NEEDLE ADAPTER AND ASSEMBLY TO FORM AN INJECTION DEVICE FOR ADMINISTERING A FLUID TO A SUBJECT

Abstract

The invention relates to a needle adapter for forming an injection device for administering a fluid to a subject. It also describes an assembly for forming an injection device for administering a fluid to a subject, comprising a needle adapter body. Methods for assembling the needle adapter and the assembly are further described, as are methods for administering a fluid to a subject using the device, and the injection equipment and devices comprising it.

Description

NEEDLE ADAPTER AND ASSEMBLY FOR FORMING AN INJECTION DEVICE FOR ADMINISTERING A FLUID TO A SUBJECT FIELD OF THE INVENTION The present invention relates to a needle adapter and an assembly for forming an injection device for delivering a fluid to a subject. The invention also relates to methods for assembling the needle adapter and the assembly, methods for delivering a fluid to a user, and injection equipment and devices comprising the same. BACKGROUND OF THE INVENTION A wide variety of injection devices are known in the field, the most common being a standard plastic medical syringe equipped with a detachable stainless steel needle. These syringes are used to deliver active agents such as drugs and vaccines via various routes of administration that require different injection depths, such as intradermal (ID), intravenous (IV), subcutaneous (SC), or intramuscular (IM) injections. While standard plastic medical syringes are relatively inexpensive to manufacture due to their simple mechanical structure, they lack any built-in features to assist with controlled skin penetration to a predefined depth. Therefore, the correct use of standard syringes for the aforementioned routes of administration depends on the skill of the person administering the active agent. Morbidity and mortality from infectious diseases have been drastically reduced thanks to vaccination, which is the most cost-effective public health measure for preventing the spread of disease. (Lambert et al., Can successful vaccines teach us how to induce efficient protective immune responses? Nature Medicine. 2005; 11: S54-S62). The three main routes of vaccine administration include ID injection, SC injection, and IM injection. Interestingly, most vaccines are administered by IM injection, even though muscle is not a highly immunogenic organ (Hutin et al., Use of injections in healthcare settings worldwide, 2000: literature review and regional estimates. British Medical Journal. 2003; 327:1075-1078; Hohlfeld and Engel, The immunobiology of muscle. Immunology Today. 1994; 15: 269-274).The skin, on the other hand, is a much more attractive site for vaccination due to the large number of resident dendritic cells and the efficient drainage to the lymph nodes (Debenedictis et al., Immune functions of the skin. Clinics in Dermatology. 2001; 19:573-585; Kupper and Fuhlbrigge, Immunological surveillance in the skin: mechanisms and clinical consequences. Nature Reviews Immunology. 2004; 4:211-222), with the result that smaller doses of antigen could induce an immune response equivalent to the standard dose. Antigen trafficking studies have shown that ID vaccination leads to more efficient antigen migration to lymph nodes than conventional IM administration (Steinman and Branchereau, Taking dendritic cells into medicine. Nature. 2007; 449: 419-426; Valladeau and Saeland, Cutaneous dendritic cells. Seminars in Immunology.2005; 17: 273-283; Sugita et al., Epidermal keratinocyte-mediated innate immunity promotes acquired immunity involving Langerhans cells and T cells in the skin. Clinical and Experimental Immunology. 2007; 147: 176-183). However, skin vaccines have not been widely adopted because intradermal injection (ID) requires specialized training and, even with training, is not reliably targeted to the skin. (Flynn et al., Influence of needle gauge on the Mantoux skin test. Chest. 1994; 106:1463-1465). Today, most ID injections are administered by specially trained personnel using a conventional hypodermic needle, via the Mantoux technique. The needle should be inserted into the skin at an angle of 5 to 15 degrees.Historically, the difficulties associated with this injection modality in the skin have limited its use, although fractionated doses of some vaccines are effective when injected into the skin. The skin, as the primary interface between the body and the environment, provides the first line of defense against a wide range of microbial pathogens. (Debenedictis et al., Immune functions of the skin. Clinics in Dermatology. 2001; 19:573-585; Kupper and Fuhlbrigge, Immune surveillance in the skin: mechanisms and clinical consequences. Nature Reviews Immunology. 2004; 4:211-222). Although skin-directed immunization has been used for decades, its application beyond a few vaccines has been hampered by the lack of a simple and reliable skin vaccination technology. An alternative method to intradermal injection is intradermal microinjection. Microneedle skin vaccination has the potential to improve both the immunology and logistics of vaccination.Compared to IM injections, microneedle skin vaccines eliminate or reduce the pain and apprehension felt by patients, eliminate or reduce the risk of needlestick injuries, and allow for greater vaccination coverage, as skin vaccines can be administered by minimally trained medical professionals or by the patient themselves. The need for safe, cost-effective, and efficient vaccine administration and the growing understanding of the mechanisms of immune responses induced by targeting the innermost layers of the skin have driven the engineering of novel delivery devices for innermost injection. (Wang et al., Precise microinjection into the skin using hollow microneedles. 2006; 126: 1080-1087; Kim and Prausnitz, Enabling skin vaccination using novel delivery technologies. Drug Delivery and Translational Research. 2011; 21(1):7-12). Specifically, these advanced delivery technologies employ microneedles inserted 1.5 mm perpendicularly into the skin, injecting approximately 100-200 pL of a liquid vaccine into the dermal layers. Promising clinical data with some vaccines highlight the potential for reduced-dose immunization via this ID route (Zehrung et al., Intradermal delivery for vaccine dose economy: current issues overview. Vaccine. 2013; 31(34): 3392-3395). ID injections have the potential to increase vaccine efficacy in targeted populations and can help increase vaccine access, reduce costs, and alleviate the logistical burdens of immunization programs, particularly in low-resource settings. New devices are being developed for easier and more reliable identification administration that can serve as alternatives to the Mantoux technique and help promote the implementation of dose-saving identification vaccination strategies. The range of new identification delivery devices includes adapters for traditional needles and syringes that control the depth and angle of needle penetration, mini-needles, micro-needles, and identification fluid jet injectors. (Zehrung et al., Intradermal delivery to save vaccine doses: an overview of current issues. Vaccine. 2013; 31(34): 3392-3395). Most of these devices are currently only available for research purposes. WO2013156524(A1) describes a highly sophisticated injection device. It comprises a leg for placement on the skin, a movable double-ended needle, and a reservoir containing a liquid for delivery. The device has a highly sophisticated mechanism to ensure a specific sequence of events. First, the device must be unlocked. Then, one end of the needle enters the reservoir. Next, the reservoir and needle move within the device, and the other end of the needle penetrates the skin. In other words, a double-ended needle enters a pre-filled reservoir on one end and penetrates the skin on the other. Subsequently, the reservoir is emptied by pushing down the plunger, and finally, the needle retracts. This device is ideal for intradermal injections. Another highly sophisticated assembly for forming an injection device is described in WO2017168015 (A1). The assembly includes a leg for placement on skin; a body comprising at least one needle, wherein the body is movably mounted on the leg to allow movement of the needle toward the skin. The needle extends beyond a second contact surface by a predefined distance to limit the depth of needle penetration. The assembly further includes a first friction means to prevent movement of the body relative to the leg that could cause sudden acceleration, and a second friction means to create dynamic friction as the needle moves toward the skin to maintain skin tautness. The assembly is particularly suitable for ID injections, although it can also be used for IV, SC, or IM injections in certain modalities. There is a need for new injection devices, particularly those suitable for ID injections. This background information is provided for the purpose of disclosing information that the applicant believes may be relevant to the present invention. It is not necessarily intended to admit, nor should it be interpreted, that any of the foregoing information constitutes prior art contrary to the present invention. BRIEF DESCRIPTION OF THE INVENTION In one aspect, a needle adapter is provided to form an injection device for delivering a fluid to a subject, comprising a housing formed by a first housing part and a second housing part, the housing having a proximal end and a distal end; and a needle unit fixedly mounted within the housing. The needle unit comprises a needle shaft comprising a first end for penetrating the subject's skin and a second end connected to a needle hub, the needle hub comprising a distal end connected to the second end of the needle shaft and a proximal end comprising a pair of diametrically opposed, radially extending tabs.Each of the first housing part and the second housing part comprises at least two consecutive transverse walls or projections extending from an inner surface thereof, wherein at least two consecutive transverse walls or projections form a space between them to receive at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit to securely mount the needle unit frfrRzrn / zznza / YiAi within the housing. The proximal end of the housing together with at least two consecutive transverse walls or projections of each of the first housing part and the second housing part define a channel for receiving a syringe tip for coupling with the needle hub.The distal end of the housing comprises a first contact surface adapted to be placed on the subject's skin and a second contact surface, wherein the first end of the needle shaft extends out of the second contact surface by a predefined distance to limit the penetration depth of the needle shaft. In another aspect, an assembly is provided for forming an injection device for delivering a fluid to a subject. The assembly comprises a leg having a first contact surface adapted to be placed on the subject's skin. The leg has a tubular shape to receive a needle adapter body, and the needle adapter body itself comprises a housing formed by a first housing part and a second housing part. The housing has a proximal end and a distal end. A needle unit is fixedly mounted within the housing. The needle unit comprises a needle shaft having a first end for penetrating the subject's skin and a second end connected to a needle hub. The needle hub has a distal end connected to the second end of the needle shaft and a proximal end comprising a pair of diametrically opposed, radially extending flanges.Each of the first housing part and the second housing part comprises at least two consecutive transverse walls or projections extending from an internal surface thereof, where at least two consecutive transverse walls or projections form a space between them to receive at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit to securely mount the needle unit within the housing. The proximal end of the housing together with at least two consecutive transverse walls or projections of each of the first housing part and the second housing part define a channel for receiving a syringe tip for coupling with the needle hub.The distal end of the housing comprises a second contact surface, where the first end of the needle shaft extends beyond the second contact surface by a predefined distance to limit the penetration depth of the needle shaft. The needle adapter body is movably mounted on the leg to allow movement of the needle adapter body from a first position to a second position, wherein when the needle adapter body is in the first position, the needle shaft is in a retracted position so that the first end of the needle shaft does not extend beyond the first contact surface, and when the needle adapter body is in the second position, the first end of the needle shaft extends beyond the first contact surface and beyond the second contact surface by the predefined distance to limit the penetration depth of the needle shaft.The assembly further comprises friction means to inhibit the movement of the needle adapter body with respect to the shank when the needle adapter body is in the first position, until a predefined static friction force is overcome, and to cause or allow a sudden acceleration of the needle adapter body towards the shank to increase the needle shaft speed to increase the probability of skin penetration. BRIEF DESCRIPTION OF THE FIGURES For a better understanding of the present invention, including the development progression to arrive at the final product, reference is made to the following description, which shall be used in conjunction with the accompanying drawings, where: Figure 1(a) illustrates an example of a needle adapter according to an embodiment of the present application, in perspective view. Figure 1(b) illustrates a top view of the needle adapter shown in Figure 1(a), showing the proximal end of the housing and the channel for receiving a syringe tip formed therein. Figure 1(c) illustrates a bottom view of the needle adapter 100 shown in Figure 1(a), showing the distal end 106 of the housing 102 comprising a first contact surface 132 adapted to be placed on the subject's skin and a second contact surface 134 through which the first end 112 of the needle shaft 110 extends. Figures 2(a) and 2(b) illustrate the first part of the housing 102a and how the needle unit 108 can be coupled with it. Figure 3(a) illustrates the partially disassembled needle adapter 100 of Figure 1(a), showing the first part housing 102a, the second part housing 102b, and the needle unit 108 secured with the first part housing 102a in the first orientation. Figure 3(b) illustrates the partially disassembled needle adapter 100 of Figure 1(a), showing the first part housing 102a, the second part housing 102b, and the needle unit 108 secured with the first part housing 102a in the second orientation. frfrRzrn / zznza / YiAi Figures 4(a) and 4(b) illustrate a simplified first housing part 102a of the needle adapter 100 in which the distal end of the housing 106 lacks the first contact surface 132, to better illustrate how the variation in the placement of the needle unit 108 within the first housing part 102a affects the predefined distance d1 at which the first end of the needle shaft 112 extends out of the second contact surface 134. Figure 5 shows another simplified view of the first simplified housing part 102a shown in Figures 4(a) and 4(b) and also shows a first simplified housing position 202a of the needle adapter body 200 of assembly 201 discussed in more detail below. In the labels in Figure 5, references to the components / elements of the needle adapter body 200 of assembly 201 discussed below are provided in parentheses. Figure 6 illustrates a perspective view of the first housing part 102a, showing how a preselected portion p1 can be removed from a distal end of the first housing part 102a during assembly of the needle adapter 100 to account for manufacturer variability in needle shaft lengths. Figures 7(a) and (b) show a simplified cross-sectional view of one embodiment of the needle adapter 100 held with a syringe 146, thus forming an injection device 149 for delivering a fluid to a subject by injection. Figure 7(c) illustrates a perspective view of the injection device 149 shown in Figures 7(a) and (b). frfrRzrn / zznza / YiAi Figure 8 illustrates a series of steps that can be used to deliver a fluid to a subject by injection using the 100 needle adapter. Figure 9(a) illustrates the safety holder 152. Figure 9(b) illustrates a simplified cross-sectional view of one embodiment of the needle adapter 100 held with a syringe 146, and how the distal end 106 of the needle adapter 102 housing can be received in the open end 154 of the safety holder. Figure 9(c) illustrates the needle adapter 102 housing held with the safety holder 152, with the needle adapter 100 in a simplified cross-sectional view. Figure 9(d) illustrates the needle adapter 102 housing held with the safety holder 152, with the needle adapter 100 in a simplified cross-sectional view, and with the safety holder 152 and syringe 146 also in cross-sectional view. Figure 10 illustrates the coupling of a syringe 146 with a dosing device 160 and the coupling of the same with the needle adapter 100. Figure 11(a) illustrates an exemplary assembly 201 for forming an injection device for supplying a fluid to a subject according to a modality of the present application, in perspective view. Figure 11(b) illustrates a top view of the assembly shown in Figure 11(a), showing the proximal end of the needle adapter housing and the channel for receiving a syringe tip formed therein. frfrRzrn / zznza / YiAi Figure 11(c) illustrates another perspective view of the assembly shown in Figure 11(a). Figure 11(d) illustrates a bottom view of the assembly 201 shown in Figures 11(a) and (c), showing the distal end 233 of the leg 231 comprising a first contact surface 232 adapted to be placed on the subject's skin. The second contact surface 234 of the distal end 206 of the housing 202 of the needle adapter body 200, through which the first end 112 of the needle shaft 210 extends, is also visible through an opening 286 formed by an inner surface 288 of the leg, the inner surface of the leg being oriented in a plane substantially parallel to and separate from a tangential plane defined by the first contact surface 232. Figure 12 illustrates an exploded view of assembly 201 shown in Figures 11(a) and (c). Figures 13(a) and 13(b) illustrate the first housing part 202a and how the needle unit 208 can be coupled with it. Figures 14(a)-14(c) illustrate the attachment of the needle unit 208 to the first housing part 202a, and the attachment of the first housing part 202a to the second housing part 202b to form the housing 202 of the needle adapter body 200. Figure 15 illustrates a perspective view of the needle adapter body 200 and the leg 231, where at least two projections 274 extend from an inner surface 276 of a proximal end 278 of the leg 231 and one of at least two corresponding grooves 280 located on an outer surface 266 of the distal end 206 of the housing 202 of the needle adapter body 200 can be clearly seen. frfrAzrn / zznza / viAi Figure 16 provides an enlarged perspective view of the needle adapter body 200 to better illustrate the contours of the groove 280. Figure 17(a) illustrates one embodiment of an assembly 201 in perspective (top) and cross-sectional view (bottom) where the safety clip 264 has been removed and the needle adapter body 200 is in the first position (i.e., ready for injection). Figure 17(b) illustrates assembly 201 in perspective (top) and cross-section (bottom) with the safety clip 264 removed and the needle adapter body 200 in the second position (i.e., the needle shaft 210 penetrates the skin). Figure 17(c) illustrates assembly 201 in perspective (top) and cross-section (bottom) with the needle adapter body 200 held in a fixed, deactivated position relative to leg 231. Figure 18(a) illustrates a proposed automated assembly line for preparing assembly 201 using machine vision technology and pick-and-place robotics. Housing 1 and Housing 2 refer to the first and second housing parts 202a and 202b, Needle refers to the needle unit 208, Housing assembly refers to the assembly of the needle unit 208 onto one of the first and second housing parts 202a / 202b, Pull pin refers to the safety clip 264, and leg refers to the leg 231. The various items are placed on the production conveyor, which moves along the assembly line via a conveyor belt. Figure 18(b) illustrates the composition of the production conveyor at each stage of assembly. hbRZQn / zznzvi / YiAi Figure 19 illustrates a series of steps that can be used to deliver a fluid to a subject by injection using assembly 201. Figures 20(a) and 20(b) show a simplified cross-sectional view of an alternative embodiment of assembly 201 coupled with a syringe 246, thus forming an injection device 249 for administering a fluid to a subject by injection. As can be seen in Figures 20(a) and (b), the locking mechanism is absent, and the needle adapter body 200 is in the second position where the needle shaft 210 penetrates the skin 250 (shown in Figure 20(b)). Figure 20(c) illustrates a perspective view of the injection device 249 shown in Figures 20(a) and (b). DETAILED DESCRIPTION OF THE INVENTION Definitions Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by a person skilled in the art to which this invention pertains. As used in the specification and claims, the singular forms “a”, “one” and “the” include plural references unless the context clearly indicates otherwise. The term “comprises” as used herein shall be understood to mean that the following list is not exhaustive and may or may not include any other suitable additional item, e.g., one or more additional features, component(s), ingredient(s) and / or element(s) as appropriate. Degree terms such as “substantially,” “around,” and “approximately,” as used herein, mean a reasonable amount of deviation from the modified term so that the final result does not change significantly. These degree terms should be interpreted as including a deviation of at least ±5% from the modified term if this deviation does not negate the meaning of the modifying word. The term “fluid” as used herein shall be understood to mean any matter that can be injected through a needle, such as a liquid, a solution, a suspension, a gel, or other substances that can be injected through a needle. The terms first, second, and similar in this specification are used to distinguish between similar elements, and it is understood that these terms may be interchangeable under certain circumstances. Furthermore, the terms upper, lower, etc., in this specification are used for descriptive purposes and may not indicate relative positions. The particular features of one or more modalities of this application may be combined in any suitable manner, as will be understood by a person skilled in the art in view of the teachings of this application. Finally, the drawings provided herein are for illustrative purposes, and the elements illustrated therein may not be drawn to scale. In the drawings, similar reference numbers refer to similar parts in the various views and as described herein, unless otherwise specified. The latest generation of needle adapters and injection devices consists of a needle unit or a series of needle units that are mounted, for example, by gluing or overmolding, onto an adapter piece or other device. Such needle units typically comprise a stainless steel needle shaft, which may be made of plastic (e.g., polypropylene (PP)), metal, or potentially even glass. Regarding overmolding: In this process, a needle shaft / unit is placed in an injection molding tool within a specially designed cavity (designed to keep the needle tip and part of the shaft free of plastic). Medical-grade plastic (e.g., cyclic olefin copolymer (COC)) is then overmolded, creating a strong connection between the needle shaft and the hub / housing. The disadvantages of overmolding are that the process is difficult to automate (and even when not highly automated, it is very expensive), requires complex tooling, is particularly challenging when very short needle shafts are needed, is highly dependent on the needle's accuracy and tolerances, and the needle tip can be damaged during the process. Regarding gluing: a needle shaft can be positioned and mounted in a hub or housing (e.g., injection molded) using glue. This would require a (semi-)automatic system to hold the needle shaft, clamp the housing, position the two components together, and mount the needle shaft with, for example, silicone or UV-cured glue. The disadvantages of gluing are that it can present biocompatibility issues (where glue elements can leach / profile into the fluids to be injected, etc.), raises quality control problems (regarding positioning, device leakage, etc.), can be subject to slippage in the needle shaft / unit positioning over time (which can affect the needle shaft length for injections), is very difficult for short needle shafts, and is expensive to automate. frfrRzrn / zznza / YiAi Furthermore, current state-of-the-art needle adapters and injection devices claim to have a predefined needle protrusion length of, for example, 1 mm or, for example, 13 mm. However, as a result of current state-of-the-art manufacturing processes, it is known that the final needle lengths will be subject to production tolerances of, for example, 0.05 mm or, for example, 2 mm, as defined in the relevant ISO standards. As such, it will be understood that the current state of the art is generally preferred for long needles (e.g., +5 mm) that have wide tolerances (e.g., +: - 0.5 mm), as only then is it economical (due to the dimensions and tolerances applied). In view of the above, it will be understood that current technology may fall short when shallow penetration depths are required (which requires a shorter functional length of the needle shaft for injection, as in the case of ID injections), as it is imprecise, costly, and prone to errors. The needle adapter and assembly for forming an injection device for delivering a fluid to a subject described herein addresses the deficiencies mentioned above and allows control over the depth of penetration regardless of the intended needle length and tolerance deviations. The needle adapter and assembly of this application allows the use of needle units with longer needle shafts, such as commercially available (pre-glued) needle units comprising a needle shaft and a hub with a standard female Luer-Lok fitting, 26-34 G and 12 mm in length. Such needle units may have long needle shafts with wide tolerances, whereas the needle adapter and assembly of this application can precisely control the depth of penetration regardless of the shaft length.The needle adapter and assembly of the present application can therefore take into account and compensate for manufacturer variability in needle shafts. In one embodiment of the present application, a needle adapter is provided to form an injection device for delivering a fluid to a subject, comprising a housing formed by a first housing part and a second housing part, the housing having a proximal end and a distal end; and a needle unit fixedly mounted within the housing. The needle unit comprises a needle shaft comprising a first end for penetrating the subject's skin and a second end connected to a needle hub, the needle hub comprising a distal end connected to the second end of the needle shaft and a proximal end comprising a pair of diametrically opposed, radially extending tabs (e.g., typical needle hub tabs found on commercially available needle units comprising a needle shaft and hub having a standard female Luer-Lok fitting).Each of the first housing part and the second housing part comprises at least two consecutive transverse walls or projections extending from an internal surface thereof, wherein at least two consecutive transverse walls or projections form a space between them to receive at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the hbRZQn / zznzzi / YiAi needle unit for securely mounting the needle unit within the housing. The proximal end of the housing together with at least two consecutive transverse walls or projections of each of the first housing parts and the second housing part defines a channel that is sized and shaped to receive a syringe tip (e.g., a syringe tip having standard Luer dimensions) for mating with the needle hub.The distal end of the housing comprises a first contact surface adapted to be placed on the subject's skin and a second contact surface, wherein the first end of the needle shaft extends out of the second contact surface by a predefined distance to limit the penetration depth of the needle shaft. In another embodiment, the first housing part and the second housing part are configured to snap together to form the housing. As the expert will appreciate, snapping the first and second housing parts together is a very simple form of joining that can be quickly and easily automated, offering advantages over gluing (whose limitations are discussed earlier) or other fastening methods, such as ultrasonic welding (which may not work for welding certain plastics and would add complexity and cost to an automated assembly line). In yet another embodiment, the first and second housing parts have at least substantially similar or identical construction (which reduces tooling requirements and makes the device cheaper to manufacture). In another embodiment, at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit has a friction coupling with opposing surfaces of at least two consecutive hbRZQn / zznzzi / YiAi cross-walls or projections of each of the first housing part and the second housing part when received in the space between them. In another embodiment, the space formed by at least two consecutive transverse walls or projections of each of the first and second housing parts is configured to receive at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the stylus unit in a first and a second mounting orientation of the stylus unit, wherein: the predefined distance by which the first end of the stylus shaft extends beyond the second contact surface is a first predefined distance when the stylus unit is mounted in the first orientation, and the predefined distance by which the first end of the stylus shaft extends beyond the second contact surface is a second predefined distance when the stylus unit is mounted in the second orientation.where the first predefined distance is different from the second predefined distance. In another embodiment, each of the first part of the housing and the second part of the housing further comprises a variety of projections extending from the inner surface of a distal end thereof to form a needle guide configured to hold the needle shaft in place. In another embodiment, the variety of projections comprises at least two needle stabilizing projections arranged on both sides of the needle axis and offset from each other along a longitudinal axis of the needle axis hbRZQn / zznzhi / YiAi each of the at least two needle stabilizing projections having an inclined surface that abuts the needle axis. In another embodiment, the first contact surface is arranged along the perimeter of the distal end of the housing, and the second contact surface is arranged substantially in the center of the distal end of the housing. The second contact surface may be arranged at one end of a stabilizing projection of the needle that may extend substantially in the center from the distal end of the housing. In yet another form, the casing is generally cylindrical in shape. In another modality, each of the first part of the casing and the second part of the casing have a generally semi-cylindrical shape. In another embodiment, a method is provided for assembling the needle adapter defined above, the method comprising: obtaining the first housing part and the second housing part; obtaining the needle unit; optionally, measuring a length of the needle shaft and removing a preselected portion from a distal end of each of the first housing part and the second housing part based on the length of the needle shaft; mounting the needle unit onto one of the first housing part and the second housing part by inserting at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit into the space formed between at least two consecutive walls or transverse projections; and coupling the first housing part and the second housing part together to form the housing. In another embodiment, a method is provided for assembling the needle adapter defined above, the method comprising: obtaining the first housing part and the second housing part; obtaining the needle unit; measuring the length of the needle shaft; determining whether the needle unit is to be mounted in the first orientation mentioned above or in the second orientation mentioned above based on the length of the needle shaft; optionally, removing a preselected portion from a distal end of each of the first housing part and the second housing part based on the length of the needle shaft and depending on whether the needle unit is to be mounted in the first orientation or in the second orientation;mounting the needle unit in one of the first housing part and the second housing part in the first or second orientation by inserting at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit into the space formed between at least two consecutive transverse walls or projections; and coupling the first housing part and the second housing part together to form the housing. In another embodiment of the method described above for assembling the needle adapter defined above, the preselected portion of the distal end of each of the first housing part and the second housing part is removed, comprising cutting the preselected portion of the distal end of each of the first housing part and the second housing part, as by laser cutting. In another form of the method described above for assembling the needle adapter defined above, the method is automated. In another embodiment, an assembly is provided to form an injection device for delivering a fluid to a subject. The assembly comprises a leg having a first contact surface adapted to be placed on the subject's skin, the leg having a tubular shape to receive a needle adapter body, and a needle adapter body. The needle adapter body comprises a housing formed by a first housing part and a second housing part, the housing having a proximal end and a distal end; and a needle unit fixedly mounted within the housing.The needle unit comprises a needle shaft comprising a first end for penetrating the subject's skin and a second end connected to a needle hub, the needle hub comprising a distal end connected to the second end of the needle shaft and a proximal end comprising a pair of diametrically opposed tabs extending radially (e.g., the typical needle hub tabs that would be found on commercially available needle units comprising a needle shaft and hub having a standard female Luer-Lok fitting).Each of the first housing part and the second housing part comprises at least two consecutive transverse walls or projections extending from an internal surface thereof, wherein at least two consecutive transverse walls or projections form a space between them to receive at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit to securely mount the needle unit within the housing. The proximal end of the housing together with at least two consecutive transverse walls or projections of each of the first housing parts and the second housing part defines a channel that is sized and shaped to receive a syringe tip (e.g., a syringe tip having standard Luer dimensions) for mating with the needle hub.The distal end of the housing comprises a second contact surface, wherein the first end of the needle shaft extends beyond the second contact surface by a predefined distance to limit the penetration depth of the needle shaft. The needle adapter body is movably mounted on the leg to allow movement of the needle adapter body from a first position to a second position, wherein when the needle adapter body is in the first position, the needle shaft is in a retracted position so that the first end of the needle shaft does not extend beyond the first contact surface, and when the needle adapter body is in the second position, the first end of the needle shaft extends beyond the first contact surface and beyond the second contact surface by the predefined distance to limit the penetration depth of the needle shaft.The assembly further comprises friction means to inhibit the movement of the needle adapter body with respect to the shank when the needle adapter body is in the first position, until a predefined static friction force is overcome, and to cause or allow a sudden acceleration of the needle adapter body towards the shank to increase the speed of the needle shaft to increase the probability of penetration into the skin. In another embodiment, the space formed by at least two consecutive transverse walls or projections of each of the first housing parts and the second housing part is configured to receive at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the stylus unit in a first and a second mounting orientation of the stylus unit, wherein: the predefined distance by which the first end of the stylus shaft extends beyond the second contact surface is a first predefined distance when the stylus unit is mounted in the first orientation, and the predefined distance by which the first end of the stylus shaft extends beyond the second contact surface is a second predefined distance when the stylus unit is mounted in the second orientation.where the first predefined distance is different from the second predefined distance. In another embodiment, at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit has a friction coupling with the opposing surfaces of at least two consecutive walls or transverse projections of each of the first housing part and the second housing part when received in the space between them. In another embodiment, the first housing part and the second housing part are configured to snap together to form the housing. As noted earlier, snap-fitting the first and second housing parts is a very simple form of joining that offers advantages over gluing (whose limitations are discussed earlier) or other joining methods, such as ultrasonic welding. In yet another embodiment, the first and second housing parts have at least substantially similar or identical construction (which reduces tooling requirements and makes the device more economical to manufacture). hbRZQn / zznzAi / YiAi In yet another embodiment, each of the first housing part and the second housing part further comprises a variety of projections extending from the inner surface of a distal end thereof to form a needle guide configured to hold the needle shaft in place. In yet another form, the variety of projections comprises at least two needle stabilizing projections arranged on either side of the needle axis and offset from each other along a longitudinal axis of the needle axis, each of the at least two needle stabilizing projections having an inclined surface that abuts the needle axis. In another embodiment, the first contact surface is arranged along the perimeter of a distal end of the leg, and the second contact surface is arranged substantially in the center of the distal end of the carcass. The second contact surface may be arranged at one end of a stabilizing projection of the needle that may extend substantially in the center from the distal end of the carcass. In yet another embodiment, the housing is generally cylindrical. In another embodiment, each of the first and second parts of the housing is generally semi-cylindrical. In another embodiment, the first friction means comprises at least two projections extending from an inner surface of a proximal end of the leg that is in contact with at least two corresponding grooves located on an outer surface of the distal end of the needle adapter body housing, wherein a radial dimension defined by at least two projections before the assembly of the needle adapter body and the leg is smaller than a radial dimension defined by at least two corresponding grooves, static friction being provided by radial clamping.However, it shall be understood that the first means of friction could equivalently comprise at least two projections extending from an outer surface of the body that is in contact with at least two corresponding grooves located on an inner surface of the leg, wherein a radial dimension defined by at least two projections before the assembly of the body and the leg is greater than a radial dimension defined by the grooves, static friction being provided by radial clamping. In another embodiment, at least two corresponding grooves are configured to prevent decoupling of the leg from the needle adapter body by limiting the movement of the leg in an axial direction away from the needle adapter body after coupling by at least two projections extending from the inner surface of the proximal end of the leg with at least two corresponding grooves. In another configuration, at least two corresponding slots are generally oriented parallel to a longitudinal axis of the housing. In another embodiment, the assembly further comprises at least two deactivation slots located on the outer surface of the distal end of the needle adapter body housing, wherein each of at least two deactivation slots intersects one of at least two corresponding slots at an angle (e.g., from about 25° to about 65°, e.g., about 45°) with respect to the longitudinal axis of the housing, such that axial movement of the leg away from the needle adapter body and rotation of the leg with respect to the needle adapter body engages at least two projections with at least two deactivation slots, wherein each of at least two deactivation slots comprises an indentation complementary to a shape of each of at least two projections for fixedly engaging each of at least two projections.such that the needle adapter body is held in a fixed and deactivated position with respect to the leg, wherein the first end of the needle shaft does not extend beyond the first contact surface when the needle adapter body is in the fixed and deactivated position with respect to the leg. In another embodiment, the assembly further comprises a locking mechanism to provide a locked mode and an unlocked mode of the device, wherein the locked mode is a mode of the assembly in which the needle adapter body is prevented from moving axially towards the leg, even when an axial force greater than the predefined static friction is exerted on the needle adapter body with respect to the leg; the unlocked mode being a mode of the assembly in which the needle adapter body is allowed to move towards the leg when an axial force greater than the predefined static friction is applied to the needle adapter body with respect to the leg.In another embodiment, the locking mechanism comprises a removable safety clip configured to engage with a portion of the outer surface of the housing to keep the leg and needle adapter body separated from each other to prevent the needle adapter body from moving axially toward the leg. In another embodiment, a method is provided for assembling the above-described assembly, wherein the assembly optionally further comprises a locking mechanism comprising a removable safety clip hbRZQn / zznzzi / YiAi configured to engage with a portion of the outer surface of the housing to keep the shank and needle adapter body separated from each other to prevent the needle adapter body from moving axially toward the shank, the method comprising: obtaining the shank; obtaining the first housing portion and the second housing portion forming the housing of the needle adapter body; obtaining the needle unit; optionally, obtaining the removable safety clip; optionally, measuring a length of the needle shaft and removing a preselected portion from a distal end of each of the first housing portion and the second housing portion according to the length of the needle shaft;Mount the needle unit into one of the first housing part and the second housing part by inserting at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit into the space formed between at least two transverse walls or projections; couple the first housing part and the second housing part together to form the needle adapter body housing; engage the removable safety clip, if present, with the outer surface portion of the housing; and secure the needle adapter leg and body. In another embodiment, a method is provided for assembling the above-described assembly wherein the assembly optionally further comprises a locking mechanism comprising a removable safety clip configured to engage with a portion of the outer surface of the housing to keep the stylus leg and the needle adapter body separated from each other to prevent the needle adapter body from moving axially toward the leg, the method comprising: obtaining the leg; obtaining the first housing portion and the second housing portion forming the housing of the needle adapter body; obtaining the needle unit; optionally, obtaining the removable safety clip; measuring the length of the needle shaft; determining whether the needle unit is to be mounted in the first orientation or the second orientation based on the length of the needle shaft;Optionally, remove a preselected portion from a distal end of each of the first housing part and the second housing part, depending on the needle shaft length and whether the needle unit is to be mounted in the first or second orientation; mount the needle unit in one of the first housing part and the second housing part in the first or second orientation by inserting at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit into the space formed between at least two consecutive transverse walls or projections; and couple the first housing part and the second housing part together to form the needle adapter body housing; engage the removable safety clip, if present, with the portion on the outer surface of the housing; and secure the needle adapter leg and body. In another embodiment of the method described above, coupling the shank and the needle adapter body comprises coupling at least two projections extending from the inner surface of the proximal end of the shank with at least two corresponding grooves located on the outer surface of the distal end of the needle adapter body housing. In another embodiment of the method described above for assembling the assembly defined above, remove the preselected portion of the distal end of each of the first housing part and the second housing part, comprising cutting the preselected portion of the distal end of each of the first housing part and the second housing part, for example, by laser cutting. In another form of the method described above for assembling the set defined above, the method is automated. In another embodiment, a method is provided for administering a fluid to a subject by injection, the method comprising: (a) obtaining the needle adapter described above; (b) obtaining a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe (the channel being sized and shaped to receive the tip of the syringe / other dosing device for coupling with the needle hub), wherein the syringe or other dosing device is loaded with the fluid to be administered to the subject; (c) inserting the tip of the syringe or other dosing device into the channel provided at the proximal end of the housing for securing the tip to the needle hub; (d) coupling the first skin contact surface with the subject;(e) pushing the housing against the skin to allow the first end of the needle shaft to penetrate the skin; (f) expelling fluid from the syringe or other dosing device through the needle shaft into the subject; and (g) optionally, coupling the needle adapter with a safety holder, wherein the safety holder has an open end to receive at least the distal end of the needle adapter housing and a closed end, the closed end comprising opposing wings to stabilize the safety holder on a horizontal surface. hhRZQn / zznzu / YiAi In another embodiment, a method is provided for administering a fluid to a subject by injection, the method comprising: (a) obtaining the assembly described above, wherein the needle adapter body is in the first position; (b) obtaining a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe (the channel being sized and shaped to receive the tip of the syringe / other dosing device for coupling with the needle hub), wherein the syringe or other dosing device is loaded with the fluid to be administered to the subject; (c) inserting the tip of the syringe or other dosing device into the channel disposed in the proximal end of the needle adapter housing to engage the tip with the needle hub; (d) coupling the first contact surface of the leg with the subject's skin;(e) pushing the needle adapter body housing towards the leg to move the needle adapter body from the first position to the second position, thereby causing the first end of the needle shaft to penetrate the skin; and (f) expelling fluid from the syringe or other dosing device through the needle shaft into the subject. In another embodiment, wherein the assembly described above comprises a needle adapter housing with deactivation slots, a method is provided for administering a fluid to a subject by injection, the method comprising: (a) obtaining the assembly, wherein the needle adapter body is in the first position; (b) obtaining a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe (the channel being sized and shaped to receive the tip of the syringe / other dosing device for coupling with the needle hub), wherein the syringe or other dosing device is loaded with the fluid to be administered to the subject;(c) inserting the tip of the syringe or other dosing device into the channel provided at the proximal end of the needle adapter housing to secure the tip to the needle hub; (d) engaging the first contact surface of the shank with the subject's skin; (e) pushing the needle adapter body housing toward the shank in an axial direction to move the needle adapter body from the first position to the second position, thereby causing the first end of the needle shaft to penetrate the skin; (f) expelling the fluid from the syringe or other dosing device through the needle shaft into the subject;and (g) pulling the needle adapter body housing away from the shank in an axial direction and rotating the shank relative to the needle adapter body to engage at least two projections with at least two deactivation slots and permanently engaging each of these projections to at least two projections in the indentation in each of at least two deactivation slots, so that the needle adapter body is held in the fixed deactivated position relative to the shank. In yet another embodiment where the assembly described above comprises a needle adapter housing with deactivation slots, as well as a locking mechanism comprising a removable safety clip, a method is provided for administering a fluid to a subject by injection, the method comprising: (a) obtaining the assembly described above, wherein the needle adapter body is in the first position; (b) obtaining a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe (the channel being sized and shaped to receive the tip of the syringe / other dosing device for coupling with the needle hub), wherein the syringe or other dosing device is loaded with the fluid to be administered to the subject;(c) inserting the tip of the syringe or other dosing device into the channel provided at the proximal end of the needle adapter housing to secure the tip to the needle hub; (d) engaging the first contact surface of the shank with the subject's skin; (e) pushing the needle adapter body housing toward the shank in an axial direction to move the needle adapter body from the first position to the second position, thereby causing the first end of the needle shaft to penetrate the skin; (f) expelling the fluid from the syringe or other dosing device through the needle shaft into the subject;and (g) pulling the needle adapter body housing away from the shank in an axial direction and rotating the shank relative to the needle adapter body to engage at least two projections with at least two deactivation slots and permanently engaging each of these projections to at least two projections in the indentation in each of at least two deactivation slots, such that the needle adapter body is held in the fixed deactivated position relative to the shank; the method further comprising removing the safety clip from the outer surface of the housing after step (c) and before step (d), or after step (d) and before step (e). Other dosing devices that could be used instead of a syringe with the needle adapter and assembly of the present application could include pre-filled multi-chamber containers (e.g., dual chambers for lyophilized substances and diluents), with a means for hbRZQn / zznzzi / YiAi mixing the chamber components and means for expelling them from the dosing device (e.g., by means of a plunger, etc.). In another embodiment, equipment is provided comprising: the needle adapter described above to form an injection device for delivering a fluid to a subject; a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe, wherein the syringe or other dosing device is optionally loaded with the fluid to be delivered to the subject; optionally, a vial containing the fluid to be delivered to the subject; optionally, a removable needle unit or other means for drawing the fluid from the optional vial into the syringe or other dosing device, the removable needle unit being removable to allow the tip of the syringe or other dosing device to be inserted into the channel of the housing;Optionally, a safety stand, wherein the safety stand has an open end for receiving at least the distal end of the needle adapter housing and a closed end, the closed end comprising opposing wings for stabilizing the safety stand on a horizontal surface; and optionally, instructions for use. In another embodiment, equipment is provided comprising: the assembly described above to form an injection device for delivering a fluid to a subject; a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe, wherein the syringe or other dosing device is optionally loaded with the fluid to be delivered to the subject; optionally, a vial containing the fluid to be delivered to the subject; optionally, a removable needle unit or other means for withdrawing the fluid from the optional vial to the syringe or other dosing device, the removable needle unit being removable to allow the tip of the syringe or other dosing device to be inserted into the channel of the housing; and optionally, instructions for use. In another embodiment, an injection device is provided comprising: the needle adapter described above; and a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe, wherein the syringe or other dosing device is optionally loaded with the fluid to be delivered to the subject. In yet another embodiment, an injection device is provided comprising: the assembly described above; and a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe, wherein the syringe or other dosing device is optionally loaded with the fluid to be delivered to the subject. The various parts of the needle adapter, as well as the assembly to form an injection device for delivering a fluid to a subject, can be formed from plastic materials, particularly medical-grade plastic (e.g., cyclic olefin copolymer (COC)), and can be manufactured by a number of different methods, such as precision casting, additive manufacturing, 3D printing, and injection molding. In one embodiment, the parts are manufactured by injection molding. The tolerances of such processes can be precisely controlled, for example, on the order of 0.01 mm. 0.02 mm or 0.03 mm, allowing for precise construction of the devices, including the accurate implementation of the frictional forces described in more detail below. It will be evident to a person skilled in the art that the present needle adapter, as well as the assembly forming an injection device for delivering a fluid to a subject, can be used to deliver various drugs or vaccines. These devices are particularly suitable for delivering injections at a very precise angle and / or depth of penetration, such as for ID injections with the needle oriented almost perpendicular to the skin and typically inserted to a very precise and predefined depth, for example, around 1.0 mm with a tolerance of + / - 0.10 mm or + / - 0.05 mm, or even less, but other specific angles can also be used. However, it will be understood that the present invention is not limited to ID injections, and can also be used for IV, SC, or IM injections, although in these cases the needle would normally be much longer, for example, at least 5 mm or at least 10 mm.As the skilled worker will appreciate, the angle and / or depth of penetration and / or the positioning of the device can be chosen differently for such types of injections. In one embodiment, the needle adapter described herein allows the fluid to be administered with one hand, and such devices are therefore suitable for self-administration. For example, with regard to the needle adapter, a syringe containing a fluid with an active agent can be loaded, the syringe having a plunger for dispensing it. The user can then insert the tip of the syringe into the channel provided at the proximal end of the housing. Next, the first contact surface of the needle adapter can be placed against the skin, and the needle adapter can be pressed into the skin to insert the first end of the needle shaft. Finally, force can be applied to the syringe plunger (e.g., with the index or middle finger) to deliver the fluid through the needle shaft into the user's body. In another embodiment, the needle adapter can be used to deliver multiple doses of a liquid. In another embodiment, the needle adapter can be attached to a dosing device that is compatible with a syringe (where the syringe tip enters the device's channel and the dosing device controls the amount of liquid delivered in a single dose). In yet another embodiment, the needle adapter can be attached to another dosing device that has a dispensing tip similar in size and shape to a syringe tip, such as a syringe tip with standard Luer dimensions. In another configuration, the assembly described in this document allows the fluid to be administered with one hand, and therefore such devices are suitable for self-administration. For example, a syringe can be loaded with a fluid containing an active agent, the syringe having a plunger for dispensing it. The user can then insert the tip of the syringe into the channel provided at the proximal end of the needle adapter body housing.The administration steps may include: 1) holding the assembly with one hand (e.g., between the thumb and middle finger), 2) gently placing the assembly on the skin, 3) pushing the needle adapter body towards the shank until the frictional force is overcome, thereby inserting the first end of the needle shaft into the skin (with almost 100% probability of hbRZQn / zznzzi / YiAi penetration and with a predefined depth of penetration of high accuracy), and 4) applying force to the syringe plunger (e.g., with the pointing or index finger) to deliver the fluid through the needle shaft to the subject.In other embodiments, the administration steps may include disengaging a locking mechanism, such as a removable safety clip, to activate the device before pushing the needle adapter body toward the shank to insert the first end of the needle shaft into the skin, as described above and in more detail below. In another embodiment, the administration steps may include placing the needle adapter body in a fixed, deactivated position relative to the shank after administering the fluid to the subject. The assembly described herein is particularly suitable for single use. In another embodiment, the needle adapter body can be attached to another dosing device that has a dispensing tip similar in size and shape to a syringe tip, such as a syringe tip with standard Luer dimensions. The channel is understood to be sized and shaped to receive the syringe tip / other dosing device and to engage with the needle hub. It will also be appreciated that the present needle adapter, as well as the assembly for forming an injection device to deliver a fluid to a subject, requires only minimal skill and experience to administer the fluid correctly, in contrast to, for example, the Mantoux technique for administering ID injections. Furthermore, the risk of non-penetration or incomplete penetration (to the predefined penetration depth) of the needle shaft into the skin is drastically reduced or almost completely eliminated, as is the risk of inserting the needle shaft too deeply. Therefore, with the present needle adapter and assembly, skin penetration and needle tip placement at a predefined depth are virtually guaranteed. This can help reduce the pain experienced by the subject and / or improve the therapeutic effect of the administered active ingredient. With respect to the assembly described above, no spring is required to insert the needle shaft (and, as such, no internal or external mechanism to compress, hold, and release such a spring). Instead, with the assembly in this application, a force / pressure / potential energy and / or kinetic energy is generated / provided by the hand and / or forearm and / or fingers of the person holding the assembly. However, the device contains a mechanism (through static friction) that enables or disables this (external) force from having an effect. A spring may be used in an injection device that uses this assembly, for example, to actuate a plunger, but this is unrelated to the insertion of the needle shaft into the skin. The frictional means, which establish or define the force / pressure / potential energy that will be generated before the needle begins to move, can be defined passively, for example, by a clamping force between parts of the needle adapter body (also referred to here as the “body”) and the shank (described in more detail below). This will cause the needle to accelerate suddenly when the static frictional force is overcome, so that the needle will penetrate the skin at a relatively high speed (for example, between 2 m / s and 15 m / s, or any other suitable speed). The predefined static frictional force can be a value in the range of approximately 1.0 to approximately 20.0 Newtons, or approximately 1.5 to approximately 15 Newtons, or approximately 2.0 to approximately 10 Newtons, or approximately 5.0 to approximately 7 Newtons.5 Newtons; preferably, the static friction force is at least approximately 2.0 Newtons. The optimum penetration speed and therefore the optimum friction can be chosen differently for different needle units (e.g., different diameters, different lengths, different angles, etc.) and different custom assemblies (e.g., having different surface features of the grooves and / or projections) can be manufactured with different needle units. In one modality, the angle between a longitudinal axis of the needle shaft and a tangential plane defined by the first contact surface is a value in the range of, for example, approximately 5° to approximately 175°, approximately 10° to approximately 170°, approximately 60° to approximately 120°, approximately 80° to approximately 100°, or approximately 90°. Therefore, the present needle adapter and assembly allow intradermal (ID) injections at a predefined angle, which differs from the Mantoux technique, which administers drugs ID at an angle of approximately 5° to approximately 15° and is known to be painful for patients. It is believed that inserting the needle at an angle close to 90° will be significantly less painful and may also allow the injected fluid to be better distributed among the cells. In one modality, the predefined distance by which at least one needle shaft extends beyond the second contact surface is in the range of 0.25 to 12.0 mm, 0.25 to 5.00 mm, or 0.25 to 2.00 mm. A distance of 5.0 mm to 12.0 mm, for example, 10 mm to 120 mm, may be particularly suitable for IM injections. A distance of 0.25 mm to 8.00 mm, for example, 1.00 mm to 5.00 mm, may be particularly suitable for SC injections. A distance of 0.25 mm to 3.00 mm may be particularly suitable for ID injections. Figure 1(a) illustrates an example of a needle adapter 100 according to an embodiment of the present application, in perspective view. The needle adapter 100 includes a housing 102 formed by a first housing part 102a and a second housing part 102b. The housing has a proximal end 104 and a distal end 106. Figure 1(b) illustrates a top view of the needle adapter 100 shown in Figure 1(a), showing the proximal end 104 of the housing 102 of the needle adapter 100 of Figure 1(a). Figure 1(c) illustrates a bottom view of the needle adapter shown in Figure 1(a). In the present embodiment, the first housing part 102a and the second housing part 102b are of identical construction and can be formed by injection molding of medical-grade plastic (e.g., COC), resulting in very economical production.In the embodiment shown, the housing 102 has a generally cylindrical shape, and each of the first part of the housing 102a and the second part of the housing 102b has a generally semi-cylindrical shape. A needle unit 108 is fixedly mounted inside the housing 102. Figures 2(a) and 2(b) illustrate the first part of the housing 102a and the manner in which the needle unit 108 can be coupled to it, i.e., in a first orientation as shown in Figure 2(a), and a second orientation as shown in Figure 2(b). After securing the needle unit 108 with the first housing part 102a, the second housing part 102b is coupled with the first housing part 102a to form the needle adapter 100. As the expert will appreciate, it is equally possible for the needle unit to be coupled with the second housing part 102b in the same way as shown for the first housing part 102a in figures 2(a) and 2(b), since the first housing part 102a and the second housing part 102b are of identical construction. Figure 3(a) shows the components of needle adapter 100 with needle unit 108 coupled with the first housing part 102a in the first orientation, along with the second housing part 102b which is configured to couple with the first housing part 102a to form housing 102. Figure 3(b) shows the component parts of needle adapter 100 with needle unit 108 coupled with the first housing part 102a in the second orientation, along with the second housing part 102b which is configured to couple with the first housing part 102a to form housing 102. As can be seen more clearly in Figures 2(a) and 2(b) and Figures 3(a) and 3(b), the needle unit 108 comprises: a needle shaft 110 comprising a first end 112 for penetrating the subject's skin and a second end 114 connected to a needle hub 116. The needle hub 116 comprises a distal end 118 connected to the second end of the needle shaft 114 and a proximal end 120 comprising a pair of diametrically opposed, radially extending tabs 122. In the embodiment shown, the needle hub 116 has the typical needle hub tabs found on commercially available needle units comprising a needle shaft and hub having a standard female Luer-Lok fitting.Each of hbRZQn / zznzzi / YiAi the first part of the housing 102a and the second part of the housing 102b comprises at least two consecutive transverse walls or projections 124 extending from an inner surface 126 thereof, wherein at least two consecutive transverse walls or projections 124 form a space 128 between them to receive at least a portion of one or both of the pair of diametrically opposed tabs 122 extending radially from the needle unit 108 to securely mount the needle unit 108 within the housing 102. The proximal end 104 of the housing 102 together with at least two consecutive transverse walls or projections 124 of each of the first part of the housing 102a and the second part of the housing 102b define a channel 130 for receiving a syringe tip to engage with the needle hub 116.The distal end 106 of the housing 102 comprises a first contact surface 132 adapted to be placed on the subject's skin and a second contact surface 134, wherein the first end of the needle shaft extends beyond the second contact surface by a predefined distance “d1” to limit the penetration depth of the needle shaft 110. In the embodiment shown, the first contact surface 132 is arranged along the perimeter of the distal end 106 of the housing 102, and the second contact surface 134 is arranged substantially in the center of the distal end 106 of the housing 102. Specifically, the second contact surface is arranged at one end of a needle stabilizing projection 135 that extends substantially in the center from the distal end of the housing. Figures 4(a) and 4(b) illustrate a simplified first part of the housing 102a of the needle adapter 100, where the distal end of the housing 106 lacks the first contact surface 132, to better illustrate how varying the placement of the needle unit 108 within the first part of the housing 102a impacts the predefined distance d1 by which the first end of the needle shaft 112 extends beyond the second contact surface 134. As noted above, as a result of current state-of-the-art manufacturing processes, it is known that final needle lengths will be subject to production tolerances of, for example, 0.05 mm or, for example, 2 mm, as defined in specific ISO standards. The needle adapter described herein allows control of the penetration depth independently of the intended needle length and tolerance deviations.The needle adapter of this application allows the use of needle units with longer needle shafts, such as commercially available (pre-glued) needle units comprising a needle shaft and a hub with a standard female lug-lock fitting, for example, 26-34 G and 12 mm in length. Such needle units may have long needle shafts with wide tolerances, while the needle adapter of this application can precisely control the penetration depth regardless of this tolerance. Therefore, the needle adapter of this application can account for and compensate for manufacturer variability in needle shafts. As can be seen in Figures 2(a) and 2(b), 3(a) and 3(b), and 4(a) and 4(b), the space 128 formed by at least two consecutive transverse walls or projections 124 of the first housing part 102a is configured to receive at least a portion of one or both of the pair of diametrically opposed tabs 122 extending radially from the stylus unit 108 in one of a first orientation (Figure 4(a)) and a second orientation frfrRzrn / zznza / YiAi (Figure 4(b)) of mounting the stylus unit. As is more clearly seen in Figures 4(a) and 4(b), the first and second orientations of mounting the stylus unit can differ from each other by a rotation of approximately 90 degrees.There are stepped stops or flanges 125 on at least one of at least two consecutive transverse walls or projections 124 of the first housing part 102a, which engage with the distal end 118 of the needle hub 116 and facilitate the fixed mounting of the needle unit 108 in either the first or second orientation. The tabs 122 of the needle unit 108 have a frictional engagement with opposing surfaces of at least two consecutive transverse walls or projections 124 of each of the first housing part 102a and the second housing part 102b when received in the space 128 between them, thus avoiding the need to use less desirable means of fixedly mounting the needle unit within the housing, such as gluing, overmolding, etc., as discussed above. As best shown in Figure 4(a), the predefined distance d1 by which the first end 112 of the needle shaft 110 extends out of the second contact surface 134 is a first predefined distance dia when the needle unit 108 is mounted in the first orientation (i.e., when the distal end 118 of the needle hub 116 is oriented with the radially and diametrically opposite pair of tabs 122 extending directly into and out of the plane of the paper in Figure 4(a); this is also referred to herein as the tabs being arranged in a “vertical” position, or V position).As best shown in Figure 4(b), the predefined distance d1 by which the first end 112 of the needle shaft 110 extends out of the second contact surface 134 is a second predefined distance d1b when the needle unit 108 is mounted in the second orientation (i.e., when the distal end 118 of the needle hub 116 is oriented with the pair of diametrically opposed tabs 122 extending radially and side to side as shown in Figure 4(b); this is also referred to herein as tabs arranged in the “horizontal” position, or Position H). As illustrated in Figures 4(a) and 4(b), the first predefined distance d1 is different from the second predefined distance d1b. Again, although the above description refers to the first housing part 102a, it shall be understood that the first housing part 102a is interchangeable with the second housing part 102b, since they are of identical construction. Figure 5 shows a further simplified view of the first simplified housing part 102a shown in Figures 4(a) and 4(b) and also shows a first simplified housing position 202a of the needle adapter body 200 of assembly 201 discussed in more detail below. References to the components / elements of the needle adapter body 200 of assembly 201 discussed below will be provided in parentheses in the labels in Figure 5 and in the following description. The needle unit 108 (208) mates with the first housing part 102a (202a). Figure 5 illustrates the impact of the orientation of the needle unit 108 (208) on the predefined distance d1 (d2) that the first end 112 (212) of the needle shaft 110 (210) extends beyond the second contact surface 134 (234). Table 1 illustrates this in more detail: hbRZQn / zznzji / YiAi Table 1 Ll=Actual length of needle shaft L2=Length of needle shaft within the device L3=Predefined distance di (d2), i.e., penetration depth of the needle shaft Tab orientation 122 (222) Delta relative to the desired di (d2) of 0.85 mm 11.750 11.000 0.750 Position H -0.100 11.800 11.000 0.800 Position H -0.050 11.850 11.000 0.850 Position H 0.000 11.900 11.000 0.900 Position H 0.050 11.950 11.000 0.950 Position H 0.100 12.000 11.250 0.750 Position V -0.100 12.050 11.250 0.800 Position V -0.050 12.100 11.250 0.850 Position V 0.000 12.150 11.250 0.900 Position V 0.050 12.200 11.250 0.950 Position V 0.100 In Figure 5, L1 indicates the length of the needle shaft 110 (210), for example, 12 mm. L2 indicates the length of the needle shaft within the device (2 possible orientations), for example, 11.00 mm with the radially and diametrically opposite pair of tabs 122 (222) extending directly into and out of the plane of the paper (vertical position) and, for example, 11.25 mm with the diametrically opposite pair of tabs 122 (222) extending radially and side to side (horizontal position). L3 indicates the predefined distance d1 (e.g., d1a or d1b for needle adapter 100; d2a or d2b for needle adapter body 200 of assembly 201) that the first end 112 (212) of the needle shaft 110 (210) extends out of the second contact surface 134 (234) (i.e., needle shaft penetration depth). With reference to Table 1, in the case of a 31G needle, an exemplary desired length L3 (predefined distance d1 (d2)) is 0.85 mm. It is further desired that this value be within a specific tolerance of, for example, + / - 0.10 mm (i.e., a tolerance width of 0.20 mm, which varies L3 from 0.75 to 0.95 mm). From the inventors' experience, it is known that a standard 31G needle of, for example, L1 12 mm has a manufacturing tolerance that can significantly exceed the desired specific tolerance of, for example, + / - 0.10 mm. As such, in the absence of a means in the present needle adapter to account for manufacturer variability in needle shafts, the ability to use commercially available needle units would be severely hampered.However, by having the ability to mount the needle unit 108 (208) in two different orientations within the housing 102 (202) to adjust the predefined distance d1 (d2) that the first end 112 (212) of the needle shaft 110 (210) extends from the second contact surface 134 (234), it is possible to practically double the tolerance width to, for example, 0.45 mm, as illustrated in Figure 5 and Table 1. For example, if the 2 L2 positions have a distance difference of, for example, 0.25 mm (11.00 vs. 11.25 mm), it is possible to operate within the specified tolerance of, for example, + / - 0.10 mm for needle shaft lengths ranging from 11.75 to 12.20 mm (which, in the inventors' experience, is closer to reality).As such, the needle assembly and adapter (discussed later) of the present application have a very significant benefit in that they can take into account and compensate for manufacturer variability in needle shafts. As can be seen in Figures 2(a) and (b), and 3(a) and (b), the first housing part 102a and the second housing part 102b are configured to snap together to form the housing 102. This is achieved by means of fasteners (i.e., snaps) 136 projecting from the inner surface of each of the first housing part 102a and the second housing part 102b, which are configured to engage with complementary grooves 138 formed within an inner housing portion of each of the first housing part 102a and the second housing part 102b in a snap fit. Each of the first part of the housing 102a and the second part of the housing 102b also has complementary ribs 140a and 140b that further assist in securing the first part of the housing 102a and the second part of the housing 102b to form the housing 102.As such, snapping the first part of housing 102a and the second part of housing 102b together to form housing 102 is a simple and straightforward means of permanently joining these two components of housing 102, requiring no use of glue or other means to join these components. As can be seen in particular from Figures 3(a) and (b) and Figures 4(a) and (b) (also present in Figures 2(a) and 2(b), although not specifically labelled to facilitate reading the other figure labels), each of the first housing part 102a and the second housing part 102b further comprises an array of projections 142 extending from the inner surface 126 of a distal end thereof to form a needle guide 144 configured to retain the needle shaft 110 in place. In the embodiment shown, the array of projections comprises at least two needle-stabilizing projections 142 disposed on each side of the needle shaft 110 and offset from each other along a longitudinal axis of the needle shaft 110, each of at least two stabilizing projections 142 having an inclined surface bearing on the needle shaft.These features of the needle adapter stabilize the needle shaft and hold it in a fixed position when assembling the first part of housing 102a and the second part of housing 102b to form housing 102. hhRZQn / zznzu / YiAi In the embodiments shown in Figures 1(a)-(c), 2(a) and (b), etc., the angle between a longitudinal axis of the needle shaft 110 and a tangential plane defined by the first contact surface 132 is approximately 90°. Those skilled in the art will understand that this angle can be varied (e.g., to be in the range of, e.g., from approximately 50° to approximately 175°, from approximately 10° to approximately 170°, from approximately 60° to approximately 120°, e.g., from approximately 80° to approximately 100°) by adjusting the angle at which at least two consecutive transverse walls or projections 124 extend from the inner surface 126 of the first / second housing part (102a / 102b) together with the positioning of other support features (e.g., the needle guide 144). As noted above, the features of the needle adapter 100 can take into account and compensate for manufacturer variability in needle shafts by having the ability to mount the needle unit 108 in two different orientations within the housing 102. If it is necessary to further adjust the predefined distance d1 that the first end 112 of the needle shaft 110 extends from the second contact surface 134, this can be done during the assembly of the needle adapter.Therefore, a method for assembling the needle adapter may comprise: obtaining the first housing part 102a and the second housing part 102b; obtaining the needle unit 108; measuring the length of the needle shaft 110; determining whether the needle unit 108 is to be mounted in the first orientation or the second orientation based on the length of the needle shaft 110; optionally, removing a preselected part p1 from a distal end of each of the first housing part 102a and the second housing part 102b based on the length of the needle shaft 110 and based on whether the needle unit 108 is to be mounted in the first orientation or the second orientation.The needle unit can then be mounted into one of the first housing part 102a and the second housing part 102b in the first or second orientation by inserting at least a portion of one or both of the pair of diametrically opposed tabs 122 extending radially from the needle unit 108 into the space 128 formed between at least two consecutive transverse walls or projections 124; and coupling the first housing part 102a and the second housing part 102b together to form the housing 102. Figure 6 illustrates a perspective view of the first housing part 102a, showing how a preselected portion p1 from a distal end of the first housing part 102a can be removed during assembly of the needle adapter 100 to account for manufacturer variability in needle shaft lengths (the preselected portion p1 is shown in exaggerated detail for ease of visualization).It will be understood that the same preselected part p1 of a distal end of the second housing part 102b would also be removed during the assembly of the needle adapter 100. Removing the preselected portion p1 from the distal end of each of the first housing part 102a and the second housing part 102b may comprise cutting the preselected portion p1 from the distal end of each of the first housing part 102a and the second housing part 102b, such as by laser cutting. The assembly process may be further automated so that a vision / imaging system (“Machine Vision”) on an automated assembly line (e.g., based on CCD cameras) can determine the needle shaft length (e.g., with an accuracy of 0.005 mm), the orientation of the needle unit, and whether the removal of a preselected portion from the distal end of each of the first housing part and the second housing part is required. A method for delivering a fluid to a subject by injection using the needle adapter described above may comprise: (a) obtaining the needle adapter; (b) obtaining a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe, wherein the syringe or other dosing device is loaded with the fluid to be delivered to the subject; (c) inserting the tip of the syringe or other dosing device into the channel provided at the proximal end of the housing to engage the tip with the needle hub; (d) coupling the first contact surface with the subject's skin; (e) pushing the housing against the skin to allow the first end of the needle shaft to penetrate the skin; and (f) expelling the fluid from the syringe or other dosing device through the needle shaft into the subject. Figures 7(a) and (b) show a simplified cross-sectional view of one embodiment of the needle adapter 100 held with a syringe 146, thus forming an injection device 149 for delivering a fluid to a subject by injection. Figure 7(c) illustrates a perspective view of the injection device 149 shown in Figures 7(a) and (b). As shown in Figures 7(a) and (b), the tip 148 of the syringe (or other dosing device) can be inserted into the channel 130 arranged in the proximal end 104 of the housing 102 to secure the tip 148 with the needle hub 116. As shown in Figure 7(b), the first contact surface 132 mates with the subject's skin 150. Pushing the housing 102 against the skin 150 allows the first end 112 of the needle shaft 110 (extending from the second contact surface 134) to penetrate the skin 150. The fluid can then be expelled from the syringe 146 (or other dosing device) through the needle shaft 110 into the subject. Figure 8 illustrates a series of steps that can be used to deliver a fluid to a subject by injection using the 100 needle adapter. After step 6, the syringe, used removable needle unit, and needle adapter can be disposed of in an appropriate sharps container. The 100 needle adapter described above is particularly suitable for delivering multiple injections of a fluid to a subject. Multiple injections of a fluid may be desirable in certain applications, such as stem cell transplantation. The predefined distance d1 (penetration depth of the 110 needle shaft) for such applications could be, for example, around 1.5 mm. To increase safety, the needle adapter housing 102 could be secured in a safety holder 152 with the first protruding end 112 of the needle shaft 110 to prevent needlestick injuries when the device is not in use (e.g., before or after injection). Figures 9(a)-(d) illustrate a safety holder 152, wherein the safety holder 152 has an open end 154 to receive at least the distal end 106 of the needle adapter housing 102 and a closed end. 156, comprising the closed end 156 and opposing wings 158 for stabilizing the safety holder 152 on a horizontal surface. Figure 9(a) illustrates the safety holder 152. Figure 9(b) illustrates a simplified cross-sectional view of one embodiment of the needle adapter 100 held with a syringe 146, and how the distal end 106 of the needle adapter housing 102 can be received in the open end 154 of the safety holder. Figure 9(c) illustrates the needle adapter housing 102 held with the safety holder 152, with the needle adapter 100 in a simplified cross-sectional view. Figure 9(d) illustrates the needle adapter housing 102 held with the safety holder 152, with the needle adapter 100 in a simplified cross-sectional view, and with the safety holder 152 and the syringe also in cross-sectional view.In the embodiment shown, the safety support 152 includes an indentation around the perimeter of the open end 154 that is configured to fit with the first contact surface 132 of the needle adapter housing 102. As previously stated, the needle adapter 100 can be attached to a dosing device 160 that is compatible with a syringe 146, where the tip of the syringe 148 enters the channel 130 (not shown) of the needle adapter 100 and the dosing device has a plunger 162 that controls the amount of fluid delivered in a single dose. This can allow for multiple-dose injections, such as between, for example, 0.01 or 0.2 ml, or 0.05 mL. Figure 10 illustrates the attachment of a syringe 146 to a dosing device 160, and the attachment of the syringe to the needle adapter 100. Fasteners such as snap fittings or clips could be used to achieve a stable connection between the dosing device 160 and the needle adapter. 100. Alternatively or additionally, as indicated above, other dosing devices besides a syringe may be coupled with the needle adapter 100, wherein the other dosing devices comprise a dispensing tip that is similar in size and shape to a syringe tip. Such other dosing devices could include pre-filled multi-chamber containers (e.g., dual chambers for lyophilized substances and diluents), with means for mixing the chamber components and means for ejecting them from the dosing device (e.g., by means of a plunger, etc.). Figures 11(a) and (c) illustrate an assembly 201 to form an injection device for delivering a fluid to a subject in two slightly different perspective views. Figure 11(b) illustrates a top view of the assembly shown in Figures 11(a) and (c), and Figure 11(d) illustrates a bottom view of the assembly shown in Figures 11(a) and (c). Figure 12 illustrates an exploded view of the assembly shown in Figures 11(a) and (c). As can be seen in Figures 11(a)-(d) and Figures 12, the assembly 201 comprises a leg 231 comprising a first contact surface 232 adapted to be placed on the subject's skin, the leg 231 having a tubular shape to receive a needle adapter body 200. As shown in Figure 12, the needle adapter body 200 comprises: a housing 202 formed by a first housing part 202a and a second housing part 202b, the housing 202 having a proximal end 204 and a distal end 206; and a needle unit 208 fixedly mounted within the housing 202. As with the needle adapter 100 described above, in the present embodiment, the first housing part 202a and the second housing part 202b are of identical construction and can be formed by injection molding of medical-grade plastic (e.g., COC), resulting in very economical production. In the embodiment shown, the housing 202 has a generally cylindrical shape, and each of the first part of the housing 202a and the second part of the housing 202b has a generally semi-cylindrical shape. Figures 13(a) and 13(b) illustrate the first housing portion 202a and how the needle unit 208 can be coupled thereto, showing the first housing portion 202a in front and side view with the needle unit 208 coupled thereto. With reference to Figure 12 and Figures 13(a) and (b), the needle unit 208 comprises: a needle shaft 210 comprising a first end 212 for penetrating the subject's skin and a second end 214 connected to a needle hub 216. The needle hub 216 comprises a distal end 218 connected to the second end 214 of the needle shaft 210 and a proximal end 220 comprising a pair of diametrically opposed, radially extending tabs 222 (only one of which is visible in Figures 12 and 13(a)).In the configuration shown, the 216 needle hub has the typical needle hub tabs that would be found on commercially available needle units comprising a needle shaft and hub that has a standard female LuerLok fitting. Each of the first housing part and the second housing part comprises at least two consecutive transverse walls or projections 224 extending from an inner surface 226 thereof, wherein at least two consecutive transverse walls or projections 224 form a space 228 between them to receive at least a portion of one or both of the pair of diametrically opposed tabs 222 extending radially from the needle unit 208 to securely mount the needle unit 208 within the housing 202. The proximal end 204 of the housing 202 together with at least two consecutive transverse walls or projections 224 of each of the first housing part 202a and the second housing part 202b define a channel 230 for receiving a syringe tip to engage with the needle hub 216.The distal end 206 of the housing 202 comprises a second contact surface 234, wherein the first end 212 of the needle shaft 210 extends beyond the second contact surface 234 by a predefined distance d2 (e.g., d2a or d2b) to limit a penetration depth of the needle shaft. In the embodiment shown, the first contact surface 232 is arranged along the perimeter of a distal end 233 of the leg 231, and the second contact surface 234 is arranged substantially at the center of the distal end 206 of the housing 202. Specifically, the second contact surface 234 is arranged at one end of a stabilizing projection of the needle 235 that extends substantially at the center from the distal end 206 of the housing 202. As will be described in more detail below, the needle adapter body 200 is movably mounted on the leg 231 to allow movement of the needle adapter body 200 from a first position to a second position, wherein: when the needle adapter body 200 is in the first position, the needle shaft 210 is in a retracted position so that the first end 212 of the needle shaft 210 does not extend beyond the first contact surface 232, and when the needle adapter body 200 is in the second position, the first end 212 of the needle shaft 210 extends beyond the first contact surface 232 and out of the second contact surface 234 by the predefined distance d2 to limit the penetration depth of the needle shaft.The assembly further comprises a friction means for inhibiting the movement of the needle adapter body 200 with respect to the leg 231 when the needle adapter body 200 is in the first position, until a predefined static friction force is overcome, and for causing or permitting a sudden acceleration of the needle adapter body 200 towards the leg 231 to increase the speed of the needle shaft 210 to increase the possibility of penetration into the skin. As noted above, Figures 13(a) and 13(b) illustrate the first part of the housing 202a and how the needle unit 208 can be coupled to it, i.e., in a first orientation as shown in Figure 13(a), and a second orientation as shown in Figure 13(b). Similar to that described above with respect to the needle adapter 100, the variation in the placement of the needle unit 208 within the first part of the housing 202a affects the predefined distance d2 by which the first end of the needle shaft 212 extends beyond the second contact surface 234. As noted above, as a result of current state-of-the-art manufacturing processes, the final needle lengths are known to be subject to production tolerances of, for example, 0.05 mm or, for example, 2 mm, as defined in the relevant ISO standards.The needle adapter body, which is part of the assembly described herein, allows control of the penetration depth independently of the intended needle length and tolerance deviations. Therefore, assembly 201 of this application allows the use of needle units with longer needle shafts, such as commercially available (pre-glued) needle units comprising a needle shaft and a hub with a standard female Luer-Lok fitting, for example, 26-34 G and 12 mm in length. Such needle units may have long needle shafts with wide tolerances, whereas assembly 201 of this application can precisely control the penetration depth independently of this, thus taking into account and compensating for manufacturer variability in needle shafts. As best seen in Figures 13(a) and (b), the space 228 formed by at least two consecutive transverse walls or projections 224 of the first part of the housing 102a is configured to receive at least a portion of one or both of the pair of diametrically opposed tabs 222 extending radially from the needle unit 208 in one of a first (Figure 13(a)) and second (Figure 13(b)) orientations of mounting the needle unit 208. As best seen in Figures 13(a) and 13(b), the first and second orientations of mounting the needle unit may differ from each other by a rotation of approximately 90 degrees.The stepped stops or shoulders 225 are present on at least one of at least two consecutive transverse walls or projections 224 of the first part of the housing 202a, which engage with the distal end 218 of the needle hub 216 and facilitate the fixed mounting of the needle unit 208 in either the first or second orientation. The tabs 222 of the needle unit 208 have a frictional engagement with the opposing surfaces of at least two consecutive transverse walls or projections 224 of each of the first part of the housing 202a and the second part of the housing 202b when received in the space 228 between them, thus avoiding the need to use less desirable means of fixedly mounting the needle unit within the housing, such as gluing, overmolding, etc., as discussed above. Continuing with reference to Figures 13(a) and (b), the predefined distance d2 by which the first end 212 of the needle shaft 210 extends out of the second contact surface 234 is a first predefined distance d2a when the needle unit 208 is mounted in the first orientation (i.e., when the distal end 218 of the needle hub 216 is oriented with the pair of radially and diametrically opposite extending tabs 222 extending directly into and out of the plane of the paper in Figure 13(a) - this is also referred to here as the tabs being arranged in a “vertical” position, or Position V).As best shown in Figure 13(b), the predefined distance d2 by which the first end 212 of the needle shaft 210 extends out of the second contact surface 234 is a second predefined distance d2b when the needle unit 208 is mounted in the second orientation (i.e., when the distal end 218 of the needle hub 216 is oriented with the pair of diametrically opposed tabs 222 extending radially and side to side as shown in Figure 13(b); this is also referred to herein as tabs arranged in a “horizontal” position, or Position H). As illustrated in Figures 13(a) and 13(b), the first predefined distance d2a is different from the second predefined distance d2b.Again, although the above description refers to the first part of housing 202a, it will be understood that the first part of frfrRzrn / zznza / YiAi housing 202a is interchangeable with the second part of housing 202b, since they are of identical construction. As indicated above, Figure 5 depicts a first position of simplified housing 202a of the needle adapter body 200 of the assembly 201 discussed in more detail above. In the labels of Figure 5 and in the preceding description thereof, references to the components / elements of the needle adapter body 200 of assembly 201 are provided in parentheses. This description will not be repeated here for the sake of brevity. However, with reference to Figure 5 and its accompanying description, as well as to Table 1, it will be clear to the person skilled in the art that the assembly of the present application has a very significant advantage in that it can account for and compensate for manufacturer variability in needle shafts. As shown in Figures 14(a)-(c), after the needle unit 208 is secured to the first housing part 202a (Figure 14(a)), the second housing part 202b is coupled to the first housing part 202a (Figure 14(b)) to form the needle adapter body 200 (Figure 14(c)). As the expert will appreciate, it is equally possible for the needle unit to be coupled to the second housing part 202b in the same manner as shown for the first housing part 202a in Figures 14(a)-(c), since the first housing part 202a and the second housing part 202b are of identical construction. As can be seen in Figures 12-14, the first housing part 202a and the second housing part 202b are configured to snap together to form housing 202. This is achieved by means of fasteners (i.e., snaps) 236 projecting from the inner surface hbRZQn / zznzAi / YiAi of each of the first housing part 202a and the second housing part 202b, which are configured to engage with complementary grooves 238 formed within an inner housing portion of each of the first housing part 202a and the second housing part 202b in a snap-fit ​​engagement. Each of the first part of the housing 202a and the second part of the housing 202b also has complementary ribs 240a and 240b that further assist in the engagement of the first part of the housing 202a and the second part of the housing 202b to form the housing 202.As such, snapping the first part of housing 202a and the second part of housing 202b together to form housing 202 is a simple and straightforward means of permanently joining these two components of housing 202, requiring no use of glue or other means to join these components. With reference to Figures 12-14, each of the first housing part 202a and the second housing part 202b further comprises an array of projections 242 extending from the inner surface 226 of a distal end thereof to form a needle guide 244 configured to retain the needle shaft 210 in place. In the embodiment shown, the array of projections comprises at least two needle-stabilizing projections 242 arranged on either side of the needle shaft 210 and offset from each other along a longitudinal axis of the needle shaft 210, each of at least two stabilizing projections 242 having an inclined surface that bears on the needle shaft. These features of the needle adapter stabilize the needle shaft and hold it in a fixed position when the first housing part 202a and the second housing part 202b are assembled to form the housing 202. hbRZQn / zznzji / YiAi As with the needle adapter 100 described above, the angle between a longitudinal axis of the needle shaft 210 and a tangential plane defined by the first contact surface 232 is approximately 90°. Those skilled in the art will understand that this angle can be varied (e.g., to be in the range of, for example, approximately 5° to approximately 175°, approximately 10° to approximately 170°, approximately 60° to approximately 120°, for example, approximately 80° to approximately 100°) by adjusting the angle at which at least two consecutive transverse walls or projections 224 extend from the inner surface 226 of the first / second housing part (202a / 202b), along with the positioning of other supporting features (e.g., needle guide 244) and the leg 231, etc. As previously stated, the needle adapter body 200 is movably mounted on the leg 231 to allow movement of the needle adapter body 200 from a first position to a second position. In the configuration shown in Figures 11(a)-(d) and 12, a locking mechanism is present to provide a locked mode and an unlocked mode of the device. The locked mode is a mode of the assembly in which the needle adapter body 200 is prevented from moving axially toward the leg 231, even when an axial force greater than the predefined static friction is exerted on the needle adapter body 200 with respect to the leg 231. The unlocked mode is a mode of the assembly in which the needle adapter body 200 is permitted to move toward the leg 231 when an axial force greater than the predefined static friction is applied to the needle adapter body 200 with respect to the leg 231.The hbRZQn / zznzzi / YiAi locking mechanism shown in Figures 11(a)-(d) and 12 comprises a removable safety clip 264 configured to engage with a portion of the outer surface 266 of the housing 202 to keep the leg 231 and the needle adapter body 200 separated from each other to prevent the needle adapter body 200 from moving axially toward the leg 231. The removable safety clip 264 is formed from an elastic material (e.g., medical-grade plastic) and has a first leg 268 and a second leg 270 extending from a handle or grip 272, wherein the first leg 268 and the second leg 270 define a general C-shape to engage with the outer surface 266 of the housing 202.Other alternative locking mechanisms are known in the art, such as those described in WO2017168015 (A1), for example, the assembly could be unlocked when the leg is rotated with respect to the needle adapter body around the longitudinal axis, resulting in an assembly in the “unlocked state”, allowing the needle adapter body to move towards the leg. As also noted above, the assembly comprises a friction means to inhibit the movement of the needle adapter body 200 relative to the leg 231 when the needle adapter body 200 is in the first position, until a predefined static friction force is overcome, and to cause or permit a sudden acceleration of the needle adapter body 200 toward the leg 231 to increase the speed of the needle shaft 210 to increase the possibility of skin penetration. The predefined static friction force may be a value in the range of approximately 1.0 to approximately 20.0 Newtons, or approximately 1.5 to approximately 15 Newtons, or approximately 2.0 to approximately 10 Newtons, or approximately 5.0 to approximately 7.5 Newtons; preferably, the static friction force is at least approximately 2.0 Newtons. In the embodiment shown in Figure 12, the friction means comprise at least two projections 274 extending from an inner surface 276 of a proximal end 278 of the leg 231, which is in contact with at least two corresponding grooves 280 located on an outer surface 266 of the distal end 206 of the housing 202 of the needle adapter body 200, wherein a radial dimension rd1 defined by at least two projections 274 before the assembly of the needle adapter body 200 and the leg 231 (see Figure 15) is smaller than a radial dimension rd2 defined by at least two corresponding grooves 280 (see Figure 17(a)-(b)), static friction being provided by radial clamping. This is described in more detail below. At least two corresponding grooves 280 are generally oriented parallel to a longitudinal axis of the housing 202. The first means of friction shall be understood to comprise equivalently at least two projections extending from an outer surface of the body that is in contact with at least two corresponding grooves located on an inner surface of the leg, wherein a radial dimension defined by at least two projections prior to the assembly of the body and leg is greater than a radial dimension defined by the grooves, static friction being provided by radial clamping. Figure 15 illustrates a perspective view of the needle adapter body 200 and the leg 231, in which at least two projections 274 extending from an inner surface 276 of a proximal end 278 of the leg 231 and at least two corresponding grooves 280 located on an outer surface 266 of the distal end 206 of the housing 202 of the needle adapter body 200 can be clearly seen. Figure 16 provides an enlarged perspective view of the needle adapter body 200 to better illustrate the contours of the groove 280. As can be seen more clearly in Figure 16, at least two corresponding grooves 280 (one shown) are configured to prevent the leg 231 from disengaging from the needle adapter body 200 by limiting the movement of the leg 231 away from the needle adapter body 200 following the engagement of at least two projections 274 extending from the inner surface 276 of the proximal end 278 of the leg 231 with at least two corresponding grooves 280. The groove portion 280a of each of at least two corresponding grooves 280 is angled slightly towards the center of the needle adapter body 200 to facilitate the initial engagement of at least two projections 274 with at least two corresponding grooves 280.However, once at least two projections 274 engage with at least two corresponding grooves 280 and move toward the distal end 206 of the housing 202 to reach the groove portion 280b of each of at least two corresponding grooves 280, it can be seen that the movement of the leg 231 away from the needle adapter body 200 is limited by a flange 281 formed between the groove portion 280b and the groove portion 280a (which projects upward from the groove portion 280b at an angle of approximately 90 degrees). At this point, static friction is provided by the radial clamping, as previously described.When the locking mechanism disengages and the predefined static friction force is exceeded—that is, when hbRZQn / zznzzi / YiAi exerts an axial force greater than the predefined static friction on the needle adapter body relative to the shank—at least two protrusions 274 move toward the grooved portion 280c of each of at least two corresponding grooves 280, where the friction between the surfaces undergoes a sudden decrease and / or drops to zero. This causes or allows a sudden acceleration of the needle adapter body 200 toward the shank 231 to increase the speed of the needle shaft 210 and thus increase the likelihood of skin penetration. As shown in Figures 15 and 16, the assembly further comprises at least two deactivation slots 282 located on the outer surface 266 of the distal end 206 of the housing 202 of the needle adapter body 100, where each of at least two deactivation slots 282 intersects one of at least two corresponding slots 280 at an angle theta (Θ) (about 25° to about 65°, for example, about 45°) with respect to the longitudinal axis of the housing 202, such that axial movement of the leg 231 away from the needle adapter body 200 and rotation of the leg 231 relative to the needle adapter body 200 engages at least two projections 274 with at least two deactivation slots 282 (one is shown), where each of at least two deactivation slots 282 comprises an indentation 284 complementary to a form of each of at least two projections 274 for securely fastening each of at least two projections 274,so that the needle adapter body 200 is held in a fixed off position with respect to leg 231, wherein the first end 212 of the needle shaft 210 does not extend beyond the first contact surface 232 when the needle adapter body 200 is in the fixed off position with respect to leg 231. hhRZQn / zznzu / YiAi Figure 17(a) illustrates one embodiment of an assembly 201 in perspective (top) and cross-section (bottom) in which the safety clip 264 has been removed and the needle adapter body 200 is in the first position (i.e., ready for injection). Figure 17(b) illustrates the assembly 201 in perspective (top) and cross-section (bottom; showing the subject's skin 250) in which the safety clip 264 has been removed and the needle adapter body 200 is in the second position (i.e., the needle penetrates the skin). Figure 17(c) illustrates the assembly 201 in perspective (top) and cross-section (bottom) where the needle adapter body 200 is held in a fixed off position with respect to the leg 231 (from the second position, it involves an axial movement of the leg 231 away from the needle adapter body 200 and rotation of the leg 231 with respect to the needle adapter body 200). As shown in Figures 17(a)-(c), the movement of the device from the first position to the second position causes or permits a sudden acceleration of the needle adapter body 200 towards the leg 231, and the needle stabilizer projection 235 passes through an opening 286 formed by an inner surface 288 of the leg 231 as it accelerates towards the skin 250. As previously stated, the features of the needle adapter body 200 of assembly 201 can account for and compensate for manufacturer variability in needle shafts by allowing the needle unit 208 to be mounted in two different orientations within the housing 202. If it is necessary to further adjust the predefined distance d2 that the first end 212 of the needle shaft 210 extends from the second contact surface 234, this can be done during assembly of the device. Therefore, one method for assembling the assembly may include: obtaining the leg 231; obtaining the first housing part 202a and the second housing part 202b, forming the housing 202 of the needle adapter body 200; obtaining the needle unit 208; obtaining the removable safety clip 264; and measuring the length of the needle shaft 210. determine whether the 208 needle unit is to be mounted in the first orientation or the secondorientation based on the length of the needle shaft 210; optionally, removing a preselected portion p2 from a distal end of each of the first housing part 202a and the second housing part 202b depending on the length of the needle shaft 210 and depending on whether the needle unit 208 is to be mounted in the first orientation or the second orientation; mounting the needle unit 208 in one of the first housing part 202a and the second housing part 202b in the first or second orientation by inserting at least a portion of one or both of the pair of diametrically opposed tabs 222 extending radially from the needle unit 208 into the space 228 formed between at least two consecutive transverse walls or projections 224; and coupling the first housing part 202a and the second housing part 202b together to form the housing 202 of the needle adapter body 200; attach the removable safety clip 264 to the part of theouter surface 266 of the housing 202; and coupling the leg 231 and the needle adapter body 200. Coupling the leg 231 and the needle adapter body 200 comprises coupling at least two projections 274 extending from the inner surface 276 of the proximal end 278 of the leg 231 with at least two corresponding grooves 280 located on the outer surface 266 of the distal end 206 of the housing 202 of the hbRZQn / zznzzi / YiAi needle adapter body 200. The preselected portion p2 of a distal end of each of the first housing part 202a and the second housing part 202b can be removed from the needle stabilizing projection 235, similarly to how shown in Figure 6 with respect to the needle adapter 100 described above. Removing the preselected portion p2 from the distal end of each of the first housing part 202a and the second housing part 202b may comprise cutting the preselected portion p2 from the distal end of eachone of the first housing part 202a and the second housing part 202b, as laser cut. The assembly process can be further automated by using a vision / imaging system (“Machine Vision”) on an automated assembly line (e.g., based on CCD cameras) that incorporates robotic “pick and place” technology to assemble the device. The overall assembly process can proceed as follows: 1. Prefabricated components: housing cover, i.e., first and second housing parts 202a and 202b (2x, injection molded); safety clip 264 (injection molded); leg 231 (injection molded); needle unit 208 (preferably obtained from an FDA-approved source) 2. Supply of components in the system (manual or (semi)automatic): in feeders (e.g., for injection-molded components); in trays or racks (e.g., for needle units) The following steps 3 or 4 can be executed in parallel or in random order relative to each other. frfrRzrn / zznza / YiAi 3. An imaging system that measures the exact length of the needle shaft 112 (e.g., with an accuracy of 0.005 mm) 4. Two housing covers (202a and 202b) are prepared / supplied in the automated system. Step 5 is optional 5. The stabilizing protrusion of the needle 235 on both housing covers 202a and 202b can be laser engraved to improve the final length of the needle shaft for skin penetration) 6. The needle is placed in 1 housing cover (202a), for example, horizontal wings or, for example, vertical wings to compensate for the length deviations of step 3. 7. The second housing cover (e.g., identical) (202b) is mounted (e.g., automatically) (e.g., snapped into place). Step 8 is optional / related to quality 8. Take measurements (images) of the residual length (penetration) of the needle shaft. 9. Safety clip 264 is installed 10. Install pin 231 Figure 18(a) illustrates a proposed automated assembly line for preparing assembly 201 using machine vision and robotic pick-and-place technology. “Housing 1” and “Housing 2” refer to the first and second housing parts 202a and 202b, “Needle” refers to the needle unit 208, “Housing Mount” refers to the mounting of the needle unit 208 on one of the first and second housing parts 202a / 202b, “Extraction Pin” refers to the safety clip 264, and “Leg” refers to the leg 231. frfcRzrn / zznza / YiAi The various components are placed on the production conveyor, which moves along the assembly line via a conveyor belt. Figure 18(b) illustrates the composition of the production conveyor at each stage of assembly. The components can be held in the holder by engaging grooves that can be formed during their injection molding, and / or they can be held in place by a slight vacuum or other means known to those skilled in the art. As the skilled worker will appreciate, it is very convenient to be able to manufacture assembly 201 from pre-molded, injection-molded components that can be assembled by press-fitting (as opposed to using glue or other joining methods). Furthermore, the ability to automate the manufacturing of assembly 201 significantly reduces production costs. However, it is, of course, also possible to manufacture assembly 201 manually. A method for administering a fluid to a subject by injection using the assembly 201 may comprise: (a) obtaining the assembly 201, wherein the needle adapter body 200 is in the first position; (b) obtaining a syringe 246 or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe, wherein the syringe 246 or other dosing device is loaded with the fluid to be administered to the subject; (c) inserting the tip 248 of the syringe 246 or the other dosing device into the channel 230 disposed in the proximal end 204 of the needle adapter housing 202 to engage the tip with the needle hub 216; (d) engaging the first contact surface 232 of the shank 231 with the subject's skin;(e) pushing the housing 202 of the needle adapter body 200 towards the leg 231 in an axial direction to move the needle adapter body 200 from the first position to the second position, thereby causing the first end 212 of the needle shaft 210 to penetrate the skin; (f) expelling fluid from the syringe 246 or other dosing device through the needle shaft 210 into the subject; and (g) pull the housing 202 of the needle adapter body 200 away from the leg 231 in an axial direction and rotate the leg 231 with respect to the needle adapter body 200 to engage at least two projections 274 with at least two deactivation slots 284 and fixably engage each of at least two projections 274 in the indentation 284 in each of at least two deactivation slots 282, so that the needle adapter body 200 is held in the fixed deactivated position with respect to the leg;further comprising the method of removing the safety clip 264 from the outer surface 266 of the housing 202 after step (c) and before step (d), or after step (d) and before step (e). As indicated above, other dosing devices could include pre-filled multi-chamber containers (e.g., double chambers for lyophilized substances and diluents), with means for mixing the chamber components and means for ejecting them from the dosing device (e.g., via a plunger, etc.). Figure 19 illustrates a series of steps that can be used to deliver a fluid to a subject by injection using assembly 201. As stated above, the assembly 201 described herein is particularly suitable for single use. Figures 20(a) and (b) show a simplified cross-sectional view of one embodiment of the assembly 201 coupled with a syringe 246, thus forming an injection device 249 for delivering a fluid to a subject by injection. As can be seen in Figures 20(a) and (b), the locking mechanism is absent, and the needle adapter body 200 is in the second position in which the needle shaft 210 penetrates the skin 250 (shown in Figure 20(b)). Figure 20(c) illustrates a perspective view of the injection device 249 shown in Figures 20(a) and (b). Although the present invention has been described with reference to preferred embodiments, it should be understood that modifications and variations may be made without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the scope and reach of the invention and the attached claims.

Claims

1. A needle adapter for forming an injection device for delivering a fluid to a subject comprising: a housing formed by a first housing part and a second housing part, wherein the housing has a proximal end and a distal end; a needle unit fixedly mounted within the housing, wherein the needle unit comprises: a needle shaft comprising a first end for penetrating the subject's skin and a second end connected to a needle hub, the needle hub comprising a distal end connected to the second end of the needle shaft and a proximal end comprising a pair of diametrically opposed, radially extending flanges;wherein each of the first housing part and the second housing part comprises at least two consecutive walls or transverse projections extending from an inner surface thereof, wherein at least two consecutive walls or transverse projections form a space between them to receive at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit to securely mount the needle unit within the housing; wherein the proximal end of the housing together with at least two consecutive walls or transverse projections of each of the first housing part and the second housing part define a channel for receiving a syringe tip for coupling with the needle hub;wherein the distal end of the housing comprises a first contact surface adapted to be placed on the subject's skin and a second contact surface, wherein the first end of the needle shaft extends out of the second contact surface by a predefined distance to limit a penetration depth of the needle shaft.

2. The needle adapter according to claim 1, wherein the space formed by at least two consecutive transverse walls or projections of each of the first housing part and the second housing part is configured to receive at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit in a first and a second mounting orientation of the needle unit, wherein: the predefined distance by which the first end of the needle shaft extends beyond the second contact surface is a first predefined distance when the needle unit is mounted in the first orientation, and the predefined distance by which the first end of the needle shaft extends beyond the second contact surface is a second predefined distance when the needle unit is mounted in the second orientation,where the first predefined distance is different from the second predefined distance.

3. The needle adapter according to claim 1 or 2, wherein at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit has a friction coupling with opposing surfaces of at least two consecutive transverse walls or projections of each of the first housing part and the second housing part when received in the space between them.

4. The needle adapter according to any of claims 1-3, wherein the first housing part and the second housing part are configured to snap together to form the housing.

5. The needle adapter according to any of claims 1-4, wherein each of the first housing part and the second housing part further comprises a variety of projections extending from the inner surface of a distal end thereof to form a needle guide configured to hold the needle shaft in place.

6. The needle adapter according to claim 5, wherein the array of projections comprises at least two needle stabilizing projections arranged on both sides of the needle shaft and offset from each other along a longitudinal axis of the needle shaft, each of at least two needle stabilizing projections having an inclined surface that rests on the needle shaft.

7. The needle adapter according to any of claims 1-6, wherein the first contact surface is arranged along the perimeter of the distal end of the housing, and the second contact surface is arranged substantially centrally on the distal end of the housing. hbRZQn / zznzzi / YiAi 8. The needle adapter according to any of claims 1-7, wherein the first housing part and the second housing part have at least substantially similar or identical construction.

9. The needle adapter according to any of claims 1-8, wherein the housing is generally cylindrical in shape.

10. The needle adapter according to any of claims 1-9, wherein each of the first housing part and the second housing part have a generally semi-cylindrical shape.

11. An assembly for forming an injection device for delivering a fluid to a subject, the assembly comprising: a leg comprising a first contact surface adapted to be placed on the subject's skin, the leg having a tubular shape to receive a needle adapter body; a needle adapter body comprising: a housing formed by a first housing part and a second housing part, the housing having a proximal end and a distal end; a needle unit fixedly mounted within the housing, wherein the needle unit comprises: a needle shaft comprising a first end for penetrating the subject's skin and a second end connected to a needle hub, the needle hub comprising a distal end connected to the second end of the needle shaft and a proximal end comprising a pair of diametrically opposed, radially extending flanges;hfrRZQn / zznzu / YiAi wherein each of the first housing part and the second housing part comprises at least two consecutive walls or transverse projections extending from an inner surface thereof, wherein at least two consecutive walls or transverse projections form a space between them to receive at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit to securely mount the needle unit within the housing; wherein the proximal end of the housing together with at least two consecutive walls or transverse projections of each of the first housing part and the second housing part define a channel for receiving a syringe tip for coupling with the needle hub;and wherein the distal end of the housing comprises a second contact surface, wherein the first end of the needle shaft extends out of the second contact surface by a predefined distance to limit the penetration depth of the needle shaft;the needle adapter body being movably mounted on the leg to allow movement of the needle adapter body from a first position to a second position, wherein: when the needle adapter body is in the first position, the needle shaft is in a retracted position so that the first end of the needle shaft does not extend beyond the first contact surface, and when the needle adapter body is in the second position, the first end of the needle shaft extends beyond the first contact surface and out of the second contact surface by a predefined distance to limit the penetration depth of the needle shaft;hbRZQn / zznzzi / YiAi further comprising a friction means for inhibiting the movement of the needle adapter body relative to the shank when the needle adapter body is in the first position, until a predefined static friction force is overcome, and for causing or permitting a sudden acceleration of the needle adapter body towards the shank to increase the speed of the needle shaft to increase the possibility of penetration into the skin.; 12. The assembly according to claim 11, wherein the space formed by at least two consecutive transverse walls or projections of each of the first housing part and the second housing part is configured to receive at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit in a first and a second mounting orientation of the needle unit, wherein: the predefined distance by which the first end of the needle shaft extends beyond the second contact surface is a first predefined distance when the needle unit is mounted in the first orientation, and the predefined distance by which the first end of the needle shaft extends beyond the second contact surface is a second predefined distance when the needle unit is mounted in the second orientation,where the first predefined distance is different from the second predefined distance. hbRZQn / zznzzi / YiAi, 13. The assembly according to claim 11 or 12, wherein at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit has a friction coupling with the opposing surfaces of at least two consecutive walls or transverse projections of each of the first housing portion and the second housing portion when received in the space between them.

14. The assembly according to any of claims 11-13, wherein the first housing part and the second housing part are configured to snap together to form the housing.

15. The assembly according to any of claims 11-14, wherein each of the first housing part and the second housing part further comprises a variety of projections extending from the inner surface of a distal end thereof to form a needle guide configured to hold the needle shaft in place.

16. The assembly according to claim fifteen, wherein the array of projections comprises at least two needle stabilizing projections arranged on each side of the needle axis and offset from each other along a longitudinal axis of the needle axis, each of the at least two needle stabilizing projections having an inclined surface that abuts the needle axis.

17. The assembly according to any of claims 11-16, wherein the first contact surface is arranged along the perimeter of a distal end of the leg, and the second contact surface is arranged substantially in the center of the distal end of the housing.

18. The assembly according to any of claims 11-17, wherein the first part of the housing and the second part of the housing have at least substantially similar or identical construction.

19. The assembly in accordance with any of claims 11-18, wherein the housing is generally cylindrical in shape.

20. The assembly according to any of claims 11-19, wherein each of the first housing part and the second housing part have a generally semi-cylindrical shape.

21. The assembly according to any of claims 11-20, wherein the friction means comprises at least two projections extending from an inner surface of a proximal end of the leg that is in contact with at least two corresponding grooves located on an outer surface of the distal end of the needle adapter body housing, wherein a radial dimension defined by at least two projections prior to the assembly of the needle adapter body and the leg is smaller than a radial dimension defined by at least two corresponding grooves, static friction being provided by radial clamping.

22. The assembly according to claim 21, wherein at least two corresponding grooves are configured to prevent decoupling of the leg from the needle adapter body by limiting the movement of the leg away from the needle adapter body after coupling by at least two projections extending from the inner surface hhRzcn / zznzAi / YiAi of the proximal end of the leg with at least two corresponding grooves.

23. The assembly according to claim 21 or 22, wherein at least two corresponding slots are generally oriented parallel to a longitudinal axis of the housing.

24. The assembly according to claim 23, further comprising at least two deactivation slots located on the outer surface of the distal end of the needle adapter body housing, wherein each of the at least two deactivation slots intersects one of at least two corresponding slots at an angle with respect to the longitudinal axis of the housing, such that axial movement of the leg away from the needle adapter body and rotation of the leg with respect to the needle adapter body engages with at least two projections having at least two deactivation slots, wherein each of the at least two deactivation slots comprises an indentation complementary to the shape of each of the at least two projections for securely fastening each of the at least two projections, such that the needle adapter body is held in a fixed deactivated position relative to the leg,where the first end of the needle shaft does not extend beyond the first contact surface when the needle adapter body is in the fixed, deactivated position relative to the leg.

25. The assembly according to any of claims 11-24, further comprising a locking mechanism to provide a locked mode and an unlocked mode of the device, the locked mode being a mode of the assembly in which the needle adapter body is prevented from moving axially towards the leg, even when an axial force greater than the predefined static friction is exerted on the needle adapter body with respect to the leg; the unlocked mode being a mode of the assembly in which the needle adapter body is permitted to move towards the leg when an axial force greater than the predefined static friction is applied to the needle adapter body with respect to the leg.

26. The assembly according to claim 25, wherein the locking mechanism comprises a removable safety clip configured to engage with a portion of the outer surface of the housing to keep the leg and needle adapter body separated from each other to prevent the needle adapter body from moving axially towards the leg.

27. A method for assembling the needle adapter according to claim 1, the method comprising: obtaining the first housing part and the second housing part; obtaining the needle unit; optionally, measuring a length of the needle shaft and removing a preselected portion from a distal end of each of the first housing part and the second housing part based on the length of the needle shaft; mounting the needle unit onto one of the first housing part and the second housing part by inserting at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit into the space formed between at least two transverse walls or projections; and coupling the first housing part and the second housing part together to form the housing.

28. A method for assembling the needle adapter according to claim 2, the method comprising: obtaining the first housing part and the second housing part; obtaining the needle unit; measuring the length of the needle shaft; determining whether the needle unit is to be mounted in the first orientation or the second orientation based on the length of the needle shaft; optionally, removing a preselected portion from a distal end of each of the first housing part and the second housing part based on the length of the needle shaft and on whether the needle unit is to be mounted in the first orientation or the second orientation;mounting the needle unit in one of the first housing part and the second housing part in the first or second orientation by inserting at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit into the space formed between at least two consecutive transverse walls or projections; and coupling the first housing part and the second housing part together to form the housing.

29. The method according to claim 27 or 28, in frfrRzrn / zznza / YiAi wherein at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit has a friction coupling with the opposing surfaces of at least two consecutive walls or transverse projections of each of the first housing portion and the second housing portion when received in the space between them.

30. The method according to any of claims 27-29, wherein the first housing part and the second housing part are configured to snap together to form the housing.

31. The method according to any of claims 27-30, wherein each of the first housing part and the second housing part further comprises a variety of projections extending from the inner surface of a distal end thereof to form a needle guide configured to hold the needle shaft in place.

32. The method according to claim 31, wherein the variety of projections comprises at least two needle stabilizing projections disposed on each side of the needle shaft and offset from each other along a longitudinal axis of the needle shaft, each of the at least two needle stabilizing projections having an inclined surface that abuts the needle shaft when the needle unit is mounted on one of the first housing part and the second housing part.

33. The method according to any of claims 27-32, wherein the first contact surface is arranged along the perimeter of the distal end of the housing, and the second contact surface is arranged substantially in the center of the distal end of the housing.

34. The method according to any of claims 27-33, wherein the first part of the housing and the second part of the housing have at least substantially similar or identical construction.

35. The method in accordance with any of claims 27-34, wherein the housing is generally cylindrical in shape.

36. The method according to any of claims 27-35, wherein each of the first housing part and the second housing part have a generally semi-cylindrical shape.

37. The method according to any of claims 27-36, wherein the removal of the preselected portion of the distal end of each of the first housing part and the second housing part comprises cutting the preselected portion of the distal end of each of the first housing part and the second housing part, for example, by laser cutting.

38. The method in accordance with any of claims 27-37, wherein the method is automated.

39. A method for assembling the assembly according to claim 11, wherein the assembly optionally further comprises a locking mechanism comprising a removable safety clip configured to engage with a portion of the outer surface of the housing to keep the shank and the needle adapter body separated from each other to prevent the needle adapter body from moving axially toward the shank, the method comprising: obtaining the shank; obtaining the first housing portion and the second housing portion forming the housing of the needle adapter body; obtaining the needle unit; optionally, obtaining the removable safety clip; optionally, measuring a length of the needle shaft and removing a preselected portion from a distal end of each of the first housing portion and the second housing portion according to the length of the needle shaft;Mount the needle unit into one of the first housing part and the second housing part by inserting at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit into the space formed between at least two transverse walls or projections; couple the first housing part and the second housing part together to form the needle adapter body housing; engage the removable safety clip, if present, with the outer surface portion of the housing; and secure the needle adapter leg and body.

40. A method for assembling the assembly according to claim 12, wherein the assembly optionally further comprises a locking mechanism comprising a removable safety clip configured to engage with a portion of the outer surface of the housing to keep the leg and the needle adapter body separated from each other to prevent the needle adapter body from moving axially toward the leg, the method comprising: obtaining the leg; obtaining the first housing portion and the second housing portion forming the housing of the needle adapter body; obtaining the needle unit; optionally, obtaining the removable safety clip; measuring the length of the needle shaft; determining whether the needle unit is to be mounted in the first orientation or the second orientation based on the length of the needle shaft;Optionally, remove a preselected portion from a distal end of each of the first housing part and the second housing part, depending on the needle shaft length and whether the needle unit is to be mounted in the first or second orientation; mount the needle unit in one of the first housing part and the second housing part in the first or second orientation by inserting at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit into the space formed between at least two consecutive walls or transverse projections; and couple the first housing part and the second housing part together to form the needle adapter body housing; engage the removable safety clip, if present, with the portion on the outer surface of the housing;and secure the needle adapter leg and body. hbRZQn / zznzzi / YiAi; 41. The method according to claim 39 or 40, wherein at least a portion of one or both of the pair of diametrically opposed tabs extending radially from the needle unit has a friction coupling with the opposing surfaces of at least two consecutive walls or transverse projections of each of the first housing portion and the second housing portion when received in the space between them.

42. The method according to any of claims 39-41, wherein the first housing part and the second housing part are configured to snap together to form the housing.

43. The method according to any of claims 39-42, wherein each of the first housing part and the second housing part further comprises a variety of projections extending from the inner surface of a distal end thereof to form a needle guide configured to hold the needle shaft in place.

44. The method according to claim 43, wherein the variety of projections comprises at least two needle stabilizing projections arranged on each side of the needle axis and offset from each other along a longitudinal axis of the needle axis, each of the at least two needle stabilizing projections having an inclined surface that abuts the needle axis.

45. The method according to any of claims 39-44, wherein the first contact surface is arranged along the perimeter of a distal end of the leg, and the second contact surface is arranged substantially centrally on the distal end of the housing.

46. ​​The method according to any of claims 39-45, wherein the first part of the housing and the second part of the housing have at least substantially similar or identical construction.

47. The method in accordance with any of claims 39-46, wherein the housing is generally cylindrical in shape.

48. The method according to any of claims 39-47, wherein each of the first housing part and the second housing part have a generally semi-cylindrical shape.

49. The method according to any of claims 39-48, wherein the friction means comprises at least two projections extending from an inner surface of a proximal end of the leg that is in contact with at least two corresponding grooves located on an outer surface of the distal end of the needle adapter body housing, wherein a radial dimension defined by at least two projections prior to assembly of the needle adapter body and the leg is smaller than a radial dimension defined by at least two corresponding grooves, static friction being provided by radial clamping;wherein attaching the shank and the needle adapter body comprises attaching at least two projections extending from the inner surface of the proximal end of the shank to at least two corresponding grooves located on the outer surface of the distal end of the needle adapter body frfcRzrn / zznza / YiAi; 50. The method according to claim 49, wherein at least two corresponding grooves are configured to prevent decoupling of the leg from the needle adapter body by limiting the movement of the leg away from the needle adapter body after coupling by at least two projections extending from the inner surface of the proximal end of the leg with at least two corresponding grooves.

51. The method according to claim 49 or 50, wherein at least two corresponding grooves are generally oriented parallel to a longitudinal axis of the housing.

52. The method according to claim 51, wherein the assembly further comprises at least two deactivation slots located on the outer surface of the distal end of the needle adapter body housing, wherein each of the at least two deactivation slots intersects one of at least two corresponding slots at an angle with respect to the longitudinal axis of the housing, such that axial movement of the leg away from the needle adapter body and rotation of the leg with respect to the needle adapter body engages with at least two projections having at least two deactivation slots, wherein each of the at least two deactivation slots comprises an indentation complementary to the shape of each of the at least two projections for securely fastening each of the at least two projections, such that the needle adapter body is held in a fixed deactivated position relative to the leg,frfrAzrn / zznza / viAi where the first end of the needle shaft does not extend beyond the first contact surface when the needle adapter body is in the fixed off position relative to the leg.

53. The method according to any of claims 39-52, wherein removing the preselected portion from the distal end of each of the first housing part and the second housing part comprises cutting the preselected portion from the distal end of each of the first housing part and the second housing part, for example, by laser cutting.

54. The method in accordance with any of claims 39-53, wherein the method is automated.

55. A method for administering a fluid to a subject by injection, the method comprising: (a) obtaining the needle adapter according to any one of claims 1-10; (b) obtaining a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe, wherein the syringe or other dosing device is loaded with the fluid to be administered to the subject; (c) inserting the tip of the syringe or other dosing device into the channel provided in the proximal end of the housing for securing the tip to the needle hub; (d) coupling the first skin contact surface with the subject; (e) pushing the housing against the skin to allow the first end of the needle shaft to penetrate the skin; (f) expelling the fluid from the syringe or other dosing device through the needle shaft into the subject;and (g) optionally, coupling the needle adapter with a safety holder, wherein the safety holder has an open end for receiving at least the distal end of the needle adapter housing and a closed end, the closed end comprising opposing wings for stabilizing the safety holder on a horizontal surface.; 56. A method for administering a fluid to a subject by injection, the method comprising: (a) obtaining the assembly according to any one of claims 11-26, wherein the needle adapter body is in the first position; (b) obtaining a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe, wherein the syringe or other dosing device is loaded with the fluid to be administered to the subject; (c) inserting the tip of the syringe or other dosing device into the channel provided in the proximal end of the needle adapter housing for securing the tip to the needle hub; (d) coupling the first contact surface of the leg with the subject's skin;(e) pushing the needle adapter body housing towards the leg to move the needle adapter body from the first position to the second position, thereby causing the first end of the needle shaft to penetrate the skin; and (f) expelling fluid from the syringe or other dosing device through the needle shaft into the subject.

57. A method for administering a fluid to a subject by injection, the method comprising: (a) obtaining the assembly according to claim 24, wherein the needle adapter body is in the first position; (b) obtaining a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe, wherein the syringe or other dosing device is loaded with the fluid to be administered to the subject; (c) inserting the tip of the syringe or other dosing device into the channel provided in the proximal end of the needle adapter housing for securing the tip to the needle hub; (d) coupling the first contact surface of the leg with the subject's skin;(e) pushing the needle adapter body housing toward the shank in an axial direction to move the needle adapter body from the first position to the second position, thereby causing the first end of the needle shaft to penetrate the skin; (f) expelling fluid from the syringe or other dosing device through the needle shaft into the subject; and (g) pulling the needle adapter body housing away from the shank in an axial direction and rotating the shank relative to the needle adapter body to engage at least two projections with at least two disengagement slots and fixably engage each of at least two projections in the indentation in each of at least two disengagement slots, so that the needle adapter body is held in the fixed disengagement position relative to the shank;further comprising the method of removing the safety clip from the outer surface of the housing after step (c) and before step (d), or after step (d) and before step (e).; 59. An apparatus comprising: the needle adapter according to any of claims 1-10; a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe, wherein the syringe or other dosing device is optionally loaded with the fluid to be delivered to the subject; optionally, a vial containing the fluid to be delivered to the subject; optionally, a removable needle unit or other means for drawing the fluid from the optional vial into the syringe or other dosing device, the removable needle unit being removable to permit the tip of the syringe or other dosing device to be inserted into the channel of the housing;Optionally, a safety stand, wherein the safety stand has an open end for receiving at least the distal end of the hbRZQn / zznzzi / YiAi needle adapter housing and a closed end, the closed end comprising opposing wings for stabilizing the safety stand on a horizontal surface; and optionally, instructions for use.

60. An apparatus comprising: the assembly according to any one of claim 1126; a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe, wherein the syringe or other dosing device is optionally loaded with the fluid to be delivered to the subject; optionally, a vial containing the fluid to be delivered to the subject; optionally, a removable needle unit or other means for withdrawing the fluid from the optional vial to the syringe or other dosing device, the removable needle unit being removable to permit the tip of the syringe or other dosing device to be inserted into the channel of the housing; and optionally, instructions for use.

61. An injection device comprising: the needle adapter according to any of claims 1-10; and a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe, wherein the syringe or other dosing device is optionally loaded with a fluid for delivery to a subject.

62. An injection device comprising: hbRZQn / zznzzi / YiAi 100 the assembly according to any of claims 1126; and a syringe or other dosing device, wherein the other dosing device comprises a dispensing tip that is similar in size and shape to the tip of a syringe, wherein the syringe or other dosing device is optionally loaded with a fluid for delivery to a subject.

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