A urinary catheter and methods of manufacturing a urinary catheter

Abstract

A urinary catheter and a method of manufacturing a urinary catheter is disclosed. The disclosed method includes the step of using gas-assisted injection moulding, where gas is injected into the melt so as to provide an interior surface of the urinary catheter. This process provides a lower pressure in the mould cavity compared to a regular injection moulding process. Use of gas-assisted injection moulding to provide a urinary catheter is also disclosed.

Description

[0001]A urinary catheter and methods of manufacturing a urinary catheter The invention relates to a urinary catheter as well as methods of manufacturing a urinary catheter. Brief Description of the Drawing The accompanying drawings are included to provide a further understanding of embodiments and are incorporated into and a part of this specification. The drawings illustrate embodiments and together with the description serve to explain principles of embodiments. Other embodiments and many of the intended advantages of embodiments will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts. Figure 1 illustrates a urinary catheter comprising a flex-tip. Figure 2 illustrates a urinary catheter comprising a nelaton tip. Figures 3A to 3D illustrate steps in a manufacturing process of a urinary catheter including gas-assisted injection moulding. Figures 4 and 5 illustrate mould cavities, which can be used in a manufacturing process of a urinary catheter as disclosed herein. Figure 6 illustrates theoretical curves showing pressure as a function of time for a prior art injection moulding process and for a manufacturing process of a urinary catheter including gas-assisted injection moulding process as disclosed herein. Figure 7 illustrate a close-up photo of a portion of a tubular portion of a urinary catheter as disclosed herein. Figures 8-12 schematically illustrate tubular portions of urinary catheters manufactured by gas-assisted injection moulding as disclosed herein. Figures 13A, 14A, illustrate mould cavities and manufacturing processes of a urinary catheter including gas-assisted injection moulding as disclosed herein and figures 13B, 14B illustrate urinary catheters obtained by the manufacturing processes as disclosed herein. Figure 15 illustrates an example of a mould cavity and manufacturing process including gas-assisted injection moulding as disclosed herein. Figures 16, 16A, 16B and 17 illustrate a test set-up and theoretical considerations for dynamic mechanical analysis. Figures 18 and 19 illustrate SEM images of surfaces of urinary catheters. Detailed Description Examples relate to a method of manufacturing a urinary catheter, the urinary catheter comprising a tubular portion, a tip portion, and an outlet portion, the tubular portion comprising an exterior surface and an interior surface defining an interior lumen and a catheter wall extending between the exterior surface and the interior surface, wherein the method comprises the steps of ^ providing a melt of a polymeric material, ^ providing a mould cavity for the melt, the mould cavity defining at least the tip portion and the exterior surface of the urinary catheter, ^ providing an inlet nozzle for the mould cavity, the inlet nozzle comprising a gas-injection nozzle, ^ injecting the melt into the mould cavity so as to fill the mould cavity to a first limit, ^ providing a gas pin for the mould cavity, and ^ injecting gas through the gas pin via the gas-injection nozzle into the melt in the mould cavity, so as to provide an interior lumen wherein the method comprises filling the mould cavity to the first limit with melt and injecting gas into the melt in such a way that the tip portion of the urinary catheter is formed by an overflow of the melt. Further examples relate to a urinary catheter obtained by the method as disclosed above. Even further examples relate to a urinary catheter comprising ^ a tip portion in a proximal insertion portion of the urinary catheter ^ a tubular portion extending from the tip portion and longitudinally to a distal end of the tubular portion, the tubular portion comprising a wall defining an exterior surface and an interior surface defining an interior lumen, wherein the urinary catheter is obtained by gas-assisted injection moulding and wherein the tip portion is obtained by balancing an overflow of melt from the injection moulding process such that the tip portion of the urinary catheter is formed by the overflow of melt, wherein the exterior surface of the tubular portion is a result of an interior surface of the mould cavity and the interior lumen is a result of gas being injected into the melt in the mould cavity. Moreover, examples relate to the use of gas-assisted injection moulding to provide a urinary catheter comprising a tip portion. Examples include the use of gas-assisted injection moulding to provide a urinary catheter comprising a tip portion and an outlet portion. The method of manufacturing a urinary catheter as disclosed herein provides an easily controllable method for providing urinary catheter. Normally, when injection moulding is used for manufacture of elongated structures, such as urinary catheters, typically, pressure in the mould has to be substantial prior to a holding phase. Typically, this is due to the melt having to be put under sufficient pressure to flow entirely around an inner core, which defines the interior lumen of the finished urinary catheters. Thus, in these prior art processes there is very limited room inside the mould cavity. Using gas-assisted injection moulding alleviates the need for an inner core, because the gas flowing into the melt will define the interior lumen of the urinary catheter. Therefore, the pressure inside the cavity can be much lower. A urinary catheter provided by the method disclosed herein will have less resident tension in the material than urinary catheters provided by other methods. This is contemplated to be a result of the lower pressure in the mould cavity during the injection moulding, as gas is used to define the interior lumen rather than an inner core. Furthermore, due to the lower pressure in the mould cavity, the flash resulting from any parting line in the mould cavity will be very small, potentially small enough to simply be ignored in the final product. By using gas-assisted injection moulding it is possible to provide urinary catheters, which already include a tip portion, when they are removed from the mould cavity. It is further possible to provide urinary catheter, which includes a tip portion as well as an outlet portion, when they are removed from the mould cavity. Thereby the post-processing of the urinary catheters will be less extensive. In the following, whenever referring to a proximal end of an element of the invention, the referral is to the end adapted for insertion. Whenever referring to the distal end of an element, the referral is to the end opposite the insertion end. In other words, the proximal end is the end closest to the user, when the catheter is to be inserted, and the distal end is the opposite end – the end furthest away from the user when the catheter is to be inserted. The same definitions apply to the mould cavity used in the manufacturing methods, the proximal end / portion of the mould cavity forms the tip portion of the urinary catheter, and the distal end / portion of the mould cavity forms the opposite end of the urinary catheter, where a handle or connector may later be added. The longitudinal direction is the direction from the distal to the proximal end. The radial direction is the direction perpendicular to the longitudinal direction, which corresponds to the direction across the tubular portion of the catheter. An intermittent urinary catheter typically comprises a tubular portion with an exterior surface, an interior lumen (interior catheter lumen), a catheter wall extending between the exterior surface and the interior lumen and drainage openings extending from the exterior surface of the tubular portion to an interior surface of the tubular portion. The interior surface of the tubular portion defines the interior lumen. The drainage openings are each provided with an exterior annular edge and an interior annular edge and a drainage opening wall. The drainage openings are positioned in a proximal portion of the intermittent urinary catheter. The intermittent urinary catheter is provided with an outlet at a distal end of the catheter; the outlet may be in the form of a connector or a handle or may be coupled to a collecting bag. Usually, intermittent urinary catheters are from size 6 FR (or CH6) to size 18 FR (or CH18). FR (or French size or Charriere (CH)) is a standard gauge for catheters approximately corresponding to the outer circumference in mm. More accurately, the outer diameter of the catheter in mm corresponds to FR divided by 3. Thus 6 FR corresponds to a catheter with an outer diameter of 2 mm and 18 FR corresponds to a catheter with an outer diameter of 6 mm. In context of this disclosure, an outlet portion may in examples mean a handle portion of the urinary catheter. In other examples the outlet portion may refer to a connector portion of the urinary catheter. Some commercially available urinary catheters are provided with a handle portion functioning as the outlet portion of the urinary catheters, for example SpeediCath ® Compact Female marketed by Coloplast A / S or SpeediCath ® Compact Eve also marketed by Coloplast A / S. Other commercially available urinary catheters are provided with a connector, which is configured for being attached to an extension tube. Examples are SpeediCath ® or SpeediCath ® Flex both marketed by Coloplast A / S. In the context of this disclosure, an inlet nozzle is used to indicate a nozzle allowing for inflow of gas into the mould cavity. In some examples disclosed herein, the melt may also be injected into the mould cavity through the same inlet nozzle. In other examples disclosed herein, the melt may be injected into the mould cavity through one or more gate- points, which are different from the inlet nozzle. Urinary catheters manufactured by a process as described herein include a tubular portion with an exterior surface and an interior lumen, as mentioned above. The structure of the exterior surface will bear traces of an interior surface of the mould cavity, including any parting line in the mould cavity. As mentioned above, the flash resulting from any parting line in the mould cavity will potentially be so small that they can be ignored on the final product. In particular, if the final urinary catheter is going to be provided with a hydrophilic coating of the type that swells extensively under influence of liquid. The interior lumen of the final urinary catheter will be formed as a result of gas being injected into the melt. This gas will assist the melt inside the mould cavity in travelling in a direction corresponding to the proximal end portion of the finalised urinary catheter product and eventually form the tip portion of the urinary catheter. Examples disclosed here relate to the filling of the mould cavity to a first limit with injecting gas into the melt in such a way that the tip portion of the urinary catheter is formed by an overflow of the melt. In examples of this disclosure, it has been found that an overflow out of the cavity can be dispensed with, by balancing the filling of melt into the mould cavity to a first limit and thus forming the proximal portion, in particular the tip portion, of the urinary catheter by an overflow of the melt. In other words, the disclosed method provides that the overflow of the melt is retained inside the mould cavity in such a way that no melt flows out of the mould cavity during the gas injection. This includes filling the mould cavity to a first limit, which is less than 100 % and subsequently injecting gas into the mould cavity thereby distributing or pushing forwards the melt towards the proximal end of the mould cavity, thus forming the proximal portion of the urinary catheter. In examples, the first limit is 70% of the volume of the mould cavity. In examples, the first limit is 80% of the volume of the mould cavity. In these examples, the controlling of the overflow may be dispensed with, which provides a more simple setup in the manufacturing process. Other examples include and relate to overflow of melt leaving the mould cavity at a proximal end of the mould cavity through an overspill channel formed in the proximal end of the mould cavity. In some instances, it may be an advantage to let the overflow leave the cavity at the tip portion of the urinary catheter. For this purpose, in examples the mould cavity is provided with an overspill channel at a proximal end of the mould cavity. As a result, the tip portion of the urinary catheter may be provided with a surplus mass at a proximal end. This surplus mass will be able to be removed by breaking it off from the tip portion of the final urinary catheter and this will leave a small proximal opening into the interior lumen of the tubular portion. Breaking off involves the process of removing or separating in the moulding cycle, which may be done by handling it in the demoulding process. Such a small proximal opening in a urinary catheter is sometimes used as a pre- draining opening to assist a user by indicating the correct position of the urinary catheter in the bladder. As soon as the small proximal opening reaches the urine in the bladder, a small amount of urine will flow into the interior lumen of the tubular portion and flow through the urinary catheter to leave the catheter at the outlet end. Due to the flow length through the catheter, there will be a slight delay in time between the small proximal opening reaching the urine in the bladder and the user using the catheter observing urine leaving the catheter. This delay may match the time it takes to correctly position the regular drainage openings of the urinary catheter, typically provided in the catheter wall so as to allow the drainage openings to completely drain urine from the bladder. If a small proximal opening is not present, a user using a urinary catheter may be instructed to enter the urinary catheter in the urinary canal until urine is observed leaving the outlet and then pull the catheter slightly in a distal (outwards) direction so as to ensure correct positioning of the drainage openings in the bladder. This forth and back manoeuvre can be dispensed with when the urinary catheter is provided with a small proximal opening. Such a small proximal opening may be around 0.1 mm or 0.2 mm across the opening or slightly larger such as 0.4, 0.5 or up to 1 mm across the opening. Examples also include relate to the overflow of melt leaving the mould cavity through a plurality of radially extending overspill channels in the mould cavity. Examples include providing six (6) or eight (8) or ten (10) or more overspill channels leading to generation of a corresponding plurality of surplus masses at the side wall of the tubular portion of the urinary catheter. In examples twenty (20) overspill channels are provided with the mould cavity leading to twenty (20) surplus masses at the side wall of the tubular portion of the urinary catheter. When these surplus masses are removed by breaking them off the tubular portion, they leave openings in the side wall of the urinary catheter, which can be used as drainage openings for draining urine from the bladder. This is a novel way of providing multiple drainage openings in a urinary catheter, which significantly reduces production steps and hence time and costs. Such drainage openings can suitably be between 0.1 mm and 1.5 mm as the largest dimension across the drainage openings. In examples the polymeric material for the melt can be selected from one or more of ^ thermoplastic urethanes (TPU) ^ polyolefins in general, for example polyethylene (PE) and polypropylene (PP), ^ Polyvinyl chloride (PVC) ^ Thermoplastic elastomers (TPE) These materials are all good candidates for using during a gas-assisted injection moulding process as described. In examples the gas injected is an inert gas. In related examples, the inert gas is Nitrogen or Carbon Dioxide. In examples the tip portion is a nelaton tip. In examples the tip portion is a flex tip. In the context of this disclosure, a flex tip means that the tip portion transitions from the tubular portion of the urinary catheter to a necked portion, with an outer diameter that is less than the outer diameter of the tubular portion. This necked portion transitions in a proximal direction to a bulb, which forms the proximal end of the urinary catheter. The bulb may have a diameter which is larger than, or smaller than or approximately equal to the diameter of the tubular portion, but in any case, larger than the outer diameter of the necked portion. The bulb may be sphere-shaped, olive- shaped or any similar shape. In examples the tip portion is a coudé tip. In the context of this disclosure, a coudé tip means that the tip portion transitions from the tubular portion through a bend to a rounded off closed tip. In examples the catheter wall comprises a thickness from the exterior surface of the tubular portion to the interior surface of the tubular portion. In examples, the thickness of the catheter wall is substantially the same in a distal portion of the tubular portion and in a proximal portion of the tubular portion. In the context of this disclosure, substantially the same means within 5 %, such that if the thickness in a distal portion is 0.7 mm, then the thickness in the proximal portion is between 0.67 and 0.73 mm. In other examples, the thickness of the catheter wall is larger in a distal portion of the tubular portion than in a proximal portion of the tubular portion. In the context of this disclosure, larger means above 5 %, such as between 5 and 10 % or even larger. For example, the thickness in a proximal portion may be 0.7 mm, and a thickness in the distal portion may be between 0.75 and 0.77 mm. Another example is that the thickness in a proximal portion may be 0.7 mm and a thickness in the distal portion may be 0.8-0.9 mm or 1.0 or 1.1 mm. In examples, a first outer diameter of the tubular portion of the proximal portion of the urinary catheter is smaller than a second outer diameter of the tubular portion of the distal portion of the urinary catheter. The difference in diameter can be obtained either by making a stepwise increase in the diameter of the tubular portion or by making a continuous increase in the diameter of the tubular portion. In examples the first outer diameter of the tubular portion is around 4 mm, corresponding to a CH 12 catheter and the second outer diameter of the of the tubular portion is around 5.3 mm, corresponding to a CH 16 catheter. Other examples include the first outer diameter corresponding to a CH 10 (3.3 mm) and the second outer diameter corresponding to a CH 14 (4.7 mm). In examples, the melt filling phase is followed by a gas injection phase. In examples the filling phase lasts approximately 0.8 s, such as between 0.6 and 1.0 s and the gas injection phase lasts approximately 4 s, such as between 3 s and 5 s. In prior art injection moulding processes, the melt filling phase may be of similar length, and this is then followed by a holding phase under high pressure in the mould cavity of up to a time of 4-5 s. By using the method as disclosed herein, the pressure in the mould cavity can be markedly reduced. The pressure may be reduced by up to 50 % at the end of the melt filling phase and even more reduced during the gas-injection phase, such that the pressure during the gas-injection phase is around 10 % of the pressure during a holding phase under a prior art injection moulding process. In examples, the pressure inside the mould cavity is below 1600 bar (160 MPa) during the melt filling phase and below 200 bar (20 MPa) during the gas-injection phase. In a prior art injection moulding process, the pressure inside the mould cavity is much higher as it is described below in relation to figure 6. Reducing the pressure has the advantage of reducing the requirements for closing of the mould cavity. Furthermore, if the mould cavity comprises a parting line, fins on the final product at this parting line will be markedly reduced compared to products produced by the prior art injection moulding process under higher pressure in the mould cavity. Moreover, reduction of the pressure inside the mould cavity will influence the resulting urinary catheter in that the resident tension in the urinary catheter will be reduced, because the polymer material used in the manufacturing process according to the disclosure will be subjected only to low pressures and uniform pressures along the length of the urinary catheter during the processing. In other words, the uniform cavity pressure on the whole length of the part will reduce tension and warpage of the urinary catheter. More gate-points Examples relate to the injection of melt in the cavity being done by having a single gate- point or alternatively, by having two or more gate-points. More than one gate-point may be an advantage in relation to speed of the moulding process, because by injection in more than one gate-point, the time spend to fill the cavity as well as the distance the melt should travel, will be lowered compared to injection in a single gate-point. In examples, the mould includes two gate points positioned at opposite ends of the mould cavity, such that there is a first gate point at a proximal end of the mould cavity and a second gate point at a distal end of the mould cavity. In examples the mould includes two gate points positioned at a distance between them, such that one gate point is around a middle portion of a proximal portion of the mould cavity and another gate point is around a middle portion of a distal portion of the mould cavity. In examples, two gate points may be positioned between 15 and 25 cm from each other, such as around 20 cm from each other. In examples the mould includes two gate points positioned close together around a middle portion of the mould cavity. In examples, the mould includes three gate points positioned at a distance from each other such as 10-15 cm apart along the length of the mould cavity. In examples the mould includes four gate points positioned at a distance from each other such as 7-10 cm apart along the length of the mould cavity. Examples relate to a method as disclosed herein, wherein the melt is provided as two shots of material so as to allow for co-injection of the melt into the mould cavity. The co-injection may be done either simultaneously or sequentially. By simultaneous co- injection is meant that the two (or more) melts are entered into the mould cavity simultaneously – however, not necessarily through the same gate-point. If two melts are injected into the mould cavity at the same gate point and simultaneously, they may still not intermix completely; it depends on the flowability of each of the two melt materials as well as the processing of the melt materials. For example, one material may flow faster than the other material and will then form the skin at the interior surface of the mould cavity. The other material will then form an inner layer such that the result will be a urinary catheter with a layered tubular portion. It may alternatively be that one material flows towards the proximal end of the mould cavity whereas the other material will set at the distal end of the mould cavity. This will result a urinary catheter which is lengthwise divided. In examples there is provided a urinary catheter as disclosed herein, wherein the urinary catheter is co-injected using gas-assisted injection moulding. In examples, the method further includes a step of removing the urinary catheter from the mould cavity. Removing the urinary catheter from the mould cavity makes the urinary catheter available for post-processing. Examples relate to a method, which further includes the step of coating the exterior surface of the urinary catheter with a hydrophilic coating. Examples relate to a method, which further includes the step of providing drainage openings in the wall. Drainage openings are typically provided in urinary catheters that include closed tip portions, such as a flex-tip or a nelaton tip or the like. In examples the drainage openings are provided by punching. In examples the drainage openings are provided by laser-ablation. In examples relating to urinary catheters, the urinary catheter is an intermittent urinary catheter. Intermittent urinary catheters are configured for being used for draining the bladder by inserting the intermittent urinary catheter into the bladder, drain the bladder and removing the urinary catheter again. This process usually takes about 5-10 minutes and is usually done by the user him- / herself. Examples relate to a urinary catheter obtained by the methods disclosed above and wherein the exterior surface of the urinary catheter is configured to have a liquid contact angle of above 90, or above 100 degrees, such as above 110 degrees. Such a contact angle provides a urinary catheter with a surface with low surface energy. This provides the effect of reducing any formation of bumps at the surface, when holes are cut in the urinary catheter, as further explained below in Example 1. Examples relate to a urinary catheter obtained by the methods disclosed above and wherein the tangens delta value of the material of the manufactured urinary catheter is below 0.1, such as below 0.9. This is believed to be the result of the manufacturing method leading to less resident tension in the polymeric material. Furthermore, there may be less warpage in the urinary catheter as mentioned above. The resulting urinary catheter is believed to potentially be easier to handle for users as explained below in Example 2. Examples include and relate to a urinary catheter obtained by the method as mentioned above including a mould cavity with a plurality of radially extending overspill channels in the mould cavity, wherein the urinary catheter comprises drainage openings resulting from the overspill channels in the mould cavity leaving drainage openings at the side wall of the tubular portion. In examples, the plurality of drainage openings in the final urinary catheter can suitably include 6, 8, 10, 12, 16, 20, 30, 40 or 50 drainage openings. This provides for a urinary catheter with drainage openings that can be tailored according to characteristics of the overspill channels. For example, drainage openings closer to the proximal end of the final urinary catheter can be smaller than drainage openings closer to the distal end of the final urinary catheter, or vice versa, or differently sized drainage openings can be placed alternately along the length of urinary catheter. Other examples include and relate to drainage openings having circular cross sections combined with drainage openings having elliptical or oval or rectangular cross-sections. The combinations of these different drainage openings cross-sections can lead to improved drainage of urine from the bladder and / or other or additional beneficial characteristics of the urinary catheter. Examples include and relate to a urinary catheter as disclosed herein, wherein the urinary catheter includes a flex tip as defined above, and wherein that flex tip is hollow. By hollow is meant that the flex tip is not solid, but rather that the interior lumen of the tubular portion extends into the tip portion and hollows out the tip portion. At least the necked portion of the flex tip will include an interior lumen, and the interior lumen will also extend at least partially into a bulb of the tip portion. This allows for configuring drainage openings to extend into the tip portion, and thus potentially provide for a drainage of urine closer to the very proximal end of the urinary catheter. Furthermore, a hollow flex tip will be even more flexible as the necked portion of the flex tip is hollowed out and includes an interior lumen. This allows for the necked portion to bend easier than compared to a solid necked portion. Examples include and relate to a urinary catheter as disclosed herein, wherein the exterior surface of the tubular portion has a controlled surface roughness. A controlled surface roughness may be determined by specific parameters, for example Ra or VDI. As an example, the VDI value may be controlled to be between 15 and 35. A controlled surface roughness may for example be obtained by grit-blasting or EDM (electrical discharge machining) the mould cavity. An interior surface obtained by EDM will be reproducible. A surface roughness of a urinary catheter which is obtained by using a mould cavity with a an EDM-processed interior surface will be different from a surface roughness of a urinary catheter obtained by extrusion. In case extrusion is used, the surface roughness can be shown to be periodic and finned oppositely of the machining direction, the surface roughness of the catheter resembling sharkskin. In processes applying injection moulding a melt into a mould cavity with an EDM-processed interior surface, the surface roughness can be shown to be randomised. So, for the same or similar Ra value, the resulting Rdc value or Rz value can be different for the two different manufacturing processes. Moreover, in the latter method, the resulting surface roughness of the urinary catheter can be much more well-defined and controlled, as it will be influenced only by the interior surface of the mould cavity and not by any other parameters in the manufacturing process, such as temperature, machining speed and other parameters, which influences the catheter surface roughness parameters in an extrusion process. Examples Various tests showing differences between urinary catheters obtained by gas-assisted injection moulding and extruded urinary catheters were performed. Examples – test specimens. Various tests were performed to compare extruded samples of tubes with tubes manufactured by gas assisted injection moulding as disclosed herein. 5 extruded samples numbered “EX 1” to “EX 5” were prepared and compared to 5 samples manufactured by gas-assisted injection moulding; these were numbered “GI 1” to “GI 5”. All of the samples were tubes in a size suitable for being used for manufacturing urinary catheters (CH 12). In a first step, the outer diameter (OD), the inner diameter (ID) and the wall thickness (WT) of each tube specimen were determined by use of a profile projector of the type Marvision MMA 420. These test results were used in calculation of torsion modulus and tangens delta (see Example 2 below). Table 1 here below show the OD, ID and WT for each test specimen. Table 1 Example 1 – test of surface tension The surface tension of the surfaces was determined by determining the contact angle of water on the surface. This is a measure of the surface tension of the surfaces, because higher surface tension will lead to a higher repellence of the water from the surface. A high repellence may be problematic in relation to a later coating process. The tests were done by using a mobile surface analyzer. A mobile surface analyzer from Krüss were used in these tests. The tests relate to measurement of the contact angle of a drop of liquid on a solid surface. In these tests, one drop of water on the surface was used. The tests were done at 23°C. The mobile surface analyzer has various settings and in these tests the setting “double sessile drop” were used. The analyzer can be set in Circle method mode or Ellipse method mode. Initial testing showed that the measurements were more stable by using the Circle method mode. Each test specimen was set in a fixture developed for the purpose so as to make the test specimen easier to handle and to reduce variation caused by using a handheld apparatus to measure the contact angle. Results of the tests are shown in Table 2 below. Table 2 The results show that there is a significant difference between the contact angles of the test specimens manufactured by gas-assisted injection moulding (GI 1- GI 5) and the test specimens manufactured by extrusion (EX 1 – EX 5). The test specimens manufactured by gas-assisted injection moulding have a contact angle value between 113 and 120, whereas the contact angle values of the extruded test specimens are between 71 and 74. These means that the surface of the test specimens manufactured by gas-assisted injection moulding is more hydrophobic than the extruded test specimens. It also means that the extruded test specimens have a higher surface energy than the test specimens manufactured by gas-assisted injection moulding. The high surface energy may be a result of the resident tension in the material, which may be due to the fact that extrusion and injection moulding without assistance of gas involve tensioning the processed material to a much greater extent than gas-assisted injection moulding as disclosed herein. This is because extrusion involves a rather high pressure of the material in the extruder screw, which will lead to tension in the material during processing, and this tension will be embedded and resident in the material following processing. In a similar, and probably to an even greater extent, injection moulding using an inner core and without the use of gas, involves very high pressures in the cavity mould – see figure 6 below. This will also lead to embedding and fixing of tension in the material following processing. Opposite to this, the very low pressures in the cavity mould, which are used when processing material using gas-assisted injection moulding, will lead to almost no tension being embedded and resident in the material following processing. A low surface energy may lead to materials, where bumps or protrusions, which may occur during cutting holes in the material, will be reduced or even completely alleviated. This is due to the fact that low surface energy materials are less prone to have the effect of so-called “spring-back” at the surface, when the surface is penetrated by a cutting tool. For high surface energy materials, the “spring-back” occur, because the energy resident in the surface will suddenly be released, when a hole is cut, and the material will seek back to the original non-tensioned state. Thus, for high surface energy materials bumps are sometimes observed, and even though they are not problematic in use and maybe even be advantageous in some uses, low surface energy materials may be an option to alleviate these bumps. This may be an advantage in some uses, such as drainage openings on urinary catheters. Example 2 – test of dynamic modulus DMA The materials were tested using a method called DMA-method (Dynamic Mechanical Analysis). In this method the materials are subjected to torsional force as illustrated schematically in figures 15, 15A, 15B. When a visco-elastic material is subjected to a force, the induced stress in the material and the resulting strain will have an elastic part and a viscous part. In the DMA-method a sinusoidal force (stress σ) is applied to a material and the resulting displacement (strain ε) is measured. For a perfectly elastic solid, the resulting strain and the stress will be perfectly in phase. For a purely viscous fluid, there will be a 90 degree phase lag of strain with respect to stress. Visco-elastic polymers have the characteristics in-between, where some phase lag will occur during DMA tests. Stress σ and strain ε may be expressed as below: Stress: ^^ ൌ ^^^ ∙ ^^^^^^^^^^^ ^ ^^^Strain: ^^ ൌ ^^^ ∙ ^^^^^^^^^^^^where ω is frequency of strain oscillation, t is time, δ is phase lag between stress and strain. The storage modulus measures the stored energy, representing the elastic portion, and the loss modulus measures the energy dissipated as heat, representing the viscous portion. In other words, the storage modulus represents the immediate response in the material and the loss modulus represents the response occurring over time (the relaxation) of the material. The tensile storage and loss moduli are defined as follows: Storage Modulus: ^^ᇱൌఙబఌ^ ^బ ∙ cos ^^Loss Modulus: Phase angle, Tan (delta): Similarly, for measuring in torsion as shown in figure 13, we can define the shear storage and loss moduli, G' and G''. Complex variables can also be used to express the moduli E and G as follows: ^^ ൌ ^^ᇱ ^ ^^^^ᇱᇱ^^ ൌ ^^ᇱ ^ ^^^^′′where ^^ ൌ √െ1Figure 15 shows a test setup for measuring the G moduli (G’, G’’ and G*) and tangens delta (tanδ) in a material. A test specimen 1 in the form of a short tube with an outer diameter OD and an inner diameter ID (figure 15A) is inserted between an upper clamp 2 and a lower clamp 3. A rod 4 is used to turn the lower clamp 3. When the specimen 1 is subjected to small oscillations of the lower clamp 3, a cross-section of the material will behave as shown in figure 15B. In figure 15B, h indicates the height of the specimen and B is the amplitude of the oscillations induced by the rod – thus the maximum distance a part of the specimen will move is illustrated as 2B at the bottom of the figure. The material will be subjected to torsion and thus allows measuring of shearing moduli. The material is subjected to a sinusoidal strain as indicated above and the resulting stress includes contribution from the storage and the loss as well. The phase shift part of the stress represents the loss and the part in phase with the strain represents the storage. Thus, by determining the phase shift and the amplitude of the stress, it is possible to determine the tangens delta value and the nominal value of the G- modulus. As mentioned earlier, the strain is measured as: ^^ ൌ ^^^ ∙ sin^^^^^^And the induced stress is: ^^ ൌ ^^^^^^ ∙ ^^^ ∙ sin^^^^^ ^ ^^^The stress can also be expressed by the storage and loss moduli in shearing: ^^ ൌ ^^ᇱ^^^^ ∙ ^^^ ∙ sin^^^^^^ ^ ^^ᇱᇱ^^^^ ∙ ^^^ ⋅ cos^^^^^^It can be seen that A(ω) corresponds to the nominal value of the G-modulus and tan δ to the ratio between the loss and the storage modulus: ^^′′ tan ^^ ൌ^^′ A(ω) and δ can be determined from the stress and strain curves, as it appears from figure 14. Results of the testing is shown in Table 3 below Table 3 The results show that the nominal value of the torsion modulus is much higher for the test specimens manufactured by gas-assisted injection moulding than for the test specimens manufactured by extrusion. Opposite to this, it seems that the extruded specimen has a higher phase lag (tangens delta value) than the specimens manufactured by gas-assisted injection moulding. These tests therefore shows that gas-assisted injection moulding will lead to test specimens having a high degree of immediate response to stress induced on them (a high elastic portion) and a low degree of phase lag in the response to stress (a low viscous portion) compared to extruded test specimens, which have a higher degree of phase lag in response to stress (a high viscous portion). The high degree of viscous behaviour of the extruded test specimens may be due to the fact that extrusion and injection moulding without assistance of gas involve tensioning the processed material to a much greater extent than gas-assisted injection moulding as disclosed herein. This is also referred to above in Example 1. A further effect of the low degree of resident tension in urinary catheter manufactured by gas-assisted injection moulding is that such a urinary catheter will be limp and without any tendency to be difficult to bend in one direction or another and without any tendency to stand out by itself, as is sometimes the case with urinary catheters processed by other manufacturing processes. This may potentially lead to a urinary catheter which is easier to handle for user. Detailed Description of the Drawing In figure 1, a urinary catheter 10 as disclosed herein is schematically illustrated. The urinary catheter comprises an elongated tubular portion 11 extending from a proximal portion 12 to a distal portion 13 of the urinary catheter. The tubular portion 11 comprises a wall 14 with a thickness t extending from an exterior surface 15 to an interior surface 16. The interior surface forms an interior lumen 17 of the urinary catheter. Drainage openings 18 may be provided in the wall 14 extending from the exterior surface 15 through the wall 14 to the interior surface 16. In figure 1 only one drainage opening 18 is illustrated, however the urinary catheter can include two or more, such as a plurality, of drainage openings, such as up to 80, or even more than 80 drainage openings. The urinary catheter comprises a tip portion 19 in the proximal portion 12 of the urinary catheter, such that a proximal end 20 of the tip portion 19 is the proximal end of the urinary catheter 10. In the example illustrated in figure 1, the tip portion 19 comprises a flex-tip, which in the context of this disclosure refers to a tip portion comprising a necked portion 21 followed in the proximal direction by a bulb 22. The urinary catheter illustrated in figure 1 also comprises a connector 23 in the distal portion 13 of the catheter 10. Figure 2 schematically illustrates another urinary catheter 30 as disclosed herein. The difference between the urinary catheter 10 of figure 1 and the urinary catheter 30 of figure 2 is that the urinary catheter 30 in figure 2 comprises a tip portion 39 with a nelaton tip, which in the context of this disclosure refers to a tip portion comprising a rounded off proximal end 40. Figures 3A to 3D illustrate steps in a gas assisted injection moulding manufacturing process for a urinary catheter as disclosed herein. The figures illustrate schematically cross-sectional views of melt 50 in a mould cavity 60. In figure 3A, the melt 50 (molten polymeric material) is shown to be injected into the mould cavity 60. The melt 50 begins to solidify as indicated by skin layer 51 where the melt 50 meets / engages with the interior surface 61 of the mould cavity 60, thereby gradually forming the exterior surface (compare reference number 15 in fig.1) of the urinary catheter 10. The mould cavity 60 disclosed in figures 3A-3D is configured for forming a urinary catheter with a nelaton tip, as for example disclosed in figure 2. This means that in a proximal end 62 of the mould cavity 60, the mould cavity 60 is rounded off in a half spherical configuration. In figure 3B, the gas 52 is being injected and flows into a central portion of the melt 50 as indicated. The presence of the gas 52 additionally pushes the melt 50 further into the mould cavity 60 as illustrated. Figure 3C illustrates how the gas 52 displaces the melt 50 gradually and proximally into the mould cavity 60, whereby the melt 50 solidifies along the interior surface 61 of the mould cavity 60 and ultimately reaches the proximal end 62 of the mould cavity 60. As indicated above, part of the melt 50 solidifies immediately upon contact with the interior surface 61 of the mould cavity 60 and thereby creates a skin layer 51. Therefore, the melt 50 is only able to keep flowing in the central portion 63 of the mould cavity 60. This further means that the gas 52 is only able to flow into and displace the central portion of the melt (as indicated particularly in figure 3B). Figure 3D illustrates how ultimately all of the melt 50 has solidified along the interior surface 61 of the mould cavity – and further how the gas 52 has displaced all of the melt 50 along the interior surface 61 and towards the proximal end 62 of the mould cavity. Figures 4 and 5 illustrate two different mould cavities 160, 260 in which a urinary catheter can be moulded in a manufacturing method according to the disclosure. An insert nozzle 170, 270 is, in the illustrated examples, used for forming the distal portion of the urinary catheter. As mentioned in relation to the urinary catheter 10 illustrated in figure 1, the distal portion 13 of the urinary catheter 10 may comprise a connector 23, which according to the disclosed method can be moulded integrally with the tubular portion 11 of the urinary catheter 10. The arrow at the top of figures 4 and 5 indicates that gas is injected through the insert nozzle 170, 270, and that the insert nozzles 170, 270 are provided with a through-going cavity 171, 271 allowing for the gas to pass through. The mould cavities 160, 260 has a longitudinal parting line 165, 265. This parting line 165, 265 allows for the mould to be opened for removal of the final urinary catheter. The parting line 165, 265 is optional and the urinary catheter can instead be removed by pulling the final urinary catheter out of the mould cavity (i.e., in the upward direction in figures 4 and 5). Urinary catheters manufactured by the method as disclosed herein can be easily removed from the mould cavity 160, 260, as the catheters have less resident tension in the material compared to prior art injection moulded urinary catheters. In the illustrated examples in figures 4 and 5, the mould cavities 160, 260 each comprise two mould cavity portions 160a, 160b and 260a, 260b (left / right), divided at the parting lines 165, 265, the mould cavity portions 160a, 160b, 260a, 260b are configured to be moved laterally compared to the longitudinal direction of the mould cavity. This is indicated by the arrows going from left to right on each of the mould cavity portions 160a, 160b, 260a, 260b. In the illustrated examples and method disclosed, the mould cavity is filled to a first limit 166, 266, such that there is an adequate amount of melt in the mould cavity, which allows for the remaining proximal portion of the urinary catheter to be formed by the melt, when the gas is injected into the melt. One difference between the mould cavities 160, 260 disclosed in figures 4 and 5 lies mainly in a difference between the tip portions 162, 262. In figure 4, the tip portion 162 of the mould cavity is configured to provide a flex-tip (see above for a description of a flex- tip). In figure 5, the tip portion 262 is configured to provide a nelaton tip. Figure 6 illustrates a theoretical consideration of pressure inside a mould cavity as a function of the time. The full curve 310 towards the top illustrates pressure inside a mould cavity in a prior art injection moulding process, whereas the dashed curve 320 at the lower level illustrates pressure inside the mould cavity in a gas-assisted injection moulding process as disclosed herein. Ranges are indicated towards the left of the figure. Here, full curve 310 indicates that the range of peak pressure for the prior art injection moulding process is between 1700 bar (170 MPa) and 2800 bar (280 MPa) (indicated as full horizontal lines), whereas dashed curve 320 illustrates the range of peak pressure for the gas-assisted injection moulding process as disclosed herein to be between 500 bar (50 MPa) and 1600 bar (160 MPa) (indicated by dashed horizontal lines). As it appears, there is a significant difference between the pressures according to the two curves 310 and 320. For example, it appears that the peak pressure point 311 reaches around 2500 bar (250 MPa) at the full curve 310, whereas the peak pressure point 321 only reaches around 1300 bar (130 MPa) at the dashed curve 320. The end of the melt filling phase is indicated as the vertical full line 330. The peak pressure is reached at the end of the melt filling phase, which is indicated at the horizontal axis as lasting approx.0.8 s. At this point, in a prior art injection moulding process, the mould cavity is filled around 98 %. In a gas- assisted injection moulding as disclosed herein, the mould cavity may only be filled around 70 % or 80 % at this point, which allows for the melt to be retained inside the mould cavity. For higher percentages of melt filling, an overspill channel as mentioned above can be used. Following the melt filling phase, there is a holding phase for prior art injection moulding. For the gas-assisted injection moulding process disclosed herein, the holding phase also includes a gas-injection phase. The difference between the pressures for the prior art and the novel process is also significant for the holding phase, which is illustrated as the portion of the curves 312, 322 to the right in figure 6. The vertical dashed line 340 indicates the time of transition into the holding / gas-injection phase, which is from approx.2 s and onwards. According to the prior art process, the curve portion 312 is at a level of around 900 bar (90 MPa) during most of the holding phase, whereas according to the method disclosed herein the curve portion 322 is at a level of around 100 bar (10 MPa) for the entire gas-injection (holding) phase. The ranges of the holding phase are indicated as full lines being between 600 bar and 1200 bar (60-120 MPa) for the curve portion 312 and as dashed lines between 10 and 200 bar (1-20 MPa) for the curve portion 322. Figure 7 is a magnified picture illustrating a portion of a tubular portion 411 of a urinary catheter produced by the method disclosed herein. At the exterior surface 415, drainage openings 418 are provided. It can be seen that the surface surrounding the drainage openings 418 is smooth and without protrusions or deformations. It is contemplated that the smooth surface of the exterior surface 415 of the catheter is due to the gas-injection moulding method disclosed herein working at low pressures in the mould cavity and without leaving any resident tension in the urinary catheter as explained above. Therefore, the resulting catheters will have less resident tension in the material following the manufacturing process according to the disclosure. Figures 8-10 illustrate three different urinary catheters, which may be obtained by gas- assisted injection moulding according to the disclosure. The relative dimensions between width and length of the urinary catheters may not be to scale in these figures, as the urinary catheters may be much longer than illustrated compared to the illustrated width. The urinary catheters illustrated in figures 8-10 can all be obtained by co-injection moulding used in connection with gas-assisted injection moulding, as mentioned above. In the embodiment of figure 8, the urinary catheter 510 includes a tubular portion 511, which is divided lengthwise into a proximal portion 512 and a distal portion 513, as indicated at the division 525. There are various ways to obtain such a urinary catheter by using co-injection in relation to gas-assisted injection moulding. One option is to use sequential gas-assisted injection moulding such that a first shot of melt is entered into the cavity followed in sequence by a second shot of melt and then followed by gas being injected into the cavity. As the first shot of melt hardens at the interior surface of the mould cavity, it will form a skin at a distal end of the catheter, i.e. form the distal portion 513 of the urinary catheter. The second shot of melt will flow proximally beyond this first shot of melt and form the proximal portion 512 of the urinary catheter. Finally, the gas will enter and form the interior lumen 517 of the tubular portion of the urinary catheter. Another option is to use several gate-points along the length of the mould cavity. In an example a first gate point at a middle of the proximal portion of the urinary catheter and a second gate-point at a middle of the distal portion of the urinary catheter can be used. The two shots of melt may be entered simultaneously and allowed to flow to the distal and proximal end, respectively, as well as flow towards each other and form the division between the proximal portion and the distal portion. The two shots may also be entered sequentially, if it is believed to be an advantage to allow the first melt to initiate setting before entering the second melt. The gate-points may be positioned in other positions as well, such as in the proximal end and distal end of the mould cavity or close to each other at a middle portion of the mould cavity. Depending on the materials used in the first and second shot, the division 525 may be more or less pronounced. If two shots of the same material are used, the division may be obliterated, whereas, if two different materials is used, the division may be more pronounced. In figure 8, the division 525 is indicated as a well-defined, pronounced division between the proximal portion 512 and the distal portion 513. By using this method, it is possible to obtain a catheter which is more flexible in the proximal end than in the distal end. The division 525 may also be used to indicate a division between drainage portion including drainage openings (the proximal portion) and a portion of the catheter without drainage openings (the distal portion). The division 525 may also be used to indicate an estimated insertion portion of the catheter (the proximal portion) and a distal portion, which can be used to handle the catheter. In figure 9, a urinary catheter 530 obtained by gas-assisted co-injection moulding is illustrated. The urinary catheter 530 includes a first outer layer 531 and a second inner layer 532. The urinary catheter 530 can be obtained by a first shot of melt being entered into the mould cavity forming a skin layer at the entire length of the mould cavity and followed by a second shot of melt being entered into the mould cavity. This will then be followed by gas being introduced into the mould cavity so as to form the interior lumen of the urinary catheter. A layered urinary catheter can be an advantage for various purposes. For example, providing the second inner layer 532 can be useful for providing a necessary buckling strength to the catheter but can have surface properties, which are not as compatible with the mucosal tissue of the urethra and bladder as could be desired. In that case, it can be an advantage to provide a first outer layer, which has good compatibility with the mucosal tissue of the urethra and bladder. Figure 10 illustrates another embodiment of a urinary catheter 540 obtained by gas- assisted co-injection moulding. The urinary catheter includes a distal portion 543 and a proximal portion 542. In the example, this is obtained by co-injection in that a first shot of melt is injected into the mould cavity to form the exterior layer of the distal portion. Following injection of the first shot, a second shot of melt is injected into the mould cavity and flow towards the proximal end and forms the proximal portion of the urinary catheter as well as forming an inner lining to the exterior layer of the distal portion. As a final shot, gas is injected to form the interior lumen. In the illustrated example, the distal portion has a thicker catheter wall with a thickness t2 which is larger than the thickness t1 of the proximal portion – however, this need not be the case as the catheter wall may have a similar thickness throughout the length of the catheter. An exterior layer in the distal portion of the catheter as illustrated can provide an increased buckling strength in that portion of the catheter, whereas the proximal portion of the catheter can be more flexible and thus easier to steer round the S-bent in a male urethra, for example. Figure 11 illustrate a urinary catheter 550, which may be obtained by gas-assisted injection moulding as disclosed herein. As disclosed in relation to figures 8-10 above, the relative dimensions between width and length of the urinary catheters may not be to scale in this figure, as the urinary catheters may be much longer than illustrated compared to the illustrated width. The urinary catheter 500 include a difference in diameter over the length of the urinary catheter. In a proximal portion 552 of the urinary catheter, the outer diameter D1 is smaller than the outer diameter D2 of a distal portion 553 of the urinary catheter. This may be an advantage in relation to handling of the urinary catheter, as a larger diameter D2 is easier to hold on to for a user. Furthermore, the smaller diameter D1 makes it easier to pass the S-bent in a male urethra. In the illustrated urinary catheter 550, the inner diameter d1 in the proximal portion is also smaller than the inner diameter d2 in the distal portion. However, this need not be the case, as the wall thickness in the distal portion may as an alternative increase. In case the inner diameter d1 of the proximal portion is smaller, as illustrated, an increase flow may be obtained because the flow will have a tendency to become more laminar rather than turbulent. Figure 12 illustrate a portion of a urinary catheter 560 including a tip portion 569. Only a portion of a tubular portion 561 is illustrated including an interior lumen 567 of the tubular portion. In this example, the tip portion 569 is a flex tip as shown in figure 1 with a proximal end 570 and a necked portion 571 followed in a proximal direction by a bulb 572. The urinary catheter 560 of figure 11 differs from the urinary catheter 10 in figure 1 in that the tip portion 569 is hollow in the sense that the interior lumen 567 extends into the tip portion 569 and provides a hollow flex-tip. Figure 13A illustrates a portion of a mould cavity 660, which, as illustrated, includes a portion of a urinary catheter 610 with a tubular portion 611, of which only a (proximal) portion is illustrated and a tip portion 619. Figure 13B illustrates a portion of the final urinary catheter 610, when it has been removed or ejected from the mould cavity 660. The tip portion 619 is in this example shown as a flex tip with a necked portion 621 followed in proximal direction by a bulb 622, however, it might as well be another type of tip portion, as mentioned above. Figure 13A illustrates how the melt 650 has been formed into the tubular portion and the tip portion by injection of gas 652 as indicated by the arrow. In a proximal end 662 of the mould cavity, the mould cavity is provided with an overspill channel 663, which leads to an overspill cavity 664. The overspill channel 663 may be used for allowing melt from a potential overfilling of the mould cavity to leave the mould cavity into an overspill cavity 664. This can provide a urinary catheter with a surplus mass 625 (figure 13A), which, by later removal by breaking off the surplus mass 625, advantageously can leave a proximal opening 626 in the proximal end 620 of the urinary catheter (figure 13B). Figures 14A and 14B are similar to figures 13A, 13B and illustrate a portion of a mould cavity 760 and a urinary catheter 710. Figure 14A illustrates a portion of a mould cavity 760, which includes a portion of a urinary catheter 710 with a tubular portion 711, of which only a (proximal) portion is illustrated and a tip portion 719. Figure 14B illustrates a portion of the urinary catheter 710, when it has been removed or ejected from the mould cavity. Similar to figure 13B, the tip portion 719 is in this example shown as a flex tip with a necked portion 721 followed in proximal direction by a bulb 722. Figure 14A illustrates how the melt 750 has been formed into the tubular portion and the tip portion 719 by injection of gas 752 as indicated by the arrow. The mould cavity 760 includes in the example illustrated in figure 14A a number of overspill channels 763a, 763b, 763c, 763d – a total of eight (8) overspill channels are shown, however the reference numbers only refer to four of the overspill channels on the one side of the mould cavity, but the four overspill channels on the opposite side are similar. In the illustrated example, the two proximal-most overspill channels 763a, 763b are narrower across than the two distal-most overspill channels 763c, 763d (this also applies to the opposite overspill channels, not indicated with reference numbers). The overspill channels lead to a first overspill cavity 764a and an opposite second overspill cavity 764b on the opposite side of the mould cavity. The overspill channels 763a, 763b, 763c, 763d suitably provides a urinary catheter with surplus masses 725 (figure 14A), which by later removal by breaking off the surplus masses 725, advantageously can leave a plurality of (here eight shown) drainage openings 727 in the urinary catheter (figure 14B). The drainage openings 727 allow for urine to drain into the interior lumen of the tubular portion 711. The drainage openings 727 are illustrated as having different sizes, such that the proximal-most drainage openings are smaller across than the distal-most drainage openings. The size is determined by the characteristics of the overspill channels 763a, 763b, 763c, 763d. Figure 15 is intended to illustrate how more than one gate point can be used in manufacturing a urinary catheter as disclosed herein. In figure 15, a mould cavity 860 as described in relation to figure 4 is shown, but with the difference that this mould cavity 860 includes two gate points 861, 862, which are positioned such that the melt flows towards the mould cavity 860 in a lateral direction, whereas in figure 4, the melt flows towards the mould cavity in a longitudinal direction. Two gate points are shown in fig.15, however, as mentioned above, three, four or more gate points can be used. Figures 16, 16A, 16B illustrate a schematic representation of a test setup used in carrying out Dynamic Mechanical Analysis (DMA) of the final urinary catheter manufactured by the gas-injection injection moulding according to the disclosure, and determining G-moduli (G’, G’’ and G*) and tangens delta as explained above in Example 2. Figure 16 illustrates a test specimen 1 as mentioned above inserted in a test set-up between an upper clamp 2 and a lower clamp 3. The upper clamp is held still during the testing, whereas the lower clamp 3 moves as a result of turning a rod 4. The rod 4 is configured to turn alternately to the left and right as indicated by the arrows in figure 16 and thus subjects the test specimen 1 to torsion along the length (h) of the specimen as indicated in figure 16B. A cross-sectional view of the test specimen 1 in shown in figure 16A, indicating an outer diameter OD and an inner diameter ID, referred to in Example – test specimen above. Figure 16B indicates that the end of the specimen closest to the turning rod 4 will be subjected to an amplitude of between minus b and plus b – in total 2b. Figure 17 illustrates the relationship between stress and strain for a specimen subjected to sinusoidal stress in the manner of testing DMA as shown in figures 16, 16A, 16B. The viscous portion illustrated by delta (δ) is shown as the phase shift between the stress at the lower curve and the strain at the upper curve. The height of the sinus-curve is an indication for the nominal value of the of the torsion module G*. Figures 18-19 show SEM representations of a surface of a test specimen of a urinary catheter obtained by extrusion, figure 18, and a surface on a test specimen of a urinary catheter manufactured by gas-assisted injection moulding (figure 19). As it appears, the surface on the extruded test specimen includes longitudinally extending fins on the surface of the catheter, sometimes referred to as shark-skin surface. This is a result of the extrusion process. Ref no.5 in figure 18 indicates some of these fins on the surface. The fins occur regularly over the surface, and all extend in the same direction on the surface. Contrary thereto, the surface on the gas-assisted injection moulded test specimen shown in figure 19 is random. This surface is a result of the inner surface of the mould cavity and does not depend on any particular process parameter. Ref. no.6 indicates areas that seems to be slightly higher than other areas on the surface, but no pattern appears on the surface. The difference in surface structure influences the surface tension as mentioned above under Example 1. Examples and features described in this disclosure, may be combined with each other (“mixed and matched”), unless specifically noted otherwise.

Claims

Claims 1. A method of manufacturing a urinary catheter, the urinary catheter comprising a tubular portion, a tip portion, and an outlet portion, the tubular portion comprising an exterior surface and an interior surface defining an interior lumen and a catheter wall extending between the exterior surface and the interior surface, wherein the method comprises the steps of ^ providing a melt of a polymeric material, ^ providing a mould cavity for the melt, the mould cavity defining at least the tip portion and the exterior surface of the urinary catheter, ^ providing an inlet nozzle for the mould cavity, the inlet nozzle comprising a gas-injection nozzle, ^ injecting the melt into the mould cavity so as to fill the mould cavity to a first limit, ^ providing a gas pin for the mould cavity, and ^ injecting gas through the gas pin via the gas-injection nozzle into the melt in the mould cavity, so as to provide an interior lumen wherein the method comprises filling the mould cavity to the first limit with melt and injecting gas into the melt in such a way that the tip portion of the urinary catheter is formed by an overflow of the melt.

2. The method as claimed in claim 1, wherein the overflow of the melt is retained inside the mould cavity in such a way that no melt flows out of the mould cavity during the gas-injection.

3. The method as claimed in claim 2, wherein the first limit is 70% of the volume of the mould cavity.

4. The method as claimed in claim 2, wherein the first limit is 80% of the volume of the mould cavity.

5. The method as claimed in claim 1, wherein the overflow of the melt leaves the mould cavity through a longitudinally extending overspill channel in a proximal end of the mould cavity.

6. The method as claimed in claim 1, wherein the overflow of the melt leaves the mould cavity through a plurality of radially extending overspill channels in the mould cavity.

7. The method as claimed in any of the preceding claims, wherein the gas is an inert gas.

8. The method as claimed in claim 7, wherein the inert gas is Nitrogen or Carbon Dioxide.

9. The method as claimed in any of the preceding claims, wherein the tip portion is a nelaton tip.

10. The method as claimed in any of the preceding claims, wherein the tip portion is a flex tip.

11. The method as claimed in any of the preceding claims, wherein the tip portion is a coudé tip.

12. The method as claimed in any of the preceding claims, wherein the polymeric material is selected from the one or more of ^ thermoplastic urethanes (TPU) ^ polyolefins, such as polyethylene (PE) or polypropylene (PP), ^ Polyvinyl chloride (PVC) ^ Thermoplastic elastomers (TPE) 13. The method as claimed in any of the preceding claims, wherein the gas pin comprises an exterior surface configured to provide an interior surface of the outlet portion of the urinary catheter.

14. The method as claimed in any of the preceding claims, wherein a melt filling phase is followed by a gas injection phase.

15. The method as claimed in claim 14, wherein the melt filling phase lasts between 0.6 s and 1.0 s and the gas injection phase lasts between 3 s and 5 s.

16. The method as claimed in any of the preceding claims, wherein a pressure inside the mould cavity is below 160 MPa during a melt filling phase.

17. The method as claimed in any of the preceding claims, wherein a pressure inside the mould cavity is below 20 MPa during a gas-injection phase.

18. The method as claimed in any of the preceding claims, wherein the injection of melt in the cavity is done through a single gate-point.

19. The method as claimed in any of claims 1 to 17, wherein the injection of melt in the cavity is done through two or more gate-points.

20. The method as claimed in any of the preceding claims, wherein the melt is provided as two shots of material so as to allow for co-injection of the melt into the mould cavity.

21. The method as claimed in any of the preceding claims, further including a step of removing the urinary catheter from the mould cavity.

22. The method as claimed in claim 21, further including a step of coating the exterior surface of the urinary catheter with a hydrophilic coating.

23. The method as claimed in any of claims 21-22, further including a step of providing urine drainage openings in the catheter wall.

24. The method as claimed in claim 23, wherein the urine drainage openings are provided by punching.

25. The method as claimed in claim 23, wherein the urine drainage openings are provided by laser-ablation.

26. A urinary catheter obtained by the method as claimed in any of claims 1 to 25.

27. The urinary catheter as claimed in claim 26, wherein the urinary catheter is an intermittent urinary catheter.

28. The urinary catheter as claimed in claim 26, wherein the exterior surface of the urinary catheter is configured to have a liquid contact angle of above 100 degrees, such as above 110 degrees.

29. The urinary catheter as claimed in any of claims 26-28, wherein the tangens delta value of the material of the urinary catheter is below 0.

1.

30. A urinary catheter obtained by the method as claimed in claim 6, wherein the urinary catheter comprises urine drainage openings resulting from the plurality of radially extending overspill channels in the mould cavity.

31. A urinary catheter obtained by the method as claimed in claim 10, wherein the flex tip is hollow.

32. A urinary catheter comprising ^ a tip portion in a proximal insertion portion of the urinary catheter, ^ a tubular portion extending from the tip portion and longitudinally to a distal end of the tubular portion, the tubular portion comprising a wall defining an exterior surface and an interior surface defining an interior lumen, wherein the urinary catheter is obtained by gas-assisted injection moulding and wherein the tip portion is obtained by an overflow of melt from the injection moulding process such that the tip portion of the urinary catheter is formed by the overflow of melt, wherein the exterior surface of the tubular portion is a result of an interior surface of the mould cavity and the interior lumen is a result of gas being injected into the melt in the mould cavity.

33. The urinary catheter as claimed in claim 32, wherein the exterior surface of the tubular portion has a controlled surface roughness.

34. Use of gas-assisted injection moulding for providing a urinary catheter comprising a tip portion.

35. Use of gas-assisted injection moulding for providing a urinary catheter comprising a tip portion and an outlet portion.

36. Use of gas-assisted injection moulding comprising the step of using a mould cavity comprising a plurality of radially extending overspill channels, wherein the overflow of melt leaves the mould cavity through the overspill channels thereby providing a urinary catheter comprising drainage openings.

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