Method for removing gas inclusions from surgical suture material and an associated device

Abstract

The rolling unit (2) and its method serve to stiffen surgical suture material and are used in devices for cutting such suture material to length. The rolling elements (213 and 223) are equipped with a heating cartridge and a temperature sensor. The rolling elements (213 and 223) are moved orthogonally to each other, with the suture material (12) positioned orthogonally to the rolling elements. The distance between the rolling elements is predetermined by a curved path (31).

Description

The present invention relates to a roller unit suitable for use in a thread cutting device for homogenizing a thermoplastic thread material as used for surgical threads, in particular for removing gas inclusions present in the thread material, and to a thread material processed with such a roller unit. The present invention also relates to a method for homogenizing a thermoplastic filamentary material, in particular for removing gas inclusions present in the filamentary material, according to the preamble of claim 10.The filamentary material used in surgery is either a monofilament or a multifilament filament. The monofilament thread consists of a single filament constituting the thread. The multifilament yarn consists of a plurality of very thin individual yarns which are twisted, twisted or interlaced with one another. Surgical suture material is offered in various lengths and with one or two needles, reinforced or non-reinforced. Non-armed threads are usually used in surgery with Ehr needles, as shown for example in WO 2017 / 170670 A1.In drilled needles, the filamentary material is inserted axially into the drilled needle and held in place by deforming the needle steel. This process is called armor and results in armor. The ready-to-use end product, a reinforced needle with filamentary material, is offered on the market as shown in Fig. 1.The production of needle-armed surgical suture material is simplified if the suture ends of the mono- as well as the multifilament threads are stiffened. Multifilament threads are also intended to prevent their end from raggeding. In the case of monofilament threads, it is desirable in particular to make them more round and more compact so that they hold better in the reinforced needle.EP 0 806 177 B1 discloses an apparatus for producing surgical suture material with stiffened, non-fraying suture ends without the need to dip the suture or suture ends into a binding resin agent. The device disclosed here consists essentially of dilatation means for tensioning the thread material, a two-part heating tool for producing a local melt connection, wherein the heating tool comes into contact with the thread to be processed, and a cutting device for cutting off thread material cut to length.However, the heating tool disclosed in this EP 0 806 177 B1 has disadvantages for the processing of thread materials with significant gas inclusions.Gas inclusions can be seen in an otherwise translucent thermoplastic from the fact that the material has a milky appearance. The multiple reflection and refraction of the light at the gas inclusions generates a reflection of the light. A typical example is a thermoplastic made of polytetrafluoroethylene, which appears white in the untreated state. A feature of these thermoplastics is "flow" under pressure. By escaping the gas inclusions, the thermoplastic yields over time.However, the flow of the thermoplastic is not desirable in the case of a reinforced needle-thread combination, since after a certain time (depending on the composition of the thermoplastic, it may take days to months) the thread material dissolves in the reinforcement and falls out of the reinforcement hole at the latest during surgical sewing.It is therefore an object of the present invention to provide an apparatus which allows to remove any gas inclusions from the end portion of the filamentary material which is subsequently used for the needle reinforcement. As already mentioned above, during degassing a previously white thread becomes translucent at the degassed location.A further object of the present invention is to design the resulting translucent filament piece as round as possible. This ensures that a large-area, long-term and load-bearing positive and non-positive connection with the thread material can be achieved during reinforcement.This object is achieved according to the invention by a device according to claim 1 and a method according to claim 9, in particular by a rolling unit for homogenizing a thermoplastic thread material as used for surgical threads, or for removing gas inclusions from such a thread material, wherein this rolling unit is suitable for use in a thread cutting device. This thread cutting device comprises at least two rolling elements, the distance of which is determined by a control device and which is controlled by two drives arranged orthogonally in such a way that at least one of the rolling elements follows a curved path, whereby the thread material is moved orthogonally to the drives in such a way that the cross-sectional area of the thread material is reduced and is preferably brought into a circular shape.Preferred embodiments of the device according to the invention have the features of dependent claims 2-8. The thread material produced thereby is homogeneous, or translucent, in the rolling region and has a reduced cross-sectional area.A method suitable for producing such a thread material according to the invention has the features of claim 9 and in particular uses a rolling station according to claim 1, wherein the cross section in the rolling region of the hot thread material is reduced and translucent with a rolling movement.Further preferred embodiments of the method have the features of dependent claims 10 - 12, in particular the rolling movement is carried out several times and an axial tension of at most 0.1N is exerted on the thread material during the rolling movement. In a preferred embodiment of the method, after the translucence has been reached and after the rolling movement has ended, the thread material is cooled under an axial tensile force.In the following, the processing of a thermoplastic filament made of polytetrafluoroethylene is to be considered in more detail by way of example and for the detailed description of the invention. This is because in the normal case its gas content is much higher than in the case of other thermoplastics and a particular attention should therefore be paid to this material. Moreover, among the thermoplastics, polytetrafluoroethylene has particular properties. In particular, polytetrafluoroethylene has the highest melting point of all thermoplastics. It is therefore also an object of the present invention to process thermoplastic filaments which have a high melting point.The melting point of polytetrafluoroethylene is 327° C., which must be reached at least in order that a permanent removal of gas inclusions is possible at all. By the application of external pressure, this value can also be lowered by a few degrees. At 327° C., however, polytetrafluoroethylene does not yet become liquid but rather softened in a gel-like manner.Polytetrafluoroethylene is not known to be a readily viscous liquid phase, as is other thermoplastics, since the material begins to decompose at temperatures above 400° C. Fluorophosgene (COF2) is thereby released. This is a highly toxic pyrolysis product which can lead to diseases such as teflon or polymer fever. For this reason, accurate temperature control is to be ensured in terms of working safety and exceeding 400° C. should be prevented.All filamentary materials, regardless of which thermoplastic, are extruded products which are stretched immediately after extrusion, i.e. upon cooling. When heated again in the direction of the melting point, these contract. However, this contraction can be prevented when an axial tension is applied to the thread and prevents the contraction. Polytetrafluoroethylene shows this typical thermoplastic behavior more clearly than other thermoplastics.The high temperatures required force the skilled person to make use of solutions which are stable at high temperatures during the construction. This excludes components in the vicinity of the roller unit which age extremely rapidly due to the action of temperature. Thus, highly precise electronic linear axes (e.g. SMC LESH8-RJ-50) can be operated only up to 60° C. according to the data sheet. Because of the spread of heat from the roller unit, therefore, linear electronic axes as a drive for the roller unit would be defective shortly. In the present invention, therefore, curve plates with a roller and temperature-resistant pneumatic drives with linear guides are used, which operate precisely and with a long service life even at high temperatures. The roller is pressed against the cam plate with the pressure force of the pneumatic drive.A particular consideration is given to the fact that the device according to the invention is suitable for the production of medical products. Thus, the components contacting the thread must not leave any abrasion on the thread, which is also not permissible for medical reasons. Likewise, no fibrous heat insulating mats are allowed because their fibers could settle on the surface of the surgical suture.The present invention uses a chromium steel cage 1.4301 disposed around the rolling elements for heat insulation. The rolling element is mechanically connected to the cage only at a few points. The heat exchange is thus greatly reduced since the rolling elements are thus packed into an air cushion. Chromium steel of grade 1.4301 is furthermore one of the worst metallic heat conductors (about 30 W / mK), which further reduces the heat conduction to the drive. The heat conduction is furthermore further reduced by an air cushion (approximately 1 mm thick) provided between the cage and the drive elements. The cage with a base surface of 900 mm 2 is in direct contact with the drive only at 28 mm 2 in this case. This means that the air cushion covers 97% of the base area, while the metallic contact area is only 3%.The drives for traversing the curved path are arranged orthogonally, i.e. at a 90° angle to one another. The orthogonality lies within the normal manufacturing tolerances, which for angles at + / - 20 degree minutes (Swiss standard SN258440-m). In the orthogonal arrangement of the drives, as shown in the present figures, these are horizontal and vertical. However, all other orthogonal arrangements are also conceivable, such as, for example. 45° vertically upward to right and 45° vertically upward to left.For a better understanding of the present invention, the orthogonal axes for defining the axial directions are referred to below as the distance axis and the roll axis, which is appropriate for the orthogonal arrangement of the drives. The terms distance drive for the first linear motion element and roll drive for the motion element orthogonal thereto are likewise used.The rolling element is preferably made of steel. Steel is also dimensionally stable at a temperature of 400° C. In a preferred embodiment, the tool steel 1.2083 is used because it has good machinability and a high hardness acceptance and is also low in distortion. For this purpose, it conducts the heat better than the steel of the cage and is free of rust under the given conditions.The rolling element is heated to the required operating temperature via the cartridge heater. In order to generate a heat field which is as homogeneous as possible on the contact surface, the temperature sensor is preferably parallel to the cartridge heater and as close as possible to the rolling surface.The present invention, the advantages and properties thereof are to be explained by way of example below with reference to the figures.The following are shown: FIG. 1 is a representation of an armed needle FIG. 2 shows a mechanical construction of the rolling station, rolling drive retracted, spacer drive extended FIG. 3 shows a mechanical construction of the rolling station, roller drive extended, spacer drive extended FIG. 4 shows the shape of the cam plate FIG. 5 shows the structure of the rolling surface with stop elements FIG. 6a shows the rolling of the thread at the beginning FIG. 6b shows the rolling of the thread FIG. 6c shows the sliding of the thread FIG. 7 shows filamentary material with gas inclusionsFIG. 1 shows a reinforced needle (11), wherein the thread (12) is inserted and pressed axially into the drilled needle opening (13).FIG. 2 shows a rolling unit (2) according to the invention in the starting position for rolling. The spacer drive has already been retracted. The rolling surface (41) already contacts the yarn material (12), whereby the latter is heated and begins to shrink if no tension is applied to the yarn. The structuring of the rolling surface ( 41) is not shown. The structuring forms an adhesion resistance which helps the thread to roll. Only two end stops ( 44, 45) are shown, the stops ( 42, 43) are not shown for the sake of better clarity.FIG. 3 shows the roller unit (2) in the end position, consisting of a vertically moving spacer heating element (21), a heat-insulating cage (210), which consists of a 1.5 mm thick Inox sheet 1.4301. Included therein is the rolling element (213). A roller (241) is fastened to the heat-insulating cage (210), which roller is advantageously designed as a metal ball bearing without lubricant. The cage ( 210) is connected to the spacer drive ( 250) only via a few connecting elements (not shown). The majority of the intermediate surface formed is an air buffer (251) of about 1 mm thickness.FIG. 3 furthermore shows the other rolling element ( 223) which is driven by the second rolling drive ( 260). It otherwise contains the same elements as in the first rolling element (21), i.e. cage (220), rolling element (223), air gap (261).FIG. 3 also shows the bores in the rolling elements ( 213, 223). The bores (221 or 221) near the rolling surface (41, not shown here) are provided for the introduction of the temperature sensor (preferably a PT100 control sensor) and a further bore (212 or 222) for the heater cartridge with a maximum power of about 250 W. With the aid of a programmable logic controller, the value of the temperature sensor is read out and the temperature of the rolling surface ( 41) is constantly controlled with the aid of a software PID or a fuzzy logic control circuit (not shown) and via controlled activation of the heater cartridge. It has been found that with this embodiment the temperature on the rolling surface (41, 41b) fluctuates less than + / - 1 C° at 390 C°.Since both heating plates can have different desired temperatures, a separate heating control circuit can be provided for both heating plates.In contrast to the rolling element ( 21) with the spacer axis ( 25), a cam plate ( 240) is provided on the cage for the rolling element ( 22) with the rolling axis ( 26). The cam plate (240) defines the distance between the two rolling surfaces (41 and 41b).FIG. 4 shows a possible shape of the contour of the cam plate ( 240). The curved web (31) is rolled over the roller (241). The starting point (33) defines the starting distance between the two rolling surfaces (41 and 41b). The starting point (33) is designed such that the thread is not yet touched by both rolling surfaces. In the case of a 0.3 mm thick yarn material, the cam disc is accordingly about 0.4 mm at the starting point (33). The rolling process runs over the curve (31) to the end point (34). The height (32) of the curve is dimensioned such that the thread is tapered during rolling. A 0.3 mm thick yarn material is thus tapered in the rolling region, for example, to 0.2 mm, while the curve length corresponds to the distance between the starting and end points (x) of the rolling drive (260) (in the example shown, 30 mm). The drives generate the movement (A)-(B)-(C)-(D), which can be repeated several times.FIG. 5 shows a top view of the lower rolling surface ( 41) and of the inserted thread material ( 12). In order for the thread to roll cleanly on the rolling surface (41), a structure on the rolling surface (41) is expedient. A parallel corrugation in the direction of the thread is shown. This corrugation can be applied fine-mechanically or electrochemically. However, other corrugations may also be provided, such as a cross-corrugation (50).The starting stops (42, 43) just before the starting position of the rolling surface and the ending stops (44, 45) are not needed in the case of slip-free rolling. However, it is found that from time to time it occurs that the thread does not roll but adheres to one rolling surface and slides on the other rolling surface. During sliding / gluing, however, the thread makes a greater path than during rolling (see FIG. 5 ). Since the transition from rolling to sliding is unpredictable, it is possible for the thread to slide out of the rolling surface (41) when rolling several times. Therefore, it needs to prevent starting and ending stops (42-45) just as well. However, the stops must be at least 5 mm away from the heating element, so that they are not heated too much by infrared radiation from the hot heating plate and the thread then remains stuck to it when in contact.Figure 6a schematically shows the starting position of the rolling of the yarn (12) with the two rolling surfaces (41 and 41b). Here too (x) shows the distance from the start to the end point of the roller drive. FIG. 6 bshows the displacement of the thread material when it rolls, namely half the distance (x / 2) of the movement of the rolling surface ( 41 b). Otherwise, the thread slides all the way (x), as shown in Fig. 6c. If the rolling movement is now repeated a plurality of times, wherein the sliding / rolling cannot be predicted, the thread may fall out on the inner side ( 61) or the outer side ( 62) (FIG. 6 a).FIG. 7 shows filamentary material with gas inclusions (71). The thread can be tapered in the rolling region if, after the rolling phase, the thread is put under tension in a controlled manner (for example with a tensile force=2.4 N in the case of a polytetrafluoroethylene thread of 0.3 mm diameter). The tapering ( 72) in the rolling region is stopped by the cooling and the associated hardening of the thread material ( 12). It has been found that it is possible to taper the thread material ( 12) from 0.3 mm to 0.2 mm, which corresponds to a diameter reduction of 33%. The cut ( 73) takes place at a point of the taper ( 72) and thus allows the taper ( 72) to be connected to the needle ( 11) in a reinforcement ( 13).During the rolling, rolling is preferably carried out with as little tensile stress as possible. A minimum tension of up to a maximum of 0.1 Newton in the axial direction of the yarn can, with certain yarn materials, prevent the yarn from being flattened during sliding / rolling and, accordingly, produce a more round end product.It goes without saying that the rolling station according to the invention can be used not only for monofilament threads but also for multifilament threads. Although less gas inclusions are pressed out in the case of multi-filament threads, it has been shown that multi-filament threads are homogenized under the action of heat and rolling pressure and become stiff and tapered.

Claims

Roller unit (2) of a thread cutting device, for homogenizing a thermoplastic thread material (12) for surgical threads and for removing gas inclusions in the thread material (12), characterized in that this roller unit (2) comprises two orthogonally arranged drives (250, 260) and two roller elements (213, 223), the distance between which can be determined by a control device, which control device controls the two orthogonally arranged drives (250, 260) in such a way that, during operation, at least one of the roller elements follows a curved path (31) in order to move the thread material (12) orthogonally to the drives (250, 260) in such a way that the cross-sectional area of the thread material is reduced in the roller region and is brought into a shape that is as circular as possible, wherein at least one roller element (213, 223) can be heated with the aid of a control circuit.The rolling unit (2) according to claim 1, characterized in that at least one rolling surface (41, 41b) of the rolling elements (213, 223) is structured.Rolling unit according to claim 1, characterised in that each rolling element (213, 223) is integrated into a cage (210, 220) with air gap.Roller unit according to Claim 1, characterized in that an air cushion (251, 261) is present between the cage (210, 220) and the drive (250, 260).Roller unit according to claim 1, characterised in that it is provided with at least one stop element (42-45).Roller unit according to claim 1, characterised in that the control device comprises at least one cam plate (240) with a roller (241) for guiding the roller element (213, 223) along the cam track (31).The rolling unit according to claim 6, characterized in that the at least one cam plate (240) maintains the distance between the rolling surfaces (41, 41b) to be monotonously reduced, wherein the distance is always greater than zero.Yarn material (12) processed with a roller unit (2) according to claim 1, characterized in that the yarn material is translucent and homogeneous in the roller area.Method for removing gas inclusions from filamentary material (12), characterized in that a rolling unit (2) according to claim 1 is used for this purpose, wherein the cross section of the hot filamentary material (12) is reduced with a rolling movement (B)(C) in order to let the filamentary material become translucent and homogeneous in the rolling region.Method according to Claim 9, characterized in that the rolling movement (B)(C) is carried out a plurality of times.Method according to claim 9, characterised in that an axial tensile force of at most 0.1 N is exerted on the thread material (12) during the rolling movement (B)(C).Method according to claim 10, characterised in that after the translucence has been reached and the rolling movement (B)(C) has ended, the thread material (12) is cooled under an axial tension.

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