Patent Application
20120303058
The invention relates to a novel thermoforming process in particular for the manufacture of surgical composite structures, such as tissue fixation implants. The implants are commonly referred to as anchors because they generally anchor a suture to the target tissue. In addition, the invention relates to novel surgical structures obtainable by the process.
Tissue fixation implants generally function as suture anchors, thus providing an attachment spot for a suture in a desired tissue. The suture can, for example, be joined with a needle extending from its end and the implant is joined to some other point of the suture, for example at the other end of the suture. In addition, implants can be joined with sutures or other distinct members to form other kinds of surgical devices.
Tissue fixation implants of the present kind are conventionally manufactured by injection molding. U.S. Pat. No. 5,964,783 (Grafton et al.) discloses an injection molded suture anchor with insert suture. The suture anchor comprises a biodegradable polymer body molded around a loop of suture, the body shaped so as to have a drive head and screw thread spirals. The suture comprises irregularities, such as knots, which hold the suture within the body. The anchor is manufactured by insert-molding, i.e. by placing the suture within an injection mold and injecting polymer into the mold. U.S. Pat. No. 7,226,469 (Benavitz et al.) discloses another insert-molded suture anchor.
A problem associated with prior art is that the natural adhesion of the suture and an injection molded implant is in many applications not mechanically sufficient for the application and therefore knots or loops are needed within the implant to hold the suture in place. Knots or loops are, however, not always desired or even possible to use. A knot may decrease the tensile strength of the suture and limit the maximum tension force to which the suture may be subjected. On the other hand, the intended use or the implant may not allow use of a suture loop. For example, in some designs (such as shown in
Another disadvantage of known melt processing techniques is that most known suture materials do not withstand high processing temperatures that may be required by these. For example, the mechanical properties of ultra high molecular weight polyethylene sutures are considerably weakened at temperatures above about 110° C.
It is an aim of the invention to solve at least part of the above problems and to provide a novel manufacturing process for surgical composite devices, combining two or more distinct members, such as a polymeric implant body and a suture. It is also an aim to provide corresponding surgical composite devices. A particular aim of the invention is to provide composite surgical devices in which the fixation force between the distinct members in the implant is high.
An aim of the invention is also to provide a manufacturing process which can be used for a wider scope of materials of the distinct members and their combinations, in particular with respect to their heat stability.
In particular, it is an object of the invention to provide a manufacturing method which can be used for manufacturing surgical composite devices having a self-reinforced structure, and a corresponding surgical device.
The invention is based on the idea that the distinct members are affixed to each other in a thermoforming process simultaneously giving one of the members, i.e., the tissue fixation implant, its final shape.
Thus, the method according to the invention for manufacturing a composite surgical device comprising a tissue fixation implant and a protruding member, such as a suture, attached to the implant comprises
According to a typical embodiment, the protruding member is flexible. In particular, the protruding member can be a suture or similar fibrous element. However, other biocompatible members, in particular braided structures can also be joined with the implant using the present method. The protruding member can also be rigid, such as a self-reinforced rod or a similar element.
According to one aspect, the composite surgical device according to the invention comprises
According to a second aspect, the composite surgical device comprises a bioabsorbable tissue fixation implant and a suture, in particular a knotless suture, integrally joined with the bioabsorbable tissue fixation implant, wherein the pull-out force of the suture from the implant is equal or close to tensile strength of suture.
According to one embodiment, the suture is joined at one end with a surgical needle to form a surgical kit.
More specifically, the invention is defined in the independent claims.
The invention provides significant advantages. In particular, thermoforming has been found to firmly attach sutures and the like braided structures to implants. That is, the pull-out strength of the suture from the implant is high. This is evidenced by way of examples later in this document. It is also an advantage of the invention that the thermoforming process is by nature solvent-free, extending the scope of materials that can be used for the implant and for the suture.
In particular, many biostabile high-temperature polymers, such as UHMWPE and PEEK, are difficult to affix to an implant by conventional techniques but can be processed using the present thermoforming method because there is no need to reach the melting temperature of the polymer or the deformation temperature of the protruding member (which is usually less than the melting temperature of many bio stabile polymers).
A composite surgical device wherein the protruding member is a suture and the pull-out tensile force of the suture from the implant is 35 N or more, and even 40 N or more, can be manufactured using the method according to the invention.
In addition to merely fixing the suture or other protruding member to implant, a high-quality implant can be produced in the same process. For example, defects on surface of the implant can be avoided in a thermoforming process. As the temperature of the preform material is kept typically below its melting point, the material, due to its high viscosity, is not prone to exit the mold cavity through the mold seams or suture orifice(s). However, it is preferred that the distance between the inner wall of the orifice(s) and the suture is 0.1 mm at maximum.
The method of the invention differs from injection molding and other melt processing methods, such as extrusion, insert injection molding, transfer molding etc. In the present method processing temperatures can be kept relatively low, enabling material combinations which are not possible by using conventional melt processing method. As complete melting is not required or desired in the present method, the present manufacturing process can be carried out at low temperatures, for most biocompatible implant materials at temperatures below 150° C. Even lower temperatures can be used (for example because of the durability of the suture), provided that a preform material having a glass transition temperature low enough is chosen. Thus, materials and material combinations can be used where one or all components are temperature sensitive or where components are not otherwise compatible or processable in molten form. Therefore, high strength of both implant and suture materials can be maintained in the process. To mention only one example, the method is well suited for ultra high molecular weight polyethylene sutures not compatible with melt processing, in which case the thermoforming temperature is preferably less than 110° C.
One advantage of the invention is that biodegradable polymers can be used as implant and/or suture material. Processing at low temperatures maintains the molecular mass of the polymer. In other words, chemical degradation of the polymer in not initiated in the process.
Moreover, the present invention makes it possible to produce self-reinforced implant structures having strong bonding with the suture, provided that the implant preform is made from self-reinforced material. That is, thermoforming does not cause self-reinforcement to relax, provided that the temperature is kept sufficiently low (typically a temperature below Tm of the preform is sufficiently low) and provided that the process is fast enough and the preform is under compression during the heating phase of thermoforming. It is also beneficial if the compression distance or duration during the compression phase is relatively short in order not to cause the reinforcing structure of the preform to lose its structure at least completely. Thus, in general, at least 10%, preferably at least 30%, most suitably at least 50% of the self-reinforcement is maintained in the process.
The present thermoforming process can be easily automated and is well suited for mass production.
The term “composite surgical device” refers to any such surgical device that is manufactured from two or more parts, typically made of different materials or at least in different processes. Typically, the implant is made of first polymer or polymer blend and the suture or other member is made of a second polymer or polymer blend.
The terms “(tissue fixation) implant” and “implant body” refer to any biocompatible and thermoformable body that can be left temporarily or permanently within human or animal tissue. In typical applications, the implant is relatively small, preferably having a maximum dimension of 2 cm or less. In particular, the implant may be an implant used in reconstructive surgery for holding desired tissue in a desired shape or in place with respect to other tissues. Large application areas of the invention are in the fields of sports medicine and trauma surgery, in particular arthroscopic surgery. For example, the present surgical device may be or form part of a meniscal repair device, suture anchor of any kind, or cross-pin ACL fixation device.
The term “protruding member” refers to any member attachable to the implant by the present process such that it extends from the outer surface of the implant to serve a particular surgical purpose, in particular attachment of the implant to another implant, surgical needle and/or tissue. Most importantly, the term includes various surgical sutures, fibers and fibrous elements. However, also rigid protruding members in their final form or as a preform can be used. Not only the implant body but also the protruding member can be shaped by thermoforming in the process. The protruding member can have a self-reinforced or unreinforced structure.
The term “fixation zone” means a region, such as a cannulation in or groove on the polymer preform serving to receive the suture before the thermoforming stage is begun. During the thermoforming stage, the fixation zone deforms and intimately mates with and bonds to the suture such that the desired fixation of the suture and the implant is achieved.
The term “defomation temperature” of a protruding member means a temperature where the protruding member, such as a suture, starts to permanently lose its strength, in particular tensile strength, due to irreversible chemical or physical processes. Usually, this temperature corresponds to the glass transition temperature Tg of the suture material.
Further embodiments and advantages of the invention will now be described in detail with reference to the attached drawings.
The invention describes a solvent-free method to connect two distinct members into single composite structure by thermoforming, i.e., using heat and pressure. In the following description, a suture and bioabsorbable tissue fixation implant preform, are frequently used as examples of the distinct members. The preform forms the implant after thermoforming. However, it must be noted that the invention allows also other types of member to be joined, as mentioned above and will be described also later in this document.
The composite product according to the invention may be a suture anchor or some other braid/bioabsorbable body arrangement connecting several implant parts together. Typically, the implant or at least one of several implants of the suture arrangement is an anchor-type part designed to be immobilized to a tissue, such as bone, cartilage, skin, muscle or internal organ, for allowing binding of the tissue to another tissue location using for example a suture or metal implant. A non-comprehensive list of examples of products where the invention can be utilized includes various forms of suture anchors, implants containing a continuous suture, implants containing an endless braid or fiber loop, implants having a self-reinfoced and/or oriented body, and implants having a textured body surface.
Generally speaking, both the implant and the suture can be either biostabile or bioabsorbable. However, typically at least the implant is bioabsorbable for removing the need of a separate removal operation.
At least the following implant types can be manufactured using the invention:
The suture is preferably braided, i.e. a multifilament suture. This increases the strength of the suture. In addition, the adhesion between the implant thermoformed according to the present process is increased as compared with plain sutures, as the polymer fills inter-filament microstructures on the surface of the suture. The suture material can be natural or artificial, for example, polyethylene, polypropylene, polyester, polyetheretherketone (PEEK) or Ultra High Molecular Weight polyethylene (UHMWPE), nylon, silk, steel or blend thereof (non-absorbable suture) or polyglycolic acid, polylactic acid, caprolactone or blend thereof or catgut (absorbable suture). According to a preferred embodiment, the suture is polymeric. The suture may be coated or uncoated. In principle, all commercially available surgically usable suture thread types, whether biodegradable or biostabile, can be used within the invention.
The implant, i.e., preform material comprises or essentially consists of thermoplastic polymer or polymer blend. A non-comprehensive list of bioabsorbable (resorbable) polymers, copolymers and terpolymers which may be utilized to manufacture bioabsorbable polymeric fibers and bioabsorbable polymeric bodies usable within the invention comprises: polyglycolide (PGA), copolymers of glycolide: glycolide/L-lactide copolymers(PGA/PLLA) glycolide/trimethylene carbonate copolymers (PGA/TMC); polylactides (PLA) stereocopolymers of PLA: poly-L-lactide (PLLA) poly-DL-lactide (PDLLA) L-lactide/DL-lactide copolymers, other copolymers of PLA: lactide/tetramethylglycolide copolymers, Lactide/trimethylene carbonate copolymers, lactide/d-valerolactone copolymers, lactide/[epsilon]-caprolactone copolymers, terpolymers of PLA: lactide/glycolide/trimethylene carbonate terpolymers, lactide/glycolide/[epsilon]-caprolactone terpolymers, PLA/polyethylene oxide copolymers, polydepsipeptides, unsymmetrically 3,6-substituted poly-1,4-dioxane-2,5-diones, polyhydroxyalkanoates: polyhydroxybutyrates (PHB), PHB/b-hydroxyvalerate copolymers, (PHB/PHV) poly-b-hydroxypropionate (PHPA), poly-p-dioxanone (PDS), poly-d-valerolactone-poly-e-caprolactone, methylmethacrylate-N-vinyl pyrrolidone copolymers, polyesteramides, polyesters of oxalic acid polydihydropyrans-polyalkyl-2-cyanoacrylates, polyurethanes (PU), polyvinylalcohol (PVA), polypeptides, poly-b-malic acid (PM LA), poly-b-alkanoic acids, polycarbonates, polyorthoesters, polyphosphates, polyanhydrides, and tyrosine derived polycarbonates, polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyetheretherketoneketone (PEEKK), polyetherketoneetherketone (PEKEK) or Ultra High Molecular Weight polyethylene (UHMWPE), -propylene (UHMWPP), or derivatives, copolymers or mixtures thereof. In addition, composites of a bioactive component and polymer can be used. The bioactive component can comprise, for example, bioactive bioceramic and/or glass, hydroxyapatite (HA), other calcium phosphates, such as tricalcium phosphates (TCP), combinations of different calcium phosphates, such as HA/TCP, calcium carbonate and/or calcium sulphate.
The adhesion of the suture to the implant may be even increased by using an adhesion-promoting agent which is applied to the contact zone of the suture and the preform or mixed with the preform material. For example, polymer with lower melting point than the preform material (or totally amorphous polymer) and/or a polymer with lower molar mass than the preform material can be used as an adhesion promoter between the polymeric implant body and the suture.
According to one embodiment, the implant is manufactured from self-reinforced polymer preform material, i.e. material containing a specific molecular orientation and/or reinforcing component increasing its strength at least in one torsional or tensile direction. Torsional strength in a longitudinal direction is of particular importance in structures similar to that presented in
The compression duration is preferably less than 10 min, in particular less than 60 s, typically 1-60 s.
Self-reinforcing of the implant preform can be achieved e.g. by solid state deformation, like with free or die drawing, biaxial drawing, compression, hydrostatic extrusion or ram extrusion as combined with drawing. Orientation and/or self-reinforcing techniques, which can be applied to manufacture the materials of the invention have been described in many publications, like in U.S. Pat. No. 4,968,317, EPO Pat. No. 0423155, EPO Pat. No. 0442911, FI Pat. No. 88111, FI Pat. No. 98136, U.S. Pat. No. 6,221,075 and U.S. Pat. No. 4,898,186, the entire disclosures of which are incorporated herein by way of this reference.
According to one embodiment the thermoformed implant serves to mechanically join two or more separate sutures. In other words, there are at least two sutures brought into the mold cavity before the thermoforming process starts such that they are all affixed to the implant by heat and pressure. This kind of implant having several sutures connected into one implant body can be used to connect sutures of the same type or, in particular, of different types. That is, the invention can be used to connect sutures having differing properties with respect to their material, strength, diameter, bioabsorbancy or market price, for example.
According to one embodiment, the present device comprises a bioabsorbable portion (e.g. implant and/or suture portion which is left within the body) and a biostabile portion (e.g. suture portion assisting in insertion/fixation of the device).
The suture can be permanently or impermanently connected, at one or both ends, to a surgical needle in order to form a ready-to-use surgical instrument.
In the following, the thermoforming process and a thermoforming apparatus suitable for carrying out the invention are described in more detail with reference to
According to one embodiment, the thermoforming process comprises
According to one embodiment, the mold comprises a heatable first mold portion, and a second mold portion, i.e., a piston, moveable with respect to the first mold portion. For being able to keep the suture within the preform during molding, there is provided at least one orifice residing on the first or second mold portion or, in the case of a through-running suture, both. The heating of the preform is achieved by heating the first mold portion. The pressure, for its part, is achieved by moving the piston with respect to the first mold portion. The piston is typically moved along the direction of the suture for achieving the desired pressure on the mold cavity.
The first mold portion preferably comprises at least two mold halves compressible against each other in a direction perpendicular to the direction of movement of the piston. The mold cavity 25 is defined by mold members, which can be opened. Preferably, the mold comprises two first mold members 24A and 24B, typically providing horizontal compression, and a second mold member 26, providing vertical compression. The suture 22 passes out of the mold cavity through one or more orifices provided at or between the mold members. In a typical embodiment, the second mold member 26, acting as a piston, comprises a through-hole having a diameter slightly (e.g. 0,01-0,2 mm) larger than the diameter of the suture 22.
It is to be noted that the mold arrangement can also be in any other orientation and that the compression directions may vary from oblique to perpendicular. According to another example, the first mold members 24A and 24B are arranged to provide vertical compression and the second mold member 26 horizontal compression. In a still another example, both compressions take place in the horizontal plane.
The compression may also be multidirectional by nature, which is achievable by hydrostatic compression means, for example.
The thermoforming process gives the final design to the whole implant 28 and integrally binds the suture to the implant. Therefore, the mold cavity 25 typically comprises a textured inner wall so as to manufacture a tissue fixation implant 28 having a corresponding surface texture.
According to one embodiment, the method comprises, as the first step, manufacturing the preform itself. This can be carried out by conventional plastic processing methods such as insert or injection molding, extrusion, machining, etc. Preform manufacturing could also include self-reinforcing, which can lead to stronger end-products, because the thermoforming process can be designed so that the majority, or at least significant portion of the self-reinforcing molecular orientation will be maintained during the process.
In the thermoforming process the preform material will generally be heated to a temperature range over Tg but below Tm, and the final form will be achieved by simultaneous presence of heat and pressure, thus resembling compression molding. For example, for a polylactide implant, the optimal temperature is in the range 65-170° C., in particular 110-150° C. In particular when manufacturing self-reinforced implants, the preform is heated under a predetermined pressure and temperature high enough to compress the preform onto suture but low enough not to relax self-reinforcement of the preform completely.
According to a practical example, the method comprises the following steps:
The mold 40 comprises a pathway for the piston 46, the actual mold cavity and a capillary bore for the suture. In addition, the mold comprises two sets of bores. The first set 43 is placed in the vicinity of the mold cavity and is designed to receive heating means, such as heating resistors or heated fluid circulation. The second set 44 is placed farther from the mold cavity and are designed to receive cooling means such as cool fluid circulation.
It is to be noted that the suture need not be conveyed to the mold cavity through the piston but may also go through a channel in the main mold halves or between any of these parts. In addition, for manufacturing structures as shown in
The following examples are intended to further clarify advantages of the invention.
Several methods to connect non-absorbable suture and bioabsorbable polylactide have been tested and according to these trials the thermoforming process yielded into most favourable results. The first thermoforming trials were made by placing the polylactide billet horizontally between the mold plates. These first trials resulted in lower pull-out force than the tensile strength of the suture (tensile strength was 53.8 N), but the load was on acceptable level, that is, regularly over 35 N (cf. suture tensile strength with knot was less than 30 N). Results of the trials are shown in
To improve the adhesion between suture (polyester) and polylactide a vertical mold was manufactured to increase molding pressure and to make the process more accurate. The billet was aligned vertically and suture was passed through the plunger (piston), as described in detail above.
Results of the trials are shown in
A thermoforming process was done similarly to that presented in Example 2 using polylactide billet and HiFi suture (UHMWPE). Samples of implants having a suture with and without a knot inside the implant body were tested. Results of the trials are shown in
The specimens having a knot in the suture within the distal end of the implant demonstrated higher pull-out forces than specimens shown in Example 2.
A thermoforming process was done similarly to that presented in Examples 2 and 3. Polylactide specimens containing both polyester and HiFi suture (UHMWPE) were manufactured and long term adhesion between implant body and suture was analyzed several times within 12 weeks using an in vitro soak study in phosphate buffer solution at 37° C. Polyester suture samples were all knotless, while all HiFi suture specimens included a single knot within the distal end of the implant.
Results of the in vitro study are shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 20096285 | Dec 2009 | FI | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FI2010/050997 | 12/3/2010 | WO | 00 | 8/14/2012 |
| Number | Date | Country | |
|---|---|---|---|
| 61266824 | Dec 2009 | US |
