NL9201037A - Bio-resorbable barrier element - Google Patents

Abstract

The invention relates to a bio-resorbable barrier element, which barrier element includes a flexurally rigid shielding section 1 made of plastic. As a result it is simple to implant and resistant to mechanical stresses, and great freedom with regard to the choice and form of the space to be shielded by means of the barrier element is made possible. <IMAGE>

Description

Short designation: Bio-absorbable barrier element

The invention relates to a barrier element according to the preamble of claim 1.

Such barrier elements are known from a publication by Caton et al. Entitled "Synthetic Bioabsorbable Barrier for Regeneration in Human Periodontal Defects" in the Journal of Dental Research 69: special issue, 1990, Abstract # 1336.

These known barrier elements are designed as fabrics of bio-absorbable fiber material. An advantage of these known barrier elements is that they no longer have to be removed after being fitted. Such an additional operation involves renewed damage to the patient's tissue, poses a psychological burden on the patient and also costs extra time and money.

A drawback of these known barrier elements, however, is that they are difficult to apply and the area of application is limited, because the fabric has to be stretched over the space to be screened. For example, when used to restore dental support tissue or dental implants, this implies that the use of such barrier elements remains out of the reach of most dentists with general practice.

A further drawback of these known barrier elements is that they have a low stability when placed, so that there is a relatively high risk that the space in which osteogenesis is intended is not sufficiently kept free. When used in dental surgery, these barrier elements often appear to deform after implantation, due to tissue pressure and possibly also forces exerted during chewing.

Furthermore, barrier elements made from PTFE (also referred to by the brand name Teflon) are known and are marketed under the designation "GORETEX

Periodontal Material ". These barrier elements must be removed again after healing. Furthermore, these barrier elements have practically the same mechanical properties as the barrier elements described above, so that they have corresponding drawbacks.

The object of the invention is to counteract these drawbacks by providing a barrier element which is easy to install and provides reliable shielding of the space in which osteogenesis is intended.

This object is achieved according to the present invention by applying the characterizing measures according to claim 1 to a barrier element of the type described in the preamble.

Since the barrier element according to the invention comprises a bending-rigid plastic-shaped shielding section, this does not have to be clamped during implantation, but can simply be arranged such that the shielding section extends along the space to be shielded, the shape of which the shielding portion determines the shape of the space in which osteogenesis will occur. Due to the bending stiffness of the shielding part, the barrier element according to the invention is more resistant to mechanical loads, so that the space in which osteogenesis is intended is more reliably kept free.

A further advantage of the barrier element according to the invention is that it offers greater freedom as regards the shape of the space in which osteogenesis is allowed to occur.

A still further advantage of the barrier element according to the invention is that it can also serve as a support element for keeping parts of bone tissue positioned relative to each other which are to grow together. The barrier element according to the invention thus makes it possible to regrow parts of bone tissue between which bone tissue has been lost, without transplanting bone tissue to replace the lost bone tissue.

The invention can also be embodied in an assembly of parts according to claim 24, which also comprises fastening means with which the barrier element according to the invention can be quickly and easily attached to bone tissue.

The invention can further be embodied in a mandrel according to claim 25 or 26 for rolling up a barrier element according to the invention into a tube, a method according to claim 27 for manufacturing a barrier element according to the invention and an injection molding machine according to claim 28 for applying the method according to claim 27.

The invention is explained in more detail below with reference to a few exemplary embodiments, wherein reference is made to the drawing. In each schematic representation: Fig. 1 shows a cross-sectional view along the line II-II in Fig. 2 of an exemplary embodiment of the invention, Fig. 2 shows a top view of the barrier element according to Fig. 1, Fig. 3 view according to fig. 1 of a further embodiment of the invention, fig. 3-6 sectional views of application examples of the barrier elements according to Figs. 1-3, FIG. 7 is a front view of a further exemplary embodiment of the invention, FIG. 8 is a sectional view along line VIII-VIII in FIG. 7, FIG. 9 is a view in accordance with FIG. 7 of a further exemplary embodiment of the invention, fig. 10 is a sectional view along line XX in fig. 9, fig. 11 and 12 are perspective views of each barrier element rolled up into a tube, FIG. 13 is an exploded view of a mandrel around which a barrier element of FIG. 12 is wrapped, and FIG. 14 is an exploded view of an example of application of a barrier element rolled up into a tube.

• The barrier elements shown each comprise a form-retaining shielding part 1, which resists arbitrary deformations and returns to its original shape at body temperature after deformation (of course, provided that certain maximum deformations are not exceeded during deformation).

The known barrier elements consist of woven material or of material with, in terms of mechanical stability, papery properties. These barrier elements are not bending rigid and have been given a specific shape and must be stretched over the space to be screened. With the barrier element according to the invention, the shape of the shield is fixed when the barrier element is formed, so that it does not have to be clamped during implantation, but can simply be applied over the desired shielding space by attaching to the adjoining bone tissue. Moreover, due to the dimensional stability of the shield 1, the barrier element according to the invention is more resistant to mechanical loads than a known space-spanning barrier element, so that the space in which osteogenesis is intended is more reliably kept free.

The barrier element according to the invention can be made in a wide variety of shapes and sizes, so that greater freedom is obtained in the shape of the space in which osteogenesis is caused to occur.

Furthermore, the barrier element according to the invention can also serve as a support element for keeping parts of bone tissue which have to grow together, positioned relative to each other, whereby the possibility is obtained of reconnecting parts of bone tissue between which bone tissue has been lost. to let grow. Bone tissue transplantation instead of the lost bone tissue can then be omitted. Examples of barrier elements suitable for such applications are shown in Figs. 7-14.

The plastic is preferably a polylactic acid or a copolymer of lactic acid and glycolide. Such polymers are commercially available under the trade name PURASORB from Purac Biochem e.g. in Gorinchem, the Netherlands.

In order to obtain the greatest possible dimensional stability, the shielding parts 1 have a wall of solid material, which wall, incidentally, can be composed of several mutually different materials.

The barrier element according to the invention can be efficiently manufactured by injection molding.

The exemplary embodiments shown in Figures 1-6 each have a central, cup-shaped shielding part 1 and a thin-walled, ring-shaped part 2 running along the edge of the cup-shaped part 1. The cup-shaped shielding part 1 shields a space within which osteogenesis can take place and the thin-walled part 2 around the shielding part 1 forms a flexible flange with which the barrier element can be reliably attached to a piece of bone tissue 3 (fig. 4-6).

The thin-walled portion preferably has a thickness decreasing from the shielding portion 1, so that it is relatively stiff in the region of the shielding portion and forms a support surface for transmitting forces exerted on the shielding portion 1 to the adjacent bone tissue.

Fig. 4 shows a human mandible bone 3, an upper part 16 of which has become too narrow to attach a dental implant to it. A barrier element according to the invention is attached adjacent the top edge of the jaw bone to the inside of the jaw bone by means of fasteners 15 (these are discussed in more detail below). In the space bounded by the shield 1, a broadening of the jaw bone will grow, in which a dental implant can then be reliably attached.

Figs. 5 and 6 show a barrier element according to the invention fitted over a cavity 16 formed in a jaw bone. The flexible edge is fastened to the bone 3 by means of fasteners 15.

Figs. 4-6 illustrate the importance of a highly flexible rim that can closely follow the shape of the bone.

It is noted that the barrier element according to the invention can also be arranged on the side of a bone part opposite the side to which a dental implant is to be attached in order to allow additional bone tissue to grow on that opposite side, in which the implant can protrude.

The barrier element according to the invention can also be designed as a blank, which can be rolled up into a tube 4, as shown in Figs. 7-14. Such a sleeve 4 can be wound around separated parts 5, 6 (fig. 14) of a bone, so that firstly these parts 5 and 6 are positioned and oriented relative to each other and secondly a space between these parts 5, 6, in which bone can form again.

With the barrier elements according to Figs. 13 and 14, flexible sections are formed in that the blanks wound into tubes have strips 7 of decreasing thickness which, after winding, form the ends of the tubes formed. As well as the flexible parts 2 of the barrier elements according to Figs. 1-6, upon attachment of the barrier element, the flexible portions 7 can effectively adapt to the shape of the adjacent bone tissue, so that a good seal between the barrier element and the adjacent bone tissue is obtained.

In order to promote an effective sealing of the connection between the barrier element and the bone tissue, the flexible part 2 can furthermore be disc-shaped. When attaching the barrier element, for example in places indicated by the arrows 9, the flexible edge 2 is then pressed against the bone tissue along the outer edge with additional bias. Also when attached to a relatively narrow bone section, as shown in fig.

6, an improved connection to the bone 3 is then obtained.

Also with the barrier elements according to Figs. 1-6 it is advantageous for sealing the connection between the barrier element and the bone tissue 3 (see Figs. 4-6) when the wall thickness of the flexible part of the shielding part 1 decreases.

In order to obtain an improved sealing, the barrier element can further be provided with a bent sealing lip 8.

With a barrier element according to Figs. 7-9, an increased pressing force of the flexible rim 7, and thus an improved sealing, can be obtained if, in the state of being rolled up into a tube, the diameter of the tube along the ends is smaller than in an intermediate part of the tube .

A tubular barrier element of such shape can be obtained by wrapping the barrier element about a mandrel 10 having two coaxially spaced sections 17 of a tapered diameter, the largest diameter sections of which face each other . The barrier element can be heated during winding or afterwards, so that it can adapt to the shape of the mandrel by plastic deformation. When a poly-lactic acid is used as the material for the barrier element, heating to a temperature of about 70 ° C is sufficient to enable such a plastic deformation.

In order to heat the barrier element during winding, the mandrel may be provided with means for heating the mandrel, such as a heating element or a space for heated liquid.

After cooling, the barrier element can be taken off the mandrel 10 again. It should then be flexible so that it can still be bent open to fit around bone sections, such as bone sections 5, 6.

A barrier element according to the invention can advantageously be fastened by means of fasteners with a shaft which is shaped such that, by applying a force, it can be placed only in the longitudinal direction of the shaft in a matching bore in bone tissue. Such fasteners, which are the subject of applicant's Dutch patent application entitled "Fastener for attaching an implant to bone tissue", can be made with a shaft with a particularly small diameter and can be arranged at a small distance, which is advantageous for obtaining a good connection between barrier element and bone tissue. A further advantage of these fasteners is that they can be applied very quickly, so that the operating time is shortened and a relatively large number of fasteners can be used without serious objection in terms of the time it takes to apply.

The barrier element shown in Fig. 12 is formed such that more layers are formed in the middle region upon winding, but substantially one layer is formed in the region of the ends. This provides an additional reinforcement of the barrier element in the region of the fracture of the bone and the shielded space between the bone parts 5 and 6.

When an object of polylactic acid material breaks down in the body of a human or animal, the material gradually degrades from the moment of implantation, which is reflected in the decrease in molecular weight. When the molecular weight reaches a certain value, the material becomes soluble and a large part of the material disappears from the object within a certain period of time. According to the publication by Schakenraad and Dijkstra mentioned in the introduction, the molecular weight at which the material becomes soluble for copolymers of DL-lactide and glycolide is about 5000 - 10,000 and disappears in a period of about 30-60 days about 90%. of the material of the barrier element.

During the said period, in which most of the mass loss occurs, a relatively large amount of material is released in the body, to which the body reacts. If a larger barrier element is used, this reaction can be undesirably strong.

The barrier elements according to the elements shown in Figs. 7-10 illustrative embodiments of the invention each comprise a first portion 11 made of a first resorbable material and a group of second portions 12 (only a few of which are referenced by reference numerals for clarity) made of a second resorbable material. The materials have such a structure and composition that the material of the first part 11 degrades on average more slowly after implantation than the material of the second parts 12.

As a result, most of the material from the second parts 12 is released in an earlier period than most of the material from the first part 11. Because the release of most of the material from the barrier element is spread over two periods, the amount of material released per unit time during those periods is significantly smaller than with a corresponding object made from a single material. The body will show less intensive reactions due to the smaller amount of material released per unit time. Furthermore, the strength of the barrier element does not decrease relatively abruptly but gradually, so that it can be better adapted to the increase in strength of the bone area to be healed.

Preferably, the structure and composition of said materials is such that after implantation, the material of the first portion 11 begins to become soluble after substantially all of the material of the further portions 12 has dissolved or degraded. This avoids an overlap between the periods in which both materials largely disappear. An overlap between the two periods can lead to a temporarily increased supply of material released from the barrier element, which can lead to a temporary enhanced reaction. However, if the flow rate of material released at the beginning and end of both periods is lower than in the middle portion of those periods, the periods may overlap slightly without this leading to a temporarily increased flow rate of material released.

A very reliable time difference between periods in which most of the material from each of the two parts 11 and 12 can be obtained if the material of the first part 11 has a different composition than the material of the second parts 12.

Suitable materials are, for example, copolymers of DL-lactide and glycolide, the glycolide content of the material of the second part 12 being higher than the glycolide content of the material of the first part 11.

A favorable time between the periods in which most of the material of the second portions 12 and the first portion 11 degrades can be obtained if the molar percentage of glycolide in the material of the second portion is between 65 and 90% and the molar percentage glycolide in the material of the first part is between 40 and 65%.

If a relatively long residence time of the first part 11 is desired, a poly (L-lactide) can advantageously be used for this.

However, it is also possible to use material with a substantially identical composition for the first and further parts. In addition, a shift of the periods in which the material of the first resp. the second part is largely released from the barrier element when the structure of the material of the first part 11 is more crystalline than the structure of the material of the second parts 12. Use of material of identical composition for the first and further sections offer the advantage that a single extruder screw can suffice during manufacture.

for a further description of process parameters affecting crystallinity, reference is made to a publication by Offergeld, Michaeli and Menges entitled 'The Injection Molding of Resorbable Implants' in ANTEC '89, p. 1282-1286.

Incidentally, it is also possible to design the barrier element such that the sections with different degradation speeds gradually merge into one another. To this end, for example, when forming a barrier element in a mold, the mold can be locally heated and cooled, so that parts of the barrier element cool quickly and other parts slowly. The slowly cooled sections will have a more amorphous structure and the fast cooled sections will have a more crystalline structure.

A still further spread of the periods in which material is released from the barrier element can be achieved if, according to a further embodiment (not shown) of the invention, the barrier element comprises a third part made of a third absorbable material, wherein the material of that third part has such a structure and composition that on average it degrades faster after implantation than the material of the second part. Insofar as suitable materials with sufficiently different degradation rates are available, a further increase in the number of parts from materials with mutually different degradation rates can also be advantageous.

In the exemplary embodiments of the invention shown in Figures 7-10, the first part 11 each forms a frame and the further second parts 12 each fill up a residual space between that frame and the outer surface / lacquer of the barrier element. This offers the advantage that the deterioration of the parts which can be broken down most quickly starts immediately after implantation, because they are located on the outside of the barrier element. Furthermore, the boundaries between the portions, if present, extend to or at least near the surface of the barrier element. By transporting material along these boundaries, accelerated degradation is possible in its region.

The barrier elements according to Figures 7-10 can each be wound up into a tube. The first portion 11 has ribs 13, and the second portions 12 form voids of cavities between those ribs. This keeps the barrier element closed and retains considerable stability and buckling stiffness when the second portions 12 are gone. Keeping the barrier element closed is important in order to keep surrounding tissue out of the space shielded by the barrier element, so that the progress of osteogenesis is not hindered by penetration of other faster growing tissue.

The barrier elements according to the illustrated embodiments can be plastically deformed after moderate heating. For polylactic acid, heating to a temperature of about 70 ° C, for example, in a bath with hot water is generally sufficient to allow plastic deformation. As a result, the shape of the barrier element can still be adapted during the operation in which it is to be implanted.

Openings through which fasteners can be inserted preferably extend through the first portion 11 which has the lowest degradation rate so that after disappearance of second portions 12 of the barrier element, the remnants 11 of the barrier element remain fixed in place.

The barrier element according to Figures 7 and 8 is provided with recesses 14 for centering a drill. These recesses 14 are arranged in such a way that bores made from these recesses extend through the first part 11.

The barrier element according to the invention can advantageously be manufactured by introducing a first amount of material into a mold, then increasing the cavity of the mold by displacing parts of the mold and then introducing a second amount of material into the mold . The formed first part does not have to be removed from the mold, so that the risk of enclosing contamination between the first part and the subsequently injected second part is minimized.

Shrinkage of the first portion allows material from further, second portions to not only penetrate voids or residual spaces between the first portion and the enlarged die space, but also to penetrate between the first portion and unexpanded portions of the die, and thus encloses the first part. However, this is not serious, because it is only a thin layer of material that also degrades and disappears relatively quickly.

For the use of this method, an injection molding machine provided with a mold holder and at least two extruder screws arranged for injecting material into the same mold in that mold holder can advantageously be used. This allows different materials to be brought into the same mold in a simple manner and in quick succession.

However, it is also possible to produce a barrier element according to the invention by first forming a first part in a first mold and then placing it in a second mold, where second, further parts are formed around the first part.

A suitable manufacturing method for forming barrier elements with a constant cross-section profile, such as the barrier element according to Figs. 9 and 10, is coextrusion.

Many other embodiments than the one shown are conceivable within the scope of the invention. For example, it is possible to give the barrier element a simple sandwich structure.

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Claims (28)

Bio-resorbable barrier element for keeping surrounding tissue outside a bone adjacent space to obtain osteogenesis, characterized in that it comprises a flexural rigid plastic-formed shielding portion (1). Barrier element according to claim 1, characterized in that the shielding part (1) has a solid material wall. Barrier element according to claim 1, characterized in that it is designed as an injection molded product. Barrier element according to one of the preceding claims, characterized by a central, cup-shaped shielding section (1) and a thin-walled, annular section (2) running along the edge of the shielding section (1). Barrier element according to one of the preceding claims, characterized in that it is designed as a blank, which can be rolled up into a tube (4). Barrier element according to any one of the preceding claims, characterized by a relatively rigid central part (1) and at least one flexible part (2, 7) along an outer edge of the central part. Barrier element according to claim 6, characterized in that the flexible part (2) is disc-spring-shaped. Barrier element according to claims 6 or 7, characterized in that the wall thickness of the flexible part (2) of the central part (1) decreases. Barrier element according to any one of claims 6-8, characterized in that the flexible part (2) comprises a bent sealing lip (8). Barrier element according to claims 5 and any one of claims 6-9, characterized in that two flexible sections (7) extend along the ends of the tube in the state rolled up into a tube (4). Barrier element according to claim 10, characterized in that in the condition rolled up into a tube (4), the diameter of the tube in the unloaded state along the ends is smaller than in an intermediate part of the tube. Barrier element according to any one of the preceding claims, characterized by bores for mounting fasteners. Barrier element according to any one of the preceding claims, characterized by recesses (14) for centering a perforating member. Barrier element according to any one of the preceding claims, characterized by a composite structure, comprising a first part (11) made of a first absorbable material and a second part (12) made of a second absorbable material, wherein said materials have a structure and composition such that the material of the first part (11) degrades on average more slowly after implantation than the material of the second part (12). Barrier element according to claim 14, characterized in that the structure and composition of said materials is such that after implantation the material of the first part (11) begins to become soluble after substantially all the material of the second part (12) is solved or broken off. Barrier element according to claim 14 or 15, characterized in that the material of the first part (11) has a different composition than the material of the second part (12). Barrier element according to claim 16, characterized in that both materials are copolymers of DL-lactide and glycolide, the glycolide content of the material of the second part being higher than the glycolide content of the material of the first part. Barrier element according to claim 17, characterized in that the molar percentage of glycolide in the material of the second part is between 65 and 90% and the molar percentage of glycolide in the material of the first part is between 40 and 65% amounts. Barrier element according to claim 14 or 15, characterized in that the material of the first part (11) has substantially the same composition as the material of the second part (12), the structure of the material of the first part is more crystalline than the structure of the material of the second part. Barrier element according to any one of claims 14-19, characterized by a third part with a structure and composition such that the material of that third part degrades on average faster after implantation than the material of the second part. Barrier element according to any one of claims 14 to 20, characterized in that the first part (11) forms a frame and the second part (12) fills at least a residual space between said frame and the outer surface of the barrier element . Barrier element according to claim 12 and any one of claims 14-21, characterized in that the openings for fasteners are arranged in said first part. Barrier element according to claim 13 and any one of claims 14-22, characterized in that the recesses (14) for centering a drill are arranged in said first part. Assembly of parts, comprising a barrier element according to any one of the preceding claims and fastening means (15) with a shaft, which is shaped such that by exerting a force only in the longitudinal direction of the shaft in a matching bore in bone fabric can be attached. A mandrel for coiling a barrier element according to claim 11, characterized by two coaxially spaced sections (17) with a tapered diameter, the largest diameter sections facing each other. A mandrel for rolling up a barrier element according to claim 5, 10 or 11 into a tube, characterized by means for heating the mandrel. 27. A method of manufacturing a barrier element from absorbable polymer material, characterized in that a first amount of material is introduced into a mold, then the cavity of the mold is enlarged by displacing parts of the mold and then a second amount of material is introduced into the mold. An injection molding machine for manufacturing a barrier element from absorbable polymeric material, characterized by a die holder and at least two extruder screws arranged for injecting material into the same die in said die holder.