GB2560484A

GB2560484A - Foil structure

Info

Publication number: GB2560484A
Application number: GB1410517.5A
Authority: GB
Inventors: Bernhard Nicolai
Original assignee: Nobel Biocare Services AG
Current assignee: Nobel Biocare Services AG
Priority date: 2014-06-12
Filing date: 2014-06-12
Publication date: 2018-09-19
Also published as: GB201410517D0

Abstract

A foil structure 1 for covering graft material 54 in a bone graft site in a bone augmentation process comprises a perforated thin metal sheet 2, such as anodised titanium, provided with a coating layer 5 of a biocompatible polymer, preferably parylene, forming a non-adherent cell surface. The perforation through-holes have a diameter of 1 micrometer or less, allowing nutrients to pass but hindering the passage of pathogens. The coating 5 may comprise an active coating for release of a substance over time.

Description

(54) Title of the Invention: Foil structure

Abstract Title: Perforated foil cover for bone graft site (57) A foil structure 1 for covering graft material 54 in a bone graft site in a bone augmentation process comprises a perforated thin metal sheet 2, such as anodised titanium, provided with a coating layer 5 of a biocompatible polymer, preferably parylene, forming a non-adherent cell surface. The perforation through-holes have a diameter of 1 micrometer or less, allowing nutrients to pass but hindering the passage of pathogens. The coating 5 may comprise an active coating for release of a substance over time.

I t I t

308 l₀₉ Fig. 5D

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

1/3

2/3

Fig. H

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303 /307 J / ΐ z

Fig. 5D

308

7V 309

TITLE

Foil structure

TECHNICAL FIELD

The invention relates to a foil structure for covering a bone graft site in a bone augmentation process. It further related to a method for producing the foil structure, a method for carrying out a bone augmentation process using the foil structure and a kit comprising the foil structure and fastening means.

BACKGROUND

Generally, bone stock is an important indicator for stability of an implant. More specifically, the higher the bone density, the more likely is the tissue able to provide the support necessary for fixing the implant postoperatively. Consequently, defects in the bone tissue, bone loss or decreased bone volume may have an adverse effect on the implantation result. Particularly in dentistry, this is a challenge, since bone tissue in this region is limited. In addition, reduced amounts of bone tissue may occur after removal of a tooth or there might be less bone stock due to osteoporosis. Also, maxillofacial surgery and cysts leading to large defects in relation to bone mass may require vertical as well as lateral crest augmentation. Thus, for obtaining a good base of bone stock for an implant and to achieve a stable anchoring of the implant within the bone tissue, it is recommendable to increase the bone volume, in particular when bone volume is decreased or is missing due to various reasons.

Bone augmentation techniques are generally based on providing bone graft material to the site of reduced bone volume or to the size of the bone defect. In order to keep the bone graft material in place, meshes or membranes are used for so-called guided bone regeneration. Besides covering up the site of the defect, these membranes or meshes also provide an initial exterior shape to the augmented bone tissue. Thus, they require the mechanical integrity in order to stabilize and protect the intended shape of the new bone tissue so that the bone graft material is prevented from experiencing too much relative movement in relation to itself as well as to the adjacent bone tissue of the defect. Metal meshes have been used in the past for these purposes. However, there is a risk of the graft being contaminated by pathogens or migrating cells as these may pass over the metal mesh into the graft site. In particular epithelial cells migrate faster than connective tissue cells and have the potential to at least contravene with the healing process at the graft site.

There is therefore a need to overcome the problems mentioned above.

SUMMARY

It is an objective of the present invention to provide a foil structure that gives mechanical stability in order to prevent relative movements of the bone graft material situated in the bone defect as well as to reduce the risk of contamination of the graft material or the site of the defect caused by migrating cells and pathogens, which can lead to inflammatory response and have an adverse effect on the resulting tissue. It is also an object of the invention to allow sufficient nutrition supply to the graft site in order to support the regeneration of bone tissue. It is also an object to minimize undesired cell adherence to the foil structure. These objects are achieved by a foil structure of claims 1.

The intention concerns a foil structure for covering a bone graft site in a bone augmentation process wherein the foil structure comprises a perforated metal sheet provided with a coating layer adapted to prevent cell adherence, wherein the foil structure exhibits a plurality of through holes each of which having a diameter of 1 pm or less.

The limited size of the plurality of through-holes prevents migrating cells and pathogens to pass the foil structure. Compared to mesh-type covering structures with less control of the size of the passages through the structure, the inventive foil structure thus reduce the risk of contamination of the graft material or the defect bone site. Migrating cells and pathogens can lead to both inflammatory response and have an adverse effect on the resulting tissue, which is avoided with the use of the inventive foil structure. In addition, the through-holes allow the necessary nutrients needed for the generation of new tissue at the bone graft site to pass the foil structure.

Further, the metal sheet of the foil structure provides mechanical stability such that the foil structure is easily handled by the dental surgeon placing it at the bone graft site and such that the foil structure prevents compression of the augmented area. The healing and regeneration of bone defects by bone substitutes (autograft, allograft and alloplast) must not be disturbed by movement of the regenerative material, dislocation of augment material may lead to fibrous tissue generation. Such mechanical stability is difficult to achieve with structures based on polymer membrane or similar material.

Moreover, the coating layer provides plasticity allowing for bending, contouring and adaption to provide a desired shape in order to fit the bone graft site. The coating layer also prevents osseointegration and ingrowth/attachment of soft tissue to the foil structure. The coating layer therefore facilitates secure and uneventful removal of the foil structure after regeneration is complete.

The surfaces of the metal sheet are preferably smooth or polished. Such a surface prevents or at least reduces osseointegration at the bone graft site. A smooth surface may be accomplished by electropolishing the metal sheet.

According to one aspect of the invention the metal sheet is provided with perforation holes and wherein the through-holes of the foil structure coincide with the perforation holes of the metal sheet. The perforation holes also form through-holes but formally only through the metal sheet. That is, the through-holes remain at the position of the perforation holes as the coating layer is applied to the metal sheet.

In one aspect of the invention the perforation holes of the metal sheet are achieved by means of etching, laser drilling, photolithography, half etching or other suitable method to achieve perforation holes of controlled and preferably uniform diameter.

The metal sheet, and thereby the foil structure, is preferably provided with as many perforation holes as possible while still maintaining the stability and plasticity of the metal sheet.

The metal sheet perforation holes may have a diameter that is larger than that of the foil structure through-holes as the perforation holes can be narrowed down to a desired crosssectional diameter when applying the coating layer onto the metal layer.

According to one aspect of the invention the perforation holes have a larger diameter than the diameter of the through-holes exhibited by the foil structure. In such a design, the coating layer narrows the diameter of the perforation holes such as to create through-holes of smaller diameter.

According to one aspect of the invention the foil structure exhibits a plurality of through-holes each of which having a diameter of 0,05 - 0,45 pm. The through-hole diameter is defined as the diameter of the narrowest passage of the through-hole in a direction perpendicular to the direction of extension of the through-hole. Examples of microorganism diameters include mycoplasm: 0,3 pm, streptococci: 0,5 pm, staphylococcus aureus: 1 pm, escherichia coli: 0,5 2 pm. Bacteria range in size from 0.2-2 microns in width or diameter, and up to 1-10 microns in length for the nonspherical species. The limited through-hole diameter therefore hinders most of such extraneous organisms from entering the bone graft site through the foil structure.

The through-holes may have any suitable geometrical shape such as cylindrical shape or conical shape as long as the diameter is set such that the narrowest part of each through-hole hinders undesired pathogens and migrating cells to pass, still allowing nutrients to pass the foil structure. The through-hole of the foil structure has preferably the same geometrical shape as the perforation holes of the metal sheet.

According to one aspect of the invention the metal sheet of the foil structure has a thickness of less than 50 pm.

According to one aspect of the invention the metal sheet has a thickness of more than 10 pm.

According to one aspect of the invention the metal sheet has a thickness of 15-30 pm.

The thickness of the sheet should be as thin as possible while still being manageable by the surgeons handling it. The thickness range mentioned herein is thin enough to allow flexibility and thick enough to allow stability to the foil structure. The thickness of the coating layer in combination with the thickness of the metal sheet determines the final thickness of the foil structure, and thereby determines its mechanical stability and plasticity.

According to one aspect of the invention an upper side and a lower side of the metal sheet is provided with a coating layer. The lower side is defined as the side intended to face the bone graft site and the upper side it defined as the opposing side, i.e. the side facing the gum tissue if gum tissue is available to cover the bone graft site. The metal sheet can be provided with a coating layer at its upper side only, at its lower side only or at both the upper and the lower side. Preferably at least the lower surface of the metal sheet, intended to face the bone graft site when applied to the site, is provided with a coating layer. The thickness of the coating layer can vary between the two sides, i.e. the lower layer can be thicker than the lower layer or the other way around.

According to one aspect of the invention the coating layer comprises a biocompatible polymer. The coating layer is preferably parylene. Parylene coatings are thin, non-porous polymeric coatings. Parylene is an inert, hydrophobic, optical transparent, biocompatible, polymeric coating material. The optical transparency of a parylene coating layer provides the foil structure with the colour of the metal sheet, wherein the foil structure is tissue coloured if the metal sheet has been anodized.

Another example of a coating is polytetrafluoroethylene (PTFE).

The coating layer material is chosen to hinder newly grown bone tissue to grow attached to the bone augmentation sheet. After regeneration of the bone is complete, the foil structure can thereby be removed without the risk of removing any cells from to graft site. In other solutions cells may grow attached to the surface of the sheet which face the graft site and may be removed and thus lost from the graft site upon removal of the sheet.

According to one aspect of the invention the metal sheet is anodized. The metal sheet thereby has a tissue-like colour and is less visible when covering the bone graft site in a subject e.g. a site in the mouth.

According to one aspect of the invention the coating layer has a thickness of 0,1 to 10 pm. The thickness is arranged with respect to the desired diameter of the through-holes of the foil structure.

The coating layer is preferably applied by physical vapor deposition (PVD). The coating layer may thereby be applied as a very thin layer distributed over the metal sheet.

According to one aspect of the invention the coating layer comprises an active coating such that a substance of the coating layer is released over time from the coating layer. Active coating includes drug eluting silk coating comprising covalently bound substances by noncovalent dimerization as known as such in the art (for example EP2703017). The substance released from the active coating layer is an active substance such as, but not limited to, antibiotics, anticoagulants such as heparin, encapsulated cells or growth hormones.

According to one aspect of the invention the metal sheet is titanium. Titanium metal sheet provides the foil structure with the desired mechanical stability. A titanium sheet is easily perforated such that a plurality of perforation holes are formed. Another suitable material is titanium nitride.

The invention further relates to a method for producing a foil structure as described herein. The method comprise the steps of providing a metal sheet, generating a plurality of perforation-holes through the metal sheet and coating the metal sheet with a coating layer adapted to prevent cell adherence. The coating layer at least partly enters the perforation holes of the metal sheet such that through-holes of controlled diameter form in the foil structure.

The generation of the plurality of perforation holes through the metal sheet may be achieved by means of etching, laser drilling, photolithography, half etching or other suitable method to achieve through-holes of controlled and uniform diameter. The perforation holes of the metal sheet are generated such that the through-holes of the foil structure, after application of a coating layer, each have a diameter of 1 pm or less.

According to one aspect of the invention the method comprises the step of applying the coating layer by physical vapor deposition (PVD), wherein the coating layer is deposited under vacuum through condensation out of the gaseous phase as a non-porous and transparent polymeric film on the substrate material. Due to the gaseous deposition the coating reaches and coats even areas and structures which are not coatable with liquid based processes, such as e.g. sharp edges or tops or thin and deep gaps. In one run a coating layer with thicknesses in the range of 0,1 to 10 pm can be deposited.

According to one aspect of the invention the method further comprise the step of anodizing the sheet material before coating the metal sheet with a coating layer. The anodization of a metal sheet comprising titanium produces a tissue-like colour (pink, yellow, red). The foil structure is therefore less visible and more discrete than a metal-coloured foil structure.

The invention also relates to a method for carrying out a bone augmentation process, comprising the steps of applying bone graft material to a defect bone site such that a bone graft site is formed and covering the bone graft site with a foil structure as described herein.

According to one aspect of the invention the method for carrying out a bone augmentation process further comprises the step of securing the foil structure to the bone graft site with fastening means. The fastening means is suitably pins, sutures, screws, staples, bone glue, polyurethane glue etc. The fastening means are preferably biocompatible.

The invention also relates to a kit, comprising a foil structure and fastening means as described herein.

It is to be understood that the term plurality of through-holes refers to the large majority of the through-holes of the foil structure. A fraction of the through-holes may have a diameter that deviates slightly from the values given, for instance due to random variations in the production of the perforation holes of the metal sheet. The benefit of the invention can still be achieved. The foil structure may also contain a few larger holes for e.g. screws.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described in detail with reference to the figures, wherein:

Figure 1

Figure 2

Figure 3 Figures 4 Figure 5a-d shows, in perspective view, a bone foil structure according to the invention covering a jaw bone graft site;

shows, in cross-sectional side view, a foil structure according to the invention covering a jaw bone graft site;

shows a foil structure according to the invention;

shows, in exploded view, a part of the foil structure of Figure 3; and shows, in a cross-sectional side view, through-holes of the foil structure according to the invention.

DETAILED DESCRIPTION OF DRAWINGS

In the description of the invention given below reference is made to the following figures in which one embodiment is exemplified. The invention is however not limited to the embodiment shown in the figures, and the figures are simply to be seen as a way of illustrating a mode of the invention.

Figures 1-4 show an embodiment of foil structure 1. Figures 5A-D shows four different examples of through-holes of a foil structure 1 as shown in Figures 1-4.

Figure 1 shows a jaw of a patient comprising an upper jaw, a lower jaw (mandible) 52, a set of upper teeth 51 and a set of lower teeth, wherein part of the mandible 52 is defect, missing a couple of teeth and in need of vertical bone regeneration. The defect mandible 52 site is filled with graft material 54 and covered by a foil structure 1. The foil structure 1 is provided with fastening means 10, wherein the fastening means 10 are arranged such as to hold the foil structure 1 in place. The fastening means 10 are screws in this example. The plasticity of the foil structure 1 allows the foil structure 1 to be formed around the bone graft site thereby providing it with a desirable shape i.e shaped in vertical line with the rest of the mandible.

Moreover, the foil structure 1 provides stability to the graft material 54, hindering it from moving around and thus facilitates a correctly sculptured mandible 52. The epithelial gum tissue 55 covering the foil structure after positioning and fastening is obsolete in Figure 1 for the purpose of a better view. The epithelial gum tissue 55 at the graft site (defect mandible part) is preferably folded over the foil structure 1 and stitched up such as to cover the graft site during the bone regeneration time. Once the bone regeneration of the defect mandible site is completed the gum tissue is opened and then the foil structure 1 is removed from the graft site. If epithelial gum tissue is covering the foil structure 1 during regeneration then the epithelial gum tissue is surgically removed to expose the foil structure 1 before its removal. In the example of Figure 1 a dental implant 56 is provided to the bone graft site prior to the adding of the graft material 54 such that the graft material 54 is allowed to grow around the dental implant. The foil structure 1 is arranged to cover the dental implant. Dental implants may also be attached to the regenerated graft site, i.e. after the regeneration phase is over and the foil structure 1 is removed from the site.

Figure 2 shows a cross-section of the bone graft site and the foil structure 1 as seen in Figure 1. The foil structure 1 comprises a metal sheet 2 provided with a coating layer 5. The metal sheet is titanium and the coating layer 5 is a biocompatible polymer preferably parylene. The coating layer 5 provides stability to the thin sheet of metal material 2 and it also provides a smooth contact surface which is non-adherent for epithelial cells or bone cells in contact with the foil structure 1. The foil structure 1 is therefore easily removed as neither the epithelial gum tissue 55 not the newly regenerated bone tissue adheres to the foil structure during the regeneration phase. The gum tissue 55 covering the foil structure 1 is not shown in Figure 2.

The foil structure 1 is provided with through-holes (not shown in Figures 1 and 2) which allow nutrients to pass the foil structure and enter the bone graft site, but hinders pathogens to pass the foil structure. The foil structure therefore functions as a membrane.

Figure 3 shows the perforated foil structure 1 of Figures 1-2 comprising through-holes 3. The through-holes 3 have a diameter of 1 pm or less at its narrowest cross-section; i.e. the narrowest part, horizontally, of the through-holes of vertical extension have a maximum diameter 1 pm. The through-holes 3 allow necessary nutrients to pass the foil structure 1 and enter the bone graft site yet hinder extraneous pathogens to pass from the outside of the bone graft site into the bone graft site. Inflammatory response and other effects on the regenerating tissue are thereby avoided.

Uniform through-holes 3 are distributed across the foil structure 1, as seen in Figure 3. The through-holes 3 are homogenous, evenly, distributed across the entire foil structure 1.

Figure 4 shows a perforated metal sheet 2 provided with uniform perforation holes 31. The perforation holes 31 are evenly distributed over the entire metal sheet. The coating layer 2 is omitted from Figure 4.

In Figure 5A-D two different through-hole geometries are illustrated. In Figure 5A the thoughhole 3 has a cylindrical geometry, the same geometry as the perforation holes of the metal sheet. The foil structure 1 is provided with a coating layer 5. The coating layer 5 is provided to the metal sheet 2 such that is covers to the upper surface 6, intended to face the gum tissue, the lower surface 8, intended to face the bone tissue, as well as the edges 9 and inner side 7, facing the through-hole 3. The coating layer 5 thereby controls the diameter L of the throughhole 3 by its thickness. A cylindrical though-hole such as the ones shown in Figures 5A-B is for example achieved by laser drilling.

In Figure 5B, wherein the though-hole 103 has cylindrical geometry like in Figure 5A, the coating layer 105 only covers the edges 109 of the through-hole 103. The inner side 107 of the through-hole 103 is not covered. Still, the thickness of the coating layer 105 controls the diameter L of the through-hole by creating the narrowest passage at the edges 109. The thickness of the coating layer 105 also determines the thickness t of the foil structure 1 in combination with the thickness of the metal sheet 102. A cylindrical though-hole such as the ones shown in Figures 5A-B is for example achieved by laser drilling.

In Figure 5C-D the though-hole 3 has a conical geometry. The perforation holes of the metal sheet have a likewise conical geometry. A conical though-hole such as the ones shown in Figures 5C-D is for example achieved by etching. The metal sheet 202 of Figure 5C is provided with a coating layer 205, wherein the coating layer 205 covers to the upper surface 206, intended to face the gum tissue, the lower surface 208, intended to face the bone tissue, as well as the edges 209 of the metal sheet 206 and the inner side 207 facing the through-hole 203. In Figure 5D the metal sheet 302 is covered by a coating layer 305 at its upper surface 206 and its lower surface 308. The edged 309 are covered whereas the inner surface 307 of the through-hole 303 is not coated.

By applying the coating layer 5, 105, 205, 305 to the through-hole 3, 103, 203, 303 diameter L can be narrower than the diameter of the hole in the metal sheet, i.e. the distance across the inner sides 7, 107, 207, 307 of the metal sheet through-hole. Hence, the through-holes 3, 103,

203, 303 can be made narrower than what would be possible with mere etching, laser, micro drilling etc of the metal sheet 2,102, 202, 302. The through-holes 3,103, 203, 303 can thereby be made small enough to keep migrating cells and pathogens from passing the foil structure 1, 101, 201, 301, which is a benefit of the invention.

Reference signs mentioned in the claims should not be seen as limiting the extent of the matter protected by the claims, and their sole function is to make claims easier to understand.

As will be realised, the invention is capable of modification in various obvious respects, all without departing from the scope of the appended claims. Accordingly, the drawings and the description thereto are to be regarded as illustrative in nature, and not restrictive.

Claims

1. Foil structure (1) for covering a bone graft site in a bone augmentation process, characterized in that the foil structure (1) comprises a perforated metal sheet (2) provided with a coating layer (5) adapted to prevent cell adherence, wherein the foil structure (1) exhibits a plurality of through-holes (3) each of which having a diameter of 1 pm or less.

2. Foil structure (1) according to claim 1, wherein the metal sheet is provided with perforation holes (31) and wherein the plurality of through-holes (3) of the foil structure (1) coincides with the perforation holes (31) of the metal sheet (2).

3. Foil structure (1) according to claim 2, wherein the perforation holes (31) have a larger diameter than the diameter of the plurality of through-holes exhibited by the foil structure (1).

4. Foil structure (1) according to any of the preceding claims, wherein the foil structure (1) exhibits a plurality of through-holes (3) each of which having a diameter of 0,05 0,45 pm.

5. Foil structure (1) according to any of the preceding claims, wherein the metal sheet (2) has a thickness of less than 50 pm.

6. Foil structure (1) according to any of the preceding claims, wherein the metal sheet (2) has a thickness of more than 10 pm.

7. Foil structure (1) according to any of the preceding claims, wherein the metal sheet (2) has a thickness of 15-30 pm.

8. Foil structure (1) according to any of the preceding claims, wherein an upper side (6) and a lower side (8) of the metal sheet (2) is provided with a coating layer (5).

9. Foil structure (1) according to any of the preceding claims, wherein the coating layer (5) comprises a biocompatible polymer.

10. Foil structure (1) according to any of the preceding claims, wherein the coating layer (5) has a thickness in the range of 0,1 to 10 pm.

11. Foil structure (1) according to any of the preceding claims, wherein the coating layer (5) comprises an active coating such that a substance of the coating layer is released over time from the coating layer (5).

12. Foil structure (1) according to any of the preceding claims, wherein the metal sheet (2) is titanium.

13. Foil structure (1) according to claim 12, wherein the titanium metal sheet (2) is anodized.

14. Method for producing a foil structure (1) according to any of the above claims, wherein the method comprise the steps of:

providing a metal sheet (2), generating a plurality of perforation holes (31) through the metal sheet (2), and coating the metal sheet (2) with a coating layer (5) adapted to prevent cell adherence.

15. Method to produce a foil structure (1) according to claim 14, wherein the method further comprise the step of:

anodizing the sheet material (2) before coating the metal sheet (2) with a coating layer (5).

16. Method for carrying out a bone augmentation process, comprising the steps of:

applying bone graft material (54) to a defect bone site such that a bone graft site is formed, covering the bone graft site with a foil structure (1) according to any of the claims 1-13.

17. Method for carrying out a bone augmentation process according to claim 16, further

5 comprising the step of:

securing the foil structure (1) to the bone graft site with fastening means (10).

18. Kit comprising a foil structure (1) according to any of the claims 1-13 and fastening means (10).

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Robert Crowshaw

8 January 2015