U.S. patent application number 11/688912 was filed with the patent office on 2008-09-25 for porous orthapedic materials coated with demineralized bone matrix.
Invention is credited to Karen Troxel, Jennifer Woodell-May.
Application Number | 20080233203 11/688912 |
Document ID | / |
Family ID | 39523709 |
Filed Date | 2008-09-25 |
United States Patent
Application |
20080233203 |
Kind Code |
A1 |
Woodell-May; Jennifer ; et
al. |
September 25, 2008 |
POROUS ORTHAPEDIC MATERIALS COATED WITH DEMINERALIZED BONE
MATRIX
Abstract
A biomaterial comprising a porous biocompatible structure and a
demineralized bone extract coated onto into the pores of the
biocompatible structure are provided. The biomaterial may also
comprise a demineralized bone gelatin where the gelatin may be
coated over the extract coating or mixed with the extract coating
before being applied to the biocompatible structure. Methods for
making the biomaterial are also provided.
Inventors: |
Woodell-May; Jennifer;
(Warsaw, IN) ; Troxel; Karen; (Warsaw,
IN) |
Correspondence
Address: |
BOSE MCKINNEY & EVANS LLP;2700 FIRST INDIANA PLAZA
135 NORTH PENNSYLVANIA
INDIANAPOLIS
IN
46204
US
|
Family ID: |
39523709 |
Appl. No.: |
11/688912 |
Filed: |
March 21, 2007 |
Current U.S.
Class: |
424/549 ;
427/2.22; 427/2.24; 427/2.27; 623/11.11 |
Current CPC
Class: |
A61L 31/10 20130101;
A61L 2430/02 20130101; A61L 31/005 20130101; A61L 31/124 20130101;
A61L 27/3608 20130101; A61L 31/10 20130101; A61L 2420/02 20130101;
A61L 27/045 20130101; A61L 27/54 20130101; A61L 27/58 20130101;
A61L 27/042 20130101; A61L 2420/06 20130101; A61L 27/56 20130101;
A61L 31/146 20130101; A61L 2300/414 20130101; C08L 89/06 20130101;
A61L 27/06 20130101; A61L 2300/606 20130101; A61L 27/12 20130101;
A61L 2300/30 20130101; A61L 27/047 20130101 |
Class at
Publication: |
424/549 ;
427/2.22; 427/2.24; 427/2.27; 623/11.11 |
International
Class: |
A61K 35/32 20060101
A61K035/32; A61F 2/02 20060101 A61F002/02; A61L 27/04 20060101
A61L027/04; A61L 27/28 20060101 A61L027/28; A61L 27/54 20060101
A61L027/54 |
Claims
1. A biomaterial comprising: a porous biocompatible structure
comprising interconnected pores, wherein the pores comprise
interior walls and are interconnected by passageways; an aqueous
demineralized bone extract coating comprising growth factors,
proteins or a combination thereof; a demineralized bone gelatin
coating comprising a demineralized bone matrix gelatin; and wherein
the demineralized bone extract coating and the demineralized bone
gelatin coating cover the interior walls and passageways.
2. The biomaterial of claim 1 wherein the demineralized bone
extract coating and the demineralized bone gelatin matrix coating
are combined into a single coating material which covers the
interior walls and passageways.
3. The biomaterial of claim 1 wherein the demineralized bone
extract coating covers the interior walls and passageways and the
demineralized bone gelatin coating covers the demineralized bone
extract coating.
4. The biomaterial of claim 1 wherein the demineralized bone
extract coating and the demineralized bone gelatin coating are
dried on interior walls and passageways.
5. The biomaterial of claim 1 wherein the demineralized bone
extract coating is an acid soluble demineralized bone coating.
6. The biomaterial of claim 1 wherein the demineralized bone
extract coating is a guanidine hydrochloride extract.
7. The biomaterial of claim 1 wherein the porous biocompatible
structure comprises a porous metal, hydroxyapatite or xenograft
demineralized cancellous bone.
8. The biomaterial of claim 7 wherein the metal is stainless steel,
titanium, a titanium alloy, tantalum or a cobalt-chromium
alloy.
9. The biomaterial of claim 7 wherein the hydroxyapatite comprises
tricalcium phosphate.
10. The biomaterial of claim 7 wherein the hydroxyapatite comprises
a coralline hydroxyapatite.
11. The biomaterial of claim 1 wherein the pores have a size of
from about 5 microns to about 1000 microns.
12. The biomaterial of claim 1 wherein the pores have an average
diameter of from about 200 microns to about 500 microns.
13. The biomaterial of claim 1 wherein the biomaterial has a form
of granules, blocks, cylinders or pre-formed shapes such as hip or
knee augments, hip or knee implants, or other orthopedic
devices.
14. The biomaterial of claim 1 wherein the biomaterial is used as
an orthopedic implant.
15. A biomaterial comprising: a porous biocompatible structure
comprising interconnected pores, wherein the pores comprise
interior walls and are interconnected by passageways; and an
aqueous demineralized bone extract coating comprising growth
factors, proteins or a combination thereof, wherein the
demineralized bone extract coating covers the interior walls and
passageways.
16. The biomaterial of claim 15 wherein the demineralized bone
extract coating is an acid soluble demineralized bone extract
coating.
17. The biomaterial of claim 15 wherein the demineralized bone
extract coating is a guanidine hydrochloride demineralized bone
extract coating.
18. The biomaterial of claim 15 wherein the demineralized bone
extract coating comprises a growth factor.
19. The biomaterial of claim 18 wherein the growth factor is a bone
morphogenic protein, TGF-.beta., IGF-1, VEGF, PDGF, FGF, EGF or
mixtures thereof.
20. The biomaterial of claim 15 wherein the porous biocompatible
structure is metal, wherein the metal is stainless steel, titanium,
a titanium alloy, tantalum or a cobalt-chromium alloy.
21. The biomaterial of claim 15 wherein the porous biocompatible
structure is xenograft demineralized cancellous bone.
22. The biomaterial of claim 15 wherein the porous biocompatible
structure is hydroxyapatite, the hydroxyapatite comprising
tricalcium phosphate or a coralline hydroxyapatite.
23. The biomaterial of claim 15 wherein the pores have an average
diameter of from about 200 microns to about 500 microns.
24. The biomaterial of claim 15 further comprising a demineralized
bone gelatin coating.
25. The biomaterial of claim 24 wherein the demineralized bone
gelatin coating and the demineralized bone extract are combined
into a single coating material which covers the interior walls and
passageways.
26. The biomaterial of claim 24 wherein the demineralized bone
extract coating covers the interior walls and passageways and the
demineralized bone gelatin coating covers the acid soluble
demineralized bone coating.
27. The biomaterial of claim 15 wherein the biomaterial has a form
of granules, blocks, cylinders or pre-formed shapes such as hip or
knee augments, hip or knee implants, or other orthopedic
devices
28. An orthopedic implant comprising: a porous biocompatible
structure comprising interconnected pores, wherein the pores
comprise interior walls and are interconnected by passageways and
wherein the pores have an average diameter of from about 200
microns to about 500 microns; and an aqueous demineralized bone
extract coating comprising growth factors, proteins or a
combination thereof, wherein the demineralized bone extract coating
covers the interior walls and passageways, wherein the bone extract
coating is dried on the interior walls and passageways.
29. The orthopedic implant of claim 28 wherein the porous
biocompatible structure is coralline hydroxyapatite.
30. The orthopedic implant of claim 28 wherein the demineralized
bone extract is an acid soluble extract.
31. The orthopedic implant of claim 28 wherein the demineralized
bone extract is a guanidine hydrochloride extract.
32. The biomaterial of claim 28 further comprising a demineralized
bone gelatin coating, wherein the demineralized bone gelatin
coating and the demineralized bone extract are combined into a
single coating material which covers the interior walls and
passageways.
33. The biomaterial of claim 28 further comprising a demineralized
bone gelatin coating, wherein the demineralized bone extract
coating covers the interior walls and passageways and the
demineralized bone gelatin coating covers the acid soluble
demineralized bone coating.
34. A method of preparing a biomaterial comprising: a. mixing
demineralized bone with an aqueous solution, the aqueous solution
comprising a weak acid or guanidine hydrochloride, and wherein the
mixing proceeds with constant agitation at a temperature of no
greater than 50.degree. C. for a time period of from about 8 hours
to about 96 hours to prepare a demineralized bone extract; b.
separating the demineralized bone extract from any remaining
solids; c. diluting, removing or neutralizing the weak acid or
guanidine hydrochloride in the demineralized bone extract; d.
coating a porous biocompatible structure with the demineralized
bone extract, wherein the porous biocompatible structure has a
porosity comprising interconnected pores, the pores comprising
interior walls and interconnected by passageways, and wherein the
demineralized bone extract infiltrates the pores and coats the
interior walls and passageways; and e. drying the applied
demineralized bone extract onto the porous biocompatible
structure.
35. The method of claim 34 wherein the aqueous solution comprises a
weak acid, wherein the weak acid is citric acid, lactic acid, malic
acid, acetic acid or a combination thereof.
36. The method of claim 34 wherein the aqueous solution comprises a
weak acid, the weak acid having a concentration of from about 2 M
to about 3 M.
37. The method of claim 34 wherein the weak acid or the guanidine
hydrochloride is neutralized by adjusting the pH to from about 6.5
to about 7.5 by titrating with a counterion.
38. The method of claim 34 wherein the aqueous solution comprises
guanidine hydrochloride, the guanidine hydrochloride having a
concentration of from about 3 M to about 6 M.
39. The method of claim 34 wherein the weak acid or the guanidine
hydrochloride is removed from the demineralized bone extract by
dialysis, ultrafiltration, hollow fiber filtration or crossflow
filtration.
40. The method of claim 34 wherein an amount of demineralized bone
mixed with the aqueous solution is from about 4 grams to about 7
grams of demineralized bone per about 100 grams of aqueous
solution.
42. The method of claim 34 wherein the mixing proceeds for a time
period of from about 24 hrs to about 96 hrs.
43. The method of claim 34 wherein the demineralized bone extract
infiltrates the pores under vacuum.
44. The method of claim 34 wherein the demineralized bone extract
infiltrates the pores by capillary action.
45. The method of claim 34 wherein the porous biocompatible
material comprises a metal, hydroxyapatite or xenograft
demineralized cancellous bone.
46. The method of claim 45 wherein the metal is stainless steel,
titanium, a titanium alloy, tantalum or a cobalt-chromium
alloy.
47. The method of claim 45 wherein the hydroxyapatite is a
coralline hydroxyapatite.
48. The method of claim 34 wherein the pores have an average
diameter of from about 200 microns to about 500 microns.
49. The method of claim 34 wherein the demineralized bone extract
is mixed with a collagen gel before coating the porous
biocompatible material and wherein the porous biocompatible
material is coated with the combined demineralized bone extract and
collagen gel.
50. The method of claim 34 further comprising: f. mixing the solids
separated out in step b with an aqueous saline solution to form a
suspension; g. heating the suspension to a temperature of from
about 85.degree. C. to about 130.degree. C. at a pressure of at
least 15 psig, dissolving the demineralized bone to produce a
demineralized bone gelatin; and h. mixing the demineralized bone
gelatin with the demineralized bone extract before coating the
biocompatible structure.
51. The method of claim 34 further comprising the steps of: f.
mixing the solids separated out in step b with an aqueous saline
solution to form a suspension; g. heating the suspension to a
temperature of from about 85.degree. C. to about 130.degree. C. at
a pressure of at least 15 psig, dissolving the demineralized bone
to produce a demineralized bone gelatin solution; h. applying the
demineralized bone gelatin solution over the dried demineralized
bone extract on the biocompatible structure, wherein the
demineralized bone gelatin solution infiltrates the pores and coats
the interior walls and passageways; i. allowing the applied
demineralized bone gelatin solution to gel; and j. lyophilizing the
biocompatible structure and the applied demineralized bone gelatin
solution.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to coated porous orthopedic
materials and more specifically to porous orthopedic materials
coated with demineralized bone matrix extracts comprising growth
factors.
[0002] Prosthetic devices and bone implants can either be made of
resorbable or non-resorbable materials. In particular, current bone
graft materials include autografts (bone material obtained from the
patient), allografts (cadaver bone and bone material typically
obtained from tissue banks); xenografts (bone materials from
animals), and a variety of artificial or synthetic bone substitute
materials. Such bone substitute materials include materials that
are biocompatible with existing bone, tendon, cartilage and
ligaments, and may comprise metals, ceramics, or composite
materials. Although synthetic materials can be designed to have
porous structures that can accommodate de-novo bone in-growth, they
are generally considered inadequate as being
non-osteoinductive.
[0003] The prior art has extracted growth factors from
demineralized bone matrix (DBM) to be used as a surface coating or
a putty to induce bone growth into implant materials. Demineralized
bone matrix (DBM) is a well characterized osteoinductive resorbable
material containing growth factors, osteogenic proteins and
collagen, which has also been extracted from DBM to be used as a
gel coating for implant materials. U.S. Patent Application No.
2003/0044445 discloses a DBM soluble extract of proteins that is
dried, reconstituted and then mixed with demineralized bone
particles to provide a bone filling material. However, there is no
teaching of applying a DBM soluble extract to a porous synthetic
implant material where the extract coats within the pores.
[0004] Alternatively, U.S. Pat. No. 6,576,249 discloses a method
for preparing a bone gel and bone putty by dissolving DBM in water,
allowing it to form a gel and mixing it with non-demineralized bone
particles to form putty. The '249 patent does not disclose using
this material as a coating. The presence of the bone particles in
the material would prohibit it from coating the pores of a porous
implant material.
[0005] U.S. Pat. No. 6,376,573 discloses a porous ceramic implant
material of coralline hydroxyapatite having a coating within the
pores of the material. The coating however, is used to reinforce
the implant material and not to promote bone growth. The coating
therefore cannot fill the pores, but must only be on the walls of
the pores. This is accomplished by adding the coating as a liquid
and then catalyzing the conversion to a polymeric material in
situ.
[0006] As can be seen, there is a need for a coating material for
porous implants that promotes bone growth, allowing the integration
of the implant within the patient. It would be desirable for the
coating to comprise growth factors, including osteoinductive
proteins to promote the bone growth.
SUMMARY OF THE INVENTION
[0007] In one aspect of the present invention there is provided a
biomaterial comprising a porous biocompatible structure comprising
interconnected pores, wherein the pores comprise interior walls and
may be interconnected by passageways, an aqueous demineralized bone
extract coating comprising growth factors, proteins or a
combination thereof, a demineralized bone gelatin coating
comprising a demineralized bone matrix gelatin, and wherein the
demineralized bone extract coating and the demineralized bone
gelatin coating may cover the interior walls and passageways. The
demineralized bone extract coating and the demineralized bone
gelatin coating may be combined into a single coating before being
applied to the porous biocompatible substrate. Alternatively, the
demineralized bone extract coating may be applied to the porous
biocompatible substrate and then the demineralized bone gelatin
coating may be applied over the demineralized bone extract
coating.
[0008] In another aspect of the present invention, there is
provided a biomaterial comprising a porous biocompatible structure
comprising interconnected pores, wherein the pores comprise
interior walls and are interconnected by passageways and an aqueous
demineralized bone extract coating comprising growth factors,
proteins or a combination thereof, wherein the demineralized bone
extract coating covers the interior walls and passageways.
[0009] In a further aspect of the present invention, there is
provided an orthopedic implant comprising a porous biocompatible
structure comprising interconnected pores, wherein the pores
comprise interior walls and are interconnected by passageways and
wherein the pores have an average diameter of from about 200
microns to about 500 microns and an aqueous demineralized bone
extract coating comprising growth factors, proteins or a
combination thereof, wherein the demineralized bone extract coating
covers the interior walls and passageways, wherein the bone extract
coating is dried on the interior walls and passageways.
[0010] In yet another aspect of the present invention there is
provided a method of preparing a biomaterial comprising mixing
demineralized bone with an aqueous solution, the aqueous solution
comprising a weak acid or guanidine hydrochloride, and wherein the
mixing proceeds with constant agitation at a temperature of no
greater than 50.degree. C. for a time period of from about 8 hours
to about 96 hours to prepare a demineralized bone extract;
separating the demineralized bone extract from any remaining
solids; diluting, removing or neutralizing the weak acid or
guanidine hydrochloride in the demineralized bone extract; coating
a porous biocompatible structure with the demineralized bone
extract, wherein the porous biocompatible structure has a porosity
comprising interconnected pores, the pores comprising interior
walls and interconnected by passageways, and wherein the
demineralized bone extract infiltrates the pores and coats the
interior walls and passageways; and drying the applied
demineralized bone extract onto the porous biocompatible structure.
The method may further comprise the steps of mixing the solids
separated from the extract with an aqueous saline solution to form
a suspension; heating the suspension to a temperature of from about
85.degree. C. to about 130.degree. C. at a pressure of at least 15
psig, dissolving the demineralized bone to produce a demineralized
bone gelatin; and mixing the demineralized bone gelatin with the
demineralized bone extract before coating the biocompatible
structure. Alternatively, the method may further comprise the steps
of mixing the solids separated from the extract with an aqueous
saline solution to form a suspension; heating the suspension to a
temperature of from about 85.degree. C. to about 130.degree. C. at
a pressure of at least 15 psig, dissolving the demineralized bone
to produce a demineralized bone gelatin solution; applying the
demineralized bone gelatin solution over the dried demineralized
bone extract on the biocompatible structure, wherein the
demineralized bone gelatin solution infiltrates the pores and coats
the internal walls and passageways; allowing the applied
demineralized bone gelatin solution to gel; and lyophilizing the
biocompatible structure and the applied demineralized bone gelatin
solution.
[0011] These and other features, aspects and advantages of the
present invention will become better understood with reference to
the following drawings, description and claims.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The following detailed description is of the best currently
contemplated modes of carrying out the invention. The description
is not to be taken in a limiting sense, but is made merely for the
purpose of illustrating the general principles of the invention,
since the scope of the invention is best defined by the appended
claims.
[0013] Broadly, the present invention provides a biomaterial
comprising a porous biocompatible structure that may be coated with
a demineralized bone (DBM) extract comprising growth factors that
increase de novo bone growth into the porous composite material.
Methods are also provided for making the biomaterial of the present
invention. The biomaterial may further comprise a demineralized
bone gelatin coating over the extract coating or the demineralized
bone extract may be combined with the gelatin coating. The
biomaterial is coated such that the pores and any connecting
passageways are coated to support, but not block, bone growth into
the biomaterial. The biomaterial may be in a form such as, but not
limited to, granules, blocks, cylinders or pre-formed shapes such
as hip or knee augments, hip or knee implants, or other orthopedic
devices.
[0014] The biomaterial of the present invention may comprise a
porous biocompatible structure where the porous biocompatible
structure comprises pores interconnected by passageways. The porous
biocompatible structure may be coated with an osteoinductive
coating such that the coating is not only on the surface but may
also coat the pores and passageways. It has been discovered that by
coating the pores and the passageways, bone growth into the porous
material may be scattered throughout most of the implant compared
to the porous biomaterial alone or the porous biomaterial with just
a gelatin coating. In contrast to the present invention, coatings
of the prior art coat the outer surface of a biomaterial with a
gelatin coating and are not designed to be used solely on a porous
substrate. Many of the coatings of the prior art comprise
demineralized bone powder which, although finely milled, prohibits
the coating from completely coating the pores and passageways of a
porous biomaterial and may even clog the pores. Other coatings of
the prior art have been designed to strengthen porous biomaterials
and are not osteoinductive.
[0015] In one embodiment, the biomaterial of the present invention
may comprise a porous biocompatible structure which may comprise
interconnected pores. The pores may comprise interior walls and may
be connected by passageways. In one illustrative embodiment, the
pores may have an average size from about 5 microns to 1000 microns
or from about 200 microns to about 500 microns. In another
illustrative embodiment, the porous biocompatible structure may be
resorbable as new bone is formed or may be non-resorbable. The
resorbable biocompatible structure may be, but not limited to,
hydroxyapatite. The hydroxyapatite may be tricalcium phosphate such
as, but not limited to, Calcigen.RTM. PSI. Alternatively, the
hydroxyapatite may be a coralline hydroxyapatite such as, but not
limited to, the coralline hydroxyapatite described in U.S. Pat. No.
4,976,736 (herein incorporated by reference), known under the trade
name Pro Osteon.TM.. By way of non-limiting example, the coralline
hydroxyapatite may be Pro Osteon.TM. 200 or Pro Osteon.TM. 500
which may have an average pore size of 200 microns and 500 microns,
respectively. In an alternate illustrative embodiment, the
resorbable biocompatible structure may be, but not limited to,
xenograft demineralized cancellous bone. The demineralized
cancellous bone may be formed from cancellous bone from an animal
such as, but not limited to, pig, cow or horse. The cancellous bone
may be cleaned to remove all blood and marrow from the pores. The
bone is then demineralized in hydrochloric acid or any other
procedure known in the art. Following the demineralization, the
bone may be washed and extracted guanidine hydrochloride. The
remaining porous collagen structure that may have the architecture
of cancellous bone may then be used in the present invention. In a
further illustrative embodiment the porous biocompatible structure
may be non-resorbable. By way of a non-limiting example, the
non-resorbable biocompatible structure may comprise porous metal
where the metal may be stainless steel, titanium, titanium alloy,
tantalum or cobalt-chromium alloy. Examples of porous metal for use
as implant material may be found in U.S. Pat. No. 6,206,924 and
Publish Application Nos. 2006/0241776 and 2006/0241781, all of
which are incorporated herein by reference. The porous
biocompatible structure may have a form such as, but not limited
to, granules, blocks, cylinders or pre-formed shapes such as hip or
knee augments, hip or knee implants, or other orthopedic
devices
[0016] The biomaterial may further comprise an aqueous
demineralized bone extract coating comprising growth factors,
proteins or a combination thereof. It will be appreciated that many
growth factors may be proteins and the two categories are not
mutually exclusive, one is not a subset of the other. The growth
factors or proteins may be osteoinductive, helping to promote de
novo growth of new bone. Non-limiting examples of growth factors
may be bone morphogenic proteins, particularly BMP-2 and BMP-7,
TGF-.beta., IGF-1, VEGF, PDGF, FGF, EGF or mixtures thereof. The
aqueous demineralized bone extract coating may also comprise
biologic solutions such as, but not limited to, blood, platelet
rich plasma, platelet poor plasma concentrated plasma, bone marrow
aspirate, concentrated bone marrow aspirate or combinations
thereof.
[0017] In one illustrative embodiment, the aqueous demineralized
bone extract may be an acid soluble demineralized bone extract. The
acid soluble extract may be produced by mixing demineralized bone
matrix (DBM) with a weak acid such as, but not limited to citric
acid, acetic acid, lactic acid, malic acid or mixtures thereof. The
mixture may be stirred or agitated from about 8 hours to about 96
hours at a temperature not greater than 50.degree. C. At
temperatures greater than 50.degree. C. there may be inactivation
of the growth factors and/or proteins. The extract may then be
filtered to remove any remaining solids, the acid neutralized or
removed and used to coat the porous biocompatible structure.
[0018] In another illustrative embodiment, the aqueous
demineralized bone extract may be a guanidine hydrochloride
demineralized bone extract. The guanidine hydrochloride
demineralized bone extract may be produced by mixing DBM with a
solution of guanidine hydrochloride where the guanidine
hydrochloride may be from about 3M to about 6M. The mixture may be
stirred or agitated from about 8 hours to about 96 hours at a
temperature not greater than 50.degree. C. The extract may then be
filtered to remove any remaining solids, the guanidine
hydrochloride neutralized or removed and used to coat the porous
biocompatible structure. Although not wishing to be bound by
theory, the guanidine hydrochloride demineralized bone extract may
have a higher protein content than the acid soluble demineralized
bone extract as it may be more likely to dissolve some of the
DBM.
[0019] The aqueous demineralized bone extract coating may be
applied to the porous biocompatible structure in a manner that
allows for the coating to be delivered to the pores and
passageways. For example, the coating may be applied under
vacuum.
[0020] Alternatively, the coating may be applied by placing the
material in the extract and allowing the extract to enter the pores
and passageways by capillary action. Once the coating is applied to
the biocompatible structure it may be dried onto the structure.
[0021] In another embodiment the biomaterial of the present
invention may further comprise a demineralized bone gelatin
coating. The demineralized bone gelatin coating may be formed from
the remaining solids after the extract is filtered or it may be
formed from a different demineralized bone sample. Alternatively,
it may be formed from partially purified or isolated collagen. The
demineralized bone or collagen may be mixed with a saline solution,
water or any other biocompatible solution and heated under pressure
to dissolve the demineralized bone matrix or collagen to form the
demineralized bone gelatin coating. The coating may then be coated
over the demineralized bone extract coating or it may be mixed with
the demineralized bone extract coating and the mixture of the
extract and gelatin coatings may then be applied to the
biocompatible structure to give only a single coating. The
demineralized gelatin coating is applied such that it coats the
pores and the passageways. As with the demineralized bone extract
coating, the gelatin coating, either alone or combined with the
extract coating, may be applied under vacuum or it may coat the
pores through capillary action. After application to the
biocompatible structure, the demineralized bone gelatin coating may
be dried. The demineralized bone gelatin coating may be less
viscous at higher temperatures making it easier to apply to the
biocompatible structure. However, care should be taken so that the
demineralized bone gelatin coating is not at a temperature high
enough to inactivate the growth factors and/or proteins of the
demineralized bone extract coating.
[0022] It will be appreciated that although the embodiments
describe a single coating, more than one coating of either the
extract and/or the gelatin may be applied. If more than one coat is
applied, the individual coats may be dried before the next coat is
applied.
[0023] In one embodiment, the present invention provides a method
of preparing a biomaterial comprising mixing DBM with an aqueous
solution of a weak acid or guanidine hydrochloride with constant
agitation for a set amount of time to produce an aqueous
demineralized bone extract, filtering the extract solution to
remove any remaining solids, neutralizing or removing the weak acid
or guanidine hydrochloride and coating the porous biocompatible
structure with the extract. The amount of DBM may be from about 2 g
to about 10 g per 100 g of solution. The DBM may be in any form,
including, but not limited to, powder, granules, fragments, slices,
pellets, slices or shavings. It will be appreciated that the
concentration of growth factors and/or proteins in the extract may
be related to both the amount of DBM used and the form, as well as
the strength of aqueous solution. The aqueous solution may comprise
any biologically compatible aqueous solution, particularly those in
which growth factors and proteins may be stable in. Examples of
such solutions may be, but not limited to, Tris buffer, Tris
buffered saline, phosphate buffer and phosphate buffered saline. In
one illustrative embodiment, the solution may be a weak acid
solution where the weak acid may be, but not limited to, citric
acid, lactic acid, malic acid, ascorbic acid or combinations
thereof. Any weak acid known in the art may be used. The
concentration of the weak acid solution may be from about 2 M to
about 3 M. In a second illustrative embodiment, the solution is a
guanidine hydrochloride solution where the concentration of the
guanidine hydrochloride solution may be from about 3 M to about 6
M.
[0024] The DBM may be mixed with the aqueous solution for a set
amount of time with constant agitation at a temperature not greater
than 50.degree. C. The amount of time that the DBM and aqueous
solution may be mixed may be from about 8 hours to about 96 hours.
In one illustrative embodiment, the DBM and aqueous solution may be
mixed together from about 24 hours to about 96 hours. The DBM and
aqueous solution may be mixed together with constant agitation
during that time. Constant agitation may be obtained by, but not
limited to, stirring, shaking, ultrasound or any combination
thereof as well as any other methods of agitating a mixture. The
mixing may be carried out at a temperature that may be conducive to
extracting growth factors and/or proteins from the DBM, but where
growth factors and/or proteins may be stable. In an illustrative
embodiment, the temperature may be no greater than 50.degree. C. In
another illustrative embodiment, the temperature may be room
temperature.
[0025] After mixing for the appropriate amount of time, the
resulting demineralized bone extract may be separated from any
insoluble DBM remaining. This separation may occur by any number of
processes such as, but not limited to, decanting, filtering or
centrifuging. In one illustrative embodiment, the solution may be
filtered to remove any soluble DBM remaining. The size of the sieve
or filter will depend on the size of the DBM particles remaining,
which may further depend on the initial form of DBM. In one
illustrative embodiment, the filter may be from about 50 microns to
about 300 microns. The filter may be a sieve, paper, scintered
glass, woven or non-woven fabric, or any other means of filtering
that is known in the art.
[0026] The demineralized bone extract may be diluted, neutralized
or the weak acid or guanidine hydrochloride removed. Methods for
doing this may be, but not limited to, titration, dialysis,
liquid-liquid extraction, hollow fiber filtration, ultrafiltration,
crossflow filtration or precipitation. In one illustrative
embodiment aqueous solution may be neutralized to a pH of from
about 6.5 to about 7.5 by titration with an appropriate counterion.
Such methods are well known in the art. In another illustrative
embodiment, the weak acid or guanidine hydrochloride may be removed
by dialysis, hollow fiber filtration, ultrafiltration or crossflow
filtration against a biologically compatible buffer, such as, but
not limited to, Tris, TBS, phosphate, PBS or water, where the pH of
the buffer may be from about 6.5 to about 7.5. The molecular weight
cutoff of the dialysis membrane will depend on the size of the
proteins and/or growth factors desired in the solution. The
dialysis, hollow fiber filtration, ultrafiltration or crossflow
filtration membrane may have, for example, a molecular weight cut
off less than or equal to 12 Kd or from about 10 Kd to about 12 Kd.
It is well known in the art how to select the molecular weight cut
off of dialysis tubing to retain the desired molecules within the
sample.
[0027] Once neutralized, a porous biocompatible structure may be
coated with the demineralized bone extract. The demineralized bone
extract may be applied to the biocompatible structure such that the
demineralized bone extract infiltrates the pores and passageways of
the biocompatible structure. In one illustrative embodiment, the
demineralized bone extract may be applied to the biocompatible
structure under vacuum. In another illustrative embodiment the
demineralized bone extract may be applied to the biocompatible
structure by dipping the structure into the extract and allowing it
to infiltrate the pores and passageways by capillary action. After
the demineralized bone extract has been applied to the
biocompatible structure, it may be dried onto the biocompatible
structure. The demineralized bone extract may be dried onto the
structure by lyophilization, vacuum, heating at a temperature not
greater than 50.degree. C. or a combination thereof.
[0028] In another embodiment, the method of the present invention
may further comprise making a demineralized bone gelatin. The
demineralized bone gelatin may be coated over the demineralized
bone extract or it may be mixed with the extract before coating to
form a single coating. The demineralized bone gelatin may be formed
by mixing DBM with an aqueous saline solution such as, but not
limited to PBS, TBS or a sodium chloride solution, to form a
suspension. The suspension may be treated to increased temperature
and pressure such as, but not limited to, autoclaved. In one
illustrative embodiment, the solution may be heated to a
temperature of from about 85.degree. C. to about 130.degree. C. at
a pressure of at least about 15 psig. The DBM may be dissolved to
produce a demineralized bone gelatin. Methods for forming a
demineralized bone gelatin are known in the art. The DBM may be the
solids removed during the filtering step while forming the
demineralized bone extract or it may be fresh DBM. Alternatively,
it will be appreciated that since the demineralized bone gelatin
comprises mainly collagen, collagen of any purity may be
substituted for the DBM.
[0029] The demineralized bone gelatin may be coated over the dried
demineralized bone extract coating on the biocompatible structure
such that the gelatin coats the pores and passageways.
Alternatively, the demineralized bone gelatin may be mixed with the
demineralized bone extract prior to the extract being coated onto
the biocompatible structure to form a single coating. The single
coating comprising the demineralized bone extract and gelatin may
then be applied to the biocompatible structure such that the pores
and passageways are coated. It will be appreciated that the
demineralized bone gelatin may be less viscous at higher
temperatures, making it easier to apply to the biocompatible
structure. If the demineralized bone gelatin is applied to the
biocompatible structure in a less viscous form such as a solution,
it should be allowed to gel before any other steps are performed.
Care should be taken so that the demineralized bone gelatin coating
is not at a temperature high enough to inactivate the growth
factors and/or proteins of the demineralized bone extract
coating.
[0030] Once applied, the demineralized bone gelatin, either alone
or mixed with the demineralized bone extract, may be dried onto the
biocompatible structure. The demineralized bone gelatin may be
dried onto the structure by lyophilization, vacuum, heating at a
temperature not greater than 50.degree. C. or a combination
thereof.
[0031] It should be understood, of course, that the foregoing
relates to exemplary embodiments of the invention and that
modifications may be made without departing from the spirit and
scope of the invention as set forth in the following claims.
* * * * *