U.S. patent application number 09/739214 was filed with the patent office on 2002-05-23 for partially demineralized cortical bone constructs.
Invention is credited to Gertzman, Arthur A., Sunwood, Moon Hae.
Application Number | 20020061328 09/739214 |
Document ID | / |
Family ID | 27101914 |
Filed Date | 2002-05-23 |
United States Patent
Application |
20020061328 |
Kind Code |
A1 |
Gertzman, Arthur A. ; et
al. |
May 23, 2002 |
Partially demineralized cortical bone constructs
Abstract
The invention is directed toward a sterile bone structure for
application to a bone defect site to promote new bone growth at the
site comprising a partially demineralized cortical bone structure,
said bone structure comprising a cross sectional surface are
ranging from 85% to 95% of the original bone surface area before
demineralization with the remaining partially demineralized
cortical bone structure having an outer demineralized layer ranging
in thickness from about 0.05 mm to about 0.14 mm and a mineralized
core.
Inventors: |
Gertzman, Arthur A.; (Stony
Point, NY) ; Sunwood, Moon Hae; (Old Tappan,
NJ) |
Correspondence
Address: |
GIPPLE & HALE
6665-A Old Dominion Drive
McLean
VA
22101
US
|
Family ID: |
27101914 |
Appl. No.: |
09/739214 |
Filed: |
December 19, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09739214 |
Dec 19, 2000 |
|
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09677891 |
Oct 3, 2000 |
|
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Current U.S.
Class: |
424/428 ;
514/152; 514/16.7; 514/2.4; 514/28; 514/39 |
Current CPC
Class: |
A61F 2002/30843
20130101; A61F 2002/2817 20130101; A61L 31/005 20130101; A61F
2002/30894 20130101; A61L 27/365 20130101; A61F 2002/3023 20130101;
A61F 2002/30059 20130101; A61L 27/3608 20130101; A61F 2/28
20130101; A61F 2002/2839 20130101; A61L 27/3683 20130101; A61L
27/3691 20130101; A61L 2430/02 20130101; A61F 2230/0069 20130101;
A61F 2/447 20130101; A61F 2/446 20130101; A61F 2/3094 20130101;
A61F 2002/302 20130101; A61F 2230/0065 20130101; Y10S 514/801
20130101; A61F 2310/00293 20130101; Y10S 514/802 20130101; A61F
2002/30892 20130101; A61L 27/3847 20130101; A61B 17/86
20130101 |
Class at
Publication: |
424/428 ; 514/28;
514/39; 514/12; 514/152 |
International
Class: |
A61K 009/00; A61K
038/17 |
Claims
What we claim is:
1. A sterile bone structure for application to a bone defect site
to promote new bone growth at the site comprising a partially
demineralized cortical bone structure with a central mineral bone
core section, said bone structure after the demineralization
process retaining a cross sectional surface area ranging from about
85% to about 95% of the original mineralized bone surface area
before demineralization with the remaining partially demineralized
cortical bone structure comprising an outer demineralized layer
ranging from about 0.05 mm to about 0.08 mm in thickness.
2. A sterile bone structure as claimed in claim 1 wherein said
structure includes bone morphogenic proteins in excess of the
amount naturally occurring in allogenic bone.
3. A sterile bone structure as claimed in claim 1 wherein said
structure is a pin.
4. A sterile bone structure as claimed in claim 1 wherein said
structure is a plate.
5. A sterile bone structure as claimed in claim 1 wherein said
structure is a screw.
6. A sterile bone structure as claimed in claim 1 wherein said
structure is a rod.
7. A sterile bone structure as claimed in claim 1 wherein said
structure is a wedge.
8. A sterile bone structure as claimed in claim 1 wherein said
structure is a rod.
9. A sterile bone structure as claimed in claim 1 wherein said
structure is a composite bone structure.
10. A sterile bone structure as claimed in claim 1 wherein said
structure is an anchor.
11. A sterile bone structure as claimed in claim 1 wherein said
structure is a fusion ring.
12. A sterile bone structure as claimed in claim 1 wherein said
structure is a fusion block.
13. A sterile malleable bone composition as claimed in claim 1
including antimicrobial and/or antibiotics such as erythromycin,
bacitracin, neomycin, penicilin polymyxin B, tetracycline,
viomycin, chloromycetin and streptomycin, cefazolin ampicillin,
azactam tobramycin, clindamycin and gentamycin added to the
demineralized layer of said bone structure.
14. A sterile bone structure as claimed in claim 1 including a
soluble silver compound added to said demineralized layer of said
bone structure.
15. A sterile bone structure as claimed in claim 14 wherein said
soluble silver compound contains silver in a range of 10 to 10,000
parts per million.
16. A sterile bone structure as claimed in claim 14 wherein said
silver compound is taken from a group consisting essentially of
silver nitrate, silver chloride, silver oxide, silver sulphate,
silver phosphate, silver acetate, silver perchlorate, or silver
tartrate.
17. A sterile bone structure for application to a bone defect site
to promote new bone growth at the site comprising a partially
demineralized cortical bone structure with a central mineral bone
section, said bone structure after the demineralization process
retaining a cross sectional surface area ranging from about 85% to
about 95% of the original mineralized bone surface area before
demineralization with the remaining partially demineralized
cortical bone structure comprising an outer demineralized portion
ranging from about 5% to about 15% of the cross sectional area of
the demineralized cortical bone structure.
18. A sterile partially demineralized bone structure for
application to a bone defect site to promote new bone growth at the
site comprising a partially demineralized cortical bone structure
with a thickness in excess of 2 mm having an outer surface layer of
demineralized bone having a thickness ranging from about 0.05 mm to
about 0.11 mm and a central mineralized section.
19. A sterile partially demineralized bone structure for
application to a bone defect site to promote new bone growth at the
site comprising a partially demineralized cortical bone structure
with a thickness in excess of 2 mm having an outer surface layer of
demineralized bone having a thickness ranging from about 0.14 mm to
about 0.17 mm and a central mineralized section having a cross
sectional area of at least 2 times the cross sectional area of said
demineralized layer.
20. A sterile partially demineralized bone structure for
application to a bone defect site to promote new bone growth at the
site comprising a partially demineralized cortical bone structure
with a thickness in excess of2 mm having an outer surface layer of
demineralized bone having a thickness ranging from about 0.08 mm to
about 0.11 mm and a central mineralized section having a cross
sectional area of at least 3 times the cross sectional area of said
demineralized layer.
21. A method for partially demineralizing a formed cortical bone
structure comprising the steps of: a) soaking a formed cortical
bone structure in an acid solution for a time period at a
temperature less than about 30.degree. C. to remove a layer of the
cortical bone structure and produce a demineralized layer on the
cortical bone structure ranging from about 0.05 mm to about 0.08 mm
with the remaining area comprising mineralized bone; b) agitating
the acid solution and immersed cortical bone structure; c) removing
the cortical bone structure from the acid solution and washing the
cortical bone structure until the wash discard is at about a
neutral pH; d) packaging the cortical bone structure in a moisture
permeable container; and e) lyophilizing the cortical bone
structure.
22. A method as claimed in claim 21 wherein said acid solution is
hydrochloric acid ranging in acid concentrations from about 0.1 N
to about 2.0 N HCl.
23. A method as claimed in claim 21 wherein said acid solution
consists of a group consisting of hydrochloric acid, sulfuric acid,
phosphoric acid, mineral acids and organic acids.
24. A method as claimed in claim 21 wherein said acid solution is a
chelating agent ethylene diamine tetra acetic acid.
25. A method for partially demineralizing a formed bone structure
comprising the steps of: a) soaking a formed cortical bone
structure having a thickness greater than 1.5 mm in an acid
solution for 30 to 90 minutes at ambient temperature to remove a
layer of the cortical bone structure ranging from 0.12 mm to 0.40
mm of the surface area and produce bone structure with a
mineralized center section and a demineralized layer around said
mineralized center section ranging in thickness from about 0.08 mm
to about 0.14 mm; b) simultaneously agitating the acid solution and
immersed cortical bone structure by stirring same; c) removing the
partially demineralized cortical bone structure from the acid
solution and washing the cortical bone structure with sterile pure
water until the wash discard is at about a neutral pH; d)
lyophilizing the cortical bone structure; and e) packaging the
cortical bone structure in a moisture permeable container.
26. A method as claimed in claim 25 wherein said acid solution is
hydrochloric acid ranging in acid concentrations from about 0.1 N
to about 2.0 N HCl.
27. A method as claimed in claim 25 wherein said acid solution
consists of a group consisting of hydrochloric acid, sulfuric acid,
phosphoric acid, mineral acids and organic acids.
28. A method as claimed in claim 25 wherein said acid solution is a
chelating agent ethylene diamine tetra acetic acid.
29. A method as claimed in claim 25 wherein said acid solution has
a temperature ranging from between 4.degree. C. and 30.degree.
C.
30. A method as claimed in claim 25 wherein said acid solution has
an ambient temperature.
31. A method for partially demineralizing a formed bone structure
comprising the steps of: a) soaking a formed cortical bone
structure in an aqueous antibiotic solution; b) placing the soaked
cortical bone structure in an aqueous detergent at about 95 degrees
F.; c) applying ultrasonic energy to enhance penetration of said
detergent; d) washing the shaped cortical bone structure for at
least 60 minutes in an alcohol/water solution; e) soaking a formed
cortical bone structure in an acid solution for 15 to 30 minutes to
remove a layer of the cortical bone structure and produce a
demineralized layer ranging from about 0.05 mm to 0.08 mm in
thickness; f) agitating the acid solution with an immersed cortical
bone structure; g) removing the cortical bone structure from the
acid solution and washing the cortical bone structure until the
wash discard is at about a neutral pH; h) lyophilizing the cortical
bone structure; and i) packaging the cortical bone structure in a
moisture permeable container.
32. A method as claimed in claim 31 wherein said acid solution
consists of a group consisting of hydrochloric acid, sulfuric acid,
phosphoric acid, mineral acids and organic acids.
33. A method as claimed in claim 31 wherein said acid solution is a
chelating agent ethylene diamine tetra acetic acid.
34. A method as claimed in claim 31 wherein said acid solution is
hydrochloric acid having a concentration ranging from about 0.1 N
to about 2.0 N HCl and said acid soaking takes place at a
temperature ranging from between 4.degree. C. and 30.degree. C.
35. A method as claimed in claim 31 wherein said aqueous antibiotic
solution is Gentamysin.
36. A method as claimed in claim 31 wherein after step g), BMP is
added to the demineralized layer.
37. A method as claimed in claim 31 wherein after step g),
antimicrobial and/or antibiotics such as erythromycin, bacitracin,
neomycin, penicillin, polymyxin B, tetracycline, viomycin,
chloromycetin and streptomycin, cefazolin, ampicillin, azactam,
tobramycin, clindamycin and gentamycin is added to the
demineralized layer.
38. A method as claimed in claim 31 wherein after step g), soluble
silver compound is added to the demineralized layer.
39. A method as claimed in claim 31 wherein said soluble silver
compound contains silver in a range of 10 to 10,000 parts per
million.
Description
RELATED APPLICATION
[0001] The present invention is a continuation-in-part of U.S.
patent application Ser. No. 091677,891 filed Oct. 3, 2000.
FIELD OF INVENTION
[0002] The present invention is generally directed toward a
surgical bone product and more specifically is a shaped partially
demineralized allograft bone device or construct with a mineralized
central section.
BACKGROUND OF THE INVENTION
[0003] The use of substitute bone tissue dates back around 1800.
Since that time research efforts have been undertaken toward the
use of materials which are close to bone in composition to
facilitate integration of bone grafts. Development have taken place
in the use of grafts of a mineral nature such as corals,
hydroxyapatites, ceramics or synthetic materials such as
biodegradable polymer materials. Surgical implants should be
designed to be biocompatible in order to successfully perform their
intended function. Biocompatibility may be defined as the
characteristic of an implant acting in such a way as to allow its
therapeutic function to be manifested without secondary adverse
affects such as toxicity, foreign body reaction or cellular
disruption.
[0004] Human allograft tissue is widely used in orthopaedic,
neuro-, maxillo facial, podiatric and dental surgery. The tissue is
valuable because it is strong, biointegrates in time with the
recipient patient's tissue and can be shaped either by the surgeon
to fit the specific surgical defect or shaped commercially in a
manufacturing environment. Contrasted to most synthetic absorbable
or nonabsorbable polymers or metals, allograft tissue is bioinert
and integrates with the surrounding tissues. Allograft bone occurs
in two basic forms; cancerous and cortical. Cortical bone is a
highly dense structure comprised of triple helix strands of
collagen fiber, reinforced with hydroxyapatite. The cortical bone
is a compound structure and is the load bearing component of long
bones in the human body. The hydroxyapatite component is
responsible for the high compressive strength of the bone while the
collagen fiber component contributes in part to torsional and
tensile strength.
[0005] Many devices of varying shapes and forms can be fabricated
from allograft cortical tissue by machining and surgical implants
such as pins, rods, screws, anchors, plates, intervertebral spacers
and the like have been made and used successfully in human surgery.
These engineered shapes are used by the surgeon in surgery to
restore defects in bone to the bone's original anatomical shape.
This treatment is well known in the art and is commercially
available as demineralized bone.
[0006] Allograft bone is a logical substitute for autologous bone.
It is readily available and precludes the surgical complications
and patient morbidity associated with obtaining autologous bone as
noted above. Allograft bone is essentially a collagen fiber
reinforced hydroxyapatite matrix containing active bone morphogenic
proteins (BMP) and can be provided in a sterile form. The
demineralized form of allograft bone is naturally both
osteoinductive and osteoconductive. The demineralized allograft
bone tissue is fully incorporated in the patient's tissue by a well
established biological mechanism. It has been used for many years
in bone surgery to fill the osseous defects previously
discussed.
[0007] Demineralized allograft bone is usually available in a
lyophilized or freeze dried and sterile form to provide for
extended shelf life. The bone in this form is usually very coarse
and dry and is difficult to manipulate by the surgeon. One solution
to use such freeze dried bone has been provided in the form of a
commercially available product, GRAFTON.RTM., a registered
trademark of Osteotech Inc., which is a simple mixture of glycerol
and lyophilized, demineralized bone powder of a particle size in
the range of 0.1 cm to 1.2 cm as is disclosed in U.S. Pat. No.
5,073,373 issued Dec. 17,1991 forming a gel. Similarly U.S. Pat.
No. 5,290,558 issued Mar. 1, 1994, discloses a flowable
demineralized bone powder composition using a osteogenic bone
powder with large particle size ranging from about 0.1 to about 1.2
cm. mixed with a low molecular weight polyhydroxy carrier
possessing from 2 to about 18 carbons comprising a number of
classes of different compounds such as monosaccharides,
disaccharides, water dispersible oligosaccharides and
polysaccharides.
[0008] A recent version of GRAFTON.RTM. product uses relatively
large demineralized particles in the carrier to create a
heterogenous mixture which provides body or substance to the
composition. This material is useful in filling larger defects
where some degree of displacement resistance is needed by the
filler.
[0009] The advantages of using the bone particle sizes as disclosed
in the 5,073,373 and 5,290,558 patents previously discussed were
compromised by using bone lamellae in the shape of threads or
filaments having a median length to median thickness ratio of about
10:1 and higher while still retaining the low molecular weight
glycerol carrier. This later prior art is disclosed in U.S. Pat.
Nos. 5,314,476 issued May 24, 1994 and 5,507,813 issued Apr. 16,
1996 and the tissue forms described in these patents are known
commercially as the GRAFTON.RTM. Putty and Flex, respective
[0010] The combination of natural cortical bone with very desirable
mechanical strength and the addition of synthetic (recombinant)
BMPs provides a superior form of tissue for surgical use retaining
all of the mechanical properties of the cortical component and the
accelerated healing offered by the BMP's.
[0011] U.S. Pat. No. 5,972,368 issued on Oct. 26, 1999 discloses
the use of cortical contructs (e.g. a cortical dowel for spinal
fusion) which are cleaned to remove all of the cellular material,
fat, free collagen and non-collagenous protein leaving structural
or bound collagen which is associated with bone mineral to form the
trabecular struts of bone. It is stated that the natural
crystalline structure of bone is maintained without the risk of
disease transmission or significant immunogenicity. Thus the shaped
bone is processed to remove associated non-collagenous bone
proteins while maintaining native bound collagen materials and
naturally associated bone minerals. Recombinant BMP-2 is then
dripped onto the dowel surface. It could also be added to the
cortical bone by soaking in the BMP-2 solution. As noted, this
reference teaches the removal of all non-collagenous bone proteins
which necessarily include all the naturally occurring BMP's and
relies upon the addition of recombinant BMP-2 in a specific and
empirically determined concentration. The naturally occurring BMP's
are present in a concentration unique for each specific BMP protein
and has been optimized by nature. The '368 patent teaches complete
removal of the natural BMP's by demineralization and relies solely
on the added rhBMP's. The surface of a machined cortical bone
surface is characterized by a wide variety of openings resulting
from exposure by the machining process of the Haversian canals
present throughout cortical bone. These canals serve to transport
fluids throughout the bone to facilitate the biochemical processes
occurring within the bone. They occur at variable angles and depths
within the bone. Hence, when the machining occurs, the opening will
be varied and unpredictable resulting in a highly variable and
uncontrolled amount of BMP entering the surface of the bone.
[0012] In WO99/39,757 published Aug. 12, 1999, an osteoimplant is
disclosed which uses partially demineralized bone elements and
adjacent surface-exposed collagen to form chemical linkages to bond
the elements into a solid aggregate. It is noted in the Description
of the Preferred Embodiments, that "when prepared from bone derived
elements that are only superficially demineralized" that the
osteoimplant will possess a fairly high compression strength
approaching that of natural bone. FIG. 2 illustrates bone-derived
stacked sheets having a fully or partially demineralized outer
surface 21 with surface exposed collagen and a nondemineralized or
partially demineralized core 22. As noted in Example 1, the bone
sheets approximately 1.5 mm thick were placed in a 0.6 N HCl
solution for 1.5 hours with constant stirring, washed in water for
5 minutes and soaked for 1.5 hours in phosphate buffered saline. In
Example 3 the bone-derived sheets from cortical bone were treated
for 10 minutes in 0.6 N HCl to expose surface collagen. Bone cubes
derived from human cancellous bone were treated to expose surface
collagen at the outer borders of the cube. In Example 4, human
cortical bone-derived sheets approximately 1 mm thick were surface
demineralized for 15 minutes in 0.6 N HCl and in Example 5, human
cortical bone derived sheets approximately 2 mm thick were surface
demineralized for 1 hour in 06 N HCl.
[0013] U.S. Pat. No. 5,899,939, issued May, 1999, to the same
inventor as the foreign patent noted in the paragraph above,
discloses a bone derived implant made up of one or more layers of
fully mineralized or partially demineralized cortical bone, and
optionally one or more layers of some other material. The layers of
the implant are assembled into a unitary structure to provide an
implant.
[0014] In U.S. Pat. No. 5,861,167, issued Jan. 19, 1999, a tooth
root is shown to have selective parts of the surface removed by
acid to improve subsequent attachment of the tooth in conjunction
with periodontal surgery. Similarly U.S. Pat. No. 5,455,041
utilized treatment by demineralizing the tooth root surface with
citric acid applied for one minute to effect reattachment of
collagen fibers to the root surface and adding growth factors onto
the surface of the demineralized root
[0015] Partial demineralization of bone is also disclosed in the
Journal of Surgical Research Vol. 59, pages 614-620 (1995) in the
article Sterilization of Partially Demineralized Bone Matrix: The
Effects of Different Sterilization Techniques on Osteogenetic
Properties where particles of bone of 500 microns were treated for
24 hours at 4 degrees C. with 0.6 N HCl with the extent of
decalcification determined to be 20% and placed in the bone site.
New bone formation was noted after the passage of six weeks.
[0016] In French Patent Applications Numbers 2,582,517 and
2,582,518 treatment of fragments of bones taken from animals,
primarily cattle were partially demineralized and tanned with
glutaraldehyde. The bone elements to be implanted are cut to the
desired shape from an ox bone which has been subjected to a
treatment comprising a degreasing step with an organic solvent such
as ethanol, a demineralization step with a calcium extraction agent
such as hydrochloric acid and tanning with glutaraldehyde and
subsequent washings. Similar demineralization of bone is shown in
U.S. Pat. No. 5,585,116 issued Dec. 17, 1996. This patent also
notes that it is known that partial demineralization facilitates
integration of a bone graft. This is accordingly followed by
different complementary steps which are intended either to
deproteinize the bone completely or to act on the nature of the
proteins which then remain linked within the bone matrix or else to
increase this proportion of proteins.
[0017] It is desirable to make the surface of the bone more
conductive to receiving BMP's and other additives without losing
the desirable high mechanical strength properties of the cortical
bone. It is also desirable to leave most of the naturally occurring
protein intact in the bone in such a way as to expose just enough
of the bone surface to free the natural BMP's present on the
surface. Since demineralization also reduces the cross sectional
area of the bone construct, the bone construct must retain its
shape and structural integrity.
[0018] Accordingly, the prior art only partially addresses the
problems inherent in correcting surgical defects.
SUMMARY OF THE INVENTION
[0019] The present invention is directed toward the treatment of
the surface of cortical bone constructs to modify the surface by
removing a layer of the inorganic mineral hydroxyapatite material
leaving the mechanical properties of the bone constructs
substantially unchanged while providing a surface that allows the
addition of BMP's and other desirable additives to be introduced to
the surface and thereby enhance the healing rate of the cortical
bone in surgical procedures.
[0020] The subject formulation is a demineralized bone structure
for application to a bone defect site to promote new bone growth at
the site comprising a partially demineralized cortical bone
structure, said bone structure comprising a cross sectional surface
are ranging from 85% to 95% of the original bone surface area
before demineralization with the remaining partially demineralized
cortical bone structure comprising an outer demineralized layer
ranging in thickness from about 0.05% to about 0.14%. The structure
is designed to present the bone matrix and a demineralized surface
layer for reception of bone morphogenetic proteins (BMP) and other
desired additives. The macro structure of the highly porous
demineralized surface layer serves both as an osteoconductive
matrix and to signal the patient's tissue and cells to initiate the
growth of new bone (osteoinduction).
[0021] It can be seen that the prior art has attempted to replicate
to some degree the present invention by flash demineralization of
the surface or full demineralization of the structure.
[0022] It is thus an object of the invention to provide a shaped
bone implant construct having a partially demineralized cortical
bone layer with an interior mineralized bone section to provide
compression strength to the implant bone construct.
[0023] It is an object of the invention to utilize a partially
demineralized shaped bone implant structure to approximate the
mechanical strength characteristics of natural bone to provide
overall strength and initial durability to the structure.
[0024] It is yet another object of the invention to provide a
partially demineralized shaped bone implant structure to provide a
strong implant structure of a predetermined shape and size for
implantation.
[0025] It is also an object of the invention to provide a bone
derived structure which can effective hold medical and biological
composition which promote new bone growth and accelerate
healing.
[0026] It is an additional object of the invention to use a BMP
additive in the demineralized layer of the bone structure.
[0027] It is an still additional object of the invention to use a
soluble silver additive in the demineralized layer of the bone
structure.
[0028] It is also an object of the invention to create a bone
structure which can be easily handled by the physician.
[0029] These and other objects, advantages, and novel features of
the present invention will become apparent when considered with the
teachings contained in the detailed disclosure which along with the
accompanying drawings constitute a part of this specification and
illustrate embodiments of the invention which together with the
description serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a perspective view of a partially demineralized
rod or dowel according to the invention;
[0031] FIG. 2 is a perspective view of a partially demineralized
screw according to the invention;
[0032] FIG. 3 is a perspective view of a partially demineralized
anchor according to the invention;
[0033] FIG. 4 is a perspective view of a partially demineralized
wedge according to the invention;
[0034] FIG. 5 is a perspective view of a partially demineralized
fusion ring according to the invention;
[0035] FIG. 6 is a perspective view of a partially demineralized
composite structure according to the invention;
[0036] FIG. 7 is a photograph of a 35.times. enlarged cross
sectional view of a partially demineralized rod treated with 0.6 N
HCl for 30 minutes;
[0037] FIG. 8 is a photograph of a 35.times. enlarged cross
sectional view of a partially demineralized rod treated with 0.6 N
HCl for 60 minutes;
[0038] FIG. 9 is a photograph of a 35.times. enlarged cross
sectional view of a partially demineralized rod treated with 0.6 N
HCl for 90 minutes;
[0039] FIG. 10 is a photograph of a 35.times. enlarged cross
sectional view of a partially demineralized rod treated with 0.6 N
HCl for 120 minutes;
[0040] FIG. 11 is a photograph of a 35.times. enlarged cross
sectional view of a partially demineralized rod treated with 0.6 N
HCl for 180 minutes;
[0041] FIG. 12 is a graph showing bending displacement in relation
to acid soak time; and
[0042] FIG. 13 is a graph showing weight loss during partial
demineralization in relation to acid soak time.
DETAILED DESCRIPTION OF THE INVENTION
[0043] The present invention is directed towards a treated
partially demineralized cortical bone construct which can be placed
in a bone defect area to heal bone defects. The term cortical bone
construct means any shaped bone device such as rods, pins, dowels,
screws, plates, wedges, fusion rings, intervertaebral spacers and
composite assemblies. The aforementioned listing is exemplary only
and is not to construed as restrictive.
[0044] The preferred embodiment and the best mode as shown in FIGS.
1 and 7-11 and shows a cylindrical cortical bone construct 10 with
its surface 12 modified by acid treatment to remove a layer of the
inorganic, mineral, hydroxyapatite bone material in such a way as
to leave the mechanical properties substantially unchanged. While
the bone material is referred to as hydroxyapatite in this
application, in actuality the chemistry and structure of natural
bone mineral is different as natural bone mineral contains
carbonate ions, magnesium, sodium, hydrogen phosphate ions and
trace elements and a different crystalline structure than
hydroxyapatite.
[0045] The unique features of bone that makes it desirable as a
surgical material are, its ability to slowly resorb and be
integrated into the space it occupies while allowing the bodies own
healing mechanism to restore the repairing bone to its natural
shape and function by a mechanism known in the art as creeping
substitution. The second feature is the high mechanical strength
arising from the collagen fiber reinforced hydroxyapatite compound
structure. The creeping substitution mechanism, takes considerable
time and some forms of cortical bone in their natural, unmodified
biological state have been found to persist for over one year
before completely remodeling. Thus a means of accelerating the rate
of biointegration of cortical bone would improve the rate of
healing and benefit the recipient patient.
[0046] It is well known that bone contains osteoinductive elements
known as bone morphogenetic proteins (BMP). These BMP's are present
within the compound structure of cortical bone and are present at a
very low concentrations, e.g. 0.003%. Based upon the work of
Marshall Urist as shown in U.S. Pat. No. 4,294,753, issued Oct. 13,
1981 the proper demineralization of cortical bone will expose the
BMP and present these osteoinductive factors to the surface of the
demineralized material rendering it significantly more
osteoinductive. The removal of the bone mineral leaves exposed
portions of collagen fibers allowing the addition of BMP's and
other desirable additives to be introduced to the demineralized
outer treated surface of the bone structure and thereby enhances
the healing rate of the cortical bone in surgical procedures. The
treatment process also exposes the naturally occurring BMP's at the
surface and renders the surface with biological properties similar
to full demineralized bone (DBM). The inner mass 14 of the bone
mineral of the shaped construct would be left intact to contain the
naturally occurring BMP's and trace elements as noted above. Such a
product would be beneficial in spinal fusion, fracture fixation and
similar orthopaedic and neurological procedures where rapid healing
without loss of strength of implant is required. Partially
demineralized rods 16 as shown in FIGS. 1 and FIGS. 7-11 will
retain various degrees of stiffness inversely proportional to the
degree of demineralization and retention of core mass. The
partially demineralized rods have a demineralized outer section 18
of exposed collagen matrix and a cortical bone core 20.
[0047] Experiments conducted by the Applicants have discovered that
the surface of cortical bone constructs can be modified by acid
treatment to remove a layer of the inorganic, mineral,
hydroxyapatite material in such a way as to leave the mechanical
properties substantially unchanged or to provide a construct having
suitable compression and bending strength. This then allows the
addition of BMP's and other desirable additives to be introduced to
the surface and thereby enhance the healing rate of the cortical
bone in surgical procedures. The process also exposes the naturally
occurring BMP's near the surface and renders the surface with
biological properties similar to fully demineralized bone (DMB).
The inner mass of the bone construct would be left intact to
contain the naturally occurring BMP's.
[0048] It was found that when allograft cortical pins of 2.0 mm
diameter were treated as noted below in Example 1; and the pins
were soaked for 15 to 30 minutes in a 0.6 N solution of HCl that
there was minimal loss of bending strength of the rod even when the
diameter of the rod was reduced from 3 to 5% and the outer layer
was demineralized. The demineralized layer ranged from about 0.05
to about 0.08 mm reducing the mineralized portion diameter from
0.10 mm to 0.16 mm after 15 to 30 minutes of soaking in the 0.6 N
HCl acid bath.
EXAMPLE 1
[0049] Allograft cortical bone pins were prepared by machining
femoral or tibial cortical bone. Pins were prepared with diameter
of approximately 2.0 mm and a length of 4 cm. The bulk bone
segments from which the pins were cut were chemically cleaned
before machining by soaking:
[0050] 1) 30 minutes in an aqueous antibiotic solution of
Gentamycin. This reduces and eliminates any bioburden introduced by
handling the bone.
[0051] 2) 30 minutes in an aqueous detergent at 95.degree. F. using
ultrasonic energy to enhance penetration. This loosens and removes
the lipid elements present in and on the bone.
[0052] 3) 60 minutes in a 70/30% v/v ethanol/water solution. This
further removes any lipid elements remaining after the detergent
wash in step 2, above.
[0053] 4) The final cut pins were given a final soak in a fresh
solution of the ethanol/water cleaning solution.
[0054] 5) The pins were cut in half and then immersed in a 0.6 N
solution of Hydrochloric Acid (HCl). Half of each pin was immersed
for varying times and the other half was retained as an untreated
control.
[0055] 6) The acid treatment was done at room temperature,
23.degree. C.
[0056] 7) Acid immersion was done for 30, 60, 90, 120 and 180
minutes. The pins were immersed in the acid solution and agitated
with gentle mechanical stirring.
[0057] 8) After the appropriate elapsed time the pins were removed,
washed with sterile, pure (USP Sterile) water until the wash
discard was at neutral pH.
[0058] 9) The pins were then lyophilized and packaged in a moisture
permeable container.
[0059] For purpose of this example, the above treatments were done
in a laboratory setting. In a commercial process, the procedures
would be done in a sterile, clean room facility.
[0060] The acid treatment can be controlled to remove a small layer
of the bone mineral layer leaving a highly porous and compressible
surface layer while inducing no change to the inner mass of the
construct. By controlling the acid concentration, temperature and
time of exposure, a layer up to 0.06 mm can be removed and a layer
0.08 mm demineralized and have the cortical pin experience
substantially no loss of mechanical properties as measured by a
three-point bending test. This is an unexpected result in that mass
loss should have a deleterious effect on bending resistance since
the bending moment of a cylindrical beam is a function of the third
power of the diameter.
[0061] The surface demineralized pins were characterized as
follows:
1 Weight Loss. % Demineralization Time (n = 3) [0.6 N HC1 @
23.degree. C.] Average Std Dev 30 minutes 31.8 3.2 60 38.1 1.9 90
48.2 1.2 120 56.1 6.4 180 64.9 2.9
[0062] The thickness of the demineralized layer was also measured.
For each treated pin, the thickness of the demineralized layer was
measured six times by starting at the top of the bone traveling
clockwise approximately 60.degree.. The following data was
measured:
2 Thickness of Demineralized Layer Demineralization Time (mm) [0.6
N HC1 @ 23.degree. C] Average (n = 6) 30 minutes 0.08 60 0.11 90
0.14 120 0.17 180 0.25
[0063] The treated and control pins were subjected to a three-point
bending test. Force-displacement calculations were made from the
test results as are shown in FIG. 12. Bending displacement appears
to be directly proportional to the acid soak time after 30 minutes.
It is noteworthy that the bending displacement is equivalent for
the 30 minute soak time and the untreated control Also note that
the 30 minute acid treatment did reduce the diameter of the pin
0.12 mm Scanning electron micrographs of the treated and control
pins were made and can be seen in the FIGS. 7, 8, 9, 10, and 11
reflecting photographs of the same. It can be clearly seen that the
Haversian canals can be seen in the cross-section of the acid
treated pins and show the removal of the mineral layer at the
surface at 35.times., revealing the open pores in the demineralized
layer exposed by the acid treatment.
[0064] This data demonstrates that surface demineralization can be
achieved to remove significant amounts of the surface mineral layer
without affecting the bulk mechanical strength.
[0065] Similar treatments were done for other machined cortical
shapes using 0.6 N HCl at 23.degree. C. for 10 minutes:
[0066] Example 2 Anterior lumbar intervertebral fusion ring
(FRA)
[0067] Example 3 Posterior lumbar intervertebral fusion block
(PLIF)
[0068] Example 4 Anterior cervical fusion ring (ACF)
[0069] Example 5 Allograft bone screw.
[0070] In all these examples, the surface of the machined cortical
shape was modified without loss of the key details and dimensions
machined into the surface.
[0071] The following shows the diameter change, the change in
surface morphology, and the size of the demineralized layers in
cylindrical pins that were demineralized in 0.6 N HCl in 30, 60,
90, 120, and 180 minutes.
[0072] 1. Diameter chance
[0073] The diameter of each pin was measured in 3 places along the
pin. The measurements were recorded on the length of the photograph
at 1.5 cm, 6.5 cm, and 11.5 cm on the pin. Each measurement is
recorded in the tables below. The bottom column in each "difference
between the treated and untreated pins" is the actual size
difference. The pin was magnified .times.35 so that the
measurements were each divided by 35 to arrive at the actual
difference diameter change.
3 Pin 1-30 minute soak Untreated: Pin 1-B1 Left Side Middle Right
Side Measurement 6.6 cm 6.4 cm 6.5 cm Treated: Pin 1-B2 Left Side
Middle Right Side Measurement 6.0 cm 6.0 cm 6.2 cm Difference
between the treated and untreated pins Left Side Middle Right Side
Measurement 0.6 cm 0.4 cm 0.3 cm Actual 0.017 cm 0.011 cm 0.009 cm
Difference Average diameter change for pin 1: 0.012 cm (0.12 mm)
Pin 2-60 minute soak Untreated: Pin 2-A2 Left Side Middle Right
Side Measurement 6.9 cm 7.1 cm 6.5 cm Treated: Pin 2-A2 Left Side
Middle Right Side Measurement 6.3 cm 6.3 cm 6.2 cm Difference
between the treated and untreated pins Left Side Middle Right Side
Measurement 0.6 cm 0.8 cm 0.3 cm Actual 0.017 cm 0.023 cm 0.009 cm
difference Average diameter change for pin 2: 0.016 cm (0.16 mm)
Pin 3-90 minute soak Untreated: Pin 3-C1 Left Side Middle Right
Side Measurement 7.1 cm 7.1 cm 6.9 cm Treated: Pin 3-C2 Left Side
Middle Right Side Measurement 5.9 cm 5.6 cm 5.4 cm Difference
between the treated and untreated pins Left Side Middle Right Side
Measurement 1.2 cm 1.5 cm 1.5 cm Actual 0.034 cm 0.043 cm 0.043 cm
difference Average diameter change for pin 3: 0.040 cm (0.4 mm) Pin
4-120 minute soak Untreated: Pin 4-A1 Left Side Middle Right Side
Measurement 6.9 cm 6.8 cm 6.6 cm Treated: Pin 4-A2 Left Side Middle
Right Side Measurement 5.1 cm 5.2 cm 4.9 cm Difference between the
treated and untreated pins Left Side Middle Right Side Measurement
1.8 cm 1.6 1.7 Actual 0.051 cm 0.046 cm 0.049 cm Difference Average
diameter change for pin 4: 0.049 cm (0.49 mm) Pin 5-180 minute soak
Untreated: Pin 5-A2 Left Side Middle Right Side Measurement 6.9 cm
6.9 cm 6.7 cm Treated: Pin 5-A2 Left Side Middle Right Side
Measurement 5.3 cm 4.6 cm 5.0 cm Difference between the treated and
untreated pins Left Side Middle Right Side Measurement 1.6 cm 2.3
cm 1.3 cm Actual 0.046 cm 0.066 cm 0.037 cm difference Average
diameter change for pin 5: 0.050 cm (0.50 mm)
[0074] 2. Surface Morphology
[0075] The surfaces of the treated pins were compared to the
surfaces of the untreated pins.
4 Pin Number Surface Morphology 1-B1 Particles are held very
tightly together. There are small gaps in the bone. It looks
somewhat rigid. 1-B2 Looks looser than 1-B1. Very rough looking.
Can see loose particles. There are many holes in the bone. Appears
to have more dimension/depth than 1-B1. 2-A1 Particles are held
tightly together. There are many small gaps in the bone. 2-A2 There
are many loose particles. The a gaps are wider than 2-A1. 3-C1 Very
dense and rigid-looking. Particles are held tightly together. 3-C2
Not as dense as 3-C1. There are many small surface holes and a
couple of loose particles. 4-A1 Particles held tightly together.
Surface appears very rigid. 4-A2 Surface smoother than 4-A1. There
are many surface holes (some deep enough to see the next layer some
just forming). A couple of loose particles. 5-A1 Very dense and
rigid. Small gaps. 5-A2 Smoother than 5-A1. Many surface holes.
Towards the top of the slide, the bone appears bumpy. Gaps are
wider than in 5-A1.
[0076] 3. Thickness of the Demineralized Layer:
[0077] For each treated pin, the thickness of the demineralized
layer was measured 6 times and the average per pin was calculated
and recorded. Note: The measurements started at the top of the bone
and recorded clockwise at approximately 60.degree. intervals. (A
magnifying glass with a cm ruler on it was used to measure the
demineralized layer of each pin).
5 Pin Measurement Number Average Number 1 2 3 4 5 6 Thickness 1-B2
0.09 mm 0.09 mm 0.06 mm 0.11 mm 0.06 mm 0.09 mm 0.08 mm 2-A2 0.11
mm 0.09 mm 0.09 mm 0.11 mm 0.14 mm 0.11 mm 0.11 mm 3-C2 0.14 mm
0.06 mm 0.03 mm 0.17 mm 0.29 mm 0.14 mm 0.14 mm 4-A2 0.17 mm 0.20
mm 0.20 mm 0.17 mm 0.11 mm 0.14 mm 0.17 mm 5-A2 0.26 mm 0.23 mm
0.20 mm 0.23 mm 0.29 mm 0.29 mm 0.25 mm
[0078] 4. Results
[0079] The length of acid soak has an effect on the diameter of the
pin. While longer the pin is soaked in 0.6 N HCl, the more the
diameter changes in size (the diameter gets smaller), a relatively
constant diameter was reached after the 120 minutes of soak in the
HCC. The average diameter change for the pin soaked for 30 minutes
was 0.12 mm; for 60 minutes was 0.16 mm; for 90 minutes was 0.40
mm; and for 120 minutes was 0.49 mm and 180 minutes was 0.50 mm.
The cross-section slides show that while the diameter of the pins
decreased at an increased amount from soak minutes 60 to 90
lessening from soak minutes 90 to 120, it remaining substantially
constant thereafter. The thickness of the demineralized layer
increased almost linearly.
[0080] The surface morphology was also affected by the acid soaks.
All the pins were viewed under a magnification of 100.times.. The
slides of the untreated pins looked rigid, the particles were
tightly held into place making the bone to appear dense, and there
were small gaps on some sections of the bones. The slides of the
treated pins looked completely different than the untreated pins.
The treated-pin slides show loose particles, surface holes, widened
gaps, and the bones appear to be less dense.
[0081] Overall, the length of acid soak time affects the three
areas tested in this study:
[0082] 1. The longer the pin soaks in 0.6 N HCl, the actual
diameter of the pin decreases up until 120 minutes of acid
soak.
[0083] 2. The longer the pin is in the acid soak, the thickness of
the demineralized layer on the bone increases and the core
mineralized portion decreases.
[0084] 3. The acid also has an effect on the surface morphology of
the bone. It changes the surface morphology from appearing very
dense and rigid (when untreated) to having loose particles and
becoming somewhat smoother (when treated).
[0085] It is valuable to add soluble silver (e.g. AgNO.sub.3) to
the surface treated cortical bone structure. This will provide
biostatic properties to the construct, i.e., it will inhibit any
growth of microorganisms which may be resident on the surface of
the cortical tissue or adjacent to it in the surrounding tissue. At
sufficiently high concentrations, the silver cation will be fully
biocidal. Thus, silver ranging from 10 to 10,000 parts per million
may be used.
[0086] It is also envisioned to add soluble silver to the surface
after treatment to provide biostatic properties inhibiting any
growth of microorganisms which may be resident on the surface of
the cortical tissue or adjacent to it in the surrounding tissue.
Silver which can be added is can be taken from a group consisting
of silver nitrate and other soluble or slightly soluble silver
compounds such as silver chloride, silver oxide, silver sulphate,
silver phosphate, silver acetate, silver perchlorate or silver
tartrate.
[0087] It is also possible to add one or more rhBMP's to the
surface of the treated bone shape by soaking and being able to use
a significantly lower concentration of the rare and expensive
recombinant human BMP to achieve the same acceleration of
biointegration. The addition of other useful treatment agents such
as vitamins, hormones, antibiotics, antiviral and other therapeutic
agents could also be added to the surface modified layer. BMP
directs the differentiation of pluripotential mesenchymal cells
into osteoprogenitor cells which form osteoblasts. The ability of
freeze dried demineralized cortical bone to facilitate this bone
induction principle using BMP present in the bone is well known in
the art. However, the amount of BMP varies in the bone depending on
the age of the bone donor and the bone processing. Sterilization is
an additional problem in processing human bone for medical use as
boiling, autoclaving or irradiation over 2.0 Mrads is sufficient to
destroy or alter the BMP present in the bone matrix.
[0088] The time, temperature and acid concentration can be adjusted
to achieve a set of process conditions that will give the same
physical result as the above noted examples. Temperature could be
lowered to 4.degree. C. and allow the process time to increase to
one hour (a four fold increase in process time). Temperatures much
above 30.degree. C. will result in too rapid a rate of
hydroxyapatite removal and result in a highly variable shape.
Conditions could be adjusted to use acid concentrations from about
0.1 N to about 2.0 N HCl. Lower concentrations will result in a
very slow rate of mineral layer removal, not conducive to a
commercial process. Higher concentrations will result in a too
rapid rate of mineral removal and to a highly varied and
uncontrolled surface. Other acids could be used; sulfuric,
phosphoric or other mineral acids, organic acids such as acetic;
chelating agents such as ethylene diamine tetra acetic acid or
other weak acids would also be suitable.
[0089] Any number of medically useful substances can be
incorporated in the invention by adding the substances to the
composition at any steps in the mixing process or directly to the
final composition. Such substances include collagen and insoluble
collagen derivatives, hydroxyapatite and soluble solids and/or
liquids dissolved therein. Also included are antiviricides such as
those effective against HIV and hepatitis; antimicrobial and/or
antibiotics such as erythromycin, bacitracin, neomycin, penicillin,
polymyxin B, tetracycline, viomycin, chloromycetin and
streptomycin, cefazolin, ampicillin, azactam, tobramycin,
clindamycin and gentamycim It is also envisioned that amino acids,
peptides, vitamins, co-factors for protein synthesis; hormones;
endocrine tissue or tissue fragments; synthesizers; enzymes such as
collagenase, peptidases, oxidases; polymer cell scaffolds with
parenchymal cells; angiogenic drugs and polymeric carriers
containing such drugs; collagen lattices; biocompatible surface
active agents, antigenic agents; cytoskeletal agents; cartilage
fragments, living cells such as chondrocytes, bone marrow cells,
mesenchymal stem cells, natural extracts, tissue transplants,
bioadhesives, transforming growth factor (TGF-beta), insulin-like
growth factor (IGF-1); growth hormones such as somatotropin; bone
digestors; antitumor agents; fibronectin; cellular attractants and
attachment agents; immuno-suppressants; permeation enhancers, e.g.
fatty acid esters such as laureate, myristate and stearate
monoesters of polyethylene glycol, enamine derivatives, alpha-keto
aldehydes can be added to the composition.
[0090] All products can also be done in an aseptic environment to
maintain a sterile final product or sterilized after production.
The cortical bone structure is then placed in a moisture permeable
inner container which is placed in a moisture barrier outer
container.
[0091] The principles, preferred embodiments and modes of operation
of the present invention have been described in the foregoing
specification. However, the invention should not be construed as
limited to the particular embodiments which have been described
above. Instead, the embodiments described here should be regarded
as illustrative rather than restrictive. Variations and changes may
be made by others without departing from the scope of the present
invention as defined by the following claims:
* * * * *