U.S. patent application number 10/828316 was filed with the patent office on 2004-10-07 for composition for filling bone defects.
Invention is credited to Gertzman, Arthur A., Sunwoo, Moon Hae.
Application Number | 20040197373 10/828316 |
Document ID | / |
Family ID | 31886632 |
Filed Date | 2004-10-07 |
United States Patent
Application |
20040197373 |
Kind Code |
A1 |
Gertzman, Arthur A. ; et
al. |
October 7, 2004 |
Composition for filling bone defects
Abstract
The invention is directed toward a formable bone composition for
application to a bone defect site to promote new bone growth at the
site which comprises a new bone growth inducing compound of
demineralized lyophilized allograft bone particles. The particle
size ranges from about 0.1 mm to about 1.0 cm and is mixed in a
hydrogel carrier containing a sodium phosphate saline buffer, the
hydrogel component of the carrier ranging from about 1.0 to 5.0% of
the composition and a pH between 6.8-7.4 with one or more additives
of a cellular material, growth factor, demineralized bone chips or
mineralized bone chips.
Inventors: |
Gertzman, Arthur A.; (Stony
Point, NY) ; Sunwoo, Moon Hae; (Old Tappan,
NJ) |
Correspondence
Address: |
JOHN S. HALE
GIPPLE & HALE
6665-A OLD DOMINION DRIVE
MCLEAN
VA
22101
US
|
Family ID: |
31886632 |
Appl. No.: |
10/828316 |
Filed: |
April 21, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10828316 |
Apr 21, 2004 |
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10222807 |
Aug 19, 2002 |
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10222807 |
Aug 19, 2002 |
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09515656 |
Feb 29, 2000 |
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6437018 |
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10222807 |
Aug 19, 2002 |
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09031750 |
Feb 27, 1998 |
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6030635 |
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10222807 |
Aug 19, 2002 |
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09365880 |
Aug 3, 1999 |
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Current U.S.
Class: |
424/423 ;
514/11.3; 514/16.7; 514/8.1; 514/8.2; 514/8.6; 514/8.9;
514/9.1 |
Current CPC
Class: |
A61L 2430/02 20130101;
A61L 27/3821 20130101; A61K 35/32 20130101; A61L 27/3683 20130101;
A61F 2002/30059 20130101; A61L 27/3804 20130101; A61L 24/0094
20130101; A61F 2310/00359 20130101; A61K 35/32 20130101; A61L
24/0031 20130101; A61K 38/1875 20130101; A61L 27/3608 20130101;
A61F 2/28 20130101; A61L 27/3847 20130101; A61L 24/0005 20130101;
A61L 27/52 20130101; A61K 38/1875 20130101; A61L 27/48 20130101;
A61L 27/52 20130101; A61L 27/365 20130101; A61L 27/3834 20130101;
C08L 5/08 20130101; C08L 5/08 20130101; A61K 2300/00 20130101; A61K
2300/00 20130101 |
Class at
Publication: |
424/423 ;
514/012 |
International
Class: |
A61K 038/18 |
Claims
1. (canceled)
2. A sterile formable bone composition as claimed in claim 21
wherein said bone particles are allograft cortical bone ranging
from 100 microns to 850 microns in size at a concentration ranging
from 20% to 35% by weight of the composition.
3. (Canceled)
4. (Canceled)
5. (Canceled)
6. (Canceled)
7. A sterile formable bone composition as claimed in claim 21
wherein said bone particles are taken from a group consisting of
allograft bone, cortical allograft bone, corticalcancellous bone,
cancellous bone, autologous bone and xenograft bone
8. A sterile formable bone composition as claimed in claim 21
wherein said composition includes bone chips taken from a group
consisting of partially demineralized chips and non demineralized
chips having a particle size ranging from 0.1 mm to 1.0 cm which
are added to said viscous carrier at a concentration of about 5% to
about 25%.
9. (Canceled)
10. A sterile formable bone composition as claimed in claim 21
including a cellular material taken from a group consisting of
living cells and cell elements such as chondrocytes, red blood
cells, white blood cells, platelets, blood plasma, bone marrow
cells, mesenchymal stem cells, pluripotential cells, osteoblasts,
osteoclasts, and fibroblasts, epithelial cells, and endothelial
cells. These cells or cell elements or combinations of the same are
present at a concentration of 10.sup.5 to 10.sup.8 per cc of the
carrier
11. (Canceled)
12. (Canceled)
13. (Canceled)
14. (Canceled)
15. (Canceled)
16. (Canceled)
17. (Canceled)
18. (Canceled)
19. (Canceled)
20. (Canceled)
21. A sterile formable bone composition for application to a bone
defect site to promote new bone growth at the site comprising a
demineralized osteoinductive and osteoconductive bone particles in
an aqueous carrier solution, the bone particles being added to a
viscous carrier at a concentration ranging from 5-50%(w/w), the
carrier comprising a hydrogel taken from a group consisting of
chitosan and sodium alginate in a phosphate buffered aqueous
solution, said hydrogel ranging from about 5.0% to about 20.0% by
weight of the aqueous carrier solution and said hydrogel component
having a molecular weight ranging from ten thousand to three
hundred thousand Daltons with a stable viscosity at a temperature
ranging from about 22.degree. C. to about 37.degree. C. and said
composition having a pH ranging from about 6.8 to about 7.4 and a
growth factor additive added to said composition, said growth
factor comprising one or more of a group consisting of transforming
growth factor (TGF-beta), insulin growth factor (IGF-1); platlet
derived growth factor (PDGF), vascular endothelial growth factor
(VEGF), fibroblast growth factor (FGF) (numbers 1-23), osteopontin,
growth hormones such as somatotropin cellular attractants and
attachment agents.
22. A sterile formable bone composition as claimed in claim 21
including a cellular material additive taken from a group
consisting of living cells and cell elements such as chondrocytes,
red blood cells, white blood cells, platelets, blood plasma, bone
marrow cells, mesenchymal stem cells, pluripotential cells,
osteoblasts, osteoclasts, and fibroblasts, epithelial cells, and
endothelial cells. These cells or cell elements or combinations of
the same are present at a concentration of 10.sup.5 to 10.sup.8 per
cc of the carrier
23. A sterile malleable bone composition for application to a bone
defect site to promote new bone growth at the site comprising
demineralized osteoinductive and osteoconductive bone particles in
an aqueous carrier solution, the bone particles being added to a
viscous carrier at a concentration ranging from 5-50%(w/w), the
carrier comprising a hydrogel taken from a group consisting of
chitosan and sodium alginate in a phosphate buffered aqueous
solution, said hydrogel ranging from about 5.0% to about 20.0% by
weight of the aqueous carrier solution and cellular material taken
from a group consisting of living cells, cell elements such as red
blood cells, white blood cells, platelets, blood plasma,
pluripotential cells, osteoblasts, osteoclasts, and fibroblasts,
epithelial cells, and endothelial cells present at a concentration
of 10.sup.5 to 10.sup.8 per cc of the carrier, said hydrogel
component having a molecular weight ranging from ten thousand to
three hundred thousand Daltons with a stable viscosity and said
composition having a pH ranging from about 6.8 to about 7.4
24. A sterile formable bone composition as claimed in claim 23
including growth factor additive added to said composition, said
growth factor comprising one or more of a group consisting of
transforming growth factor (TGF-beta), insulin growth factor
(IGF-1); platlet derived growth factor (PDGF), vascular endothelial
growth factor (VEGF), fibroblast growth factor (FGF) (numbers
1-23), osteopontin, growth hormones such as somatotropin cellular
attractants and attachment agents.
25. A sterile formable bone composition as claimed in claim 23
including growth factor additive added to said composition
comprising one or more of a group consisting of fibroblast growth
factor (FGF) (numbers 1-23) in the amount of 2-4 milligrams in 10
cc of carrier solution.
Description
RELATED APPLICATIONS
[0001] This is a continuation-in-part of U.S. patent application
Ser. No. 09/515,656, filed Feb. 29, 2000 and issued into U.S. Pat.
No. 6,437,018 on Aug. 20, 2002 and continuation-in-part of U.S.
patent application Ser. No. 09/031,750, filed Feb. 27, 1998 and
issued into U.S. Pat. No. 6,030,635 on Feb. 29, 2000 and
continuation-in-part of U.S. patent application Ser. No.
09/365,880, filed Aug. 3,1999, which is a continuation application
of U.S. patent application Ser. No. 09/031,750.
FIELD OF INVETION
[0002] The present invention is generally directed toward a
surgical bone product and more specifically is a composition for
filling bone defects using demineralized allograft bone particles,
partially demineralized allograft bone particles or whole bone
particles mixed in a fluid carrier having an isotonic phosphate
buffer and a high molecular weight viscous excipient derived from
the class of biomaterials known as hydrogels which contains cell
material and/or growth factors.
BACKGROUND OF THE INVENTION
[0003] 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] Formable compositions are used to correct surgical defects
that may be caused by trauma, pathological disease, surgical
intervention or other situations where defects need to be managed
in osseous surgery. It is important to have the defect filler in
the form of a stable, viscous formable composition to facilitate
the placement of the bone growth medium into the surgical site
which is usually uneven in shape and depth. The surgeon will take
the composition on a spatula or other instrument and trowel it into
the site or take it in his/her fingers to shape the bone inducing
material into the proper configuration to fit the site being
corrected. It is also important that the defect filler be
biocompatible and have the correct osmolality and pH and not cause
any additional trauma at the surgical site.
[0005] Many products have been developed in an attempt to treat
this surgical need for a biocompatible formable material. One such
example is autologous bone particles or segments recovered from the
patient. When removed from the patient, the segments or bone
particles are wet and viscous from the associated blood. This works
very well to heal the defect but requires significant secondary
surgery resulting in lengthening the surgery, extending the time
the patient is under anesthesia and increasing the cost. In
addition, a significant increase in patient morbidity is attendant
in this technique as the surgeon must take bone from a non-involved
site in the patient to recover sufficient healthy bone, marrow and
blood to perform the defect filling surgery. This leads to
significant post-operative pain.
[0006] Another product group involves the use of inorganic
materials to provide a matrix for new bone to grow at the surgical
site. These inorganic materials include hydroxyapatite obtained
from sea coral or derived synthetically. Either form may be mixed
with the patient's blood and/or bone marrow to form a gel or a
putty. Calcium sulfate or plaster of Paris may be mixed with water
to similarly form a putty. These inorganic materials are
osteoconductive but are bioinert and do not absorb or become
remodeled into natural bone. They consequently remain in place
indefinitely as a brittle, foreign body in the patient's
tissue.
[0007] Allograft bone is a logical substitute for autologous bone.
It is readily available and precludes the surgical complications
and patient morbidity associated with 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.
[0008] It is well known in the art that for several decades
surgeons have used a patient's own blood as a vehicle in which to
mix the patient's bone chips or bone powder, or demineralized bone
powder so as to form a defect filling paste. Blood is a useful
carrier because it is available from the bleeding operative site,
is non-immunogenic to the patient and contains bone morphogenic
proteins which facilitate wound healing through new bone growth.
However, stored blood from other patients has the deficiencies that
any blood transfusion would have; such as blood type compatibility,
possibility of transmission of disease and unknown concentration of
BMP which are to a great extent dependent upon the age of the
donor.
[0009] While blood contains from forty percent (40%) to fifty
percent (50%) cell mass, it is a satisfactory carrier for
demineralized bone powder because it contains both mono- and
polysaccharides which contribute to the blood viscosity and provide
the bulk viscosity to the paste created by mixing the bone powder
and blood. Specific monosaccharides in blood are glucose at a
concentration of 60-100 mg/100 ml (0.1%) and polysaccharides such
as hexose and glucosamine at approximately 0.1%. Glucuronic acid is
also present at approximately 0.4-1.4 mg/100 ml (average
0.01%).
[0010] The problems inherent with using the patients blood as a
carrier for demineralized bone powder are the difficulties of
mixing the same at the operating site, the difficulty in obtaining
a bone paste consistency which can be easily applied to the
surgical area, the guesswork in mixing a usable composition at the
site and the problem of having a bone paste or gel which will
promote optimum bone replacement growth and not be carried away by
the body fluids at the operation site or simply fall out of the
bone defect site. In an attempt to solve these and other problems,
there have been a number of other attempts using other alternative
mixtures and compositions.
[0011] 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
gel, 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 (1000
microns to 12,000 microns) as is disclosed in U.S. Pat. No.
5,073,373.
[0012] GRAFTON works well to allow the surgeon to place the
allograft bone material at the site. However, the carrier, glycerol
has a very low molecular weight (92 Daltons) and is very soluble in
water, the primary component of the blood which flows at the
surgical site. Glycerol also experiences a marked reduction in
viscosity when its temperature rises from room temperature
(typically 22.degree. C. in an operating room) to the temperature
of the patient's tissue, typically 37.degree. C. This combination
of high water solubility and reduced viscosity causes the allograft
bone material with a glycerol carrier to be "runny" and to flow
away from the site almost immediately after placement; this
prevents the proper retention of the bone material within the site
as carefully placed by the surgeon.
[0013] These problems with GRAFTON gel have been attempted to be
resolved by using a much larger particle size of allograft bone,
specifically lamellae or slivers of bone created by milling or
slicing the bone before mixing it with the glycerol carrier. This
improves both the bulk viscosity and the handling characteristics
of the mixture but still leaves the problem of the fast rate of
dissipation of the carrier and some bone due to the solubility of
the glycerol carrier. The larger particles of demineralized bone
may also retard the development of new bone by the patient because
the large bony lamellae do not pack as well as the smaller grainy
particles of bone. This will leave more open space and could
lengthen the time required to grow new bone and properly fill the
defect. Another deficiency of using the bony lamellae is that the
ends of the bony fragments are uneven and when packed into the
surgical defect, uneven filaments of bone are left protruding out
from the defect which can compromise the healing rate.
[0014] U.S. Pat. No. 5,290,558 discloses a flowable demineralized
bone powder composition using an osteogenic bone powder with large
particle size ranging from about 0.1 to about 1.2 cm. mixed with a
low molecular weight polyhydroxy compound possessing from 2 to
about 18 carbons including a number of classes of different
compounds such as monosaccharides, disaccharides, water dispersible
oligosaccharides and polysaccharides.
[0015] Hence, the advantages of using the smaller bone particle
sizes as disclosed in the U.S. Pat. No. 5,073,373 gel patent were
compromised by using bone lamellae in the shape of threads or
filaments and retaining the low molecular weight glycerol carrier.
This later prior art is disclosed in U.S. Pat. Nos. 5,314,476 and
5,507,813 and the tissue forms described in these patents are known
commercially as the GRAFTON.RTM. Putty and Flex, respectively.
[0016] The use of the very low molecular weight glycerol carrier
also requires a very high concentration of glycerol to be used to
achieve the bulk viscosity. Glycerol and other similar low
molecular weight organic solvents are toxic and irritating to the
surrounding tissues.
[0017] U.S. Pat. No. 5,356,629 discloses making a rigid composition
in the nature of a bone cement to fill defects in bone by mixing
biocompatible particles preferably polymethylmethacrylate coated
with polyhydroxyethylmethacrylate in a matrix selected from a group
which lists hyaluronic acid to obtain a molded semi-solid mass
which can be suitably worked for implantation into bone. The
hyaluronic acid can also be utilized in monomeric form or in
polymeric form preferably having a molecular weight not greater
than about one million Daltons. It is noted that the
nonbioabsorbable material which can be used to form the
biocompatible particles can be derived from xenograft bone,
homologous bone, autogenous bone as well as other materials. The
bioactive substance can also be an osteogenic agent such as
demineralized bone powder, in addition to morselized cancerous
bone, aspirated bone marrow and other autogenous bone sources. The
average size of the particles employed is preferably about 0.1 to
about 3.0 mm, more preferably about 0.2 to about 1.5 mm, and most
preferably about 0.3 to about 1.0 mm. It is inferentially mentioned
but not taught that particles having average sizes of about 7,000
to 8,000 microns, or even as small as about 100 to 700 microns can
be used. However, the biocompatible particles used in this
reference are used in a much greater weight ranging from 35% to 70%
by weight then that taught by the present invention. This is simply
a cement used for implantation of hip prosthesis and is not used to
promote bone growth.
[0018] U.S. Pat. No. 5,830,493 is directed toward a composite
porous body (hyaluronic acid listed in a group of compounds)
comprising a porous frame and a surface layer comprising a
bioabsorbable polymer material formed on the surface. A bone
morphogenetic protein (BMP) is carried on the surface and inside of
the composite porous body. There is no demineralization of bone and
the reference appears only to be relevant to show the addition of
BMP to a bone forming graft.
[0019] Another attempt to solve the bone composition problem is
shown in U.S. Pat. No. 4,172,128 which discloses demineralized bone
material mixed with a carrier to reconstruct tooth or bone material
by adding a mucopolysaccharide to a mineralized bone colloidal
material. The composition is formed from a demineralized coarsely
ground bone material, which may be derived from human bones and
teeth, dissolved in a solvent forming a colloidal solution to which
is added a physiologically inert polyhydroxy compound such as
mucopolysaccharide or polyuronic acid in an amount which causes
orientation when hydrogen ions or polyvalent metal ions are added
to form a gel. The gel will be flowable at elevated temperatures
above 35.degree. C. and will solidify when brought down to body
temperature. Example 25 of the patent notes that
mucopolysaccharides produce pronounced ionotropic effects and that
hyaluronic acid is particularly responsible for spatial
cross-linking. Unfortunately this bone gel is difficult to
manufacture and requires a premolded gel form.
[0020] U.S. Pat. No. 4,191,747 teaches a bone defect treatment with
coarsely ground, denatured bone meal freed from fat and ground into
powder. The bone meal is mixed with a polysaccharide in a solution
of saline and applied to the bone defect site.
[0021] Another prior art product is the formulation of
demineralized allograft bone particles in collagen. Both bovine and
human collagen have been used for this application. Bovine collagen
carries the risk of an immunogenic reaction by the recipient
patient. Recently, it has been found that a disease of cattle,
bovine spongioform encephalopathy (BSE) is transmitted from bovine
tissue to humans. Thus, bovine tissue carries a risk of disease
transmission and is not a desirable carrier for allograft
tissue.
[0022] Human collagen is free of these animal based diseases.
However, collagen absorbs slowly in the human body, particularly in
a bony site with usually a low degree of vascularity. The slow
absorption of collagen can delay the growth of new bone and result
in the formation of scar tissue at the site. This could result in a
non-bony healing and a result with much less tensile strength.
[0023] Accordingly, the prior art as embodied in the glycerol and
other carrier based technology to deliver demineralized allograft
bone to a surgical osseous site is replete with problems and only
partially addresses the problems inherent in the correcting
surgical defects.
SUMMARY OF THE INVENTION
[0024] The subject formulation is a complex mixture of
osteoinductive bone particles and a viscous hydrogel based on a
high molecular weight material with a sodium based phosphate buffer
acting as a carrier or delivery vehicle for the osteoinductive
particles which are mixed with living cells and/or cell elements or
with a bone growth additive. The viscous formulation is designed to
present the bone material and its bone morphogenetic proteins
(BMP), and the macrostructure of the bone particles to serve both
as an osteoconductive matrix and to signal the patient's tissue and
cells to initiate the growth of new bone (osteoinduction). The
formulation is used primarily in contact with bleeding bone. This
condition is created either from trauma or a surgical procedure,
that may involve drilling, sawing, grinding or scraping the bone to
achieve a bleeding condition. In surgery, the bone is traumatized
or surgically cut exposing blood capillaries, Haversian canals
(micro-channels in the bone), periosteum (the protective tissue
lining around bone), muscle and other structures in the surgical
site. Bleeding at the site is considered a favorable condition to
enhance healing of the wound site by bringing to the site the
patient's own cytokines, i.e., proteins and other molecules which
are the body's mechanism to carry out the healing process. Any
interference with the blood cell mechanism would be considered
non-biocompatible and an adverse outcome.
[0025] In order for the bone material to be osteoinductive,
interference either from the traumatized cells or the formulation
must be at a minimum, i.e., a biocompatible condition should be
established and maintained. Several specific properties have been
established in the formulation to create a functional and
therapeutic material. These properties pertain to both physical
characteristics and to the achieving of a biocompatible or
physiologically friendly condition.
[0026] It is an object of the invention to utilize bone material in
a particle size that is useful to achieve the malleability
characteristics that maximizes the amount of bone in the
formulation.
[0027] It is an additional object of the invention to use a non
toxic aqueous solution carrier with a sodium phosphate buffer for
the bone particles to present the composition in a state of
physiological osmolality at the wound site.
[0028] It is also an object of the invention to create a bone
defect material which can be easily handled by the physician and
does not degenerate when contacting blood flow at the surgical
site.
[0029] It is another object of the invention to create a bone
defect material which uses cellular material such as living cells
and cell elements.
[0030] It is still another object of the invention to create a bone
defect material which has a stable viscosity from 22.degree. to
37.degree. C.
[0031] It is an additional object of the invention to create a bone
defect material with an isotonic pH.
[0032] It is yet another object of the invention to use a growth
factor in the bone composition.
DESCRIPTION OF THE INVENTION
[0033] The present invention is directed towards a demineralized or
partially demineralized bone particle composition to heal bone
defects.
[0034] A formable composition with a useful bulk viscosity has been
achieved by using a soluble biomaterial, hydrogel. The balance of
the carrier formulation is an aqueous solution and preferably
includes the addition of a material component, namely, a sodium
based phosphate buffer in a sterile saline or salt carrying water
which avoids the toxic problems with the high concentrations of the
low molecular weight organic solvents of the prior art.
[0035] The particle size of demineralized, lyophilized, allograft
bone when mixed with high molecular weight stable viscosity
hydrogels in a suitable carrier produces a formable composition
with clinically useful bone inducing properties. The formable
property permits the surgeon to shape the bone composition to
exactly fit the surgical defect. Manipulation of the "lump" of
formable bone composition may be done without it sticking to the
gloves of the surgeon, behaving somewhat like a wet clay used in
sculpting.
[0036] It is an important aspect of the present invention that the
implant matrix must remain at the wound site and not be washed away
by the flowing blood and other fluids brought to the site by the
healing mechanism. This is achieved by both the viscous and
hydrogel state of the carrier. While viscous, the aqueous carrier
is a high molecular weight macromolecule held together with water
linkages (hydrogen bonds) and is not readily dissolved and washed
away by the blood and fluids at the wound site.
[0037] Thus, the therapeutic formable bone composition will not be
dissipated by being, washed away and will be present to be
osteoinductive.
[0038] The amount of demineralized bone material (DBM) is maximized
to achieve the optimum balance of osteoinductivity and physical
handling properties. Too much matrix bone may create a gritty or
sandy condition in which the DBM is not ideally enclosed by the
surrounding viscous matrix and the DBM bone particles would be too
easily washed away. Conversely, if the bone concentration is too
low, the osteoinductivity would be less than optimum. Bone
concentration in the composition is in the range of about 20% to
about 50%.
[0039] The types of demineralized bone used in the invention are
cortical and corticocancellous bone particles. However other bone
materials such as partially demineralized chips or granules having
the particle size of 0.1 mm to 1.0 cm or non demineralized chips or
granules derived from cortical bone having the particle size of 0.1
mm to 1.0 cm can be added to the demineralized bone. Similarly
living cells and cell elements and/or growth factors can be added
to the composition.
[0040] The primary role of a carrier is to serve as a delivery
vehicle. The bulk viscosity of the carrier achieves the design goal
of good handling properties by balancing the molecular weight and
concentration of the hydrogel used in the formulation. For example,
a very high molecular weight hydrogel would use a lower
concentration compared to a formulation in which the hydrogel
molecular weight was considerably lower with a higher concentration
used to achieve the same bulk viscosity. The nominal formulation
uses a 660,000 Dalton molecular weight hydrogel (sodium
hyaluronate, or HA). This HA material is used at a 1-5%
concentration in water or phosphate buffered saline to achieve the
bulk viscosity required for the formulation.
[0041] If the balance of molecular weight and concentration were
not optimized, the results would be a runny, excessively fluid
formulation that would not stay at the surgical site. While
Hydrogel molecular weights as low as 150,000 Dalton with a
concentration as high as about 10-15% would give a good bulk
viscosity, concentrations with corresponding viscosity above this
level cannot be filtered to achieve sterility required by a
surgical implant. Guidelines for sterility require a statistical
assurance of no more surviving microorganisms than one in one
million. This cannot be achieved above a concentration of about
5-6% hydrogel of a molecular weight of 660,000 to 700,000 Daltons.
Very much higher concentrations would result in a semi solid not
having desirable handling properties as it would lose the desirable
malleability required for a defect filling formulation.
[0042] The carriers for the formable bone composition are
preferably taken from higher molecular weight hydrogels such as: 1)
Sodium Hyaluronate 6.6.times.10.sup.5-2.6.times.10.sup.6 Daltons
and its derivatives; and 2) Lesser molecular weight hydrogels such
as 3) Chitosan about 10,000 to 300,000 Daltons; 4) Sodium Alginate
about 10,000 to 300,000 Daltons; 5) Dextran about 20,000 to 40,000
Daltons; 6) carboxymethylcellulose (CMC) about 20,000 to 40,000
Daltons and 7) hydroxypropylmethylcellulose (HPMC) about 20,000 to
40,000 Daltons. Other non hydrogel substances which can be used are
collagen.
[0043] The natural condition for blood plasma as well as synovial
fluid, cerebrospinal fluid, aqueous humor (fluid within the globe
of the eye) is at a pH of 7.3-7.4 (reference, Principles of
Biochemistry, Chapters 34 & 35; White, Handler and Smith,
McGraw Hill, NY, 1964). At very slight changes in pH, blood cells
will shift their equilibrium of hemoglobin. This hemoglobin
concentration will change over the small pH range of 7.3 to 7.7
(White et al p. 664). In addition, at significantly lower pH values
in the acidic range, protein molecules will denature, i.e.,
degrade. Thus, it is important to maintain any surgical implant
which is intimate contact with blood at a biocompatible condition
of about pH 7.2-7.4.
[0044] It is important to note that the body has many complex and
redundant mechanisms to maintain its biochemical balance. The blood
pH can be adjusted by several means to its normal, physiologic pH.
Hence the presence of a non-physiologic material at the site of a
bleeding bone wound will eventually be overcome and any
non-biocompatible condition will return to normal pH. The preferred
formulation will start out and maintain pH within the range of 6.8
to 7.4 without stressing the body's biochemical mechanisms when the
bone composition material is applied at the wound site.
[0045] In achieving physiologic pH, the formulation uses a
phosphate buffer based on an aqueous system of the two phosphate
anions, HPO.sub.4 .sup.-2 and H.sub.2 PO.sub.4.sup.-1. This buffer
system is used both to neutralize the acid used to demineralize the
bone and to buffer the sodium hyaluronate viscous hydrogel carrier.
It is important to neutralize the acid (hydrochloric acid) used to
demineralize the bone so as to assure that there is no residue of
this very strong acid which could overwhelm the buffermg capacity
of the phosphate system used to buffer the sodium hyaluronate
carrier.
[0046] The pH is adjusted to the physiologic a range of 6.8 to 7.4
pH or preferably 7.2-7.4 pH by using either or both of dibasic
sodium phosphate or monobasic sodium phosphate and adjusting the
solution with saline, i.e., a sodium chloride solution. The sodium
chloride is chosen instead of only water so as to control the final
osmolality of the formulation to preclude dehydration of the
surrounding cells.
[0047] The buffer introduced contains sodium and phosphate ions
which will remain in solution due to the high solubility of sodium
phosphate. Calcium ions in the extracellular fluid will react with
the phosphate ions to result in the precipitation of insoluble
calcium phosphate salt. More phosphate ions will ionize from the
associated state of the phosphate buffer to introduce more
phosphate ions that will, in turn react with more calcium and
precipitate yet more insoluble calcium phosphate. The calcium
phosphate will deposit at the wound site where the buffered
formulation was placed by the surgeon. This results in an increase
in the presence of calcium at the wound site. The bone regeneration
mechanism will utilize calcium starting 7-10 days after the wound
starts healing by the well-known osteochondral healing mechanism.
Hence, the selection of the sodium phosphate buffer to achieve the
physiologic pH provides a means to increase the calcium
concentration in the precise location where calcium will be needed
to grow new bone.
[0048] Thus, the invention induces the presence of soluble calcium
at the bone defect site. This will encourage new bone growth
through the normal biochemical mechanism. Soluble calcium can be
attracted to the surgical site by using a sodium phosphate buffer
of pH 6.8-7.2 in lieu of isotonic saline. The phosphate buffer
attracts calcium cations to the site from the surrounding healthy
bone and creates an equilibrium concentration of the calcium
precisely at the site of healing where it is most desirable to grow
new bone.
[0049] It is a well known principal of physiology that osmotic
pressure must be maintained within a narrow range to assure healthy
conditions for the many cell types present in normal or surgically
wounded cells. The condition of normal osmotic pressure is referred
to as an isotonic state and is quantified in humans by the value of
about 300 mOsmol/Kg. The sodium hyaluronate (HA) formulation is
buffered to isotonic conditions using sodium chloride as the ionic
salt to supplement the sodium phosphate. Were the sodium
hyaluronate formulation to be buffered without the supplemental
saline, the final hydrogel would only reach an osmolality of less
than 50 mOsmol/Kg.
[0050] At this low osmolality, the extra cellular environment at
the wound site would be in a state of hypotonicity and result in
the inflow of large quantities of water to the cells and blood
cells at the wound site to normalize the osmotic pressure. This
will result in a greater than optimum degree of hydration of the
cells and inhibit wound healing in general and bone growth in
particular. Hemolysis may occur due to excess fluid in the
cells.
[0051] Sodium hyaluronate in the form of the sodium salt is
generally described as an acid mucopolysaccharide. It is envisioned
that suitable amounts of bone morphogenic proteins (BMP) can be
added to either the gel or putty at any stage in the mixing process
to induce accelerated healing at the bone site. BMP directs the
differentiation of pluripotential mesenchymal cells into
osteoprogenitor cells which form osteoblasts. The ability of freeze
dried demineralized cortical bone to transfer 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 and irradiation over 2.0 mrads is sufficient
to destroy or alter the BMP present in the bone matrix.
[0052] A product with satisfactory formability and handling
properties could have a sodium hyaluronate molecular weight ranging
from 690,0000 to 1,200,000 Daltons with a sodium hyaluronate
concentration ranging from 0.75-2.0% with a bone concentration
ranging from 25-27% with a particle size of 100-820 microns. This
resulted in HA solution viscosities ranging from about 1,800 cps to
about 13,000 cps. It was also found that a putty product with
optimal formability and handling properties would have a molecular
weight ranging from 690,000 to 1,200,000 Daltons with a sodium
hyaluronate concentration ranging from 2.0-4.5% with a bone
concentration ranging from 30-33% with a particle size of 100-820
microns. This resulted in HA solution viscosities ranging from
about 6,000 cps to about 275,000 cps. Less molecular weight
hydrogels are used by increasing the percentage of hydrogel added
to the carrier. As an example, the aforenoted chitosan and sodium
alginate at a range of 100,000 to 3,000,000 Daltons molecular
weight are used in a concentration of 15% to 20% while the lower
weight Dextran, CMC and HPMC in a concentration of 15% to 30%.
Osmolality ranges from 280 to 320.
[0053] Additives which are beneficial to bone growth and are added
into the formable composition are living cells and cell elements
such as chondrocytes, red blood cells, white blood cells,
platelets, blood plasma, bone marrow cells, mesenchymal stem cells,
pluripotential cells, osteoblasts, osteoclasts, and fibroblasts,
epithelial cells, and endothelial cells. These cells or cell
elements or combinations of the same are present at a concentration
of 10.sup.5 to 10.sup.8 per cc of carrier and are added into the
composition at time of surgery.
[0054] Growth factor additives which can be used in the present
invention either at the time of packaging or at surgery depending
on the stability of the growth factor are transforming growth
factor (TGF-beta), insulin growth factor (IGF-1); platlet derived
growth factor (PDGF), vascular endothelial growth factor (VEGF),
fibroblast growth factor (FGF) (numbers 1-23), osteopontin, growth
hormones such as somatotropin cellular attractants and attachment
agents.
[0055] Any number of medically useful substances can be used 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,
hydroxy apatite, tricalcium phosphate and soluble solids and/or
liquids dissolved therein.
[0056] 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 gentamycin.
[0057] 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,
[0058] In the following examples the molecular weight of the
various carrier components used is as follows:
EXAMPLE I
[0059] A formable putty of 2% solution sodium hyaluronate in
isotonic saline with 250-420 micron cortical allograft bone
demineralized powder @ 30%.
[0060] 502 milligrams of freeze dried demineralized cortical
allograft bone of particle size ranging from 250-420 microns was
mixed into 1,170 milligrams of a 2% solution of sodium hyaluronate
in isotonic saline with a phosphate buffer. The bone component is
added to achieve a bone concentration of 30% (w/w). The mixture was
well stirred and allowed to stand for 2-3 hours at room temperature
to provide a malleable putty with excellent formability
properties.
EXAMPLE II
[0061] A flowable gel of 250-420 micron particle size demineralized
cortical allograft bone granules in a 1% solution of sodium
hyaluronate at a 25% (w/w) of bone content.
[0062] 503 milligrams of allograft freeze dried demineralized
cortical bone was mixed into 1,502 milligrams of a 1% solution of
sodium hyaluronate having a viscosity ranging from 2,000 cps to
6,000 cps in an aqueous solution of a sodium chloride based
phosphate buffer. The mixture at room temperature provided a
flowable gel.
EXAMPLE III
[0063] A flowable gel of 250-420 micron particle size demineralized
cortical allograft granules in a 1% solution of sodium hyaluronate
at a 30%(w/w) of bone content.
[0064] 501 milligrams of allograft freeze dried demineralized
cortical bone was mixed into 1,167 milligrams of a 1% solution of
sodium hyaluronate in isotonic saline phosphate buffer. The bone
component is added to achieve a bone concentration of 30%(w/w). The
mixture was well stirred and allowed to stand for 2-3 hours at room
temperature. This provided a flowable gel.
EXAMPLE IV
[0065] A flowable gel of 420-850 micron particle size demineralized
cortical allograft granules in a 1% solution of sodium hyaluronate
at a 25%(w/w) of bone content.
[0066] 501 milligrams of allograft freeze dried demineralized
cortical bone was mixed into 1,501 milligrams of a 1% solution of
sodium hyaluronate in isotonic saline phosphate buffer. The bone
component is added to achieve a bone concentration of 25%(w/w). The
mixture was well stirred and allowed to stand for 2-3 hours at room
temperature. This provided a flowable gel.
EXAMPLE V
[0067] A malleable putty of 250-710 micron particle size
demineralized cortical allograft granules in a 4.4% solution of
sodium hyaluronate at a 30% (w/w) of bone content.
[0068] 90 grams of freeze-dried demineralized cortical allograft
bone were mixed into 210 grams of a 4.4% solution of sodium
hyaluronate (660,000 Daltons) in phosphate buffered saline with pH
7.3, viscosity of 207,000 cps and osmolality of 337 mOsmol/Kg. The
bone component was added to achieve a bone concentration of 30%
(w/w). The mixture at room temperature provided a malleable
putty.
EXAMPLE VI
[0069] A flowable gel of 250-710 micron particles of demineralized
cortical allograft granules in a 1.9% solution of sodium
hyaluronate at 25% (w/w) of bone content.
[0070] 75 g of freeze-dried demineralized cortical allograft bone
was mixed into 225 g of 1.9% solution of sodium hyaluronate
(660,000 Daltons) in phosphate buffered saline with pH 7.3,
viscosity of 8,700 cps and osmolality of 314 mOsmol/Kg. The bone
component was added to achieve a bone concentration of 25% (w/w).
The mixture at room temperature provided a flowable gel.
[0071] A flowable gel can be made up of about 25-30% demineralized
bone powder (particle size in a range of 250-850 microns) mixed
into a high molecular weight hydrogel carrier in solution, such as
1% to 2% sodium hyaluronate, with greater ranges for chitosan and
sodium alginate such as 5% to 20% and still greater ranges for
Dextran, CMC and HPMC such as 15% to 30%.
[0072] A flowable putty can be made up of about 30-35%
demineralized bone powder (particle size in a range of 250-850
microns) mixed into a high molecular weight hydrogel carrier in
solution, such as 4% to 5% sodium hyaluronate, with greater
percentage ranges for chitosan and sodium alginate such as 10% to
20% and still greater ranges for Dextran, CMC and HPMC such as 20%
to 30%.
[0073] Osmolality for all compositions ranged from 280 to 320
mOsmol/Kg.
[0074] In Examples 1-6 living cells and cell elements such as
chondrocytes, red blood cells, white blood cells, platelets, blood
plasma, bone marrow cells, mesenchymal stem cells, pluripotential
cells, osteoblasts, osteoclasts, and fibroblasts, epithelial cells,
and endothelial cells have been added into the composition. These
cells or cell elements or combinations of the same are present at a
concentration of 10.sup.5 to 10.sup.8 per cc of carrier and are
added into the composition at time of surgery.
[0075] Similarly growth factor additives can be used in the present
composition either at the time of packaging or at surgery depending
on the stability of the growth factor are transforming growth
factor (TGF-beta), insulin growth factor (IGF-1); platlet derived
growth factor (PDGF), vascular endothelial growth factor (VEGF),
fibroblast growth factor (FGF) (numbers 1-23), osteopontin, growth
hormones such as somatotropin cellular attractants and attachment
agents. Fiberblast growth factor is added in the amount of 2 to 4
milligrams in 10 cc of carrier solution.
[0076] The mixing of the demineralized bone powder into hydrogel
solution is undertaken in a sterile chamber. The mixed formable
bone composition is then placed in a sterile container such as an
impervious syringe barrel or vial, sealed and placed in a sterile
sealed package to which stable growth factors are added with the
cell material and unstable growth factors added to the composition
at the time of surgery.
[0077] One process commonly used to achieve sterility is sterile
filtration of the sodium hyaluronate (HA) followed by aseptic
mixing of the bone and HA. Another method is to irradiate the HA
material first and then continue with aseptic mixing of the bone.
Irradiation sources of either electron beam or gamma (Cobalt 60
isotope) are commercially available.
[0078] 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:
* * * * *