bone graft substitutes

1. ‘ Ideal bone graft substitute’-should be biocompatible,
bioresorbable,osteoconductive,osteoinductive, structurally
similar to bone ,easy to use and cost effective..

2. Need for graft substitutes
Limitations of Autogenous bone graft:
Increased morbidity of surgical procedure.
Increased anaesthesia time,
Increased blood loss.
Post op donor site complications
Limited amount of graft material.

3. LAURENCIN classification
Bone graft substitutes classified into 5 major cetegories
1. Allograft based.
2. Factor based.
3. Cell based.
4. Ceramic based.
5. Polymer based.

4. CLASS Description Example Properties of action
Allograft based Allograft bone used alone or in
combination
Allegro,Orthoblast,Grafto
n.
Osteoconductive.
Osteoinductive.
Factor based Natural and recombinant growth
factors usd alone or in
combination.
TGF-B , PDGF,FGF,BMP. Osteoinductive
Osteoinductive and
osteoconductive with
carrier materials.
Cell based Cells used to generate new tissue
alone or seeded onto a support
matrix.
Mesenchymal stem cells. Osteogenic.
Both osteogenic and
osteoconductive with
carrier materials.
Ceramic based Includes calcium
phosphate,calcium sulfate,and
bioactive glass used alone or in
combination.
Osteograft,Osteoset,Nova
bone.
Osteoconductive.
Limited osteoinductive
when mixed
bonemarrow.
Polymer based Includes degradable and
nondegradable polymers used
alone and in combination with
Cortoss,OPLA,
Immix.
Osteoconductive.
Bioresorbable in
degradable polymer.

5. ALLOGRAFT BASED substitutes
Uses allograft bone with or without other elements.
Comes in many forms and many preparations-freeze
dried,irradiated and decalcified.
DEMINERALISED BONE MATRIX (DBM)-
chemosterilised,antigen extracted,surface demineralised
autolysed-allogeneic bone .
DBM is generally mixed with a carrier –glycerol,calcium
sulfate powder,sodium hyaluronate ,gelatin.

6.  DBM sterilised by gamma irradiation and ethylene
oxide-1.decreases the risk of disease transmission.
2.decreases the osteoinduvtive activity.
 Contraindications to DBM-
1.Severe vascular or neurological disease.
2.fever.
3.Uncontrolled DM.

7. 4.Severe Degenerative Bone disease.
5.Pregnancy.
6.Hypercalcemia.
7.Renal compromise.
8.Pott disease,or osteomyelitis or sepsis at the surgical
site.

8. Complications of allograft:
 Transmission of disease.
 Variable osteoinductive strength.
 Infection of graft.(large allografts for structural
replacement have the greatest risk of disease
transmission.)
DBM is much less likely to transmit infection .

9. GROWTH FACTOR BASED substitutes
URIST first discovered BMP in 1965,when he
recognised its ability to induce enchondral bone
formation.
Growth factors are a part of a very large group of
cytokines.
Growth factors commonly involved are:
1.TGF-β.2.IGF.3.PDGF.4.VEGF.5.b FGF.
Most of the BMP’s used today are in the bone super
family transforming growth factor –β.

10. This super family includes the inhibin/activin family,
mulleraian-inhibiting substance family, and the
decapentaloplegic family.
IGF and TGF-β mostly modulate the synthesis of
cartilage matrix.
bFGF has a powerful mitogenic factor which stimulates
the differentiation of chondrocytes.
bFGF is produced locally in bone during the initial
phase of fracture healing and is known to stimulate
cartilage and bone forming cells.

11. BMP’s shown to have osteogenic properties are-
1.BMP 2,7-key role in osteoblast differentiation.
2.BMP-3 – induces bone formation.
3.BMP-4 – regulates the formation of teeth,limbs and
bone from mesoderm.
4.BMP-5 –functions in cartilage develoment.
6.BMP-6- role in joint integrity in adults.
7.BMP -8a – involved in Bone and cartilage development.
BMP’s are group of noncollagenous glycoproteins that
belong to the TGF-β super family.

12. BMP’s are produced by recombinant technology and
are designated rhBMP.
Presently only two proteins have been isolated,
produced, and approved for use in humans-rhBMP-2,
and rhBMP-7.
The synthetic biodegradable polymer/interconnected
porous calcium hydroxyapatite ceramics(IP-CHA)
composite is an excellent combination carrier/scaffold
delivery system for rhBMP-2.
BMP -2,7 are water soluble and require a carrier to
remain in the operative area.

13. Representation of BMP action sites
B
bBMP 2,6,9 BMP 2,4,7,9 Most BMP’s
Pluripotent
MSC
Osteoprogenitor
cell
Osteoblast Osteocyte

14. MOA of rhBMP’s is :chemotaxis,mitogenesis, and cell
differentiation.
rhBMP’s differ in the type of cell induced to
differentiate:
-rhBMP-2 acts on the mesenchymal stem cell and
preosteoblast to differentiate into osteoblasts while
rhBMP-7 acts only on the preosteoblast.
Uses of rhBMP’s: 1.Spinal fusion
2.Treatment of open tibial fractures.
3.Maxillofacial surgeries.

15. Complications of rhBMP’s
Problems with the implant-bending,breaking
subsidence or migration, and loosening,
-neurological complications-paralysis,nerve and spinal
cord damage,dural tears,sexual dysfunction,bowel and
bladder dysfunction.
-General organ complications-respiratory failure, GIT
problems.

16. In anterior cervical spine-anterior soft tissue swelling,
-dysphagia,tracheostomies
-airway related complications
In posterior cervical spine-seroma pressing on the cord
In posterior lumbar spine-osteolysis,
-neurological deterioration
-ectopic and hypertrophic
bone formation.
-wound complications.

17. GROWTH
FACTOR
SOURCE FUNCTIONS
1.TGF-β Platelets,T-Cells,
macrophages,endothe
lial cells,fibroblasts.
1.Chemotactic for PMN’s,macrophages,
lymphocytes,fibroblasts.
2.StimulatesTIMPsynthesis,angiogenesis,fibroplasia.
3.Inhibits production of MMP’s.
2.FGF
-1-Acidic.
-2-Basic
Macrophages ,mast
cells,T-cells,
endothelial cells,
fibroblasts
1.Chemotactic for fibroblasts.
2.Mitogenic for fibroblasts & keratinocytes.
3.Stimulates keratinocyte migration.
4.Angiogenesis ,wound contraction.
3.VEGF
Isoforms-
A,B,C,D.
Many types of cells 1.Increased vascular permeability.
2.Mitogenic for endothelial cells.
3.Angiogenesis.
4.PDGF
Isoforms-
A,B,C,D.
Platelets,macrophage
s,endothelial
cells,keratinocytes,
1.Chemotactic for PMN’s,macrophages,fibroblasts.
2.Mitogenic for fibroblasts,endothelial cells.
3.Stimulates production of MMP’s,fibronectin,HA.

18. CELL BASED substitutes
Most frequently used cell based graft is autologous
bone marrow.
Bone marrow contains hemopoietic stem cells as well
as ‘mesenchymal stem cells’ or ‘stromal cells.’
BM stromal cells depending on the tissue environment
can generate- osteoblasts,chondrocytes,adipocytes,
myoblasts,endothelial cell precursors,hemopoietic
stem cells.

19. Collection of Stem cells
Bone marrow aspiration.
Mesenchymal stem cells(MSC’s) are isolated and
cultured in flasks.
After several passages ,a sufficient number of MSC are
collected.Trephination and collection of MSC from the
flasks.MSC are then loaded in the scaffold.
Aspiration should be done at multiple sites to decrease
dilution by blood.

20. Role of stem cells in orthopaedics
1.Nonunion.
2.Delayed union.
3.Stabilisation of fracture .
4.Segemental bone defects.
5.Femoral head
osteonecrosis.
6.Spinal fusion
7.Physeal and bone cysts.
8.Osteochondral defects.
9.Articular cartilage defects.

21. BM aspiration procedure
Done under aseptic condition and general anaesthesia.
3mm incision at anterior iliac crests on both sides and
needles (16 or 18 guaze) passed deep into iliac crests.
BM is aspirated with 10ml syringes ,rinsed with a buffer
solution containing 400ml of phosphate buffered saline
solution,25000 u of heparin and 100ml of albumin,to
avoid clotting.
Contents in syringes are transferred to BM collection
unit,to obtain final volume of 400 ml of BM.

23. Percutaneous Autologous bone
grafting for nonunion
MSC are aspirated from BM iliac crest.
Centrifugation of aspirate is done on cell separator.
Centrifugation produces a buffy coat,that contains the
‘progenitor cells’,the source of angiogenic and
osteogenic cytokines.
Buffy coat is taken into a syringe for intraosseous
injection and using a trocar placed in nonunion gap.

24. CERAMIC BASED substitutes
 Bioceramics – specially designed ceramics for the repair
and reconstruction of diseased or damaged parts of the
body.
 Types-1.single crystals.
2.polycrystalline.
3.glass.
4.glass – ceramics.
5.composites.

25. -
 Clinical success requires
1.Stable interface with connective tissue .
2.Matching of mechanical behaviour of implant with the
tissue to be replaced.
 No material implanted is inert and all elicit a response:
1.Material – toxic - surrounding tissue dies.
2.Material –nontoxic,biologically inactive-fibrous tissue
forms.
3.Material –nontoxic,biologically active-interfacial bond
forms.
4.material-nontoxic  dissolves-surrounding tissue replaces
it.

26. Type of ceramic Type of aattachment Example
1.Dense,nonporo
us,nearly inert.
Attach by bone growth into surface
irregularities,by press fitting into a defect.
(MORPHOLOGICAL FIXATION.)
•Al2O3(single crystal
and polycrystalline).
2.Porous inert
implant.
Bone ingrowth occurs,which mechanically
attaches the bone to the material.
(BIOLOGICAL FIXATION.)
•Al2O3(porous
polycrystalline),
•HA coated porous
materials.
3.Dense,nonporo
us surface
reactive ceramics
Attach directly by chemical bonding with
bone.-(BIOACTIVE FIXATION.)
•Bioactive glasses.
•Bioactive glass
ceramics.
•HA.
4.Dense ,porous/
nonporous
resorbable
Slowly replaced by bone. •Calcium sulfate
•TCP
•Calcium phosphate

27. Level of reactivity of an implant influences the
thickness of the interfacial zone (layer between the
material and the tissue).
Inert biomaterial-Interface is not chemically /
biologically bonded, leading to relative movement at
interface thus decreasing the function of the implant.
‘Bioactive Material’-that elicits a specific biological
response at the interface resulting in formation of a
bond between tissue and the material.

28. Type 1(nearly inert,nonporous) ceramics
Bone at an interface with type 1,nearly inert implant is
often structurally weak due to disease,localised death of
bone or the stress sheilding of the implant prevents the
bone from being loaded.
High density,high purity Alumina(Al2O3)-1st bioceramic
widely used clinically
Al2O3-used in load bearing hip prosthesis,dental
implants because of

29. 1. Excellent corrosion resistance
2. Good biocompatibility and very thin capsule formation
permitting cementless fixation of prostheses.
3. High wear resistance.
4. High strength.
- Most alumina devices are very fine grained
polycrystalline alpha Al2O3.
- Alumina with an average grain size of <4 µm and >99.7%
purity exhibits good flexural strength and excellent
compressive strength.

30. An average increase in grain size to >7µm can decrease
the mechanical properties by about 20%.
The primary use of alumina is for the ball of the hip
joint with the acetabular component being ultra high
molecular wt PE.
Other clinical applications of alumina include-
1.Knee prostheses.2.bone screws.3.alveolar ridge of jaw
bone .4.maxillofacial reconstruction.5.ossicular bone
reconsruction.

31. Medical grade alumina used as femoral balls in total hip
replacement.

32. Type 2(porous ceramics)
Potential advantage-inertness combined with
mechanical stability of highly convoluted interface
developed when bone grows into the pores of ceramic.
The micro structure of certain corals makes an ideal
investment material for the casting of stuctures with
controlled pore sizes.
The most promising coral gene PORITES has pores
with size of 140-160 µm with all pores interconnected.

33. Another coral gene ‘GONIOPORA’ has larger pore size
of 200-1000µm.
REPLAMINEFORM process- duplicating the porous
microstructure of corals that have a high degree of
uniform pore size and interconnection.
The advantage of the above process is that the pore
size and microstucture are uniform,contolled with
interconnections of pores.
Procedure-1.To machine the coral with proper
microstructure into desired shape.

34. 2.The machined coral shape is fired to drive off
carbondioxide from lime stone forming ‘CALCIA’.
3.Calcia structure serves as investment material for
forming the porous material.
 The limitation with type-2 porous implants is that for
the tissue to remain viable and healthy, it is necessary
for the pores to be >100-150µm in diameter to provide a
blood supply to the ingrown tissue.
 Ageing of porous ceramics leads to decrease in
strength ,posing question as to the successful longterm
application of porous material.

35. INGROWTH OF BONE WITHIN> 100µm OF ALUMINA
BICERAMIC

36. Bioactive glasses  glass ceramics
 Certain compositions of glasses,ceramics ,glass ceramics
and composites have been shown to bond to bone-
Bioactive ceramics.
 A common characteristic of bioactive glasses and bioactive
ceramics is a time dependent,kinetic modification of the
surface that occurs upon implantation.
 The surface forms a biologically active ‘Hydroxycarbonate
Apatite’ (HCA) layer which provides the bonding interface
with tissues.

37.  The HCA phase that forms on bioactive implants is
equivalent chemically and structurally to the mineral phase
in bone.
 The interfacial strength of adhesion is equivalent or greater
than the cohesive strength of implant or tissue.
 Therefore failure occurs either in the implant or in the
bone but almost never in the interface.
 Many bioactive silica glasses are based upon the formula-’
45 S 5 ‘: 45 – wt % of SiO2
S – networker former
5 – 5 to 1 molar ratio of Ca to P

38.  The collagenous constitutent of soft tissue can strongly
adhere to the bioactive silica glasses.
 The dense HCA – Collagen agglomerates mimic the
nature of bonding between tendons and ligaments
composed entirely of collagen fibrils and bone which is
a composite of HCA crystals and collagen.
 Three key compositional features of these glasses
distinguish them from traditional Na2O-CaO-SiO2
glasses:
1.<60 mol% SiO2

39. 2.High Na2O and high CaO content
3.High Cao/P2O5 ratio.

40. 1.SEM micrograph of collagen fibrills incorporated within
the HCA layer growing on a 45S5 Bioglass invitro.
2.Close up of the HCA crystals bonding to a collagen fibrill.

41. Stage Reaction
1. Rapid exchange of Na+ or K+ with H+ or H3O+ from solution.
(Ion exchange)
2. Loss of soluble silica in the form of Si(OH)4 to the solution,resulting from
breaking of Si-O-Si bonds and formation of Si-OH at the glass solution
interface.(Silica network dissolution)
3. Condensation and repolymerisation of a SiO2 rich layer on the surface
4. Migration of Ca2+ and PO4 groups to the surface through the SiO2 rich
layer forming a CaO-P2O5 rich film
5. Crystallisaton of the amorphous CaO-P2O5 film by incorporation of OH-,
CO3,or F- anions from solution to form a mixed
Hydroxyl,Carbonate,Fluoroapatite layer.
Reaction stages of a bioactive implant

42. Sequence of interfacial reactions involved in forming a bond
between tissue and bioactive ceramics.

43. Calcium phosphate ceramics
 The stable phase of calcium phosphate ceramics
depend considerably upon temperature and presence of
water.
 At pH<4.2 the stable phase is CaHPO4.2H2O.
(Dicalcium phosphate or Brushite).
 At pH>4.2 the stable phase is Ca 10(PO4)6(OH)2.
(Hyroxyapatite).
 At higher temperatures-other phases are stable.
1.Ca3(PO4)2- Tricalcium phosphate.

44.  2.Ca4P2O9 – tetracalcium phosphate.
The unhydrated high temperature calcium phosphate
phases interact with body water or body fluids at 37ºc
to form HA.
 The HA forms on exposed surfaces of TCP by the
following reaction:
4Ca3(PO4)2 +2H2O Ca10(PO4)6(OH)2+2Ca2+
2HPO4-
-The presence of micropores in the sintered material can
increase the solubility of these phases.

45.  Sintering of calcium phosphate ceramics usually occurs in
the range of 1000ºc to 1500ºc following compaction of the
powder into a desired shape.
 Sintering reduces the amount of carbonated apatite, an
unstable and weakly soluble form of HA.
 Tensile and compressive strength and fatigue resistance
depend on the total volume of porosity.
 Porosity -1.micropores:<1µm , due to incomplete sintering.
2.macropores:>100µm in diameter,to permit bone
growth.

46.  In clinical practice calcium phosphate ceramics should
be used as
1.powders.
2.Small unloaded implants in middle ear.
3.Dental implants with reinforcing metal ports.
4.Coatings on metal implants.
5.Low loaded porous implants where bone growth acts
as reinforcing phase.
6.Bioactive phase in a polymer –bioactive ceramic
composite.

47.  Bonding mechanism:a cellular bone matrix from
differentiated osteoblasts appear at the surface
,producing a narrow amorphous electron dense band
only 3-5µm wide. Between this area and the cells
collagen bundles are seen.
As the site matures the bonding zone shrinks to a depth
of only 0.05-0.2µm and thus normal bone attached
through a thin epitaxial layer to the bulk implant.

48.  Resorption / biodegradation of calcium phosphate
ceramics is caused by
1.Physiochemical dissolution .
2.Physical disintegration.
3.Biological factors.
 All calcium phosphate ceramics biodegrade to varying
degrees in the following order:
α-TCP > β –TCP > HA.

49.  Rate of biodegradation increase as :
1.Surface area increase.
2.Crystallinity decrease.
3.Crystal perfection decrease.
4.Crystal and grain size decrease.
5.Ionic substitution of CO3,Mg2+ in HA take place
 Factors which decrease rate of biodegradation:
1.F – substitution in HA .
2.Mg2+ substitution in β-TCP.
3.Decreased β-TCP/HA ratio in biphasic calcium phosphate.

50. Composite ceramics
 Certain restrictions in the use of bioceramics due to
1.Uncertain life lifetime under complex stress status.
2.Slow crack growth.
3.Cyclic fatigue.
 Two creative approaches to these mechanical
limitations:
-use of bioactive ceramics as 1.coatings
2.composites.

51.  Composites and coatings involve all 3 types of
biomaterials-nearly inert,resorbable,bioactive.
 Goal : 1.To increase the flexural strength and strain to
failure.
2.decrease the elastic modulus.
 Most bioceramics are much stiffer than bone and many
exhibit poor fracture toughness.
 One approach to achieve properties analougous to bone is
to stiffen a compliant biocompatible synthetic polymer
such as PE,with a higher modulus ceramic second phase –
like HA powder.

52.  The mechanical properties of PE-HA composite are
close to/superior to those of bone.
 Calcium phosphate –collagen composite:
-collagen promotes mineral deposition by providing
binding sites for matrix proteins.
-types 1 ,3 collagen have been combined with HA,TCP,
and autologous bone marrow to form a graft material
devoid of structural support but augments fracture
healing.

53. PE-HA composite used as a sleeve for the
stem of a total hip implant.

54. Coatings
 Commonly used material for coating are :1.carbon.
2.HA.
 Three types of carbon are used in biomedical devices:
1.LTI variety of pyrolytic carbon.
2.Glassy (vitreous) carbon.
3.Ultralow –temperature isotropic (ULTI) form of vapor
deposited carbon.

55.  HA used as a coating on porous metal surfaces for
fixation of orthopaedic prostheses.
 This method combines type 2 & 3 methods of
fixation.(biological & bioactive).
 The plasma spray coating of HA is generally preffered,
which substantially increase early stage interfacial
bond strength of implants.

56. Calcium sulfate(POP)
 In a crystalline structure dscribed as alphahemihydrate
acts primarily as osteoconductive bone void filler.
 Uses -1.filling of cysts,bone cavities,benign bone
lesions and segmental defects.
2.expansion of grafts used for spinal fusion.
3.filling of bone graft harvest sites.

57. POLYMER BASED substitutes
 Polymers for graft substitutes include :
-natural/synthetic.
-Biodegradable/nonbiodegradable.
 Nonbiodegradable natural and synthetic polymers are
composites of polymer and ceramic.
 Biodegradable natural and synthetic materials include
-polyglycolic acid(PGA)
-poly(lactic-co-glycolic )acid.

58. Miscellaneous bone graft substitutes
 CORALLINE HYDROXYAPATITE:
-CHIROFF first observed that corals from marine
invertebrates have skeleton with a structure similar to
both cortical and cancellous bone with
interconnecting porosity.
-processed by a hydrothermal exchange method that
converts the coral calcium phosphate to crystalline HA
with pore diameters 200µm -500µm and in a structure
very similar to that of human trabecular bone.