Comparative in vivo study of six hydroxyapatite‐based bone graft substitutes

Improvement of synthetic bone graft substitutes as suitable alternatives to a patient's own bone graft remains a challenge in biomaterials research. Our goal was to answer the question of whether improved osteoinductivity of a material would also translate to better bone‐healing orthotopically. Three porous biphasic calcium phosphate (BCP) ceramics (BCPA, BCPB, and BCPC), consisting of hydroxyapatite and β‐tricalcium phosphate, a porous biphasic calcium phosphate ceramic reinforced with a bioresorbable polylactic acid to improve its mechanical properties (BCPC+), a pure hydroxyapatite ceramic (HA), and a carbonated apatite ceramic (CA) were implanted intramuscularly and orthotopically by using a transverse process model in 11 goats for 12 weeks. BCPA and BCPB had similar chemical composition but differed in their microstructure. BCPB was not osteoinductive at all, but BCPA induced ectopic bone formation in 9 of 11 animals. Orthotopically, BCPA performed better than BCPB in both the amount and rate of bone formation. BCPC, similar to BCPA structurally and physicochemically, showed comparable results ectopically and orthotopically. Addition of resorbable polymer to BCPC made the material less osteoinductive (4 of 11 animals) and delayed bone formation orthotopically. Neither HA nor CA were osteoinductive, and their orthotopic performance was inferior to the osteoinductive ceramics. The results of the present study showed that material‐derived osteoinduction significantly enhanced bone healing orthotopically, and that this material property appeared more sensitive for predicting orthotopic performance than physicochemical and structural characteristics. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1363–1370, 2008     

Bone integration within calcium phosphate ceramic by creation of posterior inter-articular lumbar spine fusions in dogs

Following earlier experiments in which several calcium phosphate ceramics were tested, the aim of this study was to evaluate bone integration within a macroporous biphasic calcium ceramic (M.B.C.P.) in comparison to autologous bone grafts, by producing posterior lumbar spine fusions in dogs. Five dogs were used. 40 posterior lumbar joints were exposed; 38 articular surfaces were removed, 27 M.B.C.P. and 5 autologous bone grafts were implanted; 6 joints were kept free of implant for control purposes. Fixation with a metal rod was performed using Luque's method. Tetracycline was used for a double marking of bone growth. Joints were removed at 4 weeks in 1 dog, 8 weeks in two and 13 weeks in the remaining 2 dogs. Demineralized and non demineralized sections were examined. After 1 month, sections with M.B.C.P. showed early signs of mineralization of the scar tissue between the biomaterial and one of the facets of the joint. Fluoroscopy revealed an absence of bone growth in the pores at the center of the ceramic implant. After 3 months, a number of M.B.C.P. blocks had become integrated into both sides of the joint; however some microfractures in the biomaterial with discontinuity between the mineralized areas was seen. Macroporous calcium phosphate ceramic leads to revascularization allowing bone reconstruction. Similarities in the kinetics and mechanisms of bone integration between the ceramic and autologous bone grafts are demonstrated.     

Demineralized bone matrix and hydroxyapatite/tri-calcium phosphate mixture for bone healing in rats

Purpose: Hydroxyapatite/tri-calcium phosphate (HA/TCP) mixture is an osteoconductive material used as a bone graft substitute, and demineralised bone matrix (DBM) is an osteoinductive material. A combination of DBM and HA/TCP mixture would probably create a composite with both osteoconductive and osteoinductive properties. The purpose of this study was to determine the effect of the combination of DBM and HA/TCP mixture on healing of rat radius segmental defects. Methods: Twenty-four adult male Wistar rats were used. Bilateral radial defects were created in each animal. Radial defects were implanted with DBM, HA/TCP mixture and a combination of both substances. Control defects were left unfilled. Ten weeks after implantation, the animals were sacrificed, and the radii were evaluated by radiograhic and histopathological studies. Results: The use of DBM alone demonstrated improved healing on radiographic and histological studies compared to other groups and the control group. There were no differences between the other two groups and the control group. Conclusion: The DBM group showed the best healing response. Combined use of DBM and HA/TCP mixture did not improve bone healing, and the osteoinductive properties of DBM were inhibited by HA/TCP mixture.     

Ectopic bone formation by microporous calcium phosphate ceramic particles in sheep muscles

Calcium phosphate ceramics are widely used in bone reconstructive surgery because of their osteconductive properties. However, these materials generally lack osteoinductive properties required to support bone healing in large defects. In this article, we study the osteoinductive potential of calcium phosphate ceramic particles implanted for 6 months into the dorsal muscles of eight adult female sheep. Microporous biphasic calcium phosphate (MBCP) granules of 1–2 mm composed of hydroxyapatite and beta-tricalcium phosphate (60/40) had macropores of 450 μm, micropores of 0.43 μm, and a specific surface area of 1.8 m²/g. After 6 months in the back muscles of sheep, the explants composed of MBCP granules were hard and encapsulated by normal muscle tissue. Ectopic bone formation with Haversian structures was observed in close contact with the MBCP granules in histological sections. Back-scattered electron microscopy and micro-computed tomography indicated that approximately 10% of well-mineralized bone with mature osteocytes had formed between or upon the granules. The ectopic bone showed trabeculae bridging the MBCP granules. Both the number and thickness of the trabeculae formed between the MBCP particles were comparable to those measured in spongious bone. The overall results therefore confirmed the presence of mature bone after intramuscular implantation of MBCP granules. The different hypotheses explaining ectopic bone formation induced by MBCP granules are discussed. Synthetic bone substitutes with osteoinductive properties could be used in bone reconstructive surgery.     

Hydroxyapatite and tricalcium phosphate bone graft substitutes

Autografts have consistently outperformed calcium phosphate implants in most experimental models and clinical applications. However, human trials in metaphyseal defects demonstrate comparable results with autograft, hydroxyapatite, and TCP. Diaphyseal fractures and segmental defects represent more challenging problems, with less predictable results achieved with the synthetic bone graft substitutes. Improvements in the pore configuration, mechanical properties, and osteoinductive capacity of these implants should widen their future clinical application.     

Cytocompatibility of porous biphasic calcium phosphate granules with human mesenchymal cells by a multiparametric assay

This work aims to evaluate the cytocompatibility of injectable and moldable restorative biomaterials based on granules of dense or porous biphasic calcium phosphates (BCPs) with human primary mesenchymal cells, in order to validate them as tools for stem cell‐induced bone regeneration. Porous hydroxyapatite (HA) and HA/beta‐tricalcium phosphate (β‐TCP) (60:40) granules were obtained by the addition of wax spheres and pressing at 20 MPa, while dense materials were compacted by pressing at 100 MPa, followed by thermal treatment (1100°C), grinding, and sieving. Extracts were prepared by 24‐h incubation of granules on culture media, with subsequent exposition of human primary mesenchymal cells. Three different cell viability parameters were evaluated on the same samples. Scanning electron microscopy analysis of the granules revealed distinct dense and porous surfaces. After cell exposition to extracts, no significant differences on mitochondrial activity (2,3‐bis(2‐methoxy‐4‐nitro‐5‐sulfophenly)‐5‐[(phenylamino) carbonyl]‐2H‐tetrazolium hydroxide) or cell density (Crystal Violet Dye Elution) were observed among groups. However, Neutral Red assay revealed that dense materials extracts induced lower levels of total viable cells to porous HA/β‐TCP (P < 0.01). Calcium ion content was also significantly lower on the extracts of dense samples. Porogenic treatments on BCP composites do not affect cytocompatibility, as measured by three different parameters, indicating that these ceramics are well suited for further studies on future bioengineering applications.     

Enhanced Bone Bonding of the Hydroxyapatite/β‐Tricalcium Phosphate Composite by Electrical Polarization in Rabbit Long Bone

A review of the osteogenic cell activity and new bone growth in the regions bordering negatively charged surfaces of polarized Hydroxyapatite/β‐tricalcium phosphate (HA/TCP) composites implanted in the long bone in rabbits was conducted. Polarized and non‐polarized HA/TCP specimens were implanted into the right and left femoral condyle, respectively (each n = 10). After 3 and 6 weeks, five rabbits were sacrificed in each group, and histological analysis was administered. Large cuboidal‐shaped osteoblastic cells were predominantly observed lining the newly formed bone on the negatively charged surface (N‐surface) in the polarized HA/TCP implants. The TRAP‐positive multinucleated cells were observed extensively in the newly formed bone on the N‐surfaces compared with the 0‐surface and adhered directly to the HA/TCP composite. The bone area (B.Ar) value, newly formed bone area contacting the implant, and contact length (C.Le) value, percentage length of newly formed bone directly attaching to the implant, on both the 0‐ and N‐surface increased significantly with time in each group. Both the B.Ar and C.Le value on the N‐surface were significantly greater than those on the 0‐surface after 3 and 6 weeks. The number of TRAP‐positive cells/total length value on the N‐surface was significantly greater than that on the 0‐surface after 3 and 6 weeks postoperatively. It is hypothesized that electrical charge acquired by electrical polarization treatment may modify the biochemical and biophysical processes of the osteogenic cells, resulting in enhanced new bone formation and direct bonding between the recipient bone and implants.     

The evaluation of a biphasic calcium phosphate ceramic for use in grafting long-bone diaphyseal defects

The effectiveness of a sintered hydroxyapatite-tricalcium phosphate (HA-TCP) ceramic in bridging large diaphyseal defects in the canine ulna was studied. One-hundred percent morselized HA-TCP, a 50:50 mixture of morselized HA-TCP, and autogenous cancellous bone, and 100% autogenous cancellous bone were used to bridge 2.5-cm defects in the left ulnae of three groups of six dogs each. At 24 weeks the ulnae were explanted and studied by radiography, microradiography, mechanical testing, and histology. Pure HA/TCP was not osteoinductive, and four of six ulnae in this group progressed to a fibrous nonunion. The HA/TCP-cancellous bone mixture and pure cancellous bone were approximately equal in effect, leading to good callus formation at 4 weeks and strong bony union by 24 weeks, with no evidence of bioincompatibility. Morselized HA/TCP promises to be useful as a graft extender when mixed with autogenous cancellous bone.     

Major bone defect treatment with an osteoconductive bone substitute

A bone defect can be provoked by several pathological conditions (e.g. bone tumours, infections, major trauma with bone stock loss) or by surgical procedures, required for the appropriate treatment. Surgical techniques currently used for treating bone defects may count on different alternatives, including autologous vascularized bone grafts, homologous bone graft provided by musculoskeletal tissue bank, heterologous bone graft (xenograft), or prostheses, each one of them dealing with both specific advantages and complications and drawbacks. The main concerns related to these techniques respectively are: donor site morbidity and limited available amount; possible immune response and viral transmission; possible animal-derived pathogen transmission and risk of immunogenic rejection; high invasiveness and surgery-related systemic risks, long post-operative. physical recovery and prostheses revision need. Nowadays, an ideal alternative is the use of osteoconductive synthetic bone substitutes. Many synthetic substitutes are available, used either alone or in combination with other bone graft. Synthetic bone graft materials available as alternatives to autogeneous bone include calcium sulphates, special glass ceramics (bioactive glasses) and calcium phosphates (calcium hydroxyapatite, HA; tricalcium phosphate, TCP; and biphasic calcium phosphate, BCP). These materials differ in composition and physical properties fro each other and from bone (De Groot in Bioceramics of calcium phosphate, pp 100–114, 1983; Hench in J Am Ceram Soc 74:1487–1510, 1994; Jarcho in Clin Orthop 157:259–278, 1981; Daculsi et al. in Int Rev Cytol 172:129–191, 1996). Both stoichiometric and non-stoichiometric HA-based substitutes represent the current first choice in orthopedic surgery, in that they provide an osteoconductive scaffold to which chemotactic, circulating proteins and cells (e.g. mesenchymal stem cells, osteoinductive growth factors) can migrate and adhere, and within which progenitor cells can differentiate into functioning osteoblasts (Szpalski and Gunzburg in Orthopedics 25S:601–609, 2002). Indeed, HA may be extemporarily combined either with whole autologous bone marrow or PRP (platelet rich plasma) gel inside surgical theatre in order to favour and accelerate bone regeneration. A case of bifocal ulnar bone defect treated with stoichiometric HA-based bone substitute combined with PRP is reported in here, with a 12-month-radiographic follow-up.     

Spinal Fusion of an Unstable Atlantoaxial Fracture in a Completely Tetraplegic Patient Using Silicate-Substituted Calcium Phosphate

Bone graft harvesting from the iliac crest constitutes the gold standard in spinal surgery due to its osteogenic, osteoconductive and osteoinductive properties. Large amounts of autograft can provoke complications like donor site morbidity, pain and the need for a second operation. Therefore, research into bone graft substitutes is of great interest. Silicate-substituted calcium phosphate (Actifuse^TM Synthetic Bone Graft, ApaTech Ltd, London) was used in combination with morselized corticocancellous graft in a transarticular stabilization (modified Magerl) of a completely tetraplegic patient with an unstable atlantoaxial fracture. Computed tomography showed bone bridging between the segment C1/C2, the surface of the implant and the remodeled bone at follow-up at 8 months. The use of silicate-substituted calcium phosphate as a bone graft extender in spinal surgery could be an alternative to autografting from the iliac crest. Vegetative symptoms are often underestimated but can be triggered by donor site morbidity or pain in patients after spinal cord injury.     

Massive bone reconstruction with heat‐treated bone graft loaded autologous bone marrow‐derived stromal cells and β‐tricalcium phosphate composites in canine models

Bone marrow‐derived stromal cells (BMSCs) contain mesenchymal stem cells that are capable of forming various mesenchymal tissues. We hypothesized that BMSCs and β‐tricalcium phosphate (β‐TCP) composites would promote the remodeling of large‐sized autologous devitalized bone grafts; therefore, the aim of this study was to evaluate the effects of the composites on the remodeling of autologous devitalized bone grafts. Autologous BMSCs cultured in culture medium containing dexamethasone (10^?7 M) were loaded into porous β‐TCP granules under low‐pressure. Theses BMSC/TCP composites were put into the bone marrow cavity of autologous heat‐treated bone (femoral diaphysis, 65‐mm long, 100°C, 30 min) and put back to the harvest site. In the contralateral side, β‐TCP without BMSC were used in the same manner as the opposite side as the control. Treatment with the BMSC/TCP composites resulted in a significant increase in thickness, bone mineral density, and matured bone volume of the cortical bone at the center of the graft compared to the control. Histological analysis showed matured regenerated bone in the BMSC loaded group. These results indicate that BMSC/TCP composites facilitated bone regeneration and maturation at the graft site of large‐sized devitalized bone. This method could potentially be applied for clinical use in the reconstruction of large bone defects such as those associated with bone tumors. © 2013 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 31:1308–1316, 2013

     

Bone ingrowth into two porous ceramics with different pore sizes: an experimental study

Many properties of porous calcium phosphate ceramics have been described, but how pore size influences bony integration of various porous ceramics remains unclear. This study was performed to quantify the bony ingrowth and biodegradability of two porous calcium phosphate ceramics with four different pore size ranges (45-80 microm, 80-140 microm, 140-200 microm, and 200-250 microm). Hydroxyapatite (HA) and beta-tricalcium phosphate (TCP) cylinders were implanted into the femoral condyles of rabbits and were left in situ for up to 12 months. The percentage of bone ingrowth and the depth of ingrowth within the pores were determined. Biodegradability of the implants was also evaluated. Bone ingrowth occurred at a higher rate into the TCP than into the HA ceramics with the same pore size ranges. The amount of newly formed bone was statistically smaller (p < 0.05) into ceramics with 45-80 microm pore size than with larger pore size, whatever the implantation time for HA and until four months for TCP. No statistical difference was noted between the three highest pore size ranges. No implant degradation was noted up to four months. Our results suggest that a pore size above 80 microm improves bony ingrowth in both HA and TCP ceramics. Bone formation was higher in the TCP than in the HA implants.     

The effect of different mineral frames on ectopic bone formation in mouse hind leg muscles induced by native reindeer bone morphogenetic protein

Introduction Bone morphogenetic proteins (BMPs) require carrier material for slow release and framing material for osteoconduction.Materials and methods The effect of a frame on early bone formation induced by partially purified native reindeer BMP in composite implants containing 3 mg of BMP, type IV collagen and tricalcium phosphate (TCP/Col/BMP) or hydroxyapatite (HA/Col/BMP) or biphasic tricalcium phosphate-hydroxyapatite (TCP/HA/Col/BMP) or biocoral (NC/Col/BMP) was evaluated using a mouse hind leg muscle pouch model. Collagen with native reindeer BMP (Col/BMP) and corresponding implants without native reindeer BMP served as controls. Evaluation was done by incorporation of ⁴⁵Ca, radiographically and histologically 3 weeks after the implantation.Results None of the implants without native reindeer BMP were able to induce new bone visible on radiographs. The area of new bone formation in the Col/BMP (p=0.026) and TCP/HA/Col/BMP (p=0.012) groups was significantly greater than in the TCP/Col/BMP group. The optical density of the new bone area was significantly greater in the TCP/HA/Col/BMP group than in the TCP/Col/BMP (p=0.036) or Col/BMP (p=0.02) groups. ⁴⁵Ca incorporation was many times greater in all the groups containing native reindeer BMP than in the corresponding groups without BMP. In the Col/BMP (p=0.046) and TCP/HA/Col/BMP (p=0.046) groups, ⁴⁵Ca incorporation was significantly greater than in the TCP/Col/BMP group. No significant differences were found in any parameters between HA/Col/BMP and NC/Col/BMP groups and the other BMP-containing groups.Conclusions Hydroxyapatite, biocoral and biphasic tricalciumphosphate-hydroxyapatite are equally good as framing material for native reindeer BMP, while tricalciumphosphate is somewhat worse. Osteoinduction of native reindeer BMP works well with collagen alone.     

Current Application of β‐tricalcium Phosphate Composites in Orthopaedics

Presently, bioceramic materials have been extensively used in spinal surgery as bone grafts; however, there are some limitations for bioceramic materials. Calcium sulfate is rapidly absorbed in vivo, the degradation of which often occurs prior to the formation of new bones. Hydroxyapatite (HA) is hardly absorbed, which blocks the formation of new bones and remodeling, and results in poor local stability or permanent stress concentration. Only β‐tricalcium phosphate (β‐TCP) is relatively balanced between scaffold absorption and bone formation. And it is a good biodegradable ceramic material that could supply a large quantity of calcium ion and sulfate ion as well as scaffold structure for bone regeneration. However, the problem of single β‐TCP is lack of osteoinductivity and osteogenicity, which restricts its application. Therefore β‐TCP composite materials have been used in the field of orthopaedics in recent decades, which fully use excellent properties of other bone repairing materials, such as biodegradability, osteoinductivity, osteogenicity and osteoconductivity. These materials make up for the deficiencies of single β‐TCP and endow β‐TCP with more biological and physical properties.     

Submicron‐surface structured tricalcium phosphate ceramic enhances the bone regeneration in canine spine environment

Calcium phosphate ceramics with submicron‐scaled surface structure can trigger bone formation in non‐osseous sites and are expected to enhance bone formation in spine environment. In this study, two tricalcium phosphate ceramics having either a submicron‐scaled surface structure (TCP‐S) or a micron‐scaled one (TCP‐B) were prepared and characterized regarding their physicochemical properties. Granules (size 1–2 mm) of both materials were implanted on either left or right side of spinous process, between the two lumbar vertebrae (L3‐L4), and in paraspinal muscle of eight beagles. After 12 weeks of implantation, ectopic bone was observed in muscle in TCP‐S explants (7.7 ± 3.7%), confirming their ability to inductively form bone in non‐osseous sites. In contrast, TCP‐B implants did not lead to bone formation in muscle. Abundant bone (34.1 ± 6.6%) was formed within TCP‐S implants beside the two spinous processes, while limited bone (5.1 ± 4.5%) was seen in TCP‐B. Furthermore, the material resorption of TCP‐S was more pronounced than that of TCP‐B in both the muscle and spine environments. The results herein indicate that the submicron‐scaled surface structured tricalcium phosphate ceramic could enhance bone regeneration as compared to the micron‐scaled one in spine environment. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1865–1873, 2016.     

A long-term study on defect filling and bone ingrowth using a canine fiber metal total hip model.

When performing primary and revision total hip arthroplasty (THA), bone defects are often encountered. At present, grafting osseous defects with autogeneic bone is a common means of treatment. In this study, defects in bone were created in the femora and acetabula of dogs being treated with cementless THA with a fiber metal implant (Group A) or a hydroxyapatite tricalcium phosphate (HA/TCP) sprayed implant (Group B). The following methods of defect filling were compared: (1) leaving defects unfilled, (2) filling with autogeneic bone graft, (3) filling with a 50:50 mixture of autograft and a biphasic ceramic composed of HA/TCP, and (4) filling with a collagen-HA/TCP-bone marrow mixture. Analysis of defect healing and the extent of ingrowth into the overlying fiber metal, at defect sites and sites distant from defects, was made at six, 12, and 24 weeks postimplantation. Defect healing was enhanced at six and 12 weeks in all grafted groups when compared with ungrafted controls. Bone ingrowth into the porous fiber metal overlying the defects was not significantly affected by grafting the defects, compared with the ungrafted defects. The extent of bone ingrowth into the fiber metal acetabular implant at sites away from the defects increased during the entire study. In contrast, the extent of bone ingrowth on the femoral side was maximal at 12 weeks. The HA/TCP coating enhanced ingrowth into the acetabular component at 12 weeks, compared with the uncoated prosthesis, but did not enhance ingrowth on the femoral side. The data from this study demonstrate that defect healing is enhanced with graft materials. However, this does not necessarily result in increased ingrowth into porous surfaces overlying osseous defects. General bone ingrowth and ingrowth at defect sites at 12 weeks postimplantation can be enhanced on the acetabular side with the use of HA/TCP-sprayed implants. However, no positive effect is seen with the use of an HA/TCP-sprayed femoral implant.     

Interaction of allogeneic demineralized bone matrix and porous hydroxyapatite bioceramics in lumbar interbody fusion in rabbits

Bone repair by autograft is effective in clinical practice. However, serious problems arise when a considerable volume of transplant is needed, as with spinal fusion procedures. The use of bone substitutes combined with osteoinductive agents may contribute to the solution of such problems. In this study, the effectiveness of such a procedure was tested in an experimental model of interbody fusion in rabbits in which the incorporation of a porous hydroxyapatite block (HA) was enhanced by the addition of allogeneic demineralized bone matrix (DBM). The latter was used as a delivery system for the osteoinductive activity of the bone morphogenetic protein contained in the matrix. A group implanted with combined HA + DBM showed significantly earlier stabilization of the fusion when compared to groups implanted with DBM alone, HA alone, and bone autografts. On the other hand, the general results of the fusion with HA + DBM were superimposable on those of autografts. With further research, the combination of a bone substitute and an osteoinductive agent may constitute an alternative to the use of bone autografts.     

Formation of carbonate-apatite crystals after implantation of calcium phosphate ceramics

Summary The aims of this study were (1) to determine at the crystal level, the nonspecific biological fate of different types of calcium phosphate (Ca−P) ceramics after implantation in various sites (osseous and nonosseous) in animals and (2) to investigate the crystallographic association of newly formed apatitic crystals with the Ca−P ceramics. Noncommercial Ca−P ceramics identified by X-ray diffraction as calcium hydroxylapatite (HA), beta-tricalcium phosphate (β-TCP), and biphasic calcium phosphates (BCP) (consisting of β-TCP/HA=40/60) were implanted under the skin in connective tissue, in femoral lamellar cortical bone, articular spine bone, and cortical mandibular and mastoidal bones of animals (mice, rabbits, beagle dogs) for 3 weeks to 11 months. In humans, HA or β-TCP granules were used to fill periodontal pockets, and biposies of the implanted materials were recovered after 2 and 12 months. Results of this study demonstrated the following: (1) the presence of needle-like microcrystals (new crystals) associated with the Ca−P ceraiic macrocrystals in the microporous regions of the implants regardless of the sites of implantation (osseous or nonosseous), type of Ca−P ceramics (HA, β-TCP, BCP), type of species used (mice, rabbits, dogs, humans), or duration of implantation; (2) decrease in the area occupied by the ceramic crystals and the subsequent filling of the spaces between the ceramic crystals by the new crystals; (3) these new crystals were identified as apatite by electron diffraction and as carbonate-apatite by infrared absorption spectroscopy; (4) high resolution transmission electron microscopy (Hr TEM) revealed one family of apatite lattice fringes in the new crystals in continuity with the lattice planes of the HA of β-TCP ceramic crystals; (5) Hr TEM also demonstrated the presence of linear dislocations at the junction of the new apatite crystals and ceramic crystals. It is suggested that the formation of the CO₃ apatite crystals associated with the implanted Ca−P ceramic is due to dissolution/precipitation and secondary nucleation involving an epitatic growing process and not to an osteogenic property of the ceramic.     

Repair of rat calvarial defects using Si‐doped hydroxyapatite scaffolds loaded with a bone morphogenetic protein‐2‐related peptide

Tissue engineering promises therapies ideal for treating conventional large bone injuries and defects. In the present study, we developed a novel Si‐HA scaffold loaded with a synthetic BMP‐2‐related peptide, P28, and tested its ability to repair a critical‐sized calvarial defect. We created a calvarial defect (5 mm in diameter) in the parietal bone of 32 rats and implanted one of the following biomaterials: No implant (control), Si‐HA, P28/Si‐HA, or rhBMP‐2/Si‐HA. As assessed by micro CT imaging and histological evaluations, the P28/Si‐HA scaffold promoted bone recovery to a similar degree as the rhBMP‐2/Si‐HA scaffold. In addition, both P28/Si‐HA and rhBMP‐2/Si‐HA promoted recovery better than Si‐HA alone. The novel P28/Si‐HA scaffold might represent a promising biomaterial for future bone tissue engineering applications. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1874–1882, 2016.     

Relevance of osteoinductive biomaterials in critical-sized orthotopic defect.

Several publications have shown the phenomenon of osteoinduction by biomaterials to be real. However, whether the ability of a biomaterial to initiate bone formation in ectopic implantation sites improves the performance of such osteoinductive biomaterial in clinically relevant orthotopic sites remains unclear. No studies have been published in which osteoinductive potential of a biomaterial is directly related to its performance orthotopically. In this study, we compared osteoinductive and nonosteoinductive biphasic calcium-phosphate (BCP) ceramics ectopically and in a clinically relevant critical-sized orthotopic defect in goats. The two materials, BCP1150 and BCP1300, had similar chemical compositions, crystallinities, and macrostructures, but their microstructures differed significantly. BCP1150, sintered at a lower temperature, had a large amount of micropores, small average crystal size, and hence a high specific surface area. In contrast, BCP1300, with few micropores, had a significantly lower specific surface area as compared to BCP1150. Twelve-week intramuscular implantation in goats (n = 10) showed that bone was induced in all BCP1150 implants, while no signs of bone formation were found in any of the BCP1300 implants. After 12 weeks of implantation in a bilateral critical-sized iliac wing defect in the same goats, BCP1150 showed significantly more bone than BCP1300. In addition, the analysis of fluorochrome markers, which were administered to the animals 4, 6, and 8 weeks after implantation to follow the bone growth dynamics, showed an earlier start of bone formation in BCP1150 as compared to BCP1300. Significantly better performance of an osteoinductive ceramic in a critical-sized orthotopic defect in a large animal model in comparison to a nonosteoinductive ceramic suggests osteoinduction to be clinically relevant. Further improvement of material osteoinductive properties is thus a significant step forward in the search for alternatives for autologous bone graft.