Eric Goyenvalle

Macroporous biphasic calcium phosphate ceramics versus injectable bone substitute: a comparative study 3 and 8 weeks after implantation in rabbit bone

Macroporous biphasic calcium phosphate ceramics (MBCP) and a calcium phosphate injectable bone substitute (IBS), obtained by the association of biphasic calcium phosphate (BCP) ceramic granules and an aqueous solution of a cellulosic polymer, were compared in the same animal model. The two tested biomaterials were implanted in distal femoral osseous defects in rabbits. Qualitative and quantitative histological evaluation was performed three and eight weeks after implantation to investigate bone colonization and ceramic biodegradation associated with the two bone substitutes.Both biomaterials expressed osteoconduction properties and supported the apposition of a well-mineralized lamellar newly-formed bone. Bone colonization occurred much earlier and faster for IBS than for MBCP implants, although the respective rates of newly-formed bone after eight weeks of implantation did not differ significantly. For both biomaterials, ceramic resorption occurred regularly throughout the implantation period, though to a greater extent with IBS than with MBCP implants.The associated polymer in IBS produced intergranular spaces allowing body fluids to reach each BCP ceramic granule immediately after implantation, which may have favored osteoblastic activity, new bone formation and ceramic resorption. This completely interconnected open macroporosity could account for the earlier and more satisfactory bone substitution achieved with IBS.

Developments in injectable multiphasic biomaterials. The performance of microporous biphasic calcium phosphate granules and hydrogels

Calcium phosphate bioceramic granules associated with hydrosoluble polymers were developed as bone substitutes for various maxillofacial and orthopaedic applications. These injectable bone substitutes, support and regenerate bone tissue and resorb after implantation. The efficiency of these multiphasic materials is due to the osteogenic and osteoconductive properties of the microporous biphasic calcium phosphate. The associated hydrosoluble polymers are considered as carriers in order to achieve the rheological properties of injectable bone substitutes (IBS). In this study, we used 2 semi synthetic hydrosoluble polymers of polysaccharidic origin. The hydroxy propyl methyl cellulose (HPMC), with and without silane, was combined with microporous BCP granules. The presence of silane induced considerable gelation of the suspension. The 2 IBS used (without gelation, IBS1, with gelation, IBS2) were implanted in critical size femoral epiphysis defects in rabbits. No foreign body reactions were observed in either sample. However, because of the higher density from gelation, cell colonisation followed by bone tissue ingrowth was delayed over time with IBS2 compared to the IBS1 without gelation. The results showed resorption of the BCP granule and bone ingrowth at the expense of both IBS with different kinetics. This study demonstrates that the hydrogel cannot be considered merely as a carrier. The gelation process delayed cell and tissue colonisation by slow degradation of the HPMC Si, compared to the faster release of HPMC with IBS1, in turn inducing faster permeability and spaces for tissue ingrowth between the BCP granules.

Mandibular Segmental Defect Regenerated With Macroporous Biphasic Calcium Phosphate, Collagen Membrane, and Bone Marrow Graft in Dogs

OBJECTIVE To reconstruct segmental mandibulectomy using calcium phosphate ceramics and collagen membrane with a delayed bone marrow grafting in experimental animals. DESIGN Defects of segmental mandibulectomy were filled with calcium phosphate granules and wrapped with a collagen membrane in 4 dogs and left empty as a control in 2 dogs. Two months later, a bone marrow graft was injected into the center of the implants. Animals were humanely killed after a 16-week delay. SUBJECTS Six adult beagles were included in this study. INTERVENTION Segmental mandibulectomy. MAIN OUTCOME MEASURE Bone ingrowth and material resorption in the reconstructed segment. RESULTS Successful osseous colonization bridged the whole length of the defects. The good new bone formation at the center and the periosteum-like formation at the periphery suggest the osteoinductive role of the bone marrow graft and the healing scaffold role of the membrane. CONCLUSIONS This model succeeded in regenerating a large segmental defect in the mandible. An investigation with a postimplantation radiation delivery schedule is required with the use of this model, which should be considered as a preclinical study for a bone tissue engineering approach in patients with cancer-related bone defects.

Bilayered calcium phosphate coating to promote osseointegration of a femoral stem prosthesis.

A bilayered bioactive-gradient coating, consisting of a superficial layer of biphasic calcium phosphate (BCP) and a deep layer of hydroxyapatite (HA), promotes faster osseointegration and higher shear strength in non-loading conditions than do monolayer BCP or HA coatings. This study evaluated the biofunctionality of this coating in weight-bearing conditions at 6 and 12 months. The coating was plasma-sprayed on the metaphyseal portion of a sandblasted Ti6Al4V canine femoral prosthesis implanted using the surgical press-fit technique. An identical uncoated stem served as the control. Metaphyseal bone-to-implant apposition was increased for coated (∼90% and 80% respectively at 6 and 12 months) as compared to uncoated implant (∼7% at 6 and 12 months). Limited bone apposition was observed at the diaphyseal level. After 12 months, the uncoated implant interface consisted of well-organized, active fibrous tissue, whereas only inactive fibrous tissue interposition was observed at diaphyseal levels of the coated implant. At 6 months, the mineralization apposition rate (MAR) was similar, regardless of implant or bone structures. At 12 months, a significant decrease of MAR was observed around the uncoated implant. Transmission electron microscopy studies of the interface showed precipitation of biological apatite crystals in close association with mineralized collagenous bone matrix. Our results suggest a direct relationship between bioactivity and enhanced bone formation. The sandwich coating used is effective in promoting massive metaphyseal osseointegration, which ensures mechanical stability for early weight-bearing and should prevent long-term complications.

Injectable biphasic calcium phosphate bioceramic: The HYDROS concept.

A new biphasic calcium phosphate ceramic material has been developed in our laboratory. It is composed of 60% of hydroxyapatite and 40% of beta-tricalcium phosphate, based on three granulometries (submicron, round microporous 80-200 mum and macro microporous 0.5-1 mm particles) and hydrated with water leading the formation of a putty filler for bone repair. Biocompatibility and osteogenicity were tested by filling femoral epiphyses critical size bone defect and lumbar muscles in rabbit. After 3, 6 and 12 weeks of implantation, explants were treated for histology. Results revealed the biocompatibility of the material and intensive resorption of the submicron particle fraction followed by important bone ingrowth whereas osteoconduction was provided by the larger particles.

Bone Mass and Bone Quality Are Altered by Hypoactivity in the Chicken

Disuse induces a rapid bone loss in adults; sedentarity is now recognized as a risk factor for osteoporosis. Hypoactivity or confinement also decrease bone mass in adults but their effects are largely unknown and only few animal models have been described. We have used 10 chickens of the rapidly growing strain 857K bred in a large enclosure (FREE group); 10 others were confined in small cages with little space to move around (HYPO group). They were sacrificed at 53 days and femurs and tibias were evaluated by texture analysis, dual energy X-ray densitometry, microcomputed tomography (microCT) and histomorphometry. Hypoactivity had no effect on the length and diameter of the bones. Bone mineral density (BMD), microCT (trabecular bone volume and trabecular microarchitecture) and texture analysis were always found significantly reduced in the animals of the HYPO group. BMD was reduced at both femur and tibia diaphysises; BMD of the metaphysis was significantly reduced in the femur but not in the tibia. An increase in osteoid volume and surfaces was noted in the HYPO group. However, there was no alteration of the mineral phase as the osteoid thickness did not differ from control animals. Bone loss was much more pronounced at the lower femur metaphysis than at the upper metaphysis of the tibia. At the tibia, only microarchitectural changes of trabecular bone could be evidenced. The confined chicken represents a new method for the study of hypodynamia since these animals do not have surgical lesions.

β-TCP granules mixed with reticulated hyaluronic acid induce an increase in bone apposition

β beta-tricalcium phosphate (β-TCP) granules are suitable for repair of bone defects. They have an osteoconductive effect shortly after implantation. However, dry granules are difficult to handle in the surgical room because of low weight and lack of cohesion. Incorporation of granules in a hydrogel could be a satisfactory solution. We have investigated the use of hyaluronic acid (HyA) as an aqueous binder of the granules. β-TCP granules were prepared by the polyurethane foam technology. Commercially available linear (LHya) and reticulated hyaluronic acid (RHyA) in aqueous solution were used to prepare a pasty mixture that can be handled more easily than granules alone. Thirteen New Zealand White rabbits (3.5-3.75 kg) were used; a 4 mm hole was drilled in each femoral condyle. After flushing, holes were filled with either LHyA, RHyA, dry β-TCP granules alone, β-TCP granules + LHyA and β-TCP granules + RHyA. Rabbits were allowed to heal for one month, sacrificed and femurs were harvested and analysed by microCT and histomorphometry. The net amount of newly formed bone was derived from measurements done after thresholding the microCT images for the material and for the material+bone. LHyA and RHyA did not result in healing of the grafted area. LHyA was rapidly eluted from the grafted zone but allowed deposition of more granules, although the amount of formed bone was not significantly higher than with β-TCP granules alone. RHyA permitted the deposition of more granules which induced significantly more bone trabeculae without inducing an inflammatory reaction. RHyA appears to be a good vehicle to implant granules of β-TCP, since HyA does not interfere with bone remodeling.

Effect of Sintering Process of HA/TCP Bioceramics on Microstructure, Dissolution, Cell Proliferation and Bone Ingrowth

The purpose of this study was to determine the effect of sintering conditions on microporosity of and cell proliferation and bone ingrowth on biphasic calcium phosphate (BCP) bioceramics. Discs were prepared from a calcium-deficient apatite preparation that upon sintering at 1050oC and above, results in a BCP with 60% hydroxyapatite (HA)/ 40% beta-tricalcium phosphate (β-TCP) ratio. The discs were divided into groups which were sintered under different conditions of heating rate (programmed vs. non-programmed) and temperature (1050°C vs. 1200°C). The discs were characterized in terms of composition (HA/β-TCP ratio), surface morphology, surface area, surface microporosity, per cent microporosity, and dissolution properties. The in vitro effect of sintering conditions on cell proliferation was determined using an established mouse fibroblast cell line (L929). Results demonstrated the following: (a) the HA/β-TCP ratio remained 60/40 regardless of sintering conditions; (b) the % microporosity, surface microporosity, surface area of the BCP and cell proliferation on the BCP significantly decreased with increasing sintering temperature, and (c) the extent of dissolution decreased with decreasing per cent microporosity. The in vivo study indicated no tissue adverse reaction and direct bone contact with the implant surface, confirming the biocompatibility of the BCP bioceramics. Resorption of the BCP and bone ingrowth was directly related to the sintering temperature: the higher the temperature, the lower the resorption and the bone ingrowth. Results of this study indicate that per cent microporosity of the BCP bioceramics affects its dissolution properties and cell response. The study demonstrates that optimum per cent microporosity elicits optimum cell response and should be considered to provide osteogenic/osteoinductive property to bioceramics.

Repairing segmental defect with a composite associating collagen membrane and MBCP+® combined with total bone marrow graft in irradiated bone defect: an experimental study in Rabbit.

The aim of this study was to study bone marrow quality from various location and species for reconstruction of segmental critical size defect in irradiated weigh bearing bone. Sample of bone marrow aspirates from rabbits and Beagle dog were analyzed. Rabbits were implanted with a composite associating resorbable collagen membrane plus micro macroporous biphasic calcium phosphate (MBCP®) and autologous bone marrow (BM) injected after irradiation. Bone marrow samples were found to be significantly less rich in tibia than in humerus and ilium in Dog and less rich in Dog than in Rabbit (p<0,05). Successful osseous colonization bridging of the defect were obtain at 16 weeks in all animals. Identical repartition of bone ingrowth and residual ceramic at the different levels of the implant suggest an osteoinduction role of the bone marrow graft in the center of the defect. This model succeeded in reconstruct a large segmental defect in weight bearing and irradiated bone in rabbit.

In Vivo Comparative Study of Two Injectable/Moldable Calcium Phosphate Bioceramics

Calcium phosphate bioceramic granules associated with hydrosoluble polymers formed putties currently more used in clinical applications as they are easy to handle (injectability, moldability). In this study, 2 kinds of materials were tested in rabbit bone defects. The first one is InOss (Biomatlante), a microporous biphasic CaP granules (BCP, HA/TCP mixture) with polysaccharidic hydrogel; and the second one is Actifuse ABX (Baxter/Apatech), pure hydroxyapatite granules containing silicate (HA-Si) with blocks copolymer hydrogel (poloxamer), . The aim of this study was to compare osteogenic properties of two kinds of CaP putties containing HA-Si versus BCP and the kinetic of resorption of their hydrogel. Data have demonstrated that both hydrogels increase the handling properties. Bone regeneration was observed in the two types of sample, however at 3 weeks, Actifuse ABX hydrogel was not totally absorbed, while InOss hydrogel was no longer observed. The second difference observed was osteoconduction. Newly formed bone over the time period studied was moreover in close contact with BCP granules than with HA-Si granules. Larger granules resorption on time was observed for BCP compared to HA-Si. Resorption of Actifuse ABX remains limited and explains the faster kinetic of absorption for InOss. This study demonstrates biocompatibility, absorbability and bone ingrowth at the expense of the two types of putty injectable/moldable bioceramic used for bone regeneration.