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A new class of biomimetic, bioresorbable apatitic calcium phosphate cement (CPC) biomaterial was recently developed. The handling characteristics and the ability to harden at body temperature in the presence of physiological saline makes it an attractive clinical bone substitute and delivery vehicle for therapeutic agents in orthopaedic applications. The major challenge with the material system consists in formulating an injectable paste with options for cell delivery in order to regenerate new bone faster with high quality. In this study, three different additives and/or viscosity modifiers (carboxymethylcellulose, silk and alginate) were incorporated into the CPC matrix. Injectability, cell viability and cell proliferation were evaluated by SEM, chemical content, and gene expression for osteogenesis of hMSCs. Injectable composites of CPC-gels for cell protection were achieved. The alginate provided the best outcomes, based on cell proliferation, ALP and collagen production, and osteogenic transcript increases for ALP, type I collagen, BSP and OP. Osteogenic analysis indicated lineage-specific differentiation of hMSCs into osteogenic outcomes in this CPC matrix. The results suggest that gel mixed CPC combination materials can be used as a cell delivery vehicle for bone regeneration.

A new class of osteoconductive and osteoinductive combination biomaterials composed of calcium phosphate cement (CPC), demineralized bone matrix (DBM) and a water-soluble viscosity modifier were prepared and characterized in-vitro and in-vivo. In previous studies, a range of combinations formulations were tested in order to compare their performance characteristic. In-vitro characterization results show that the mechanical strength is decreased when the amount of DBM increases. However, DBM does not affect the CPC’s ability to set hard and convert to nanocrystalline apatitic calcium phosphate, which shares the chemical structure of natural bone as seen in x-ray diffraction. It is known that the DBM alone is osteoinductive. In-vivo osteoinductivity testing of the formulations in an intramuscular, athymic rat model demonstrated that the combination material is also osteoinductive. Two formulations were chosen for in-vivo efficacy testing based on the results of in-vitro and in-vivo characterization. These formulations were studied using rabbit critical-sized femoral core defect model. The formulations were composed of DBM with particle sizes of 250 to 710 μm, carboxymethyl-cellulose (CMC) as the viscosity modifier and weight percent compositions of 50% DBM/ 45% CPC/ 5% CMC and 60% DBM/ 30% CPC/ 10% CMC. Bone integration and healing was graded at 6, 12, and 24 weeks. The two formulations were compared to the gold standard autograft at 12 weeks and to an empty defect as the negative control at 24 weeks. Based on micro-computed topography (μCT), both formulations allowed for continuity of bone throughout the defect region at all time points. No differences in dense area fraction were seen between two formulations at 6 weeks (p = 0.8661). There was no significant statistical difference between the two formulations and autograft at 12 weeks (p = 0.2467). At 24 weeks, both formulations had significantly higher dense area fractions than empty controls (p = 0.0001). Histologically, the biology of the treatment areas appeared to have returned to normal by 24 weeks with CPC appearing to be the principal osteogenic inducer. In conclusion, these combinations of CPC and DBM offers significant advantages (handling, mechanical properties and osteoinductivity) over current DBM products and can be an effective alternative to autograft in healing of bone defects.

Alpha-bsm® is a first generation self-setting, injectable and moldable apatitic calcium phosphate cement (CPC) based on amorphous calcium phosphate (ACP). ACP was prepared using low temperature double decomposition technique, from a calcium solution (0.16 M), and phosphate solution (0.26 M) in a basic (pH~13) media. ACP was than stabilized using three crystal growth inhibitors (CO32-, Mg2+, P2O74-), freeze-dried, and heated (450 °C, 1h) to remove additional moisture and some inhibitors. Dicalcium phosphate dehydrate (DCPD) was also prepared using wet chemistry at room temperature from calcium and phosphate solution, respectively, 0.3 M and 0.15 M. ACP and DCPD powder were combined at a 1:1 ratio and ground to produce Alpha-bsm® bone cement. The cement is supplied as a powder and when mixed with an appropriate amount (0.8 ml/g) of physiological saline at room temperature, forms an injectable putty-like paste. The paste has a working time of about 45 minutes at room temperature, when stored in a moist environment. The setting reaction proceeds isothermically at body temperature (37°C) in less than 20 minutes, forming a hardened, porous (total porosity 50 to 60%), low crystalline (40% comparing with HA), apatitic calcium phosphate cement with a compressive strength range of 10 to 12 MPa. Extensive pre-clinical studies (rabbit radius critical sized defect, canine tibia osteotomy, sheep tibia, primate fibula fracture healing, and primate fibula critical size defect) demonstrate that Alpha-bsm® undergoes remodeling in conjunction with new bone formation. The next generation of Bone Substitute Materials (Beta-bsmTM and Gamma-bsm TM) are formulated based on the Alpha-bsm® chemistry but differ in powder processing (e.g. milling) technique. These materials are also self-setting, injectable and/or moldable apatitic calcium phosphate cements with improved handling and mechanical properties. The setting & hardening reaction of these new CPCs proceeds isothermically in less than 5 minutes at 37°C and once hardened demonstrate a compressive strength of 30 to 50 MPa. The final product (after full conversion) is a low crystalline (40% compared with Hydroxyapatite), calcium deficient (Ca/P atomic ratio = 1.45) carbonated apatite similar to the composition and structure of natural bone mineral (crystal size: length = 26 nm, width thickness = 8 nm). A desirable feature of these cements is their high surface chemistry (with specific surface area of about 180-200 m2/g) which is ideal for remodeling and controlled release of growth factors. A pilot rabbit critically sized femoral defect study comparing the three synthetic family products demonstrate that they share similar remodeling and resorption characteristics up to 52 weeks. Physico-chemical and mechanical performance of these next generation CPCs are favorable when compared with existing CPCs in the market, specifically material working time (at room temperature), cohesivity in a wet environment and fast setting & hardening rate (at body temperature).