Development and in vivo testing of gelatin and silk-fibroin based calcium phosphate bone cement

Calcium phosphate cement bone replacement materials are used in biomedical and dental applications as composites and coatings, due to their physical and chemical similarity to bone structure. Bone cements are used in hard tissue repair by inducing new bone formation as well as supporting internal fixation. This study was conducted with the aim to produce, characterize and apply gelatin and silk based calcium phosphate cements. The composition of bone cement was based mainly on an inorganic component consisting of hydroxyapatite, tetracalcium phosphate, disodium phosphate, carbonate and an organic component consisting of gelatin and silk fibroin. The various formulations studied varied from each other in terms of gelatin concentration, water content, setting temperature, setting time and the use of Na+ versus Ca++ as the carbonate cation. The bone cement setting time was determined mechanically using the Vicat Testing Method. Cement samples were further characterized by contact angle analysis, XRD, SEM and FTIR to determine their hydrophilicity, crystal structure, morphology and molecular bonding pattern. The mechanical properties of the cements were studied using the Universal Testing Device. In vivo performance tests were conducted on Sprague-Dawley rats using 3 mm wide defects formed on both sides of the calvarium. The results of characterization indicated formation of Ca-P based bone cement with a minimum setting time of 16.5±0.5 minutes. Among the various formulations studied, cement 80C-3/37 demonstrated a contact angle of 28.8°±1.78, formation of hydroxyapatite crystals with crystal size of approximately 135 nm, Ca/P ratio of 1.71, Calcium solubility of 73.96 μg/μl, Phosphate solubility of 0.24 μg/μl, mechanical strength of 0.31±0.25 MPa, and a setting time of 16.5±0.5 min. The in-vivo testing histological scores indicated time-based bone healing in the experimental groups with the superior healing in cement 80C-3/37 implanted animals, wheres the four-week group demonstrating partial and the eight week group complete healing and replacement of the defect by the newly formed calvarial bone.