Properties of Gelatin/Carbonate apatite composite compared to bovine bone

Bone is a composite of approximately 65% inorganic phase (carbonate apatite, CHA) and a 35% organic phase (mostly collagen). Several commercial composites consisting of natural or synthetic polymers and calcium phosphates ( hydroxyapatite, tricalcium phosphate) are recommended for use in bone repair.

Objective: The purpose of this study was to compare the physico-chemical properties of gelatin/carbonate apatite composites with that of bovine bone.  Native (Gel) or cross-linked (Gel*) was used. Methods: The CHA was prepared by hydrolysis method. The gelatin (denatured collagen) was cross-linked using Genipin. Genipin is a natural cross-linking agent with significantly less toxicity than gluteraldehyde. Gelatin composites with CHA were prepared in the 35/65 weight ratios by mixing and freeze-drying.The composites were characterized using x-ray diffraction (XRD), FT-IR spectroscopy, scanning electron microscopy (SEM) and thermogravimetry (TGA). Dissolution properties were determined in acidic buffer (0.1M KAc, pH 6, 37^oC).  Mechanical strength was determined using 3-point bend test. Bovine bone was similarly characterized for comparison. In vitro cell response (proliferation) to the composites was determined using human osteosarcoma cell line (MG63).  Results: The composition and crystallite size of the CHA were similar to that of the bone mineral. Gel/CHA composites with organic/inorganic ratio (35/65) showed several physico-chemical properties similar to that of bone.  The properties included: crystallinity (reflecting crystal size of the inorganic phase); composition; FT-IR spectra; thermal stability; dissolution and mechanical strength. Gel*/CHA compared to Gel/CHA composites showed lower elastic modulus, flexural strength, dissolution rate, swelling and higher porosity. Greater cell proliferation was observed on the composites compared to that on the gelatin or on CHA alone. Conclusion: The Gel*/CHA composites presented several properties similar to those of bovine bone and may have potential as bone substitute materials. [Supported by funds from L.Linkow Professorship in Implant Dentistry].