Gelatin-apatite bone mimetic co-precipitates incorporated within biopolymer matrix to improve mechanical and biological properties useful for hard tissue repair.

Synthetic biopolymers are commonly used for the repair and regeneration of damaged tissues. Specifically targeting bone, the composite approach of utilizing inorganic components is considered promising in terms of improving mechanical and biological properties. We developed gelatin-apatite co-precipitates which mimic the native bone matrix composition within poly(lactide-co-caprolactone) (PLCL). Ionic reaction of calcium and phosphate with gelatin molecules enabled the co-precipitate formation of gelatin-apatite nanocrystals at varying ratios. The gelatin-apatite precipitates formed were carbonated apatite in nature, and were homogeneously distributed within the gelatin matrix. The incorporation of gelatin-apatite significantly improved the mechanical properties, including tensile strength, elastic modulus and elongation at break, and the improvement was more pronounced as the apatite content increased. Of note, the tensile strength increased to as high as 45 MPa (a four-fold increase vs. PLCL), the elastic modulus was increased up to 1500 MPa (a five-fold increase vs. PLCL), and the elongation rate was ~240% (twice vs. PLCL). These results support the strengthening role of the gelatin-apatite precipitates within PLCL. The gelatin-apatite addition considerably enhanced the water affinity and the acellular mineral-forming ability in vitro in simulated body fluid; moreover, it stimulated cell proliferation and osteogenic differentiation. Taken together, the GAp-PLCL nanocomposite composition is considered to have excellent mechanical and biological properties, which hold great potential for use as bone regenerative matrices.

Functional composite nanofibers of poly(lactide-co-caprolactone) containing gelatin-apatite bone mimetic precipitate for bone regeneration.

Functional nanofibrous materials composed of gelatin-apatite-poly(lactide-co-caprolactone) (PLCL) were produced using an electrospinning process. A gelatin-apatite precipitate, which mimicked bone extracellular matrix, was homogenized in an organic solvent using various concentrations of PLCL. A fibrous structure with approximate diameters of a few hundred nanometers was successfully generated. Apatite nanocrystallines were found to be effectively distributed within the polymeric matrix of the gelatin-PLCL. The addition of a small amount of gelatin-apatite into PLCL significantly improved the tensile strength of the nanofiber by a factor of 1.8. Moreover, tissue cell growth on the composite nanofiber was enhanced. Osteogenic differentiation of the cells was significantly stimulated by the composite nanofiber compared with the pure PLCL nanofiber. When implanted in a rat calvarium for 6weeks the composite nanofiber supported defect closure and new bone formation better than the pure PLCL nanofiber, as deduced from micro-computed tomography and histological analyses. Based on these results, the gelatin-apatite-PLCL composite nanofiber developed in this study is considered to be potentially useful as a bone tissue regeneration matrix.

Development of robotic dispensed bioactive scaffolds and human adipose-derived stem cell culturing for bone tissue engineering.

Bioactive and degradable scaffolds made from bioactive glass-polycaprolactone with a mineralized surface and a well-defined three-dimensional (3D) pore configuration were produced using a robotic dispensing technique. Human adipose-derived stem cells (hASCs) were cultured on the 3D scaffolds, and the osteogenic development of cells within the scaffolds was addressed under a dynamic flow perfusion system for bone tissue engineering. The bioactive glass component introduced within the composite assisted in the surface mineralization of the 3D scaffolds. The hASCs initially adhered well and grew actively over the mineralized surface, and migrated deep into the channels of the 3D scaffold. In particular, dynamic perfusion culturing helped the cells to proliferate better on the 3D structure compared to that under static culturing condition. After 4 weeks of culturing by dynamic perfusion, the cells not only covered the scaffold surface completely but also filled the pore channels bridging the stems. The osteogenic differentiation of the hASCs with the input of osteogenic factors was stimulated significantly by the dynamic perfusion flow, as determined by alkaline phosphate expression. Overall, the culturing of hASCs upon the currently developed 3D scaffold in conjunction with the dynamic perfusion method may be useful for tissue engineering of bone.