Gelatin Reinforced with Hydroxyapatite Nanofibers
Gelatin is commonly used in biomedical applications as it is derived from collagen, yet has lower costs and can retain information signals such as the Arginyl-glycyl- aspartic acid (RGD) tri-peptide which is known to promote cell adhesion [10, 11]. Furthermore, it has a low-toxicity, is non-immunogenic, and has good biodegradability and biocompatibility . For applications, in which the extracellular matrix has a low elastic modulus, such as in the case of artificial skin, pure gelatin is appropriate. However, in mimicking tougher tissues such as bone, it is necessary to enhance the strength through composite structures that can withstand the stresses to which the human skeleton is subject to. This can be effectively done by enhancing gelatin with nanoscale hydroxyapatite (HA), which is found in natural bone and has a much higher elastic modulus. Hence, HA-gelatin composites appear to be a promising materials selection, as it is possible to increase the flexibility of gelatin to the desired stiffness by the appropriate concentration of HA. The optimum scaffold microstructure should be porous enough so as to allow bone ingrowth, however, a high porous microstructure results in low mechanical stability. The addition of HA nanorods can allow a retention of the porous microstructure of gelatin, while increasing the strength of the gelatin fibers. In addition, to the presence of HA, the cross-linking agent can further regulate the microstructure, surface roughness and compression strength of such nanocomposites. It should be noted that in addition to hydroxyapatite being used as a secondary phase reinforcement in scaffolds for tissue regeneration, one of its main applications is in bone implants where it can also be used as the main matrix material that is reinforced with nanofibers and nanotubers (such as carbon nanotubes) in order to increase its fracture toughness, and wear resistance.
In the following sub-sections a gelatin-HA nanocomposite as presented in  is summarized.