Nano-scaled hydroxyapatite/polymer composite IV. Fabrication and cell adhesion properties of a three-dimensional scaffold made of composite material with a silk fibroin substrate to develop a percutaneous device

Abstract

Nano-scaled sintered hydroxyapatite (HAp) particles with an a-axis length of 87 ± 23 nm, a c-axis length of 236 ± 81 nm, and a mean aspect ratio (c/a) of 2.72 were covalently linked onto a silk fibroin (SF) substrate chemically modified by graft polymerization with γ-methacryloxypropyl trimethoxysilane (MPTS). Graft polymerization with poly(MPTS) on SF was conducted by free-radical initiation in a water solvent with pentaethylene glycol dodecyl ether as a nonionic surfactant. The alkoxysilyl groups of the graft polymers avoided hydrolysis and maintained their activity in coupling with the hydroxyl groups on the HAp surface despite the use of water as the reaction solvent. The weight gain of poly(MPTS) on SF increased with increasing the reaction time, eventually reaching a plateau value of about 15 wt% after 50 min of reaction time. After HAp covalent coating, the particles separated or aggregated into several crystals, as shown by scanning electron microscopic observation. L929 fibroblast cells adhered more plentifully on HAp-coated SF compared to untreated SF and hydrolyzed poly(MPTS)-grafted SF during 24 h or 48 h of incubation. The cells adhered only on the HAp surface but not at all on the dehydrated grafted surface of SF without HAp. A button-shaped prototype for a percutaneous device was manufactured by transplantation of HAp-coated SF fibers of about 100 µm in length onto silicone moldings using an adhesive, and the device showed good cell adhesiveness.