Synthesis and characterization of collagen–hydroxyapatite immobilized on polydopamine grafted stainless steel

Hydroxyapatite (HA) and collagen have been coated on metallic implants to accelerate osseointegration. Most methods to coat HA require high sintering temperature, high cost and high energy power while the methods to coat collagen commonly produce unstable coating. Therefore, in this study, a polydopamine film was used as an intermediate layer to immobilize HA and collagen type I on a medical grade stainless steel (SS316L) implant to overcome those disadvantages. The SS316L disks were pre-treated and grafted with a polydopamine film. It was then covalently immobilized with collagen fibers at different immersion times (6, 12 and 24h). The disks were further biomineralized with HA in simulated body fluid (SBF) for 7days. The film surfaces were characterized by FTIR, FESEM-EDX, XRD and contact angle analyses to investigate the chemical composition, morphology, crystallinity and wettability properties. The collagen and carbonated HA (lath-like surface) were successfully immobilized on the polydopamine film with less agglomeration as the immersion time in the collagen solution increased. Increasing the immersion time accelerated the activation of carboxylic groups in the collagen to form an amide cross-linkage for heterogenous nucleation of HA. Furthermore, the crystallinity and wettability properties were also enhanced with the closest theoretical Ca/P ratio. As a conclusion, the immobilization of collagen at 24h has produced better HA formation and wettability property that might be beneficial for the attachment and proliferation of osteoblast cells on biomedical implants. Graphical abstract [Display omitted] •HA and collagen were successfully immobilized on polydopamine grafted SS316L.•Less agglomerated carbonate HA (lath-like surface) on HA-24Coll-dopa•HA-24Coll-dopa improved the coating crystallinity and wettability.