Incorporation of bioactive collagen type I and biomineralised hydroxyapatite on polydopamine grafted stainless steel

Abstract

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 immobilise HA and collagen type I on a medical grade stainless steel (SS316L) due to its versatile, strong and stable properties. The SS316L disks were pre-treated and grafted with a polydopamine film. Then, they were covalently immobilised with collagen fibers at different immersion time (6, 12 and 24 hours). The disks were further biomineralised with HA in 1.5× simulated body fluid (SBF) solution for 7 days. The coated surfaces were characterised using FTIR, FESEM-EDX, XRD and contact angle analyses to investigate its chemical composition, morphology, crystallinity and wettability properties. The characterisation analyses showed that increased in collagen immersion time have induced the formation of amide cross-linkage between collagen and polydopamine. Longer immersion time has also produced less agglomerated carbonate HA with a nano lath-like surface. The disks with longest collagen immersion time were selected and subjected to in vitro test with human fetal osteoblasts (hFOB). The cell attachment, viability and differentiation were examined through FESEM, Alamar Blue reduction assay and Alkaline Phosphatase (ALP) assay respectively. The disks immobilised with HA and collagen presented highest proportion of cell adhesion, highest viability percentage with 31.8% of reduction potential and highest production level of ALP activity at 6.4 μIU/L compared to the bare SS316L disks and the disks immobilised with collagen. It can be concluded that, the polydopamine film has acted as an intermediate layer for the immobilisation of bioactive HA and collagen which projects a promising technique in the development of bioactive implant coating.