BI-Layer biomimetic protein coatings on HF-Treated commercial pure magnesium for potential bone implant applications

Abstract

Magnesium-based biomaterials have a great potential as biodegradable bone repair implants due to its mechanical properties which similar to natural bone, osteoconductive and osteogenic potential that promote the formation of new bones. The degradation of magnesium (Mg) has became the most crucial characteristic with regards to its success as bone implants. Additionally, good cellular response and attachment are desirable to allow the implant to be fully integrated with the human biological system. However, rapid degradation of Mg in the physiological environment hinders its clinical application. In order to improve Mg, as an ideal bone implant, a biocompatible protective surface coating that can reduce the biodegradation rate with better cell/surface interactions on pure Mg was developed. The present study aimed to develop bi-layer coatings to functionalise pure Mg surface, composed of nontoxic elements that decelerated the degradation rate in physiological solution while enhancing the cellular response of osteoblast cells (hFOB) on the treated surface of pure Mg. The hydrofluoride (HF) conversion surface treatment was applied as the first coating layer and acted as a protective film to decelerate the fast degradation rate. Then, biomimetic protein coatings from fetal bovine serum (FBS) and/or collagen type I were applied as the second coating layer to enhance cell/surface interactions of the implants. The in-vitro assessment was used to investigate the biodegradation performances of the developed bi-layered coatings. The treated surface and bi-layer coating were then subjected to FESEM, SEM, EDS measurement, XRD, ATR-FTIR, contact angle and protein release for surface characterisation analyses. The degradation rate was examined through in-vitro semi-static immersion, TAFEL extrapolation and EIS test in DMEM + 10% FBS solution. The bioactivity, biocompatibility and osteogenic differentiation measurements also have been conducted. Protein adsorption was detected with a complex chemical composition through the presence of amide, PO|- and CO|- groups incorporated fluoride ions on the treated surface. After 21 days immersion, both biomimetic protein coatings showed higher corrosion rate compared with the pure Mg but lower corrosion rate than the surface treated Mg. For long-term evaluation by the EIS test, the biomimetic collagen/apatite coating demonstrated a better protective corrosion product layer in the electrochemical corrosion by gradually increasing the charge transfer resistance value until 21 days immersion through a self-healing process. For the cytotoxicity test, after 28 days immersion, the collagen/apatite surface coated showed higher cell viability with 74.1% better cell adhesion and proliferation as well as forming 3D hFOB cells cellular network. Besides, both protein coatings can accelerate the osteogenic differentiation of hFOB cells. Collagen/apatite coating induced the highest ALP activity and gradually increased the Ca and collagen accumulation production in ECM. The 3D porous scaffold was also well accepted by hFOB cells for attachment, spreading, migrations and cell ingrowth. This research study concludes that the biomimetic collagen type I coating could be used to control implant degradation rate for long-term and enhance cell/surface interactions.