Deposition of functional biomedical coating via drop-on-demand micro-dispensing technique

Abstract

Silicon-substituted hydroxyapatite (SiHA) and silver-substituted hydroxyapatite (AgHA) have been shown to provide enhanced bioactivity and anti-bacterial properties over pure hydroxyapatite (HA), respectively. In this work, a dual-layer nanoSiHA-nanoAgHA/nanoHA (nSiHA-nAgHA/nHA) coating consisted of a bottom nHA layer and a top hybrid nSiHA-nAgHA layer was developed and fabricated via the Drop-on-Demand (DoD) micro-dispensing technique, to achieve fast bone growth and reduce bacterial adhesion. Phase-pure nHA, nSiHA containing 0.7 wt.% silicon (Si), and nAgHA containing 0.5 wt.% silver (Ag) powders were synthesised in-house via a wet precipitation method, and deposited onto the glass substrates using the DoD technique. Dispensing parameters were optimised using Taguchi method with an L16 orthogonal array. The S/N ratio and ANOVA analysis revealed that the parameters of on-time and pressure had more significant effects on the droplet formation. The dual-layer coating retained its physicochemical properties of as-synthesised powders, and exhibited a thickness of 34.5 ? 1.0 ?m. It exhibited a critical load of 69 mN before failure, and Si and Ag were uniformly distributed on the top layer. In addition, adipose-derived stem cells grew and differentiated well on the dual-layer coatings, with up-regulated expression of alkaline phosphatase activity, type I collagen and osteocalcin. The growth of S.aureus was inhibited on the dual-layer coating within 24 h. In short, this report evaluates the capability of DoD micro-dispensing technique for the deposition of dual-layer nSiHA-nAgHA/nHA coatings, and explores the physicochemical, mechanical and biological properties of coatings, indicating its potential usage in the orthopaedic implants.