Abstract
The enhancement of the biological properties of Ti by surface doping with hydroxyapatite (HA) is of great significance, especially for orthodontic applications. This study addressed the effects of HA particle size in the electrolyte suspension on the characteristics and biological properties of thin titania-based coatings produced on Ti-6Al-4V alloy by plasma electrolytic oxidation (PEO). Detailed morphological investigation of the coatings formed by a single-stage PEO process with two-step control of the electrical parameters was performed using the Minkowski functionals approach. The surface chemistry was studied by glow discharge optical emission spectroscopy and Fourier transform infrared spectroscopy, whereas mechanical properties were evaluated using scratch tests. The biological assessment included in vitro evaluation of the coating bioactivity in simulated body fluid (SBF) as well as studies of spreading, proliferation and osteoblastic differentiation of MC3T3-E1 cells. The results demonstrated that both HA micro- and nanoparticles were successfully incorporated in the coatings but had different effects on their surface morphology and elemental distributions. The micro-particles formed an irregular surface morphology featuring interpenetrated networks of fine pores and coating material, whereas the nanoparticles penetrated deeper into the coating matrix which retained major morphological features of the porous TiO2 coating. All coatings suffered cohesive failure in scratch tests, but no adhesive failure was observed; moreover doping with HA increased the coating scratch resistance. In vitro tests in SBF revealed enhanced bioactivity of both HA-doped PEO coatings; furthermore, the cell proliferation/morphometric tests showed their good biocompatibility. Fluorescence microscopy revealed a well-organised actin cytoskeleton and focal adhesions in MC3T3-E1 cells cultivated on these substrates. The cell alkaline phosphatase activity in the presence of ascorbic acid and β-glycerophosphate was significantly increased, especially in HA nanoparticle-doped coatings.
Highlights
Bone consist of an extracellular matrix and the mineral hydroxyapatite (HA) phase
This work has investigated the effects of HA particle size in single-stage Plasma electrolytic oxidation (PEO) with the two-step control of electrical parameters on the coating characteristics and biological properties
It has been demonstrated that both micro- and nanoparticles can be successfully incorporated from electrolyte suspensions into the growing coatings this would result in different surface morphology and distribution of chemical elements across the coating
Summary
Bone consist of an extracellular matrix and the mineral hydroxyapatite (HA) phase. The latter has been wellcharacterised and widely used in orthodontics to stimulate osteogenesis. Due to the brittle nature of HA ceramics, there has been growing interest in HA-coated metallic dental implants. Synthesising crystalline HA with a uniform porous morphology using PEO treatments in calcium-based electrolytes is challenging.[10,11,12,13] various post-treatments have been proposed to crystallise or deposit the crystalline HA onto the coatings, including electrodeposition,[14,15] hydrothermal[16] and chemical[17] treatments, which complicates the coating procedure
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