Abstract
For many years, calcium phosphate coatings to tailor the degradation behavior of magnesium and magnesium-based alloys for orthopaedic applications have received lots of research attention. However, prolong degradation behavior, its effect on biological and mechanical properties as well as osteoblastic response to single-step hydrothermally deposited calcium phosphate coatings remain poorly documented. In this study, Alamar blue assay, cell attachment, live/dead assay, and qRT-PCR were done to study the biological response of the coatings. Furthermore, immersion testing in SBF for 28 days and compression testing of the degraded samples were carried out to examine the degradation behavior and its effect on mechanical properties. The results indicated that coatings have a significant influence on both the substrate performance and structural integrity of coated AZ91-3Ca alloy. Immersion test revealed that coating deposited at pH 7, 100°C (CP7100) improves the hydrogen evolution rate by 65% and the degradation rate by 60%. As the degradation performance of coated samples improves so does the mechanical strength. CP7100 samples successfully retained 90% of their compressive strength after 14 days of immersion while bare AZ91-3Ca alloy lost its mechanical integrity. Furthermore, biological studies show that cells are happily proliferating, differentiating, and adhering to the coating surfaces, which indicates, improved osteointegration and osteogenesis with no sign of alkaline poisoning. qRT-PCR results showed that calcium phosphate coatings enhanced the mRNA levels for RUNX2, Col1A, and ALP that may exhibit a speedy bone recovery. Thus, calcium phosphate coatings produced via a single-step hydrothermal method improve the degradation behavior, mechanical integrity and stimulate the differentiation of osteoblast lining. This leads toward faster bone regeneration, which shows a great potential of these coatings to be used on degradable implants as a bioactive protective layer.
Highlights
Magnesium is an exceptionally lightweight metal with excellent mechanical properties
The present study demonstrated that the CaP coatings deposited by the single-step hydrothermal method reduced the degradation rate by 60% and hydrogen gas evolution rate (HER) by 65% as compared to bare AZ91-3Ca alloy
MC3T3-E1 pre-osteoblast cells culturing with coated samples and live/dead assay tests show no significant difference in cell proliferation on coating and positive control
Summary
Magnesium is an exceptionally lightweight metal with excellent mechanical properties. The chloride ions present in the physiological environment react with Mg(OH) layer and convert it into soluble magnesium chloride with evolution of hydrogen gas This exposes the magnesium substrate to be further attacked by surrounding water and faster corrosion followed by abrupt hydrogen evolution (Staiger et al, 2006; Brar et al, 2009). Abrupt hydrogen evolution increases the localized pH, which harshly affects the biological process as the alkalization increases rapidly around the implant surroundings (Song, 2007; Lorenz et al, 2009; Schumacher et al, 2014) These shortcomings are currently a limiting factor for magnesium-based alloys to be safely used in load-bearing orthopaedic applications
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