Electrochemical study of the in vitro degradation of plasma-sprayed hydroxyapatite/bioactive glass composite coatings after heat treatment

In vitro comparisons of microscale and nanoscale calcium silicate particles

Calcium silicate (CaSi) materials have been used for bone repair and generation due to their osteogenic properties. Tailoring the surface chemistry and structure of CaSi can enhance its clinical performance. There is no direct comparison between microscale and nanoscale CaSi particles. Therefore, this article aimed to compare and evaluate the surface chemistry, structure, and in vitro properties of microscale CaSi (μCaSi) and nanoscale CaSi (nCaSi) particles synthesized by the sol-gel method and precipitation method, respectively. As a result, the semi-crystalline μCaSi powders were assemblies of irregular microparticles containing a major β-dicalcium silicate phase, while the amorphous nCaSi powders consisted of spherical particles with a size of 100 nm. After soaking in a Tris-HCl solution, the amount of Si ions released from nCaSi was higher than that released from μCaSi, but there was no significant difference in Ca ion release between the two CaSi particles. Compared to microscale CaSi (μCaSi), nanoscale CaSi (nCaSi) significantly enhanced the growth and differentiation of human mesenchymal stem cells (hMSC) and inhibited the function of RAW 264.7 macrophages. In the case of antibacterial activity against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus), nanoscale nCaSi displayed a higher bacteriostatic ratio, a greater growth inhibition zone and more reactive oxygen species (ROS) production than microscale μCaSi. The conclusion is that nanoscale CaSi had greater antibacterial and osteogenic activity compared to microscale CaSi. Next generation CaSi-based materials with unique properties are emerging to meet specific clinical needs.

A Comprehensive Review of Bioactive Glass Coatings: State of the Art, Challenges and Future Perspectives

Bioactive glasses are promising biomaterials for bone and tissue repair and reconstruction, as they were shown to bond to both hard and soft tissues stimulating cells towards a path of regeneration and self-repair. Unfortunately, due to their relatively poor mechanical properties, such as brittleness, low bending strength and fracture toughness, their applications are limited to non-load-bearing implants. However, bioactive glasses can be successfully applied as coatings on the surface of metallic implants to combine the appropriate mechanical properties of metal alloys to bioactivity and biocompatibility of bioactive glasses. In this review, several available coating techniques to coat metal alloys using bioactive glasses are described, with a special focus on thermal spraying, which nowadays is the most used to deposit coatings on metallic implants.

Component effects of bioactive glass on corrosion resistance and in vitro biological properties of apatite-matrix coatings

BACKGROUND

Surface modification of metallic implants is critical for improving the clinical performance of the dental and orthopedic devices. Bioactive glasses exhibit different levels of cellular function and physicochemical behavior; however, there have been few previous studies on the effect of constituents of the bioactive glasses on the in vitro osteogenic activity and corrosion resistance of apatite-based coatings.

OBJECTIVE

The objective of this work was to investigate the effect of SiO2, CaO, Na2O, and P2O5 on plasma-sprayed apatite coatings on Ti alloy substrates for tailoring the properties of implants making them suitable for clinical applications.

METHODS

The corrosion potential and corrosion current of various coatings in simulated body fluid (SBF) were examined. MG63 cell proliferation, differentiation, and mineralization of plasma-sprayed apatite-matrix coatings were evaluated.

RESULTS

The SiO2 and CaO-containing HA (HSC) coating had a higher corrosion potential than the other three coatings, while SiO2-containing HA (HS) coating displayed the highest corrosion current among all coatings. The effect of the oxides on cell functions followed the order SiO2 > CaO > P2O5 > Na2O in terms of cell attachment, proliferation, differentiation, and mineralization.

CONCLUSIONS

The flexibility in oxide doping may allow for the tunable biological properties and corrosion-resistant ability of the apatite coatings.