Antimicrobial Electrodeposited Silver-Containing Calcium Phosphate Coatings.

Biocompatible antimicrobial coatings may enhance the function of many orthopedic implants by combating infection. Hydroxyapatite is a choice mineral for such a coating as it is native to bone and silver would be a possible antimicrobial agent as it is also commonly used in biomedical applications. The aim of the research is to develop a silver-containing calcium phosphate (Ag/Ca-P) coating via electrochemical deposition on titanium substrates as this allows for controlled coating buildup on complex shapes and porous surfaces. Two different deposition approaches are explored: one-step Ag/Ca-P(1) deposition coatings, containing silver ions as microsized silver phosphate particles embedded in the Ca-P matrix; and via a two-step method (Ag/Ca-P(2)) where silver is deposited as metallic silver nanoparticle on the Ca-P coating. The Ag/Ca-P(1) coating displays a bacterial reduction of 76.1 ± 8.3% via Ag-ion leaching. The Ag/Ca-P(2) coating displays a bacterial reduction of 83.7 ± 4.5% via contact killing. Interestingly, by preincubation in phosphate-buffered saline solution, bacterial reduction improves to 97.6 ± 2.7 and 99.7 ± 0.4% for Ag/Ca-P(1) and Ag/Ca-P(2) coatings, respectively, due to leaching of formed AgClx(x-1)- species. The biocompatibility evaluation indicates that the Ag/Ca-P(1) coating is cytotoxic towards osteoblasts while the Ag/Ca-P(2) coating shows excellent compatibility. The electrochemical deposition of highly bactericidal coatings with excellent biocompatibility will enable us to coat future bone implants even with complex or porous structures.

Mechanical and biological properties of electrodeposited calcium phosphate coatings.

Calcium phosphate (CaP) coatings were electrochemically deposited on titanium substrates. By increasing the electrodeposition time (from 1 to 30 min), the coating thickness increases but also the surface morphology of the CaP coatings is greatly affected going from smooth to plate-like, featuring elongated plates, ribbon-like and finally sharp needle structures. Micro-stretch tests reveal that, regardless of the coating morphology and thickness, the electrodeposited CaP coatings have strong adhesion with the titanium substrates and their failure mode is cohesive failure. The effects of different morphologies on cellular behavior such as adhesion, viability, proliferation, and osteogenic gene expression were studied. The surface morphology of CaP coatings has a remarkable effect on cell attachment, proliferation, and viability. A smooth surface results in better adhesion of the cells, whereas the presence of sharp needles and ribbons on rough surfaces restricts cell adhesion and consequently cell proliferation and viability. The improved cell adhesion and viability on the smoother surface can be attributed to the higher contact area between the cell and the coating, while the needle-like morphology inflicts damage to the cells by physically disrupting the cell wall. There is no significant difference in the level of osteoblast gene expression when osteosarcoma cells are cultured on coatings with different morphologies. Our study provides crucial insights into the optimum electrodeposition procedures for CaP coating formation leading to both good cell-material interaction and sufficient mechanical properties. This can be achieved with relatively thin coatings produced by short electrodeposition times.