Biomimetic organic-inorganic nanocomposite coatings for titanium implants.
In order to evaluate the biocompatibility and bioactivity of recently described nanocomposite coatings, consisting of polyelectrolyte multilayers interspersed with calcium apatite crystals, extensive cell culture tests have been applied to coated and uncoated chemically etched titanium plates. The coatings had top calcium phosphate layers (PLL/PGA)10CaP[(PLL/PGA)5CaP]4 (A) or top polyelectrolyte multilayers, (PLL/PGA)10CaP[(PLL/PGA)5CaP]4 (PLL/PGA)5, (B), where PLL and PGA are poly-l-lysine and poly-l-glutamic acid respectively and CaP is calcium deficient apatite. Before testing coated samples were crosslinked and subsequently stored for extended periods of time (18 or 32 weeks) under dry, sterile conditions. Nonspecific activities, e.g. cell adhesion, proliferation, vitality, activity of mitochondrial dehydrogenases and cell morphology in contact with the material surfaces were tested using the cell-line MC3T3-E1, while for testing osteoblast specific activities, (collagen type I synthesis and alkaline phosphatase activity) SAOS-2 cells were used. The results show excellent biological properties of chemically etched titanium which were even surpassed by surfaces covered with coating B, while coating A (top crystal layer) adversely affected cell proliferation and performance. The effect is explained by morphological observations, showing inhibited spreading of the cells on the rough surfaces of coating A. The results also show that coatings, when shelved under dry and sterile conditions are stable for up to 8 months.