Synthesis of a poly(L-lysine)-calcium phosphate hybrid on titanium surfaces for enhanced bioactivity

Titanium has been a successful implant material owing to its excellent strength to weight ratio, toughness, and bioinert oxide surface. Significant progress has been made on the improvement of titanium's bioactivity by coating its oxide surface with calcium phosphates and bioactive molecules. Here, we report on the coating of titanium with a poly(L-lysine)-calcium phosphate hybrid material with a nanoscale texture. This hybrid coating was grown by first nucleating seed crystals of calcium phosphate, directly on the Ti surface and then exposing this surface to solutions containing Ca(2+), PO(4)(3-), and poly(L-lysine). The resultant hybrid coating was characterized by electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, and elemental analysis. This material contained 14% by weight poly(L-lysine), and this organic component decreased greatly the dimensions of the surface features, thus enhancing surface area relative to the inorganic control. The highly textured hybrid material was more susceptible than the control to acidic and enzymatic degradation. The amino acid cysteine was covalently linked to the hybrid material, demonstrating the potential of this coating for further functionalization. These hybrid coatings may prove useful in enhancing the bioactivity of titanium.