Formation and in Vivo Evaluation of Carbonate Apatite and Carbonate Apatite/CaCO₃ Composite Films Using the Thermal Substrate Method in Aqueous Solution

Abstract

We have studied the formation and carried out an in vivo evaluation of carbonate apatite (CO₃-Ap) and CO₃-Ap/CaCO₃ composite coatings on titanium substrates using the thermal substrate method. The coatings were formed on commercial pure titanium rods (diameter = 2 mm, length = 5 mm) and plates (thickness = 0.3 mm) by the thermal substrate method in an aqueous solution that contained Ca(H₂PO₄)₂, CaCl₂, and NaHCO₃. The coating experiments were conducted at 40–140°C and pH=8 for periods of 15 or 30 min. The coating temperature and NaHCO₃ of the solution had a significant influence on the surface morphology (net-like, plate-like, needle-like, or sphere-like), the phase (single phase of CO₃-Ap or binary phase of CO₃-Ap and CaCO₃), and the carbonate content in the precipitated films. A subsequent autoclave treatment also had an effect on the films. A coated rod was implanted in a 10 weeks old male rat’s tibia with a non-coated titanium rod being used as a control. The constructs were retrieved after a period of 14 d postimplantation and examined for new bone formation and for tissue response in the cancellous and cortical bone parts, respectively. Single-phase sphere-like CO₃-Ap had high osteoconductivity in the cortical bone region, and this increased with increasing carbonate content in the films. However, the osteoconductivity of the CO₃-Ap/CaCO₃ composite coatings decreased with increasing total carbonate content.