Micro/Nanoporous Modification On Medical Titanium Surface And Functional Composite Coatings

Hydroxyapatite (HA) coatings on titanium substrates have been widely used in hard tissue replacement surgery. However, the artificial HA coatings still have many differents from natural bone, and do not show any anti-inflammatory action. In order to improve the biological and antibacterial properties as well as the bonding strength with the substrate of the HA coatings, two kinds of functional coatings containing protein (BSA) and antibiotic (Gentamicin) were produced respectively on nanotublar titanium surfaces through biomimetic and co-deposition. The nanostructured surfaces were preceding prepared by anodic oxidation and heat treatment at 450℃.During the preparation of BSA/HA coatings, four kinds of samples, including TiO2 nanotublar surfaces with diameter of 50,100 and 170nm, micro/nanoporous structural surfaces with dozens of micron porous and nanotubes with 100nm diameter were prepared. The growth process of HA coatings on the samples were studied respectively, in order to investigate the influence of different morphology and diameters of nanotubes on the HA coating formation. Also, the bonding strength of the coating samples were tested. The formation of HA coatings were easier on micro/nanoporous structural surface than that of on the other titania nanotublar surfaces. For nanotubes with different diameters, the TiO2 nanotube layers with 170nm diameter has better mineralization ability compared to nanotubes with 100nm and 50nm diameter. The formation ability of HA increased with the increasing of the nanotube diameter. The pre-mineralization in vacuum increased growth rate of the coating and significantly enhanced the bonding strength. The bonding strength between the coating and the nanotube layers with large diameter is higher than that with the small diameter. The micro/nanoporous sample owns the maximal strength of 18MPa.For drug loaded HA coatings, I have investigated the effect of the gentamicin concentration on the coating formation. Bacteria culture testing was ultilized to evaluate the antimicrobial property of the coating. The calcium phosphate coatings could be deposited on samples when the concentration of gentamicin sustains in a range of 0-1000mg/L in coating solution. Ca/P coating formation enhance by the increasing of the drug concentration. A concentration higher than 1200mg/L hindered the growth of calcium phosphate crystals on nanotublar surfaces. The test of bacteria culture showed that the incorporation of gentamicin in HA coating could significantly inhibit reproduction of esherichia coli and staphylococcus albus.The release of BSA and gentamicin were also measured in vitro. After mineralization for 24h, the loaded amount of BSA into the coating on the substrate with nanotube layers of 170nm diameter was around 1.87mg for concentration of 1000mg/L. And the deposition rate of BSA was 18.7%. After 15 days immersion, the release of BSA from HA coating was 44%. For the drug loaded coatings, HA coating were loaded with gentamicin by immersing in gentamicin coating solution of 1000mg/L for 48h. With a 8.36mg loaded amount of gentamicin, about 87.5% was released within 15 days. The amount of gentamicin released from the coating has exceeded the minimal inhibitory concentration (MIC) in 12 days.All the results indicate that through pre-mineralization in vacuum and then biomimetic co-deposition methods, HA coating containing biomolecules can fastly formed on micro/nanoporous structural surface which has high bonding strength to the substrates. These method would be a promising way to prepare titanium-based bioacitive coatings. Besides, the antibiotics loaded HA coatings could be used to prevent post-surgical infections in orthopaedics or trauma.