Poly-L-Lysine-Dnalayer By Layer Modification On Medical Titanium Surface And Its Biological Properties

Titanium and titanium alloys have good biocompatibility and mechanical properties, such as low modulus, high strength, corrosion resistance and excellent fatigue resistance. As a result, they have been extensively used in orthopaedic fields. However, titanium and its alloys cannot meet clinical requirements for that even if a titanium implant osseo-integrates. Surface modification for biomaterials was often used to improve their biocompatibility. There are two parts in this study, one part is that a layer-by-layer (LBL) self-assembly technique, based on the polyelectrolyte-mediated electrostatic adsorption of poly-l-lysine (PLL) and DNA, was used to the formation of multilayer on titanium surfaces. Then bovine serum albumin (BSA) adsorption, biomineralization and osteoblast culture of modified surfaces were studied. The other is some highly-ordered nanotube arrays on titanium surfaces were obtained by anodization. After further heat treatment, PLL and DNA were assembled onto the titanium nanotublar surfaces. Then protein adsorption and biomineralization tests were conducted to investigate bioactivity of samples. Finally, cellular behaviors of osteoblast cell on surfaces with different morphology and component were evaluated in vitro.X-ray photoelectron spectroscopy (XPS) and water contact angle measurement indicated that PLL and DNA were assembled onto titanium and titanium oxide nanotubes successfully. And these data provides the evidence that PLL and DNA were combined together through electrostatic attractions between P-O- and NH3+ rather than physical adsorption. Quartz crystal microbalance dissipation (QCM-D) was used to monitor the self-assemble process of PLL and DNA on titanium. The mass of self-assembled layers were obtained using QCM-D. The stability of PLL layer and DNA layer on titanium in HEPEs solution under 37℃was both excellent. Zeta potential of the LBL-coated microparticles was measured by dynamic light scattering (DLS). The data of zeta potential showed that the surface terminated with PLL displayed positive charge while the surface terminated with DNA diaplayed negative charge, which further confirmed the electrostatic attraction between PLL and DNA.In protein adsorption test, the measurement with ultraviolet (UV) spectrophotometer revealed that the LBL films enhanced ability of BSA adsorption onto titanium/titanium oxide nanotubes. The adsorption quantity of BSA on the surface terminated with PLL was higher than that of the surface terminated with DNA, and the samples of Ti/P/D/P and TNT/P/D/P absorbed BSA most. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) showed that samples of assembled PLL or/and DNA had better bioactivity in inducing HA formation. Thus the assembling of poly-l-lysine (PLL) and DNA onto the surface of titanium/titanium oxide nanotubes in turn via a layer-by-layer self-assembly technology can improve the bioactivity of titanium/titanium oxide nanotubes.In osteoblast culture test, alamar blue measurement showed that the PLL/DNA-modified films have higher cell viability (p<0.02) than Ti/TiO2 nanotube without modification after 3 and 7 days culture, respectively. Still, the alkaline phosphatase activity (ALP) assay revealed a better differentiated phenotype on three types of multilayered surfaces compared to non-coated controls. The sample Ti/P/D/P and TNT/P/D/P displayed much more amount of cells and much more cells connected and overlapped. What's more, cells on TiO2 nanotubes showed much more cell adhesion than the smooth Ti, which demonstrated that the TiO2 nanotubes can affect the abilities of cells adhesion, spread and colonization.Collectively, our results suggest that PLL/DNA were successfully employed to surface engineer titanium via LBL technique, and enhanced its cell biocompatibility. When anodization and LBL were coexisted, they would be mutual promotion of cells adhesion, spread and colonization.