OBJECTIVETo provide a basis for surface modification of polyelectrolyte multilayer films (PEM) on implants by exploring the effects of immobilization of PEM on titanium surfaces on their cell biological effects.

METHODSBy using plasmid of bone morphogenetic protein-2 (pBMP-2)-loaded lipopolysaccharide-amine nanopolymersomes (pLNP) as cationic polyelectrolytes and hyaluronic acid (HA) as anionic polyelectrolytes. PEM were constructed on alkaline-heat treated titanium surfaces via layer by layer self-assembly(LbL) technique. A successive deposition of HA and pLNP on titanium surfaces was defined as one cycle of assembly. The morphology of titanium surface before and after assembly treatment was observed by scanning electron microscopy (SEM). The ultraviolet (UV) spectra and surface contact angles of PEM with different self-assembly cycles were measured. The adhesion and proliferation of mesenchymal stem cell (BMSC) on surfaces of group A (4 cycles of assembly, with outermost layer of pLNP), group B (4.5 cycles of assembly, with outermost layer of HA), blank control (polished titanium, Ti group) and alkaline-heat treated titanium (Ti-OH group) were investigated. Cell differentiation indexed by alkaline phosphatase activity (ALP) and in situ transfection of BMSC on surfaces of group A, Ti, negative control [4 cycles of assembly without pBMP- 2] were evaluated.

RESULTSSelf assembly of PEM made the titanium surface become relatively smooth. DNA absorption peaked appear at 260 nm in UV spectra, and the absorption intensity increased with assembly, suggesting the successful construction of PEM. After alkali- heat treatment, the surface contact angle of titanium decreased from (62.6±4.9) ° to (8.1±2.2) °. During LbL, with alternately introducing pLNP and HA, the contact angle increased in a jagged mode at a gradually decreased rate, which further proved the success of assembly. Cell adhesion for group A at 0.5 and 1 h was 0.415±0.085 and 0.426±0.048, which was significantly higher than those for group B (0.299±0.012, 0.355±0.022), Ti-OH group (0.225±0.007, 0.260±0.010) and Ti group (0.302±0.056, 0.339±0.028) (P < 0.01). Cell proliferation for group A and B at 3, 5 and 7 d were significantly higher than those for Ti and Ti-OH group (P < 0.01). ALP in group A at day 7 was 261±58, which was significantly higher than those in group B and Ti group. Group A had in situ transfection capability for BMSC.

CONCLUSIONSPEM with good cell biological effects can be constructed successfully on titanium surfaces using gene- loaded lipopolysaccharide- amine nanopolymersomes and hyaluronic acid.