Surface Modification Of Poly(D,L-lactide) Via Bioactive Surfactant And Functional Microsphere

Getting the inspiration from modern bionics, bioconjugate surfactants were explored to surface tailoring of poly(D,L-lactide) (PLA) to promote the cytocompatibility for tissue engineering application. The self-segregation of cholesterol tethered surfactant was used to present the hydrophobic bioactive ligand in PLA surface. Biofunctional microspheres stabilized with ligand tethered surfactant were deposited onto PLA surface to fabricate discrete ligand domain in micro-scale. And the electrostatic deposition of nanosphere onto cytophobic polyelectrolyte multilayer was explored to develop discrete ligand domain in nano-scale. The cytocompatibility test on above modified PLA surface was then investigated.Surface modification of PLA with bioactive surfactant—A novel amphiphilic cholesterol-poly(ethylene glycol)-poly(D,L-lactic acid) copolymer (Chol-EG_n-LA_m) was synthesized via bulk ring-opening polymerization of D,L-lactide using cholesterol-poly(ethylene glycol) initiator. The gel permeation chromatography (GPC) and nuclear magnetic resonance spectroscopy (~1H-NMR) results indicated that the product had the expected structure with low polydispersity. Chol-EG_n-LA_m was used as the bioactive surface additive to blend with PLA. The surface of modified PLA membrane was investigated by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle. The results revealed that the cholesterol tethered PEG chain could self-segregate to the surface. The osteoblast cell line (MC3T3) test indicated that the cholesterol-containing oligomers had no toxicity to the osteoblast cells and could improve the cytocompatibility. The molecular weight of the PEG 'spacer' was found to be an important character for the cytocompatibility. The Chol-EG_n-LA_m with 30 ethylene glycol units reduced the osteoblast adhesion and proliferation, whereas Chol-EG_n-LA_m with 15 and 5 ethylene glycol units promoted osteoblast attachment and growth greatly. The self-segregation of the Chol-EG_n-LA_m in PLA provided as an easy method to present the hydrophobic bioactive ligand in PLA surface.Surface modification of PL A with biofunctional microsphere—The amino acid and RGD tethered PEO-PPO-PEO was prepared via methyl sulfonyl chloride method, which is verified by 'H-NMR, Fourier transform infrared(FTIR) and ultra violet (UV) spectra . The PLA microsphere was prepared by oil in water method using ligand tethered PEO-PPO-PEO as surfactant. The scanning electronic microscopy (SEM) and confocal laser scanning microscopy (CLSM) showed that the microsphere had a narrow size distribution (2-5 um). The functional microsphere was dispersed on the surface of PLA by spin-coating method. The PLA surface with biofunctional domain in micro-scale was then constructed via simply heating method. The osteoblast cell culture on the modified PLA surface showed that the cell preferred to adhere on the biofuntional microsphere. The alkaline amino acid and RGD improved the cytocompatibility more significantly than aspartic acid. The high density of microsphere on the PLA surface was benefit to improve the cytocompatibility.The micrometer-sized microsphere with different surface charge was prepared by oil in water method using PEO-PPO-PEO, cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfonate (SDS) as surfactants respectively. The PLA surface with discrete micro-domain in different charge was then constructed via similar spin-coating and heating method. A significant higher chondrocyte attachment and proliferation was found in the surface modified with the microsphere with positive charge. However, too high density positive charge prevented cell from adhering and proliferating. The optimum charge density to promote the cytocompatibility of PLA was found.Surface tailor of PLA via electrostatic self-assemble technique— Cytophilic and cytophobic surfaces of PLA were prepared via electrostatic self-assemble technique. Poly (L-lysine) (PLL) and sodium alginate (ALG) multilayers were constructed in the solution with different salt concentration. The osteoblasts culture result revealed that the multilayer films showed cytophilic in low salt concentration, whereas showed cytophobic in high salt concentration and in phosphate buffer solution (PBS). The cytophobic multilayer films could remain stable more than three days in PBS at 37 °C.The bioactive nanospheres were prepared by oil in water method using gelatin assurfactant. The functional nanospheres had narrow size distribution (20-30 nm), which was verified by AFM and size distribution test. The electrostatic assemble of the functional nanospheres onto cytophobic multilayers was explored to develop discrete ligand domain in nano-scale. The AFM results revealed that the density of the nanosphere increased with the increase of adsorption time. The chondrocyte adhesion and proliferation showed that the cytocompatibility of the modified multilayer films was increased with the increase of the density of the nanoshpere.