Aixue Liu

Surface modification of bioactive glass nanoparticles and the mechanical and biological properties of poly(L-lactide) composites

Novel bioactive glass (BG) nanoparticles/poly(L-lactide) (PLLA) composites were prepared as promising bone-repairing materials. The BG nanoparticles (Si:P:Ca=29:13:58 weight ratio) of about 40nm diameter were prepared via the sol-gel method. In order to improve the phase compatibility between the polymer and the inorganic phase, PLLA (M(n)=9700Da) was linked to the surface of the BG particles by diisocyanate. The grafting ratio of PLLA was in the vicinity of 20 wt.%. The grafting modification could improve the tensile strength, tensile modulus and impact energy of the composites by increasing the phase compatibility. When the filler loading reached around 4 wt.%, the tensile strength of the composite increased from 56.7 to 69.2MPa for the pure PLLA, and the impact strength energy increased from 15.8 to 18.0 kJ m(-2). The morphology of the tensile fracture surface of the composite showed surface-grafted bioactive glass particles (g-BG) to be dispersed homogeneously in the PLLA matrix. An in vitro bioactivity test showed that, compared to pure PLLA scaffold, the BG/PLLA nanocomposite demonstrated a greater capability to induce the formation of an apatite layer on the scaffold surface. The results of marrow stromal cell culture revealed that the composites containing either BG or g-BG particles have much better biocompatibility compared to pure PLLA material.

The Surface Modification of Hydroxyapatite Nanoparticles by the Ring Opening Polymerization of γ-Benzyl-L-glutamate N-carboxyanhydride

The surface modification of hydroxyapatite (HA) nanoparticles by the ring opening polymerization (ROP) of gamma-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) was proposed to prepare the poly(gamma-benzyl-L-glutamate) (PBLG)-grafted HA nanoparticles (PBLG-g-HA) for the first time. HA nanoparticles were firstly treated by 3-aminopropylthriethoxysilane (APS) and then the terminal amino groups of the modified HA particles initiated the ROP of BLG-NCA to obtain PBLG-g-HA. The process was monitored by XPS and FT-IR. The surface grafting amounts of PBLG on HA ranging from 12.1 to 43.1% were characterized by thermal gravimetric analysis (TGA). The powder X-ray diffraction (XRD) analysis confirmed that the ROP only underwent on the surface of HA nanoparticles without changing its bulk properties. The SEM measurement showed that the PBLG-g-HA hybrid could form an interpenetrating net structure in the self-assembly process. The PBLG-g-HA hybrid could maintain higher colloid stability than the pure HA nanoparticles. The in vitro cell cultures suggested the cell adhesion ability of PBLG-g-HA was much higher than that of pure HA.

Surface Modification of Hydroxyapatite Nanoparticles with Thermal-Responsive PNIPAM by ATRP

Hydroxyapatite (HA) nanoparticles grafted by poly(N-isopropylacrylamide) (PNIPAM) brushes (PNIPAM-g-HA) have been synthesized by the surface-initiated atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAM). The surface grafting amount of PNIPAM ranges from 15.5% to 46.4%. PNIPAM-g-HA has been characterized by FT-IR spectroscopy, thermal gravimetric analysis, X-ray diffraction, and scanning electron microscopy (SEM). The UV transmittance spectra and the particle size analysis of PNIPAM-g-HA in aqueous solution demonstrates that the PNIPAM-g-HA possess reversible thermal stimuli responsive properties. An in vitro bioactivity assessment indicates that PNIPAM-g-HA can induce the mineralization of Ca(2+) and HPO(4) (2-) and possesses an excellent bioactivity. The cell culture results show that the cells adhered to the surface of PNIPAM-g-HA grow better than on HA, and the area of the cells on the surface of PNIPAM-g-HA is much greater than for HA, which proves that the PNIPAM-g-HA has a better biocompatibility than HA.

NOVEL COMPOSITES OF POLY(L-LACTIDE) AND SURFACE MODIFIED BIOACTIVE SiO2-CaO-P2O5 GEL NANOPARTICLES: MECHANICAL AND BIOLOGICAL PROPERTIES

Bioactive SiO2-CaO-P2O5 gel (BAG) nanoparticles with 40 nm in diameter were synthesized by the sol-gel route and further modified via the ring-opening polymerization of lactide on the surface of particles. Surface modified BAG (mBAG) was introduced in poly(L-lactide) (PLLA) matrix as bioactive filler. The dispersibility of mBAG in PLLA matrix was much higher than that of rough BAG particles. Tensile strength of the mBAG/PLLA composite could be increased to 61.2 MPa at 2 wt% filler content from 53.4 MPa for pure PLLA. The variation of moduli of the BAG/PLLA and mBAG/PLLA composites always showed an enhancement tendency with the increasing content of filler loading. The SEM photographs of the fracture surfaces showed that mBAG could be homogeneously dispersed in the PLLA matrix, and the corrugated deformation could absorb the rupture energy effectively during the breaking of materials. In vitro bioactivity tests showed that both BAG and mBAG particles could endow the composites with ability of the calcium sediment in SBF, but the surface modification of BAG particles could weaken this capability to some extent. Biocompatibility tests showed that both BAG and mBAG particles could facilitate the attachment and proliferation of the marrow cells on the surface of the composite.