Shuying Gu

Bone marrow stromal cells cultured on poly (lactide-co-glycolide)/nano-hydroxyapatite composites with chemical immobilization of Arg-Gly-Asp peptide and preliminary bone regeneration of mandibular defect thereof

Polyethyleneimine (PEI) was used to create active groups on the poly (lactide-co-glycolide)/nano-hydroxyapatite (PLGA/NHA) surface and Arg-Gly-Asp (RGD) was grafted on the active groups and novel PLGA/NHA 2-D membranes and 3D scaffolds modified with RGD were obtained. X-ray photoelectron spectrum (XPS) results show that sulfur displays only on the modified surface. The RGD-modified PLGA/NHA materials also have much lower static water contact angle and much higher water-absorption ability, which shows that after chemical treatment, the modified materials show better hydrophilic properties. Atomic force microscope (AFM) shows that after surface modification, the surface morphology of PLGA is greatly changed. All these results indicate that RGD peptide has successfully grafted on the surface of PLGA. Rabbit bone marrow stromal cells (MSCs) were seeded in the 2D membranes and 3D scaffolds materials. The influences of the RGD on the cell attachment, growth and differentiation, and proliferation on the different materials were studied. The modified scaffolds were implanted into rabbits to observe preliminary application in regeneration of mandibular defect. The PLGA/NHA-RGD presents better results in bone regeneration in rabbit mandibular defect.

Solvent-free ionic molybdenum disulphide (MoS2) nanofluids

Solvent-free nanofluids are synthesized by functionalizing nanoscale MoS2 from hydrothermal synthesis with a charged corona and an ionic oligomeric canopy. The nanofluids are homogeneous amber-like fluids with Newtonian flow behavior. They are potential candidates for the lubrication of micro/nanoelectromechanical systems (MEMS/NEMS).

Improved shape memory performance of star-shaped POSS-polylactide based polyurethanes (POSS-PLAUs)

Star-shaped polyhedral oligomeric silsesquioxane multi-arm polylactides (POSS-PLA) with various arm lengths were synthesized by ring opening polymerization of D,L-lactide. Then, the star-shaped POSS-PLA based polyurethanes (POSS-PLAUs) were synthesized by cross-linking POSS-PLAs with various PLA arm lengths and polytetramethylene ether (PTMEG) with hexamethylene diisocyanate (HDI). Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) were utilized to characterize the structures of the materials. Differential scanning calorimetry (DSC) experiments were carried out to investigate the glass transition temperature (Tg) of POSS-PLAUs and crystallinity of PTMEG. Dynamic mechanical analysis (DMA) and stress relaxation experiments were used to study the dynamic mechanical properties and stress relaxation behaviors of POSS-PLAUs. Cyclic thermal mechanical and physical shape recovery tests were used to study the shape memory properties. The effects of POSS and PLA arm length on the mechanical, thermal properties and the shape memory behaviors were investigated. In our system, PLA arm length has no significant effect on glass transition temperature (Tg). Tg increases with the POSS content in the networks due to the obstructed movement of the polymer chains caused by caged POSS. E′ increases from POSS-PLAU110 to POSS-PLAU530 due to the decreasing of PTMEG content. Dynamic mechanical analysis reveals a similar relationship of glass transition temperature to POSS content. The stress relaxation curves show an increase in initial stress in POSS-PLAUs with longer arm length due to lower PTMEG content. The relaxation ratio is higher for the polymer with shorter PLA arm length. The quick relaxation above the triggering temperature of POSS-PLAU with shorter PLA arm length is favorable for quick shape recovery. All the POSS-PLAUs have excellent shape memory properties with high shape fixity ratios above 99%, shape recovery ratios around 84% for the first cycle and above 89% for the second cycle. POSS-PLAUs with the shorter arm length show faster recovery speed due to the higher content of POSS cores.

Polylactide-based polyurethane shape memory nanocomposites (Fe3O4/PLAUs) with fast magnetic responsiveness

Polylactide-based polyurethane shape memory nanocomposites (Fe3O4/PLAUs) with fast magnetic responsiveness are presented. For the purpose of fast response and homogeneous dispersion of magnetic nanoparticles, oleic acid was used to improve the dispersibility of Fe3O4 nanoparticles in a polymer matrix. A homogeneous distribution of Fe3O4 nanoparticles in the polymer matrix was obtained for nanocomposites with low Fe3O4 loading content. A small agglomeration was observed for nanocomposites with 6 wt% and 9 wt% loading content, leading to a small decline in the mechanical properties. PLAU and its nanocomposites have glass transition around 52 °C, which can be used as the triggering temperature. PLAU and its nanocomposites have shape fixity ratios above 99%, shape recovery ratios above 82% for the first cycle and shape recovery ratios above 91% for the second cycle. PLAU and its nanocomposites also exhibit a fast water bath or magnetic responsiveness. The magnetic recovery time decreases with an increase in the loading content of Fe3O4 nanoparticles due to an improvement in heating performance for increased weight percentage of fillers. The nanocomposites have fast responses in an alternating magnetic field and have potential application in biomedical areas such as intravascular stent.

Biodegradable Shape Memory Polyurethanes with Controllable Trigger Temperature

A series of random copolymers (PCLAs) were synthesized by ring-opening polymerization of D,L-lactide (LA) and ε-caprolactone (CL) with different molar ratios. PCLA based polyurethanes (PCLAUs) were obtained by chain-extending of PCLA and polytetramethylene ether (PTMEG) with hexamethylene diisocyanate (HDI). All the PCLAUs exhibit good shape memory properties with high shape fixity ratios above 98% and shape recovery ratios above 82% in the first cycle and 91% in the second cycle. PCLAUs with less CL content show faster recovery speed and PCLAUs with more CL content show higher shape recovery ratio. The trigger temperature can be tuned or controlled around body temperature by adjusting the molar ratio of LA to CL. The PCLAUs have potential applications in implant biomedical devices, especially for minimally invasive deployable devices.

Effects of heat treatment on the thermal and mechanical properties of ramie fabric-reinforced poly(lactic acid) biocomposites

Laminated biocomposites based on ramie fabric and poly(lactic acid) were prepared through hot compression molding followed by direct cooling (without heat treatment) or melt crystallization (with heat treatment). The effects of heat treatment and ramie fabric reinforcement on the thermal and mechanical properties of poly(lactic acid) composites were studied. X-ray diffraction and differential scanning calorimetry measurements confirmed that the heat treatment was able to promote the formation of crystals and enhance the crystallinity of poly(lactic acid), and the addition of ramie fabric also accelerated the crystallization rate of poly(lactic acid). Hence, heat treatment and ramie fabric reinforcement both can improve the thermal stability of poly(lactic acid) biocomposites remarkably. The heat deflection temperature of poly(lactic acid)/24 wt% ramie fabric biocomposite with heat treatment was up to 149.3℃, with a highest increase of 90.7℃. The mechanical properties of the ramie fabric-reinforced poly(lactic acid) biocomposites were also improved after heat treatment.

Preparation and properties of ramie fabric-reinforced thermoset poly lactic acid composites

Ramie fabric-reinforced thermoset poly lactic acid composites were produced from ramie fabrics and methacrylated four-armed star-shaped poly lactic acid resin by hot press molding. The resin was brushed uniformly on the surface of ramie fabrics. The properties of the composites were investigated by mechanics performance test, water absorption test, dynamic mechanical analysis, thermogravimetric analysis, and scanning electron microscopy. The result shows that ramie content should be properly controlled at as much as 48%. The composite with 8% alkali treatment obtained higher tensile strength and flexural strength, as well as decreased impact strength caused by surface treatment. The composite with treated ramie fabrics had slightly better water resistance and thermal stability than those without surface treatment because of enhanced interfacial adhesion between fabrics and matrix. The DMA results and morphologies of the composites confirmed the improvement of ramie–matrix interface bonding.

Fabrication and Characterization of Electrospun Poly(L-Lactic Acid)and Poly(L-Lactide-Co-Glycolide) Mats as Wound Dressing

Electrospun poly (L-lactic acid) (PLLA) and poly (L-lactide -co -glycolide) (PLGA) mats were fabricated as wound dressings. The in vitro degradation behavior was studied in phosphate buffer solution (PBS, pH 7.4) at 37degC for 6 days. Structural and morphological changes during degradation were investigated with gel permeation chromatography (GPC) and scanning electron microscopy (SEM). Both of the electrospun biopolymer mats showed stable degradation rate without losing the fibrous structure. Water adsorption ability, water retention ability and water vapor permeability were monitored comparing with PLGA casting film. The results indicates that the electrospun PLLA and PLGA mats are suitable for wound dressing and PLGA mat is more preferable.