Zhongcheng Zhou

Bone-like apatite formation on HA/316L stainless steel composite surface in simulated body fluid

Abstract HA/316L stainless steel(316L SS) biocomposites were prepared by hot-pressing technique. The formation of bone-like apatite on the biocomposite surfaces in simulated body fluid(SBF) was analyzed by digital pH meter, plasma emission spectrometer, scanning electron microscope(SEM) and energy dispersive X-ray energy spectrometer(EDX). The results indicate that the pH value in SBF varies slightly during the immersion. It is a dynamic process of dissolution-precipitation for the formation of apatite on the surface. With prolonging immersion time, Ca and P ion concentrations increase gradually, and then approach equilibrium. The bone-like apatite layer forms on the composites surface, which possesses benign bioactivity and favorable biocompatibility and achieves osseointegration, and can provide firm fixation between HA60/316L SS composite implants and human body bone.

Preparation and bioactivity of sol-gel macroporous bioactive glass

Abstract Bioactive glass is well known for its ability of bone regeneration, and sol-gel bioactive glass has many advantages compared with melt-derived bioactive glass. 3-D scaffold prepared by the sol-gel method is a promising substrate material for bone tissue engineering and large-scale bone repair. Porous sol-gel glass in the CaO-SiO 2 -P 2 O 5 system with macropores larger than 100 μm was prepared by the addition of stearic acid as a pore former. The diameter of the pore created by the pore former varied from 100 to 300 μm. The formation of a hydroxyapatite layer on the glass was analyzed by studying the surface of the porous glass by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and Raman spectra after they had been immersed in simulated body fluid (SBF) for some time, and the porous glass shows good bioactivity.

Non-linear Viscoelastic Rheological Properties of PCC/PEG Suspensions

The shear thinning and shear thickening rheological properties of PCC/PEG suspension were investigated with the increase of oscillatory amplitude stress at different constant frequencies. The results show that the complex viscosity was initially independent of stress amplitude and obvious shear thinning occurred, then dramatic shear thickening took place after reaching the minimum viscosity. Typically, in a constant frequency of 5 rad/s, the elastic modulus, viscous modulus, and tanδ (δ is the out-of-phase angle) vs. the stress amplitude was investigated. It is found that the elastic modulus initially appeared to be independent of stress amplitude and then exhibited a rapid decrease, but the viscous modulus was independent of amplitude stress at lower amplitude stress. After reaching the minimum value the viscous modulus showed a rapid increase. On the other hand, tanδ increased from 0.6 to 92, which indicates that the transition from elastic to viscous had taken place and tanδ showed a steep increase when shear thickening occurred. Lissajous plots are shown for the dissipated energy vs. different maximum stress amplitude in the shear thinning and shear thickening regions. The relationship of dissipated energy vs. maximum stress amplitude was determined, which follows a power law. In the shear thinning region the exponent was 1.91, but it steeply increases to 3.97 in the shear thickening region.

Preparation of poly-L-lactide/bioactive glass composite and evaluation of cytotoxicity in vitro

Abstract Bioactive and bioresorbable composite materials were fabricated from poly-L-lactide and bioactive glass (average particle size 6.8 μm) by a solvent evaporation technique. Cellular cultivation in vitro and MTT assay were conducted for evaluating the influence on morphology, growth and proliferation of cultured fibroblasts. The results of cytotoxicity testing show that cells cultured in extracts of PLLA/BG and on the surface of composites demonstrate normal growth and proliferation. The bioactive glass in PLLA composite facilitates both adhesion and proliferation of rat fibroblasts on PLLA/bioactive glass composite film.

The Preparation and Properties of Bioactive Composites Based on Modification Bioactive Glass and Poly(Lactide-Co-Glycolide)

PLGA/bioactive glass composites were prepared as promising bone-repairing materials. The bioactive glass was fabricated by Sol-gel method. Surface Modification was done to improve the phase compatibility between polymer and the inorganic phase. PLGA/bioactive glass composites were successfully prepared via solution dispersion method. Composites films with different content of bioactive glass were obtained. The mechanical properties of composites were characterized by the three-point-bending test and composites films were investigated by in vitro bioactive test. These results indicate that the fractions of bioactive glass in composites produce no significant influence on mechanical properties. Compared to pure PLGA film the PLGA/bioactive glass composites demonstrate greater capability to induce the formation of apatite particles on the film surface.

Synthesis of Poly-L-Lactide for Scaffold Materials by Melt-Solid Polycondensation

Poly-L-lactide (PLLA) with low viscosity average molecular mass for scaffold materials was synthesized by melt-solid condensation polymerization and characterized by IR, XRD, and 1H-NMR. The influences of catalyst (LaCl3/C7H8SO3) concentration, polymerization temperature and polymerization time on the viscosity average molecular mass of poly-L-lactide acid (PLLA) were investigated. Poly-L-lactide with a viscosity average relative molecular mass of about 7.2 × 104 was obtained when melt-solid polycondensation was conducted with first preheating at 110°C for 4 h and solid polycondensation at 150°C for 20 h; the catalyst concentration was 0.4 wt. %. PLLA was made into porous materials by using sodium hydrogen carbonate particulates as the porogen to foam. Scanning electron microscope observation indicates that the sample is highly porous and well distributed with good interconnections between pores and the pore size of porous materials in the range of 300–500 μm and it can be used as scaffold for bone tissue engineering.

Effect of preparation routes on activity of Ag-MnOx/C as electrocatalysts for oxygen reduction reaction in alkaline media

Abstract The effect of preparation routes on the physical characteristics and activity of the Ag-MnOx/C composites toward the oxygen reduction reaction (ORR) in alkaline media were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy-dispersion spectroscopy (EDS) as well as scanning electron microscopy (SEM) and electrochemical techniques. The results show that more Ag and Mn species present on the surface of the Ag-MnOx/C composite prepared by two-step route (Ag-MnOx/C-2) compared to the one prepared by one-step route (Ag-MnOx/C-1), which contributes to its superior activity toward the ORR. The higher electron transfer number involved in the ORR can be observed on the Ag-MnOx/C-2 composite and its specific mass kinetic current at −0.6 V (vs Hg/HgO) is 46 mA/μg, which is 23 times that on the Ag/C. The peak power density of zinc–air battery with the Ag-MnOx/C-2 air electrode reaches up to 117 mW/cm2.

Influence of Non-isothermal Melt Crystallization on the Thermal Behavior and Morphology of Poly-L-lactide

Abstract The influence of non-isothermal melt crystallization on thermal behavior and morphology of poly-L-lactide (PLLA) was investigated by differential scanning calorimetry (DSC), polarizing micrograph (POM), and scanning electron microscopy (SEM). Crystallization performed at lower cooling rate (2 °C·min−1) was accompanied by a change of the kinetics around 118 °C. The glass transition temperature of PLLA decreased with the increase in cooling rate. The crystallinity at the end of crystallization and the size of PLLA spherulites increased with decrease in cooling rate, and PLLA became almost amorphous when cooled at a rapid rate of 10 °C·min−1. PLLA biodegradable material with a spherulite structure was obtained by using a compression mould and controlling the cooling rates, and spherulites developed rapidly at lower cooling rates. The fracture surfaces of PLLA at low cooling rates were more compact and smoother, but more brittle, than those at high cooling rates.

Viscoelastic Behavior and Ability of Dissipating Energy of SiO2 Dispersions under Stress Shear

Abstract The viscoelastic behavior and the ability of dissipating energy of fumed silica dispersions in ethylene glycol, propylene glycol, and butylene glycol have been studied under oscillation stress shear. The systems show linear viscoelastic, shear thinning, and shear thickening behaviors as the shear stress (σ) increases. In linear viscoelastic region, the storage modulus (G′) and loss modulus (G″) remain unchanged; in shear thinning region, G′ decreases and the sequence of the decreasing degree of G′ is EG/SiO2>PG/SiO2> BG/SiO2; however, G″ remains unchanged with σ increasing; in shear thickening region, both G′ and G″ increase as σ increases. The magnitude of G″ is larger than that of G′ over the studied range of stress, indicating that the dispersions mainly possess viscous property, and the energy dissipated is larger than the energy stored. The dissipated energies (Ed) of EG/SiO2, PG/SiO2, and BG/SiO2 dispersions increase with the maximum strain (γ0) increasing in a second power relation under low shear stress; however, in the shear thickening region, the Ed of EG/SiO2, PG/SiO2, and BG/SiO2 dispersions show an exponential increase with γ0 increasing by the exponents of n=2.79, 4.93, and 4.88, respectively.

Fabrication of Degradable Bone-Like Substitutes Based on Poly-L-lactide and β-tricalcium Phosphate

Composite bone-like substitutes composed of poly-L-lactide (PLLA) and β-tricalcium phosphate (β-TCP) (average particle size: 4.43 μm) were fabricated and the properties were investigated. β-TCP was prepared by wet chemical precipitation, followed by calcining at 800°C. Composite films were obtained by completely mixing dissolved PLLA with granules of β-TCP; the agglomerated β-TCP powder granules were distributed homogeneously in the PLLA matrix. PLLA/β-TCP composite materials were obtained by cold and hot pressing the composite film at a pressure of 130 MPa and temperature of 185°C–195°C. With increase of the amount of β-TCP powder, the bending strength of the composites decreased while the bending modulus increased. The fracture mechanism of the composites was significantly influenced by the content of β-TCP powder, from ductile fracture to brittle fracture as the β-TCP powder content increased.