Papers by Author: Xiao Feng Chen

Abstract: The bioactive glasses 58S was first prepared using sol-gel technique and the 45S5 bioactive glass was prepared through melting method. The above bioactive glasses were then grounded into fine powders, and each of the glass powders and their mixtures was doped with the porogen in certain ratios respectively. The bioactive porous materials were finally produced through sintering. We investigated the microstructure, surface morphologies, bending strength and bioactivity of the porous materials via in vitro method combined with DTA, SEM and FTIR techniques. The results show that the porous material made from the 58S and 45S5 mixture possesses the best bioactivity and bio-mineralization function among all samples, thus is a very promising bioactive material for bone defects filling or bone tissue engineering scaffolds.

Abstract: The emulsion combining sol-gel method was used to prepare spherical bioactive glass in the present work. This method involves a two-stage synthesis process: the pre-hydrolysis of tetraethyl orthosilicate (TEOS) in an aqueous acidic solution using templates, and afterward the fabrication of silica spheres by pH induced rapid gelation in a W/O emulsion. Through controlling the two stages separately, the particle size and morphology of silica spheres can be adjusted. These results indicated that emulsion method could supply a good way to prepare glass microspheres.

Abstract: A kind of poly(N-isopropylacrylamide) (PNIPAM) gel was synthesized by radical polymerization of N-isopropylacrylamide monomer in the present of crosslinker N,N-Methylenebisacylamide using short reaction time. This kind of PNIPAM gel exhibits higher swelling ratio at low temperature and much faster deswelling rate than conventional gel, which could be attributed to the presence of loops, dangling chains and other incomplete structure in the gel caused by short reaction time.

Abstract: In this paper, a strain gradient model is constructed to predict the bending size dependence of the elastic property of nanofibers under three-point tests. The model prediction shows that there are two kinds of size dependency for the bending tests: one is related to the diameter of the nanofiber, which can be named as Diameter Size Dependency (D-SD), the other is related to the length of the nanofiber, which can be termed as Length Size Dependency (L-SD). Mechanical testing on PCL nanofibers was performed to verify the model for D-SD, and good agreement is found between the model prediction and the data obtained in the experiment. The model can be applied to explain the size dependency in bending test for polymeric nanofibers.

Abstract: In this paper, a higher order strain gradient model is constructed to predict this size dependence of the elastic property of nanofibers under uniaxial tensile tests. We can show that the size effects in tensile test can be explained using a new model based on the higher order strain gradient elasticity (HSGE). A series of mechanical testing were performed to verify the model, and good agreement is found between the model prediction and the data obtained in the experiment. Compared with the model prediction based on surface effect (SE), our model can better capture the size effect in tensile test.

Abstract: In this paper, a high order strain gradient (HSGE) model is constructed to predict the bending size dependence of the elastic property of nanofibers under three-point tests. The model can be applied to explain the size dependency in bending test for polymeric nanofibers.

Abstract: A micromechanical model is constructed for the elastic modulus of nano-fibrous scaffold. The nano-fibrous scaffold was obtained using electrospinning method with polymeric materials, and was supposed to be created with linear elastic strain rods that are straight in the range of rod length. Statistical theory was introduced to model the random distribution of fiber segment length and the percolation effect was also studied. Model predictions were verified using experimental data. This model can be used to study the relationship between the elastic modulus of the scaffold with respect to the fiber concentration, fiber diameter and fiber orientation.

Abstract: The aim of this study was to develop a novel injectable hydroxyapatite for bone repair materials. This study was based on the in situ setting properties of calcium phosphate cement (CPC), which properties were improved. The solid phase consisted of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA). The liquid phase was the weak acidic solution of chitosan. The CPC powder was mixed with the chitosan solution to form a paste that could conform to the bone cavity even for irregularly shaped cavities. All the by-production disappeared by neutralization reaction. The CPC paste could then set in situ to form hydroxyapatite (HA) as the final product. The chemical process of CPC hydration was studied. The process was controlled by dissolution and precipitation chemical reaction. The kinetic model of hydration reaction was established. The effects of preparing conditions, such as powder to liquid ratio and particle size, on setting time and compressive strength were investigated systematically. The optimal condition was that the liquid phase contained 3% chitosan, 5% citric acid and 15% glucose (wt%), powder to liquid ratio was 0.8 g/ml, and powders were respectively ground for 40 hours.

Abstract: In the present study, an Intelligent Multi-parameter Simulated Evaluation in vitro （IMSE system） was used to study the deposition properties of apatite formation on the surface of biphasic calcium phosphate porous ceramic (BCP) from static and dynamic r-SBF. Results showed that apatite formed on the surface of BCP from static and dynamic r-SBF differed between each other. In static r-SBF, ions were transferred by diffusion, which could not compensate the consuming of calcium ions, and mist apatite layer was formed on the surface of samples. But in the dynamic r-SBF, simulated fluid was adjusted precisely and flowed forcedly, the concentrations of ions were homogeneous; with the compensation of ions, calcium and phosphate were supersaturated, and the free energy of apatite formation was negative, bone-like apatite sheets were formed on the surface of samples.

Abstract: Papers reported that the pH value was rising slowly with the prolonging of soaking time when bioglass was studied into simulated body fluids, and it influenced the formation of apatite layer on the surface of bioglass obviously. An Intelligent Multi-parameter in vitro Simulated Evaluation （IMSE system） was used to study the bio-mineralization properties of 58S bioglass. The deposition of apatite formation on the surface of bioglass (BG) from dynamic r-SBF was studied systemically with IMSE system, which could control and stable such parameters as temperature, fluid rate, ion concentrations and pH value etc. precisely. Results showed that the rate of apatite formation was slowed down when pH value was stabled at about 7.35.