Functionalization and reduction of graphene oxide with p-phenylene diamine for electrically conductive and thermally stable polystyrene composites.

A facile and efficient approach was developed to simultaneously functionalize and reduce graphene oxide (GO) with p-phenylene diamine (PPD) by simple refluxing. This was possible by the nucleophilic substitution reaction of epoxide groups of GO with amine groups of PPD aided by NH(3) solution. As a consequence, electrical conductivity of GO-PPD increased to 2.1 × 10(2) S/m, which was nearly 9 orders of magnitude higher than that of GO. Additionally, after the incorporation of GO-PPD in polystyrene (PS), the composites exhibited a sharp transition from electrically insulating to conducting behavior with a low percolation threshold of ~0.34 vol %, which was attributed to the improved dispersion and the reduction of GO-PPD. Thermal stability of the PS/GO-PPD composite was also ~8 °C higher than that of PS.

Effects of fluid viscoelasticity on the performance of an axial blood pump model.

An aqueous Xanthan gum solution (XGS) was used as blood analog fluid to explore the influence of fluid viscoelasticity on the performance of an axial blood pump model. For comparison, a 39 wt% Newtonian aqueous glycerin solution (GS), the common fluid in blood pump tests, was also used as a working fluid. The experimental results showed that a higher head curve was obtained using XGS in the pump than using GS. The heads of the XGS that were computed using the viscoelastic turbulence model agreed well with the measured data. In contrast, the standard k-ε turbulence model failed to provide satisfactory predictions for the XGS. The computational results revealed that in most parts of the pump model flow fields, the Reynolds shear stress values and turbulent dissipation rates of the XGS were all lower than those of the GS. The hemolysis index of the pump model using the XGS was calculated to be only one-third of that using the GS.

An experimental study of Newtonian and non-Newtonian flow dynamics in an axial blood pump model.

The head curves of a 1.5:1 new axial blood pump model were measured using five working fluids at five rotational speeds. The working fluids were water, a 39wt% aqueous glycerin solution (GS), and three aqueous xanthan gum solutions (XGSs) with different concentrations. The flow velocities and shear stresses in the mechanical clearance between the casing and rotor were investigated using a laser Doppler velocimeter and hot-film sensor. At every rotational speed, the experiment in which viscous GS was used in the pump model showed a head curve lower than that obtained using water, whereas the head obtained using viscoelastic XGS was higher than that generated using water. A maximum difference of 65.8% between the heads measured in the 0.06% XGS and GS experiments was detected. The higher head produced by the XGS may have originated from the drag-reduction effect of XGS viscoelasticity. The measurements showed that a reverse washout flow at a velocity of 0.05-0.11m/s occurs in the clearance. This reverse washout flow is crucial to preventing flow stagnation and accompanying thrombus formation. The wall shear stress and the Taylor number of the rotating Couette-like flow in the clearance both indicated that it is a turbulent flow.

[Effects of traditional Chinese medicine on the differentiation of mesenchymal stem cells to osteoblasts].

OBJECTIVE: To investigate the effects of traditional Chinese medicine on the differentiation of mesenchymal stem cells (MSC) to osteoblasts. METHODS: Six male Beagle dogs weighed 10-15 kg each were divided into three groups, group A: medicine serum group, group B: non-medicine serum group and group C: bovine serum group. The serum of group A was obtained from the femoral artery of 2 Beagle dogs drinking equivalent dose of traditional Chinese medicine according to body surface area for 7 continuous days. The serum of group B was collected from the femoral artery of 2 Beagle dogs fed with equal volume of normal saline for 7 days. The serum of group C was fetal bovine serum. The tibia marrow was harvested from another 2 Beagle dogs and MSC were isolated and purified by density gradient centrifugation. MSC were cultured in DMEM solution with fetal bovine serum. After MSC were digested by trypsin, MSC were cultured in DMEM solution with the osteogeneic inducer, which contained dexamethasone, antiscorbutic and beta-glycerophosphate. Morphological and histological changes of the MSC were observed under an inverted microscope. Alizarin monosulfonate and nitric acid argentum staining was performed to observe the calcium deposition. MSC were curtured in DMED solution with medicine serum (group A), non-medicine serum (group B) and bovine serum (group C) respectively. The growth curve was detected by the methyl thiazolyl tetrazolium (MTT). The alkaline phosphatase (ALP) activities were detected to observe the differentiation of MSC. RESULTS: The original MSC were observed as fibroblast-like cell shapes. After the osteogeneic inducer was added, MSC were polygon cells with a few polyprocess. Calcium deposition appeared during 10-14 days and alizarin monosulfonate and Von Kossa staining presented positive. MTT results showed that the number of adherent cells of group A was more than that of group B and that of group C significantly after 6 days (P < 0.05). ALP detection proved that ALP activity of group A was more than that of group B and that of group C significantly after 5 days (P < 0.05). CONCLUSIONS: The traditional Chinese medicine promotes the differentiation of MSC to osteoblasts and osteogenesis.