Kangde Yao

Electrospinning of chitosan solutions in acetic acid with poly(ethylene oxide)

Electrospinning of chitosan solutions with poly(ethylene oxide) (PEO) in an aqueous solution of 2 wt% acetic acid was studied. The properties of the chitosan/PEO solutions, including conductivity, surface tension and viscosity, were measured. Morphology of the electrospun chitosan/PEO was observed by using scanning electron micrographs. Results showed that the ultrafine fibers could be generated after addition of PEO in 2:1 or 1:1 mass ratios of chitosan to PEO from 4-6 wt% chitosan/PEO solutions at 15 kV voltage, 20 cm capillary-collector distance and flow rate 0.1 ml/h. During electrospinning of the chitosan/PEO solutions, ultrafine fibers with diameters from 80 nm to 180 nm were obtained, while microfibers with visually thicker diameters could be formed as well. Results of X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and differential scanning calorimeter exhibited the larger electrospun microfibers were almost entirely made from PEO, while the electrospun ultrafine fibers mainly contained chitosan.

Degradation of electrospun PLGA-chitosan/PVA membranes and their cytocompatibility in vitro.

Nanofibrious composite poly(lactide-co-glycolide) (PLGA) and chitosan/poly(vinyl alcohol) (PVA) membranes were prepared by simultaneously electrospinning PLGA and chitosan/PVA from two different syringes. The in vitro degradation of PLGA and cross-linked composite membranes was examined for up to 10 weeks in phosphate-buffered saline (PBS, pH 7.4) at 37°C. The pH of PBS, the weight average molecular weight of PLGA, fiber morphology and mechanical properties, including tensile strength, Youngs modulus and elongation-at-break, were measured as a function of degradation time. The fibrous composite membranes were further investigated as a promising scaffold for human embryo skin fibroblasts (hESFs) culture. The cell adhesion and morphology of hESFs seeded on each electrospun membrane was observed using scanning electron microscope and inverted phase contrast microscopy after Wright–Giemsa staining. The introduction of chitosan/PVA component changed the hydrophilic/hydrophobic balance and, thus, influenced degradation behavior and mechanical properties of the composite membranes during degradation. The cells could not only favorably attach and grow well on the composite membranes, but were also able to migrate and infiltrate the membranes. Therefore, the results suggest that the composite membranes can positively mimic the structure of natural extracellular matrices and have the potential for application as three-dimensional tissue-engineering scaffolds.

Comparative observation of accelerated degradation of poly(L-lactic acid) fibres in phosphate buffered saline and a dilute alkaline solution

Abstract Accelerated degradation of poly( l - lactic acid) (PLLA) fibres was carried out in phosphate buffered saline (PBS) (pH 7.4) and a dilute NaOH solution (pH 11.0) at 80xa0°C for up to 7–8 days. Characterization of the viscosity-average molecular weight, the mass loss, the thermal behaviours, the morphology and the tensile properties of the PLLA fibres was performed. The results suggested that the PLLA fibres degraded in PBS followed a typical bulk degradation mechanism, but the PLLA fibres degraded in the dilute NaOH solution showed both bulk degradation and surface erosion. The melting temperature of the fibres measured by differential scanning calorimetry decreased notably in both media, while the crystallinity increased. Scanning electron microscopy showed many microcracks on the fibre surfaces across the fibre axis after degradation. Apparently because of these morphological defects and the sharp drop of the molecular weight, the fibres lost their tensile strengths almost completely after 5 days of accelerated degradation. By that time, the mass of the fibres had begun to decrease. The results generated in the accelerated degradation of fibres in PBS as well as in dilute NaOH at 80xa0°C could have useful implications for the in vitro degradation of PLLA fibres at 37xa0°C.

Surface degradation of poly(L-lactic acid) fibres in a concentrated alkaline solution

Abstract Surface degradation of poly( l -lactic acid) (PLLA) fibres was studied by incubating them in a concentrated NaOH solution at 37xa0°C for several hours. Characterization of the viscosity-average molecular weight, the mass, the morphology, the thermal behaviours and the tensile properties of the PLLA fibres were investigated. After surface degradation, the viscosity-average molecular weight of PLLA did not drop but apparently showed a slight increase. The diameter and the mass of the PLLA fibres dropped significantly. The fibres lost their surface smoothness and a regular rough topology was generated after 2.5 h of degradation. Thermal studies by differential scanning calorimetry showed that the melting temperatures of the PLLA fibres increased notably but the crystallinity did not change. The tensile properties of the PLLA fibres did not show significant changes in 1 h of degradation. After 2.5 h of degradation, the values of the tensile modulus apparently increased slightly, but the ultimate strength and the maximum elongation showed substantial decreases. The 3% offset strength did not exhibit significant changes during all the degradation. Results suggested that the degradation of PLLA fibres in the concentrated alkaline solution followed a surface erosion mechanism. The effects of degradation may be advantageous in applications where cell attachment is important.

Montmorillonite clay/poly(methyl methacrylate) hybrid resin and its barrier property to the plasticizer within poly(vinyl chloride) composite

A poly(methyl methacrylate) (PMMA)-clay hybrid resin was prepared via bulk polymerization methyl methacrylate monomer in the presence of montmorillonite intercalated with an ammonium salt of dctadecylamine. The products were characterized by infrared spectroscopy, X-ray diffraction, pyrolysis gas chromatography, and transmission electron microscopy. Results confirm that the resin is intercalated with PMMA molecules. The layer spacing of montmorillonite are enlarged, whereas the silicate layers are homogeneously dispersed individually. When the PMMA-clay hybrid was blended with plasticized poly(vinyl chloride), the resulting composite exhibited excellent barrier property in preventing the plastizers migration from the inner matrix to the surface of the product. This is presumably caused by barrier property of the silicate layers dispersed in the composite.

Study of phase behavior on chitosan/viscose rayon blend film

A blend of chitosan and viscose rayon was investigated. A film was made from regenerating the blend of chitosan and viscose rayon. The film was characterized by various techniques, including Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and transmission electron microscopy (TEM). The phase behavior of the blend is influenced by its composition with or without carboxymeth-ylated chitosan (CM-Cs). Characterization of the chitosan/viscose rayon (Cs/VR) blend by DSC and DMA suggests partial compatibility of chitosan with VR and lack of compatibility in the remaining cases. Results of the TEM show that the addition of CM-Cs into the blend can improve the compatibility of Cs with VR.

β-TCP/MCPM-based premixed calcium phosphate cements

Novel premixed calcium phosphate cements (CPCs) were prepared by combining cement liquids comprised of glycerol or polyethylene glycol with CPC powders that consisted of beta-tricalcium phosphate (beta-TCP) and monocalcium phosphate monohydrate (MCPM). Changing the powder to liquid mass ratio enabled the setting time to be regulated, and improved the compressive strength of the CPCs. Although some ratios of the new premixed CPCs had long setting times, these ranged from 12.4 to 27.8 min which is much shorter than the hour or more reported previously for a premixed CPC. The premixed CPCs had tolerable washout resistance before final setting, and the cements had strengths matching that of cancellous bone (5-10 MPa); their maximum compressive strength was up to 12 MPa. The inflammatory response around the premixed CPCs implanted in the subcutaneous tissue in rabbits was more prominent than that of apatite cement. These differences might be due to the much faster resorption rate of the premixed CPCs.

A study on mechano‐electro‐chemical behavior of chitosan/poly(propylene glycol) composite fibers

Chitosan (CS) and poly(ethylene glycol) (PEG) composite fibers were prepared via solution spinning. The fibers were then crosslinked with epichlorohydrin (ECH) and glutaraldehyde (GA). Data indicated that the swelling behavior of CS-PEG fibers exhibited pH sensitivity, and crosslinking could change the mechanical properties of fibers. Moreover, the mechano-electro-chemical (MEC) performance showed that the bending direction of fiber specimen would invert at a critical concentration of both of the crosslinking agents. i.e., in a 0.1% HCl aqueous solution under a dc electric field, as the ECH concentration was more than 9.0 × 10−3M or GA concentration was more than 5.64 × 10−4M, the CS-PEG fibers bent to the cathode, while they bent to the anode if ECH or GA concentration was less than the above values respectively. The mechanisms involve variation in the fixed charge density on the macromolecular network as well as difference in the mechanical properties of the fibers.

Rat osteoblast functions on the o-carboxymethyl chitosan-modified poly(D,L-lactic acid) surface.

In this study, the functions of rat osteoblasts on o-carboxymethyl chitosan-modified poly(D,L-lactic acid) (PDLLA) films were investigated in vitro. The surface characterization was measured by contact angle and electron spectroscopy for chemical analysis (ESCA). Cell adhesion and proliferation were used to assess cell behavior on the modified surface and control. The MTT assay was used to determined cell viability and alkaline phosphatase (ALP) activity was performed to evaluate differentiated cell function. Compared to the control films, cell adhesion of osteoblasts on o-carboxymethyl chitosan-modified PDLLA films was significantly higher (p < 0.05) after 6 and 8 h culture, and osteoblast proliferation was also significantly hlgher (p < 0.01) between 4 and 7 days. The MTT assay suggested cell viability of osteoblasts cultured on o-carboxymethyl chitosan modified PDLLA films was significantly greater (p < 0.05) than that seeded on control one, and the ALP activity of cells cultured on modified PDLLA films was significantly higher (p < 0.01) than that found on control. These results give the first evidence that o-carboxymethyl chitosan could be used to modify PDLLA surface for improving biocompatibility.

Kinetics analysis of the curing reaction of fast cure epoxy prepregs

In this article, the curing kinetics of two fast cure flip-chip epoxy encapsulants under both isothermal and nonisothermal conditions are investigated by differential scanning calorimetry. The method allows determination of the most suitable kinetic model and corresponding parameters. The kinetic analysis suggests that the two-parameter autocatalytic model is more appropriate to describe the kinetics of the curing reaction. There are certain differences between the kinetic data from isothermal and that from nonisothermal measurements. The apparent activation energy Ea and pre-exponential factor A of E-AB1 determined from nonisothermal experiments were higher than the isothermal values, whereas the Ea and A of E-RV2 determined from both methods are relatively close.