Jin-Lin Han

Antibacterial activity and biocompatibility of a chitosan–γ-poly(glutamic acid) polyelectrolyte complex hydrogel

In this study, we prepared a polyelectrolyte complex (PEC) hydrogel comprising chitosan as the cationic polyelectrolyte and gamma-poly(glutamic acid) (gamma-PGA) as the anionic polyelectrolyte. Fourier transform infrared spectroscopy revealed that ionic complex interactions existed in the chitosan-gamma-PGA PEC hydrogels. The compressive modulus increased upon increasing the degree of complex formation in the chitosan-gamma-PGA PEC hydrogel; the water uptake decreased upon increasing the degree of complex formation. At the same degree of complex formation, the compressive modulus was larger for the chitosan-dominated PEC hydrogels; the water uptake was larger for the gamma-PGA-dominated ones. Scanning electron microscopy images revealed the existence of interconnected porous structures (pore size: 30-100mum) in all of the chitosan-gamma-PGA PEC hydrogels. The chitosan-gamma-PGA PEC hydrogels also exhibited antibacterial activity against Escherichia coli and Staphylococcus aureus. In addition, in vitro cell culturing of 3T3 fibroblasts revealed that all the chitosan-gamma-PGA PEC hydrogels were effective in promoting cell proliferation, especially the positively charged ones (chitosan-dominated). Therefore, the chitosan-gamma-PGA polyelectrolyte hydrogel appears to have potential as a new material for biomedical applications.

Graft interpenetrating polymer networks of urethane-modified bismaleimide and epoxy (I): mechanical behavior and morphology

Polyurethanes (PU) based on poly(butylene adipate) [PU(PBA)] and poly(oxypropylene) [PU(PPG)] polyols are employed as a graft agent to prepare interpenetrating polymer networks of urethane-modified bismaleimide (UBMI) and the diglycidyl ether of bisphenol A (Ep) (UBMI/Ep graft-IPNs). The UBMI is introduced and partially grafted to the epoxy by PU graft agents, and then simultaneous bulk polymerization technique is used to prepare the graft-IPNs. All the PU graft agents were characterized by infrared (IR). The tensile strength of both the UBMI/Ep graft-IPNs with PU(PBA) and PU(PPG) graft agent systems increased to a maximum value with increasing UBMI content in the system and then decreased with further increasing the UBMI content. For both kinds of PU with various molecular weight in the UBMI/Ep graft-IPNs, the Izod impact strength increased with the UBMI contents increasing. The better compatibility of PU(PBA)-based UBMI/Ep graft-IPNs led to higher impact strength. On the contrary, the fracture energy (GIC value) of the resultant UBMI/Ep graft-IPN showed that the UBMI/Ep graft-IPN with PU(PPG) graft agent had much higher GIC value than that with PU(PBA) graft agent. The morphology of this IPN with PU(PBA) graft agent exhibited a homogeneous one-phase system, while the UBMI/Ep graft-IPN with PU(PPG) graft agent showed a two-phase morphology with the UBMI particles dispersed in the epoxy matrix.

Kinetic study of acid depolymerization of chitosan and effects of low molecular weight chitosan on erythrocyte rouleaux formation.

In this study, the depolymerization of chitosan was carried out in an acetic acid aqueous solution and was followed by viscometry for molecular weight determination. It was found that the depolymerization rate increased with elevated temperatures and with high acid concentrations. Based on FTIR analysis, the chitosan was depolymerized randomly along the backbone; no other structural change was observed during the acid depolymerization process. Revealed in the TGA study, the degradation temperature and char yield of LMWCs (low molecular weight chitosan) were molecular weight dependent. The blood compatibility of LMWCs was also investigated: rouleaux formation was observed when erythrocyte contacted with LMWCs, which showed that LMWCs are able to interfere with the negatively charged cell membrane through its polycationic properties. Furthermore, as regards a kinetics investigation, the values of M(n) (number-average molecular weight) were obtained from an experimentally determined relationship. The kinetics study showed that the complex salt, formed by amine on chitosan and acetic acid, acted as catalyst. Finally, the activation energy for the hydrolysis of the glycosidic linkage on chitosan was calculated to be 40kJ/mol; the mechanism of acid depolymerization is proposed. In summary, LMWCs could be easily and numerously generated with acid depolymerization for further biological applications.

Development of chitosan/ dicarboxylic acid hydrogels as wound dressing materials

Two different dicarboxylic acids (glutamic acid and succinic acid), instead of acetic acid, were used simultaneously as solubilizing and crosslinking agents in the preparation of chitosan-based hydrogel. Sustained, homogeneous and transparent hydrogels were formed with amide linkage formations. X-ray diffraction and Fourier transformed infrared (FTIR) were used to examine the crystal structure and chemical composition of chitosan/glutamic acid (C/G) hydrogel and chitosan/ succinic acid (C/S) hydrogel, respectively. The in vitro cell cultures confirmed that the amine group was effective in promoting cell affinity. Histological examinations revealed that reepithelialization and regeneration of tissue was achieved 50% faster by dressing the wound with the C/G hydrogels. This chitosan/dicarboxylic acid hydrogel system has potential as wound dressing material.Two different dicarboxylic acids (glutamic acid and succinic acid), instead of acetic acid, were used simultaneously as solubilizing and crosslinking agents in the preparation of chitosan-based hydrogel. Sustained, homogeneous and transparent hydrogels were formed with amide linkage formations. X-ray diffraction and Fourier transformed infrared (FTIR) were used to examine the crystal structure and chemical composition of chitosan/glutamic acid (C/G) hydrogel and chitosan/ succinic acid (C/S) hydrogel, respectively. The in vitro cell cultures confirmed that the amine group was effective in promoting cell affinity. Histological examinations revealed that reepithelialization and regeneration of tissue was achieved 50% faster by dressing the wound with the C/G hydrogels. This chitosan/dicarboxylic acid hydrogel system has potential as wound dressing material.

Polyaniline nano-composites with large negative dielectric permittivity

Two polyaniline (PANI)/polymer nano-composites exhibiting huge negative dielectricpermittivity have been synthesized for the first time. These novel chemical processes open a new approach for fabrication of the negative index materials (NIMs), since most of the NIMs prepared today are obtained by a structural approach – by putting together two structured materials that exhibit separately a negative permittivity and a negative permeability. We found the negative permittivity of these nano-composites is a function of the content of the dopant (i.e., PANI) as well as of the frequency. The generation of huge negative permittivity can be rationalized by the well-dispersed PANI-DBSA nano-particles which form a pseudo-continuous conductive pathway in these nano-composites.

Chitosan Membrane with Surface-bonded Growth Factor in Guided Tissue Regeneration Applications

The potential of surface covalently bonded rhBMP-2 biodegradable chitosan membrane was examined for guided tissue regeneration (GTR) applications. A chitosan surface-bonded rhBMP-2 membrane was produced via amide bond formation between chitosan and rhBMP-2 using EDC/NHS as the catalyst. The chitosan surface-bonded rhBMP-2 membrane retained more than 70% of the initial rhBMP-2 after 4 weeks of incubation, whereas the chitosan surface-adsorbed rhBMP-2 membrane retained only 30%. The surface-bonded rhBMP-2 did not denature, but expressed sustained biological activity, such as osteoblast cell adhesion, proliferation, and differentiation. X-ray images and histology of an in vivo segmental bone defect rabbit model showed that the chitosan surface-bonded rhBMP-2 membrane induced new bone formation. The chitosan surface-bonded rhBMP-2 membrane has the potential as a bioactive material for GTR.

Tissue response to chitosan/γ-PGA polyelectrolyte complex using a rat model:

In this study, the in vivo soft tissue response of chitosan/γ-poly(glutamic acid) (γ-PGA) polyelectrolyte complex (PEC) using a rat model was assessed using chitosan as a cationic polyelectrolyte and γ-PGA as an anionic polyelectrolyte; four groups of chitosan/γ-PGA PECs were synthesized according to the molar ratio of amine groups of chitosan to the carboxylic acid groups of γ-PGA. Different soft tissue responses to chitosan/γ-PGA PEC were observed between the epithelium and the muscle. In the epithelium, the wound dressed with chitosan/γ-PGA PEC healed faster than the control, with chitosan attracting polymorphonuclear (PMN) cells and γ-PGA creating a hydrophilic environment. In the muscle, a quantitative evaluation of the tissue response revealed that different degradation phenomena were evoked by different compositions of chitosan/γ-PGA PEC. After implantation for 28 days, the chitosan/γ-PGA PEC with chitosan dominating showed extensive surface erosion and superficial fragmentation surrounded by infla...In this study, the in vivo soft tissue response of chitosan/g-poly(glutamic acid) (g-PGA) polyelectrolyte complex (PEC) using a rat model was assessed using chitosan as a cationic polyelectrolyte and g-PGA as an anionic polyelectrolyte; four groups of chitosan/g-PGA PECs were synthesized according to the molar ratio of amine groups of chitosan to the carboxylic acid groups of g-PGA. Different soft tissue responses to chitosan/g-PGA PEC were observed between the epithelium and the muscle. In the epithelium, the wound dressed with chitosan/g-PGA PEC healed faster than the control, with chitosan attracting polymorphonuclear (PMN) cells and g-PGA creating a hydrophilic environment. In the muscle, a quantitative evaluation of the tissue response revealed that different degradation phenomena were evoked by different compositions of chitosan/g-PGA PEC. After implantation for 28 days, the chitosan/g-PGA PEC with chitosan dominating showed extensive surface erosion and superficial fragmentation surrounded by inflammatory cells, while chitosan/g-PGA PECs with g-PGA dominating elicited minimal degradation. These results confirm that the degradation of PECs can be controlled by tailoring the chitosan/g-PGA PECs for different purposes. It appears that different local tissue conditions in muscle and epithelium may be involved in this difference.

Rapid fabrication of 2D and 3D photonic crystals and their inversed structures.

In this paper a new technique is proposed for the fabrication of two-dimensional (2D) and three-dimensional (3D) photonic crystals using monodisperse polystyrene microspheres as the templates. In addition, the approaches toward the creation of their corresponding inversed structures are described. The inversed structures were prepared by subjecting an introduced silica source to a sol-gel process; programmed heating was then performed to remove the template without spoiling the inversed structures. Utilizing these approaches, 2D and 3D photonic crystals and their highly ordered inversed hexagonal multilayer or monolayer structures were obtained on the substrate.

Effects of types and length of soft-segments on the physical properties and blood compatibility of polyurethanes.

Segmented polyurethane (SPU) materials based on different soft-segment component (PPG, PTMO and PBA) and various length of soft-segment (molecular weight of PBA: 500, 700 and 1000) were synthesized in this research. The soft-segment components were synthesized from polyether-polyols (PPG and PTMO) or from polyester-polyol (PBA). The physical properties and structure characterization of the synthesized SPUs were fully investigated using differential scanning calorimetry (DSC) analysis, and stress-strain measurements. Blood compatibility was evaluated with the platelet adhesion ratio (PAR) and the morphological observation for adhering platelets. Our results showed that the physical properties and blood compatibility of SPUs were closely related to its composition, which was controlled by (1) the types of the soft-segment component employed and (2) the length of soft segments. Polyether-polyol-based SPUs exhibited greater phase separations, poorer tensile strengths, and better blood compatibility, compared with polyester-polyol-based SPUs. SPUs with shorter soft-segment component exhibited greater phase mixing, higher tensile strength, but lower blood compatibility of SPUs, as compared with its counterparts with longer soft-segment component.