Key Engineering Materials Vols. 342-343

Abstract: To improve the conventional and commercially-available medical adhesives such as cyanoacrylate, aldehyde-based, and fibrin glue, new bioadhesive has been prepared using medical and food additives as starting materials. Aldehyde groups could be easily introduced in dextran in the presence of sodium periodate in aqueous media, and the extent of the introduction could also be controlled. In vitro degradation speed of the hydrogel prepared by mixing of aldehyded dextran with ε-poly(L-lysine) at 37oC significantly varied by acetic anhydride concentration added to ε-poly(L-lysine) from < 5h to > 5 weeks. Bonding strength of the glue was 4 times higher than that of commercial fibrin glue and almost no cytotoxicity was observed, suggesting the development of novel self-degradable bioadhesive.

Abstract: Superporous hydrogels (SPHs) with interconnected pores of several hundreds micrometers were prepared using radical polymerization of acrylic acid (AA) and acrylamide (AAm) in the presence of N,N’-methylenebisacrylamide (BIS). A gas blowing method using bicarbonate as a foaming agent was applied to introduce the porous structure under different pH conditions (pH 2~7). The pore structures of the prepared SPHs were examined by a scanning electron microscope. The SPHs obtained at pHs of 4.5 and 4.75 were observed to have a interconnected pore structure with homogeneous distribution and swell to an equilibrium state within several minutes. The O2 plasma reactor has been used for surface modification of SPHs. The plasma-treated SPHs showed much faster swelling behavior due to the improvement of surface hydrophilicity. The swelling ratio of SPHs was also enhanced by using a wetting agent, such as triacetin and glycerol, during a washing procedure.

Abstract: In order to elucidate the relationship between the structure and biological activity such as anti-HIV and blood anticoagulant activity, sulfonated polysaccharides and amino-polysaccharides having pentofuranosidic structures were synthesized. These sulfonated polysaccharides had potent anti-HIV activity in spite of low molecular weights, and which was dependent on the degree of sulfonation. For the blood anticoagulant activity, the conformation of polymer backbone and sulfamide group plays an important role on the interactions with the blood anticoagulant factor.

Abstract: Linear and Star-shaped PCL-b-PEG copolymers were synthesized through a two step process, including the first step to synthesize the star-shaped PCL through ring-opening polymerization of Γ-caprolactone initiated from multi-functional alcohol under the existence of tin(II) ethylhexanoate [Sn(Oct)2] catalyst, and the following step to couple the obtained star-shaped PCL with PEG segments using bi-functional linker. The structure of the polymers was confirmed by IR, NMR, GPC, et al. The aggregation behaviors of the star-shape copolymers were compared with that of the linear block copolymer with corresponding molecular weight of each arm, and the influences of structure factors were discussed.

Abstract: A new type of thermotropic main-chain liquid crystalline polyurethanes containing biphenyl units was synthesized by polyaddition reaction of diisocyanates such as 2,6-tolylene diisocyanate, 2,5-tolylene diisocyanate, 2,4-tolylene diisocyanate, and 1,4-phenylene diisocyanate, with 4,4′-Bis(8-hydroxyoctoxy)biphenyl (BP8). The structure of the monomer and the corresponding polymers were confirmed using FT-IR and 1H-NMR spectroscopic methods. BP8 exhibited a smectic type mesophase, however, nematic phases were found for all synthesized liquid crystalline polyurethanes except for 1,4-phenylene diisocyanate/BP8 based polyurethane. For example, polyurethane 2,5-TDI/BP8 exhibited monotropic liquid crystallinity in the temperature ranging from 172 to 160 °C on the cooling stage. Properties of these polyurethanes were studied by differential scanning calorimetry (DSC), and optical polarizing microscopy. The FT-IR study indicated that the hydrogen bonding among urethane linkages attributed to the mesomorphism.

Abstract: To enhance the stability of liposomes in systemic circulation, a number of liposomes modified with hydrophilic polymer such as poly(ethylene oxide) have been developed. In this study, the comb-type copolymer was prepared as a surface modifier of liposome and the polymer was anchored onto the lipid bi-layer via hydrophobic interaction between aliphatic chain of phospholipids and hydrophobic chain of the polymer. The comb-type copolymer was synthesized by radical polymerization of octadecyl acrylate (ODA), hydroxy-poly-(oxyethylene) methacrylate (HPOEM) and 2-Hydroxyethyl methacrylate (HEMA). The structure of the comb-type copolymer was confirmed by 1H-NMR analysis. The stability of the comb-type copolymer-incorporated liposomes (CCIL) in serum was investigated by measuring the amount of protein adsorbed onto liposomes. The CCIL showed a much lower amount of adsorbed protein than the other liposomes. Those results indicated that the stability of CCIL in serum was higher than those of the other liposomes. Thus, the comb-type copolymer composed of ODA-HPOEM-HEMA can be a promising surface modifier for enhancement of the stability of liposomes in systemic circulation.

Abstract: In this study, poly(ε-caprolactone) (PCL)/multiwalled carbon nanotube (MWCNT) composites with different contents of MWCNTs were successfully prepared by solution compounding, a method which could make them good competitors for commodity materials such as general purpose plastics, while allowing them to keep their complete biodegradability. For the homogeneous dispersion of the MWCNTs in the polymer matrix, oxygen-containing groups were introduced on their surface. The mechanical properties of the PCL/MWCNT composites were effectively increased due to the incorporation of the MWCNTs. The composites were characterized using scanning electron microscopy, in order to obtain information on the dispersion of the MWCNTs in the polymeric matrix. In the case of the composites containing 2.0 wt% of MWCNTs in their matrix, the strength and modulus of the composites were increased by 18.4% and 178.4%, respectively. In addition, the dispersion of the MWCNTs in the PCL matrix resulted in a substantial decrease in the electrical resistivity of the composites as the MWCNT loading was increased from 0 to 2.0 wt%.

Abstract: We prepared composite films consisting of two biocompatible materials, bacterial cellulose and silk fibroin. Aqueous silk fibroin solution and bacterial cellulose excreted by Acetobacter xylinum were used to fabricate the composite films. It was verified by field emission scanning electron microscopy and X-ray diffraction that the two components were finely blended and that the silk fibroin was crystallized during the composition of the films. The silk fibroin penetrated well between the individual fibrils of the bacterial cellulose, while the water molecules inside the pellicular bacterial cellulose were evaporating. The composite films did not dissolve in water due to the crystallization of the silk fibroin in the composite films. We also observed the change in the mechanical properties of the composite films according to the water content. The composite films became more flexible and tougher when they were dipped in water, whereas they were very brittle in the dehydrated state.

Abstract: Though hyaluronic acid (HA)-based hydrogel has drawn great attention in biomedical society, it’s long molecular weights sometimes have been problematic due to its difficulty in handling. After reduction of its high molecular weight into smaller sizes with various concentrations of hydrogen chloride solutions, its chemical and biological properties have been examined by changes in viscosity, FTIR spectroscopy and gel permeation chromatography as well as cellular interactions. While FTIR analysis indicated maintenance of its original chemical structures, its viscosity has been remarkably reduced and its extent was dependent upon the employment of acid concentrations. After controlling its molecular weight to approximately 100 kDa and coupling of aminopropymethacrylate to the treated HA, we evaluated in vitro cellular interactions and cell proliferations of the HA-poly(ethylene oxide) (PEO) hydrogel.

Abstract: Characterization of an hyaluronic acid (HA)-poly(ethylene oxide) (PEO) hydrogel was performed by changing the number of side arms in a PEO molecule. Verification of grafting chemistry and mechanical strength, as well as swelling behaviors and surface morphologies of the HA-PEO hydrogels were analyzed by employing different x-linking molecular weights (MW) of PEO ranging from 1.7 to 5.0 kDa at a fixed low MW HA in the hydrogel network. Methacrylation to the HA successfully obtained via Michael type reaction between the methacrylate arm groups in HA and the thiol end groups in PEO was observed by XPS. Hydrogel formation was markedly dependent upon the numbers of thiol groups in the PEO molecule. Furthermore the lower MW PEO-based HA hydrogel demonstrated stronger mechanical properties but lower water absorption and the smaller pore sizes on its surface and cross section.