Chee-Youb Won

Synthesis and characterization of dextran-maleic acid based hydrogel.

A new class of hydrogel precursor, dextran-maleic acid (Dex-MA), was synthesized by the reaction of dextran with maleic anhydride in the presence of the catalyst triethylamine. The effects of temperature, time, catalyst amount, and reactant concentration on the degree of substitution (DS) by MA was studied to establish an optimum reaction condition. The new hydrogel precursor had excellent solubility in various common organic solvents. The hydrogels based on Dex-MA precursor were made by the irradiation of Dex-MA with a long wave UV lamp. The Dex-MA hydrogels showed a very high swelling ratio in water, and the magnitude of swelling depended on the pH of the medium and the DS by MA. The Dex-MA hydrogels exhibited the highest swelling ratio in neutral pH, followed by acidic (pH 3) and alkaline pH (10). The most distinctive characteristic of Dex-MA hydrogels was that a carboxylic acid group was generated by the reaction of dextran with maleic anhydride. As a result, the swelling ratio increased with an increase of the DS of the MA segment (ionizable moiety that affects swelling ratio) in the Dex-MA hydrogel.

Synthesis and characterization of biodegradable network hydrogels having both hydrophobic and hydrophilic components with controlled swelling behavior

A new class of biodegradable hydrogels, consisting of hydrophobic poly(D,L)lactic acid (PDLLA) and hydrophilic dextran segments with a polymer network structure, was synthesized with UV photopolymerization. Unsaturated vinyl groups first were introduced onto the PDLLA and dextran polymer backbones, then followed by a crosslinking reaction of diacrylate-terminated PDLLA and dextran acrylate. The chemical crosslinking forced the hydrophobic PDLLA and hydrophilic dextran segments to mix with each other in the network hydrogels. The new polymers were characterized by standard polymer characterization methods such as NMR, Fourier transform infrared spectroscopy, and gel permeation chromatography. The effects of reaction time, temperature, and molar ratio of the reactants on the incorporation of acrylate onto the polymer backbone were examined. A series of hydrogels with different dextran/PDLLA composition ratios was prepared, and their swelling behaviors were studied. These new bicomponent network hydrogels had a wide range of hydrophilicity to hydrophobicity that was difficult to achieve in totally hydrophilic hydrogels.

Synthesis and characterization of biodegradable hydrophobic–hydrophilic hydrogel networks with a controlled swelling property

A biodegradable polymer network hydrogel system with both hydrophilic and hydrophobic components was synthesized and characterized. The hydrophilic and hydrophobic components were dextran and poly(D,L)lactic acid (PDLLA), respectively. These two polymers were chemically modified for incorporating unsaturated groups for subsequent UV crosslinking to generate a hydrogel with a three-dimensional network structure. The effects of the reaction conditions on the synthesis of a dextran derivative of allyl isocyanate (dex-AI) were studied. All newly synthesized materials were characterized by Fourier transform infrared and NMR. The swelling property of the hydrogels was studied in buffer solutions of different pHs. The results of this study showed that a wide-range swelling property was obtained by changes in the dex-AI/PDLLA composition ratio, the type and degree of unsaturated groups incorporated into dextran, and the UV photocrosslinking time. The solvent extraction effect on the swelling property of the hydrogels was also studied.

Synthesis and characterization of biodegradable poly(L‐aspartic acid‐co‐PEG)

The melt polycondensation reaction of the prepolymer prepared from N-(benzyloxycarbonyl)-L-aspartic acid anhydride (N-CBz-L-aspartic acid anhydride) and low molecular weight poly(ethylene glycol) (PEG) using titanium isopropoxide (TIP) as a catalyst produced the new biodegradable poly(L-aspartic acid-co-PEG). This new copolymer had pendant amine functional groups along the polymer backbone chain. The optimal reaction conditions for the preparation of the prepolymer were obtained by using a 0.12 mol % of p-toluenesulfonic acid with PEG 200 for 48 h. The weight-average molecular weight of the prepolymer increased from 1,290 to 31,700 upon melt polycondensation for 6 h at 130°C under vacuum using 0.5 wt % TIP as a catalyst. The synthesized monomer, prepolymer, and copolymer were characterized by FTIR, 1H- and 13C-NMR, and UV spectrophotometers. Thermal properties of the prepolymer and the protected copolymer were measured by DSC. The glass transition temperature (Tg) of the prepolymer shifted to a significantly higher temperature with increasing molecular weight via melt polycondensation reaction, and no melting temperature was observed. The in vitro hydrolytic degradation of these poly(L-aspartic acid-co-PEG) was measured in terms of molecular weight loss at different times and pHs at 37°C. This pH-dependent molecular weight loss was due to a simple hydrolysis of the backbone ester linkages and was characterized by more rapid rates of hydrolysis at an alkaline pH. These new biodegradable poly(L-aspartic acid-co-PEG)s may have potential applications in the biomedical field.

Novel biodegradable copolymers containing pendant amine functional groups based on aspartic acid and poly(ethylene glycol)

Abstract A new biodegradable poly( l -aspartic acid-co-poly(ethylene glycol)) having pendant amine functional groups was synthesized by the melt polycondensation reaction of prepolymer prepared from N -(benzyloxycarbonyl)- l -aspartic acid anhydride ( N -Z- l -aspartic acid anhydride) and poly(ethylene glycol). The synthesized polymer was characterized by FT i.r., 1 H n.m.r., d.s.c., g.p.c. and solubility. The weight-average molecular weight of the prepolymer increased about 11 times via melt polycondensation at 160°C in a vacuum for

Synthesis of starch-based drug carrier for the control/release of estrone hormone

The objective of this study was to provide new synthetic route to prepare starch as a potential carrier for controlled release of drugs. A starch was modified with bromoacetyl bromide in order to provide more reactive sites for coupling of bioactive estrone and a suitable spacer between the drug carrier and the hormone. The degree of substitution (D.S.) per anhydroglucose (AHG) unit was calculated from the bromine content and ranged from 0.11 to 2.29, depending on the ratio of bromoacetyl bromide to starch. The starch-estrone conjugate was then synthesized by reacting bromoacetylated starch with the sodium salt of estrone. The structures of bromoacetylated starch and starch-estrone conjugate were determined by means of FTIR,1H NMR,13C NMR and UV. Additionally, X-ray diffraction patterns showed the amorphous character of the bromoacetylated starches.

Inulin polysaccharide having pendant amino acids : Synthesis and characterization

Inulin polysaccharide was esterified with N-protected α-amino acids (N,N′-di-benzylocarbonyl-L-lysine and N-benzylocarbonyl-glycine) under a mild condition (room temperature) and within short reaction times (6 h). The esterification reactions were conducted in the presence of dicyclohexylcarbodiimide and 4-(dimethylamino)pyridine as a catalyst. The optimal reaction time (6 h) was determined by monitoring the concentration of free carboxylic acid of the N-protected amino acids during the reaction. The degree of substitution per fructose unit was 0.95 for inulin-lysine and 1.01 for inulin-glycine. The resulting biopolymer was deprotected by catalytic transfer hydrogenation method using 1,4-cyclohexadiene as an effective hydrogen donor. The structures, molecular weight, and thermal properties of the amino acid esters of inulin were determined by Fourier transform infrared spectroscopy, 1H and 13C NMR, UV, viscosity, and dicyclohexylcarbodiimide. This new modified inulin polysaccharide would have the potential as a biomaterial for biomedical applications.

Synthesis of unsaturated poly(ether amide)s based on amine‐terminated poly(ethylene glycol)

Novel water-soluble unsaturated poly(ether amide)s (PEAs) were synthesized by low-temperature polycondensation of fumaryl chloride and amine-terminated poly(ethylene glycol) (Jeffamine®). The unsaturated copolymers were further chemically modified with thiols to provide reactive pendant functional groups. Hydrogels based on these copolymers were prepared by copolymerization of the PEA with N-vinyl pyrrolidone exposure to ultraviolet (UV) irradiation. The resulting hydrogels exhibited a high swelling ratio, and the magnitude of swelling depended on the molecular weight of Jeffamine®. The swelling ratio and equilibrium water content tended to increase with increasing chain length of the Jeffamine® used in copolymer synthesis.