Biomedical subjects

E T Kang

Publications and source records attributed to E T Kang.

43 records · Page 3Linked to original sources

PubMedDate not supplied

Covalent immobilization of glucose oxidase on the surface of polyaniline films graft copolymerized with acrylic acid.

Glucose oxidase (GOD) was covalently immobilized on the electroactive polyaniline (PAN) film with surface-grafted acrylic acid (AAc) polymer through the amide linkage formation between amino groups of GOD and the carboxyl groups of the grafted AAc polymer chains in the presence of a water-soluble carbodiimide. The surface structure and composition of the graft-modified and enzyme-functionalized PAN films were characterized by angle-resolved X-ray photoelectron spectroscopy (XPS). The amounts of immobilized GOD and its activity were also investigated. It was shown that the amount of immobilized GOD increased linearly with the concentration of surface-grafted AAc polymer chains. The decrease in activity of the immobilized GOD was considered to be due to, among other factors, the reduced accessibility of glucose molecules to the active sites of the enzyme and the conformational change of the GOD molecules as a result of the covalent immobilization. However, the immobilized enzyme was less sensitive to thermal inactivation as compared to that of the free form. The optimum pH value of GOD was not affected by the immobilization reaction and the pH stability range was considerably widened. The immobilized GOD also exhibits a significantly improved stability during storage in buffer solution over that of the free enzyme.

Acrylic Resins↗

PubMedDate not supplied

Immobilization of galactose ligands on acrylic acid graft-copolymerized poly(ethylene terephthalate) film and its application to hepatocyte culture.

Surface modification of argon-plasma-pretreated poly(ethylene terephthalate) (PET) films via UV-induced graft copolymerization with acrylic acid (AAc) was carried out. Galactosylated surfaces were then obtained by coupling a galactose derivative (1-O-(6'-aminohexyl)-D-galactopyranoside) to the AAc graft chains with the aid of a water-soluble carbodiimide (WSC) and N-hydroxysulfosuccinimide (sulfo-NHS). The modified PET films were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and water contact-angle measurements. The galactosylated PET films were used as substrates for hepatocyte culture. The effects of surface carboxyl group concentration on the extent of galactose ligand immobilization, the extent of hepatocyte attachment, and the surface morphology were investigated. The amount of the galactose ligands immobilized on the PET surface increased with the AAc polymer graft concentration. AFM images revealed that the surface roughness of the PET film increased after graft copolymerization with AAc, but did not change appreciably with the subsequent immobilization of the galactose ligands. At the surface carboxyl group concentration of about 0.56 micromol/cm(2) or galactose ligand concentration of about 0.51 micromol/cm(2), the hepatocyte culture on the galactosylated surface exhibited the optimum concentration and physiological functions and formed aggregates or spheroids after just 1 day of culture. The albumin and urea synthesis functions of these hepatocytes were comparable to or higher than those of the hepatocytes cultured on the collagen-modified PET substrates.

Acrylates↗

PubMedDate not supplied

Assessment of in vitro bioactivity of hyaluronic acid and sulfated hyaluronic acid functionalized electroactive polymer.

Electrically conductive polypyrrole (PPY) was surface functionalized with hyaluronic acid (HA) and sulfated hyaluronic acid (SHA) to improve its surface biocompatibility. The immobilization of HA on the PPY film was facilitated by the use of a cross-linker having the appropriate functional groups. The biological activity of the HA functionalized PPY film was assessed by means of an in vitro PC12 cell culture. The cell attachment on different substrates was studied and determined by bicinchoninic acid protein analysis. Cell attachment on the HA functionalized PPY film surface was significantly enhanced in the presence of nerve growth factor. The SHA functionalized PPY film was obtained by the sulfonation of the immobilized HA using pyridinesulfonate. The retention of the biological activity of the immobilized HA after sulfonation was evaluated by the in vitro assessment of the plasma recalcification time (PRT) and platelet adhesion on the substrate. The PRT observed from the SHA functionalized PPY film was significantly prolonged compared with the HA functionalized PPY. Some reduction of platelet adhesion was observed for the SHA functionalized PPY film, compared with that of the HA functionalized PPY film.

Animals↗

PubMedDate not supplied

Covalent immobilization of glucose oxidase on well-defined poly(glycidyl methacrylate)-Si(111) hybrids from surface-initiated atom-transfer radical polymerization.

A simple one-step procedure was employed for the covalent immobilization of an atom-transfer radical polymerization (ATRP) initiator, via the robust Si-C bond, on the hydrogen-terminated Si(111) surface (Si-H surface). Well-defined poly(glycidyl methacrylate) [P(GMA)] brushes, tethered directly on the (111)-oriented single-crystal silicon surface, were prepared via surface-initiated ATRP. Kinetics study on the surface-initiated ATRP of glycidyl methacrylate revealed that the chain growth from the silicon surface was consistent with a "controlled" process. A relatively high concentration of glucose oxidase (GOD; above 0.2 mg/cm2) could be coupled directly to the well-defined P(GMA) brushes via the ring-opening reaction of the epoxide groups with the amine moieties of the enzyme. The resultant GOD-functionalized P(GMA) brushes, with the accompanying hydroxyl groups from the ring-opening reaction of the epoxide groups, serves as an effective spacer to provide the GOD with a higher degree of conformational freedom and a more hydrophilic environment. An equivalent enzyme activity above 1.6 units/cm2 [micromoles of beta-D-(+)-glucose oxidized to d-gluconolactone per minute per square centimeter] and a corresponding relative activity of about 60% could be readily achieved. The immobilized GOD also exhibited an improved stability during storage over that of the free enzyme. The GOD-functionalized silicon substrates are potentially useful to the development of silicon-based glucose biosensors.

Biosensing Techniques↗

PubMedDate not supplied

Surface-active and stimuli-responsive polymer--Si(100) hybrids from surface-initiated atom transfer radical polymerization for control of cell adhesion.

A simple two-step method was developed for the covalent immobilization of atom-transfer radical polymerization (ATRP) initiators on the hydrogen-terminated Si(100) (Si-H) surface. Well-defined functional polymer-Si hybrids, consisting of covalently tethered brushes of poly(ethylene glycol) monomethacrylate (PEGMA) polymer, N-isopropylacrylamide (NIPAAm) polymer, and NIPAAm-PEGMA copolymers and block copolymers on Si-H surfaces, were prepared via surface-initiated ATRP. Kinetics study revealed that the chain growth from the silicon surface was consistent with a "controlled" process. Surface cultures of the cell line 3T3-Swiss albino on the hybrids were evaluated. The PEGMA graft-polymerized silicon [Si-g-P(PEGMA)] surface is very effective in preventing cell attachment and growth. At 37 degrees C [above the lower critical solution temperature (LCST, approximately 32 degrees C) of NIPAAm], the seeded cells adhered, spread, and proliferated on the NIPAAm graft polymerized silicon [Si-g-P(NIPAAm)] surface. Below the LCST, the cells detached from the Si-g-P(NIPAAm) surface spontaneously. Incorporation of PEGMA units into the NIPAAm chains of the Si-g-P(NIPAAm) surface via copolymerization resulted in more rapid cell detachment during the temperature transition. The "active" chain ends on the Si-g-P(PEGMA) and Si-g-P(NIPAAm) hybrids were also used as the macroinitiators for the synthesis of diblock copolymer brushes. Thus, not only are the hybrids potentially useful as stimuli-responsive adhesion modifiers for cells in silicon-based biomedical microdevices but also the active chain ends on the hybrid surfaces offer opportunities for further surface functionalization and molecular design.

3T3 Cells↗

PubMedDate not supplied

Heparin-coupled poly(poly(ethylene glycol) monomethacrylate)-Si(111) hybrids and their blood compatible surfaces.

Well-defined (nearly monodispersed) poly(poly(ethylene glycol)monomethacrylate)-Si hybrids were prepared via surface-initiated atom transfer radical polymerization (ATRP) of the poly(ethylene glycol)monomethacrylate (PEGMA) macromonomer on the hydrogen-terminated Si(111) surface (Si-H surface). Both the active chloride groups at the chain ends (from the ATRP process) and the chloride groups converted from some ( approximately 32%) of the -OH groups of the Si-C bonded PEGMA polymer, or P(PEGMA), brushes were used as leaving groups for the covalent coupling of heparin. For the heparinized P(PEGMA)-Si hybrid surfaces, protein adsorption and platelet adhesion were significantly suppressed. The well-defined and dense P(PEGMA) brushes, prepared from surface-initiated ATRP, had allowed the immobilization of a relatively high concentration of heparin (about 14 mug/cm(2)). The resulting silicon surface exhibited significantly improved antithrombogenecity with a plasma recalcification time (PRT) of about 150 min. The persistence of high bioactivity for the immobilized heparin on the hybrid surfaces can be attributed to the biocompatibility of the PEGMA units, as well as their role as spacers in providing the immobilized heparin with a higher degree of conformational freedom in a more hydrophilic environment. Thus, the heparin-coupled P(PEGMA)-Si hybrids with anti-fouling and antithrombogenic surfaces are potentially useful in silicon-based implantable devices and tissue engineering.

Acrylates↗

PubMedDate not supplied

Collagen-coupled poly(2-hydroxyethyl methacrylate)-Si(111) hybrid surfaces for cell immobilization.

To improve the biocompatibility of silicon-based implantable micro- and nanodevices, and to tailor silicon surfaces for controlled cell immobilization, well-defined functional polymer-Si(111) hybrids, consisting of nearly monodispersed poly(2-hydroxyethyl methacrylate [P(HEMA)] with covalently coupled collagen and tethered (Si-C bonded) on the silicon surfaces, were prepared. HEMA was graft polymerized on the hydrogen-terminated Si(111) surface (Si-H surface) via surface-initiated atom transfer radical polymerization (ATRP) to give rise to the Si-g-P(HEMA) hybrid. The active chloride end groups preserved throughout the ATRP process and the chloride groups converted from some (approximately 20%) of the OH groups of the P(HEMA) brushes were used as the leaving groups for nucleophilic reaction with the -NH2 groups of collagen to give rise to the Si-g-P(HEMA)-collagen surface conjugates. These hybrid surfaces were evaluated by culturing 3T3 fibroblasts. The biocompatible Si-g-P(HEMA) hybrid surface resisted attachment and growth of this cell line. The Si-g-P(HEMA)-collagen hybrid surfaces, on the other hand, exhibited good cell adhesion and growth characteristics, and the extent of cell immobilization could be controlled by adjusting the amount of immobilized collagen. Thus, incorporating the collagen-coupled P(HEMA) onto silicon surfaces via robust Si-C bonds may endow the silicon substrates with new and interesting properties for potential applications in silicon-based implantable devices, such as molecular sensors and biochips.

3T3 Cells↗