Polysaccharides, such as heparin, hyaluronan, and chitosan, were partially derivatized with a styryl or a methacryloyl group by condensation at a carboxyl or an amino group of the polysaccharides with 4-vinylaniline or 4-vinylbenzoic acid. The degree of substitution depended on the reaction conditions. These compounds with low degrees of derivatization produced water-swollen hydrogels only at relatively high concentrations (30−40 wt %) in the presence of a carboxylated camphorquinone upon visible light irradiation. A high degree of derivatization of heparin increased the gel yield and concomitantly reduced the degree of swelling. The copolymerization of these vinylated polysaccharides with styrenated gelatin considerably reduced the degree of swelling. Tubular photoconstructs were prepared by photocopolymerization of vinylated polysaccharide and vinylated gelatin. The mixing of diacrylated poly(ethylene glycol) with vinylated polysaccharide improved the burst strength of photogels against the gradual infusion of water. These photocurable polysaccharides may be used as photocured scaffolds in tissue-engineered devices.

Heparin terminally grafted with a thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAM), was prepared by sequential steps of chemical modification of one terminal group of heparin, leading to its dithiocarbamylation as an iniferter (initiator-transfer agent-terminator), followed by quasi-living photopolymerization, thereby producing PNIPAM with a molecular weight (mol wt) ranging from 2 × 10 3 to 1 × 10 5 g/mol at the terminus of heparin (PNIPAM-heparin). The lower critical solution temperature depended on the mol wt of PNIPAM. Higher-mol-wt PNIPAM-heparin completely precipitated at 34 °C. The adsorptivity on the poly(ethylene terephthalate) (PET), poly(styrene) (PST), and segmented polyurethane (PU) films was assessed by wettability measurement and surface chemical compositional analysis using X-ray photoelectron spectroscopy. The temperature-dependent amount of adsorbed PNIPAM-heparin was quantitatively determined by a confocal laser scanning microscope (CLSM) using fluorescence-labeled PNIPAM-heparin. The relative degree of heparin complexation with antithrombin III (ATIII) was assessed based on fluorescence intensity using the avidin-biotinylated enzyme complex assay technique under a CSLM. The results showed that irrespective of the type of polymer films, higher-mol-wt PNIPAM-heparin adsorbed better and was more stable than lower-mol-wt PNIPAM-heparin at 40 and 20 °C, an effect which was more enhanced on a hydrophobic surface (PST) than on polar surfaces (PET and PU). The desorption of PNIPAM-heparin did not occur even in the serum-containing medium. In addition, higher complexation capability with ATIII was observed for higher-mol-wt PNIPAM-heparin probably due to its higher adsorption capability. The desorption of PNIPAM-heparin was noted at 20 °C. Thus, it is concluded that PNIPAMheparin exhibits thermoresponsiveness of surface biofunctionality.

Terminally alkylated heparin was prepared by reducing the terminal end of heparin and subsequent lactone formation, followed by ring-opening reaction with alkylamine. The alkyl groups used include butyl, octyl, lauryl, and stearyl. These alkylated heparins adsorbed on the poly(ethylene terephthalate) film from their respective aqueous solutions. The adsorptivity and its stability in buffer solution, complexation compatibility with antithrombin III (ATIII), were enhanced with larger alkyl-group-derivatized heparins. These were assessed using a confocal laser scanning microscope. The "heparin surfactant" developed here may be used for ensured short-term "system antithrombogenicity" of assembled extracorporeal circulatory devices or circuits.

The aim of this study was to create a dense albuminated layer, a heparinized layer, and a mixed layer on a poly(acrylic acid)-grafted surface via visible light induced photopolymerization. The procedure is comprised of four reaction steps: first, by visible light irradiation, acrylic acid (AA) was graft-polymerized on a segmented polyurethane (SPU) film that was preimpregnated with camphorquinone. The second step was adsorption of multiply styrenated albumin or styrenated heparin or their mixture, followed by visible light irradiation in the presence of carboxylated camphorquinone. The third step was covalent bonding between polyAA graft chain and polymerized biomacromolecule and between polymerized biomacromolecule to enforce the formation of a stable immobilized multilayer. X-ray photoelectron spectroscopic and Fourier transform-infrared spectroscopic measurements were conducted to analyze the surfaces formed at each step. Confocal laser scanning microscopy was utilized to determine the thickness of the biomacromolecule-immobilized layer with several tenths of a micrometer thickness. Platelet adhesion was markedly reduced on polymerized albuminated, polymerized heparinized, and copolymerized layers, whereas adhesive and proliferative potentials of endothelial cells, which were comparable to those of commercial tissue culture dishes, were observed on these surfaces. Co-immobilization of fibronectin and basic fibroblast growth factor enhanced these potentials. These densely multilayered surfaces may be suitable for artificial and tissue-engineered devices.

The antiproliferative activity of alkylated heparin, in which the terminal end of heparin is derivatized with an alkyl group (butyl, octyl, lauryl, stearyl), was examined using vascular smooth muscle cells. The proliferation of cells, which were growth-arrested prior to addition of heparin, was inhibited in proportion to both increase in the chain length of the alkyl group of alkylated heparin and alkylated heparin concentration in the serum-containing medium. The antiproliferative activity of stearyl group derivatized heparin was significantly stronger than that of nonmodified heparin. Little proliferation was observed at high dose (500 microg/mL). Confocal laser scanning microscopic observation indicated that alkylated heparin was accumulated on the cell membranes at an early incubation time, followed by homogeneous distribution of intracellular space. The therapeutic potential of alkylated heparin for preventing restenosis after balloon angioplasty is discussed.