Biomedical Applications. (biomedical + applications)

Distribution by Scientific Domains

Selected Abstracts

Photoinitiating polymerization to prepare biocompatible chitosan hydrogels

Xiaohong Hu
Abstract Chitosan hydrogels were prepared from water soluble chitosan derivatives (chitosan-MA-LA, CML) by photoinitiating polymerization under the existence of Irgacure2959 and the irradiation of UV light. The CML was obtained by amidation of the amine groups of chitosan with lactic acid and methacrylic acid. Gelation time of the hydrogel could be adjusted within a range of 5,50 min, and controlled by factors such as the degree of MA substitution, initiator concentration, existence of oxygen, and salt. The dry hydrogel adsorbed tens to hundred times of water, forming a highly hydrated gel. The swelling ratio was smaller at the higher degree of MA substitution, higher pH, and higher salt concentration. Rheological test showed that the hydrogel is elastomeric in the measuring frequency range, with a storage modulus and loss modulus of 0.8,7 kPa and 10,100 Pa, respectively. In vitro culture of chondrocytes demonstrated that the cells could normally proliferate in the extractant of the hydrogels, showing no cytotoxicity at lower initiator concentration. By contrast, the extractant of the hydrogel made by the redox initiating system, i.e., ammonium persulfate (APS) and N,N,N,,N,-tetramethylethylenediamine (TEMED), showed apparent cytotoxicity. Thus, the chitosan hydrogels initiated by the Irgacure2959 have better comprehensive properties, in particular better biocompatibility, and are more suitable for biomedical applications. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Chitosan-alginate films prepared with chitosans of different molecular weights

Xiao-Liang Yan
Abstract Chitosan-alginate polyelectrolyte complex (CS-AL PEC) is water insoluble and more effective in limiting the release of encapsulated materials compared to chitosan or alginate. Coherent CS-AL PEC films have been prepared in our laboratory by casting and drying suspensions of chitosan-alginate coacervates. The objective of this study was to evaluate the properties of the CS-AL PEC films prepared with chitosans of different molecular weights. Films prepared with low-molecular-weight chitosan (Mv 1.30 105) were twice as thin and transparent, as well as 55% less permeable to water vapor, compared to films prepared with high-molecular-weight chitosan (Mv 10.0 105). It may be inferred that the low-molecular-weight chitosan reacted more completely with the sodium alginate (Mv 1.04 105) than chitosan of higher molecular weight. A threshold molecular weight may be required, because chitosans of Mv 10.0 105 and 5.33 105 yielded films with similar physical properties. The PEC films exhibited different surface properties from the parent films, and contained a higher degree of chain alignment with the possible formation of new crystal types. The PEC films exhibited good in vitro biocompatibility with mouse and human fibroblasts, suggesting that they can be further explored for biomedical applications. 2001 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 58: 358,365, 2001 [source]

Production and processing of spider silk proteins

John G. Hardy
Abstract Natural spider silk fibers have impressive mechanical properties (outperforming many man-made fibers) and are, moreover, biocompatible, biodegradable, and produced under benign conditions (using water as a solvent at ambient temperature). The problems associated with harvesting natural spider silks inspired us to devise a method to produce spider silk-like proteins biotechnologically (the first subject tackled in this highlight); we subsequently discuss their processing into various materials morphologies, and some potential technical and biomedical applications. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3957,3963, 2009 [source]

Sugars-grafted aliphatic biodegradable poly(L -lactide- co -carbonate)s by click reaction and their specific interaction with lectin molecules

Changhai Lu
Abstract A novel biodegradable aliphatic poly(L -lactide- co -carbonate) bearing pendant acetylene groups was successfully prepared by ring-opening copolymerization of L -lactide (LA) with 5-methyl-5-propargyloxycarbonyl-1,3-dioxan-2-one (PC) in the presence of benzyl alcohol as initiator with ZnEt2 as catalyst in bulk at 100 C and subsequently used for grafting 2-azidoethyl ,- D -glucopyranoside and 2-azidoethyl ,-lactoside by the typical "click reaction," that is Cu(I)-catalyzed cycloaddition of azide and alkyne. The density of acetylene groups in the copolymer can be tailored by the molar ratio of PC to LA during the copolymerization. The aliphatic copolymers grafted with sugars showed low cytotoxicity to L929 cells, improved hydrophilic properties and specific recognition and binding ability with lectins, that is Concanavalin A (Con A) and Ricinus communis agglutinin (RCA). Therefore, this kind of sugar-grafted copolymer could be a good candidate in variety of biomedical applications. 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3204 ,3217, 2007 [source]

Characterization of ring-opening polymerization of genipin and pH-dependent cross-linking reactions between chitosan and genipin

Fwu-Long Mi
Abstract In this study, a novel chitosan-based polymeric network was synthesized by crosslinking with a naturally occurring crosslinking agent,genipin. The results showed that the crosslinking reactions were pH-dependent. Under basic conditions, genipin underwent a ring-opening polymerization prior to crosslinking with chitosan. The crosslink bridges consisted of polymerized genipin macromers or oligomers (7 , 88 monomer units). This ring-opening polymerization of genipin was initiated by extracting proton from the hydroxyl groups at C-1 of deoxyloganin aglycone, followed by opening the dihydropyran ring to conduct an aldol condensation. At neutral and acidic conditions, genipin reacted with primary amino groups on chitosan to form heterocyclic amines. The heterocyclic amines were further associated to form crosslinked networks with short chains of dimmer, trimer, and tetramer bridges. An accompanied reaction of nucleophilic substitution of the ester group on genipin by the primary amine group on chitosan would occur in the presence of an acid catalysis. The extent in which chitosan gels crosslinked with genipin was significantly dependent on the crosslinking pH values: 39.9 3.8% at pH 5.0, 96.0 1.9% at pH 7.4, 45.4 1.8% at pH 9.0, and 1.4 1.0% at pH 13.6 (n = 5, p < 0.05). Owing to the different crosslinking extents and different chain lengths of crosslink bridges, the genipin-crosslinked chitosan gels showed significant difference in their swelling capability and their resistance against enzymatic hydrolysis, depending on the pH conditions for crosslinking. These results indicated a direct relationship between the mode of crosslinking reaction, and the swelling and enzymatic hydrolysis properties of the genipin-crosslinked chitosan gels. The ring-opening polymerization of genipin and the pH-dependent crosslinking reactions may provide a novel way for the preparation and exploitation of chitosan-based gels for biomedical applications. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1985,2000, 2005 [source]