Hydrogel thermal

Amphiphilic peptides lonically crosslinked micro- and nano-spheres Biotinylated microspheres Photopolymerizable hydrogels Thermally activated crosslinked gels Two-component polyurethanes Alginates... 

Thermosensitive hydrogels Thermally-sensitive hydrogels Intelligent gels... 

Water content indirectly affects other lens characteristics. Water evaporation from the lens can result in a dry eye sensation and subsequent desiccative erosion of the cornea. Clinical studies have shown the incidence of corneal erosion as a result of lens desiccation to be a material-dependent and water-content-dependent phenomenon (25,26). The nature of water and sodium ions in hydrogels has been studied primarily by nmr and thermal techniques (27,28). An empirical relationship between water mobility in contact lens polymers and desiccative staining has been proposed (29). 

Hydrogel lenses are obtained by photo or thermal polymerisation of monomers in bulk or in solution. A variety of thermal and photo catalysts have been used in hydrogel formulations. 

Collier JH, Hu BH, Ruberti JW et al (2001) Thermally and photochemically triggered self-assembly of peptide hydrogels. J Am Chem Soc 123 9463-9464... 

Pochan DJ, Schneider JP, Kretsinger J et al (2003) Thermally reversible hydrogels via intramolecular folding and consequent self- assembly of a de novo designed peptide. J Am Chem Soc 125 11802-11803... 

AS Hoffman, A Afrassiabi, LC Dong. Thermally reversible hydrogels II. Delivery and selective removal of substances from aqueous solutions. J Controlled Release 4 213-222, 1986. 

A Afrassiabi, AS Hoffman, LA Cadwell. Effect of temperature on the release rate of biomolecules from thermally reversible hydrogels. J Membrane Sci 33 191-200,... 

TG Park, AS Hoffman. Immobilization of Arthrobacter simplex in thermally reversible hydrogels Effect of gel hydrophobicity on steroid conversion. Biotech Prog 7 383-390, 1991. 

Another class of environmentally sensitive materials that are being targeted for use in drug delivery applications is thermally sensitive polymers. This type of hydrogel exhibits temperature-sensitive swelling behavior... 

El Sherbiny IM, Lins RJ, Abdel-Bary EM, Harding DRK (2005) Preparation, characterization, swelling and in vitro drug release behaviour of poly [N-acryloylglycine-chitosan interpoly-meric pH and thermally-responsive hydrogels. European Polymer Journal 41 2584-2591. 

Dong, L. C., Yan, Q., and Hoffman, A. S. Controlled release of amylase from a thermal and pH-sensitive, macroporous hydrogel. J. Controlled Release 1992, 19, 171-178. 

We show here that when an enzyme is immobilized within such gels it may be "switched" on and off reversibly as the temperature is cycled. Such catalytic hydrogels may be used to control reactions by a thermal feedback mechanism. 

In this paper we have immobilized an enzyme within a thermally reversible hydrogel. Immobilized enzymes have been used in a variety of applications, ranging from treatment of diseases to sensors, assays, and industrial processes (15-20). When an enzyme is immobilized within a gel which exhibits reversible shrinking and swelling as the ten rature is raised and lowered through the LCST of the gel matrix polymer, the enzyme may be switched off and on as the substrate diffusion rate is regulated by the gel pore size (5). In adcfition to enzymes, a variety... 

Figure 1. Schematic of synthesis of enzyme immobilized within hydrogel exhibiting thermally reversible shrinking and swelling.

Thermal and pH sensitive heterogeneous copolymer hydrogels which contain silicone rubber domains within a temperature and pH sensitive copolymer of NIPA and acrylic acid have been synthesized by Dong et al. [60]. These materials contained macropores when swollen and collapsed much faster than homopolymers of iV-isopropylacrylamide. Biocatalyst immobilization using copolymers of NIPA and NN - dimethylaminopropylmethacrylamide have also been studied [61]. 

Several other studies have also been made in an attempt to account theoretically for the phase transition in terms different from those of the Flory-Huggins theory. Otake et al. [55] thus proposed a theoretical model that takes hydrophobic interaction into account in explaining the thermally induced discontinuous volume collapse of hydrogels. In addition, Prausnitz et al. [56] proposed a lattice model, an improvement of which was made to explain the swelling curves of gels consisting of /V,/V -methylenebis(acrylamide) (MBA)-crosslinked copolymers of AAm with [(methacrylamide)propyl]trimethyl-ammonium chloride (MAPTAC) [57],... 

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