Thermoresponsive materials poly

MA1 Maeda, T., Kanda, T., Yonekura, Y., Yamamoto, Y., and Aoyagi, T., Hydioxylated poly(A-isopropylacrylamide) as functional thermoresponsive materials. Biomacromolecules, 1, 545, 2006. 

Temperature variations may result in reversible changes in properties such as structural arrangement, size, solubihty, and shape. Many materials designed for biomedical or biotechnology appHcations are confined to a narrow temperature spectrum in order to be effective in a physiological environment. The following thermoresponsive materials are discussed in the next section poly(N-iso-propylacrylamide (PNIPAAm), polymer brushes, and shape-memory polymers. 

Materials that typify thermoresponsive behavior are polyethylene—poly (ethylene glycol) copolymers that are used to functionalize the surfaces of polyethylene films (smart surfaces) (20). When the copolymer is immersed in water, the poly(ethylene glycol) functionaUties at the surfaces have solvation behavior similar to poly(ethylene glycol) itself. The abiUty to design a smart surface in these cases is based on the observed behavior of inverse temperature-dependent solubiUty of poly(alkene oxide)s in water. The behavior is used to produce surface-modified polymers that reversibly change their hydrophilicity and solvation with changes in temperatures. Similar behaviors have been observed as a function of changes in pH (21—24). 

The group of Goldfarb and coworkers have in recent years explored how (spin-labeled) thermoresponsive triblock copolymers of the Pluronic -type (PEO-PPO-PEO, poly(ethylene oxide)-poly(propyleneoxide)-poly(ethyleneoxide)) can be used to build templates, e.g., for the formation of mesoporous frameworks [93, 94]. These structures bear great potential as carrier materials for catalysts and hence could aid societal needs in energy and sustainability. 

Pretsch, T. (2010) Triple-shape properties of a thermoresponsive poly(ester urethane). Smart Materials and Structures, 19, paper 015006 (7 pages). 

The hexagonaUy ordered mesoporous silicas with different pore sizes (10,17,30 nm) materials were tested as carrier, in smart controlled drug (Indomethacin (I)) release using the thermoresponsive poly(iV-isopropylacrylamide) (PNIPAm) hybrid nanoporous structures during stepwise temperature changes between 25°C and 40°C (Chang et al. 2004). 

CHR Christova, D., Velichkova, R., Loos, W., Goethals, E.J., and DuPrez, F., New thermoresponsive polymer materials based on poly(2-ethyl-2-oxazoline) segments. Polymer, 44, 2255, 2003. 

Lendlein et al. demonstrated the possibilities to design thermoresponsive macroscopic self-folding objects using shape-memory polymers based on different poly(e-caprolactone) [12]. At low temperature, the materials are in their temporary shape. The films recover their permanent shape and irreversibly fold by heating, which could be accompanied by a change of transparency. 

Thermoresponsive control over the display of RGD peptides has been demonstrated by Okano and co-workers (Ebara et al., 2004). A temperature-sensitive copolymer, poly(A-isopropylacrylamide-co-2-carboxyisopropylacrylamide), is grafted on a surface and then decorated with RGD by attachment of the peptide to the carboxylic acid functionalities of the polymer. Cell adhesion is promoted at temperatures above the LCST but reduced below the LCST. This is explained with a modulation of the availability of the peptide at the material surface above the LCST, the polymer is collapsed and the peptide is available at the surface, whereas below the LCST, the polymer becomes soluble and the expanding polymer chains prevent access to the peptide (Figure 3.7(c)). 

Nitschke, M., Gramm, S., Gbtze, T., Valtink, M., Drichel, J., Voit, B., et al. (2007). Thermoresponsive poly(NiPAAm-co-DEGMA) substrates for gentle harvest of human comeal endothelial cell sheets. Journal of Biomedical Materials Research A, 80, 1003-1010. 

Jones, D. M., Smith, R. R., Huck, W. T. S., and Alexander, C. 2002. Variable adhesion of micropattemed thermoresponsive polymer brushes AFM investigations of poly(N-isopropylacrylamide) brushes prepared by surface-initiated polymerizations. Advanced Materials 14 1130-34. 

SI-IMP has been used for synthesis of different types of stimuli-responsive polymer brushes that are responsive to several external stimuli, such as pFI, temperature, and ionic strength [28,58-65]. Because materials interact with their surroundings via their interfaces, the ability to fashion soft interfacial layers and tune the range, extent, and type of physicochemical interactions across interfaces is central to a variety of applications. Rahane et al. carried out sequential SI-IMP of two monomers to create bilevel poly(methacrylic acid)-Woc/c-poly(N-isopropylacrylamide) (PMAA-b-PNIPAM) block copolymer brushes that can respond to multiple stimuli [28]. They observed that each strata in the bilevel PMAA-b-PNIPAM brush retained its customary responsive characteristics PMAA being a "weak" polyelectrolyte swells as pH is increased and the thermoresponsive PNIPAM block collapses as temperature is raised through the volume phase transition temperature due to its lower critical solution temperature (LCST) behavior. As a result of ions added to make buffer solutions of various pH and because of the effect of surface confinement, the swollen-collapse transition of the PNIPAM layer occurs at a... 

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