Hydrogel thermo

Jeong and coworkers have reported peptide-based thermo-gelling systems using PEG-b-polyAla as an injectable cellular scaffold [315]. The polymer aqueous solution undergoes sol-gel transition as temperature increases. The fraction of the p-sheet structure of the poly Ala dictated the population and thickness of fibrous nanostructure in the hydrogel, which affected the proliferation and protein... 

Thermosensitive hydrogels, 13 743 THERMOSET Thermoset recycling pyramid, 13 780-781 Thermoset elastomers, 20 71 Thermoset epoxy resins, curing of, 10 421 Thermoset flexible polyurethane foams properties of, 25 461 Thermoset matrix composites, 21 456 Thermo set molding properties of diallyl isophthalate, 2 262t Thermoset polymers, 25 455 cured, 10 425... 

Brazel, C. S. and Peppas, N. A. Synthesis and characterization of thermo- and chemomechanically responsive poly(A-isopropylacrylamide-co-methacryhc acid) hydrogels. Macromolecules 1995, 28, 8016-8020. 

From this perspective, temperature-responsive hydrogels are reviewed as agents in the design of effective polymeric structures for thermo-responsiveness as Intelligent Materials . 

Poly(vinyl methyl ether), PVME, is a thermo-sensitive polymer. The aqueous solution has a Lower Critical Solution Temperature (LCST) of 37 °C. Therefore, PVME is soluble in water below its LCST, but insoluble above its LCST. When an aqueous solution of PVME is irradiated with y-rays the solution becomes PVME hydrogel [18, 19]. The gel shows thermo-sensitivity similar to the solution, and swells below 37 °C and shrinks above this temperature. It is important to form a fine porous gel structure to obtain quick response gels. There are two methods for the purpose. One is a method using micro-phase separation by heating. The other is a method using micro-phase separation by blending of polymer solutions. 

Fig. 18. Thermo-mechanical response of PVME hydrogels Ln gel length at 40 °C,...

Fig. 21. Thermo-mechanical response of fibrous PVME hydrogel...

Harmon, M.E., Tang, M., Frank, C.W., A microfluidic actuator based on thermo-responsive hydrogels. Polymer 2003, 44, 4547M556. 

Chacon D, Hsieh YL, Kurth MJ, Krochta JM (2000) Swelling and protein absorp-tion/desorption of thermo-sensitive lactitol-based polyether polyol (LPEP) hydrogels. Polymer 41 8257-8262... 

Kondo, A., and Fukuda, H., Preparation of thermo-sensitive magnetic hydrogel microspheres for antibody and application to enzyme immobilization, J. Ferment. Bioeng., 41, 99, 1994. 

Recently a polyrotaxane composed of multiple methylated a-CD rings threaded on a high molecular weight PEO chain and end-capped by bulky adamantyl groups was synthesized (Fig. 17) and investigated in terms of its thermo-reversible sol-gel transition and hydrogel formation [87],... 

Physical hydrogels were formed induced by self-assembled water-insoluble and crystalline polypseudorotaxane domains which act as physical crosslinking points. Such physical hydrogels include the polypseudorotaxane systems of a-CD threading on PEO or its copolymers, a-CD threaded on PEI, PL, or their copolymers, and even 3-CD or y-CD threaded PPO or PEI copolymers. The thermo-reversible and thixotropic properties of these supramolecular hydrogels have inspired their applications as injectable drug delivery systems. Physical hydrogels induced by physical interaction of threaded CD molecules in polyrotaxanes were also developed. 

Kim, J.H. Lee, T.R. Thermo- and pH-responsive hydrogel-coated gold nanoparticles. Chem. Mater. 2004, 16, 3647-3651. 

Stile RA. Healy KE (2001) Thermo-responsive peptide-modified hydrogels for tissue regeneration. BioMacromolecules 2 185-194... 

An advantage of radiochemical induced cross-linking is the possibility to combine polymers with different properties. For that purpose, the polymers were separately dissolved in water. The solutions were mixed and irradiated. (Gottlieb et al. 2005) describes the synthesis of temperature-sensitive hydrogel blends of PVME (as thermo-sensitive polymer) and the radiation-cross-linkable polymer PVP (a polymer that is applied in pharmaceutics). The experiments show that the gelation dose of the blend is between the gelation doses of the two pure polymers. 

Proton NMR imaging was used to study the volume phase transition in a thermo-responsive hydrogel (Ganapathy et al. 2000). The thermally induced volume phase transition was clearly seen in the proton image. The shrinking of a polyelectrolyte gel under the application of an electrical DC field was observed in real time (Hotta and Ando 2002). 

Orakdogen N, Okay O (2006) Reentrant conformation transition in poly(N, N-dimethylacryla-mide) hydrogels in water-organic solvent mixtures. Polymer 47 561-568 Panayiotou M, Freitag R (2005) Influence of the synthesis conditions and ionic additives on the swelling behaviour of thermo-responsive polyalkylacrylamide hydrogels. Polymer 46 6777-6785... 

The probably simplest controllable basic functionality consists of a thermo-sensitve hydrogel and a directly attached resistive heater (Fig. 10a) (Richter et al. 2003 Arndt et al. 2000). As a function of the electrical power per Joule heat the hydrogel can be heated above its volume phase transition temperature. 

Microvalves are the simplest hydrogel-based components. The gel actuator is directly placed within a valve chamber (Fig. 11a). The thermo-sensitive PNIPAAm is swollen at room temperature and closes the valve. For opening the attached resistive heater has to be activated. Exceeding the volume phase transition temperature of approximately 34 °C the gel shrinks and opens the valve seat. 

In presence of certain substances, the phase transition temperature of thermo-sensitive hydrogels is altered. This phenomenon is used to design electrothermi-cally adjustable hydrodynamic microtransistors, which are also called chemostat microvalves (Richter et al. 2007a). The valve seat of the device (Fig. 14a) is tempered by a heater and an integrated temperature sensor is used for a closed-loop control. The volume phase transition temperature of PNIPAAm decreases with increasing alcohol content in water (Fig. 14b, solid symbols). Therefore, each critical alcohol concentration or volume phase transition correlates with one characteristic isotherm. Tempered at a particular isotherm the valve switches at a certain concentration (Fig. 14b, open symbols). 

Hatakeyama H, Kikuchi A, Yamato M et al (2007) Patterned biofunctional designs of thermo-responsive surfaces for spatiotemporally controlled cell adhesion, growth, and thermally induced detachment. Biomaterials 28 3632-3643 Hem DL, Hubbell JA (1998) Incorporation of adhesion peptides into nonadhesive hydrogels useful for tissue resurfacing. J Biomed Mater Res 39 266-276 Huang J, Wang XL, Chen XZ et al (2003) Temperature-sensitive membranes prepared by the plasma-induced graft polymerization of N-isopropylacrylamide into porous polyethylene membranes. J Appl Polym Sci 89 3180-3187... 

Nitschke M, Zschoche S, Baier A et al (2004) Low pressure plasma immobilization of thin hydrogel films on polymer surfaces. Surf Coat Technol 185 120-125 Nitschke M, Gramm S, Gotze T et al (2007a) Thermo-responsive poly(NiPAAm-co-DEGMA) substrates for gentle harvest of human comeal endothelial cell sheets. J Biomed Mater Res A 80 1003-1010... 

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