Temperature-sensitive hydrogels

Thermosensitive Hydrogels Temperature-sensitive polymers have been studied extensively and many of these exhibit the LOST in aqueous solution. The volume-phase transition of a thermosensitive hydrogel was first reported for PNlPAm hydrogel in water (90). After that, a large number of hydrogels based on NIPAm has been prepared and the phase transition upon temperature change have been studied. 

DC Harsh, SH Gehrke. Controlling the swelling characteristics of temperature-sensitive cellulose ether hydrogels. J Controlled Release 17 175-186, 1991. 

X Huang, H Unno, T Akehata, O Hirasa. Analysis of kinetic behavior of temperature-sensitive water-absorbing hydrogel. J Chem Eng Jpn 20 123-128, 1987. 

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... 

Nabeshima, Y., Ding, Z. L., Chen, G. H., Hoffman, A. S., Taira, H., Kataoka, K., and Tsuruta, T., Slow release of heparin from a hydrogel made from polyamine chains to a temperature-sensitive polymer backbone, in Advanced Biomaterials in Biomedical Engineering and Drug Delivery Systems (N. Ogata, et al., Eds.), pp. 315-316. Springer, Tokyo (1996). 

Figure 7 Schematic diagram of the mechanism of temperature sensitivity of hybrid hydrogels.

In this work, we generated new PMAA/PNIPAAm IPN hydrogels with both pH and temperature sensitivities by the interpenetration of the pH-sensitive and temperature-sensitive polymer networks. 

At pH 4.3, there is no significant transition detected around 32°C. Transition temperatures are detected and increase as pH increases. This is because, at low pH, the aggregation of PMAA decreases the mobility of the PNIPAAm network as well as the water uptake of the IPN, resulting in drastically lowering the temperature sensitivity of the IPN hydrogel. However, at higher pH value, the swollen PMAA allows the PNIPAAm to have a higher mobility, which makes the IPN more temperature sensitive. 

Fig. 74. Phase change behavior of pH and temperature-sensitive polymers and hydrogels [452]...

Trank SJ (1988) Design and application of temperature-sensitive hydrogels. Thesis, University of Minnesota, Minnesota... 

Applications of responsive gels in biotechnology have also been examined. For example, Dong and Hoffman proposed the use of temperature sensitive hydrogels for the immobilization of enzymes in bioreactors [110]. Enzyme activity can be turned on and off by causing the gel to swell or shrink when shrunken, the enzyme activity is turned off, since the pores are blocked to the substrate. Different applications are possible for this system besides enhanced bioreactor performance, including bioassays. 

The large contraction change shown by curve 2 is due to polymer dehydration or precipitation induced by complexation between PEO and PMAA. It is evident that the dehydration or precipitation is enhanced by complexation compared to curve 1. Furthermore, curve 2 indicates a reversible contraction/ recovery change, suggesting that complexation and dissociation occur reversibly with temperature changes within the PMAA gel. This drastic contraction change can be applied to temperature sensitive hydrogels as well. 

Explain the potential uses of (i) temperature-sensitive and (ii) pH-sensitive hydrogels in advanced drag delivery. 

Gottlieb R, Kaiser C, Gohs U, Arndt KF (2007) Temperature sensitive hydrogels based on hydroxypropylcellulose by high energy irradiation. Macromol Symp 254 361-369... 

Schmidt T, Monch JI, Arndt KF (2006) Temperature-sensitive hydrogel pattern by electron-beam lithography. Macromol Mater Eng 291(7) 755-761... 

Theiss D, Schmidt T, Arndt KF (2004) Temperature-sensitive poly(vinyl methyl ether) hydrogel beads. Macromol Symp 210 465 174... 

Ruel-Gariepy, E., and Leroux, J. C. (2004), In situ-forming hydrogels—Review of temperature-sensitive systems, Eur. J. Pharm. Biopharm., 58,409-426. 

Grass G, Farra R, Caliceti P, Carenza M, and Grass M. Temperature-sensitive hydrogels Potential therapeutic applications. Am. J. Drug Delivery 2005 3(4) 239-251. 

Some of the temperature-sensitive hydrogels are also pH sensitive. The pH sensitivity of the hydrogels is due to the presence of weakly acidic... 

Caliceti, P. Salmaso, S. Lante, A. Yoshida, M. Katakai, R. Martellini, F. Mei, L.H.I. Carenza, M. Controlled release of biomolecules from temperature-sensitive hydrogels prepared by radiation polymerization. J. Control. Release 2001, 75, 173-181. 

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