Thermoresponse polymer gel

Luo, Q., Mutlu, S., Gianchandani, Y. B., Svec, E, Frdchet, J. M. J. (2003). Monohthic valves for microfluidic chips based on thermoresponsive polymer gels. Electrophoresis, 24, 3694-3702. 

Luo Q, Mutlu S, Gianchandani YB et al (2003) Monolithic valves for microfiuidic chips based on thermoresponsive polymer gels. ELECTROPHORESIS 24 3694-3702. doi 10.1002/... 

Fig. 9 Diffusion of glucose through thermoresponsive polymer gel membranes.

In this section, the volumetric phase transition of the dye-modified, thermoresponsive polymer gel by irradiation of light has been reviewed. Using this principle, the amount of transmitted light can be reduced discontinuously by irradiating any gel made of any polymer that will shrink when heat is used. Furthermore, it is also possible to develop a gel that swells by irradiation of light and increases the intensity of the transmitted light discontinuously. In diis case, it is necessary for the gel to swell discontinuously when light is not irradiated. 

Fig. 10 Water recovery and reuse system using a thermoresponsive polymer gel.

PCR products may be purified by gel extraction from agarose gels, though this is a time-consuming process. The rapid thermal precipitation of amplicons via thermoresponsive polymers incorporated during the PCR process itself represents a clear advantage over established methods for amphcon purification for certain applications. 

The third method of gelation involves alginate gel formation dependent on temperature. An example of this includes control of alginate gel concentration in a specified area when thermoresponsive polymers such as N-isopropylacrylamide and poly(ethylene glycol)-co-poly(e-caprolactone) (PEG-PCL) serve as interpenetrating networks and prevent alginate gelation until certain temperatures are achieved [67]. 

Chemomechanical gels that function with phase transition caused by temperature changes Various pol)maers exhibit reversible phase transition in aqueous solution due to temperature variations. Representative examples include poly(vinyl methyl ether) (PVME) and poly(N-isopropylacrylamide) (PNIPAAm) [16, 17]. Common features of thermoresponsive polymers are the coexistence of hydrophilic and hydro-phobic portions in the same polymer chain. Increased hydrophobic interaction at an elevated temperature causes phase separation to take place. Gels obtained by crosslinking these polymers also show thermo-responsivity. The PNIPAAm gel shows the phase transition at 33°C in pure water. It swells at a temperature below the transition and vice versa (see Fig. 5) [18]. 

Polymer gels with amino acid groups or peptides in their side chains have been synthesized [22,23]. The copol)mier gel between methacryloyl-L-alanine methyl ester (MA-L-AlaOMe) and 2-hydroxypropyl methacrylate (HPMA) shows thermoresponsivity. However, as the HPMA fraction increases, the thermoresponsivity decreased. This gel not only shows thermoresponsivity but also pH responsivity. When the gel is made by irradiating y-rays onto a sequential polypeptide, elastin, also shows thermoresponsivity [24]. These materials consist of biocompatible amino acids and peptides and therefore applications in biorelated areas are possible. 

Thermoineversible gels, 189 Thermoresponsive chromatography, 136-9 Thermoresponsive gels, 68-71 Thermoresponsive polymers, fixation, 185-7 Thermoresponsive surface... 

A thermoresponsive polymer hydrogel can be synthesized by copolymerizing these acrylamide-type monomers and a difunctional monomer such as methylenebisacrylamide. Hirokawa and other researchers studied the temperature dependence of the degree of swelling of a thermoresponsive poly(N-isopropylacrylamide) gel in pure water [18]. It was observed that a discontinuous volumetric phase transition occurred around the LCST of the polymer and the volume change was 8 times. 

An aqueous solution of poly(vinyl methylether), which is one of the thermoresponsive polymers, dehydrates due to the thermal motion of hydrating water around the methoxy groups and exhibits phase transition (see Fig. 3) [19]. This transition is reversible with respeet to the temperature ehanges, and the transition temperature depends on the concentration of salt in the aqueous solution (see Fig. 4). The poly(vinyl methylether) aqueous solution erosslinks by irradiating x-rays or an electron beam and forms a hydrogel. Similar to the aqueous solution, this gel also shows thermoresponsivity. It swells and shrinks depending on temperature. Its volume changes are illustrated in Fig. 5 [20]. 

Hollow silica gels were prepared using PNlPAAm by Liu et al. Rhodamine B was taken as the model drug, it was observed that the LCST of the PNlPAAm was increased to 40.6°C, which indicates a good performance of temperature-dependent phase transition. To further confirm the temperature responsiveness of the system, the release study was carried out at 25°C and 40°C. it was observed that 82.5% of the RHB was released for 12 h at 25°C while 86.5% was released at 40°C in 12 h. Thus, this indicates the prepared microgels achieve thermoresponsive controlled release behavior and were also found to be biocompatible [36]. Some of the applications of thermoresponsive polymers in drug delivery are summarised in Table 20.1. 

There are two main applications of thermoresponsive polymers in tissue engineering [1] as substrates that enable the cell growth and proliferation and [2] as injectable gels. The cells can be well encapsulated with the polymer and then when injected into the body due to change in LCST of the polymer, it forms a physical gel and the cells get encapsulated within the 3D structure of the gel. The in situ formation of cell/scaffold contrast by thermoresponsive systems can be used to deliver growth factors, cells to the desired site [20]. 

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