Thermo-sensitive polymers

YH Bae, T Okano, R Hsu, SW Kim. Thermo sensitive polymers as on-off switches for drug release. Makromol Chem Rapid Commun 8 581-483, 1987. 

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. 

Polymers of 4,5-dihydrooxazole have been studied for some time, and copolymers have been prepared for such uses as adhesives and coatings. A thermo-sensitive polymer, prepared by copolymerization of 2-isopropyl-4,5-dihydrooxazole and ethylene glycol dimethylacrylate, was developed for bioapplications <92CL1643>. The first polymers of 2,3-dihydrooxazoles were reported <85JHC417>. 

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. 

More complex pattern can be written by electron beam lithography. This is shown on example of the thermo-sensitive polymer PVME deposited on a silicon substrate in Fig. 18. The patterns attached to the substrate show the same sensitivity as bulk polymer networks. 

It is well known that membranes of various kinds of phospholipids undergo phase transitions, such as a gel-to-liquid crystalline transition and a lamellar-to-hexagonal transition. These phase transitions have been used for the design of stimuli-sensitive liposomes. The, temperature sensitization of liposomes has been attempted using thermo-sensitive polymers that exhibit a lower critical solution temperature (CST). Attachment of these polymers to liposomes could give temperature-sensitive functionalities to the liposomes. ... 

Chemical structure of thermo-sensitive polymer poly(N-isopropyl acrylamide), known as NIPAAm. 

Demonstration of a thermo-sensitive polymer below and above its LCST. Below LCST, the polymer is hydrophilic and remains in solution form. As temperature is increased to above its LCST, the polymer becomes insoluble and collapses to form a gel. 

Chemical structure of thermo-sensitive polymer poly(N-isopropyl acrylamide-co-hydroxyethyl methacrylate acrylate), or poly(NIPAAm-co-HEMA-acrylate). By the copolymerization of HEMA-acrylate, a hydrophobic monomer, the LCST of the polymer decreases. 

Chemical structure of chitosan, a natural thermo-sensitive polymer. 

Makromolekulare Chemie, Rapid Communications 8, No. 10, Oct. 1987, p.481-5 THERMO-SENSITIVE POLYMERS AS ON-OFF SWITCHES FOR DRUG RELEASE... 

In this study, pH/thermo-sensitive polymer beads were prepared using statistical terpolymers of NIPAAm, BMA and AA and investigated for oral delivery of polypeptide drugs. Loading efficiency into the beads was studied as a function of M. 

SHI 95] Shiroya T., Yasui M., Fujimoto K. et al, Control of enzymatic activity using thermo sensitive polymers , Colloids and Surfaces B Biointer faces, vol. 4, pp. 275-285, 1995. 

Rastan, A. J., et al. (2010). EacUitated anastomosis using a reverse thermo-sensitive polymer for temporary coronary occlusion in off-pump minimally invasive direct coronary artery bypass surgery. Interactive Cardiovascular and Thoracic Surgery, 11(5), 532-536. 

Uyama, H. and Kobayashi, S. (1992) A novel thermo-sensitive polymer. Poly(2-/so-propyl-2-oxazoline), Chem Lett, 1643-1646, doi 10.1246/cl.l992.1643. 

Purushotham and Ramanujan (2010) presented a case study in which iron oxide (Fej04) mNPs were coated with a thermo-sensitive polymer, PNIPAM, and used for simultaneous magnetic hyperthermia and controlled... 

S.A. Deshmukh, S.K. Sankaranarayanan, D.C. Mancini, Vibrational spectra of proximal water in a thermo-sensitive polymer undergoing conformational transition across the lower critical solution temperature. J. Phys. Chem. B 116(18), 5501-5515 (2012)... 

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