Thermosensitive drug release

Alternatively, this type of thermosensitive microcapsule can be prepared even with already established pharmaceutical ingredients. As is well known, hydro-xypropyl cellulose (HPC), the commonly used binder and coating substrate (Table 1), has a lower critical solution temperature (LCST) around 44° C, and its water solubility drastically changes across the LCST. Negatively thermosensitive drug release microcapsules... 

Fig. 7 Particle exhibiting negatively thermosensitive drug release.

Ichikawa, H. Fukumori, Y. New applications of acrylic polymers for thermosensitive drug release. STP Pharma 1997, 7 (6), 529-545. 

Shin, Y, Chang, J.H., Liu, J., WiUiford, R., Shin, Y, and Exarhos, G.J. 2001. Hybrid nanogels for sustainable positive thermosensitive drug release. J. Control. Release 73 1—6. 

Figure 15 Mechanisms of drug release from thermosensitive monolithic devices.

Controlled-release technology based on the external temperature-activated release can find application in diverse industrial fields. In the pharmaceutical area, for example, the deviation of the body temperature from the normal temperature (37°C) in the physiological presence of the pathogens or pyrogens can be utilized as a useful stimulus that induces the release of the therapeutic agents from a thermosensitive controlled-release system. Physically controlled temperature using a heat source such as the microwaves from outside the body can also be used for temperature-activated antitumor drug release combined with the local hyperthermic treatment of cancer. 

The membranes of the thermosensitive controlled-release microcapsules were constructed by a random mixing Aquacoat (Table 1) with the latex particles having poly(EA/MMA/2-hydroxyethyl methacrylate) core and poly(A-isopropylacrylamide (NIPAAm)) shell. This is an example where the membrane has the random two-phase structure as shown in Fig. 5. The microcapsules exhibited a thermosensitive release of water-soluble drug. The mechanism is explained in Fig. 6. When the temperature was changed in a stepwise manner between 30 and 50°C, the microcapsules showed an on-off pulsatile release. This on-off response was reversible. 

Jeong B, Bae YH, Kim SW. Drug release from hiodegradahle injectable thermosensitive hydrogel of PEG-PLGA-PEG triblock copolymers. J Contr Rel 2000 63 155-163. 

In vitro cytotoxicity studies with drug-loaded micelles have also shown greater cytotoxicity above the LCST, resulting from thermally induced drug release. These results suggest that combination therapy can be implemented, using both thermosensitive systems and local hyperthermic treatment of tumors, primarily at 42°C. The coupled treatment may prove to be more... 

Despite successful results from in vitro studies, however, the clinical applications of systems that are based on polyNlPAAm may be limited, becanse poly-NIPAAm is nondegradable and insoluble. In addition, a major problem of polyNIPAAm-based drug deUvery systems is that thermal treatment is required for controlled destabilization of the micelles and concurrent drug release, which is not always feasible in clinical situations. Therefore, to overcome the disadvantages of polyNIPAAm, controlled biodegradable systems that use polyester block copolymers as thermosensitive polymers have been investigated. 

Tokuyama, H. and Y. Kato, Preparation of thermosensitive polymeric organogels and their drug release behaviors. European Polymer Journal, 2010.46(2) 277-282. 

Zhang, J. Misra, R.D.K. 2007, Magnetic drug-targeting carrier encapsulated with thermosensitive smart polymer Core-shell nanoparticle carrier and drug release response , Acta Biomaterialia, vol. 3, no. 6, pp. 838-850. 

Wang, Q., Y. Zhao, et al. (2007). Thermosensitive phase behavior and drug release of in situ gelable poly(N-isopropylacrylamide-co-acrylamide) microgels. Colloid Polymer Science 285(5) 515-521. 

Prabaharan, M. and Mano, J.F. (2007) A novel pH and thermosensitive N,0-carboxymethylchitosan-graft-poly(N-isopropylacrylamide) hydrogel for drug release. e-Polymers, 043,1-14. 

Keywords Thermosensitive, Composite Hydrogel, Degradation, Pluronic, Drug Release. 

Jeong, B., Bae, Y.H., Kim, S.W. Drug release from biodegradable injectable thermosensitive hydrogel of peg-plga-peg triblock copolymers. Journal of Controlled Release 63,155-163 (2000)... 

Thermosensitive liposomes are made from phospholipids whose membrane undergoes the gel-to-liquid crystalline phase transition a few degrees above physiological temperature. Increasing the temperature of a mmor s cells using an external source may induce drug release from thermosensitive liposomes at the tumor site [17,18], It has been recently shown that when certain copolymers incorporate in liposome bilayers, the vesicles become thermosensitive and the tumor targeting is enhanced upon induction of hyperthermia [19],... 

NIR-Controllable Drug Release Based on Thermosensitive Pol5miers... 

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