Temperature-sensitive hydrogels

Thermo-sensitive polymers are appealing materials for several therapeutic applications, such as in regenerative medicine and in situ drug release. These macromolecules are characterized by the ability to undergo swelling/deswelling processes during temperature change-induced phase transitions. Swelling and shrinking temperatures depend on the specific physicochemical properties, namely salt concentration or pH, of the thermo-sensitive gels as well as the incubation environment. An understanding of the mechanisms underlying the gel-swelling equilibrium and kinetics is necessary for the selection of an appropriate gel in relation to the specific pharmaceutical application. Thermo-sensitive polymers used in medicine include polyacrylamides, polyvinyls, polyethers, polysaccharides, and polyphosphazenes. A few of them have been successfully used as 3-dimentional supports for cell cultivation, allowing for the production of scaffolds with excellent biologic properties for application in regenerative medicine. Stem cells that can undergo specific differentiation under the appropriate stimulation have also been cultivated. The ability of drug/polymer solutions to turn into gels at physiologic temperature has been exploited for local drug delivery. The prolonged in situ presence and slow drug release enhances the therapeutic performance of antibiotics used in urogenital pathologies, anti-inflammatory agents, and anticancer drugs. The reduced toxicity as well as lower fluctuations in peak-to-trough drug concentrations make these systems superior to traditional gels. Thermo-sensitive hydrogels have also been demonstrated to be interesting formulations for the delivery of biotechnological drugs. Proteins and oligonucleotides can be loaded under mild conditions, stabilized, and released at a controlled rate. Finally, thermo-reversible polymers have been investigated for protein conjugation to enhance the physicochemical, biologic, immunologic, and pharmacokinetic properties of biotechnological products.