Abstract
Various natural and synthetic polymers are capable of showing thermoresponsive properties and their hydrogels are finding a wide range of biomedical applications including drug delivery, tissue engineering and wound healing. Thermoresponsive hydrogels use temperature as external stimulus to show sol-gel transition and most of the thermoresponsive polymers can form hydrogels around body temperature. The availability of natural thermoresponsive polymers and multiple preparation methods of synthetic polymers, simple preparation method and high functionality of thermoresponsive hydrogels offer many advantages for developing drug delivery systems based on thermoresponsive hydrogels. In textile field applications of thermoresponsive hydrogels, textile based transdermal therapy is currently being applied using drug loaded thermoresponsive hydrogels. The current review focuses on the preparation, physico-chemical properties and various biomedical applications of thermoresponsive hydrogels based on natural and synthetic polymers and especially, their applications in developing functionalized textiles for transdermal therapies. Finally, future prospects of dual responsive (pH/temperature) hydrogels made by these polymers for textile based transdermal treatments are mentioned in this review.
Highlights
Hydrogels made of hydrophilic components are porous, three-dimensional, interpenetrating, polymeric network containing large amounts of water or biological fluids without losing their structure at physiological temperature and pH [1,2,3]
A thermoresponsive double gel was prepared by incorporating κ-carrageenan and MC mixtures in water and it showed double thermal gel-sol-gel transition upon heating [112]. This system showed a very interesting and reversible thermal behavior as liquid state of the system was found between the low-temperature and high-temperature gel-state and state of the system could be altered by easy temperature tuning [112]. Another injectable thermosensitive hydrogel was prepared from a blend of MC and chitosan (CS) for tissue engineering and it was formed under mild conditions via addition of salts, such as NaCl, Na3 PO4, NaHCO3 and glycerophosphate, without applying organic solvent, high temperature or harsh pH [113]
Thermoresponsive systems based on hydrogels from poly(N-isopropylacrylamide) and its copolymers are subject of extensive research and pNIPAAm based hydrogel materials are useful for developing drug delivery systems, sensors and actuators, separation operations in biotechnology, processing of agricultural products [135]
Summary
Hydrogels made of hydrophilic components are porous, three-dimensional, interpenetrating, polymeric network containing large amounts of water or biological fluids without losing their structure at physiological temperature and pH [1,2,3]. The source, structure, properties and biomedical applications of natural thermoresponsive polymers, including chitosan, cellulose, gelatin and synthetic thermoresponsive polymers like poly(N-isopropylacrylamide) (pNIPAAm), Pluronics® or Poloxamers namely pluronic F127 (PF127), are discussed in this review. Several chemical modifications on the polymeric backbone of such compounds are included in the Polymers 2018, 10, x FOR PEER REVIEW review to discuss and overcome the shortcomings of thermogels with the polymers alone Some other natural such as xyloglucan, dextran, poly(γ-glutamate) elastin elastin like elastin polymers, like polypeptide/oligopeptide and synthetic polymersand such as and polyoxazoline, polypeptide/oligopeptide andpoly(ethylene synthetic polymers such as polyoxazoline, poly(organophosphazenes), poly(organophosphazenes), glycol)/biodegradable polyester copolymers, can form poly(ethylene glycol)/biodegradable polyester copolymers, can form thermoresponsive hydrogels, thermoresponsive hydrogels, which find versatile biomedical applications especially for developing which find versatile biomedical applications especially for developing drug delivery systems drug delivery systems [15].
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