Thermogelling Polymer Hydrogels

Physically crosslinked PNIPAM-based hydrogels were described for the first time by Han et al [51], who synthesized poly(N-isopropylacrylamide-co-acrylic acid) (p(NIPAM-co-AA)) to prepare thermosensitive matrices that were used in follow-up studies for biomedical purposes, particularly as synthetic matrices in refillable bio-artifidal pancreas. Encapsulated Langeran islets showed good viability, and the cellladen artificial matrices showed insulin release [52,53]. Similarly and more recently, p(NIPAM) networks were crosslinked using N, N -methylenebisacrylamide (BIS) and used for bovine serum albumin (BSA) release studies in vitro. The release of the protein 

Name structure Behavior Protein release/application 

Pluronics PEO-PPO-PEO LCST Insulin, urease, inter-leukin-2, several growth factors 

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In this chapter, biodegradable IP systems that can form hydrogels after injection into the body are introduced. Especially, recent progress in biodegradable copolymer systems exhibiting temperature-responsive sol-gel transition (thermogelling polymer) is mainly introduced from the viewpoint of polymer nanoarchitectonics. 

Reverse thermogelling polymers used to act as an effective injectable thermogel usually possess block architectures and a balanced structure of hydrophobicity and hydrophilicity. As temperature increases, the association of the polymers occurs due to increased hydrophobic interactions to show a temperature-sensitive sol-to-gel transition at a critical temperature, namely, lower critical solution temperature (LCST). Typical reverse thermogelling polymers include poly(N-substimted acrylamide)-based block copolymers [7-11], poly(vinyl ether)-based block copolymers, poly(ethylene oxide) (PEO)/poly(propylene oxide) (PPO)-based block copolymers [12-17] and PEG/polyester block copolymers [18-23], The representative structures of each class are shown in Fig. 1. In most cases, PEG was used as a hydrophilic block. All the themogelling hydrogels formed from the amphiphilic block copolymers mentioned above exhibit a sol-gel phase-transition in the physiological conditions in a tunable manner and have been intensively studied in recent years. 

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