Tissue engineering PNIPAM

Certain Af-substituted acrylamide polymers exhibit phase separation characteristics with associated changes in their properties upon heating above a certain lower critical solution temperature (LCST) [38 0]. Polymers based on Al-isopropyl acrylamide (NIPAM) are the best-known examples. The homopolymer has an LCST of 32°C in aqueous solution [41]. NIPAM can also be polymerized with a wide variety of comonomers, and with the appropriate choice of comonomer, the LCST can be controlled to near physiological temperatures [42,43]. Poly(Af-isopropylacrylamide) (PNIPAM) polymers have therefore recently been investigated for use in drug delivery [44,45], biomolecule separation [46], and tissue engineering [47] applications. 

The most widely investigated temperature-responsive biomedical polymer is poly(A-isopropyl acrylamide) (pNIPAM). This polymer is the focus of Chapter 1 in this book, and therefore it will not be discussed in depth here. However, pNIPAM has been paired with polyampholyte copolymers and applied to nanoparticle separations (Das et al., 2008), drug delivery (Bradley, Liu, Keddie, Vincent, Burnett, 2009 Bradley, Vincent, Burnett, 2009), and tissue engineering applications (Xu et al., 2008). In a related system, latridi et al. (2011) also used the LCST-responsive properties of polyethylene glycol methacrylate (PEGMA) copolymerized with methac-rylic acid and 2-(diethylamino) ethyl methacrylate in a temperature- and pH-sensitive doxorubicin drug delivery system. However, the primary focus of this study was to demonstrate the pH-dependent release properties as discussed earlier. 

Armes et al. [58] synthesized, via ATRP, biocompatible, thermoresponsive ABA triblock copolymers in which the onter A blocks are comprised of PNIPAm and the central B block is poly(2-methacryloyloxyethyl phosphorylcholine). This novel system is soluble in dilnte aqueous solution but forms free-standing physical gels at 37 °C due to hydro-phobic associations of the PNIPAm segments. The gelation process is reversible and shows potential applications in drug delivery and tissue engineering. 

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