Mechanical properties of PNIPAM based hydrogels: A review

•Mechanical properties of native thermoresponsive PNIPAM hydrogels are discussed.•Strategies to improve the mechanical properties are comprehensively appraised.•These include interpenetrating polymer network, nanocomposite and copolymerization.•Few applications of enhanced strength PNIMPAM based hydrogels are highlighted.•Future areas of research in PNIPAM hydrogel are mentioned.

Materials which adjust their properties in response to environmental factors such as temperature, pH and ionic strength are rapidly evolving and known as smart materials. Hydrogels formed by smart polymers have various applications. Among the smart polymers, thermoresponsive polymer poly(N-isopropylacrylamide)(PNIPAM) is very important because of its well defined structure and property specially its temperature response is closed to human body and can be finetuned as well. Mechanical properties are critical for the performance of stimuli responsive hydrogels in diverse applications. However, native PNIPAM hydrogels are very fragile and hardly useful for any practical purpose. Intense researches have been done in recent decade to enhance the mechanical features of PNIPAM hydrogel. In this review, several strategies including interpenetrating polymer network (IPN), double network (DN), nanocomposite (NC) and slide ring (SR) hydrogels are discussed in the context of PNIPAM hydrogel.