Significant enhancement of elasticity in alginate-clay nanocomposite hydrogels with PEO-PPO-PEO copolymers

The mechanical properties of a new type of nanocomposite gel, consisting of varying concentrations of the biopolymer alginate and the synthetic clay Laponite^®, together with the temperature-sensitive copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO, trade name Pluronic^® F127), are reported. These “ALP” gels (alginate-Laponite^®-Pluronic^®) were prepared and studied using rheology. Gels with multiple networks and gelation mechanisms have been explored as one strategy to strengthen and stiffen conventional hydrogels, which usually consist of a single polymer network. This work shows that the ALP gels exhibit significantly higher storage and loss modulus (G′, G″) values than gels composed of only alginate and Laponite^®. Moreover, the interaction between the components appears to be synergistic; that is, the resulting multicomponent hydrogels are much more elastic than the additive effects of individual components. For example, the G′ of one series of the nanocomposite gels containing F127 Pluronic^® experiences two orders of magnitude enhancement compared to its respective control containing only alginate and Laponite^®. Furthermore, the ALP gels show a 20-40x enhancement in storage modulus, with values as high as 10,000–20,000 Pa, over the 30–55 °C temperature range. The large degree of enhancement in the storage modulus of the ALP gels with addition of Pluronic^® is quite remarkable, compared to alginate-Laponite^® gels on their own at comparable concentrations and temperatures, which form relatively weak gels. These results provide a simple strategy for significantly increasing the mechanical properties of polymer hydrogels used in biomaterials applications.