Injectable ultra soft hydrogel with natural nanoclay

Soft hydrogels based on a transient network of wormlike surfactant micelles containing bentonite nanoclay tactoids as physical cross-links were developed. The network was composed of mixed micelles of nontoxic zwitterionic surfactant oleylamidopropyldimethylcarboxybetaine and an anionic surfactant sodium dodecyl sulfate. It was demonstrated that before nanoclay addition the solution has pronounced viscoelastic properties with zero-shear viscosity of 100 Pa s and plateau modulus around 7 Pa, which were attributed to the formation of an entangled micellar network. The solution demonstrated pronounced shear thinning behavior provided by the elongation of wormlike micellar chains in flow direction. Upon addition of non-exfoliated nanoclay particles, the zero-shear viscosity increases by an order of magnitude, while the useful property of shear-induced thinning is retained. Oscillation amplitude tests show that viscoelastic fluid becomes hydrogel upon addition of nanoclay, because elastic response was observed even at large stress amplitudes. This behavior was attributed to the formation of nanoclay- wormlike micelles junctions. Prepared soft hydrogel is a promising candidate for injection applications, because of its self-assembled structure providing pronounced shear-thinning behavior and fast recovery of rheological properties at rest. In this nanocomposite material, nanoclay tactoids strengthen the hydrogels and can serve as reservoirs for the delivery of various substances.