Hydrogel Nanocomposites with Independently Tunable Rheology and Mechanics

Abstract

Hydrogels are an attractive class of biomaterials for minimally invasive local drug delivery given their injectability, tunability, high water content, and biocompatibility. Broad applicability though is challenged: relatively modest mechanical properties restrict use to soft tissues, while flow properties necessary for injectability limit implantation to dried, enclosed tissues to minimize material migration during gelation. To address these dual concerns, we designed an injectable nanocomposite hydrogel based on dextran aldehyde and a poly(amido amine) dendrimer doped with phyllosilicate nanoplatelet fillers. Balance of components allows for exfoliation of nanoplatelets, significantly changing macromer solution flow, facilitating injection and manipulation in a wide variety of implantation contexts while enhancing compressive modulus of hydrogels at low loading. Importantly, rheological and mechanical effects were dependent on aspect ratio, with high aspect ratio nanoplatelets having much stronger effects on mechanics and low aspect ratio nanoplatelets having stronger effects on rheology, enabling nearly independent control of rheological and mechanical properties. Nanoplatelets enhanced hydrogel properties at a filler loading substantially lower than that of comparably sized nanoparticles. We present a model to explain the role that aspect ratio plays in control of rheology and mechanics in nanoplatelet-containing hydrogels, with lessons for further nanocomposite hydrogel development. This low-cost biocompatible material may be useful as a drug delivery platform in challenging implantation environments. Keywords: aspect ratio; hydrogel; mechanics; nanocomposite; nanoplatelet; phyllosilicate; rheology