In the realm of soft nanotechnology, hydrogel micro‐ and nanoparticles represent a versatile class of responsive materials. Over the last decade, our group has investigated the synthesis and physicochemical properties of a variety of synthetic hydrogel particles. From these efforts, several particle types have emerged with potentially enabling features for biological applications, including nanogels for targeted drug delivery, microlenses for biosensing, and coatings for biomedical devices. For example, core/shell nanogels have been used to encapsulate and deliver small interfering RNA to ovarian cancer cells; nanogels used in this fashion may improve therapeutic outcomes for a variety of macromolecular therapeutics. Microgels arranged as multilayers on implantable biomaterials greatly minimize the host inflammatory response to the material. Furthermore, the triggered release of drugs (i.e., insulin) has been demonstrated from similar assemblies. The goal of this feature article is to highlight developments in the design of responsive microgels and nanogels in the context of our recent efforts and in relation to the community that has grown up around this fascinating class of materials.

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Deformation of 570-nm radius poly(N-isopropylacrylamide-co-acrylic acid) microgels passing through individual 375- to 915-nm radius nanopores in glass has been investigated by the resistive-pulse method. Particle translocation through nanopores of dimensions smaller than the microgel yields electrical signatures reflecting the dynamics of microgel deformation. Translocation rates, and event duration and peak shape, are functions of the conductivities of microgel and electrolyte. Our results demonstrate that nanopore resistive-pulse methods provide new fundamental insights into microgel permeation through porous membranes.

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