Ultrasoft, highly deformable microgels.

Microgels are colloidally stable, hydrogel microparticles that have previously been used in a range of (soft) material applications due to their tunable mechanical and chemical properties. Most commonly, thermo and pH-responsive poly(N-isopropylacrylamide) (pNIPAm) microgels can be fabricated by precipitation polymerization in the presence of the co-monomer acrylic acid (AAc). Traditionally pNIPAm microgels are synthesized in the presence of a crosslinking agent, such as N,N'-methylenebisacrylamide (BIS), however, microgels can also be synthesized under 'crosslinker free' conditions.

Tunable swelling and rolling of microgel membranes.

The tunable swelling and rolling of films assembled via layer-by-layer (LbL) methods from poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAm-co-AAc) microgels and poly(ethylenimine) (PEI) have been systematically studied. Microgel/PEI films assembled at pH 7.4 display a high degree of in-plane swelling at low pH that dramatically increases the film area and drives self-delamination from the substrate to form a free-standing film.

Microgel film dynamics modulate cell adhesion behavior.

A material's mechanical properties greatly control cell behavior at the cell–substrate interface. In this work, we demonstrate that microgel multilayers have unique elastic and viscoelastic-like properties that can be modulated to produce morphological changes in fibroblasts cultured on the film. Protein adsorption is also examined and the data are contrasted with the number of cells adhered.

Plastic deformation, wrinkling, and recovery in microgel multilayers.

Microgel multi-layer films assembled from anionic particles and linear polycation were prepared on elastomeric substrates and their self-healing properties studied. Dried films were imaged during mechanical deformation and were determined to undergo plastic deformation in response to linear strain, leading to film buckling upon strain relaxation. Hydration leads to rapid reorganization of the film building blocks, permitting recovery of the film to the undamaged state.

Dynamic materials from microgel multilayers.

Multilayer coatings made from hydrogel microparticles (microgels) are conceptually very simple materials: thin films composed of microgel building blocks held together by polyelectrolyte "glue". However, the apparent simplicity of their fabrication and structure belies extremely complex properties, including those of "dynamic" coatings that display rapid self-healing behavior in the presence of solvent. This contribution covers our work with these materials and highlights some of the key findings regarding damage mechanisms, healing processes, film structure/composition, and how the variation of fabrication parameters can impact self-healing behavior.