Materials with switchable mechanical properties are widespread in living organisms and endow many species with traits that are essential for their survival. Many of the mechanically morphing materials systems found in nature are based on hierarchical structures, which are the basis for mechanical robustness and often also the key to responsive behavior. Many “operating principles” involve cascades of events that translate cues from the environment into changes of the overall structure and/or the connectivity of the constituting building blocks at various levels. These concepts permit dramatic property variations without significant compositional changes. Inspired by the function and the growing understanding of the operating principles at play in biological materials with the capability to change their mechanical properties, significant efforts have been made toward mimicking such architectures and functions in artificial materials. Research in this domain has rapidly grown in the last two decades and afforded many examples of bioinspired materials that are able to reversibly alter their stiffness, shape, porosity, density, or hardness upon remote stimulation. This review summarizes the state of research in this field.

We report a simple temperature-responsive bioconjugate system comprising superfolder green fluorescent protein (sfGFP) decorated with poly[(oligo ethylene glycol) methyl ether methacrylate] (PEGMA) polymers. We used amber suppression to site-specifically incorporate the non-canonical azide-functional amino acid p-azidophenylalanine (pAzF) into sfGFP at different positions. The azide moiety on modified sfGFP was then coupled using copper-catalyzed “click” chemistry with the alkyne terminus of a PEGMA synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. The protein in the resulting bioconjugate was found to remain functionally active (i.e., fluorescent) after conjugation. Turbidity measurements revealed that the point of attachment of the polymer onto the protein scaffold has an impact on the thermoresponsive behavior of the resultant bioconjugate. Furthermore, small-angle X-ray scattering analysis showed the wrapping of the polymer around the protein in a temperature-dependent fashion. Our work demonstrates that standard genetic manipulation combined with an expanded genetic code provides an easy way to construct functional hybrid biomaterials where the location of the conjugation site on the protein plays an important role in determining material properties. We anticipate that our approach could be generalized for the synthesis of complex functional materials with precisely defined domain orientation, connectivity, and composition.

The potential control over monomer sequence in the ring-opening metathesis polymerization of functional norbornenes is explored based on the difference in reactivity of endo and exo isomers. This kinetic approach allows the rapid consumption of the exo-norbornene and insertion onto the growing poly(norbornene) chain within a narrow region of the overall polymer chain, whilst maintaining a homogeneous backbone. We herein demonstrate that this can be achieved using a range of functional monomers easily derived from commercially available precursors while their polymerization is carried out in a controlled manner.

L-Proline functionalized PMMA nanogels with a range of catalyst functionalization (0.5–15 wt%) and cross-linking densities (0–50 wt%) were prepared via emulsion polymerization. The catalyst efficiency in water was investigated using a model asymmetric aldol reaction and an unprecedented reduction in catalyst loading, whilst maintaining high catalytic activity, is reported. In these reactions, a marked effect on selectivity was observed and determined to be dependent on the hydrophobicity of the nanogel particles. Furthermore, the effect of increasing cross-linking density on the catalytic efficiency of these particles (and their core–shell analogues) was explored and a significant reduction in activity was observed.