This work focused on the synthesis and aqueous self‐assembly of a series of novel hyperbranched star copolymers with a hyperbranched poly[3‐ethyl‐3‐(hydroxymethyl)oxetane] (HBPO) core and many linear poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA) arms. The copolymers can synchronously form unimolecular micelles (around 10 nm) and large multimolecular micelles (around 100 nm) in water at room temperature. TEM measurements have provided direct evidence that the large micelles are a kind of multimicelle aggregates (MMAs) with the basic building units of unimolecular micelles. It is the first demonstration of the self‐assembly mechanism for the large multimolecular micelles generated from the solution self‐assembly of hyperbranched copolymers.magnified image

Highly resilient synthetic hydrogels were synthesized by using the efficient thiol-norbornene chemistry to cross-link hydrophilic poly(ethylene glycol) (PEG) and hydrophobic polydimethylsiloxane (PDMS) polymer chains. The swelling and mechanical properties of the hydrogels were well-controlled by the relative amounts of PEG and PDMS. In addition, the mechanical energy storage efficiency (resilience) was more than 97% at strains up to 300%. This is comparable with one of the most resilient materials known: natural resilin, an elastic protein found in many insects, such as in the tendons of fleas and the wings of dragonflies. The high resilience of these hydrogels can be attributed to the well-defined network structure provided by the versatile chemistry, low cross-link density, and lack of secondary structure in the polymer chains.

Cyclic poly(5-hydroxy-1-cyclooctene) (PACOE) was synthesized by ring-expansion metathesis polymerization (REMP), and thiol-ene chemistry was used to cross-link the internal double bonds in the PACOE backbone. This created a novel network material (gels formed from cyclic polymers) with unique structural units, where the cyclic PACOE main chains, which serve as secondary topological cross-linkages, were connected by primary intermolecular chemical cross-linkages. The resulting properties were notably different from those of traditional chemically cross-linked linear PACOE gels, whose gel fraction (GF) and modulus (G) increased while the swelling ratio (Q) decreased with increasing initial polymer concentration in the gel precursor solution (C(0)). For the gels formed from cyclic polymers, however, the GF, Q, and G all simultaneously increased as C(0) increased at the higher range. Furthermore, at the same preparation state (same C(0)), the swelling ability and the maximum strain at break of the gels formed from cyclic polymers were always greater than those of the gels formed from linear polymers, and these differences became more pronounced as C(0) increased.

Poly(ethylene glycol) (PEG)/polydimethylsiloxane (PDMS) hydrogels were synthesized by cross-linking norbornene end-functionalized polymers with a tetrafunctional thiol using thiol−norbornene chemistry. The swelling capacity and mechanical properties, including the Young's modulus (E) and fracture toughness (G c ), of the hydrogels were characterized and quantified as a function of the volume fractions of PEG and PDMS. E and G c increased simultaneously with the volume fraction of PDMS. The moduli of the hydrogels were quantitatively described and predicted as a function of the volume fraction ratio of PEG to PDMS using the Voigt and Reuss models. The fracture toughness was well described by the Lake−Thomas theory at low volume fractions of PDMS. As the volume fraction of PDMS increased, PDMS not only controlled the swelling capacity of the hydrogels but also contributed to hydrogel toughness.

In this study we investigated the mechanical properties of composite hydrogels based on a polyacrylamide (PAAm) matrix with embedded temperature sensitive poly(N-isopropylacrylamide) (PNiPAM) microgels. We analysed the mechanical properties of the composite material with tensile tests, shear and cavitation rheology. The results of the different experiments displayed an enhancement of mechanical stability with increasing concentration of incorporated microgels. The improved stability is related to an increase of physical cross-linking points due to the incorporation of the microgels. The incorporation of temperature responsive microgel particles introduces temperature sensitive mechanical behaviour of the composite hydrogels. The collapse of the microgels inside the polyacrylamide matrix leads to a change of the volume of the filler particles as well as to a change from a soft filler to a hard filler. The influence of the hard particles on the mechanical stability of the matrix is much stronger which leads to materials with enhanced mechanical properties at high temperatures.

The anisotropic mechanical properties of bovine eye lenses were measured using cavitation rheology over a range of length scales. The technique involves inducing a cavity at the tip of a syringe needle in different regions of the lens. Effective Young's moduli of the nucleus and cortex of the lens were determined, as approximately 11.8 and 0.8 kPa, respectively, on macroscopic length scales. We also measured the mechanical properties of the lens on the length scale of a single cell, suggesting that the stiffness significantly decreased from that in the bulk measurements for both the nucleus and cortex. In addition, during the growth of the cavity anisotropic propagation in the cortex was observed, while in the nucleus, the propagation was isotropic. We further explored the elasticity of the cavity deformation, showing both elastic and inelastic deformation occurred in the nucleus with equal contributions while deformation in the cortex was elastic and reversible.

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