Elasticity, one of the most important properties of a soft material, is difficult to quantify in polymer networks because of the presence of topological molecular defects in these materials. Furthermore, the impact of these defects on bulk elasticity is unknown. We used rheology, disassembly spectrometry, and simulations to measure the shear elastic modulus and count the numbers of topological "loop" defects of various order in a series of polymer hydrogels, and then used these data to evaluate the classical phantom and affine network theories of elasticity. The results led to a real elastic network theory (RENT) that describes how loop defects affect bulk elasticity. Given knowledge of the loop fractions, RENT provides predictions of the shear elastic modulus that are consistent with experimental observations.

Efficient, one-pot preparation of synthetically challenging, high molecular weight (MW), narrowly dispersed brush block copolymers and random copolymers in high conversions was achieved by ring-opening metathesis (co)polymerization (ROMP) of various macromonomers (MMs) using the highly active, fast-initiating ruthenium olefin metathesis catalyst (H2IMes)(pyr)2(Cl)2RuCHPh. A series of random and block copolymers were prepared from a pair of MMs containing polylactide (PLA) and poly(n-butyl acrylate) (PnBA) side chains at similar MWs. Their self-assembly in the melt state was studied by small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). In brush random copolymers containing approximately equal volume fractions of PLA and PnBA, the side chains segregate into lamellae with domain spacing of 14 nm as measured by SAXS, which was in good agreement with the lamellar thickness measured by AFM. The domain spacings and order−disorder transition temperatures of brush random copolymers were insensitive to the backbone length. In contrast, brush block copolymers containing approximately equal volume fractions of these MMs self-assembled into highly ordered lamellae with domain spacing over 100 nm. Their assemblies suggested that the brush block copolymer backbone adopted an extended conformation in the ordered state.

Internal hemorrhaging is a leading cause of death after traumatic injury on the battlefield. Although several surgical approaches such as the use of fibrin glue and tissue adhesive have been commercialized to achieve hemostasis, these approaches are difficult to employ on the battlefield and cannot be used for incompressible wounds. Here, we present shear-thinning nanocomposite hydrogels composed of synthetic silicate nanoplatelets and gelatin as injectable hemostatic agents. These materials are demonstrated to decrease in vitro blood clotting times by 77%, and to form stable clot-gel systems. In vivo tests indicated that the nanocomposites are biocompatible and capable of promoting hemostasis in an otherwise lethal liver laceration. The combination of injectability, rapid mechanical recovery, physiological stability, and the ability to promote coagulation result in a hemostat for treating incompressible wounds in out-of-hospital, emergency conditions.

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