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Abstract An aqueous emulsion of conducting polymer is commonly applied on a substrate to form a coating after drying. The coating, however, disintegrates in water. This paper reports a coating prepared using a mixture of two emulsions: an aqueous emulsion of conducting polymer, and an aqueous emulsion of hydrophobic and rubbery chains copolymerized with silane coupling agents. When applied on a substrate and dried, particles of the mixed emulsion merge into a continuous film. While the conducting polymer forms percolated nanocrystals, the silane groups crosslink the rubbery chains and interlink the rubbery chains to the substrate. The percolated nanocrystals make the coating highly conductive. The covalent network of hydrophobic polymer chains stabilizes the coating in water. The high conductivity and stability in water may enable broad applications. 

We mix the amphiphilic monomer acrylic acid, the hydrophobic polymer poly(methyl methacrylate), and water. We report various morphologies, which we interpret by invoking that the amphiphilic monomer can bridge the hydrophobic polymer and water. 

Hydrogels are being developed to bear loads. Applications include artificial tendons and muscles, which require high strength to bear loads and low hysteresis to reduce energy loss. However, simultaneously achieving high strength and low hysteresis has been challenging. This challenge is met here by synthesizing hydrogels of arrested phase separation. Such a hydrogel has interpenetrating hydrophilic and hydrophobic networks, which separate into a water-rich phase and a water-poor phase. The two phases arrest at the microscale. The soft hydrophilic phase deconcentrates stress in the strong hydrophobic phase, leading to high strength. The two phases are elastic and adhere through topological entanglements, leading to low hysteresis. For example, a hydrogel of 76 weight % water, made of poly(ethyl acrylate) and poly(acrylic acid), achieves a tensile strength of 6.9 megapascals and a hysteresis of 16.6%. This combination of properties has not been realized among previously existing hydrogels. 

Electronic devicesforrecording neuralactivityinthe nervoussyste m needto bescalableacrosslargespatialandte mporalscales whilealso providing millisecondandsingle-cellspatiote mporalresolution. H o w e v e r, e xi s ti n g hi g h- r e s ol u ti o n n e u r al r e c o r di n g d e vi c e s c a n n o t achievesi multaneousscalability on bothspatialandte mporallevels due toatrade-offbetweensensordensityand mechanicalflexibility. Here weintroduceathree-di mensional(3D)stackingi mplantableelectronic platfor m,basedonperfluorinateddielectricelasto mersandtissue-levelsoft multilayerelectrodes,thatenablesspatiote mporallyscalablesingle-cell neuralelectrophysiologyinthenervoussyste m. Ourelasto mersexhibit stable dielectric perfor mancefor overayearin physiologicalsolutions andare10,000ti messofterthanconventional plastic dielectrics. By leveragingthese uniquecharacteristics we developthe packaging of lithographednano metre-thickelectrodearraysina3Dconfiguration with across-sectionaldensityof7.6electrodesper100μ m2.Theresulting3D integrated multilayersoftelectrodearrayretainstissue-levelflexibility, reducingchronici m muneresponsesin mouse neuraltissues,and de monstratestheabilitytoreliablytrackelectricalactivityinthe mouse brain orspinalcord over months without disruptingani mal behaviour. 

Biological tissues, such as cartilage, tendon, ligament, skin, and plant cell wall, simultaneously achieve high water content and high load-bearing capacity. The high water content enables the transport of nutrients and wastes, and the high load-bearing capacity provides structural support for the organisms. These functions are achieved through nanostructures. This biological fact has inspired synthetic mimics, but simultaneously achieving both functions has been challenging. The main difficulty is to construct nanostructures of high load-bearing capacity, characterized by multiple properties, including elastic modulus, strength, toughness, and fatigue threshold. Here we develop a process that self-assembles a nanocomposite using a hydrogel-forming polymer and a glass-forming polymer. The process separates the polymers into a hydrogel phase and a glass phase. The two phases arrest at the nanoscale and are bicontinuous. Submerged in water, the nanocomposite maintains the structure and resists further swelling. We demonstrate the process using commercial polymers, achieving high water content, as well as load-bearing capacity comparable to that of polyethylene. During the process, a rubbery stage exists, enabling us to fabricate objects of complex shapes and fine features. We conduct further experiments to discuss likely molecular origins of arrested phase separation, swell resistance, and ductility. Potential applications of the nanocomposites include artificial tissues, high-pressure filters, low-friction coatings, and solid electrolytes. 

Longer and stronger; stiff but not brittle Hydrogels are highly water-swollen, cross-linked polymers. Although they can be highly deformed, they tend to be weak, and methods to strengthen or toughen them tend to reduce stretchability. Two papers now report strategies to create tough but deformable hydrogels (see the Perspective by Bosnjak and Silberstein). Wanget al. introduced a toughening mechanism by storing releasable extra chain length in the stiff part of a double-network hydrogel. A high applied force triggered the opening of cycling strands that were only activated at high chain extension. Kimet al. synthesized acrylamide gels in which dense entanglements could be achieved by using unusually low amounts of water, cross-linker, and initiator during the synthesis. This approach improves the mechanical strength in solid form while also improving the wear resistance once swollen as a hydrogel. —MSL 

"This paper studies the lap shear, in which both the adhesive and adherends are elastic, but the adhesive is much softer than the adherends. The shear lag model identifies a length, called the shear lag length Ls. The energy release rate of a debond crack is affected by the elasticity of both the adhesive and adherends. Their relative importance is characterized by the ratio of the length of the remaining joint, L, to the shear lag length, Ls. In the short-joint limit, L/Ls→0, the adherends do not deform, and the elasticity of the adhesive gives the energy release rate. In the long-joint limit, L/Ls→∞, the interior of the adhesive does not deform, and the elasticity of the adherends gives the energy release rate. The shear lag model gives an approximate expression of the energy release rate for all values of L/Ls. This expression is in excellent agreement with the results obtained by finite element calculations, so long as the crack is long compared to the thickness of the adhesive."