This article reports the first hydrogel with the strength and modulus of cartilage in both tension and compression, and the first to exhibit cartilage‐equivalent tensile fatigue strength at 100 000 cycles. These properties are achieved by infiltrating a bacterial cellulose (BC) nanofiber network with a poly(vinyl alcohol) (PVA)–poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid sodium salt) (PAMPS) double network hydrogel. The BC provides tensile strength in a manner analogous to collagen in cartilage, while the PAMPS provides a fixed negative charge and osmotic restoring force similar to the role of aggrecan in cartilage. The hydrogel has the same aggregate modulus and permeability as cartilage, resulting in the same time‐dependent deformation under confined compression. The hydrogel is not cytotoxic, has a coefficient of friction 45% lower than cartilage, and is 4.4 times more wear‐resistant than a PVA hydrogel. The properties of this hydrogel make it an excellent candidate material for replacement of damaged cartilage.

The ability to 3D print lithium ion batteries (LIBs) in an arbitrary geometry would not only allow the battery form factor to be customized to fit a given product design but also facilitate the use of the battery as a structural component. A major hurdle to achieving this goal is the low ionic conductivity of the polymers used for 3D printing. This article reports the development of anode, cathode, and separator materials that enable 3D printing of complete lithium ion batteries with low cost and widely available fused filament fabrication (FFF) 3D printers. Poly(lactic acid) (PLA) was infused with a mixture of ethyl methyl carbonate, propylene carbonate, and LiClO 4 to obtain an ionic conductivity of 0.085 mS cm −1 , a value comparable to that of polymer and hybrid electrolytes. Different electrically conductive (Super P, graphene, multiwall carbon nanotubes) and active (lithium titanate, lithium manganese oxide) materials were blended into PLA to determine the relationships among filler loading, conductivity, charge storage capacity, and printability. Up to 30 vol % of solids could be mixed into PLA without degrading its printability, and an 80:20 ratio of conductive to active material maximized the charge storage capacity. The highest capacity was obtained with lithium titanate and graphene nanoplatelets in the anode, and lithium manganese oxide and multiwall carbon nanotubes in the cathode. We demonstrate the use of these novel materials in a fully 3D printed coin cell, as well as 3D printed wearable electronic devices with integrated batteries.

This article demonstrates a two-step method to 3D print double network hydrogels at room temperature with a low-cost ($300) 3D printer. A first network precursor solution was made 3D printable via extrusion from a nozzle by adding a layered silicate to make it shear-thinning. After printing and UVcuring, objects were soaked in a second network precursor solution and UV-cured again to create interpenetrating networks of poly(2-acrylamido-2-methylpropanesulfonate) and polyacrylamide. By varying the ratio of polyacrylamide to cross-linker, the trade-off between stiffness and maximum elongation of the gel can be tuned to yield a compression strength and elastic modulus of 61.9 and 0.44 MPa, respectively, values that are greater than those reported for bovine cartilage. The maximum compressive (93.5 MPa) and tensile (1.4 MPa) strengths of the gel are twice that of previous 3D printed gels, and the gel does not deform after it is soaked in water. By 3D printing a synthetic meniscus from an X-ray computed tomography image of an anatomical model, we demonstrate the potential to customize hydrogel implants based on 3D images of a patient's anatomy.

This article reports a synthesis that yields 4.4 g of Cu nanowires in 1 h, and a method to coat 22 g of Cu nanowires with Ag within 1 h. Due to the large diameters of Cu nanowires (≈240 nm) produced by this synthesis, a Ag:Cu mol ratio of 0.04 is sufficient to coat the nanowires with ≈3 nm of Ag, and thereby protect them from oxidation. This multigram Cu‐Ag core–shell nanowire production process enabled the production of the first nanowire‐based conductive polymer composite filament for 3D printing. The 3D printing filament has a resistivity of 0.002 Ω cm, >100 times more conductive than commercially available graphene‐based 3D printing filaments. The conductivity of composites containing 5 vol% of 50‐µm‐long Cu‐Ag nanowires is greater than composites containing 22 vol% of 20‐µm‐long Ag nanowires or 10‐µm‐long flakes, indicating that high‐aspect ratio Cu‐Ag nanowires enable the production of highly conductive composites at relatively low volume fractions. The highly conductive filament can support current densities between 2.5 and 4.5 × 105 A m−2 depending on the surface‐to‐volume ratio of the printed trace, and was used to 3D print a conductive coil for wireless power transfer.

The generation of renewable electricity is variable, leading to periodic oversupply. Excess power can be converted to hydrogen via water electrolysis, but the conversion cost is currently too high. One way to decrease the cost of electrolysis is to increase the maximum productivity of electrolyzers. This study investigated how nano-and microstructured porous electrodes could improve the productivity of hydrogen generation in a zero-gap, flow-through alkaline water electrolyzer. Three nickel electrodesfoam, microfiber felt, and nanowire felt-were studied to examine the tradeoff between surface area and pore structure on the performance of alkaline electrolyzers. Although the nanowire felt with the highest surface area initially provided the highest performance, this performance quickly decreased as gas bubbles were trapped within the electrode. The open structure of the foam facilitated bubble removal, but its small surface area limited its maximum performance. The microfiber felt exhibited the best performance because it balanced high surface area with the ability to remove bubbles. The microfiber felt maintained a maximum current density of 25,000 mA cm -2 over 100 hrs without degradation, which corresponds to a hydrogen production rate 12.5-and 50-times greater than conventional proton-exchange membrane and alkaline electrolyzers, respectively.Flow-through alkaline electrolysis with a Ni microfiber felt improved the maximum H 2 production rate by 50 times relative to conventional alkaline electrolyzers. Compared to Ni-Cu nanowires and Ni foam, Ni microfiber felt provided the most surface area for water splitting without blocking the removal of gas bubbles.