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 catalytic oxidation of carbon monoxide to carbon dioxide by gold nanoclusters loaded onto cerium oxide supports is an important reaction that has been increasingly tailored for use in hydrogen fuel cells. It has been known that there are simultaneous mechanisms that involve coordination of both the dioxygen and carbon monoxide to the gold, as well as one in which the dioxygen is contributed in the form of lattice oxygen while the gold still coordinates the carbon monoxide. The latter has been shown to be the more potent, and it is for this reason that modulating the cerium oxide support is of vital interest. The present work provides compelling evidence that the rate-limiting step in this process is the coordination of the lattice oxygen. Exploratory studies of the control or this step via doping the cerium oxide support are also presented.

Key hurdles for replacing damaged cartilage with an equivalent synthetic construct are the development of a hydrogel with a strength that exceeds that of cartilage and fixation of this hydrogel onto the surface of an articulating joint. This article describes the first hydrogel with a tensile and compressive strength (51 and 98 MPa) that exceeds those of cartilage (40 and 59 MPa), and the first attachment of a hydrogel to a metal backing with a shear strength (2.0 MPa) that exceeds that of cartilage on bone (1.2 MPa). The hydrogel strength is achieved through reinforcement of crystallized polyvinyl alcohol with bacterial cellulose. The high attachment strength is achieved by securing freeze-dried bacterial cellulose to a metal backing with an adhesive and a shape memory alloy clamp prior to infiltration and crystallization of the polyvinyl alcohol. The bacterial cellulose-reinforced polyvinyl alcohol is three times more wear resistant than cartilage over one million cycles and exhibits the same coefficient of friction. These advances in hydrogel strength and attachment enable the creation of a hydrogel-based implant for durable resurfacing of damaged articulating joints.

Inspired by the avoidance of toxic chemical crosslinkers and harsh reaction conditions, this work describes a poly(vinyl alcohol)‐based (PVA) double‐network (DN) hydrogel aimed at maintaining biocompatibility through the combined use of bio‐friendly additives and freezing–thawing cyclic processing for the application of synthetic soft‐polymer implants. This DN hydrogel is studied using techniques that characterize both its chemical and mechanical behavior. A variety of bio‐friendly additives are screened for their effectiveness at improving the toughness of the PVA hydrogel system in monotonic tension. Starch is selected as the best additive for further tensile testing as it brings about a near 30% increase in ultimate tensile strength and maintains ease of processing. This PVA–starch DN sample is then studied for its tensile fatigue properties through cyclic, strain‐controlled testing to develop a fatigue life curve. Though an increase in monotonic tensile strength is observed, the PVA–starch DN hydrogel does not bring about an improvement in the fatigue behavior as compared to the control. Although synthetic hydrogel reinforcement is widely researched, this work presents the first fatigue analysis of its kind and it is intended to serve as a guide for future fatigue studies of reinforced hydrogels.

This work describes a semester-long learning module designed to equip students with the analytical and practical skills necessary to be successful in an interdisciplinary polymer research environment. This learning module combines laboratory experiments involving both synthesis and materials characterization with lectures in polymer theory, and encourages chemists and engineers to learn alongside one another. Specifically, students learn air-free Schlenk technique to facilitate the atom transfer radical polymerization (ATRP) of a series of homo- and copolymers made from n-butyl methacrylate (BMA) and methyl methacrylate (MMA) monomers. Students analyze these polymers using techniques that traverse the interdisciplinary spectrumincluding Gel Permeation Chromatography (GPC), Proton-Nuclear Magnetic Resonance (1H NMR) spectroscopy, Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and Dynamic Mechanical Analysis (DMA)and learn about the theory and mathematics behind the measurements. Ultimately, this hands-on experience in polymer material design bridges the structure–property relationships taught by classical and applied polymer theory.

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Tensile fatigue behavior is commonly overlooked as researchers pursue the toughest hydrogels. This work describes a poly(vinyl alcohol) (PVA) hydrogel prepared through freezing–thawing (FT) processing to achieve varied monotonic strength and toughness. The monotonic tensile responses of relatively strong and weak versions of the hydrogel are studied with cylindrical hole and crack‐like flaws of different sizes to develop an understanding of monotonic strength in the presence of two different, extreme defect types. The monotonic strength of the samples with cylindrical defects is reasonably predicted using nominal stress which accounts for a loss of load‐bearing area, while linear‐elastic fracture mechanics gives a first‐order approximation of the impact of crack‐like flaw size on monotonic strength. A subset of key defected samples are further subjected to cyclic loading and fatigue failure at varying stress amplitude. The cylindrical defect samples outperformed cracked samples in fatigue, and the utilization of four FT cycles instead of two improved both monotonic toughness and fatigue properties. This work represents the first tensile fatigue analysis on defected hydrogel materials, sheds light on the behavior of hydrogels in cyclic loading environments, and evaluates both the monotonic toughness and fatigue behavior of soft materials with and without defects.

The repair of a cartilage lesion with a hydrogel requires a method for long‐term fixation of the hydrogel in the defect site. Attachment of a hydrogel to a base that allows for integration with bone can enable long‐term fixation of the hydrogel, but current methods of forming bonds to hydrogels have less than a tenth of the shear strength of the osteochondral junction. This communication describes a new method, nanofiber‐enhanced sticking (NEST), for bonding a hydrogel to a base with an adhesive shear strength three times larger than the state‐of‐the‐art. An example of NEST is described in which a nanofibrous bacterial cellulose sheet is bonded to a porous base with a hydroxyapatite‐forming cement followed by infiltration of the nanofibrous sheet with hydrogel‐forming polymeric materials. This approach creates a mineralized nanofiber bond that mimics the structure of the osteochondral junction, in which collagen nanofibers extend from cartilage into a mineralized region that anchors cartilage to bone.