Nonspecific protein adsorption and/or microbial adsorption on biomedical materials adversely affects the efficacy of a range of biomedical systems, from implants and biosensors to nanoparticles. To address this problem, antibiofouling polymers can be coated on biomedical devices or built into nanoparticles to confer protein and/or microbial repellent properties. The current review provides an overview of the range of synthetic polymers currently used to this end and explores their biomedical potential. The most widely-used antifouling polymer, poly(ethylene glycol) (PEG) is reviewed alongside several promising alternatives, including zwitterionic polymers, poly(hydroxyfunctional acrylates), poly(2-oxazoline)s, poly (vinylpyrrolidone), poly(glycerol), peptides and peptoids. For each material, notable applications for both nanomedicine and macroscopic surface coatings are highlighted.

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Efficient nonprecious‐metal oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts are key for the commercial viability of fuel cells, metal–air batteries, and water‐splitting systems. Thus, high‐performance ORR and OER electrocatalysts in acidic electrolytes are needed to support high‐efficiency proton exchange membrane (PEM)‐based systems. Herein, we report a new approach to design and prepare an ultrathin N‐doped holey carbon layer (HCL) on a graphene sheet that exhibits outstanding bifunctional ORR/OER activities in both alkaline and acidic media. The edge sites of HCL are utilized to achieve selective doping of highly active pyridinic‐N. The sandwiched graphene sheet provides mechanical support, stabilizes HCL structure and promotes charge transfer. The synergetic effect of the catalyst structure overcomes the drawbacks of holey graphene approaches. The resulting ORR and OER performances are equal to or better than the top‐ranked electrocatalysts.

Three-dimensional (3D) printing technology has been recognized as an emerging advanced fabrication technology in both industry and academia. Direct ink writing (DIW), a type of 3D printing technology, can build 3D structures through the deposition of custom-made inks, printing devices with complex architectures, excellent mechanical properties and enhanced functionalities. DIW can greatly facilitate the fabrication of miniaturized or flexible electronic components. These components are potentially useful for their applications in advanced wearable devices. This article highlights recent advancements in 3D direct ink written electronic components with an emphasis on their potential applications for wearable devices. The relationship among ink formulations, DIW techniques and printed devices is highlighted. In particular, the DIW-assisted fabrication of key components in wearable electronics, including power generation (nanogenerators), energy storage (e.g. lithium ion batteries) and energy consuming products (e.g. strain sensors) are reviewed in terms of performance metrics and fabrication strategies. Optimized ink preparations, evolving DIW techniques, and device designs can work synergistically to enhance the development of printed advanced wearable devices.

Graphene oxide (GO) is promising for a variety of applications due to its excellent dispersibility and processability. However, current chemical oxidation routes have several drawbacks, including the use of explosive oxidizing agents, residual metal ions contaminations, and the creation of irreparable hole defects on the GO sheet. The electrochemical exfoliation and oxidation of graphite is a potentially greener approach without the need for extensive purification steps. Most reported electrochemical methods employ a single preformed bulk graphite as electrode, which limits their scalability, reproducibility, and degree of oxidation. Herein, we reported a novel mechanically assisted electrochemical method to produce graphene oxide directly from graphite flakes. The electrochemically derived graphene oxide (EGO) shows a good degree of oxidation but with less physical defects than chemically derived graphene oxide (CGO). EGO has good dispersibility in water and various solvents and, in particular, displays better long-term stability in ethanol when compared with CGO. Notably, unlike conventional CGO, EGO can undergo facile thermal conversion at 200 °C in air to conductive thermally processed EGO, which is highly desirable for heat/chemical-sensitive applications.

Although direct ink writing (DIW) is a versatile 3D printing technique, progress in DIW has been constrained by the stringent rheological requirements for printable conductive nanocomposites, particularly at smaller length scales. In this work, we overcome these challenges using an aqueous nanocomposite ink with polydimethylsiloxane (PDMS) submicrobeads and an electrochemically-derived graphene oxide (EGO) nanofiller. This nanocomposite ink possesses a thixotropic, self-supporting viscoelasticity. It can be easily extruded through very small nozzle openings (as small as 50 µm) allowing for the highest resolution PDMS DIW reported to date. With a mild thermal annealing, the DIW-printed device exhibits low resistivity (1660 Ω•cm) at a low percolation threshold of EGO (0.83 vol%) owing to the unique nanocomposite structure of graphene-wrapped elastomeric beads. The nanocomposite ink was used to print wearable, macro-scale strain sensing patches, as well as remarkably small, micron-scale pressure sensors. The large-scale strain sensors have excellent performance over a large working range (up to 40% strain), with high gauge factor (20.3), and fast responsivity (83 ms) while the micron-scale pressure sensors demonstrated high pressure sensitivity (0.31 kPa -1 ) and operating range (0.248-500 kPa). Ultrahigh resolution, multimaterial layer-by-layer deposition allows the engineering of microscale features into the devices, features which can be used to tune the piezoresistive mechanism and degree of piezoresistivity.

Reproducible and in-depth studies of the electrochemical graphite intercalation and oxidation processes were carried out with the use of an electrochemical Tee-cell setup. The electrochemical method allowed simpler and greater controllability over the level of oxidation/functionalization, relative to the commonly employed chemical oxidation approach (e.g. the modified Hummers method). Extensive characterization was carried out to understand the properties of the electrochemically-derived graphite oxide (EGrO) and it was found that the abundance of each functionality is highly dependent on the electrochemical reaction time or by varying the concentration of the electrolyte (perchloric acid) employed.Notably, the amount of oxygen functional groups on EGrO could be as high as 30 wt.%, but the degree of oxidation did not proceed beyond the generation of carbonyl species. The controllable oxidation level of the EGrO makes it an attractive precursor for many applications, such as electronics and nanocomposites.

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