Close monitoring of vital physiological parameters is often key in following the evolution of certain medical conditions (e.g., diabetes, infections, post-operative status or post-traumatic injury). The allocation of trained medical staff and specialized equipment is, therefore, necessary and often translates into a clinical and economic burden on modern healthcare systems. As a growing field, transient electronics may establish fully bioresorbable medical devices capable of remote real-time monitoring of therapeutically relevant parameters. These devices could alert remote medical personnel in case of any anomaly and fully disintegrate in the body without a trace. Unfortunately, the need for a multitude of biodegradable electronic components (power supplies, wires, circuitry) in addition to the electrochemical biosensing interface has halted the arrival of fully bioresorbable electronically active medical devices. In recent years molybdenum (Mo) and tungsten (W) have drawn increasing attention as promising candidates for the fabrication of both energy-powered active (e.g., transistors and integrated circuits) and passive (e.g., resistors and capacitors) biodegradable electronic components. In this review, we discuss the latest Mo and W-based dissolvable devices for potential biomedical applications and how these soluble metals could pave the way towards next-generation fully transient implantable electronic systems.

Nanostructured materials have attracted considerable interest over the last few decades to enhance sensing capabilities thanks to their unique properties and large surface area. In particular, noble metal nanostructures offer several advantages including high stability, non-toxicity and excellent electrochemical behaviour. However, in recent years the great expansion of point-of-care (POC) and wearable systems and the attempt to perform measurements in tiny spaces have also risen the need of increasing sensors miniaturization. Fast constant potential electrodeposition techniques have been proven to be an efficient way to obtain conformal platinum and gold nanostructured layers on macro-electrodes. However, this technique is not effective on micro-electrodes. In this paper, we investigate an alternative one-step deposition technique of platinum nanoflowers on micro-electrodes by linear sweep voltammetry (LSV). The effective deposition of platinum nanoflowers with similar properties to the ones deposited on macro-electrodes is confirmed by morphological analysis and by the similar roughness factor (~200) and capacitance (~18 $\mathsf{\mu }$ F/mm ${}^2$ ). The electrochemical behaviour of the nanostructured layer is then tested in an solid-contact (SC) $L{i}^{+}$ -selective micro-electrode and compared to the case of macro-electrodes. The sensor offers Nernstian calibration with same response time (~15 s) and a one-order of magnitude smaller limit of detection (LOD) ( $2.6\times {10}^{-6}$ ) with respect to the macro-ion-selective sensors (ISE). Finally, sensor reversibility and stability in both wet and dry conditions is proven.

A facile and clean-room compatible approach to Ni nitride (Ni_xN_y) synthesis is proposed, based on a reactive sputtering deposition technique. Ni_xN_y thin films were deposited at different N₂ partial pressures, after which their electrocatalytic properties towards glucose oxidation were investigated. Relative to the bare Ni, Ni_xN_y thin films sputtered at low N₂ partial pressures exhibited a decreased linear range (0–5 mM) and sensitivity. Contrarily, Ni_xN_y thin films sputtered at high N₂ partial pressures displayed an increase in sensitivity of ≈30% in the same linear range (0–10 mM) as for Ni. The Ni_xN_y films showed a clear morphological change from a flat thin film (Ni) to a faceted nanostructure whose characteristic dimensions decreased with increasing N₂.

Ionic conductive hydrogels have emerged as promising candidates for wearable sensors thanks to their stretchability and conductivity. However, it is still challenging to fabricate hydrogels simultaneously with balanced mechanical strength, ionic conductivity, and sensitivity. In this work, PVA/Pullulan/NaCl ionic hydrogels were prepared by soaking frozen-thawed PVA/Pullulan hydrogels in NaCl solutions. Due to the synergy of the semi-interpenetrating network between PVA and pullulan as well as the salting-out effect due to NaCl, the hydrogels exhibited a large tensile strength of 2.72 MPa. The presence of Na+ and Cl− ions endowed the hydrogels with superb ionic conductivity (up to 10.44 S/m). The hydrogel was assembled as a strain sensor, which displayed good sensitivity (up to 5.98) and was utilized for the detection of human joint movements. Additionally, hydrogel sensors can provide efficient information transmission through Morse code. As such, the presented PVA/Pullulan/NaCl hydrogels suggested a promising prospect for the next generation of wearable sensors.