The conversion of various polymer substrates into Laser-Induced Graphene (LIG) with a CO₂ laser in ambient condition is recently emerging as a simple method for obtaining patterned porous graphene conductors, with a myriad of applications in sensing, actuation and energy. In this paper a method is presented for embedding porous LIG (LIG-P) or LIG fibers (LIG-F) into a thin (~50 μm) and soft medical grade polyurethane (MPU) providing excellent conformal adhesion on skin, stretchability and maximum breathability, to boost the development of various unperceivable monitoring systems on skin. The effect of varying laser fluence and geometry of the laser scan process on the LIG micro-nanostructure morphology and on the electrical and electro-mechanical properties of LIG/MPU composites under tensile stretching is investigated. A peculiar and distinct behavior is observed for either LIG-P and LIG-F. Excellent stretchability without permanent impairing of conductive properties is revealed up to 100% strain and retained after hundreds of cycles of stretching tests. A distinct piezoresistive behavior, with GF of 40, opens the way to various potential strain/pressure sensing applications. A novel method based on laser scribing is then introduced for providing Vertical Interconnect Access (VIA) into LIG/MPU conformable epidermal sensors. This simplifies the achievement of stable connections to an external measurement device, as this represents a typical weakness of many epidermal devices so far. Three examples of minimally invasive LIG/MPU epidermal sensing proof of concepts are presented: as electrodes for electromyographic (EMG) recording on limb and as piezoresistive sensors for touch and respiration detection on skin. Long-term wearability and functioning up to several days and under repeated stretching tests is demonstrated.

In the growing field of conformable electronics, tattoo technology has emerged from among the various approaches so farHere, temporary tattoo paper is adopted as unconventional substrate to build up transferable body compliant devices, which establishes a stable and long-lasting interface with the skin. Tattoo-based devices have shown their capabilities in multiple fields, with the main application in human health biomonitoring. Such an approach is advancing to become state-of-the-art, overcoming some limits of existing technologies, as in the case of skin-contact electrodes and sweat analysis. Temporary tattoo has also been adopted in other fields, such asorganic electronics, the development of organic solar cells, and transferable edible transistors. Multiple and complementary fabrication approaches on temporary tattoos have been demonstrated, spanning from traditional vacuum-based deposition methods to various printing technologies. In this review, together with reporting and discussing the main fabrication methods and applications of tattoo technology, we describe the main features of the tattoo substrate. New insights into its material composition and properties are given, discussing the pros and cons in comparison to other approaches adopted in conformable electronics. Together with providing a comprehensive and up to date review of advancements in tattoo technology, this review aims to contribute in a better understanding of the capabilities offered by such a low cost and versatile substrate. This can help in opening up new research for emerging applications, like in the relevant field of sustainable electronics.

The article describes an easy-to-implement and print-ready composition for inkjet printing of magnetic structures, which can be used for security printing, coding, and marking, magnetic device fabrication or creation of micro-antennas.

The fabrication of a fully printed, lead‐free, polymer piezoelectric transducer is presented and the characterization of its structural, dielectric, and ferroelectric properties at different processing stages is demonstrated. The performance of poly(vinylidene fluoride‐trifluoroethylene) transducers with resonance frequency analyses, acoustic power measurements, and pulse‐echo experiments is evaluated. Notably, for the first time for a fully printed transducer, an optimal performance in the medical ultrasound range (1 W cm⁻², which is promising for applications in epidermal and wearable electronics. Overall, the findings provide a strong foundation for future research in the area of flexible ultrasound transducers.