Thin-film electronic devices can be integrated with skin for health monitoring and/or for interfacing with machines. Minimal invasiveness is highly desirable when applying wearable electronics directly onto human skin. However, manufacturing such on-skin electronics on planar substrates results in limited gas permeability. Therefore, it is necessary to systematically investigate their long-term physiological and psychological effects. As a demonstration of substrate-free electronics, here we show the successful fabrication of inflammation-free, highly gas-permeable, ultrathin, lightweight and stretchable sensors that can be directly laminated onto human skin for long periods of time, realized with a conductive nanomesh structure. A one-week skin patch test revealed that the risk of inflammation caused by on-skin sensors can be significantly suppressed by using the nanomesh sensors. Furthermore, a wireless system that can detect touch, temperature and pressure is successfully demonstrated using a nanomesh with excellent mechanical durability. In addition, electromyogram recordings were successfully taken with minimal discomfort to the user.

The prolonged and continuous monitoring of mechanoacoustic heart signals is essential for the early diagnosis of cardiovascular diseases. These bodily acoustics have low intensity and low frequency, and measuring them continuously for long periods requires ultrasensitive, lightweight, gas-permeable mechanoacoustic sensors. Here, we present an all-nanofiber mechanoacoustic sensor, which exhibits a sensitivity as high as 10,050.6 mV Pa−1 in the low-frequency region (<500 Hz). The high sensitivity is achieved by the use of durable and ultrathin (2.5 µm) nanofiber electrode layers enabling a large vibration of the sensor during the application of sound waves. The sensor is ultralightweight, and the overall weight is as small as 5 mg or less. The devices are mechanically robust against bending, and show no degradation in performance even after 1,000-cycle bending. Finally, we demonstrate a continuous long-term (10 h) measurement of heart signals with a signal-to-noise ratio as high as 40.9 decibels (dB).

Smad1, Smad5 and Smad9 (also known as Smad8) are activated by phosphorylation by bone morphogenetic protein (BMP)-bound type I receptor kinases. We examined the role of Smad1, Smad5, and Smad9 by creating constitutively active forms (SmadDVD). Transcriptional activity of Smad9DVD was lower than that of Smad1DVD or Smad5DVD, even though all three SmadDVDs associated with Smad4 and bound to the target DNA. The linker region of Smad9 was sufficient to reduce transcriptional activity. Smad9 expression was increased by the activation of BMP signaling, similar to that of inhibitory Smads (I-Smads), and Smad9 reduced BMP activity. In contrast to I-Smads, however, Smad9 did not inhibit the type I receptor kinase and suppressed the constitutively active Smad1DVD. Smad9 formed complexes with Smad1 and bound to DNA but suppressed the transcription of the target gene. Taken together, our findings suggest that Smad9 is a new type of transcriptional regulator in BMP signaling.

The importance of continuous monitoring of skin hydration in daily life, to aid in the diagnosis of skin diseases, is rising. Electrodes that can be worn directly on the skin are attracting attention as an effective means. However, they should not inhibit natural water evaporation from the skin and should not cause inflammation or irritation even if they are attached to the body for long periods of time. In this study, nanomesh electrodes that have previously been reported to exhibit high biocompatibility are also found to exhibit high water vapor permeability, resulting in properties that prevent skin dampness. Furthermore, the skin impedance measured using nanomesh electrodes is found to correlate with the hydration level of skin measured using existing medical equipment. This study provides a new approach to measure skin hydration in conditions close to bare skin. Skin is the outermost organ of the body and acts as a barrier separating the inside of the body from the outside world. Skin is essential to prevent the entry of pathogens and contaminants from the outside environment into the body, as well as to prevent excessive evaporation of water from the body. The stratum corneum, the outermost layer of the skin, serves as a barrier that inhibits water evaporation from the skin called trans-epidermal water loss (TEWL). [1] When the stratum corneum is damaged, the water in skin evaporates more easily to the outside world, making the skin prone to dryness. [2] Therefore, it is important to measure the skin hydration levels to assess the barrier function of the stratum corneum. The evaluation of the stratum corneum's barrier function has attracted significant attention from the cosmetic and medical fields as it is useful for understanding the characteristics of an individual's skin and diagnosing skin diseases such as atopic dermatitis, [3] ichthyosis vulgaris, [4] and psoriasis. [5] Skin hydration levels are commonly measured indirectly by measuring the skin's electrical properties, such as the skin impedance and skin capacitance. This is because the higher the hydration level of the skin, the higher the conductivity and dielectric constant. [6,7] In the medical community, the electrical properties of the skin are measured using probes with rigid electrodes