undergo negligible changes when stretched and bent in this manner (figs. S5 and S6). Stretching the ECG EES uniaxially by up to 16% (Fig. 1C) and the PPG EES by up to 13% results in strains in the electronics and antenna structures that remain below the limits for plastic deformation (~0.3%; figs. S7 to S9). Even with 20% stretching, the changes in the inductance, Q factor, and resonant frequency of the antennas are minimal (< 5%) (figs. S10 and S11). Figure 1D shows pictures of a PPG EES with its red LED activated, captured with and without external illumination. Images in Fig. 1, E and F, compare clinicalstandard technologies to our devices, as deployed on a realistic model of a neonate. Existing systems require a collection of separate electrodes, sensors, and limb-strapped systems paired to base units with hard-wired connections. An ECG requires three adhesive-backed electrodes with adjoining wires to monitor HR, HRV, and RR. Commonly used electrodes for this purpose (e.g., Red Dot, 3M Company) may require additional adhesives that further increase the risk of skin injury. Measurements of SpO2 rely on limb-based devices for PPG (e.g., LNCS Neo SpO2 sensor, Masimo), typically wrapped around the entire foot, with an additional wired interface. Continuous measurements of skin temperature, necessary to monitor for signs of hypothermia, involve another adhesive-backed sensor (e.g., HNICU-22, DeRoyal) and adjoining wire. Collectively, then, vital signs monitoring in the conventional manner requires at least four electrodes and one limb-deployed device, with five wires for Chung et al., Science 363, eaau0780 (2019) 1 March 2019 2 of 12 Fig. 1. Schematic illustrations and photographic images of ultrathin, skin-like wireless modules for full vital signs monitoring in the neonatal intensive care unit (NICU) with comparisons to clinical-standard instrumentation. (A) Schematic illustration of wireless, battery-free modules for recording electrocardiogram (ECG) and photoplethysmogram (PPG) data and skin temperature. The ionic liquid in the microfluidic channel contains blue dye for visualization purposes. (B) Images of devices draped over the fingers of a life-sized, transparent mannequin hand to illustrate the sizes and physical form factors of these devices. (C) Image of an ECG EES stretched uniaxially in the horizontal direction by ~16%. (D) Device for capturing PPG data during operation in a lighted and a dark room. PD, photodiode. (E and F) NICU setting with a life-sized neonate doll configured with conventional measurement hardware (E) and with a binodal (chest and foot) deployment of skin-like wireless devices designed to provide the same functionality and measurement fidelity (F). (G) Functional block diagram showing analog front end of each EES, components of the NFC SoC including microcontroller, GPIO, and radio interface, with a host reader platform that includes an NFC reader module and a BLE interface with circular buffer. RESEARCH | RESEARCH ARTICLE Downloaded from https://www.science.org on July 15, 2022 external connection to yield HR, HRV, RR, skin temperature, and SpO2. The block diagram in Fig. 1G summarizes the system architecture and overall wireless operation of our systems. The ECG EES includes two epidermal electrodes, an instrumentation amplifier, analog filters, an inverting amplifier, and a NFC system-on-a-chip (SoC) (fig. S12). The PPG EES includes a pair of small-scale LEDs that emit in the red (640 nm) and infrared (IR) (940 nm), a photodiode, LED drivers, an external power circuit, analog filters, an inverting amplifier, and a NFC SoC (fig. S13). A 14-bit analog-to-digital converter (ADC) operating at a sampling frequency of 200 Hz digitizes the signals captured by each module. The RF loop antennas in both the ECG EES and PPG EES serve dual purposes in power transfer and in data communication. The standard NFC protocol at 13.56 MHz supports only low-speed, low-fidelity applications such as contactless payments and wireless identification (15); thus, substantial modification in both the transponder and host reader systems at ISO15693 was required to support data transfer rates sufficient for NICU monitoring (hundreds of Hz). The results enable continuous streaming of data at rates of up to 800 bytes/s with dual channels, which is orders of magnitude larger than those previously achieved in NFC sensors (15–17). A key to realizing such high rates is in minimizing the overhead associated with transfer by packaging data into six blocks (24 bytes) in a circular buffer. Reading occurs with a NFC host Chung et al., Science 363, eaau0780 (2019) 1 March 2019 3 of 12 Fig. 2. Fundamental aspects of mechanical stresses and soft adhesion at the interface with the skin. (A) Simulation results for the deformed geometry and distribution of strain in the copper layer of an ECG EES during uniaxial stretch (~16%). (B) Simulation results for the distribution of shear and normal stresses at the interface between an ECG EES and underlying skin during deformation for devices without (left) and with (right) the microfluidic channel. Stresses in the latter case are less than ~20 kPa, the threshold of skin sensation. (C) Simulation results for the distribution of von Mises stress on the skin due to peeling of a conventional NICU adhesive (left) and the ECG EES adhesive (right). (D) Simulation result for the time dependence of the peel force during removal of a conventional NICU adhesive and the ECG EES adhesive from the skin. (E) Images that highlight experimental studies of peeling of a conventional NICU adhesive (left) and the ECG EES adhesive (right) from the skin of a healthy adult. (F) Experimental measurement of the time dependence of the peel force during removal of a conventional NICU adhesive and the ECG EES adhesive from the skin. (G) Simulation results that highlight the role of the microfluidic channel in the peel force associated with removal of an ECG EES from the skin, with emphasis on the initial, non–steady-state regime during peel initiation. The circles denote the instants of initial delamination, when the interfacial cohesive strength is reached. The inset shows the normal stress distribution, syy, along the interface at the