mm). The force scales with 1 – a (fig. S21)—that is, the area of contact between the EES and the skin. This scaling also applies to other patterns of holes (e.g., figs. S22 and S23 for square patterns without and with 45° rotation, respectively). For sufficiently small holes (e.g., 200 mm; see figs. S24 to S28), the relation between the peel force and time depends only on 1 – a and is approximately independent of pattern. Oscillations in the force only appear for holes larger than the characteristic size of the cohesive zone (~500 mm, as in Fig. 2I). An optimized approach to reducing interface stresses and peel forces, therefore, combines microfluidic channel structures with small perforation holes, the latter of which can be naturally accommodated within the open network designs characteristic of epidermal electronics (Fig. 1A). Compatibility with medical imaging techniques used in the NICU Magnetic resonance imaging (MRI) is essential in the NICU because of its ability to deliver precise assessment of white matter, gray matter, and posterior fossa abnormalities with functional capabilities that exceed those of ultrasound (23, 24). The EES platforms exploit designs that minimize disturbances in the time-dependent magnetic fields associated with MRI scanning, thereby reducing distortions and shadowing artifacts in the final images and eliminating any parasitic heating from magnetically induced eddy currents. Calculations of the gradients of the magnetic field density near electrodes with Chung et al., Science 363, eaau0780 (2019) 1 March 2019 5 of 12 Fig. 4. Visualization of radiolucent properties through medical imaging. (A) A coronal MRI image collected from the mid-dorsum of a rat cadaver with an ECG EES mounted on the skin. (B) A coronal MRI image collected from the mid-dorsum of a rat cadaver with conventional ECG leads mounted on the skin. (C) An x-ray image collected from the right flank of a rat cadaver with an ECG EES mounted on the skin. (D) An x-ray image collected from the right flank of a rat cadaver with conventional ECG leads mounted on the skin. RESEARCH | RESEARCH ARTICLE Downloaded from https://www.science.org on July 15, 2022 different structures (mesh, solid, and commercial electrodes, see fig. S29) on biological tissues in a 3-T MRI scanner reveal the underlying effects. The results show that mesh electrodes induce the weakest disturbance to the magnetic field among mesh (layout of Fig. 1A), solid (i.e., no mesh), and commercial electrodes with similar overall sizes and geometries (Fig. 3, A and C) for both the in-plane |∇pB| and out-of-plane |∇zB| gradient of the magnetic field density. The maximum value of |∇pB| for the mesh electrode is smaller than that of the commercial electrode by a factor of ~3 (Fig. 3E), whereas |∇zB| is smaller by a factor of 4 (Fig. 3F). The mesh design also has advantages in its soft, flexible mechanics and associated benefits in interfacial stresses and adhesion, as described previously. Additional simulations guide selection of designs that ensure that the resonant frequencies of the EES have no overlap with the working frequencies of typical MRI scanners (64 MHz, 128 MHz, 298 MHz, and 400 MHz for 1.5-T, 3-T, 7-T, and 9.4-T MRI scanners, respectively; Fig. 3G), thereby avoiding large gradients of the magnetic field density (Fig. 3, B and D, and figs. S30 and S31). Similar simulations for the PPG EES indicate gradients of the magnetic field density that are smaller than those for the ECG EES (fig. S32). These features allow the devices to remain in place on neonates undergoing MRI imaging to mitigate the risks of injury and complications with removal and re-adhesion. Experiment and simulation results also yield information on parasitic heating during an MRI scan. Full three-dimensional multi-physics modeling shows that, at the end of a single scan for 0.5 ms, the copper layer of an ECG EES undergoes heating by only 1°C (Fig. 3H). The resultant maximum temperature change at the skin interface is 0.04°C, far below the threshold for sensation, due to the insulating effects of the polydimethylsiloxane (PDMS) and the microfluidic Chung et al., Science 363, eaau0780 (2019) 1 March 2019 6 of 12 Fig. 5. Operational characteristics of the ECG EES. (A) Block diagram of in-sensor analytics for peak detection from ECG waveforms. (B) ECG signals acquired simultaneously from an ECG EES (blue) and a gold standard (red), with detected peaks (green). (C) Comparison of heart rate determined using data from the ECG EES and a gold standard. (D) Respiration rate extracted from oscillations of the amplitudes of peaks extracted from the ECG waveforms. (E) Comparison of respiration rate determined using data from the ECG EES and manual count by a physician. (F) Comparison of skin temperature determined by the ECG EES and a gold-standard thermometer. (G) Thermal image of the chest collected using an IR camera. (H) Temperature wirelessly measured using an ECG EES. (I) Bland-Altman plot for heart rate collected from three healthy adults using an ECG EES and a clinical-standard system. (J) Bland-Altman plot for respiratory rate collected from three 157 lbs 5 cm HAND ECG EES FACE 2 cm 36.7 °C 22.4 °C RESEARCH | RESEARCH ARTICLE Downloaded from https://www.science.org on July 15, 2022 channel. The maximum change in temperature occurs ~0.24 s after initiating the scan (Fig. 3H and fig. S33). This time scale is on the same order as that for heat conduction (0.1 s) in the microfluidic channel (fig. S33). Experimental measurements support these findings. Figure 3I shows the change of temperature during an MRI scan (3-T MAGNETOM Prisma, Siemens Healthineers), measured on a sample of phantom skin (designed to match the conductivity and dielectric constant of tissue at 33 MHz) at a location underneath the ECG EES near the loop antenna and adjacent to the device. The results show a temperature difference of ~0.1°C. Figure 3J presents measurements in the middle region of the ECG EES where the values of |∇zB| and |∇pB| are comparable to those for bare phantom skin. Simulation results for the PPG EES suggest even smaller changes in temperature than those for the ECG EES (fig. S34). Additional testing with