Microsupercapacitors (MSCs) with excellent flexibility and electrochemical capacitance are promising energy storage devices for wearable electronics. In this paper, we present a 3D porous poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/graphene composite sponge (PGCS) fabricated via a facile self-assembly process for highly stretchable, high areal capacitance MSCs. The proposed self-assembly process enables simultaneously the following in one-step: (1) separation of PSS and PEDOT from PEDOT:PSS, (2) reduction of graphene oxide (GO) into reduced graphene oxide (rGO), and (3) integration of PEDOT and rGO into a hybrid 3D composite. By tuning the mass ratio of PEDOT:PSS and GO, PGCSs with different porosities, mechanical properties, conductivities, and capacitances can be obtained. With the incorporation of PEDOT into rGO, the PGCS exhibits enhanced electrochemical performance and better mechanical flexibility. The fabricated stretchable MSC exhibits a high areal specific capacitance (19.3 mF cm⁻² at a scan rate of 20 mV s⁻¹), good electrochemical stability (88.6% retention of specific capacitance after 5000 cycles), and a remarkable stretchability (87.1% retention of specific capacitance after 50% stretching). This facile approach provides a general strategy for synergistic self-assembly of composite sponges and the design of stretchable 3D MSCs, suitable for energy storage devices with high stretchability and high energy density.

Stretchable micro-supercapacitors (MSCs) with high power density and small size have been intensively researched in the recent years. However, to date, the stretchability of the overall device is still limited by the lack of a stretchable electrode material, which results in significant performance degradation, particularly in the highly stretched state. Herein, a new method for designing natively stretchable MSCs capable of maintaining high electrochemical performance in a highly (200%) stretched state is presented. The electrode is based on the novel incorporation of the bis(trifluoromethane) sulfonamide lithium salt (LiTFSI) and poly(vinyl alcohol) (PVA) into a PEDOT:PSS hydrogel. The resultant PEDOT:PSS-LiTFSI-PVA hydrogel is operated with a PVA/H₂SO₄ electrolyte to deliver an unprecedented level of combined performance such as a large areal capacitance of 44.5 mF cm⁻², a power density of 0.04 mW cm⁻² at an area energy density of 0.004 mW h cm⁻², and an excellent stretchability of 200% while retaining 93% of the original capacitance. The MSCs deliver highly stable performance even under extensive stretching, showing a high 92% capacitance retention after 2000 cycles of 100%-strain stretching. The proposed MSC architecture is compatible with laser patterning, which enables rapid fabrication, and reflects a highly practical approach for realizing high performance, mechanically robust micro energy storage devices.

Cardiovascular disease, like hypertension, is one of the top killers of human life and early detection of cardiovascular disease is of great importance. However, traditional medical devices are often bulky and expensive, and unsuitable for home healthcare. In this paper, we proposed an easy and inexpensive technique to estimate continuous blood pressure from the heart sound signals acquired by the microphone of a smartphone. A cold-pressor experiment was performed in 32 healthy subjects, with a smartphone to acquire heart sound signals and with a commercial device to measure continuous blood pressure. The Fourier spectrum of the second heart sound and the blood pressure were regressed using a support vector machine, and the accuracy of the regression was evaluated using 10-fold cross-validation. Statistical analysis showed that the mean correlation coefficients between the predicted values from the regression model and the measured values from the commercial device were 0.707, 0.712, and 0.748 for systolic, diastolic, and mean blood pressure, respectively, and that the mean errors were less than 5 mmHg, with standard deviations less than 8 mmHg. These results suggest that this technique is of potential use for cuffless and continuous blood pressure monitoring and it has promising application in home healthcare services.

Heart rate variability is a useful clinical tool for autonomic function assessment and cardiovascular disease diagnosis. To investigate the dynamic changes of sympathetic and parasympathetic activities during the cold pressor test, we used a time-varying autoregressive model for the time-frequency analysis of heart rate variability in 101 healthy subjects. We found that there were two sympathetic peaks (or two parasympathetic valleys) when the abrupt changes of temperature (ACT) occurred at the beginning and the end of the cold stimulus and that the sympathetic and parasympathetic activities returned to normal in about the last 2 min of the cold stimulus. These findings suggested that the ACT rather than the low temperature was the major cause of the sympathetic excitation and parasympathetic withdrawal. We also found that the onsets of the sympathetic peaks were 4-26 s prior to the ACT and the returns to normal were 54-57 s after the ACT, which could be interpreted as the feedforward and adaptation of the autonomic regulation process in the human body, respectively. These results might be helpful for understanding the regulatory mechanisms of the autonomic system and its effects on the cardiovascular system.