A non-invasive, flexible, lightweight, and wearable system for real-time ECG monitoring in freely moving mice

Fig. 1. Design and fabrication of epidermal electrodes. a Finite element analysis map of epidermal electrodes under different stretching shapes. b The conformal contact model for epidermal electrodes. c The preparation process of epidermal electrodes. d Section schematic of epidermal electrodes in the preparation process. e, f Epidermal electrode transfer process. g Photos of epidermal electrodes attached to the abdomen, legs, and heart surface of a mouse. h Photos of epidermal electrodes attached to the legs of the mouse

Fig. 2. Performance test of epidermal electrodes. a Performance of epidermal electrodes under different mechanical deformations. b Tensile test results of the epidermal electrodes. c Effects of epidermal electrode attachment on the limbs of mice. d Resistance changes of epidermal electrodes under segmented stretching conditions. e Adhesion force test between the electrode and mouse skin

Fig. 3. Design and Implementation of a flexible mouse ECG monitoring system. a Physical diagram of the FPCB. b 3D diagram of the FPCB. c Bending diagram of the FPCB. d Functional block diagram. e Circuit module block diagram. f Algorithm flowchart

Fig. 4. Design of a wearable mouse ECG monitoring system. a Design diagram of the ECG backpack. b Photo of the mouse without the backpack. c Photos and details of the mouse wearing the backpack. d Overall testing scenario

Fig. 5. The functional testing of epidermal electrodes. a Electrode placement method for ECG signal acquisition in mice. b Pictures of the mouse’s leg after using two types of electrodes. c Mouse ECG signals tested using two electrodes. d Test of interference immunity of an ECG acquisition system using epidermal electrodes. e Test of interference immunity of an ECG acquisition system using needle electrodes. f Test of interference immunity of an ECG acquisition system using needle electrodes. g Test of interference immunity of an ECG acquisition system using epidermal electrodes

Fig. 6. Long-term stability and biocompatibility evaluation of the ECG monitoring system. a ECG waveforms recorded on Day 0, Day 1, Day 3, and Day 5. b Serum biochemical indices (ALT, AST, BUN, and CRE). c, d Hematoxylin and Eosin (H&E) stain present in ×400 magnification. ns not significant

Fig. 7. Psychological stress indicators in mice following ECG monitoring system wear. a, b Trajectory maps of mice during the open field test. c Total locomotor distance. d Average movement velocity. e Number of entries into the center zone. f Duration spent in the center zone. g–i Serum levels of corticosterone (CORT), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α). ns not significant

Fig. 8. Results of ECG signal testing in mice model of myocardial infarction. a, b Testing electrocardiographic signals in mice with myocardial infarction using two types of electrodes. c, d Monitoring electrocardiographic signals in normal and myocardial infarction mice using epidermal electrodes. e Hematoxylin and Eosin (H&E) stain present in ×400 magnification. f Masson Staining present in ×400 magnification

Fig. 9. The proposed system is mounted on the back of the mouse to collect ECG signals