Fig. 6: Laser ablation for integrated wireless bioresorbable cardiac systems.
a Schematic illustration of the components used to construct the cardiac devices. b Photograph of the multi-sensing element. Constituent components include, from bottom to top: a bottom WPU encapsulation (thickness: ~100 µm), a tri-arm Y-shaped layer with three pairs of bottom electrodes, three single-arm floating electrodes, and a tri-arm Y-shaped top cover, and another top WPU encapsulation. The hole on each arm close to the center aids device mounting with a customized accessory. The hole close to the end facilitates suturing. c Photograph of the flexible cable. The element possesses six independent Zn traces (thickness: 5 µm) on a CA substrate (thickness: 35 µm), with a uniform PLGA layer as the top encapsulation (thickness: ~10 µm). d Photograph of the wireless module. The element adopts three Zn inductors (thickness: 25 µm) with different inductance values on a PLA substrate (thickness: 50 µm). A pair of PLGA layers serves as top and bottom encapsulation (thickness: 50 µm). e Working principle of the device. Strains along each arm lead to changes in the relative position between the floating electrode and the pair of bottom electrodes. This change in position leads to a corresponding change in capacitance that, in turn, changes the frequency of the resonance. f Photograph of the complete device for measuring strains on the surface of cardiac tissue in large animals. In vivo acute evaluations in an ovine model. g Schematic illustration of a device designed for measurements on the LV of an ovine animal. The multi-sensing element integrates on the LV. The wireless module lies in the dorsal subcutaneous area. A flexible cable provides an electrical interface. h Raw data from one sensing unit. i Filtering the raw data yields the respiration rate (duration: ~4–5 s; bandpass <1 Hz; marked red) and the heart rate (duration: ~0.9 s; bandpass: 40–200 Hz; marked blue). Quantitative assessment of principal strains (εx, j; εy, k) and shear strain (γxy, l) of the ovine LV.
