Fig. 1.

In vitro electric coupling and optical pacing. (A) Illustration of the proposed MF–SiNW hybrid methodology. SiNWs are seeded on MFs and allowed to hybridize. The MF–SiNW hybrids can be harvested and cocultured with CMs or injected into heart tissue, where they provide high-resolution photomodulation. (B) SEM images of coaxial p-i-n SiNWs. (Top) One-dimensional morphology of an SiNW. (Bottom) Representative cross-section of a randomly broken SiNW, where the coaxial feature is clear. (Scale bars, 100 nm.) (C) Confocal images of cytoplasmatic (calcein AM, green) and membranal (CellMask, red) staining show that SiNWs are internalized by MFs. The SiNWs (white) are detected by reflected light. Yellow dashed lines represent 2 cross-sectioned z-n slices. (Scale bars, 10 µm.) (D) Longer pulse durations (1 ms or 5 ms, 1 mW) for SiNW stimulation increase the likelihood of provoking an AP in neighboring CMs. Results shown for 2 different SiNWs. Error bars represent SE of the mean from >20 stimulations for each SiNW. (E) Effect of photomodulation on MF–SiNW/CM coculture. (Top Left) Bright-field image shows perinuclear arrangement of SiNWs within MF; arrowhead indicates stimulated SiNW. (Top Right) Fluorescent Ca²⁺ imaging in analyzed ROIs 1 to 3. (Bottom Left) Heat map of AP propagation before photopacing shows unsynchronized CM beating in ROI 1 and 3, and no electrical activity in ROI 2. (Bottom Right) Following ∼400 s of photopacing (5 ms, 1 mW, 1.3 Hz), all regions are completely active and synchronized. Field of view: 169 μm × 169 μm. (F) Summary of activity in all ROIs following optical stimulation of MF–SiNW hybrid. Results are plotted as the average of the time intervals between consecutive APs for each ROI. Black line, pacing rate of laser pulse. (G) dF/F vs. time of electrical activity of ROI 1; initial slow rate of electrical activity gradually increases and synchronizes with the laser pulses.