## 3 Results
Tracking of each cell began at the origin, with positive y-displacement indicating cathodal migration. DC EF stimulation via galvanotaxis increased cell recruitment and migration within the bovine cartilage defect (Figure 8C,D) compared to controls (Figure 8A,B). Assessing the depth of the defect region following DC EF exposure, approximately 86% of adherent cells had migrated at least 40 \(\upmu\)m in the EF group, compared to 38% in the controls (Figure 8E; \(p<0.001\)). Additionally, EF stimulation increased the directed velocity of FLS into the defect site (28.2 \(\upmu\)m/h) relative to untreated controls (8.9 \(\upmu\)m/h) (Figure 8E; \(p<0.001\)). Following DC EF exposure, viability of the cartilage construct was also assessed using a live/dead cytotoxicity assay. The assay is based on Calcein AM permeating the cells with intact membranes, producing a green fluorescence (live), while Ethidium Homodimer permeates the nuclei of dead cells to produce a red fluorescence (dead) [49]. Compared to untreated controls from initial harvest (Figure 9A), viability of the cartilage construct remained consistent with minimal dead cells under DC EF exposure (Figure 9B). Dead cells were visible along the circumference of the annulus region where the 1 mm sub-core was removed from the cartilage construct. The ring of dead cells was not as profound in the cartilage explants exposed to EF stimulation compared to control samples. **Study 4. Characterize the effect of PEMF stimulation on modulating the migration of endogenous and/or exogenous FLS repair cells into a cartilage defect model. **  
PEMF stimulation for 48 h enhanced the migration of FLS into the cartilage defect region compared to untreated controls across both timepoints (Figure 10A-F). The number of migrated FLS was significantly elevated under PEMF exposure, where 78% of adherent  
Figure 8: Representative confocal images of Dil-stained FLS migrating into DAPI-labeled bovine cartilage defect. (**A**) Top and (**B**) side view of control (CTL) explants showing minimal FLS migration into the cartilage construct. (**C**) Top and (**D**) side view of explant exposed to DC EFs for 3 h showing significant FLS migration through the depth of the defect region (Scale bar = 200 \(\upmu\)m). (**E**) Percent migration and (**F**) directed velocity of FLS into the cartilage defect for CTL and EF treated groups (\(n=4\) cartilage explants). Figure 9: Representative live/dead images of (**A**) control and (**B**) DC EF treated cartilage explants following DC EF stimulation for 3 h (Scale bar = 100 \(\upmu\)m). cells had migrated at least 40 \(\upmu\)m into the defect area compared to 17% in the sham group (Figure 10G; \(p<0.001\)). Histological staining of the synovium on cartilage explant model was performed to further assess cell migration into the defect site. In this case, the 1 mm cores that were removed from each 4 mm bovine cartilage plug were reinserted in order to characterize intrinsic repair of the defect region via PEMF-induced cell migration. A piece of bovine synovium was placed in direct apposition to the cartilage construct and the explants were exposed to PEMF treatment for up to 7 days. Structural morphology of the cartilage plugs and the migration of FLS as well as native chondrocytes were visualized with H&E staining. Compared to controls (Figure 11A-D), PEMF treatment slightly improved cell migration within the defect region of the cartilage construct over time (Figure 11E-G). The defect ring at the sub-cored interface visually showed enhanced cellular migration and repair by day 7 of PEMF stimulation compared to day 0 controls, as the cell-free defect region exhibited gradual closure across each timepoint. Figure 11: H&E-stained bovine cartilage explants to assess defect repair for (**A–D**) control and (**E–G**) PEMF treated samples (Scale bar = 300 \(\upmu\)m). A uniform defect region was formed by removing 1 mm subcores and reinserting the annuli into the cartilage explant. Arrows indicate areas of closure along the cell-free defect region.