## 4 Discussion
The EF parameters of this study were optimized to preserve FLS viability under the tested conditions while also maximizing DC EF exposure to promote migration, suggesting that novel bioreactors can be designed to investigate 3D tissue specimens and subsequent cell migration analysis under galvanotaxis stimulation. Following a similar procedure, PEMF contributed to increased FLS migration into the bovine cartilage defect region, suggesting that PEMF exposure can promote intrinsic repair. This finding supports previous studies that have shown PEMF treatment improves cartilage graft growth and healing in both a time- and direction-dependent manner [37]. H&E staining of the defect region reveled improved repair under PEMF following 7 days of EF exposure. Whether the repair process was initiated by FLS from the overlying synovium or native chondrocytes from the articular cartilage surface is yet to be determined. However, recent studies have shown that PEMF treatment can induce MSC differentiation to promote immunomod and improve cartilage regeneration in vitro and in vivo [53]. The multi-lineage differentiation capabilities of MSCs combined with PEMF stimulation have been shown to promote osteogenesis and chondrogenesis in joint repair [54; 57]. With appropriate stimulation, FLS have also been shown to possess a multi-lineage potential to differentiate into chondrocytes and exhibit characteristics of the native cartilaginous environment [61; 62]. The accelerated repair of the bovine cartilage defect region in the current study may be induced by a combination of PEMF stimulated chondrocyte migration and potential chondrogenesis of native FLS into the injured site, contributing to an improved healing response compared to untreated controls. PCR analysis of PEMF treated explants revealed that gene expression of chondrogenic and synovium ECM markers were upregulated compared to no-PEMF controls. These results may reflect the contribution of gene expression from cells recruited to the wound site and those derived from the entirety of the cartilage construct. PEMF-induced chondrogenesis in situ may further contribute to increased cartilage ECM constituents in injured joints [53]. Biochemistry analysis revealed that DNA levels were consistent between PEMF and control treated specimens, suggesting that EF stim ulation did not induce cell damage for both synovium and cartilage explants. Collagen and GAG content differed significantly between PEMF and untreated samples, suggesting that EF stimulated environments may affect cell sensitivity and metabolism [43; 63]. While lower GAG and collagen content have been shown to be characteristic features associated with cartilage damage, PEMF treatment contributed to elevated matrix constituents for both bovine synovium and cartilage tissue, indicative of its pro-anabolic effect [34; 64; 65; 66; 67; 68]. Histological analysis of both explants confirmed the differences observed in GAG and collagen levels under PEMF exposure compared to controls. Future studies will aim to optimize PEMF and DC EF culture conditions. While the current galvanotaxis set-up did not allow for examination of bi-directional cell migration, the system can be modified by culturing labeled FLS on multiple surfaces of the cartilage hydrogel or explant model to further investigate preferential migration towards the cathode (\(-\)). In addition, mechanisms that mediate differences in cell attachment versus interactions between the examined substrates can be distinguished in order to confirm the role of PEMFs and DC EF stimulation in promoting FLS migration. While the present PEMF and galvanotaxis systems were unable to perform real-time cell tracking, both procedures allowed for the maintenance of aseptic conditions, multiple treatments over time, and subsequent cell and tissue analyses. Overall, both PEMFs and galvanotaxis DC EF treatments can enhance synovial cell-mediated cartilage repair using clinically relevant stimulation parameters.