## 4 Discussion  
The presented studies characterized the use of PEMFs and DC EF galvanotaxis to promote the migratory behavior and healing capacity of native bovine FLS. The bovine model is widely used in musculoskeletal research and has yielded significant insights to cartilage biology, synovial activation, and regenerative medicine. Previous studies from our laboratory have demonstrated that bovine synovium (engineered and native) respond similarly to pro-inflammatory cytokines as native human synovium, supporting future efforts to develop more effective strategies for promoting repair and restoring joint health [46]. Electrotherapeutic stimulation is yet to be fully explored in the context of promoting intrinsic cartilage repair via FLS modulation. Given its proximity to the underlying cartilage, synovium-derived cells have been implicated in localized repair of injured lesions along  
Figure 14: Gene expression of bovine cartilage explants normalized to day 0 controls using (**A**) cartilage (ACAN, COL2, COL10, COL11) and (**B**) synovium (COL1, COL3, COL4, COL5) ECM markers following 7 days of PEMF stimulation with parallel untreated controls (\(n\) = 6; \({}^{*}\)\(p\) < 0.05, \({}^{**}\)\(p\) < 0.01). Figure 13: Histological staining of PEMF treated explants. (**A**,**B**) H&E, (**C**,**D**) Safranin O, and (**E**,**F**) Picrosirius Red staining of bovine synovium explants (Scale bar = 100 \(\upmu\)m). (**G**,**H**) Safranin O and (**I**,**J**) Picrosirius Red staining of 4 mm bovine cartilage plugs with 1 mm subcores that were reinserted into the explant forming a circular defect region (Scale bar = 400 \(\upmu\)m). the articular surface [50; 51; 52]. Combined with the use of electrotherapeutic strategies, direct homing of resident FLS can further be enhanced, thus expediting the rate of cartilage repair without surgical interventions. Compared to untreated controls, PEMF exposure enhanced bovine FLS migration during wound closure, suggesting that EF stimulation can promote FLS movement in vitro. While no immediate effects of PEMF were observed directly following injury, sustained improvement in the rate of FLS wound closure was evident by 24 h, contributing to current literature findings that support the use of PEMFs in modulating gradual migration of other cell types including MSCs, chondrocytes, osteoblasts, and meniscal derived cells [37; 53; 54; 55; 56; 57]. From a 2D environment, the migration of bovine FLS was further investigated within a 3D collagen hydrogel via galvanotaxis. In the collagen substrate, bovine FLS exhibited migration toward the cathode with increased incremental and overall speeds of movement, suggesting that DC EF stimulation can promote the directed migration of FLS under 3D culture conditions. In this study, FLS migration was tracked by identifying the centroid and tracing the path followed by each cell within the collagen hydrogel. However, this method of cell tracking may have underestimated the displacement of the cells in the galvanotaxis chamber. FLS may have formed additional focal matrix adhesions with the surrounding collagen gel, potentially contributing to delayed migration rates [58; 59]. Following FLS migration within a 3D collagen hydrogel, a custom galvanotaxis chamber was designed in order to assess cell movement within a biological substrate. EF strengths of magnitudes similar to those used to promote 2D galvanotaxis was applied to track cell migration into the defect of the bovine cartilage explant. FLS migrated into the defect region at an average velocity of 28.2 \(\upmu\)m/h with an EF strength of 6 V/cm and a current density equal to 73 mA/cm\({}^{2}\). These values are comparable to physiologic conditions exhibited by chondrocytes in vivo, where cells can be exposed to field strengths and current densities with magnitudes of up to 15 V/cm and 100 mA/cm\({}^{2}\), respectively [60].