Fig. 2.

Design and development of a magnetic array for in vivo MICA activation. a Determining the minimum magnetic field strength required for cell activation. MICA activation of MNP-labelled HEK-293 NFΚ-β reporter cells at increasing magnetic field strengths (corresponding to a decrease in distance between cells and the magnetic array). Data represents the mean luminescence (RLU) ± SEM (n = 3). b MICA activation of MNP-labelled and unlabelled STRO-4 positive ovine mesenchymal stem cells (oMSCs) towards osteogenesis (Alizarin red staining) in 6-well monolayer cell culture plates at a field strength of 0.13 and 2.55 KG and compared to static and unlabelled controls (n = 3), scale bar; 1 cm. c Quantification of bony nodules generated in monolayer as a result of MICA activation at either field strength (0.13 and 2.55 KG) and compared to static and unlabelled controls. Data represents the average number of visible bone nodules across 3 wells of a 6-well plate. d Schematic representing the size and location of the defect within the femoral condyle relative to the position of the magnetic array. “X” marks the location of MNP-labelled cells furthest away from the magnet i.e 2.5 cm in the ovine model. e Fabrication of six magnetic arrays containing neodymium iron boron magnets of varying dimensions. f Comparative magnetic field strength from arrays 1–6 at a distance of 2.5 cm. Data represents the average magnetic field strength at six random points on each magnet per array ± S.D. Red dashed line represents minimum magnetic field strength (0.13 KG) required to activate cells. g 3D Magnetic profile of array 4 at a distance of 0.5 cm demonstrating alternating poles. h Accelerometer data for sheep donors 4, 6 and 12 highlighting most active periods (red boxes) within a 24 h period. i Picture of a sheep fitted with the adapted truss housing magnetic array 4 within the pouch corresponding to the location of the defect. Statistical significance is represented by *P < 0.05, ***P < 0.001 and ns is no significance