Fig 1.
The fabrication process for the magnetically-actuated beam.
a) a negative mold for the beam is created via photolithography, b) A mixture of PDMS with magnetic particles is cured in the mold with any excess removed via a razor blade, c) the beam is removed after curing and magnetized in a large magnetic field generated by two permanent magnets, d) the magnetic beam is then glued to a glass slide using liquid PDMS and tape as a spacer and again cured, e) the final device when the spacer is removed after the device has been fully cured. f) Experiment demonstrating that the magnetic mixture has no effect on cell death compared to conventional plastic cultureware. N = 3.
Fig 2.
Schematics showing the magnetic actuator.
a) Side view of the fully assembled device where the magnetic beam sits a distance h above the cell surface, b) top view of the device is shown with the adhesive film border on the bottom slide and the magnetic device glued to the top glass slide. c) and d) show scenarios where the gap height h can be coincidentally reduced either due to the device being angled downwards due to gravity (c) or as a result of thick spacer or a thick layer of glue pushing the whole structure downwards (d). e) A 3D rendering of the geometry is shown. This is the geometry used in the finite element analysis. The red square shows the region where shear stress calculations were performed.
Fig 3.
Experimental setup to test magnetic actuator.
a) A schematic of the experimental setup is shown, b) the actual coils when placed around the microscope are shown. The 1D Helmholtz coils are specifically designed to fit around a fluorescent microscope. The coils are connected to an amplifier and power supply for current generation.
Fig 4.
Simulation results for magnetic beam flow generation.
a) 2D Couette flow principle; b) magnetic flux density generated by the coils (shown for 2 s for posterity but this takes place over several minutes); c) the resulting theoretical deflection profile of the beam if the magnetic flux density in (b) is applied. This is also the profile used in the finite element analysis and the tangential derivative is used to determine the theoretical velocities shown in parts (e) and (g). d) The theoretical beam tip velocity magnitude as well as the cycle averaged velocity is shown for the deflection profile seen in (c). e) and g) are plotted using Eq 7 with theoretical velocities determined using the tangential derivative of the deflection profile and the numerical velocities determined from the finite element simulations. f) and h) show the shear stress with varying gap heights and beam tip deflection based on Eq 6 using theoretical and numerical velocities.
Fig 5.
Osteocyte calcium response under magnetic actuator stimulation.
a) The shear stress map obtained using Eq 6 with velocities obtained from finite element simulations is overlaid with the locations of all responding cells from multiple trials that are coded with the time it takes to respond. The dotted line shows the typical viewing window in experiments and the range of the beam oscillation is also overlaid on the map. b) A representative image obtained of the Fura-2 AM stained cells along with the beam is shown which corresponds to the dotted lines on the shear stress map. Scale bar = 50 μm. c) A plot of the cell response time vs distance from the tip of the beam with a linear regression performed is shown, showing an increase in response time for cells further away from the stimulated region. A total of 3 trials and 39 cells were recorded, with an r2 value of 0.59 for the linear regression.
Fig 6.
Sample calcium response curves resulting from magnetic actuation.
a) Three cells are plotted with respect to their positions from the tip of the beam, positioned in regions with different shear stress values; b) the calcium response of the corresponding cells from part (a) are shown.