Process steps for integration of spatially and geometrically defined electrospun fibers into PDMS based microfluidic channels. (1) Polyurethane solution containing BME is electrospun directly onto a glass substrate; (2) the electrospun network is exposed to DUV through a quartz mask causing the BME to form radicals which results in crosslinking of the fiber network; (3) development of the patterns by immersion in THF, dissolving the noncrosslinked areas, followed by rinsing in de-ionized water; (4) substrate is dried and the first layer is complete (5) Process steps 1–4 are repeated consecutively to form new additional fiber pads having different geometries, alignment or fiber diameter; (6) PDMS is molded, aligned and cured onto the glass substrate to form the microfluidic channel around the electrospun patterns; (7) complete microfluidic channel comprising electrospun fibers.
(a) Scanning electron micrograph of electrospun fiber pads with alternating fiber orientation (alternating vertical and horizontal). The fiber pads are 250 × 200 μm with pitch of 400 μm (center to center distance). (b) Magnified view of (a) showing a fiber pad with vertical fiber orientation to the left and one with horizontal orientation to the right. (c) Scanning electron micrograph of a vertical cross section of the probing channel. The long fiber pad is positioned within the channel, the pad boundaries are indicated by a dashed black line. The PDMS (top) and glass (bottom) are irreversibly bonded and the fiber pad does not disturb the bond. (d) Light micrograph (top view) of electrospun fiber pads within the microfluidic chip. The fiber pads are positioned along the probing channel.
(a) Simulated color coded concentration gradients in the microfluidic network (x-y plane). Left side: overview of the gradient network and downstream probing channel. The two measurement positions 1 and 2 are indicated. Right side: Magnification of the concentration gradient within the probing channel simulated for flow velocities of 0.075, 1.5, and 15 mm/s. (b) Bright field micrograph of an electrospun fiber pad in the microfluidic probing channel. The position for the intensity line profile measurement (position 2) is indicated in the figure, as well as the direction of flow. (c) Fluorescence micrograph of soluble sodium fluorescein gradient; the image was taken at the same position as indicated in (b) at a flow velocity of 7.5 mm/s. (d) Fluorescence intensity line profiles measured in microfluidic channels with fiber pads. The profiles were taken at the two different positions indicated in (a). Intensity line profiles are shown for flow velocities of 0.075, 1.5, and 15 mm/s. (e) Comparison of intensity line profiles in channels with (fiber) and without fiber pads (flat) measured at positions 1 and 2. These measurements were all done at a flow velocity of 7.5 mm/s.
(a) Simulated flow velocity profile in the probing channel, fiber pad indicated with a white line, for an average inflow velocity of 1.5 mm/s (x-z plane coordinates given in μm). (b) Simulated shear stress in the bottom half of the probing channel with similar simulation parameters as A. (c) Simulated vorticity magnitude at the edge of the fiber pad with similar simulation parameters as A and B.
(a) Simulated relative concentration line profiles for different fiber mat thicknesses for an average inflow velocity of 1.5 mm/s. The line profiles were taken 2 μm above each simulated fiber mat. (b), (c) and (d) Color coded relative concentration (red = high, blue = low) shown as cross-sections in the z-y plane and flow streamlines shown in red along the channel for 5, 20, and 40 μm thick fiber mats.
(a) False color fluorescence micrograph of 3T3 fibroblast cells after 24 h of culture in the microfluidic network on electrospun fibers. Individual fluorescence channels shown in (b)-(d). (b) Red = actin filaments stained with Alexa Fluor555 phalloidin, (c) Green = autofluorescence of the fibers and (d) Blue = DNA stained with DAPI. (e) and (f) False colored fluorescence micrographs of cells situated in the microfluidic channel at different positions along the length of the probing channel (g) False colored fluorescence micrograph of a single cell on a fiber pad. All same color scheme as A.
(a) False color fluorescence micrograph of a neurosphere on laminin coated aligned electrospun fibers after 24 h of culture in a Petri dish. Green = GFAP and Blue = DNA stained with DAPI. (b) False color fluorescence micrograph of a neurosphere cultured on similar conditions than (a), but on a laminin coated flat glass surface. (c) False color fluorescence micrograph of neural stem cells in a microfluidic channel with a SDF-1a gradient increasing concentration from the bottom to top of the figure (as indicated by the wedge) partly on aligned electrospun fibers on the right side of the image(all surfaces coated with laminin) after 24 h of culture. Red = Actin filaments stained with Alexa Fluor555 phalloidin and Blue = DNA stained with DAPI. D-F) False color fluorescence micrograph of neural stem cells in a microfluidic chip cultured under similar conditions as (c) showing the three different conditions: without fibers (d), fibers orientated in parallel to the gradient (e) and fibers orientated perpendicular to the gradient (f).
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