Fabrication of 3D Biomimetic Microfluidic Networks in Hydrogels - PubMed (original) (raw)
Fabrication of 3D Biomimetic Microfluidic Networks in Hydrogels
Keely A Heintz et al. Adv Healthc Mater. 2016 Sep.
Abstract
A laser-based hydrogel degradation technique is developed that allows for local control over hydrogel porosity, fabrication of 3D vascular-derived, biomimetic, hydrogel-embedded microfluidic networks, and generation of two intertwining, yet independent, microfluidic networks in a single construct.
Keywords: biomimetic; laser-based degradation; microfluidic; tissue engineering; vascularized constructs.
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Figures
Figure 1. Fabrication of Microfluidic Channels in PEGDA Hydrogels
(A) A 5% 3.4 kDa PEGDA hydrogel is photopolymerized against a PDMS master to create reservoirs. A 790 nm, 140 fs pulsed laser focused through a 20X(NA1.0) water immersion objective is raster scanned in desired 3D configurations to locally degrade the hydrogel. The hydrogel is fluorescently labeled via photocoupling of a monoacrylate fluorescent PEG-RGDS to visualize degraded volumes. The reservoirs are filled with a fluorescent species (dextran (Dex), bovine serum albumin (BSA), nano- or microspheres) and the microchannels imaged via confocal microscopy. (B: left column) Time-lapse images of PEGDA during laser-induced degradation of a 500×100×100 μm (x,y,z) channel. (B: right column) As microbubbles form they migrate to the reservoir and coalesce to form a large bubble. The microchannel walls are depicted by dashed black lines. (C) 3D renderings of a micromolded hydrogel and microchannels filled with 10, 500, and 2000 kDa fluorescent dextran and 200 nm and 2 μm fluorescent spheres. (B) SB=50 μm.
Figure 2. Controlled Local Hydrogel Porosity and Size-Based Separation of Fluorescent Species
(A) The local hydrogel porosity was controlled by altering the laser scan speed while degrading at a constant fluence of 21.73 nJ μm−2. (A: top two rows) Z-projections of a 3D image stack depicting the eosin Y and fluorescent PEG-RGDS show where the hydrogel (lighter regions) was degraded to form microchannels (darker regions). (A: bottom two rows) Z-projections of fluorescent 10 and 2000 kDa dextran perfused into the microchannels are also shown. (A,B: channel on far left side) A slow scan speed, 0.005 μm μs−1, induced total hydrogel degradation resulting in a completely open microchannel as observed in the eosin Y and fluorescent PEG-RGDS (A) images and (B) intensity profiles. (A,B: channels from left to right) Increasing the scan speed induced partial hydrogel degradation resulting in microchannels containing some polymer but with an increased pore size relative to the unmodified base hydrogel as indicated by the (A,B: 4th row) inability for 2000 kDa dextran to perfuse into these channels and (A,B: 3rd row) decreased intensity of 10 kDa dextran. (A: 4th row) The white box (389×37.4 μm) indicates where the (B) intensity measurements were acquired for each z-projection. (A,B) The vertical dashed lines, indicated by the black arrows, are in the same location for orientation purposes. (C) The degradation parameters used to create the microchannels in (A) were applied in a gradient fashion by increasing the scan speed from left to right to create a long rectangular channel (white lines indicate channel walls) that allowed for size-based separation of fluorescent species (2000 kDa dextran and 2 μm spheres) during flow; Q = 10 μL min−1. Normalized intensity profiles measured for each fluorescent species were plotted as a function of distance from the channel entrance. (A,C) SB=50 μm.
Figure 3. 3D Vascular -Derived Microfluidic Networks
(A) A confocal image stack of (red) cerebral cortex vasculature was used to fabricate a (green) biomimetic microfluidic network in a PEGDA hydrogel. The in vivo and in vitro microfluidic networks were skeletonized for quantitative analysis. (B) Four metrics were used to quantity the microfluidic networks. (C) The insets in (A) are expanded to demonstrate the ability to recapitulate the dense, tortuous in vivo vascular network in PEGDA. (D) Microchannels were seeded with mouse brain endothelial cells, fluorescently labeled with DAPI (blue: nucleus) and ZO-1 (green: tight junctions), and imaged via confocal microscopy. (D) SB=50 μm.
Figure 4. Transport Between 3D Intertwining Microchannels
(A) A 3D model containing two independent yet intertwining microchannels (20×20 μm: x,y) was designed in SolidWorks; the white arrows in the 2D projection indicate the flow direction. (B) The 3D model was used to fabricate two microfluidic networks in PEGDA and the microchannels were exposed to (red) 70 kDa dextran and (green) BSA. Orange in the 3D renderings indicates transport of the two fluorescent species from their respective microchannel, through the hydrogel, into the adjacent channel. (B: right panel) Looking down the central axis of the intertwining channels shows that the two networks come within 15 μm of each other but never directly connect. (C) Time-lapse confocal images of species movement show (green) 2000 kDa dextran and (red) BSA filling their respective microchannel and transport through the hydrogel into the adjacent channel. (D) White dotted boxes in (C) indicate where intensities of 2000 kDa dextran and BSA were measured over time. (D: left graph) Normalized intensity of 2000 kDa dextran in its own channel and diffusion into the BSA channel (D: right graph). Normalized intensity of BSA in its own channel and diffusion into the 2000 kDa channel. (C) SB=20 μm.
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