Microchannels throughout a branched network are uniformly expanded and circularized.

<p>(a) A pseudo-3D network constructed from a 7 layer stack of planar PLA branched networks before and after expansion (bars, 300 µm). (b) Due to the limitations of 2D lithographic microfabrication, the initially rectangular large channels in early branch generations have smaller aspect ratios than those in later generation branches (<i>n</i> = 1: <i>w₀</i> = 498 µm, <i>h₀</i> = 33 µm; <i>n</i> = 2: <i>w₀</i> = 81 µm, <i>h₀</i> = 31 µm; <i>n</i> = 3: <i>w₀</i> = <i>h₀</i> = 31 µm; <i>n</i> = 4: <i>w₀</i> = 14 µm, <i>h₀</i> = 35 µm). The degree of circularity (i.e., aspect ratio <i>h₀</i>/<i>w₀</i> approaching unity) is simultaneously improved across all branch generations after a single expansion step (15 psi of pressurized air for 20 min at 80°C; white bar, 500 µm; black bars, 100 µm). All experiment data are mean ± sd of 3 independent experiments. (c) A 3D branched microchannel network embedded in a 1.5×5×8 cm molded PLA block by electrostatic discharge contains a distribution of microchannel diameters that are not optimal for cell seeding (upper image). After air expansion (lower image), average diameters are significantly increased throughout and the sidewall topology becomes smoother (bar, 500 µm).</p

Seeding and culture of bovine aortic endothelial cells (BAECs) throughout PLA microchannel networks.

<p>(a) Confocal microscopy shows that the interior walls of a 200 µm diameter straight circularized microchannel can be uniformly seeded with endothelial cells that subsequently are confluently cultured in a monolayer lining the channel wall. (b) Fluorescent images show BAECs survive and maintain their morphology after 5 days in the straight circularized microchannel (bar, 50 µm). (c) BAECs seeded in four generations of branched microchannel network with diameters extending below 50 µm uniformly cover all channel walls and maintain viability after 3 days of culture (bar, 50 µm).</p

Enlargement and circularization of PLA microchannels by pressure-assisted expansion.

<p>(a) Microchannels with initially rectangular cross-sectional profiles are molded in PLA using a PDMS master. (b–d) Pressurized air is injected upon heating the PLA into the rubbery state (i.e., above the glass transition temperature and below the melting temperature) causing the interior air pressure force to exceed the wall resistance. The initially rectangular channels eventually attain circular cross-sections. (e–g) Corresponding images of cross-sectional profiles obtained at different times during the expansion process (<i>w₀</i> = 81 µm, <i>h₀</i> = 31 µm) (e) before expansion; (f) 80°C, 15 psi for 15 min; and (g) 80°C, 15 psi for 25 min (expansion ratio = 5; bars, 50 µm). (h) Comparison between experimental results (symbols) and model predictions (lines) capture the expansion of initially rectangular microchannels as a function of time under different processing conditions (<i>w₀</i> = <i>h₀</i> = 31 µm). Microchannel size is expressed in terms of the instantaneous width (<i>w</i>). (i) Circular cross-sectional profiles are obtained regardless of initial rectangular channel aspect ratio (<i>h₀</i>/<i>w₀</i>; 80°C at 15 psi). (j) Cross-sectional images of channels before and after expansion under the same conditions as (i) with initial aspect ratios of 2.23 (<i>w₀</i> = 16 µm, <i>h₀</i> = 35 µm), 1.00 (<i>w₀</i> = <i>h₀</i> = 31 µm), 0.38 (<i>w₀</i> = 81 µm, <i>h₀</i> = 31 µm), and 0.07 (<i>w₀</i> = 498 µm, <i>h₀</i> = 33 µm) (white bar, 100 µm; black bar, 1000 µm). All experiment data are mean ± sd of 3 independent experiments.</p

Supplementary document for Sub-picosecond tunable mid-infrared light source for driving high-efficiency optical rectification - 6591337.pdf

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