Creating cellular and molecular patterns via gravitational force with liquid droplets
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Fabrication of a pattern using the gravitational force of a falling liquid droplet. (a) Schematic of this fabrication method. A liquid droplet with proteins such as fibronectin or filamentous actin is pipetted from a defined height onto ultrasoft PDMS that was modified by controlling the ratio of base to curing agent. This liquid droplet was then dried on the modified PDMS during the curing process, which patterned the proteins at the position of the droplet. The topography of the soft PDMS was also controlled through the indentation of the PDMS due to the gravitational force of the falling droplet. The distance between the liquid droplet and the modified PDMS was 1 cm. The patterned area can be controlled by altering the distance between the liquid droplet and the modified PDMS. (b) A graph of the elastic modulus of PDMS and the weight ratio of base to curing agent. The elastic moduli of PDMS were determined through compression tests. [(c) and (d)] Optical images of the resulting configuration of the liquid droplets with the modified PDMS. When using water, bubbles formed around the liquid pattern (c), yet the bubbles were limited when using buffered solution (d). Scale in (c) and the scale in (d). (e) Diameters of patterns vs the falling distance of liquid droplets. By increasing the falling height, a larger pattern can be obtained through our method.
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(a) Imaging schematic of molecular and cellular patterning achieved via the use of liquid droplets and gravity. (b) Fluorescent (tetramethylrhodamine isothiocyanate) images of the pattern formed by a droplet containing rhodamine fibronectin. The PDMS weight ratio of base to curing agent was 50:1 resulting in a PDMS elastic modulus of 17.6 kPa (Scale ). (c) NIH 3T3 fibroblasts were cultured on the surface after the fibronectin coated droplet pattern PDMS was treated with bovine serum albumin (3 mg in 1 ml PBS) for 1 h to block nonspecific attachment of the cells. The cells were allowed to attach and spread for at least 6 h in the local regions where the fibronectin was patterned (scale ). Local regions of cells are visualized due to the patterning and the image focal plane onthis curved structure. (d) Side view of the curved pattern formed from the droplet process. This has a high aspect ratio of 5 (vertical scale ). (e) A top-down scanning electron micrograph of this array pattern. (f) Three-dimensional profile of a single pattern fabricated through our method.
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Patterning of molecular structures using droplets. (a) Actin filaments patterned through the use of our liquid droplets technique. The PDMS weight ratio of base to curing agent was 42:1 resulting in a PDMS elastic modulus of 27.5 kPa (scale ). The actin filaments were labeled using phalloidin. (b) Higher magnification image showing individual actin filaments in the patterned region in (a) (scale ). (c) By using localized actin filaments, inorganic structures were also patterned in localized regions through crystallization (scale ).
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