Abstract
This study presents a fabrication method for spherical or ellipsoidal structures, achieved by using a liquid mold in a controlled manner. In order to verify this method, the physical relationship between liquid drops and pre-cured PDMS mixture was investigated during fabrication by altering properties such as density, viscosity, and surface tension. The results show that the lateral capillary force plays a critical role in fabricating hollow dome-like structures in a well-arranged array format. The degree of sphere of the fabricated structures was theoretically examined and was consistent with experimental data. This method is useful for fabricating hollow spherical structures with easy-to-fabricate protocols, and is affordable for general laboratories not equipped with conventional clean room facilities. Standard molding techniques for spherical structures are commonly cumbersome and difficult, since the removal process of the spherical rigid mold from the structure is almost impossible, or destructive to the fabrication. The current fabrication method uses a liquid fabrication mold, therefore providing a noninvasive means of forming spherical structures in pre-cured polymeric mixtures for micro- and meso-scale level applications. This method is also potentially beneficial for producing dynamic culture arrays with a sufficient supply of cell media to maintain controlled cellular environments that can directly induce stem cell differentiation and proliferation.
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Acknowledgments
This work was supported by a grant from the Kyung Hee University in 2010 (KHU-20100608).
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Y. Park and W. Y. Sim contributed equally to this work.
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Figure S1 Graph for quantitative measurement of evaporation over time. This graph shows the rate of evaporation of different mixtures (TIFF 185 kb)
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Figure S2 Observation of lateral movements of liquid droplets of different materials. (a) Observation of lateral movements of droplets 80% ethanol and 100% distilled water at room temperature (RT). Ethanol droplets moved a bit more actively than those of distilled water. The inlet panels show photographs of liquid droplets submerged at PDMS surface with no entrance hole (top) and entrance hole (bottom). Scale bar is 1 cm, (b) Observation of a movement of droplets of 70% ethanol and 200-μL volume at RT. Scale bar is 5 mm. Note that the final positions of the ethanol droplets were dependent on the initial drop positions, resulting in directed 2D mesoscale self-assemblies of liquid droplets at the PDMS surface. (TIFF 953 kb)
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Figure S3 Characterization for geometrical formation of liquid droplet arrays (a) Plot for the distance between droplets in array, (b) Minor-axis diameters of the droplet arrays (TIFF 57 kb)
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Figure S4 Characterization for creation of liquid droplet arrays (N=19, 50 μL). (a) Photographs of fabrication of nineteen-droplet arrays with volume 50 μL. In our experiments, 80% ethanol has only a closely-packed array form, but not coalesced. The conditions below 20% ethanol were not in contact, while 40%, 60%, and 100% ethanol were coalesced. (b) Reversed images of the arrays for clear view. Scale bar is 1 cm. (TIFF 605 kb)
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Figure S5 Characterization for creation of liquid droplet arrays (N=7, 5 μL). (a) Photographs of fabrication of seven-droplet arrays with volume 5 μL. The experimental conditions were strongly affected by evaporation due to small volume and high volatility. The conditions below 40% ethanol were non-contact, in semi-contact at 60%, in contact at 80%, and totally evaporated at 100% where the black arrows indicate the spot for disappeared droplets. Note the experiment for fabricating nineteen-droplet arrays of using 5-μL volume was not performed here, because those droplets are too hard to fabricate due to its strong volatility. (b) Reversed images of the arrays for clear view. Scale bar is 1 cm. (TIFF 475 kb)
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Park, Y., Sim, W.Y. & Lee, W.G. A controllable liquid mold for fabrication of 3D spherical structures and arrays. Microsyst Technol 18, 2093–2098 (2012). https://doi.org/10.1007/s00542-012-1690-y
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DOI: https://doi.org/10.1007/s00542-012-1690-y