Microparticulate systems are widely used for applications such as drug delivery, biological analysis, and clinical diagnosis. However, particles produced by conventional methods are typically limited to spherical shape and monolithic or core-shell structures. Based on soft lithography, we have developed a simple method to fabricate plate-like polymer microparticles. Through inducing self-folding of these 2-D precursors, we can produce 3-D particulate microstructures.
- Th is fabrication process is illustrated in F igure ( a ) . 40 m m-wide square poly prop yl methacrylate (PPMA) micropads were printed on a chitosan -coated glass slide by microContact Hot Printing using a polydimethyl siloxane (PDMS) stamp. S oybean o il was then applied onto the slide, leaving oil droplets on ly on the PPMA micropads as shown in Figure (b) due to the polarity differences between oil, PPMA and chitosan . Finally, aqueous ace t ic acid solution was added to release the micropads by dissolving the chitosan sacrificial layer . T he released micropads fold ed over the oil droplets spontaneously, forming dumpling-like microstructures as s hown in Figure (c).
The exclusive wetting of micropads by oil is a result of minimization of interfacial energy of the sys tem due to low surface tension s of P P MA and oil , and the high surface tension of chitosan . The folding of the micropads i s also driven by free - energy minimization as water replace s air in the system. S ince the oil- water interfacial tension i s larger than that of oil-air and P P MA-water, t he oil droplets that initially sp r ead on the micropads tend to shrink into a spherical shape to minimize their interfacial area in contact with water . Also due to t he strong adhesion between oil and P P MA and the compliance of the micropads , t he oil droplets force the released micropads to fold around them . The final structures are dumpling-like microcapsules with oil cores and PPMA coats.
This technique presents a simple strategy for fabricating 3-D polymeric microstructures that are difficult to produce by other technique s, as well as a method for drug and cell microencapsulation. P articulate microdevices for applications such as advanced drug delivery and tissue engineering may be fabricated using this method.
Microparticulate systems are widely used for biomedical applications such as drug delivery, biological analysis, and clinical diagnosis. However, particles produced by conventional manufacturing methods are typically limited to spherical shape, relatively wide size distributions, and monolithic or core-shell structures. Based on soft lithography, we have developed a simple method to fabricate plate-like polymer microparticles. Through inducing self-folding of the plate-like microparticles made of environment-sensitive hydrogels, we can also make 3-D particulate microstructures. The microstructures and the technique can be used to make microdevices such as sensors and drug delivery systems.
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Figure. (a) Fabrication process of dumpling-like microstructures. (b) Oil droplets on PPMA micropads attached to a chitosan sacrificial layer. The upper-left inset shows PPMA micropads before oil was applied. (c) Dumpling-like PPMA microstructures in aqueous solution of acetic acid.
Light micrograph of a hydrogel microstructure in water formed by self-folding
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