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Topographical and chemical defects on solid surfaces tend to pin three-phase contact lines of moving liquid drops. Our quantitative understanding of the pinning process is, however, still poor. Here we use an atomic force microscope to slide ≈100 pL droplets of water-glycerol mixtures over hydrophobic surfaces and measure friction forces. By using picoliter droplets, the sensitivity for detecting processes at the contact line is enhanced. We have found that only a region <200 nm around the contact line contributes to friction. By imaging isolated nanospherical defects, we could quantify the force and energy dissipation when the front and rear of the droplet passes the defect and compare it to theory.
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http://dx.doi.org/10.1103/s6ln-s593 | DOI Listing |
J Control Release
September 2025
Department of Mechanical Engineering, Ulsan National Institute of Science and Technology, UNIST-gil 50, Ulsan 44919, Republic of Korea; RecensMedical, Hwaseong 18468, Republic of Korea. Electronic address:
Transdermal drug delivery holds significant potential for treating skin conditions. Conventional methods utilizing needles or large unit drug delivery volumes often result in patient discomfort and inhomogeneous delivery. This study proposes a picoliter ice particle delivery (PIPD) technology that produces high-speed solid ice drug particles using controlled supersonic cryogenic jets for transdermal drug delivery.
View Article and Find Full Text PDFResearch (Wash D C)
August 2025
Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 101400, P. R. China.
Droplet microfluidics is a rapidly evolving technology enabling precise control and manipulation of small-volume droplets, typically ranging from picoliters to nanoliters, offering important potential for biomedical applications. By generating highly uniform droplets with size variation below 5% and at high frequencies exceeding 10,000 droplets per second using techniques such as flow focusing, this approach facilitates high-throughput experimentation with minimal reagent consumption. These features make droplet microfluidics invaluable for single-cell analysis, drug screening, and disease diagnostics.
View Article and Find Full Text PDFAdv Mater Interfaces
February 2025
Department of Genetics, Stanford University, Stanford, CA 94305, USA; Department of Bioengineering, Stanford University, Stanford, CA 94305, USA; Sarafan ChEM-H Institute, Stanford University, Stanford, CA 94305, USA; Chan Zuckerberg Biohub, San Francisco, CA 94158, USA.
Biphasic environments can enable successful chemical reactions where any single solvent results in poor substrate solubility or poor catalyst reactivity. For screening biphasic reactions at high throughput, a platform based on microfluidic double emulsions can use widely available FACS (Fluorescence Activated Cell Sorting) machines to screen millions of picoliter reactors in a few hours. However, encapsulating biphasic reactions within double emulsions to form FACS-sortable droplet picoreactors requires optimized solvent phases and surfactants to produce triple emulsion droplets that are stable over multi-hour assays and compatible with desired reaction conditions.
View Article and Find Full Text PDFAdv Sci (Weinh)
August 2025
Centre de Recherche Paul Pascal (CRPP), CNRS UMR 5031, Univ. Bordeaux, 115 Avenue du Docteur Schweitzer, Pessac, 33600, France.
Directed evolution relies on iterative cycles of variant generation, screening, and selection to identify enzyme variants with improved activities. Droplet-based microfluidics accelerates this process by enabling rapid screening of enzyme variants in water-in-oil emulsions acting as picoliter-scale microcompartments. In fluorescence-activated droplet sorting (FADS), single E.
View Article and Find Full Text PDFPhys Rev Lett
July 2025
Universidad Técnica Federico Santa María, Departamento de Física, Av. España 1680, Valparaíso 2390123, Chile.
Topographical and chemical defects on solid surfaces tend to pin three-phase contact lines of moving liquid drops. Our quantitative understanding of the pinning process is, however, still poor. Here we use an atomic force microscope to slide ≈100 pL droplets of water-glycerol mixtures over hydrophobic surfaces and measure friction forces.
View Article and Find Full Text PDF