Surface Interactions for Controlling the Microfluidic Separation of Polymeric Microspheres
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Surface Interactions for Controlling the Microfluidic Separation of Polymeric Microspheres Alireza Sadeghia, Jonathan Howsea, Steve Ebbensa, Bruno De Geestb a Chemical and Process Engineering Department, University of Sheffield, Sheffield S1 3JD b Laboratory of Pharmaceutical Technology, Faculty of Pharmaceutical Sciences, Ghent University, B-9000 Ghent ABSTRACT Applications of self-assembled monolayers (SAMs) formed by the adsorption of alkanethiols onto gold surfaces have had a widespread growth in adhesion investigations, interfacial interaction investigations and other interfacial phenomena in recent years. As computational modelling showed that modified surfaces can segregate compliant microspheres, a microfluidic flow cell was designed to roll polymeric microcapsules on surfaces with different chemistries, in order to obtain experimental data to validate previous results. Particle image velocimetry showed that rolling speed of microcapsules is affected by surface chemistry. The velocity of vesicles rolling on thiol surfaces with positive of negative charged head groups was significantly lower than vesicles rolling on thiol surfaces with a hydrocarbon chain head group and pure gold surface respectively. Since fabrication of patterned SAMs with different thiol surfaces is possible through oxidation by UV light, our results point to a facile method for carrying out a continuous separation process. INTRODUCTION For both polymeric microcapsules and biological cells, mechanical stiffness is a key parameter since it reveals the quality of the fabricated product in the former case and presence of disease in the latter case.1,2 However, assessing the mechanical properties of such nano-scale particles in an efficient, cost-effective method remains a critical challenge up to now. A number of diseases (e.g., malaria and various cancers) alter the elasticity of biological cells,3 and in some instances, the stiffness of the cell is a sign of the stage of infection.4 While researchers have developed refined approaches to measure the mechanical characteristics of diseased cells,5 there remains a critical need for simple methods to sort cells by their stiffness, and thereby enable rapid, low-cost means. In addition, scientists are now successful in fabricating new types of polymeric microcapsules6 and “polymersomes”,7 with a range of tailored chemical and mechanical properties which can be used as particles mimicking a cell’s behaviour. For instance, elastic vesicles are fabricated by using block copolymers7 while more rigid capsules are formed by fitting nanoparticles into the bounding shells.8 In order to employ these polymeric capsules in biological and chemical applications as microcarriers or microreactors, it becomes necessary to isolate species with the desired mechanical properties.
A recently developed three-dimensional computational model in which microcapsules were modeled as fluid-filled elastic shells rolling on substrates patterned with diagonal stripes showed surfaces that exhibit a simple chemical variation c
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