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Zhang L.,Tsinghua University | Hao S.,Tsinghua University | Liu B.,Tsinghua University | Shum H.C.,University of Hong Kong | And 3 more authors.
ACS Applied Materials and Interfaces | Year: 2013

We demonstrate an approach to prepare zirconium dioxide (ZrO2) microspheres by carrying out a diffusion-induced sol-gel reaction inside double emulsion droplets. A glass capillary microfluidic device is introduced to generate monodisperse water-in-oil-in-water (W/O/W) double emulsions with a zirconium precursor as the inner phase. By adding ammonia to the continuous aqueous phase, the zirconium precursor solution is triggered to gel inside the emulsions. The double emulsion structure enhances the uniformity in the rate of the sol-gel reaction, resulting in sol-gel microspheres with improved size uniformity and sphericity. ZrO2 ceramic microspheres are formed following subsequent drying and sintering steps. Our approach, which combines double-emulsion-templating and sol-gel synthesis, has great potential for fabricating versatile ceramic microspheres for applications under high temperature and pressure. © 2013 American Chemical Society. Source

Li Z.,University of Hong Kong | Mak S.Y.,University of Hong Kong | Sauret A.,Princeton University | Shum H.C.,University of Hong Kong | Shum H.C.,HKU Shenzhen Institute of Research and Innovation HKU SIRI
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2014

We report a new method to display the minute fluctuations induced by syringe pumps on microfluidic flows by using a liquid-liquid system with an ultralow interfacial tension. We demonstrate that the stepper motor inside the pump is a source of fluctuations in microfluidic flows by comparing the frequencies of the ripples observed at the interface to that of the pulsation of the stepper motor. We also quantify the fluctuations induced at different flow rates, using syringes of different diameters, and using different syringe pumps with different advancing distances per step. Our work provides a way to predict the frequency of the fluctuation that the driving syringe pump induces on a microfluidic system and suggests that syringe pumps can be a source of fluctuations in microfluidic flows, thus contributing to the polydispersity of the resulting droplets. © 2014 The Royal Society of Chemistry. Source

Kong T.,University of Hong Kong | Kong T.,HKU Zhejiang Institute of Research and Innovation HKU ZIRI | Shum H.C.,University of Hong Kong | Shum H.C.,HKU Shenzhen Institute of Research and Innovation HKU SIRI | And 2 more authors.
Biomicrofluidics | Year: 2013

We report a facile and robust microfluidic method to fabricate polymeric core-shell microspheres as delivery vehicles for biomedical applications. The characteristics of core-shell microspheres can be precisely and easily tuned by manipulating the microfluidic double emulsion templates. The addition of a shell can significantly improve the versatility as well as functionality of these microspheres as delivery vehicles. We demonstrate that the nature of the shell material plays an important role in the properties of the core-shell delivery vehicles. The release kinetics is significantly influenced by the material of the shell and other characteristics such as the thickness. For example, by adding a poly(lactic-co-glycolic acid) (PLGA) shell to an alginate core, the encapsulation efficiency is enhanced and undesired leakage of hydrophilic actives is prevented. By contrast, adding an alginate shell to PLGA core can lead to a reduction of the initial release rate, thus extending the release period of hydrophobic actives. Microfluidic fabrication enables the generation of precisely controlled core-shell microspheres with a narrow size distribution, which enables the investigation of the relationship between the release kinetics of these microspheres and their characteristics. The approach of using core-shell particles as delivery vehicles creates new opportunities to customize the release kinetics of active ingredients. © 2013 AIP Publishing LLC. Source

Chan Y.K.,University of Hong Kong | Wong D.,University of Hong Kong | Yeung H.K.,University of Hong Kong | Man P.K.,University of Hong Kong | And 2 more authors.
Investigative Ophthalmology and Visual Science | Year: 2015

PURPOSE. Silicone oil (SO) has been used as a long-term intraocular tamponade in treating retinal diseases for more than half a decade. However, its propensity to form tiny SO droplets is associated with a number of complications. Currently there is no effective way to remove such droplets from the eye cavity. In this work, a novel cleaner was developed for effective removal of these droplets. METHODS. The cleaner promotes the formation of an oil-in-water-in-oil (O/W/O) doubleemulsion that consists of the unwanted droplets as the innermost oil phase. The cleaner’s ability to encapsulate SO droplets was tested using both in vitro microdevices and ex vivo porcine eye models. The efficiency of the cleaner in removing the SO droplets was quantified using the three-dimensional (3D) printed eye model. Both the volatility and in vitro cytotoxicity of the cleaner were evaluated on three retinal cell lines. RESULTS. Cleaner 1.0 is volatile and has an evaporation rate of 0.14 mL/h at room temperature. The formation of O/W/O double-emulsion indicates the encapsulation of SO droplets by the cleaner. In the 3D printed eye model, rinsing with cleaner 1.0 led to a significant reduction of leftover SO droplets compared with 13 phosphate-buffered saline (PBS; P < 0.05; n ¼ 6). Cleaner 1.0 did not cause significant cell death (3%–6%) compared with balance salt solution (BSS; 1%–3%) in all three cell lines. The reduction in the cell viability due to cleaner 1.0, relative to that of BSS, was significant only in ARPE-19 cells (27%; P < 0.05) but not in the other two cell lines (8% and 17%, respectively; P > 0.05). CONCLUSIONS. The double-emulsification approach was effective in removing remnant droplets from the eye cavities, and the cleaner was compatible with common cell types encountered in human eyes. The mechanism of toxicity of the proposed cleaner is still unknown, therefore, further in vivo animal tests are needed for full evaluation of the physiological response before the proposed cleaner can be advanced to clinical trials for retinal surgeries. © 2015 The Association for Research in Vision and Ophthalmology, Inc. Source

Kong T.,University of Hong Kong | Kong T.,HKU Zhejiang Institute of Research and Innovation HKU ZIRI | Wang L.,University of Hong Kong | Wang L.,HKU Zhejiang Institute of Research and Innovation HKU ZIRI | And 3 more authors.
Soft Matter | Year: 2014

In this work, we have developed a facile, economical microfluidic approach as well as a simple model description to measure and predict the mechanical properties of composite core-shell microparticles made from materials with dramatically different elastic properties. By forcing the particles through a tapered capillary and analyzing their deformation, the shear and compressive moduli can be measured in one single experiment. We have also formulated theoretical models that accurately capture the moduli of the microparticles in both the elastic and the non-linear deformation regimes. Our results show how the moduli of these core-shell structures depend on the material composition of the core-shell microparticles, as well as on their microstructures. The proposed technique and the understanding enabled by it also provide valuable insights into the mechanical behavior of analogous biomaterials, such as liposomes and cells. © 2014 the Partner Organisations. Source

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