Purpose: Polymer microspheres and microcapsules are used ubiquitously in tissue engineering and drug delivery as drug depots and carriers. These microspheres and microcapsules are typically generated by emulsification process, followed by solidification or removal of the solvent. Majors challenges that limit the widespread utilization of these microspheres/microcapsules in clinical settings are 1) low encapsulation efficiency (typically well below 30%) and 2) large heterogeneity in size and properties (Shah, 2008). Using glass capillary microfluidic droplet generator allows for the formation of highly uniform single and multiple emulsions at a high rate (103–104 drops/sec) (Shah, 2008). These droplets have already been used as templates to generate microspheres and microcapsules with high uniformity and high encapsulation efficiency (essentially ~ 100%)(Chu, 2007, Kamat, 2011, Lee, 2008, Shum, 2008, Tu, 2012, Utada, 2005). Because of their chemical compatibility, these glass capillary devices are especially attractive when the emulsification process uses organic solvents that are known to degrade plastic or poly(dimethylsiloxane)-based microfluidic devices. Also the surface of the capillaries can be readily functionalized with the silane chemistry to facilitate the formation of multiple emulsions.
Method of Fabrication/Use: A schematic illustration of a glass capillary emulsion generator is shown in Glass capillaries that have outer diameters of 500 um to 1 mm are used to for the fabrication of these devices. Tapered orifices are formed by using a capillary puller, which locally heats a portion of a capillary and pulls the two ends of the capillary apart to form two capillaries with orifices. The size of the orifice can be further tuned by using a microforge. A round capillary with an orifice of 5 – 200 um (determined by the desired size of emulsions) is inserted into a square capillary, of which inner dimension matches the outer diameter of the round capillary. By inserting multiple round capillaries within a single square channel, it is possible to generate drop generators that are designed to form highly structured multiple emulsions. Once emulsions are generated using these devices, the microsphere/microcapsules can be prepared by simply evaporating the solvent or by converting the monomer in the dispersed phase of emulsions to solid particles.(Tu, 2012)
Learn more about Dr. Lee’s research here.
Chu LY, Utada AS, Shah RK, Kim JW, Weitz DA. Controllable monodisperse multiple emulsions. Angew Chem Int Ed Engl 2007; 46 (47): 8970-8974.
Kamat NP, Lee MH, Lee D, Hammer DA. Micropipette aspiration of double emulsion-templated polymersomes. Soft Matter 2011; 7 (21): 9863-9866.
Lee D, Weitz DA. Double emulsion-templated nanoparticle colloidosomes with selective permeability. Advanced Materials Sep 17 2008; 20 (18): 3498-+.
Shah RK, Shum HC, Rowat AC, Lee D, Agresti JJ, Utada AS, Chu LY, Kim JW, Fernandez-Nieves A, Martinez CJ, Weitz DA. Designer emulsions using microfluidics. Materials Today Apr 2008; 11 (4): 18-27.
Shum HC, Lee D, Yoon I, Kodger T, Weitz DA. Double emulsion templated monodisperse phospholipid vesicles. Langmuir Aug 5 2008; 24 (15): 7651-7653.
Tu F, Lee D. Controlling the stability and size of double-emulsion-templated poly(lactic-co-glycolic) acid microcapsules. Langmuir Jul 3 2012; 28 (26): 9944-9952.
Utada AS, Lorenceau E, Link DR, Kaplan PD, Stone HA, Weitz DA. Monodisperse double emulsions generated from a microcapillary device. Science Apr 22 2005; 308 (5721): 537-541.