Microfluidic Assembly of Magnetic Hydrogel Particles with Uniformly Anisotropic Structure
Original entry: Darren Yang, AP225, Fall 2010
C.H. Chen, A.R. Abate, D. Lee, E.M. Terentjev, D.A. Weitz, “Editing Microfluidic Assembly of Magnetic Hydrogel Particles with Uniformly Anisotropic Structure,” Advanced Materials, 21, 3201–3204 (2009).
Drop and bubble formation; Magnetic fluids and ferrofluids; Microemulsions; Micro-and nano-scale flow phenomena
The authors present a method to produce monodisperse magnetic particles from double emulsions formed using sequential flow-focus drop formation. This microfluidic drop formation allows the particles to be formed with high monodispersity and with consistently anisotropic internal structure. This structural anisotropy gives rise to magnetic anisotropy, allowing the particles to be rotated by a magnetic field.
Gel particles with the incorporation of an inorganic material are used in a wide range of application. For example, microparticles consisting of magnetic materials encapsulated in a polymer matrix are of great interest in drug deliver, image enhancement, and much more. There are various polymerization methods such as microemulsion and suspension polymerization were establish and implemented to produce these particles. However, these traditional techniques have limitation on size and morphology.
The authors present an alternative technique utilizing microfluidics devices. Magnetic hydrogel particles with uniform anisotropic internal structure were produced by a flow focusing drop make using double emulsions as templates.
Methods and Results
The droplets consist of the hydrophobic monomer core with magnetic material (black) that is encapsulated by a hydrophilic monomer droplet (white) suspended in fluorocarbon oil (gray). By increasing the inner flow rate, two magnetic cores could be encapsulated in the droplets, which demonstrates excellent control of emulsion morphology by the microfludics devices (Figure 1).
Figure 1. Scheme of the PDMS device for forming double emulsion droplets. The scale bar for the two images corresponds to 50mm.
Once polymerized (under UV light), the magnetic gel particles were robust and could be washed, dried, and re-dispersed into water (Figure 2).
Figure 2. a) Particles with a single magnetic core, and b) with two magnetic cores, in fluorocarbon oil. c) Single-core particles dried, and d) re-dispersed in water. The images in the second row show magnified views of the same particles. The scale bar in the top row is 50 mm and in the bottom row is 20 mm.