Fabrication and electrokinetic motion of electrically anisotropic Janus droplets in microchannels

This is the peer reviewed version of the following article: Li, M. and Li, D. (2017), Fabrication and electrokinetic motion of electrically anisotropic Janus droplets in microchannels. ELECTROPHORESIS, 38: 287–295 which has been published in final form at http://dx.doi.org/10.1002/elps.201600310. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.This paper presents experimental investigations of the fabrication and the motion of electrically anisotropic Janus droplets in a microchannel under externally applied direct current (DC) electrical field. The fabrication method of the Janus droplets is presented first. To begin, oil droplets are coated uniformly with positively charged nanoparticles in the aluminum oxide nanoparticle suspension. The electrically anisotropic Janus droplets are formed when the nanoparticles are accumulated to one side of the droplets in response to externally applied DC electric field. The surface coverage of the Janus droplets by nanoparticles can be adjusted by controlling the concentration of the nanoparticle suspension. The flow fields around the Janus droplets moving in a microchannel were observed with tracing particles. Finally, the electrokinetic velocity of the Janus droplets in a microchannel was measured. The effects of the strength of the electrical field, the surface coverage of the Janus droplets by nanoparticles, the size of the droplets as well as the electrolyte concentration on the electrokinetic velocity of the Janus droplets were studied.Natural Sciences and Engineering Research Council of Canad

Effect of surfactant on Pseudomonas aeruginosa colonization of polymer microparticles and flat films

Micro- and nanoparticles are of great interest because of their potential for trafficking into the body for applications such as low-fouling coatings on medical devices, drug delivery in pharmaceutics and cell carriers in regenerative medicine strategies. Particle production often relies on the use of surfactants to promote stable droplet formation. However, the presence of residual surfactant has been shown to complicate the surface chemistry and resultant properties. When forming particles from polymerizable monomer droplets, these polymeric surfactant chains can become physically entangled in the particle surface. Due to the key role of the outermost layers of the surface in biomaterial interactions, the surface chemistry and its influence on cells needs to be characterized. This is the first study to assess surfactant retention on microfluidic produced particles and its effect on bacterial attachment; surfactant contaminated microparticles are compared with flat films which are surfactant-free. Polymeric microparticles with an average diameter of 76 ± 1.7 μm were produced by using a T-junction microfluidic system to form monomer droplets which were subsequently photopolymerized. Acrylate based monomer solutions were found to require 2 wt% PVA to stabilize droplet formation. ToF-SIMS was employed to assess the surface chemistry revealing the presence of PVA in a discontinuous layer on the surface of microparticles which was reduced but not removed by solvent washing. The effect of PVA on bacterial (Pseudomonas aeruginosa) attachment was quantified and showed reduction as a function of the amount of PVA retained at the surface. The insights gained in this study help define the structure–function relationships of the particulate biomaterial architecture, supporting materials design with biofilm control

A high rate flow-focusing foam generator

We use a rigid axisymetric microfluidic flow focusing device to produce monodisperse bubbles, dispersed in a surfactant solution. The gas volume fraction of the dispersion collected out of this device can be as large as 90%, demonstrating that foam with solid-like viscoelastic properties can be produced in this way. The polydispersity of the bubbles is so low that we observe crystallization of our foam. We measure the diameter of the bubbles and compare these data to recent theoretical predictions. The good control over bubble size and foam gas volume fraction shows that our device is a flexible and promising tool to produce calibrated foam at a high flow rate

Spatioselective Modification of Bicompartmental Polymer Particles and Fibers via Huisgen 1,3-Dipolar Cycloaddition

Precise nano- and microscale control of the architecture of biodegradable biomaterials is desirable for several biotechnological applications such as drug delivery, diagnostics, and medical imaging. Herein, we combine electrohydrodynamic co-jetting and highly specific surface modification (via Huisgen 1,3-dipolar cycloaddition) to prepare particles and fibers with spatioselective surface modification. We first prepared biphasic particles and fibers from commercial poly(lactide- co -glycolide) copolymers via electrohydrodynamic co-jetting of two organic solutions loaded with fluorescent macromolecules and acetylene-modified PLGA derivatives. (i) Spatially controlled reaction of poly[lactide- co -(propargyl glycolide)] with O -(2-aminoethyl)- O ′-(2-azidoethyl)heptaethylene glycol and (ii) subsequent conversion of the newly introduced amino groups with fluorescence probes resulted in particles and fibers with surface modification of one hemisphere only.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/61239/1/1655_ftp.pd

Prediction and control of drop formation modes in microfluidic generation of double emulsions by single-step emulsification

Hypothesis Predicting formation mode of double emulsion drops in microfluidic emulsification is crucial for controlling the drop size and morphology. Experiments and modelling A three-phase Volume of Fluid-Continuum Surface Force (VOF–CSF) model was developed, validated with analytical solutions, and used to investigate drop formation in different regimes. Experimental investigations were done using a glue-free demountable glass capillary device with a true axisymmetric geometry, capable of readjusting the distance between the two inner capillaries during operation. Findings A non-dimensional parameter (ζ) for prediction of double emulsion formation mode as a function of the capillary numbers of all fluids and device geometry was developed and its critical values were determined using simulation and experimental data. At logζ > 5.7, drops were formed in dripping mode; the widening jetting occurred at 5 < logζ < 5.7; while the narrowing jetting was observed at logζ < 5. The ζ criterion was correlated with the ratio of the break-up length to drop diameter. The transition from widening to narrowing jetting was achieved by increasing the outer fluid flow rate at the high capillary number of the inner fluid. The drop size was reduced by reducing the distance between the two inner capillaries and the minimum drop size was achieved when the distance between the capillaries was zero

Differentially Degradable Janus Particles for Controlled Release Applications

Janus particles with differentially degradable compartments were prepared by electrohydrodynamic (EHD) co‐jetting and subsequent controlled crosslinking. These bicompartmental particles are composed of an interpenetrating polymer network of poly(ethylene oxide) and poly(acrylamide‐co‐acrylic acid) in one hemisphere and a crosslinked copolymer of dextran and poly(acrylamide‐co‐acrylic acid) segments in the second compartment. The compositional anisotropy caused differential hydrolytic susceptibility: Although both compartments were stable at pH 3.0, selective degradation of the PEO‐containing compartment pH 7.4 was observed wtihin 5 days. Janus particles with differentially degradable polymer compartments may be of interest for a range of oral drug delivery applications because of their propensity for decoupled release profiles. Submicrometer sized Janus particles are prepared by electrohydrodynamic co‐jetting. Two compartments in the polymer particles are designed to exhibit distinctive physicochemical properties depending on hydrolytic stabilities at different pHs. Although both compartments are stable at a low pH, one compartment is selectively degradable at physiological pH and temperature. Such pH responsive anisotropic particles are useful in targeted drug delivery.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92439/1/1178_ftp.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/92439/2/marc_201200054_sm_suppl.pd

Structurally Controlled Bio-hybrid Materials Based on Unidirectional Association of Anisotropic Microparticles with Human Endothelial Cells

No Abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/64554/1/4920_ftp.pd

Interdroplet bilayer arrays in millifluidic droplet traps from 3D-printed moulds

In droplet microfluidics, aqueous droplets are typically separated by an oil phase to ensure containment of molecules in individual droplets of nano-to-picoliter volume. An interesting variation of this method involves bringing two phospholipid-coated droplets into contact to form a lipid bilayer in-between the droplets. These interdroplet bilayers, created by manual pipetting of microliter droplets, have proved advantageous for the study of membrane transport phenomena, including ion channel electrophysiology. In this study, we adapted the droplet microfluidics methodology to achieve automated formation of interdroplet lipid bilayer arrays. We developed a ‘millifluidic’ chip for microliter droplet generation and droplet packing, which is cast from a 3D-printed mould. Droplets of 0.7–6.0 μL volume were packed as homogeneous or heterogeneous linear arrays of 2–9 droplets that were stable for at least six hours. The interdroplet bilayers had an area of up to 0.56 mm2, or an equivalent diameter of up to 850 μm, as determined from capacitance measurements. We observed osmotic water transfer over the bilayers as well as sequential bilayer lysis by the pore-forming toxin melittin. These millifluidic interdroplet bilayer arrays combine the ease of electrical and optical access of manually pipetted microdroplets with the automation and reproducibility of microfluidic technologies. Moreover, the 3D-printing based fabrication strategy enables the rapid implementation of alternative channel geometries, e.g. branched arrays, with a design-to-device time of just 24–48 hours