Research Interests

1. Dynamics of the microvascular system

Microvascular system, including small blood vessels (arterioles, capillaries, and venules), blood flow (microcirculation), and associated nerves, supplies oxygen and nutrients to all the 75 trillion cells that compose our body, particularly to the cells in heart and brain. Microvascular abnormalities, therefore, can deprive tissues of nutrients and oxygen and deteriorate the regulation of blood flow, which may lead to heart diseases, diabetes, and high blood pressure.

Microfluidics is an ideal approach for the study of microvascular system due to its well-controlled microenvironment and the ability to detect biological signals with high spatiotemporal resolution. We are currently interested in the study of mechanosensing of human red blood cells (RBCs) and the intercellular signaling between red cells and small blood vessels by using microfluidic approaches. In particular, we design and fabricate functional micro-devices to explore the mechanisms of deformation-induced adenosine-5'-triphosphate (ATP) release from RBCs and the signaling dynamics between red cells and endothelia cells. We expect the outcomes of our investigation will greatly add to our understanding of microvascular homeostasis and enhance our ability to treat vascular diseases with effective therapeutic strategies.


Figure. 1. Microfluidic approach for shear-triggered release of ATP.

(A) Schematic of the experimental apparatus (not to scale). A mixture of RBCs and luciferase/luciferin solution are pumped through a microfluidic constriction.

(B) Representative experimental measurements of the photon emission rate resulting from the reaction between luciferase/luciferin and ATP, measured versus position along the channel (lc = 1600 µm and wc = 20 µm). The position x = 0 is defined as where the entrance to the constriction. The approximate ATP concentration (CATP) converted from the calibration curve is shown on the right axis. We focus here only on light collected outside of the constriction; no appreciable signal was measured inside the constriction. The error bars are reported as the standard error of the mean (n = 5 different experiments). Note that the photon emission rate increases far downstream from the constriction.


 


2. Microemulsion-based functional materials

Microfluidics is one of the most promising approaches for production of microemulsions and microencapsulation. Research has shown the controlled generation of micrometer diameter droplets and bubbles, double emulsions, triple emulsions, and multiple emulsions inside microfluidic channels. Furthermore, by conducting chemical reactions inside droplets and emulsions, microparticles with desired functionality, e.g., size, shape, and composition, can be generated. The obtained microemulsions and particles find many applications from pharmaceuticals to foods and the cosmetic industry.   

 We are currently interested in microemulsion-based new functional materials for biomedical and chemical applications. In particular, we have shown the controlled generation of gas bubbles in micrometer-diameter aqueous droplets and the synthesis of thin-shell covered microbubbles, which provides a promising approach to achieve microbubble-based ultrasound contrast imaging and image-guided drug delivery materials. Along the development of effect approaches that can produce materials with desired functionality, we also conduct fundamental research to address the roles of fluid dynamics in the synthesis of functional material, particularly in a multiphase system that involves gas bubbles, liquid droplets, and colloidal particles.

 

 

Figure 2. Generation of porous polyacrylamide microparticles and their elastic properties.

a) Image of sequential formation of multi-bubbles per drop in a flow-focusing followed by a T-junction device (FFT) (Qw/Qo = 1; P = 18 psi). Scale bar 200 µm.

b) Inverted image of collected drops with encapsulated microbubbles. Scale bar 200 µm.

c) Image of an acrylamide droplet with bubbles after UV irradiation. Scale bar 50 µm.

d) Force indentation curves of dry polyacrylamide particles when photopolymerized with (□, lower curve) and without bubbles (○, upper curve). The black solid lines represent the fit by the tip model (eq 1) to the indentation data on the polyacrylamide particles when photopolymerized with bubbles (lower curve, open square, E = 3.6 ± 1.2 × 107 Pa) and without bubbles  (upper curve, open circles, Es = 8.6 ± 1.7 × 108 Pa).

 



3.
Photocatalytic multiphase reactions

 Multiphase reactions at the microscale, e.g., in microfluidic devices, have large interfacial areas, efficient heat and mass transfer, and therefore are more efficient than bulk reactions. For example, a tri-phase hydrogenation reaction has been demonstrated in a microfluidic device and the desired products were obtained within two minutes.

 We are interested in photocatalytic multiphase reactions in microfluidics and photo-induced charge transfer dynamics in bulk heterojunction solar cells for clean energy production. Projects are currently under investigation.

 

 



Figure 3.
Photoinduced Electron Transfer in a Quaterthiophene-Amide-Anthraquinone Dyad