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Making Sense of Microfluidics
* 1 , 2 , 1
1  National University of Singapore
2  Singapore Institute of Manufacturing Technology, A*STAR


Microfluidics has often been used for chemical or biological sensing, but rarely for mechanical sensing. Furthermore, conventional lab-on-chip platforms require discrete patient samples, and rely on bulky equipment such as microscope and syringe pump. Here, we revolutionized the microfluidics regime into elements compatible to our skin to enable continuous and unobtrusive biomonitoring. The aim of this presentation is to introduce the mechanosensing principle using flexible microfluidics and demonstrate its potential in disease sensing, rehabilitation monitoring, and artificial sensing.

To achieve this, we combined the principles of material science and deterministic geometry to develop a microfluidic liquid-based tactile sensor that is soft, thin, flexible, stretchable, and cost-effective to produce. The sensor comprises a unique combination of soft silicone rubber substrate and conductive fluid which forms the active liquid-based sensing element. These liquids assume the shape of the microchannels within the soft silicone elastomer due to the weak intermolecular forces of attraction between particles. As such, their shape is highly reconfigurable. Essentially, the conductive fluid is displaced in proportion to the mechanical forces exerted by the user, which corresponded to a change in its electrical resistance.The combination of a highly deformable elastomer and conductive liquid of low viscosity forms an important aspect in our approach in transducing mechanical forces to electrical changes. Microfluidic channels form the geometrical pattern that enables efficient liquid movement, realizing a sensor with high responsiveness, low creep, and low hysteresis. 

Furthermore, by modifying the contents of the silicone elastomer and conductive fluid, the device sensitivity, material hardness, viscoelasticity, and stretchability may be further tuned for different applications. We have demonstrated the utility of our sensor in numerous healthcare applications, including disease sensing, rehabilitation monitoring, and even artificial sensing. For example, we designed an elastomeric structure with a microfluidic protrusion capable of sensing surface roughness, and even recognizing Braille elements. In another application, we developed a microfluidic sensor the size of a strand of hair that can be attached to the wrist to monitor pulse pressure continuously and unobtrusively. Importantly, the possibility of imperceptible monitoring is set to create a paradigm shift in traditional clinical healthcare assessment, allowing access to the patient’s vital signs anytime, anywhere. 

Keywords: Wearable microfluidics