Ashis Kumar Sen

Passive droplet manipulation on open surfaces can be achieved by creating a wettability gradient on surfaces, which is essential in the fabrication of low cost biological and biochemical chips. We performed 3D numerical simulations to analyze the droplet motion on a broad range of wettability gradient surfaces. We found that the droplet shape evolves with time to maintain a minimum energy state, and the surface energy of the droplet is identical at a particular non-dimensional time (t∗) for different wettability gradient surfaces. Although the droplet is at various locations at a fixed t∗, the shape of the droplet is found to be identical. The physics behind this interesting phenomenon of identical droplet shape formation is explored. A co-relation for t∗ is proposed to get the dependency of t∗ on various geometrical parameters and fluid properties. Three distinct regimes of the droplet identical shape on different wettability gradient surfaces are shown using a regime plot. Along with the identical droplet shape phenomena, the detailed understanding of the dynamics of the droplet shape evolution on different wettability gradient surfaces gives an insight for better open surface passive manipulation.

Circulating tumor cells (CTC) are released from the primary tumors into the bloodstream. These CTCs hold a crucial role in cancer metastasis; hence, they could be used for early diagnosis of cancer, evaluation of cancer development, and even helpful in drug development. In recent years, many novel microfluidic-based techniques for CTCs detection and isolation are explored. However, still, they cannot fulfill the current clinical requirement because of numerous current technological limitations. The heterogeneous nature of CTCs makes it further complicated. This chapter provides current advancements in CTC detection and isolation in a microfluidics platform. Different techniques are evaluated based on various parameters, such as purity, throughput, and cell viability. We discussed the concepts, limitations, advantages, drawbacks, and challenges, and at the end, we also discussed future application prospect.

Here we report the development of a micro flow analyser that integrates digital microfluidics technology with optoelectronics for the detection of micron size droplets and particles. Digital microfluidics is employed for the encapsulation of microparticles inside droplets that self-align at the centre of a microchannel thus eliminates the need of complicated 3D focusing. Optoelectronics comprise a laser source and detectors for the measurement of forward scatter (FSC), side scatter (SSC) and fluorescence (FL) signals from the microparticles. The optoelectronics was first used with a simple 2D flow focusing channel to detect microparticles which showed uncertainty in the data due to lack of 3D focusing. The integrated device with digital microfluidics technology and optoelectronics was then used for the enumeration and detection of Rhodamine droplets of different size. Rhodamine droplets of different size were characterized based on FSC, SSC and FL. Finally, the device was used for the detection of fluorescent microbeads encapsulated inside aqueous droplets.

This work presents design, fabrication and test of a microfluidic device which employs Fahraeus-Lindqvist and Zweifach-Fung effects for cell concentration and blood cell-plasma separation. The device design comprises a straight main channel with a series of branched channels placed symmetrically on both sides of the main channel. The design implements constrictions before each junction (branching point) in order to direct cells that would have migrated closer to the wall (naturally or after liquid extraction at a junction) towards the centre of the main channel. Theoretical and numerical analysis are performed for design of the microchannel network to ensure that a minimum flow rate ratio (of 2.5:1, main channel-to-side channels) is maintained at each junction and predict flow rate at the plasma outlet. The dimensions and location of the constrictions were determined using numerical simulations. The effect of presence of constrictions before the junctions was demonstrated by comparing the performances of the device with and without constrictions. To demonstrate the performance of the device, initial experiments were performed with polystyrene microbeads (10 and 15 μm size) and droplets. Finally, the device was used for concentration of HL60 cells and separation of plasma and cells in diluted blood samples. The cell concentration and blood-plasma purification efficiency was quantified using Haemocytometer and Fluorescence-Activated Cell Sorter (FACS). A seven-fold cell concentration was obtained with HL60 cells and a purification efficiency of 70 % and plasma recovery of 80 % was observed for diluted (1:20) blood sample. FACS was used to identify cell lysis and the cell viability was checked using Trypan Blue test which showed that more than 99 % cells are alive indicating the suitability of the device for practical use. The proposed device has potential to be used as a sample preparation module in lab on chip based diagnostic platforms.

Microfluidics as a field has a plethora of applications in several fields. From heat transfer to biomedical applications, microfluidic techniques are used to deliver solutions. In the present chapter, we look into the basics of microfluidic techniques used to manipulate tiny volumes of fluids. Further, a detailed discussion on acoustofluidics, lab/organ-on-chip, biosensing, and cell manipulation follows. Section 2.4 focuses on the use of bulk and surface acoustic waves to manipulate particles and cells. Section 2.5 sheds light on the use of microfluidic chips mimicking an organ or its basic process and how the same is used to study the effect of drugs on the organs. Section 2.6 focuses on using microfluidic techniques for disease detection and prognosis monitoring. The part on Cell manipulation cuts through various active and passive techniques for cell trapping, focusing, and sorting.