Microfluidics and Bio-MEMS

Devices and Applications

Tuhin S. Santra, Tuhin S. Santra

• Publisher: Jenny Stanford Publishing
• Year: 2020
• ISBN:
  9781000769210
• Edition: 1
• Topic: Medicine
• Subtopic: Biotechnology in Medicine

The past two decades have seen rapid development of micro-/nanotechnologies with the integration of chemical engineering, biomedical engineering, chemistry, and life sciences to form bio-MEMS or lab-on-chip devices that help us perform cellular analysis in a complex micro-/nanoflluidic environment with minimum sample consumption and have potential biomedical applications. To date, few books have been published in this field, and researchers are unable to find specialized content. This book compiles cutting-edge research on cell manipulation, separation, and analysis using microfluidics and bio-MEMS devices. It illustrates the use of micro-robots for biomedical applications, vascularized microfluidic organs-on-a-chip and their applications, as well as DNA gene microarray biochips and their applications. In addition, it elaborates on neuronal cell activity in microfluidic compartments, microvasculature and microarray gene patterning, different physical methods for drug delivery and analysis, micro-/nanoparticle preparation and separation in a micro-/nanofluidic environment, and the potential biomedical applications of micro-/nanoparticles. This book can be used by academic researchers, especially those involved in biomicrofluidics and bio-MEMS, and undergraduate- and graduate-level students of bio-MEMS/bio-nanoelectromechanical systems (bio-NEMS), biomicrofluidics, biomicrofabricatios, micro-/nanofluidics, biophysics, single-cell analysis, bionanotechnology, drug delivery systems, and biomedical micro-/nanodevices. Readers can gain knowledge of different aspects of microfluidics and bio-MEMS devices; their design, fabrication, and integration; and biomedical applications. The book will also help biotechnology-based industries, where research and development is ongoing in cell-based analysis, diagnosis, and drug screening.

Chapter 1
Microfluidic Technologies for Cell Manipulation, Therapeutics, and Analysis

Amogh Kumar,^a Pallavi Shinde,^a Loganathan Mohan,^a Pallab Sinha Mahapatra,^b and Tuhin S. Santra^a

^a Department of Engineering Design, Alumni Ave, Indian Institute of Technology, Chennai, Tamil Nadu 600036, India

^b Department of Mechanical Engineering, Indian Institute of Technology, Chennai, Tamil Nadu 600036, India

[email protected], [email protected]

Biological cell studies commonly involve thousands or millions of cells together, especially in the case of clinical applications. Toward this end, conventional techniques used for research, diagnostic, and therapeutic purposes in cellular biology fall short due to their low throughput and inability to provide information about individual cells. In recent years, microfluidic technologies have come to the frontiers of research due to their seemingly vast applications and adaptability to various requirements for conducting comprehensive cell studies on chip. On the other hand, microfluidic-based single-cell analysis has emerged over the past two decades owing to high throughput combined with the ability it provides to study individual cells precisely. This chapter discusses in detail some of the prominent microfluidic strategies employed for cellular manipulation, analysis, and treatment and their feasibility in clinical applications.

1.1 Introduction

In the last three decades, the advances in microfabrication techniques have enabled us to develop several microsystem devices with various applications. The application of microsystems in biological cell studies is a growing research field that has shown several advantages over conventional methods [1–3]. The development of microsystem technology integrated with chemistry, chemical engineering, and life sciences in the form of biomicroelectromechanical systems or lab-on-a-chip (LOC) devices provides a powerful tool for cellular analysis in a micro- or nanofluidic environment. To understand cellular functions and their interactions precisely, a conventional or bulk approach involving millions of cells together can provide average information, but it cannot reveal the cellular heterogeneity characteristics and molecular dynamics [4–8]. On the other hand, micro- or nanofluidic devices have the ability to analyze cellular function precisely at the single-cell level. Micro-and nanofluidic devices can not only perform cellular manipulation, separation, and isolation but also help in cellular therapeutics and diagnostics [6–8].

In their natural environment, cells exist in heterogeneous states, with extreme variations in intracellular components, such as DNA, RNA, and proteins [9, 10]. This has been the main inspiration behind the development of micro- and nanofluidic devices for performing single-cell analysis, with such systems termed as single-cell technologies (SCTs) [4, 11]. SCTs can provide highly accurate information about individual cells and enable cell manipulation and therapeutics in a highly efficient manner [12, 13]. Obtaining extensive knowledge about the behavior of cells and various cellular and molecular pathways is the first step toward understanding the mechanisms through which diseases originate or progress as well as discovering pathways to treat those diseases. SCTs offer the possibility to conduct dynamic studies on individual cells and analyze cellular compartments [5, 14].

Recently, more advanced microfluidic techniques have emerged that allow one to study cellular functions and mechanisms precisely. The major advantage of microfluidic techniques over other conventional methods is that they provide high-throughput devices for the manipulation and analysis of cells. Microfluidic devices are fabricated using well-established microfabrication techniques, such as photolithography, soft lithography using polydimethylsiloxane (PDMS), and wet etching [15, 16]. The devices require picoliter to microliter sample volumes for performing their desired functions and enable simultaneous analysis of many cells. This, in turn, shows great promise toward adapting these devices for clinical diagnostic, therapeutic, and regenerative medicine purposes in the future [7].

This chapter discusses several microfluidic techniques currently employed for studying cellular biology. Many high-throughput microfluidic devices have been used for single-cell trapping using electro-osmotic flow manipulation, microvortex manipulation, etc. Then various microfluidic-based physical techniques, such as electroporation and mechanoporation, are discussed for single-cell therapeutic and diagnostic purposes. Finally, the prospects and applications of microfluidic technologies in cellular biology have been discussed.

1.2 Microfluidic Cell Capture Techniques

Cell capture or trapping is the first step for cellular analysis or many other applications, such as treatment, culture, and monitoring. Cells often need to be trapped or moved to a specific location on a chip for further incubation, analysis, or treatment. Many microfluidic devices have been developed to trap cells with high efficiency [17]. These devices usually do not employ any external force fields, such as optical, electric, or magnetic fields. Other conventional techniques for cell trapping, such as microscopy or patch clamp, suffer disadvantages such as high skill requirement for operation. In comparison to this, the most difficult step in employing microfluidic devices for cell trapping is the complex design and fabrication process [18]. Microfluidic devices generally allow integration with other techniques for analysis or monitoring of micro- to picoliter samples. Both droplet microfluidics and flow channels containing hydrodynamic traps are used for single-cell trapping. Recent advancements in microfabrication techniques have enabled the design of several novel microfluidic devices for single-cell trapping, a few of which are discussed in this section (Table 1.1).

Table 1.1 Microfluidic techniques for cell trapping

S. no.	Microfluidic cell trapping options	Key features	References
1	Microdroplets	Provides high throughput Allows further analysis after cell capture	[19,20]
2	Microarray devices	Provides high throughput Provides the possibility for incubation on the same chip after trapping	[21-23]
		Allows the selection and retrieval of specific cells from the microenvironment without losing any information
3	Microvortices	Involves relatively simple device fabrication and operation, unlike other methods	[24,25]
		Allows cell sorting by size
4	Dielectrophoresis and electro-osmotic flow	Allows easy patterning of single cells on a substrate	[26, 27]

1.2.1 Microdroplet-Based Cell Trapping

Fan et al. [19] introduced a microfluidic device that employed a change in flow resistance due to trapping of droplets in a channel as the driving principle for separating single cells on a chip. The device consisted of two dispensing modules: one dispensed oil, which acted as a continuous phase, and the other module dispensed the cell sample, which acted as the dispersed phase. The two inlets met at a T-junction, as shown in Fig. 1.1. Due to the shear force created by the flow rate of the continuous phase, microdroplets of the sample would break off and flow along the main channel., thus forming the dispersed phase. The main channel consisted of several snake-like bypass channels and was directly connected with them. The diameter of the main channel was equal to that of the bypass channel. Without any droplet trapping, the flow rate in the straight channels was higher than that in the bypass channels due to the variation in length.

Figure 1.1 (a) Overall schematic of a microfluidic device. (b) The T-junction where microdroplets are formed. (c) Schematic showing the main and bypass channels. (d) Imaging and analysis following cell capture. Reprinted from Ref. [19]. © IOP Publishing. Reproduced with permission. All rights reserved.

However, once a droplet was trapped in the straight channel due to the decrease in the radius of the channel after a certain length, the flow resistance of the straight channel became much higher than that of the bypass channel. As a result, the oil and the sample droplets started flowing in the bypass channel. Thus, a single droplet containing the cell was trapped at each junction in the main channel corresponding to a bypass channel. The diameters of the microdroplets were larger than the widths of the narrow parts of the main channel to ensure the droplets would not flow through the channel and to prevent the continuous phase from passing through it.

The concentration of cells in the sample and the size of the microdroplets were adjusted accordingly to obtain the maximum number of droplets encapsulating single cells. Human liver hepatocellular carcinoma (HepG2) cells were used for experimental studies. The efficiency of trapping the droplets containing single cells reached up to 60%. Following cell capture, fluorescence studies were conducted to demonstrate the device efficiency in the single-cell analysis (Fig. 1.2). Thus, with further optimization, this device could show great promise in biological applications.

Figure 1.2 (a, c) Bright-field images of cells in the device. (b, d) Fluorescence images of cells trapped in the device. Reprinted from Ref. [19]. © IOP Publishing. Reproduced with permission. All rights reserved.

Sauzade and Brouzes [20] introduced a similar device for single-cell trapping using droplet mic...