cells Review A Review of Single-Cell Adhesion Force Kinetics and Applications Ashwini Shinde 1 , Kavitha Illath 1, Pallavi Gupta 1, Pallavi Shinde 1, Ki-Taek Lim 2 , Moeto Nagai 3 and Tuhin Subhra Santra 1,* 1 Department of Engineering Design, Indian Institute of Technology Madras, Chennai 600036, Tamil Nadu, India; [email protected] (A.S.); [email protected] (K.I.); [email protected] (P.G.); [email protected] (P.S.) 2 Department of Biosystems Engineering, Kangwon National University, Chuncheon-Si, Gangwon-Do 24341, Korea; [email protected] 3 Department of Mechanical Engineering, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi, Aichi 441-8580, Japan; [email protected] * Correspondence: [email protected]; Tel.: +91-044-2257-4747 Abstract: Cells exert, sense, and respond to the different physical forces through diverse mechanisms and translating them into biochemical signals. The adhesion of cells is crucial in various develop- mental functions, such as to maintain tissue morphogenesis and homeostasis and activate critical signaling pathways regulating survival, migration, gene expression, and differentiation. More impor- tantly, any mutations of adhesion receptors can lead to developmental disorders and diseases. Thus, it is essential to understand the regulation of cell adhesion during development and its contribution to various conditions with the help of quantitative methods. The techniques involved in offering different functionalities such as surface imaging to detect forces present at the cell-matrix and deliver quantitative parameters will help characterize the changes for various diseases. Here, we have briefly reviewed single-cell mechanical properties for mechanotransduction studies using standard and recently developed techniques. This is used to functionalize from the measurement of cellular Citation: Shinde, A.; Illath, K.; deformability to the quantification of the interaction forces generated by a cell and exerted on its Gupta, P.; Shinde, P.; Lim, K.-T.; surroundings at single-cell with attachment and detachment events. The adhesive force measurement Nagai, M.; Santra, T.S. A Review of for single-cell microorganisms and single-molecules is emphasized as well. This focused review Single-Cell Adhesion Force Kinetics should be useful in laying out experiments which would bring the method to a broader range of and Applications. Cells 2021, 10, 577. research in the future. https://doi.org/10.3390/cells10030577 Keywords: single-cell adhesion; mechanotransduction; microbial cell adhesion; single-molecule Academic Editor: Daniel Bouvard adhesion Received: 28 January 2021 Accepted: 2 March 2021 Published: 5 March 2021 1. Introduction Publisher’s Note: MDPI stays neutral Within a living organism, cells gather information about their surroundings and with regard to jurisdictional claims in process them by chemical, electrical and mechanical signals. Chemical and electrical signals published maps and institutional affil- are well understood; however, there is much need to learn about mechanical signaling. iations. Along with the traditional knowledge of chemical and electric signaling as the primary mechanism, now mechanical signaling is also known to play an essential role in a vast range of biological activities. Many cells such as immune cells [1], neurons [2], endothelial cells [3], muscle cells [4] and osteocytes [5] are mechanically sensitive, and thus, they generate force. The process known as mechanotransduction is the force between the cell Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. and its surrounding that transmits mechanical signals which are converted into biochemical This article is an open access article signals. Mechanotransduction and mechanical activities play a central role in various cell distributed under the terms and processes such as cell growth [6], differentiation [7], meiosis and mitosis [8], apoptosis [9] conditions of the Creative Commons and homeostasis [10]. Thus, the malfunction of mechanical stimuli sensed by the cell can Attribution (CC BY) license (https:// have severe consequences which lead to diseases, such as vascular diseases [11], kidney creativecommons.org/licenses/by/ diseases [12], dystrophy [13] and cancer [14]. Thus, it is imperative to characterize and 4.0/). understand mechanical signaling to the same extent as chemical and electrical signaling. Cells 2021, 10, 577. https://doi.org/10.3390/cells10030577 https://www.mdpi.com/journal/cells Cells 2021, 10, 577 2 of 46 have severe consequences which lead to diseases, such as vascular diseases [11], kidney diseases [12], dystrophy [13] and cancer [14]. Thus, it is imperative to characterize and understand mechanical signaling to the same extent as chemical and electrical signaling. Cells 2021, 10, 577 The study of single-cell adhesion is one of the most important and2 of 46 complicated as- pects to understand in life sciences. Different cells adhere to their surrounding surfaces which help them to survive. It also helps in other vital cellular processes such as embryo- genesis,The study cell oforientation, single-cell adhesion morphogenesis, is one of the mostcell importantmotility, and immune complicated responses, aspects development, to understand in life sciences. Different cells adhere to their surrounding surfaces which helpand themreorganization. to survive. It alsoThe helps process in other involves vital cellular a multitude processes of such factors as embryogenesis, present both intrinsic and cellextrinsic orientation, to the morphogenesis, cell membrane, cell motility, such as immune the cytoskeleton responses, development, [15], membrane and reorga--bound adhesion nization.proteins The [16] process and involvesglycocalyx a multitude elements of factors [17]. present The transmembrane both intrinsic and extrinsicproteins, to e.g., integrins, theform cell adhesion membrane, sites such asto the anchor cytoskeleton between [15], membrane-boundthe cell and matrix adhesion or proteinsthe other [16] cell's adhesion andmolecule glycocalyx. These elements adhesion [17]. The molecules transmembrane are attached proteins, e.g., to the integrins, cytoskeleton, form adhesion the actin filament sites to anchor between the cell and matrix or the other cell’s adhesion molecule. These adhesionthrough molecules the focal are adhesion attached (FA) to the complex, cytoskeleton, which the actin is highly filament organized through the with focal a cluster of mol- adhesionecules (Figure (FA) complex, 1). which is highly organized with a cluster of molecules (Figure1). FigureFigure 1. 1.Cell Cell adhesion adhesion process: process the ligand: the onligand the artificially on the artificially tailored surface tailored binds tosurface the integrin binds to the integrin receptorsreceptors found found on the on cell the membrane. cell membrane Throughout. Throughout the adhesion the process, adhesion the actin process filament, structurethe actin filament struc- ofture the of cell the is reorganized,cell is reorganized, and a traction and forcea traction is generated force is in generated the substrate. in Externalthe substrate. stimuli External also stimuli also regulateregulate the the reorganization reorganization of cytoskeletal. of cytoskeletal. After surface After adhesion, surface the cell adhesion can interact, the with cell other can cells interact with other throughcells through membrane membrane proteins such proteins as cadherins, such selectinsas cadherins, and the selectins Immunoglobulin and the (Ig) Immunoglobulin superfamily. (Ig) super- In tissues, cell junctions, a variety of multiprotein complexes (e.g., tight junctions), can form between family. In tissues, cell junctions, a variety of multiprotein complexes (e.g., tight junctions), can form cells to promote intercellular communication and mechanical stability. (F—Force applied by cell on between cells to promote intercellular communication and mechanical stability. (F—Force applied its surrounding) (Reproduced with permission from [18]). by cell on its surrounding) (Reproduced with permission from [18]). The passive cell adhesion process is an in vitro process in static medium culture (e.g., cultureThe flasks passive or petri cell dishes), adhesion where process cells undergo is an in morphologic vitro process alterations in static driven medium by culture (e.g., passiveculture deformation flasks or petri and dynamic dishes), reorganization where cells of undergo the cytoskeleton. morphologic In in vitro alterationsconditions, driven by pas- cell adhesion progresses using passive adsorption to the surface, where the initial contact issive made deformation by the cell glycocalyx and dynamic coat, followedreorganization by attachment, of the thecytoskeleton. spreading of In the in cell vitro conditions, andcell theadhesion formation progresses of focal adhesions. using passive A recent adsorption study by Kanyo to t ethe al. surface, discovered where that thethe initial contact componentsis made by of the the cell glycocalyx glycocalyx could coat, regulate followed the speed by and attachment, magnitude ofthe adhesion spreading [19]. of the cell and Moreover,the formation an increase of focal and decreaseadhesions. in adhesion A recent can study be achieved by Kanyo by using et theiral. discovered technique. that the com- This is further modulated by the signalization process [20], flow circulation [21] or the cell- extracellularponents of matrixthe gly (ECM)cocalyx under could blood regulat flow