Force Spectroscopy and Beyond: Innovations and Opportunities

Abstract

Life operates at the intersection of chemistry and mechanics. Over the years, we have made remarkable progress in understanding life from a biochemical perspective and the mechanics of life at the single-molecule scale. Yet the full integration of physical and mechanical models into mainstream biology has been impeded by technical and conceptual barriers, including limitations in our ability to 1) easily measure and apply mechanical forces to biological systems, 2) scale these measurements from single-molecule characterization to more complex biomolecular systems, and 3) model and interpret biophysical data in a coherent way across length scales that span single molecules to cells to multicellular organisms. In this manuscript, through a look at historical and recent developments in force spectroscopy techniques and a discussion of a few exemplary open problems in cellular biomechanics, we aim to identify research opportunities that will help us reach our goal of a more complete and integrated understanding of the role of force and mechanics in biological systems.

Figure 1

Schematics for SMFS techniques. (A) OTs use focused laser beams to trap dielectric particles, such as microbeads. Mechanochemical information is teased out by applying tensile force to molecular constructs tethered to these particles. (B) Atomic force microscopes use flexible cantilevers to apply direct mechanical forces to molecules of interest, whereas (C) magnetic tweezers employ magnetic forces. (D) The centrifuge force microscope rapidly rotates to apply centrifugal forces to a sample, which typically consists of hundreds to thousands of tethered beads being pulled and observed in parallel.

Figure 2

Schematic of the assay performed to identify the role of matrix elasticity in governing the differentiation potential of mesenchymal stem cells. A softer matrix, ∼0.1–1 kPa, resulted in neurogenic differentiation, whereas a higher stiffness matrix, ∼8–17 kPa, resulted in myogenic differentiation. Even higher stiffness, ∼25–40 kPa, resulted in osteogenic differentiation. Figure reproduced with permission from Engler et al. (26). To see this figure in color, go online.

Figure 3

Cartoon representation of a self-assembled force spectrometer. Such a system has been used to measure distance-dependent pair potential between a histone pair. Figure reproduced with permission from Funke et al. (65). To see this figure in color, go online.