A novel platform for in situ investigation of cells and tissues under mechanical strain

Abstract

The mechanical micro-environment influences cellular responses such as migration, proliferation, differentiation, and apoptosis. Cells are subjected to mechanical stretching in vivo, e.g., epithelial cells during embryogenesis. Current methodologies do not allow high resolution in situ observation of cells and tissues under applied strain, which may reveal intracellular dynamics and the origin of cell mechanosensitivity. We have developed a novel polydimethylsiloxane (PDMS) substrate capable of applying tensile and compressive strain (up to 45%) to cells and tissues while allowing in situ observation with high resolution optics. The strain field of the substrate was characterized experimentally using digital image correlation (DIC) and the deformation was modeled with finite element method (FEM) using a Mooney-Rivlin hyperelastic constitutive relation. The substrate strain was found to be uniform for greater than 95% of the substrate area. As a demonstration of our system, we applied mechanical strain to single fibroblasts transfected with GFP-Actin and whole transgenic Drosophila embryos expressing GFP in all neurons during live imaging. We report three observations of biological responses due to applied strain: (1) dynamic rotation of intact actin stress fibers in fibroblasts; (2) lamellipodia activity and actin polymerization in fibroblasts; (3) active axonal contraction in Drosophila embryo motor neurons. Our novel platform may serve as an important tool in studying the mechanoresponse of cells and tissues including whole embryos.

A silicone-based stretchable micropost array membrane for monitoring live-cell subcellular cytoskeletal response

“…Second, the regularly arranged PDMS microposts can be used automatically as high-precision fiducial markers to gauge the magnitude of cell stretch, eliminating the necessary step for continuous membranes to mark their surfaces for assessments of the stretch magnitude. 29, 56–57 Third, the geometry of the PDMS micropost can be precisely controlled to regulate substrate rigidity and adhesive ECM pattern independently of effects on other surface properties. 15, 51–54 Thus, the mPAM system can serve as a new class of the synthetic biointerfacial system in which cell stretch, substrate rigidity, adhesive ECM pattern, and surface chemistry and topography can be independently controlled to facilitate characterization and study of complex biointerfacial cellular phenomena.…”

The emerging role of forces in axonal elongation

“…Lastly, Franze and Guck (2010) recently published a comprehensive review on the biophysics of neuronal growth and the susceptibility of neurons to physical cues. In brief, the methods used to study the physical properties of neurons have innovatively utilized nanowires (Hallstrom et al, 2010), force calibrated glass needles (Bernal et al, 2007), microfabricated silicon-based micromechanical force sensors (Siechen et al, 2009), optical stretchers (Lu et al, 2006), stretchable polydimethylsiloxane (PDMS) substrates (Ahmed et al , 2010), and polyacrylamide gel-based compliant substrates (Chan and Odde, 2008). Using these approaches the significant findings have been that (1) tension generation by growth cones is higher on softer (i.e.…”

“…Using these approaches the significant findings have been that (1) tension generation by growth cones is higher on softer (i.e. < ~ 1 kiloPascal) substrates (Chan and Odde, 2008), (2) glial cells provide a soft substrate that may facilitate axonal elongation (Lu et al, 2006), (3) active force generation in neurons causes them to shorten when slackened (Ahmed et al , 2010; Bernal et al , 2007), and (4) the rest tension of axons both in vivo and in vitro is in the range of 1–10 nN (Hallstrom et al , 2010; Rajagopalan et al , 2010; Siechen et al , 2009). We think there is great promise in the application of these approaches to longstanding problems in the field of molecular cell biology, not only of neurons but cells in general.…”

Dental pulp stem cells express tendon markers under mechanical loading and are a potential cell source for tissue engineering of tendon-like tissue

“…The mechanical microenvironment can affect cell proliferation, migration, differentiation, and apoptosis, as well as tissue development. 19 Different types of mechanical stimuli have been widely applied to tissue engineering of tendons. 20, 21 We used custom-fabricated springs and PGA scaffolds modified from the previous work 22, 23 to apply static stretch to DPSCs in vitro .…”