Cellular response to substrate rigidity is governed by either stress or strain

Area of Science:

• Cellular Mechanobiology
• Biomaterials Science
• Biophysics

Background:

• Cells dynamically interact with their physical environment, sensing and responding to substrate rigidity.
• Understanding the specific physical cues cells use to modulate their behavior remains an active research area.
• Existing methods for substrate functionalization can lead to protein detachment, confounding cell-substrate interaction studies.

Purpose of the Study:

• To investigate how fibroblasts' traction stress and substrate deformation vary with substrate rigidity.
• To evaluate a novel N-acryloyl-6-aminocaproic acid (ACA) based method for stable protein immobilization on elastic substrates.
• To identify physical variables that govern cellular responses to substrate stiffness.

Main Methods:

• Fabrication of polyacrylamide gels with Young's moduli ranging from 6 to 110 kPa.
• Modified substrate preparation using N-acryloyl-6-aminocaproic acid (ACA) for stable collagen immobilization.
• Measurement of cellular traction stress and substrate deformation using fibroblasts on functionalized gels.

Main Results:

• The ACA method provides more stable protein immobilization compared to sulfo-SANPAH, preventing protein removal by cells.
• On soft substrates (Young's modulus <20 kPa), substrate deformation was constant regardless of rigidity.
• On stiff substrates (Young's modulus >20 kPa), traction stress plateaued, and substrate deformation decreased with increasing rigidity.

Conclusions:

• Stable protein immobilization is crucial for accurate measurement of cell-substrate interactions.
• Sustained substrate strain on soft materials and sustained traction stress on stiff materials may dictate cellular responses to rigidity.
• Findings provide insights into the physical parameters cells utilize to interpret their mechanical environment.