Optical trapping microrheology in cultured human cells

Area of Science:

• Biophysics
• Cell Biology
• Rheology

Background:

• Understanding the mechanical properties of human epithelial cells is crucial for distinguishing between normal and cancerous cell behavior.
• Microrheology offers a powerful tool to probe cellular viscoelasticity at the microscale.

Purpose of the Study:

• To investigate and compare the microrheological properties of non-cancerous HCV29 and cancerous T24 human epithelial cell lines.
• To analyze subdiffusion dynamics and extract viscoelastic moduli using optical tweezers and a novel MSD equation.

Main Methods:

• Utilized optical tweezers to track endogenous lipid granule trajectories in live cells with high temporal resolution (1μs).
• Applied a recently developed equation for mean square displacement (MSD) to analyze subdiffusion influenced by an optical trap.
• Calculated viscoelastic moduli from the analyzed trajectories.

Main Results:

• Identical viscoelastic moduli were observed for both HCV29 and T24 cells within the frequency range of 10^2 - 10^5 Hz.
• Subdiffusion behavior with an exponent near 3/4, consistent with semiflexible polymer theory, was found in both cell lines.
• Cancerous T24 cells exhibited significantly higher MSD than non-cancerous HCV29 cells for timescales longer than 0.1s.

Conclusions:

• The observed difference in MSD at longer timescales suggests active cellular processes in cancerous cells.
• Passive microrheology may be limited in extracting low-frequency viscoelastic moduli from living cells due to these active processes.
• The study highlights distinct dynamic behaviors between cancerous and non-cancerous epithelial cells at the micro-rheological level.