Stiffness analysis of 3D spheroids using microtweezers

Area of Science:

• Biophysics
• Cell Biology
• Biomaterials Engineering

Background:

• Cell stiffness is a critical differentiator between cancerous and normal cells.
• Existing methods like atomic force microscopy are unsuitable for measuring the mechanical properties of larger 3D cellular structures such as spheroids.
• The mechanical characteristics of multicellular spheroids remain largely unstudied.

Purpose of the Study:

• To develop and validate a novel mechanical characterization method for directly measuring the stiffness of cancer spheroids.
• To compare the stiffness of cancerous and normal breast cell line spheroids.
• To establish a new tool for studying the mechanical properties of 3D cellular structures.

Main Methods:

• Development of microtweezers with replaceable SU8 and brass cantilevers for a wide force range (sub-hundred nN to mN).
• Optical tracking of cantilever bending to determine applied force and sample stiffness.
• System validation using agarose pillars of known concentrations.
• Mechanical characterization of multicellular spheroids from cancerous (T47D, BT474) and normal (MCF 10A) breast cell lines.

Main Results:

• The microtweezers successfully measured stiffness across a wide range of Young's moduli (25-100 kPa for agarose, 230-1250 Pa for spheroids).
• Cancerous T47D and BT474 spheroids exhibited Young's moduli of 420 Pa and 230 Pa, respectively.
• Normal MCF 10A spheroids showed a Young's modulus of 1250 Pa, indicating cancerous spheroids are significantly softer than normal ones.

Conclusions:

• The developed microtweezers provide a novel and effective method for characterizing the mechanical properties of multicellular spheroids.
• Cancerous breast cell spheroids are substantially softer than normal epithelial spheroids.
• This technique opens new avenues for studying the role of mechanical properties in cancer progression and disease.