Paul A Janmey

Authors:

Paul A Janmey¹, Katarzyna Pogoda², Kiet Tran³, Peter A Galie³

1. Department of Physiology, and Physics & Astronomy, University of Pennsylvania, Philadelphia, PA, USA
2. Department of Experimental Physics of Complex Systems, Institute of Nuclear Physics, Polish Academy of Sciences, PL-31342, Krakow, Poland
3. Department of Biomedical Engineering, Rowan University, Glassboro, NJ, USA

Abstract:

Embedding micron-scale ferromagnetic particles within hydrogels, including those made from extracellular matrix proteins, allows rapid and reversible tuning of gel mechanics with magnetic fields. This approach can easily be applied to cell-seeded hydrogels and is compatible with live cell imaging using light microscopy.  We characterize the dependence of magnetically-induced increases in gel stiffness in biological and synthetic gels that exhibit a range of linear or non-linear elastic responses.  The increase in storage modulus of the magnetically active gels depends on field strength but also on the magnitude of the strain, and the responses are different if the host hydrogel is linearly or non-linearly elastic. For example, application of a 4,000 Oe magnetic field to a 5 mg/mL collagen network containing 10 wt% MPs increases the shear storage modulus from 1.5 kPa to 30 kPa. Morphological studies indicate that cells within these hydrogels rapidly sense the magnetically-induced changes to ECM stiffness. Moreover, intracellular Ca²⁺ transients change within seconds of stiffening or subsequent softening, and slower changes occur in nuclear translocation of the transcription regulator YAP. Due to its flexibility, this method is broadly applicable to future studies interrogating cell mechanotransduction in three-dimensional substrates.