Measuring traction forces in long-term cell cultures

This report describes an approach to extend indefinitely the duration of traction force measurements with cells cultured on soft polyacrylamide gels. Typical observation times in traction force measurements on similar substrates have been limited to 24-48 h, but cell differentiation or responses to external stimuli often occur over much longer periods of several days or weeks. This study describes a method for covalently linking fluorescent marker beads to a polyacrylamide matrix that renders the hydrogels useful for traction force measurements over several days. This approach was validated by comparing the contractility of C2C12 murine skeletal muscle cells prior to myotube formation, after one day in culture, with that of myotubes after 7 days in culture. Measured tractions increased concurrent with the differentiation of C2C12 cells to the contractile, myotube phenotype. Covalent bead linkage thus extends the useful period during which traction force data can be obtained with cells cultured on optically transparent polyacrylamide hydrogels with controlled elastic moduli.