Finite element simulation of cell-substrate decohesion by laser-induced stress waves

Fundamental to the development and application of biomedical devices is an understanding of the adhesion of cells to substrates. There are many experimental techniques and papers dedicated to the study of cell adhesion. This work aims to elucidate on the cell detachment mechanism in a recently reported cell adhesion measurement experiment by laser-induced stress wave technique. In the experiment the absorption of an Nd:YAG laser pulse generates a stress wave of nanoseconds duration that interacts with and detaches the cell adhered to a Si substrate. Due to the ultra-short timescale involved in the experiment, details of the detachment process were not readily observable. In this work, dynamic finite element method is used to simulate the cell-substrate decohesion process under the laser-induced stress wave loading. The results show that the combined effect of nanosecond stress wave pulse and the specific cell geometry results in a complex stress-strain state along the cell-substrate interface. The principal failure mechanism is large interfacial strains realized from the cell's tendency to spread and elongate on the substrate as a result of substrate acceleration. The cells behave like a soft elastic solid during the detachment process due to the large difference between their characteristic response time and the ultra-short duration of the applied stress wave. Evolution of the cell geometry from hydrophobic to hydrophilic contact results in the same detachment process.