How can we precisely control the shape of growing microtissue in vitro? This would be a simple but profound question to design tissues with complex structures in near future. While recent progress in micro-engineering succeeded in imposing particular shape to cells in micron order, little control exists on how microtissue changes the shape as they mature. Especially, the misbalance between cell-generated forces and cell-cell and cell-substrate contacts can result in unintended tissue deformation and rupture, however, we still do not have quantitative understandings on how those parameters determines stability of microtissue. In this study, human arterial smooth muscle cells were cultured on glass substrates with submillimeter semichannels as a model case of microtissue with 3D structure and their morphology was analyzed by confocal microscopy to quantify cell sheet detachment. Variations of microchannel curvature, cellular contractility and adhesion strength of protein coating onto substrate revealed that cell sheet cause catastrophic detachment when normal stress generated by cellular contractility and surrounding geometry exceeds the adhesion strength of protein layer to substrate surface. We proposed a simple mechanical model that quantitatively explains how stability of microtissue on steric surface is determined. Our model together with first semi-quantitative phase diagram of microtissue stability can be exploited to either inhibit or purposefully induce a collective detachment of sheet-like microtissues for the use in tissue engineering and regenerative therapies.
Yamashita, H. et al. Cell sheet mechanics: how geometrical constraints induce the detachment of cell sheets from concave surfaces. doi: 10.1016/j.actbio.2016.08.044