Mohamed Elhebeary1 Taher Saif1

1, University of Illinois-Urbana Champaign, Urbana, Illinois, United States

The development of multicellular tissues is highly dependent on the mechanical forces associated with cell-cell and cell-matrix interactions. Cellular forces are measured using Traction Force Microscopy (TFM) on 2D soft substrates. However, TFM cannot provide forces in 3D tissues. Also, the effect of cross talk between cells within the tissue microenvironment cannot be captured in 2D culture. Here, we propose a technology that introduces a new device and a new method that radically changes the way we form 3D biomimetic tissues, and study them in situ. The method exploits the advances in micro-fabrication and combines them with classical theories of capillarity to offer new functionalities, namely self-assembly and self-alignment of tissues on a sensor stage. Currently there is no technology available to measure tissue force (due to cells) and tissue stiffness simultaneously. The new device closes this gap for the first time. It not only provides a time lapse measure of both force and stiffness, it allows simultaneous inspection of the microstructure of the tissue in situ, thus linking tissue biophysics with pathophysiology. Such in situ quantitative inspection will offer new insights that cannot be achieved with existing methods.

A novel design of a silicon platform, that integrates a stretching and sample self-assembly mechanisms, is introduced. First, a mixture of collagen I solution and fibroblasts (3T3) is dispensed on the silicon platform at room temperature (500x500x200 μm3). After curing, the chip is inundated in cell culture media within an incubation chamber. The small thickness of the chip (200 μm) makes it compatible with live cell microscopy and avoids any histological sectioning needed in the case of thick sample. The tissue forces are measured using an optical microscope by imaging the co-fabricated gauges on the chip and follow-up image analysis. An external 3D manipulator is used to stretch the tissue sample to measure its elastic modulus at different stages of tissue morphogenesis. Image analysis gives a displacement resolution of approximately 200 nm and a corresponding force resolution <1 µN. The proposed technology offers advantages over available techniques to study the biomimetic tissue due to the following reasons: no need to expose the sample to light which might affect its response, small size allows portability between different chambers during imaging and/or incubation, and ability to monitor the stiffness change along with microstructure development with time. Results from different cell lines showed the evolution of force with time after seeding cell/collagen mixture. Stiffness measurements of samples and effect of drugs on force relaxation are studied.