Micron-sized Device Examines Tissue Development

June 24, 2009 | Contact Author | By: Katie Schaefer
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Bioengineers at the University of Pennsylvania have created a micron–sized device that allows them to measure and manipulate cellular forces during tissue development. With the device, researchers can gauge how cells' minute mechanical forces affect cellular behavior, protein deposition and cell differentiation in a three-dimensional, in vivo-like environment that mimics how tissue actually forms in a living organism.

This work aimed to examine the physical forces generated by individual cells, and findings were published in the June issue of the Proceedings of the National Academy of Sciences. In addition to understanding tissue development, this research has implications for the testing of irregular or diseased tissue, such as beating cardiac tissue, which can be modeled and studied.

The push-and-pull of cellular forces reportedly drives the buckling, extension and contraction of cells that occur during tissue development, according to the research. These processes ultimately shape the architecture of tissues and play an important role in coordinating cell signaling, gene expression and behavior, and they are essential for wound healing and tissue homeostasis in adult organisms. For personal care, this could lead to a better understanding of the mechanisms acting in living human skin.

The study highlights the complex relationship between cellular forces, visualizes the remodeling of a matrix by living cells, and demonstrates a system to study and apply this relationship within engineered 3-D microtissue. The system was created by fabricating an array of tiny divots within a mold and immersing the mold in a culture of cells and collagen. Researchers then placed raised microcantilever posts on either side of the mold and observed the formation of a cell and collagen web of living tissue anchored to the cantilevers. These microcantilevers were used to simultaneously constrain the remodeling of a collagen gel and to report forces generated during this process.

The cantilever posts allowed the team to observe and measure the retraction and extension of the cells as they remodeled the adjacent matrix into a coherent band of tissue. Varying the mechanical stiffness of the cantilevers and collagen matrix demonstrated that the cellular forces increased with boundary or matrix rigidity, whereas the levels of proteins in the cytoskeleton and extracellular matrix also increased with levels of mechanical stress.

By mapping these relationships between cellular and matrix mechanics, cellular forces and protein expression onto a bio-chemo-mechanical model of microtissue contractility, the team demonstrated how intratissue gradients of mechanical stress can emerge from collective cellular contractility and, finally, how such gradients can be used to engineer protein composition and organization within a 3-D tissue.

The researchers see potential for high-throughput drug testing with the model, where they find research may identify new ways to increase the contractility of cardiac muscle or to relax arteries to treat hypertension. The researchers created a mathematical model of the entire process that accurately predicted the experimental results.

The study was conducted by Chris Chen, Wesley Legant, Michael T. Yang, Amit Pathak, Robert M. McMeeking and Vikram S. Deshpande. The research was funded by grants from the National Institutes of Health, an Army Research Office Multidisciplinary University Research Initiative, the Material Research Science and Engineering Center and Center for Engineering Cells and Regeneration at Penn, the US Department of Education's Graduate Assistance in Areas of National Need and the National Science Foundation's Graduate Research Fellowship.

-University of Pennsylvania