not only a complex biochemical environment but also a diverse biomechanical environment. How cells respond to variations in mechanical forces is critical in homeostasis and many diseases. The mechanisms by which mechanical forces lead to eventual biochemical and molecular responses remain undefined, and unraveling this mystery will undoubtedly provide new insight into strengthening bone, growing cartilage, improving cardiac contractility, and constructing tissues for artificial organs. In this article we review the physical bases underlying the mechanotransduction process, techniques used to apply controlled mechanical stresses on living cells and tissues to probe mechanotransduction, and some of the important lessons that we are learning from mechanical stimulation of cells with precisely controlled forces.cytoskeleton; micromanipulation; cell signaling ALL LIVING ORGANISMS face mechanical forces, from the fluid forces around a bacterium to the high forces in a human knee during stair climbing. The process of converting physical forces into biochemical signals and integrating these signals into the cellular responses is referred to as mechanotransduction. Although this review cannot cover all that has been discovered about mechanotransduction, we discuss the molecule-and cell-level structures that may participate in mechanotransduction, provide an overview of prominent techniques currently used for exerting mechanical stresses on cells, and conclude with an overview of the tissue-level response to mechanical signaling.
FORCE TRANSDUCTION PATHWAYS AND SIGNALINGForce transmission pathways at the cellular and subcellular scales. Understanding the molecular basis for mechanotransduction requires knowledge of the magnitude and distribution of forces throughout the cell at the molecular scale. At present, we have sufficient information to measure molecular scale forces in only a very few cases. We can, however, analyze the mechanisms by which force is transmitted throughout the cell and use that as a basis for speculation about the molecular mechanisms of mechanotransduction. A variety of different methods have been used to mechanically stimulate a cell, and the cellular response is multifaceted and diverse. Similarly, there are likely to be a variety of sensing mechanisms and locations within the cell where forces can be transduced from a mechanical to a biochemical signal. Despite this apparent complexity, it is probable that cells stimulated in different ways are activated by similar mechanisms at the molecular level. To identify these commonalities, it is useful to consider how externally applied forces are transmitted into and throughout the cell, as well as the magnitudes and distribution of force corresponding to these different methods of stimulation.Both continuum and microstructural approaches have been used to determine force distributions. In the case of a continuum model, the details of the microstructure are ignored, and the forces transmitted via the individual microstructural elements are described in...