Microscale Measurements of Cell and Tissue Mechanics in Three Dimensions

Two-dimensional (2D) studies have revealed that mechanical forces drive cell migration and can feedback to regulate proliferation, differentiation and the synthesis/remodeling of extracellular matrix (ECM) proteins. Whether these observations can be translated to clinical settings or be utilized for tissue engineering will depend critically on our ability to translate these findings into physiologically relevant three-dimensional (3D) environments. The general goal of this dissertation has been to develop and apply new technologies capable of extending studies of cell and tissue mechanics into 3D environments. In the first project, we measured both shear and normal traction forces exerted by cells cultured on planar substrates. We observed that focal adhesions serve as pivots about which cells generate rotational moments. In the second project, we combined enzymatically degradable synthetic hydrogels with finite element models to measure the mechanical tractions exerted by cells fully encapsulated within 3D matrices. We found that cells reach out thin protrusions and pull back inward towards the cell body with the highest forces at the tip. Cellular extensions that were invading into the surrounding matrix displayed a strong inward force 10-15 microns behind the leading tip, suggesting that growing extensions may establish a contractile waypoint, before invading further. To study the forces cells exert during tissue remodeling, we utilized photolithograpy to generate arrays of microtissues consisting of cells encapsulated in 3D collagen matrices. Microcantilevers were used to constrain the remodeling of the collagen gel and to report the forces generated during this process. We used this technique to explore the effects of boundary stiffness and matrix density within model tendon and cardiac tissues. Finally, we combined this system with a Foerster radius energy transfer (FRET) based biosensor of fibronectin conformation to reveal how tissue geometry and cell-genereated tractions cooperate to pattern matrix conformation during tissue remodeling. Together, these studies highlight novel approaches to understand the nature of cell-ECM interactions in 3D matrices. Such mechanical insights will help us to understand how physical forces drive cell migration and behavior within physiologically relevant environments

Interview with Dale Grassbaugh

Dale Grassbaugh, the father of the Grassbaugh family, talks about his family farm and about how farming has become more of a business now than simply a way of life. The business aspect is strong for the local farmers. He discusses the economic aspects for local farmers in detail.https://digital.kenyon.edu/ffp_interviews/1023/thumbnail.jp

Interview with Auctioneer John \u27Red\u27 Shaw

John Shaw discusses growing up on a farm and being in 4H, and getting involved in the auction business; specifically getting involved with agriculture sales. He also discusses how the new buyers are buying bigger sections of land and have bigger equipment, they are less likely to be small, family farms. He says the biggest change he\u27s noticed in his time is that the farms are becoming bigger and the owners are not young people, because it is so expensive to start a farm.https://digital.kenyon.edu/ffp_interviews/1038/thumbnail.jp

Interview with Dwayne Grassbaugh

Dwayne Grassbaugh discusses going to Virginia Tech and taking care of the dairy section of the farm. He also discusses what a family farm is actually like.https://digital.kenyon.edu/ffp_interviews/1031/thumbnail.jp

Interview with Cindy Grassbaugh

Cindy Grassbaugh, the second daughter of the Grassbaugh\u27s talks of growing up on a farm and having to feed the calves. She also speaks of how her brothers had more responsibilities on the farm because they were physically stronger. Cindy also talks about how she learned responsibility on the farm, and through the 4-H program.https://digital.kenyon.edu/ffp_interviews/1022/thumbnail.jp

Interview with Kathy Grassbaugh

Kathy Grassbaugh, the wife and mother of the Grassbaugh family, discusses life on a farm and whether people are born into farming or whether they can start farming at any age with any background. She also discusses how farms are getting bigger and bigger just to bring in the same prices, because of the agricultural economics at the time. However, she also discusses how being a farmer is like being your own boss and you get to control your income.https://digital.kenyon.edu/ffp_interviews/1007/thumbnail.jp

Interview with Anna Grassbaugh

Anna Grassbaugh discusses growing up on a farm, and how that has changed her outlook on life. Grassbaugh discusses her future goal of working for farmers.https://digital.kenyon.edu/ffp_interviews/1005/thumbnail.jp

Force traction microscopy: An inverse problem with pointwise observations

Force Traction Microscopy is an inversion method that allows to obtain the stress field applied by a living cell on the environment on the basis of a pointwise knowledge of the displacement produced by the cell itself. This classical biophysical problem, usually addressed in terms of Green functions, can be alternatively tackled using a variational framework and then a finite elements discretization. In such a case, a variation of the error functional under suitable regularization is operated in view of its minimization. This setting naturally suggests the introduction of a new equation, based on the adjoint operator of the elasticity problem. In this paper we illustrate the rigorous theory of the two-dimensional and three dimensional problem, involving in the former case a distributed control and in the latter case a surface control. The pointwise observations require to exploit the theory of elasticity extended to forcing terms that are Borel measure

Publisher Correction: Deep learning enables fast and dense single-molecule localization with high accuracy

In the version of this Article initially published, Jacob H. Macke and Jonas Ries were not listed as corresponding authors. Their contact information and designation as corresponding authors are now included. The error has been corrected in the online version of the Article