Cell adhesion is a critical determinant of tissue architecture and tissue organization. Cadherin proteins mediate cell-cell adhesion in a calcium-dependent manner. The functional roles for cadherin proteins early in development and in adults, as well as the multiple disease phenotypes resulting from cadherin dysregulation, underscore the importance of cadherin proteins. Cadherin structure, force, and interaction dynamics are not yet completely understood because of lack of experimental platforms to study cadherin proteins. Engineered platforms with highly defined cadherin ligands presented in a controlled manner can be used to investigate cadherin-based adhesive force. Adhesive force measurement tools such as alkanethiols and micro-fabricated force array detectors promise to meet this challenge of elucidating how cadherin complex assembly and function develop in a spatiotemporal manner in human health and disease.

The goal of this thesis was to engineer adhesive surfaces that support cadherin-based adhesion as a model system to analyze cadherin-dependent forces. We have engineered two different types of surfaces, based on self-assembled monolayers of alkanethiols on gold surfaces as well as micro-fabricated post-array detectors that present isolated and purified VE-cadherin ligands.

We demonstrated the technology of the self-assembly of alkanethiols on gold surfaces in quantifying the adhesion strength of three different endothelial cell lines. We engineered surfaces with precisely controlled cell-adhesive areas passively adsorbed with VE-cadherin. We then evaluated adhesion strength values and perturbed cadherin binding using functional blocking antibodies or calcium chelators abrogated adhesion strength. Ligand density and contact time mediate the strength of adhesion of a cell to its substrate. Functional blocking antibodies and calcium chelators eliminate adhesion strength.

We also demonstrated that micro-fabricated post-array detectors, or mPADs, allow for the direct measurement of cell-generated forces for cells interacting with adsorbed proteins on a surface. This work was the first system in which the traction forces of cells interacting with adsorbed cadherin ligands were measured. It is also the first system in which cadherin-dependent changes in traction forces upon exposure to different chemical agents were measured. This methodology provides insights into cadherin-based mechano-transduction events and provides a robust platform for further study.

Ultimately, future research into how cells strengthen cadherin-based adhesive force from weak homophilic interactions in the extracellular domain to strong forces intracellularly will rely on quantitative platforms with precise control of cadherin ligand density, an elimination of non-specific protein signaling through the immobilization of biomolecules or chemical chelators, as well as those that simplify the complexity of studying two cells in contact with one another. In this thesis, wee demonstrate two such systems that can accomplish all three things. Once mPAD technology becomes more standard in studies of cadherin-based adhesion, it can be applied to investigate emerging questions in the field, including the role of receptor trafficking in modulating adhesion strength and traction force generation, the interplay of cross-talk in cell-ECM and cell-cell adhesion, and the role of specific adhesion biomolecules in mediating adhesive force generation in several disease states.