Microengineered responsive platforms for spatial and geometrical control of multicellular organizations

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.Includes bibliographical references.Living systems are composed of complex multicellular organizations containing various cell types spatially distributed in defined microenvironments. The intricate cell-cell and cell-matrix interactions in these microenvironments regulate the cell fate, differentiation of the cells, and functions of the associated tissues. Recreating these complex associations in vitro can be highly useful for fabricating biomimetic tissues for regenerative medicine, disease models for drug discovery, and models to study embryogenesis. This thesis focused on developing microscale responsive platforms for spatial and geometrical control of multicellular organizations. The first part of the thesis describes methods to fabricate spherical and stripe microtissues of single cell types and their temperature-controlled retrieval. These microtissues were scaffold-free and can potentially produce homotypic cell-cell interactions. Microwells fabricated from poly(Nisopropylacrylamide) (PNIPAAm) responded to temperature by changing their shapes. Spherical microtissues of a single cell type were formed in responsive microwells and recovered by using shape changing properties of microwells. Elastomeric microgrooves were conformally coated with PNIPAAm to first generate stripe microtissues of a single cell type, and then harvest them by exploiting the temperature-dependent hydrophilicity and swelling change of PNIPAAm film. The second part of the thesis introduces techniques to control spatial and geometrical distribution of multiple cell types in scaffold-free and scaffold-based tissues. Shape changing properties of dynamic microwells facilitated the sequential patterning of multicompartment hydrogels. Different cell types were spatially arranged in different compartments of microgels which may lead to complex cell-matrix interactions replicating native tissues. Shape changing properties of dynamic microwells were also employed to seed different cell types at different temperatures within defined geometries to control spatial and geometrical organization of multiple cell types. Resulting scaffold-free tissues can potentially produce homotypic and heterotypic cell-cell interactions. Dynamic microstructures with different geometries could be used to recapitulate complex native tissues with controlled cell-cell and cell-matrix interactions. The techniques presented in this thesis are versatile and may potentially be useful for replicating biological complexities for a wide range of applications in tissue engineering, regenerative medicine, drug discovery, developmental biology, and cancer biology.by Halil Tekin.Ph.D