טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentYosef Andrei
SubjectIntrinsic Matrix Mechanical Stimulation of Mesenchymal
Cells in Tissue Engineering
DepartmentDepartment of Biomedical Engineering
Supervisors Professor Dror Seliktar
Professor Emeritus Joseph Mizrahi
Full Thesis textFull thesis text - English Version


Abstract

One of the primary challenges in tissue engineering is to create a scaffold that can mimic the intrinsic mechanical properties of the native tissue in order for resident cells to retain their inherent function and phenotype based on physical induction. The growing demand for better scaffolds in tissue engineering requires better insight into the importance of cell interactions with their extra cellular matrix (ECM). Individual cells are highly sensitized to external cues arising from their interactions with the ECM, which include both biochemical signals, as well as physical features of the ECM. Recent studies have underscored the direct effect of the ECM on anchorage-depended cells. For example, it has been demonstrated that some cell types will alter their phenotype when presented with a drastic change in physical milieu. In order to design a tissue replacement using a tissue engineering methodology, one needs to provide the cells with a scaffold environment that can favorably stimulate the cells to achieve the intended outcome, based in part on physical induction. In this work, we explore the relationship between the physical features imposed by the 3-D amorphous hydrogel scaffold environment (e.g. matrix stiffness, ligand density) and the mechano-sensing events that lead to augmented cell morphology in 2-D and 3-D cultures. This relationship was investigated using a biocompatible hydrogel culture system made from adducts of fibrinogen and synthetic polymers such as poly(ethylene glycol) (PEG) and Pluronics F-127. In this system, pseudo-independent control of ligand density and matrix modulus is achieved. Three kinds of cells: Smooth Muscle Cells (SMCs), Human Foreskin Fibroblasts (HFFs) and Chondrocytes (CHONs) where used to evaluate the cell-scaffold interaction in two dimensional (2-D) cultures while HFFs were encapsulated in hydrogels to evaluate the interaction in three dimensional (3-D) cultures. Microscopic fluorescence images of the embedded cells were captured to monitor and define their reactions to the changes in hydrogels properties. We concluded that the pseudo-independent control of the matrix properties provides an ability to alter cell behavior in and on hydrogels in a predictive fashion. Specifically, we found that ligand density and compliance of the encapsulating hydrogel matrix have a significant influence on the regulation of cell morphogenesis. Ultimately, identifying environmental conditions that are optimal for directing cell morphogenesis based on biophysical induction can contribute to successfully designing scaffolds that favorably affect the final outcome in tissue engineering.