Engineer cell growth using a DNA crosslinked hydrogel with static and dynamic stiffnesses

Elucidation of the interactions between cells and extracellular matrices (ECM) is critical to not only the understanding of the basic biology of development, tissue functioning and pathological conditions, but also successful design and implementation of bioscaffolds in tissue engineering applications. Mechanical characteristics, including mechanical stiffness, of the local microenvironment play an important role in cell decision making processes. Aiming at the neural tissue engineering applications, we examined the mechano-sensing of neural cells in the context of neuron-astroglia interactions, and differentiated between dendrites and axons by deploying bis- and DNA-crosslinked hydrogels. These studies revealed the complexity in the neural cell mechano-sensing which is coupled with cell-cell interactions and possesses specificity towards cellular property, cell type and stiffness range. The dynamic and changing nature of cells' local physiological environment particularly of its mechanical characteristics makes it desirable to develop a cell culture system or bioscaffold whose mechanical properties can be modulated in a controlled and temporal fashion. DNA crosslinked hydrogels offer unique opportunities for modifying mechanical properties of the substrates or scaffolds via DNA delivery during cell culture without changing environmental factors. Two types of fibroblasts, L929 and GFP fibroblasts, and spinal cord cells were subjected to the dynamic alterations in the mechanical stiffness of the DNA gels. It was found that both fibroblasts and neurons are able to sense the mechanical stiffness change. Fibroblasts respond mainly by altering morphology, focal adhesion or cytoskeletal structures whereas neurons respond largely by adjusting neurite outgrowth and adhesion properties. The significance of the current thesis work includes the following: 1. It highlights the importance of the mechanical aspects of cell-ECM interactions, particularly cellular response to static and dynamic mechanical stiffnesses. 2. It reveals the complexity in the mechano-sensing with specificity towards or dependence on cell type, cellular property and stiffness range. It can be further coupled with cell-cell interactions, and other factors including dimensionality and biological cues. 3. It adds a new dimension, Time, to the mechanical compliance of the substrate in understanding cell-ECM events. 4. It provides design guidelines for the choice of the mechanical stiffness of the bio-scaffold in tissue engineering applications.Ph.D.Includes bibliographical referencesby Xue Jian