Cell-materials interaction and its implications on stem cell fate

Human mesenchymal stem cells (hMSCs) continue to attract prominence in tissue engineering due to their immunosuppressive property, self renewability, and multi-lineage differentiation potential. While emphasis has always been placed on inducing differentiation of hMSCs into the targeted cells of interest by biological methods in the past, biophysical methods such as mechanical stimulation and cellular morphology are now emerging at a rapid pace. In the physical methods, the interaction between the cell and material is of utmost importance but systematic study of this interaction is still limited to date. In this investigation, cell-materials interaction represented by the development of focal adhesion (FA) was studied systematically and the relationship between FA and stem cell differentiation (especially myogenic differentiation) was investigated. Results indicated that the FA development of hMSCs can be modulated by micropatteming but there was a synergistic effect between FA regulation and matrix stiffness. Elongated FA could be modulated on the substrates with intermediate stiffness ((polydimethylsiloxane (PDMS) with a stiffness of 12.6 kPa and polyacrylamide (PA) gel with a stiffness of 10.2 kl'a) and with collagen type I (COLI) as the inking protein. hMSCs with elongated FA showed specific myogenic differentiation at both transcription and translation levels compared with cells with dense FA and those in control group. Mechanistic study showed that elongated FA recruited integrin ~3 clusters, activated RhoA signaling pathway, aligned stress fibers, and increased cellular tension via activation of RhoA signaling pathway and up-regulation of myosin light chain kinase (MLCK). Moreover, the interplay of cell shape and FA on hMSCs differentiation was investigated and the key role of elongated FA in driving hMSCs myogenic differentiation was confirmed. Similar shaped hMSCs with different FA morphology and distribution were induced using micropatterning technique and it was found that the elongated FA was more supportive of myogenic differentiation. Collectively, this study demonstrates a novel chemical/biological free and feasible method of inducing myogenic differentiation of hMSCs and improves our understanding of the micropatterning platform in affecting the differentiation.DOCTOR OF PHILOSOPHY (MSE