Abstract:
Stem cells have the remarkable ability to self-renew and engender various cells, and the process by which they do so makes them vital for tissue regeneration and therapeutic uses. However, stem cell therapies are limited by the lack of control over cell fate and knowledge regarding these processes in vitro. Cells adhering to the extracellular matrix are known to sense the mechanical and biochemical environment through a process known as mechanotransduction, which plays a major role in determining the cell’s behaviour. The substrate stiffness of in vitro cell culture is known to influence stem cell phenotype, and inducing dynamic changes in the substrate properties is a growing area of research. Materials designed to mimic the cell’s in vivo microenvironment will be key to understanding their behaviour and their use in modern medicines.
This thesis aims to design, develop, and characterise a hydrogel substrate capable of dynamically changing its mechanical properties to study mechanotransduction. This platform would allow two-dimensional cell studies to be performed with on-demand switching of the mechanical properties through an external stimulus. This system comprises of a hybrid poly(N-isopropylacrylamide) hydrogel fabricated with conducting polymers. Specifically, this thesis aims to control the Young’s modulus of a hydrogel through an applied voltage. Conducting polymers in their native state are stiff and unrepresentative of the in vivo microenvironment. To overcome this, their properties are combined with the physical properties of hydrogels that can be tuned to match natural tissue. The design and fabrication of the hybrid hydrogel were optimised, and its electromechanical properties were quantified. Electrochemical atomic force microscopy was optimised, and modifications were installed to characterise the hybrid hydrogel. The optimised poly(N-isopropylacrylamide) hydrogel containing the conducting polymer, polypyrrole, exhibited a fast and large change in mechanical actuation upon low voltage stimulation. Furthermore, the stiffness of the hydrogel was changed upon voltage stimulation at physiologically relevant temperatures. Finally, cells were cultured on the hybrid hydrogel, demonstrating their attachment.
The results presented in this thesis demonstrate the potential of conducting polymer hydrogels for cell mechanotransduction studies. Knowledge and control over these processes enable stem cell therapies to be safer and more accessible in modern medicines.