Abstract:
Stem cells have the remarkable ability to self-renew and differentiate into other cell
types. The cell fate is regulated precisely by the cell’s microenvironment and the
interaction of the cell with surrounding biomolecules. Cells sense their environment
through a range of receptors, two of which are integrins and growth factor receptors.
These receptors initiate cellular signalling pathways independently but also
synergistically. While independent pathways are often well understood, there is a
need for a more advanced understanding of the cross-talk between integrins and
growth factor receptors. Many of these signalling pathways cannot be studied in vivo.
Consequently, there has been tremendous progress in material systems that
resemble aspects of the cells’ microenvironment in vitro. There is currently a lack of
engineered biointerfaces to study synergistic signalling pathways between
mechanotransduction and growth factor receptor signalling.
Hence, this thesis aims to progress the development of a block copolymer-based
platform that allows for the cell-mediated release of signalling molecules upon
integrin binding. This would provide local release of biomolecules in close proximity
to the integrin binding. The system comprises a polystyrene-block-poly(ethylene
oxide) thin film containing proteins released upon exposure to an aqueous
environment. Specifically, this thesis aims to quantify and control the release of
protein from the block copolymer film. This thesis presents key milestones to
contribute to the development of the proposed platform. The film fabrication
parameters were optimised and resulted in largely defect-free films. Furthermore, the
solvent-vapour annealing procedure was optimised, which resulted in the more
reliable fabrication of cylindrical nanopatterns. Circular dichroism and an enzyme
activity showed that the protein cargo retained its enzymatic activity in the solvent
mixture used for the co-assembly of PS-b-PEO and protein cargo. The release rate
into aqueous solutions from the co-assembled protein and polymer films was
measured using detection of fluorescently labelled proteins and by an enzymatic
assay. The results show a rapid release of incorporated protein. To hinder such fast
release, the film needs to be capped. Work towards that goal in this thesis focussed
on post-fabrication functionalisation of the thin film via copper‐catalysed azide/alkyne
cycloaddition.
The results presented in this thesis lay the foundation for the future use of the
proposed system. However, particularly controlling the release from thin films in cell
culture conditions needs further development to establish cell-mediated release of
signalling molecules. Creating systems that allow for studying synergistic effects
between mechanotransduction and growth factor signalling in vitro can further
contribute to understanding stem cell behaviour in vivo. With extended knowledge
and control about cellular processes, the use of stem cells in therapeutic applications
becomes safer and more accessible to patients.