Fabrication of difficult nanostructures by injection moulding

There is an increasing demand for nanostructured polymeric surfaces for many scientific and commercial applications including the fields of cell and tissue engineering, where the study of the ways that cells interact with their environment holds great potential for the future of regenerative medicine. Current replication based fabrication techniques, such as hot embossing, which are used to produce nanostructured surfaces for this type of research are not fast enough to keep up with the growing demand for them. Injection moulding offers a high throughput alternative to these processes and can upscale the production of nanopatterned samples by several orders of magnitude. However, the nickel moulds traditionally used to injection mould micro- and nanostructures are limited to producing recessed features due to the rate at which the injected polymer cools upon contact with it. In order to replicate raised features (e.g. pillars) the polymer needs enough time to fill the nanoscale cavities of the mould before freezing. A solution to this limitation of nickel tooling is devised and implemented, using a thermally insulating tooling material that facilitates the formation of nanopillars by injection moulding. This tooling material can be patterned by a range of fabrication techniques including photolithography and nanoimprint lithography. The tooling can be used to replicate nanopatterns over underlying micron and millimetre scale topographies. This flexible solution enables the large volume production of samples containing raised poly(carbonate) nanopillars without significantly compromising cycle time. Following this, the technique is adapted in an attempt to replicate high aspect ratio nanostructures. In this section a range of non-adhesive surface coatings are tested for their abilities to enhance the replication process through the systematic analysis of their durability and the replication fidelity that they enable. Nanopillars with aspect ratios of greater than 10:1 are successfully produced and are used to fabricate surfaces for cell engineering research. This success is also demonstrative of the technique’s potential to mass produce nanostructures for other applications such as non-reflective and dry adhesive surfaces. Finally, a study is undertaken to replicate microstructures with an elastomeric polymer. The tooling solution is used to assess the minimum feature size that can be replicated with this polymer and how processing parameters and non-adhesive coatings can improve this. This thesis documents the development of a range of enabling techniques which add to the existing toolbox of nanofabrication technologies. They address a growing demand for nanostructured polymeric surfaces in cell and tissue engineering research, whilst remaining open and adaptable to any application that requires the high throughput production of nanopatterned polymeric samples