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Scottish Plastics and Rubber Association Scottish Plastics and Rubber Association

Injection Moulding Nanostructures for Medical Applications

Dr Nikolaj Gadegaard

At the February SPRA technical meeting on “Advances in Injection Moulding”, sponsored by Engel UK and held at the Dakota Hotel, Eurocentral, the two speakers, Graeme Herlihy, MD of Engel UK and Dr Nikolaj Gadegaard, University of Glasgow, informed and entertained an audience of 28, drawn from moulders, toolmakers, end users and academics, on some of the latest developments in the field of plastics injection moulding.

In the second presentation at the February SPRA meeting on Advances in Injection Moulding, Dr Nikolaj Gadegaard described some of the exciting work at the Centre for Cell Engineering at the University of Glasgow, which has been made possible through adaptation of plastics injection moulding.

demonstrating how biological cells react to different nano-patterns
The Centre for Cell Engineering has demonstrated that creating detailed surface topography, typically ‘pits’ of the order of 100 nm diameter with 300 nm spacing, can in some instances repel biological cells and in other cases attract cells and promote cell growth. They have also established that arrays of nano scale ‘pits’ or ‘pillars’ with a controlled amount of disorder are more successful than either regular arrays or totally random arrays.

injection moulding of test plaques
The nano scale surface patterns are created on nickel substrates using electron beam lithography, which is capable of producing patterns with line widths less than 10 nm. For mass production of surfaces for test programmes, plaques with the nano-scale topography were produced in polystyrene and polycarbonate by injection moulding, using the nickel masters as inserts in the mould cavity. An Engel Victory Tech 28 injection moulding machine was selected to provide the high injection pressure required to create the extremely fine moulding detail, using a compression-injection (coining) technique.

The problem of insufficient detail due to premature freezing of the melt before the nano-scale cavities were filled was solved by replacing the nickel inserts with replicas fabricated in polyimide (Kapton and Cirlex), which had lower thermal conductivity than the nickel but could stand up to repeated cycles at temperatures up to 350oC. Polyimide inserts provide much better detail than nickel inserts. The team are now looking at moulding cages in PEEK to promote bone cell growth in spine fusion procedures.

In addition to life science applications for specific elimination of cells or promotion of cell growth, the nano-pattern surfaces are attracting interest in superhydrophobicity, self cleaning surfaces and attempts to mimic the colours created by nano-scale patterns in nature, for example butterfly wings.

Overview of the complete process of injection moulding nano-scale surface patterns

Dr Gadegaard addressing SPRA members and guests

Report by Charlie Geddes, SPRA Hon. Secretary, February 2012

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