Med-Tech Innovation Nanotechnology


Manufacturing porous polymers The self-organisation technique employed to produce porous polymer surfaces is based on the Breath Figure Method first reported in 1994.14


The name relates to


the breath figures (patterns that form when a vapour is condensed onto a cold surface) of condensing water droplets that appear on the surface of polymer solutions, which lead to the structures observed above. The introduction of water vapour over a polymer/ solvent solution leads to water droplet condensation at the polymer solution surface (due to evaporative cooling at the surface), then trapping of the water droplets by the polymer, and ultimately the imprinting of their shape on the surface. This results in ordered hexagonally packed porous microstructure of micron-scale pores supported by walls of nano-scale thin films at their narrowest points. This discovery led to considerable interest in porous microstructures produced via this method. The spherical microstructure was believed to be an intrinsic feature of this system and only limited reports of any changes in this regard were found without any post-processing techniques.


Using this novel technique, a porous film or coating


with micron scale pores containing nanofeatures, whose depth, shape and function can all be controlled in a simple, robust, single step process, can be used to create porous polymer films for the medical device industry (Figure 3). The formation mechanism allows for a range of different pore geometries, thus adding significantly to the scope of potential applications. Furthermore, loading of active agents is typically achieved by solution dosing following porous film production, whereas this novel technique has the potential to load the active agents in a single step during film formation.


Advantages These porous films have many advantages over current state-of-the-art products: • Single step synthesis allows for a complete production process integrated to one machine


• Operation is simple and control over pore morphology is achieved using easily adjustable reaction conditions


• Simple production techniques potentially allow for integration of many different materials into the polymer membrane and therefore provide a diverse range of functionality for this product


• The technique used to create porous polymer surfaces is also capable of scale-up to produce high throughput thus making it suitable for industrial levels of production


• This method of production is simple, cost-effective and has low material requirements.


Burgeoning potential The remarkable self-ordering observed in these polymer samples mimics the ordering within systemsin nature in a simple and elegant manner. The vast array of nanoscale order in the natural world and how it is used to such great effect is in itself a wonder. This technique coupled with the enabling surface monitoring technologies at CRANN will


www.med-techinnovation.com


hopefully lead to a range of technologies inspired by the nano-natural world, which is all around us.


Acknowledgements We would like to thank the following contributors: Dr Chris Keely, Professor John Boland, Professor John Donegan, Professor Yurii Gun`ko, Ms Valerie Gerard, Dr Paul Miney, Dr Ronan Daly and Ms Mary Colclough.


Additional Information For more information regarding these porous polymers see the Trinity College Alumni YouTube video, http://tiny.cc/9nfc8 To find out more about how companies can work with CRANN, contact Brendan Ring, CRANN Commercialisation Manager, Trinity College Dublin, tel. +353 (0)1 896 3088, e-mail: brendan.ring@tcd.ie.


References


1. ISO/TC229 Documentary standards for nanotechnology, TR ISO, 2008.


2. D. Bazou et al., “Imaging of Human Colon Cancer Cells Using He-Ion Scanning Microscopy,” J. of Microscopy, 42, 3, 290–294 (2011).


3. S.E. McNeil, “Nanotechnology for the Biologist,” J. Leukoc. Biol., 78, 3 585–594 (2005).


4. A.S.G Curtis et al., “Cells React to Nanoscale Order and Symmetry in Their Surroundings,” IEEE Transactions on Nanobioscience, 3, 1, 61–65 (2004).


5. R.G. Flemming et al., “P. F. Effects of Synthetic Micro-and Nano-Structured Surfaces on Cell Behavior,” Biomaterials, 20, 6, 126 –135 (1999).


6. T.J. Webster et al., “Nanoceramic Surface Roughness Enhances Osteoblast and Osteoclast Functions for Improved Orthopaedic/Dental Efficacy,” Scripta Materilia, 44, 8–9, 1639–1642 (2001).


7. N. Gadegaard et al., Nano Patterned Surfaces for Biomaterials Applications,” Advances in Science and Technology, 53, 107–115 (2006).


8. S.J. Kalita et al., “Nanocrystalline Calcium Phosphate Ceramics in Biomedical Engineering,” Materials Science & Engineering, C 27, 3 441–449 (2007).


9. E. Karsenti, “Self-Organisation in Cell Biology: A Brief History,” Nature Reviews Molecular Cell Biology, 9, 255-262, (2008).


10. D. Vollath, Nanomaterials, Wiley-VCH (2008).


11. B.L. van der Hoeven et al., “Drug-Eluting Stents: Results, Promises and Problems, Intl J. of Cardiology, 99, 1 (2005).


12. S. Zhang et al., “Fabrication of Ordered Porous Polymer Film via a One-Step Strategy and Its Formation Mechanism,” Macromolecules, 42, 10, 3591–3597 (2009).


13. Mimicking Nature at the Nanoscale: Selective Transport Across a Biomimetic Nanopore – Physorg.com, www.physorg. com/news/2011-06-mimicking-nature-nanoscale-biomimetic- nanopore.html


14. G. Widawski et al., “Self-Organised Honeycomb Morphology of Star-Polymer Polystyrene Films, “ Nature, 369, 387–389 (1994).


Dr Éilis E. McGrath is Technical Marketing Officer and


Dr David A. McGovern is Commercialisation Technical Specialist at CRANN Innovating Nanoscience, Trinity College Dublin, Dublin 2, Ireland, tel. +353 (0)86 847 2564, e-mail: eilis.mcGrath@tcd.ie, www.crann.tcd.ie


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