Certain plant species are highly non-wetting – known as superhydrophobic (Figure a) – due to a rough, hydrophobic surface microstructure (Figure b, lotus leaf). Synthetically, we can engineer a number of superhydrophobic micropost surfaces (Figures c, d) by photolithography/etching and polymer molding methods.
Previously we have shown these materials can delay ice nucleation (1, 2) due to droplet bouncing (de-wetting) (Figure e). The limited surface contact can control inorganic crystal nucleation (3), and bacterial adhesion. Recently, pitcher plants provided a novel bio-inspired model for a new approach to ultra-low adhesion materials, known as ‘slippery liquid-infused porous surfaces’, or SLIPS (4). Recently we have generated transparent SLIPS layers (5), and demonstrated a robust resistance to blood clotting (6), and bacterial adhesion (7).
1. L. Mishchenko et al., ACS Nano 4, 7699-7707 (2010).; 2. L. Mishchenko, M. Khan, J. Aizenberg, B. D. Hatton, Adv. Func. Materials 23, 4577-4584 (2013).; 3. B. D. Hatton, J. Aizenberg, Nano Letters 12, 4551-4557 (2012).; 4. T. S. Wong et al., Nature 477, 443-447 (2011).; 5. N. Vogel, R. Belisle, B. D. Hatton, T. S. Wong, J. Aizenberg, Nature Communications 4, (2013).; 6. D. C. Leslie et al., Nature Biotechnology 32, 1134-1140 (2014).; 7. N. MacCallum et al., ACS Biomat. Science & Eng. 1, 43-51 (2014).
‘Bottom-up’ fabrication methods can build novel material structures at the nano- and microscale from the self-assembly of molecular or nanoscale components (Figure a). Colloids are nanoscale particles that can self-assemble and be a template for nanoporous inorganic materials, such as metal oxides, where the size and porous structure is defined by the colloidal template. Previously we have used electrophoretic deposition (8, 9), and evaporation-induced self-assembly (10) to control the assembly to deposit colloids.
(Figure b) shows SiO2 shells deposited around a template of polymer spheres (burned away) by vapour phase growth (11). We developed a method of colloidal co-assembly to directly self-assemble a matrix material around the colloidal template in one step (Figure c). We have generate metal oxide nanoporous layers (Figures d,e) over large areas, with very high surface area, novel optical properties (10, 12), and defined wetting patterns (‘W-ink’) (13). We currently explore methods for rapid, large area printing of colloidal nanostructures, for high surface area catalysis.
8. B. D. Hatton, P. S. Nicholson, J. Am. Ceramic Society 84, 571-576 (2001).; 9. T. Uchikoshi, K. Ozawa, B. D. Hatton, Y. Sakka, J. Materials Research 16, 321-324 (2001).; 10. B. D. Hatton, L. Mishchenko, S. Davis, K. H. Sandhage, J. Aizenberg. Proc. National Academy of Sciences 107, 10354-10359 (2010).; 11. B. Hatton, V. Kitaev, D. Perovic, G. Ozin, J. Aizenberg, J. Mater. Chem. 20, 6009-6013 (2010).; 12. H. Míguez, N. Tétreault, B. D. Hatton, D. Perovic, G. A. Ozin, Chemical Communications, 2736-2737 (2002).; 13. I. B. Burgess et al. J. Am. Chem. Soc. 133, 12430-12432 (2011).
The Hatton lab has a new Biosafety level 2 microbiology lab for bacterial culture (Figure a), managed by Dr. Dalal Asker. We research how surface topographies, such as regular nano- and microscale arrays, can affect the adhesion, morphology, growth and behaviour of bacteria and mammalian cells. An example (Figure b) is the effect a regular square array of Si posts, spaced 2 µm apart, has on the growth and morphology of mammalian cells to become highly elongated (mouse stem cell) (14).
We are designing new kinds of antimicrobial surfaces that significantly delay bacterial contamination and biofilm growth, to help address the problem of biomedical device infection and hospital-acquired infections. (Figures c and d) show bacterial biofilms (B. subtilis), which are dense, matrix-embedded bacterial colonies. (Figure e) shows the dangerous role that surface micro-cracks has to harbour bacterial adhesion on biomaterials (Pseudomonas aeruginosa on PDMS silicone). We currently investigate enzyme-immobilized surfaces that specifically disrupt the formation of extracellular biofilm matrix for P. aeruginosa. Also, ultra-slippery, low-adhesion surfaces (SLIPS) that can reduce bacterial cell counts significantly in continuous flow culture growth over 30 days.
14. M. A. Bucaro, Y. Vasquez, B. D. Hatton, J. Aizenberg. ACS nano 6, 6222-6230 (2012).
Microfluidic devices control the flow and mixing of fluids in small volumes, and has evolved in the past 20 years for a wide range of applications in chemistry, biology, medical diagnostics, and regenerative medicine. Devices are typically small (1 to 2 cm), with channels in the range of 10-100 Âµm cross-sectional dimensions, and made by photolithography mask/etching processes. We have focuses on methods to fabricate microfluidic layers over large areas, such as 50x50 cm2, using methods such as laser or vinyl cutting to define the channel structures (15) (Figures a, b).
Making large area microfluidics has enabled the development of adaptive, fluidic layers for the thermal control of building windows (15). (Figure e) shows the temperature change (measured by IR) of a microfluidic window (10x10 cm2, 0.1x1 mm channels) cooled from 40Â°C with the flow of cool water, which we suggest could be a means of dynamically controlling the outer temperature of building windows, using a closed fluidic network (and suitable heat exchange), or optical properties (Figures c,d).
15. Hatton, B. D.; Wheeldon, I.; Hancock, M. J.; Kolle, M.; Aizenberg, J.; Ingber, D. E. Solar Energy Materials and Solar Cells 2013, 117, 429-436.
As the world faces urgent global problems of climate change due to increasing greenhouse gas emissions, there are efforts at UofT to develop efficient, scalable processes to directly capture and chemically reduce carbon dioxide (CO2) into useful hydrocarbon fuels through photocatalysis. The Solar Fuels group (led by Prof. Geoff Ozin, Chemistry) is an interdisciplinary, multi-departmental effort at UofT, funded in 2015 by a $1M Connaught Global Challenge award, to develop large area photocalalytic reactor devices.
Photocatalysts can achieve reactions such as water splitting and CO2 reduction by photo-based excitation and catalytic surface reactions, which achieves the goals of CO2 capture, and non-fossil fuel-based hydrocarbon that uses only sunlight. Our effort is to develop large area nanoporous layers to improve the overall efficiently of photocatalysis, through colloidal self-assembly (16, 17), electrospinning and others.
16. Hatton, B. D.; Mishchenko, L.; Davis, S.; Sandhage, K. H.; Aizenberg, J. Proceedings of the National Academy of Sciences 2010, 107, (23), 10354-10359.; 17. Mishchenko, L.; Vasquez, Y.; Hatton, B. D.; Kolle, M.; Aizenberg, J. ACS Photonics 2014, 1, (1), 53-60.