Slippery Surfaces

Harvard Professor Joanna Aizenberg shows David Pogue the Nepenthes Pitcher Plant, a carnivorous plant whose slippery surface inspired a non-stick material invented by her lab.

Unwanted surface interactions are a limiting factor nearly everywhere liquid is handled or encountered: they create drag in transport systems, trigger blood clotting, nucleate aircraft icing, and promote biofouling. Despite intensive study, state-of-the-art repellent surfaces have remained poorly suited for many substances, environments, and budgets. Inspired by the carnivorous pitcher plant, we have invented a fundamentally different conceptual approach to surface design that avoids the inherent limits of current strategies. Based on this approach, we have created surfaces that show almost perfect slipperiness toward polar and organic liquids, complex substances such as blood, oil, and ketchup, a genetically diverse range of bacteria and algae, and solid materials such as ice, dust, and insects. The surfaces can be optimized to function under extreme conditions, adapt to stimuli, and self-heal, and can be constructed from a variety of low-cost materials and applied to surfaces as diverse as medical tubing, planes, and refrigerators. 

Our approach comes from the same concept the pitcher plants use to make insects slide down their leaves into their digestive juices. We infuse a porous substrate with a lubricating fluid such that the overlying film, rather than air or solid, serves as the slippery interface. Based on extensive theoretical and experimental characterization, we have defined materials requirements for the lubricant to form a locked-in, stable, inert surface. These surfaces outperform state-of-the-art surfaces in scope (water, hydrocarbons, crude oil, blood, ice, bacteria), liquid mobility (contact angle hysteresis <2.5o), resilience (recovery within 0.1-1 s); and pressure tolerance (up to ~676 atm). Since low-surface-energy porous solids are abundant from small to large sacles, highly omniphobic surfaces can be easily generated without specialized fabrication facilities. 

Currently our group is developing this technology to meet emerging needs in biomedical fluid handling, fuel transport, antifouling, anti-icing, optical imaging, harsh environments, and other areas. 


See SLIPS in action by following the links below: 

Interviews: 

"The Makers" of The Mind of the Universe features Professor Aizenberg, International science documentary series, VPRO, May 21, 2017.

Nova episode on Making Stuff Wilder, October 23, 2013. 

Deadly pitcher-plant inspires super slippery nano-surface, Reuters, February 6, 2012. 

“Extreme Biomimetics” talk by Professor Aizenberg, Disruptive Ideas, TEDxBigApple, New York, February 4, 2012. 

“Slippery when wet (or anytime)”, CBC interview with Professor Aizenberg, October 8, 2011. 

Material World, BBC interview with Professor Aizenberg, September 21, 2011. 
 


In the news: 

Slippery liquid surfaces confuse mussels to stop them from sticking to underwater structuresHarvard press release, August 17, 2017. 

ARPA-E Making Progress Toward Achieving Mission, Report by the National Academies of Sciences, Engineering, and Medicine, June 13, 2017.

Creating a slippery slope on the surface of medical implantsHarvard press release, November 1, 2016. 

An unobstructed view into the human body, Harvard press release, September 26, 2016

Harnessing engineered slippery surfaces for tissue repair, Harvard press release, May 18, 2016.

Mid-Atlantic Seabed Drilling Expedition, BBC Science in Action podcast (starting at 14:08 minutes), October 23, 2015. 

Super-slick material makes steel better, stronger, cleaner, Harvard press release, October 20, 2015. 

The secrets of secretion, Harvard press release, June 22, 2015. 

What Is ARPA-E Up to Now?, Innovation, May 2015. 

Artificial membrane system uses fluid-filled pores for smooth moving, Materials 360, April 9, 2015. 

Literally Nothing Will Stick To This New Slippery Surface, Fast Company, March 27, 2015. 

Fabrics of Life, Nature, Outlook, March 25, 2015. 

Pores for thought over separation issues, Materials Today, March 10, 2015. 

Gating mechanism under pressure, Nature, News and VIews, March 5, 2015. 

Fluid–filled pores separate materials with fine precision, Harvard press release, March 5, 2015. 

New silicone infused with silicone oil = super-slippery, and proven to keep bacteria from growing on medical tubing, Reddit, February 20, 2015. 

SLIPS team heads to Capitol Hill, Harvard press release, February 12, 2015. 

Novel non-stick material joins portfolio of slippery surface technologies, Harvard press release, February 10, 2015. 

Wyss Institute launches SLIPS company, Harvard press release, October 29, 2014. Read more at SLIPS Technologies

Carnivorous Plant Inspires Anticlotting Medical Devices, Scientific American podcast, October 15, 2014. 

Slippery When Coated: Helping Medical Devices Prevent Blood Clots, NPR, October 12, 2014. 

Bioinspired coating for medical devices repels blood and bacteria, Harvard press release, October 12, 2014. 

Super-Slick Material Keeps Ice From Forming, Technology Review, July 2, 2014. 

Scientists Modify Cotton and Polyester to Display Repellent Properties, The Crimson, February 26, 2014. 

Stain-free, self-cleaning clothing on the horizon, Harvard press release, January 13, 2014. 

Pulling On The Shade, American Scientist, September 1, 2013. 

New coating turns ordinary glass into super-slippery glass, Harvard press release, August 2, 2013. 

Fluid-Infused Porous FIlms Dynamically Adjust Transparency and Wettability, Materials 360, April 22, 2013. 

Scientists Design New Adaptive Material Inspired by Tears, Popular Mechanics, April 17, 2013. 

Morphing 'fabric' shifts shape to repel or grip water, New Scientist, April 9, 2013. 

New material can halt runny liquids on demand, BBC, April 9, 2013. 

Cry me a river of possibility: Scientists design new adpative material inspired by tears, Harvard press release, April 8, 2013. 

Ice-Phobic Surfaces that are Wet, ACS Nano, August 9, 2012. 

SLIPS Blitz Biofilms, Nature, August 9, 2012. 

Harvard scientists' breakthrough could stop biofilm formation, Food Production Daily, August 9, 2012. 

SLIPS liquid repeller is inspired by carnivorous plants, enemy to insects and graffiti artists alike, Engadget, August 3, 2012. 

Super slippery surface prevents biofilms, PNAS, July 31, 2012. 

New coating evicts biofilms for good, Harvard press release, July 30, 2012. 

Ice Curbs, National Science Foundation's Discovery Files (podcast), June 27, 2012. 

'Ice-Phobic' Airplane Wings, Wall Street Journal, June 22, 2012. 

SLIPS receives a 2012 R&D 100 Award from R&D Magazine, honoring it as one of the 100 most technologically significant products of the previous year. June 20, 2012. 

No Scraper Required: Ice Rolls Off Metal, Discovery, June 16, 2012. 

Slippery Coating Keeps Metals Frost-Free, Chemical and Engineering News, June 15, 2012. 

Keeping Metal Surfaces Ice, Frost Free, The Hindu, June 14, 2012. 

Ultra-Antifreeze Keeps Ice From Even Forming, Smithsonian, June 12, 2012. 

A new spin on anti-freeze, Harvard press release, June 11, 2012. 

Super-slippery material could mean end to having to wait for ketchup, The Telegraph, November 13, 2011. 

Slippery Slope: researchers take advice from carnivorous plant, Harvard press release, September 21, 2011. 

Slippery when wetted, Nature News and Views, September 21, 2011. 

Carnivorous plant inspires super slippery material, New Scientist, September 21, 2011. 

Pitcher plant inspires super slippery surface, Chemical and Engineering News, September 21, 2011. 

Ketchup bottle problems solved, The Telegraph, November 13, 2011. 

Carnivorous plant shows its slippery side, Financial Times, September 30, 2011. 

A great non-friction story: Researchers create ‘world’s most slippery surface’, Daily Mail, September 22, 2011. 

Scientists create wonder material, Metro Herald, p. 10, September 22, 2011. 

Copied from pitcher plants; destined for ketchup bottles, Popular Science, November 14, 2011. 

Pitcher plant perfect, Nature Chemistry, vol. 3, pp. 834, October 24, 2011. 

Pitcher plant inspires ultimate non-stick surface, Chemistry World, September 22, 2011. 

Plant technology used to create super-repellent material, The Engineer, September 26, 2011. 

Flesh-eating plant inspires super-slippery material that repels everything, Discover Online, September 21, 2011. 

Invention Solves Ketchup Dilemma, The Harvard Crimson, November 20, 2011. 

Source: Nature 
Michael Nosonovsky of the University of Wisconsin-Milwaukee: "The development of SLIPS typifies two themes that are likely to dominate the field of biomimetic and functional surfaces in coming years." 

Source: C&EN (ACS) 
Philippe Brunet, an expert on omniphobic materials at France’s University of Paris Diderot, says he is impressed by the innovative strategy. “In my opinion, this study does not simply represent an improvement in liquid-repellent surfaces, but rather a revolution in the field,” he says. “I am sure many researchers reading this paper would think as I do: ‘I wish I would have thought about these surfaces before.’” 

Source: Chemistry World (RCS) 
"This really is a new direction," says Steven Bell, director of innovative molecular materials at Queen's University Belfast, UK. "Many of us have been working on improving the durability of 'lotus effect' materials but this now offers us an alternative way to try to reach the same objectives." 

Source: ABC (Australia) 
Professor Robert Short, director of the Mawson Institute at the University of South Australia, says the results are highly impressive and the simplicity of the approach is particularly striking. 
"The combination of solids and liquids uses capillary action to bring lubricant to the surface of nano/microengineered structures," Short says. 
"Furthermore, the ability of the surface to 'heal' sets it apart from other cutting-edge approaches." 

Source: Discover 
Walter Federle from the University of Cambridge, who discovered the structure of the pitcher plant’s peristome, says,“It’s really exciting to see that this principle has inspired the authors and allowed them to develop something that could prove extremely useful.” 

Source: New Scientist 
"It's interesting that it combines self-lubrication, self-healing and self-cleaning, which are different 
processes,"
 says Michael Nosonovsky of the University of Wisconsin-Milwaukee. "It's a new type of 
smart material."

Amini S, Kolle S, Petrone L, Ahanotu O, Sunny S, Sutanto CN, Hoon S, Cohen L, Weaver JC, Aizenberg J, et al. Preventing mussel adhesion using lubricant-infused materials. Science [Internet]. 2017;357 (6352) :668-673. Publisher's VersionAbstract

Mussels are opportunistic macrofouling organisms that can attach to most immersed solid surfaces, leading to serious economic and ecological consequences for the maritime and aquaculture industries. We demonstrate that lubricant-infused coatings exhibit very low preferential mussel attachment and ultralow adhesive strengths under both controlled laboratory conditions and in marine field studies. Detailed investigations across multiple length scales—from the molecular-scale characterization of deposited adhesive proteins to nanoscale contact mechanics to macroscale live observations—suggest that lubricant infusion considerably reduces fouling by deceiving the mechanosensing ability of mussels, deterring secretion of adhesive threads, and decreasing the molecular work of adhesion. Our study demonstrates that lubricant infusion represents an effective strategy to mitigate marine biofouling and provides insights into the physical mechanisms underlying adhesion prevention.

Daniel D, Timonen JVI, Li R, Velling SJ, Aizenberg J. Oleoplaning droplets on lubricated surfaces. Nat. Phys. [Internet]. 2017;13 :1020-1025. Publisher's VersionAbstract

Recently, there has been much interest in using lubricated surfaces to achieve extreme liquid repellency: a foreign droplet immiscible with the underlying lubricant layer was shown to slide o at a small tilt angle <5◦ . This behaviour was hypothesized to arise from a thin lubricant overlayer film sandwiched between the droplet and solid substrate, but this has not been observed experimentally. Here, using thin-film interference, we are able to visualize the intercalated film under both static and dynamic conditions. We further demonstrate that for a moving droplet, the film thickness follows the Landau–Levich–Derjaguin law. The droplet is therefore oleoplaning—akin to tyres hydroplaning on a wet road—with minimal dissipative force and no contact line pinning. The techniques and insights presented in this study will inform future work on the fundamentals of wetting for lubricated surfaces and enable their rational design.

Alvarez MM, Aizenberg J, Analoui M, Andrews AM, Bisker G, Boyden ES, Kamm RD, Karp JM, Mooney DJ, Oklu R, et al. Emerging Trends in Micro- and Nanoscale Technologies in Medicine: From Basic Discoveries to Translation. ACS Nano. 2017;11 (6) :5195-5214.Abstract

We discuss the state of the art and innovative micro- and nanoscale technologies that are finding niches and opening up new opportunities in medicine, particularly in diagnostic and therapeutic applications. We take the design of point-of-care applications and the capture of circulating tumor cells as illustrative examples of the integration of micro- and nanotechnologies into solutions of diagnostic challenges. We describe several novel nanotechnologies that enable imaging cellular structures and molecular events. In therapeutics, we describe the utilization of micro- and nanotechnologies in applications including drug delivery, tissue engineering, and pharmaceutical development/testing. In addition, we discuss relevant challenges that micro- and nanotechnologies face in achieving cost-effective and widespread clinical implementation as well as forecasted applications of micro- and nanotechnologies in medicine.

Hou X, Zhang YS, Trujillo-de Santiago G, Alvarez MM, Ribas J, Jonas SJ, Weiss PS, Andrews AM, Aizenberg J, Khademhosseini A. Interplay between materials and microfluidics. Nat. Rev. Mater. 2017;2 (5) :17016.Abstract

Developments in the field of microfluidics have triggered technological revolutions in many disciplines, including chemical synthesis, electronics, diagnostics, single-cell analysis, micro- and nanofabrication, and pharmaceutics. In many of these areas, rapid growth is driven by the increasing synergy between fundamental materials development and new microfluidic capabilities. In this Review, we critically evaluate both how recent advances in materials fabrication have expanded the frontiers of microfluidic platforms and how the improved microfluidic capabilities are, in turn, furthering materials design. We discuss how various inorganic and organic materials enable the fabrication of systems with advanced mechanical, optical, chemical, electrical and biointerfacial properties — in particular, when these materials are combined into new hybrids and modular configurations. The increasing sophistication of microfluidic techniques has also expanded the range of resources available for the fabrication of new materials, including particles and fibres with specific functionalities, 3D (bio)printed composites and organoids. Together, these advances lead to complex, multifunctional systems, which have many interesting potential applications, especially in the biomedical and bioengineering domains. Future exploration of the interactions between materials science and microfluidics will continue to enrich the diversity of applications across engineering as well as the physical and biomedical sciences.

Wong T-S, Sun T, Feng L, Aizenberg J. Interfacial materials with special wettability. MRS Bulletin. 2013;38 :366-371.Abstract

Various life forms in nature display a high level of adaptability to their environments through the use of sophisticated material interfaces. This is exemplifi ed by numerous biological systems, such as the self-cleaning of lotus leaves, the water-walking abilities of water striders and spiders, the ultra-slipperiness of pitcher plants, the directional liquid adhesion of butterfl y wings, and the water collection capabilities of beetles, spider webs, and cacti. The versatile interactions of these natural surfaces with fl uids, or special wettability, are enabled by their unique micro/nanoscale surface structures and intrinsic material properties. Many of these biological designs and principles have inspired new classes of functional interfacial materials, which have remarkable potential to solve some of the engineering challenges for industrial and biomedical applications. In this article, we provide a snapshot of the state of the art of biologically inspired materials with special wettability, and discuss some promising future directions for the field.

Kovalenko Y, Sotiri I, Timonen JVI, Overton JC, Homes G, Aizenberg J, Howell C. Bacterial Interactions with Immobilized Liquid Layer. Adv. Healthcare Mater. 2017;6 (15) :1600948.Abstract

Bacterial interactions with surfaces are at the heart of many infection-related problems in healthcare. In this work, the interactions of clinically relevant bacteria with immobilized liquid (IL) layers on oil-infused polymers are investigated. Although oil-infused polymers reduce bacterial adhesion in all cases, complex interactions of the bacteria and liquid layer under orbital flow conditions are uncovered. The number of adherent Escherichia coli cells over multiple removal cycles increases in flow compared to static growth conditions, likely due to a disruption of the liquid layer continuity. Surprisingly, however, biofilm formation appears to remain low regardless of growth conditions. No incorporation of the bacteria into the layer is observed. Bacterial type is also found to affect the number of adherent cells, with more E. coli remaining attached under dynamic orbital flow than Staphylococcus aureus, Pseudomonas aeruginosa under identical conditions. Tests with mutant E. coli lacking flagella confirm that flagella play an important role in adhesion to these surfaces. The results presented here shed new light on the interaction of bacteria with IL layers, highlighting the fundamental differences between oil-infused and traditional solid interfaces, as well as providing important information for their eventual translation into materials that reduce bacterial adhesion in medical applications.

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