Fibrillar adhesives

Loading Physical Intelligence Department

Objectives:

Selected Research Results and Papers

Nature can be an inspiration for innovations in science. One such inspiration comes from the gecko lizard which can climb on walls and ceilings of almost any surface texture. Rather than using its claws or sticky substances, the gecko is able to stick to smooth surfaces through dry micro/nanofibrillar adhesion, which requires no energy to hold it to the surface and leaves no residue. The dry adhesion force comes from surface contact forces such as van der Waals forces which act between all materials in contact.

 

The gecko's amazing capability of sticking to a wide range of surfaces lies in its feet, specifically the very fine hairs on its toes. There are billions of these tiny hairs which make contact with the surface and create a huge collective surface area of contact. The hairs have physical properties which let them bend and conform to a wide variety of surface roughnesses, meaning that the gecko's secret lies in the structure of these hairs themselves.

 

The structure of the biological gecko hair is very complicated as well as very miniscule. Each hair is made from multiple sections and atop each of these microhairs sit tens to hundreds of nanohairs which are 200 nanometers in diameter in a tree-like branching structure.

 

By studying this structure, we are able to mimic the biological structures with synthetic materials. These advanced adhesives will have countless uses from space exploration robots to surgical applications to post-it notes. This reusable, self-cleaning adhesive material can be thought of as a one-sided velcro which can stick to almost everything.

 

Project Members:

Dirk-Michael Drotlef

Thomas Endlein

Sukho Song

Past Members:

Seok Kim

Paul Glass

Burak Aksak

Eugene Cheung

Mike Murphy

Yigit Menguc

Uyiosa Abusomwan

Staying sticky: contact self-cleaning of gecko-inspired adhesives

The exceptionally adhesive foot of the gecko remains clean in dirty environments by shedding contaminants with each step. Synthetic gecko-inspired adhesives have achieved similar attachment strengths to the gecko on smooth surfaces, but the process of contact self-cleaning has yet to be effectively demonstrated. Here, we present the first gecko-inspired adhesive that has matched both the attachment strength and the contact self-cleaning performance of the gecko's foot on a smooth surface. Contact self-cleaning experiments were performed with three different sizes of mushroom-shaped elastomer microfibres and five different sizes of spherical silica contaminants. Using a load-drag-unload dry contact cleaning process similar to the loads acting on the gecko foot during locomotion, our fully contaminated synthetic gecko adhesives could recover lost adhesion at a rate comparable to that of the gecko. We observed that the relative size of contaminants to the characteristic size of the microfibres in the synthetic adhesive strongly determined how and to what degree the adhesive recovered from contamination. Our approximate model and experimental results show that the dominant mechanism of contact self-cleaning is particle rolling during the drag process. Embedding of particles between adjacent fibres was observed for particles with diameters smaller than the fibre tips, and further studied as a temporary cleaning mechanism. By incorporating contact self-cleaning capabilities, real-world applications of synthetic gecko adhesives, such as reusable tapes, clothing closures and medical adhesives, would become feasible.

Y. Mengüç, M. Röhrig, U. Abusomwan, H. Hölscher, M. Sitti, “Staying sticky: contact self-cleaning of gecko-inspired adhesives”, J R Soc Interface, vol. 11, no. 94, Feb. 2014

Brief highlighted research result:

• Created many new processes to fabricate vertical, angled and hierarchical polymer micro/nanofibers with and without spatulated tip endings.

   These methods are scalable and cost-effective, and resulted in 4 issued and 3 pending patents;

• Demonstrated enhanced adhesion and shear of mushroom shaped microfibers as good as geckos on smooth surfaces;

• Demonstrated controlled adhesion and directional friction of angled fiber stems with angled spatulated tips as good as biological foot-hairs;

• Manufactured hierarchical elastomer fiber adhesives with enhanced adhesion on single-asperity rough surfaces;

• Demonstrated the mechanics of contact self-cleaning of elastomer microfiber adhesives;

• Application of fibrillar adhesives to new miniature robots: (a) non-invasive anchoring of capsule robots inside the gastrointestinal tract for

   therapeutic applications and (b) palm-sized climbing robots called Waalbots.

Selected Videos

Gecko Inspired Directional and Controllable Adhesion

Enhanced Adhesion by Gecko Inspired Hierarchical Fibrillar Adhesives

Enhanced Adhesion by Gecko Inspired Hierarchical Fibrillar Adhesives

Side view video of angled gecko inspired microfibers with mushroom tips in a shear displacement experiment

Side view video of mushroom shaped microfibers with 30µm diameter attaching to a curved glass surface

Side view video from a gecko inspired hierarchical fiber in an indentation experiment

List of Publications

2014

 

Staying sticky: contact self-cleaning of gecko-inspired adhesives

Y Mengüç, M Röhrig, U Abusomwan, H Hölscher, M Sitti

Journal of The Royal Society Interface 11 (94), 20131205

 

 

Mechanics of Load-Drag-Unload based Contact Cleaning of Gecko-inspired Fibrillar Adhesives

U Abusomwan, M Sitti

Langmuir

 

 

2013

 

Enhanced fabrication and characterization of gecko-inspired mushroom-tipped microfiber adhesives

J Song, Y Mengüç, M Sitti

Journal of Adhesion Science and Technology 27 (17), 1921-1932

 

 

Contact compliance effects in the frictional response of bioinspired fibrillar adhesives

M Piccardo, A Chateauminois, C Fretigny, NM Pugno, M Sitti

Journal of The Royal Society Interface 10 (83), 20130182

 

2012

 

Effect of retraction speed on adhesion of elastomer fibrillar structures

U Abusomwan, M Sitti

Applied Physics Letters 101 (21), 211907

 

 

Gecko-Inspired Controllable Adhesive Structures Applied to Micromanipulation

Y Mengüç, SY Yang, S Kim, JA Rogers, M Sitti

Advanced Functional Materials 22 (6), 1245-1245

 

 

2011

 

Enhancing adhesion of biologically inspired polymer microfibers with a viscous oil coating

E Cheung, M Sitti

The Journal of Adhesion 87 (6), 547-557

 

The effect of aspect ratio on adhesion and stiffness for soft elastic fibres

B Aksak, CY Hui, M Sitti

Journal of The Royal Society Interface 8 (61), 1166-1175

 

 

Piezoelectric polymer fiber arrays for tactile sensing applications

B Sümer, B Aksak, K Şsahin, K Chuengsatiansup, M Sitti

Sensor Letters 9 (2), 457-463

 

 

Enhanced adhesion of dopamine methacrylamide elastomers via viscoelasticity tuning

H Chung, P Glass, JM Pothen, M Sitti, NR Washburn

Biomacromolecules 12 (2), 342-347

 

 

Waalbot II: adhesion recovery and improved performance of a climbing robot using fibrillar adhesives

MP Murphy, C Kute, Y Mengüç, M Sitti

The International Journal of Robotics Research 30 (1), 118-133

 

 

2010

 

Microstructured elastomeric surfaces with reversible adhesion and examples of their use in deterministic assembly by transfer printing

S Kim, J Wu, A Carlson, SH Jin, A Kovalsky, P Glass, Z Liu, N Ahmed, ...

 

 

Enhanced wet adhesion and shear of elastomeric micro-fiber arrays with mushroom tip geometry and a photopolymerized p (DMA-co-MEA) tip coating

P Glass, H Chung, NR Washburn, M Sitti

Langmuir 26 (22), 17357-17362

 

 

An experimental analysis of elliptical adhesive contact

B Sümer, CD Onal, B Aksak, M Sitti

Journal of Applied Physics 107 (11), 113512

 

 

2009

 

Reversible dry micro-fibrillar adhesives with thermally controllable adhesion

S Kim, M Sitti, T Xie, X Xiao

Soft Matter 5 (19), 3689-3693

 

 

Enhanced reversible adhesion of dopamine methacrylamide-coated elastomer microfibrillar structures under wet conditions

P Glass, H Chung, NR Washburn, M Sitti

Langmuir 25 (12), 6607-6612

 

 

Enhanced adhesion by gecko-inspired hierarchical fibrillar adhesives

MP Murphy, S Kim, M Sitti

ACS applied materials & interfaces 1 (4), 849-855

 

Gecko‐Inspired Directional and Controllable Adhesion

MP Murphy, B Aksak, M Sitti

Small 5 (2), 170-175

 

2008

 

Fabrication and characterization of biologically Inspired microfiber arrays with spatulate tips

S Kim, M Sitti

International Conference on Micromanufacturing, 2008.

 

Fabrication and Characterization of Biologically Inspired Mushroom-Shaped Elastomer Microfiber Arrays

S Kim, M Sitti

ASME 2008 International Design Engineering Technical Conferences and ...

 

Modeling the soft backing layer thickness effect on adhesion of elastic microfiber arrays

R Long, CY Hui, S Kim, M Sitti

Journal of Applied Physics 104 (4), 044301

 

 

Gecko inspired micro-fibrillar adhesives for wall climbing robots on micro/nanoscale rough surfaces

B Aksak, MP Murphy, M Sitti

Robotics and Automation, 2008. ICRA 2008. IEEE International Conference on ...

 

 

2007

 

Enhanced friction of elastomer microfiber adhesives with spatulate tips

S Kim, B Aksak, M Sitti

Applied Physics Letters 91 (22), 221913

 

 

Adhesion and anisotropic friction enhancements of angled heterogeneous micro-fiber arrays with spherical and spatula tips

MP Murphy, B Aksak, M Sitti

Journal of Adhesion Science and Technology 21 (12-13), 1281-1296

 

 

Adhesion of biologically inspired vertical and angled polymer microfiber arrays

B Aksak, MP Murphy, M Sitti

Langmuir 23 (6), 3322-3332

 

 

2006

 

Biologically inspired polymer microfibers with spatulate tips as repeatable fibrillar adhesives

S Kim, M Sitti

Applied Physics Letters 89 (26), 261911-261911-3

 

 

2004

 

Modeling and design of biomimetic adhesives inspired by gecko foot-hairs

GV Shah, M Sitti

Robotics and Biomimetics, 2004. ROBIO 2004. IEEE International Conference on ...

 

 

Gecko inspired surface climbing robots

C Menon, M Murphy, M Sitti

Robotics and Biomimetics, 2004. ROBIO 2004. IEEE International Conference on ...

 

 

2003

 

Synthetic gecko foot-hair micro/nano-structures for future wall-climbing robots

M Sitti, RS Fearing

Robotics and Automation, 2003. Proceedings. ICRA'03. IEEE International ...

 

 

2002

Nanomolding based fabrication of synthetic gecko foot-hairs

M Sitti, RS Fearing

Nanotechnology, 2002. IEEE-NANO 2002. Proceedings of the 2002 2nd IEEE ...

 

 

Evidence for van der Waals adhesion in gecko setae

K Autumn, M Sitti, YA Liang, AM Peattie, WR Hansen, S Sponberg, ...

Proceedings of the National Academy of Sciences 99 (19), 12252-12256