|Fibrillar Dry Adhesive © INM|
The Program Division Functional Microstructures conducts pioneering research on functional micro- and nanopatterned surfaces. Through a suitable combination of patterning and materials, surface features are fabricated that enhance mechanical, optical, thermal or haptic functionalities. Inspired by the fascinating adhesive performance of natural structures, the group attempts to mimic such mechanisms in synthetic surfaces. Our research focuses on the switchability of adhesion to different surfaces using gecko-inspired structures and its transfer into practical applications. In collaboration with the InnvationCenter INM, we promote the transfer of our patented Gecomer® Technology into industrial applications ranging from robotic pick & place technologies through protective systems to medical surfaces.
Numerical simulations underpin the process development and the micromechanical optimization. Our group receives generous funding from international (ERC Advanced Grant, EU BioSmartTrainee project) and national (DFG, Leibniz Transfer Project) sources.
- Engineering of biomimetic surfaces: Switchable micropatterns for controlled adhesion and touch, ERC Advanced Grant „Switch2stick“, 2014-2019, Grant agreement No. 340929.
- Mikroskalige Kompositstrukturen für kontaktmechanische Wechselwirkung mit Hautoberflächen, DFG, 2015-2017, Grant agreement No. HE 7498/1-1.
- BioSmartTrainee project „Training in Bio-Inspired Design of Smart Adhesive Materials“, EU Marie Sklodowska-Curie Actions, 2015-2018, Grant agreement No. 642861.
- Upscaling and transfer of the gecko effect into industrial applications, Leibniz Association, 2016-2018, Leibniz-Competition Grant No. 493.
- Gecko material for Space applications, European Space Research and Technology Centre, 2017-2018
The adhesion of micropatterned adhesives is strongly affected by the surface roughness and texture. We explore how adhesion of micropatterned structures can be tailored even for rough surfaces. To this end, we gain new insight into the contact mechanics and identify ways to improve adhesion as a function of feature size, roughness and materials characteristics. Recently, the adhesion enhancement of gecko-like surfaces, over unpatterned surfaces, was demonstrated even for rough surfaces. These developments aim to extend the applicability of fibrillar structures to realistic surfaces.
Following the example of the gecko toe, hierarchically structured adhesives are investigated as macroscopic and microscopic models. Hierarchy is found to affect both the elastic instability (in compression) and the adhesion. Because of an increased propensity to buckling, hierarchical patterns are not always superior to conventional structures with regard to adhesion behavior. Our concepts suggest that the structure compliance needs to be tailored to achieve the best performance.
We explore the adhesion mechanisms of functional patterns against compliant material surfaces. Using novel structural designs, the effects of substrate compliance, viscoelasticity, humidity and roughness are investigated. With special systems, promising adhesion to skin models was demonstrated. Such adhesives based on the Gecomer® principle have high potential for emerging applications in clinical practice or wearable sensors.
The development of adhesives for medical applications is carried out in collaboration with the Medical School of Saarland University (UKS). In addition to adhesion, issues of biocompatibility, biodegradation and the impact of surface morphologies on cell adhesion and migration are in the center of our research. The objective is the development of a physically adhering implant with proven wound management capability.
The ability to control adhesive strength is one of the prominent features of fibrillar structures in comparison to conventional adhesives. We have successfully demonstrated the principle of mechanical actuation in robotic systems. One focus lies on the exploitation of additional stimuli for adaptive surface features, e.g. based on the shape memory effect. Other novel concepts are currently under development.
Modeling provides a necessary approach, complementary to experimental studies, to gain additional insight into new contact mechanisms. Using analytical and numerical calculations, we explore the influence of structural and materials parameters on the stress distribution in the interface. It is found that the stress singularities, which govern the adhesive performance, are sensitive to changes in feature geometry. After validation with experiments, our simulations are a helpful tool in the targeted optimization of our technology for specific applications.
INM’s Gecomer® Technology is the result of our long-term research into reliable and reversible adhesion. Stimulated by our customers’ demands regarding substrate materials, process environments and other specifications, we design and fabricate the next generation of Gecomer® Technology. Our solution provides a novel, noise-free system for handling delicate objects even in vacuum. Our energy-saving pick and place system relies on a patented attachment and detachment mechanism which enables controlled switching of the adhesion strength. Hence, switching functions without external energy, enabling energy conservation in production lines. The industry transfer is conducted in cooperation with InnovationCenter INM .
Connecting biological objects with electronics requires soft electrical contacts. To that end, we explore the fabrication of micro-fibrillar adhesion devices from electrically conductive materials. Detailed characterization of these devices reveals the relationship between adhesion properties and electrical resistivity. Their application as electrically tunable devices is also explored.