Interactive Surfaces

Molecular mechanics of soft matter

We use high-resolution force microscopy (AFM) in aqueous solution to study molecular forces at the surface of soft matter. Single-molecule force spectroscopy on hydrogels contributes to the understanding and control of the mechanisms of bioadhesion and mechanotransduction on biomaterials. In active materials, we employ light-activated molecular motors for the mechanical stimulation. For rapid force measurements on the single-molecular level, we develop novel high-throughput techniques based on tethered-particle motion in microfluidic devices.

Relevant publications:

• B. Li, A. Çolak et al.,
  Molecular stiffness cues of an interpenetrating network hydrogel for cell adhesion
  Materials Today Bio, 15 (2022) 100323.
• Y. Zheng, M.K.L. Han, R. Zhao, J. Blass, et al.,
  Optoregulated force application to cellular receptors using molecular motors
  Nature Communications, 12 (2021) 3580.
• M. Penth et al.,
  Nanomechanics of self-assembled DNA building blocks
  Nanoscale, 13 (2021) 9371-9380.
• Colak, B. Li, et al.,
  The mechanics of single cross-links which mediate cell attachment at a hydrogel surface
  Nanoscale, 11 (2019) 11596-11604.

Nanotribology

Friction force microscopy in ultra-high vacuum or in aqueous solutions reveals molecular mechanisms of friction. As one example, we investigate the limits of superlubricity in 2D materials under high local pressure. We also move our research towards a nanotribology of hydrogels and study dissipative interactions of single fluctuating polymers.

Relevant publications:

• B. Szczefanowicz, et al.,
  Formation of intermittent covalent bonds at high contact pressure limits superlow friction on epitaxial graphene,
  Physical Review Research, 5 (2023) L012049.
• K. Schellnhuber et al.,
  Single-Polymer Friction Force Microscopy of dsDNA Interacting with a Nanoporous Membrane,
  Langmuir, 40 (2024) 968-974.
• Z. Liu et al.,
  Nanoscale friction on MoS2/graphene heterostructures,
  Nanoscale, 15 (2023) 5809-5815.

Tactile perception of materials

Fingertip friction plays a key role in the tactile exploration of materials and in the perception of material properties and surfaces structures. We implement psychophysical studies to find correlations between fingertip friction and individual judgement on touch of materials.

Relevant publications:

• R. Sahli et al.,
  Tactile perception of randomly rough surfaces
  Scientific Reports, 10 (2020) 15800.
• Gedsun et al.,
  Bending as Key Mechanism in the Tactile Perception of Fibrillar Surfaces
  Advanced Materials Interfaces, 9 (2022) 2101380.
• M. Fehlberg et al.,
  Perception of Friction in Tactile Exploration of Micro-structured Rubber Samples,
  in Haptics: Science, Technology, Applications, Springer 2022, pp. 21-29.

Materials for the future of tactile communication

Materials with switchable surface structure offer opportunities to quickly convey information to humans by varying the touch experience. We develop micro-structured elastomers which change the surface shape by applied electric fields or pneumatic mechanisms. The sensory reaction to such stimulation of touch is evaluated by EEG and MEG experiments.

Relevant publications:

• N. Özgün et al.,
  Tribology of a Braille Display and EEG Correlates
  Tribol. Lett., 66 (2018) 16.