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Multi-Point Nanoindentation Method to Determine Mechanical Anisotropy in Nanofibrillar Thin Films
Dinidu Perera1, Qijue Wang1, Hannes C Schniepp1
1Department of Applied Science, William & Mary, P.O. Box 8795, Williamsburg, VA, 23187-8795, USA.
Small (Weinheim an Der Bergstrasse, Germany)
|July 3, 2022
Summary
Researchers developed a new method to measure mechanical anisotropy in materials like spider silk. This technique reveals how nanofibril orientation impacts material strength, with potential for disease diagnostics.
Area of Science:
- Materials Science
- Nanotechnology
- Biomimetics
Background:
- Oriented nanofibrillar structures in biomaterials (e.g., spider silk, wood, cartilage) confer outstanding mechanical properties.
- Characterizing mechanical anisotropy in these materials, especially at microscopic scales, is challenging.
- Spider silk's unique structure and properties make it an ideal model for studying nanofibril anisotropy.
Purpose of the Study:
- To develop and apply a novel technique for characterizing mechanical anisotropy in microscopically small samples.
- To provide a detailed nanoscale structure-property analysis of Chilean recluse spider silk.
- To investigate the role of interfibrillar binding forces and surface energy in spider silk's mechanical behavior.
Main Methods:
- Utilized atomic force microscope (AFM) indentation at multiple points.
- Combined AFM data with finite element analysis (FEA) for mechanical anisotropy assessment.
- Applied the technique to thin films of Chilean recluse spider silk.
Main Results:
- Achieved detailed directional nanoscale structure-property characterization of spider silk.
- Determined tensile and transverse elastic moduli of spider silk as 9 GPa and 1 GPa, respectively.
- Quantified the binding strength between silk nanofibrils (159 ± 13 MPa) and derived surface energy (37 mJ m⁻²), highlighting the role of van der Waals forces.
Conclusions:
- The developed AFM-FEA technique is effective for characterizing mechanical anisotropy in small, inhomogeneous samples.
- Spider silk's mechanical properties are strongly linked to its strictly oriented nanofibrillar structure and interfibrillar binding.
- The technique's versatility offers potential applications in areas like early disease diagnostics by detecting altered mechanical properties in tissues.
