Mechanical properties of collagen fibrils determined by buckling analysis

The mechanical properties of biological nanofibers such as collagen fibrils are important in many applications, ranging from tissue-engineering to cancer treatment. However, mechanical testing is not straightforward at the nanometer scale. Here, we use the theory of column-buckling to determine the bending properties of individual collagen fibrils. To achieve this, fibrils were deposited on a manually pre-stretched foil, which was then released with the fibrils attached. Atomic Force Microscopy (AFM) imaging was used to determine the tensile modulus by measuring the buckling-wavelength and the radius for each fibril. Comparison with data obtained by AFM nanoindentation and other, more sophisticated methods, shows that our results are in very good agreement. The great advantage of this simple approach is that it can be used to quickly determine mechanical properties without force or stress-strain measurements, which are challenging to obtain accurately and at high throughput at the nanoscale. The method could be applied to any nanofibers, not just collagen fibrils. STATEMENT OF SIGNIFICANCE: Collagen fibrils are the main constituent of the extracellular matrix, and alterations of their mechanical properties can have significant effects on cell adhesion and motility. This has, ultimately, implications in age-related diseases and cancer. Furthermore, tuning the mechanical properties of collagen fibrils could be an important tool in the design of artificial cell scaffolds in tissue-engineering. For these reasons, it is important to have methods that can be used to determine the mechanical properties of fibrils at the single-fibril level and, therefore, at the nanometer scale. The method presented here has the advantage of being easy to use and avoids some of the fundamental issues of more established methods.