Nanomechanical 3D Depth Profiling of Collagen Fibrils in Native Tendon

Abstract

Connective tissue displays a large compositional and structural complexity that involves multiple length scales. In particular, on the molecular and the nanometer level, the elementary processes that determine the biomechanics of collagen fibrils in connective tissues are still poorly understood. Here, we use atomic force microscopy (AFM) to determine the three-dimensional (3D) depth profiles of the local nanomechanical properties of collagen fibrils and their embedding interfibrillar matrix in native (unfixed), hydrated Achilles tendon of sheep and chickens. AFM imaging in air with controlled humidity preserves the tissue’s water content, allowing the assembly of collagen fibrils to be imaged in high resolution beneath an approximately 5–10 nm thick layer of the fluid components of the interfibrillar matrix. We collect pointwise force–distance (FD) data and amplitude–phase–distance (APD) data, from which we construct 3D depth profiles of the local tip–sample interaction forces. The 3D images reveal the nanomechanical morphology of unfixed, hydrated collagen fibrils in native tendon with a 0.1 nm depth resolution and a 10 nm lateral resolution. We observe a diversity in the nanomechanical properties among individual collagen fibrils in their adhesive and in their repulsive, viscoelastic mechanical response as well as among the contact points between adjacent collagen fibrils. This sheds new light on the role of interfibrillar bonds and the mechanical properties of the interfibrillar matrix in the biomechanics of tendon.

High-Speed Nanomechanical Mapping of the Early Stages of Collagen Growth by Bimodal Force Microscopy

“…Thus, overlap regions are thicker, stiffer, and dissipate less energy than gap regions. This tendency was similar to the one observed on thicker collagen samples . Bottom-effect corrections were applied to remove the influence of the rigidity support (∼50 GPa) on the elastic modulus measurements (see SI for details).…”

“…This tendency was similar to the one observed on thicker collagen samples. 43 Bottom-effect corrections were applied 44 to remove the influence of the rigidity support (∼50 GPa) on the elastic modulus measurements (see SI for details). The values of the elastic modulus reported here were similar to data obtained from AFM-based force–distance curves on thicker collagen fibrils (∼100 nm).…”

Accurate Wide-Modulus-Range Nanomechanical Mapping of Ultrathin Interfaces with Bimodal Atomic Force Microscopy

“…Nanoscale mechanical property mapping is one of the key achievements of atomic force microscopy (AFM). − Nanomechanical mapping is applied to facilitate the development of or to improve the characterization of materials and interfaces. − Nanomechanical measurements are widely used in mechanobiology to reveal how elastic and viscoelastic properties of proteins, cells, and the extracellular matrix influence biological processes. − …”

Nanomechanical Subsurface Characterisation of Cellulosic Fibres

“…Thus, it is possible to estimate the Young's modulus of the sample at a desired indentation spot for various indentation depths. Previously released studies have shown that this approach can be applied to soft materials such as cells (Stuhn et al 2019), polymers (Dehnert and Magerle 2018), bacteria (Longo et al 2013), graphene oxide (Dehnert et al 2016) or collagen fibrils (Magerle et al 2020).…”