Wave Propagation and Energy Dissipation in Collagen Molecules

Abstract

Collagen is the key protein of connective tissue (i.e., skin, tendons and ligaments, cartilage, among others) accounting for 25% to 35% of the whole-body protein content, and entitled of conferring mechanical stability. This protein is also a fundamental building block of bone due to its excellent mechanical properties together with carbonated hydroxyapatite minerals. While the mechanical resilience and viscoelasticity have been studied both in vitro and in vivo from the molecule to tissue level, wave propagation properties and energy dissipation have not yet been deeply explored, in spite of being crucial to understand the vibration dynamics of collagenous structures (e.g., eardrum, cochlear membranes) upon impulsive loads. By using a bottom-up atomistic modelling approach, here we study a collagen peptide under two distinct impulsive displacement loads, including longitudinal and transversal inputs. Using a one-dimensional string model as a model system, we investigate the roles of hydration and load direction on wave propagation along the collagen peptide and the related energy dissipation. We find that wave transmission and energy-dissipation strongly depend on the loading direction. Also, the hydrated collagen peptide can dissipate five times more energy than dehydrated one. Our work suggests a distinct role of collagen in term of wave transmission of different tissues such as tendon and eardrum. This study can step towards understanding the mechanical behaviour of collagen upon transient loads, impact loading and fatigue, and designing biomimetic and bio-inspired materials to replace specific native tissues such as the tympanic membrane.

Mechanics of Mineralized Collagen Fibrils upon Transient Loads

“…15,41,42 However, we predict Young's moduli that are doubled than those expected with the Haplin-Tsai analytical equations. This mismatch is due to the mechanical behavior of the collagen that is severely affected by the loading-rate, 18,22,43 and it is here manifested upon impulsive loads in contrast to the quasi-static conditions used in literature. 15 Figure 5 depicts the trend of the relaxation time (τ), along the x-axis, as a function of the input velocity vi.…”

“…This is further confirmed when comparing the relaxation time at 100 m/s with the results described in earlier studies, with values being almost halved with respect to the single peptide. 22 The dissipation behavior is mainly due to the organic component of the material, which carries most of the deformation (especially in the overlap region) in contrast to the mineral component that stores most of the stress. 21,45 Specifically, collagen peptides upon tensile loads tend to uncoil, 46 and eventually slide on the HA minerals: 47 this phenomenon also observed at a larger scale 48 is one reason for the dissipation.…”

Molecular origin of viscoelasticity in mineralized collagen fibrils

“…For both the dry and wet systems, the numerical values for the G' at are about doubled than the ones achieved at To understand the behavior under the impact or creep loading, we utilize the characterization based on the response upon axial impulses (later referred as wave propagation -"WP")). This approach is a validated technique, exploited across different scales in earlier works, able to deliver a complete description of a material or structure with a simple broadband impulsive load 26,45,52 .…”

“…Understanding the mechanics of the material upon cyclic angular loads will complement the studies on bone failure and damage in which shear deformation are more prominent than homogeneous uniaxial loads, especially at a molecular scale. Previous works have speculated on the viscoelasticity of bone at the macroscale with experiments 20,42,43 , or with simulation tools focusing on a single collagen peptide 45,46 or the mechanics of dry mineralized fibrils upon quasi-static and impulsive loads 26 . Recently, Fielder et al have presented a first study investigating role of water on the mechanical behavior of the D-period varying the %HA.…”

Four-Dimensional (Bio-)printing: A Review on Stimuli-Responsive Mechanisms and Their Biomedical Suitability

“…For example, appropriate mechanical stimulation and biomechanical signals are key factors in tendon/ligament (T/L) engineering. As the native T/L is able to respond to mechanical forces by changing structure, composition, and mechanical properties [35][36][37], smart hydrogels obtained via 4D printing cold help to achieve such a critical goal. Typical mechanical values of hydrogels (e.g., ≈0.1 MPa Young's moduli) are usually far from satisfying T/L mechanics (i.e., 1.2-1.8 GPa tensile modulus) that can be achieved only by high modulus chemically crosslinked hydrogels [38,39].…”