Effect of the Structural Water on the Mechanical Properties of Collagen-like Microfibrils: A Molecular Dynamics Study

Abstract

The objective of this paper is to investigate the role played by the structural water on the intermolecular sliding between collagen-like 1QSU peptides in a microfibril under deformation. Three modes of deformation are used to generate intermolecular sliding: forced axial stretching (case I) or sliding (case II) of a central peptide monomer (while other surrounding monomers are fixed); and cantilever bending (case III) under a terminal lateral load. The force-displacement curve of each deformation mode is derived using a module called Steered Molecular Dynamics (SMD) in a molecular dynamics package NAMD under the CHARMM22 force field. Each calculation is carried out twice, one in the presence of structural water, one without. It is found that the structural water is a weak "lubricant" in forced axial stretching (case I), but it functions as a "glue" in forced axial sliding (case II) and cantilever bending (case III). A change in the pulling speed does not significantly alter the force-displacement behavior in axial stretching (case I) and sliding (case II), but it does in cantilever bending (case III). The additional resistance contributed by the structural water is attributed to the additional energy cost in breaking the water-mediated hydrogen bonds (water bridges).

Interfacial Forces and Interfaces in Hard Biomaterial Mechanics

“…Similar interaction behavior of water at protein-mineral interface is found in nacre as well [81,82]. It also acts as glue between TC-TC interactions [24], and thereby, delays the failure of the overall system. Another interesting finding emerged out of a comparison between stress-strain curves for two different hierarchical levels is that the failure of such biocomposites is predominantly strain dependent and not a function of ultimate strength.…”

“…Previously, such MD schemes have focused on understanding the mechanical behavior and properties of TC molecules in different structural configurations [68][69][70], the hierarchical organization of TC molecules into collagen fibrils and its effect on mechanical properties [21,71], the properties of hydrated TC molecules [24,72], and the TC molecule stability with respect to changes in residue sequences [73].…”

“…Recently, it has also been shown that changes in the residue sequences of TC molecules at the interface can affect the material mechanical strength considerably [14][15][16]21]. Furthermore, it has been shown earlier that moisture can play a major role in affecting the strength of such hybrid interfaces in biological materials [22][23][24][25].…”

The effects of hydration on the collagen and gelatine phases within parchment artefacts

“…Bound water (phase II), where water molecules form bridges between neighbouring polypeptide chains and act as receptors for CH-O hydrogen bonds [9]. Free water (phase III) where water is fixed by one hydrogen bond between polypeptide chains or fixed in the hole zones at the end of the polypeptide chain, and finally transition water or unperturbed bulk water (phase IV), where water molecules are bound between the fibrils [10,11]. The total amount of structural and bound water (phase I and II) contained in collagen is approximately 0.5 g/g [12][13][14].…”

Understanding straining induced changes in thermal properties of tropocollagen-hydroxyapatite interfacial configurations

“…This work investigates the effects of changes in HAP crystal shapes, interfacial periods, strain levels on the thermal properties of a set of idealised TC-HAP biomaterials using molecular dynamics (MD) simulations. The mechanical behaviour of biological materials with a view to understand the role of TC molecules and HAP mineral has been earlier analysed using experiments (Eppell et al, 2005;Gupta et al, 2006aGupta et al, , 2006bSasaki and Enyo, 1995;Odajima, 1996a, 1996b), modelling (Gao et al, 2003;Gao and Wang, 2005;Jager and Fratzl, 2000;Ji, 2008) and simulations (Buehler, 2006a(Buehler, , 2006bDubey and Tomar, 2009;Handgraaf and Zerbetto, 2006;Radmer and Klein, 2004;Zhang et al, 2007). Experimental techniques for investigating the thermal properties of the bone material as well as other biological materials have been reported over the years.…”