ABSTRACT
Tropocollagen plays a very important role in the load bearing functionality of soft tissues. In the context of multi-scale modeling the response of tropocollagen molecules to stretch should be very carefully predicted in order to describe the mechanical behavior of soft tissues. To this end, the worm-like chain (WLC) model is often applied, although it is restricted to the entropic force regime which is essential at moderate deformations. To describe molecular forces under larger stretches several extensions of the WLC have been proposed for deoxyribonucleic acid (DNA). This contribution aims to investigate the applicability of these models in the context of tropocollagen and discusses the feasibility of their application. Finally, the models are validated in comparison to experimental data available in the literature.
Subject(s)
Tropocollagen/physiology , Entropy , Models, Biological , Stress, MechanicalABSTRACT
Changes in mineral texture (e.g. hydroxyapatite (HAP) or aragonite) and polypeptide (e.g. tropocollagen (TC)) residue sequence are characteristic features of a disease known as osteogenesis imperfecta (OI). In OI, different possibilities of changes in polypeptide residue sequence as well as changes in polypeptide helix replacement (e.g. 3 alpha1 chains instead of 2 alpha1 and 1 alpha2 chain in OI murine) exist. The cross section of the HAP crystals could be needle like or plate like. Such texture and residue sequence related changes can significantly affect the material strength at the nanoscale. In this work, a mechanistic understanding of such factors in determining strength of nanoscale TC-HAP biomaterials is presented using three dimensional molecular dynamics (MD) simulations. Analyses point out that the peak interfacial strength for failure is the highest for supercells with plate shaped HAP crystals. TC molecules with higher number of side chain functional groups impart higher strength to the TC-HAP biomaterials at the nanoscale. Overall, HAP crystal shape variation, the direction of applied loading with respect to the relative TC-HAP orientation, and the number of side chain functional groups in TC molecules are the factor that affect TC-HAP biomaterial strength in a significant manner.
Subject(s)
Amino Acid Substitution/physiology , Biocompatible Materials/chemistry , Durapatite/chemistry , Nanoparticles , Tensile Strength/physiology , Tropocollagen/chemistry , Amino Acid Sequence/genetics , Amino Acid Sequence/physiology , Amino Acid Substitution/genetics , Compressive Strength/physiology , Humans , Materials Testing , Minerals/chemistry , Models, Biological , Models, Molecular , Molecular Dynamics Simulation , Nanoparticles/chemistry , Osteogenesis Imperfecta/genetics , Tropocollagen/genetics , Tropocollagen/physiologyABSTRACT
The characteristics of PN junction in bone are investigated. Collagen (N type) and apatite (P type) complex are supposed to form this junction and their behaviour for reverse and forward bias is examined. It is suggested that mucopolysaccharides play an important role in controlling junction characteristics. There is found to be generation of photocurrent in response to infrared light; while ultra-violet light produces a permanent change in its behaviour. Magnetic field is found to enhance the optical response of the junction.
