Molecular-dynamics simulations of water in articular cartilage

Overview

Topic status: We're looking for students to study this topic.

Articular cartilage is an example of an anisotropic tissue: the collagen fibres forming its scaffold have a preferred alignment. The direction of this alignment varies with the depth from the cartilage surface, and the cross-linked collagen fibres usually form an arch-like superstructure. Characterisation of this superstructure is important for understanding of the mechanisms by which cartilage carries mechanical load and reduces stress on the bones. The organisation of collagen fibres can be studied by magnetic resonance, most notably using diffusion-tensor imaging (DTI) and spin-relaxation imaging. The following MRI parameters are typically used to visualise and quantify MR images of articular cartilage:

  • principal eigenvalue of the diffusion tensor
  • principal eigenvector of the diffusion tensor
  • fractional anisotropy of the diffusion tensor
  • longitudinal relaxation rate
  • transverse relaxation rate

Each of these parameters reflects certain aspects of the molecular hydrodynamics of water in AC and therefore reports on the organisation of the biopolymeric scaffold of the tissue. The diagnostic utility of these parameters is significantly increased when they are translated into biophysically meaningful information, such as the volume fraction of collagen or proteoglycans in the tissue, or the predominant alignment and the degree of disorder of the collagen network. The aim of this project is to develop 'calibration curves' for the translation of measured MRI parameters into quantitative biophysical information characterising the biopolymeric scaffold of AC. To do this, two techniques will be used:

  1. Monte Carlo simulations of the dynamics of water in cartilage - The objective is to calculate the dependence of the diffusion tensor on the composition of the tissue and the degree of alignment of collagen fibres. These calibration plots can then be used in reverse to infer the physical characteristics of cartilage from the results of MRI measurements;
  2. Stochastic and Molecular Dynamics simulations - These simulations are based on the interatomic interaction potentials and will be used to study the hydration state of cartilage biopolymers. This, in turn, will be used to interpret the results of spin-relaxation measurements and adapt these measurements for probing collagen fibre alignment.

This project will involve the use of QUT supercomputing facilities. You will acquire skills in computational physics and chemistry, modelling of molecular phenomena, computer programming, and biophysics.

References

  • SK de Visser, RW Crawford, JM Pope. Osteoarthr. Cartilage16, 83-89 (2008)
  • KI Momot, JM Pope, RM Wellard. NMR in Biomed. 23, 313-324 (2010)
  • KI Momot, Eur. Biophys. J., in press (2010)
Study level
Honours
Supervisors
QUT
Organisational unit

Science and Engineering Faculty

Research area

Physics

Contact
Please contact the supervisor.