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Physics and Astronomy

Photo of Dr James  Bell

Dr James Bell

Visiting Scientist


The Composition and Mechanical Properties of Articular Cartilage

My main research interest is the mechanical properties of connective tissue, with focus currently on articular cartilage (AC). AC is a soft tissue located at the ends of articulating bones in synovial joints. Its role is to act as both a shock absorber and a smooth, lubricated surface that minimises friction during articulation. To perform this job, cartilage employs a combination of mechanical, chemical and electrical principles to control the rate of deformation and fluid exudation under load. Under the effect of disease, the composition and mechanical properties change, leading to accelerated wear and degradation of the joint.

My work has included creating and analysing finite element models of cartilage under load, specifically investigating the effect of anisotropy and inhomogeneity with depth. I have also performed mechanical testing in parallel with the models to determine the variation of mechanical properties both with depth and location on the joint. I have also used the multiphoton microscopy suite to image cartilage using two-photon fluorescence (TPF) and second harmonic generation (SHG). These imaging modalities provide a means of viewing chondrocytes, elastin fibres, pericellular matrices and collagen without the use of exogenous fluorophores. I have also modified a loading rig to be mounted on the microscope stage, allowing the imaging of loaded cartilage in real time.

I collaborate on this project with Prof C. Peter Winlove, Prof Chris Smith and Dr Jessica Mansfield.

Acoustic Metamaterials

I am also involved in acoustic metamaterial research, which involves the design and analysis of materials with acoustic properties derived from their structure as opposed to their composition. I am currently working on the "acoustic double fishnet" structure, which comprises a pair of periodically perforated plates, separated by a thin gap. This structure exhibits a tunable broad stop band despite having holes running from front to back.

I use an apparatus consisting of moveable spherical mirrors with high frequency speakers to determine the transmittance of structures experimentally. Theoretical studies are based on in-house analytical codes, as well as Comsol Multiphysics.

I collaborate on this project with Dr Ian Summers, Dr Alastair Hibbins, Prof J. Roy Sambles FRS, Dr Euan Hendry and Alasdair Murray.

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