The smart behaviour of bone:
By Kevin Bell, University College London
This website is intended to give a brief overview of my work on trying to model the smart behaviour of bone. Further information can be obtained on request by E-mailing me at:
To the uninitiated, suggesting that bone exhibits smart behaviour, or indeed any behaviour at all, would seem an odd thing to do. One often sees bone portrayed in television programmes about forensic science or human archaeology, as remaining unchanging for hundreds of years. How could such a solid substance exhibit any kind of behaviour? What one must remember is that the bones seen in such programmes are long dead, just as the person they were part of.
Living bone is a very different proposition. It, like any other living system, has mechanisms for repair and growth, to feed its constituent parts and ensure that any materials needed for structural work are supplied to the correct area as and when they are required.
My work was based on a very simple model, assuming that the rate of growth of bone was in some way dependent on the strains it encountered. However, I did not consider bones to just be the large macroscopic items that comprise skeletons, but instead looked at the internal macrostructure of struts and rigid joints which form the bulk of our bones.
Fig.1: The complex internal macrostructure of bone
The model was set up on a computer. Geometrical information pertaining to the lengths, start and end points and the cross-sectional areas of the struts was fed in to a program that calculated the strains for a given load. Then the strain information was passed to a second program that evaluated the amount by which each struts area should change (be that positive or negative) based on the strain and an experimentally determined relation between strain and growth. The new geometry would then be passed back to the original program and the cycle repeated.
It was demonstrated that even using such a simple model, very complex behaviours could arise owing to the effects that the area change of one strut had on its neighbours.
This work has many important applications in the field of biophysics but there is much still to be done. The ultimate goal is to try and come up with a way of calculating how at risk an individual is from bone fracture due to a number of metabolic bone diseases. If you are interested in continuing this work then please E-mail Dr.J.Harding or Dr.A.Harker