Broken bones

I managed to squeeze in the back of one of a packed seminar session a couple of weeks ago – but the hour’s stand was worth it. I love clever science, clearly explained, especially when it seems to apply to real world problems.

The speaker was Prof Kevin Shakesheff (which incidentally kayaked down the Thames last year!). Based at Nottingham University, he presented his work on the local delivery of drug and therapeutic cells to areas of the body where tissue (for example bone) needs to be regrown – the technical term is ‘regenerative medicine’.

Pharmaceutical science is now developing regenerative therapies that help the body to grow back its own bits! These usually involve using proteins or cells that are found in the body to ‘trick’ it into regenerating damaged tissue: almost like either seeding or fertilising a garden lawn. The problem comes in that these proteins or cells are highly potent and they spread to areas of other the body causing nasty side effects (for example growth in the wrong place). The key is to make sure the proteins or cells are in the right place, at the right time at the right ‘dose’ – not easy to hit all three targets.

The overall effect comes from carefully controlling and, with chemistry, manipulating the melting point of the plastics used to make the plug.

The paste is made from two different kinds of plastic: PEG (polyethylene glycol which acts as a plasticiser) and PLGA (poly lactic co-glycolic acid). These are combined in small beads so that they are solid at room temperature but start melting at 37˚C. The results is that they can be injected into a wound as a kind of glue, but gradually melt merging, or annealing, the particles together. (A bit like the effect on a bag of ice cubes when someone leave the freezer door open too long!) But cleverly, the PEG then starts to dissolve in the body fluids, which – because its the plasticiser – drives the melting point of the plastic upwards and so it sets rigid in the shape it ‘melted into’. (Just like the refrozen ice cubes). The plug sets harder than the surrounding bone. Figure 3 in this paper has some nice examples of bone healing in a mouse femur. A similar idea, again with PLGA, can be used to repair brain tissue.


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