Polymer chemists tap the body's organs

The strained tendons and ligaments that end many sporting careers could be repaired with polymers made from our own digestive chemicals. Julien Gautrot and Julian Zhu at the University of Montreal in Canada have devised a chemical method to make degradable elastomers - polymers with elastic properties - using bile acid.

Gautrot relied on an entropy-driven ring opening metathesis polymerisation (ED-ROMP) technique to synthesise polyester chains from ring-shaped molecules made from bile acids that contain a steroid backbone in their structure. 

The ED-ROMP reaction breaks open carbon-carbon double bonds in the cyclic molecules, before forming new bonds between those carbon atoms and their neighbouring molecules, knitting them into a long polymer chain. The reaction uses a ruthenium-based Grubbs catalyst, the development of which won Robert Grubbs a share of the 2005 Nobel prize in chemistry.

’Ring opening metathesis usually involves small cyclic oligomers because these small cyclic rings have a lot of strain between atoms which can be used to break the ring,’ Gautrot told Chemistry World. ’There is very little work done in large macrocycles because they are considered to be less reactive.’ Since the reaction is driven by the change in entropy, or disorder, within the system, it avoids the use of potentially toxic coupling agents, explained Gautrot.

The elastic polymers created by Gautrot’s team have unique functional properties. ’The large molecular weights of these polymers means that, although they are elastic, they are sufficiently firm to hold their form,’ he said. ’Their mechanical properties give them the potential for use in building polymer scaffolds to support the regeneration of elastic body tissue like cartilage.’ 

Because of its elasticity and slow regeneration, damage to cartilage, common in sporting injuries, is particularly difficult to repair. 

’The fact that we can source this material from the body also means that as it degrades it only releases non-toxic substances that are already present in the body,’ added Gautrot. ’Twenty to thirty grams of bile acids are released everyday into the intestine, so it’s an abundant and sustainable source.’

It should also be possible to source larger quantities of bile acid from by-products of the meat industry, he added.

Anthony Davis, a chemist from the University of Bristol, UK, uses a bile acid called cholic acid as a source to make a variety of medically useful products. ’One major virtue of these substances is that they are thermoplastic, which means that they can be easily formed into a desired shape by heating them,’ said Davies. ’They are ideal for tissue scaffolds because, unlike most thermoplastics, they are elastic and they can be used internally because they will degrade naturally.’ 

Victoria Gill

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