Glue comes in all shapes and sizes, with just as many applications. The downside of many types of glue is that they do their job a bit too well, making them non-recyclable and bad for the environment. But you don’t want to compromise on the quality of your glue: it should really stick. Subhajit Pal, Phillip Messersmith and colleagues at the University of California, Berkeley, have developed a simple but versatile polymer based on a molecule that occurs naturally in the body: (R)-α-lipoic acid (αLA).

αLA is a small molecule with a disulfide ring and a caboxylic acid group that acts as a cofactor for enzymes in aerobic metabolism and participates in ring-opening polymerisation. It sounds great, but αLA polymers also suffer from spontaneous depolymerisation. ‘Messersmith and his group show that you can get around this by cleverly adding stabilisers and co-monomers that counteract depolymerisation’, explains Patricia Dankers, professor of biomedical materials at the TU Eindhoven, by email.

The co-monomers are almost the same as αLA, but instead of a carboxylic acid they have an N-hydroxysuccinimide ester, which stabilises the reactive parts of the molecule by forming networks. ‘Depending on which co-monomer you use, you get different types of adhesive materials’, Dankers continues. The authors show liquids, solid patches and even powders based on αLA.

‘They also show that they can depolymerise the formed polymer network on demand, regenerating the alpha-lipoic acid’, Dankers writes. ‘This way, you can use it in a sustainable way.’ Another nice feature is that the material is self-healing due to the disulfide bridges, the authors show.

In practice

The Americans have also put their superglue into practice. For example, they show that they can reseal a perforated pig stomach (ex vivo) with an αLA patch and spray. In vitro tests also seem to indicate that the glue may have anti-inflammatory properties and keep E. coli out - a pretty important property if you have medical applications in mind.

But the glue is also proving itself in living creatures. If you want to treat babies in the womb, you have to go through the amniotic membrane, which is fragile and does not repair itself, increasing the risk of amniotic rupture. So they investigated whether a preventive patch could help reduce the risk.

In pregnant mice, the researchers applied a patch to some membranes and, as there was no negative reaction to the patch, they punctured a 2 mm hole in the membrane after a few days. The amniotic sac with the patch lost up to 50% less amniotic fluid, and all the baby mice with the patch survived the procedure, while none of the baby mice without the patch survived. That sounds promising, and based on the closed-loop recycling and other applications the authors have shown, Dankers concludes: ‘It’s a wonderful combination of clever, relatively simple chemistry under physiological conditions. A truly wonderful piece of work.’

Pal, S. et al. (2024) Science 385(6711), DOI: 10.1126/science.ado6292