Nature is providing the inspiration for a range of novel self-repairing materials – by mimicking bone healing to fix ceramics, for instance, or using bacteria to heal a ‘wound’ in an undersea power cable.
Self-healing polymers are already well known. A familiar example is self-healing composite aircraft wings: if a crack appears, microcapsules in the composite matrix rupture, releasing ‘sealant’ into the crack to repair it. Recently, however, researchers have expanded the range of ‘repairable’ substances to include other promising materials – including rubber, ceramics and even electronic circuits.
Paul Race, senior lecturer in biochemistry at Bristol University, UK, heads a multi-disciplinary project to develop new types of self-healing materials. The three-year project, called Manufacturing Immortality, is in partnership with six other UK universities and involves biologists, chemists and engineers. ‘Our aim is to create new materials that can regenerate – or are very difficult to break – by combining biological and non-biological components – such as bacteria with ceramics, glass or electronics,’ says Race, whose own research interests include the stereochemistry of antibiotics, and the activities of enzymes.
The project’s approach is quite different to most polymer-based self-healing technologies, which typically rely on simple hydrogen bonds and reversible covalent bonds. ‘There are limits to the polymer chemistry approach,’ he says. ‘We’re trying to take inspiration from biology, which uses much more elaborate and powerful approaches to achieve more dramatic repair.’
Self-healing rubber links permanent covalent bonds (in red) with reversible hydrogen bonds (green). Image: Peter and Ryan Allen/ Harvard press
As an example, Race refers to what happens when we break or bone or receive a bad cut, which triggers a cascade of events in which the body detects the damage and responds appropriately. The team’s work is aimed at three broad application areas: safety critical systems; energy generation; and consumer electronics.