Self-healing image 2

Opinion Piece by Dr Merryn Haines-Gadd, University of Exeter

23 April 2021

Self-healing materials – fact or science fiction?

A field of interest for over 20 years, self-healing materials are those with the ability to repair themselves when damaged. They can be classified into two types: extrinsic self-healing – whereby healing agents inside micro-capsules or vascular networks flood to the damaged area repairing it, and intrinsic self-healing – whereby healing is an inherent functionality of the material, typically triggered by heat, light or pressure.
Developed as both coatings and bulk materials, healing has been explored within concrete, asphalt, glass, ceramics, polymers and composites. While they often drum up a great deal of excitement and intrigue when discussed, they are still a technology that has yet to fully transition from lab based innovation, into mass commercial application.
With global complex challenges such as climate change and sustainable development, focus is being placed on topics such as ‘resilience’ and ‘longevity’, opening up many opportunities for material innovation within these spaces. Moreover, considering that lifetime extension is key principle for maximising the value of products and materials within Circular Economy systems, perhaps now is the time for this shift to finally occur.
However, as Carolyn Roberts and Julie Hill offer in 2015 within Environmental Scientist: New Materials and the Circular Economy, the development of novel materials ‘is part of a radical shift in society’s use of chemistry, the implications of which are only starting to be investigated by environmental scientists.’ So, while new materials might offer exciting and enhanced functionality such as improved durability, integrity and reparability, it is vital that their circular economy and sustainability implications be anticipated as well.
This topic was central to research carried out at the Exeter Centre for Circular Economy (ECCE) as part of the EPSRC consortium ‘Manufacturing Immortality’. A research collaboration between seven UK universities: University of Bristol, University of Exeter, Heriot-Watt, Lancaster University, The University of Manchester, Northumbria University and Sheffield Hallam University, as a group we sought to not only developed new compositions of synthetic and bio-hybrid self-healing materials, but also investigate the manufacturing and sustainability effects of putting these into products as well.
At Exeter, through theoretical exploration and practice-based industrial collaboration, we examined the key benefits, opportunities and environmental challenges that these materials offer. Below is a summary of thoughts and findings from us.

Benefits they could offer:

  • Keep products in service for longer through functional durability and increased aesthetic resilience, improving the reliability and reducing the environmental of footprint of the product over its lifetime
  • Reduce the risk and cost associated with repair, especially for products in extreme and remote environments
  • Mitigate issues related to damage during installation, which could ultimately lower waste rates reducing time and resources needed for replacement
  • Improve ease of disassembly and reassembly – imagine a product with an entirely sealed casing that can be cut and re-bonded. This would ultimately reduce the number of parts and components needed to make the product.

Challenges to consider:

  • Warranties and liability – standards have yet to be defined for assessing the health and safety issues of keeping a self-healed product in service
  • Hybridization of materials – in a functional circular system materials need to be separated into biological and technical cycles, thus this must be considered when combining synthetic and bio-based components into materials
  • Environmental trade-offs – environmental assessments must be carried out to ensure that that the lifetime extension outweighs the impact of the addition of a coating to a structure or a product

Application areas to consider:
Built environment – Although self-healing concrete is one of the first innovation areas to be discussed, self-healing polymers and glass offer many possibilities for self-healing facias, windows, solar panels, flooring, sealants, lining, pipes, outdoor furniture and railings.
Products in Extreme environments – structures and products within harsh or extreme environments such as those within deep space, sub-sea or nuclear or energy generation scenarios.
Consumer products and furniture – wear and tear is one of the key drivers for why products are prematurely replaced, self-healing coatings and paints could improve the aesthetic resilience of these items.
Medical industry – some bio-hybrid materials are able to self-heal like the skin, so could be used for soft tissues adhesives, plasters, prosthetics and synthetic skin.
Transport industry – self-healing hydrogen fuel cells were developed at the Lancaster University that aim to improve the lifespan of this clean form of energy generation. Also self-healing gas tanks and tires are currently commercially available.

Overall, self-healing is an amazing technological development and presents many opportunities for innovation across multiple sectors. It does however, require a little bit more industrial collaboration and use cases examples to advance these materials further, and perhaps the construction industry is just the sector that could make this happen.

If you would like to discuss these topics in more detail please feel free to contact me on LinkedIn.

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