Scientists have turned to nature to develop a 3D vascular system that permits high-performance composite materials such as fiberglass to heal both autonomously and repeatedly. Damage to such fiber-reinforced composites, commonly used within engineered structures in aerospace, automotive, civil, naval and even sporting goods due to their effective strength-to-weight ratio, can be difficult to detect and repair using traditional approaches.
The team, from the University of Illinois at Urbana-Champaign, whose research was published in the journal Advanced Materials [Patrick et al. Adv. Mater. (2014) DOI: 10.1002/adma.201400248], were looking to solve the problem in composites of small cracks that become irreversible damaged by delamination, limiting the wider deployment of such materials in industry. They demonstrated the first repeated healing in a fiber-reinforced composite system using vasculature patterns of micro-channels that integrate dual networks that are isolated from each other – an epoxy resin and hardener acting as liquid healing agents sequestered in two different microchannel networks.
As fiber-composite laminates are produced by the weaving and stacking of multiple layers, it is comparatively easy for the structure to separate between the layers. In this new 3D vascular system, when a fracture breaks apart the separate networks, the healing agents are automatically released into the crack plane. On coming into contact with one another in situ, or within the material, they polymerize to form a structural glue at the damage site and were shown to heal the material over multiple cycles. It is important the vascular networks do not run in straight lines to allow the healing agents to mix properly once released. Therefore the vessels were overlapped, significantly improving their resilience and life span.
The team introduced the same process used for making laminates to stitch in a line made from a bio-friendly polymer (termed “sacrificial fiber”) within the composite. Once this was achieved, the system was heated to melt and evaporate the sacrificial fibers so that hollow microchannels remained, which became the vasculature for the self-healing system. The method therefore integrates seamlessly with standard manufacturing processes for polymer composites and is also highly scalable.
The approach could be used in structures prone to cyclic damage and are critically important for the safety and performance of engineered systems. The team is now continuing to explore biomimetic vasculatures through more advanced fabrication techniques, which could lead to even more complex vascular architectures, including multi-scale and branched networks.