SHAPE FORMING
changes in pressure and temperature – then this mechanism may not be the best long-term option.
MICROVASCULAR HEALING SYSTEMS To overcome the single-use limitations of the embedded capsules approach, materials scientists took a leaf out of Mother Nature’s book. As Dr Kathleen Toohey noted in a seminal 2007 study in the field of self-healing materials, “Healing in biological systems is accomplished by a pervasive vascular network that supplies the necessary biochemical components.” Toohey led a study that incorporated a similar vascular network into the substrate of an epoxy resin. Such a material contains a network of microtubes that allow the healing agent to flow to the location of damage by leveraging capillarity, or the ability of liquids in capillary tubes to flow independently of external forces. When a crack occurs, the change in surface tension in the vascular network causes the healing agent to pump to the point of damage, at which point it reacts to embedded catalyst particles and then hardens and seals the crack. With this design, microvascular healing materials can overcome the issue of repeated localised damage that limits the application of microencapsulated healing. It also boasts great potential for several
materials that are commonly used in transport, manufacturing and design. For example, carbon-fibre reinforced plastic (CFRP) is a composite material that is regularly used in transport due to its comparatively high stiffness and strength at low density and weight. For this reason, it’s increasingly used in everything from chassis and roof frames in cars to train frames and the fuselage of Boeing’s 787 Dreamliner aircraft. CFRPs have been developed with
self-healing properties by leveraging capillary networks to transport healing agents, with the healed material often not showing a significant reduction in bend strength. This is noted by G Williams in the 2007 paper, a self-healing carbon fibre reinforced polymer for aerospace applications.
INTRINSIC HEALING Both encapsulation mechanisms and microvascular structures offer promise for the field of self-healing materials. However, each of these techniques involves the development of extrinsic healing polymers, which require the use of a separate healing agent. For some materials scientists and
researchers, the goal is to develop intrinsic self-healing polymers that regenerate using dynamic chemical
bonds within the material itself. Whereas the lifespan of extrinsic healing polymers is limited by the quantity of dormant healing agent present in the material, intrinsic healing materials could theoretically offer a near-endless capacity for reparation. Achieving intrinsic healing is no
easy feat, especially for materials that would offer practical benefit to the transport industry. The typical challenges, as identified by Yu Yanagisawa in a 2018 research paper, are that “These healable materials are usually soft and deformable. Some healable materials with high mechanical robustness have also been developed by cross-linking with dynamic covalent bonds. However, in most cases, heating to high temperatures (of 120°C or more) to reorganise their cross-linked networks is necessary for the fractured portions to repair.” Research is still ongoing in this
area, particularly in developing robust materials that heal autonomically. Progress has been made, and one study achieved low elastic modulus polymers that can heal in response to temperatures of 70°C. There have also been a handful of
other materials that exhibit intrinsic self-healing properties. A notable example is self-healing ceramics, where the ceramic can repair
This is the result of the MIT/ Lamborghini collaboration
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