Smart Skins

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001 | Biomimic Research

     +   Self-healing material with microvascular networks  

What is  a self-healing polymer?

Self-healing polymer in this case is a material that is composed of microencapsulated healing agents that can regenerate with external mechanical performance; i.e. heat. According to the article, the self-healing mechanism is triggered when the capsules are ruptured, giving the substrate the required energy to heal within that localized region. The material investigated is bio-inspired designed where a microvascular network regulate the composite in the substrate to heal. If the epoxy (outer layer) is damaged then the healing agents react and repair the skin.

• How is this possible?
• the pervasive vascular system is constructed in a way that mimics a biological structure. 
• there are biochemicals embedded in the system that react to the external forces.
• this particular system mimics the human skin structure
• the human skin has two layers, the epidermal and dermal
• the epidermal contains a network of sub-layers  that continuously work to rebuild the system.
• the dermal layer supplies the epidermal with nutrients, blood, and regulates the body temperature.
• when the skin is damaged, the skin triggers the capillary network to work quickly to clot the wound. 
• once accomplished, the cells then react and mend the epidermal layer.
• this same approached in the mechanical method.

• The mechanical approach
• the outer layer (epidermal) is an epoxy coating substrate.
• this substrate contains a more 3-dimensional microvascular network.
• there are catalyst particles in the coating and network that work with the healing agent filled in the system

• The process
• if and when the skin is placed under max. street levels, cracks form
• when the skin is cracked, the substrate is filled with fluid-filled microchannels
• This fluid then react with the healing agent and the catalyst particles.
• This initiates polymerization
• re-bonding occurs
• cracks are filled and the surface strength is restored.

The Healing Agent

• it is dicyclopentadiene monomer catalyst (DCPD). 
• with benzylidenebis (tricyclohexyphosphine) dichlororuthenium
• it has a high healing performance
• a low viscosity
• this allows a nice flow to the crack plane with enough push to cover the exposed area.
• the agent remains active during the healing process
• it also dissolves quickly on contact with the monomer.
• it then polymerizes the DCPD.
• the result is a tough cross-linked polymer

 

figure 1:   diagram of capillary network in the dermis layer of human skin.

figure 3:   diagram of the self-healing the microvascular skin structure. The healing agent then seeps into the crack slowly to bond with the epoxy to heal the surface.

figure 3:   image of the microvascular skin structure bent at its maximum stress level. The epoxy coating with embedded catalyst.

figure 4:   image of the skin structure after cracks are sealed and healed