Photosynthesis for self-healing polymers

Materials World magazine
27 Nov 2018

A self-repairing polymer that continuously expands and strengthens has been developed at MIT. Khai Trung Le reports. 

A material that can extract carbon from the atmosphere to replenish itself sounds both incredible and mundane. After all, this is simply the common process of photosynthesis. However, a polymer that can grow, strengthen and self-repair simply using carbon fixation has been developed by a team led by the Massachusetts Institute of Technology (MIT), USA.

The polymer, a synthetic gel matrix comprising aminopropyl methacrylamide (APMA), glucose oxidase (GOx), and chloroplasts, is said to become stronger as it incorporates the carbon. The paper, Polymethacrylamide and carbon composites that grow, strengthen, and self-repair using ambient carbon dioxide fixation, published in Advanced Materials, notes that the glucose is produced from the embedded chloroplasts and converted to gluconolactone via the GOx, and polymerised with APMA to form a polymethacrylamide that can expand and strengthen.

The paper continues, ‘The system achieves an average growth rate of µm3 h−1 per chloroplast under ambient CO2 and illumination over 18 h, thickening with a shear modulus of 3kPa’.

Michael Strano, Professor of Chemical Engineering at MIT, said, ‘This is a completely new concept in materials science. What we call carbon-fixing materials don’t exist yet today. Imagine a synthetic material that could grow like trees, taking the carbon from the CO2 and incorporating it into the material’s backbone.’ The polymer is able to self-repair on exposure to sunlight or ‘some indoor lightning,’ he said.

Self-repairing materials have previously been developed, but they have all required outside input to function, including heating, UV lighting, mechanical stress, or chemical treatment. While the proof of concept does use a biological component – nanoceria-stabilised chloroplasts taken from spinach leaves and used as a catalyst for the conversion – given the instability of isolated chloroplasts, which stop functioning when removed from the plant within a few hours, the team state the catalyst would be replaced with a non-biological component.

The polymer can be manufactured in bulk quantities, and although the material is currently too weak to be used as a building material, the team believes the polymer could soon have applications in construction, as a crack filler or coating material.

Additionally, the material could ease transporting building materials, as it begins in soft or liquid form in transit and hardens on its own time on site.

Strano said, ‘Our work shows CO2 need not be purely a burden and a cost. It is also an opportunity in this respect. There’s carbon everywhere. We build the world with it. Humans are made of carbon. Making a material that can access the abundant carbon all around us is a significant opportunity for materials science. In this way, our work is about making materials that are not just carbon neutral,
but carbon negative.’

The team is currently optimising the material properties, and further predict it could be used in self-healing coatings and fabrics. The US Department of Energy will continue to sponsor Strano’s work.

Other self-healing materials work include efforts from Clemson University, USA, where a technique to produce self-healing polymers without the need to invest in a purpose-built factory, and the University of Tokyo, which has recently explored the self-healing properties of glass-like polyether-thioureas (see Materials World, February 2018, pg 12).

You can read the paper, Polymethacrylamide and carbon composites that grow, strengthen, and self-repair using ambient carbon dioxide fixation, at