September 21, 2021


Born to play

High-energy shape memory polymer could someday help robots flex their muscles

When stretched or deformed, shape memory polymers return to their unique designs right after heat or light is used. These products show fantastic guarantee for soft robotics, clever biomedical units and deployable house buildings, but right until now they have not been equipped to keep ample energy.

Now, scientists reporting in ACS Central Science have created a shape memory polymer that suppliers just about six moments extra energy than prior variations.

An synthetic muscle built of a stretched shape memory polymer contracts upon heating, bending a mannequin’s arm. Image credit history: Tailored from ACS Central Science 2021, DOI: 10.1021/acscentsci.1c00829

Form memory polymers alternate involving an unique, undeformed point out and a secondary, deformed point out. The deformed point out is made by stretching the polymer and is held in put by molecular alterations, these as dynamic bonding networks or pressure-induced crystallization, that are reversed with heat or light. The polymer then returns to its unique point out via the release of stored entropic energy. But it is been difficult for scientists to make these polymers complete energy-intense tasks. Zhenan Bao and colleagues required to build a new variety of shape memory polymer that stretches into a secure, hugely elongated point out, letting it to release big amounts of energy when returning to its unique point out.

The scientists included four-,4’-methylene bisphenylurea models into a poly(propylene glycol) polymer backbone. In the polymer’s unique point out, polymer chains were being tangled and disordered. Stretching brought on the chains to align and type hydrogen bonds involving urea groups, building supermolecular buildings that stabilized the hugely elongated point out. Heating brought on the bonds to split and the polymer to deal to its preliminary, disordered point out.

In assessments, the polymer could be stretched up to 5 moments its unique duration and keep up to 17.nine J/g energy –– just about six moments extra energy than prior shape memory polymers. The group demonstrated that the stretched material could use this energy to raise objects five,000 moments its individual weight upon heating. They also built an synthetic muscle by attaching the pre-stretched polymer to the higher and lower arm of a picket mannequin. When heated, the material contracted, causing the mannequin to bend its arm at the elbow. In addition to its record-large energy density, the shape memory polymer is also low-cost (uncooked products expense about $11 per lb) and easy to make, the scientists say.