A polymer that remembers its original shape after being scrunched up gives support to nanoparticles

Scientists in China have developed a polymer scaffold for functional nanoparticles that can be folded and mangled but will reform into its original shape if it is placed in water.

Materials often exhibit very different properties when shrunk down to the nanoscale. Exciting new devices can be designed when nanoscale characteristics are brought together in synergy with macroscale materials, but bespoke production processes are often needed for each new nano-composite material.

Shu-Hong Yu and colleagues at the University of Science and Technology of China have developed a simple shape memory polymer scaffold from chitosan that can be used as a host for a wide range of different functional nanoparticles, combining benefits from the macro- and nanoscale.

Chitosan solution is placed in a mould and shaped by ice crystal fingers that grow and push the chitosan polymer chains into place, forming an insoluble and robust sponge-like scaffold. If the scaffold is put into a solution of nanoparticles it becomes coated as it swells and the nanoparticles bind to the scaffold via electrostatic interactions

A shape-memory scaffold for macroscale assembly of functional nanoscale building blocks

Source: © The Royal Society of Chemistry 2014

(a) SEM images of CSS: the cross-section (left) perpendicular to the ice front and the longitudinal section (right) parallel to the ice front. The results show that CSS displays a highly ordered microstructure with aligned and interconnecting pore channels. (b) Photograph of CSS composed of “USTC” abbreviated for the University of Science and Technology of China. (c) Dried CSS can be compressed and folded randomly, and recover to its original shape quickly as soon as it was immersed in water. (d) CSSs immersed in water can be repeatedly compressed and rebound to their original shapes rapidly by absorbing water again.

A wide diversity of nanoparticles can be attached to the scaffold to make 3D shape memory materials with properties ranging from magnetism to antibacterial activity. Multifunctional materials can be created by adding two types of nanoparticles simultaneously. And no matter how many times the scaffolds are compressed and folded, if you place them in water, they will revert to their original shape.

Shu-Hong Yu says that the universal, straightforward, low cost and scalable nature of this approach shows its versatility in its ability to retain the function of a diverse range of nanoparticles in the 3D material which will have uses in a wide range of devices.

Ashutosh Tiwari an expert in biomedical devices and scaffolds at Linköping University in Sweden comments that the work ‘emphasises the emerging area of shape memory scaffolds and custom-fitted and adaptive medical devices.’ Jinsong Leng, an expert in smart materials from Harbin Institute of Technology in China, echoes these thoughts and says ‘shape memory materials that make assembly technology universal and intelligent will play an important role in both smart materials and self-assembly structures’.

Yu’s team are now working towards incorporating nanomaterials, such as graphene sheets and nanowires, into their scaffolds to fabricate more sophisticated nanocomposites.