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Actuators are materials that change their shape in response to an external stimulus. The change is usually an increase or decrease in the material's dimensions, and the stimulus is typically temperature, humidity, light, or pH.

Most actuators today are made from synthetic polymers or semiconductors, and they have good stability and reversibility properties but their life cycle typically equates to energy-intensive and/or toxic processes.

Our focus is on the use of biopolymers to fabricate actuators in a way that restreams lignocellulosic biomass as a feedstock for the bioeconomy.

With that vision, we are channeling our research into cellulose nanofibres, which we obtain by mechanical delamination of the cellulosic fibre, producing objects that present microns in length and just nanometers in cross-section.

Cellulose nanofibres have hugely attractive mechanical, optical and barrier properties, and are widely used in composites, packagings, and coatings.

Our study breaks new ground as we manage to fabricate films made of asymmetrically-arranged cellulose nanofibres that have been oxidized in order to introduce charged groups (COOH/COO^-). The films are fashioned to present a concentration gradient of responsive groups along thickness.

This is achieved by the successive deposition of functionalized and non-functionalized nanofibrillated cellulose layers, thus affording graded films where the concentration of COOH groups increases throughout the thickness.

This purposed asymmetric structural response is expected to find applications in robotics (clamps and levers for manipulation, artificial muscles and tissues, etc.).