Harvard Engineers Turn Ordinary Knitting Into Shape-Shifting Smart Fabric

Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have shown that ordinary machine-knitting techniques can produce fabrics that change shape, sense movement and act as switches. The study, led by postdoctoral researcher Kausalya Mahadevan in the lab of professor Katia Bertoldi, was published in the journal Advanced Functional Materials.

The team used weft knitting, the same method used to make hats and gloves, together with elastic yarn and a technique called plating, which places different yarns on opposite faces of the fabric. This produced thick fabrics that naturally curl into three-dimensional shapes, the same effect that makes the bottom edge of a cut T-shirt curl upward. By arranging the knit in systematic horizontal and vertical stripe patterns, the researchers made textiles that snap between stable shapes and stay there, a property called multistability, similar to a light switch that stays either on or off.

Adding thin conductive yarns turned the multistable fabric into a soft, stretchable electrical switch that changes state when the textile snaps from one shape to another. The researchers demonstrated a knitted shell that switches a light-emitting diode (LED) on and off as it moves between its stable shapes, a wearable switch worn over a knee or elbow whose snapping motion an Arduino microcontroller could detect and use to count steps, and a lampshade with three separate multistable switches that each controlled a different color of light as sections of the fabric were stretched.

Because the knitting machines used in the study resemble industrial equipment already common in garment factories, the researchers say the technique could be scaled up relatively quickly. The work also connects textiles to the field of nonlinear mechanical metamaterials, engineered structures built to bend, buckle and snap in controlled, useful ways.

The research was funded by the U.S. National Science Foundation, the Army Research Office's Multidisciplinary University Research Initiative (MURI) program and an Office of Naval Research equipment grant.