Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed machine-knitted textiles that can snap between several stable three-dimensional shapes. The fabrics combine textile design with mechanical engineering and could support applications in wearable sensors, soft switches and reconfigurable products.

The study, led by Kausalya Mahadevan in the laboratory of Professor Katia Bertoldi, appeared in Advanced Functional Materials. It explores multistability: the ability of a structure to maintain more than one shape without requiring continuous external force.

Creating Curvature Through Knitting

Manufacturers usually produce curved structures by moulding polymers and programming residual stress into the material. Instead, the Harvard team used industrial weft knitting, a common technique for making garments such as hats and gloves. This approach creates complex curvatures using yarn alone.

The researchers selected highly elastic yarns and applied a knitting method called plating, which places different yarns on each side of a fabric. This combination produced dense, thick textiles that naturally curl into three-dimensional forms. The effect uses the same basic mechanism that causes the cut edge of a T-shirt to roll up.

By adjusting yarn selection and knitting-machine settings, the team could influence how quickly and forcefully the material snapped between configurations. They then combined horizontal and vertical stripes to create fabrics with two or more stable shapes.

Mapping Material And Geometric Behaviour

The researchers systematically studied how material selection and knitted geometry affected the snap-through response. This allowed them to identify the conditions under which a textile becomes multistable.

They also developed simulations that represent the knitted structure as a continuous material. Consequently, the models can predict its overall behaviour without tracking every individual yarn. This may simplify the design of future textile-based mechanical systems.

Conductive Yarns Add Functionality

To demonstrate possible applications, the team incorporated fine conductive yarns into the fabrics. These yarns transformed the knitted structures into soft, stretchable electrical switches.

One knitted shell switched an LED on and off when it moved between stable states. Another textile, worn over a knee or elbow, generated a snapping movement that an Arduino could register to count steps. The researchers also created a reconfigurable lampshade containing three multistable switches. Each switch controlled a different colour of light.

Because the team used machinery similar to standard industrial knitting equipment, the technology may be compatible with existing textile manufacturing processes. Further development could lead to seamless fabrics that monitor movement, provide tactile feedback or change shape on demand. Potential fields include fashion, product design, interiors and wearable technology.

Source & image: Harvard John A. Paulson School of Engineering and Applied Sciences