Knitted fabrics are usually associated with warm sweaters, scarves, and blankets.
But researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have shown that knitting can do much more than keep people warm.
They have created a new type of smart fabric that can change shape, act like a switch, and even control electronic devices.
Their work could help create a new generation of wearable technology that is comfortable, flexible, and easy to produce.
The study, published in the journal Advanced Functional Materials, was led by Dr. Kausalya Mahadevan, who recently completed her Ph.D. at Harvard and is now a postdoctoral researcher in the laboratory of Professor Katia Bertoldi.
The team focused on a special property called multistability. This means an object can naturally stay in more than one stable shape without needing a constant supply of energy.
A simple example is a light switch, which stays either on or off until someone flips it. The researchers wanted to build fabrics that could behave in a similar way.
Instead of using plastics or other rigid materials, the team relied on ordinary knitting techniques commonly used in garment factories. They used a process called weft knitting, which is already widely used to make clothing such as gloves, hats, and sweaters. By carefully choosing very stretchy yarns and using a knitting method called plating, they created thick fabrics that naturally curled into three-dimensional shapes.
The different yarns were arranged so that one type appeared mainly on one side of the fabric while another appeared on the opposite side. This created built-in tension that caused the fabric to bend and curl, much like the edges of a cut T-shirt roll up on their own. By adjusting the knitting pattern, the researchers were able to create fabrics that quickly snapped between different shapes instead of changing gradually.
To better understand how the fabric behaved, the researchers tested many different designs and used computer simulations to predict how the knitted material would bend and snap. Rather than modeling every individual strand of yarn, they treated the fabric as a whole, making it much easier to study and design.
The team also showed that these smart fabrics can perform useful tasks. They knitted thin conductive threads directly into the material, allowing the fabric to act as a soft electrical switch. As the fabric snapped from one shape to another, it could turn electrical circuits on or off.
In one demonstration, a knitted shell switched an LED light on and off as it changed shape. In another, the researchers created a wearable sensor that could be placed over a knee or elbow.
Every time the joint bent enough to make the fabric snap, the movement was detected by a small Arduino microcontroller, allowing it to count steps or repeated arm movements. They also built a lampshade with three separate knitted switches, each controlling a different colored light as the fabric stretched and snapped into new positions.
Because the fabrics were made using machines already found in many clothing factories, the researchers believe the technology could be produced on a large scale without major changes to existing manufacturing methods.
The team hopes this work will lead to smart clothing that can quietly monitor body movement, provide touch-based feedback, or even change shape when needed.
By combining traditional knitting with modern engineering, they have shown that everyday fabrics could become an important part of the next generation of wearable electronics and interactive textiles.
