Knitted structures made on standard weft-knitting machines can switch shapes, sense motion and operate as soft electrical switches
Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed knitted fabrics capable of switching between stable shapes, sensing motion and functioning as soft electrical switches. The structures were produced using standard weft-knitting machines similar to those already used in garment manufacturing, offering a manufacturing-compatible approach to programmable textiles.
The research was led by Kausalya Mahadevan, a recent SEAS Ph.D. graduate who is now a postdoctoral associate in the laboratory of Katia Bertoldi, the William and Ami Kuan Danoff Professor of Applied Mechanics.
Applying Nonlinear Mechanics to Textile Structures
The Harvard team explored how principles from nonlinear solid mechanics could be incorporated into textile design. Rather than relying on polymer moulding and engineered residual stresses, which are commonly used to create shape-holding textiles, the researchers used yarn selection and knitting structures to generate the desired behaviour.
The team used highly elastic yarns together with a technique known as plating, in which different yarns are positioned on opposite faces of the fabric. This combination produced dense, thick knitted structures that naturally curl into three-dimensional forms.
The mechanism is similar to the way a cut T-shirt hem can roll upward.
Knitted Fabrics Designed for Multistability
By systematically arranging horizontal and vertical knitted stripes, the researchers created structures capable of “snapping” between two or more stable configurations and remaining in each configuration.
This characteristic, known as multistability, allows the fabric to behave in a manner comparable to a switch that remains in either an on or off state.
The researchers mapped the geometric and material conditions required to produce this behaviour. Their models were validated by treating the knitted structure as a continuous material rather than modelling individual yarns separately.
Conductive Yarns Add Electrical Functionality
The researchers incorporated thin conductive yarns into the knitted structures to create soft, stretchable electrical switches. These switches change state as the textile moves between its stable configurations.
The demonstrations included:
- A knitted shell that switched an LED on and off as it moved between stable states.
- A wearable switch placed over a knee or elbow that could be connected to an Arduino to count steps as the joint bent.
- A reconfigurable lampshade incorporating three separate multistable switches, with each switch controlling a different light colour as sections of the fabric were stretched.
Existing Knitting Equipment Used for Production
The fabrics were produced using industrial-grade knitting machines similar to those already used in garment production.
The approach connects textile engineering with the field of nonlinear mechanical metamaterials, which focuses on structures engineered to bend, buckle and snap in controlled ways to achieve specific functions.
The research was supported by the US National Science Foundation, the Army Research Office’s MURI programme, and an ONR DURIP equipment award.
Implications for Programmable Textile Manufacturing
The research demonstrates that multistable behaviour can be engineered through yarn selection and knit structure using existing knitting equipment, rather than requiring new tooling or polymer-processing methods.
This approach provides a route for incorporating shape-changing, sensing and switching functions directly into knitted textile structures while using manufacturing equipment already established in the textile industry.
Source: Apparel Resources