LEDs Enclosed in Silicone for the Development of Tender Robots
In the world of flexible and stretchable electronics, two materials have emerged as key players: polyimide and silicone. Polyimide, with its exceptional mechanical strength, heat resistance, and flexibility, serves as a sturdy base for creating stretchy circuits, while silicone, known for its elasticity, is used to construct soft robots.
To fabricate stretchy circuits using flexible circuits built on polyimide film, the general approach involves several steps. First, polyimide film is used as the flexible substrate, thanks to its ability to withstand substantial stretching and bending without breaking.
Next, the conductive traces are designed with shapes that accommodate stretching, such as serpentine, meander, or spring-like patterns. This geometric layout allows the copper conductors to elongate and compress with mechanical deformation without cracking.
Thin copper foil is then used as the conductor layer, which adheres well and remains functional when the circuit is flexed repeatedly. Suitable adhesives and coverlay films are incorporated to bond and protect the layers, ensuring durability during stretching and exposure to the environment.
For integration into stretchable substrates like silicone, flexible circuits are often embedded in a stretchable matrix. This can be achieved by layering the circuit between silicone skin layers, and using wire looping or spring-like wiring to enable expansion and contraction.
The process of making silicone skin involves layering a two-part mixture into a mold, followed by the addition of a strip of conductive fabric and an LED with its wires, and then another layer of silicone to completely cover and seal the fabric and LED in place. Tape is used to hold the fabric and LED in place while the final layer of silicone is applied.
Soft robots can be made entirely or partially from silicone. When LEDs are embedded within translucent silicone, they emit diffuse light. To limit current and prevent overheating, a large series resistor (e.g., 1K) is recommended when embedding LEDs in silicone.
An example of a claw-like gripper made entirely from silicone is shown in a video, along with demonstrations on how to wire in the LEDs without bending the wires if they are run along an axis which won't stretch. The YouTube channel Science Buddies provides a comprehensive guide on embedding LEDs in soft robots.
When it comes to wiring LEDs in soft robots, stranded wire is best for flexibility. Reduced airflow in silicone can lead to LED overheating, so it's important to use a series resistor to manage the current.
In summary, stretchy circuits on polyimide film rely on flexible substrates combined with circuit trace geometries designed to accommodate strain, protective layering, and sometimes embedding in a more elastic material like silicone for higher stretchability. This approach balances the strong, heat-resistant properties of polyimide with the need for mechanical compliance in flexible/stretchable electronics. Soft robots, on the other hand, can be made entirely or partially from silicone, offering a unique blend of flexibility and functionality.
A do-it-yourself (DIY) project could involve creating stretchy circuits using polyimide film as the flexible substrate, designing conductive traces in serpentine, meander, or spring-like patterns, and embedding the circuit in a stretchable matrix of silicone for higher stretchability.
As for soft robots, they can be fabricated entirely or partially from silicone, with appropriate usage of stranded wire for wiring LEDs, and a large series resistor to limit current and prevent overheating when LEDs are embedded within translucent silicone.
