Despite the many names owners give their robot vacuum cleaners, Dustin Bieber and Optimus Grime being two of our favourites, there’s no chance of mistaking these devices as living beings. They can deliver a clean house but not comfort.

As the population ages and robotics becomes more advanced, the prospect of lifelike robots delivering care becomes increasingly likely. Soft robotics use materials that are flexible, deformable, pliant, and that mimic skin. Sensors, lenses, and circuits are then embedded within this soft material. In a not-to-distant future, a robot could hold a sick person’s hand, simultaneously taking their temperature, heart rhythm, glucose levels, etc., all while providing a simulation of human contact and comfort.

But the end goal of soft robotics is not just a Siri with corporeal form performing human-like movements. Soft robotics allows for flexible, wearable sensors as well as minimally invasive surgeries as the material’s flexible structures navigate through the body’s confined spaces with reduced trauma to the surrounding tissue.

The challenge to the widespread adoption of soft robotics in the medical sphere is the durability and longevity of these materials. They stretch and release repeatedly as they are worn or as they moved. This can cause the various layers of the material to pull apart or delaminate. In addition, the circuits and sensors within the material are exposed to air and moisture during the fabrication process, which can cause them to degrade over time.

Researchers at TMOS, the ARC Centre of Excellence for Transformative Meta-Optical Systems, have addressed these challenges with a new fabrication technique that can create stretchable circuits and lenses within a silicone polymer without exposing it to atmospheric conditions and without needing the multiple layers that typically fail over time. This flexible polymer with embedded sensors is only 1/20th the thickness of the epidermal layer of human skin, making it an ideal for wearable and implantable devices.

This new fabrication technique, detailed in Advanced Electronic Materials, uses direct laser writing (DLW) or three-dimensional laser printing to run a highly confined laser along a pre-determined path on a silicone substrate made from combined Polydimethylsiloxane (PDMS) and graphene oxide (GO). This laser interacts with the substrate at specific depths beneath the surface, transforming the GO-PDMS material into reduced GO and carbon-rich PDMS. This carbon-rich material is conductive, and essentially, a circuit is formed within the material without it having been exposed to the atmosphere and without it needing an encapsulating layer.

The researchers also demonstrated the fabrication of stretchable flat graphitized lenses using the same method. These lenses have a broadband focusing capability in the visible region and present a potential transformation of applications from intraocular lenses for living organisms to compact lens systems in soft robotics.

Lead author Dr Litty Thekekkera from the Centre’s RMIT node says, “Using careful control of carbon doping and with extensive modelling, we have been able to demonstrate not just stretchable electronics but also a stretchable graphitised lens which is tunable with strain and has broadband focusing capability.”

TMOS Chief Investigator Madhu Bhaskaran says, “Using a laser to transform the material to create 3D structures is an exciting new way to create next-generation optical and electronic devices – it is a step process to offer functionality, enhanced stretchability, and encapsulation.”

For more information about this research,  please contact connect@tmos.org.au

3D Stretchable Devices: Laser-Patterned Electronic and Photonic Structures

Litty V Thekkekara, Ying Zhi Cheong, Md. Ataur Rahman, Sharath Sriram, Madhu Bhaskaran

Advanced Electronic Materials, 10th December 2023

Realising three-dimensional stretchable structures of functional materials with a minimum footprint on Silicone polymer is highly desirable in soft robotics, stretchable electronics, and photonics. However, material processing on a stretchable substrate requires a sophisticated deposition system with integrated substrate cooling facilities to prevent delamination of materials from the stretchable substrate due to stretching-releasing cycles and for encapsulating the functional materials. Here, a methodology to address these challenges using in situ graphitization within silicone polymer, referring to transforming the material into graphite-like structures using three-dimensional laser printing is reported. In this case, the graphitization process occurs due to the interaction of the material with a spatially controllable, tightly focused femtosecond laser beam in the confined region within the polymer. Three-dimensional printed embedded, stretchable electrodes and varifocal lenses of thickness 1/20th compared to the epidermis layer thickness of human skin, which can contribute to achieving compact, highly sensitive wearable sensing and imaging systems are demonstrated and characterized. This process will open a new door for forming non-metallic stretchable three-dimensional conductors and photonics with minimum exposure to atmospheric conditions and a pathway to interface with thin films to develop low-dimensional devices. These graphitized three-dimensional structures can make them integral to intelligent skins, e-textiles, and implantable devices.