Researches in the medical field are causing a rise in wearables and soft robotics. Recent research published in Nature explains how soft materials can be fabricated with micron resolution for complex systems like robotics and next-generation wearables.

Additive manufacturing has a wide range of applications and addresses many challenges inherited from conventional molding techniques such as human error, multistep fabrication, and manual handling. However, 3D printing soft functional robots with two-part platinum cure silicones require development to match the material performance of the molded counterparts.

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Based on previously published work, the researchers selected a thiol-ene silicone formulation that possessed excellent printability (low viscosity, rapid gelation, and high reaction conversion). They employed the use of a materials platform consisting of silicone double networks (SilDNs), offering low elastic moduli and strength not found in previous SLA elastomers. Furthermore, while meeting the process requirements of SLA, these SilDNs are also compatible with less restrictive additive manufacturing techniques like UV-curing injection molding.

“The combination of low moduli, high toughness, and high tear resistance is desirable when printing soft robotic and biomedical devices,” said the researchers. “Unlike other materials where the 3D printing process can impart anisotropy or alter performance, SilDNs can possess similar properties regardless of print orientation or layer height. These findings suggest that the condensation network crosslinks across printed layers.”

Sensors and soft actuators need tear resistance and the ability to connect to stretchable fabrics. Therefore, a good elastomer-textile bond is necessary for these devices. Wearables must be able to hold up under wear and tear and donning and doffing cycles, reports 3Dprint.com.

“By introducing the SilDN framework, we note opportunities to improve process speed and final material properties. While the photopolymerization kinetics of the thiol-ene network enables rapid 3D printing, the tin-catalyzed condensation network forms over a period of hours to prolong total manufacturing time,” says the researchers.

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The researcher 3D printed the materials on a modified bottom-up commercial desktop SLA printer (Ember by Autodesk) using a blue-light LED projector modified to use a PMP window. They also added a dye series to refine Z-axis resolution, and then in post-printing, painted the surgical simulator with SilcPigs pigments.