Printing the future of soft robots one microscopic drop at a time

A silicone material called PDMS has become foundational to technologies ranging from soft robots that safely grasp fragile objects to wearable sensors that flex naturally with the body.  The material is prized for its flexibility, durability, and biocompatibility but despite its widespread use, creating intricate and arbitrary microscale structures of it has been a manufacturing challenge—until now.

Researchers at Carnegie Mellon University have developed a way to print detailed 2D and 3D PDMS architectures with remarkable precision using aerosol jet printing. This creates new possibilities for soft electronics, biomedical devices and next-generation robotics.

Published in npj Advanced Manufacturing, the study demonstrates how the team successfully fabricated everything from microscopic lines and pillars to complex lattices and soft microfluidic channels without the molds and labor-intensive fabrication steps typically required in soft material manufacturing.

The work was led by Rahul Panat, professor of mechanical engineering, and Swastik Kushagr, Ph.D. candidate in Panat’s lab, alongside collaborators across materials science and robotics.

Aerosol jet printing, an additive manufacturing technique more commonly associated with printed electronics, creates a mist of microscopic droplets that can be precisely directed onto a surface. Compared to traditional extrusion printing that uses a conventional nozzle and limits control, aerosol jet printing allows researchers to build structures at extremely small scales while maintaining fine geometric detail.

When it comes to manufacturing PDMS, however, the process becomes more challenging.

The silicone’s flow behavior and curing properties make it difficult to print stable, high-resolution 3D structures. By carefully engineering the material formulation and optimizing the printing conditions, the CMU team enabled the ink to hold its shape as structures were built layer by layer. The ink itself remains printable for 3+ weeks without gelling, giving it an excellent shelf life. This, along with its in-situ curing of picolitre droplets, enables the formation of a wide range of complex microarchitectures, as seen in this work.

The result is a manufacturing method capable of producing soft structures measured in mere micrometers, that is, thinner than a strand of hair, while preserving the elasticity that makes PDMS so valuable.

Beyond the new ability to print tiny microscale shapes, the researchers demonstrated functional structures with real engineering potential, including compressible microlattices, robust leakproof 3D-microfluidic pathways, and magnetically responsive composites (cilia) infused with iron oxide nanoparticles. These structures maintained their integrity even under mechanical deformation, an important characteristic for soft systems designed to bend, stretch, and move.

This ability to directly print such architectures could streamline how researchers prototype flexible devices. Traditionally, fabricating PDMS microsystems often requires complex lithography, molds or sacrificial templates that can take days to prepare and limits structural design flexibility. Aerosol jet printing, on the other hand, offers a more direct, single-step, and customizable approach, allowing designs to be rapidly modified and produced with minimal post-processing.

That flexibility may prove especially valuable in fields where rapid iteration is critical, like in biomedical engineering, where the technique could be used to develop implantable devices or lab-on-a-chip systems capable of analyzing fluid samples.

“This work signifies a broader shift in additive manufacturing toward multifunctional microscale systems,” said Panat. “More often, we are looking for ways to integrate mechanical, electronic and fluidic capabilities into a single manufacturing platform to reduce complexity while still enabling more compact and more capable devices.”

Because aerosol jet printing can deposit material onto complex and non-conformal surfaces, the team’s approach may eventually allow conductive materials, magnetic sensors and actuators, and soft structural elements to be fabricated together in a single process.

Moving forward, the team will look into the fundamentals behind the formation of such complex microarchitectures, extending the range of printable materials with other functionality such as integrating conductive features directly into the soft PDMS architectures.