Printed Nanomaterial-based Devices for Programmable Thermal and Mechanical Actuation

Abstract

Demand for adaptable, lightweight, and human-compatible technologies continues to grow across fields like robotics, healthcare, and aerospace. Traditional actuation systems, such as motors, hydraulic cylinders, and combustion engines, offer limited human contact given their rigidity, bulk, and incompatibility with vulnerable biological surfaces. In contrast, soft materials, which are often composed of materials like polymers, hydrogels, and composites, have emerged as a compelling alternative, offering capabilities such as bending, stretching, and conforming to complex surfaces. The incorporation of soft materials can make systems highly versatile for applications ranging from biomedical implants to deployable space structures.The development of soft actuators has historically been driven by the emergence of advanced materials, from shape memory alloys to electroactive polymers. Despite these advances, significant challenges persist in achieving faster actuation speeds, enhanced safety, improved durability, and increased versatility in fabrication. Overcoming these obstacles necessitates a shift toward miniaturized, programmable, and biocompatible systems. This imperative, in turn, underscores the need to investigate novel materials that offer superior electrical, thermal, and mechanical properties when integrated into conventional device architectures or when prototyping new system designs. Conductive 2D nanomaterials (NMs) such as graphene, MXenes, and other metallic nanostructures offer unique properties that are not able to be realized by their bulk counterparts and their incorporation into thin films has opened new possibilities for actuation design. When combined with digitally controlled additive manufacturing methods, especially aerosol jet and inkjet printing, these NMs enable the precise, scalable fabrication of custom electronic devices directly onto a wide range of substrates, including those that are soft, flexible, porous, or even biological. This convergence of material capability and fabrication freedom allows for demonstration of the promise of printed actuation devices for diverse applications. In this dissertation, advancements in NM-based ink development and AJP technology make possible the fabrication of printed transducers, microscale thermal systems, and soft actuators. Process-level innovations are introduced that enhance dimensional control for realizing targeted performance characteristics with relevance to several research fields. A central contribution of this research is the development of a speed-thickness calibration model that supports fine-tuning dimensional control of AJP printed films. Reading the generated calibration curve informs the user of the appropriate speed required for achieving a desired thickness for printed features. Thickness proves critical for voltage requirements of electronic devices, as well as the mechanical responsiveness of soft actuators. Particularly for soft actuators, the ability to engineer dimensionality at the microscale was shown to influence the relationship between light exposure and actuation force—a key relationship that drives multiple commonly reported performance metrics including power input threshold, bend angle, displacement, etc. Furthermore, a speed-thickness calibration is presented as an additional tool for future additive manufacturing researchers working with printable conductive NMs and serves as a new method for improved device-to-device uniformity. The advancements in AJP are applied to the fabrication of acoustofluidic devices. Using a AgNW ink formulation, an AJP process was employed for directly printing interdigitated transducers (IDTs) onto a series of piezoelectric substrates, for realizing multiple sets of acoustofluidic devices operating at frequencies ranging from 5 –20 MHz. As an example of the device-to-device uniformity, a set of six AgNW IDTs achieved a consistent resonant frequency of 9.89 ± 0.09 MHz. Notably, acoustofluidic devices could immediately be employed for droplet manipulation without post-processing methods typically required in conventional fabrication, such as treatments involving high temperatures, strong vacuum, harsh chemicals, and oxygen plasma. Further advancements to AJP printing allowed for the realization of improved 2D control and consistency, demonstrated by the fabrication of eighteen microscale resistive thermal detectors (RTDs), for localized heating and thermal sensing, exhibiting resistance values within the tight distribution of 54.0 ± 4.6 Ω. Representative devices demonstrated thermal stability during continuous operation above 50 °C over seven days, with a minor decrease in temperature of only 1.2 ± 0.4 °C, demonstrating their promise as suitable candidates for use in controlled heating applications, such as transdermal drug delivery systems. When tested under both ambient and aqueous conditions, including use within a Franz cell diffusion system, electronically insulated heaters maintained consistent thermal performance and demonstrated a reliable temperature coefficient of resistance for self-monitored electrothermally induced temperature elevation for oxycodone release from thermally-responsive drug-loaded films. The use of AJP to fabricate these microheaters provides a pathway to engineer integrated, programmable thermal systems directly onto wearable or flexible substrates. Soft actuators based on MXene-cellulose nanofiber (MXene-CNF) composite inks were also developed in this work. These actuators were printed onto lightweight, flexible, and porous polycarbonate (PC) membranes at room-temperature, allowing for multiple successive, precise, and reversible cycles, particularly for small bending motions under low-power stimulus. Further, this dissertation presents the first fully printed multi-stimulus actuators fabricated using AJP. Multi-stimulus devices were designed to respond to both electrical input (below 2.5 V) and near-infrared (NIR) light (below 10 mW/mm²), demonstrating rapid and reversible thermomechanical actuation for powering via direct electric wiring as well as by wireless, battery-free control. Looking forward, this work advances the development of new nanomaterial inks that offer tunable optical, electrical, mechanical, and thermal properties without compromising printability. A future direction would be the incorporation of real-time process monitoring tools into the AJP system process, such as sensors for aerosol characteristics and feedback-driven print control, which could enhance reproducibility across long prints and large device arrays. There is also significant potential in printing more electronic components to develop fully self-contained platforms for custom, on-the-fly electronic solutions, integrating printed sensing and actuating components into a range of applications. In summary, this dissertation work overcomes scientific obstacles for fabricating functional nanomaterial-based devices across multiple modalities using aerosol jet printing. It contributes several innovations in process modeling, ink-substrate interactions, and device design that can support the next generation of scalable, adaptive electronics, with specific relevance for transdermal drug delivery and soft robotic systems. While broader integration remains a future goal, the work presented here establishes critical groundwork for enabling precise, programmable, and reproducible printed NM-enabled electronics.