Traditional 3D printing approaches typically rely on thermal or photochemical processes to solidify resins and polymers. However, these modalities often encounter limitations when miniaturizing complex geometries on pliable materials, particularly at microscale dimensions required for lab-on-a-chip systems and soft microfluidics. Proximal sound printing circumvents such bottlenecks by deploying highly localized ultrasound energy to initiate polymerization reactions in liquid monomers precisely where needed. This sub-millimeter accuracy is achieved by positioning the ultrasound transducers closer to the target substrate, effectively focusing the acoustic energy and enabling fine control over solidification.

The science underpinning this innovation revolves around the capacity of focused sound waves to induce chemical cross-linking in photo- and thermo-sensitive polymers without relying on external heat or light sources. Unlike previous direct sound printing techniques developed by the same research group, which demonstrated proof-of-concept but suffered from limited resolution and reproducibility, this proximal approach achieves vastly improved feature size control and power efficiency. The reduction in acoustic power requirements not only conserves energy but also minimizes thermal deformation of delicate polymeric materials, leading to enhanced structural fidelity.

One of the most remarkable outcomes of this technique is its ability to fabricate complex assemblies comprised of multiple materials and heterogeneous structures in a single, streamlined printing process. This multi-material printing capability is a critical advantage for constructing functional microsystems exhibiting diverse properties, such as flexible strain sensors integrated directly with microfluidic circuitry for real-time biochemical analysis. The ability to pattern these devices directly on soft substrates heralds new possibilities in wearable health monitors and implantable biomedical devices that demand both miniaturization and mechanical compliance.

Concordia’s team led by Professor Muthukumaran Packirisamy and PhD candidate Shervin Foroughi, collaborating with Mohsen Habibi from the University of California at Davis, has published their findings in the prestigious journal Microsystems & Nanoengineering. Their published study meticulously details experimental setups where focused ultrasound transducers were operated in close proximity to silicone and other polymeric substrates, triggering localized cross-linking reactions and thus solidifying the material layer-by-layer into finely detailed three-dimensional microstructures.

The implications of proximal sound printing extend beyond the laboratory and poised for industrial relevance, particularly in scenarios demanding rapid prototyping of microdevices with stringent dimensional tolerances. This technique’s enhanced repeatability and precision potentially reduce material waste and shorten production cycles, making it an appealing alternative to conventional lithography or laser-based processes which can be prohibitively expensive and less adaptable to soft polymeric materials.

Moreover, the sound-based printing approach addresses critical challenges in microfabrication where ultraviolet or visible light penetration is limited, or where heat-sensitive components preclude the use of traditional thermal curing. The ultrasound-induced polymerization mechanism thus constitutes a non-invasive alternative that expands the materials palette available for next-generation microelectronics and sensing platforms.

Looking forward, this technology promises transformative impacts on the development of soft robotics, flexible electronics, and portable diagnostic tools. The capacity to print intricate microchannels, integrated sensors, and responsive polymer structures directly onto flexible bases streamlines device packaging and enhances mechanical robustness. Such integration facilitates the production of lightweight, adaptable medical devices and wearable systems capable of continuous health monitoring or environmental detection in real time.

The research team acknowledges the foundational role of earlier sound printing methods, emphasizing that the critical advance of reducing the standoff distance between the ultrasound source and the printing interface grants unprecedented control over feature geometry and consistency. By employing proximal sound printing, they achieved features as small as tenths of a millimeter, representing a roughly tenfold improvement over their previous demonstrations.

From a technical perspective, the key to this improvement lies in the manipulation of acoustic focal zones and the refinement of polymer chemistry to optimize responsiveness to ultrasound stimuli. The researchers tailored polymer formulations to achieve rapid and reproducible curing kinetics when subjected to controlled ultrasonic intensities. This synergy of materials engineering and acoustics enables direct fabrication of microstructures without intermediate masking or post-processing steps.

Given these advances, proximal sound printing stands to revolutionize fabrication workflows in laboratories and factories where microscale devices form the backbone of innovation. This technology offers a versatile, energy-efficient, and adaptable route to creating next-generation microsystems crucial for biomedical engineering, sensor technologies, and nanomanufacturing.

Financial support for this research was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC), reflecting the strategic importance of this innovation in advancing Canadian and global capabilities in advanced manufacturing and materials science.

Subject of Research: Not applicable
Article Title: Proximal sound printing: direct 3D printing of microstructures on polymers
News Publication Date: 8-Jan-2026
Web References: https://www.nature.com/articles/s41378-025-01035-w
References: Muthukumaran Packirisamy, Mohsen Habibi, Shervin Foroughi, “New sound-based 3D printing method enables finer, faster microdevices,” Microsystems & Nanoengineering, DOI: 10.1038/s41378-025-01035-w
Image Credits: Concordia University
Keywords: Nanotechnology, Nanofabrication, Polymer engineering

Passivation, broadly understood as the process through which a material surface forms a protective oxide layer preventing further corrosion or machining, plays a pivotal role in ECM technologies. Traditionally, this phenomenon has been inferred indirectly through post-process analyses or theoretical models, which limit the understanding of its dynamic behavior during machining. The current study circumvents these limitations by deploying an innovative experimental setup that facilitates live monitoring of passivation layers in situ during the machining process, a feat rarely achieved with such clarity until now.

Electrochemical machining, celebrated for its ability to machine complex geometries without inducing thermal or mechanical stresses, relies intricately on the interplay between metal dissolution and oxide layer formation. This balance determines machining accuracy, surface finish, and tool longevity. Yet, the exact dynamics of oxide layer growth, breakdown, and regeneration under varying machining parameters remained elusive. Arshad and colleagues’ operando approach effectively captures these dynamic changes, offering quantitative and qualitative data on passivation kinetics and enabling the fine-tuning of process parameters for optimal machining outcomes.

One of the study’s notable innovations involves integrating laser assistance within the ECM framework. Laser-ECM combines localized laser heating with electrolytic dissolution, which can accelerate machining rates and enhance material removal efficiency. However, laser-induced thermal effects complicate the electrochemical environment, potentially impacting passivation behavior unpredictably. The research team’s real-time investigation reveals how laser irradiation modulates the formation and stability of passivation films, identifying specific thresholds where the passivation layer either strengthens or breaks down, significantly influencing machining precision.

The experimental methodology employed represents a sophisticated convergence of electrochemical sensors, high-speed imaging, and spectroscopic techniques adapted for operando conditions. This multidisciplinary setup allowed the researchers to observe the nascent oxide films’ evolution on metal surfaces during actual machining, capturing transient phenomena such as micro-passivation and localized breakdown events. Such high temporal and spatial resolution insights were previously unattainable, marking this research as a paradigm shift in ECM process monitoring.

Beyond the fundamental scientific implications, the operational benefits of this research are profound. By elucidating the correlation between passivation dynamics and process variables such as current density, electrolyte composition, and laser power, operators can now anticipate and manipulate passivation to mitigate defects such as overcutting or undercutting. This predictive capability translates into enhanced manufacturing reliability, reduced waste, and lower processing times, offering a competitive edge in sectors demanding extreme precision, including aerospace, biomedical device fabrication, and microelectronics.

Moreover, the authors demonstrate that passivation phenomena are not merely passive protective mechanisms but active participants in shaping the machining topology. The fine interplay between passivation layer growth and electrical parameters can be exploited to engineer surface roughness at the microscale, paving the way for customized surface properties without additional finishing processes. This revelation opens intriguing possibilities for functionalizing component surfaces during machining, integrating production and surface treatment in a single step.

Another intriguing aspect uncovered by Arshad et al. is the spatial heterogeneity of passivation within the machining zone. The operando measurements revealed localized zones where passivation formations evolved differently due to micro-variations in electrolyte flow, temperature gradients, and electric field distributions. Understanding this heterogeneity is crucial for advancing ECM techniques, as it helps designers address inconsistencies affecting dimensional accuracy and surface integrity in complex part geometries.

The research also broaches the challenge of scaling these findings for industrial application. While the laboratory-scale setup delivers invaluable data, translating operando measurement techniques to fully automated, high-speed manufacturing environments will require further innovation in sensor miniaturization, data processing, and real-time control algorithms. However, the foundational knowledge gained serves as an essential stepping stone toward smarter, self-optimizing ECM machines capable of adjusting parameters on-the-fly based on live passivation feedback.

Environmental and economic implications of enhanced passivation understanding are equally significant. ECM processes traditionally utilize specialized electrolytes and generate waste products that require careful management. With real-time insights into passivation, process engineers can optimize electrolyte usage and machining cycles, minimizing chemical consumption and waste generation. This aligns well with growing sustainability initiatives in manufacturing, promoting greener production methods without sacrificing performance.

From a broader scientific perspective, this research illustrates the growing power of operando techniques across materials and manufacturing science domains. Being able to capture phenomena as they unfold in operational environments ushers a new era where theoretical concepts meet tangible, actionable insights. Arshad and colleagues’ work exemplifies this trend, highlighting how advanced characterization tools and methodological innovation forge pathways toward fully integrated digital manufacturing ecosystems.

The implications for training and workforce development should also not be overlooked. As machines become equipped with advanced sensors that monitor passivation and other critical phenomena, operators and engineers will require new competencies in data interpretation, process optimization, and machine learning integration. This evolution signals a shift toward more interdisciplinary skill sets blending electrochemistry, materials science, and data analytics, indicative of future manufacturing workforce demands.

Further research directions suggested by this study are manifold. Extending operando monitoring to other machining techniques, such as abrasive or chemical milling, could reveal similarly critical transient phenomena influencing process efficiency and materials integrity. Additionally, exploring passivation behavior across diverse material classes — from metals to composites and emerging alloys — could broaden applicability and drive cross-disciplinary innovation.

Ultimately, the findings presented in this seminal paper herald a new age where precise, on-machine, and real-time understanding of passivation not only solves longstanding manufacturing challenges but also inspires novel machining strategies yet to be conceived. This blend of fundamental science and practical engineering insight invigorates the manufacturing sector’s capacity to innovate, compete, and sustainably meet the complex demands of tomorrow’s technologies.

As industries continue to push the boundaries of miniaturization, customization, and material complexity, the ability to govern passivation phenomena dynamically will underpin competitive advantage. The pioneering work of Arshad, Saxena, and Reynaerts thus stands as a keystone achievement — a beacon illuminating the intricate dance of chemical, thermal, and electrical factors woven into the fabric of modern electrochemical machining.

Subject of Research: Passivation phenomenon during Electrochemical Machining (ECM) and Laser-ECM processes, with operando and on-machine evaluation of passivation layer formation and evolution.

Article Title: Operando evaluation of passivation phenomenon during ECM/Laser-ECM: direct and on-machine evidence of passivation evolution.

Article References:
Arshad, M.H., Saxena, K.K. & Reynaerts, D. Operando evaluation of passivation phenomenon during ECM/Laser-ECM: direct and on-machine evidence of passivation evolution. npj Adv. Manuf. 2, 7 (2025). https://doi.org/10.1038/s44334-025-00017-0

Image Credits: AI Generated