Biocompatible 3D-Printed Micro-Optofluidic Devices for Cell Concentration Monitoring

The increasing demand for precision, efficiency, and scalability in life sciences and biomedical research has driven the development of advanced microfluidic and lab-on-a-chip (LOC) devices. Accurate cell concentration measurement is critical for applications like cell culture, drug development, diagnostics, and tissue engineering. Microfluidic devices utilize techniques such as flow cytometry, impedance spectroscopy, digital microfluidics, and image analysis methods, though challenges like invasiveness, complexity, and cost persist. Micro-optofluidic (MoF) devices ad dress these limitations offering non-invasive, label-free, real-time monitoring by combining fluid manipulation with optical com ponents, enabling light-based analytical capabilities. This work addresses issues of similar geometries previously fabricated using polydimethylsiloxane (PDMS) and soft lithography techniques, such as surface deformation due to swelling, lack of permanent bonding, low dimensional accuracy from PDMS’ softness and ther mal expansion, high fabrication costs, time-intensive procedures, and the ongoing investigation into the feasibility of single-step PDMS device printing (Saitta et al., 2022). In this context, this study aims to design, fabricate, and validate two MoF devices, 3D printed via Projection Micro-Stereolithography (PμSL). It enables the production of monolithic microstructures integrating optical and fluidic functionalities with micron-level precision (10μm), rapid turn-around times, and the ability to print complex shapes as single piece without the need for assembly or support materials. By using a novel biocompatible resin, the precision, optical trans parency, and material compatibility for biomedical applications are achieved. The devices feature a T-junction microchannel for two-phase flow generation and micrometric dead-end slots for optical fiber insertion, enabling light-based sensing. They were designed at two different microscales: the first device has microchannels and optical fiber slots with 500μm square cross-sections, while for the second these components sizes are scaled down to 200μm. The working principles allow for two-phase low monitoring and cell concentration detection, using optical absorption, where light transmission variations are correlated with f luid or cell interactions within the microchannels. Experimental validation demonstrated the devices’ ability to detect air-water slug flows and measure yeast cell concentrations suspended in phosphate-buffered saline solutions. Key operational parameters, i.e., flow rates and laser input power, were optimized using a Design of Experiments methodology to ensure repeatability. A comparative study of the two MoF devices evaluated the effects of scaling down microchannel dimensions on optical and fluidic performance. Results showed that both devices were capable of distinguishing biological fluids with varying cell concentrations. The smaller showed superior sensitivity in detecting lower cell concentrations, highlighting the potential for developing devices with microchannels comparable to individual cells, enabling real-time cell counting based on optical signals. This study demonstrates the potential of PμSL-fabricated MoF devices for real-time, label-free, and non-invasive biosensing applications. It advances the integration of micro-optofluidic and biomaterials in LOC technologies, offering solutions for next-generation diagnostics and biomedical research.