Comparing Microfluidic Performance of Three-Dimensional (3D) Printing Platforms

Multipath Projection Stereolithography for Three-Dimensional Printing Microfluidic Devices

Although many lab-on-chip applications require inch-sized devices with microscale feature resolution, achieving this via current 3D printing methods remains challenging due to inherent trade-offs between print resolution, design complexity, and build sizes. Inspired by microscopes that can switch objectives to achieve multiscale imaging, we report a new optical printer coined multipath projection stereolithography (MPS) specifically designed for printing microfluidic devices. MPS is designed to switch between high-resolution (1× mode, ∼10 μm) and low-resolution (3× mode, ∼30 μm) optical paths to generate centimeter-sized constructs (3 × 6 cm) with a feature resolution of ∼10 μm. Illumination and projection systems were designed, resin formulations were optimized, and slicing software was integrated with hardware with the goal of ease of use. Using a test case of micromixers, we show that user-defined CAD models can be directly input to an automated slicing software to define printing of low-resolution features via the 3× mode with embedded microscale fins via 1× mode. A new computational model, validated using experimental results, was used to simulate various fin designs, and experiments were conducted to verify simulated mixing efficiencies. New 3D out-of-plane micromixer designs were simulated and tested. To show broad applications of MPS, multichambered chips and microfluidic devices with microtraps were also printed. Overall, MPS can be a new fabrication tool to rapidly print a range of lab-on-chip applications.

3D Printing in Biocatalysis and Biosensing: From General Concepts to Practical Applications

3D printing has matured into a versatile technique that offers researchers many different printing methods and materials with varying properties. Nowadays, 3D printing is deployed within a myriad of different applications, ranging from chemistry to biotechnology -including bioanalytics, biocatalysis or biosensing. Due to its inherent design flexibility (which enables rapid prototyping) and ease of use, 3D printing facilitates the relatively quick and easy creation of new devices with unprecedented functions.. This review article describes how 3D printing can be employed for research in the fields of biochemistry and biotechnology, and specifically for biocatalysis and biosensor applications. We survey different relevant 3D printing techniques, as well as the surface activation and functionalization of 3D-printed materials. Finally, we show how 3D printing is used for the fabrication of reaction ware and enzymatic assays in biocatalysis research, as well as for the generation of biosensors using aptamers, antibodies, and enzymes as recognition elements.

A feedback-driven brain organoid platform enables automated maintenance and high-resolution neural activity monitoring

The analysis of tissue cultures, particularly brain organoids, requires a sophisticated integration and coordination of multiple technologies for monitoring and measuring. We have developed an automated research platform enabling independent devices to achieve collaborative objectives for feedback-driven cell culture studies. Our approach enables continuous, communicative, non-invasive interactions within an Internet of Things (IoT) architecture among various sensing and actuation devices, achieving precisely timed control of in vitro biological experiments. The framework integrates microfluidics, electrophysiology, and imaging devices to maintain cerebral cortex organoids while measuring their neuronal activity. The organoids are cultured in custom, 3D-printed chambers affixed to commercial microelectrode arrays. Periodic feeding is achieved using programmable microfluidic pumps. We developed a computer vision fluid volume estimator used as feedback to rectify deviations in microfluidic perfusion during media feeding/aspiration cycles. We validated the system with a set of 7-day studies of mouse cerebral cortex organoids, comparing manual and automated protocols. The automated protocols were validated in maintaining robust neural activity throughout the experiment. The automated system enabled hourly electrophysiology recordings for the 7-day studies. Median neural unit firing rates increased for every sample and dynamic patterns of organoid firing rates were revealed by high-frequency recordings. Surprisingly, feeding did not affect firing rate. Furthermore, performing media exchange during a recording showed no acute effects on firing rate, enabling the use of this automated platform for reagent screening studies.

Microfluidic Nanoparticle Separation for Precision Medicine

A deeper understanding of disease heterogeneity highlights the urgent need for precision medicine. Microfluidics, with its unique advantages, such as high adjustability, diverse material selection, low cost, high processing efficiency, and minimal sample requirements, presents an ideal platform for precision medicine applications. As nanoparticles, both of biological origin and for therapeutic purposes, become increasingly important in precision medicine, microfluidic nanoparticle separation proves particularly advantageous for handling valuable samples in personalized medicine. This technology not only enhances detection, diagnosis, monitoring, and treatment accuracy, but also reduces invasiveness in medical procedures. This review summarizes the fundamentals of microfluidic nanoparticle separation techniques for precision medicine, starting with an examination of nanoparticle properties essential for separation and the core principles that guide various microfluidic methods. It then explores passive, active, and hybrid separation techniques, detailing their principles, structures, and applications. Furthermore, the review highlights their contributions to advancements in liquid biopsy and nanomedicine. Finally, it addresses existing challenges and envisions future development spurred by emerging technologies such as advanced materials science, 3D printing, and artificial intelligence. These interdisciplinary collaborations are anticipated to propel the platformization of microfluidic separation techniques, significantly expanding their potential in precision medicine.

Rapid Biofabrication of an Advanced Microphysiological System Mimicking Phenotypical Heterogeneity and Drug Resistance in Glioblastoma

Microphysiological systems (MPSs) reconstitute tissue interfaces and organ functions, presenting a promising alternative to animal models in drug development. However, traditional materials like polydimethylsiloxane (PDMS) often interfere by absorbing hydrophobic molecules, affecting drug testing accuracy. Additive manufacturing, including 3D bioprinting, offers viable solutions. GlioFlow3D, a novel microfluidic platform combining extrusion bioprinting and stereolithography (SLA) is introduced. GlioFlow3D integrates primary human cells and glioblastoma (GBM) lines in hydrogel-based microchannels mimicking vasculature, within an SLA resin framework using cost-effective materials. The study introduces a robust protocol to mitigate SLA resin cytotoxicity. Compared to PDMS, GlioFlow3D demonstrated lower small molecule absorption, which is relevant for accurate testing of small molecules like Temozolomide (TMZ). Computational modeling is used to optimize a pumpless setup simulating interstitial fluid flow dynamics in tissues. Co-culturing GBM with brain endothelial cells in GlioFlow3D showed enhanced CD133 expression and TMZ resistance near vascular interfaces, highlighting spatial drug resistance mechanisms. This PDMS-free platform promises advanced drug testing, improving preclinical research and personalized therapy by elucidating complex GBM drug resistance mechanisms influenced by the tissue microenvironment.

Transformation gap from research findings to large-scale commercialized products in microfluidic field

The field of microfluidics has experienced rapid growth in the last several decades, yet it isn't considered to be a large industry comparable to semiconductor and consumer electronics. In this review, we analyzed the entire process of the transformation from research findings to commercialized products in microfluidics, as well as the significant gap during the whole developing process between microchip fabrication in R&D and large-scale production in the industry. We elaborated in detail on various materials in the microfluidics industry, including silicon, glass, PDMS, and thermoplastics, discussing their characteristics, production processes, and existing products. Despite challenges hindering the large-scale commercialization of microfluidic chips, ongoing advancements and applications are expected to integrate microfluidic technology into everyday life, transforming it into a commercially viable field with substantial potential and promising prospects.

Recent advances in microfluidic technology of arterial thrombosis investigations

Microfluidic technology has emerged as a powerful tool in studying arterial thrombosis, allowing researchers to construct artificial blood vessels and replicate the hemodynamics of blood flow. This technology has led to significant advancements in understanding thrombosis and platelet adhesion and aggregation. Microfluidic models have various types and functions, and by studying the fabrication methods and working principles of microfluidic chips, applicable methods can be selected according to specific needs. The rapid development of microfluidic integrated system and modular microfluidic system makes arterial thrombosis research more diversified and automated, but its standardization still needs to be solved urgently. One key advantage of microfluidic technology is the ability to precisely control fluid flow in microchannels and to analyze platelet behavior under different shear forces and flow rates. This allows researchers to study the physiological and pathological processes of blood flow, shedding light on the underlying mechanisms of arterial thrombosis. In conclusion, microfluidic technology has revolutionized the study of arterial thrombosis by enabling the construction of artificial blood vessels and accurately reproducing hemodynamics. In the future, microfluidics will place greater emphasis on versatility and automation, holding great promise for advancing antithrombotic therapeutic and prophylactic measures.

Democratizing Access to Microfluidics: Rapid Prototyping of Open Microchannels with Low-Cost LCD 3D Printers

Microfluidics offer user-friendly liquid handling for a range of biochemical applications. 3D printing microfluidics is rapid and cost-effective compared to conventional cleanroom fabrication. Typically, microfluidics are 3D printed using digital light projection (DLP) stereolithography (SLA), but many models in use are expensive (≥$10,000 USD), limiting widespread use. Recent liquid crystal display (LCD) technology advancements have provided inexpensive (<$500 USD) SLA 3D printers with sufficient pixel resolution for microfluidic applications. However, there are only a few demonstrations of microfluidic fabrication, limited validation of print fidelity, and no direct comparisons between LCD and DLP printers. We compared a 40 μm pixel DLP printer (∼$18,000 USD) with a 34.4 μm pixel LCD printer (<$380 USD). Consistent with prior work, we observed linear trends between designed and measured channel widths ≥4 pixels on both printers, so we calculated accuracy above this size threshold. Using a standard IPA-wash resin and optimized parameters for each printer, the average error between designed and measured widths was 2.11 ± 1.26% with the DLP printer and 15.4 ± 2.57% with the 34.4 μm LCD printer. Printing with optimized conditions for a low-cost water-wash resin designed for LCD-SLA printers resulted in an average error of 2.53 ± 0.94% with the 34.4 μm LCD printer and 5.35 ± 4.49% with a 22 μm LCD printer. We characterized additional parameters including surface roughness, channel perpendicularity, and light intensity uniformity, and as an application of LCD-printed devices, we demonstrated consistent flow rates in capillaric circuits for self-regulated and self-powered delivery of multiple liquids. LCD printers are an inexpensive alternative for fabricating microfluidics, with minimal differences in fidelity and accuracy compared with a 40X more expensive DLP printer.

Revolutionizing biocatalysis: A review on innovative design and applications of enzyme-immobilized microfluidic devices

Integrating microfluidic devices and enzymatic processes in biocatalysis is a rapidly advancing field with promising applications. This review explores various facets, including applications, scalability, techno-commercial implications, and environmental consequences. Enzyme-embedded microfluidic devices offer advantages such as compact dimensions, rapid heat transfer, and minimal reagent consumption, especially in pharmaceutical optically pure compound synthesis. Addressing scalability challenges involves strategies for uniform flow distribution and consistent residence time. Incorporation with downstream processing and biocatalytic reactions makes the overall process environmentally friendly. The review navigates challenges related to reaction kinetics, cofactor recycling, and techno-commercial aspects, highlighting cost-effectiveness, safety enhancements, and reduced energy consumption. The potential for automation and commercial-grade infrastructure is discussed, considering initial investments and long-term savings. The incorporation of machine learning in enzyme-embedded microfluidic devices advocates a blend of experimental and in-silico methods for optimization. This comprehensive review examines the advancements and challenges associated with these devices, focusing on their integration with enzyme immobilization techniques, the optimization of process parameters, and the techno-commercial considerations crucial for their widespread implementation. Furthermore, this review offers novel insights into strategies for overcoming limitations such as design complexities, laminar flow challenges, enzyme loading optimization, catalyst fouling, and multi-enzyme immobilization, highlighting the potential for sustainable and efficient enzymatic processes in various industries.

Towards a 3D-Printed Millifluidic Device for Investigating Cellular Processes

Microfluidic devices (µFDs) have been explored extensively in drug screening and studying cellular processes such as migration and metastasis. However, the fabrication and implementation of microfluidic devices pose cost and logistical challenges that limit wider-spread adoption. Despite these challenges, light-based 3D printing offers a potential alternative to device fabrication. This study reports on the development of millifluidic devices (MiFDs) for disease modeling and elucidates the methods and implications of the design, production, and testing of 3D-printed MiFDs. It further details how such millifluidic devices can be cost-efficiently and effortlessly produced. The MiFD was developed through an iterative process with analytical tests (flow tests, leak tests, cytotoxicity assays, and microscopic analyses), driving design evolution and determination of the suitability of the devices for disease modeling and cancer research. The design evolution also considered flow within tissues and replicates interstitial flow between the main flow path and the modules designed to house and support organ-mimicking cancer cell spheroids. Although the primary stereolithographic (SLA) resin used in this study showed cytotoxic potential despite its biocompatibility certifications, the MiFDs possessed essential attributes for cell culturing. In summary, SLA 3D printing enables the production of MiFDs as a cost-effective, rapid prototyping alternative to standard µFD fabrication for investigating disease-related processes.

3D-printed thermally expanded monolithic foam for solid-phase extraction of multiple trace metals

Digital light processing (DLP) 3DP, commercial acrylate-based photocurable resins, and thermally expandable microspheres-incorporated flexible photocurable resins were employed to fabricate an SPE column with a thermally expanded monolithic foam for extracting Mn, Co, Ni, Cu, Zn, Cd, and Pb ions prior to the determination using inductively coupled plasma mass spectrometry. After optimization of the thermally activated foaming, the design and fabrication of the SPE column, and the automatic analytical system, the DLP 3D-printed SPE column with the thermally expanded monolithic foam extracted the metal ions with up to 14.8-fold enhancement (relative to that without incorporating the microspheres), with absolute extraction efficiencies all higher than 95.6%, and method detection limits in the range from 0.5 to 5.2 ng L-1. We validated the reliability and applicability of this method by determination of the metal ions in several reference materials (CASS-4, SLRS-5, 1643f, and Seronorm Trace Elements Urine L-2) and spiked seawater, river water, ground water, and human urine samples. The results illustrated that to incorporate the thermally expandable microspheres into the photocurable resins with a post-printing heating treatment enabled the DLP 3D-printed thermally expanded monolithic foam to substantially improve the extraction of the metal ions, thereby extending the applicability of SPE devices fabricated by vat photopolymerization 3DP techniques.

Fully 3D-Printed Miniature Soft Hydraulic Actuators with Shape Memory Effect for Morphing and Manipulation

Miniature shape-morphing soft actuators driven by external stimuli and fluidic pressure hold great promise in morphing matter and small-scale soft robotics. However, it remains challenging to achieve both rich shape morphing and shape locking in a fast and controlled way due to the limitations of actuation reversibility and fabrication. Here, fully 3D-printed, sub-millimeter thin-plate-like miniature soft hydraulic actuators with shape memory effect (SME) for programable fast shape morphing and shape locking, are reported. It combines commercial high-resolution multi-material 3D printing of stiff shape memory polymers (SMPs) and soft elastomers and direct printing of microfluidic channels and 2D/3D channel networks embedded in elastomers in a single print run. Leveraging spatial patterning of hybrid compositions and expansion heterogeneity of microfluidic channel networks for versatile hydraulically actuated shape morphing, including circular, wavy, helical, saddle, and warping shapes with various curvatures, are demonstrated. The morphed shapes can be temporarily locked and recover to their original planar forms repeatedly by activating SME of the SMPs. Utilizing the fast shape morphing and locking in the miniature actuators, their potential applications in non-invasive manipulation of small-scale objects and fragile living organisms, multimodal entanglement grasping, and energy-saving manipulators, are demonstrated.

Functionality integration in stereolithography 3D printed microfluidics using a "print-pause-print" strategy

Stereolithography 3D printing, although an increasingly used fabrication method for microfluidic chips, has the main disadvantage of producing monolithic chips in a single material. We propose to incorporate during printing various objects using a "print-pause-print" strategy. Here, we demonstrate that this novel approach can be used to incorporate glass slides, hydrosoluble films, paper pads, steel balls, elastic or nanoporous membranes and silicon-based microdevices, in order to add microfluidic functionalities as diverse as valves, fluidic diodes, shallow chambers, imaging windows for bacteria tracking, storage of reagents, blue energy harvesting or filters for cell capture and culture.

Portable IC system enabled with dual LED-based absorbance detectors and 3D-printed post-column heated micro-reactor for the simultaneous determination of ammonium, nitrite and nitrate

BACKGROUND

The on-site and simultaneous determination of anionic nitrite (NO2-) and nitrate (NO3-), and cationic ammonium (NH4+), in industrial and natural waters, presents a significant analytical challenge. Toward this end, herein a 3D-printed micro-reactor with an integrated heater chip was designed and optimised for the post-column colorimetric detection of NH4+ using a modified Berthelot reaction. The system was integrated within a portable and field deployable ion chromatograph (Aquamonitrix) designed to separate and detect NO2- and NO3-, but here enabled with dual LED-based absorbance detectors, with the aim to provide the first system capable of simultaneous determination of both anions and NH4+ in industrial and natural waters.

RESULTS

Incorporating a 0.750 mm I.D. 3D-printed serpentine-based microchannel for sample-reagent mixing and heating, the resultant micro-reactor had a total reactor channel length of 1.26 m, which provided for a reaction time of 1.42 min based upon a total flow rate of 0.27 mL min-1, within a 40 mm2 printed area. The colorimetric reaction was performed within the micro-reactor, which was then coupled to a dedicated 660 nm LED-based absorbance detector. By rapidly delivering a reactor temperature of 70 °C in just 40 s, the optimal conditions to improve reaction kinetics were achieved to provide for limits of detection of 0.1 mg L-1 for NH4+, based upon an injection volume of just 10 μL. Linearity for NH4+ was observed over the range 0-50 mg L-1, n = 3, R2 = 0.9987. The reactor was found to deliver excellent reproducibility when included as a post-column reactor within the Aquamonitrix analyser, with an overall relative standard deviation below 1.2 % for peak height and 0.3 % for peak residence time, based upon 6 repeat injections.

SIGNIFICANCE

The printed post-column reactor assembly was integrated into a commercial portable ion chromatograph developed for the separation and detection of NO2- and NO3-, thus providing a fully automated system for the remote and simultaneous analysis of NO2-, NO3-, and NH4+ in natural and industrial waters. The fully automated system was deployed externally within a greenhouse facility to demonstrate this capability.

A review of the recent achievements and future trends on 3D printed microfluidic devices for bioanalytical applications

3D printing has revolutionized the manufacturing process of microanalytical devices by enabling the automated production of customized objects. This technology promises to become a fundamental tool, accelerating investigations in critical areas of health, food, and environmental sciences. This microfabrication technology can be easily disseminated among users to produce further and provide analytical data to an interconnected network towards the Internet of Things, as 3D printers enable automated, reproducible, low-cost, and easy fabrication of microanalytical devices in a single step. New functional materials are being investigated for one-step fabrication of highly complex 3D printed parts using photocurable resins. However, they are not yet widely used to fabricate microfluidic devices. This is likely the critical step towards easy and automated fabrication of sophisticated, complex, and functional 3D-printed microchips. Accordingly, this review covers recent advances in the development of 3D-printed microfluidic devices for point-of-care (POC) or bioanalytical applications such as nucleic acid amplification assays, immunoassays, cell and biomarker analysis and organs-on-a-chip. Finally, we discuss the future implications of this technology and highlight the challenges in researching and developing appropriate materials and manufacturing techniques to enable the production of 3D-printed microfluidic analytical devices in a single step.

Three-Dimensional Printed Teeth in Endodontics: A New Protocol for Microcomputed Tomography Studies

This study aimed to describe a support material removal protocol (SMRP) from inside the root canals of three-dimensional printed teeth (3DPT) obtained by the microcomputed tomography (microCT) of a natural tooth (NT), evaluate its effectiveness by comparing the 3DPT to NT in terms of internal anatomy and behaviour toward endodontic preparation, and evaluate if 3DPT are adequate to assess the differences between two preparation systems. After the SMRP, twenty 3DPT printed by PolyJet™ were microCT scanned before preparation and thereafter randomly assigned into two groups (n = 10). One group and NT were prepared using ProTaper Gold® (PTG), and the other group with Endogal® (ENDG). MicroCT scans were carried out after preparation, and the volume increase, volume of dentin removed, centroids, transportation, and unprepared areas were compared. For the parameters evaluated, no significant differences were found between the 3DPT and NT before and after preparation (p > 0.05), and no significant differences were found between the 3DPT PTG group and the 3DPT ENDG group (p > 0.05). It can be concluded that the SMRP described is effective in removing the support material SUP706B™. PolyJet™ is adequate for printing 3DPT. Furthermore, 3DPT printed with high-temperature RGD525™ have similar behaviour during endodontic preparation with PTG as the NT, and 3DPT can be used to compare two preparation systems.

A 3D printed sheath flow interface for surface enhanced Raman spectroscopy (SERS) detection in flow

Surface enhanced Raman spectroscopy (SERS) is an effective technique for detecting molecules in aqueous solutions due to its insensitivity to water, which makes it especially useful for biological samples. Utilizing SERS in flow can aid in a variety of applications such as metabolomics, pharmaceuticals, and diagnostics. The ability to 3D print complex objects enables rapid dissemination of prototypes. A 3D printed flow cell for sheath flow SERS detection has been developed that can incorporate a variety of planar substrates. The 3D printed flow cell incorporates hydrodynamic focusing, a sheath flow, that confines the analyte near the SERS substrate. Since the SERS signal obtained relies on the interaction between analyte molecules and nanostructures, sheath flow increases the detection efficiency and eliminates many issues associated with SERS detection in solution. This device was optimized by analyzing both molecules and particles with and without using sheath flow for SERS detection. Our results show that the flow rates can be optimized to increase the SERS signal obtained from a variety of analytes, and that the signal was increased when using sheath flow. This 3D printed flow cell offers a straightforward method to disseminate this technology and to facilitate online SERS detection.

Raman spectroscopy-based microfluidic platforms: A promising tool for detection of foodborne pathogens in food products

Rapid and sensitive detection of foodborne pathogens in food products is paramount for ensuring food safety and public health. In the ongoing effort to tackle this issue, detection methods are continually researched and upgraded to achieve rapidity, sensitivity, portability, and cost-effectiveness. This review addresses the critical need for improved technique by focusing on Raman spectroscopy-based microfluidic platforms, which have shown potential in revolutionizing the field of foodborne pathogen analysis offering point-of-care diagnosis and multiplex detection. The key problem lies in the persistent threat of compromised food quality and public health due to inadequate pathogen detection. The review elucidates the various trapping strategies employed in a microfluidic platform, including optical trapping, electrical trapping, mechanical trapping, and acoustic trapping for the capture of microbial cells. Subsequently, the review delves into the key aspects of the application of microbial detection in food products, highlighting recent advances and challenges in the field. The integrated technique allows point-of-care application assessment, which is an attractive quality for in-line and real-time detection of foodborne pathogens. However, the application of the technique in food products is limited and requires further research to combat the complexity of the food matrix, reduced costs of production, and ensure real-time use for diverse pathogens. Ultimately, this review aims to propel advancements in microbial detection, thus promoting enhanced food safety through state-of-the-art technologies.

Advancing 3D printed microfluidics with computational methods for sweat analysis

The intricate tapestry of biomarkers, including proteins, lipids, carbohydrates, vesicles, and nucleic acids within sweat, exhibits a profound correlation with the ones in the bloodstream. The facile extraction of samples from sweat glands has recently positioned sweat sampling at the forefront of non-invasive health monitoring and diagnostics. While extant platforms for sweat analysis exist, the imperative for portability, cost-effectiveness, ease of manufacture, and expeditious turnaround underscores the necessity for parameters that transcend conventional considerations. In this regard, 3D printed microfluidic devices emerge as promising systems, offering a harmonious fusion of attributes such as multifunctional integration, flexibility, biocompatibility, a controlled closed environment, and a minimal requisite analyte volume-features that leverage their prominence in the realm of sweat analysis. However, formidable challenges, including high throughput demands, chemical interactions intrinsic to the printing materials, size constraints, and durability concerns, beset the landscape of 3D printed microfluidic devices. Within this paradigm, we expound upon the foundational aspects of 3D printed microfluidic devices and proffer a distinctive perspective by delving into the computational study of printing materials utilizing density functional theory (DFT) and molecular dynamics (MD) methodologies. This multifaceted approach serves manifold purposes: (i) understanding the complexity of microfluidic systems, (ii) facilitating comprehensive analyses, (iii) saving both cost and time, (iv) improving design optimization, and (v) augmenting resolution. In a nutshell, the allure of 3D printing lies in its capacity for affordable and expeditious production, offering seamless integration of diverse components into microfluidic devices-a testament to their inherent utility in the domain of sweat analysis. The synergistic fusion of computational assessment methodologies with materials science not only optimizes analysis and production processes, but also expedites their widespread accessibility, ensuring continuous biomarker monitoring from sweat for end-users.

3D-printed extraction devices fabricated from silica particles suspended in acrylate resin

In recent years, there has been an increasing worldwide interest in the use of alternative sample preparation methods. Digital light processing (DLP) is a 3D printing technique based on using UV light to form photo-curable resin layer upon layer, which results in a printed shape. This study explores the application of this technique for the development of novel drug extraction devices in analytical chemistry. A composite material consisting of a photocurable resin and C18-modified silica particles was employed as a sorbent device, demonstrating its effectiveness in pharmaceutical analysis. Apart from estimating optimal printing parameters, microscopic examination of the material surface, and sorbent powder to resin ratio, the extraction procedure was also optimised. Optimisation included the type and amount of sample matrix additives, desorption solvent, sorption and desorption times, and proper number of sorbent devices needed in extraction protocol. To demonstrate this method's applicability for sample analysis, the solid-phase extraction followed by gas chromatography coupled with mass spectrometry (SPE-GC-MS) method was validated for its ability to quantify benzodiazepine-type drugs. This evaluation confirmed good linearity in the concentration range of 50-1000 ng/mL, with R2 values being 0.9932 and 0.9952 for medazepam and diazepam, respectively. Validation parameters proved that the presented method is precise (with values ranging in-between 2.98 %-7.40 %), and accurate (88.81 % to 110.80 %). A negative control was also performed to investigate possible sorption properties of the resin itself, proving that the addition of C18-modified silica particles significantly increases the extraction efficiency and repeatability. The cost-effectiveness of this approach makes it particularly advantageous for single-use scenarios, eliminating the need for time-consuming sorbent-cleaning procedures, common in traditional solid-phase extraction techniques. Future optimisation opportunities include refining sorbent size, shape, and geometry to achieve lower limits of quantification. As a result of these findings, 3D-printed extraction devices can serve as a viable alternative to commercially available SPE or solid-phase microextraction (SPME) protocols for studying new sample preparation approaches.

Toward 3D printed microfluidic artificial lungs for respiratory support

Microfluidic artificial lungs (μALs) are a new class of membrane oxygenators. Compared to traditional hollow-fiber oxygenators, μALs closely mimic the alveolar microenvironment due to their size-scale and promise improved gas exchange efficiency, hemocompatibility, biomimetic blood flow networks, and physiologically relevant blood vessel pressures and shear stresses. Clinical translation of μALs has been stalled by restrictive microfabrication techniques that limit potential artificial lung geometries, overall device size, and throughput. To address these limitations, a high-resolution Asiga MAX X27 UV digital light processing (DLP) 3D printer and custom photopolymerizable polydimethylsiloxane (PDMS) resin were used to rapidly manufacture small-scale μALs via vat photopolymerization (VPP). Devices were designed in SOLIDWORKS with 500 blood channels and 252 gas channels, where gas and blood flow channels were oriented orthogonally and separated by membranes on the top and bottom, permitting two-sided gas exchange. Successful devices were post-processed to remove uncured resin from microchannels and assembled with external tubing in preparation for gas exchange performance testing with ovine whole blood. 3D printed channel dimensions were 172 μm-tall × 320 μm-wide, with 62 μm-thick membranes and 124 μm-wide support columns. Measured outlet blood oxygen saturation (SO2) agreed with theoretical models and rated flow of the device was 1 mL min-1. Blood side pressure drop was 1.58 mmHg at rated flow. This work presents the highest density of 3D printed microchannels in a single device, one of the highest CO2 transfer efficiencies of any artificial lung to date, and a promising approach to translate μALs one step closer to the clinic.

A Versatile Photocrosslinkable Silicone Composite for 3D Printing Applications

Embedded printing has emerged as a valuable tool for fabricating complex structures and microfluidic devices. Currently, an ample of amount of research is going on to develop new materials to advance its capabilities and increase its potential applications. Here, we demonstrate a novel, transparent, printable, photocrosslinkable, and tuneable silicone composite that can be utilized as a support bath or an extrudable ink for embedded printing. Its properties can be tuned to achieve ideal rheological properties, such as optimal self-recovery and yield stress, for use in 3D printing. When used as a support bath, it facilitated the generation microfluidic devices with circular channels of diameter up to 30 μm. To demonstrate its utility, flow focusing microfluidic devices were fabricated for generation of Janus microrods, which can be easily modified for multitude of applications. When used as an extrudable ink, 3D printing of complex-shaped constructs were achieved with integrated electronics, which greatly extends its potential applications towards soft robotics. Further, its biocompatibility was tested with multiple cell types to validate its applicability for tissue engineering. Altogether, this material offers a myriad of potential applications (i.e., soft robotics, microfluidics, bioprinting) by providing a facile approach to develop complicated 3D structures and interconnected channels.

Toward an open-source 3D-printable laboratory

Premise

Low-cost, repairable lab equipment is rare within the biological sciences. By lowering the costs of entry using 3D printing and open-source hardware, our goal is to empower both amateur and professional scientists to conduct research.

Methods

We developed a modular system of 3D-printable designs called COBLE (Collection of Bespoke Laboratory Equipment), including novel and remixed 3D-printable lab equipment that can be inexpensively printed, assembled, and repaired for a fraction of the cost of retail equivalents.

Results

Here we present novel tools that utilize 3D printing to enable a wide range of scientific experiments. We include additional resources for scientists and labs that are interested in utilizing 3D printing for their research.

Discussion

By describing the broad potential that 3D-printed designs can have in the biological sciences, we hope to inspire others to implement and improve upon these designs, improving accessibility and enabling science for all.

Three-Dimensional Rock Core-Like Microstructure Fabricated by Additive Manufacturing for Petroleum Engineering

To improve the recovery rate of oil in the formation, oil recovery technology has been continuously studied. Considering the experimental cost and data measurement in oil recovery research, laboratory oil recovery is the most effective method. The rock core model used in the simulation directly affects whether the research results are credible. However, the current three-dimensional rock core model manufacturing methods and corresponding models lack of reproducible, customizable, and visualized characteristics. In this study, a reproducible rock core model of microsphere accumulation based on the structure of natural rock core was designed and manufactured by microstereolithography. Oil recovery experiments and simulation studies show that the rock core model has similar flow characteristics to natural rock cores. In addition, resin rock core models with different structures and hydrogel rock core models with deformability are also manufactured by microstereolithography and used for simulation analysis. This research provides an effective and reproducible rock core structure model for the experiment of oil recovery research.

Projection Micro-Stereolithography to Manufacture a Biocompatible Micro-Optofluidic Device for Cell Concentration Monitoring

In this work, a 3D printed biocompatible micro-optofluidic (MoF) device for two-phase flow monitoring is presented. Both an air-water bi-phase flow and a two-phase mixture composed of micrometric cells suspended on a liquid solution were successfully controlled and monitored through its use. To manufacture the MoF device, a highly innovative microprecision 3D printing technique was used named Projection Microstereolithography (PμSL) in combination with the use of a novel 3D printable photocurable resin suitable for biological and biomedical applications. The concentration monitoring of biological fluids relies on the absorption phenomenon. More precisely, the nature of the transmission of the light strictly depends on the cell concentration: the higher the cell concentration, the lower the optical acquired signal. To achieve this, the microfluidic T-junction device was designed with two micrometric slots for the optical fibers' insertion, needed to acquire the light signal. In fact, both the micro-optical and the microfluidic components were integrated within the developed device. To assess the suitability of the selected biocompatible transparent resin for optical detection relying on the selected working principle (absorption phenomenon), a comparison between a two-phase flow process detected inside a previously fully characterized micro-optofluidic device made of a nonbiocompatible high-performance resin (HTL resin) and the same made of the biocompatible one (BIO resin) was carried out. In this way, it was possible to highlight the main differences between the two different resin grades, which were further justified with proper chemical analysis of the used resins and their hydrophilic/hydrophobic nature via static water contact angle measurements. A wide experimental campaign was performed for the biocompatible device manufactured through the PμSL technique in different operative conditions, i.e., different concentrations of eukaryotic yeast cells of Saccharomyces cerevisiae (with a diameter of 5 μm) suspended on a PBS (phosphate-buffered saline) solution. The performed analyses revealed that the selected photocurable transparent biocompatible resin for the manufactured device can be used for cell concentration monitoring by using ad hoc 3D printed micro-optofluidic devices. In fact, by means of an optical detection system and using the optimized operating conditions, i.e., the optimal values of the flow rate FR=0.1 mL/min and laser input power P∈{1,3} mW, we were able to discriminate between biological fluids with different concentrations of suspended cells with a robust working ability R2=0.9874 and Radj2=0.9811.

Microfluidic platforms in diagnostic of ovarian cancer

The most important reason for death from ovarian cancer is the late diagnosis of this disease. The standard treatment of ovarian cancer includes surgery and chemotherapy based on platinum, which is associated with side effects for the body. Due to the nonspecific nature of clinical symptoms, developing a platform for early detection of this disease is needed. In recent decades, the advancements of microfluidic devices and systems have provided several advantages for diagnosing ovarian cancer. Designing and manufacturing new platforms using specialized technologies can be a big step toward improving the prevention, diagnosis, and treatment of this group of diseases. Organ-on-a-chip microfluidic devices are increasingly used as a promising platform in cancer research, with a focus on specific biological aspects of the disease. This review focusing on ovarian cancer and microfluidic application technologies in its diagnosis. Additionally, it discusses microfluidic platforms and their potential future perspectives in advancing ovarian cancer diagnosis.

3D Printing of Individualized Microfluidic Chips with DLP-Based Printer

Microfluidic chips have shown their potential for applications in fields such as chemistry and biology, and 3D printing is increasingly utilized as the fabrication method for microfluidic chips. To address key issues such as the long printing time for conventional 3D printing of a single chip and the demand for rapid response in individualized microfluidic chip customization, we have optimized the use of DLP (digital light processing) technology, which offers faster printing speeds due to its surface exposure method. In this study, we specifically focused on developing a fast-manufacturing process for directly printing microfluidic chips, addressing the high cost of traditional microfabrication processes and the lengthy production times associated with other 3D printing methods for microfluidic chips. Based on the designed three-dimensional chip model, we utilized a DLP-based printer to directly print two-dimensional and three-dimensional microfluidic chips with photosensitive resin. To overcome the challenge of clogging in printing microchannels, we proposed a printing method that combined an open-channel design with transparent adhesive tape sealing. This method enables the rapid printing of microfluidic chips with complex and intricate microstructures. This research provides a crucial foundation for the development of microfluidic chips in biomedical research.

Versatile Microfluidics for Biofabrication Platforms Enabled by an Agile and Inexpensive Fabrication Pipeline

Microfluidics have transformed diagnosis and screening in regenerative medicine. Recently, they are showing much promise in biofabrication. However, their adoption is inhibited by costly and drawn-out lithographic processes thus limiting progress. Here, multi-material fibers with complex core-shell geometries with sizes matching those of human arteries and arterioles are fabricated employing versatile microfluidic devices produced using an agile and inexpensive manufacturing pipeline. The pipeline consists of material extrusion additive manufacturing with an innovative continuously varied extrusion (CONVEX) approach to produce microfluidics with complex seamless geometries including, novel variable-width zigzag (V-zigzag) mixers with channel widths ranging from 100-400 µm and hydrodynamic flow-focusing components. The microfluidic systems facilitated rapid mixing of fluids by decelerating the fluids at specific zones to allow for increased diffusion across the interfaces. Better mixing even at high flow rates (100-1000 µL min-1 ) whilst avoiding turbulence led to high cell cytocompatibility (>86%) even when 100 µm nozzles are used. The presented 3D-printed microfluidic system is versatile, simple and efficient, offering a great potential to significantly advance the microfluidic platform in regenerative medicine.

Development of hybrid scaffolds with biodegradable polymer composites and bioactive hydrogels for bone tissue engineering

The development of treatments for critical-sized bone defects has been considered an important topic in the biomedical field because of the high demand for transplantable bone grafts. Following the concept of tissue engineering, implantation of biocompatible porous scaffolds carrying cells and regulating factors is the most efficient strategy to stimulate clinical bone regeneration. With the advancement in the development of 3D-printing techniques, scaffolds with highly controllable architectures can be fabricated to further improve healing efficacies. However, challenges such as the limited biocompatibility of resin materials and poor cell-carrying capacities still exist in the application of current scaffolds. In this study, a novel biodegradable polymer, poly (ethylene glycol)-co-poly (glycerol sebacate) acrylate (PEGSA), was synthesized and blended with hydroxyapatite (HAP) nanoparticles to produce osteoinductive and photocurable resins for 3D printing. The composites were optimized and applied in the fabrication of gyroid scaffolds with biomimetic characteristics and high permeability, followed by the combination of bioactive hydrogels containing Wharton's jelly-derived mesenchymal stem cells (WJMSC) to increase the efficiency of cell delivery. The promotion of osteogenesis from 3D-printed scaffolds was confirmed in-vivo while the hybrid scaffolds were proven to be great platforms for WJMSC culture and differentiation in-vitro. These results indicate that the proposed hybrid systems, combining osteoinductive 3D-printed scaffolds and cell-laden hydrogels, have great potential for bone tissue engineering and are expected to be applied in the treatment of bone defects based on active tissue regeneration.

Tunable resins with PDMS-like elastic modulus for stereolithographic 3D-printing of multimaterial microfluidic actuators

Stereolithographic 3D-printing (SLA) permits facile fabrication of high-precision microfluidic and lab-on-a-chip devices. SLA photopolymers often yield parts with low mechanical compliancy in sharp contrast to elastomers such as poly(dimethyl siloxane) (PDMS). On the other hand, SLA-printable elastomers with soft mechanical properties do not fulfill the distinct requirements for a highly manufacturable resin in microfluidics (e.g., high-resolution printability, transparency, low-viscosity). These limitations restrict our ability to print microfluidic actuators containing dynamic, movable elements. Here we introduce low-viscous photopolymers based on a tunable blend of the monomers poly(ethylene glycol) diacrylate (PEGDA, Mw ∼ 258) and the monoacrylate poly(ethylene glycol methyl ether) methacrylate (PEGMEMA, Mw ∼ 300). In these blends, which we term PEGDA-co-PEGMEMA, tuning the PEGMEMA content from 0% to 40% (v/v) alters the elastic modulus of the printed plastics by ∼400-fold, reaching that of PDMS. Through the addition of PEGMEMA, moreover, PEGDA-co-PEGMEMA retains desirable properties of highly manufacturable PEGDA such as low viscosity, solvent compatibility, cytocompatibility and low drug absorptivity. With PEGDA-co-PEGMEMA, we SLA-printed drastically enhanced fluidic actuators including microvalves, micropumps, and microregulators with a hybrid structure containing a flexible PEGDA-co-PEGMEMA membrane within a rigid PEGDA housing. These components were built using a custom "Print-Pause-Print" protocol, referred to as "3P-printing", that allows for fabricating high-resolution multimaterial parts with a desktop SLA printer without the need for post-assembly. SLA-printing of multimaterial microfluidic actuators addresses the unmet need of high-performance on-chip controls in 3D-printed microfluidic and lab-on-a-chip devices.

Fabricating and Laminating Films with Through-Holes and Engraved/Protruding Structures for 3D Micro/Nanofluidic Platforms

Micro/nanofluidic devices have become popular for delicately processing biological, material, and chemical samples. However, their reliance on 2D fabrication schemes has hindered further innovation. Here, a 3D manufacturing method is proposed through the innovation of laminated object manufacturing (LOM), which involves the selection of building materials as well as the development of molding and lamination techniques. Fabrication of interlayer films is demonstrated with both multi-layered micro-/nanostructures and through-holes, using an injection molding approach and establishing strategic principles of film design. Utilization of the multi-layered through-hole films in LOM allows reducing the number of alignments and laminations by at least two times compared to conventional LOM. Using a dual-curing resin for film fabrication, a surface-treatment-free and collapse-free lamination technique is shown for constructing 3D multiscale micro/nanofluidic devices with ultralow aspect ratio nanochannels. The 3D manufacturing method enables the development of a nanochannel-based attoliter droplet generator capable of 3D parallelization for mass production, which implies the remarkable potential to extend numerous existing 2D micro/nanofluidic platforms into a 3D framework.

A review on inertial microfluidic fabrication methods

In recent decades, there has been significant interest in inertial microfluidics due to its high throughput, ease of fabrication, and no need for external forces. The focusing efficiency of inertial microfluidic systems relies entirely on the geometrical features of microchannels because hydrodynamic forces (inertial lift forces and Dean drag forces) are the main driving forces in inertial microfluidic devices. In the past few years, novel microchannel structures have been propounded to improve particle manipulation efficiency. However, the fabrication of these unconventional structures has remained a serious challenge. Although researchers have pushed forward the frontiers of microfabrication technologies, the fabrication techniques employed for inertial microfluidics have not been discussed comprehensively. This review introduces the microfabrication approaches used for creating inertial microchannels, including photolithography, xurography, laser cutting, micromachining, microwire technique, etching, hot embossing, 3D printing, and injection molding. The advantages and disadvantages of these methods have also been discussed. Then, the techniques are reviewed regarding resolution, structures, cost, and materials. This review provides a thorough insight into the manufacturing methods of inertial microchannels, which could be helpful for future studies to improve the harvesting yield and resolution by choosing a proper fabrication technique.

TiO2 nanoparticle-Coated 3D-Printed porous monoliths enabling highly sensitive speciation of inorganic Cr, As, and Se

Post-printing functionalization can enhance the functionality and applicability of analytical devices manufactured using three-dimensional printing (3DP) technologies. In this study we developed a post-printing foaming-assisted coating scheme-through respective treatments with a formic acid (30%, v/v) solution and a sodium bicarbonate (0.5%, w/v) solution incorporating titanium dioxide nanoparticles (TiO2 NPs; 1.0%, w/v)-for in situ fabrication of TiO2 NP-coated porous polyamide monoliths in 3D-printed solid phase extraction columns, thereby enhancing the extraction efficiencies of Cr(III), Cr(VI), As(III), As(V), Se(IV), and Se(VI) for speciation of inorganic Cr, As, and Se species in high-salt-content samples when using inductively coupled plasma mass spectrometry. After optimizing the experimental conditions, the 3D-printed solid phase extraction columns with the TiO2 NP-coated porous monoliths extracted these species with 5.0- to 21.9-fold enhancements, relative to those obtained with the uncoated monolith, with absolute extraction efficiencies ranging from 84.5 to 98.3% and method detection limits ranging from 0.7 to 32.3 ng L-1. We validated the reliability of this multi-elemental speciation method through determination of these species in four reference materials [CASS-4 (nearshore seawater), SLRS-5 (river water), 1643f (fresh water), and Seronorm Trace Elements Urine L-2 (human urine); relative errors between certified and measured concentrations: 5.6 to +4.0%] and spike analyses of seawater, river water, agriculture waste, and human urine samples (spike recoveries: 96-104%; relative standard deviations of these measured concentrations all below 4.3%). Our results demonstrate that post-printing functionalization has great potential for future applicability in 3DP-enabling analytical methods.

Rapid microfluidics prototyping through variotherm desktop injection molding for multiplex diagnostics

In this work, we demonstrate an inexpensive method of prototyping microfluidics using a desktop injection molding machine. A centrifugal microfluidic device with a novel central filling mechanism was developed to demonstrate the technique. We overcame the limitations of desktop machines in replicating microfluidic features by variotherm heating and cooling the mold between 50 °C and 110 °C within two minutes. Variotherm heating enabled good replication of microfeatures, with a coefficient of variation averaging only 3.6% attained for the measured widths of 100 μm wide molded channels. Using this methodology, we produced functional polystyrene centrifugal microfluidic chips, capable of aliquoting fluids into 5.0 μL reaction chambers with 97.5% accuracy. We performed allele-specific loop-mediated isothermal amplification (AS-LAMP) reactions for genotyping CYP2C19 alleles on these chips. Readouts were generated using optical pH sensors integrated onto chips, by drop-casting sensor precursor solutions into reaction chambers before final chip assembly. Positive reactions could be discerned by decreases in pH sensor fluorescence, thresholded against negative control reactions lacking the primers for nucleic acid amplification and with time-to-results averaging 38 minutes. Variotherm desktop injection molding can enable researchers to prototype microfluidic devices more cost-effectively, in an iterative fashion, due to reduced costs of smaller, in-house molds. Designs prototyped this way can be directly translated to mass production, enhancing their commercialization potential and positive impacts.

Vat photopolymerization 3D printed microfluidic devices for organ-on-a-chip applications

Organs-on-a-chip, or OoCs, are microfluidic tissue culture devices with micro-scaled architectures that repeatedly achieve biomimicry of biological phenomena. They are well positioned to become the primary pre-clinical testing modality as they possess high translational value. Current methods of fabrication have facilitated the development of many custom OoCs that have generated promising results. However, the reliance on microfabrication and soft lithographic fabrication techniques has limited their prototyping turnover rate and scalability. Additive manufacturing, known commonly as 3D printing, shows promise to expedite this prototyping process, while also making fabrication easier and more reproducible. We briefly introduce common 3D printing modalities before identifying two sub-types of vat photopolymerization - stereolithography (SLA) and digital light processing (DLP) - as the most advantageous fabrication methods for the future of OoC development. We then outline the motivations for shifting to 3D printing, the requirements for 3D printed OoCs to be competitive with the current state of the art, and several considerations for achieving successful 3D printed OoC devices touching on design and fabrication techniques, including a survey of commercial and custom 3D printers and resins. In all, we aim to form a guide for the end-user to facilitate the in-house generation of 3D printed OoCs, along with the future translation of these important devices.

Centrifugation-Assisted Three-Dimensional Printing of Devices Embedded with Fully Enclosed Microchannels

The challenges in reliably removing the sacrificial material from fully enclosed microfluidic channels hinder the use of three-dimensional (3D) printing to create microfluidic devices with intricate geometries. With advances in printer resolution, the etching of sacrificial materials from increasingly smaller channels is poised to be a bottleneck using the existing techniques. In this study, we introduce a microfabrication approach that utilizes centrifugation to effortlessly and efficiently remove the sacrificial materials from 3D-printed microfluidic devices with densely packed microfeatures. We characterize the process by measuring the etch rate under different centrifugal forces and developed a theoretical model to estimate process parameters for a given geometry. The effect of the device layout on the centrifugal etching process is also investigated. We demonstrate the applicability of our approach on devices fabricated using inkjet 3D printing and stereolithography. Finally, the advantages of the introduced approach over commonly used injection-based etching of sacrificial material are experimentally demonstrated in direct comparisons. A robust method to postprocess additively manufactured geometries composed of intricate microfluidic channels can help utilize both the large printing volume and high spatial resolution afforded by 3D printing in creating a variety of devices ranging from scaffolds to large-scale microfluidic assays.

Tuning the fabrication of knotted reactors via 3D printing techniques and materials

Although three-dimensional (3D) printing technologies can customize a diverse range of devices, cross-3D printing technique/material comparisons aimed at optimizing the fabrication of analytical devices have been rare. In this study, we evaluated the surface features of the channels in knotted reactors (KRs) fabricated using fused deposition modeling (FDM) 3D printing [with poly(lactic acid) (PLA), polyamide, and acrylonitrile butadiene styrene filaments], and digital light processing and stereolithography 3D printing with photocurable resins. Also, their ability to retain Mn, Co, Ni, Cu, Zn, Cd, and Pb ions was evaluated to achieve the maximal sensitivities of these metal ions. After optimizing the techniques and materials for 3D printing of the KRs, the retention conditions, and the automatic analytical system, we observed good correlations (R > 0.9793) for the three 3D printing techniques in terms of the surface roughnesses of their channel sidewalls with respect to the signal intensities of their retained metal ions. The FDM 3D-printed PLA KR provided the best analytical performance, with the retention efficiencies of the tested metal ions all being greater than 73.9% and with the detection limits of the method ranging from 0.1 to 5.6 ng L^-1. We used this analytical method to perform analyses of the tested metal ions in several reference materials (CASS-4, SLEW-3, 1643f, and 2670a). Spike analyses of complicated real samples verified the reliability and applicability of this analytical method, highlighting the possibility of tuning 3D printing techniques and materials to optimize the fabrication of mission-oriented analytical devices.

A Regression Approach to Model Refractive Index Measurements of Novel 3D Printable Photocurable Resins for Micro-Optofluidic Applications

In this work, a quadratic polynomial regression model was developed to aid practitioners in the determination of the refractive index value of transparent 3D printable photocurable resins usable for micro-optofluidic applications. The model was experimentally determined by correlating empirical optical transmission measurements (the dependent variable) to known refractive index values (the independent variable) of photocurable materials used in optics, thus obtaining a related regression equation. In detail, a novel, simple, and cost-effective experimental setup is proposed in this study for the first time for collecting the transmission measurements of smooth 3D printed samples (roughness ranging between 0.04 and 2 μm). The model was further used to determine the unknown refractive index value of novel photocurable resins applicable in vat photopolymerization (VP) 3D printing techniques for manufacturing micro-optofluidic (MoF) devices. In the end, this study proved how knowledge of this parameter allowed us to compare and interpret collected empirical optical data from microfluidic devices made of more traditional materials, i.e., Poly(dimethylsiloxane) (PDMS), up to novel 3D printable photocurable resins suitable for biological and biomedical applications. Thus, the developed model also provides a quick method to evaluate the suitability of novel 3D printable resins for MoF device fabrication within a well-defined range of refractive index values (1.56; 1.70).

Engraving of stainless-steel wires to improve optical quality of closed-loop wire-guided flow jet systems for optical and X-ray spectroscopy

This paper describes performance enhancement developments to a closed-loop pump-driven wire-guided flow jet (WGJ) for ultrafast X-ray spectroscopy of liquid samples. Achievements include dramatically improved sample surface quality and reduced equipment footprint from 7 × 20 cm2 to 6 × 6 cm2, cost, and manufacturing time. Qualitative and quantitative measurements show that micro-scale wire surface modification yields significant improvements to the topography of the sample liquid surface. By manipulating their wettability, it is possible to better control the liquid sheet thickness and to obtain a smooth liquid sample surface, as demonstrated in this work.

Establishment of a Perfusion Process with Antibody-Producing CHO Cells Using a 3D-Printed Microfluidic Spiral Separator with Web-Based Flow Control

Monoclonal antibodies are increasingly dominating the market for human therapeutic and diagnostic agents. For this reason, continuous methods-such as perfusion processes-are being explored and optimized in an ongoing effort to increase product yields. Unfortunately, many established cell retention devices-such as tangential flow filtration-rely on membranes that are prone to clogging, fouling, and undesirable product retention at high cell densities. To circumvent these problems, in this work, we have developed a 3D-printed microfluidic spiral separator for cell retention, which can readily be adapted and replaced according to process conditions (i.e., a plug-and-play system) due to the fast and flexible 3D printing technique. In addition, this system was also expanded to include automatic flushing, web-based control, and notification via a cellphone application. This set-up constitutes a proof of concept that was successful at inducing a stable process operation at a viable cell concentration of 10-17 × 106 cells/mL in a hybrid mode (with alternating cell retention and cell bleed phases) while significantly reducing both shear stress and channel blockage. In addition to increasing efficiency to nearly 100%, this microfluidic device also improved production conditions by successfully separating dead cells and cell debris and increasing cell viability within the bioreactor.

Research on the Comparison Properties of PDMS Specimens Demolding Processes and the Mechanical Performance of Hollow-Solid Ratios of Flexible Telescopic Rods

The main motivation of this work was to demonstrate a hollow telescopic rod structure that could be used for minimally invasive surgery. The telescopic rods were fabricated using 3D printing technology to make mold flips. During fabrication, differences in biocompatibility, light transmission, and ultimate displacement were compared between telescopic rods fabricated via different processes, so as to select the appropriate process. To achieve these goals, flexible telescopic rod structures were designed and 3D-printed molds were fabricated using Fused Deposition Modeling (FDM) and Stereolithography (SLA) techniques. The results showed that the three molding processes had no impact on the doping of the PDMS specimens. However, the FDM molding process had lower surface flatness accuracy compared to SLA. The SLA mold flip fabrication exhibited superior surface accuracy and light transmission compared to the other methods. The sacrificial template method and the use of HTL direct demolding technique had no significant impact on cellular activity and biocompatibility, but the mechanical properties of the PDMS specimens were weakened after swelling recovery. The height and radius of the hollow rod were found to have a significant impact on the mechanical properties of the flexible hollow rod. The hyperelastic model was fitted appropriately with the mechanical test results, and the ultimate elongation increased with an increase in hollow-solid ratios under the uniform force.

Ultrahigh-Throughput Enzyme Engineering and Discovery in In Vitro Compartments

Novel and improved biocatalysts are increasingly sourced from libraries via experimental screening. The success of such campaigns is crucially dependent on the number of candidates tested. Water-in-oil emulsion droplets can replace the classical test tube, to provide in vitro compartments as an alternative screening format, containing genotype and phenotype and enabling a readout of function. The scale-down to micrometer droplet diameters and picoliter volumes brings about a >107-fold volume reduction compared to 96-well-plate screening. Droplets made in automated microfluidic devices can be integrated into modular workflows to set up multistep screening protocols involving various detection modes to sort >107 variants a day with kHz frequencies. The repertoire of assays available for droplet screening covers all seven enzyme commission (EC) number classes, setting the stage for widespread use of droplet microfluidics in everyday biochemical experiments. We review the practicalities of adapting droplet screening for enzyme discovery and for detailed kinetic characterization. These new ways of working will not just accelerate discovery experiments currently limited by screening capacity but profoundly change the paradigms we can probe. By interfacing the results of ultrahigh-throughput droplet screening with next-generation sequencing and deep learning, strategies for directed evolution can be implemented, examined, and evaluated.

The Additive Manufacturing Approach to Polydimethylsiloxane (PDMS) Microfluidic Devices: Review and Future Directions

This paper presents a comprehensive review of the literature for fabricating PDMS microfluidic devices by employing additive manufacturing (AM) processes. AM processes for PDMS microfluidic devices are first classified into (i) the direct printing approach and (ii) the indirect printing approach. The scope of the review covers both approaches, though the focus is on the printed mold approach, which is a kind of the so-called replica mold approach or soft lithography approach. This approach is, in essence, casting PDMS materials with the mold which is printed. The paper also includes our on-going effort on the printed mold approach. The main contribution of this paper is the identification of knowledge gaps and elaboration of future work toward closing the knowledge gaps in fabrication of PDMS microfluidic devices. The second contribution is the development of a novel classification of AM processes from design thinking. There is also a contribution in clarifying confusion in the literature regarding the soft lithography technique; this classification has provided a consistent ontology in the sub-field of the fabrication of microfluidic devices involving AM processes.

Low-Viscosity Polydimethylsiloxane Resin for Facile 3D Printing of Elastomeric Microfluidics

Microfluidics is a rapidly advancing technology with expansive applications but has been restricted by slow, laborious fabrication techniques for polydimethylsiloxane (PDMS)-based devices. Currently, 3D printing promises to address this challenge with high-resolution commercial systems but is limited by a lack of material advances in generating high-fidelity parts with micron-scale features. To overcome this limitation, a low-viscosity, photopolymerizable PDMS resin was formulated with a methacrylate-PDMS copolymer, methacrylate-PDMS telechelic polymer, photoabsorber, Sudan I, photosensitizer, 2-isopropylthioxanthone, and a photoinitiator, 2,4,6-trimethyl benzoyl diphenylphosphine oxide. The performance of this resin was validated on a digital light processing (DLP) 3D printer, an Asiga MAX X27 UV. Resin resolution, part fidelity, mechanical properties, gas permeability, optical transparency, and biocompatibility were investigated. This resin produced resolved, unobstructed channels as small as 38.4 (±5.0) µm tall and membranes as thin as 30.9 (±0.5) µm. The printed material had an elongation at break of 58.6% ± 18.8%, Young's modulus of 0.30 ± 0.04 MPa, and was highly permeable to O₂ (596 Barrers) and CO₂ (3071 Barrers). Following the ethanol extraction of the unreacted components, this material demonstrated optical clarity and transparency (>80% transmission) and viability as a substrate for in vitro tissue culture. This paper presents a high-resolution, PDMS 3D-printing resin for the facile fabrication of microfluidic and biomedical devices.

3D printed microfluidics: advances in strategies, integration, and applications

The ability to construct multiplexed micro-systems for fluid regulation could substantially impact multiple fields, including chemistry, biology, biomedicine, tissue engineering, and soft robotics, among others. 3D printing is gaining traction as a compelling approach to fabricating microfluidic devices by providing unique capabilities, such as 1) rapid design iteration and prototyping, 2) the potential for automated manufacturing and alignment, 3) the incorporation of numerous classes of materials within a single platform, and 4) the integration of 3D microstructures with prefabricated devices, sensing arrays, and nonplanar substrates. However, to widely deploy 3D printed microfluidics at research and commercial scales, critical issues related to printing factors, device integration strategies, and incorporation of multiple functionalities require further development and optimization. In this review, we summarize important figures of merit of 3D printed microfluidics and inspect recent progress in the field, including ink properties, structural resolutions, and hierarchical levels of integration with functional platforms. Particularly, we highlight advances in microfluidic devices printed with thermosetting elastomers, printing methodologies with enhanced degrees of automation and resolution, and the direct printing of microfluidics on various 3D surfaces. The substantial progress in the performance and multifunctionality of 3D printed microfluidics suggests a rapidly approaching era in which these versatile devices could be untethered from microfabrication facilities and created on demand by users in arbitrary settings with minimal prior training.

Application of 3D Printing Technology in Sensor Development for Water Quality Monitoring

The development of sensors for water quality monitoring is crucial to protect water quality, aquatic biota and human health. Traditional sensor manufacturing methods have significant drawbacks, such as low fabrication freedom, limited material choice and expensive manufacturing cost. As a possible alternative method, 3D printing technologies are increasingly popular in sensor development due to their high versatility, fast fabrication/modification, powerful processing of different materials and ease of incorporation with other sensor systems. Surprisingly, a systematic review examining the application of 3D printing technology in water monitoring sensors has not yet been conducted. Here, we summarized the development history, market share and advantages/disadvantages of typical 3D printing techniques. Specifically focused on the 3D-printed sensor for water quality monitoring, we then reviewed the applications of 3D printing in the development of sensors' supporting platform, cell, sensing electrode as well as all-3D-printed sensors. The fabrication materials and processing, and the sensor's performances regarding detected parameters, response time and detection limit/sensitivity, were also compared and analyzed. Finally, the current drawbacks of 3D-printed water sensors and potential directions for future study were discussed. This review will substantially promote the understanding of 3D printing technology used in water sensor development and benefit the protection of water resources.

Scalable Liposome Synthesis by High Aspect Ratio Microfluidic Flow Focusing

Microfluidic flow focusing provides an efficient approach to the generation of nanoscale lipid vesicles of tunable size and low size variance. Scalable nanoliposome synthesis over a wide range of production rates can be readily achieved using a high aspect ratio flow focusing device fabricated by widely available additive manufacturing methods. Here we detail methods for the manufacture and operation of a 3D-printed microfluidic flow focusing technology enabling the synthesis of liposomes with modal diameters ranging from ca. 50-200 nm at production rates up to several hundred milligrams lipid per hour.

V, Ortega-Aguilera R, Zapata PA, Cataño FA, Mestra AS. Numerical Study About Nanofluids of Spherical and Tube-Shaped TiO2 Nanomaterials on the Thermal Performance and Entropy Generation of Different Cross-Section Microchannel Heat Sinks

We numerically evaluated the thermal performance of microchannel heat sinks, considering rectangular, hexagonal, and circular cross-sections. Moreover, as a passive heat transfer augmentation technique, dimples were added to improve the rectangular microchannel heat sinks. These simulations use nanofluids based on TiO2 nanoparticles or nanotubes dispersed in bidistilled water as working fluids. The mathematical model considered variable thermophysical properties of the nanofluids; for this purpose, polynomial fittings correlate the dependence of the thermophysical properties on the temperature. We considered a heat flux of q″ = 50 W/cm2 at the microchannel’s lower surface as a boundary condition along with laminar flow conditions. The numerical simulations allowed the Nusselt numbers and entropy generation calculation, which were the basis for the thermal performance calculation. Regarding the effect of TiO2 nanoparticles shape, spherical TiO2 nanoparticles based nanofluids using rectangular microchannels improve the Nusselt number. Moreover, the frictional entropy decreases with nanofluids based on TiO2 nanotubes, but the thermal entropy decreases with nanofluids based on TiO2 nanotubes. Incorporating dimples in the rectangular microchannel enhances the Nusselt numbers and lowers the entropy generation. Considering the Reynolds number range and from the perspective of Nusselt number and entropy generation, we concluded that the microchannels must be operated at a high Reynolds number to improve the microchannel heat sinks thermal performance.

A Solution to the Clearance Problem of Sacrificial Material in 3D Printing of Microfluidic Devices

3D-printing is poised to enable remarkable advances in a variety of fields, such as artificial muscles, prosthetics, biomedical diagnostics, biofuel cells, flexible electronics, and military logistics. The advantages of automated monolithic fabrication are particularly attractive for complex embedded microfluidics in a wide range of applications. However, before this promise can be fulfilled, the basic problem of removal of sacrificial material from embedded microchannels must be solved. The presented work is an experimental proof of principle of a novel technique for clearance of sacrificial material from embedded microchannels in 3D-printed microfluidics. The technique demonstrates consistent performance (~40-75% clearance) in microchannels with printed width of ~200 µm and above. The presented technique is thus an important enabling tool in achieving the promise of 3D printing in microfluidics and its wide range of applications.