3D printed fittings and fluidic modules for customizable droplet generators

3D Printed Customizable Microsampling Devices for Neuroscience Applications

Multifunctional devices that incorporate chemical or physical measurements combined with ways to manipulate brain tissue via drug delivery, electrical stimulation, or light for optogenetics are desired by neuroscientists. The next generation in vivo brain devices will likely utilize the extensive flexibility and rapid processing of 3D printing. This Perspective demonstrates how close we are to this reality for advanced neuroscience measurements. 3D printing provides the opportunity to improve microsampling-based devices in ways that have not been previously available. Not only can 3D printing be used for actual device creation, but it can also allow printing of peripheral objects necessary to assemble functional devices. The most probable 3D printing set up for microsampling devices with appropriate nm to μm feature size will likely require 2-photon polymerization-based printers. This Perspective describes the advantages and challenges for 3D printing of microsampling devices as an initial step to meet the next generation device needs of neuroscientists.

Three-Dimensional Printing Enabled Droplet Microfluidic Device for Real-Time Monitoring of Single-Cell Viability and Blebbing Activity

Droplet-based microfluidics with the characteristics of high throughput, low sample consumption, increasing reaction speed, and homogeneous volume control have been demonstrated as a useful platform for biomedical research and applications. The traditional fabrication methods of droplet microfluidics largely rely on expensive instruments, sophisticated operations, and even the requirement of an ultraclean room. In this manuscript, we present a 3D printing-based droplet microfluidic system with a specifically designed microstructure for droplet generation aimed at developing a more accessible and cost-effective method. The performance of droplet generation and the encapsulation capacity of the setup were examined. The device was further applied to measure the variation in cell viability over time and monitor the cell's blebbing activity to investigate its potential ability and feasibility for single-cell analysis. The result demonstrated that the produced droplets remained stable enough to enable the long-time detection of cell viability. Additionally, cell membrane protrusions featuring the life cycle of bleb initiation, expansion, and retraction can be well-observed. Three-dimensional printing-based droplet microfluidics benefit from the ease of manufacture, which is expected to simplify the fabrication of microfluidics and expand the application of the droplet approach in biomedical fields.

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.

A 3D-Printed Standardized Modular Microfluidic System for Droplet Generation

Droplet-based microfluidics has a variety of applications, such as material synthesis and single-cell analysis. In this paper, we propose a modular microfluidic system using projection micro-stereolithography three-dimensional (3D) printing technology for droplet generation. All modules are designed using a standard cubic structure with a specific leakage-free connection interface. Versatile droplets, including single droplets, alternating droplets, merged droplets, and Janus particles, have been successfully produced. The droplet size and the generation rate can be flexibly controlled by adjusting the flow rates. The influence of the flow rate fraction between the discrete phase and the continuous phase over the generation of the alternating and merged droplets is discussed. Furthermore, the 'UV curing' module can be employed to solidify the generated droplets to avoid coalescence and fix the status of the Janus particles. The proposed modular droplet generators are promising candidates for various chemical and biological applications, such as single-cell incubation, screening of protein crystallization conditions, synthesis of nanoparticles, and gene delivery. In addition, we envision that more functional modules, e.g., valve, microreactor, and detection modules, could be developed, and the 3D standardized modular microfluidics could be further applied to other complex systems, i.e., concentration gradient generators and clinical diagnostic systems.

A Monolithic 3D Printed Axisymmetric Co-Flow Single and Compound Emulsion Generator

We report a microfluidic droplet generator which can produce single and compound droplets using a 3D axisymmetric co-flow structure. The design considered for the fabrication of the device integrated a user-friendly and cost-effective 3D printing process. To verify the performance of the device, single and compound emulsions of deionized water and mineral oil were generated and their features such as size, generation frequency, and emulsion structures were successfully characterized. In addition, the generation of bio emulsions such as alginate and collagen aqueous droplets in mineral oil was demonstrated in this study. Overall, the monolithic 3D printed axisymmetric droplet generator could offer any user an accessible and easy-to-utilize device for the generation of single and compound emulsions.

Design and fabrication of micro/nanofluidics devices and systems

This chapter provides an overview of the science, engineering, and design methods required in the development of micro/nanofluidic devices. Section 2 provides the scientific background of fluid mechanics and physical phenomena in micro/nanoscale. Section 3 gives a brief overview of the existing fabrication techniques employed in micro/nanofluidics. The techniques are grouped into three categories: (1) subtractive manufacturing, (2) formative manufacturing, and (3) additive manufacturing. The advantages and disadvantages of each manufacturing technique are also discussed. Implementation of the fluidic devices beyond laboratory demonstrations is not trivial, which requires a good understanding of the problems of interest and the end-users. To that end, Section 4 introduces the design thinking approach and its application to develop micro/nanofluidic devices. Finally, Section 5 concludes the chapter with future outlooks.

3D Printing to Increase the Flexibility of the Chemical Synthesis of Biologically Active Molecules: Design of On-Demand Gas Generation Reactors

The development of new drugs is accelerated by rapid access to functionalized and D-labeled molecules with improved activity and pharmacokinetic profiles. Diverse synthetic procedures often involve the usage of gaseous reagents, which can be a difficult task due to the requirement of a dedicated laboratory setup. Here, we developed a special reactor for the on-demand production of gases actively utilized in organic synthesis (C2H2, H2, C2D2, D2, and CO2) that completely eliminates the need for high-pressure equipment and allows for integrating gas generation into advanced laboratory practice. The reactor was developed by computer-aided design and manufactured using a conventional 3D printer with polypropylene and nylon filled with carbon fibers as materials. The implementation of the reactor was demonstrated in representative reactions with acetylene, such as atom-economic nucleophilic addition (conversions of 19-99%) and nickel-catalyzed S-functionalization (yields 74-99%). One of the most important advantages of the reactor is the ability to generate deuterated acetylene (C2D2) and deuterium gas (D2), which was used for highly significant, atom-economic and cost-efficient deuterium labeling of S,O-vinyl derivatives (yield 68-94%). Successful examples of their use in organic synthesis are provided to synthesize building blocks of heteroatom-functionalized and D-labeled biologically active organic molecules.

Hydrophilic modification of SLA 3D printed droplet generators by photochemical grafting

Few droplet generators manufactured using desktop stereolithography 3D printers have been reported in the literature. Moreover, 3D printed microfluidic chips are typically hydrophobic, limiting their application to water in oil droplets. Herein, we present designs for concentric and planar 3D printed microfluidic devices suitable for making polymeric microparticles using an off-the-shelf commercial stereolithography printer and resin. The devices consist of a microscope slide, binder clips, and printed components. Channels were modified by an ultraviolet grafting of methacrylic acid to the surface of chips, yielding a hydrophilic coating without modification to the bulk polymer. The water contact angle decreased from 97.0° to 25.4° after grafting. The presence of the coating was confirmed by microscopy and spectroscopy techniques. Polystyrene microparticles in the <100 μm size range were generated with varying molecular weights using the described microfluidic chips. Our work provides a facile method to construct droplet generators from commercial stereolithography printers and resins, and a rapid surface modification technique that has been under-utilized in 3D printed microfluidics. A wide range of microfluidic devices for other applications can be engineered using the methods described.

A versatile method of manufacturing and directly modifying the surfaces of 3D printed microfluidic devices was developed. The device functionality was demonstrated by producing o/w emulsions that yielded polystyrene microspheres.

Evaluation of 3D-printed molds for fabrication of non-planar microchannels

Replica obtained from micromolds patterned by simple photolithography has features with uniform heights, and attainable microchannels are thus quasi-two-dimensional. Recent progress in three-dimensional (3D) printing has enabled facile desktop fabrication of molds to replicate microchannels with varying heights. We investigated the replica obtained from four common techniques of 3D printing-fused deposition modeling, selective laser sintering, photo-polymer inkjet printing (PJ), and stereolithography (SL)-for the suitability to form microchannels in terms of the surface roughness inherent to the mechanism of 3D printing. There have been limited quantitative studies that focused on the surface roughness of a 3D-printed mold with different methods of 3D printing. We discussed that the surface roughness of the molds affected (1) transparency of the replica and (2) delamination pressure of poly(dimethylsiloxane) replica bonded to flat glass substrates. Thereafter, we quantified the accuracy of replication from 3D-printed molds by comparing the dimensions of the replicated parts to the designed dimensions and tested the ability to fabricate closely spaced microchannels. This study suggested that molds printed by PJ and SL printers were suitable for replica molding to fabricate microchannels with varying heights. The insight from this study shall be useful to fabricate 3D microchannels with controlled 3D patterns of flows guided by the geometry of the microchannels.

3D printing direct to industrial roll-to-roll casting for fast prototyping of scalable microfluidic systems

Microfluidic technologies have enormous potential to offer breakthrough solutions across a wide range of applications. However, the rate of scale-up and commercialization of these technologies has lagged significantly behind promising breakthrough developments in the lab, due at least in part to the problems presented by transitioning from benchtop fabrication methods to mass-manufacturing. In this work, we develop and validate a method to create functional microfluidic prototype devices using 3D printed masters in an industrial-scale roll-to-roll continuous casting process. There were no significant difference in mixing performance between the roll-to-roll cast devices and the PDMS controls in fluidic mixing tests. Furthermore, the casting process provided information on the suitability of the prototype microfluidic patterns for scale-up. This work represents an important step in the realization of high-volume prototyping and manufacturing of microfluidic patterns for use across a broad range of applications.

Enabling intensification of multiphase chemical processes with additive manufacturing

Fixed bed supports of various materials (metal, ceramic, polymer) and geometries are used to enhance the performance of many unit operations in chemical processes. Consider first metal and ceramic monolith support structures, which are typically extruded. Extruded monoliths contain regular, parallel channels enabling high throughput because of the low pressure drop accompanying high flow rate. However, extruded channels have a low surface-area-to-volume ratio resulting in low contact between the fluid phase and the support. Additive manufacturing, also referred to as three dimensional printing (3DP), can be used to overcome these disadvantages by offering precise control over key design parameters of the fixed bed including material-of-construction and total bed surface area, as well as accommodating system integration features compatible with continuous flow chemistry. These design parameters together with optimized extrinsic process conditions can be tuned to prepare customizable separation and reaction systems based on objectives for chemical process and/or the desired product. We discuss key elements of leveraging the flexibility of additive manufacturing to intensification with a focus on applications in continuous flow processes and disperse, multiphase systems enabling a range of scalable chemistry spanning discovery to manufacturing operations.

Three-Dimensional Printed Devices in Droplet Microfluidics

Droplet microfluidics has become the most promising subcategory of microfluidics since it contributes numerous applications to diverse fields. However, fabrication of microfluidic devices for droplet formation, manipulation and applications is usually complicated and expensive. Three-dimensional printing (3DP) provides an exciting alternative to conventional techniques by simplifying the process and reducing the cost of fabrication. Complex and novel structures can be achieved via 3DP in a simple and rapid manner, enabling droplet microfluidics accessible to more extensive users. In this article, we review and discuss current development, opportunities and challenges of applications of 3DP to droplet microfluidics.

Microfluidic Chips for Life Sciences-A Comparison of Low Entry Manufacturing Technologies

Microfluidic water-in-oil droplets are a versatile tool for biological and biochemical applications due to the advantages of extremely small monodisperse reaction vessels in the pL-nL range. A key factor for the successful dissemination of this technology to life science laboratory users is the ability to produce microfluidic droplet generators and related accessories by low-entry barrier methods, which enable rapid prototyping and manufacturing of devices with low instrument and material costs. The direct, experimental side-by-side comparison of three commonly used additive manufacturing (AM) methods, namely fused deposition modeling (FDM), inkjet printing (InkJ), and stereolithography (SLA), is reported. As a benchmark, micromilling (MM) is used as an established method. To demonstrate which of these methods can be easily applied by the non-expert to realize applications in topical fields of biochemistry and microbiology, the methods are evaluated with regard to their limits for the minimum structure resolution in all three spatial directions. The suitability of functional SLA and MM chips to replace classic SU-8 prototypes is demonstrated on the basis of representative application cases.