Improving the Resolution of 3D-Printed Molds for Microfluidics by Iterative Casting-Shrinkage Cycles

Hydrogel-based 3D fabrication of multiple replicas with varying sizes and materials from a single template via iterative shrinking

3D printing technologies have been widely used for the rapid prototyping of 3D structures, but their application in a broader context has been hampered by their low printing throughput. For the same structures to be produced in a variety of sizes and materials, each must be printed separately, which increases time and cost. Replicating 3D-printed structures in a variety of sizes using a molding process with size-tunable molds could be a solution, but it has only been applied to simple structures, such as those with tapered or vertical profiles. This work demonstrates the generation of multiple replicas of varying sizes and materials from a single 3D-printed template with complex geometries by using molds made of stretchable hydrogel that shrink isotropically. We optimize hydrogel compositions to synthesize a hydrogel that is highly stretchable and shrinks isotropically in all directions. The high stretchability of this hydrogel allows for the removal of complex 3D-printed templates from hydrogel molds. The cavities of the hydrogel molds are then filled with polycaprolactone (PCL) and dried at 80 °C. As the hydrogel shrinks due to drying, the melted PCL fragments completely fill the cavities. The entire process can be repeated to produce multiple replicas in a variety of sizes and materials. Replicas that are one-tenth of the size of the original printed template can be produced. Finally, we demonstrate how our method can be used to reduce the size of interconnected geometries, which would be impossible to achieve using traditional molding processes.

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.

Highly flexible elastomer microfluidic chip for single cell manipulation

New materials and fabrication technologies have significantly boosted the development of lab-on-a-chip technologies and functionalities. In this work, we developed a highly flexible elastomer microfluidic chip with a microchannel with a minimum width of ∼5 μm manufactured by imprinting onto an SU-8 template. We found that the deformation induced in the microstructures by manual stretching of the chip is higher than that for the chip itself, which we attribute to the stress concentration of microstructures. Here, we demonstrate that the elastomer enables the manipulation of single cells, such as dynamic trapping-releasing operations, by simply stretching and releasing the elastomer chip.

Modular microfluidic systems cast from 3D-printed molds for imaging leukocyte adherence to differentially treated endothelial cultures

Microfluidic systems are very useful for in vitro studies of interactions between blood cells and vascular endothelial cells under flow, and several commercial solutions exist. However, the availability of customizable, user-designed devices is largely restricted to researchers with expertise in photolithography and access to clean room facilities. Here we describe a strategy for producing tailor-made modular microfluidic systems, cast in PDMS from 3D-printed molds, to facilitate studies of leukocyte adherence to endothelial cells. A dual-chamber barrier module was optimized for culturing two endothelial cell populations, separated by a 250 μm wide dividing wall, on a glass slide. In proof-of-principle experiments one endothelial population was activated by TNFα, while the other served as an internal control. The barrier module was thereafter replaced with a microfluidic flow module, enclosing both endothelial populations in a common channel. A suspension of fluorescently-labeled leukocytes was then perfused through the flow module and leukocyte interactions with control and TNFα-treated endothelial populations were monitored in the same field of view. Time-lapse microscopy analysis confirmed the preferential attachment of leukocytes to the TNFα-activated endothelial cells. We conclude that the functionality of these modular microfluidic systems makes it possible to seed and differentially activate adherent cell types, and conduct controlled side-by-side analysis of their capacity to interact with cells in suspension under flow. Furthermore, we outline a number of practical considerations and solutions associated with connecting and switching between the microfluidic modules, and the advantages of simultaneously and symmetrically analyzing control and experimental conditions in such a microfluidic system.

3D-printed miniaturized fluidic tools in chemistry and biology

3D printing (3DP), an additive manufacturing (AM) approach allowing for rapid prototyping and decentralized fabrication on-demand, has become a common method for creating parts or whole devices. The wide scope of the AM extends from organized sectors of construction, ornament, medical, and R&D industries to individual explorers attributed to the low cost, high quality printers along with revolutionary tools and polymers. While progress is being made but big manufacturing challenges are still there. Considering the quickly shifting narrative towards miniaturized analytical systems (MAS) we focus on the development/rapid prototyping and manufacturing of MAS with 3DP, and application dependent challenges in engineering designs and choice of the polymeric materials and provide an exhaustive background to the applications of 3DP in biology and chemistry. This will allow readers to perceive the most important features of AM in creating (i) various individual and modular components, and (ii) complete integrated tools.

3D nanofabrication inside rapid prototyped microfluidic channels showcased by wet-spinning of single micrometre fibres

Microfluidics is an established multidisciplinary research domain with widespread applications in the fields of medicine, biotechnology and engineering. Conventional production methods of microfluidic chips have been limited to planar structures, preventing the exploitation of truly three-dimensional architectures for applications such as multi-phase droplet preparation or wet-phase fibre spinning. Here the challenge of nanofabrication inside a microfluidic chip is tackled for the showcase of a spider-inspired spinneret. Multiphoton lithography, an additive manufacturing method, was used to produce free-form microfluidic masters, subsequently replicated by soft lithography. Into the resulting microfluidic device, a three-dimensional spider-inspired spinneret was directly fabricated in-chip via multiphoton lithography. Applying this unprecedented fabrication strategy, the to date smallest printed spinneret nozzle is produced. This spinneret resides tightly sealed, connecting it to the macroscopic world. Its functionality is demonstrated by wet-spinning of single-digit micron fibres through a polyacrylonitrile coagulation process induced by a water sheath layer. The methodology developed here demonstrates fabrication strategies to interface complex architectures into classical microfluidic platforms. Using multiphoton lithography for in-chip fabrication adopts a high spatial resolution technology for improving geometry and thus flow control inside microfluidic chips. The showcased fabrication methodology is generic and will be applicable to multiple challenges in fluid control and beyond.

Straightforward and Ultrastable Surface Modification of Microfluidic Chips with Norepinephrine Bitartrate Improves Performance in Immunoassays

Polymers are commonly used materials for microfluidic chip fabrication, because they are standardized in fabrication and low in cost. However, most polymeric materials that are readily fabricated on the industrial scale are hydrophobic, which is inconvenient for the injection and flow of the aqueous solution, resulting in poor analytical performance for biochemical assays. In this work, we present a straightforward and ultrastable surface modification process for polymeric chips. A one-step modification by using norepinephrine bitartrate monohydrate as a modification reagent is completed at room temperature. The hydrophilicity of the polymeric surfaces increases dramatically. Surface modification is stable for at least 2.5 years, allowing for autoinjection of aqueous solution into the channels. The chips are applied in the immunoassay of alpha-fetoprotein (AFP). The low nonspecific adsorption after modification results in significantly decreased background noise, optimized signal-to-noise ratios (SNR), and dramatically enhanced reproducibility of the immunoassay. Thirty clinical human serum samples are analyzed; these results strongly correlated with the values obtained using commercial test kits. We anticipate that this surface modification method can be used for immunoassay devices in analytical and biosensing technology.

3D Micropatterned All-Flexible Microfluidic Platform for Microwave-Assisted Flow Organic Synthesis

A large-area, all-flexible, microwaveable polydimethoxysilane microfluidic reactor was fabricated by using a 3D printing system. The sacrificial microchannels were printed on polydimethoxysilane substrates by a direct ink writing method using water-soluble Pluronic F-127 ink and then encapsulated between polydimethoxysilane layers. The structure of micron-sized channels was analyzed by optical and electron microscopy techniques. The fabricated flexible microfluidic reactors were utilized for the acetylation of different amines under microwave irradiation to obtain acetamides in shorter reaction times and good yields by flow organic synthesis.