Microfluidic Connectors Research Articles

Characterization and Evaluation of 3D-Printed Connectors for Microfluidics.

3D printing is regarded as a useful tool for the fabrication of microfluidic connectors to overcome the challenges of time consumption, clogging, poor alignment and bulky fixtures existing for current interconnections. 3D-printed connectors without any additional components can be directly printed to substrate with an orifice by UV-assisted coaxial printing. This paper further characterized and evaluated 3D-printed connectors fabricated by the proposed method. A process window with an operable combination of flow rates was identified. The outer flow rate could control the inner channel dimensions of 3D-printed connectors, which were expected to achieve less geometric mismatch of flow paths in microfluidic interfaces. The achieved smallest inner channel diameter was around 120 µm. Furthermore, the withstood pressure of 3D-printed connectors was evaluated to exceed 450 kPa, which could enable microfluidic chips to work at normal pressure.

Directly Printed Hollow Connectors for Microfluidic Interconnection with UV-Assisted Coaxial 3D Printing

Effective and reliable interconnections are crucial for microfluidics to connect with the macro world. Current microfluidic interfaces are still bulky, expensive, or with issues of clogging and material limitation. In this study, a novel ultraviolet (UV)-assisted coaxial three-dimensional (3D) printing approach was proposed to fabricate hollow microfluidic connectors with advantages of rapid prototyping, fixture-free, and materials compatible. An assembled coaxial nozzle was designed to enable co-flow extrusion, where the inner flow (water) served as the sacrificial layer and the outer flow (adhesive) was cured for shell formation. Furthermore, a converged UV-LED light source was attached to the coaxial nozzle for UV curing of adhesives. UV rheological characterizations were performed to study the UV curing kinematics, and the gelation time was employed to describe the state transition behaviors of UV curable adhesives used in the study. To explore requirements for successful hollow connectors direct printing, processing criteria such as co-flow regime and pre-cure time were investigated. The hollow connectors with an inner channel diameter of ~150 μ m and a height of 5 mm were successfully printed on polymethyl methacrylate (PMMA) and glass substrate. The integration feasibility of the proposed method was also demonstrated by the presented microfluidic device with printed hollow connectors.

Object-In-Fluid Framework in Modeling of Blood Flow in Microfluidic Channels

We present a fully three-dimensional computational model of red blood cells and their flow in a fluid. This model includes all components necessary to capture important physical and biological aspects of the cell flow. It comprises descriptions of elasticity of the cell membrane, cell-cell interactions, two-way cell-fluid interaction, and adhesion of cell to surfaces. Using this model, we analyze different processes involving flow of cells. We present the results of ongoing research concerning the development of model for cell adhesion, the analysis of microfluidic devices with periodic obstacle arrays, the optimization of microfluidic connectors and biological process of red blood cells formation from reticulocytes.

A multifunctional, plug-and-play and low-cost microfluidic connector system based on electronics standard

In this study, we utilized the electrical engineering standard of a 2.54 mm pin-header connector to create two standard microfluidic connectors and two accessories for different applications.

Easy-to-realise Polyvinylsiloxane Microfluidic Connectors for PDMS Chips

The connection of tubes to a polydimethylsiloxane (PDMS) device can usually not be realised easily. Tube connectors embedded in the PDMS structure have a large foot print. Thick layers of PDMS in which the tubes or needles can hold hinders the visualisation of sample within the device. In this contribution we present microfluidic connectors for PDMS chips realized by easy-to-use elastomeric impression material polyvinylsiloxane (PVS). PVS cylinders were added to a pre-cured PDMS chip and ready to use within five minutes without the need of exposure to high temperatures or the use of additional glues. The robustness of the PVS connectors has been demonstrated through pull-tests and liquid pressure tests.

Capillary microchannel fabrication using plasma polymerized TMDS for fluidic MEMS technology

This paper reports the first use of cold plasma deposition of polymerizable monomers for the fast, cost-effective and easy fabrication of buried air microchannels. A new method named ‘plasma polymerization on sacrificial layer’ (PPSL) is presented. It consists in the direct polymerization of tetramethyldisiloxane (TMDS) on a photopatterned sacrificial layer. Channels are formed with only one lithographic mask and without any etching or bonding process. The use of polymerized TMDS allows rapid creation of capillarity-driven flow systems with the channel width ranging from 4 to 700 µm without pillars. Channels are characterized and successfully tested. Capillary forces draw water, as well as aqueous solution into the channel from the inlet reservoir to the outlet one, avoiding the need of microfluidic connectors with the surrounding environment. Filling of the capillaries is very fast. It reaches the initial velocity of 4.4 cm s−1 with the geometries and water used here. In addition, PPSL easily allows the building of transparent channel networks directly on processed electrochemical or electromagnetic components. An example of one such integrated fluidic microelectromechanical system (MEMS) is described.

Microfluidic connectors by ultrasonic welding

We attempted ultrasonic welding as a technique for the bonding of connectors to microfluidic devices. Different schemes of the method were explored based on different designs of the connectors to achieve a strong, minimal dead-volume connection. Results showed that without the use of inserts, there would be unwanted flow of melt material into the conduit of the connector causing blockage. With the small scale of welding, the use of inserts and proper fixture designs were necessary to block or direct melt flow during the process. The process times were well within 1 s. Two connectors were also simultaneously welded on a microfluidic device to demonstrate the possibility of further increase in productivity in the technique. The device was able to withstand a minimum of 6 bars (gauge) pressure. Where dead-volume is not a concern, it was possible to create connection without the use of an insert by employing different connector geometry and changing the scheme of the welding. It was found out that the width of the welding zone is limited by the width of the sleeve (application of ultrasonic energy to the connector). Hence, the welding zone would proceed no further towards the conduit and causing blockage.

Microbioreactors for Bioprocess Development

As a step toward high-throughput bioprocess development, we present design, fabrication, and characterization of polymer based microbioreactors integrated with automated sensors and actuators. The devices are realized, in increasing levels of complexity, in poly(dimethylsiloxane) and poly(methyl methacrylate) by micromachining and multilayer thermal compression bonding procedures. Online optical measurements for optical density, pH, and dissolved oxygen are integrated. Active mixing is made possible by a miniature magnetic stir bar. Plug-in-and-flow microfluidic connectors and fabricated polymer micro-optical lenses/connectors are integrated in the microbioreactors for fast set up and easy operation. Application examples demonstrate the feasibility of culturing microbial cells, specifically Escherichia coli, in 150 μL-volume bioreactors in batch, continuous, and fed-batch operations. (JALA 2007;12:143–51)

Hand-Held Microanalytical Instrument for Chip-Based Electrophoretic Separations of Proteins

The design, fabrication, and demonstration of a hand-held microchip-based analytical instrument for detection and identification of proteins and other biomolecules are reported. The overall system, referred to as muChemLab, has a modular design that provides for reliability and flexibility and that facilitates rapid assembly, fluid and microchip replacement, troubleshooting, and sample analysis. Components include two independent separation modules that incorporate interchangeable fluid cartridges, a 2-cm-square fused-silica microfluidic chip, and a miniature laser-induced fluorescence detection module. A custom O-ring sealed manifold plate connects chip access ports to a fluids cartridge and a syringe injection port and provides sample introduction and world-to-chip interface. Other novel microfluidic connectors include capillary needle fittings for fluidic connection between septum-sealed fluid reservoirs and the manifold housing the chip, enabling rapid chip priming and fluids replacement. Programmable high-voltage power supplies provide bidirectional currents up to 100 microAlpha at 5000 V, enabling real-time current and voltage monitoring and facilitating troubleshooting and methods development. Laser-induced fluorescence detection allows picomolar (10(-11) M) detection sensitivity of fluorescent dyes and nanomolar sensitivity (10(-9) M) for fluorescamine-labeled proteins. Migration time reproducibility was significantly improved when separations were performed under constant current control (0.5-1%) as compared to constant voltage control (2-8%).