Interconnected reversible lab-on-a-chip technology

Leakage pressures for gasketless superhydrophobic fluid interconnects for modular lab-on-a-chip systems

Chip-to-chip and world-to-chip fluidic interconnections are paramount to enable the passage of liquids between component chips and to/from microfluidic systems. Unfortunately, most interconnect designs add additional physical constraints to chips with each additional interconnect leading to over-constrained microfluidic systems. The competing constraints provided by multiple interconnects induce strain in the chips, creating indeterminate dead volumes and misalignment between chips that comprise the microfluidic system. A novel, gasketless superhydrophobic fluidic interconnect (GSFI) that uses capillary forces to form a liquid bridge suspended between concentric through-holes and acting as a fluid passage was investigated. The GSFI decouples the alignment between component chips from the interconnect function and the attachment of the meniscus of the liquid bridge to the edges of the holes produces negligible dead volume. This passive seal was created by patterning parallel superhydrophobic surfaces (water contact angle ≥ 150°) around concentric microfluidic ports separated by a gap. The relative position of the two polymer chips was determined by passive kinematic constraints, three spherical ball bearings seated in v-grooves. A leakage pressure model derived from the Young-Laplace equation was used to estimate the leakage pressure at failure for the liquid bridge. Injection-molded, Cyclic Olefin Copolymer (COC) chip assemblies with assembly gaps from 3 to 240 µm were used to experimentally validate the model. The maximum leakage pressure measured for the GSFI was 21.4 kPa (3.1 psig), which corresponded to a measured mean assembly gap of 3 µm, and decreased to 0.5 kPa (0.073 psig) at a mean assembly gap of 240 µm. The effect of radial misalignment on the efficacy of the gasketless seals was tested and no significant effect was observed. This may be a function of how the liquid bridges are formed during the priming of the chip, but additional research is required to test that hypothesis.

Large-Area and High-Throughput PDMS Microfluidic Chip Fabrication Assisted by Vacuum Airbag Laminator

One of the key fabrication steps of large-area microfluidic devices is the flexible-to-hard sheet alignment and pre-bonding. In this work, the vacuum airbag laminator (VAL) which is commonly used for liquid crystal display (LCD) production has been applied for large-area microfluidic device fabrication. A straightforward, efficient, and low-cost method has been achieved for 400 × 500 mm² microfluidic device fabrication. VAL provides the advantages of precise alignment and lamination without bubbles. Thermal treatment has been applied to achieve strong PDMS⁻glass and PDMS⁻PDMS bonding with maximum breakup pressure of 739 kPa, which is comparable to interference-assisted thermal bonding method. The fabricated 152 × 152 mm² microfluidic chip has been successfully applied for droplet generation and splitting.

Gecko gaskets for self-sealing and high-strength reversible bonding of microfluidics

We report in this work a novel reversible bonding technique for elastomeric microfluidic devices by integrating gecko-inspired dry adhesives with microfluidic channels which greatly enhances the bonding strength of reversibly sealed channels. The concept is applicable to nearly any elastomer and can be used to bond against any smooth surface which allows for van der Waals interactions. It does not require any solvents or glues or sources for plasma activation or thermal-compressive loading to aid the bonding process and is achievable at zero extra cost. We also demonstrate a quick fabrication technique involving soft master thermo-compressive molding of these microfluidic devices with thermoplastic elastomers. The resultant devices can be used for both pressure driven and non-pressure driven flows. We report the maximum contained pressure of these devices manufactured from two grades of styrene ethylene butylene styrene (SEBS) by conducting a burst pressure test with various substrates.

Solder-based chip-to-tube and chip-to-chip packaging for microfluidic devices

Constructing a microsystem compatible with a large variety of chemistries requires a system design that will be robust in the presence of different compounds and at a wide range of conditions. Although microreactors themselves can accommodate a great span of conditions, few packaging schemes are compatible with cryogenic temperatures, high pressures, and aggressive organic solvents. Solder-based connections are designed and implemented on silicon-based microreactors and are demonstrated to withstand elevated pressures (up to 200 atm), a wide range of temperatures (-78 to 160 degrees C) and a variety of solvent systems. Through the deposition of metal bonding pads directly onto silicon and glass surfaces, solder-based chip-to-tube connections can be reliably formed using handheld soldering tools. Packaging techniques are also described for fluidic chip-to-chip bonds, facilitating direct connection of microfluidic modules. This method greatly expands the utility of microfluidic reactors while enabling easy and reproducible fluidic packaging.

Microfluidic system integration in sample preparation chip-sets - a summary

An increasing complexity of microfluidic chips and systems used for biochemical assay applications calls for the development of new strategies towards their functionality integration in order to achieve optimum assay performance. Approaches to an integration of microfluidic chips into diagnostic fluidic systems are reviewed with the emphasis on the selection of assay application, integration scheme, interfacing, and fabrication platform. In particular, we discuss a system containing polymer microfluidic chip-sets capable of cell pre-concentration from a complex sample matrix using immunomagnetic separations.