Christiane Neumann

Connecting microfluidic chips using a chemically inert, reversible, multichannel chip-to-world-interface

In this paper we present a reusable, chemically inert, multichannel Chip-to-World-Interface (CWI). The concept of this interface is based on a force fit connection similar to the hollow screw connectors known from high-performance liquid chromatography (HPLC) instruments. It allows contamination free connection of up to 100 thermoplastic tubes to microfluidic chips made from various materials e.g., epoxy polymers, glass and polydimethylsiloxane (PDMS). The spacing of the tubes is fixed whereas the outer dimensions of the CWI can be adapted to the microfluidic chip it should be used with. We demonstrate that such a CWI with 100 tubes is pressure-tight up to (at least) 630 kPa (6.3 bar) pressure and the connection easily sustains flow rates above 4 ml min(-1). The presented CWI is designed such that the fluid probed in the microfluidic chip is in direct contact only with the tube material and the material from which the microfluidic chip is made. This not only enables fluid transport without dead volume, it also ensures that CWI itself will not be contaminated or contaminate the samples being probed. Using polytetrafluoroethylene (PTFE, Teflon®) tubing we demonstrate that the CWI can even be used with harsh organic solvents such as dichloromethane or dimethylformamide during continuous solvent probing over several hours without damage to the CWI or leakage. This CWI therefore effectively allows using almost all types of organic solvents in microfluidic applications.

Rapid bonding of polydimethylsiloxane to stereolithographically manufactured epoxy components using a photogenerated intermediary layer.

We describe a low cost, photo-induced, room-temperature bonding technique for bonding epoxy components to flexible PDMS membranes in less than half an hour. Bond strengths (~350 kPa) were characterized by ISO-conform tensile testing for a popular stereolithography resin and found comparable bond strengths as reported for PDMS/PDMS bonds.

Rapid bonding of polydimethylsiloxane (PDMS) to various stereolithographically (STL) structurable epoxy resins using photochemically cross-linked intermediary siloxane layers

In this paper we present a fast, low cost bonding technology for combining rigid epoxy components with soft membranes made out of polydimethylsiloxane (PDMS). Both materials are commonly used for microfluidic prototyping. Epoxy resins are often applied when rigid channels are required, that will not deform if exposed to high pressure. PDMS, on the other hand, is a flexible material, which allows integration of membrane valves on the chip. However, the integration of pressure driven components, such as membrane valves and pumps, into a completely flexible device leads to pressure losses. In order to build up pressure driven components with maximum energy efficiency a combination of rigid guiding channels and flexible membranes would be advisable. Stereolithographic (STL) structuring would be an ideal fabrication technique for this purpose, because complex 3D-channels structures can easily be fabricated using this technology. Unfortunately, the STL epoxies cannot be bonded using common bonding techniques. For this reason we propose two UV-light based silanization techniques that enable plasma induced bonding of epoxy components. The entire process including silanization and corona discharge bonding can be carried out within half an hour. Average bond strengths up to 350 kPa (depending on the silane) were determined in ISO-conform tensile testing. The applicability of both techniques for microfluidic applications was proven by hydrolytic stability testing lasting more than 40 hours.

Rapid prototyping of glass microfluidic chips

In academia the rapid and flexible creation of microfluidic chips is of great importance for microfluidic research. Besides polymers glass is a very important material especially when high chemical and temperature resistance are required. However, glass structuring is a very hazardous process which is not accessible to most members of the microfluidic community. We therefore sought a new method for the rapid and simple creation of transparent microfluidic glass chips by structuring and sintering amorphous silica suspensions. The whole process from a digital mask layout to a microstructured glass sheet can be done within two days. In this paper we show the applicability of this process to fabricate capillary driven microfluidic systems.

Fluidic Platforms and Components of Lab-on-a-Chip devices

In recent years the distribution of Lab-on-a-chip devices as well as micro-total analysis systems in applications such as analytical chemistry, biochemistry, biotechnology, microsystems technology, or clinical diagnostics has increased significantly. In order to allow multiple assays to be carried out on this devices components that enable fast tests and quantitative measurements are needed. The first systems which fulfilled these requirements were paper based devices. The development of these systems was based on chromatographic techniques. The basic principle is already known as so termed spot tests since the 1930s. The trend to take more and more applications out of the laboratory to the user started the development of a large number of platforms for point of care devices. These platforms can be driven by different ways, e.g., pressure, capillary flow, or electro kinetic effects. Complex applications need additional fluidic components such as pumps, valves, sensors, or mixers. In this chapter different fluidic platforms as well as fluidic components will be described. Applications of platforms and integrated components are exemplarily demonstrated by means of case studies.

A chemically inert multichannel chip-to-world interface to connect microfluidic chips

Within the last decades more and more microfluidic systems for applications in chemistry, biology or medicine were developed. Most of them need a connection between the chip and its macroscopic environment e.g., pumps. Numerous concepts for such interconnections are known from literature but most of them allow only a small number of connections and are neither chemically inert nor contamination-free. We developed a chemically inert, reusable, multichannel Chipto- World-Interface (CWI) based on a force fit connection. This principle is comparable to hollow screws as used in highperformance liquid chromatography. The CWI can be used to connect chips, made of different materials, e.g., glass, polydimethylsiloxane (PDMS), or epoxy polymers, with up to 100 thermoplastic tubes. The dimensions of the CWI and the number of connections can be individually adapted depending on the chip dimensions but the pitch between the tubes is fixed. Due to the design of the CWI the fluid is only in contact with the chip and the tubing material, thus leading to a contamination free and zero dead volume interconnection. Using tubes of polytetrafluorethylene (PTFE, Teflon®) even enables probing with organic solvents like dimethylformamide, dichloromethane or tetrahydrofuran over several hours without leakage or corrosion of the CWI. During experiments the CWI with 100 connections resisted pressure up to 630 kPa (6.3 bar) and sustained flow rates higher than 4 ml/min.

Microfluidics on liquid handling stations (μF-on-LHS): a new industry-compatible microfluidic platform

Since the early days microfluidics as a scientific discipline has been an interdisciplinary research field with a wide scope of potential applications. Besides tailored assays for point-of-care (PoC) diagnostics, microfluidics has been an important tool for large-scale screening of reagents and building blocks in organic chemistry, pharmaceutics and medical engineering. Furthermore, numerous potential marketable products have been described over the years. However, especially in industrial applications, microfluidics is often considered only an alternative technology for fluid handling, a field which is industrially mostly dominated by large-scale numerically controlled fluid and liquid handling stations. Numerous noteworthy products have dominated this field in the last decade and have been inhibited the widespread application of microfluidics technology. However, automated liquid handling stations and microfluidics do not have to be considered as mutually exclusive approached. We have recently introduced a hybrid fluidic platform combining an industrially established liquid handling station and a generic microfluidic interfacing module that allows probing a microfluidic system (such as an essay or a synthesis array) using the instrumentation provided by the liquid handling station. We term this technology “Microfluidic on Liquid Handling Stations (μF-on-LHS)” – a classical “best of both worlds”- approach that allows combining the highly evolved, automated and industry-proven LHS systems with any type of microfluidic assay. In this paper we show, to the best of our knowledge, the first droplet microfluidics application on an industrial LHS using the μF-on-LHS concept.