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Micro Total Analysis Systems. 1. Introduction, Theory, and Technology

After having reviewed some aspects of microfluidic system preparation in the first part (1), in this second part of the review we will cover a number of standard operations (namely: sample preparation, sample injection, sample manipulation, reaction, separation, and detection) as well as some biological applications of micro total analysis systems (namely: cell culture, polymerase chain reaction, DNA separation, DNA sequencing, and clinical diagnostics). As previously, we will include papers issued from different scientific journals as well as useful abstracts from three conference proceedings: MEMS, Transducers, and μTAS. In this second part, we do not include the period covered by the history section (1975-1997) from part 1 but try to cover the relevant examples of the literature published between January 1998 and March 2002. We briefly describe articles that struck us as needing special attention, while more “standard” papers are dutifully reported in groups of interest. An article might be included in more than one section, depending on the ideas developed in it.

Micro total analysis systems. 2. Analytical standard operations and applications.

Micro total analysis systems. Recent developments.

Micro total analysis systems. Latest advancements and trends.

Polymers have assumed the leading role as substrate materials for microfluidic devices in recent years. They offer a broad range of material parameters as well as material and surface chemical properties which enable microscopic design features that cannot be realised by any other class of materials. A similar range of fabrication technologies exist to generate microfluidic devices from these materials. This review will introduce the currently relevant microfabrication technologies such as replication methods like hot embossing, injection molding, microthermoforming and casting as well as photodefining methods like lithography and laser ablation for microfluidic systems and discuss academic and industrial considerations for their use. A section on back-end processing completes the overview.

Polymer microfabrication technologies for microfluidic systems

Flexible polyimide probes with microelectrodes and embedded microfluidic channels for simultaneous drug delivery and multi-channel monitoring of bioelectric activity.

This paper describes the development of polyimide-based microfluidic devices. A layer transfer and lamination technique is used to fabricate flexible microfluidic channels in various shapes and with a wide range of dimensions. High bond strengths can be achieved by cure cycle adaptation and surface treatment of the polyimide layers prior to bonding. The polyimide microchannels can be combined with metallization layers to fabricate electrodes inside and outside channels. The resulting devices can be used for flexible fluidic and electrical connectors, implantable fluid delivery devices, microelectrodes with embedded fluidic channels, chip-based flow cytometry and for a great variety of other applications in medical, chemical or biological research.

Polyimide-based microfluidic devices

The following paper describes a sacrificial layer method for the manufacturing of microfluidic devices in polyimide and SU-8. The technique uses heat-depolymerizable polycarbonates embedded in polyimide or SU-8 for the generation of microchannels and sealed cavities. The volatile decomposition products originating from thermolysis of the sacrificial material escape out of the embedding material by diffusion through the cover layer. The fabrication process was studied experimentally and theoretically with a focus on the decomposition of the sacrificial materials and their diffusion through the polyimide or SU-8 cover layer. It is demonstrated that the sacrificial material removal process is independent of the actual channel geometry and advances linearly with time unlike conventional sacrificial layer techniques. The fabrication method provides a versatile and fast technique for the manufacturing of microfluidic devices for applications in the field of μTAS and Lab-on-a-Chip.

Polyimide and SU-8 microfluidic devices manufactured by heat-depolymerizable sacrificial material technique

A new noninvasive approach for intraocular pressure (IOP) measurement allowing continuous monitoring over prolonged periods, regardless of patient's position and activities. The key element of this measurement method is a soft contact lens (1) including at least one strain gage (2) longitudinally arranged around the center of the contact lens and capable of measuring precisely spherical deformations of the eyeball induced by changes in IOP. This information is transmitted with wires or (preferably) wirelessly in real time to an external recording system (14). The system is placed in the same way as a normal corrective contact lens, no anesthesia is required and patient vision remains almost completely unimpaired.

Intraocular pressure recording system

This paper reports on polyimide microfluidic devices fabricated by photolithography and a layer transfer lamination technology. The microchannels are sealed by laminating an uncured polyimide film on a partially cured layer and subsequent imidization. Selected areas of the microchannels were irradiated with heavy ions of several hundred MeV and the generated ion tracks are chemically etched to submicron pores of high aspect ratio. The ion beam parameters and the track etching conditions define density, length, diameter and shape of the pores. Membrane permeability and separation performance is demonstrated in cross-flow filtration experiments. The devices can be used for selective delivery or probing of fluids to biological tissue, e.g. drug delivery or microdialysis. For chip-based devices the filters can be used as a sample pre-treatment unit for filtration or concentration of particles or molecules.

http://iopscience.iop.org/article/10.1088/0960-1317/14/3/002/pdf

Stefan Metz

Papers

Flexible polyimide probes with microelectrodes and embedded microfluidic channels for simultaneous drug delivery and multi-channel monitoring of bioelectric activity.

Polyimide-based microfluidic devices

Polyimide and SU-8 microfluidic devices manufactured by heat-depolymerizable sacrificial material technique

Intraocular pressure recording system

Polyimide microfluidic devices with integrated nanoporous filtration areas manufactured by micromachining and ion track technology