This paper describes a procedure that makes it possible to design and fabricate (including sealing) microfluidic systems in an elastomeric materialpoly(dimethylsiloxane) (PDMS)in less than 24 h. A network of microfluidic channels (with width >20 μm) is designed in a CAD program. This design is converted into a transparency by a high-resolution printer; this transparency is used as a mask in photolithography to create a master in positive relief photoresist. PDMS cast against the master yields a polymeric replica containing a network of channels. The surface of this replica, and that of a flat slab of PDMS, are oxidized in an oxygen plasma. These oxidized surfaces seal tightly and irreversibly when brought into conformal contact. Oxidized PDMS also seals irreversibly to other materials used in microfluidic systems, such as glass, silicon, silicon oxide, and oxidized polystyrene; a number of substrates for devices are, therefore, practical options. Oxidation of the PDMS has the additional advantage that it ...

Rapid prototyping of microfluidic systems in poly(dimethylsiloxane)

Soft lithography is an alternative to silicon-based micromachining that uses replica molding of nontraditional elastomeric materials to fabricate stamps and microfluidic channels. We describe here an extension to the soft lithography paradigm, multilayer soft lithography, with which devices consisting of multiple layers may be fabricated from soft materials. We used this technique to build active microfluidic systems containing on-off valves, switching valves, and pumps entirely out of elastomer. The softness of these materials allows the device areas to be reduced by more than two orders of magnitude compared with silicon-based devices. The other advantages of soft lithography, such as rapid prototyping, ease of fabrication, and biocompatibility, are retained.

http://science.sciencemag.org/content/sci/288/5463/113.full.pdf

Monolithic microfabricated valves and pumps by multilayer soft lithography

High-density microfluidic chips contain plumbing networks with thousands of micromechanical valves and hundreds of individually addressable chambers. These fluidic devices are analogous to electronic integrated circuits fabricated using large scale integration (LSI). A component of these networks is the fluidic multiplexor, which is a combinatorial array of binary valve patterns that exponentially increases the processing power of a network by allowing complex fluid manipulations with a minimal number of inputs. These integrated microfluidic networks can be used to construct a variety of highly complex microfluidic devices, for example the microfluidic analog of a comparator array, and a microfluidic memory storage device resembling electronic random access memories.

https://science.sciencemag.org/content/sci/298/5593/580.full.pdf

Microfluidic large scale integration

/pdf/micro-total-analysis-systems-1-introduction-theory-and-27f7corp18.pdf

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

We survey progress over the past 25 years in the development of microscale devices for pumping fluids. We attempt to provide both a reference for micropump researchers and a resource for those outside the field who wish to identify the best micropump for a particular application. Reciprocating displacement micropumps have been the subject of extensive research in both academia and the private sector and have been produced with a wide range of actuators, valve configurations and materials. Aperiodic displacement micropumps based on mechanisms such as localized phase change have been shown to be suitable for specialized applications. Electroosmotic micropumps exhibit favorable scaling and are promising for a variety of applications requiring high flow rates and pressures. Dynamic micropumps based on electrohydrodynamic and magnetohydrodynamic effects have also been developed. Much progress has been made, but with micropumps suitable for important applications still not available, this remains a fertile area for future research.

https://microfluidics.stanford.edu/Publications/Micropumps_Cooling/Laser%20Review%20of%20Micropumps%20in%20JMM.pdf

A review of micropumps

An overview is given of research activities in the field of fluid components or systems built with microfabrication technologies. This review focuses on the fluidic behaviour of the various devices, such as valves, pumps and flow sensors as well as the possibilities and pitfalls related to the modelling of these devices using simple flow theory. Finally, a number of microfluidic systems are described and comments on future trends are given.

https://iopscience.iop.org/article/10.1088/0960-1317/3/4/002/pdf

Microfluidics-a review

On the representability of soil water samples in space and time: Impact of heterogeneous solute transport pathways underneath a sandy field.

The geological map sheet Møn covers the island of Møn, the smaller adjacent islands Langø, Lindholm and Nyord as well as adjacent parts of Sjælland and Lolland. It comprises the geodetic map sheets 1511 I and 1511 II and areas on bordering sheets. Møn is surrounded by the Baltic Sea with the bay of Hjelm Bugt to the south, the straits of Grønsund and Ulvsund to the west, and the bays of Stege Bugt and Fakse Bugt to the north.
Møn is divided into three glaciomorphological areas, namely a high, hilly landscape of Høje Møn to the east, a hummocky to parallel ridge landscape to the west and areas of marine deposits around Nyord and Ulvshale. The composite ridge landscape of Høje Møn constitutes a glaciotectonic complex comprising four individual glaciodynamic sequences, with the hill Aborrebjerg as the highest point (143 m a.s.l.). The parallel ridge hills consist of thrust-fault-displaced chalk sheets with superimposed glacial deposits. The thrust sheets are up to 80 m thick, of which 60 m constitute Maastrichtian chalk. The vertical displacement of the thrust sheets is about 150 m measured from the primary, undeformed pre-Quaternary surface located 25–30 m below sea level. The pre-Quaternary surface consists of chalk of Late Maastrichtian age, which forms a carbonate platform in the subsurface of Møn about 27 m below sea level. Chalk displaced by glacial tectonics is not restricted to Høje Møn but also appears in smaller thrust sheets and rafts in the small-ridged landscape around Stege Nor. In the chalk sheets along Møns Klint, most of the Late Maastrichtian succession is exposed. Cliff sections with chalk are also exposed at Hvideklint along the south coast of the island. However, here the glaciotectonic shear deformation has commonly altered the lithology into a chalk glacitectonite.
The oldest Quaternary units deposited on the pre-Quaternary unconformity are Saalian till as well as sand and clay from the Eemian Interglacial. These units are overlain by Early Weichselian sand. The next Quaternary succession, the Ristinge Klint Till Formation, was deposited during the Ristinge ice advance in the early Middle Weichselian about 55 000–50 000 years ago. Then followed the Kraneled Formation (new formation) consisting of fluvial and lacustrine deposits. The following Klintholm Till Formation (adjusted formation) was deposited during the Klintholm ice advance 35 000–32 000 years ago. The Klintholm Till Formation is overlain by a more than 10 m thick unit of greyish glaciolacustrine clay with dropstones. Glaciofluvial sand with thin-layered intercalations of laminated mud and diamictites of the Kobbelgård Formation (new formation) are related to this unit and interpreted as deposited in a huge, partly ice dammed lake covering a large part of the present Baltic Sea and the southern part of Kattegat 32 000 to 28 000 years ago. The Kobbelgård Formation is overlain by sand and gravel of the Stubberup Have Formation (new formation) and tills of the Mid Danish Till Formation deposited by the NE Ice Advance from central Sweden about 23 000–20 000 years ago.
Relatively shortly after the NE ice had melted away, the Young Baltic Ice advanced from the eastern part of the Baltic area. North-directed compressive deformation during this advance created the glaciotectonic complex of Møns Klint including the new unit Møns Klint Glaciodynamic Sequence. In the southern part of the complex, a steeply inclined imbricated fan was formed; towards the foreland to the north, the thrust faults became gently dipping and the tip-zone of thrusting is located under the landslides at Liselund. The composite ridges form a characteristic hilly landscape with elongate crests trending E–W.
The curved coastline along Hjelm Bugt was formed by a glacial lobe, north of which a push moraine was built up. A number of spillways striking radially northward from the lobe were formed by meltwater discharged from its glacier ports, including the Borre, Maglemose and Røddinge depressions. Deposition of sand and gravel of the Ny Borre Formation (new formation) took place at this time. During the advance of the Young Baltic Ice over southern Denmark to the Eastern Jutland stationary line, a relatively thin lodgement till of the Lolland Till Formation was deposited, which is rich in chalk due to its truncation of the upthrusted chalk sheets.
Towards the end of the Weichselian glaciation c. 17 000 years ago, the Young Baltic Ice melted back, leaving a residual ice cap in Skåne from where a recessive ice advance towards south-west reached Møns Klint, resulting in superimposed glaciotectonic deformation. During the Late Weichselian, freshwater lakes in the Hjelm, Tøvelde and Høje Møn areas were filled by clay and gyttja, with deposition that continued into the Holocene.
During the Holocene, the former spillways were turned into fjords during the Atlantic transgression. Marine deposits mirroring the Littorina Sea are thus found in Maglemose and Borre Sømose. After the Atlantic transgression had established a sea level more or less corresponding to that of today, accretion of marine forelands and formation of a spit system started. In particular, this is the case for the areas of Ulvshale and Nyord. At the same time, vegetation migrated out into the numerous fjords, and peat began to accumulate. The last phase of sedimentation is confined to the formation of beach ridges in the coastal areas, typically covered by aeolian dunes, as can be seen on the coast at Klintholm Havn and Råbylille as well as along the north-eastern coast of Ulvshale.

P Gravesen

Papers

Microfluidics-a review

On the representability of soil water samples in space and time: Impact of heterogeneous solute transport pathways underneath a sandy field.

Descriptive text to the Geological map of Denmark, 1:50 000, Møn 1511 I, 1511 IV and 1512 II