Biomedical Engineering Reference
In-Depth Information
This should come as no surprise, since the physical behavior of materials is non-linear and
unpredictable, especially when materials are formulated or in combination. Two examples
will suffi ce: high temperature ceramic superconductors and insulators above their critical
temperatures or at non-ideal stoichiometries; composite structures may show several times
the strength or impact resistance than would be expected from their component materials.
Materials discovery will always require a good deal of trial and error, factors that may be
mitigated by techniques that permit the simultaneous synthesis of large numbers of mate-
rials, followed by rapid or parallel screening for desired properties.
In material science, new phosphors have been discovered for eventual use in fl uores-
cent lighting, fl at-panel displays, and computer screens. An inkjet-based combinatorial
chemistry synthesizer has been designed and built. A new, effi cient blue photolumines-
cent composite has also been found. A library of electronic materials has been quickly
tested in actual devices. A thin fi lm material has been developed that has a higher die-
lectric constant than silicon dioxide, the insulator most commonly used in dynamic
random-access memory (DRAM) computer chips. Studies suggest that combinatorial
methods will be very useful in identifying superior materials for superconducting mag-
netoresistive applications as well, within classes of both known materials and entirely
new ones. Numerous screening methods, ranging from NMR-on-chip to infrared ther-
mography to activated resins, are being perfected. Moreover, the software that enables
users to keep track of all these is commercially available.
11.5.4.3 Chemical and biological analysis
LOC-based chemical analysis systems consist of fl ow injection analysis as well as bio-
logical molecule analysis. Microfl uidic injection analysis includes liquid/gas chroma-
tography (LC, GC) or capillary electrophoresis (CE). The fi rst micromachined fl ow
injection analysis (FIA) system was a gas chromatograph developed by Terry [182],
which consists of a long capillary column, active valve with magnetic actuation, and a
detector element on a silicon wafer. Since then, different LOC chromatography devices
have been reported [183, 184]. These miniaturized systems demonstrated good perform-
ance. The fi rst capillary electrophoretic LOC was based on electroosmotic effect [185,
186], in which the capillaries are micromachined by silicon wet etching and sealed by
anodic binding and separation. The LOC separation effi ciency was improved by syn-
chronized cyclic capillary electrophoresis [186]. More functions such as mixing, reaction
[187], and sample detection with fl uorescence [188] were incorporated onto the chip.
Almost all genetic tests today use one of two techniques: sequencing, which is more
comprehensive and versatile, or hybridization, which is faster and more effi cient for
small pieces of genes. Rapid identifi cation of genes or gene sequences has become one of
the aims of the medical diagnostics business. Hybridization techniques lend themselves
well to a combinatorial approach, and this has become the entry point into genetics for
LOC developers. During the past few years, the HGP has provided the impetus for the
evolution and maturation of DNA sequencing using capillary electrophoresis (CE), an
important theme in LOC development. Recently, researchers have been looking ahead
to the next generation of sequencer, a microfabricated chip-based electrophoresis system
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