Biomedical Engineering Reference
In-Depth Information
changes in cell volume during apoptotic commitment [44], with earlier work showing
the application to electronic nuclear volume (ENV) and DNA content using a NPE
Quanta [45, 46]. Again, the fact that cells are in suspension for flow applications
provides convenient methods for the evaluation of novel, fluid-based approaches in
drug delivery research. For example, ultrasound-directed drug delivery using micro-
bubbles is a promisingmethod [47] and flow cytometry has been used to investigate the
effect of ultrasound exposure parameters on the “sonoporation“ [48]. Here we
selectively review some interesting innovations applicable to fluid-based platforms.
In flow cytometry, object manipulation technologies determine the method and
performance envelope of cell presentation and separation. It is important to appreciate
that other solutions may be available when preparative cell separation is an intrinsic
requirement of a diagnostic, biotechnological, or biomedical application. Matrix-
based separation methods such as affinity chromatography have to overcome the
problems of the availability of compatible matrices with convenient pore sizes and the
means of elution of cells from the affinity capture surface surfaces. In this area, a novel
solution is the use of supermacroporous monolithic high-elasticity cryogels with
highly interconnected large (10-100
m) pores permitting cell detachment through
mechanical compression [49]. There continue to be advances in cell separation using
micro- and nanoscale technologies, offering advantages over conventional, macro-
scale separation systems in terms of sample volumes, low cost, portability, and
potential for integration with other analytical techniques [50]. A recent review [51]
has discussed various cell separation principles based on size, magnetic attraction,
fluorescence, and adhesion to surfaces in addition to new emerging technologies such
as affinity capture planar flow cell arrays, dielectrophoresis, field flow methods, and
column separation devices. Such approaches stand alongside FACS for applications
in medicine and biotechnology [51, 52].
m
2.3.1 Pneumatic Delivery
There is an expansion in the size range within which flow cytometry can now operate
as interest arises in more diverse and complex model systems. Here one issue is the
problem of hydrodynamic focusing becoming inherently limiting due to the potential
impact of high sheath pressures on object integrity and downstream cell viability. The
COPAS
instruments of Union Biometrica provide analysis and low-stress (2-5 psi)
pneumatic sorting of biological objects up to 1500
m including small multicellular
animals (e.g., Caenorhabditis elegans, and the eggs and larvae of Drosophila, Hydra,
Xenopus, mosquitoes, Medaka, and zebrafish D. rerio). A drug compound library
might be tested by arraying the library in the wells of a microtiter plate, and then
dispensing a model system such as nematodes into each well with subsequent
aspiration of well content for reanalysis. Thus, of particular interest to the drug
discovery and development sector is the potential for the analysis and isolation of
large cells and cell clusters (e.g., adipocytes, duct cells (kidney, breast, pancreas),
hepatocytes, pancreatic islet cells, imaginal discs, stem cells, and clusters). For
automated detection and sorting of live D. rerio embryos from dead eggs, the COPAS
XL instrument (operating on size and optical parameters) has been used on
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