We study the mobility of short ssDNA fragments (approximately 30-500 bases) separated by capillary electrophoresis in entangled polymer solutions. Although this corresponds to what is commonly called the Ogston regime, the corresponding sieving concept has never been defined properly nor tested quantitatively. We consider three formulas that have been suggested to fit data in this range of ssDNA sizes, and we discuss how their free parameters are related to actual physical parameters. We test these formulas with new data obtained in our laboratory using a commercial poly-N,N-dimethylacrylamide sieving matrix. Our results show that all three formulas provide decent fits. However, the traditional Ogston equation produces fitting parameters that appear to lack physical meaning. Surprisingly, all three approaches predict that the effective pore size and fiber radius are almost equal. This is the first step towards the development of a systematic approach to optimizing sequencing systems for this size range.

This work reports the synthesis and characterisation of new amphiphilic hyaluronan (HA) grafted with poly(3-hydroxyalkanoates) (PHAs) conjugates. Hydrolytic depolymerisation of PHAs was used for the synthesis of defined oligo(3-hydroxyalkanoates)-containing carboxylic terminal moieties. A kinetic study of the depolymerisation was followed to prepare oligomers of required molecular weight. PHAs were coupled with hydroxyl groups of HA mediated by N, N'-carbonyldiimidazole (CDI) or HSTU Tetramethyl-O-(N-succinimidyl) uronium hexafluorophosphate. For the first time, the covalent bonding of oligo derivatives of P(3-hydroxybutyrate), P(3-hydroxyoctanoate), P(3-hydroxyoctanoate-co-3-hydroxydecanoate) and P(3-hydroxyoctanoate-co-3-hydroxydecanoate-co-3-hydroxydodecanoate) and HA was achieved by "grafting to" strategy. Achieved grafting degree was a function of hydrophobicity of PHA, Mw and polarity of the solvent. The most suitable reaction conditions were observed for oligo (3-hydroxybutyrate) grafted to HA (grafting degree of 14%). Graft copolymers were characterized by FT-IR, NMR, DSC and SEC-MALLS. Graft copolymers can be physically loaded with hydrophobic drugs and may serve as drug delivery system.

Controlling and manipulating liquids and analytes at the sub-millimeter scale is a challenge that frequently requires new methods to be developed. Indeed, scaling-down of traditional macroscopic ideas often fails. For instance, pumping liquids using pressure differences is often impractical and counterproductive because the resulting parabolic flow profile deforms sample zones. As the size of the system shrinks, the surface-to-volume ratio increases and interfacial effects become dominant. This actually opens new possibilities since the phenomenon of electroosmotic flow (EOF), wherein a fluid is made to move relative to a stationary charged boundary, can then be exploited to design efficient microfluidic devices. In this chapter, we review the fundamental principles of EOF as well as some of the methods used to coat channel walls and reduce the impact of EOF in situations where it would be unfavorable for the device performance.

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