Jordan J. Wilson

Ventilator-associated pneumonia (VAP) is a life-threatening condition most frequently associated with the use of endotracheal tubes (ETs). This study describes the development of macroporous p(HEMA) hydrogels as removable antimicrobial liners for ETs to help prevent VAP. Hydrogels were prepared by free-radical polymerisation using varying sodium chloride concentrations and 40% or 60% w/w water. Increasing NaCl concentration enhanced porosity but reduced mechanical strength and improved swelling and gentamicin loading of hydrogels containing 60% w/w but not 40% w/w water. Gentamicin release was more controlled at lower NaCl concentrations, whereas hydrogels with higher porosity promoted rapid release. The formulation containing 60% w/w water and 0.1 M NaCl provided the best balance of mechanical integrity, drug uptake, sustained antimicrobial activity, and reduced bacterial adherence. Nebulisation studies showed that gentamicin-loaded hydrogels eradicated adherent bacteria and prevented recovery of viable organisms after repeated bacterial challenges. These findings indicate that macroporous p(HEMA) hydrogel liners offer a promising strategy for reducing endotracheal tube-associated infection.

Thermoresponsive hydrogels demonstrate tremendous potential as sustained drug delivery systems. However, progress has been limited as formulation of a stable biodegradable thermosensitive hydrogel remains a significant challenge. In this study, free radical polymerization was exploited to formulate a biodegradable thermosensitive hydrogel characterized by sustained drug release. Highly deacetylated chitosan and N-isopropylacrylamide with distinctive physical properties were employed to achieve a stable, hydrogel network at body temperature. The percentage of chitosan was altered within the copolymer formulations and the subsequent physical properties were characterized using ¹H-NMR, FTIR, and TGA. Viscoelastic, swelling, and degradation properties were also interrogated. The thermoresponsive hydrogels were loaded with RALA/pEGFP-N1 nanoparticles and release was examined. There was sustained release of nanoparticles over three weeks and, more importantly, the nucleic acid cargo remained functional and this was confirmed by successful transfection of the NCTC-929 fibroblast cell line. This tailored thermoresponsive hydrogel offers an option for sustained delivery of macromolecules over a prolonged considerable period.

Oligodeoxynucleotides incorporating internucleotide phosphoroselenolate linkages have been prepared under solid-phase synthesis conditions using dimer phosphoramidites. These dimers were constructed following the high yielding Michaelis–Arbuzov (M–A) reaction of nucleoside H-phosphonate derivatives with 5′-deoxythymidine-5′-selenocyanate and subsequent phosphitylation. Efficient coupling of the dimer phosphoramidites to solid-supported substrates was observed under both manual and automated conditions and required only minor modifications to the standard DNA synthesis cycle. In a further demonstration of the utility of M–A chemistry, the support-bound selenonucleoside was reacted with an H-phosphonate and then chain extended using phosphoramidite chemistry. Following initial unmasking of methyl-protected phosphoroselenolate diesters, pure oligodeoxynucleotides were isolated using standard deprotection and purification procedures and subsequently characterised by mass spectrometry and circular dichroism. The CD spectra of both modified and native duplexes derived from self-complementary sequences with A-form, B-form or mixed conformational preferences were essentially superimposable. These sequences were also used to study the effect of the modification upon duplex stability which showed context-dependent destabilisation (−0.4 to −3.1 °C per phosphoroselenolate) when introduced at the 5′-termini of A-form or mixed duplexes or at juxtaposed central loci within a B-form duplex (−1.0 °C per modification). As found with other nucleic acids incorporating selenium, expeditious crystallisation of a modified decanucleotide A-form duplex was observed and the structure solved to a resolution of 1.45 Å. The DNA structure adjacent to the modification was not significantly perturbed. The phosphoroselenolate linkage was found to impart resistance to nuclease activity.