Dual action antimicrobial surfaces via combined nitric oxide and silver release.

Recent research has demonstrated that silver sulfadiazine and small molecule nitric oxide (NO) donors kill a number of bacterial species synergistically in solution-based assays. Herein, we report on multilayered silica-based xerogels that release both NO and silver. Release of each agent was achieved by exposing amine-modified xerogels to high pressures of NO, and doping silver nitrate (AgNO3) into an alkyl-silane xerogel. Total achievable releases were 3.5 µmol cm(-2) and 1.7 ppm for NO and Ag+, respectively, with release of each agent controlled independent of the other. The NO/Ag+-releasing coating reduced bacterial adhesion and exhibited greater-than-additive killing against both Pseudomonas aeruginosa and Staphylococcus aureus. In contrast, cytotoxicity assays against L929 fibroblasts suggest that the combination does not cause greater-than-additive killing to mammalian cells. Such materials may prove useful in the design of biomedical devices prone to infection such as bone and surgical screws.

Superhydrophobic nitric oxide-releasing xerogels.

Superhydrophobic nitric oxide (NO)-releasing xerogels were prepared by spray-coating a fluorinated silane/silica composite onto N-diazeniumdiolate NO donor-modified xerogels. The thickness of the superhydrophobic layer was used to extend NO release durations from 59 to 105h. The resulting xerogels were stable, maintaining superhydrophobicity for up to 1month (the longest duration tested) when immersed in solution, with no leaching of silica or undesirable fragmentation detected. The combination of superhydrophobicity and NO release reduced viable Pseudomonas aeruginosa adhesion by >2-logs. The killing effect of NO was demonstrated at longer bacterial contact times, with superhydrophobic NO-releasing xerogels resulting in 3.8-log reductions in adhered viable bacteria vs. controls. With no observed toxicity to L929 murine fibroblasts, NO-releasing superhydrophobic membranes may be valuable antibacterial coatings for implants as they both reduce adhesion and kill bacteria that do adhere.

Nitric oxide-releasing xerogels synthesized from N-diazeniumdiolate-modified silane precursors.

Nitric oxide (NO)-releasing xerogel materials were synthesized using N-diazeniumdiolate-modified silane monomers that were subsequently co-condensed with an alkoxysilane. The NO-release characteristics were tuned by varying the aminosilane structure and concentration. The resulting materials exhibited maximum NO release totals and durations ranging from 0.45-3.2 µmol cm(-2) and 20-90 h, respectively. The stability of the xerogel networks was optimized by varying the alkoxysilane backbone identity, water to silane ratio, base catalyst concentration, reaction time, and drying conditions. The response of glucose biosensors prepared using the NO-releasing xerogel (15 mol % N-diazeniumdiolate-modified N-2-(aminoethyl)-aminopropyltrimethoxysilane) as an outer sensor membrane was linear (R(2) = 0.979) up to 24 mM glucose. The sensitivity (3.4 nA mM(-1)) of the device to glucose was maintained for 7 days in phosphate buffered saline. The facile sol-gel synthetic route, along with the NO release and glucose biosensor characteristics, demonstrates the versatility of this method for biosensor membrane applications.

Inaccuracies of nitric oxide measurement methods in biological media.

Despite growing reports on the biological action of nitric oxide (NO) as a function of NO payload, the validity of such work is often questionable due to the manner in which NO is measured and/or the solution composition in which NO is quantified. To highlight the importance of measurement technique for a given sample type, NO produced from a small-molecule NO donor (N-diazeniumdiolated l-proline, PROLI/NO) and a NO-releasing xerogel film were quantified in a number of physiological buffers and fluids, cell culture media, and bacterial broth by the Griess assay, a chemiluminescence analyzer, and an amperometric NO sensor. Despite widespread use, the Griess assay proved to be inaccurate for measuring NO in many of the media tested. In contrast, the chemiluminescence analyzer provided superb kinetic information in most buffers but was impractical for NO analysis in proteinaceous media. The electrochemical NO sensor enabled greater flexibility across the various media with potential for spatial resolution, albeit at lower than expected NO totals versus either the Griess assay or chemiluminescence. The results of this study highlight the importance of measurement strategy for accurate NO analysis and reporting NO-based biological activity.

Local delivery of nitric oxide: targeted delivery of therapeutics to bone and connective tissues.

Non-invasive treatment of injuries and disorders affecting bone and connective tissue remains a significant challenge facing the medical community. A treatment route that has recently been proposed is nitric oxide (NO) therapy. Nitric oxide plays several important roles in physiology with many conditions lacking adequate levels of NO. As NO is a radical, localized delivery via NO donors is essential to promoting biological activity. Herein, we review current literature related to therapeutic NO delivery in the treatment of bone, skin and tendon repair.

Decreasing bacterial colonization of external fixation pins through nitric oxide release coatings.

OBJECTIVE: Bacterial infection of the pin tract represents the most common complication associated with external fixation. This study was designed to evaluate the antibacterial activity of nitric oxide (NO)-releasing xerogel films applied to commercially pure titanium pins in a rat model. METHODS: Pins were coated with xerogel solution through a dip-coating procedure. Half of the xerogel-coated implant pins were modified into NO donors and served as the NO-releasing group, whereas the remaining pins were left unmodified to serve as non-NO-releasing xerogel-coated controls. Acid-etched pins served as uncoated controls. Animal selection was randomized and every rat had one pin from each of the three groups randomly allocated to the third, fourth, or fifth tail vertebrae. Quantification of bacterial infection was performed 48 days postoperatively and the tissue-implant interface was inspected for clinical signs of infection on Days 14 and 28 postimplantation. RESULTS: Pin tract bacterial colony counts of the NO-releasing group (170,000 ± 181,000) were significantly lower than both the xerogel-coated group (677,000 ± 675,000) and the control group (1,181,000 ± 2,717,000) 48 days postoperatively (P < 0.05). No significant difference in colony counts was observed between the xerogel-coated group and the control group. The NO-releasing group also had significantly fewer clinical signs of infection than both the coated and the control groups on postoperative Day 28 (P < 0.05). CONCLUSION: The application of NO-releasing xerogel coatings can inhibit bacterial colonization of external fixation pins both during the initial postsurgical period and up to 48 days postimplantation.