Sterilization Effects on Nitric Oxide-Releasing Glucose Sensors.

Nitric oxide (NO) release from S-nitrosothiol-modified mesoporous silica nanoparticles imbedded in the diffusion limiting layer of a glucose sensor has been demonstrated as an effective strategy for mitigating the foreign body response common to sensor implantation, resulting in improved analytical performance. With respect to potential clinical translation of this approach, the effects of sterilization on NO-releasing biosensors require careful evaluation, as NO donor chemistry is sensitive to temperature and environment. Herein, we evaluated the influence of multiple sterilization methods on 1) sterilization success; 2) NO payload; and 3) sensor performance to establish the commercialization potential of NO-releasing glucose sensors. Sensors were treated with ethylene oxide gas, the most common sterilization method for intricate medical devices, which led to undesirable (i.e., premature) release of NO. To reduce NO loss, alternative sterilization methods that were studied included exposure to ultraviolet (UV) light and immersion in 70% ethanol (EtOH). Sterilization cycle times required to reach a 10-6 sterility assurance level were determined for both UV light and 70% EtOH against Gram-negative and -positive bacteria. The longest sterilization cycle times (258 s and 628 s for 70% EtOH and UV light, respectively) resulted in a negligible impact on benchtop sensor performance. However, sterilization with 70% ethanol resulted in a reduced NO-release duration. Ultraviolet light exposure for ~10 min proved successful at eliminating bacteria without compromising NO payloads or durations and presents as the most promising method for sterilization of these sensors. In addition, storage of NO-releasing sensor membranes at -20 and -80°C resulted in preservation of NO release for 6 and 12 months, respectively.

Planar carbon electrodes for real-time quantification of hydrogen sulfide release from cells.

A planar electrode system was developed to permit the real-time, selective detection of hydrogen sulfide (H2S) from stimulated cells. Planar carbon electrodes were produced via stencil printing carbon ink through a laser cut vinyl mask. Electrodes were preconditioned using a constant potential amperometry methodology to prevent sensor drift resulting from elemental sulfur adsorption. Modification with a bilaminar coating (electropolymerized ortho-phenylenediamine and a fluorinated xerogel) facilitated high selectivity to H2S. To demonstrate the biological application of this planar sensor system, H2S released from 17ß-estradiol-stimulated human umbilical vein endothelial cells (HUVECs) was quantified in situ in real-time. Stimulated HUVECs released sustained H2S levels for hours before returning to baseline. Cellular viability assays demonstrated negligible cell cytotoxicity at the electrochemical potentials required for analysis.

Combination of Nitric Oxide Release and Surface Texture for Mitigating the Foreign Body Response.

The tissue response to polyurethane (PU)-coated implants employing active and/or passive FBR mitigation techniques was evaluated over a 28 day study in a diabetic swine model. Active FBR mitigation was achieved through the sustained release of nitric oxide (NO) from a mesoporous silica nanoparticle-doped PU coating. Passive FBR mitigation was achieved through the application of a foam- or fiber-based topcoat. These topcoats were designed to possess topographical features known to promote tissue integration with foam-coated implants having pore sizes of approximately 50 µm and fiber-coated implants consisting of fiber diameters of less than 1 µm. Nitric oxide-release profiles were minimally impacted by the presence of either topcoat. Inflammatory cell density and collagen density at the implant-tissue interface were assessed at 7, 14, 21, and 28 days following implantation. Nitric oxide-releasing implants had significantly lower inflammatory cell density and collagen density than non-NO-releasing controls. The presence of a topcoat did not significantly impact inflammatory cell density, though top-coated textured implants resulted in significantly lower collagen density, irrespective of NO release. Overall, coatings that combine NO release with surface texture demonstrated the greatest potential for tissue-based biomedical device applications.