Despite innovative surgical techniques and use of current frontal sinus stents from different materials, the problem of treatment failure with consecutive reoperation remains present. The aim of our study is to investigate biocompatibility, degradation kinetics, and functionality of a newly developed fluoride-coated magnesium-based nasal stent. A minipig anatomy of frontal sinus adapted design and an external surgical approach were developed and established. The functionality of the stents was evaluated endoscopically. The stent-tissue blocks were analysed after 90 and 180 days using microcomputed tomography (µ-CT), histology, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Functional evaluation revealed an unobstructed stent lumen in all cases. Histological analysis showed moderate mucosal hyperplasia with a mild, nonspecific inflammatory response, and nonosteoconductive effect. Rejection reactions or necrosis did not occur. The volumetric analysis of the stents showed 51% volume loss after 180 days. The EDS analysis did not detect any neodymium (Nd) in the mucosa or bone. The Mg-2 wt % Nd stents are a promising option when treating the narrow passages following paranasal sinus surgery. In particular, its good biocompatibility and good functionality facilitate the re-epithelization of these constricted passages. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 350-365, 2017.
Magnesium alloys are currently being investigated for use as resorbable biomaterials. Various applications for magnesium based implant materials have already been presented. Currently, stents and structures that sustain diseased or narrowed vessels seem to be the most promising areas. This study focuses on the use of a magnesium fluoride (MgF2 ) coated magnesium neodymium based alloy (MgNd2 ) and its use as a postsurgery stent material to avoid proliferation in the sinus region. Simple cylindrical shaped specimens were sown to the sinus' mucosa of pigs and left in place for different periods of time to investigate the long-term corrosion resistance of the alloy and its coating during direct contact with physiological tissue. Investigations made within this study explicitly focused on the corrosive behavior of the alloy in the region of a physiological sinus. Thus, losses in mass and volume, and element analyses were considered to obtain information about the specimens' corrosion performance over time. Furthermore, micrographs support the alloy specific corrosion type analyses which focus on grain boundary effects. This study demonstrates the general in vivo applicability of fluoride coated MgNd2 . The progress of corrosion was determined to be adequate and homogeneous over a total period of 180 days.
Biodegradable and biocompatible magnesium alloys appear to be very promising not only for temporary clinical application but also for developing deformable and degradable medical implants. This study analyzes the in vivo degradation behavior and the impact on the paranasal sinuses of the highly ductile Mg-2 wt%Nd alloy (MgNd2) in order to provide a basis for a satisfying stent system for the therapy of a chronic sinusitis. Moreover, in vitro tests were carried out on primary porcine nasal epithelial cells (PNEC). For the in vivo tests, cylindrical MgNd2 specimens were implanted into the sinus' mucosa of minipigs. During and after a total period of 180 days the long-term biodegradation and biocompatibility properties after direct contact with the physiological tissue were analyzed. Biodegradation was investigated by measuring the mass and volume losses of the MgNd2 specimens as well as by performing element analyses to obtain information about the degradation layer. The influence on the surrounding tissue of paranasal sinuses was evaluated by endoscopic and histopathological examinations of the mucosa. Here, only a locally unspecific chronic infection was found. The degradation rate showed a maximum after 45 days postsurgery and was determined to decrease subsequently. In vitro experiments using PNEC showed adequate biocompatibility of MgNd2. This study demonstrates a good in vivo biocompatibility for MgNd2 in the system of paranasal sinuses and underlines the promising properties of alloy MgNd2 for biodegradable nasal stent applications.
Chronic rhinosinusitis (CRS) is a common disease in the general population that is increasing in incidence and prevalence, severely affecting patients’ quality of life. Medical treatment for CRS includes self-management techniques, topical and oral medical treatments, and functional endoscopic sinus surgery (FESS). FESS is a standard procedure to restore sinus ventilation and drainage by physically enlarging the inflamed sinus passageways. Nasal drug-releasing stents are implanted to keep the surgically expanded aperture to the sinus frontalis open. The outcome of such an intervention is highly variable. We defined the anatomical structures which should be removed, along with ‘no-go areas’ which need to be preserved during FESS. Based on these definitions, we used cone beam computed tomography (CBCT) images to measure the dimensions of the frontal neo-ostium in 22 patients. We demonstrate anatomical variability in the volume and diameter of the frontal sinus recess after surgery. This variability could be the cause of therapy failure of drug-eluting implants after FESS in some patients. Implants individually made to fit a given patient’s postsurgical anatomy may improve the therapeutic outcome.
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