Balloon-expandable trilayer nitrided iron/Zn/poly-D,L-lactic acid metallic tracheal stent: structural characterization, mechanical performance, and short-term safety evaluation in rabbits.

BACKGROUND: Pediatric airway stenosis and tracheomalacia may require airway stenting to maintain patency. However, conventional metallic or silicone airway stents are associated with frequent complications such as granulation, mucus plugging, and migration. Although bioresorbable polymer stents reduce long-term indwelling, degradation fragments may still pose a risk of airway obstruction. Therefore, a tracheal stent designed to provide reliable early mechanical support, favorable tissue compatibility, and potential long-term bioresorption remains needed. This study aims to develop and evaluate a biodegradable tracheal stent with improved mechanical performance and biocompatibility.

METHODS: A balloon-expandable trilayer tracheal stent was fabricated with a load-bearing nitrided iron (Fe-N) framework, a zinc (Zn) buffering layer, and an outer poly-D,L-lactic acid (PDLLA) coating. The layered structure and composition were verified by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). Radial compression testing was performed and compared with a pure iron stent of the same geometry. Stent extracts were prepared to evaluate in vitro biocompatibility using BEAS-2B cells, including scratch assay, 5-ethynyl-2'-deoxyuridine (EdU) assay, Transwell assay, terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL), cytoskeleton staining, and live/dead staining. Immunological safety was assessed using RAW264.7 macrophages, with lipopolysaccharide (LPS) as a positive control, by immunofluorescence for cluster of differentiation 86 (CD86), interleukin-1 beta (IL-1β), inducible nitric oxide synthase (iNOS), and interleukin-6 (IL-6) and by reverse transcription quantitative polymerase chain reaction (RT-qPCR) for related messenger RNAs (mRNAs). For in vivo evaluation, the stent was delivered and deployed under flexible bronchoscopy in male New Zealand White rabbits. Tissues were collected at 1 week, 1 month, and 2 months for hematoxylin and eosin (H&E) and Masson staining of the trachea, and histology of the lungs and major organs (heart, liver, spleen, and kidney).

RESULTS: Characterization confirmed successful construction of the designed trilayer structure. Radial compression testing showed that the Fe-N stent provided higher radial support than the pure iron stent with the same geometry. In vitro, extracts showed no obvious cytotoxic or pro-inflammatory effects. The extracts also did not induce inflammatory activation in RAW264.7 macrophages, whereas the LPS group showed the expected inflammatory response. In rabbits, the stent could be delivered and deployed by bronchoscopy with balloon expansion. Histology showed early mucosal injury followed by progressive repair, with no obvious progressive granulation, persistent fibrotic remodeling, distal lung injury, or major-organ damage.

CONCLUSIONS: The balloon-expandable trilayer Fe-N/Zn/PDLLA metallic tracheal stent demonstrated feasible delivery and deployment in rabbits, provided the mechanical basis required for airway support, and showed favorable in vitro and short-term in vivo biosafety with a repair-dominant tissue response. These findings support further optimization and long-term evaluation of this trilayer metallic airway stent design, particularly regarding its degradation behavior, durability of radial support, and long-term biosafety.