Design of a Biocompatible Drug-Eluting Tracheal Stent in Mice with Laryngotracheal Stenosis

Abstract

Laryngotracheal stenosis (LTS) is a pathologic narrowing of the subglottis and trachea leading to extrathoracic obstruction and significant shortness of breath. LTS results from mucosal injury from a foreign body in the trachea, leading to tissue damage and a local inflammatory response that goes awry, leading to the deposition of pathologic scar tissue. Treatment for LTS is surgical due to the lack of effective medical therapies. The purpose of this method is to construct a biocompatible stent that can be miniaturized to place into mice with LTS. We demonstrated that a PLLA-PCL (70% poly-L-lactide and 30% polycaprolactone) construct had optimal biomechanical strength, was biocompatible, practicable for an in vivo placement stent, and capable of eluting drug. This method provides a drug delivery system for testing various immunomodulatory agents to locally inhibit inflammation and reduce airway fibrosis. Manufacturing the stents takes 28-30 h and can be reproduced easily, allowing for experiments with large cohorts. Here we incorporated the drug rapamycin within the stent to test its effectiveness in reducing fibrosis and collagen deposition. Results revealed that PLLA-PCL tents showed reliable rapamycin release, were mechanically stable in physiological conditions, and were biocompatible, inducing little inflammatory response in the trachea. Further, the rapamycin-eluting PLLA-PCL stents reduced scar formation in the trachea in vivo.

Figure 1:. Rapamycin PLLA-PCL elution.

The PLLA-PCL construct containing 1% rapamycin demonstrated a consistent and predictable release of rapamycin over a 14 day period. Data points represent the mean ± SEM of sampled elution (n = 3).

Figure 2:. Stent casting.

(A) The PLLA-PCL solution was allowed to dry around a 22 G angiocatheter. (B) The cast was then removed from the angiocatheter. (C) Stents were cut to 3 mm lengths for use in the mouse model.

Figure 3:. Transoral stent placement in mice.

(A) The stent was loaded onto an empty angiocatheter and placed transorally into the trachea. (B) The black dye marking on the stent may be seen through a transcervical incision to confirm its position in the mouse trachea. (C) Representative drawing of the stent in situ in the diseased mouse trachea.

Figure 4:. In situ images of stent.

(A-B) The stent with black dye markings may be seen in situ in the murine trachea. (C) An image of the stent and the murine laryngotracheal complex after harvest at 21 days.

Figure 5:. Stent biocompatibility.

Immunofluorescent staining for F4/80 (macrophages, red chromophore) and CD3 (green chromophore, T-lymphocytes) at day 4 revealed minimal inflammatory cells in the (A) uninjured trachea and (B) trachea with PLLA-PCL stent. This contrasts with (C) an injured trachea, with a thickened lamina propria and the presence of numerous cells with positive F4/80 and CD3 staining.