Evaluation of poly-L-lactic acid and polyglycolic acid resorbable stents for repair of tracheomalacia in a porcine model

Early preclinical evaluation of a novel, computer aided designed, 3D printed, bioresorbable posterior cricoid scaffold

OBJECTIVES

The posterior cricoid split with rib graft is a procedure that elegantly corrects pediatric posterior glottic stenosis and subglottic stenosis. Currently, the procedure requires harvesting of rib cartilage which leaves room for optimization. With use of three dimensional printing technology, our objective was to design a device that would negate the need for costal cartilage harvesting in this procedure.

METHODS

An optimized, novel polycaprolactone scaffold was designed using computer aided design software and three dimensional printing. A pilot proof of concept study was conducted with implantation of the device in three porcine animal subjects. Device was evaluated by post-procedural clinical course, endoscopic exams, post-mortem exam, and histological evaluation.

RESULTS

A series of variably sized scaffolds were created. The scaffolds showed structural integrity and successfully expanded the cricoid cartilage in the porcine model study. Post-operative endoscopy and clinical exams demonstrated no signs of implant instability or failure. Gross and histologic exams showed successful mucosalization over the scaffold and cartilage ingrowth by six weeks.

CONCLUSION

This porcine animal pilot study demonstrated early success of a computer-aided designed, 3D printed, bioresorbable PCL posterior graft scaffold. The scaffolds eliminate the need for costal cartilage harvesting and had excellent surgical usability. The scaffolds functioned as designed, offering proof of concept and grounds for further evaluation to expand on this small pilot study with larger animal studies and continued design refinement.

Computational modeling of airway instability and collapse in tracheomalacia

Background

Tracheomalacia (TM) is a condition of excessive tracheal collapse during exhalation. Both acquired and congenital forms of TM are believed to result from morphological changes in cartilaginous, fibrous and/or smooth muscle tissues reducing airway mechanical properties to a degree that precipitates collapse. However, neither the specific amount of mechanical property reduction nor the malacic segment lengths leading to life threatening airway collapse in TM are known. Furthermore, the specific mechanism of collapse is still debated.

Methods

Computational nonlinear finite element models were developed to determine the effect of malacic segment length, tracheal diameter, and reduction in tissue nonlinear elastic properties on the risk for and mechanism of airway collapse. Cartilage, fibrous tissue, and smooth muscle nonlinear elastic properties were fit to experimental data from preterm lambs from the literature. These elastic properties were systematically reduced in the model to simulate TM.

Results

An intriguing finding was that sudden mechanical instability leading to complete airway collapse occurred in airways when even a 1 cm segment of cartilage and fibrous tissue properties had a critical reduction in material properties. In general, increased tracheal diameter, increased malacic segment length coupled with decreased nonlinear anterior cartilage/fibrous tissue nonlinear mechanical properties increased the risk of sudden airway collapse from snap through instability.

Conclusion

Modeling results support snap through instability as the mechanism for life threatening tracheomalacia specifically when cartilage ring nonlinear properties are reduced to a range between fibrous tissue nonlinear elastic properties (for larger diameter airways > 10 mm) to mucosa properties (for smaller diameter airways < 6 mm). Although reducing posterior tracheal smooth muscle properties to mucosa properties decreased exhalation area, no sudden instability leading to collapse was seen in these models.

Biodegradable Airway Stents - Bench to Bedside: A Comprehensive Review

Airway stents are indicated to treat symptomatic narrowing or to close fistulas of the central airways. They are generally divided into two types: the silicone stents and the metallic stents. Unlike in malignancies, removability is a major objective of temporary stenting in benign conditions, which poses the challenge of a new rigid bronchoscopic procedure under general anesthesia and stent removal with all its attendant risks and costs. The concept of a biodegradable (BD) stent that could maintain the patency of an airway for a predetermined duration of time is very appealing. These BD stents would gradually degrade and eventually vanish from the airway once they are no longer needed. Such stents are currently an area of intense research. Another very promising concept of drug delivery with such stents is also a very exciting area of current research. The aim of this comprehensive review is to discuss all pertinent available literature on the use of BD materials in various clinical applications and to extensively review all animal and humans trials involving BD airway stents.

Treatment of severe porcine tracheomalacia with a 3-dimensionally printed, bioresorbable, external airway splint

IMPORTANCE

The study demonstrates use of a novel intervention for severe tracheobronchomalacia (TBM).

OBJECTIVE

To test a novel, 3-dimensionally (3D) printed, bioresorbable airway splint for efficacy in extending survival in a porcine model of severe, life-threatening TBM.

DESIGN AND PARTICIPANTS

A randomized, prospective animal trial was used to evaluate an external airway splint as treatment of severe, life-threatening TBM in a multi-institutional, multidisciplinary collaboration between a biomedical engineering department and an academic animal surgery center. Six 2-month-old Yorkshire pigs underwent tracheal cartilage division and inner tracheal lumen dissociation and were randomly assigned to splint treatment (n = 3) or control groups (n = 3). Two additional pigs had the splint placed over their normal trachea.

INTERVENTIONS

A 3D-printed, bioresorbable airway splint was assessed in a porcine animal model of life-threatening TBM. The open-cylindrical, bellow-shaped, porous polycaprolactone splint was placed externally and designed to suspend the underlying collapsed airway. Two additional animals were splinted without model creation.

MAIN OUTCOMES AND MEASURES

The observer-based Westley Clinical Croup Scale was used to assess the clinical condition of animals postoperatively. Animal survival time was noted.

RESULTS

Complete or nearly complete tracheal lumen collapse was observed in each animal, with resolution of symptoms in all of the experimental animals after splint placement. Using our severe TBM animal model, survival was significantly longer in the experimental group receiving the airway splint after model creation than in the control group (P = .0495).

CONCLUSIONS AND RELEVANCE

A multidisciplinary effort producing a computer-aided designed, computer-aided manufactured bioresorbable tracheobronchial splint was tested in a porcine model of severe TBM and was found to extend survival time. Mortality in the splinted group was ascribed to the TBM model based on the lack of respiratory distress in splinted pigs, long-term survival in animals implanted with the splint without TBM, and necropsy findings.

[Tracheobronchomalacia in adults: breakthroughs and controversies]

Tracheobronchomalacia (TBM) in adults is a disease defined by a reduction of more than 50% of the airway lumen during expiration. It encompasses many etiologies that differ in their morphologic aspects, pathophysiological mechanisms and histopathologies. TBM is encountered with increasing frequency, as it is more easily diagnosed with new imaging techniques and diagnostic bronchoscopy, as well as because of its frequent association with Chronic Obstructive Pulmonary Disease (COPD), which represents the most frequent etiology for acquired TBM in adults. A distinction between TBM in association with failure of the cartilaginous part of the airways and TBM affecting only the posterior membranous part is emerging since their physiopathology and treatment differ. The therapeutic management of TBM should be as conservative as possible. Priority should be given to identification and treatment of associated respiratory diseases, such as asthma or COPD. Surgery addressing extrinsic compression (thyroid goiter or tumor, for example) may be necessary. Noninvasive ventilation can be considered in patients with increasing symptoms. Endoscopic options, such as the placement of stents, should only be used as palliative or temporary solutions, because of the high complication rates. Symptomatic improvement after stenting might be helpful in selecting patients in whom a surgical management with tracheobronchoplasty can be useful.

Tracheobronchomalacia and excessive dynamic airway collapse

Tracheobronchomalacia and excessive dynamic airway collapse are two separate forms of dynamic central airway obstruction that may or may not coexist. These entities are increasingly recognized as asthma and COPD imitators. The understanding of these disease processes, however, has been compromised over the years because of uncertainties regarding their definitions, pathogenesis and aetiology. To date, there is no standardized classification, diagnosis or management algorithm. In this article we comprehensively review the aetiology, morphopathology, physiology, diagnosis and treatment of these entities.

Surgisis patch tracheoplasty in a rodent model for tracheal stenosis

BACKGROUND

Tracheal stenosis is a challenging surgical problem that can require reconstruction using autologous grafts or artificial stents. In this study, we evaluate the efficacy of Surgisis, a commercially available, biocompatible, acellular matrix, in the repair of a critical-size tracheal defect.

METHODS

A full-thickness defect (2 mm x 6 mm) was created in tracheal rings 4 through 6 in adult rats. A piece of 8-ply Surgisis (Cook; Bloomington, IN) was sutured to the edges of the defect with interrupted 8-0 polypropylene sutures. In control animals, the defect was closed primarily. The trachea was harvested at 4 weeks and prepared for histologic evaluation using conventional techniques. Cross-sectional area and perimeters were calculated using imaging software.

RESULTS

Tracheal defects without patch repair (n = 3) resulted in tracheal stenosis and immediate death. Animals that underwent Surgisis patch repair of tracheal defects (n = 10) tolerated the procedure well and had no audible stridor or evidence of respiratory distress. Eight of ten animals survived 4 weeks. The tracheal lumen was patent with no evidence of contracture or degradation of the Surgisis. Histologically, neovascularization of the Surgisis was noted with moderate inflammation. The surface of the Surgisis patch was covered ith a lining of ciliated epithelial cells.

CONCLUSION

In the rodent model, Surgisis appears to be an efficacious method for the patch repair of partial circumferential tracheal defects. Surgisis appears to be a safe and promising means of facilitating neovascularization and tissue regeneration. The long-term use of Surgisis warrants further investigation.

Comparison of resorbable poly-L-lactic acid-polyglycolic acid and internal Palmaz stents for the surgical correction of severe tracheomalacia

Tracheomalacia (TM) is associated with expiratory airway collapse and potentially fatal respiratory distress. Internal and external tracheal stents and, recently, resorbable biopolymers have been used to treat this condition. In this study, the efficacy and biocompatibility of internal Palmaz stents and external poly-L-lactic acid-polyglycolic acid (PLPG) stents were compared in a model of severe TM induced in piglets. The tracheas were repaired with one of two stenting methods, and the animals survived for up to 16 weeks. Weight gain, adverse respiratory signs and symptoms, tracheal or lung histopathologic changes, and internal and external tracheal diameters were measured. The animals in the PLPG group uniformly were free of respiratory distress and tracheal stenosis or inflammation, whereas all animals in the Palmaz group developed respiratory distress as a result of pneumonia or tracheal stenosis caused by intraluminal granulation tissue. In conclusion, superior efficacy of external, resorbable PLPG stents was found relative to internal Palmaz stents for the surgical repair of severe TM.