Experimental repair of tracheal defect using a bioabsorbable copolymer

A systematic review of simulated laryngotracheal reconstruction animal models

OBJECTIVES

Review of the literature to identify practical, high-fidelity, commercially available animal models for simulation training and surgical skills maintenance in laryngotracheal reconstruction (LTR).

METHODS

A systematic review of PubMed and Embase databases was conducted independently by two authors, according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Search terms included "laryngotracheal reconstruction," "laryngotracheoplasty," "pig and larynx," "sheep and larynx," and "rabbit and larynx." Articles were then assessed, identifying model cost and availability, model validation, feasibility as a training tool, and verisimilitude to pediatric LTR.

RESULTS

In total, 79 articles were considered suitable for inclusion in the study, incorporating both in vitro and in vivo models. Models utilized included rabbit (n = 69), pig (n = 7), sheep (n = 1), and goat (n = 2). The rabbit model was similar in size to the neonate, but differences in laryngeal anatomy and cartilage texture made graft insertion difficult. The anatomy of the pig, sheep, and goat larynges more closely resembled the pediatric patient, allowing improved grafting, but corresponded more in size to that of an older child. Commercial availability of the pig and sheep was considered greatest, and was reflected in cost. None of the animal models identified in the literature have been validated as a simulation tool.

CONCLUSIONS

The rabbit, sheep and pig models seemed to demonstrate the greatest potential for use as advanced pediatric airway surgery simulation models, with the rabbit model being most utilized in the literature. However, as yet there have been no models formally validated as a simulation training tool. Laryngoscope, 129:235-243, 2019.

A rational tissue engineering strategy based on three-dimensional (3D) printing for extensive circumferential tracheal reconstruction

Extensive circumferential tracheal defects remain a major challenging problem in the field of tracheal reconstruction. In this study, a tissue-engineered tracheal graft based on three-dimensional (3D) printing was developed for extensive circumferential tracheal reconstruction. A native trachea-mimetic bellows scaffold, a framework for a tissue-engineered tracheal graft, was indirectly 3D printed and reinforced with ring-shaped bands made from medical grade silicone rubber. A tissue-engineered tracheal graft was then created by stratifying tracheal mucosa decellularized extracellular matrix (tmdECM) hydrogel on the luminal surface of the scaffold and transferring human inferior turbinate mesenchymal stromal cell (hTMSC) sheets onto the tmdECM hydrogel layer. The tissue-engineered tracheal graft with critical length was anastomosed end-to-end to the native trachea and complete re-epithelialization was achieved on the entire luminal surface within 2 months in a rabbit model with no post-operative complications. With this successful result, the present study reports the preliminary potential of the tissue-engineered tracheal graft as a rational tissue engineering strategy for extensive circumferential tracheal reconstruction.

A novel tissue-engineered trachea with a mechanical behavior similar to native trachea

A novel tissue-engineered trachea was developed with appropriate mechanical behavior and substantial regeneration of tracheal cartilage. We designed hollow bellows scaffold as a framework of a tissue-engineered trachea and demonstrated a reliable method for three-dimensional (3D) printing of monolithic bellows scaffold. We also functionalized gelatin sponge to allow sustained release of TGF-β1 for stimulating tracheal cartilage regeneration and confirmed that functionalized gelatin sponge induces cartilaginous tissue formation in vitro. A tissue-engineered trachea was then created by assembling chondrocytes-seeded functionalized gelatin sponges into the grooves of bellows scaffold and it showed very similar mechanical behavior to that of native trachea along with substantial regeneration of tracheal cartilage in vivo. The tissue-engineered trachea developed here represents a novel concept of tracheal substitute with appropriate mechanical behavior similar to native trachea for use in reconstruction of tracheal stenosis.

Overexpression of CXCR4 in tracheal epithelial cells promotes their proliferation and migration to a stromal cell-derived factor-1 gradient

Tracheal reconstruction has been an important issue in clinic, but it is limited for the ability of epithelial regeneration. Several reports have shown that stromal cell-derived factor-1 (SDF-1) and chemokine receptor CXCR4 play an important role in cell proliferation and migration of multiple cell types. But there is no report of SDF-1 and CXCR4 in tracheal cells. In this paper, the rat tracheal epithelial cells covered with cilium were isolated and cultured using two enzyme digestions, and CXCR4 lentivirus was constructed and infected to the tracheal cells successfully. The results showed that the expression of CXCR4 which was covered on cellular membrane majorly was low in normal cells, and the cell proliferation was increased accompanied with the increase in SDF-1 concentration. The cell proliferation, migration and intracellular free calcium were increased significantly in CXCR4 lentivirus infected groups in a dose-dependent manner, and these effects could be inhibited after CXCR4 inhibitor AMD3100 treated because the expression of CXCR4 was decreased. Our findings indicate that the activation of CXCR4 may promote tracheal cell proliferation and migration to the sites of airway injury where SDF-1 is regulated.

Development of a 3D bellows tracheal graft: mechanical behavior analysis, fabrication and an in vivo feasibility study

Artificial tracheal grafts should have not only enough compressive strength to maintain an open tracheal lumen, but also sufficient flexibility for stable mechanical behavior, similar to the native trachea at the implant site. In this study, we developed a new 3D artificial tracheal graft using a bellows design for considering its mechanical behavior. To investigate the mechanical behavior of the bellows structure, finite element method (FEM) analysis in terms of longitudinal tension/compression, bending and radial compression was conducted. The bellows structure was then compared with the cylinder structure generally used for artificial tracheal grafts. The FEM analysis showed that the bellows had outstanding flexibility in longitudinal tension/compression and bending. Moreover, the bellows kept the lumen open without severe luminal deformation in comparison with the cylinder structure. A three-dimensional artificial tracheal graft with a bellows design was fabricated using indirect solid freeform fabrication technology, and the actual mechanical test was conducted to investigate the actual mechanical behavior of the bellows graft. The fabricated bellows graft was then applied to segmental tracheal reconstruction in a rabbit model to assess its applicability. The bellows graft was completely incorporated into newly regenerated connective tissue and no obstruction at the implanted site was observed for up to 8 weeks after implantation. The data suggested that the developed bellows tracheal graft could be a promising alternative for tracheal reconstruction.

Modification of macroporous titanium tracheal implants with biodegradable structures: tracking in vivo integration for determination of optimal in situ epithelialization conditions

Previously, we showed that macroporous titanium implants, colonized in vivo together with an epithelial graft, are viable options for tracheal replacement in sheep. To decrease the number of operating steps, biomaterial-based replacements for epithelial graft and intramuscular implantation were developed in the present study. Hybrid microporous PLLA/titanium tracheal implants were designed to decrease initial stenosis and provide a surface for epithelialization. They have been implanted in New Zealand white rabbits as tracheal substitutes and compared to intramuscular implantation samples. Moreover, a basement membrane like coating of the implant surface was also designed by Layer-by-Layer (LbL) method with collagen and alginate. The results showed that the commencement of stenosis can be prevented by the microporous PLLA. For determination of the optimum time point of epithelialization after implantation, HPLC analysis of blood samples, C-reactive protein (CRP), and Chromogranin A (CGA) analyses and histology were carried out. Following 3 weeks the implant would be ready for epithelialization with respect to the amount of tissue integration. Calcein-AM labeled epithelial cell seeding showed that after 3 weeks implant surfaces were suitable for their attachment. CRP readings were steady after an initial rise in the first week. Cross-linked collagen/alginate structures show nanofibrillarity and they form uniform films over the implant surfaces without damaging the microporosity of the PLLA body. Human respiratory epithelial cells proliferated and migrated on these surfaces which provided a better alternative to PLLA film surface. In conclusion, collagen/alginate LbL coated hybrid PLLA/titanium implants are viable options for tracheal replacement, together with in situ epithelialization.

Tracheal defect repair using a PLGA-collagen hybrid scaffold reinforced by a copolymer stent with bFGF-impregnated gelatin hydrogel

PURPOSE

We studied the regenerated cartilage in tracheal defect repair and compared the bio-materials used versus native trachea using basic fibroblast growth factor (bFGF)-impregnated gelatin hydrogel.

MATERIALS AND METHODS

A full-thickness anterior defect was created in the cervical trachea of 15 experimental rabbits. The defect was implanted with a hybrid scaffold of poly(lactic-co-glycolic acid) (PLGA) knitted mesh and collagen sponge. The implanted trachea was reinforced with a copolymer stent of polycaprolactone and poly(lactic acid) coarse fiber mesh. A gelatin hydrogel was used for providing a sustained release of bFGF. The reconstructed tracheas were divided into three groups with wrapped materials; without gelatin hydrogel (control group, n = 5), a gelatin hydrogel with saline (gelatin group, n = 5), and a gelatin hydrogel with 100 microg of bFGF (bFGF group, n = 5). One of the five rabbits in each group at 1 month after operation, one at 3 months, and three at 6 months were killed and the engineered tracheas were evaluated histologically. Biomechanical properties were evaluated on samples at 6 months postoperatively.

RESULTS

The rigid support in the defect portion was maintained during 6 months postoperatively. The newly regenerated cartilages were recognized between the host cartilage stumps at 3 months postoperatively in the bFGF group, and limited new cartilage growth and epithelialization were observed at 6 months postoperatively.

CONCLUSIONS

The experiment shows that using bFGF, better mechanical strength was obtained but with poor cartilage growth.