Spatial and Temporal Analysis of Host Cells in Tracheal Graft Implantation

Assessing the Biocompatibility and Regeneration of Electrospun-Nanofiber Composite Tracheal Grafts

OBJECTIVE

Composite tracheal grafts (CTG) combining decellularized scaffolds with external biomaterial support have been shown to support host-derived neotissue formation. In this study, we examine the biocompatibility, graft epithelialization, vascularization, and patency of three prototype CTG using a mouse microsurgical model.

STUDY DESIGN

Tracheal replacement, regenerative medicine, biocompatible airway splints, animal model.

METHOD

CTG electrospun splints made by combining partially decellularized tracheal grafts (PDTG) with polyglycolic acid (PGA), poly(lactide-co-ε-caprolactone) (PLCL), or PLCL/PGA were orthotopically implanted in mice (N = 10/group). Tracheas were explanted two weeks post-implantation. Micro-Computed Tomography was conducted to assess for graft patency, and histological analysis was used to assess for epithelialization and neovascularization.

RESULT

Most animals (greater than 80%) survived until the planned endpoint and did not exhibit respiratory symptoms. MicroCT confirmed the preservation of graft patency. Grossly, the PDTG component of CTG remained intact. Examining the electrospun component of CTG, PGA degraded significantly, while PLCL+PDTG and PLCL/PGA + PDTG maintained their structure. Microvasculature was observed across the surface of CTG and infiltrating the pores. There were no signs of excessive cellular infiltration or encapsulation. Graft microvasculature and epithelium appear similar in all groups, suggesting that CTG did not hinder endothelialization and epithelialization.

CONCLUSION

We found that all electrospun nanofiber CTGs are biocompatible and did not affect graft patency, endothelialization and epithelialization. Future directions will explore methods to accelerate graft regeneration of CTG.

LEVEL OF EVIDENCE

N/A Laryngoscope, 134:1155-1162, 2024.

Optimization of Chondrocyte Viability in Partially Decellularized Tracheal Grafts

OBJECTIVE

Advancements in tissue-engineered tracheal replacement (TETR) show promise for the use of partially decellularized tracheal grafts (PDTG) to address critical gaps in airway management and reconstruction. In this study, aiming to leverage the immunoprivileged nature of cartilage to preserve tracheal biomechanics, we optimize PDTG for retention of native chondrocytes.

STUDY DESIGN

Comparison in vivo murine study.

SETTING

Research Institute affiliated with Tertiary Pediatric Hospital.

METHODS

PDTG were created per a shortened decellularization protocol using sodium dodecyl sulfate, then biobanked via cryopreservation technique. Decellularization efficiency was characterized by DNA assay and histology. Viability and apoptosis of chondrocytes in preimplanted PDTG and biobanked native trachea (control) was assessed with live/dead and apoptosis assays. PDTG (N = 5) and native trachea (N = 6) were orthotopically implanted in syngeneic recipients for 1-month. At the endpoint, microcomputed tomography (micro-CT) was employed to interrogate graft patency and radiodensity in vivo. Vascularization and epithelialization were qualitatively analyzed using histology images following explant.

RESULTS

PDTG exhibited complete decellularization of all extra-cartilaginous cells and reduced DNA content compared to control. Chondrocyte viability and nonapoptotic cell populations were improved utilizing biobanking and shorter decellularization time. All grafts remained patent. Evaluation of graft radiodensity at 1 month revealed elevation of Hounsfield units in both PDTG and native compared to host, with PDTG showing higher radiodensity than native. PDTG supported complete epithelialization and functional reendothelialization 1-month postimplantation.

CONCLUSION

Optimizing PDTG chondrocyte viability is a key component to successful tracheal replacement. Ongoing research seeks to evaluate the acute and chronic immunogenicity of PDTG.

Successful Early Neovascularization in Composite Tracheal Grafts

OBJECTIVE

Long-segment tracheal defects require tissue replacement for successful reconstruction. Rapid revascularization is imperative to maintain graft function. We previously showed that partially decellularized tracheal grafts (PDTG) and composite tracheal grafts (CTG; PDTG supported by a 3-dimensionally printed external splint) regenerate respiratory epithelium and may support the regeneration of endothelial cells (CD31+). However, the capability of graft endothelial cells to organize or contribute to tracheal revascularization remains unclear. In this study, we quantified endothelial cells (CD31+) and neovessel formation in PDTG and CTG. We hypothesize that PDTG and CTG support tracheal neovascularization to a similar extent as surgical (syngeneic tracheal graft [STG]) and native trachea (NT) controls.

STUDY DESIGN

The animal study, a randomized control trial.

SETTING

Center for Regenerative Medicine, Nationwide Children's Hospital.

METHODS

PDTG was created via an established decellularization protocol. Segmental tracheal reconstruction was performed with STG, PDTG, or CTG using a mouse microsurgical model. NT was used as a nonsurgical control. At 1 month, mice were euthanized, grafts harvested, sectioned, and stained with CD31 and hematoxylin and eosin. Neovessel formation was quantified by the number of formed blood vessels in the lamina propria and vessel size (vessel/graft area, mm2 ).

RESULTS

Decellularization eliminated all endothelial cells and there were no perfused vessels at implantation. At 1 month, PDTG and CTG supported neovessel formation with tubular vessels lined with endothelial cells. There was no difference in the number or size of vessels compared to controls.

CONCLUSION

PDTG and CTG support tracheal endothelial cell regeneration and neovessel formation. Future directions to assess the function, kinetics, and distribution of graft neovessels are needed.

Regeneration of tracheal neotissue in partially decellularized scaffolds

Extensive tracheal injury or disease can be life-threatening but there is currently no standard of care. Regenerative medicine offers a potential solution to long-segment tracheal defects through the creation of scaffolds that support the generation of healthy neotissue. We developed decellularized tracheal grafts (PDTG) by removing the cells of the epithelium and lamina propria while preserving donor cartilage. We previously demonstrated that PDTG support regeneration of host-derived neotissue. Here, we use a combination of microsurgical, immunofluorescent, and transcriptomic approaches to compare PDTG neotissue with the native airway and surgical controls. We report that PDTG neotissue is composed of native tracheal cell types and that the neoepithelium and microvasculature persisted for at least 6 months. Vascular perfusion of PDTG was established within 2 weeks and the graft recruited multipotential airway stem cells that exhibit normal proliferation and differentiation. Hence, PDTG neotissue recapitulates the structure and function of the host trachea and has the potential to regenerate.

Tissue-engineered composite tracheal grafts create mechanically stable and biocompatible airway replacements

We tested composite tracheal grafts (CTG) composed of a partially decellularized tracheal graft (PDTG) combined with a 3-dimensional (3D)-printed airway splint for use in long-segment airway reconstruction. CTG is designed to recapitulate the 3D extracellular matrix of the trachea with stable mechanical properties imparted from the extraluminal airway splint. We performed segmental orthotopic tracheal replacement in a mouse microsurgical model. MicroCT was used to measure graft patency. Tracheal neotissue formation was quantified histologically. Airflow dynamic properties were analyzed using computational fluid dynamics. We found that CTG are easily implanted and did not result in vascular erosion, tracheal injury, or inflammation. Graft epithelialization and endothelialization were comparable with CTG to control. Tracheal collapse was absent with CTG. Composite tracheal scaffolds combine biocompatible synthetic support with PDTG, supporting the regeneration of host epithelium while maintaining graft structure.