Tissue-engineered tracheal implants: Advancements, challenges, and clinical considerations

Understanding the anatomical basis of anorectal fistulas and their surgical management: exploring different types for enhanced precision and safety

Anorectal fistulas remain one of the most challenging conditions in colorectal surgery and require precise anatomical knowledge for successful management. This comprehensive review synthesizes the current evidence on the anatomical foundations of fistula development and treatment, particularly focusing on the cryptoglandular hypothesis and its clinical implications. A systematic analysis of the recent literature has examined the relationship between anatomical structures and fistula formation, classification systems, diagnostic modalities, and therapeutic approaches. The review revealed that anatomical considerations fundamentally influence treatment outcomes, with modern imaging techniques achieving up to 98% accuracy in delineating fistula anatomy. Key findings demonstrate that surgical success rates vary significantly based on anatomical complexity: 92-97% for simple fistulas versus 40-95% for complex cases using sphincter-sparing techniques. Emerging minimally invasive approaches and regenerative therapies, including mesenchymal stem cells, show promising results with 50-60% healing rates in complex cases. Special considerations are needed for complex cases such as Crohn's disease-related and rectovaginal fistulas. This review provides surgeons with an evidence-based framework for selecting optimal treatment strategies based on anatomical considerations, emphasizing the importance of preserving the anal sphincter function while achieving complete fistula eradication. Integrating advanced imaging, surgical techniques, and emerging therapies offers new possibilities for improving patient outcomes. This review aimed to bridge the gap between anatomical knowledge and practical surgical application, enhance clinical decision-making, and improve patient outcomes in anorectal fistula management.

Dynamic single-cell transcriptomic reveals the cellular heterogeneity and a novel fibroblast subpopulation in laryngotracheal stenosis

BACKGROUND

Laryngotracheal stenosis (LTS), a pathological narrowing of the upper airway caused by excessive extracellular matrix (ECM) deposition, often leads to dyspnea and even respiratory failure. However, systematic studies addressing the specific subpopulations and their contribution to LTS development still remain underexplored.

RESULTS

We collected laryngotracheal tissue at multiple time points of LTS rat model, established by injuring their laryngotracheal lining, and performed dynamic single-cell RNA sequencing (scRNA-seq) to elucidate the transcriptomic atlas of LTS development. The results showed, from the inflammatory state to the repair/fibrotic state, infiltration of immune cells such as monocyte macrophages decreased and fibroblast increased. We delineated the markers and functional status of different fibroblasts subsets and identified that fibrotic fibroblasts may originate from multiple fibroblast subpopulations, including a new subpopulation characterized by the expression of chondrogenic markers such as Ucma and Col2a1, we designated this subcluster as chondrocyte injury-related fibroblasts (CIRF). Furthermore, we categorized monocytes/macrophages into several subtypes and identified that SPP1 high macrophages represented the largest macrophage subpopulation in LTS, providing evidence to clarify the importance of SPP1 macrophages in fibrosis disease. Our findings also revealed the interactions among these cells to explore the molecular mechanism associated with LTS pathogenesis.

CONCLUSIONS

Our study, for the first time, conducted dynamic scRNA-seq on LTS, revealing the cellular heterogeneity and providing a valuable resource for exploring the intricate molecular landscape of LTS. We propose CIRF may represent a tissue-specific fibroblast lineage in LTS and potentially originate from cells in the perichondrium of the trachea and transform into fibrotic fibroblasts. Integration of our study with those of other respiratory fibrotic diseases will allow for a comprehensive understanding of airway remodeling in respiratory diseases and exploring potential new therapeutic targets for their treatment.

The role of the glutathione pathway in tracheal regeneration with aortic allografts through antioxidant-driven tissue integration

Tracheal regeneration remains a major challenge due to the lack of efficient graft integration and functional restoration. Current approaches fail to address oxidative stress-induced tissue remodeling. Here, we show that the glutathione pathway plays a pivotal role in tracheal regeneration with aortic allografts by modulating redox homeostasis and promoting host-graft integration. Through transcriptomic profiling, histological analyses, and functional assessment, we demonstrate that antioxidant-driven tissue remodeling enhances epithelialization, neovascularization, and extracellular matrix organization, thereby improving graft stability and biomechanical properties. These findings provide mechanistic insights into oxidative stress-mediated tissue remodeling and suggest that targeting redox signaling could optimize bioengineered tracheal grafts for clinical translation.

Decellularization techniques: unveiling the blueprint for tracheal tissue engineering

Certain congenital or acquired diseases and defects such as tracheo-oesophageal fistula, tracheomalacia, tracheal stenosis, airway ischemia, infections, and tumours can cause damage to the trachea. Treatments available do not offer any permanent solutions. Moreover, long-segment defects in the trachea have no available surgical treatments. Tissue engineering has gained popularity in current regenerative medicine as a promising approach to bridge this gap. Among the various tissue engineering techniques, decellularization is a widely used approach that removes the cellular and nuclear contents from the tissue while preserving the native extracellular matrix components. The decellularized scaffolds exhibit significantly lower immunogenicity and retain the essential biomechanical and proangiogenic properties of native tissue, creating a foundation for trachea regeneration. The present review provides an overview of trachea decellularization advancements, exploring how recellularization approaches can be optimized by using various stem cells and tissue-specific cells to restore the scaffold's structure and function. We examine critical factors such as mechanical properties, revascularization, and immunogenicity involved in the transplantation of tissue-engineered grafts.

Tracheal transplantation: lessons learned that may apply to lung transplantation

PURPOSE OF REVIEW

The purpose of this review is to explore the lessons learned from experimental and human tracheal transplantation to determine if this information may be applied to lung transplantation.

RECENT FINDINGS

Experimental work in animal models and the recent human tracheal transplantation suggests that a robust tracheal vascular supply prevents anastomotic complications. Further, this work demonstrates that tracheal allografts undergo a progressive chimerism as recipient epithelium repopulates the allograft. In contrast to most vascularized composite allografts such as hand and face transplantation that experience high rates of rejection, the tracheal allograft did not demonstrate rejection. This may suggest that tissue chimerism plays a role in evading immune-mediated allograft rejection.

SUMMARY

While anastomotic complications and chronic allograft rejection are the most common complications related to lung transplantation, the findings associated with tracheal transplantation may have implications for both reducing complications associated with lung transplantation.

Hybrid 3D bioprinting for advanced tissue-engineered trachea: merging fused deposition modeling (FDM) and top-down digital light processing (DLP)

In this present study, we introduce an innovative hybrid 3D bioprinting methodology that integrates fused deposition modeling (FDM) with top-down digital light processing (DLP) for the fabrication of an artificial trachea. Initially, polycaprolactone (PCL) was incorporated using an FDM 3D printer to provide essential mechanical support, replicating the structure of tracheal cartilage. Subsequently, a chondrocyte-laden glycidyl methacrylated silk fibroin hydrogel was introduced via top-down DLP into the PCL scaffold (PCL-Sil scaffold). The mechanical evaluation of PCL-Sil scaffolds showed that they have greater flexibility than PCL scaffolds, with a higher deformation rate (PCL-Sil scaffolds: 140.9% ± 5.37% vs. PCL scaffolds: 124.3% ± 6.25%) and ability to withstand more force before fracturing (3.860 ± 0.140 N for PCL-Sil scaffolds vs. 2.502 ± 0.126 N for PCL scaffolds, ***P< 0.001). Both types of scaffolds showed similar axial compressive strengths (PCL-Sil scaffolds: 4.276 ± 0.127 MPa vs. PCL scaffolds: 4.291 ± 0.135 MPa). Additionally, PCL-Sil scaffolds supported fibroblast proliferation, indicating good biocompatibility.In vivotesting of PCL-Sil scaffolds in a partial tracheal defect rabbit model demonstrated effective tissue regeneration. The scaffolds were pre-cultured in the omentum for two weeks to promote vascularization before transplantation. Eight weeks after transplantation into the animal, bronchoscopy and histological analysis confirmed that the omentum-cultured PCL-Sil scaffolds facilitated rapid tissue regeneration and maintained the luminal diameter at the anastomosis site without signs of stenosis or inflammation. Validation study to assess the feasibility of our hybrid 3D bioprinting technique showed that structures, not only the trachea but also the vertebral bone-disc and trachea-lung complex, were successfully printed.

Challenges and Opportunities in Developing Tracheal Substitutes for the Recovery of Long-Segment Defects

Tracheal resection and reconstruction procedures are necessary when stenosis, tracheomalacia, tumors, vascular lesions, or tracheal injury cause a tracheal blockage. Replacement with a tracheal substitute is often recommended when the trauma exceeds 50% of the total length of the trachea in adults and 30% in children. Recently, tissue engineering and other advanced techniques have shown promise in fabricating biocompatible tracheal substitutes with physical, morphological, biomechanical, and biological characteristics similar to native trachea. Different polymers and biometals are explored. Even with limited success with tissue-engineered grafts in clinical settings, complete healing of tracheal defects remains a substantial challenge due to low mechanical strength and durability of the graft materials, inadequate re-epithelialization and vascularization, and restenosis. This review has covered a range of reconstructive and regenerative techniques, design criteria, the use of bioprostheses and synthetic grafts for the recovery of tracheal defects, as well as the traditional and cutting-edge methods of their fabrication, surface modification for increased immuno- or biocompatibility, and associated challenges.

Revolutionizing tracheal reconstruction: innovations in vascularized composite allograft transplantation

Tracheal defects, particularly those extending over long segments, present substantial challenges in reconstructive surgery due to complications in vascularization and integration with host tissues. Traditional methods, such as extended tracheostomies and alloplastic stents, often result in significant morbidity due to mucus plugging and mechanical erosion. Recent advances in vascularized composite allograft (VCA) transplantation have opened new avenues for effective tracheal reconstruction. This article reviews the evolution of tracheal reconstruction techniques, focusing on the shift from non-vascularized approaches to innovative revascularization methods that enhance graft integration and functionality. Key advancements include indirect revascularization techniques and the integration of regenerative medicine, which have shown promise in overcoming historical barriers to successful tracheal transplantation. Clinical case studies are presented to illustrate the complexities and outcomes of recent tracheal transplantation procedures, highlighting the potential for long-term success through the integration of advanced vascular engineering and immune modulation strategies. Furthermore, the role of chimerism in reducing graft rejection and the implications for future tracheal transplantation and tissue engineering efforts are discussed. This review underscores the transformative potential of VCA in tracheal reconstruction, paving the way for more reliable and effective treatments for extensive tracheal defects.