Tracheobronchial transplantation with a stem-cell-seeded bioartificial nanocomposite: a proof-of-concept study

Nanotechnology: The Future for Diagnostic and Therapeutic Intervention in Cardiovascular Diseases is Here

With advances in technology and medicine over the last 3 decades, cardiovascular medicine has evolved tremendously. Nanotechnology provides a promising future in personalized precision medicine. In this review, we delve into the current and prospective applications of nanotechnology and nanoparticles in cardiology. Nanotechnology has allowed for point-of-care testing such as high-sensitivity troponins, as well as more precise cardiac imaging. This review is focused on 3 diseases within cardiology: coronary artery disease, heart failure, and valvular heart disease. The use of nanoparticles in coronary stents has shown success in preventing in-stent thrombosis, as well as using nanosized drug delivery medications to prevent neointimal proliferation in a way that spares systemic toxicity. In addition, by using nanoparticles as drug delivery systems, nanotechnology can be utilized in the delivery of goal-directed medical therapy in heart failure patients. It has also been shown to improve cell therapy in this patient population by helping in cell retention of grafts. Finally, the use of nanoparticles in the manufacturing of bioprosthetic valves provides a promising future for the longevity and success of cardiac valve repair and replacement.

Global Bibliometric and Visualized Analysis of Tracheal Tissue Engineering Research

The development of tracheal tissue engineering (TTE) has seen a rapid growth in recent years. The purpose of this study was to investigate the global status, trends, and hotspots of TTE research based on bibliometrics and visualization analysis. Publications related to TTE were retrieved and included in the Web of Science Core Collection. VOSviewer and CiteSpace were used to generate knowledge maps. Six hundred fifty-five publications were identified, and the quantity of the annual publications worldwide was on the increase. International collaboration is a widespread reality. The United States led the world in the field of trachea tissue engineering, whereas University College London was the institution with the greatest contribution. In addition, Biomaterials had a great influence in this field, attracting the largest number of papers. Moreover, the topics of TTE research largely concentrated on the biomechanical scaffold preparation, the vascularization and epithelialization of scaffold, the tracheal cartilage regeneration, and the tissue-engineered tracheal transplantation. And the research on the application of decellularization and 3D printing for the construction of a tissue-engineered trachea was likely to receive more widespread attention in the future. Impact statement In recent years, tracheal tissue engineering (TTE) has experienced rapid growth. In this study, we investigated the worldwide status and trends of TTE research, and revealed the countries, institutions, journals, and authors that had made significant contributions to the field of TTE. Moreover, the possible research hotspots in the future were predicted. According to our research, researchers can gain a better understanding of the trends in this field, and stay informed of the most current research by tracking key journals, institutions, and authors.

Application of aortic allograft in trachea transplantation

BACKGROUND

The use of tracheal implants for tracheal reconstruction remains a challenge in thoracic medicine due to the complex structure of the trachea in mammalian organisms, including smooth muscles, cartilage, mucosa, blood vessels, cilia, and other tissues, and the difficulty in achieving tracheal regeneration using implants from either allografts or synthetic biomaterials.

METHODS

This project used the Lee-Sung strain pig, a swine breed local to Taiwan, as the experimental subject. The aorta of the pig was harvested, decellularized to form the scaffold, and transplanted into the trachea of allogeneic pigs together with growth factors. Postoperative physiological function and tissue changes were observed. The postoperative physiological parameters of the LSP were monitored, and they were sacrificed after a certain period to observe the pathological changes in the tracheal epithelial cells and cartilages.

RESULTS

Overall, six LSP tracheal transplantations were performed between March 4, 2020, and March 10, 2021. These included aortic patch anastomosis for pig 1 and aortic segmental anastomosis for pigs 2-6. The shortest and longest survival periods were 1 day and 147 days, respectively. Excluding the pig that survived for only 1 day due to a ruptured graft anastomosis, all other subjects survived for over 1 month on average.

CONCLUSION

In this study, we grafted a decellularized porcine aorta into a recipient pig with a tracheal defect. We found cryopreservation of the allogeneic aorta transplantation was a feasible and safe method for the management of airway disease, and immunosuppressants were unnecessary during the treatment course.

Pre-epithelialized cryopreserved tracheal allograft for neo-trachea flap engineering

Background: Tracheal reconstruction presents a challenge because of the difficulty in maintaining the rigidity of the trachea to ensure an open lumen and in achieving an intact luminal lining that secretes mucus to protect against infection. Methods: On the basis of the finding that tracheal cartilage has immune privilege, researchers recently started subjecting tracheal allografts to "partial decellularization" (in which only the epithelium and its antigenicity are removed), rather than complete decellularization, to maintain the tracheal cartilage as an ideal scaffold for tracheal tissue engineering and reconstruction. In the present study, we combined a bioengineering approach and a cryopreservation technique to fabricate a neo-trachea using pre-epithelialized cryopreserved tracheal allograft (ReCTA). Results: Our findings in rat heterotopic and orthotopic implantation models confirmed that tracheal cartilage has sufficient mechanical properties to bear neck movement and compression; indicated that pre-epithelialization with respiratory epithelial cells can prevent fibrosis obliteration and maintain lumen/airway patency; and showed that a pedicled adipose tissue flap can be easily integrated with a tracheal construct to achieve neovascularization. Conclusion: ReCTA can be pre-epithelialized and pre-vascularized using a 2-stage bioengineering approach and thus provides a promising strategy for tracheal tissue engineering.

Bioengineering lungs: An overview of current methods, requirements, and challenges for constructing scaffolds

Chronic respiratory diseases remain a significant health burden worldwide. The only option for individuals with end-stage lung failure remains Lung Transplantation. However, suitable organ donor shortages and immune rejection following transplantation remain a challenge. Since alternative options are urgently required to increase tissue availability for lung transplantation, researchers have been exploring lung bioengineering extensively, to generate functional, transplantable organs and tissue. Additionally, the development of physiologically-relevant artificial tissue models for testing novel therapies also represents an important step toward finding a definite clinical solution for different chronic respiratory diseases. This mini-review aims to highlight some of the most common methodologies used in bioengineering lung scaffolds, as well as the benefits and disadvantages associated with each method in conjunction with the current areas of research devoted to solving some of these challenges in the area of lung bioengineering.

The Growing Medical Need for Tracheal Replacement: Reconstructive Strategies Should Overcome Their Limits

Breathing, being predominantly an automatic action, is often taken for granted. However, respiratory diseases affect millions of people globally, emerging as one of the major causes of disability and death overall. Among the respiratory dysfunctions, tracheal alterations have always represented a primary challenge for clinicians, biologists, and engineers. Indeed, in the case of wide structural alterations involving more than 50% of the tracheal length in adults or 30% in children, the available medical treatments are ineffective or inapplicable. So far, a plethora of reconstructive approaches have been proposed and clinically applied to face this growing, unmet medical need. Unfortunately, none of them has become a well-established and routinely applied clinical procedure to date. This review summarizes the main clinical reconstructive attempts and classifies them as non-tissue engineering and tissue engineering strategies. The analysis of the achievements and the main difficulties that still hinder this field, together with the evaluation of the forefront preclinical experiences in tracheal repair/replacement, is functional to promote a safer and more effective clinical translation in the near future.

Successful Total Tracheal Replacement by Cryopreserved Aortic Allograft in a Patient Post-COVID-19 Infection

This is the first report to our knowledge of a successful total tracheal replacement in a post-COVID-19 patient by cryopreserved aortic allograft. The graft was anastomosed to the cricoid and carina; a silicon stent was inserted to ensure patency. The patient was extubated on the operative table and was immediately able to breathe, speak, and swallow. No immunosuppression was administered. Three weeks after surgery, the patient was discharged from hospital in excellent health, and was able to resume his normal lifestyle, work, and activity as an amateur cyclist. Two months after surgery, the patient assumes aerosol with saline solution three times per day and no other therapy; routine bronchoscopy to clear secretions is no longer needed.

Design and In Vivo Testing of Novel Single-Stage Tendon Graft Using Polyurethane Nanocomposite Polymer for Tendon Reconstruction

Severe trauma, failure of prior surgical repair, delayed presentation and excessive scarring around the flexor tendon bed often necessitate a two-stage surgical reconstruction, where a silicone spacer is used in the first stage to recreate the fibro-osseous tunnel through which the tendon graft can glide in the second stage. This staged procedure involves great commitment on the part of both patient and surgeon, over the course of several months, involving a prolonged period of rehabilitation that can be quite disruptive to the patient's life and work. Reducing this from a two-stage into a single-stage procedure, therefore, has the potential to reduce rehabilitation time and cost, expedite return to work, and improve outcomes. To address this, we developed polyurethane (PU) nanocomposite, as an engineered tendon sheath, for treatment of delayed flexor tendon division as a single-stage procedure. The clinically conformant tubular grafts were tested for their efficacy in the peroneus tertius tendon of 6 Mule sheep for 3 months. Semi-quantitative histological assessment was carried out by analysing four descriptive layers: tendon, tendon/polymer sheath interface, polymer sheath, and polymer sheath/surrounding tissue. Four (out of 6) of the implanted PU nanocomposites showed moderate to substantial healing of the injured tendons, with minimal adhesion after repair, ensuring good gliding movement. No statistical differences were observed in tendon repair based on intra-regional variation in the explanted grafts, indicating homogeneity in tendon repair. Overall, the PU nanocomposite bears morphological stability and functionality for tendon repair, in single-stage surgical reconstruction, demonstrating promising evidence for clinical translation.

Facial Cartilaginous Reconstruction-A Historical Perspective, State-of-the-Art, and Future Directions

Importance: Reconstruction of facial deformity poses a significant surgical challenge due to the psychological, functional, and aesthetic importance of this anatomical area. There is a need to provide not only an excellent colour and contour match for skin defects, but also a durable cartilaginous structural replacement for nasal or auricular defects. The purpose of this review is to describe the history of, and state-of-the-art techniques within, facial cartilaginous surgery, whilst highlighting recent advances and future directions for this continually advancing specialty. Observations: Limitations of synthetic implants for nasal and auricular reconstruction, such as silicone and porous polyethylene, have meant that autologous cartilage tissue for such cases remains the current gold standard. Similarly, tissue engineering approaches using unrelated cells and synthetic scaffolds have shown limited in vivo success. There is increasing recognition that both the intrinsic and extrinsic microenvironment are important for tissue engineering and synthetic scaffolds fail to provide the necessary cues for cartilage matrix secretion. Conclusions and Relevance: We discuss the first-in-man studies in the context of biomimetic and developmental approaches to engineering durable cartilage for clinical translation. Implementation of engineered autologous tissue into clinical practise could eliminate donor site morbidity and represent the next phase of the facial reconstruction evolution.

Current Strategies for Tracheal Replacement: A Review

Airway cancers have been increasing in recent years. Tracheal resection is commonly performed during surgery and is burdened from post-operative complications severely affecting quality of life. Tracheal resection is usually carried out in primary tracheal tumors or other neoplasms of the neck region. Regenerative medicine for tracheal replacement using bio-prosthesis is under current research. In recent years, attempts were made to replace and transplant human cadaver trachea. An effective vascular supply is fundamental for a successful tracheal transplantation. The use of biological scaffolds derived from decellularized tissues has the advantage of a three-dimensional structure based on the native extracellular matrix promoting the perfusion, vascularization, and differentiation of the seeded cell typologies. By appropriately modulating some experimental parameters, it is possible to change the characteristics of the surface. The obtained membranes could theoretically be affixed to a decellularized tissue, but, in practice, it needs to ensure adhesion to the biological substrate and/or glue adhesion with biocompatible glues. It is also known that many of the biocompatible glues can be toxic or poorly tolerated and induce inflammatory phenomena or rejection. In tissue and organ transplants, decellularized tissues must not produce adverse immunological reactions and lead to rejection phenomena; at the same time, the transplant tissue must retain the mechanical properties of the original tissue. This review describes the attempts so far developed and the current lines of research in the field of tracheal replacement.

Insulin-like growth factor 1 promotes the extension of Tracheal Epithelium in an in Vitro Tracheal organ culture model

OBJECTIVE

Rapid epithelialization is crucial to maintain tracheal patency and prevent potential graft failure in tracheal reconstruction after tracheal resection for cancer with tracheal infiltration or tracheal stenosis. Insulin-like growth factor 1 is a liver-secreted endocrine molecule that controls cell proliferation, differentiation, and apoptosis and has been reported to promote epithelialization in several organs. Here, we utilized mouse tracheal organ cultures to examine the effect of insulin-like growth factor 1 on tracheal epithelialization.

METHODS

The trachea was resected from thirteen-week-old female ICR mice, and cut into small plate-shaped tracheal sections. First, the expression of insulin-like growth factor 1 receptor was assessed by immunohistochemistry. Secondly, the tracheal sections were cultured for seven days in the culture medium, and the morphological change during the seven-day culture was assessed by immunohistochemistry, hematoxylin and eosin staining, and scanning electron microscopy. Moreover, the tracheal sections were cultured for 48 h with different concentration of insulin-like growth factor 1 (0, 0.1, 1 and 10 µg/mL) in the culture medium, and the extension length of the tracheal epithelium during culture was measured in order to assess the effect of topical IGF1 on tracheal epithelialization.

RESULTS

Immunohistochemistry showed that insulin-like growth factor 1 receptor was expressed in tracheal epithelium. Immunohistochemistry, hematoxylin and eosin staining, and scanning electron microscopy showed that the tracheal organ cultures were stable for at least seven days without apparent morphological damage. The effect of insulin-like growth factor 1 on tracheal epithelialization was examined in plate-shaped tracheal sections cultured in medium supplemented with or without insulin-like growth factor 1 for 48 h. We also found that the epithelial edge of plate-shaped tracheal sections extended further along the surface of the tracheal section in culture medium containing insulin-like growth factor 1 compared with that in culture medium without insulin-like growth factor 1.

CONCLUSION

The current study using an in vitro mouse tracheal organ culture model demonstrated that topical insulin-like growth factor 1 treatment promoted the extension of tracheal epithelium, suggesting the potential utility of insulin-like growth factor 1 in aiding rapid tracheal epithelialization in patients requiring tracheal reconstruction using tissue-engineered tracheas.

Rapid Preparation Method for Preparing Tracheal Decellularized Scaffolds: Vacuum Assistance and Optimization of DNase I

Decellularized scaffolds are an effective way for tracheal tissue engineering to perform alternative treatments. However, clinically used decellularized tracheal scaffolds have a long preparation cycle. The purpose of this study is to improve the efficiency of decellularization by vacuum assistance and optimizing the concentration of DNase I in the decellularization process and to quickly obtain tracheal decellularized scaffolds. The trachea of New Zealand white rabbits was decellularized with 2, 4, 6, and 8 KU/mL DNase I under vacuum. The performance of the decellularized tracheal scaffold was evaluated through histological analysis, immunohistochemical staining, DNA residue, extracellular matrix composition, scanning electron microscopy, mechanical properties, cell compatibility, and in vivo experiments. Histological analysis and immunohistochemical staining showed that compared with the native trachea, the hierarchical structure of the decellularized trachea remained unchanged after decellularization, nonchondrocytes were effectively removed, and the antigenicity of the scaffold was significantly weakened. Deoxyribonucleic acid (DNA) quantitative analysis showed that the amount of residual DNA in the 6-KU group was significantly decreased. Scanning electron microscopy and mechanical tests showed that small gaps appeared in the basement membrane of the 6-KU group, and the mechanical properties decreased. The CCK-8 test results and in vivo experiments showed that the 6-KU group's acellular scaffold had good cell compatibility and new blood vessels were visible on the surface. Taken together, the 6-KU group could quickly prepare rabbit tracheal scaffolds with good decellularization effects in only 2 days, which significantly shortened the preparation cycle reducing the required cost.

Bone marrow mesenchymal stem cell-derived exosomes promote rotator cuff tendon-bone healing by promoting angiogenesis and regulating M1 macrophages in rats

BACKGROUND

Rotator cuff tears (RCTs) often require reconstructive surgery. Tendon-bone healing is critical for the outcome of rotator cuff reconstruction, but the process of tendon-bone healing is complex and difficult. Mesenchymal stem cells (MSCs) are considered to be an effective method to promote tendon-bone healing. MSCs have strong paracrine, anti-inflammatory, immunoregulatory, and angiogenic potential. Recent studies have shown that MSCs achieve many regulatory functions through exosomes. The purpose of this study was to explore the role of bone marrow mesenchymal stem cell-derived exosomes (BMSC-Exos) in tendon-bone healing.

METHODS

Our study found that BMSC-Exos promote the proliferation, migration, and angiogenic tube formation of human umbilical vein endothelial cells (HUVECs). The mechanism by which BMSC-Exos achieve this may be through the regulation of the angiogenic signaling pathway. In addition, BMSC-Exos can inhibit the polarization of M1 macrophages and inhibit the secretion of proinflammatory factors by M1 macrophages. After rotator cuff reconstruction in rats, BMSC-Exos were injected into the tail vein to analyze their effect on the rotator cuff tendon-bone interface healing.

RESULTS

It was confirmed that BMSC-Exos increased the breaking load and stiffness of the rotator cuff after reconstruction in rats, induced angiogenesis around the rotator cuff endpoint, and promoted growth of the tendon-bone interface.

CONCLUSION

BMSC-Exos promote tendon-bone healing after rotator cuff reconstruction in rats by promoting angiogenesis and inhibiting inflammation.

The current status and outlook of trachea transplantation

PURPOSE OF REVIEW

The trachea is an enigmatic organ due to its complex morphology. Although circumferential tracheal defects are extremely difficult to repair with autologous tissue or with an allotransplant, the trachea has been touted as the first organ that could be regenerated. This review provides a comprehensive evaluation of the published evidence in tracheal tissue replacement surgery.

RECENT FINDINGS

In recent years, reports of successful tracheal regeneration have attracted great interest. Despite descriptions of the trachea as a perhaps uniquely regeneratable tissue since 2008, critical reporting provided insights into the more complex realities of tracheal regeneration attempts and led to the retraction of some articles making tracheal regeneration claims. Allotransplantation of the trachea is hindered by numerous difficult obstacles. The most promising approach developed thus far for difficult-to-repair patch airway defects is tracheal allotransplantation, which allows for tapering and withdrawal of immunosuppressive therapy.

SUMMARY

Restoration of a long-segment circumferential tracheal defect remains an unmet challenge. Future clinical studies require thoroughly documented visual evidence of outcomes to reduce confusion surrounding tracheal replacement and to prevent future scandals like those seen previously in the tracheal regeneration story. VIDEO ABSTRACT: http://links.lww.com/COOT/A6.

Bioengineered airway epithelial grafts with mucociliary function based on collagen IV- and laminin-containing extracellular matrix scaffolds

Current methods to replace damaged upper airway epithelium with exogenous cells are limited. Existing strategies use grafts that lack mucociliary function, leading to infection and the retention of secretions and keratin debris. Strategies that regenerate airway epithelium with mucociliary function are clearly desirable and would enable new treatments for complex airway disease.Here, we investigated the influence of the extracellular matrix (ECM) on airway epithelial cell adherence, proliferation and mucociliary function in the context of bioengineered mucosal grafts. In vitro, primary human bronchial epithelial cells (HBECs) adhered most readily to collagen IV. Biological, biomimetic and synthetic scaffolds were compared in terms of their ECM protein content and airway epithelial cell adherence.Collagen IV and laminin were preserved on the surface of decellularised dermis and epithelial cell attachment to decellularised dermis was greater than to the biomimetic or synthetic alternatives tested. Blocking epithelial integrin α2 led to decreased adherence to collagen IV and to decellularised dermis scaffolds. At air-liquid interface (ALI), bronchial epithelial cells cultured on decellularised dermis scaffolds formed a differentiated respiratory epithelium with mucociliary function. Using in vivo chick chorioallantoic membrane (CAM), rabbit airway and immunocompromised mouse models, we showed short-term preservation of the cell layer following transplantation.Our results demonstrate the feasibility of generating HBEC grafts on clinically applicable decellularised dermis scaffolds and identify matrix proteins and integrins important for this process. The long-term survivability of pre-differentiated epithelia and the relative merits of this approach against transplanting basal cells should be assessed further in pre-clinical airway transplantation models.

Biomedical grafts for tracheal tissue repairing and regeneration "Tracheal tissue engineering: an overview"

Airway system is a vital part of the living being body. Trachea is the upper respiratory portion that connects nostril and lungs and has multiple functions such as breathing and entrapment of dust/pathogen particles. Tracheal reconstruction by artificial prosthesis, stents, and grafts are performed clinically for the repairing of damaged tissue. Although these (above-mentioned) methods repair the damaged parts, they have limited applicability like small area wounds and lack of functional tissue regeneration. Tissue engineering helps to overcome the above-mentioned problems by modifying the traditional used stents and grafts, not only repair but also regenerate the damaged area to functional tissue. Bioengineered tracheal replacements are biocompatible, nontoxic, porous, and having 3D biomimetic ultrastructure with good mechanical strength, which results in faster and better tissue regeneration. Till date, the bioengineered tracheal replacements studies have been going on preclinical and clinical levels. Besides that, still many researchers are working at advance level to make extracellular matrix-based acellular, 3D printed, cell-seeded grafts including living cells to overcome the demand of tissue or organ and making the ready to use tracheal reconstructs for clinical application. Thus, in this review, we summarized the tracheal tissue engineering aspects and their outcomes.

Synthetic tracheal grafts seeded with bone marrow cells fail to generate functional tracheae: First long-term follow-up study

OBJECTIVE

Synthetic tracheal grafts seeded with autologous bone marrow-mononuclear cells (BM-MNCs) have been described as becoming living and functional grafts representing a promising option for tracheal replacement for pathologies unamenable by segmental resection or autologous repair. This study aimed to present the first long-term follow-up of these procedures in humans.

METHODS

We retrospectively analyzed 3 patients who received synthetic tracheal grafts seeded with BM-MNCs implanted.

RESULTS

Patient 1 was a 37-year-old man with mucoepidermoid carcinoma, the first-ever human to receive a synthetic tracheal graft seeded with BM-MNCs. Patient 2 was a 30-year-old man with adenoid cystic carcinoma, and patient 3 was a 22-year-old woman with an iatrogenic tracheal injury. All patients developed graft-related complications necessitating multiple surgical reinterventions. Patient 1 was hospitalized for 8 months before dying from respiratory failure secondary to graft dehiscence 32 months after implantation. Patient 2 died 3.5 months after implantation from undisclosed causes. Patient 3 received a second synthetic tracheal graft after 11 months and an allogeneic trachea and lung transplantation 45 months after the primary implantation. Patient 3 underwent 191 surgical interventions after the primary implantation and spent 55 months in the intensive care unit before dying from airway bleeding. All patients' bronchoscopic, histologic, and radiologic investigations demonstrated graft-associated complications, including anastomotic fistulae and obstructive granulation tissue, without graft vascularization, mucosal lining, or integration into adjacent tissues.

CONCLUSIONS

Synthetic tracheal grafts seeded with BM-MNCs do not become living functional tracheal grafts and lead to debilitating complications and death.

Tracheal Replacement Therapy with a Stem Cell-Seeded Graft: Lessons from Compassionate Use Application of a GMP-Compliant Tissue-Engineered Medicine

Tracheal replacement for the treatment of end‐stage airway disease remains an elusive goal. The use of tissue‐engineered tracheae in compassionate use cases suggests that such an approach is a viable option. Here, a stem cell‐seeded, decellularized tissue‐engineered tracheal graft was used on a compassionate basis for a girl with critical tracheal stenosis after conventional reconstructive techniques failed. The graft represents the first cell‐seeded tracheal graft manufactured to full good manufacturing practice (GMP) standards. We report important preclinical and clinical data from the case, which ended in the death of the recipient. Early results were encouraging, but an acute event, hypothesized to be an intrathoracic bleed, caused sudden airway obstruction 3 weeks post‐transplantation, resulting in her death. We detail the clinical events and identify areas of priority to improve future grafts. In particular, we advocate the use of stents during the first few months post‐implantation. The negative outcome of this case highlights the inherent difficulties in clinical translation where preclinical in vivo models cannot replicate complex clinical scenarios that are encountered. The practical difficulties in delivering GMP grafts underscore the need to refine protocols for phase I clinical trials. Stem Cells Translational Medicine2017;6:1458–1464

Trachea Engineering Using a Centrifugation Method and Mouse-Induced Pluripotent Stem Cells

The outcomes of tracheal transplantation for the treatment of airway stenosis are unsatisfactory. We investigated the feasibility of regeneration of the trachea using a rat decellularized tracheal scaffold and mouse-induced pluripotent stem (iPS) cells for in vivo transplantation. The rat trachea was first decellularized using a detergent/enzymatic treatment method. We successfully established a centrifugation method that can transplant cells onto the luminal surface of the decellularized rat tracheal scaffold circumferentially. Two types of mouse iPS cells were differentiated into definitive endoderm cells and transplanted onto the luminal surface of the decellularized tracheal matrix scaffold using this centrifugation method. For in vivo study, normal rat tracheas, no-cell rat tracheal scaffolds, or rat tracheal scaffolds recellularized with rat tracheal epithelial cells (EGV-4T) were orthotopically transplanted on F344 rats, and rat tracheal scaffolds recellularized with mouse iPS cells were transplanted on F344/NJc1-rnu/rnu rats. Rats transplanted with no-cell scaffolds or scaffolds recellularized with EGV-4T survived for 1 month, although airway stenosis was observed. One of the F344/NJc1-rnu/rnu rats transplanted with rat trachea regenerated using mouse iPS cells survived over 5 weeks. Histological analysis indicated the cause of death was airway stenosis due to colonic cellular proliferation of undifferentiated iPS cells. Re-epithelialization with numerous ciliated epithelial cells was observed in one of the rats transplanted with trachea bioengineered using iPS cells. In this study, we present a simple and efficient tracheal tissue engineering model using a centrifugation method in a small-animal model. Tissue-engineered trachea using decellularized tracheal scaffolds and iPS cells is potentially applicable for tracheal transplantation.

Challenges With the Development of Biomaterials for Sustainable Tissue Engineering

The field of tissue engineering has tantalizingly offered the possibility of regenerating new tissue in order to treat a multitude of diseases and conditions within the human body. Nevertheless, in spite of significant progress with in vitro and small animal studies, progress toward realizing the clinical and commercial endpoints has been slow and many would argue that ultimate goals, especially in treating those conditions which, as yet, do not have acceptable conventional therapies, may never be reached because of flawed scientific rationale. In other words, sustainable tissue engineering may not be achievable with current approaches. One of the major factors here is the choice of biomaterial that is intended, through its use as a "scaffold," to guide the regeneration process. For many years, effective specifications for these biomaterials have not been well-articulated, and the requirements for biodegradability and prior FDA approval for use in medical devices, have dominated material selection processes. This essay argues that these considerations are not only wrong in principle but counter-productive in practice. Materials, such as many synthetic bioabsorbable polymers, which are designed to have no biological activity that could stimulate target cells to express new and appropriate tissue, will not be effective. It is argued here that a traditional 'scaffold' represents the wrong approach, and that tissue-engineering templates that are designed to replicate the niche, or microenvironment, of these target cells are much more likely to succeed.

Long-Segment Tracheal Reconstruction With Free Radial Forearm Flap Reinforced by Rib Cartilage

Long-segment tracheal reconstruction remains a challenge. The ideal tracheal substitute should be an epithelialized tube to prevent stenosis and sufficiently rigid to maintain airflow patency. An autologous technique using a radial forearm free flap reinforced by rib cartilage has been recently described for tracheal reconstruction. We report here two cases of complex tracheal reconstruction with a modification of this technique, which consists of the creation of two independent skin paddles to allow the reconstruction of the trachea and a second adjacent defect (eg, cervical skin, esophagus). Airway patency was achieved with no stenosis, prolonged stenting, fistula, or necrosis after 26 and 44 months, respectively. We suggest that the satisfactory outcome obtained with this modified technique is a valuable option for tracheal and adjacent defect reconstruction without the need for a second flap.

Factors Influencing Poor Outcomes in Synthetic Tissue-Engineered Tracheal Replacement

OBJECTIVES

Humans receiving tissue-engineered tracheal grafts have experienced poor outcomes ultimately resulting in death or the need for graft explantation. We assessed the performance of the synthetic scaffolds used in humans with an ovine model of orthotopic tracheal replacement, applying standard postsurgical surveillance and interventions to define the factors that contributed to the complications seen at the bedside.

STUDY DESIGN

Large animal model.

SETTING

Pediatric academic research institute.

SUBJECTS AND METHODS

Human scaffolds were manufactured with an electrospun blend of polyethylene terephthalate and polyurethane reinforced with polycarbonate rings. They were seeded with autologous bone marrow-derived mononuclear cells and implanted in sheep. Animals were evaluated with routine bronchoscopy and fluoroscopy. Endoscopic dilation and stenting were performed to manage graft stenosis for up to a 4-month time point. Grafts and adjacent native airway were sectioned and evaluated with histology and immunohistochemistry.

RESULTS

All animals had signs of graft stenosis. Three of 5 animals (60%) designated for long-term surveillance survived until the 4-month time point. Graft dilation and stent placement resolved respiratory symptoms and prolonged survival. Necropsy demonstrated evidence of infection and graft encapsulation. Granulation tissue with signs of neovascularization was seen at the anastomoses, but epithelialization was never observed. Acute and chronic inflammation of the native airway epithelium was observed at all time points. Architectural changes of the scaffold included posterior wall infolding and scaffold delamination.

CONCLUSIONS

In our ovine model, clinically applied synthetic tissue-engineered tracheas demonstrated infectious, inflammatory, and mechanical failures with a lack of epithelialization and neovascularization.

Collagen sponge scaffolds containing growth factors for the functional regeneration of tracheal epithelium

Tracheal epithelia have barrier and mucociliary clearance functions that prevent invasion of extraneous particles and infectious materials. Hence, following tracheal reconstructions, functional and morphological regeneration of epithelia is required to prevent respiratory declines and infectious diseases. Although growth factors (GFs) promote the regeneration of tracheal epithelial morphologies, it remains unclear whether tracheal grafts containing GFs are beneficial for regeneration of tracheal epithelial functions. Thus, we fabricated collagen sponge scaffolds containing insulin-like GF-1 (IGF-1) and the basic fibroblast, hepatocyte, and epidermal GFs (bFGFs, HGFs, and EGFs, respectively), and we evaluated the effects of the grafts on the functional regeneration of tracheal epithelia. Partial tracheal defects were imposed surgically, and collagen sponges containing IGF-1, bFGF, HGF, or EGF were then transplanted to defect sites. Subsequent immunofluorescence studies suggested that EGF and bFGF contribute to regular distributions of tight junction molecules, and tracer permeability assays suggested that EGF and bFGF promote regeneration of barrier function. Increased ciliogenesis was also observed using scanning electron microscopy in reconstructed regions treated with EGF- and bFGF-supplemented collagen sponges. However, bFGF-supplemented collagen sponges led to greater microsphere transport than did EGF-supplemented sponges. The present data suggested that collagen sponge scaffold containing bFGF promotes functional regeneration of tracheal epithelial tissues.

Evaluation of Cilia Function in Rat Trachea Reconstructed Using Collagen Sponge Scaffold Seeded with Adipose Tissue-Derived Stem Cells

The tracheal lumen is essential for conducting air to the lung alveoli and for voice production. However, patients with severe tracheal stenosis and malignant tumors invading the trachea often require tracheal resection. Recently, various reported tissue engineering methods for tracheal reconstruction show that regeneration of ciliated epithelium in the reconstructed areas, as well as preservation of the luminal structure is possible. However, only few studies report on the mucociliary transport function in reconstructed tracheae. We investigated mucociliary transport function within rat tracheal epithelium, reorganized after autologous adipose tissue-derived stem cell (ASC) transplantation. Rat ASCs were expanded in culture, and then seeded in a collagen sponge, which was physically supported with a polypropylene framework. The ASC-seeded collagen sponge was transplanted into the rat tracheal defect. We then examined the motility and transport function of cilia generated in the transplanted area using ciliary beat frequency (CBF) and microsphere movement analyses. Our data suggested that autologous ASC transplantation promoted ciliogenesis, consistent with previous reports. The CBF analysis revealed that motility of the cilia generated in the ASC group was comparable to that observed in the normal rat tracheal epithelium. Transport function in the ASC group was higher than that in the control group. These data suggested that autologous ASC transplantation increased ciliated cells in the reconstructed area without significantly disrupting cilia motility, thereby promoting transport function regeneration. Autologous ASC transplantation is expected to be beneficial in morphological and functional regeneration of tracheal epithelium. Anat Rec, 303:471-477, 2020. © 2019 American Association for Anatomy.

Seeding and Implantation of a Biosynthetic Tissue-engineered Tracheal Graft in a Mouse Model

Treatment options for congenital or secondary long segment tracheal defects have historically been limited due to an inability to replace functional tissue. Tissue engineering holds great promise as a potential solution with its ability to integrate cells and signaling molecules into a 3-dimensional scaffold. Recent work with tissue engineered tracheal grafts (TETGs) has seen some success but their translation has been limited by graft stenosis, graft collapse, and delayed epithelialization. In order to investigate the mechanisms driving these issues, we have developed a mouse model for tissue engineered tracheal graft implantation. TETGs were constructed using electrospun polymers polyethylene terephthalate (PET) and polyurethane (PU) in a mixture of PET and PU (20:80 percent weight). Scaffolds were then seeded using bone marrow mononuclear cells isolated from 6-8 week-old C57BL/6 mice by gradient centrifugation. Ten million cells per graft were seeded onto the lumen of the scaffold and allowed to incubate overnight before implantation between the third and seventh tracheal rings. These grafts were able to recapitulate the findings of stenosis and delayed epithelialization as demonstrated by histological analysis and lack of Keratin 5 and Keratin 14 basal epithelial cells on immunofluorescence. This model will serve as a tool for investigating cellular and molecular mechanisms involved in host remodeling.

Mobilization of Transplanted Bone Marrow Mesenchymal Stem Cells by Erythropoietin Facilitates the Reconstruction of Segmental Bone Defect

Reconstruction of segmental bone defects poses a tremendous challenge for both orthopedic clinicians and scientists, since bone rehabilitation is requisite substantially and may be beyond the capacity of self-healing. Bone marrow mesenchymal stem cells (BMSCs) have been identified as an optimal progenitor cell source to facilitate bone repair since they have a higher ability for proliferation and are more easily accessible than mature osteoblastic cells. In spite of the potential of BMSCs in regeneration medicine, particularly for bone reconstruction, noteworthy limitations still remain in previous application of BMSCs, including the amount of cells that could be recruited, the compromised bone migration of grafted cells, reduced proliferation and osteoblastic differentiation ability, and likely tumorigenesis. Our current work demonstrates that BMSCs transplanted through the caudal vein can be mobilized by erythropoietin (EPO) to the bone defect area and participate in regeneration of new bone. Based on the histological analysis and micro-CT findings of this study, EPO can dramatically promote the effects on the osteogenesis and angiogenesis efficiency of BMSCs in vivo. Animals that underwent EPO+BMSC administration demonstrated a remarkable increase in new bone formation, tissue structure organization, new vessel density, callus formation, and bone mineral density (BMD) compared with the BMSCs alone and control groups. At the biomechanical level, we demonstrated that combing transplantation of EPO and BMSCs enhances bone defect reconstruction by increasing the strength of the diaphysis, making it less fragile. Therefore, combination therapy using EPO infusion and BMSC transplantation may be a new therapeutic strategy for the reconstruction of segmental bone defect.

Mouse Model of Tracheal Replacement With Electrospun Nanofiber Scaffolds

OBJECTIVES

The clinical experience with tissue-engineered tracheal grafts (TETGs) has been fraught with graft stenosis and delayed epithelialization. A mouse model of orthotopic replacement that recapitulates the clinical findings would facilitate the study of the cellular and molecular mechanisms underlying graft stenosis.

METHODS

Electrospun nanofiber tracheal scaffolds were created using nonresorbable (polyethylene terephthalate + polyurethane) and co-electrospun resorbable (polylactide-co-caprolactone/polyglycolic acid) polymers (n = 10/group). Biomechanical testing was performed to compare load displacement of nanofiber scaffolds to native mouse tracheas. Mice underwent orthotopic tracheal replacement with syngeneic grafts (n = 5) and nonresorbable (n = 10) and resorbable (n = 10) scaffolds. Tissue at the anastomosis was evaluated using hematoxylin and eosin (H&E), K5+ basal cells were evaluated with the help of immunofluorescence testing, and cellular infiltration of the scaffold was quantified. Micro computed tomography was performed to assess graft patency and correlate radiographic and histologic findings with respiratory symptoms.

RESULTS

Synthetic scaffolds were supraphysiologic in compression tests compared to native mouse trachea ( P < .0001). Nonresorbable scaffolds were stiffer than resorbable scaffolds ( P = .0004). Eighty percent of syngeneic recipients survived to the study endpoint of 60 days postoperatively. Mean survival with nonresorbable scaffolds was 11.40 ± 7.31 days and 6.70 ± 3.95 days with resorbable scaffolds ( P = .095). Stenosis manifested with tissue overgrowth in nonresorbable scaffolds and malacia in resorbable scaffolds. Quantification of scaffold cellular infiltration correlated with length of survival in resorbable scaffolds (R² = 0.95, P = .0051). Micro computed tomography demonstrated the development of graft stenosis at the distal anastomosis on day 5 and progressed until euthanasia was performed on day 11.

CONCLUSION

Graft stenosis seen in orthotopic tracheal replacement with synthetic tracheal scaffolds can be modeled in mice. The wide array of lineage tracing and transgenic mouse models available will permit future investigation of the cellular and molecular mechanisms underlying TETG stenosis.

Differential epithelial growth in tissue-engineered larynx and trachea generated from postnatal and fetal progenitor cells

Postnatal organ-specific stem and progenitor cells are an attractive potential donor cell for tissue-engineering because they can be harvested autologous from the recipient and have sufficient potential to regenerate the tissue of interest with less risk for ectopic growth or tumor formation compared to donor cells from embryonic or fetal sources. We describe the generation of tissue-engineered larynx and trachea (TELT) from human and mouse postnatal organoid units (OU) as well as from human fetal OU. Mouse TELT contained differentiated respiratory epithelium lining large lumens, cartilage and smooth muscle. In contrast, human postnatal TE trachea, formed small epithelial lumens with rare differentiation, in addition to smooth muscle and cartilage. Human fetal TELT contained the largest epithelial lumens with all differentiated cell types as well as smooth muscle and cartilage. Increased epithelial cytokeratin 14 was identified in both human fetal and postnatal TELT compared to native trachea, consistent with regenerative basal cells. Cilia in TELT epithelium also demonstrated function with beating movements. While both human postnatal and fetal progenitors have the potential to generate TELT, there is more epithelial growth and differentiation from fetal progenitors, highlighting fundamental differences in these cell populations.

Cardiovascular stents: overview, evolution, and next generation

Compared to bare-metal stents (BMSs), drug-eluting stents (DESs) have been regarded as a revolutionary change in coronary artery diseases (CADs). Releasing pharmaceutical agents from the stent surface was a promising progress in the realm of cardiovascular stents. Despite supreme advantages over BMSs, in-stent restenosis (ISR) and long-term safety of DESs are still deemed ongoing concerns over clinically application of DESs. The failure of DESs for long-term clinical use is associated with following factors including permanent polymeric coating materials, metallic stent platforms, non-optimal drug releasing condition, and factors that have recently been supposed as contributory factors such as degradation products of polymers, metal ions due to erosion and degradation of metals and their alloys utilizing in some stents as metal frameworks. Discovering the direct relation between stent materials and associating adverse effects is a complicated process, and yet it has not been resolved. For clinical success it is of significant importance to optimize DES design and explore novel strategies to overcome all problems including inflammatory response, delay endothelialization, and sub-acute stent thrombosis (ST) simultaneously. In this work, scientific reports are reviewed particularly focusing on recent advancements in DES design which covers both potential improvements of existing and recently novel prototype stent fabrications. Covering a wide range of information from the BMSs to recent advancement, this study mostly sheds light on DES's concepts, namely stent composition, drug release mechanism, and coating techniques. This review further reports different forms of DES including fully biodegradable DESs, shape-memory ones, and polymer-free DESs.

Aortic allografts: final destination?-a summary of clinical tracheal substitutes

The patient population in desperate need for an airway substitute are individuals with long segment tracheal defects that are considered, technically, inoperable. Regardless of the underlying etiology, benign or malignant growing processes, this patient category enters a palliative setting or require tracheal transplantation. Different airway substitutes have been categorized by Grillo as follows; tracheal transplantation, autogenous tissue, non-viable tissue, tissue-engineering and foreign materials. These fields have been explored in the past in animal models and in clinical patients. Research on airway replacement has been exposed to a level of controversies in the past years. The field has been turbulent and apocryphal. In particular, the area of tissue-engineering using stem cells has suffered from a major set-back leaving scientists, clinicians and ethical committees skeptical. Recently, a hopeful study emerged using aortic allografts as tracheal substitutes in patients with airway defects. The initial results seem promising and reliable. The developments of the field at this point seem striking and hopeful. The focus of this review is to shed light on developments in the field of aortic allografts as substitute for tracheal replacement.

How to build a lung: latest advances and emerging themes in lung bioengineering

Chronic respiratory diseases remain a major cause of morbidity and mortality worldwide. The only option at end-stage disease is lung transplantation, but there are not enough donor lungs to meet clinical demand. Alternative options to increase tissue availability for lung transplantation are urgently required to close the gap on this unmet clinical need. A growing number of tissue engineering approaches are exploring the potential to generate lung tissue ex vivo for transplantation. Both biologically derived and manufactured scaffolds seeded with cells and grown ex vivo have been explored in pre-clinical studies, with the eventual goal of generating functional pulmonary tissue for transplantation. Recently, there have been significant efforts to scale-up cell culture methods to generate adequate cell numbers for human-scale bioengineering approaches. Concomitantly, there have been exciting efforts in designing bioreactors that allow for appropriate cell seeding and development of functional lung tissue over time. This review aims to present the current state-of-the-art progress for each of these areas and to discuss promising new ideas within the field of lung bioengineering.

Feasibility of Bioengineered Tracheal and Bronchial Reconstruction Using Stented Aortic Matrices

IMPORTANCE

Airway transplantation could be an option for patients with proximal lung tumor or with end-stage tracheobronchial disease. New methods for airway transplantation remain highly controversial.

OBJECTIVE

To establish the feasibility of airway bioengineering using a technique based on the implantation of stented aortic matrices.

DESIGN, SETTING, AND PARTICIPANTS

Uncontrolled single-center cohort study including 20 patients with end-stage tracheal lesions or with proximal lung tumors requiring a pneumonectomy. The study was conducted in Paris, France, from October 2009 through February 2017; final follow-up for all patients occurred on November 2, 2017.

EXPOSURES

Radical resection of the lesions was performed using standard surgical techniques. After resection, airway reconstruction was performed using a human cryopreserved (-80°C) aortic allograft, which was not matched by the ABO and leukocyte antigen systems. To prevent airway collapse, a custom-made stent was inserted into the allograft. In patients with proximal lung tumors, the lung-sparing intervention of bronchial transplantation was used.

MAIN OUTCOMES AND MEASURES

The primary outcome was 90-day mortality. The secondary outcome was 90-day morbidity.

RESULTS

Twenty patients were included in the study (mean age, 54.9 years; age range, 24-79 years; 13 men [65%]). Thirteen patients underwent tracheal (n = 5), bronchial (n = 7), or carinal (n = 1) transplantation. Airway transplantation was not performed in 7 patients for the following reasons: medical contraindication (n = 1), unavoidable pneumonectomy (n = 1), exploratory thoracotomy only (n = 2), and a lobectomy or bilobectomy was possible (n = 3). Among the 20 patients initially included, the overall 90-day mortality rate was 5% (1 patient underwent a carinal transplantation and died). No mortality at 90 days was observed among patients who underwent tracheal or bronchial reconstruction. Among the 13 patients who underwent airway transplantation, major 90-day morbidity events occurred in 4 (30.8%) and included laryngeal edema, acute lung edema, acute respiratory distress syndrome, and atrial fibrillation. There was no adverse event directly related to the surgical technique. Stent removal was performed at a postoperative mean of 18.2 months. At a median follow-up of 3 years 11 months, 10 of the 13 patients (76.9%) were alive. Of these 10 patients, 8 (80%) breathed normally through newly formed airways after stent removal. Regeneration of epithelium and de novo generation of cartilage were observed within aortic matrices from recipient cells.

CONCLUSIONS AND RELEVANCE

In this uncontrolled study, airway bioengineering using stented aortic matrices demonstrated feasibility for complex tracheal and bronchial reconstruction. Further research is needed to assess efficacy and safety.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01331863.

A reassessment of tracheal substitutes-a systematic review

Background

Tracheal substitutes remain an active area of research. For rare patients with large or complex defects that cannot be repaired primarily, replacement of the airway may represent the only treatment option. The present systematic review aims to assess the clinical successes and setbacks of current methods of airway replacement.

Methods

Systematic review using Medline and PubMed from 01 January 2000 to 01 October 2017 focusing on clinical translation of circumferential or near circumferential (>270°) tracheal substitutes. Studies were identified using key phrases including terms such as "tracheal replacement", "tracheal regeneration", "tracheal transplant", "tracheal tissue engineering", and "tracheal substitution". Animal or non-clinical studies were excluded. Reviews were included if they contained clinical updates.

Results

Twenty-one studies were included in assessment comprising a mix of case reports, case studies, and a single review with clinical updates on prior studies. Since 2001, 41 patients have undergone a reported circumferential or near circumferential tracheal substitution through four underlying methodologies including allotransplantation, autologous tissue reconstruction, bioprosthetic reconstruction, and tissue engineered reconstruction. Each modality has unique advantages and disadvantages with varying success in clinical application.

Conclusions

The need for tracheal substitution remains a difficult clinical problem without an ideal prosthetic or graft material. While various modalities have had limited clinical success, further laboratory work is necessary before tracheal substitutes can become widely adopted, especially in the case of tissue engineered conduits, which have been setback by premature clinical translation.

A reassessment of tracheal substitutes-a systematic review

Background

Tracheal substitutes remain an active area of research. For rare patients with large or complex defects that cannot be repaired primarily, replacement of the airway may represent the only treatment option. The present systematic review aims to assess the clinical successes and setbacks of current methods of airway replacement.

Methods

Systematic review using Medline and PubMed from 01 January 2000 to 01 October 2017 focusing on clinical translation of circumferential or near circumferential (>270°) tracheal substitutes. Studies were identified using key phrases including terms such as "tracheal replacement", "tracheal regeneration", "tracheal transplant", "tracheal tissue engineering", and "tracheal substitution". Animal or non-clinical studies were excluded. Reviews were included if they contained clinical updates.

Results

Twenty-one studies were included in assessment comprising a mix of case reports, case studies, and a single review with clinical updates on prior studies. Since 2001, 41 patients have undergone a reported circumferential or near circumferential tracheal substitution through four underlying methodologies including allotransplantation, autologous tissue reconstruction, bioprosthetic reconstruction, and tissue engineered reconstruction. Each modality has unique advantages and disadvantages with varying success in clinical application.

Conclusions

The need for tracheal substitution remains a difficult clinical problem without an ideal prosthetic or graft material. While various modalities have had limited clinical success, further laboratory work is necessary before tracheal substitutes can become widely adopted, especially in the case of tissue engineered conduits, which have been setback by premature clinical translation.

Tracheal replacement

Tracheal reconstruction is one of the greatest challenges in thoracic surgery when direct end-to-end anastomosis is impossible or after this procedure has failed. The main indications for tracheal reconstruction include malignant tumours (squamous cell carcinoma, adenoid cystic carcinoma), tracheoesophageal fistula, trauma, unsuccessful surgical results for benign diseases and congenital stenosis. Tracheal substitutes can be classified into five types: 1) synthetic prosthesis; 2) allografts; 3) tracheal transplantation; 4) tissue engineering; and 5) autologous tissue composite. The ideal tracheal substitute is still unclear, but some techniques have shown promising clinical results. This article reviews the advantages and limitations of each technique used over the past few decades in clinical practice. The main limitation seems to be the capacity for tracheal tissue regeneration. The physiopathology behind this has yet to be fully understood. Research on stem cells sparked much interest and was thought to be a revolutionary technique; however, the poor long-term results of this approach highlight that there is a long way to go in this research field. Currently, an autologous tissue composite, with or without a tracheal allograft, is the only long-term working solution for every aetiology, despite its technical complexity and setbacks.