Moving towards in situ tracheal regeneration: the bionic tissue engineered transplantation approach

Mechanochemistry-Induced Universal Hydrogel Surface Modification for Orientation and Enhanced Differentiation of Skeletal Muscle Myoblasts

Micropatterned surface substrates containing topographic cues offer the possibility of programming tissue organization as a cell template by guiding cell alignment, adhesion, and function. In this study, we developed and used a force stamp method to grow aligned micropatterns with tunable chemical properties and elasticity on the surface of hydrogels based on a force-triggered polymerization mechanism of double-network hydrogels to elucidate the underlying mechanisms by which cells sense and respond to their mechanical and chemical microenvironments. In this work, we describe the impact of aligned micropatterns on the combined effects of microstructural chemistry and mechanics on the selective adhesion, directed migration, and differentiation of myoblasts. Our investigations revealed that topographically engineered substrates with hydrophobic and elevated surface roughness significantly enhanced myoblast adhesion kinetics. Concurrently, spatially ordered architectures facilitated cytoskeletal reorganization in myocytes, establishing biomechanically favorable niches for syncytial myotube development through extracellular matrix (ECM) physical guidance. Reverse transcription PCR analysis and immunofluorescence revealed that the expression of differentiation-specific genes, myosin heavy chain, and myogenic regulatory factors Myf5 and MyoD was upregulated in muscle cells on the aligned patterned scaffolds. These results suggest that the aligned micropatterns can promote muscle cell differentiation, making them potential scaffolds for enhancing skeletal differentiation.

An overview of nasal cartilage bioprinting: from bench to bedside

Nasal cartilage diseases and injuries are known as significant challenges in reconstructive medicine, affecting a substantial number of individuals worldwide. In recent years, the advent of three-dimensional (3D) bioprinting has emerged as a promising approach for nasal cartilage reconstruction, offering potential breakthroughs in the field of regenerative medicine. This paper provides an overview of the methods and challenges associated with 3D bioprinting technologies in the procedure of reconstructing nasal cartilage tissue. The process of 3D bioprinting entails generating a digital 3D model using biomedical imaging techniques and computer-aided design to integrate both internal and external scaffold features. Then, bioinks which consist of biomaterials, cell types, and bioactive chemicals, are applied to facilitate the precise layer-by-layer bioprinting of tissue-engineered scaffolds. After undergoing in vitro and in vivo experiments, this process results in the development of the physiologically functional integrity of the tissue. The advantages of 3D bioprinting encompass the ability to customize scaffold design, enabling the precise incorporation of pore shape, size, and porosity, as well as the utilization of patient-specific cells to enhance compatibility. However, various challenges should be considered, including the optimization of biomaterials, ensuring adequate cell viability and differentiation, achieving seamless integration with the host tissue, and navigating regulatory attention. Although numerous studies have demonstrated the potential of 3D bioprinting in the rebuilding of such soft tissues, this paper covers various aspects of the bioprinted tissues to provide insights for the future development of repair techniques appropriate for clinical use.

A Contemporary Review of Trachea, Nose, and Ear Cartilage Bioengineering and Additive Manufacturing

The complex structure, chemical composition, and biomechanical properties of craniofacial cartilaginous structures make them challenging to reconstruct. Autologous grafts have limited tissue availability and can cause significant donor-site morbidity, homologous grafts often require immunosuppression, and alloplastic grafts may have high rates of infection or displacement. Furthermore, all these grafting techniques require a high level of surgical skill to ensure that the reconstruction matches the original structure. Current research indicates that additive manufacturing shows promise in overcoming these limitations. Autologous stem cells have been developed into cartilage when exposed to the appropriate growth factors and culture conditions, such as mechanical stress and oxygen deprivation. Additive manufacturing allows for increased precision when engineering scaffolds for stem cell cultures. Fine control over the porosity and structure of a material ensures adequate cell adhesion and fit between the graft and the defect. Several recent tissue engineering studies have focused on the trachea, nose, and ear, as these structures are often damaged by congenital conditions, trauma, and malignancy. This article reviews the limitations of current reconstructive techniques and the new developments in additive manufacturing for tracheal, nasal, and auricular cartilages.

Synergistic Effects of SDS and H2O2 Combinations on Tracheal Scaffold Development: An In Vitro Study Using Goat Trachea

Currently, a tissue-engineered trachea has been popularly used as a biological graft for tracheal replacement in severe respiratory diseases. In the development of tissue-engineered tracheal scaffolds, in vitro studies play a crucial role in allowing researchers to evaluate the efficacy and safety of scaffold designs and fabrication techniques before progressing to in vivo or clinical trials. This research involved the decellularization of goat trachea using SDS, H2O2, and their combinations. Various quantitative and qualitative assessments were performed, including histological analysis, immunohistochemistry, and biomechanical testing. Hematoxylin and eosin staining evaluated the cellular content, while safranin O-fast green and Masson's trichrome staining assessed glycosaminoglycan content and collagen distribution, respectively. The immunohistochemical analysis focused on detecting MHC-1 antigen presence. Tensile strength measurements were conducted to evaluate the biomechanical properties of the decellularized scaffolds. The results demonstrated that the combination of SDS and H2O2 for goat tracheal decellularization yielded scaffolds with minimal cellular remnants, low toxicity, preserved ECM, and high tensile strength and elasticity. This method holds promise for developing functional tracheal scaffolds to address severe respiratory diseases effectively.

Tracheal replacement with aortic grafts: Bench to clinical practice

Tracheal reconstruction following extensive resection for malignant or benign lesions remains a major challenge in thoracic surgery. Numerous studies have attempted to identify the optimal tracheal replacement with different biological or prosthetic materials, such as various homologous and autologous tissues, with no encouraging outcomes. Recently, a few clinical studies reported attaining favorable outcomes using in vitro or stem cell-based airway engineering and also with tracheal allograft implantation following heterotopic revascularization. However, none of the relevant studies offered a standardized technology for airway replacement. In 1997, a novel approach to airway reconstruction was proposed, which involved using aortic grafts as the biological matrix. Studies on animal models reported achieving in-vivo cartilage and epithelial regeneration using this approach. These encouraging results inspired the subsequent application of cryopreserved aortic allografts in humans for the first time. Cryopreserved aortic allografts offered further advantages, such as easy availability in tissue banks and no requirement for immunosuppressive treatments. Currently, stented aortic matrix-based airway replacement has emerged as a standard approach, and its effectiveness was also verified in the recently reported TRITON-01 study. In this context, the present review aims to summarize the current status of the application of aortic grafts in tracheal replacement, including the latest advancements in experimental and clinical practice.

Long-term longitudinal study on swine VML model

BACKGROUND

Volumetric Muscle Loss (VML), resulting from severe trauma or surgical ablation, is a pathological condition preventing myofibers regeneration, since skeletal muscle owns the remarkable ability to restore tissue damage, but only when limited in size. The current surgical therapies employed in the treatment of this pathology, which particularly affects military personnel, do not yet provide satisfactory results. For this reason, more innovative approaches must be sought, specifically skeletal muscle tissue engineering seems to highlight promising results obtained from preclinical studies in VML mouse model. Despite the great results obtained in rodents, translation into human needs a comparable animal model in terms of size, in order to validate the efficacy of the tissue engineering approach reconstructing larger muscle mass (human-like). In this work we aim to demonstrate the validity of a porcine model, that has underwent a surgical ablation of a large muscle area, as a VML damage model.

RESULTS

For this purpose, morphological, ultrasound, histological and fluorescence analyses were carried out on the scar tissue formed following the surgical ablation of the peroneus tertius muscle of Sus scrofa domesticus commonly called mini-pig. In particular, the replenishment of the damaged area, the macrophage infiltration and the vascularization at different time-points were evaluated up to the harvesting of the scar upon six months.

CONCLUSION

Here we demonstrated that following VML damage, there is an extremely poor regenerative process in the swine muscle tissue, while the formation of fibrotic, scar tissue occurs. The analyses performed up to 180 days after the injury revealed the development of a stable, structured and cellularized tissue, provided with vessels and extracellular matrix acquiring the status of granulation tissue like in human.

Tissue Engineering for Tracheal Replacement: Strategies and Challenges

The critical feature in trachea replacement is to provide a hollow cylindrical framework that is laterally stable and longitudinally flexible, facilitating cartilage and epithelial tissue formation. Despite advanced techniques and sources of materials used, most inherent challenges are related to the complexity of its anatomy. Limited blood supply leads to insufficient regenerative capacity for cartilage and epithelium. Natural and synthetic scaffolds, different types of cells, and growth factors are part of tissue engineering approaches with varying outcomes. Pre-vascularization remains one of the crucial factors to expedite the regenerative process in tracheal reconstruction. This review discusses the challenges and strategies used in tracheal tissue engineering, focusing on scaffold implantation in clinical and preclinical studies conducted in recent decades.

A Novel Decellularized Trachea Preparation Method for Rapid Construction of a Functional Tissue Engineered Trachea to Repair Tracheal Defects

Long segment trachea defects are repaired by tracheal substitution, while the decellularized technology has been effectively employed to prepare tissue engineering trachea (TET). However, its clinical application is restrictied by...

Extracellular Matrix Scaffold Using Decellularized Cartilage for Hyaline Cartilage Regeneration

The repair of osteochondral defects is among the top ten medical needs of humans in the 21st centuries with many countries facing rapidly aging population involved with osteoarthritis as a major contributor to global disease burden. Tissue engineering methods have offered new windows of hope to treat such disorders and disabilities. Regenerative approaches to cartilage injuries require careful replication of the complex microenvironment of the native tissue. The decellularized hyaline cartilage derived from human allografts or xenografts is potentially an ideal scaffold, simulating the mechanical and biochemical properties, as well as biological microarchitecture of the hyaline cartilage. There have been many attempts to regenerate clinically viable hyaline cartilage tissue using decellularized cartilage-derived extracellular matrix with stem cell technology. This chapter describes the reproducible methods for hyaline cartilage decellularization and recellularization. In addition, quality control and characterization requirements of the product at each step, as well as the clinical applications of final product have been discussed.

Directly construct microvascularization of tissue engineering trachea in orthotopic transplantation

Tissue engineering technology provides effective alternative treatments for tracheal reconstruction. The formation of a functional microvascular network is essential to support cell metabolism and ensure the long-term survival of grafts. However, given the lack of an identifiable vascular pedicle of the trachea that could be anastomosed to the blood vessels directly in the recipient's neck, successful tracheal transplantation faces significant challenges in rebuilding the adequate blood supply of the graft. Herein, we describe a one-step method to construct microvascularization of tissue-engineered trachea in orthotopic transplantation. Forty rabbit tracheae were decellularized using a vacuum-assisted decellularization (VAD) method. Histological appearance and immunohistochemical (IHC) analysis demonstrated efficient removal of cellular components and nuclear material from natural tissue, which was also confirmed by 4'-6-diamidino-2-phenylindole(DAPI) staining and DNA quantitative analysis, thus significantly reducing the antigenicity. Scanning electron microscopy (SEM), immunofluorescence (IF) analysis, GAG and collagen quantitative analysis showed that the hierarchical structures, composition and integrity of the extracellular matrix (ECM) were protected. IF analysis also demonstrated that basic fibroblast growth factor (b-FGF) was preserved during the decellularization process, and also exerted biocompatibility and proangiogenic properties by the chick chorioallantoic membrane(CAM) assay. Xenotransplantation assays indicated that the VAD tracheal matrix would no longer induced inflammatory reactions implanted in the body for 4 weeks after treated by VAD more than 16 h. Furthermore, we seeded the matrix with bone marrow-derived endothelial cells (BMECs) in vitro and performed in vivo tracheal patch repair assays to prove the biocompatibility and neovascularization of VAD-treated tracheal matrix, and the formation of a vascular network around the patch promoted the crawling of surrounding ciliated epithelial cells to the surface of the graft. We conclude that this natural VAD tracheal matrix is non-immunogenic and no inflammatory reactions in vivo transplantation. Seeding with BMECs on the grafts and then performing orthotopic transplantation can effectively promote the microvascularization and accelerate the native epithelium cells crawling to the lumen of the tracheal graft.

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.

Vascularization strategies for tissue engineering for tracheal reconstruction

Tissue engineering technology provides effective alternative treatments for tracheal reconstruction. The formation of a functional microvascular network is essential to support cell metabolism and ensure the long-term survival of grafts. Although several tracheal replacement therapy strategies have been developed in the past, the critical significance of the formation of microvascular networks in 3D scaffolds has not attracted sufficient attention. Here, we review key technologies and related factors of microvascular network construction in tissue-engineered trachea and explore optimized preparation processes of vascularized functional tissues for clinical applications.

Applications of decellularized materials in tissue engineering: advantages, drawbacks and current improvements, and future perspectives

Decellularized materials (DMs) are attracting more and more attention because of their native structures, comparatively high bioactivity, low immunogenicity and good biodegradability, which are difficult to be imitated by synthetic materials. Recently, DMs have been demonstrated to possess great potential to overcome the disadvantages of autografts and have become a kind of promising material for tissue engineering. In this systematic review, we aimed to not only provide a quick access for understanding DMs, but also bring new ideas to utilize them more appropriately in tissue engineering. Firstly, the preparation of DMs was introduced. Then, the updated applications of DMs derived from different tissues and organs in tissue engineering were comprehensively summarized. In particular, their advantages, drawbacks and current improvements were emphasized. Moreover, we analyzed and proposed future perspectives.

Maneuvering the Migration and Differentiation of Stem Cells with Electrospun Nanofibers

Electrospun nanofibers have been extensively explored as a class of scaffolding materials for tissue regeneration, because of their unique capability to mimic some features and functions of the extracellular matrix, including the fibrous morphology and mechanical properties, and to a certain extent the chemical/biological cues. This work reviews recent progress in applying electrospun nanofibers to direct the migration of stem cells and control their differentiation into specific phenotypes. First, the physicochemical properties that make electrospun nanofibers well-suited as a supporting material to expand stem cells by controlling their migration and differentiation are introduced. Then various systems are analyzed in conjunction with mesenchymal, neuronal, and embryonic stem cells, as well as induced pluripotent stem cells. Finally, some perspectives on the challenges and future opportunities in combining electrospun nanofibers with stem cells are offered to address clinical issues.

Rapid preparation of decellularized trachea as a 3D scaffold for organ engineering

OBJECTIVE

To shorten the preparation time of rabbit decellularized tracheal matrix through a modified detergent-enzymatic method with higher concentration of DNase (50 kU/mL), providing an experimental and theoretical basis for clinical decellularization technology.

METHODS

The control group was a natural trachea, and the experimental group was a tracheal matrix subjected to two and four decellularization cycles. The performance of each group of samples was evaluated by histology and immunohistochemical staining, scanning electron microscopy, biomechanical property testing, inoculation and cytotoxicity tests, and allograft experiments.

RESULTS

The results showed that the nuclei of the nonchondral areas of the tracheal stroma were essentially completely removed and MHC-I and MHC-II antigens were removed after two decellularization cycles. Histological staining and scanning electron microscopy showed that the extracellular matrix was retained and the basement membrane was intact. Cell inoculation and proliferation tests confirmed that the acellular tracheal matrix had good biocompatibility, and the proliferation capacity of bone mesenchymal stem cells on the matrix was increased in the experimental group compared with the control group (p < 0.05). Histological staining and CD68 molecular marker analysis after the allograft experiment showed that the inflammatory response of the acellular tracheal matrix was weak and the infiltration of surrounding macrophages was reduced.

CONCLUSION

A modified detergent-enzymatic method with an increased DNase (50 kU/mL) concentration requires only two cycles (4 days) to obtain a decellularized rabbit tracheal matrix with a short preparation time, good biocompatibility, suitable mechanical properties, and reduced preparation cost.

The long and winding road: stem cells for cystic fibrosis

INTRODUCTION

Cystic fibrosis (CF) is a genetic syndrome with a high mortality rate due to severe lung disease. Despite having several drugs targeting specific mutated CFTR proteins already in clinical trials, new therapies, based on stem cells, are also emerging to treat those patients.

AREAS COVERED

The authors review the main sources of stem cells, including embryonic stem cells (ESCs), induced-pluripotent stem cells (iPSCs), gestational stem cells, and adult stem cells, such as mesenchymal stem cells (MSCs) in the context of CF. Furthermore, they describe the main animal and human models of lung physiology and pathology, involved in the optimization of these stem cell-applied therapies in CF.

EXPERT OPINION

ESCs and iPSCs are emerging sources for disease modeling and drug discovery purposes. The allogeneic transplant of healthy MSCs, that acts independently to specific mutations, is under intense scrutiny due to their secretory, immunomodulatory, anti-inflammatory and anti-bacterial properties. The main challenge for future developments will be to get exogenous stem cells into the appropriate lung location, where they can regenerate endogenous stem cells and act as inflammatory modulators. The clinical application of stem cells for the treatment of CF certainly warrants further insight into pre-clinical models, including large animals, organoids, decellularized organs and lung bioengineering.

Exploiting decellularized cochleae as scaffolds for inner ear tissue engineering

Background

Use of decellularized tissues has become popular in tissue engineering applications as the natural extracellular matrix can provide necessary physical cues that help induce the restoration and development of functional tissues. In relation to cochlear tissue engineering, the question of whether decellularized cochlear tissue can act as a scaffold and support the incorporation of exogenous cells has not been addressed. Investigators have explored the composition of the cochlear extracellular matrix and developed multiple strategies for decellularizing a variety of different tissues; however, no one has investigated whether decellularized cochlear tissue can support implantation of exogenous cells.

Methods

As a proof-of-concept study, human Wharton’s jelly cells were perfused into decellularized cochleae isolated from C57BL/6 mice to determine if human Wharton’s jelly cells could implant into decellularized cochlear tissue. Decellularization was verified through scanning electron microscopy. Cocheae were stained with DAPI and immunostained with Myosin VIIa to identify cells. Perfused cochleae were imaged using confocal microscopy.

Results

Features of the organ of Corti were clearly identified in the native cochleae when imaged with scanning electron microscopy and confocal microscopy. Acellular structures were identified in decellularized cochleae; however, no cellular structures or lipid membranes were present within the decellularized cochleae when imaged via scanning electron microscopy. Confocal microscopy revealed positive identification and adherence of cells in decellularized cochleae after perfusion with human Wharton’s jelly cells. Some cells positively expressed Myosin VIIa after perfusion.

Conclusions

Human Wharton’s jelly cells are capable of successfully implanting into decellularized cochlear extracellular matrix. The identification of Myosin VIIa expression in human Wharton’s jelly cells after implantation into the decellularized cochlear extracellular matrix suggest that components of the cochlear extracellular matrix may be involved in differentiation.

Tissue-engineered trachea: A review

Tracheal replacement is performed after resection of a portion of the trachea that was impossible to reconnect via direct anastomosis. A tissue-engineered trachea is one of the available options that offer many advantages compared to other types of graft. Fabrication of a functional tissue-engineered trachea for grafting is very challenging, as it is a complex organ with important components, including cartilage, epithelium and vasculature. A number of studies have been reported on the preparation of a graftable trachea. A laterally rigid but longitudinally flexible hollow cylindrical scaffold which supports cartilage and epithelial tissue formation is the key element. The scaffold can be prepared via decellularization of an allograft or fabricated using biodegradable or non-biodegradable biomaterials. Commonly, the scaffold is seeded with chondrocytes and epithelial cells at the outer and luminal surfaces, respectively, to hasten tissue formation and improve functionality. To date, several clinical trials of tracheal replacement with tissue-engineered trachea have been performed. This article reviews the formation of cartilage tissue, epithelium and neovascularization of tissue-engineered trachea, together with the obstacles, possible solutions and future. Furthermore, the role of the bioreactor for in vitro tracheal graft formation and recently reported clinical applications of tracheal graft were also discussed. Generally, although encouraging results have been achieved, however, some obstacles remain to be resolved before the tissue-engineered trachea can be widely used in clinical settings.

An Investigation of Topics and Trends of Tracheal Replacement Studies Using Co-Occurrence Analysis

This study evaluated tracheal regeneration studies using scientometric and co-occurrence analysis to identify the most important topics and assess their trends over time. To provide the adequate search options, PubMed, Scopus, and Web of Science (WOS) were used to cover various categories such as keywords, countries, organizations, and authors. Search results were obtained by employing Bibexcel. Co-occurrence analysis was applied to evaluate the publications. Finally, scientific maps, author's network, and country contributions were depicted using VOSviewer and NetDraw. Furthermore, the first 25 countries and 130 of the most productive authors were determined. Regarding the trend analysis, 10 co-occurrence terms out of highly frequent words were examined at 5-year intervals. Our findings indicated that the field of trachea regeneration has tested different approaches over the time. In total, 65 countries have contributed to scientific progress both in experimental and clinical fields. Special keywords such as tissue engineering and different types of stem cells have been increasingly used since 1995. Studies have addressed topics such as angiogenesis, decellularization methods, extracellular matrix, and mechanical properties since 2011. These findings will offer evidence-based information about the current status and trends of tracheal replacement research topics over time, as well as countries' contributions.

Mechanical Characterization and Constitutive Modeling of Human Trachea: Age and Gender Dependency

Tracheal disorders can usually reduce the free lumen diameter or wall stiffness, and hence limit airflow. Trachea tissue engineering seems a promising treatment for such disorders. The required mechanical compatibility of the prepared scaffold with native trachea necessitates investigation of the mechanical behavior of the human trachea. This study aimed at mechanical characterization of human tracheas and comparing the results based on age and gender. After isolating 30 human tracheas, samples of tracheal cartilage, smooth muscle, and connective tissue were subjected to uniaxial tension to obtain force-displacement curves and calculate stress-stretch data. Among several models, the Yeoh and Mooney-Rivlin hyperelastic functions were best able to describe hyperelastic behavior of all three tracheal components. The mean value of the elastic modulus of human tracheal cartilage was calculated to be 16.92 ± 8.76 MPa. An overall tracheal stiffening with age was observed, with the most considerable difference in the case of cartilage. Consistently, we noticed some histological alterations in cartilage and connective tissue with aging, which may play a role in age-related tracheal stiffening. No considerable effect of gender on the mechanical behavior of tracheal components was observed. The results of this study can be applied in the design and fabrication of trachea tissue engineering scaffolds.

Tissue Engineered Airways: A Prospects Article

An ideal tracheal scaffold must withstand luminal collapse yet be flexible, have a sufficient degree of porosity to permit vascular and cellular ingrowth, but also be airtight and must facilitate growth of functional airway epithelium to avoid infection and aid in mucocilliary clearance. Finally, the scaffold must also be biocompatible to avoid implant rejection. Over the last 40 years, efforts to design and manufacture the airway have been undertaken worldwide but success has been limited and far apart. As a result, tracheal resection with primary repair remains the Gold Standard of care for patients presenting with airway disorders and malignancies. However, the maximum resectable length of the trachea is restricted to 30% of the total length in children or 50% in adults. Attempts to provide autologous grafts for human application have also been disappointing for a host of different reasons, including lack of implant integration, insufficient donor organs, and poor mechanical strength resulting in an unmet clinical need. The two main approaches researchers have taken to address this issue have been the development of synthetic scaffolds and the use of decellularized organs. To date, a number of different decellularization techniques and a variety of materials, including polyglycolic acid (PGA) and nanocomposite polymers have been explored. The findings thus far have shown great promise, however, there remain a significant number of caveats accompanying each approach. That being said, the possibilities presented by these two approaches could be combined to produce a highly successful, clinically viable hybrid scaffold. This article aims to highlight advances in airway tissue engineering and provide an overview of areas to explore and utilize in accomplishing the aim of developing an ideal tracheal prosthesis. J. Cell. Biochem. 117: 1497-1505, 2016. © 2016 Wiley Periodicals, Inc.

In vitro characterization of design and compressive properties of 3D-biofabricated/decellularized hybrid grafts for tracheal tissue engineering

Infection or damage to the trachea, a thin walled and cartilage reinforced conduit that connects the pharynx and larynx to the lungs, leads to serious respiratory medical conditions which can often prove fatal. Current clinical strategies for complex tracheal reconstruction are of limited availability and efficacy, but tissue engineering and regenerative medicine approaches may provide viable alternatives. In this study, we have developed a new "hybrid graft" approach that utilizes decellularized tracheal tissue along with a resorbable polymer scaffold, and holds promise for potential clinical applications. First, we evaluated the effect of our decellularization process on the compression properties of porcine tracheal segments, and noted approximately 63% decrease in resistance to compression following decellularization. Next we developed four C-shape scaffold designs by varying the base geometry and thickness, and fabricated polycaprolactone scaffolds using a combination of 3D-Bioplotting and thermally-assisted forming. All scaffolds designs were evaluated in vitro under three different environmental testing conditions to determine the design that offered the best resistance to compression. These were further studied to determine the effect of gamma radiation sterilization and cyclic compression loading. Finally, hybrid grafts were developed by securing these optimal design scaffolds to decellularized tracheal segments and evaluated in vitro under physiological testing conditions. Results show that the resistance to compression offered by the hybrid grafts created using gamma radiation sterilized scaffolds was comparable to that of fresh tracheal segments. Given that current clinical attempts at tracheal transplantation using decellularized tissue have been fraught with luminal collapse and complications, our data support the possibility that future embodiments using a hybrid graft approach may reduce the need for intraluminal stenting in tracheal transplant recipients.

Effect of cell seeding on neotissue formation in a tissue engineered trachea

BACKGROUND

Surgical management of long segment tracheal disease is limited by a paucity of donor tissue and poor performance of synthetic materials. A potential solution is the development of a tissue-engineered tracheal graft (TETG) which promises an autologous airway conduit with growth capacity.

METHODS

We created a TETG by vacuum seeding bone marrow-derived mononuclear cells (BM-MNCs) on a polymeric nanofiber scaffold. First, we evaluated the role of scaffold porosity on cell seeding efficiency in vitro. We then determined the effect of cell seeding on graft performance in vivo using an ovine model.

RESULTS

Seeding efficiency of normal porosity (NP) grafts was significantly increased when compared to high porosity (HP) grafts (NP: 360.3 ± 69.19 × 10(3) cells/mm(2); HP: 133.7 ± 22.73 × 10(3) cells/mm(2); p<0.004). Lambs received unseeded (n=2) or seeded (n=3) NP scaffolds as tracheal interposition grafts for 6 weeks. Three animals were terminated early owing to respiratory complications (n=2 unseeded, n=1 seeded). Seeded TETG explants demonstrated wound healing, epithelial migration, and delayed stenosis when compared to their unseeded counterparts.

CONCLUSION

Vacuum seeding BM-MNCs on nanofiber scaffolds for immediate implantation as tracheal interposition grafts is a viable approach to generate TETGs, but further preclinical research is warranted before advocating this technology for clinical application.

In vivo generation of a mature and functional artificial skeletal muscle

Extensive loss of skeletal muscle tissue results in mutilations and severe loss of function. In vitro-generated artificial muscles undergo necrosis when transplanted in vivo before host angiogenesis may provide oxygen for fibre survival. Here, we report a novel strategy based upon the use of mouse or human mesoangioblasts encapsulated inside PEG-fibrinogen hydrogel. Once engineered to express placental-derived growth factor, mesoangioblasts attract host vessels and nerves, contributing to in vivo survival and maturation of newly formed myofibres. When the graft was implanted underneath the skin on the surface of the tibialis anterior, mature and aligned myofibres formed within several weeks as a complete and functional extra muscle. Moreover, replacing the ablated tibialis anterior with PEG-fibrinogen-embedded mesoangioblasts also resulted in an artificial muscle very similar to a normal tibialis anterior. This strategy opens the possibility for patient-specific muscle creation for a large number of pathological conditions involving muscle tissue wasting.

Autologous Peripheral Blood Mononuclear Cells as Treatment in Refractory Acute Respiratory Distress Syndrome

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a devastating disorder. Despite enormous efforts in clinical research, effective treatment options are lacking, and mortality rates remain unacceptably high.

OBJECTIVES

A male patient with severe ARDS showed no clinical improvement with conventional therapies. Hence, an emergent experimental intervention was performed.

METHODS

We performed intratracheal administration of autologous peripheral blood-derived mononuclear cells (PBMCs) and erythropoietin (EPO).

RESULTS

We found that after 2 days of initial PBMC/EPO application, lung function improved and extracorporeal membrane oxygenation (ECMO) support was reduced. Bronchoscopy and serum inflammatory markers revealed reduced inflammation. Additionally, serum concentration of miR-449a, b, c and miR-34a, a transient upregulation of E-cadherin and associated chromatin marks in PBMCs indicated airway epithelial differentiation. Extracellular vesicles from PBMCs demonstrated anti-inflammatory capacity in a TNF-α-mediated nuclear factor-x03BA;B in vitro assay. Despite improving respiratory function, the patient died of multisystem organ failure on day 38 of ECMO treatment.

CONCLUSIONS

This case report provides initial encouraging evidence to use locally instilled PBMC/EPO for treatment of severe refractory ARDS. The observed clinical improvement may partially be due to the anti-inflammatory effects of PBMC/EPO to promote tissue regeneration. Further studies are needed for more in-depth understanding of the underlying mechanisms of in vivo regeneration.

Optimal amount of basic fibroblast growth factor in gelatin sponges incorporating β-tricalcium phosphate with chondrocytes

BACKGROUND

A gelatin sponge with slowly releasing basic fibroblast growth factor (b-FGF) enhances chondrogenesis. This study investigated the optimal amount of b-FGF in gelatin sponges to fabricate engineered cartilage.

MATERIALS AND METHODS

b-FGF (0, 10, 100, 500, 1000, and 2000 μg/cm(3))-impregnated gelatin sponges incorporating β-tricalcium phosphate (β-TCP) were produced. Chondrocytes were isolated from the auricular cartilage of C57B6J mice and expanded. The expanded auricular chondrocytes (10×10(6) cells/cm(3)) were seeded onto the gelatin sponges, which served as scaffolds. The construct assembly was implanted in the subcutaneous space of mice through a syngeneic fashion. Thereafter, constructs were retrieved at 2, 4, or 6 weeks.

RESULTS

(1) Morphology: The size of implanted constructs was larger than the size of the scaffold with 500, 1000, and 2000 μg/cm(3) b-FGF-impregnated gelatin sponges incorporating β-TCP at 4 and 6 weeks after implantation. (2) The weight of the constructs increased roughly proportional to the increase in volume of the b-FGF-impregnated scaffold at 2, 4, and 6 weeks after implantation, except in the 2000 μg/cm(3) b-FGF-impregnated constructs group. (3) Histological examination: Extracellular matrix in the center of the constructs was observed in gelatin sponges impregnated with more than 100 μg/cm(3) b-FGF at 4 weeks after implantation. The areas of cells with an abundant extracellular matrix were positive for cartilage-specific marker type 2 collagen in the constructs. (4) Protein assay: Glycosaminoglycan and collagen type 2 expression were significantly increased at 4 and 6 weeks on implantation of gelatin sponges impregnated with more than 100 μg/cm(3) b-FGF. At 6 weeks after implantation, the ratio of type 2 collagen to type 1 collagen in constructs impregnated with 100 μg/cm(3) or more b-FGF was higher than that in mice auricular cartilage.

CONCLUSION

Gelatin sponges impregnated with more than 100 μg/cm(3) b-FGF incorporating β-TCP with chondrocytes (10×10(6) cells/cm(3)) can fabricate engineered cartilage at 4 weeks after implantation.

Advances in tracheal reconstruction

SUMMARY

A recent revival of global interest for reconstruction of long-segment tracheal defects, which represents one of the most interesting and complex problems in head and neck and thoracic reconstructive surgery, has been witnessed. The trachea functions as a conduit for air, and its subunits including the epithelial layer, hyaline cartilage, and segmental blood supply make it particularly challenging to reconstruct. A myriad of attempts at replacing the trachea have been described. These along with the anatomy, indications, and approaches including microsurgical tracheal reconstruction will be reviewed. Novel techniques such as tissue-engineering approaches will also be discussed. Multiple attempts at replacing the trachea with synthetic scaffolds have been met with failure. The main lesson learned from such failures is that the trachea must not be treated as a "simple tube." Understanding the anatomy, developmental biology, physiology, and diseases affecting the trachea are required for solving this problem.

Advances in tracheal reconstruction

Summary:

A recent revival of global interest for reconstruction of long-segment tracheal defects, which represents one of the most interesting and complex problems in head and neck and thoracic reconstructive surgery, has been witnessed. The trachea functions as a conduit for air, and its subunits including the epithelial layer, hyaline cartilage, and segmental blood supply make it particularly challenging to reconstruct. A myriad of attempts at replacing the trachea have been described. These along with the anatomy, indications, and approaches including microsurgical tracheal reconstruction will be reviewed. Novel techniques such as tissue-engineering approaches will also be discussed. Multiple attempts at replacing the trachea with synthetic scaffolds have been met with failure. The main lesson learned from such failures is that the trachea must not be treated as a “simple tube.” Understanding the anatomy, developmental biology, physiology, and diseases affecting the trachea are required for solving this problem.

Future directions for the management of pain in osteoarthritis

Osteoarthritis (OA) is the predominant form of arthritis worldwide, resulting in a high degree of functional impairment and reduced quality of life owing to chronic pain. To date, there are no treatments that are known to modify disease progression of OA in the long term. Current treatments are largely based on the modulation of pain, including NSAIDs, opiates and, more recently, centrally acting pharmacotherapies to avert pain. This review will focus on the rationale for new avenues in pain modulation, including inhibition with anti-NGF antibodies and centrally acting analgesics. The authors also consider the potential for structure modification in cartilage/bone using growth factors and stem cell therapies. The possible mismatch between structural change and pain perception will also be discussed, introducing recent techniques that may assist in improved patient phenotyping of pain subsets in OA. Such developments could help further stratify subgroups and treatments for people with OA in future.

Airway transplantation

No definitive solution has been discovered for replacing long segments or the entire trachea in humans. Most of this challenge stems from the specific function and mechanics that are almost impossible to replicate except in the setting of an allotransplantation, which requires lifelong immunosuppressive medication. Recently, tissue engineering provided significant evidence concerning the next promising therapeutic alternative for tracheal replacement. Underlying mechanism and pathways of cell-surface interactions, cell migration, and differentiation are essential to understand the complexity of tracheal tissue regeneration. Tracheal replacement remains challenging but initial steps toward an ideal therapeutic concept have been made.

Hydrogels preserve native phenotypes of valvular fibroblasts through an elasticity-regulated PI3K/AKT pathway

Matrix elasticity regulates proliferation, apoptosis, and differentiation of many cell types across various tissues. In particular, stiffened matrix in fibrotic lesions has been shown to promote pathogenic myofibroblast activation. To better understand the underlying pathways by which fibroblasts mechano-sense matrix elasticity, we cultured primary valvular interstitial cells (VICs) isolated from porcine aortic valves on poly(ethylene glycol)-based hydrogels with physiologically relevant and tunable elasticities. We show that soft hydrogels preserve the quiescent fibroblast phenotype of VICs much better than stiff plastic plates. We demonstrate that the PI3K/AKT pathway is significantly up-regulated when VICs are cultured on stiff gels or tissue culture polystyrene compared with freshly isolated VICs. In contrast, myofibroblasts de-activate and pAKT/AKT decreases as early as 2 h after reducing the substrate modulus. When PI3K or AKT is inhibited on stiff substrates, myofibroblast activation is blocked. When constitutively active PI3K is overexpressed, the myofibroblast phenotype is promoted even on soft substrates. These data suggest that valvular fibroblasts are sensing the changes in matrix elasticity through the PI3K/AKT pathway. This mechanism may be used by other mechano-sensitive cells in response to substrate modulus, and this pathway may be a worthwhile target for treating matrix stiffness-associated diseases. Furthermore, hydrogels can be designed to recapitulate important mechanical cues in native tissues to preserve aspects of the native phenotype of primary cells for understanding basic cellular responses to biophysical and biochemical signals, and for tissue-engineering applications.

Tracheal replacement for primary tracheal cancer

PURPOSE OF REVIEW

To summarize the so far applied clinical methods of tracheal replacement, comparing pros and cons of conventional and tissue-engineered approaches.

RECENT FINDINGS

Several strategies have been most recently described to replace the trachea-like aortic homografts, allotransplantation, and tissue engineering. Allotransplantation requires lifelong immunosuppression and this may be ethically questioned being not a lifesaving procedure. Tissue-engineered tracheal transplantation has been clinically applied using biological or bioartificial tubular or bifurcated scaffolds reseeded with mesenchymal stromal cells, and bioactive molecules boosting regeneration and promoting neovascularization.

SUMMARY

Tracheal tissue engineering may be a promising alternative to conventional allotransplantation in adults and children. Different methods have been developed and are currently under active clinical investigation, and await long-term results.

Engineering functional epithelium for regenerative medicine and in vitro organ models: a review

Recent advances in the fields of microfabrication, biomaterials, and tissue engineering have provided new opportunities for developing biomimetic and functional tissues with potential applications in disease modeling, drug discovery, and replacing damaged tissues. An intact epithelium plays an indispensable role in the functionality of several organs such as the trachea, esophagus, and cornea. Furthermore, the integrity of the epithelial barrier and its degree of differentiation would define the level of success in tissue engineering of other organs such as the bladder and the skin. In this review, we focus on the challenges and requirements associated with engineering of epithelial layers in different tissues. Functional epithelial layers can be achieved by methods such as cell sheets, cell homing, and in situ epithelialization. However, for organs composed of several tissues, other important factors such as (1) in vivo epithelial cell migration, (2) multicell-type differentiation within the epithelium, and (3) epithelial cell interactions with the underlying mesenchymal cells should also be considered. Recent successful clinical trials in tissue engineering of the trachea have highlighted the importance of a functional epithelium for long-term success and survival of tissue replacements. Hence, using the trachea as a model tissue in clinical use, we describe the optimal structure of an artificial epithelium as well as challenges of obtaining a fully functional epithelium in macroscale. One of the possible remedies to address such challenges is the use of bottom-up fabrication methods to obtain a functional epithelium. Modular approaches for the generation of functional epithelial layers are reviewed and other emerging applications of microscale epithelial tissue models for studying epithelial/mesenchymal interactions in healthy and diseased (e.g., cancer) tissues are described. These models can elucidate the epithelial/mesenchymal tissue interactions at the microscale and provide the necessary tools for the next generation of multicellular engineered tissues and organ-on-a-chip systems.

Airway transplantation: a challenge for regenerative medicine

After more than 50 years of research, airway transplantation remains a major challenge in the fields of thoracic surgery and regenerative medicine. Five principal types of tracheobronchial substitutes, including synthetic prostheses, bioprostheses, allografts, autografts and bioengineered conduits have been evaluated experimentally in numerous studies. However, none of these works have provided a standardized technique for the replacement of the airways. More recently, few clinical attempts have offered encouraging results with ex vivo or stem cell-based engineered airways and tracheal allografts implanted after heterotopic revascularization. In 1997, we proposed a novel approach: the use of aortic grafts as a biological matrix for extensive airway reconstruction. In vivo regeneration of epithelium and cartilage were demonstrated in animal models. This led to the first human applications using cryopreserved aortic allografts that present key advantages because they are available in tissue banks and do not require immunosuppressive therapy. Favorable results obtained in pioneering cases have to be confirmed in larger series of patients with extensive tracheobronchial diseases.

Regenerative medicine primer

The pandemic of chronic diseases, compounded by the scarcity of usable donor organs, mandates radical innovation to address the growing unmet needs of individuals and populations. Beyond life-extending measures that are often the last available option, regenerative strategies offer transformative solutions in treating degenerative conditions. By leveraging newfound knowledge of the intimate processes fundamental to organogenesis and healing, the emerging regenerative armamentarium aims to boost the aptitude of human tissues for self-renewal. Regenerative technologies strive to promote, augment, and reestablish native repair processes, restituting organ structure and function. Multimodal regenerative approaches incorporate transplant of healthy tissues into damaged environments, prompt the body to enact a regenerative response in damaged tissues, and use tissue engineering to manufacture new tissue. Stem cells and their products have a unique aptitude to form specialized tissues and promote repair signaling, providing active ingredients of regenerative regimens. Concomitantly, advances in materials science and biotechnology have unlocked additional prospects for growing tissue grafts and engineering organs. Translation of regenerative principles into practice is feasible and safe in the clinical setting. Regenerative medicine and surgery are, thus, poised to transit from proof-of-principle studies toward clinical validation and, ultimately, standardization, paving the way for next-generation individualized management algorithms.

The effect of decellularization of tracheal allografts on leukocyte infiltration and of recellularization on regulatory T cell recruitment

Tracheal transplantation without immunosuppressive therapy has been accomplished with a tissue-engineering approach using decellularized biological scaffolds in combination with recipient progenitor cells. The mechanisms of immune response directed towards these tracheal allografts have not been fully determined. In this study, we evaluated the immunogenicity of these grafts at the protein level, and functionally, in vitro and in vivo in a large animal model. Long-segment circumferential tracheal allografts were decellularized using two different protocols and recellularized using recipient mesenchymal stromal cells (MSC) and tracheal epithelial progenitor cells (TEC). Residual MHCI and MHCII immunostaining was found surrounding the submucosal glands despite cyclical decellularization. In an in vitro lymphocyte proliferation assay, CD4+ T cells continued to proliferate on decellularized pieces and this proliferation was inhibited by co-culture with autologous MSC. Allografts were heterotopically transplanted under a muscle flap in the neck of the recipients and decellularization was found to delay leukocyte infiltration but resulted in eventual cartilage degradation. Recellularization prevented this infiltration up to 3 weeks post-transplantation and allowed for preservation of the cartilage. The immune cells found within these grafts included a significant number of CD4+CD25+Foxp3+ regulatory T cells. Furthermore, gene expression of anti-inflammatory cytokines, such as IL-10 and TGF-β1, involved in proliferation, differentiation and function of regulatory T cells was found in these grafts. These results indicate that the immunological modification induced by recellularized tracheal scaffolds is an active process involving the recruitment of immunosuppressive cells, rather than simply the removal of donor-derived antigenic components.

Regenerative medicine for the respiratory system: distant future or tomorrow's treatment?

Regenerative medicine (RM) is a new field of biomedical science that focuses on the regeneration of tissues and organs and the restoration of organ function. Although regeneration of organ systems such as bone, cartilage, and heart has attracted intense scientific research over recent decades, RM research regarding the respiratory system, including the trachea, the lung proper, and the diaphragm, has lagged behind. However, the last 5 years have witnessed novel approaches and initial clinical applications of tissue-engineered constructs to restore organ structure and function. In this regard, this article briefly addresses the basics of RM and introduces the key elements necessary for tissue regeneration, including (stem) cells, biomaterials, and extracellular matrices. In addition, the current status of the (clinical) application of RM to the respiratory system is discussed, and bottlenecks and recent approaches are identified. For the trachea, several initial clinical studies have been reported and have used various combinations of cells and scaffolds. Although promising, the methods used in these studies require optimization and standardization. For the lung proper, only (stem) cell-based approaches have been probed clinically, but it is becoming apparent that combinations of cells and scaffolds are required to successfully restore the lung's architecture and function. In the case of the diaphragm, clinical applications have focused on the use of decellularized scaffolds, but novel scaffolds, with or without cells, are clearly needed for true regeneration of diaphragmatic tissue. We conclude that respiratory treatment with RM will not be realized tomorrow, but its future looks promising.

Production and utilization of acellular lung scaffolds in tissue engineering

Pulmonary disease is a worldwide public health problem that reduces the quality of life and increases the need for hospital admissions as well as the risk for premature death for those affected. For many patients, lung transplantation is the only chance for survival. Unfortunately, there is a significant shortage of lungs for transplantation and since the lung is the most likely organ to be damaged during procurement many lungs deemed unacceptable for transplantation are simply discarded. Rather than discarding these lungs they can be used to produce three-dimensional acellular (AC) natural lung scaffolds for the generation of engineered lung tissue. AC scaffolds are lungs whose original cells have been destroyed by exposure to detergents and physical methods of removing cells and cell debris. This creates a lung scaffold from the skeleton of the lungs themselves. The scaffolds are then used to support adult, stem or progenitor cells which can be grown into functional lung tissue. Recent studies show that engineered lung tissues are capable of surviving after in vivo transplantation and support limited gas exchange. In the future engineered lung tissue has the potential to be used in clinical applications to replace lung functions lost following injury or disease. This manuscript discusses recent advances in development and use of AC scaffolds to support engineering of lung tissues.

Tracheal regeneration: evidence of bone marrow mesenchymal stem cell involvement

OBJECTIVES

Recent advances in airway transplantation have shown the ability of ex vivo or in vivo tracheal regeneration with bioengineered conduits or biological substitutes, respectively. Previously, we established a process of in vivo-guided tracheal regeneration using vascular allografts as a biological scaffold. We theorized that tracheal healing was the consequence of a mixed phenomenon associating tracheal contraction and regeneration. The aim of the present study was to determine the role that bone marrow stem cells play in that regenerative process.

METHODS

Three groups of 12 rabbits underwent a gender-mismatched aortic graft transplantation after tracheal resection. The first group received no cells (control group), the second group had previously received autologous green fluorescent protein-labeled mesenchymal stem cell transplantation, and the third group received 3 labeled mesenchymal stem cell injections on postoperative days 0, 10, and 21.

RESULTS

The clinical results were impaired by stent complications (obstruction or migration), but no anastomotic leakage, dehiscence, or stenosis was observed. The rabbits were killed, and the trachea was excised for analysis at 1 to 18 months after tracheal replacement. In all 3 groups, microscopic examination showed an integrated aortic graft lined by metaplastic epithelium. By 12 months, immature cartilage was detected among disorganized elastic fibers. Positive SRY gene detection served as evidence for engraftment of cells derived from the male recipient. EF-green fluorescent protein detection showed bone marrow-derived mesenchymal stem cell involvement.

CONCLUSIONS

The results of the present study imply a role for bone marrow stem cells in tracheal regeneration after aortic allografting. Studies are necessary to identify the local and systemic factors stimulating that regenerative process.