Bioengineered trachea using autologous chondrocytes for regeneration of tracheal cartilage in a rabbit model

Biomimetic Trachea Engineering via a Modular Ring Strategy Based on Bone-Marrow Stem Cells and Atelocollagen for Use in Extensive Tracheal Reconstruction

The fabrication of biomimetic tracheas with a architecture of cartilaginous rings alternately interspersed between vascularized fibrous tissue (CRVFT) has the potential to perfectly recapitulate the normal tracheal structure and function. Herein, the development of a customized chondroitin-sulfate-incorporating type-II atelocollagen (COL II/CS) scaffold with excellent chondrogenic capacity and a type-I atelocollagen (COL I) scaffold to facilitate the formation of vascularized fibrous tissue is described. An efficient modular ring strategy is then adopted to develop a CRVFT-based biomimetic trachea. The in vitro engineering of cartilaginous rings is achieved via the recellularization of ring-shaped COL II/CS scaffolds using bone marrow stem cells as a mimetic for native cartilaginous ring tissue. A CRVFT-based trachea with biomimetic mechanical properties, composed of bionic biochemical components, is additionally successfully generated in vivo via the alternating stacking of cartilaginous rings and ring-shaped COL I scaffolds on a silicone pipe. The resultant biomimetic trachea with pedicled muscular flaps is used for extensive tracheal reconstruction and exhibits satisfactory therapeutic outcomes with structural and functional properties similar to those of native trachea. This is the first study to utilize stem cells for long-segmental tracheal cartilaginous regeneration and this represents a promising method for extensive tracheal reconstruction.

3D Printed Biomimetic PCL Scaffold as Framework Interspersed With Collagen for Long Segment Tracheal Replacement

The rapid development of tissue engineering technology has provided new methods for tracheal replacement. However, none of the previously developed biomimetic tracheas exhibit both the anatomy (separated-ring structure) and mechanical behavior (radial rigidity and longitudinal flexibility) mimicking those of native trachea, which greatly restricts their clinical application. Herein, we proposed a biomimetic scaffold with a separated-ring structure: a polycaprolactone (PCL) scaffold with a ring-hollow alternating structure was three-dimensionally printed as a framework, and collagen sponge was embedded in the hollows amid the PCL rings by pouring followed by lyophilization. The biomimetic scaffold exhibited bionic radial rigidity based on compressive tests and longitudinal flexibility based on three-point bending tests. Furthermore, the biomimetic scaffold was recolonized by chondrocytes and developed tracheal cartilage in vitro. In vivo experiments showed substantial deposition of tracheal cartilage and formation of a biomimetic trachea mimicking the native trachea both structurally and mechanically. Finally, a long-segment tracheal replacement experiment in a rabbit model showed that the engineered biomimetic trachea elicited a satisfactory repair outcome. These results highlight the advantage of a biomimetic trachea with a separated-ring structure that mimics the native trachea both structurally and mechanically and demonstrates its promise in repairing long-segment tracheal defects.

Transplantation of a 3D-printed tracheal graft combined with iPS cell-derived MSCs and chondrocytes

For successful tracheal reconstruction, tissue-engineered artificial trachea should meet several requirements, such as biocompatible constructs comparable to natural trachea, coverage with ciliated respiratory mucosa, and adequate cartilage remodeling to support a cylindrical structure. Here, we designed an artificial trachea with mechanical properties similar to the native trachea that can enhance the regeneration of tracheal mucosa and cartilage through the optimal combination of a two-layered tubular scaffold and human induced pluripotent stem cell (iPSC)-derived cells. The framework of the artificial trachea was fabricated with electrospun polycaprolactone (PCL) nanofibers (inner) and 3D-printed PCL microfibers (outer). Also, human bronchial epithelial cells (hBECs), iPSC-derived mesenchymal stem cells (iPSC-MSCs), and iPSC-derived chondrocytes (iPSC-Chds) were used to maximize the regeneration of tracheal mucosa and cartilage in vivo. After 2 days of cultivation using a bioreactor system, tissue-engineered artificial tracheas were transplanted into a segmental trachea defect (1.5-cm length) rabbit model. Endoscopy did not reveal granulation ingrowth into tracheal lumen. Alcian blue staining clearly showed the formation of ciliated columnar epithelium in iPSC-MSC groups. In addition, micro-CT analysis showed that iPSC-Chd groups were effective in forming neocartilage at defect sites. Therefore, this study describes a promising approach for long-term functional reconstruction of a segmental tracheal defect.

Deconstructing tissue engineered trachea: Assessing the role of synthetic scaffolds, segmental replacement and cell seeding on graft performance

The ideal construct for tracheal replacement remains elusive in the management of long segment airway defects. Tissue engineered tracheal grafts (TETG) have been limited by the development of graft stenosis or collapse, infection, or lack of an epithelial lining. We applied a mouse model of orthotopic airway surgery to assess the impact of three critical barriers encountered in clinical applications: the scaffold, the extent of intervention, and the impact of cell seeding and characterized their impact on graft performance. First, synthetic tracheal scaffolds electrospun from polyethylene terephthalate / polyurethane (PET/PU) were orthotopically implanted in anterior tracheal defects of C57BL/6 mice. Scaffolds demonstrated complete coverage with ciliated respiratory epithelium by 2 weeks. Epithelial migration was accompanied by macrophage infiltration which persisted at long term (>6 weeks) time points. We then assessed the impact of segmental tracheal implantation using syngeneic trachea as a surrogate for the ideal tracheal replacement. Graft recovery involved local upregulation of epithelial progenitor populations and there was no evidence of graft stenosis or necrosis. Implantation of electrospun synthetic tracheal scaffold for segmental replacement resulted in respiratory distress and required euthanasia at an early time point. There was limited epithelial coverage of the scaffold with and without seeded bone marrow-derived mononuclear cells (BM-MNCs). We conclude that synthetic scaffolds support re-epithelialization in orthotopic patch implantation, syngeneic graft integration occurs with focal repair mechanisms, however epithelialization in segmental synthetic scaffolds is limited and is not influenced by cell seeding. STATEMENT OF SIGNIFICANCE: The life-threatening nature of long-segment tracheal defects has led to clinical use of tissue engineered tracheal grafts in the last decade for cases of compassionate use. However, the ideal tracheal reconstruction using tissue-engineered tracheal grafts (TETG) has not been clarified. We addressed the core challenges in tissue engineered tracheal replacement (re-epithelialization and graft patency) by defining the role of cell seeding with autologous bone marrow-derived mononuclear cells, the mechanism of respiratory epithelialization and proliferation, and the role of the inflammatory immune response in regeneration. This research will facilitate comprehensive understanding of cellular regeneration and neotissue formation on TETG, which will permit targeted therapies for accelerating re-epithelialization and attenuating stenosis in tissue engineered airway replacement.

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.

Head to Knee: Cranial Neural Crest-Derived Cells as Promising Candidates for Human Cartilage Repair

A large array of therapeutic procedures is available to treat cartilage disorders caused by trauma or inflammatory disease. Most are invasive and may result in treatment failure or development of osteoarthritis due to extensive cartilage damage from repeated surgery. Despite encouraging results of early cell therapy trials that used chondrocytes collected during arthroscopic surgery, these approaches have serious disadvantages, including morbidity associated with cell harvesting and low predictive clinical outcomes. To overcome these limitations, adult stem cells derived from bone marrow and subsequently from other tissues are now considered as preferred sources of cells for cartilage regeneration. Moreover, with new evidence showing that the choice of cell source is one of the most important factors for successful cell therapy, there is growing interest in neural crest-derived cells in both the research and clinical communities. Neural crest-derived cells such as nasal chondrocytes and oral stem cells that exhibit chondrocyte-like properties seem particularly promising in cartilage repair. Here, we review the types of cells currently available for cartilage cell therapy, including articular chondrocytes and various mesenchymal stem cells, and then highlight recent developments in the use of neural crest-derived chondrocytes and oral stem cells for repair of cartilage lesions.

Regeneration of Tracheal Tissue in Partial Defects Using Porcine Small Intestinal Submucosa

Background

Surgical correction of tracheal defects is a complex procedure when the gold standard treatment with primary end-to-end anastomosis is not possible. An alternative treatment may be the use of porcine small intestinal submucosa (SIS). It has been used as graft material for bioengineering applications and to promote tissue regeneration. The aim of this study was to evaluate whether SIS grafts improved tracheal tissue regeneration in a rabbit model of experimental tracheostomy.

Methods

Sixteen rabbits were randomized into two groups. Animals in the control group underwent only surgical tracheostomy, while animals in the SIS group underwent surgical tracheostomy with an SIS graft covering the defect. We examined tissues at the site of tracheostomy 60 days after surgery using histological analysis with hematoxylin and eosin (H&E) staining and analyzed the perimeter and area of the defect with Image-Pro® PLUS 4.5 (Media Cybernetics).

Results

The average perimeter and area of the defects were smaller by 15.3% (p = 0.034) and 21.8% (p = 0.151), respectively, in the SIS group than in the control group. Histological analysis revealed immature cartilage, pseudostratified ciliated epithelium, and connective tissue in 54.5% (p = 0.018) of the SIS group, while no cartilaginous regeneration was observed in the control group.

Conclusions

Although tracheal SIS engraftment could not prevent stenosis in a rabbit model of tracheal injury, it produced some remarkable changes, efficiently facilitating neovascularization, reepithelialization, and neoformation of immature cartilage.

Engineered Tissue-Stent Biocomposites as Tracheal Replacements

Here we report the creation of a novel tracheal construct in the form of an engineered, acellular tissue-stent biocomposite trachea (TSBT). Allogeneic or xenogeneic smooth muscle cells are cultured on polyglycolic acid polymer-metal stent scaffold leading to the formation of a tissue comprising cells, their deposited collagenous matrix, and the stent material. Thorough decellularization then produces a final acellular tubular construct. Engineered TSBTs were tested as end-to-end tracheal replacements in 11 rats and 3 nonhuman primates. Over a period of 8 weeks, no instances of airway perforation, infection, stent migration, or erosion were observed. Histological analyses reveal that the patent implants remodel adaptively with native host cells, including formation of connective tissue in the tracheal wall and formation of a confluent, columnar epithelium in the graft lumen, although some instances of airway stenosis were observed. Overall, TSBTs resisted collapse and compression that often limit the function of other decellularized tracheal replacements, and additionally do not require any cells from the intended recipient. Such engineered TSBTs represent a model for future efforts in tracheal regeneration.

Autologous Cell Seeding in Tracheal Tissue Engineering

Purpose of Review

There is no consensus on the best technology to be employed for tracheal replacement. One particularly promising approach is based upon tissue engineering and involves applying autologous cells to transplantable scaffolds. Here, we present the reported pre-clinical and clinical data exploring the various options for achieving such seeding.

Recent Findings

Various cell combinations, delivery strategies, and outcome measures are described. Mesenchymal stem cells (MSCs) are the most widely employed cell type in tracheal bioengineering. Airway epithelial cell luminal seeding is also widely employed, alone or in combination with other cell types. Combinations have thus far shown the greatest promise. Chondrocytes may improve mechanical outcomes in pre-clinical models, but have not been clinically tested. Rapid or pre-vascularization of scaffolds is an important consideration. Overall, there are few published objective measures of post-seeding cell viability, survival, or overall efficacy.

Summary

There is no clear consensus on the optimal cell-scaffold combination and mechanisms for seeding. Systematic in vivo work is required to assess differences between tracheal grafts seeded with combinations of clinically deliverable cell types using objective outcome measures, including those for functionality and host immune response.

Electronic supplementary material

The online version of this article (10.1007/s40778-017-0108-2) contains supplementary material, which is available to authorized users.

Circumferential Three-Dimensional-Printed Tracheal Grafts: Research Model Feasibility and Early Results

BACKGROUND

Methods for tracheal graft research have presented persistent challenges to investigators, and three-dimensional (3D)-printed biosynthetic grafts offer one potential development platform. We aimed to develop an efficient research platform for customizable circumferential 3D-printed tracheal grafts and evaluate feasibility and early structural integrity with a large-animal model.

METHODS

Virtual 3D models of porcine subject tracheas were generated using preoperative computed tomography scans. Two designs were used to test graft customizability and the limits of the construction process. Designs I and II used 270-degree and 360-degree external polycaprolactone scaffolds, respectively, both encompassing a circumferential extracellular matrix collagen layer. The polycaprolactone scaffolds were made in a fused-deposition modeling 3D printer and customized to the recipient's anatomy. Design I was implanted in 3 pigs and design II in 2 pigs, replacing 4-ring tracheal segments. Data collected included details of graft construction, clinical outcomes, bronchoscopy, and gross and histologic examination.

RESULTS

The 3D-printed biosynthetic grafts were produced with high fidelity to the native organ. The fabrication process took 36 hours. Grafts were implanted without immediate complication. Bronchoscopy immediately postoperatively and at 1 week demonstrated patent grafts and appropriate healing. All animals lived beyond a predetermined 1-week survival period. Bronchoscopy at 2 weeks showed significant paraanastomotic granulation tissue, which, along with partial paraanastomotic epithelialization, was confirmed on pathology. Overall survival was 17 to 34 days.

CONCLUSIONS

We propose a rapid, reproducible, resource efficient method to develop various anatomically precise grafts. Further graft refinement and strategies for granulation tissue management are needed to improve outcomes.

Clinical Translation of Tissue Engineered Trachea Grafts

OBJECTIVE

To provide a state-of-the-art review discussing recent achievements in tissue engineered tracheal reconstruction.

DATA SOURCES AND REVIEW METHODS

A structured PubMed search of the current literature up to and including October 2015. Representative articles that discuss the translation of tissue engineered tracheal grafts (TETG) were reviewed.

CONCLUSIONS

The integration of a biologically compatible support with autologous cells has resulted in successful regeneration of respiratory epithelium, cartilage, and vascularization with graft patency, although the optimal construct composition has yet to be defined. Segmental TETG constructs are more commonly complicated by stenosis and delayed epithelialization when compared to patch tracheoplasty.

IMPLICATIONS FOR PRACTICE

The recent history of human TETG recipients represents revolutionary proof of principle studies in regenerative medicine. Application of TETG remains limited to a compassionate use basis; however, defining the mechanisms of cartilage formation, epithelialization, and refinement of in vivo regeneration will advance the translation of TETG from the bench to the bedside.

Repair of extrahepatic bile duct defect using a collagen patch in a Swine model

Extrahepatic bile duct (EBD) injury can happen during surgery. To repair a defect of the EBD and prevent postoperative biliary complications, a collagen membrane was designed. The collagen material was porous, biocompatible, and degradable and could maintain its shape in bile soaking for about 4 weeks. The goal was to induce rapid bile duct tissue regeneration. Twenty Chinese experimental hybrid pigs were used in this study and divided into a patch group and a control group. A spindle-shaped defect (20 mm × 6 mm) was made in the anterior wall of the lower EBD in the swine model, and then the defect was reconstructed using a collagen patch with a drainage tube and wrapped with greater omentum. Ultrasound was performed at 2, 4, 8, and 12 weeks postoperatively. Liver function tests and white blood cell count (WBC) were measured. Hematoxylin-eosin staining, cytokeratin 7 immunohistochemical staining, and Van Gieson's staining of EBD were used. The diameter and thickness of the EBD at the graft site were measured. There was no significant difference in liver function tests or WBC in the patch group compared with the control group. No evidence of leakage or stricture was observed, but some pigs developed biliary sludge or stone at 4 and 8 weeks. The drainage tube was lost within 12 weeks. The neo-EBD could withstand normal biliary pressure 2 weeks after surgery. Histological study showed the accessory glands and epithelial cells gradually regenerated at graft sites from 4 weeks, with increasing vessel infiltration and decreasing inflammation. The collagen fibers became regular with full coverage of epithelial cells. The statistical analysis of diameter and thickness showed no stricture formation at the graft site, but the EBD wall was slightly thicker than in the normal bile duct due to collagen fiber deposition. The structure of the neo-EBD was similar to that of the normal EBD. The collagen membrane patch associated with a drainage tube and wrapped with greater omentum effectively induced the regeneration of the EBD defect within 12 weeks.