Experimental study on a new tracheal prosthesis made from collagen-conjugated mesh

Replacement of a 5-cm intrathoracic trachea with a tissue-engineered prosthesis in a canine model

BACKGROUND

Critical obstacles must be addressed before clinical application of artificial tracheas. The major complications of long tracheal replacement include anastomotic dehiscence and stenosis owing to poor vascularity and incomplete re-epithelialization. The objective of this report was to clarify whether pre-incubation of the prosthesis in the omentum could be applicable for reconstruction of a long segment of the intrathoracic trachea in a canine model.

METHODS

The framework of an artificial trachea was fabricated from a polypropylene mesh tube and coated with 1% neutral atelocollagen inside and outside the lumen. The prosthesis was placed in the omentum of nine healthy male beagle dogs for 3 weeks. Then, the pedicled prosthesis was used to replace a 50 mm long section of intrathoracic trachea. Results were evaluated bronchoscopically, macroscopically, and histologically.

RESULTS

After 3 weeks of abdominal incubation, the prostheses were incorporated into the host tissue. None of the dogs showed dehiscence of the anastomosis or infection of the prostheses during the postoperative period. Seven of the nine dogs survived for more than 1 year. One dog died of a bowel obstruction resulting from a diaphragmatic hernia 3 months after replacement, and another died due to reasons unrelated to the prosthesis at 6 months. Bronchoscopic examination revealed no stenosis or dehiscence, and microscopic examination of all dogs showed that the luminal surface was covered by newly regenerated connective tissue and respiratory epithelium.

CONCLUSIONS

Pedicled omentum-prosthesis complexes may allow successful reconstruction of a long segment of the intrathoracic trachea.

Evaluation of regenerated tracheal cilia function on a collagen-conjugated scaffold in a canine model

OBJECTIVES

It is unclear whether the movement and function of the regenerated cilia on collagen-conjugated artificial trachea are the same as those of normal cilia. This study assessed the ciliary beat frequency (CBF) and ciliary transport functions (CTFs) of regenerated cilia in a canine model.

METHODS

A tracheal defect introduced into the anterior portion of the cervical trachea of an adult beagle dog was covered with a collagen-conjugated prosthesis. Two months later, the trachea was harvested along the long axis, both from normal and regenerated regions. The cilia were stained with isothiocyanate-conjugated wheat germ agglutinin, and their movement was monitored with a high-speed camera to analyse CBF and CTF. Four samples each were obtained from the regenerated and normal regions for CBF analysis and 7 samples each were obtained for CTF analysis.

RESULTS

The wheat germ agglutinin-stained cells showed well-regulated beats in both the regenerated and normal regions of the trachea. Mean CBF in the regenerated and normal regions did not differ significantly (7.11 ± 0.41 vs 7.14 ± 1.09 Hz; P = 981). By contrast, CTF was significantly lower in the regenerated region than in the normal region (30.0 ± 6.62 vs 7.43 ± 0.58 μm/s; P = 0.005).

CONCLUSIONS

Mean CBF in the regenerated and normal regions did not differ significantly at 2 months. The CTF in the regenerated region recovered partially but remained lower than those in the normal region. Methods are needed to improve the CTF of regenerated cilia.

Replacement of Rat Tracheas by Layered, Trachea-Like, Scaffold-Free Structures of Human Cells Using a Bio-3D Printing System

Current scaffold-based tissue engineering approaches are subject to several limitations, such as design inflexibility, poor cytocompatibility, toxicity, and post-transplant degradation. Thus, scaffold-free tissue-engineered structures can be a promising solution to overcome the issues associated with classical scaffold-based materials in clinical transplantation. The present study seeks to optimize the culture conditions and cell combinations used to generate scaffold-free structures using a Bio-3D printing system. Human cartilage cells, human fibroblasts, human umbilical vein endothelial cells, and human mesenchymal stem cells from bone marrow are aggregated into spheroids and placed into a Bio-3D printing system with dedicated needles positioned according to 3D configuration data, to develop scaffold-free trachea-like tubes. Culturing the Bio-3D-printed structures with proper flow of specific medium in a bioreactor facilitates the rearrangement and self-organization of cells, improving physical strength and tissue function. The Bio-3D-printed tissue forms small-diameter trachea-like tubes that are implanted into rats with the support of catheters. It is confirmed that the tubes are viable in vivo and that the tracheal epithelium and capillaries proliferate. This tissue-engineered, scaffold-free, tubular structure can represent a significant step toward clinical application of bioengineered organs.

Reconstruction of Ovine Trachea with a Biomimetic Composite Biomaterial

The aim of this study was to evaluate a novel composite material for tracheal reconstruction in an ovine model. A polymer containing various forms of carbon fibers (roving, woven, and nonwoven fabric) impregnated with polysulfone (PSU) was used to create cylindrical tracheal implants, 3 cm in length and 2.5 cm in diameter. Each implant, reinforced with five rings made of PSU-impregnated carbon-fiber roving, had three external layers made of carbon-fiber woven fabric and the inner layer formed of carbon-fiber nonwoven fabric. The inner surface of five implants was additionally coated with polyurethane (PU), to promote migration of respiratory epithelium. The implants were used to repair tracheal defects (involving four tracheal rings) in 10 sheep (9-12 months of age; 40-50 kg body weight). Macroscopic and microscopic characteristics of the implants and tracheal anastomoses were examined 4 and 24 weeks after implantation. At the end of the follow-up period, outer surfaces of the implants were covered with the tissue which to various degree resembled histological structure of normal tracheal wall. In turn, inner surfaces of the prostheses were covered only with vascularized connective tissue. Inner polyurethane coating did not improve the outcomes of tracheal reconstruction and promoted excessive granulation, which contributed to moderate to severe stenosis at the tracheal anastomoses. The hereby presented preliminary findings constitute a valuable source of data for future research on a tracheal implant being optimally adjusted for medical needs.

A Modular Strategy to Engineer Complex Tissues and Organs

Currently, there are no synthetic or biologic materials suitable for long-term treatment of large tracheal defects. A successful tracheal replacement must (1) have radial rigidity to prevent airway collapse during respiration, (2) contain an immunoprotective respiratory epithelium, and (3) integrate with the host vasculature to support epithelium viability. Herein, biopolymer microspheres are used to deliver chondrogenic growth factors to human mesenchymal stem cells (hMSCs) seeded in a custom mold that self-assemble into cartilage rings, which can be fused into tubes. These rings and tubes can be fabricated with tunable wall thicknesses and lumen diameters with promising mechanical properties for airway collapse prevention. Epithelialized cartilage is developed by establishing a spatially defined composite tissue composed of human epithelial cells on the surface of an hMSC-derived cartilage sheet. Prevascular rings comprised of human umbilical vein endothelial cells and hMSCs are fused with cartilage rings to form prevascular-cartilage composite tubes, which are then coated with human epithelial cells, forming a tri-tissue construct. When prevascular- cartilage tubes are implanted subcutaneously in mice, the prevascular structures anastomose with host vasculature, demonstrated by their ability to be perfused. This microparticle-cell self-assembly strategy is promising for engineering complex tissues such as a multi-tissue composite trachea.

Regeneration of the Junctional Epithelium and Connective Tissue after Transplantation of Detergent-Processed Allo-Teeth

The authors have developed a new artificial dental implant and evaluated it in a dog model in terms of its potential to produce: I) regeneration of junctional epithelium; II) regeneration and attachment of connective tissue. The implants were constructed from allo-teeth. We removed the cell components from the periodontal ligaments of these teeth with a detergent (1% TritonX-100); the remaining acellular periodontal ligament acted as an extracellular matrix upon which regeneration and attachment could proceed. We placed 10 of these implants in the just-extracted sites of three beagle dogs. We observed regeneration of both junctional epithelium and connective tissue at all implant sites after 3 months. The connective tissue was attached in all cases. Use of the acellular periodontal ligament as an extracellular matrix may facilitate regeneration of host periodontal ligament tissue, thus contributing to recovery of host immunological defense and long-term oral function.

Development of New Tracheal Prosthesis: Autogenous Mucosa-Lined Prosthesis Made from Polypropylene Mesh

Reliable tracheal or tissue graft has not been developed yet for the reconstruction of large, circumferential tracheal defects. Major limitations were anastomotic dehishence and stenosis, which were attributed to the poor epithelinisation of the prosthetic graft. We developed a new tracheal prosthesis that has a viable lined and well-vasculised mucosa. The prosthesis consists of Prolene® mesh reinforced with polypropylene rings, and is coated with gelatin. In addition, we lined the luminal surface of the prosthesis with transplanted autogenous oral mucosa and wrapped the prosthesis with greater omentum. Animal experiments were performed using 10 adult mongrel dogs. The transplanted mucosa and wrapped greater omentum tightly adhered to the prosthesis to make a single unit within two weeks. The mucosa survived well, was well vasculised by new vessels from greater omentum and showed normal histology. Complete surgical resection and replacement of a thoracic trachea (3 cm in length, 6 tracheal rings) were carried out in 2 dogs, which survived well with normal activity. We concluded that this highly biocompatible tracheal prosthesis could be very useful for step-wise reconstruction of tracheal defects.

Effects of artificial tracheal fixation on tracheal epithelial regeneration and prevention of tracheal stenosis

CONCLUSION

Tight fixation of the artificial trachea is important for epithelialization and tracheal stenosis.

OBJECTIVE

The authors have developed an artificial trachea and have used it for tracheal reconstruction. Although various studies on tracheal reconstruction have been conducted, no studies have examined the effect of artificial tracheal fixation on tracheal stenosis and regeneration. Therefore, the purpose of the present study was to evaluate the effect of artificial tracheal fixation.

STUDY DESIGN

Preliminary animal experiment.

METHODS

Artificial tracheae were implanted into rabbits with partial tracheal defects. Tracheal stenosis and regeneration of the tracheal epithelium on the artificial tracheae were evaluated by endoscopic examination, scanning electron microscopic analysis, and histological examination. The artificial tracheae fixed to the tracheal defects were classified into three groups (0-point, 4-point, and 8-point) by the number of fixation points.

RESULTS

At 14 and 28 days post-implantation, the luminal surface of the implantation area was mostly covered with epithelium in all fixation groups. However, a small amount of granulation tissue was observed in the 0-point fixation group at 14 days post-implantation. Moreover, tracheal stenosis did not occur in the 8-point fixation group, but stenosis was detected in the other groups.

PLGA-PTMC-Cultured Bone Mesenchymal Stem Cell Scaffold Enhances Cartilage Regeneration in Tissue-Engineered Tracheal Transplantation

The treatment of long-segment tracheal defect requires the transplantation of effective tracheal substitute, and the tissue-engineered trachea (TET) has been proposed as an ideal tracheal substitute. The major cause of the failure of segmental tracheal defect reconstruction by TET is airway collapse caused by the chondromalacia of TET cartilage. The key to maintain the TET structure is the regeneration of chondrocytes in cartilage, which can secrete plenty of cartilage matrices. To address the problem of the chondromalacia of TET cartilage, this study proposed an improved strategy. We designed a new cell sheet scaffold using the poly(lactic-co-glycolic acid) (PLGA) and poly(trimethylene carbonate) (PTMC) to make a porous membrane for seeding cells, and used the PLGA-PTMC cell-scaffold to pack the decellularized allogeneic trachea to construct a new type of TET. The TET was then implanted in the subcutaneous tissue for vascularization for 2 weeks. Orthotopic transplantation was then performed after implantation. The efficiency of the TET we designed was analyzed by histological examination and biomechanical analyses 4 weeks after surgery. Four weeks after surgery, both the number of chondrocytes and the amount of cartilage matrix were significantly higher than those contained in the traditional stem-cell-based TET. Besides, the coefficient of stiffness of TET was significantly larger than the traditional TET. This study provided a promising approach for the long-term functional reconstruction of long-segment tracheal defect, and the TET we designed had potential application prospects in the field of TET reconstruction.

Tissue Engineering for Regeneration of the Tracheal Epithelium

Objectives:

The slowness of epithelialization on the artificial trachea that has been successfully used in humans is a problem. The purpose of this study was to develop a way to regenerate the epithelium on the surface of this artificial trachea.

Methods:

In an in vitro study, isolated rat tracheal epithelial cells were seeded on a collagenous gel that was stratified on a collagenous sponge. Histologic and immunohistochemical examinations were made. In an in vivo study, we transplanted grafts with green fluorescent protein–positive tracheal epithelial cells onto the tracheal defects of normal rats. At 3, 7, 14, and 30 days after the operation, histologic and immunohistochemical examinations were made.

Results:

In the in vitro study, the 3 layers — the epithelium, gel, and sponge — could be observed. The epithelium expressed cytokeratin 14, cytokeratin 18, and occludin. In the in vivo study, the artificial trachea was covered with epithelium at 3 days after operation, and then the epithelium differentiated from single- or double-stratified squamous epithelium into columnar ciliated epithelium. Green fluorescent protein–positive cells were found 3 days after operation.

Conclusions:

We believe that the method used in our experiment is an effective way to regenerate the epithelium on the surface of an artificial trachea. With further experimentation, this method should be suitable for clinical application.

Cricoid Regeneration Using in Situ Tissue Engineering in Canine Larynx for the Treatment of Subglottic Stenosis

The purpose of the present study was to evaluate the efficacy of cricoid regeneration via in situ tissue engineering in a canine larynx for the treatment of subglottic stenosis. As the tissue scaffold, a Marlex mesh tube coated by collagen sponge was used for a rigid airway framework and for tissue regrowth around the tube. On 5 dogs, the larynx was exposed and the anterior third of the cricoid cartilage was resected. The tube was anastomosed to the lower edge of the thyroid cartilage and to the first tracheal cartilage. By postoperative endoscopic examination at 3 to 7 months, no airway obstruction was observed in any of the dogs. There was granulation tissue in 2 dogs and slight mesh exposure in 1 dog, but they were asymptomatic. Confluent regeneration of the epithelium over the scaffold and good incorporation of the scaffold mesh into the host tissue were observed after surgery.

Effect of Structural Differences in Collagen Sponge Scaffolds on Tracheal Epithelium Regeneration

OBJECTIVE

We developed an in situ regeneration-inducible artificial trachea composed of a porcine collagen sponge and polypropylene framework and used it for tracheal reconstruction. In the present study, collagen sponges with different structures were prepared from various concentrations of collagen solutions, and their effect on the regeneration of tracheal epithelium was examined.

METHODS

Collagen sponges were prepared from type I and III collagen solutions. The structures of the sponges were analyzed using scanning electron microscopy (SEM). Artificial tracheae, which were formed using the collagen sponges with different structures, were implanted into rabbits, and regeneration of the tracheal epithelium on the artificial tracheae was evaluated by SEM analysis and histological examination.

RESULTS

The SEM analysis showed that collagen sponges prepared from 0.5% and 1.0% collagen solutions had a porous structure. However, the sponges prepared from a 1.5% collagen solution had a nonporous structure. After implantation of artificial tracheae prepared from 0.5% and 1.0% collagen solutions, their luminal surfaces were mostly covered with epithelium within 14 days. However, epithelial reorganization occurred later on artificial tracheae prepared from the 1.5% collagen solution.

CONCLUSION

Collagen sponges with a porous structure are suitable for regeneration of the tracheal epithelium in our artificial trachea.

Engineered cartilaginous tubes for tracheal tissue replacement via self-assembly and fusion of human mesenchymal stem cell constructs

There is a critical need to engineer a neotrachea because currently there are no long-term treatments for tracheal stenoses affecting large portions of the airway. In this work, a modular tracheal tissue replacement strategy was developed. High-cell density, scaffold-free human mesenchymal stem cell-derived cartilaginous rings and tubes were successfully generated through employment of custom designed culture wells and a ring-to-tube assembly system. Furthermore, incorporation of transforming growth factor-β1-delivering gelatin microspheres into the engineered tissues enhanced chondrogenesis with regard to tissue size and matrix production and distribution in the ring- and tube-shaped constructs, as well as luminal rigidity of the tubes. Importantly, all engineered tissues had similar or improved biomechanical properties compared to rat tracheas, which suggests they could be transplanted into a small animal model for airway defects. The modular, bottom up approach used to grow stem cell-based cartilaginous tubes in this report is a promising platform to engineer complex organs (e.g., trachea), with control over tissue size and geometry, and has the potential to be used to generate autologous tissue implants for human clinical applications.

Decellularized tracheal extracellular matrix supports epithelial migration, differentiation, and function

Tracheal loss is a source of significant morbidity for affected patients with no acceptable solution. Interest in engineering tracheal transplants has created a demand for small animal models of orthotopic tracheal transplantation. Here, we examine the use of a decellularized graft in a murine model of tracheal replacement. Fresh or decellularized tracheas harvested from age-matched female donor C57BL/6 mice were transplanted into syngeneic recipients. Tracheas were decellularized using repeated washes of water, 3% Triton X-100, and 3 M NaCl under cyclic pressure changes, followed by disinfection with 0.1% peracetic acid/4% ethanol, and terminal sterilization by gamma irradiation. Tracheas were explanted for immunolabeling at 1, 4, and 8 weeks following surgery. Video microscopy and computed tomography were performed to assess function and structure. Decellularized grafts supported complete reepithelialization by 8 weeks and motile cilia were observed. Cartilaginous portions of the trachea were maintained in mice receiving fresh transplants, but repopulation of the cartilage was not seen in mice receiving decellularized transplants. We observed superior postsurgical survival, weight gain, and ciliary function in mice receiving fresh transplants compared with those receiving decellularized transplants. The murine orthotopic tracheal transplant provides an appropriate model to assess the repopulation and functional regeneration of decellularized tracheal grafts.

Cell sources for trachea tissue engineering: past, present and future

Trachea tissue engineering has been one of the most promising approaches to providing a potential clinical application for the treatment of long-segment tracheal stenosis. The sources of the cells are particularly important as the primary factor for tissue engineering. The use of appropriate cells seeded onto scaffolds holds huge promise as a means of engineering the trachea. Furthermore, appropriate cells would accelerate the regeneration of the tissue even without scaffolds. Besides autologous mature cells, various stem cells, including bone marrow-derived mesenchymal stem cells, adipose tissue-derived stem cells, umbilical cord blood-derived mesenchymal stem cells, amniotic fluid stem cells, embryonic stem cells and induced pluripotent stem cells, have received extensive attention in the field of trachea tissue engineering. Therefore, this article reviews the progress on different cell sources for engineering tracheal cartilage and epithelium, which can lead to a better selection and strategy for engineering the trachea.

Cross-linking of gelatin with carbodiimides

Carbodiimides were employed for cross-linking of gelatin through amide bond formation to avoid any foreign bond incorporation into the cross-linked gelatin molecules. Cross-linking of gelatin was performed not in aqueous solution but in the form of a film under a heterogenous condition. Ethanol-water mixtures were used as the reaction medium to prevent dissolution of gelatin films. The optimal ethanol concentration in the ethanol-water mixtures was around 80 vol%, and the water content of the cross-linked gelatin film attained after swelling with water at 25 degrees C was as low as 55 wt%. A water-soluble carbodiimide (l-ethyl-3[3-dimethylaminoprophyl] carbodiimide) was more effective for gelatin cross-linking than a water-insoluble carbodiimide (1,3-dicyclohexyl carbodiimide). The optimal temperature for cross-linking with the water-soluble carbodiimide ranged between 15 and 25 degrees C. It was concluded that gelatin cross-linking with carbodiimides is as effective as that with glutaraldehyde, which is most widely used despite the toxicity, at least, so far as the water content of cross-linked gelatin film is concerned.

Laryngeal regeneration using tissue engineering techniques in a canine model

OBJECTIVES

We previously reported that polypropylene mesh covered with collagen sponge is a useful material for the regeneration of the trachea and the cricoid cartilage. The aim of this study was to regenerate larynges after partial hemilaryngectomy with this new biomaterial.

METHODS

A left partial hemilaryngectomy was performed on 12 adult beagles. The defect size was about 1.8 x 1.0 cm. Both sides of polypropylene mesh were coated with either 1% or 3% collagen sponge. This scaffold was wrapped in fascia lata harvested from the left thigh and then fixed in place over the defect. Endoscopic examinations were performed periodically. Six months after treatment, 3-dimensional computed tomographic scanning was performed. Vibratory examinations were also performed with excised larynges.

RESULTS

In the 1% collagen group, exposure or dislocation of the mesh was found in 3 of 6 cases, but in the 3% group, no exposure of the mesh was seen. The morphological findings in the vocal fold were better in the 3% group than in the 1% group, but a difference in the vertical levels of the vocal folds was found in both groups.

CONCLUSIONS

This study suggests that 3% collagen-coated polypropylene mesh wrapped with autologous fascia is a useful material for laryngeal regeneration.

Tissue-engineered airway and "in situ tissue engineering"

Since the 1980s, tissue engineering has become one of the major areas of endeavor in medical research, applying the principles of biology and engineering to the development of functional substitutes for damaged tissue. Using this technology, various attempts have been made to create and apply a tissue-engineered prosthetic trachea, or airway. In addition to the conventional tissue engineering approach, a new substantially different concept has been advocated in Japan since 2000. This is "in situ tissue engineering," where a tissue is created not in vitro but in vivo, exploiting the potential of the living body for wound healing. An artificial trachea created by in situ tissue engineering has already been applied in human patients for reconstruction of airway defects, and promising results have been obtained. This article reviews recent progress in the relatively new field of airway reconstruction employing tissue engineering.

Tracheal defect repair using a PLGA-collagen hybrid scaffold reinforced by a copolymer stent with bFGF-impregnated gelatin hydrogel

PURPOSE

We studied the regenerated cartilage in tracheal defect repair and compared the bio-materials used versus native trachea using basic fibroblast growth factor (bFGF)-impregnated gelatin hydrogel.

MATERIALS AND METHODS

A full-thickness anterior defect was created in the cervical trachea of 15 experimental rabbits. The defect was implanted with a hybrid scaffold of poly(lactic-co-glycolic acid) (PLGA) knitted mesh and collagen sponge. The implanted trachea was reinforced with a copolymer stent of polycaprolactone and poly(lactic acid) coarse fiber mesh. A gelatin hydrogel was used for providing a sustained release of bFGF. The reconstructed tracheas were divided into three groups with wrapped materials; without gelatin hydrogel (control group, n = 5), a gelatin hydrogel with saline (gelatin group, n = 5), and a gelatin hydrogel with 100 microg of bFGF (bFGF group, n = 5). One of the five rabbits in each group at 1 month after operation, one at 3 months, and three at 6 months were killed and the engineered tracheas were evaluated histologically. Biomechanical properties were evaluated on samples at 6 months postoperatively.

RESULTS

The rigid support in the defect portion was maintained during 6 months postoperatively. The newly regenerated cartilages were recognized between the host cartilage stumps at 3 months postoperatively in the bFGF group, and limited new cartilage growth and epithelialization were observed at 6 months postoperatively.

CONCLUSIONS

The experiment shows that using bFGF, better mechanical strength was obtained but with poor cartilage growth.

Biodegradable polymer coating promotes the epithelization of tissue-engineered airway prostheses

OBJECTIVE

We have developed a prosthesis that includes a collagen layer for tracheobronchial reconstruction and applied it in a canine model. In previous studies luminal epithelization remained partial or rather slow because of the early disintegration of the collagen layer. We have improved this type of prosthesis by coating the luminal surface with a biodegradable polymer, which serves to protect the collagen layer. The effect of the polymer coating on the epithelization of the luminal surface of the prosthesis was examined.

METHODS

The main frame consisted of a polypropylene mesh tube, measuring 15 mm in inner diameter and 30 mm in length, with reinforcing rings. Collagen extracted from porcine skin was conjugated to this frame. The luminal surface was coated with a polymer, poly (L-lactic-acid-co-epsilon-caprolactone). In 5 beagle dogs the left main bronchus was replaced with this prosthesis, periodic bronchoscopic observations were conducted, and microscopic evaluations were performed.

RESULTS

All dogs survived until they were killed, except for 1 animal in which pneumonia developed, and this animal died at 13 months after replacement. None of the dogs showed adverse complications caused by the prosthesis. Bronchoscopic observations revealed that the polymer remained on the luminal surface for 2 weeks. The luminal surface in 4 dogs was completely covered with ciliated columnar epithelium or nonciliated squamous epithelium, and 90% epithelization was achieved in 1 dog.

CONCLUSIONS

The biodegradable polymer coating protected the collagen layer and promoted better epithelization. This improved epithelization on the luminal surface could therefore potentially increase the success rates in airway replacement with artificial prostheses.

In situ tissue engineering for tracheal reconstruction using a luminar remodeling type of artificial trachea

BACKGROUND

After successful trials of tracheal reconstruction using mesh-type prostheses in canine models, the technique has been applied clinically to human patients since 2002. To enhance tissue regeneration, we have applied a new tissue engineering approach to this mesh-type prosthesis.

METHODS

The prosthesis consists of a polypropylene mesh tube reinforced with a polypropylene spiral and atelocollagen layer. The cervical tracheas of 18 beagle dogs were replaced with the prosthesis. The collagen layer was soaked with peripheral blood in 6 of the dogs, with bone marrow aspirate in another 6, and with autologous multipotential bone marrow-derived cells (mesenchymal stem cells) in another 6. The dogs were humanely killed at 1 to 12 months after the operation.

RESULTS

All 18 dogs survived the postoperative period. Bronchoscopically, 3 of 4 dogs in the peripheral blood group showed stenosis, whereas no stenosis was evident in all 8 of the dogs in the bone marrow and mesenchymal stem cell groups 6 months after the operation. Faster epithelialization and fewer complications, such as mesh exposure and luminal stenosis, were observed in these two groups than in the peripheral blood group. Histologically, the cells from autologous bone marrow were found to proliferate into the tracheal tissue during the first month. Cilial movement in these two groups was faster than that in the peripheral blood group and recovered to 80% to 90% of the normal level.

CONCLUSIONS

Bone marrow aspirate and mesenchymal stem cells enhance the regeneration of the tracheal mucosa on this prosthesis. This in situ tissue engineering approach may facilitate tracheal reconstruction in the clinical setting.

In situ tissue engineering of the cricoid and trachea in a canine model

OBJECTIVES

The purpose of the current study was to demonstrate the efficacy of in situ tissue engineering of the cricoid and trachea in a canine model.

METHODS

Marlex mesh tube reinforced with polypropylene threads and covered by collagen sponge was used as a tissue scaffold for airway regeneration in 9 beagle dogs. The anterior half of the cricoid cartilage was resected in 5 dogs, whereas the cricoid cartilage and cervical trachea were simultaneously resected in 4 dogs. The tissue scaffold was implanted into the resultant defect.

RESULTS

Endoscopic examination showed no airway obstruction for a postoperative period of 3 to 40 months in all dogs. Granulation tissue was observed in 2 dogs, and slight mesh exposure in 1 dog, although all were asymptomatic. Light microscopy and electron microscopy showed the endolaryngeal and endotracheal lumen to be covered by ciliated epithelium. According to strain-force measurement, the framework was firmly supported by regenerated tissue, as well as the normal cricoid and trachea.

CONCLUSIONS

Our current tissue scaffold provides a rigid framework for the airway, and the collagen coating invites tissue regrowth around the tube. This study presents the possibility of successful reconstruction of the cricoid and trachea with epithelial regeneration by means of in situ tissue engineering.

Replacement of the left main bronchus with a tissue-engineered prosthesis in a canine model

BACKGROUND

Stenosis of the left main bronchus caused by inflammatory diseases and neoplasms is a serious clinical problem because it can cause obstructive pneumonia and may require pneumonectomy. As an alternative to various treatments currently available, including balloon dilatation, stenting, and bronchoplasty, we propose the use of a prosthesis developed based on the concept of in situ tissue engineering for replacement of the left main bronchus.

METHODS

The main frame of the tissue-engineered prosthesis is a polypropylene mesh tube, 12 to 15 mm in inner diameter and 30 mm in length, with reinforcing rings. Collagen extracted from porcine skin is conjugated to this frame. A consecutive series of 8 beagle dogs underwent replacement of the left main bronchus with this tissue-engineered prosthesis.

RESULTS

All dogs survived the postoperative period with no morbidity except 1, which required intravenous administration of antibiotic for a week for pneumonia and recovered. Three dogs were euthanized for examination at 3 and 4 months after bronchus replacement, and the other five were monitored for more than 1 year. In two dogs, histologic examination revealed that the luminal surface was completely covered with ciliated columnar epithelium or nonciliated squamous epithelium. Exposure of the polypropylene mesh to various degrees was observed in 6 dogs, but the prosthesis remained stable and no adverse effects such as infection, sputum retention, or dehiscence were observed.

CONCLUSIONS

These long-term results suggest that our tissue-engineered prosthesis is applicable for replacement of the left main bronchus.

Human nasal turbinates as a viable source of respiratory epithelial cells using co-culture system versus dispase-dissociation technique

OBJECTIVE

To compare a co-culture system with a conventional dispase-dissociation method for obtaining functional human respiratory epithelial cells from the nasal turbinates for tissue engineering application.

METHODS

Human respiratory epithelial cells were serially passaged using a co-culture system and a conventional dispase-dissociation technique. The growth kinetics and gene expression levels of the cultured respiratory epithelial cells were compared. Four genes were investigated, namely cytokeratin-18, a marker for ciliated and secretory epithelial cells; cytokeratin-14, a marker for basal epithelial cells; MKI67, a proliferation marker; and MUC5B, a marker for mucin secretion. Immunocytochemical analysis was performed using monoclonal antibodies against the high molecular-weight cytokeratin 34 beta E12, cytokeratin 18, and MUC5A to investigate the protein expression from cultured respiratory epithelial cells.

RESULTS

Respiratory epithelial cells cultured using both methods maintained polygonal morphology throughout the passages. At passage 1, co-cultured respiratory epithelial showed a 2.6-times higher growth rate compared to conventional dispase dissociation technique, and 7.8 times higher at passage 2. Better basal gene expression was observed by co-cultured respiratory epithelial cells compared to dispase dissociated cells. Immunocytochemical analyses were positive for the respiratory epithelial cells cultured using both techniques.

CONCLUSION

Co-culture system produced superior quality of cultured human respiratory epithelial cells from the nasal turbinates as compared to dispase dissociation technique.

[Tissue engineering of respiratory epithelium. Regenerative medicine for reconstructive surgery of the upper airways]

Reconstruction of long tracheal defects remains an unsolved surgical problem. Tissue engineering of respiratory epithelium is therefore of utmost surgical and scientific interest. Successful cultivation and reproduction of respiratory epithelium in vitro is crucial to seed scaffolds of various biomaterials with functionally active respiratory mucosa. Most frequently, the suspension culture as well as the tissue or explant cultures are used. Collagenous matrices, synthetic and biodegradable polymers, serve as carriers in studies. It is essential for clinical practice that mechanically stable biomaterials be developed that are resorbable in the long term or that cartilaginous constructs produced in vitro be employed which are seeded with respiratory epithelium before implantation. Vascularization of a bioartificial matrix for tracheal substitution is also prerequisite for integration of the constructs produced in vitro into the recipient organism. Here, the state of the art of research, perspectives and limitations of tracheal tissue engineering are reviewed.

Tracheal replacements: Part 2

In this review, we summarize the history of tracheal reconstruction and replacement as well as progress in current tracheal substitutes. In Part 1, we covered the historical highlights of grafts, flaps, tube construction, and tissue transplants and addressed the progress made in tracheal stenting as a means of temporary tracheal support. In Part 2 we analyze solid and porous tracheal prostheses in experimental and clinical trials and provide a summary of efforts aimed at generating a bioengineered trachea. In both parts, we provide an algorithm on the spectrum of options available for tracheal replacement.

Tracheal remodeling: comparison of different composite cultures consisting of human respiratory epithelial cells and human chondrocytes

The reconstruction of extensive tracheal defects is still an unsolved challenge for thoracic surgery. Tissue engineering is a promising possibility to solve this problem through the generation of an autologous tracheal replacement from patients' own tissue. Therefore, this study investigated the potential of three different coculture systems, combining human respiratory epithelial cells and human chondrocytes. The coculture systems were analyzed by histological staining with alcian blue, immunohistochemical staining with the antibodies, 34betaE12 and CD44v6, and scanning electron microscopy. The first composite culture consisted of human respiratory epithelial cells seeded on human high-density chondrocyte pellets. For the second system, we used native articular cartilage chips as base for the respiratory epithelial cells. The third system consisted of a collagen membrane, seeded with respiratory epithelial cells and human chondrocytes onto different sides of the membrane, which achieved the most promising results. In combination with an air-liquid interface system and fibroblast-conditioned medium, an extended epithelial multilayer with differentiated epithelial cells could be generated. Our results suggest that at least three factors are necessary for the development towards a tracheal replacement: (1) a basal lamina equivalent, consisting of collagen fibers for cell-cell interaction and cell polarization, (2) extracellular factors of mesenchymal fibroblasts, and (3) the presence of an air-liquid interface system for proliferation and differentiation of the epithelial cells.

Experimental regeneration of canine larynx: a trial with tissue engineering techniques

CONCLUSION

Since this tissue engineering technique is cost-effective and is less invasive to patients, it may replace conventional approaches in laryngeal reconstructive surgeries.

OBJECTIVE

Laryngeal cancer is one of the most prevalent cancers in the head and neck region, and frequently requires surgical resection. Although there are many ways to reconstruct the larynx after resection, donor tissue is usually required. Recently, tissue engineering techniques have become widely accepted in clinical medicine and have already been applied to some organs. This animal experiment was designed to elucidate the efficacy of laryngeal regeneration using tissue engineering technique.

MATERIALS AND METHODS

A bioartificial scaffold was designed from a replica of a canine larynx. A dental cast was used to replicate the intricate inside shape of the larynx. After copying its shape on a polypropylene mesh sheet, this sheet was coated with spongy collagen from porcine skin. A hemilaryngectomy was performed on beagle dogs under general anesthesia. Then the scaffold, preclotted with a mixture of peripheral blood and bone marrow-derived stromal cells, was implanted and fixed. The postoperative status was examined fiberscopically.

RESULTS

On the eighth day after the operation, the surface of the implant was covered with soft tissue. Finally, the implant was completely covered with regenerated mucosa.

Development of tracheal prostheses made of porous titanium: a study on sheep

Authors report the development of a biomaterial to be used for tracheal and laryngeal reconstruction. This experimentation follows the replacement of trachea in rats with porous titanium implants. The aim of the study is to test this type of prosthesis on sheep, whose trachea is of comparable size to that of humans. Six ewes were implanted with porous titanium implants after resection of 5 cm of trachea. The planned period for the implantation was from 3 to 6 months before the sacrifice of the animals for histological analysis. After a simple immediate postoperative course, the implantations developed complications of tracheal patency, responsible for four deaths (tracheal obstruction by mucous plug n = 2, inferior necrosis of trachea n = 1, pneumopathy n = 1). The two remaining sheep presented no complications. The mechanical performance of the prostheses was good. The histological results showed an inflammatory stenosis of the tracheo-prosthetic junctions, which was not the direct result of death. The protheses were integrated by the surrounding tissue, but endoprosthetic colonisation by pseudostratified ciliated columnar epithelium was low or nil. The absence of endoprosthetic lining was responsible for the complications. The biocompatibility of the biomaterial is not in question, but the surgical procedure will have to be modified by an endoprosthetic mucous graft before implantation so as to accelerate healing process.

Cell delivery in regenerative medicine: the cell sheet engineering approach

Recently, cell-based therapies have developed as a foundation for regenerative medicine. General approaches for cell delivery have thus far involved the use of direct injection of single cell suspensions into the target tissues. Additionally, tissue engineering with the general paradigm of seeding cells into biodegradable scaffolds has also evolved as a method for the reconstruction of various tissues and organs. With success in clinical trials, regenerative therapies using these approaches have therefore garnered significant interest and attention. As a novel alternative, we have developed cell sheet engineering using temperature-responsive culture dishes, which allows for the non-invasive harvest of cultured cells as intact sheets along with their deposited extracellular matrix. Using this approach, cell sheets can be directly transplanted to host tissues without the use of scaffolding or carrier materials, or used to create in vitro tissue constructs via the layering of individual cell sheets. In addition to simple transplantation, cell sheet engineered constructs have also been applied for alternative therapies such as endoscopic transplantation, combinatorial tissue reconstruction, and polysurgery to overcome limitations of regenerative therapies and cell delivery using conventional approaches.

Tissue Engineered Epithelial Cell Sheets for the Creation of a Bioartificial Trachea

To successfully engineer a bioartificial tracheal replacement, it is believed that the regeneration of a functional epithelial lining is a key requirement. In the present study, rabbit tracheal epithelial cells were cultured on temperature-responsive culture dishes, under normal culture conditions at 37 degrees C. By simple temperature reduction to 20 degrees C, the cultured epithelial cells were noninvasively harvested as intact sheets, without the use of any proteolytic enzymes. Support Dacron grafts that had been subcutaneously implanted for 4 weeks to allow for host tissue and vessel infiltration were then opened, and the tracheal epithelial cell sheets were transplanted to the luminal surface without sutures. These fabricated constructs were then used as tracheal replacements, in a rabbit model. Four weeks after transplantation, results showed that the tracheal grafts were covered by a mature, pseudostratified columnar epithelium. In contrast, control constructs that did not receive cell sheet transplantation demonstrated only a thin, immature epithelium at the center of the replacement graft. These results therefore demonstrate that these tracheal epithelial cell sheets can create an epithelial lining on the luminal surface of a bioartificial trachea.

On the Use of Unsealed Polypropylene Mesh as Tracheal Replacement

The necessity of a cervical tracheal replacement arises with thyroid carcinoma, which occasionally infiltrates the trachea extensively, the rare primary tracheal tumors and, sporadically, benign stenoses. In the present study, we used an uncoated porous polypropylene prosthesis as cervical tracheal replacement in sheep. Specifically, we implanted a tracheal prosthesis of polypropylene mesh as a cervical tracheal replacement in five sheep, protecting the airways with self-expanding stents. Healing-in of the prostheses was checked bronchoscopically. The animals were killed after increasing survival times (7, 28, 64, 68, and >90 days), and incorporation of the prosthesis was examined macroscopically, microangiographically and histologically. Although medium-term survival was possible with a sufficiently wide airway, all animals were ultimately euthanized because of complications (airway stenosis, prolapse of prosthesis). Nevertheless, the results show that replacement of the cervical trachea with a polypropylene mesh can be successful under different experimental conditions.

Estimation of Interaction Between Human Keratinocytes and Xenogenic Collagen in vitro

This paper describes the interaction observed between human keratinocytes and xenogenic collagen in vitro modified by HCl. Human keratinocytes were cultivated for 3-10 days, on modified and control support. Their growth, morphology and interaction with support were analyzed. It was found that on both control and experimental (modified) collagen cells proliferated in a similar way. Within 3-10 days, the culture became multilayered and mature and differentiation of cells was visible. Using electron microscope elements of basal membrane interacting with support were seen. On modified support processes of cells penetrating the support are occasionally seen. By use of the immunofluorescent, cytochemical techniques was found the presence of: BP-180 (antigen), beta(4) integrin, laminin 5 and collagen IV, VII, VIIc. On the modified support the above listed elements appeared between 3 and 7 days of culture, whereas on the control between 7th and 10th days. On 10th day of culture, the presence of elements of basal membranes became less evident. Results give some hope for using xenogenic, modified collagen as support of keratinocytes culture in process of human skin engineering.

Development of .BETA.-tricalcium Phosphate/Collagen Sponge Composite for Bone Regeneration

Synthetic biomaterials have been developed and used for bone grafting. Here, we developed a biodegradable sponge composite for bone tissue engineering by combining beta-tricalcium phosphate (beta-TCP) and collagen. In addition, we sought to determine the optimal beta-TCP granules/collagen ratio by evaluating and bone formation in vivo. Porous beta-TCP granules were mixed with atelocollagen hydrochloride solution at various ratios--0.02, 0.05, 0.1, and 0.2 g/mL. The resultant mixtures were freeze-dried and subjected to dehydrothermal treatment in vacuo. The final composites obtained were designated beta-TCP/collagen sponge composites (beta-TCP/CS). Through compression testing, it was found that the stress values for beta-TCP/CS (0.2 g/mL) were higher than those of the other three composites over the whole strain range. Histological evaluation at four weeks after implantation revealed that the collagen sponge had degraded and newly formed bone was present on the surface of the beta-TCP granules. At 12 weeks, the beta-TCP granules were completely degraded and remodeling of the lamellar bone was observed.

Experimental study of replacing circumferential tracheal defects with new prosthesis

PURPOSE

To investigate the feasibility of using a new tracheal prosthesis made of biomaterials to replace extensive circumferential tracheal defects.

DESCRIPTION

Three types of tracheal prostheses were developed and studied. Type I prosthesis was used in 8 mongrel dogs (group A), type II in 4 dogs (group B), and type III in 4 dogs (group C).

EVALUATION

In group A, one died from prosthetic dehiscence, another from anastomotic leakage, and the others had uneventful postoperative courses. The implanted prosthesis was completely incorporated with the recipient trachea, where different lengths of reepithelialization occurred on the luminal surface of the reconstructed trachea. Macroscopic examination showed scattered and different sizes of neo-ossification surrounding the implanted prosthesis. The prosthesis was radioopaque when exposed to routine x rays. In contrast, a relatively high number of complications occurred postoperatively in groups B and C.

CONCLUSIONS

Type I tracheal prosthesis, with further improvements, may be the optimal tracheal graft to replace circumferential tracheal defects, and appears very promising for clinical application.

Collagenous matrices as release carriers of exogenous growth factors

We have investigated the use of natural and synthetic collagenous matrices as carriers of exogenous growth factors. A bladder acellular matrix (BAM) was processed from rat bladder and compared with sponge matrix of porcine type 1 collagen. The lyophilized matrices were rehydrated by the aqueous solutions of basic fibroblast growth factor (bFGF), hepatocyte growth factor (HGF), platelet derived growth factor-BB (PDGF-BB), vascular endothelial growth factor (VEGF), insulin like growth factor-1 (IGF-1) and heparin binding epidermal growth factor-like growth factor (HB-EGF), to obtain the matrix incorporating each growth factor. The rehydration method enabled the growth factor protein to distribute into the matrix homogeneously. In vivo release test in the mouse subcutis revealed that, the property of BAM for growth factor release was similar to that of collagen sponge. Among the growth factors examined, bFGF release was the most sustained, followed by HGF and PDGF-BB. bFGF released from the two matrices showed similar in vivo angiogenic activity at the mouse subcutis in a dose-dependent manner. These findings demonstrate that the collagenous matrices function as release carriers of growth factors. This feature is promising to create a scaffold, which has a nature to control the tissue regeneration actively.

Tissue regeneration based on tissue engineering technology

Recent development of biomedical engineering as well as basic biology and medicine has enabled us to induce cell-based regeneration of body tissue to self-repair defective tissue or substitute biological functions of damaged organs. For successful tissue regeneration, it is indispensable to give cells an environment suitable for regeneration induction. Tissue engineering is a newly emerging biomedical technology for creating an environment for tissue regeneration with various biomaterials. The paper presented here overviews recent research data on tissue regeneration based on tissue engineering, and briefly explains the key technology of tissue engineering.

Replacement of a tracheal defect with a tissue-engineered prosthesis: early results from animal experiments

OBJECTIVES

The major problems in the development of tracheal prosthesis are anastomotic dehiscence and stenosis, caused by poor epithelialization of the prosthetic graft. We developed a novel tracheal prosthesis with viable mucosa transplanted from the oral cavity and reported excellent long-term results after thoracic tracheal replacements in dogs. In the current study, we used tissue-engineering techniques to construct a mucosal prosthetic lining from skin cells and evaluated its usefulness in tracheal replacement.

METHODS

Abdominal skin patches (5 x 10 cm) were harvested from 10 adult mongrel dogs. The epithelial cells were separated, cultured in vitro for 4 weeks, and then seeded onto a porous polylactic glycolic acid scaffold (6 x 8 cm) to construct a lining mucosa. This was then mounted onto the prosthesis framework, made with polypropylene mesh reinforced with polypropylene rings. The mucosa-lined prosthesis was wrapped with the greater omentum of the same dog and placed in the peritoneal cavity for 1 week. Complete surgical resection and replacement of a thoracic tracheal segment (5 cm in length, just above the carina) was then performed using the prosthesis.

RESULTS

The animals regained full activity and survived with normal activity. Bronchoscopy at 1 week and at 1 and 2 months revealed no stenosis in the anastomosis.

CONCLUSIONS

This highly biocompatible tracheal prosthesis could prove useful for the reconstruction of large, circumferential tracheal defects.

Experimental study of a new tracheal prosthesis: Pored Dacron tube

OBJECTIVE

This study was designed to evaluate how various sizes and densities of pores in Dacron tubing might enhance its utility as a tracheal prosthesis.

METHODS

A vascular prosthesis made of knitted external velour polyester was prepared for pore formation with a laser. The first set compared different pore sizes (300, 500, and 700 microm) and pore densities (25/cm(2) or 100/cm(2)). Grafts were reinforced with an externally heat-sealed silicone ring. The second set tested grafts with a pore density of 64/cm(2) and a pore size of 500 microm internally reinforced with a stainless-steel spiral stent. In all experiments, a canine mediastinal trachea 10 cartilage rings in length was resected, and the prosthesis was then implanted with an omental flap.

RESULTS

Lower pore size and density (300 microm, 25 pores/cm(2)) led to essentially no tissue ingrowth. Larger pore size (700 microm) and low density (25 pores/cm(2)) led to rapid and excessive ingrowth of granulation. Midrange pore size (500 microm) and high density (100 pores/cm(2)) invited steady tissue ingrowth, but marked luminal stenosis eventually developed. Stent-reinforced prostheses with 500-microm pores at 64 pores/cm(2), as used in the second set, maintained an average patency rate of 60% or more (range, 20%-100%) at least 12 months after implantation.

CONCLUSION

Our data show that porosity is a key factor for tissue growth through our Dacron tracheal prostheses. This artificial trachea model has led to long-term survivors up to 27 months after the operation and seems promising as a basic model for clinical tracheal repair.

Novel approach to regeneration of periodontal tissues based on in situ tissue engineering: effects of controlled release of basic fibroblast growth factor from a sandwich membrane

To regenerate periodontal tissues, a sandwich membrane composed of a collagen sponge scaffold and gelatin microspheres containing basic fibroblast growth factor (bFGF) in a controlled-release system was developed according to the new concept of "in situ tissue engineering." A three-walled alveolar bone defect (3 x 4 x 4 mm) was made bilaterally in edentulous regions created mesially to the canines in both the maxilla and mandible of nine beagle dogs. A sandwich membrane with or without bFGF (100 microg) was implanted in each defect (each group, n = 18). During weeks 1, 2, and 4, histologic evaluation and histometric analyses were performed on three dogs. Throughout the 4 weeks, vascularization and osteogenesis were active only in the bFGF-treated group (p < 0.01). New cementum was formed (2.4 +/- 0.9 mm) on the exposed root surface at 4 weeks, and functional recovery of the periodontal ligament was indicated in part by the perpendicular orientation of regenerated collagen fibers. In the control group, epithelial downgrowth and root resorption occurred and the defects were filled with connective tissue. Thus, our sandwich membrane induced successful regeneration of the periodontal tissues in a short period of time.

Regenerative repair of the mandible using a collagen sponge containing TGF-beta1

INTRODUCTION

Alveolar bone resorption and atrophy of the mandible are a major challenge for regeneration medicine. In the present investigation, a collagen sponge that contained TGF-beta1 was placed at a mandibular defect and the osteogenic effects of collagen-TGF-beta1, complex were evaluated.

MATERIAL AND METHODS

The Pm2, Pm3, and Pm4 teeth on both sides of the mandibles of 12 adult beagle dogs (9.0-12.0 kg) were extracted. After the extraction-site wounds healed, a bone defect (10.0 x 15.0 mm-wide, 10.0 mm-deep or 10.0 x 10.0 mm-wide, 10.0 mm-deep) was created on the mandible. A collagen sponge (10.0 x 10.0 x 10.0 mm) that contained TGF-beta1 (1.0 microg, 5.0 microg, or 10.0 microg, in physiological saline) was placed at the bottom of the defect and the overlying mucous membrane was sutured with 4-0 prolene. As a control, a collagen sponge that contained physiological saline only was placed in a defect on the opposite side. Two weeks after the surgery the wounds above the bone defects on both the control and TGF-beta1-treated sides had healed completely.

RESULTS

At four, six, or eight weeks post-operatively animals were killed. Soft X-ray and bone-salt measurement analyses confirmed clearly that there was greater calcified bone formation in the defects into which TGF-beta1 had been incorporated than with the control defects. The implanted collagen sponges were fully resorbed and the bone tissue had regenerated from the bottom of the defects on the TGF-beta1, side by four weeks. On the control side, no such regeneration was observed.

CONCLUSIONS

These results indicate that TGF-beta1, released slowly from a collagen sponge was effective in promoting bone remodeling when applied to mandibular defects in adult dogs.

Tracheal replacement: a critical review

This review discusses the need for tracheal replacement, distinct from resection with primary anastomosis, the requirements for replacement, and the many efforts over the past century to accomplish this goal experimentally and clinically. Approaches have included use of foreign materials, nonviable tissue, autogenous tissue, tissue engineering, and transplantation. Biological problems in each category are noted.