Rat Tracheal Cartilage Regeneration Using Mesenchymal Stem Cells Derived From Human iPS Cells

Tracheal cartilage provides structural support to the airways to enable breathing. However, it can become damaged or impaired, sometimes requiring surgical resection and reconstruction. Previously, we clinically applied an artificial trachea composed of a polypropylene mesh and collagen sponge, with a favorable postoperative course. However, the artificial trachea presents a limitation, as the mesh is not biodegradable and cannot be used in pediatric patients. Compared to a polypropylene mesh, regenerated cartilage represents an ideal material for reconstruction of the damaged trachea. The use of mesenchymal stem cells (MSCs) as a source for cartilage regeneration has gained widespread acceptance, but challenges such as the invasiveness of harvesting and limited cell supply persist. Therefore, we focused on the potential of human-induced pluripotent stem cell (hiPSC)-derived mesenchymal stem cells (iMSCs) for tracheal cartilage regeneration. In this study, we aimed to regenerate tracheal cartilage on an artificial trachea as a preliminary step to replace the polypropylene mesh. iMSCs were induced from hiPSCs through neural crest cells and transplanted with a polypropylene mesh covered with a collagen sponge into the damaged tracheal cartilage in immunodeficient rats. Human nuclear antigen (HNA)-positive cells were observed in all six rats at 4 weeks and in six out of seven rats at 12 weeks after transplantation, indicating that transplanted iMSCs survived within the tracheal cartilage defects of rats. The HNA-positive cells coexpressed SOX9, and type II collagen was detected around HNA-positive cells in four of six rats at 4 weeks and in three of seven rats at 12 weeks after transplantation, reflecting cartilage-like tissue regeneration. These results indicate that the transplanted iMSCs could differentiate into chondrogenic cells and promote tracheal cartilage regeneration. iMSC transplantation thus represents a promising approach for human tracheal reconstruction.

Airway ciliated cells regenerated on collagen sponge implants acquire planar polarities towards nearby edges of implanted areas

Tissue-engineered tracheae have been developed to replace defective tracheae. However, the direction of ciliated cells in the regenerated epithelium remains unclear. We investigated planar polarity formed in the regenerated airway epithelium after tracheal graft implantation. We partially resected the rat trachea and implanted a collagen scaffold. The direction of the basal foot was assessed by transmission electron microscopy. Immunofluorescence staining was performed to examine the biased distribution of Vangl1 and Frizzled6 proteins. The direction of mucociliary transport was analyzed by video microscopy. Our results showed that the basal feet of cilia in the proximal and distal regions of the implanted areas were respectively oriented toward the proximal and distal directions. The biased distribution of Vangl1 and Frizzled6, and the directions of mucociliary transport showed that planar polarities formed in the regenerated epithelium were oriented toward the proximal, distal, left, and right directions in the proximal, distal, left, and right regions of the implanted area. These polarities persisted until nine months after implantation. Hence, the results suggest that planar polarities formed in epithelia regenerated on tracheal grafts are directed toward the nearby edges of implanted areas and are preserved for a prolonged period. The polarities can, at least partially, contribute to clearing external materials from the implanted areas by transporting them to a normal region.

Transplantation of multiciliated airway cells derived from human iPS cells using an artificial tracheal patch into rat trachea

Tracheal resection is often performed for malignant tumours, congenital anomalies, inflammatory lesions, and traumatic injuries. There is no consensus on the best approach for the restoration of tracheal functionality in patients with tracheal defects. Artificial grafts made of polypropylene and collagen sponge have been clinically used by our group. However, 2 months are required to achieve adequate epithelialization of the grafts in humans. This study aimed to investigate the feasibility of transplantation therapy using an artificial trachea with human-induced pluripotent stem cell (hiPSC)-derived multiciliated airway cells (hiPSC-MCACs). Collagen vitrigel membrane, a biocompatible and absorbable material, was used as a scaffold to cover the artificial trachea with hiPSC-MCACs. Analyses of hiPSC-MCACs on collagen vitrigel membrane were performed by immunocytochemistry and electron microscopy and by assessing ciliary beat frequency. Along with the artificial trachea, hiPSC-MCACs were transplanted into surgically created tracheal defects of immunodeficient rats. The survival of transplanted cells was histologically evaluated at 1 and 2 weeks after the transplantation. The hiPSC-MCACs exhibited motile cilia on collagen vitrigel membrane. The surviving hiPSC-MCACs were observed in the endotracheal epithelium of the tracheal defect at 1 and 2 weeks after transplantation. These results suggest that hiPSC-MCAC is a useful candidate for tracheal reconstruction.

Large animal models for long-segment tracheal reconstruction: a systematic review

BACKGROUND

The reconstruction of extensive tracheal defects is an unresolved problem. Despite decades of research, a reliable and practical substitute remains to be found. While there have been clinical reports of successful long-segment tracheal reconstruction, reproducibility and widespread applicability of these techniques have yet to be achieved. Large animals such as the dog, pig, sheep, and goat have comparable tracheal morphology and physiology to humans making them useful preclinical models to screen potential therapeutic strategies.

MATERIALS AND METHODS

The literature was reviewed to identify large animal models commonly used for tracheal reconstruction. A systematic search of PubMed and EMBASE was performed for large animal studies reporting on the reconstruction of long-segment tracheal and carinal defects. Fifty-seven studies were identified for analysis.

RESULTS

There is no standard large animal model available for tracheal research. In recent years, livestock species have gained favor over dogs as animal models in this field. The minimum requirements for successful tracheal replacement are rigidity, vascularity, and epithelial lining. Early attempts with synthetic prostheses were met with disappointing results. An autologous tracheal substitute is ideal but hindered by limited donor site availability and the lack of a dominant vascular pedicle for microsurgical reconstruction. Although tracheal allotransplantation enables like-for-like replacement, there are unresolved issues relating to graft vascularity, immunosuppression, and graft preservation. Tissue engineering holds great promise; however, the optimal combination of scaffold, cells, and culture conditions is still indeterminate.

CONCLUSIONS

Despite impressive advances in tracheal reconstruction, a durable substitute for extended tracheal defects continues to be elusive.

Long-term preservation of planar cell polarity in reversed tracheal epithelium

Background

Planar cell polarity (PCP) coordinates the patterning and orientation of cells and their structures along tissue planes, and although its acquisition during the formation of airway epithelium has been described, the mechanisms for its maintenance and reconstruction are poorly understood. We aimed to clarify whether ambient environment change by orthotropic autologous transplantation affected PCP at the cellular level.

Methods

We performed orthotropic autologous transplantation by inverting tracheal segments in rats, and then performed morphological evaluation by microscopy. The PCP of the tracheal epithelium was assessed over time by analyzing the directions of mucociliary transport and ciliary beat, the positional relationship between the basal body and basal foot, and the bias of Vang-like protein 1 (Vangl1) at 2, 4, and 6 months postoperatively.

Results

After 2 months, the directions of mucociliary transport and ciliary beat were preserved toward the lung in the inverted tracheal segments. The positional relationship between the basal body and the basal foot, and the bias of Vangl1, also indicated preservation of PCP in the inverted tracheal segments. Similar results were obtained at 6 months.

Conclusion

The PCP of ciliated epithelium was preserved in reversed trachea, even after long-term observation.

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0726-y) contains supplementary material, which is available to authorized users.

In Situ Tissue Engineering of the Bile Duct Using Polypropylene Mesh-Collagen Tubes

Multiple attempts have been made to replace biliary defects with a variety of materials. Recently, successful biliary reconstruction using the Gore-Tex vascular graft has been reported experimentally and clinically We designed a new artificial bile duct consisting of collagen sponge and polypropylene mesh. We presently evaluated the feasibility of using this prosthesis as a scaffold for bile duct tissue regeneration in a canine model. Our prosthesis, a sponge made from porcine dermal collagen, is reinforced with a polypropylene mesh cylinder. We used the prosthesis to reconstruct the middle portion of the common bile duct in seven beagle dogs to evaluate its efficacy. While one dog died of biliary stricture 8 months after operation, six survived without problems to scheduled time points for tissue evaluation at 1 to 12 months. All prostheses had become completely incorporated into the host. A confluent epithelial lining was observed within 3 months. In cholangiograms the prosthesis displayed long-term patency in the six dogs and provided satisfactory bile drainage for up to 12 months. Our graft thus shows promise for repair of biliary defects and should lead to development of a new treatment for biliary reconstruction.

Implantation of Induced Pluripotent Stem Cell-Derived Tracheal Epithelial Cells

OBJECTIVES

Compared with using autologous tissue, the use of artificial materials in the regeneration of tracheal defects is minimally invasive. However, this technique requires early epithelialization on the inner side of the artificial trachea. After differentiation from induced pluripotent stem cells (iPSCs), tracheal epithelial tissues may be used to produce artificial tracheas. Herein, we aimed to demonstrate that after differentiation from fluorescent protein-labeled iPSCs, tracheal epithelial tissues survived in nude rats with tracheal defects.

METHODS

Red fluorescent tdTomato protein was electroporated into mouse iPSCs to produce tdTomato-labeled iPSCs. Embryoid bodies derived from these iPSCs were then cultured in differentiation medium supplemented with growth factors, followed by culture on air-liquid interfaces for further differentiation into tracheal epithelium. The cells were implanted with artificial tracheas into nude rats with tracheal defects on day 26 of cultivation. On day 7 after implantation, the tracheas were exposed and examined histologically.

RESULTS

Tracheal epithelial tissue derived from tdTomato-labeled iPSCs survived in the tracheal defects. Moreover, immunochemical analyses showed that differentiated tissues had epithelial structures similar to those of proximal tracheal tissues.

CONCLUSIONS

After differentiation from iPSCs, tracheal epithelial tissues survived in rat bodies, warranting the use of iPSCs for epithelial regeneration in tracheal defects.

Bioengineered Trachea with Fibroblasts in a Rabbit Model

Objectives

Although our group has had mostly successful results with clinical application of a tracheal prosthesis, delayed epithelial regeneration remains a problem. In our previous studies using rats, it was demonstrated that tracheal fibroblasts accelerated proliferation and differentiation of the tracheal epithelium in vitro and in vivo. The purpose of this study was to evaluate the effects of fibroblasts on epithelial regeneration in larger tracheal defects in rabbits.

Methods

We developed a bioengineered scaffold, the luminal surface of which was coated with fibroblasts. This scaffold was implanted into tracheal defects in 12 rabbits (bioengineered group), and scaffolds without fibroblasts were implanted in 12 rabbits (control group). The regenerated epithelium was histologically examined by light microscopy, scanning electron microscopy, and immunohistochemical studies.

Results

In the bioengineered group, a stratified squamous epithelium was observed on the surface 7 days after transplantation. However, in the control group, the scaffolds were exposed. Fourteen days after implantation, a columnar ciliated epithelium was observed in the bioengineered group. The average thickness of the regenerated epithelium in the bioengineered group was significantly greater than that in the control group.

Conclusions

This study indicated that fibroblasts had a stimulatory effect that hastened regeneration of the epithelium in large tracheal defects.

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.

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.

Regenerative Medicine of the Trachea: The First Human Case

Objectives:

The objective of the present study was to demonstrate regenerative medicine of the tracheal tissue by using an in situ tissue engineering technique for airway reconstruction.

Methods:

Based on the previous successful experimental animal studies, the current regenerative technique was applied to repair of the trachea of a 78-year-old woman with thyroid cancer. A Marlex mesh tube covered by collagen sponge was used as a tissue scaffold. The operative intervention included right hemithyroidectomy, resection of the trachea, and tracheoplasty using the scaffold. The right half of three rings of the trachea was resected, and the scaffold material was sutured to the defect of the trachea.

Results:

After 2 weeks, the mesh collagen structure of the artificial material could be seen with endoscopy in most of the implanted area. The artificial material was covered with epithelial growth after 2 months. Epithelialization continued to cover the artificial material completely for 2 years without any complications.

Conclusions:

The current regenerative technique avoided tracheotomy, a second operation, and deformity. Good epithelialization has been observed on the tracheal luminal surface without any complications for 2 years. Although long-term observation is required, regenerative medicine of the tracheal tissue appears feasible for airway reconstruction.

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.

Optimal bovine collagen concentration to achieve tracheal epithelial coverage of collagen sponges

OBJECTIVES/HYPOTHESIS

Artificial tracheas prepared using a collagen sponge and polypropylene mesh have been implanted in patients who received tracheal resections, but epithelialization in the reconstructed area is slow. We determined the optimal bovine atelocollagen concentration necessary for the rapid and complete tracheal epithelial coverage of collagen sponge implants.

STUDY DESIGN

Preliminary animal experiment.

METHODS

Collagen sponges were prepared using lyophilizing 0.5%, 0.7%, and 1.0% atelocollagen solutions (0.5%, 0.7%, and 1.0% sponges) and were analyzed using scanning electron microscopy. Partial tracheal defects were prepared in rabbits and reconstructed using sponges. Epithelial regeneration in the reconstructed area was evaluated by endoscopic, histological, and scanning electron microscope analyses.

RESULTS

All sponges had a membranous structural framework, and numerous fibrous structures filled the spaces within the framework in the 0.5% sponges. The membranous structure in the 0.7% sponges branched at many points, and intermembrane spaces were frequently observed. Conversely, the membranous structure in the 1.0% sponges was relatively continuous, thick, and closely arranged. Two weeks after implantation, tracheal defects were entirely covered with epithelium in two of the four and three of the four of the 0.5% and 0.7% sponge-implanted rabbits, respectively. The collagen sponges remained exposed to the tracheal lumen in four of the four rabbits in the 1.0% sponge group. Ciliogenesis in the center of the epithelialized region was detected only in the 0.7% sponge group.

CONCLUSION

Collagen sponges prepared from various concentrations of bovine atelocollagen have different structures. Complete epithelial coverage was achieved in more rabbits implanted with sponges prepared using the 0.7% bovine atelocollagen solution than in those implanted with sponges prepared from the 0.5% and 1.0% solutions.

LEVEL OF EVIDENCE

NA Laryngoscope, 126:E396-E403, 2016.

Regeneration of tracheal epithelium using mouse induced pluripotent stem cells

Conclusion The findings demonstrated the potential use of induced pluripotent stem cells for regeneration of tracheal epithelium. Objective Autologous tissue implantation techniques using skin or cartilage are often applied in cases of tracheal defects with laryngeal inflammatory lesions and malignant tumor invasion. However, these techniques are invasive with an unstable clinical outcome. The purpose of this study was to investigate regeneration in a tracheal defect site of nude rats after implantation of ciliated epithelium that was differentiated from induced pluripotent stem cells. Method Embryoid bodies were formed from mouse induced pluripotent stem cells. They were cultured with growth factors for 5 days, and then cultured at the air-liquid interface. The degree of differentiation achieved prior to implantation was determined by histological findings and the results of real-time polymerase chain reaction. Embryoid bodies including ciliated epithelium were embedded into collagen gel that served as an artificial scaffold, and then implanted into nude rats, creating an 'air-liquid interface model'. Histological evaluation was performed 7 days after implantation. Results The ciliated epithelial structure survived on the lumen side of regenerated tissue. It was demonstrated histologically that the structure was composed of ciliated epithelial cells.

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.

Visualization of mouse induced pluripotent stem cells for evaluation of tracheal regeneration

CONCLUSION

Visualization of mouse induced pluripotent stem (iPS) cells with the use of a fluorescent protein was successfully achieved for evaluation of tracheal regeneration.

OBJECTIVES

Tracheal epithelial cells derived from iPS cells are expected to be a useful cell source for tracheal regeneration. Our previous study demonstrated that mouse iPS cells differentiated into tracheal epithelial cells. However, when they are implanted into tracheal defects in experimental animals, it is difficult to determine whether the regenerated tracheal epithelium is in fact derived from iPS cells. The purpose of this study was to develop a visualization technique for iPS cells for evaluation of tracheal regeneration.

METHODS

Fluorescent marker tdTomato was transfected into iPS cells. Tracheal epithelial cells were generated from tdTomato-labeled iPS cells using embryoid body formation to detect the expression of tdTomato. The artificial material with tdTomato-labeled iPS cells was implanted into tracheal defects in nude rats. The survival and distribution of tdTomato-labeled iPS cell-derived cells were examined using the IVIS Imaging System and immunostaining.

RESULTS

The expression of tdTomato was detected in both undifferentiated cells and tracheal epithelial cells in vitro. tdTomato-labeled iPS cell-derived cells were successfully detected in the tracheal defects by IVIS Imaging System and immunostaining.

Tissue engineered scaffolds for an effective healing and regeneration: reviewing orthotopic studies

It is commonly stated that tissue engineering is the most promising approach to treat or replace failing tissues/organs. For this aim, a specific strategy should be planned including proper selection of biomaterials, fabrication techniques, cell lines, and signaling cues. A great effort has been pursued to develop suitable scaffolds for the restoration of a variety of tissues and a huge number of protocols ranging from in vitro to in vivo studies, the latter further differentiating into several procedures depending on the type of implantation (i.e., subcutaneous or orthotopic) and the model adopted (i.e., animal or human), have been developed. All together, the published reports demonstrate that the proposed tissue engineering approaches spread toward multiple directions. The critical review of this scenario might suggest, at the same time, that a limited number of studies gave a real improvement to the field, especially referring to in vivo investigations. In this regard, the present paper aims to review the results of in vivo tissue engineering experimentations, focusing on the role of the scaffold and its specificity with respect to the tissue to be regenerated, in order to verify whether an extracellular matrix-like device, as usually stated, could promote an expected positive outcome.

Are synthetic scaffolds suitable for the development of clinical tissue-engineered tubular organs?

Transplantation of tissues and organs is currently the only available treatment for patients with end-stage diseases. However, its feasibility is limited by the chronic shortage of suitable donors, the need for life-long immunosuppression, and by socioeconomical and religious concerns. Recently, tissue engineering has garnered interest as a means to generate cell-seeded three-dimensional scaffolds that could replace diseased organs without requiring immunosuppression. Using a regenerative approach, scaffolds made by synthetic, nonimmunogenic, and biocompatible materials have been developed and successfully clinically implanted. This strategy, based on a viable and ready-to-use bioengineered scaffold, able to promote novel tissue formation, favoring cell adhesion and proliferation, could become a reliable alternative to allotransplatation in the next future. In this article, tissue-engineered synthetic substitutes for tubular organs (such as trachea, esophagus, bile ducts, and bowel) are reviewed, including a discussion on their morphological and functional properties.

Evaluation of the use of induced pluripotent stem cells (iPSCs) for the regeneration of tracheal cartilage

The treatment of laryngotracheal stenosis remains a challenge as treatment often requires multistaged procedures, and successful decannulation sometimes fails after a series of operations. Induced pluripotent stem cells (iPSCs) were generated in 2006. These cells are capable of unlimited symmetrical self-renewal, thus providing an unlimited cell source for tissue-engineering applications. We have previously reported tracheal wall regeneration using a three-dimensional (3D) scaffold containing iPSCs. However, the efficiency of differentiation into cartilage was low. In addition, it could not be proven that the cartilage tissues were in fact derived from the implanted iPSCs. The purpose of this study was to evaluate and improve the use of iPSCs for the regeneration of tracheal cartilage. iPSCs were cultured in vitro in a 3D scaffold in chondrocyte differentiation medium. After cultivation, differentiation into chondrocytes was examined. The ratio of undifferentiated cells was analyzed by flow cytometry. The 3D scaffolds were implanted into tracheal defects, as an injury site, in 24 nude rats. Differentiation into chondrocytes in vitro was confirmed histologically, phenotypically, and genetically. Flow cytometric analysis demonstrated that the population of undifferentiated cells was decreased. Cartilage tissue was observed in the regenerated tracheal wall in 6 of 11 rats implanted with induced iPSCs, but in none of 13 rats implanted with the control and noninduced iPSCs. The expression of cartilage-specific protein was also demonstrated in vivo in 3D scaffolds containing iPSCs. The presence of the GFP gene derived from iPSCs was confirmed in samples of cartilage tissue by the combination of laser microdissection (LMD) and polymerase chain reaction (PCR) techniques. Our study demonstrated that iPSCs have the potential to differentiate into chondrogenic cells in vitro. Cartilage tissue was regenerated in vivo. Our results suggest that iPSCs could be a new cell source for the regeneration of tracheal cartilage.

Regeneration of tracheal epithelium using a collagen vitrigel-sponge scaffold containing basic fibroblast growth factor

OBJECTIVES

Our group has had good results in tracheal mucosal regeneration using a collagen vitrigel-sponge scaffold in an animal model. In this study, the effectiveness of this scaffold with the application of basic fibroblast growth factor (b-FGF) was investigated.

METHODS

A collagen vitrigel-sponge scaffold was fabricated with simultaneous addition of b-FGF. Three types of collagen vitrigel-sponge scaffolds were made: no b-FGF, 10 ng of b-FGF, and 100 ng of b-FGF. At 3, 5, 7, and 14 days after implantation in rats, the tracheas were removed and histologically evaluated. The regeneration of mucosal epithelium and the subepithelial layer was evaluated.

RESULTS

Mucosal epithelium, including pseudostratified epithelium and ciliated cells, regenerated earlier in the scaffolds when b-FGF was applied than when b-FGF was not applied. Regeneration of the subepithelial layer, infiltration of inflammatory cells and fibroblasts, and angiogenesis were promoted earlier in the scaffolds with b-FGF application.

CONCLUSIONS

Our technique for tracheal reconstruction using collagen vitrigel-sponge scaffolds with b-FGF application affords a feasible approach for accelerating the regeneration of the intraluminal surface and subepithelial layer of tracheal tissue.

Collagen vitrigel scaffold for regenerative medicine of the trachea: experimental study and quantitative evaluation

CONCLUSION

Our technique for tracheal regeneration using a collagen vitrigel scaffold affords a feasible approach for accelerating epithelial regeneration on the intraluminal surface of the host tracheal defect.

OBJECTIVES

The purpose of the study was to quantitatively evaluate the effectiveness of a collagen vitrigel scaffold for the regeneration of the tracheal epithelium.

METHODS

The collagen vitrigel scaffold was developed by conjugating a collagen vitrigel membrane to a collagen sponge to promote both epithelial cell growth and mesenchymal cell infiltration. The collagen vitrigel scaffold was implanted into tracheal defects in rats as the vitrigel model, and a conventional collagen sponge was implanted as a control model. The structure of the regenerated tissue was observed and thickness of the epithelium was quantitatively evaluated by histological examination.

RESULTS

Histological findings showed the surface of the collagen vitrigel scaffold to be flat in comparison with that of the conventional collagen sponge. At 7, 14, and 28 days post-implantation, the average thickness of the regenerated epithelial layer in the vitrigel model group was greater than that in the control group.

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.

Potential of induced pluripotent stem cells for the regeneration of the tracheal wall

OBJECTIVES

Our previous studies focused on basic research and the clinical applications of an artificial trachea. However, the prefabricated artificial trachea cannot be utilized for pediatric airways, because the tracheal frame needs to expand as the child develops. The purpose of this study was to evaluate the potential of induced pluripotent stem (iPS) cells for the regeneration of the tracheal wall.

METHODS

We cultured iPS cells in a 3-dimensional (3-D) scaffold in chondrocyte differentiation medium (bioengineered scaffold model), and the results were compared with those in a 3-D scaffold without iPS cells (control scaffold model). The 3-D scaffolds were implanted into tracheal defects in 8 nude rats. After 4 weeks, the regenerated tissue was histologically examined.

RESULTS

Implanted iPS cells were confirmed to exist in all 5 rats implanted with bioengineered scaffolds. Cartilage-like tissue was observed in the regenerated tracheal wall in 2 of the 5 rats in the bioengineered scaffold model, but in none of the 3 rats in the control scaffold model.

CONCLUSIONS

Implanted iPS cells were confirmed to exist in the bioengineered scaffold. Cartilage-like tissue was regenerated in the tracheal defect. This study demonstrated the potential of iPS cells in the regeneration of the tracheal wall.

A tissue-engineering approach for stenosis of the trachea and/or cricoid

CONCLUSION

This new regenerative therapy shows great potential for the treatment of stenosis of the trachea and/or cricoids (STC).

OBJECTIVES

To estimate the potential of tissue-engineered artificial trachea (AT) for treatment of STC in clinical applications. We previously reported that AT was a useful material for implantation into a tracheal defect after resection of cancer. There are many causes of stenosis of the respiratory tract and STC is particularly difficult to treat.

METHODS

The AT was a spiral stent composed of Marlex mesh made of polypropylene and covered with collagen sponge made from porcine skin. Three patients with STC were treated by this tissue-engineering method. All of them suffered from STC caused by long endotracheal intubations. They underwent a two-stage operation. In the first operation, after resection of the stenotic regions, the edge of the tracheal cartilage was sutured to the edge of the skin. The tracheal lumen was exposed and a T-shaped cannula was inserted into the large tracheostoma. At 3 weeks to 2 months after the first operation, the trachea and skin were separated. The trimmed AT with venous blood and basic fibroblast growth factor (b-FGF) was then implanted into the cartilage defect.

RESULTS

Postoperatively, all patients were able to breathe easily and had no discomfort in their daily activities. Six months after the second operation, we observed enough air space in the trachea and cricoid by computed tomography (CT) imaging and fiber endoscopy.

Bioengineered Trachea with Fibroblasts in a Rabbit Model

Objectives:

Although our group has had mostly successful results with clinical application of a tracheal prosthesis, delayed epithelial regeneration remains a problem. In our previous studies using rats, it was demonstrated that tracheal fibroblasts accelerated proliferation and differentiation of the tracheal epithelium in vitro and in vivo. The purpose of this study was to evaluate the effects of fibroblasts on epithelial regeneration in larger tracheal defects in rabbits.

Methods:

We developed a bioengineered scaffold, the luminal surface of which was coated with fibroblasts. This scaffold was implanted into tracheal defects in 12 rabbits (bioengineered group), and scaffolds without fibroblasts were implanted in 12 rabbits (control group). The regenerated epithelium was histologically examined by light microscopy, scanning electron microscopy, and immunohistochemical studies.

Results:

In the bioengineered group, a stratified squamous epithelium was observed on the surface 7 days after transplantation. However, in the control group, the scaffolds were exposed. Fourteen days after implantation, a columnar ciliated epithelium was observed in the bioengineered group. The average thickness of the regenerated epithelium in the bioengineered group was significantly greater than that in the control group.

Conclusions:

This study indicated that fibroblasts had a stimulatory effect that hastened regeneration of the epithelium in large tracheal defects.

Glottal reconstruction with a tissue engineering technique using polypropylene mesh: a canine experiment

OBJECTIVES

The larynx must be resected in some cases of cancer or stenosis, and various techniques are generally employed to fill the resulting defect. No ideal way, however, has been established to restore vocal function after this form of insult. The aim of this preliminary feasibility study in a canine model was to investigate the effectiveness of a polypropylene-based tissue engineering approach to repair a partial glottal defect.

METHODS

Eight dogs were used in this study. A laryngeal defect involving resection of the left vocal fold was created through a thyroid cartilage window. A scaffold made of polypropylene and collagen was preclotted and wrapped with autologous fascia lata, inserted through the window, and sutured to the laryngeal defect in 5 dogs. The defect was reconstructed with an adjacent sternohyoid muscle flap in 3 control dogs. The surgical site was evaluated 3 months after operation by fiberscopic examination, computed tomographic imaging, histologic evaluation, and study of excised larynges.

RESULTS

On fiberscopic examination, the experimental group implants were completely covered with regenerated mucosa in all cases, and a favorable vocal fold contour was found in 4 of the 5 cases. One case was characterized by a concave vocal fold shape and red granulation. In the control group, the muscle flap was replaced by scarred mucosa with a concave vocal fold contour in 2 cases, and there was soft white granulation at the anterior resected edge in the third case. The histologic data revealed the regeneration of lined epithelium, subepithelial tissue, and muscle structure in both groups. The excised larynx phonatory data revealed reduced vibratory amplitude in the experimental group compared with the control group; however, excised phonation was not achieved in 2 of the 3 cases in the control group.

CONCLUSIONS

This polypropylene-based tissue engineering technique appears to be a viable tool for glottal reconstruction; however, additional refinement is required to maximize long-term phonatory function.

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 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.

Clinical Application of in Situ Tissue Engineering Using a Scaffolding Technique for Reconstruction of the Larynx and Trachea

Objectives:

The objective of the present study was to demonstrate the efficacy of the clinical application of in situ tissue engineering using a scaffolding technique for laryngeal and tracheal tissue.

Methods:

We have developed a tissue scaffold made from a Marlex mesh tube covered by collagen sponge. Based on successful animal experimental studies, in situ tissue engineering with a scaffold implant was applied to repair the larynx and trachea in 4 patients.

Results:

In 1 patient with subglottic stenosis, the thyroid cartilage, cricoid cartilage, and cervical trachea with scarring and granulation were resected and reconstructed by use of the scaffold. In 3 patients with thyroid cancer, the trachea and cricoid cartilage with tumor invasion were resected and the scaffold was implanted into the defect. Postoperative endoscopy during the observation period of 8 to 34 months showed a well-epithelialized airway lumen without any obstruction.

Conclusions:

Our current technique of in situ tissue engineering using a scaffold shows great potential for use in the regeneration of airway defects.

Regeneration of the Trachea Using a Bioengineered Scaffold with Adipose-Derived Stem Cells

Objectives:

Our group has developed and clinically applied an artificial graft made from a collagen sponge scaffold for the regeneration of tracheal tissue. However, the artificial graft requires about 2 months for epithelial regeneration. The purpose of the present study was to accelerate the regeneration process of the trachea through the effective use of a bioengineered scaffold. Adipose-derived stem cells (ASCs) with multilineage differentiation capability were used. In our study, we implanted a bioengineered scaffold that included autologous ASCs into tracheal defects in rats.

Methods:

Collagen gel, including ASCs labeled with monomeric yellow fluorescent protein, was layered onto the surface of the collagen sponge to form a bioengineered scaffold. This scaffold was implanted into the tracheal defects in rats. A control scaffold without ASCs was also implanted.

Results:

On day 14 after implantation, a pseudostratified columnar epithelium with well-differentiated ciliated and goblet cells and neovascularization was observed in rats that received the implant with the bioengineered scaffold that included ASCs.

Conclusions:

These results suggested that implanted ASCs accelerated neovascularization and epithelialization on the regenerated trachea. Thus, our newly developed bioengineered scaffold contributes to tracheal regeneration.

Regeneration of Tracheal Epithelium Utilizing a Novel Bipotential Collagen Scaffold

Objectives:

The purpose of the present study was to evaluate the effectiveness of a novel bipotential collagen scaffold as a bioengineered trachea for the regeneration of the tracheal epithelium.

Methods:

The bipotential collagen scaffold was developed by conjugating a collagen vitrigel membrane to a collagen sponge in order to promote both epithelial cell growth and mesenchymal cell infiltration. The bipotential collagen scaffold was transplanted into tracheal defects in rats, and a conventional collagen sponge was implanted as a control model. Histologic examinations were undertaken to evaluate the results.

Results:

The bioengineered trachea was covered with epithelium in the vitrigel model, but not in the control model, at 7 days after implantation. At 14 days after implantation, the bioengineered trachea was covered with epithelium involving the basal cell layer in the vitrigel model. At 28 days after implantation, a columnar ciliated epithelium was observed only in the vitrigel model.

Conclusions:

Our technique for trachea reconstruction using a novel bipotential collagen scaffold affords a feasible approach for accelerating epithelial regeneration on the intraluminal surface of the host tracheal defect.

Effect of Fibroblasts on Epithelial Regeneration on the Surface of a Bioengineered Trachea

Objectives:

Our group applied a tracheal prosthesis, which was composed of polypropylene as the frame and collagenous sponge as the scaffold, to the first human case and had successful results. The objective of this study was to find a way to acquire more rapid re-epithelialization with fibroblasts on this tracheal prosthesis.

Methods:

Tracheal epithelial cells, which were isolated from the trachea of rats, were suspended in a collagenous gel. The collagenous gel with fibroblasts was layered on a collagenous sponge. The grafts of this “bioengineered trachea” were implanted into tracheal defects of rats, and the regenerated epithelium on the grafts was histologically examined.

Results:

Seven days after implantation, stratified squamous epithelium covered almost all of the surface of the gel, and some of the implanted fibroblasts in the gel were lined up just below the epithelium. Fourteen days after implantation, columnar and cuboidal ciliated epithelium covered almost all of the surface of the defects, and the implanted fibroblasts had disappeared. The numbers of regenerated epithelial cells at 14 days after implantation were larger than those of control models without fibroblasts, with statistical significance.

Conclusions:

The results suggested that the grafts of bioengineered trachea composed of collagenous sponge and collagenous gel with tracheal fibroblasts accelerated epithelial differentiation and proliferation in vivo.

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.

Carinal Replacement With an Aortic Allograft

BACKGROUND

Carinal replacement after extensive resection remains a tremendous challenge in thoracic surgery. In previous studies, we demonstrated that an aortic graft could be a valuable tracheal substitute. The goal of this new study was to evaluate the reconstruction of the carina using a stent supported bifurcated aortic allograft.

METHODS

In 15 sheep the replacement of the tracheobronchial bifurcation with an aortic allograft was performed under cardiopulmonary bypass. A temporary stent prevented airway collapse. No immunosuppression was used. Aortic segments were retrieved at regular intervals up to 24 months after implantation.

RESULTS

All animals survived the initial aortic allograft operation. Six animals died postoperatively (1 of graft necrosis, 2 of pneumonia, and 3 of bronchial fistula). The remaining 9 animals were in good condition until they were euthanized. Stent removal was tolerated after 9 months in 3 animals. Progressive transformation of the arterial graft initially into extensive inflammatory tissue, and after 3 to 6 months into a tracheal tissue comprising a well-differentiated epithelium and cartilage was confirmed by histology.

CONCLUSIONS

This study showed that regeneration of a functional tissue can be obtained after replacement of the carina with an aortic allograft. The origin and mechanisms of this regenerative process remains to be discovered. These results represent an important hope for the reconstruction of the carina after extensive resection, especially for cancer lesions. In human application, the systemic use of omentoplasty or myoplasty should further reduce its risk of complication.

Cranial Bone Regeneration Using a Composite Scaffold of Beta-Tricalcium Phosphate, Collagen, and Autologous Bone Fragments

OBJECTIVE

The aim of our study was to examine the tissue response and new bone formation induced by beta-tricalcium phosphate (beta-TCP), collagen, and autologous bone fragments with fibrin glue implanted into a cranial bone defect.

MATERIALS AND METHODS

Granulated beta-TCP and collagen from porcine skin were mixed and freeze-dried. The weight ratio of both materials was 98:2. The composite scaffold for bone regeneration was composed of this artificial material and autologous bone fragments. Five adult beagle dogs were used. A cranial bone defect (2 cmx2 cm) was created in each dog. The animals were divided into two groups. In group 1 (n=3), the cranial bone defect was closed by replacing the original free bone flap, and the residual fissure and burr holes were filled with the composite scaffold with fibrin glue. In group 2 (n=2), the bone defect was closed only by replacing the original free bone flap. Three months after the treatment, computed tomography and histologic examinations were done in all animals.

RESULTS

In all dogs in group 1, the defects were almost closed by new bone; whereas in group 2, the defects were filled with fibrous tissues instead of bone.

CONCLUSION

This study showed that the composite scaffold made of beta-TCP, collagen, and autologous bone fragments with fibrin glue enabled reconstruction of cranial bone defects without the usual fixation materials.

Surgical relief of causalgia with an artificial nerve guide tube: Successful surgical treatment of causalgia (Complex Regional Pain Syndrome Type II) by in situ tissue engineering with a polyglycolic acid-collagen tube

Two patients with causalgia associated with allodynia and finger contracture were treated surgically with a bioresorbable nerve guide tube made from polygycolic acid and collagen: the injured segment of the digital nerve was resected and the resulting gap (25 and 36mm) was bridged with the tube. In both cases, a neuroma was found on the injured nerve and many sprouting branches were. After reconstruction, the causalgia and allodynia disappeared and movement of the fingers recovered during the following 6 months. Functional recovery was objectively identified for 1 year and 9 months. Both patients regained full use of their finger and were free of discomfort for up to 24 and 18 months, respectively. Since the first description of causalgia in 1864, there has been no definitive treatment for this intractable burning pain. Our experience shows that at least some types of causalgia can be resolved successfully by surgery.

Effect of basic fibroblast growth factor on vascularization in esophagus tissue engineering

We carried out an experimental study to evaluate the effect of basic fibroblast growth factor (bFGF)-containing collagen gel on vascularization in esophageal tissue engineering. We compared an acellular collagen sponge scaffold and an acellular collagen gel scaffold in combination with bFGF using a canine model. The construct was implanted in the cervical esophagus and the regenerated tissue was evaluated one month after surgery. Histological analysis confirmed a significantly large amount of blood vessels in the bFGF-containing collagen gel group as compared to the collagen gel group without bFGF (bFGF (-)). However, in the collagen sponge groups, no difference was observed between the bFGF (+) group and the bFGF (-) group. These results showed that bFGF-containing collagen gel is suitable not only for an acellular scaffold for tissue engineering but also for an effective tropic factor vehicle in vivo.

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.