Esophageal tissue engineering: A new approach for esophageal replacement

Circumferential Esophageal Reconstruction Using a Tissue-engineered Decellularized Tunica Vaginalis Graft in a Rabbit Model

BACKGROUND

Pediatric surgeons have faced esophageal reconstruction challenges for decades owing to a variety of congenital and acquired conditions. This work aimed to introduce a reproducible and efficient approach for creating tissue-engineered esophageal tissue using bone marrow mesenchymal stem cells (BMSCs) cultured in preconditioned mediums seeded on a sheep decellularized tunica vaginalis (DTV) scaffold for partial reconstruction of a rabbit's esophagus.

METHODS

DTV was performed using SDS and Triton X-100 solutions. The decellularized grafts were employed alone (DTV group) or after recellularization with BMSCs cultured for 10 days in preconditioned mediums (RTV group) for reconstructing a 3 cm segmental defect in the cervical esophagus of rabbits (n = 20) after the decellularization process was confirmed. Rabbits were observed for one month, after which they were euthanized, and the reconstructed esophagi were harvested for histological analysis.

RESULTS

Six rabbits in the DTV group and eight rabbits in the RTV group survived until the end of the one-month study period. Despite histological examination demonstrating that both grafts completely repaired the esophageal defect, the RTV graft demonstrated a histological structure similar to that of the normal esophagus. The reconstructed esophagi in the RTV group revealed the arrangement of the different layers of the esophageal wall with the formation of newly formed blood vessels and Schwann-like cells.

CONCLUSION

DTV xenograft is a novel scaffold that promotes cell adhesion and differentiation and might be effectively utilized for regenerating esophageal tissue, paving the way for future clinical trials in pediatric patients.

Recent advances in the treatment of gastrointestinal motility disorders in children

INTRODUCTION

Pediatric gastrointestinal motility disorders represent some of the most challenging clinical conditions with largely undefined pathogenetic pathways and therefore limited therapeutic options. Herein, we provide an overview of the recent advances in treatment options for these disorders and their clinical impact.

AREAS COVERED

PubMed and Medline databases were searched for relevant articles related to the treatment of achalasia, esophageal atresia, gastroparesis, PIPO and constipation published between 2017 and 2022. In this article, we review and summarize recent advances in management of gastrointestinal motility disorders in children with a particular focus on emerging therapies as well as novel diagnostic modalities that help guide their application or develop new, more targeted treatments.

EXPERT OPINION

Gastrointestinal motility disorders represent one of the most challenging conundrums in pediatric age and despite significant advances in investigative tools, the palette of treatment options remain limited. Overall, while pharmacological options have failed to bring a curative solution, recent advances in minimal invasive therapeutic and diagnostic techniques have emerged as potential keys to symptom and quality of life improvement, such as ENDOFLIP, POEM, cine-MRI, fecal microbiota transplantation.

Recent Methods for Modifying Mechanical Properties of Tissue-Engineered Scaffolds for Clinical Applications

The limited regenerative capacity of the human body, in conjunction with a shortage of healthy autologous tissue, has created an urgent need for alternative grafting materials. A potential solution is a tissue-engineered graft, a construct which supports and integrates with host tissue. One of the key challenges in fabricating a tissue-engineered graft is achieving mechanical compatibility with the graft site; a disparity in these properties can shape the behaviour of the surrounding native tissue, contributing to the likelihood of graft failure. The purpose of this review is to examine the means by which researchers have altered the mechanical properties of tissue-engineered constructs via hybrid material usage, multi-layer scaffold designs, and surface modifications. A subset of these studies which has investigated the function of their constructs in vivo is also presented, followed by an examination of various tissue-engineered designs which have been clinically translated.

Decellularized esophageal tubular scaffold microperforated by quantum molecular resonance technology and seeded with mesenchymal stromal cells for tissue engineering esophageal regeneration

Current surgical options for patients requiring esophageal replacement suffer from several limitations and do not assure a satisfactory quality of life. Tissue engineering techniques for the creation of customized “self-developing” esophageal substitutes, which are obtained by seeding autologous cells on artificial or natural scaffolds, allow simplifying surgical procedures and achieving good clinical outcomes. In this context, an appealing approach is based on the exploitation of decellularized tissues as biological matrices to be colonized by the appropriate cell types to regenerate the desired organs. With specific regard to the esophagus, the presence of a thick connective texture in the decellularized scaffold hampers an adequate penetration and spatial distribution of cells. In the present work, the Quantum Molecular Resonance^® (QMR) technology was used to create a regular microchannel structure inside the connective tissue of full-thickness decellularized tubular porcine esophagi to facilitate a diffuse and uniform spreading of seeded mesenchymal stromal cells within the scaffold. Esophageal samples were thoroughly characterized before and after decellularization and microperforation in terms of residual DNA content, matrix composition, structure and biomechanical features. The scaffold was seeded with mesenchymal stromal cells under dynamic conditions, to assess the ability to be repopulated before its implantation in a large animal model. At the end of the procedure, they resemble the original esophagus, preserving the characteristic multilayer composition and maintaining biomechanical properties adequate for surgery. After the sacrifice we had histological and immunohistochemical evidence of the full-thickness regeneration of the esophageal wall, resembling the native organ. These results suggest the QMR microperforated decellularized esophageal scaffold as a promising device for esophagus regeneration in patients needing esophageal substitution.

Bio-Engineered Scaffolds Derived from Decellularized Human Esophagus for Functional Organ Reconstruction

Esophageal reconstruction through bio-engineered allografts that highly resemble the peculiar properties of the tissue extracellular matrix (ECM) is a prospective strategy to overcome the limitations of current surgical approaches. In this work, human esophagus was decellularized for the first time in the literature by comparing three detergent-enzymatic protocols. After decellularization, residual DNA quantification and histological analyses showed that all protocols efficiently removed cells, DNA (<50 ng/mg of tissue) and muscle fibers, preserving collagen/elastin components. The glycosaminoglycan fraction was maintained (70–98%) in the decellularized versus native tissues, while immunohistochemistry showed unchanged expression of specific ECM markers (collagen IV, laminin). The proteomic signature of acellular esophagi corroborated the retention of structural collagens, basement membrane and matrix–cell interaction proteins. Conversely, decellularization led to the loss of HLA-DR expression, producing non-immunogenic allografts. According to hydroxyproline quantification, matrix collagen was preserved (2–6 µg/mg of tissue) after decellularization, while Second-Harmonic Generation imaging highlighted a decrease in collagen intensity. Based on uniaxial tensile tests, decellularization affected tissue stiffness, but sample integrity/manipulability was still maintained. Finally, the cytotoxicity test revealed that no harmful remnants/contaminants were present on acellular esophageal matrices, suggesting allograft biosafety. Despite the different outcomes showed by the three decellularization methods (regarding, for example, tissue manipulability, DNA removal, and glycosaminoglycans/hydroxyproline contents) the ultimate validation should be provided by future repopulation tests and in vivo orthotopic implant of esophageal scaffolds.

Development of Bio-artificial Esophageal Tissue Engineering Utilization for Circumferential Lesion Transplantation: A Narrative Review

The esophagus is the gastrointestinal tract's primary organ that transfers bolus into the stomach with peristaltic motion. Therefore, its lesions cause a significant disturbance in the nutrition and digestive system. Esophageal disease treatment sometimes requires surgical procedures that involve removal and circumferential full-thickness replacement. Unlike other organs, the esophagus has a limited regeneration ability and cannot be transplanted from donors. There are various methods of restoring the esophageal continuity; however, they are associated with certain flaws that lead to a non-functional recovery. As an exponentially growing science, tissue engineering has become a leading technique for the development of tissue replacement to repair damaged esophageal segments. Scaffold plays a significant role in the process of tissue engineering, as it acts as a template for the regeneration of growing tissue. A variety of scaffolds have been studied to replace the esophagus. Due to the many tissue quality challenges, the results are still inadequate and need to be improved. The success of esophageal tissue regeneration will finally depend on the scaffold's capability to mimic natural tissue properties and provide a qualified environment for regeneration. Thereby, scaffold fabrication techniques are fundamental. This article reviews the recent developments in esophageal tissue engineering for the treatment of circumferential lesions based on scaffold biomaterial engineering approaches.

Decellularization of porcine esophageal tissue at three diameters and the bioscaffold modification with EETs-ECM gel

Damaged complex modular organs repair is a current clinical challenge in which one of the primary goals is to keep their biological response. An interesting case of study it is the porcine esophagus since it is a tubular muscular tissue selected as raw material for tissue engineering. The design of esophageal constructs can draw on properties of the processed homologous extracellular matrix (ECM). In this work, we report the decellularization of multilayered esophagus tissue from 1-, 21- and 45-days old piglets through the combination of reversible alkaline swelling and detergent perfusion. The bioscaffolds were characterized in terms of their residual composition and tensile mechanical properties. The biological response to esophageal submucosal derived bioscaffolds modified with ECM gel containing epoxyeicosatrienoic acids (EETs) was then evaluated. Results suggest that the composition (laminin, fibronectin, and sulphated glycosaminoglycans/sGAG) depends on the donor age: a better efficiency of the decellularization process combined with a higher retention of sGAG and fibronectin is observed in piglet esophageal scaffolds. The heterogeneity of this esophageal ECM is maintained, which implied the preservation of anisotropic tensile properties. Coating of bioscaffolds with ECM gel is suitable for carrying esophageal epithelial cells and EETs. Bioactivity of EETs-ECM gel modified esophageal submucosal bioscaffolds is observed to promote neovascularization and antiinflammatory after rabbit full-thickness esophageal defect replacement.

Engineered Full Thickness Electrospun Scaffold for Esophageal Tissue Regeneration: From In Vitro to In Vivo Approach

Acquired congenital esophageal malformations, such as malignant esophageal cancer, require esophagectomy resulting in full thickness resection, which cannot be left untreated. The proposed approach is a polymeric full-thickness scaffold engineered with mesenchymal stem cells (MSCs) to promote and speed up the regeneration process, ensuring adequate support and esophageal tissue reconstruction and avoiding the use of autologous conduits. Copolymers poly-L-lactide-co-poly-ε-caprolactone (PLA-PCL) 70:30 and 85:15 ratio were chosen to prepare electrospun tubular scaffolds. Electrospinning apparatus equipped with two different types of tubular mandrels: cylindrical (∅ 10 mm) and asymmetrical (∅ 10 mm and ∅ 8 mm) were used. Tubular scaffolds underwent morphological, mechanical (uniaxial tensile stress) and biological (MTT and Dapi staining) characterization. Asymmetric tubular geometry resulted in the best properties and was selected for in vivo surgical implantation. Anesthetized pigs underwent full thickness circumferential resection of the mid-lower thoracic esophagus, followed by implantation of the asymmetric scaffold. Preliminary in vivo results demonstrated that detached stitch suture achieved better results in terms of animal welfare and scaffold integration; thus, it is to be preferred to continuous suture.

Circumferential esophageal replacement by a decellularized esophageal matrix in a porcine model

BACKGROUND

Tissue engineering is an attractive alternative to conventional esophageal replacement techniques using intra-abdominal organs which are associated with a substantial morbidity. The objective was to evaluate the feasibility of esophageal replacement by an allogenic decellularized esophagus in a porcine model. Secondary objectives were to evaluate the benefit of decellularized esophagus recellularization with autologous bone marrow mesenchymal stromal cells and omental maturation of the decellularized esophagus.

METHODS

Eighteen pigs divided into 4 experimental groups according to mesenchymal stromal cells recellularization and omental maturation underwent a 5-cm long circumferential replacement of the thoracic esophagus. Turbo green florescent protein labelling was used for in vivo mesenchymal stromal cells tracking. The graft area was covered by a stent for 3 months. Clinical and histologic outcomes were analyzed over a 6-month period.

RESULTS

The median follow-up was 112 days [5; 205]. Two animals died during the first postoperative month, 2 experienced an anastomotic leakage, 13 experienced a graft area stenosis following stent migration of which 3 were sacrificed as initially planned after successful endoscopic treatment. The stent could be removed in 2 animals: the graft area showed a continuous mucosa without stenosis. After 3 months, the graft area showed a tissue specific regeneration with a mature epithelium and muscular cells. Clinical and histologic results were similar across experimental groups.

CONCLUSION

Circumferential esophageal replacement by a decellularized esophagus was feasible and allowed tissue remodeling toward an esophageal phenotype. We could not demonstrate any benefit provided by the omental maturation of the decellularized esophagus nor its recellularization with mesenchymal stromal cells.

A narrative review of esophageal tissue engineering and replacement: where are we?

Long-gap esophageal defects, whether congenital or acquired, are very difficult to manage. Any significant surgical peri-esophageal dissection that is performed to allow for potential stretching of two ends of a defect interrupts the esophageal blood supply and leads to complications such as leak and stricture, even in the youngest, healthiest patients. The term “congenital” applied to these defects refers mainly to long-gap esophageal atresia (LGA). Causes of acquired long-segment esophageal disruption include recurrent leaks and fistulae after primary repair, refractory GERD, caustic ingestions, cancer, and strictures. 5,000–10,000 patients per year in the US require esophageal replacement. Gastric, colonic, and jejunal pull-up surgeries are fraught with high rates of both short and long term complications thus creating a space for a better option. Since the 1970’s many groups around the world have been unsuccessfully attempting esophageal replacement with tissue-engineered grafts in various animal models. But, recent advances in these models are now combining novel technologic advances in materials bioscience, stem-cell therapies, and transplantation and are showing increasing promise to human translational application. Transplantation has been heretofore unsuccessful, but given modern improvements in transplant microsurgery and immunosuppressive medications, pioneering trials in animal models are being undertaken now. These rapidly evolving medical innovations will be reviewed here.

Development of a Decellularized Porcine Esophageal Matrix for Potential Applications in Cancer Modeling

Many decellularized extracellular matrix-derived whole organs have been widely used in studies of tissue engineering and cancer models. However, decellularizing porcine esophagus to obtain decellularized esophageal matrix (DEM) for potential biomedical applications has not been widely investigated. In this study a modified decellularization protocol was employed to prepare a porcine esophageal DEM for the study of cancer cell growth. The cellular removal and retention of matrix components in the porcine DEM were fully characterized. The microstructure of the DEM was observed using scanning electronic microscopy. Human esophageal squamous cell carcinoma (ESCC) and human primary esophageal fibroblast cells (FBCs) were seeded in the DEM to observe their growth. Results show that the decellularization process did not cause significant loss of mechanical properties and that blood ducts and lymphatic vessels in the submucosa layer were also preserved. ESCC and FBCs grew on the DEM well and the matrix did not show any toxicity to cells. When FBS and ESCC were cocultured on the matrix, they secreted more periostin, a protein that supports cell adhesion on matrix. This study shows that the modified decellularization protocol can effectively remove the cell materials and maintain the microstructure of the porcine esophageal matrix, which has the potential application of studying cell growth and migration for esophageal cancer models.

Trends in 3D bioprinting for esophageal tissue repair and reconstruction

In esophageal pathologies, such as esophageal atresia, cancers, caustic burns, or post-operative stenosis, esophageal replacement is performed by using parts of the gastrointestinal tract to restore nutritional autonomy. However, this surgical procedure most often does not lead to complete functional recovery and is instead associated with many complications resulting in a decrease in the quality of life and survival rate. Esophageal tissue engineering (ETE) aims at repairing the defective esophagus and is considered as a promising therapeutic alternative. Noteworthy progress has recently been made in the ETE research area but strong challenges remain to replicate the structural and functional integrity of the esophagus with the approaches currently being developed. Within this context, 3D bioprinting is emerging as a new technology to facilitate the patterning of both cellular and acellular bioinks into well-organized 3D functional structures. Here, we present a comprehensive overview of the recent advances in tissue engineering for esophageal reconstruction with a specific focus on 3D bioprinting approaches in ETE. Current biofabrication techniques and bioink features are highlighted, and these are discussed in view of the complexity of the native esophagus that the designed substitute needs to replace. Finally, perspectives on recent strategies for fabricating other tubular organ substitutes via 3D bioprinting are discussed briefly for their potential in ETE applications.

Strategies for treating oesophageal diseases with stem cells

There is a wide range of oesophageal diseases, the most general of which are inflammation, injury and tumours, and treatment methods are constantly being developed and updated. With an increasingly comprehensive understanding of stem cells and their characteristics of multilineage differentiation, self-renewal and homing as well as the combination of stem cells with regenerative medicine, tissue engineering and gene therapy, stem cells are playing an important role in the treatment of a variety of diseases. Mesenchymal stem cells have many advantages and are most commonly applied; however, most of these applications have been in experimental studies, with few related clinical trials for comparison. Therefore, the methods, positive significance and limitations of stem cells in the treatment of oesophageal diseases remain incompletely understood. Thus, the purpose of this paper is to review the current literature and summarize the efficacy of stem cells in the treatment of oesophageal diseases, including oesophageal ulceration, acute radiation-induced oesophageal injury, corrosive oesophageal injury, oesophageal stricture formation after endoscopic submucosal dissection and oesophageal reconstruction, as well as gene therapy for oesophageal cancer.

Successful muscle regeneration by a homologous microperforated scaffold seeded with autologous mesenchymal stromal cells in a porcine esophageal substitution model

BACKGROUND

Since the esophagus has no redundancy, congenital and acquired esophageal diseases often require esophageal substitution, with complicated surgery and intestinal or gastric transposition. Peri-and-post-operative complications are frequent, with major problems related to the food transit and reflux. During the last years tissue engineering products became an interesting therapeutic alternative for esophageal replacement, since they could mimic the organ structure and potentially help to restore the native functions and physiology. The use of acellular matrices pre-seeded with cells showed promising results for esophageal replacement approaches, but cell homing and adhesion to the scaffold remain an important issue and were investigated.

METHODS

A porcine esophageal substitute constituted of a decellularized scaffold seeded with autologous bone marrow-derived mesenchymal stromal cells (BM-MSCs) was developed. In order to improve cell seeding and distribution throughout the scaffolds, they were micro-perforated by Quantum Molecular Resonance (QMR) technology (Telea Electronic Engineering).

RESULTS

The treatment created a microporous network and cells were able to colonize both outer and inner layers of the scaffolds. Non seeded (NSS) and BM-MSCs seeded scaffolds (SS) were implanted on the thoracic esophagus of 4 and 8 pigs respectively, substituting only the muscle layer in a mucosal sparing technique. After 3 months from surgery, we observed an esophageal substenosis in 2/4 NSS pigs and in 6/8 SS pigs and a non-practicable stricture in 1/4 NSS pigs and 2/8 SS pigs. All the animals exhibited a normal weight increase, except one case in the SS group. Actin and desmin staining of the post-implant scaffolds evidenced the regeneration of a muscular layer from one anastomosis to another in the SS group but not in the NSS one.

CONCLUSIONS

A muscle esophageal substitute starting from a porcine scaffold was developed and it was fully repopulated by BM-MSCs after seeding. The substitute was able to recapitulate in shape and function the original esophageal muscle layer.

Tissue Engineered Esophageal Patch by Mesenchymal Stromal Cells: Optimization of Electrospun Patch Engineering

Aim of work was to locate a simple, reproducible protocol for uniform seeding and optimal cellularization of biodegradable patch minimizing the risk of structural damages of patch and its contamination in long-term culture. Two seeding procedures are exploited, namely static seeding procedures on biodegradable and biocompatible patches incubated as free floating (floating conditions) or supported by CellCrown^TM insert (fixed conditions) and engineered by porcine bone marrow MSCs (p-MSCs). Scaffold prototypes having specific structural features with regard to pore size, pore orientation, porosity, and pore distribution were produced using two different techniques, such as temperature-induced precipitation method and electrospinning technology. The investigation on different prototypes allowed achieving several implementations in terms of cell distribution uniformity, seeding efficiency, and cellularization timing. The cell seeding protocol in stating conditions demonstrated to be the most suitable method, as these conditions successfully improved the cellularization of polymeric patches. Furthermore, the investigation provided interesting information on patches’ stability in physiological simulating experimental conditions. Considering the in vitro results, it can be stated that the in vitro protocol proposed for patches cellularization is suitable to achieve homogeneous and complete cellularizations of patch. Moreover, the protocol turned out to be simple, repeatable, and reproducible.

Mechanical stimuli enhance simultaneous differentiation into oesophageal cell lineages in a double-layered tubular scaffold

The tissue-engineered oesophagus serves as an alternative and promising therapeutic approach for long-gap oesophageal replacement. This study proposes an advanced in vitro culture platform focused on construction of the oesophagus by combining an electrospun double-layered tubular scaffold, stem cells, biochemical reagents, and biomechanical factors. Human mesenchymal stem cells were seeded onto the inner and outer surfaces of the scaffold. Mechanical stimuli were applied with a hollow organ bioreactor along with different biochemical reagents inside and outside of the scaffold. Electrospun fibres in a tubular scaffold were found to be randomly and circumferentially oriented for the inner and outer surfaces, respectively. Amongst the two types of mechanical stimuli, the intermittent shear flow that can simultaneously cause circumferential stretching due to hydrostatic pressure, and shear stress caused by flow on the inner surface, was found to be more effective for simultaneous differentiation into epithelial and muscle lineage than steady shear flow. Under these conditions, the expression of epithelial markers on the inner surface was significantly observed, although it was minimal on the outer surface. Muscle differentiation showed the opposite expression pattern. Meanwhile, the mechanical tests showed that the strength of the scaffold was improved after incubation for 14 days. We have developed a potential platform for tissue-engineered oesophagus construction. Specifically, simultaneous differentiation into epithelial and muscle lineages can be achieved by utilizing the double-layered scaffold and appropriate mechanical stimulation.

Management of long gap esophageal atresia: A systematic review and evidence-based guidelines from the APSA Outcomes and Evidence Based Practice Committee

BACKGROUND

Treatment of the neonate with long gap esophageal atresia (LGEA) is one of the most challenging scenarios facing pediatric surgeons today. Contributing to this challenge is the variability in case definition, multiple approaches to management, and heterogeneity of the reported outcomes. This necessitates a clear summary of existing evidence and delineation of treatment controversies.

METHODS

The American Pediatric Surgical Association Outcomes and Evidence Based Practice Committee drafted four consensus-based questions regarding LGEA. These questions concerned the definition and determination of LGEA, the optimal method of surgical management, expected long-term outcomes, and novel therapeutic techniques. A comprehensive search strategy was crafted and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were utilized to identify, review and report salient articles.

RESULTS

More than 3000 publications were reviewed, with 178 influencing final recommendations. In total, 18 recommendations are provided, primarily based on level 4-5 evidence. These recommendations provide detailed descriptions of the definition of LGEA, treatment techniques, outcomes and future directions of research.

CONCLUSIONS

Evidence supporting best practices for LGEA is currently low quality. This review provides best recommendations based on a critical evaluation of the available literature. Based on the lack of strong evidence, prospective and comparative research is clearly needed.

TYPE OF STUDY

Treatment study, prognosis study and study of diagnostic test.

LEVEL OF EVIDENCE

Level II-V.

Optimization of Decellularization Procedure in Rat Esophagus for Possible Development of a Tissue Engineered Construct

Background: Current esophageal treatment is associated with significant morbidity. The gold standard therapeutic strategies are stomach interposition or autografts derived from the jejunum and colon. However, severe adverse reactions, such as esophageal leakage, stenosis and infection, accompany the above treatments, which, most times, are life threating. The aim of this study was the optimization of a decellularization protocol in order to develop a proper esophageal tissue engineered construct. Methods: Rat esophagi were obtained from animals and were decellularized. The decellularization process involved the use of 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS) and sodium dodecyl sulfate (SDS) buffers for 6 h each, followed by incubation in a serum medium. The whole process involved two decellularization cycles. Then, a histological analysis was performed. In addition, the amounts of collagen, sulphated glycosaminoglycans and DNA content were quantified. Results: The histological analysis revealed that only the first decellularization cycle was enough to produce a cellular and nuclei free esophageal scaffold with a proper extracellular matrix orientation. These results were further confirmed by biochemical quantification. Conclusions: Based on the above results, the current decellularization protocol can be applied successfully in order to produce an esophageal tissue engineered construct.

Multi-stage bioengineering of a layered oesophagus with in vitro expanded muscle and epithelial adult progenitors

A tissue engineered oesophagus could overcome limitations associated with oesophageal substitution. Combining decellularized scaffolds with patient-derived cells shows promise for regeneration of tissue defects. In this proof-of-principle study, a two-stage approach for generation of a bio-artificial oesophageal graft addresses some major challenges in organ engineering, namely: (i) development of multi-strata tubular structures, (ii) appropriate re-population/maturation of constructs before transplantation, (iii) cryopreservation of bio-engineered organs and (iv) in vivo pre-vascularization. The graft comprises decellularized rat oesophagus homogeneously re-populated with mesoangioblasts and fibroblasts for the muscle layer. The oesophageal muscle reaches organised maturation after dynamic culture in a bioreactor and functional integration with neural crest stem cells. Grafts are pre-vascularised in vivo in the omentum prior to mucosa reconstitution with expanded epithelial progenitors. Overall, our optimised two-stage approach produces a fully re-populated, structurally organized and pre-vascularized oesophageal substitute, which could become an alternative to current oesophageal substitutes.

Combining decellularised scaffolds with patient-derived cells holds promise for bioengineering of functional tissues. Here the authors develop a two-stage approach to engineer an oesophageal graft that retains the structural organisation of native oesophagus.

3D bioprinting of tissues and organs for regenerative medicine

3D bioprinting is a pioneering technology that enables fabrication of biomimetic, multiscale, multi-cellular tissues with highly complex tissue microenvironment, intricate cytoarchitecture, structure-function hierarchy, and tissue-specific compositional and mechanical heterogeneity. Given the huge demand for organ transplantation, coupled with limited organ donors, bioprinting is a potential technology that could solve this crisis of organ shortage by fabrication of fully-functional whole organs. Though organ bioprinting is a far-fetched goal, there has been a considerable and commendable progress in the field of bioprinting that could be used as transplantable tissues in regenerative medicine. This paper presents a first-time review of 3D bioprinting in regenerative medicine, where the current status and contemporary issues of 3D bioprinting pertaining to the eleven organ systems of the human body including skeletal, muscular, nervous, lymphatic, endocrine, reproductive, integumentary, respiratory, digestive, urinary, and circulatory systems were critically reviewed. The implications of 3D bioprinting in drug discovery, development, and delivery systems are also briefly discussed, in terms of in vitro drug testing models, and personalized medicine. While there is a substantial progress in the field of bioprinting in the recent past, there is still a long way to go to fully realize the translational potential of this technology. Computational studies for study of tissue growth or tissue fusion post-printing, improving the scalability of this technology to fabricate human-scale tissues, development of hybrid systems with integration of different bioprinting modalities, formulation of new bioinks with tuneable mechanical and rheological properties, mechanobiological studies on cell-bioink interaction, 4D bioprinting with smart (stimuli-responsive) hydrogels, and addressing the ethical, social, and regulatory issues concerning bioprinting are potential futuristic focus areas that would aid in successful clinical translation of this technology.

Regenerative medicine for the esophagus

Advances in tissue engineering techniques have made it possible to use human cells as biological material. This has enabled pharmacological studies to be conducted to investigate drug effects and toxicity, to clarify the mechanisms underlying diseases, and to elucidate how they compensate for impaired organ function. Many researchers have tried to construct artificial organs using these techniques, but none has succeeded in growing a whole organ. Unlike other digestive organs with complicated functions, such as the processing and absorption of nutrients, the esophagus has the relatively simple function of transporting content, which can be replicated easily by a substitute. In regenerative medicine, various combinations of materials have been applied, including scaffolding, cell sources, and bioreactors. Exciting results of tissue engineering techniques for the esophagus have been reported. In animal models, replacing full-thickness and full-circumferential defects remains challenging because of stenosis and leakage after implantation. Although many reports have manipulated various scaffolds, most have emphasized the importance of both epithelial and mesenchymal cells for the prevention of stenosis. However, the results of repair of partial full-thickness defects and mucosal defects have been promising. Two successful approaches for the replacement of mucosal defects in a clinical setting have been reported, although in contrast to the many animal models, there are few pilot studies in humans. We review the recent results and evaluate the future of regenerative medicine for the esophagus.

Esophageal reconstruction: Combined application of muscle tissue flap and inner chitosan tube stent in rabbits

BACKGROUND

Esophageal reconstruction is the key issue in esophageal surgery. However, currently there is no satisfied technique to repair esophagus after surgery.

OBJECTIVE

To combine an inner chitosan stent and a muscle tissue with vascular pedicle to repair the esophageal defect in cervical segment.

METHODS

Esophageal defect was repaired using the combination of a muscle tissue flap and a chitosan tube stent in experimental group while only muscle tissue flap was utilized in controls for comparison. One animal in each group was sacrificed at week 3, 6 and 9 after operation respectively to exam the healing status. Barium X-ray was used to evaluate the esophageal status in 12 weeks.

RESULTS

Histology showed the inflammatory response in 3 weeks after surgery, the chitosan stent was partially absorbed in 6 weeks, and there was no obvious fibrotic proliferation in experimental group; while the fibrotic proliferation and esophageal stenosis were obvious in controls, the chitosan stent was completely absorbed in 9 weeks, and squamous epidermis cells were observed. Twelve weeks later, the barium swallow went smoothly through the esophagus with noticeable peristalsis in the experimental group; esophageal stenosis without peristalsis was observed in controls.

CONCLUSION

The combination of chitosan stent and muscle tissue flap is feasible to reconstruct a partial defect in esophagus.

Surgical techniques for esophageal replacement in children

PURPOSE

Surgical techniques for esophageal replacement (ER) in children include colon interposition, gastric tube, gastric transposition, and jejunal interposition. This review evaluates the merits and demerits of each.

METHOD

Surgical techniques, complications, and outcome of ER are reviewed over last seven decades.

RESULTS

Colon interposition is the time-tested procedure with minimal and less serious complications. Long-term complications include reflux, halitosis, colonic segment dilatation, and anastomotic stricture, sometimes requiring surgical interventions especially for dilatation and reflux. Gastric tube is technically more risky, and associated with early serious complications like prolonged leak in neck or mediastinum, graft necrosis, and ischemia leading to stricture of the tube. Long-term results are good. Gastric transposition is much simpler, can be performed in emergency and in newborns. It involves a single anastomosis in the neck. Post-operative complications include gastric stasis, bile reflux, restricted growth, and decreased pulmonary functional capacity. Jejunal interposition has not been used extensively due to short mesentery but long-term results are good in expert hands.

CONCLUSION

Colon is the most preferred and safest organ for ER. Stomach is a vascular and muscular organ with lower risk of ischemia. Gastric tube is a demanding technique. Jejunum or ileum is alternative for redo cases.

Decellularized material as scaffolds for tissue engineering studies in long gap esophageal atresia

INTRODUCTION

Esophageal atresia refers to an anomaly in foetal development in which the esophagus terminates in a blind end. Whilst surgical correction is achievable in most patients, when a long gap is present it still represents a major challenge associated with higher morbidity and mortality. In this context, tissue engineering could represent a successful alternative to restore oesophageal function and structure. Naturally derived biomaterials made of decellularized tissues retain native extracellular matrix architecture and composition, providing a suitable bed for the anchorage and growth of relevant cell types. Areas covered: This review outlines the various strategies and challenges in esophageal tissue engineering, highlighting the evolution of ideas in the development of decellularized scaffolds for clinical use. It explores the interplay between clinical needs, ethical dilemmas, and manufacturing challenges in the development of a tissue engineered decellularized scaffold for oesophageal atresia. Expert opinion: Current progress on oesophageal tissue engineering has enabled effective repair of patch defects, whilst the development of a full circumferential construct remains a challenge. Despite the different approaches available and the improvements achieved, a gold standard for fully functional tissue engineered oesophageal constructs has not been defined yet.

Design of a Bioabsorbable Multilayered Patch for Esophagus Tissue Engineering

A gold standard for esophagus reconstruction is not still available. The present work aims to design a polymer patch combining synthetic polylactide-co-polycaprolacton and chitosan biopolymers, tailoring patch properties to esophageal tissue characteristics by a temperature-induced precipitation method, to get multilayered patches (1L, 2L, and 3L). Characterization shows stable multilayered patches (1L and 2L) by selection of copolymer type, and their M _w . In vitro investigation of the functional patch properties in simulated physiologic and pathologic conditions demonstrates that the chitosan layer (patch 3L) decreases patch stability and cell adhesion, while improves cell proliferation. Patches 2L and 3L comply with physiological esophageal pressure (3-5 kPa) and elongation (20%).

The Surgical Correction of Congenital Deformities: The Treatment of Diaphragmatic Hernia, Esophageal Atresia and Small Bowel Atresia

BACKGROUND

More than half of all congenital deformities can be detected in utero. The initial surgical correction is of paramount importance for the achievement of good long-term results with low surgical morbidity and mortality.

METHODS

Selective literature review and expert opinion.

RESULTS

Congenital deformities are rare, and no controlled trials have been performed to determine their optimal treatment. In this article, we present the prenatal assessment, treatment, and long-term results of selected types of congenital deformity. Congenital diaphragmatic hernia (CDH) affects one in 3500 live-born infants, while esophageal atresia affects one in 3000 and small-bowel atresia one in 5000 to 10,000. If a congenital deformity is detected and its prognosis can be reliably inferred from a prenatal assessment, the child should be delivered at a specialized center (level 1 perinatal center). The associated survival rates are 60-80% after treatment for CDH and well over 90% after treatment for esophageal or small-bowel atresia. Despite improvements in surgical correction over the years, complications and comorbidities still affect 20-40% of the treated children. These are not limited to surgical complications in the narrow sense, such as recurrence, postoperative adhesions and obstruction, stenoses, strictures, and recurrent fistulae, but also include pulmonary problems (chronic lung disease, obstructive and restrictive pulmonary dysfunction), gastrointestinal problems (dysphagia, gastro-esophageal reflux, impaired intestinal motility), and failure to thrive. Moreover, the affected children can develop emotional and behavioral disturbances. Minimally invasive surgery in experienced hands yields results as good as those of conventional surgery, as long as proper selection criteria are observed.

CONCLUSION

Congenital deformities should be treated in recognized centers with highly experienced interdisciplinary teams. As no randomized trials of surgery for congenital deformities are available, longitudinal studies and registries will be very important in the future.

Decellularized scaffolds in regenerative medicine

Allogeneic organ transplantation remains the ultimate solution for end-stage organ failure. Yet, the clinical application is limited by the shortage of donor organs and the need for lifelong immunosuppression, highlighting the importance of developing effective therapeutic strategies. In the field of regenerative medicine, various regenerative technologies have lately been developed using various biomaterials to address these limitations. Decellularized scaffolds, derived mainly from various non-autologous organs, have been proved a regenerative capability in vivo and in vitro and become an emerging treatment approach. However, this regenerative capability varies between scaffolds as a result of the diversity of anatomical structure and cellular composition of organs used for decellularization. Herein, recent advances in scaffolds based on organ regeneration in vivo and in vitro are highlighted along with aspects where further investigations and analyses are needed.

Nondestructive measurement of esophageal biaxial mechanical properties utilizing sonometry

Malignant esophageal pathology typically requires resection of the esophagus and reconstruction to restore foregut continuity. Reconstruction options are limited and morbid. The esophagus represents a useful target for tissue engineering strategies based on relative simplicity in comparison to other organs. The ideal tissue engineered conduit would have sufficient and ideally matched mechanical tolerances to native esophageal tissue. Current methods for mechanical testing of esophageal tissues both in vivo and ex vivo are typically destructive, alter tissue conformation, ignore anisotropy, or are not able to be performed in fluid media. The aim of this study was to investigate biomechanical properties of swine esophageal tissues through nondestructive testing utilizing sonometry ex vivo. This method allows for biomechanical determination of tissue properties, particularly longitudinal and circumferential moduli and strain energy functions. The relative contribution of mucosal-submucosal layers and muscular layers are compared to composite esophagi. Swine thoracic esophageal tissues (n  =  15) were tested by pressure loading using a continuous pressure pump system to generate stress. Preconditioning of tissue was performed by pressure loading with the pump system and pre-straining the tissue to in vivo length before data was recorded. Sonometry using piezocrystals was utilized to determine longitudinal and circumferential strain on five composite esophagi. Similarly, five mucosa-submucosal and five muscular layers from thoracic esophagi were tested independently. This work on esophageal tissues is consistent with reported uniaxial and biaxial mechanical testing and reported results using strain energy theory and also provides high resolution displacements, preserves native architectural structure and allows assessment of biomechanical properties in fluid media. This method may be of use to characterize mechanical properties of tissue engineered esophageal constructs.

Tissue-engineered artificial oesophagus patch using three-dimensionally printed polycaprolactone with mesenchymal stem cells: a preliminary report

OBJECTIVES

There has been a recent focus on 3D printing with regard to tissue engineering. We evaluated the efficacy of a 3D-printed (3DP) scaffold coated with mesenchymal stem cells (MSCs) seeded in fibrin for the repair of partial oesophageal defects.

METHODS

MSCs from rabbit bone marrow were cultured, and a 3DP polycaprolactone (PCL) scaffold was coated with the MSCs seeded in fibrin. The fibrin/MSC-coated 3DP PCL scaffold was implanted on a 5 × 10 mm artificial oesophageal defect in three rabbits (3DP/MSC group) and 3DP PCL-only scaffolds were implanted in three rabbits (3DP-only group). Three weeks post-procedure, the implanted sites were evaluated radiologically and histologically.

RESULTS

None of the rabbits showed any infection, stenosis or granulation on computed tomography. In the 3DP/MSC group, the replaced scaffolds were completely covered with regenerating mucosal epithelium and smooth muscle cells as determined by haematoxylin and eosin and Desmin staining. However, mucosal epithelium and smooth muscle cell regeneration was not evident in the 3DP-only group.

CONCLUSIONS

Use of the 3DP scaffold coated with MSCs seeded in fibrin resulted in successful restoration of the shape and histology of the cervical oesophagus without any graft rejection; thus, this is a promising material for use as an artificial oesophagus.

Surface modification of a POSS-nanocomposite material to enhance cellular integration of a synthetic bioscaffold

Polyhedral oligomeric silsesquioxane poly(carbonate-urea) urethane (POSS-PCU) is a versatile nanocomposite biomaterial with growing applications as a bioscaffold for tissue engineering. Integration of synthetic implants with host tissue can be problematic but could be improved by topographical modifications. We describe optimization of POSS-PCU by dispersion of porogens (sodium bicarbonate (NaHCO₃), sodium chloride (NaCl) and sucrose) onto the material surface, with the principle aim of increasing surface porosity, thus providing additional opportunities for improved cellular and vascular ingrowth. We assess the effect of the porogens on the material's mechanical strength, surface chemistry, wettability and cytocompatibilty. Surface porosity was characterized by scanning electron microscopy (SEM). There was no alteration in surface chemistry and wettability and only modest changes in mechanical properties were detected. The size of porogens correlated well with the porosity of the construct produced and larger porogens improved interconnectivity of spaces within constructs. Using primary human bronchial epithelial cells (HBECs) we demonstrate moderate in vitro cytocompatibility for all surface modifications; however, larger pores resulted in cellular aggregation. These cells were able to differentiate on POSS-PCU scaffolds. Implantation of the scaffold in vivo demonstrated that larger pore sizes favor cellular integration and vascular ingrowth. These experiments demonstrate that surface modification with large porogens can improve POSS-PCU nanocomposite scaffold integration and suggest the need to strike a balance between the non-porous surfaces required for epithelial coverage and the porous structure required for integration and vascularization of synthetic scaffolds in future construct design.

Regenerative medicine in otorhinolaryngology

BACKGROUND

Tissue engineering using biocompatible scaffolds, with or without cells, can permit surgeons to restore structure and function following tissue resection or in cases of congenital abnormality. Tracheal regeneration has emerged as a spearhead application of these technologies, whilst regenerative therapies are now being developed to treat most other diseases within otolaryngology.

METHODS AND RESULTS

A systematic review of the literature was performed using Ovid Medline and Ovid Embase, from database inception to 15 November 2014. A total of 561 papers matched the search criteria, with 76 fulfilling inclusion criteria. Articles were predominantly pre-clinical animal studies, reflecting the current status of research in this field. Several key human research articles were identified and discussed.

CONCLUSION

The main issues facing research in regenerative surgery are translation of animal model work into human models, increasing stem cell availability so it can be used to further research, and development of better facilities to enable implementation of these advances.

Acellular bi-layer silk fibroin scaffolds support functional tissue regeneration in a rat model of onlay esophagoplasty

Surgical management of long-gap esophageal defects with autologous gastrointestinal tissues is frequently associated with adverse complications including organ dysmotility, dysphagia, and donor site morbidity. In order to develop alternative graft options, bi-layer silk fibroin (SF) scaffolds were investigated for their potential to support functional tissue regeneration in a rodent model of esophageal repair. Onlay esophagoplasty was performed with SF matrices (N = 40) in adult rats for up to 2 m of implantation. Parallel groups consisted of animals implanted with small intestinal submucosa (SIS) scaffolds (N = 22) or sham controls receiving esophagotomy alone (N = 20). Sham controls exhibited a 100% survival rate while rats implanted with SF and SIS scaffolds displayed respective survival rates of 93% and 91% prior to scheduled euthanasia. Animals in each experimental group were capable of solid food consumption following a 3 d post-op liquid diet and demonstrated similar degrees of weight gain throughout the study period. End-point μ-computed tomography at 2 m post-op revealed no evidence of contrast extravasation, fistulas, strictures, or diverticula in any of the implant groups. Ex vivo tissue bath studies demonstrated that reconstructed esophageal conduits supported by both SF and SIS scaffolds displayed contractile responses to carbachol, KCl and electrical field stimulation while isoproterenol produced tissue relaxation. Histological (Masson's trichrome and hematoxylin and eosin) and immunohistochemical (IHC) evaluations demonstrated both implant groups produced de novo formation of skeletal and smooth muscle bundles positive for contractile protein expression [fast myosin heavy chain (MY32) and α-smooth muscle actin (α-SMA)] within the graft site. However, SF matrices promoted a significant 4-fold increase in MY32+ skeletal muscle and a 2-fold gain in α-SMA+ smooth muscle in comparison to the SIS cohort as determined by histomorphometric analyses. A stratified squamous, keratinized epithelium expressing cytokeratin 5 and involucrin proteins was also present at 2 m post-op in all experimental groups. De novo innervation and vascularization were evident in all regenerated tissues indicated by the presence of synaptophysin (SYP38)+ boutons and vessels lined with CD31 expressing endothelial cells. In respect to SIS, the SF group supported a significant 4-fold increase in the density of SYP38+ boutons within the implant region. Evaluation of host tissue responses revealed that SIS matrices elicited chronic inflammatory reactions and severe fibrosis throughout the neotissues, in contrast to SF scaffolds. The results of this study demonstrate that bi-layer SF scaffolds represent promising biomaterials for onlay esophagoplasty, capable of producing superior regenerative outcomes in comparison to conventional SIS scaffolds.

Operating RegenMed: development of better in-theater strategies for handling tissue-engineered organs and tissues

Tissue engineering ex vivo and direct cellular application with bioscaffolds in vivo has allowed surgeons to restore and establish function throughout the human body. The evidence for regenerative surgery is growing, and consequently there is a need for the development of more advanced regenerative surgery facilities. Regenerative medicine in the surgical field is changing rapidly and this must be reflected in the design of any future operating suite. The theater environment needs to be highly adaptable to account for future significant advances within the field. Development of purpose built, combined operating suites and tissue-engineering laboratories will provide the facility for modern surgeons to treat patients with organ deficits, using bespoke, regenerated constructs without the need for immunosuppression.

Bone marrow stromal cell-derived extracellular matrix promotes osteogenesis of adipose-derived stem cells

Adipose-derived stem cells (ASCs) can differentiate into multiple cell lineages and favor adipogenesis rather than osteogenesis. Because the extracellular matrix (ECM) component of the stem cell niche is important in stem cell differentiation, we hypothesized that ECM produced by human bone marrow stromal cells (BM-ECM) could enhance the osteogenic potential of ASCs during in vitro expansion. We have compared the replication and osteogenic differentiation of ASCs expanded on BM-ECM versus tissue culture plastic (TCP) in vitro and in vivo. During the first two passages, ASC proliferation on BM-ECM was 3.27-fold greater than that on TCP. ASCs expanded on BM-ECM formed more osteogenic colonies and higher expression of osteogenic markers than ASCs expanded on TCP. In nude mice, ASCs that had been expanded on BM-ECM formed more new bone tissue than those expanded on TCP. The data indicate that BM-ECM can be used to promote the osteogenic fate of ASCs.

Organ bioengineering for the newborn

Regenerative medicine has recently been established as an emerging interdisciplinary field focused on the repair; replacement or regeneration of cells, tissues and organs. It involves various disciplines, which are focused on different aspects of the regeneration process such as cell biology, gene therapy, bioengineering, material science and pharmacology. In this article, we will outline progress on tissue engineering of specific tissues and organs relevant to paediatric surgery.

Difficult esophageal atresia: trick and treat

Although most patients with esophageal atresia (EA) and tracheo-esophageal fistula (TEF) may benefit from "standard" management, which is deferred emergency surgery, some may present unexpected elements that change this paradigm. Birth weight, associated anomalies, and long gap can influence the therapeutic schedule of the patients with EA/TEF and can make their treatment tricky. As a consequence, detailed information on these aspects gives the power to develop a decision-making process as correct as possible. In this article, we will review the most important factors influencing the treatment of patients with EA/TEF and will share our experience on the diagnostic and therapeutic tips that may provide pivotal help in the management of such patients.

Airway tissue engineering: an update

INTRODUCTION

Prosthetic materials, autologous tissues, cryopreserved homografts and allogeneic tissues have thus far proven unsuccessful in providing long-term functional solutions to extensive upper airway disease and damage. Research is therefore focusing on the rapidly expanding fields of regenerative medicine and tissue engineering in order to provide stem cell-based constructs for airway reconstruction, substitution and/or regeneration.

AREAS COVERED

Advances in stem cell technology, biomaterials and growth factor interactions have been instrumental in guiding optimization of tissue-engineered airways, leading to several first-in-man studies investigating stem cell-based tissue-engineered tracheal transplants in patients. Here, we summarize current progress, outstanding research questions, as well as future directions within the field.

EXPERT OPINION

The complex immune interaction between the transplant and host in vivo is only beginning to be untangled. Recent progress in our understanding of stem cell biology, decellularization techniques, biomaterials and transplantation immunobiology offers the prospect of transplanting airways without the need for lifelong immunosuppression. In addition, progress in airway revascularization, reinnervation and ever-increasingly sophisticated bioreactor design is opening up new avenues for the construction of a tissue-engineered larynx. Finally, 3D printing is a novel technique with the potential to render microscopic control over how cells are incorporated and grown onto the tissue-engineered airway.

Tissue engineering of the esophagus

Esophageal atresia occurs in 1 out of 3000 births. Current treatments involve esophageal replacement by using more distal parts of the gastrointestinal tract, such as the stomach, jejunum, and colon. Significant complications are associated with each treatment option. Tissue engineering may provide a therapeutic alternative for esophageal replacement. This article addresses the progress in esophageal tissue engineering using acellular and cell-seeded approaches. In addition, we discuss the potential direction of future approaches by critically appraising the results in the recent literature.

Stem cell-based organ replacements-airway and lung tissue engineering

Tissue engineering requires the use of cells seeded onto scaffolds, often in conjunction with bioactive molecules, to regenerate or replace tissues. Significant advances have been made in recent years within the fields of stem cell biology and biomaterials, leading to some exciting developments in airway tissue engineering, including the first use of stem cell-based tissue-engineered tracheal replacements in humans. In addition, recent advances within the fields of scaffold biology and decellularization offer the potential to transplant patients without the use of immunosuppression.

Esophageal replacement: overcoming the need

Three developments which have contributed to the declining necessity for esophageal replacement are improvement in the management of esophageal atresia, prevention of caustic injuries to the esophagus, and early antireflux surgery for intractable gastro-esophageal reflux. Despite these advances, replacement of the esophagus may still be necessary. The two most commonly used procedures for replacing the esophagus are colonic interposition and gastric transposition. Experience with 236 gastric transposition operations reveals a mortality of 2.5%, leak rate of 12%, and stricture of 20%. The follow-up shows a satisfaction of over 90%. New methods of overcoming the need for esophageal replacement are in progress with tissue engineering with a scaffold to produce a tubular graft to bridge the gap in the continuity of the esophagus.

Decellularized scaffolds as a platform for bioengineered organs

PURPOSE OF REVIEW

Patients suffering from end-stage organ failure requiring organ transplantation face donor organ shortage and adverse effect of chronic immunosuppression. Recent progress in the field of organ bioengineering based on decellularized organ scaffolds and patient-derived cells holds great promise to address these issues.

RECENT FINDINGS

Perfusion-decellularization is the most consistent method to obtain decellularized whole-organ scaffolds to serve as a platform for organ bioengineering. Important advances have occurred in organ bioengineering using decellularized scaffolds in small animal models. However, the function exhibited by bioengineered organs has been rudimentary. Pluripotent stem cells seem to hold promise as the ideal regenerative cells to be used with this approach but the techniques to effectively and reliably manipulate their fate are still to be discovered. Finally, this technology needs to be scaled up to human size to be of clinical relevance.

SUMMARY

The search for alternatives to allogeneic organ transplantation continues. Important milestones have been achieved in organ bioengineering with the use of decellularized scaffolds. However, many challenges remain on the way to producing an autologous, fully functional organ that can be transplanted similar to a donor organ.

Seamless vascularized large-diameter tubular collagen scaffolds reinforced with polymer knittings for esophageal regenerative medicine

A clinical demand exists for alternatives to repair the esophagus in case of congenital defects, cancer, or trauma. A seamless biocompatible off-the-shelf large-diameter tubular scaffold, which is accessible for vascularization, could set the stage for regenerative medicine of the esophagus. The use of seamless scaffolds eliminates the error-prone tubularization step, which is necessary when emanating from flat scaffolds. In this study, we developed and characterized three different types of seamless tubular scaffolds, and evaluated in vivo tissue compatibility, including vascularization by omental wrapping. Scaffolds (luminal Ø ∼ 1.5 cm) were constructed using freezing, lyophilizing, and cross-linking techniques and included (1) single-layered porous collagen scaffold, (2) dual-layered (porous+dense) collagen scaffold, and (3) hybrid scaffold (collagen+incorporated polycaprolacton knitting). The latter had an ultimate tensile strength comparable to a porcine esophagus. To induce rapid vascularization, scaffolds were implanted in the omentum of sheep using a wrapping technique. After 6 weeks of biocompatibility, vascularization, calcification, and hypoxia were evaluated using immunohistochemistry. Scaffolds were biocompatible, and cellular influx and ingrowth of blood vessels were observed throughout the whole scaffold. No calcification was observed, and slight hypoxic conditions were detected only in the direct vicinity of the polymer knitting. It is concluded that seamless large-diameter tubular collagen-based scaffolds can be constructed and vascularized in vivo. Such scaffolds provide novel tools for esophageal reconstruction.

Immunomodulatory effect of a decellularized skeletal muscle scaffold in a discordant xenotransplantation model

Decellularized (acellular) scaffolds, composed of natural extracellular matrix, form the basis of an emerging generation of tissue-engineered organ and tissue replacements capable of transforming healthcare. Prime requirements for allogeneic, or xenogeneic, decellularized scaffolds are biocompatibility and absence of rejection. The humoral immune response to decellularized scaffolds has been well documented, but there is a lack of data on the cell-mediated immune response toward them in vitro and in vivo. Skeletal muscle scaffolds were decellularized, characterized in vitro, and xenotransplanted. The cellular immune response toward scaffolds was evaluated by immunohistochemistry and quantified stereologically. T-cell proliferation and cytokines, as assessed by flow cytometry using carboxy-fluorescein diacetate succinimidyl ester dye and cytometric bead array, formed an in vitro surrogate marker and correlate of the in vivo host immune response toward the scaffold. Decellularized scaffolds were free of major histocompatibility complex class I and II antigens and were found to exert anti-inflammatory and immunosuppressive effects, as evidenced by delayed biodegradation time in vivo; reduced sensitized T-cell proliferative activity in vitro; reduced IL-2, IFN-γ, and raised IL-10 levels in cell-culture supernatants; polarization of the macrophage response in vivo toward an M2 phenotype; and improved survival of donor-derived xenogeneic cells at 2 and 4 wk in vivo. Decellularized scaffolds polarize host responses away from a classical TH1-proinflammatory profile and appear to down-regulate T-cell xeno responses and TH1 effector function by inducing a state of peripheral T-cell hyporesponsiveness. These results have substantial implications for the future clinical application of tissue-engineered therapies.

Preparation and characterization of a biologic scaffold from esophageal mucosa

Biologic scaffolds composed of extracellular matrix (ECM) are commonly used to facilitate a constructive remodeling response in several types of tissue, including the esophagus. Surgical manipulation of the esophagus is often complicated by stricture, but preclinical and clinical studies have shown that the use of an ECM scaffold can mitigate stricture and promote a constructive outcome after resection of full circumference esophageal mucosa. Recognizing the potential benefits of ECM derived from homologous tissue (i.e., site-specific ECM), the objective of the present study was to prepare, characterize, and assess the in-vivo remodeling properties of ECM from porcine esophageal mucosa. The developed protocol for esophageal ECM preparation is compliant with previously established criteria of decellularization and results in a scaffold that maintains important biologic components and an ultrastructure consistent with a basement membrane complex. Perivascular stem cells remained viable when seeded upon the esophageal ECM scaffold in-vitro, and the in-vivo host response showed a pattern of constructive remodeling when implanted in soft tissue.

Cationic antimicrobial polymers and their assemblies

Cationic compounds are promising candidates for development of antimicrobial agents. Positive charges attached to surfaces, particles, polymers, peptides or bilayers have been used as antimicrobial agents by themselves or in sophisticated formulations. The main positively charged moieties in these natural or synthetic structures are quaternary ammonium groups, resulting in quaternary ammonium compounds (QACs). The advantage of amphiphilic cationic polymers when compared to small amphiphilic molecules is their enhanced microbicidal activity. Besides, many of these polymeric structures also show low toxicity to human cells; a major requirement for biomedical applications. Determination of the specific elements in polymers, which affect their antimicrobial activity, has been previously difficult due to broad molecular weight distributions and random sequences characteristic of radical polymerization. With the advances in polymerization control, selection of well defined polymers and structures are allowing greater insight into their structure-antimicrobial activity relationship. On the other hand, antimicrobial polymers grafted or self-assembled to inert or non inert vehicles can yield hybrid antimicrobial nanostructures or films, which can act as antimicrobials by themselves or deliver bioactive molecules for a variety of applications, such as wound dressing, photodynamic antimicrobial therapy, food packing and preservation and antifouling applications.