Regenerative signals for intestinal epithelial organoid units transplanted on biodegradable polymer scaffolds for tissue engineering of small intestine

Composite Scaffolds Based on Intestinal Extracellular Matrices and Oxidized Polyvinyl Alcohol: A Preliminary Study for a New Regenerative Approach in Short Bowel Syndrome

Pediatric Short Bowel Syndrome is a rare malabsorption disease occurring because of massive surgical resections of the small intestine. To date, the issues related to current strategies including intestinal transplantation prompted the attention towards tissue engineering (TE). This work aimed to develop and compare two composite scaffolds for intestinal TE consisting of a novel hydrogel, that is, oxidized polyvinyl alcohol (OxPVA), cross-linked with decellularized intestinal wall as a whole (wW/OxPVA) or homogenized (hW/OxPVA). A characterization of the supports was performed by histology and Scanning Electron Microscopy and their interaction with adipose mesenchymal stem cells occurred by MTT assay. Finally, the scaffolds were implanted in the omentum of Sprague Dawley rats for 4 weeks prior to being processed by histology and immunohistochemistry (CD3; F4/80; Ki-67; desmin; α-SMA; MNF116). In vitro studies proved the effectiveness of the decellularization, highlighting the features of the matrices; moreover, both supports promoted cell adhesion/proliferation even if the wW/OxPVA ones were more effective (p < 0.01). Analysis of explants showed a continuous and relatively organized tissue wall around the supports with a connective appearance, such as myofibroblastic features, smooth muscle, and epithelial cells. Both scaffolds, albeit with some difference, were promising; nevertheless, further analysis will be necessary.

Novel Electrohydrodynamic Printing of Nanocomposite Biopolymer Scaffolds

In this paper, we uncover a new method for the preparation of biopolymer scaffolds and demonstrate its potential for the development of organs with the aid of tissue engineering. Two novel nanocomposite polymers, a nonbiodegradable polyhedral oligomeric silsesquioxane-poly (carbonate-urea)urethane and a biodegradable polyhedral oligomeric silsesquioxane-polycaprolactone-poly(carbonate-urea)urethane, have been subjected to flow in an electric field. Electrically forced microthreading of the polymers occurs and a three-dimensional print-patterning device was used to deposit fine (<50 µm) threads of polymer according to a predesigned architecture to prepare scaffolds. The technique can offer tremendous potential in the development of organs.

Gastrointestinal tissue engineering

Tissue engineering is an emerging discipline that combines engineering principles and the biological sciences toward the development of functional replacement tissue. Virtually every tissue in the body has been investigated and tremendous advances have been made in many areas. This article focuses on the gastrointestinal tract and reviews the current status of bioengineering gastrointestinal tissues, including the esophagus, stomach, small intestine and colon. Although progress has been achieved, there continues to be significant challenges that need to be addressed.

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.

Whole-organ re-engineering: a regenerative medicine approach to digestive organ replacement

Recovery from end-stage organ failure presents a challenge for the medical community, considering the limitations of extracorporeal assist devices and the shortage of donors when organ replacement is needed. There is a need for new methods to promote recovery from organ failure and regenerative medicine is an option that should be considered. Recent progress in the field of tissue engineering has opened avenues for potential clinical applications, including the use of microfluidic devices for diagnostic purposes, and bioreactors or cell/tissue-based therapies for transplantation. Early attempts to engineer tissues produced thin, planar constructs; however, recent approaches using synthetic scaffolds and decellularized tissue have achieved a more complex level of tissue organization in organs such as the urinary bladder and trachea, with some success in clinical trials. In this context, the concept of decellularization technology has been applied to produce whole organ-derived scaffolds by removing cellular content while retaining all the necessary vascular and structural cues of the native organ. In this review, we focus on organ decellularization as a new regenerative medicine approach for whole organs, which may be applied in the field of digestive surgery.

Tissue engineering for neuromuscular disorders of the gastrointestinal tract

The digestive tract is designed for the optimal processing of food that nourishes all organ systems. The esophagus, stomach, small bowel, and colon are sophisticated neuromuscular tubes with specialized sphincters that transport ingested food-stuffs from one region to another. Peristaltic contractions move ingested solids and liquids from the esophagus into the stomach; the stomach mixes the ingested nutrients into chyme and empties chyme from the stomach into the duodenum. The to-and-fro movement of the small bowel maximizes absorption of fat, protein, and carbohydrates. Peristaltic contractions are necessary for colon function and defecation.

Generating intestinal tissue from stem cells: potential for research and therapy

Intestinal resection and malformations in adult and pediatric patients result in devastating consequences. Unfortunately, allogeneic transplantation of intestinal tissue into patients has not been met with the same measure of success as the transplantation of other organs. Attempts to engineer intestinal tissue in vitro include disaggregation of adult rat intestine into subunits called organoids, harvesting native adult stem cells from mouse intestine and spontaneous generation of intestinal tissue from embryoid bodies. Recently, by utilizing principles gained from the study of developmental biology, human pluripotent stem cells have been demonstrated to be capable of directed differentiation into intestinal tissue in vitro. Pluripotent stem cells offer a unique and promising means to generate intestinal tissue for the purposes of modeling intestinal disease, understanding embryonic development and providing a source of material for therapeutic transplantation.

Intestinal tissue engineering: current concepts and future vision of regenerative medicine in the gut

Functional tissue engineering of the gastrointestinal (GI) tract is a complex process aiming to aid the regeneration of structural layers of smooth muscle, intrinsic enteric neuronal plexuses, specialized mucosa, and epithelial cells as well as interstitial cells. The final tissue-engineered construct is intended to mimic the native GI tract anatomically and physiologically. Physiological functionality of tissue-engineered constructs is of utmost importance while considering clinical translation. The construct comprises of cellular components as well as biomaterial scaffolding components. Together, these determine the immune response a tissue-engineered construct would elicit from a host upon implantation. Over the last decade, significant advances have been made to mitigate adverse host reactions. These include a quest for identifying autologous cell sources like embryonic and adult stem cells, bone marrow-derived cells, neural crest-derived cells, and muscle derived-stem cells. Scaffolding biomaterials have been fabricated with increasing biocompatibility and biodegradability. Manufacturing processes have advanced to allow for precise spatial architecture of scaffolds to mimic in vivo milieu closely and achieve neovascularization. This review will focus on the current concepts and the future vision of functional tissue engineering of the diverse neuromuscular structures of the GI tract from the esophagus to the internal anal sphincter.

Regenerative medicine as applied to solid organ transplantation: current status and future challenges

In the last two decades, regenerative medicine has shown the potential for "bench-to-bedside" translational research in specific clinical settings. Progress made in cell and stem cell biology, material sciences and tissue engineering enabled researchers to develop cutting-edge technology which has lead to the creation of nonmodular tissue constructs such as skin, bladders, vessels and upper airways. In all cases, autologous cells were seeded on either artificial or natural supporting scaffolds. However, such constructs were implanted without the reconstruction of the vascular supply, and the nutrients and oxygen were supplied by diffusion from adjacent tissues. Engineering of modular organs (namely, organs organized in functioning units referred to as modules and requiring the reconstruction of the vascular supply) is more complex and challenging. Models of functioning hearts and livers have been engineered using "natural tissue" scaffolds and efforts are underway to produce kidneys, pancreata and small intestine. Creation of custom-made bioengineered organs, where the cellular component is exquisitely autologous and have an internal vascular network, will theoretically overcome the two major hurdles in transplantation, namely the shortage of organs and the toxicity deriving from lifelong immunosuppression. This review describes recent advances in the engineering of several key tissues and organs.

Intestinal stem cell organoid transplantation generates neomucosa in dogs

BACKGROUND AND AIMS

Intestinal stem cell organoid transplantation generates functional intestinal neomucosa and has been used therapeutically to improve nutrient absorption and cure bile acid malabsorption in rats. We hypothesized that intestinal organoids can be harvested and transplanted to generate intestinal neomucosa in a large animal model.

MATERIALS AND METHODS

In group 1, 2-month old beagles (n = 6) underwent autotransplantation of intestinal organoids prepared from a segment of their own ileum. In group 2, intestinal organoids were harvested from fetuses and allotransplanted into 10-month old mother animals (n = 4). Tissues were harvested after 4 weeks and analyzed by hematoxylin and eosin histology and fluorescent microscopy.

RESULTS

Large numbers of viable organoids were harvested in both groups. In group 1, no neomucosal growth was identified in any of the engraftment sites after autotransplantation of juvenile organoids. In group 2, neomucosal growth with large areas of crypts and villi was identified in 11 of 12 polyglycolic acid scaffolds after allotransplantation of fetal organoids. The neomucosa resembled normal canine mucosa in structure and composition.

CONCLUSIONS

Intestinal stem cell organoid transplantation can be used to generate neomucosa in dogs. This is the first report of successful generation of intestinal neomucosa using intestinal stem cell organoid transplantation in a large animal model.

Stem cells as a potential future treatment of pediatric intestinal disorders

All surgical disciplines encounter planned and unplanned ischemic events that may ultimately lead to cellular dysfunction and death. Stem cell therapy has shown promise for the treatment of a variety of ischemic and inflammatory disorders where tissue damage has occurred. As stem cells have proven beneficial in many disease processes, important opportunities in the future treatment of gastrointestinal disorders may exist. Therefore, this article will serve to review the different types of stem cells that may be applicable to the treatment of gastrointestinal disorders, review the mechanisms suggesting that stem cells may work for these conditions, discuss current practices for harvesting and purifying stem cells, and provide a concise summary of a few of the pediatric intestinal disorders that could be treated with cellular therapy.

A perfusion bioreactor for intestinal tissue engineering

BACKGROUND

Short gut syndrome is a devastating clinical problem with limited long-term treatment options. A unique characteristic of the normal intestinal epithelium is its capacity for regeneration and adaptation. Despite this tremendous capacity in vivo, one of the major limitations in advancing the understanding of intestinal epithelial differentiation and proliferation has been the difficulty in maintaining primary cultures of normal gut epithelium in vitro. A perfusion bioreactor system has been shown to be beneficial in long-term culture and bioengineering of a variety of tissues. The purpose of this study is to design and fabricate a perfusion bioreactor for intestinal tissue engineering.

MATERIALS AND METHODS

A perfusion bioreactor is fabricated using specific parameters. Intestinal epithelial organoid units harvested from neonatal rats are seeded onto biodegradable polymer scaffolds and cultured for 2 d in the bioreactor. Cell attachment, viability, and survival are assessed using MTT assay, scanning electron micrograph, and histology.

RESULTS

A functional perfusion bioreactor was successfully designed and manufactured. MTT assay and scanning electron micrograph demonstrated successful attachment of viable cells onto the polymer scaffolds. Histology confirmed the survival of intestinal epithelial cells seeded on the scaffolds and cultured in the perfusion bioreactor for 2 days.

CONCLUSIONS

A functional perfusion bioreactor can be successfully fabricated for the in-vitro cultivation of intestinal epithelial cells. With further optimization, the perfusion bioreactor may be a useful in in-vitro system for engineering new intestinal tissue.

Comparison of polyester scaffolds for bioengineered intestinal mucosa

INTRODUCTION

Biodegradable polyester scaffolds have proven useful for growing neointestinal tissue equivalents both in vitro and in vivo. These scaffolds allow cells to attach and grow in a 3-dimensional space while nutrient flow is maintained throughout the matrix. The purpose of this study was to evaluate different biopolymer constructs and to determine mucosal engraftment rates and mucosal morphology.

HYPOTHESIS

We hypothesized that different biopolymer constructs may vary in their ability to provide a good scaffolding onto which intestinal stem cell organoids may be engrafted.

STUDY DESIGN

Eight different microporous biodegradable polymer tubes composed of polyglycolic acid (PGA), polylactic acid, or a combination of both, using different fabrication techniques were seeded with intestinal stem cell clusters obtained from neonatal rats. Three different seeded polymer constructs were subsequently placed into the omentum of syngeneic adult recipient rats (n = 8). Neointestinal grafts were harvested 4 weeks after implantation. Polymers were microscopically evaluated for the presence of mucosal growth, morphology, scar formation and residual polymer.

RESULTS

Mucosal engraftment was observed in 7 out of 8 of the polymer constructs. A maximal surface area engraftment of 36% (range 5-36%) was seen on nonwoven, randomly entangled, small fiber PGA mesh coated with aerosolized 5% poly-L-lactic acid. Villous and crypt development, morphology and created surface area were best on PGA nonwoven mesh constructs treated with poly-L-lactic acid. Electrospun microfiber PGA had poor overall engraftment with little or no crypt or villous formation.

CONCLUSION

Intestinal organoids can be engrafted onto biodegradable polyester scaffoldings with restitution of an intestinal mucosal layer. Variability in polymer composition, processing techniques and material properties (fiber size, luminal dimensions and pore size) affect engraftment success. Future material refinements should lead to improvements in the development of a tissue-engineered intestine.

Hyaluronic acid based materials for intestine tissue engineering: a morphological and biochemical study of cell-material interaction

A wide number of gastro-intestinal disorders are associated with structural alterations of this district leading to an impaired gastrointestinal function. The study of cell material interactions represents one of the major issues for the development of tissue engineering purposes. Benzyl esters of hyaluronic acid are promising materials because they exhibit good tissue compatibility and are available in various configurations. In this work they have been studied for the possible application of intestinal cell growth and functioning. The preliminary investigation on the morphologic and biochemistry data obtained by monitoring the growth and differentiation of intestinal epithelial cells on two hyaluronic acid benzyl esters is reported. Two types of materials structures were studied: a three dimensional matrix and a macroporous flat sheet membrane. Caco-2 cell line was used: these cells undergo spontaneous enterocytic differentiation after several days in culture. The differentiation status of these cells grown on different materials was used as a parameter of biocompatibility and cell functioning. The status of cell growth and differentiation was monitored by studying cell morphology using scanning electron microscopy. The results obtained were confirmed by biochemical determinations. Although both the configurations of the two polymers exhibited good compatibility with respect to intestinal cells, only the flat sheet membrane proved to induce cell differentiation, leading us to the conclusion that it is a promising substrate for the proposed application.

Optical tissue window: a novel model for optimizing engraftment of intestinal stem cell organoids

BACKGROUND

Intestinal malabsorption disorders and short bowel syndrome lead to significant morbidity. We recently demonstrated that grafting of intestinal organoids can grow a bioengineered intestinal neomucosa and cure bile acid malabsorption in rats. Now we have developed a novel system that permits direct observation of intestinal organoids in vivo to optimize conditions for engraftment.

METHODS

Optical Windows were created in C57BL/6J mice by externalizing an omental pedicle into a dorsal skin flap chamber. Following creation of windows, 5000 intestinal organoids from green-fluorescent protein transgene (GFP)+ donor mice were seeded directly either on omentum or on polyglycolic acid (PGA) disks that had been placed on omentum at 1 or 5 days. Engraftment of green fluorescent cells was evaluated on postseeding days 1, 3, 5, 7, 10, 12, and 21 using fluorescence microscopy.

RESULTS

An initial group had seeding onto omentum (n = 5) or biopolymer disks (n = 5) on postoperative day 1. After 7 days, there was mucosal cell engraftment onto omental tissue and biopolymers. GFP+ organoids engrafted significantly better when seeded onto biopolymers compared to omentum (P < 0.05). In a second study with increased sample size (n = 24) up to day 12, all four groups demonstrated adherence and growth. However, GFP+ organoids seeded onto delayed PGA biopolymer demonstrated significantly better engraftment (P < 0.05).

CONCLUSIONS

This novel system allows continuous in vivo observation of engrafted cells that are seeded on externalized omentum. The use of PGA mesh biopolymer may improve engraftment of intestinal organoids.

To Make a New Intestinal Mucosa

A number of clinical conditions are caused by disorders affecting the mucosal lining of the gastrointestinal tract. Some patients suffer from a loss of mucosal surface area due to congenital defects or due to surgical resections ("short bowel syndrome"). Other patients have inborn or acquired defects of certain mucosal functions (e.g., glucose-galactose malabsorption, bile acid malabsorption). Many patients with these mucosal disorders could be more effectively treated if healthy mucosa were available in larger quantities as a replacement or functional supplement. We therefore developed methods to transplant mucosal stem cells from one part of the intestine to another and to make bioengineered intestinal mucosa. We generated an animal model of bile acid malabsorption using rats that underwent resection of the distal 25% of their small intestine (ileum). This resulted in significant losses of bile acids with the fecal excretions in these animals. We subsequently harvested ileal stem cell clusters from neonatal donors, removed the mucosa from a segment of proximal intestine (jejunum), and implanted the stem cell clusters into the debrided segment of jejunum. After four weeks, the animals had developed a functional "neomucosa." We inserted the "neo-ileal" segment into continuity as a substitute ileum. Postoperative measurements of fecal bile acid excretion showed that we were able to reverse the malabsorption syndrome in this model. This was the first reported neo-mucosa-based treatment of a malabsorption syndrome in vivo. We subsequently studied different biodegradable PGA and PLLA scaffoldings to generate bioengineered intestinal mucosa. We implanted these materials into omentum of rats and were able to identify a PGA/PLLA hybrid material on which engraftment rates of 36% of the available surface area could be achieved. Most recently, we developed a novel technique that permits direct observation of cell-biomaterial interactions after implantation into omentum or intestine in vivo. This method will help to optimize engraftment conditions for stem cell clusters on biomaterials.

Stem cells, tissue engineering and organogenesis in transplantation

Tissue engineering is an attempt to generate living tissues for surgical transplantation. In vitro and in vivo approaches have led to the production of vascular and cardiovascular components, bones, cartilages and gastrointestinal tissues. Organogenesis has a different aim, which is to create transplantable organs from embryonic tissue implanted into the recipient's omentum. This approach has been successful in creating kidneys and pancreases in animals. The use of stem cells in organogenesis and in tissue engineering has vastly enlarged the potential for clinical applications. The technique of nuclear transfer offers the possibility of creating cells, which are genetically identical to the host. Tissue engineering and organogenesis represent the future of transplantation in medicine. The progress in this field is of tremendous importance because it can produce a new generation of morphologically complex tissues and organs. In this review, the most relevant experiences in this area are summarized, including its perspectives for therapeutical applications.

Morphologic evaluation of regenerated small bowel by small intestinal submucosa

BACKGROUND/PURPOSE

Previous studies have shown small intestinal submucosa (SIS) can be used as biodegradable scaffolds in tissue engineering small intestine. The purpose of this study is to evaluate the regeneration of neointestine and its morphology using SIS.

METHODS

A 2-cm tubular SIS graft from Sprague Dawley rat donors was interposed in the middle of a 6-cm ileal Thiry-Vella loop of Lewis rats, which was used to construct an ileostomy. The grafts were harvested at each of the time points ranging from 2 weeks to half a year after implantation, and native small intestine and grafts were investigated for morphology using histology and immunohistochemistry.

RESULTS

At the early postoperative period, SIS grafts were colonized by numerous inflammatory cells. A mucosal epithelial layer began to line the luminal surface of the graft by 4 weeks, and by 12 weeks, the luminal surface was covered completely by a layer of neomucosa. Neomucosa with typical small bowel morphology was characterized by a columnar epithelial cell layer with goblet cells, Paneth cells, absorptive enterocytes, and enteroendocrine cells. Significant differences between neomucosa by 12 weeks and 24 weeks in the measurements of mucosal thickness, villus height, and crypt depth were found. The outer walls of SIS grafts were composed of distinct bundles of well-formed smooth muscle-like cells with some fibrovascular tissue.

CONCLUSIONS

This initial study suggests that tissue engineering neointestine using SIS can develop structural features of the normal intestine. Small intestinal submucosa might be a viable material in the creation of neointestine for patients suffering short bowel syndrome.

Assessment of tissue-engineered stomach derived from isolated epithelium organoid units

OBJECTIVE

Isolated stomach epithelial organoid units developed on biodegradable polymers were transplanted to assess the feasibility of a tissue-engineered stomach.

BACKGROUND

Despite recent advances in reconstruction techniques, total gastrectomy is still accompanied by various complications. An alternative treatment would be a tissue-engineered stomach, which replaces the mechanical and metabolic functions of a normal stomach.

METHODS

Stomach epithelial organoid units isolated from neonatal rats were seeded onto biodegradable polymers. The constructs implanted into the omenta of adult rats were harvested for examination at designated times. Nine rats underwent a second operation for anastomosis.

RESULTS

The constructs resulted in cyst-like formations showing vascularized tissue with neomucosa lining the lumen. The surface morphology as assessed using scanning electron microscopy was similar to that of a native stomach. Immunohistochemical staining for alpha-actin smooth muscle and gastric mucin indicated the presence of a smooth muscle layer and a well-developed gastric epithelium, respectively. The luminal surface of the anastomosed tissue-engineered stomach was well-covered with epithelium.

CONCLUSIONS

Epithelium-derived stomach organoid units seeded on biodegradable polymers and transplanted into donor rats were shown to vascularize, survive, and regenerate into complex tissue resembling native stomach. Anastomosis between the units and native small intestine may have the potential to stimulate epithelial growth. This research may provide insight into new approaches to alleviate complications following total gastrectomy.

Use of omentum as an in vivo cell culture system in tissue engineering

Many modifications of in vitro culture techniques have been applied to promote tissue formation, resulting in limitations. Because the omentum is composed of lobes of adipose tissue with abundant blood vessels and has been used for organ reconstruction, we used the omentum as an in vivo culture system to promote cellular proliferation upon the scaffold. Two kinds of autogenous cells, oral epithelial cells and rib chondrocytes, obtained from canine were isolated and then seeded on porous poly-lactic-glycolic acid scaffolds of a pre-determined shape and size. Comparison was performed in two groups. In Group 1, cell-polymer constructs were cultured in vitro for 2 weeks, and in group 2, cell-polymer constructs were cultured in vitro for 1 week following the same protocol as group 1 but were then implanted into the omentum of same canines for the next week. We performed histologic analysis of tissue formation between the two groups. In group 1, seeded cells were presented spatially along the porous polymer surface only. However, in group 2, the cell-polymer constructs maintained their original dimensions and showed formation of a multicell layered structure with abundant blood vessels. We concluded that the use of the omentum as an in vivo culture medium offers possibilities as an efficient and effective method for tissue engineering with greater vascularization and more consistent cell spacing throughout the construct.

[Apoptosis participation in the acute rejection of intestinal transplantation in rats]

BACKGROUND

Intestinal transplantation is a possible treatment for patients with short bowel syndrome, aiming the reintroduction of oral diet. However, the major obstacle in this procedure is the strong rejection. Delay in rejection diagnosis may be irreversible and lethal.

AIM

To define method for early diagnosis of rejection based on the apoptosis from intestinal allograft.

MATERIAL AND METHODS

Isogenic rats Brown-Norway (BN) and Lewis (LEW) were submitted to intestinal heterotopic allotransplantation and divided in two groups: LEW donor to LEW recipient isograft group C and BN donor to LEW recipient allograft group (Tx). According to the day of sacrifice, Tx group were subdivided in three subgroups with eight animals each as follow: Tx3-- sacrificed at third postoperative day (POD), Tx5 -- sacrificed at fifth POD and Tx7 -- sacrificed at seventh POD. Eight animals from control group were subdivided in three moments according to the time of biopsy from the graft as follow: C3 -- biopsy at third POD; C5 -- biopsy at fifth POD and C7 -- biopsy at seventh POD. All animals from control group were sacrificed at seventh POD. Rejection parameters were compared between the control groups (C3 vs C5, C3 vs C7 and C5 vs C7, and allograft group (Tx3 vs Tx5, Tx3 vs Tx7 and Tx5 vs Tx7). The same parameters were analyzed between the control group and allograft groups ( C3 vs Tx3, C5 vs Tx5 and C7 vs Tx7). In C group no statistical significant difference regarding the expression of the apoptotic cells were detected, while in Tx group, the presence of apoptotic cells were remarkable since the third postoperative day.

Angiogenesis in tissue-engineered small intestine

Tissue-engineered intestine offers promise as a potential novel therapy for short bowel syndrome. In this study we characterized the microvasculature and angiogenic growth factor profile of the engineered intestine. Twenty-three tissue-engineered small intestinal grafts were harvested from Lewis rat recipients 1 to 8 weeks after implantation. Architectural similarity to native bowel obtained from juvenile rats was assessed with hematoxylin and eosin-stained sections. Capillary density, measured after immunohistochemical staining for CD34, was expressed as number of capillaries per 1000 nuclei. Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) tissue levels were measured by ELISA and normalized to total protein. Over the 8-week period cysts increased in volume (0.5 cm(3) at week 1 versus 12.6 cm(3) at week 8) and mass (1.30 +/- 0.29 versus 9.74 +/- 0.3 g; mean +/- SEM). Muscular and mucosal layers increased in thickness, but capillary density remained constant (82.95 +/- 4.81 capillaries per 1000 nuclei). The VEGF level was significantly higher in juvenile rat bowel than in engineered cyst (147.6 +/- 23.9 versus 42.3 +/- 3.4 pg/mg; p < 0.001). Tissue bFGF levels were also higher (315 +/- 65.48 versus 162.3 +/- 15.09 pg/mg; p < 0.05). The mechanism driving angiogenesis differs in engineered intestine and in normal bowel. VEGF and bFGF delivery may prove useful for bioengineering of intestine.

Transplantation of the urinary bladder and other organs in the subcutaneous tissue induces cyst formation and epithelialization: its potential usefulness in regenerative medicine

Certain hollow organs are known to form cysts when heterologously transplanted. In order to examine the usefulness of the phenomenon for regenerative medicine, rat urinary bladders and other organs were allo-transplanted under the subcutaneous tissue of the back. These transplanted tissues very often formed cysts covered with epithelia. The epithelia covered an area about twice the original size. In the case of the urinary bladder, the epithelium started moving from the edge of the transplants around day 3 after the operation, and as time proceeded, the tela submucosa and tunica muscularis also moved to encircle the epithelium, and formed the wall of the cyst. The basal laminae were formed under the newly expanded epithelium slightly behind the leading tip. All of the organs tested had the capability of cyst formation and epithelialization, although their rate differed between organs. The results are discussed with reference to the potential use of cyst formation for regenerating damaged organs.

SHAPE-DEFINING SCAFFOLDS FOR MINIMALLY INVASIVE TISSUE ENGINEERING

BACKGROUND

Minimally invasive surgical procedures are increasingly important in medicine, but biomaterials consistent with this delivery approach that allow one to control the structure of the material after implantation are lacking. Biomaterials with shape-memorizing properties could permit minimally invasive delivery of cell transplantation constructs and enable the formation of new tissues or structures in vivo in desired shapes and sizes.

METHODS

Macroporous alginate hydrogel scaffolds were prepared in a number of predefined geometries, compressed into significantly smaller, different "temporary" forms, and introduced into immunocompromised mice by means of minimally invasive surgical delivery through a small catheter. Scaffolds were rehydrated in situ with a suspension of cells (primary bovine articular chondrocytes) or cell-free medium and delivered through the same catheter. Specimens were harvested at 1 hr to evaluate the efficacy of cell delivery and the recovery of scaffold geometry, and at 8 and 24 weeks to evaluate neotissue formation.

RESULTS

A high percentage (88%) of scaffolds that were introduced with a catheter and rehydrated with cells had recovered their original shape and size within 1 hr. This delivery procedure resulted in cartilage structures with the geometry of the original scaffold by 2 months and histologically mature appearing tissue at 6 months.

CONCLUSIONS

Shaped hydrogels, formed by covalently cross-linking, can be structurally collapsed into smaller, temporary shapes that permit their minimally invasive delivery in vivo. The rapid recovery of scaffold properties facilitates efficient cell seeding in vivo and permits neotissue formation in desired geometries.

Effect of GLP-2 on mucosal morphology and SGLT1 expression in tissue-engineered neointestine

Using tissue-engineering techniques, we have developed a neointestine that regenerates the structural and dynamic features of native small intestine. In this study, we tested neointestinal responsiveness to glucagon-like peptide 2 (GLP-2). Neointestinal cysts were engineered by seeding biodegradable polymers with neonatal rat intestinal organoid units. The cysts were matured and anastomosed to the native jejunum of syngeneic adult recipients. Animals were treated with GLP-2 [Gly2] (twice daily, 1 microg/g body wt) or vehicle alone (control) for 10 days. Rats were then killed, and tissues were harvested for analysis. Na+-glucose cotransporter (SGLT1) mRNA expression was assessed with Northern blotting and in situ hybridization. SGLT1 protein was localized by using immunofluorescence. GLP-2 administration resulted in 1.8- and 1.7-fold increases (P < 0.05) in neointestinal villus height and crypt depth, respectively. GLP-2 administration also resulted in a 2.4-fold increase (P < 0.01) in neomucosal SGLT1 mRNA expression. SGLT1 mRNA expression was localized to enterocytes throughout the villi, and SGLT1 protein was localized to the brush border of enterocytes along the entire length of villi from the neointestine of GLP-2-treated animals. The response of tissue-engineered neointestine to exogenous GLP-2 includes mucosal growth and enhanced SGLT1 expression. Therefore, tissue-engineering principles may help in dissecting the regulatory mechanisms mediating complex processes in the intestinal epithelium.

A tissue-engineered stomach as a replacement of the native stomach

BACKGROUND

Despite recent advances in reconstruction techniques, total gastrectomy is still accompanied by various complications. As an alternative treatment, we propose a tissue-engineered stomach that replaces the mechanical and metabolic functions of a normal stomach. The objective of this study was to demonstrate the function of a tissue-engineered stomach as a replacement of the native stomach.

METHODS

Tissue-engineered stomachs were formed in recipient rats from stomach epithelium organoid units isolated from neonatal donor rats. After 12 weeks, the animals underwent a second operation for replacement of the native stomachs.

RESULTS

Tissue-engineered stomachs were successfully used as a substitute of the native stomach in a rat model. An upper gastrointestinal tract study revealed no evidence of bowel stenosis or obstruction at both anastomosis sites. Histologically, the tissue-engineered stomachs had well-developed vascularized tissue with a neomucosa continuously lining the lumen and stratified smooth muscle layers. Immunohistochemical staining for alpha-actin smooth muscle showed that the smooth muscle layers were arranged in a regular fashion. Scanning electron microscopy showed that the surface topography of the tissue-engineered stomachs resembled that of native stomachs.

CONCLUSIONS

It has been demonstrated that a tissue-engineered stomach can replace a native stomach in a rat model. Replacement of the native stomach by a tissue-engineered stomach had beneficial effects on the formation of neomucosa and smooth muscle layers in the tissue-engineered stomach.

Transplante de intestino delgado

RACIONAL: Avanços da biotecnologia e o desenvolvimento de novas drogas imunossupressoras melhoraram os resultados do transplante de intestino delgado. Esse transplante é atualmente indicado para casos especiais da falência intestinal. OBJETIVO: A presente revisão realça os recentes desenvolvimentos na área do transplante de intestino delgado. MATERIAL E MÉTODO: Mais de 600 publicações de transplante de intestino delgado foram revisadas. O desenvolvimento da pesquisa, novas estratégias de imunossupressão, monitorização do enxerto e do receptor, e avanços na técnica cirúrgica são discutidos. RESULTADOS: Realizaram-se cerca de 700 transplante de intestino delgado em 55 centros: 44% intestino-fígado, 41% enxerto intestinal isolado e 15% transplante multivisceral. Rejeição e infecção são as principais limitações desse transplante. Sobrevida de 5 anos na experiência internacional é de 46% para o transplante de intestino isolado, 43% para o intestino-fígado e de cerca de 30% para o transplante multivisceral. Sobrevidas prolongadas são mais freqüentes nos centros com maior experiência. Em série de 165 transplantes intestinais na Universidade de Pittsburgh, PA, EUA, foi relatada sobrevida do paciente maior do que 75% no primeiro ano, 54% em 5 anos e 42% em 10 anos. Mais de 90% desses pacientes assumem dieta oral irrestrita. CONCLUSÃO: O transplante de intestino delgado evoluiu de estratégia experimental para uma alternativa viável no tratamento da falência intestinal permanente. Promover o refinamento da terapia imunossupressora, do manejo e prevenção de infecções, da técnica cirúrgica e da indicação e seleção adequada dos pacientes é crucial para melhorar a sobrevida desse transplante.

Tissue engineering: current state and prospects

Organ shortage and suboptimal prosthetic or biological materials for repair or replacement of diseased or destroyed human organs and tissues are the main motivation for increasing research in the emerging field of tissue engineering. No organ or tissue is excluded from this multidisciplinary research field, which aims to provide vital tissues with the abilities to function, grow, repair, and remodel. There are several approaches to tissue engineering, including the use of cells, scaffolds, and the combination of the two. The most common approach is biodegradable or resorbable scaffolds configured to the shape of the new tissue (e.g. a heart valve). This scaffold is seeded with cells, potentially derived from either biopsies or stem cells. The seeded cells proliferate, organize, and produce cellular and extracellular matrix. During this matrix formation, the starter matrix is degraded, resorbed, or metabolized. First clinical trials using skin or cartilage substitutes are currently under way. Both the current state of the field and future prospects are discussed.

Smooth muscle cell adhesion to tissue engineering scaffolds

Synthetic polyesters of lactic and glycolic acid, and the extracellular matrix molecule collagen are among the most widely-utilized scaffolding materials in tissue engineering. However, the mechanism of cell adhesion to these tissue engineering scaffolds has not been extensively studied. In this paper, the mechanism of adhesion of smooth muscle cells to these materials was investigated. Vitronectin was found to be the predominant matrix protein adsorbed from serum-containing medium onto polyglycolic acid, poly(lactic co-glycolic) acid, and collagen two-dimensional films and three-dimensional scaffolds. Fibronectin adsorbed to both materials as well, although to a much lower density. Smooth muscle cell adhesion was mediated through specific integrin receptors interacting with these adsorbed proteins, as evidenced by both immunostaining and blocking studies. The receptors involved in adhesion included the alpha(v)beta5 to vitronectin, the alpha5beta1 to fibronectin and the alpha2beta1 to collagen I. Identification of the specific receptors used to adhere to these polymers clarifies why smooth muscle tissue development differs on these scaffolds, and may allow one to design tissue formation by controlling the surface chemistry of tissue engineering scaffolds.

Long-term follow-up of tissue-engineered intestine after anastomosis to native small bowel

BACKGROUND

Our laboratory has investigated the fabrication of a tissue-engineered intestine using biodegradable polymer scaffolds. Previously we reported that isolated intestinal epithelial organoid units on biodegradable polymer scaffolds formed cysts and the neointestine was successfully anastomosed to the native small bowel. The purpose of this study was to observe the development of tissue-engineered intestine after anastomosis and to demonstrate the effect of the anastomosis over a 9-month period.

METHODS

Microporous biodegradable polymer tubes were created from polyglycolic acid. Intestinal epithelial organoid units were harvested from neonatal Lewis rats and seeded onto the polymers, which were implanted into the abdominal cavity of adult male Lewis rats followed by 75% small bowel resection (n=24). Three weeks after implantation, the unit/polymer constructs were anastomosed to the native jejunum in a side-to-side fashion. The anastomosed tissue-engineered intestine was measured by laparotomy 10, 24, and 36 weeks after the implantation (n= 14). During the laparotomy, all rats with an obstruction in their anastomosis were killed and excluded from the statistical analysis. Another five rats were also killed at 10 and 36 weeks for histological and morphometric studies.

RESULTS

All analyzed rats survived this study and significantly increased their body weight by 36 weeks. Obstruction of the anastomosis was observed in one rat at 24 weeks and in two rats at 36 weeks; however, the anastomosis was patent in the other 11 rats by 36 weeks. The tissue-engineered intestine of these 11 rats increased in length and diameter at 10, 24, and 36 weeks after anastomosis; there were statistically significant differences between each time point except between the length of 10 and 24 weeks (P<0.016 by Wilcoxon signed rank test). Histologically the inner surface of the tissue-engineered intestine was lined with well-developed neomucosa at 10 and 36 weeks; however, there were small bare areas lacking neomucosa in the tissue-engineered intestine at 36 weeks. Morphometric analysis demonstrated no significant differences in villus number, villus height, and surface length of the neomucosa at 10 and 36 weeks.

CONCLUSIONS

Anastomosis between tissue-engineered intestine and native small bowel resulted in no complications after operation and maintained a high patency rate for up to 36 weeks. The tissue-engineered intestine increased in size and was lined with well-developed neomucosa for the duration of the study.

Effects of anastomosis of tissue-engineered neointestine to native small bowel

BACKGROUND

Our laboratory is investigating the tissue engineering of small intestine using intestinal epithelial organoid units seeded onto highly porous biodegradable polymer matrices. This study investigated the effects of anastomosis of tissue-engineered intestine to native small bowel alone or combined with small bowel resection on neointestinal regeneration.

METHODS

Intestinal epithelial organoid units harvested from neonatal Lewis rats were seeded onto biodegradable polymer tubes and implanted into the omentum of adult Lewis rats as follows: (1) implantation alone (n = 9); (2) implantation followed by anastomosis to native small bowel at 3 weeks (n = 11); and (3) implantation after small bowel resection and anastomosis to native small bowel at 3 weeks (n = 8). All constructs were harvested at 10 weeks and examined by histology. Morphometric analysis of the neomucosa was obtained using a computer image analysis program.

RESULTS

Cyst development was noted in all animals. All anastomoses were patent at 10 weeks. Histology revealed the development of a vascularized tissue with a neomucosa lining the lumen of the cyst with invaginations resembling crypt-villus structures. Morphometric analysis demonstrated significantly greater villus number, villus height, crypt number, crypt area, and mucosal surface length in groups 2 and 3 compared with group 1, and significantly greater villus number, villus height, crypt area, and mucosal surface length in group 3 compared with group 2 (P < 0.05, ANOVA, Tukey test).

CONCLUSION

Intestinal epithelial organoid units transplanted on biodegradable polymer tubes can regenerate into complex tissue resembling small intestine. Anastomosis to native small bowel combined with small bowel resection and anastomosis alone contribute significant regenerative stimuli for the morphogenesis and differentiation of tissue-engineered neointestine.