Experimental assessment of small intestinal submucosa as a small bowel graft in a rat model

In Vivo Regeneration of Tubular Small Intestine With Motility: A Novel Approach by Orthotopic Transplantation of Decellularized Scaffold

BACKGROUND

Whole-intestine engineering can provide a therapeutic alternative to bowel transplantation. Intestinal components including the mucosa, muscular layer, enteric nervous system, and vasculature must be reestablished as a tubular organ to generate an artificial small intestine. This study proposes a novel approach to produce a transplantable, well-organized tubular small intestine using a decellularized scaffold.

METHODS

Male Lewis rat intestines were used to generate decellularized scaffolds. Patch or tubular grafts were prepared from the decellularized intestine and transplanted into the rat intestine orthotopically. Histological analysis of the decellularized intestine was performed up to 12 wk after transplantation.

RESULTS

Histological examination revealed abundant vascularization into the decellularized patch graft 1 wk after transplantation. Muscular and nervous components, as well as cryptogenesis, were observed in the decellularized patch graft 2 wk after transplantation. Sixteen of the 18 rats survived with normal intake of food and water after the decellularized tubular graft transplantation. Compared with silicone tube grafts, the decellularized tubular grafts significantly promoted the infiltration and growth of intestinal components including the mucosa, muscular layer, and nerve plexus from the recipients. Circular and longitudinal muscle with a well-developed myenteric plexus was regenerated, and intestinal motility was confirmed in the decellularized tubular graft 12 wk after transplantation.

CONCLUSIONS

Orthotopic transplantation of decellularized intestine enhanced the reconstruction of the well-organized tubular small intestine with an enteric nervous system in vivo. Our method using a decellularized scaffold represents a promising approach toward whole-intestine engineering and provides a therapeutic alternative for the irreversible intestinal failure.

Surgical Treatment of Short Bowel Syndrome—The Past, the Present and the Future, a Descriptive Review of the Literature

Short bowel syndrome (SBS) is a devastating disorder with both short- and long-term implications for patients. Unfortunately, the prevalence of SBS has doubled over the past 40 years. Broadly speaking, the etiology of SBS can be categorized as congenital or secondary, the latter typically due to extensive small bowel resection following diseases of the small intestine, e.g., necrotizing enterocolitis, Hirschsprung’s disease or intestinal atresia. As of yet, no cure exists, thus, conservative treatment, primarily parenteral nutrition (PN), is the first-line therapy. In some cases, weaning from PN is not possible and operative therapy is required. The invention of the longitudinal intestinal lengthening and tailoring (LILT or Bianchi) procedure in 1980 was a major step forward in patient care and spawned further techniques that continue to improve lives for patients with severe SBS (e.g., double barrel enteroplasty, serial transverse enteroplasty, etc.). With this review, we aim to provide an overview of the clinical implications of SBS, common conservative therapies and the development of operative techniques over the past six decades. We also provide a short outlook on the future of operative techniques, specifically with respect to regenerative medicine.

Evidence of glucose absorption in a neoformed intestine

Recent advances in the field of tissue regeneration are offering promising therapeutic options for the treatment of short bowel syndrome. This study aimed to evaluate the glucose absorptive capacity of a neoformed intestine obtained from a biological scaffold in a rodent model and the steadiness of the engrafted segment area. Twenty-four male Sprague–Dawley rats were used for this study. Under anesthesia, a patch of biological material (2.2 × 1.5 cm) was engrafted in the anti-mesenteric border of the small bowels of 12 rats. Twelve rats were sham-operated. Animals were studied at 4, 8, and 10 months postengraftment. Functional and histological analyses were performed. The functional analysis was performed using an 18F-FDG analog as a probe and the results were acquired with an optical imager. The intensity of the fluorescent signal emitted by the neointestine was comparable with that emitted by the native intestine in all animals and was visible after injection in the preserved mesentery. The mean intestinal volume at time of engraftment and after 10 months was 4.08 cm³ (95% CI [3.58–4.58]) and 3.26 cm³ (CI 95% [3.23–3.29]), respectively, with a mean shrinkage of 17.3% (range 10.6–23.8%), without any evidence of stenosis. Morphological analysis revealed the progression of the biological material toward a neoformed intestine similar to the native intestine, especially at 8 and 10 months. In a rodent model, we demonstrated that a neointestine, obtained from a biological scaffold showed glucose absorption and a durable increase in diameter.

The Charming World of the Extracellular Matrix: A Dynamic and Protective Network of the Intestinal Wall

The intestinal extracellular matrix (ECM) represents a complex network of proteins that not only forms a support structure for resident cells but also interacts closely with them by modulating their phenotypes and functions. More than 300 molecules have been identified, each of them with unique biochemical properties and exclusive biological functions. ECM components not only provide a scaffold for the tissue but also afford tensile strength and limit overstretch of the organ. The ECM holds water, ensures suitable hydration of the tissue, and participates in a selective barrier to the external environment. ECM-to-cells interaction is crucial for morphogenesis and cell differentiation, proliferation, and apoptosis. The ECM is a dynamic and multifunctional structure. The ECM is constantly renewed and remodeled by coordinated action among ECM-producing cells, degrading enzymes, and their specific inhibitors. During this process, several growth factors are released in the ECM, and they, in turn, modulate the deposition of new ECM. In this review, we describe the main components and functions of intestinal ECM and we discuss their role in maintaining the structure and function of the intestinal barrier. Achieving complete knowledge of the ECM world is an important goal to understand the mechanisms leading to the onset and the progression of several intestinal diseases related to alterations in ECM remodeling.

Combating COVID-19 with tissue engineering: a review

The ongoing COVID-19 pandemic triggered by SARS-CoV-2 emerged from Wuhan, China, firstly in December 2019, as well spread to almost all around the world rapidly. The main reason why this disease spreads so many people in a short time is that the virus could be transmitted from an infected person to another by infected droplets. The new emergence of diseases usually may affect multiple organs; moreover, this disease is such an example. Numerous reported studies focus on acute or chronic organ damage caused by the virus. At this point, tissue engineering (TE) strategies can be used to treat the damages with its interdisciplinary approaches. Tissue engineers could design drug delivery systems, scaffolds, and especially biomaterials for the damaged tissue and organs. In this review, brief information about SARS-CoV-2, COVID-19, and epidemiology of the disease will be given at first. After that, the symptoms, the tissue damages in specific organs, and cytokine effect caused by COVID-19 will be described in detail. Finally, it will be attempted to summarize and suggest the appropriate treatments with suitable biomaterials for the damages via TE approaches. The aim of this review is to serve as a summary of currently available tissue damage treatments after COVID-19.

Bioengineering and regeneration of gastrointestinal tissue: where are we now and what comes next?

INTRODUCTION

The field of tissue engineering and regenerative medicine has been applied to the gastrointestinal (GI) tract for a couple decades. Several achievements have been accomplished that provide promising tools for treating diseases of the GI tract.

AREAS COVERED

The work described in this review covers the traditional aspect of using cells and scaffolds to replace parts of the tract. Several studies investigated different types of biomaterials and different types of cells. A more recent approach involved the use of gut-derived organoid units that can differentiate into all gut cell layers. The most recent approach introduced the use of organ-on-a-chip concept to understand the physiology and pathophysiology of the GI system.

EXPERT OPINION

The different approaches tackle the diseases of the GI tract from different perspectives. While all these different approaches provide a promising and encouraging future for this field, the translational aspect is yet to be studied.

Extracellular Matrix Bioscaffolds for Building Gastrointestinal Tissue

Regenerative medicine is a rapidly advancing field that uses principles of tissue engineering, developmental biology, stem cell biology, immunology, and bioengineering to reconstruct diseased or damaged tissues. Biologic scaffolds composed of extracellular matrix have shown great promise as an inductive substrate to facilitate the constructive remodeling of gastrointestinal (GI) tissue damaged by neoplasia, inflammatory bowel disease, and congenital or acquired defects. The present review summarizes the preparation and use of extracellular matrix scaffolds for bioengineering of the GI tract, identifies significant advances made in regenerative medicine for the reconstruction of functional GI tissue, and describes an emerging therapeutic approach.

The extracellular matrix of the gastrointestinal tract: a regenerative medicine platform

The synthesis and secretion of components that constitute the extracellular matrix (ECM) by resident cell types occur at the earliest stages of embryonic development, and continue throughout life in both healthy and diseased physiological states. The ECM consists of a complex mixture of insoluble and soluble functional components that are arranged in a tissue-specific 3D ultrastructure, and it regulates numerous biological processes, including angiogenesis, innervation and stem cell differentiation. Owing to its composition and influence on embryonic development, as well as cellular and organ homeostasis, the ECM is an ideal therapeutic substrate for the repair of damaged or diseased tissues. Biologic scaffold materials that are composed of ECM have been used in various surgical and tissue-engineering applications. The gastrointestinal (GI) tract presents distinct challenges, such as diverse pH conditions and the requirement for motility and nutrient absorption. Despite these challenges, the use of homologous and heterologous ECM bioscaffolds for the focal or segmental reconstruction and regeneration of GI tissue has shown promise in early preclinical and clinical studies. This Review discusses the importance of tissue-specific ECM bioscaffolds and highlights the major advances that have been made in regenerative medicine strategies for the reconstruction of functional GI tissues.

Transplantation of a Human Tissue-Engineered Bowel in an Athymic Rat Model

Intestinal failure is a serious clinical condition characterized by loss of motility, absorptive function, and malnutrition. Current treatments do not provide the optimal solution for patients due to the numerous resulting complications. A bioengineered bowel that contains the necessary cellular components provides a viable option for patients. In this study, human tissue-engineered bowel (hTEB) was developed using a technique, whereby human-sourced smooth muscle cells were aligned and neoinnervated using human-sourced neural progenitor cells, resulting in the formation of intrinsically innervated smooth muscle sheets. The sheets were then rolled around hollow tubular chitosan scaffolds and implanted in the omentum of athymic rats for neovascularization. Four weeks later, biopsies of hTEB showed vascularization, normal cell alignment, phenotype, and function. During the biopsy procedure, hTEB was transplanted into the same rat's native intestine. The rats gained weight and 6 weeks later, hTEB was harvested for studies. hTEB was healthy in color with normal diameter and with digested food in the lumen, indicating propulsion of luminal content through the hTEB. Histological studies indicated neomucosa with evidence of crypts and villi structures. This study provides proof of concept that hTEB could provide a viable treatment to lengthen the gut for patients with gastrointestinal disorders.

Bioengineering the gut: future prospects of regenerative medicine

Functions of the gastrointestinal tract include motility, digestion and absorption of nutrients. These functions are mediated by several specialized cell types including smooth muscle cells, neurons, interstitial cells and epithelial cells. In gastrointestinal diseases, some of the cells become degenerated or fail to accomplish their normal functions. Surgical resection of the diseased segments of the gastrointestinal tract is considered the gold-standard treatment in many cases, but patients might have surgical complications and quality of life can remain low. Tissue engineering and regenerative medicine aim to restore, repair, or regenerate the function of the tissues. Gastrointestinal tissue engineering is a challenging process given the specific phenotype and alignment of each cell type that colonizes the tract - these properties are critical for proper functionality. In this Review, we summarize advances in the field of gastrointestinal tissue engineering and regenerative medicine. Although the findings are promising, additional studies and optimizations are needed for translational purposes.

New approaches to increase intestinal length: Methods used for intestinal regeneration and bioengineering

Inadequate absorptive surface area poses a great challenge to the patients suffering a variety of intestinal diseases causing short bowel syndrome. To date, these patients are managed with total parenteral nutrition or intestinal transplantation. However, these carry significant morbidity and mortality. Currently, by emergence of tissue engineering, anticipations to utilize an alternative method to increase the intestinal absorptive surface area are increasing. In this paper, we will review the improvements made over time in attempting elongating the intestine with surgical techniques as well as using intestinal bioengineering. Performing sequential intestinal lengthening was the preliminary method applied in humans. However, these methods did not reach widespread use and has limited outcome. Subsequent experimental methods were developed utilizing scaffolds to regenerate intestinal tissue and organoids unit from the intestinal epithelium. Stem cells also have been studied and applied in all types of tissue engineering. Biomaterials were utilized as a structural support for naive cells to produce bio-engineered tissue that can achieve a near-normal anatomical structure. A promising novel approach is the elongation of the intestine with an acellular biologic scaffold to generate a neo-formed intestinal tissue that showed, for the first time, evidence of absorption in vivo. In the large intestine, studies are more focused on regeneration and engineering of sphincters and will be briefly reviewed. From the review of the existing literature, it can be concluded that significant progress has been achieved in these experimental methods but that these now need to be fully translated into a pre-clinical and clinical experimentation to become a future viable therapeutic option.

Proposal of intestinal tissue engineering combined with Bianchi's procedure

AIM

The aim of this study is to examine the feasibility of the small intestinal submucosa (SIS) when the longitudinal staples during Bianchi's procedure are replaced with SIS graft.

METHODS

The mesentery of the bowel was separated based on the bifurcated vessels in five beagles. A 2×7-cm longitudinal half of the bowel was excised and the defect was repaired using SIS with similar blood supply in Bianchi's operation. Six months later, intestinal motility in the SIS-grafted area was recorded. Tissue preparations were obtained from the reorganized area. An organ bath technique with electrical field stimulation was applied. Both the native small intestine and grafted area were morphologically investigated using immunohistochemistry.

MAIN RESULTS

All dogs survived and thrived with no anastomotic leakage. Isoperistaltic migrating contractility during fasting was observed through the grafted segment including the reorganized area. The SIS-reorganized tissue contracted in response to an acetylcholine agonist and electrical field stimulation. The mucosa was covered with normal epithelium. Reorganization of neural and smooth muscle cells was observed.

CONCLUSIONS

SIS has the potential for use as a scaffold that promotes the formation of a physical and physiological neointestine. Our present proposal approaches a novel surgical treatment in patients with short bowel syndrome.

The use of murine-derived fundic organoids in studies of gastric physiology

KEY POINTS

An in vitro approach to study gastric development is primary mouse-derived epithelium cultured as three-dimensional spheroids known as organoids. We have devised two unique gastric fundic-derived organoid cultures: model 1 for the expansion of gastric fundic stem cells, and model 2 for the maintenance of mature cell lineages. Organoids maintained in co-culture with immortalized stomach mesenchymal cells express robust numbers of surface pit, mucous neck, chief, endocrine and parietal cells. Histamine induced a significant decrease in intraluminal pH that was reversed by omeprazole in fundic organoids and indicated functional activity and regulation of parietal cells. Localized photodamage resulted in rapid cell exfoliation coincident with migration of neighbouring cells to the damaged area, sustaining epithelial continuity. We report the use of these models for studies of epithelial cell biology and cell damage and repair.

ABSTRACT

Studies of gastric function and disease have been limited by the lack of extended primary cultures of the epithelium. An in vitro approach to study gastric development is primary mouse-derived antral epithelium cultured as three-dimensional spheroids known as organoids. There have been no reports on the use of organoids for gastric function. We have devised two unique gastric fundic-derived organoid cultures: model 1 for the expansion of gastric fundic stem cells, and model 2 for the maintenance of mature cell lineages. Both models were generated from single glands dissociated from whole fundic tissue and grown in basement membrane matrix (Matrigel) and organoid growth medium. Model 1 enriches for a stem cell-like niche via simple passage of the organoids. Maintained in Matrigel and growth medium, proliferating organoids expressed high levels of stem cell markers CD44 and Lgr5. Model 2 is a system of gastric organoids co-cultured with immortalized stomach mesenchymal cells (ISMCs). Organoids maintained in co-culture with ISMCs express robust numbers of surface pit, mucous neck, chief, endocrine and parietal cells. Histamine induced a significant decrease in intraluminal pH that was reversed by omeprazole in fundic organoids and indicated functional activity and regulation of parietal cells. Localized photodamage resulted in rapid cell exfoliation coincident with migration of neighbouring cells to the damaged area, sustaining epithelial continuity. Thus, we report the use of these models for studies of epithelial cell biology and cell damage and repair.

Arterial grafts exhibiting unprecedented cellular infiltration and remodeling in vivo: the role of cells in the vascular wall

OBJECTIVE

To engineer and implant vascular grafts in the arterial circulation of a pre-clinical animal model and assess the role of donor medial cells in graft remodeling and function.

APPROACH AND RESULTS

Vascular grafts were engineered using Small Intestinal Submucosa (SIS)-fibrin hybrid scaffold and implanted interpositionally into the arterial circulation of an ovine model. We sought to demonstrate implantability of SIS-Fibrin based grafts; examine the remodeling; and determine whether the presence of vascular cells in the medial wall was necessary for cellular infiltration from the host and successful remodeling of the implants. We observed no occlusions or anastomotic complications in 18 animals that received these grafts. Notably, the grafts exhibited unprecedented levels of host cell infiltration that was not limited to the anastomotic sites but occurred through the lumen as well as the extramural side, leading to uniform cell distribution. Incoming cells remodeled the extracellular matrix and matured into functional smooth muscle cells as evidenced by expression of myogenic markers and development of vascular reactivity. Interestingly, tracking the donor cells revealed that their presence was beneficial but not necessary for successful grafting. Indeed, the proliferation rate and number of donor cells decreased over time as the vascular wall was dominated by host cells leading to significant remodeling and development of contractile function.

CONCLUSIONS

These results demonstrate that SIS-Fibrin grafts can be successfully implanted into the arterial circulation of a clinically relevant animal model, improve our understanding of vascular graft remodeling and raise the possibility of engineering mural cell-free arterial grafts.

In vitro evaluation of bi-layer silk fibroin scaffolds for gastrointestinal tissue engineering

Silk fibroin scaffolds were investigated for their ability to support attachment, proliferation, and differentiation of human gastrointestinal epithelial and smooth muscle cell lines in order to ascertain their potential for tissue engineering. A bi-layer silk fibroin matrix composed of a porous silk fibroin foam annealed to a homogeneous silk fibroin film was evaluated in parallel with small intestinal submucosa scaffolds. AlamarBlue analysis revealed that silk fibroin scaffolds supported significantly higher levels of small intestinal smooth muscle cell, colon smooth muscle cell, and esophageal smooth muscle cell attachment in comparison to small intestinal submucosa. Following 7 days of culture, relative numbers of each smooth muscle cell population maintained on both scaffold groups were significantly elevated over respective 1-day levels—indicative of cell proliferation. Real-time reverse transcription polymerase chain reaction and immunohistochemical analyses demonstrated that both silk fibroin and small intestinal submucosa scaffolds were permissive for contractile differentiation of small intestinal smooth muscle cell, colon smooth muscle cell, esophageal smooth muscle cell as determined by significant upregulation of α-smooth muscle actin and SM22α messenger RNA and protein expression levels following transforming growth factor-β1 stimulation. AlamarBlue analysis demonstrated that both matrix groups supported similar degrees of attachment and proliferation of gastrointestinal epithelial cell lines including colonic T84 cells and esophageal epithelial cells. Following 14 days of culture on both matrices, spontaneous differentiation of T84 cells toward an enterocyte lineage was confirmed by expression of brush border enzymes, lactase, and maltase, as determined by real-time reverse transcription polymerase chain reaction and immunohistochemical analyses. In contrast to small intestinal submucosa scaffolds, silk fibroin scaffolds supported spontaneous differentiation of esophageal epithelial cells toward a suprabasal cell lineage as indicated by significant upregulation of cytokeratin 4 and cytokeratin 13 messenger RNA transcript levels. In addition, esophageal epithelial cells maintained on silk fibroin scaffolds also produced significantly higher involucrin messenger RNA transcript levels in comparison to small intestinal submucosa counterparts, indicating an increased propensity for superficial, squamous cell specification. Collectively, these data provide evidence for the potential of silk fibroin scaffolds for gastrointestinal tissue engineering applications.

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.

A study of a three-dimensional PLGA sponge containing natural polymers co-cultured with endothelial and mesenchymal stem cells as a tissue engineering scaffold

The interaction between vascular endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) in a complex hemodynamic and mechanical environment plays an important role in the control of blood vessel growth and function. Despite the importance of VSMCs, substitutes are needed for vascular therapies. A potential VSMC substitute is human adult bone marrow derived mesenchymal stem cells (hMSCs). In this study, the effect of poly(lactic-co-glycolic acid) (PLGA) scaffolds containing three natural polymers (demineralized bone particles, silk, and small intestine submucosa) on the phenotype of MSCs and SMCs cultured with or without ECs was investigated. The study objective was to create a media equivalent for a tissue engineered blood vessel using PLGA, natural polymers, and MSCs co-cultured with ECs. The PLGA containing the natural polymers silk and SIS showed increased proliferation and cell adhesion. The presence of silk and DBP promoted a MSC phenotype change into a SMC-like phenotype at the mRNA level; however these differences at the protein level were not seen. Additionally, PLGA containing SIS did not induce SMC gene or protein upregulation. Finally, the effect of ECs in combination with the natural polymers was tested. When co-cultured with ECs, the mRNA of SMC specific markers in MSCs and SMCs were increased when compared to SMCs or MSCs alone. However, MSCs, when co-cultured with ECs on PLGA containing silk, exhibited significantly increased α-SMA and calponin expression when compared to PLGA only scaffolds. These results indicate that the natural polymer silk in combination with the co-culture of endothelial cells was most effective at increasing cell viability and inducing a SMC-like phenotype at the mRNA and protein level in MSCs.

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.

Tubular scaffolds of gelatin and poly(ε-caprolactone)-block-poly(γ-glutamic acid) blending hydrogel for the proliferation of the primary intestinal smooth muscle cells of rats

The proper regeneration of intestinal muscle for functional peristalsis is the most challenging aspect of current small intestine tissue engineering. This study aimed to fabricate a hydrogel scaffold for the proliferation of intestinal smooth muscle cells (ISMCs). Tubular porous scaffolds of 10-20 wt% gelatin and 0.05-0.1 wt% poly(ε-caprolactone)-block-poly(γ-glutamic acid) blending hydrogel were cross-linked by carbodiimide and succinimide in an annular space of a glass mold. The scaffolds with higher gelatin contents degraded slower in the phosphate buffer solution. In rheological measurements, the hydrated scaffolds were elastic (all tangent delta <0.45); they responded differentially to frequency, indicating a complete viscoelastic property that is beneficial for soft tissue regeneration. Isolated rat ISMCs, with the characteristic biomarkers α-SMA, calponin and myh11, were loaded into the scaffolds by using either static or centrifugal methods. The average cell density inside the scaffolds increased in a time-dependent manner in most scaffolds of both seeding groups, although at early time points (seven days) the centrifugal seeding method trapped cells more efficiently and yielded a higher cell density than the static seeding method. The static seeding method increased the cell density from 7.5-fold to 16.3-fold after 28 days, whereas the centrifugal procedure produced a maximum increase of only 2.4-fold in the same period. In vitro degradation data showed that 50-80% of the scaffold was degraded by the 14th day. However, the self-secreted extracellular matrix maintained the integrity of the scaffolds for cell proliferation and spreading for up to 28 days. Confocal microscopic images revealed cell-cell contacts with the formation of a 3D network, demonstrating that the fabricated scaffolds were highly biocompatible. Therefore, these polymeric biomaterials hold great promise for in vivo applications of intestinal tissue engineering.

A decellularization methodology for the production of a natural acellular intestinal matrix

Successful tissue engineering involves the combination of scaffolds with appropriate cells in vitro or in vivo. Scaffolds may be synthetic, naturally-derived or derived from tissues/organs. The latter are obtained using a technique called decellularization. Decellularization may involve a combination of physical, chemical, and enzymatic methods. The goal of this technique is to remove all cellular traces whilst maintaining the macro- and micro-architecture of the original tissue.

Intestinal tissue engineering has thus far used relatively simple scaffolds that do not replicate the complex architecture of the native organ. The focus of this paper is to describe an efficient decellularization technique for rat small intestine. The isolation of the small intestine so as to ensure the maintenance of a vascular connection is described. The combination of chemical and enzymatic solutions to remove the cells whilst preserving the villus-crypt axis in the luminal aspect of the scaffold is also set out. Finally, assessment of produced scaffolds for appropriate characteristics is discussed.

Influence of mesenchymal stem cells on stomach tissue engineering using small intestinal submucosa

Small intestinal submucosa (SIS) is a biodegradable collagen-rich matrix containing functional growth factors. We have previously reported encouraging outcomes for regeneration of an artificial defect in the rodent stomach using SIS grafts, although the muscular layer was diminutive. In this study, we investigated the feasibility of SIS in conjunction with mesenchymal stem cells (MSCs) for regeneration of the gastrointestinal tract. MSCs from the bone marrow of green fluorescence protein (GFP)-transgenic Sprague-Dawley (SD) rats were isolated and expanded ex vivo. A 1 cm whole-layer stomach defect in SD rats was repaired using: a plain SIS graft without MSCs (group 1, control); a plain SIS graft followed by intravenous injection of MSCs (group 2); a SIS graft co-cultured with MSCs (group 3); or a SIS sandwich containing an MSC sheet (group 4). Pharmacological, electrophysiological and immunohistochemical examination was performed to evaluate the regenerated stomach tissue. Contractility in response to a muscarinic receptor agonist, a nitric oxide precursor or electrical field stimulation was observed in all groups. SIS grafts seeded with MSCs (groups 3 and 4) appeared to support improved regeneration compared with SIS grafts not seeded with MSCs (groups 1 and 2), by enabling the development of well-structured smooth muscle layers of significantly increased length. GFP expression was detected in the regenerated interstitial tissue, with fibroblast-like cells in the seeded-SIS groups. SIS potently induced pharmacological and electrophysiological regeneration of the digestive tract, and seeded MSCs provided an enriched environment that supported tissue regeneration by the SIS graft in the engineered stomach.

The development and implantation of a biologically derived allograft scaffold

Biologically derived scaffolds are becoming viable treatment options for tissue/organ repair and regeneration. A continuing hurdle is the need for a functional blood supply to and from the implanted scaffold. We have addressed this problem by constructing an acellular ileal scaffold with an attached vascular network suitable for implantation and immediate reperfusion with the host's blood. Using a vascular perfusion approach, a segment of porcine ileum up to 30 cm long, together with its attached vasculature, was decellularized as a single entity. The quality of the decellularized scaffold was assessed histologically and using molecular tools. To establish vascular perfusion potentials of the scaffold, a right-sided nephrectomy and end-to-end anastomosis of the decellularized scaffold's vasculature to a renal artery and vein were performed in a pig of similar size to the donor animal. Lengths of ileal scaffold, together with its attached vasculature, were successfully decellularized, with no evidence of intact cells/nuclear material or collagen degradation. The scaffold's decellularized vascular network demonstrated optimum perfusion at 1, 2 and 24 h post-implantation and the mesenteric arcade remained patent throughout the assessment. The 1, 2 and 24 h explanted scaffolds demonstrated signs of cellular attachment, with cells positive for CD68 and CD133 on the vascular luminal aspect. It is possible to decellularize clinically relevant lengths of small intestine, together with the associated vasculature, as a single segment. The functional vascular network may represent a route for recellularization for future regeneration of bowel tissue for patients with short bowel syndrome.

Small intestinal submucosa segments as matrix for tissue engineering: review

Tissue engineering (TE) is an emerging interdisciplinary field aiming at the restoration or improvement of impaired tissue function. A combination of cells, scaffold materials, engineering methods, and biochemical and physiological factors is employed to generate the desired tissue substitute. Scaffolds often play a pivotal role in the engineering process supporting a three-dimensional tissue formation. The ideal scaffold should mimic the native extracellular environment providing mechanical and biological properties to allow cell attachment, migration, and differentiation, as well as remodeling by the host organism. The scaffold should be nonimmunogenic and should ideally be resorbed by the host over time, leaving behind only the regenerated tissue. More than 40 years ago, a preparation of the small intestine was introduced for the replacement of vascular structures. Since then the small intestinal submucosa (SIS) has gained a lot of interest in TE and subsequent clinical applications, as this material exhibits key features of a highly supportive scaffold. This review will focus on the general properties of the SIS and its applications in therapeutical approaches as well as in generating tissue substitutes in vitro. Furthermore, the main problem of TE, which is the insufficient nourishment of cells within three-dimensional, artificial tissues exceeding certain dimensions is addressed. To solve this issue the implementation of another small intestine-derived preparation, the biological vascularized matrix (BioVaM), could be a feasible option. The BioVaM comprises in addition to SIS the arterial and venous mesenteric pedicles and exhibits thereby a perfusable vessel bed that is preserved after decellularization.

Regeneration and bioengineering of transplantable abdominal organs: current status and future challenges

INTRODUCTION

The most critical issue to organ transplantation is the identification of new sources of organs. The present manuscript illustrates the state-of-the-art regenerative medicine (RM) investigations aiming to manufacturing abdominal organs for transplant purposes.

AREAS COVERED

This manuscript focuses on research in the bioengineering and regeneration of kidneys, insulin-producing cells, livers and small bowel. The main technology currently under development exploits the seeding of cells on supporting scaffolding material. Despite favorable preliminary results obtained with relatively simple, hollow organs, when more complex organs are considered, the scenario changes dramatically. Investigations are still in early stages, and clinical translation is not yet foreseeable based on current knowledge and information. Obstacles are numerous but we believe the critical factor hampering success is lack of in-depth understanding of the extracellular matrix (ECM) and cell-ECM interactions, as well as the mechanisms with which organs develop in utero.

EXPERT OPINION

The success of RM to generate transplantable abdominal organs relies heavily on progress in (stem) cell therapies, developmental and ECM biology, and in the thorough understanding of the intricate relationship and interplay between cells and the ECM. This will require enormous investments in financial and medical resources, which ideally should be embarked upon by governments, the private sector and academia.

Autologous gastrointestinal reconstruction: review of the optimal nontransplant surgical options for adults and children with short bowel syndrome

Short bowel syndrome (SBS) results in loss of absorptive capacity of the development of gut, leading to malabsorption due to protein, energy, fluid, and electrolyte loss and imbalance while on enteral diet alone. Various nonsurgical and surgical therapeutic options that have emerged improve the survival outcome following SBS in both children and adults. An individualized, complex multidisciplinary approach to medical and surgical intestinal rehabilitation is needed to provide an opportunity for enteral autonomy to be possible in a patient with SBS. The remnant bowel plays a very pivotal role in autologous gastrointestinal reconstruction (AGIR) surgery. Intestinal transplantation, although promising and potentially life-saving for SBS, should be reserved for patients with failed AGIR or those who have no prospect for autologous enteral autonomy. This article reviews the evolution of nontransplant surgical management of patients with SBS.

Small intestinal submucosa seeded with intestinal smooth muscle cells in a rodent jejunal interposition model

BACKGROUND

Small intestinal submucosa (SIS) is a porcine-derived, acellular, collagen-based matrix that has been tested without seeded smooth muscle cells (SMCs) for intestinal tissue engineering. We examined the expression patterns of contractile proteins of SIS with SMCs implanted in an in vivo rodent model.

MATERIALS AND METHODS

Intestinal SMCs were isolated from Lewis rat pups. Four-ply tubular SMCs-seeded SIS or blank SIS scaffolds were implanted in an adult rat jejunal interposition model. Recipients were sacrificed at 2, 4, and 8 wk following the implantation. The retrieved specimens were examined using antibodies against contractile proteins of SMCs.

RESULTS

Cultured intestinal SMCs expressed α-smooth muscle actin (α-SMA), calponin, and less smooth muscle myosin heavy chain (SM-MHC) in vitro. Cell-seeded SIS scaffolds contracted significantly over 8 wk of implantation but were comparable to SIS scaffolds without cell seeding. Implanted cell-seeded SIS scaffolds at 2 wk expressed extensive α-SMA, some calponin, and minimal SM-MHC. At 4 wk, α-SMA-expressing cells decreased significantly, whereas calponin or SM-MHC expressing cells were rarely detected. A small number of α-SMA-expressing cells were present at 8 wk, whereas more calponin or SM-MHC expressing cells emerged in proximity with the anastomotic interface.

CONCLUSIONS

Cell-seeded SIS contracted significantly after implantation, but the expressions of contractile proteins were present at the site of SIS interposition. No organized smooth muscle was formed at the site of implantation. A better scaffold design is needed to produce structured smooth muscle.

Engineered tendon with decellularized xenotendon slices and bone marrow stromal cells: an in vivo animal study

The purpose of this study was to investigate an engineered composite of multilayer acellular tendon slices seeded with bone marrow stromal cells (BMSCs) as a possible solution for tendon reconstruction. BMSCs were harvested from 15 rabbits and infraspinatus tendons were harvested from 17 dogs. The decellularized tendons were sectioned in longitudinal slices with a thickness of 50 µm. The BMSCs were seeded on the slices and then the slices were bundled into one composite. The composite was implanted into a rabbit patellar tendon defect. Tendon slices without BMSCs were implanted into the contralateral patellar tendon as a control. The composites were evaluated by histology and qRT-PCR. The viability of BMSCs was assessed using a fluorescent marker. Histology showed viable cells between the collagen fibres on the cell-seeded side. Analysis by qRT-PCR showed higher tenomodulin, collagen type III, MMP3 and MMP13 expressions and lower collagen type I expression in the cell-seeded composite than in the tendon slices without BMSCs. We conclude that BMSCs can survive in a multilayer composite, express a tendon phenotype and enhance the metabolism of tendon in vivo. This in vivo study suggests a potential utility of this composite in tendon reconstruction.

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.

The role of basic fibroblast growth factor to enhance fetal intestinal mucosal cell regeneration in vivo

BACKGROUND/PURPOSE

The limited application of small bowel transplantation for short bowel syndrome, mainly on the account of the morbidity and long-term implications of the procedure, has led to a search for alternative therapies. The purpose of this study was to evaluate whether basic fibroblast growth factor (bFGF) could facilitate regeneration of fetal small intestinal mucosa in vivo.

METHODS

Intestinal epithelial organoid units harvested from fetal Lewis rats were injected into adult male Lewis rats whose colon was denuded of mucosa, as syngeneic recipients. One experimental group transplanted with the addition of 50 ng/ml bFGF, was compared with a control group that were transplanted without bFGF. The grafts were harvested and analyzed using histology and immunohistochemistry 3 weeks after operation.

RESULTS

There were 4 anesthetic deaths, two in each group, and 11 deaths due to adhesive ileus. In no rat did neomucosa fully cover the denuded colonic muscle throughout the whole length of lumen. Histologically, the structure of the neomucosa, when present, was normal small intestinal mucosa. The small intestinal mucosa was partially restored in 100% (6 of 6) of bFGF, and in 28.6% (2 of 7) of those not given bFGF (P = 0.0021).

CONCLUSIONS

These data demonstrate that bFGF can facilitate the restoration of intestinal epithelial cells, at least to some degree. Potentially, refinements of this technique could be used to facilitate the physiologic tissue engineering of small intestine in a way that allows it to move peristaltically, and have an application in the management of patients with short bowel syndrome.

Multilayer tendon slices seeded with bone marrow stromal cells: a novel composite for tendon engineering

The ideal scaffold for tendon engineering would possess the basic structure of the tendon, native extracellular matrix, and capability of cell seeding. The purpose of this study was to assess the tissue engineering potential of a novel composite consisting of a decellularized multilayer sliced tendon (MST) scaffold seeded with bone marrow stromal cells (BMSC). BMSC and infraspinatus tendons were harvested from 20 dogs. The tendons were sectioned in longitudinal slices with a thickness of 50 microm. The slices were decellularized, seeded with BMSC, and then bundled into one composite. The composite was incubated in culture media for 14 days. The resulting BMSC-seeded MST was evaluated by qRT-PCR and histology. The BMSC viability was assessed by a fluorescent tracking marker. Histology showed that the seeded cells aligned between the collagen fibers of the tendon slices. Analysis by qRT-PCR showed higher tenomodulin and MMP13 expression and lower collagen type I expression in the composite than in the BMSC before seeding. BMSC labeled with fluorescent tracking marker were observed in the composite after culture. Mechanical testing showed no differences between scaffolds with or without BMSC. BMSC can survive in a MST scaffold. The increased tenomodulin expression suggests that BMSC might express a tendon phenotype in this environment. This new composite might be useful as a model of tendon tissue engineering.

Intestinal regeneration by a novel surgical procedure

BACKGROUND

Treatment of short bowel syndrome is problematical. Small bowel tissue engineering has achieved modest results in animal studies. The aim of this study was to investigate intestinal regeneration in a novel surgical model.

METHODS

Roux-en-Y bypass procedures were performed on 40 Wistar rats weighing 250-350 g. Animals were killed at 1, 2, 3, 4, 8, 12 and 24 weeks after implantation with a 3-cm silicone tube. The spatio temporal relationship of intestinal regeneration was analysed using three-dimensional multislice computed tomography, and examination of sequential morphological changes on gross or histological findings and measurement of missing intestinal tissue (growth defects).

RESULTS

Progressive intestinal regeneration on a silicone tube was identifiable in 35 animals. Most adhesions were initially localized on the tube but spread to a distal site 4 weeks after implantation. Growth defects decreased with time, with a marked reduction in the first 4 weeks and a gradual reduction to week 24 after implantation. Luminal patency shown radiologically as well as sequential histological findings, such as mucosal lining, matrix remodelling and muscular regeneration, suggested that regeneration of intestinal tissue took place, not merely scar contraction.

CONCLUSION

Non-invasive as well as histomorphological assessment followed intestinal regeneration over time in this model, which provides scope for further studies.

Evaluation of small intestinal submucosa as scaffolds for intestinal tissue engineering

BACKGROUND

Biodegradable scaffolds have been used for regenerating the small intestine. The aim of this study was to evaluate the feasibility of small intestinal submucosa (SIS) as scaffolds for intestinal regeneration in a rat model.

MATERIALS AND METHODS

A tubular one-ply or four-ply SIS was interposed between isolated jejunal segments in rats. The scaffolds were harvested at 2, 4, and 8 weeks after implantation, and the specimens were examined grossly and histologically.

RESULTS

Significant contractions were observed in SIS scaffolds after implantation. The one-ply SIS contracted to 44% of its initial length at 2 weeks and continued to contract to 6% of its initial length at 8 weeks. The contraction of four-ply SIS scaffolds was less than that of the one-ply SIS, reaching 29% of its initial length at 8 weeks. Minimal epithelial and smooth muscular regeneration was observed in the SIS scaffolds after implantation.

CONCLUSIONS

A significant shrinkage was observed in the SIS scaffolds after implantation. Although the four-ply SIS contracted less than the one-ply SIS, neither scaffold supported significant amount of intestinal regeneration.

Endocrine Cell and Nerve Regeneration in Autologous In Situ Tissue-Engineered Small Intestine

BACKGROUND

The purpose of this study was to regenerate a larger size of small intestinal tissue than that of our previous study and to evaluate the regeneration of the endocrine cells (ECC) and nerve system of autologous tissue-engineered small intestine. The effect of implantation of large numbers of smooth muscle cells (SMC) for the regeneration of small intestine was also investigated.

METHODS

Two types of scaffolds with different cell densities were fabricated: low density (LD) of SMC in the scaffold and high density (HD) of SMC in the scaffold. Both scaffolds were implanted into defects of isolated ileum in a canine model. Animals were sacrificed at 8, 12, 18, and 24 weeks.

RESULTS

The area of engineered small intestine in the HD group was four times larger than that in the LD group, although that was smaller in size than the original size of the defect. There were no significant changes in the thickness of regenerated smooth muscle layer (SML) in the LD and HD groups. The numbers of endocrine cells gradually increased after implantation. At 18 weeks of regeneration, the number of ECC reached levels comparable to that of normal mucosa. The nerve fibers extended to the center of the graft area and were observed in regenerated SML and regenerated villi at 24 weeks.

CONCLUSIONS

The ECC and nerve fibers were regenerated in autologous in situ tissue-engineered small intestine. Seeding a large number of SMC was not sufficient for the regeneration of the small intestine in a tubular configuration.

Experimental evaluation of Surgisis as scaffold for neointestine regeneration in a rat model

The aim of the study was to evaluate the use of Surgisis (Cook Biotech Inc.), a porcine derived extracellular matrix already used in tissue engineering, as a scaffold for neointestinal regeneration in a rat model. A 3-cm length of tubular Surgisis graft was interposed with bilateral anastomoses in the middle of an isolated ileal loop of Sprague Dawley rats with an ileostomy. The grafts were harvested and analyzed using histology and immunohistochemistry at 24 weeks after operation. Macroscopic examination revealed neither stenosis nor adhesions in the area surrounding the neointestine. The regenerated small bowel showed a mean shrinkage of 30.7% (range 20%-40%). Histologic and immunohistochemical evaluation showed a well-developed three layers of mucosa and smooth muscle and serosa in the regenerated bowel wall that were similar to those of the normal bowel with evident neovascularization. Also, the regeneration of smooth muscle fibers and innervation were evident. The preliminary results of this study showed that Surgisis allowed rapid regeneration of mucosa and smooth muscle and therefore may be a promising material for the creation of a neointestine.

Esophageal replacement in rat using porcine intestinal submucosa as a patch or a tube-shaped graft

This study compares the efficacy of porcine intestinal submucosa (SIS) patch graft versus SIS-tube graft in esophageal replacement, using a novel esophageal regeneration model. Clinical function, as well as macroscopic and microscopic morphology were evaluated in both SIS-treated groups. We performed semi-circumferential esophageal excision followed by repair of the defect using either a SIS-patch graft (group I) or segmental esophageal excision followed by a SIS-tube interposition graft (group II) in rats. The 28-day survival rate was significantly different between the SIS-treated groups (100% in group I vs. 0% in group II). Unlike the rats in group II, which died within the first postoperative month due to esophageal dysfunction, all surviving animals in group I resumed a normal solid diet within a few days after surgery, without signs of esophageal dysfunction and gained weight. Barium swallow studies showed no evidence of fistula, significant stenosis or diverticula. No hematological or serum biochemistry abnormalities were found. By day 150 the SIS patch was replaced by esophageal-derived tissues. In the rat model, a patch graft technique using SIS appeared to induce esophageal regrowth and provided an initial and long-term satisfactory function, while a tube-shaped graft technique using SIS was unsuccessful.

Tissue engineering of small intestinal tissue using collagen sponge scaffolds seeded with smooth muscle cells

In a previously reported attempt to regenerate small intestine with autologous tissues, collagen scaffolds were used without cell seeding or with autologous mesenchymal stem cell seeding. However the regenerated intestine lacked a smooth muscle layer. To accomplish regeneration of a smooth muscle layer, this present study used collagen scaffolds seeded with the smooth muscle cells (SMC) in a canine model. Autologous SMC were isolated from stomach wall and cultured. Two types of scaffolds were fabricated: in SMC (+), cultured SMCs were mixed with collagen solution and poured into a collagen sponge; and in SMC (-), SMCs were omitted. Both scaffolds were implanted into defects of isolated ileum as a patch graft. Animals were euthanized at 4, 8, and 12 weeks; for the last time point, the ileal loop had been reanastomosed at 8 weeks. At 12 weeks, the SMC (-) group showed a luminal surface covered by a regenerated epithelial cell layer with very short villi; however only a thin smooth muscle layer was observed, representing the muscularis mucosae. In the SMC (+) group, the luminal surface was covered completely by a relatively well-developed epithelial layer with numerous villi. Implanted SMCs were seen in the lamina propria and formed a smooth muscle layer. Thus, we concluded that collagen sponge scaffolds seeded with autologous SMCs have a potential for small intestine regeneration.

Advances in short bowel syndrome: an updated review

Short bowel syndrome (SBS) continues to be an important clinical problem due to its high mortality and morbidity as well as its devastating socioeconomic effects. The past 3 years have witnessed many advances in the investigation of this condition, with the aim of elucidating the cellular and molecular mechanisms of intestinal adaptation. Such information may provide opportunities to exploit various factors that act as growth agents for the remaining bowel mucosa and may suggest new therapeutic strategies to maintain gut integrity, eliminate dependence on total parenteral nutrition, and avoid the need for intestinal transplantation. This review summarizes current research on SBS over the last few years.

Induction of smooth muscle cell-like phenotype in marrow-derived cells among regenerating urinary bladder smooth muscle cells

Tissue regeneration on acellular matrix grafts has great potential for therapeutic organ reconstruction. However, hollow organs such as the bladder require smooth muscle cell regeneration, the mechanisms of which are not well defined. We investigated the mechanisms by which bone marrow cells participate in smooth muscle formation during urinary bladder regeneration, using in vivo and in vitro model systems. In vivo bone marrow cells expressing green fluorescent protein were transplanted into lethally irradiated rats. Eight weeks following transplantation, bladder domes of the rats were replaced with bladder acellular matrix grafts. Two weeks after operation transplanted marrow cells repopulated the graft, as evidenced by detection of fluorescent staining. By 12 weeks they reconstituted the smooth muscle layer, with native smooth muscle cells (SMC) infiltrating the graft. In vitro, the differential effects of distinct growth factor environments created by either bladder urothelial cells or bladder SMC on phenotypic changes of marrow cells were examined. First, supernatants of cultured bladder cells were used as conditioned media for marrow cells. Second, these conditions were reconstituted with exogenous growth factors. In each case, a growth factor milieu characteristic of SMC induced an SMC-like phenotype in marrow cells, whereas that of urothelial cells failed. These findings suggest that marrow cells differentiate into smooth muscle on acellular matrix grafts in response to the environment created by SMC.