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

Tissue engineering of the gastrointestinal tract: the historic path to translation

The gastrointestinal (GI) tract is imperative for multiple functions including digestion, nutrient absorption, and timely waste disposal. The central feature of the gut is peristalsis, intestinal motility, which facilitates all of its functions. Disruptions in GI motility lead to sub-optimal GI function, resulting in a lower quality of life in many functional GI disorders. Over the last two decades, tissue engineering research directed towards the intestine has progressed rapidly due to advances in cell and stem-cell biology, integrative physiology, bioengineering and biomaterials. Newer biomedical tools (including optical tools, machine learning, and nuanced regenerative engineering approaches) have expanded our understanding of the complex cellular communication within the GI tract that lead to its orchestrated physiological function. Bioengineering therefore can be utilized towards several translational aspects: (i) regenerative medicine to remedy/restore GI physiological function; (ii) in vitro model building to mimic the complex physiology for drug and pharmacology testing; (iii) tool development to continue to unravel multi-cell communication networks to integrate cell and organ-level physiology. Despite the significant strides made historically in GI tissue engineering, fundamental challenges remain including the quest for identifying autologous human cell sources, enhanced scaffolding biomaterials to increase biocompatibility while matching viscoelastic properties of the underlying tissue, and overall biomanufacturing. This review provides historic perspectives for how bioengineering has advanced over time, highlights newer advances in bioengineering strategies, and provides a realistic perspective on the path to translation.

The Development of Newborn Porcine Models for Evaluation of Tissue-Engineered Small Intestine

Short bowel syndrome (SBS) is a major cause of morbidity and mortality in the pediatric population, for which treatment options are limited. To develop novel approaches for the treatment of SBS, we now focus on the development of a tissue-engineered intestine (also known as an "artificial intestine"), in which intestinal stem cells are cultured onto an absorbable bioscaffold, followed by implantation into the host. To enhance the translational potential of these preclinical studies, we have developed three clinically relevant models in neonatal piglets, which approximate the size of the human infant and were evaluated after implantation and establishment of intestinal continuity over the long term. The models included (1) a staged, multioperation approach; (2) a single operation with a de-functionalized loop of small intestine; and (3) a single operation with an intestinal bypass. The first model had complications related to multiple operations in a short time period, including surgical site infections and wound hernias. The second model avoided wound complications, but was associated with high ostomy output, local skin breakdown, and systemic dehydration with associated electrolyte imbalances. The third model was the most effective, although resulted in stoma prolapse. In summary, we have now developed and evaluated three operative methods for the long-term evaluation of the artificial intestine in the piglet, and conclude that a single operation with a de-functionalized loop of small intestine may be an optimal approach for evaluation over the long term.

Tissue engineering for the treatment of short bowel syndrome in children

Short bowel syndrome is a major cause of morbidity and mortality in children. Despite decades of experience in the management of short bowel syndrome, current therapy is primarily supportive. Definitive treatment often requires intestinal transplantation, which is associated with significant morbidity and mortality. In order to develop novel approaches to the treatment of short bowel syndrome, we and others have focused on the development of an artificial intestine, by placing intestinal stem cells on a bioscaffold that has an absorptive surface resembling native intestine, and taking advantage of neovascularization to develop a blood supply. This review will explore recent advances in biomaterials, vascularization, and progress toward development of a functional epithelium and mesenchymal niche, highlighting both success and ongoing challenges in the field.

Tissue Engineering Functional Gastrointestinal Regions: The Importance of Stem and Progenitor Cells

The intestine shows extraordinary regenerative potential that might be harnessed to alleviate numerous morbid and lethal human diseases. The intestinal stem cells regenerate the epithelium every 5 days throughout an individual's lifetime. Understanding stem-cell signaling affords power to influence the niche environment for growing intestine. The manifold approaches to tissue engineering may be organized by variations of three basic components required for the transplantation and growth of stem/progenitor cells: (1) cell delivery materials or scaffolds; (2) donor cells including adult stem cells, induced pluripotent stem cells, and in vitro expansion of isolated or cocultured epithelial, smooth muscle, myofibroblasts, or nerve cells; and (3) environmental modulators or biopharmaceuticals. Tissue engineering has been applied to the regeneration of every major region of the gastrointestinal tract from esophagus to colon, with scientists around the world aiming to carry these techniques into human therapy.

Regenerative medicine of the gastrointestinal tract

Regenerative biology/tissue engineering offers potential solutions for the repair and augmentation of diseased tissues and organs. Tissue engineering technology platforms currently under development for organ regeneration may function in part by recapitulating key mechanistic and signaling pathways associated with embryonic organogenesis. Temporal observations of observed morphological outcomes from the regeneration of tubular organs provide insights into the mechanisms of action associated with the activation of regenerative pathways in preclinical animal models and humans. These include induction of a neo-blastema, regeneration of laminarily organized mural elements (i.e., lamina propria, sub-mucosa, and muscularis), and formation of context appropriate transitional junctions at the point of anastomosis with other tissue elements. These results provide the foundation for a regenerative technology applicable to hollow organs of the gastrointestinal (GI) tract including esophagus and small intestine. Factors affecting the efficacy of observed regenerative outcomes within the GI tract include the roles of vascularization, innervations, and mesenchymal signaling. These will be discussed in the context of an overall mechanism of adult regeneration potentially applicable by the tissue engineering and regenerative medicine industry for continued development of hollow neo-organ products.

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.

Regeneration of rodent small intestine tissue following implantation of scaffolds seeded with a novel source of smooth muscle cells

Aims: To apply an organ regeneration platform technology of autologous smooth muscle cell/biomaterial combination products, previously demonstrated to be successful for urinary tissue regeneration, to the regeneration of the small intestine. Materials & methods: Patch and tubular constructs were implanted in rodent small intestines and histologically evaluated over a time course for evidence of regeneration of the laminarly organized neo-mucosa and muscle layers. Results: Laminarly organized neo-mucosa and muscle layer bundles are demonstrated as early as 8 weeks postimplantation. Conclusion: An organ regeneration technology platform of autologous smooth muscle cell/biomaterial combination products can be extended to the regeneration of the small intestine.

Tissue engineering: current strategies and future directions

Novel therapies resulting from regenerative medicine and tissue engineering technology may offer new hope for patients with injuries, end-stage organ failure, or other clinical issues. Currently, patients with diseased and injured organs are often treated with transplanted organs. However, there is a shortage of donor organs that is worsening yearly as the population ages and as the number of new cases of organ failure increases. Scientists in the field of regenerative medicine and tissue engineering are now applying the principles of cell transplantation, material science, and bioengineering to construct biological substitutes that can restore and maintain normal function in diseased and injured tissues. In addition, the stem cell field is a rapidly advancing part of regenerative medicine, and new discoveries in this field create new options for this type of therapy. For example, new types of stem cells, such as amniotic fluid and placental stem cells that can circumvent the ethical issues associated with embryonic stem cells, have been discovered. The process of therapeutic cloning and the creation of induced pluripotent cells provide still other potential sources of stem cells for cell-based tissue engineering applications. Although stem cells are still in the research phase, some therapies arising from tissue engineering endeavors that make use of autologous, adult cells have already entered the clinical setting, indicating that regenerative medicine holds much promise for the future.

Scaffold Characteristics for Functional Hollow Organ Regeneration

Many medical conditions require surgical reconstruction of hollow organs. Tissue engineering of organs and tissues is a promising new technique without harvest site morbidity. An ideal biomaterial should be biocompatible, support tissue formation and provide adequate structural support. It should degrade gradually and provide an environment allowing for cell-cell interaction, adhesion, proliferation, migration, and differentiation. Although tissue formation is feasible, functionality has never been demonstrated. Mainly the lack of proper innervation and vascularisation are hindering contractility and normal function. In this chapter we critically review the current state of engineering hollow organs with a special focus on innervation and vascularisation.

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.

Intrathoracic esophageal replacement by in situ tissue-engineered esophagus

OBJECTIVE

This study aimed to evaluate in situ tissue-engineered esophagus in a canine model after experimental resection and replacement of a full circumferential defect of the intrathoracic esophagus.

METHODS

Two types of scaffolding were fabricated. In the KF(+) group (n = 6), oral keratinocytes and fibroblasts cultured on human amniotic membrane were sheeted on polyglycolic acid felt with smooth muscle tissue and were then rolled around tubes. In the KF(-) group (n = 6), the same procedure was followed, but the keratinocytes and fibroblasts were omitted. Both scaffolds were wrapped in omentum and implanted in the abdomen. In the KF(+) group, at 3 weeks after implantation, the scaffold developed into a tube with a well-differentiated lumen of stratified squamous cells surrounded by a thick smooth muscle-like tissue (in situ tissue-engineered esophagus). A part of the esophagus was resected and replaced by the graft in the same dogs.

RESULTS

In the KF(-) group, strictures developed after esophageal replacement, with almost complete obstruction within 2 to 3 weeks. In contrast, in the KF(+) group, the in situ tissue-engineered esophagus showed good distensibility and the dogs remained without feeding problems through 420 days. Esophageal peristalsis transferred food to the stomach, despite the absence of peristaltic activity in the in situ tissue-engineered esophagus itself. The thickness of the squamous epithelial layer and the smooth muscle layer of the in situ tissue-engineered esophagus were similar to that of the adjacent native esophagus.

CONCLUSION

The in situ tissue-engineered esophagus can successfully replace the intrathoracic esophagus, and this procedure may offer a promising surgical approach to esophageal diseases.