Studies of brush border enzymes, basement membrane components, and electrophysiology of tissue-engineered neointestine

3D printing of polylactic acid: recent advances and opportunities

Bio-based polymers are a class of polymers made by living organisms, a few of them known and commercialized yet. Due to poor mechanical strength and economic constraints, they have not yet seen the extensive application. Instead, they have been an appropriate candidate for biological applications. Growing consumer knowledge of the environmental effect of polymers generated from petrochemical sources and a worldwide transition away from plastics with a lifespan of hundreds of years has resulted in greater interest in such hitherto unattainable sectors. Bio-based polymers come in various forms, including direct or "drop-in" replacements for their petrochemical counterparts with nearly identical properties or completely novel polymers that were previously unavailable, such as polylactide. Few of these bio-based polymers offer significantly improved technical specifications than their alternatives. Polylactic acid (PLA) has been well known in the last decade as a biodegradable thermoplastic source for use in 3DP by the "fused deposition modeling" method. The PLA market is anticipated to accomplish 5.2 billion US dollars in 2020 for its industrial usage. Conversely, 3DP is one of the emerging technologies with immense economic potential in numerous sectors where PLA is one of the critical options as the polymer source due to its environmentally friendly nature, glossiness, multicolor appearance, and ease of printing. The chemical structure, manufacturing techniques, standard features, and current market situation of PLA were examined in this study. This review looks at the process of 3DP that uses PLA filaments in extrusion-based 3DP technologies in particular. Several recent articles describing 3D-printed PLA items have been highlighted.

Applications of PLA in modern medicine

Polylactic acid (PLA) is a versatile biopolymer. PLA is synthesized with ease from abundant renewable resources and is biodegradable. PLA has shown promise as a biomaterial in a plethora of healthcare applications such as tissue engineering or regenerative medicine, cardiovascular implants, dental niches, drug carriers, orthopedic interventions, cancer therapy, skin and tendon healing, and lastly medical tools / equipment. PLA has demonstrated instrumental importance as a three-dimensionally (3D) printable biopolymer, which has further been bolstered by its role during the Coronavirus Disease of 2019 (Covid-19) global pandemic. As an abundant filament, PLA has created desperately needed personal protective equipment (PPE) and ventilator modifications. As polymer chemistry continues to advance, so too will the applications and continued efficacy of PLA-based modalities.

Repair and regeneration of small intestine: A review of current engineering approaches

The small intestine (SI) is difficult to regenerate or reconstruct due to its complex structure and functions. Recent developments in stem cell research, advanced engineering technologies, and regenerative medicine strategies bring new hope of solving clinical problems of the SI. This review will first summarize the structure, function, development, cell types, and matrix components of the SI. Then, the major cell sources for SI regeneration are introduced, and state-of-the-art biofabrication technologies for generating engineered SI tissues or models are overviewed. Furthermore, in vitro models and in vivo transplantation, based on intestinal organoids and tissue engineering, are highlighted. Finally, current challenges and future perspectives are discussed to help direct future applications for SI repair and regeneration.

Effect of peristaltic-like movement on bioengineered intestinal tube

The intestine is a highly heterogeneous hollow organ with biological, mechanical and chemical differences between lumen and wall. A functional human intestine model able to recreate the in vivo dynamic nature as well as the native tissue morphology is demanded for disease research and ​drug discovery. Here, we present a system, which combines an engineered three-dimensional (3D) tubular-shaped intestine model (3D In-tube) with a custom-made microbioreactor to impart the key aspects of the in vivo microenvironment of the human intestine, mimicking the rhythmic peristaltic movement. We adapted a previously established bottom-up tissue engineering approach, to produce the 3D tubular-shaped lamina propria and designed a glass microbioreactor to induce the air-liquid interface ​condition and peristaltic-like motion. Our results demonstrate the production of a villi-like protrusion and a correct spatial differentiation of the intestinal epithelial cells in enterocyte-like as well as mucus-producing-like cells on the lumen side of the 3D In-tube. This dynamic platform offers a proof-of-concept model of the human intestine.

Intestinal Crypt Organoid: Isolation of Intestinal Stem Cells, In Vitro Culture, and Optical Observation

The isolation and culture of intestinal stem cells (ISCs) was first demonstrated in the very recent decade with the identification of ISC marker Lgr5. The growth of ISCs into crypt organoids provides an in vitro model for studying the mucosal physiology, intestinal cancer tumorigenesis, and intestinal regeneration. Here, we describe two different isolation protocols and demonstrate a fixation method that aids in the confocal observation of the organoids.

Critical intestinal cells originate from the host in enteroid-derived tissue-engineered intestine

BACKGROUND

Enteroid-derived tissue-engineered intestine (TEI) contains intestinal subepithelial myofibroblasts (ISEMFs) and smooth muscle cells (SMCs). However, these cell types are not present in the donor enteroids. We sought to determine the origin of these cell types and to quantify their importance in TEI development.

MATERIALS AND METHODS

Crypts from pan-EGFP or LGR5-EGFP mice were used for enteroid culture and subsequent implantation for the production of TEI. TEI from pan-EGFP enteroids was labeled for smooth muscle alpha actin (SMA) to identify ISEMFs and SMCs and green fluorescent protein (GFP) to identify cells from pan-EGFP enteroids. Fluorescence in situ hybridization (FISH) for the Y chromosome was applied to TEI from male LGR5-EGFP enteroids implanted into female nonobese diabetic/severe combined immunodeficiency mice. To identify chemotactic effects of intestinal epithelium on ISEMFs, a Boyden chamber assay was performed.

RESULTS

Immunofluorescence of TEI from pan-EGFP enteroids revealed GFP-positive epithelium with surrounding SMA positivity and no colocalization of the two. FISH of TEI from male LGR5-EGFP enteroids implanted into female nonobese diabetic/severe combined immunodeficiency mice revealed that only the epithelium was Y chromosome positive. Chemotactic assays demonstrated increased ISEMF migration in the presence of enteroids (983 ± 133) compared to that in the presence of either Matrigel alone (357 ± 36) or media alone (339 ± 24; P ≤ 0.05).

CONCLUSIONS

Lack of GFP/SMA colocalization suggests that ISEMFs and SMCs are derived from host animals. This was confirmed by FISH which identified only epithelial cells as being male. All other cell types originated from host animals. The mechanism by which these cells are recruited is unknown; however, Boyden chamber assays indicate a direct chemotactic effect of intestinal epithelium on ISEMFs.

Advancing Intestinal Organoid Technology Toward Regenerative Medicine

With the emergence of technologies to culture intestinal epithelial cells in vitro as various forms of intestinal organoids, there is growing interest in using such cultured intestinal cells as a source for tissue engineering and regenerative medicine. One such approach would be to combine the organoid technology with methodologies to engineer the culture environment, particularly the three-dimensional scaffold materials, to generate intestines that exquisitely recapitulate their original structures and functions. Another approach to use organoids for regenerative medicine would be to urge them to mature into functional intestines by implanting them into hosts. This process includes the tissue-engineered small intestine that uses synthetic scaffolds for tissue regeneration and direct organoid transplantation that takes advantage of submucosal tissues in the native intestines as a scaffold. Further study in these subfields could lead to the development of therapeutic options to use different types of organoids with various cell types in regenerative medicine for intestinal diseases in humans.

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.

Distinct intestinal adaptation for vitamin B12 and bile acid absorption revealed in a new mouse model of massive ileocecal resection

Ileocecal resection (ICR), one of several types of intestinal resection that results in short bowel syndrome (SBS), causes severe clinical disease in humans. We here describe a mouse model of massive ICR in which 75% of the distal small intestine is removed. We demonstrate that mice underwent 75% ICR show severe clinical signs and high mortality, which may recapitulate severe forms of human SBS, despite an adaptive response throughout the remnant intestine. By using this model, we also investigated whether the epithelium of the remnant intestine shows enhanced expression of factors involved in region-specific functions of the ileum. Cubn mRNA and its protein product, which play an essential role in vitamin B12 absorption in the ileum, are not compensatory up-regulated in any part of the remnant intestine, demonstrating a clear contrast with post-operative up-regulation of genes involved in bile acid absorption. Our study suggests that functional adaptation by phenotypical changes in the intestinal epithelium is not a general feature for nutrient absorption systems that are confined to the ileum. We also propose that the mouse model developed in this study will become a unique system to facilitate studies on SBS with ICR in humans.

Summary: Genes involved in region-specific functions of the distal small intestine show distinct adaptive response following massive ileocecal resection in mice.

Bone Graft Prefabrication Following the In Vivo Bioreactor Principle

Large bone defect treatment represents a great challenge due to the difficulty of functional and esthetic reconstruction. Tissue-engineered bone grafts created by in vitro manipulation of bioscaffolds, seed cells, and growth factors have been considered potential treatments for bone defect reconstruction. However, a significant gap remains between experimental successes and clinical translation. An emerging strategy for bridging this gap is using the in vivo bioreactor principle and flap prefabrication techniques. This principle focuses on using the body as a bioreactor to cultivate the traditional triad (bioscaffolds, seed cells, and growth factors) and leveraging the body's self-regenerative capacity to regenerate new tissue. Additionally, flap prefabrication techniques allow the regenerated bone grafts to be transferred as prefabricated bone flaps for bone defect reconstruction. Such a strategy has been used successfully for reconstructing critical-sized bone defects in animal models and humans. Here, we highlight this concept and provide some perspective on how to translate current knowledge into clinical practice.

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The in vivo bioreactor principle and flap prefabrication technique is a promising strategy for bone defect reconstruction.

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The in vivo bioreactor principle focuses on using the body’s self-regenerative capacity to regenerate new tissue.

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This strategy has been successfully used to reconstruct critical-sized bone defects in humans.

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.

Production of tissue-engineered intestine from expanded enteroids

BACKGROUND

Short bowel syndrome is a life-threatening condition with few solutions. Tissue-engineered intestine (TEI) is a potential treatment, but donor intestine is a limiting factor. Expanded epithelial surrogates termed enteroids may serve as a potential donor source.

MATERIALS AND METHODS

To produce TEI from enteroids, crypts were harvested from mice and enteroid cultures established. Enteroids were seeded onto polymer scaffolds using Matrigel or culture medium and implanted in immunosuppressed mice for 4 wk. Histology was analyzed using Periodic acid-Schiff staining and immunofluorescence. Neomucosa was quantified using ImageJ software. To determine whether TEI could be produced from enteroids established from small intestinal biopsies, 2 × 2-mm pieces of jejunum were processed for enteroid culture, enteroids were expanded and seeded onto scaffolds, and scaffolds implanted for 4 wk.

RESULTS

Enteroids in Matrigel produced TEI in 15 of 15 scaffolds, whereas enteroids in medium produced TEI in 9 of 15 scaffolds. Use of Matrigel led to more neomucosal surface area compared to media (10,520 ± 2905 μm versus 450 ± 127 μm, P < 0.05). Histologic examination confirmed the presence of crypts and blunted villi, normal intestinal epithelial lineages, intestinal subepithelial myofibroblasts, and smooth muscle cells. Crypts obtained from biopsies produced an average of 192 ± 71 enteroids. A single passage produced 685 ± 58 enteroids, which was adequate for scaffold seeding. TEI was produced in 8 of 9 scaffolds seeded with expanded enteroids.

CONCLUSIONS

Enteroids can be obtained from minimal starting material, expanded ex vivo, and implanted to produce TEI. This method shows promise as a solution to the limited donor intestine available for TEI production in patients with short bowel syndrome.

Considering new methodologies in strategies for safety assessment of foods and food ingredients

Toxicology and safety assessment are changing and require new strategies for evaluating risk that are less depending on apical toxicity endpoints in animal models and relying more on knowledge of the mechanism of toxicity. This manuscript describes a number of developments that could contribute to this change and implement this in a stepwise roadmap that can be applied for the evaluation of food and food ingredients. The roadmap was evaluated in four case studies by using literature and existing data. This preliminary evaluation was shown to be useful. However, this experience should be extended by including examples where experimental work needs to be included. To further implement these new insights in toxicology and safety assessment for the area of food and food ingredients, the recommendation is that stakeholders take action in addressing gaps in our knowledge, e.g. with regard to the applicability of the roadmap for mixtures and food matrices. Further development of the threshold of toxicological concern is needed, as well as cooperation with other sectors where similar schemes are under development. Moreover, a more comprehensive evaluation of the roadmap, also including the identification of the need for in vitro experimental work is recommended.

Human and mouse tissue-engineered small intestine both demonstrate digestive and absorptive function

Short bowel syndrome (SBS) is a devastating condition in which insufficient small intestinal surface area results in malnutrition and dependence on intravenous parenteral nutrition. There is an increasing incidence of SBS, particularly in premature babies and newborns with congenital intestinal anomalies. Tissue-engineered small intestine (TESI) offers a therapeutic alternative to the current standard treatment, intestinal transplantation, and has the potential to solve its biggest challenges, namely donor shortage and life-long immunosuppression. We have previously demonstrated that TESI can be generated from mouse and human small intestine and histologically replicates key components of native intestine. We hypothesized that TESI also recapitulates native small intestine function. Organoid units were generated from mouse or human donor intestine and implanted into genetically identical or immunodeficient host mice. After 4 wk, TESI was harvested and either fixed and paraffin embedded or immediately subjected to assays to illustrate function. We demonstrated that both mouse and human tissue-engineered small intestine grew into an appropriately polarized sphere of intact epithelium facing a lumen, contiguous with supporting mesenchyme, muscle, and stem/progenitor cells. The epithelium demonstrated major ultrastructural components, including tight junctions and microvilli, transporters, and functional brush-border and digestive enzymes. This study demonstrates that tissue-engineered small intestine possesses a well-differentiated epithelium with intact ion transporters/channels, functional brush-border enzymes, and similar ultrastructural components to native tissue, including progenitor cells, whether derived from mouse or human cells.

Short bowel syndrome in children: surgical and medical perspectives

The main cause of intestinal failure in children is due to short bowel syndrome (SBS) resulting from congenital or acquired intestinal lesions. From the first lengthening procedure introduced by Bianchi, the last three decades have seen lengthening procedures established as fundamental components of multidisciplinary intestinal rehabilitation programs. Debate on indications and timing of the procedures is still open leaving SBS surgical treatment a great challenge. However, enteral autonomy is possible only with an individualized approach remembering that each SBS patient is unique. Current literature on autologous gastrointestinal reconstruction technique was reviewed aiming to assess a comprehensive pathway in SBS non-transplant management.

Stem cells and biopharmaceuticals: vital roles in the growth of tissue-engineered small intestine

Tissue engineering currently constitutes a complex, multidisciplinary field exploring ideal sources of cells in combination with scaffolds or delivery systems in order to form a new, functional organ to replace native organ lack or loss. Short bowel syndrome (SBS) is a life-threatening condition with high morbidity and mortality rates in children. Current therapeutic strategies consist of costly and risky allotransplants that demand lifelong immunosuppression. A promising alternative is the implantation of autologous organoid units (OU) to create a tissue-engineered small intestine (TESI). This strategy is proven to be stem cell and mesenchyme dependent. Intestinal stem cells (ISCs) are located at the base of the crypt and are responsible for repopulating the cycling mucosa up to the villus tip. The stem cell niche governs the biology of ISCs and, together with the rest of the epithelium, communicates with the underlying mesenchyme to sustain intestinal homeostasis. Biopharmaceuticals are broadly used in the clinic to activate or enhance known signaling pathways and may greatly contribute to the development of a full-thickness intestine by increasing mucosal surface area, improving blood supply, and determining stem cell fate. This review will focus on tissue engineering as a means of building the new small intestine, highlighting the importance of stem cells and recombinant peptide growth factors as biopharmaceuticals.

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.

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.

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.

Cell transplantation in surgical treatment of familial adenomatous polyposis coli

We developed a method of surgical treatment of familial adenomatous polyposis coli giving an opportunity to prevent the growth of new polyps in the preserved part of the rectum and consisting in transplantation of fetal cells of the epithelial origin into the rectum wall after mucosectomy. Since the rectum is partially preserved, ileorectal anastomosis can be formed after colectomy, which preserves natural bowel passage. Complex examination 4 weeks after surgery revealed the formation of normal rectal mucosa. No new polyps were detected in the rectum 1-3 years after surgery.

Tissue engineering in the development of replacement technologies

The field of tissue engineering is generating new scaffolds, bioreactors and methods for stimulating cells within complex cultures, with the aim of recreating the conditions under which cells form functional tissues. Hitherto, the primary focus of this field has been on clinical applications. However, there are many methods of in vitro tissue engineering that represent new opportunities in 3D cell culture and could be the basis for new replacement methods that either replace the use of a tissue isolated from an animal or the use of a living animal. This chapter presents an overview of tissue engineering and provides tissue-specific examples of recent advances.

Tissue engineering and regenerative medicine research perspectives for pediatric surgery

Tissue engineering and regenerative medicine research is being aggressively pursued in attempts to develop biological substitutes to replace lost tissue or organs. Remarkable degrees of success have been achieved in the generation of a variety of tissues and organs as a result of concerted contributions by multidisciplinary groups in the field of biotechnology. Engineering of an organ is a complex process which is initiated by appropriate sourcing of cells and their controlled proliferation to achieve critical numbers for seeding on biodegradable scaffolds in order to create cell-scaffold constructs, which are thereafter maintained in bioreactors to generate tissues identical to those required for replacement. Extensive efforts in understanding the characteristics of cells and their interaction with specifically tailored scaffolds holds the key to their attachment, controlled proliferation and differentiation, intercommunication, and organization to form tissues. The demand for tissue-engineered organs is enormous and this technology holds the promise to supply customized organs to overcome the severe shortages that are currently faced by the pediatric patient, especially due to organ-size mismatch. The contemporary state of tissue-engineering technology presented in this review summarizes the advances in the various areas of regenerative medicine and addresses issues that are associated with its future implementation in the pediatric surgical patient.

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.

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.

Dental-derived Stem Cells and whole Tooth Regeneration: an Overview

The need for new dental tissue-replacement therapies is evident in recent reports which reveal startling statistics regarding the high incidence of tooth decay and tooth loss. Recent advances in the identification and characterization of dental stem cells, and in dental tissue-engineering strategies, suggest that bioengineering approaches may successfully be used to regenerate dental tissues and whole teeth. Interest in dental tissue-regeneration applications continues to increase as clinically relevant methods for the generation of bioengineered dental tissues, and whole teeth, continue to improve. This paper is concerned about dental-derived stem cells and their characterization. Additionally, since conventional dental treatments partially serve the purpose for replacing missing teeth and always include possible failure rates, the potential of dental-derived stem cells in promoting whole tooth regeneration is also discussed.

KEYWORDS

Dental stem cells; Tissue engineering; Tooth regeneration.

Intestinal smooth muscle cell maintenance by basic fibroblast growth factor

Intestinal tissue engineering is a potential therapy for patients with short bowel syndrome. Tissue engineering scaffolds that promote smooth muscle cell proliferation and angiogenesis are essential toward the regeneration of functional smooth muscles for peristalsis and motility. Since basic fibroblast growth factor (bFGF) can stimulate smooth muscle proliferation and angiogenesis, the delivery of bFGF was employed to stimulate proliferation and survival of primary intestinal smooth muscle cells. Two methods of local bFGF delivery were examined: the incorporation of bFGF into the collagen coating and the encapsulation of bFGF into poly(D,L-lactic-co-glycolic acid) microspheres. Cell-seeded scaffolds were implanted into the omentum and were retrieved after 4, 14, and 28 days. The seeded cells proliferated from day 4 to day 14 in all implants; however, at 28 days, significantly higher density of implanted cells and blood vessels was observed, when 10 microg of bFGF was incorporated into the collagen coating of scaffolds as compared to scaffolds with either no bFGF or 1 microg of bFGF in collagen. Microsphere encapsulation of 1 microg of bFGF produced similar effects as 10 microg of bFGF mixed in collagen and was more effective than the delivery of 1 microg of bFGF by collagen incorporation. The majority of the implanted cells also expressed alpha-smooth muscle actin. Scaffolds coated with microsphere-encapsulated bFGF and seeded with smooth muscle cells may be a useful platform for the regeneration of the intestinal smooth muscle.

Intestinal tissue engineering: where do we stand?

Tissue engineering has revolutionized the medical field by giving us the hope of generating alternative human tissues that could replace diseased ones. On this front, the generation of tissue-engineered neo-intestine in animal models has been a great endeavor with the ultimate goal of replacing the diseased gut or to treat short gut syndrome. Although this field and the generated neo-intestine are still in their infancy, this idea is so attractive that it has fascinated all medical personnel including gastroenterologists and gastrointestinal surgeons. We herein introduce the salient features of a tissue-engineered intestine, the hopes associated with it, and the few practical constraints in developing a "mature" human tissue-engineered intestine, which would be sufficient to treat short gut syndrome.

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.

The effect of sustained delivery of vascular endothelial growth factor on angiogenesis in tissue-engineered intestine

Our group has previously created a functional neointestine that is capable of restoring absorptive function. However, the endogenous level of vascular endothelial growth factor (VEGF) is markedly reduced in the construct compared to native bowel. Therefore, we wanted to locally deliver VEGF in a sustained fashion to upregulate angiogenesis in the neointestine. Rat recombinant VEGF was encapsulated in poly(lactide-co-glycolide) microspheres by a double emulsion method. Release kinetics and bioactivity were determined in vitro. Tissue-engineered intestine was generated by seeding donor neonatal rat intestinal organoid units onto a biodegradable polyglycolic acid scaffold along with VEGF-containing or empty microspheres, and wrapped in the omentum of recipient rats. After 4 weeks, the neointestinal cysts were analyzed for morphometry, VEGF levels, epithelial proliferation, and capillary density. Sustained release of biologically active VEGF was confirmed by in vitro studies. Intestinal constructs with VEGF microspheres were significantly larger than those containing empty microspheres. Tissue VEGF levels were significantly higher in neointestine loaded with encapsulated VEGF compared to those without growth factor. Epithelial cellular proliferation and capillary density were significantly increased in the VEGF-containing neointestinal constructs compared to empty constructs. Tissue-engineered intestine responds to sustained delivery of VEGF by upregulating microvasculature and epithelial proliferation.

Prolonged Maintenance of Neointestine Using Subcutaneously Implanted Tubular Scaffolds in a Rat Model

Tissue-engineered small intestine offers a possible alternative to long-term parenteral nutrition or intestinal transplantation in patients with short bowel syndrome. The aim of this study was to investigate the prolonged development of neointestine grown on subcutaneously implanted scaffolds. Tubular polylactide-coglycolide (PLGA) scaffolds were implanted into adult Lewis rats. Four weeks after scaffold implantation, a suspension of organoid units was delivered to the lumen of each scaffold. Organoid units were manufactured from small intestine harvested from neonatal Lewis rats by partial digestion using collagenase and dispase. Scaffolds were removed at 4, 8, and 12 weeks after organoid unit implantation, processed to paraffin, and sectioned. Hematoxylin and eosin staining demonstrated well-developed and well-differentiated intestinal mucosa and a vascularised submucosa within the scaffolds at 4, 8, and 12 weeks. Appearances were similar to native small intestine. Immunohistochemistry performed using primary antibody against proliferating cell nuclear antigen, a marker for cellular proliferation, demonstrated positively staining cells within the mucosa and submucosa at all time points. In the mucosal layer these positively staining cells were found primarily in the crypts. These findings show that neointestinal mucosa can be maintained for at least 12 weeks on a subcutaneous PLGA scaffold, and the presence of actively proliferating cells at 12 weeks suggests potential for further development beyond this.

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.

Tissue-engineered small intestine improves recovery after massive small bowel resection

OBJECTIVE

Rescue with tissue-engineered small intestine (TESI) after massive small bowel resection (MSBR).

SUMMARY BACKGROUND DATA

Short bowel syndrome is a morbid product of massive small bowel resection. We report the first replacement of a vital organ by tissue engineering with TESI after MSBR.

METHODS

Ten male Lewis rats underwent TESI implantation with green fluorescent protein (GFP)-marked cells (TESI+, n = 5) or sham laparotomy (TESI-, n = 5) followed by MSBR. Side-to-side anastomosis of TESI to proximal small intestine was performed or omitted. TESIO animals underwent implantation of engineered intestine with no further surgery. Weights were measured QOD until day 40. Transit times were measured. DNA assay was performed with computer morphometry. Northern blots of RNA were probed for intestinal alkaline phosphatase (IAP) and villin. Hematoxylin and eosin, S100, and smooth muscle actin immunohistochemistry were performed. Blood was collected at sacrifice.

RESULTS

All 10 rats initially lost then regained weight. The initial rate of weight loss was higher in TESI+ versus TESI-, but the nadir was reached a week earlier with more rapid weight gain subsequently to 98% preoperative weight on day 40 in animals with engineered intestine versus 76% (P < 0.03). Serum B12 was higher at 439 pg/mL versus 195.4 pg/mL. IAP mRNA appeared greater in TESI+ than TESIO, with constant villin levels. Histology revealed appropriate architecture including nerve. GFP labeling persisted.

CONCLUSIONS

Anastomosis of TESI significantly improved postoperative weight and B12 absorption after MSBR. IAP, a marker of differentiation in intestinal epithelium, is present in TESI, and GFP labeling was accomplished.

Surgical therapy for short bowel syndrome

Patients with short bowel syndrome (SBS) suffer tremendous morbidity secondary to prolonged hospitalization and chronic parenteral nutrition (TPN). Overall, the majority of infants will adapt and ultimately become independent of TPN, but this process may require many months or years. Reasons for continued TPN dependency include bowel dysmotility, bacterial overgrowth, insufficient adaptation, or very short bowel length. It is this subpopulation of patients who may benefit from surgical procedures that optimize intestinal adaptation and increase the mucosal absorptive surface area. The goal of this review article is to summarize the process of intestinal adaptation and then to outline the surgical principles and techniques available to surgeons who treat this complicated group of patients.

Bioengineered teeth from cultured rat tooth bud cells

The recent bioengineering of complex tooth structures from pig tooth bud tissues suggests the potential for the regeneration of mammalian dental tissues. We have improved tooth bioengineering methods by comparing the utility of cultured rat tooth bud cells obtained from three- to seven-day post-natal (dpn) rats for tooth-tissue-engineering applications. Cell-seeded biodegradable scaffolds were grown in the omenta of adult rat hosts for 12 wks, then harvested. Analyses of 12-week implant tissues demonstrated that dissociated 4-dpn rat tooth bud cells seeded for 1 hr onto PGA or PLGA scaffolds generated bioengineered tooth tissues most reliably. We conclude that tooth-tissue-engineering methods can be used to generate both pig and rat tooth tissues. Furthermore, our ability to bioengineer tooth structures from cultured tooth bud cells suggests that dental epithelial and mesenchymal stem cells can be maintained in vitro for at least 6 days.

Animal models for intestinal tissue engineering

Although total parenteral nutrition prevents patients with short bowel syndrome from dying of starvation, having short bowel remains a severely debilitating condition. The best current treatment for inadequate absorptive surface area is through intestinal transplantation. However, this therapy is associated with significant morbidity and patients suffer from consequences of long-term immunosuppression. Additionally, the numbers of organs are limited. A new frontier in medicine is the field of tissue engineering. We will review the progress of intestinal bioengineering with a focus on the use of animal models. Investigators initially used autologous tissue as a patch to study intestinal regeneration. Subsequent studies focused on the use of absorbable biomaterials as a patch for tissue ingrowth. The most novel methodology consists of seeding a resorbable scaffold and implanting this construct to observe the regeneration of neointestine. Successful creation of esophagus, stomach, small bowel and colon has been demonstrated. Although these studies are preliminary, the results suggest that tissue-engineered intestine will become a real therapeutic option in the not too distant future for patients with inadequate intestinal tissue.

Intestinal tissue engineering: from regenerative medicine to model systems

BACKGROUND

Tissue engineering is a rapidly emerging field that combines the established disciplines of engineering, biology, and medicine with the goal of fabricating viable tissues and organs. Although initially targeted for applications in regenerative medicine, a novel application of this technology has been to generate experimental model systems for studying biological mechanisms and testing the efficacy of potential therapies.

METHODS

Review and analysis of the literature.

RESULTS AND CONCLUSION

We present the limitations of existing models and provide examples of how tissue engineering has allowed for the generation of new models that may overcome these limitations.

Lymphangiogenesis in tissue-engineered small intestine

BACKGROUND

Lymphangiogenesis, the formation of lymphatic vessels, has not been reported in engineered tissue. The purpose of this study was to characterize lymphangiogenesis in tissue-engineered small intestine.

METHODS

Biodegradable polymer scaffolds seeded with intestinal organoid units were implanted into syngenic recipient rats. Twenty-three neointestinal grafts were harvested from adult rat recipients 1 to 8 weeks postimplantation. Cells expressing the lymphatic endothelial marker vascular endothelial growth factor receptor (VEGFR)-3 were detected immunohistochemically. The lymphangiogenic growth factor VEGF-C was quantified by enzyme-linked immunoadsorbent assay.

RESULTS

Between the first and eighth weeks, neointestinal cysts increased in volume and mass. Muscular and mucosal layers increased in thickness and developed to resemble normal intestine histologically. The proportion of neointestinal VEGFR-3-positive cells increased and ultimately, tubular structures developed that resembled lymphatics architecturally, were distinct from CD34-positive blood vessels, and lacked luminal erythrocytes.

CONCLUSION

Lymphangiogenesis occurs in tissue-engineered small intestine. This is the first demonstration of lymphatic vessels in an engineered tissue.

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.

Tissue engineering in surgery

The demands for repair and renewal of worn out or injured human tissue continue to increase and it is now apparent that this demand cannot be met from human donors. A partial solution may be found in living related and trans-species transplantation but these approaches invoke the problems of disease transfer and ethical dilemmas. Tissue engineering is a new technology that seeks to meet these increasing demands by utilising novel cell culture methods in vitro to provide tissue replacements in vivo. This article reviews the current state of tissue engineering and its potential for use in surgery.

Tissue engineering of the gastrointestinal tract for surgical replacement: a nutrition tool of the future?

Optimal nutrition depends on the multiple complex functions performed by the gastrointestinal tract, which range from basic functions such as storage, conduit and mechanical processing to more finely regulated capabilities such as vectorial transport, immune defence and cell signalling. Surgical strategies to supply lacking gastrointestinal tract tissues have relied on either replacement by proxy (surgical substitution) or the introduction of prostheses. Tissue engineering seeks to replace missing tissues with engineered tissues that more accurately reproduce the native physiological and anatomical milieu. It is now possible to engineer several areas of the gastrointestinal tract with high fidelity, and to employ tissue-engineered bowel in replacement in animal models. These replacement models have reflected excellent anatomical and physiological recapitulation of native bowel by the tissue-engineered constructs in vivo.

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.

Tissue-engineered neomucosa: morphology, enterocyte dynamics, and SGLT1 expression topography

BACKGROUND

The standard therapy for short bowel syndrome is total parenteral nutrition, which is expensive and associated with significant morbidity and mortality. New therapeutic approaches for this disorder are needed. We have applied the techniques of tissue engineering to develop a prototype neointestine. We hypothesized that anastomosis of this neointestine to the native bowel would result in regeneration of mucosal morphology and enterocyte dynamics.

METHODS

Biodegradable polymers seeded with neonatal rat intestinal organoid units were implanted into the omenta of adult rats to form neointestinal cysts. Five weeks after implantation, side-to-side cyst-jejunal anastomoses were fashioned in one cohort of rats. Tissues were harvested from all rats at 5 months after implantation. Native jejunal (J) and non-anastomosed (N-N) and anastomosed (A-N) neointestinal tissues were assessed for morphology, epithelial cell proliferation (5-bromo-2-deoxyuridine immunohistochemistry), apoptotic rates (terminal deoxynucleotide transferase-mediated dUTP nick-end labeling assay), and SGLT1 in situ hybridization.

RESULTS

Mucosal morphology, rates and topography of enterocyte proliferation, and transporter expression in A-N neointestine recapitulated those of native jejunum. Each of these features was rudimentary in N-N neointestine.

CONCLUSIONS

These results suggest that the tissue-engineered neomucosa can develop structural and dynamic features of the normal jejunum. Anastomosis to the native intestine is an essential step for neomucosal development. Tissue engineering offers promise as a novel approach to the treatment of patients suffering from short bowel syndrome.