Elie Zakhem

Chitosan-based scaffolds for the support of smooth muscle constructs in intestinal tissue engineering.

Intestinal tissue engineering is an emerging field due to a growing demand for intestinal lengthening and replacement procedures secondary to massive resections of the bowel. Here, we demonstrate the potential use of a chitosan/collagen scaffold as a 3D matrix to support the bioengineered circular muscle constructs maintain their physiological functionality. We investigated the biocompatibility of chitosan by growing rabbit colonic circular smooth muscle cells (RCSMCs) on chitosan-coated plates. The cells maintained their spindle-like morphology and preserved their smooth muscle phenotypic markers. We manufactured tubular scaffolds with central openings composed of chitosan and collagen in a 1:1 ratio. Concentrically aligned 3D circular muscle constructs were bioengineered using fibrin-based hydrogel seeded with RCSMCs. The constructs were placed around the scaffold for 2 weeks, after which they were taken off and tested for their physiological functionality. The muscle constructs contracted in response to acetylcholine (Ach) and potassium chloride (KCl) and they relaxed in response to vasoactive intestinal peptide (VIP). These results demonstrate that chitosan is a biomaterial possibly suitable for intestinal tissue engineering applications.

Design Strategies of Biodegradable Scaffolds for Tissue Regeneration

There are numerous available biodegradable materials that can be used as scaffolds in regenerative medicine. Currently, there is a huge emphasis on the designing phase of the scaffolds. Materials can be designed to have different properties in order to match the specific application. Modifying scaffolds enhances their bioactivity and improves the regeneration capacity. Modifications of the scaffolds can be later characterized using several tissue engineering tools. In addition to the material, cell source is an important component of the regeneration process. Modified materials must be able to support survival and growth of different cell types. Together, cells and modified biomaterials contribute to the remodeling of the engineered tissue, which affects its performance. This review focuses on the recent advancements in the designs of the scaffolds including the physical and chemical modifications. The last part of this review also discusses designing processes that involve viability of cells.

Development of Chitosan Scaffolds with Enhanced Mechanical Properties for Intestinal Tissue Engineering Applications.

Massive resections of segments of the gastrointestinal (GI) tract lead to intestinal discontinuity. Functional tubular replacements are needed. Different scaffolds were designed for intestinal tissue engineering application. However, none of the studies have evaluated the mechanical properties of the scaffolds. We have previously shown the biocompatibility of chitosan as a natural material in intestinal tissue engineering. Our scaffolds demonstrated weak mechanical properties. In this study, we enhanced the mechanical strength of the scaffolds with the use of chitosan fibers. Chitosan fibers were circumferentially-aligned around the tubular chitosan scaffolds either from the luminal side or from the outer side or both. Tensile strength, tensile strain, and Young’s modulus were significantly increased in the scaffolds with fibers when compared with scaffolds without fibers. Burst pressure was also increased. The biocompatibility of the scaffolds was maintained as demonstrated by the adhesion of smooth muscle cells around the different kinds of scaffolds. The chitosan scaffolds with fibers provided a better candidate for intestinal tissue engineering. The novelty of this study was in the design of the fibers in a specific alignment and their incorporation within the scaffolds.

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.

Successful Treatment of Passive Fecal Incontinence in an Animal Model Using Engineered Biosphincters: A 3‐Month Follow‐Up Study

Fecal incontinence (FI) is the involuntary passage of fecal material. Current treatments have limited successful outcomes. The objective of this study was to develop a large animal model of passive FI and to demonstrate sustained restoration of fecal continence using anorectal manometry in this model after implantation of engineered autologous internal anal sphincter (IAS) biosphincters. Twenty female rabbits were used in this study. The animals were divided into three groups: (a) Non‐treated group: Rabbits underwent IAS injury by hemi‐sphincterectomy without treatment. (b) Treated group: Rabbits underwent IAS injury by hemi‐sphincterectomy followed by implantation of autologous biosphincters. (c) Sham group: Rabbits underwent IAS injury by hemi‐sphincterectomy followed by re‐accessing the surgical site followed by immediate closure without implantation of biosphincters. Anorectal manometry was used to measure resting anal pressure and recto‐anal inhibitory reflex (RAIR) at baseline, 1 month post‐sphincterectomy, up to 3 months after implantation and post‐sham. Following sphincterectomy, all rabbits had decreased basal tone and loss of RAIR, indicative of FI. Anal hygiene was also lost in the rabbits. Decreases in basal tone and RAIR were sustained more than 3 months in the non‐treated group. Autologous biosphincters were successfully implanted into eight donor rabbits in the treated group. Basal tone and RAIR were restored at 3 months following biosphincter implantation and were significantly higher compared with rabbits in the non‐treated and sham groups. Histologically, smooth muscle reconstruction and continuity was restored in the treated group compared with the non‐treated group. Results in this study provided promising outcomes for treatment of FI. Results demonstrated the feasibility of developing and validating a large animal model of passive FI. This study also showed the efficacy of the engineered biosphincters to restore fecal continence as demonstrated by manometry. Stem Cells Translational Medicine 2017;6:1795–1802

Is bioengineering a possibility in gastrointestinal disorders

The gastrointestinal (GI) tract is responsible for conducting multiple functions including motility, digestion and absorption. In gastrointestinal disorders, some of those functions are weakened or lost. Excision of the diseased segment of the GI tract is a common treatment; however, patients suffer from complications and low quality of life. Functional replacements are therefore needed to restore, repair or replace damaged parts of the tract. Tissue engineering and regenerative medicine provide an alternative approach to reconstruct different segments of the GI tract. The GI tract is a complex system with multiple cell types and layers. In previous years, bioengineering approaches focused on identifying an optimal cell source and scaffolding material to engineer GI tissues. In this editorial, we address some of our thoughts with regard to the recent discoveries in bioengineering the GI tract.

Enteric neural differentiation in innervated, physiologically functional, smooth muscle constructs is modulated by bone morphogenic protein 2 secreted by sphincteric smooth muscle cells

The enteric nervous system (ENS) controls gastrointestinal (GI) functions, including motility and digestion, which are impaired in ENS disorders. Differentiation of enteric neurons is mediated by factors released by the gut mesenchyme, including smooth muscle cells (SMCs). SMC‐derived factors involved in adult enteric neural progenitor cells (NPCs) differentiation remain elusive. Furthermore, physiologically relevant in vitro models to investigate the innervations of various regions of the gut, such as the pylorus and lower oesophageal sphincter (LES), are not available. Here, neural differentiation in bioengineered innervated circular constructs composed of SMCs isolated from the internal anal sphincter (IAS), pylorus, LES and colon of rabbits was investigated. Additionally, SMC‐derived factors that induce neural differentiation were identified to optimize bioengineered construct innervations. Sphincteric and non‐sphincteric bioengineered constructs aligned circumferentially and SMCs maintained contractile phenotypes. Sphincteric constructs generated spontaneous basal tones. Higher levels of excitatory and inhibitory motor neuron differentiation and secretion of bone morphogenic protein 2 (BMP2) were observed in bioengineered, innervated, sphincteric constructs compared to non‐sphincteric constructs. The addition of BMP2 to non‐sphincteric colonic SMC constructs increased nitrergic innervations, and inhibition of BMP2 with noggin in sphincteric constructs decreased functional relaxation. These studies provide: (a) the first bioengineered innervated pylorus and LES constructs; (b) physiologically relevant models to investigate SMCs and adult NPCs interactions; and (c) evidence of the region‐specific effects of SMCs on neural differentiation mediated by BMP2. Furthermore, this study paves the way for the development of innervated bioengineered GI tissue constructs tailored to specific disorders and locations within the gut. Copyright

Tissue Engineering and Regenerative Medicine: Gastrointestinal Application

The gastrointestinal (GI) tract is susceptible to multiple neurodegenerative diseases that can result in motility disorders. Current surgical treatments are associated with limited outcomes and high rates of morbidity. The GI tract consists of multiple cell types arranged in a specific alignment and location. Tissue engineering and regenerative medicine provide an alternative approach by taking into account the different layers of the tract. Finding a cell source is a major challenge with the autologous source remaining the ideal one. Apart from the cell source, different biomaterials are available for scaffolds fabrication. This unique combination of cells and scaffolds dictates the biocompatibility of the scaffold, cell attachment and survival, maintenance of cell phenotype, and mechanical properties of the scaffolds. All these factors are critical for successful regeneration outcomes. In this chapter, we will focus on the recent advances in the regeneration of different parts of the GI tract.The gastrointestinal (GI) tract is susceptible to multiple neurodegenerative diseases that can result in motility disorders. Current surgical treatments are associated with limited outcomes and high rates of morbidity. The GI tract consists of multiple cell types arranged in a specific alignment and location. Tissue engineering and regenerative medicine provide an alternative approach by taking into account the different layers of the tract. Finding a cell source is a major challenge with the autologous source remaining the ideal one. Apart from the cell source, different biomaterials are available for scaffolds fabrication. This unique combination of cells and scaffolds dictates the biocompatibility of the scaffold, cell attachment and survival, maintenance of cell phenotype, and mechanical properties of the scaffolds. All these factors are critical for successful regeneration outcomes. In this chapter, we will focus on the recent advances in the regeneration of different parts of the GI tract.

Advances in Neo-Innervation of the Gut

The gastrointestinal (GI) tract is a hollow organ composed of epithelial, muscular, and neural components, along with supporting cells, including interstitial cells of Cajal and endothelial cells, which cooperate to support digestion. The inner layer, or mucosa consists of epithelial cells that secrete digestive enzymes/acid, absorb nutrients, facilitate hormone secretion, and assess the luminal content of the gut. Constant sampling of luminal materials is coordinated by receptors expressed on the apical side of epithelial cells within the mucosa that can transmit signals to other systems such as the enteric nervous system and the gut immune system. The mucosa is surrounded by circular and longitudinal smooth muscle layers that promote the mechanical breakdown and propulsion of food within the GI tract, through coordinated contraction and relaxation events termed peristalsis. The neural component of the GI tract, the enteric nervous system, is an independent division of the peripheral nervous system responsible for regulating gut functions including motility, secretion, and absorption.