Tubular organ epithelialisation

Assembly of Rolled-Up Collagen Constructs on Porous Alumina Textiles

Developing new techniques to prepare free-standing tubular scaffolds has always been a challenge in the field of regenerative medicine. Here, we report a new and simple way to prepare free-standing collagen constructs with rolled-up architecture by self-assembling nanofibers on porous alumina (Al2O3) textiles modified with different silanes, carbon or gold. Following self-assembly and cross-linking with glutaraldehyde, collagen nanofibers spontaneously rolled up on the modified Al2O3 textiles and detached. The resulting collagen constructs had an inner diameter of approximately 2 to 4 mm in a rolled-up state and could be easily detached from the underlying textiles. Mechanical testing of wet collagen scaffolds following detachment yielded mean values of 3.5 ± 1.9 MPa for the tensile strength, 41.0 ± 20.8 MPa for the Young's modulus and 8.1 ± 3.7% for the elongation at break. No roll-up was observed on Al2O3 textiles without any modification, where collagen did not assemble into fibers, either. Blends of collagen and chitosan were also found to roll into fibrous constructs on silanized Al2O3 textiles, while fibrinogen nanofibers or blends of collagen and elastin did not yield such structures. Based on these differences, we hypothesize that textile surface charge and protein charge, in combination with the porous architecture of protein nanofibers and differences in mechanical strain, are key factors in inducing a scaffold roll-up. Further studies are required to develop the observed roll-up effect into a reproducible biofabrication process that can enable the controlled production of free-standing collagen-based tubes for soft tissue engineering.

Gelatin-grafted tubular asymmetric scaffolds promote ureteral regeneration via activation of the integrin/Erk signaling pathway

Introduction: The repair of a diseased ureter is an urgent clinical issue that needs to be solved. A tissue-engineered scaffold for ureteral replacement is currently insufficient due to its incompetent bioactivity, especially in long-segment abnormalities. The primary reason is the failure of urothelialization on scaffolds. Methods: In this work, we investigated the ability of gelatin-grafted tubular scaffold in ureteral repairment and its related biological mechanism. We designed various porous asymmetric poly (L-lactic acid) (PLLA)/poly (L-lactide-co-e-caprolactone) (PLCL) tubes with a thermally induced phase separation (TIPS) method via a change in the ratio of solvents (named PP). To regulate the phenotype of urothelial cells and ureteral reconstruction, gelatin was grafted onto the tubular scaffold using ammonolysis and glutaraldehyde crosslinking (named PP-gel). The in vitro and in vivo experiments were performed to test the biological function and the mechanism of the scaffolds. Results and Discussion: The hydrophilicity of the scaffold significantly increased after gelatin grafting, which promoted the adhesion and proliferation of urothelial cells. Through subcutaneous implantation in rats, PP-gel scaffolds demonstrated good biocompatibility. The in vivo replacement showed that PP-gel could improve urothelium regeneration and maintain renal function after the ureter was replaced with an ∼4 cm-long PP-gel tube using New Zealand rabbits as the experimental animals. The related biologic mechanism of ureteral reconstruction was detected in detail. The gelatin-grafted scaffold upgraded the integrin α6/β4 on the urothelial cell membrane, which phosphorylates the focal adhesion kinase (FAK) and enhances urothelialization via the MAPK/Erk signaling pathway. Conclusion: All these results confirmed that the PP46-gel scaffold is a promising candidate for the constitution of an engineered ureter and to repair long-segment ureteral defects.

Recent advances in biofabricated gut models to understand the gut-brain axis in neurological diseases

Increasing evidence has accumulated that gut microbiome dysbiosis could be linked to neurological diseases, including both neurodegenerative and psychiatric diseases. With the high prevalence of neurological diseases, there is an urgent need to elucidate the underlying mechanisms between the microbiome, gut, and brain. However, the standardized aniikmal models for these studies have critical disadvantages for their translation into clinical application, such as limited physiological relevance due to interspecies differences and difficulty interpreting causality from complex systemic interactions. Therefore, alternative in vitro gut–brain axis models are highly required to understand their related pathophysiology and set novel therapeutic strategies. In this review, we outline state-of-the-art biofabrication technologies for modeling in vitro human intestines. Existing 3D gut models are categorized according to their topographical and anatomical similarities to the native gut. In addition, we deliberate future research directions to develop more functional in vitro intestinal models to study the gut–brain axis in neurological diseases rather than simply recreating the morphology.

A dynamic Air Liquid Interface system for in vitro mimicking of the nasal mucosa

The development of an in vitro 3D model for the growth of the nasal mucosa cells can improve the therapy and the study of pathological states for subjects with chronic airway conditions. We have previously characterized a system consisting of a scaffold with an internal channel and a perfusion bioreactor with two independent flows provided by an external and an internal circuit, respectively. In this paper, this system was designed as a model of the nasal cavity, in which cells, grown on the inner surface of the scaffold channel, would be in contact at the same time with both culture medium, supplied by the external circuit, and air, provided with the internal flow. To ensure adequate nutrient supply to the cells in the scaffold channel, the radial diffusion of the culture medium through the porous matrix was evaluated first in qualitative and, then, in quantitative terms, demonstrating the capability of the system to control the value and direction of this flux. As a preliminary study, the culture of epithelial cells in the scaffold channel is also discussed in static, maintaining the air-liquid-interface (ALI) condition for up to three weeks. Despite minor abnormalities, such as a gap between cell layers and some detachments from the scaffold, the scaffold ensured cell survival and growth during the experimental time. This article is protected by copyright. All rights reserved.

Insulin-like growth factor 1 promotes the extension of Tracheal Epithelium in an in Vitro Tracheal organ culture model

OBJECTIVE

Rapid epithelialization is crucial to maintain tracheal patency and prevent potential graft failure in tracheal reconstruction after tracheal resection for cancer with tracheal infiltration or tracheal stenosis. Insulin-like growth factor 1 is a liver-secreted endocrine molecule that controls cell proliferation, differentiation, and apoptosis and has been reported to promote epithelialization in several organs. Here, we utilized mouse tracheal organ cultures to examine the effect of insulin-like growth factor 1 on tracheal epithelialization.

METHODS

The trachea was resected from thirteen-week-old female ICR mice, and cut into small plate-shaped tracheal sections. First, the expression of insulin-like growth factor 1 receptor was assessed by immunohistochemistry. Secondly, the tracheal sections were cultured for seven days in the culture medium, and the morphological change during the seven-day culture was assessed by immunohistochemistry, hematoxylin and eosin staining, and scanning electron microscopy. Moreover, the tracheal sections were cultured for 48 h with different concentration of insulin-like growth factor 1 (0, 0.1, 1 and 10 µg/mL) in the culture medium, and the extension length of the tracheal epithelium during culture was measured in order to assess the effect of topical IGF1 on tracheal epithelialization.

RESULTS

Immunohistochemistry showed that insulin-like growth factor 1 receptor was expressed in tracheal epithelium. Immunohistochemistry, hematoxylin and eosin staining, and scanning electron microscopy showed that the tracheal organ cultures were stable for at least seven days without apparent morphological damage. The effect of insulin-like growth factor 1 on tracheal epithelialization was examined in plate-shaped tracheal sections cultured in medium supplemented with or without insulin-like growth factor 1 for 48 h. We also found that the epithelial edge of plate-shaped tracheal sections extended further along the surface of the tracheal section in culture medium containing insulin-like growth factor 1 compared with that in culture medium without insulin-like growth factor 1.

CONCLUSION

The current study using an in vitro mouse tracheal organ culture model demonstrated that topical insulin-like growth factor 1 treatment promoted the extension of tracheal epithelium, suggesting the potential utility of insulin-like growth factor 1 in aiding rapid tracheal epithelialization in patients requiring tracheal reconstruction using tissue-engineered tracheas.

Adhesion of fibroblast cells on thin films representing surfaces of polymeric scaffolds of human urethra rationalized by molecular models of integrin binding: cell adhesion on polymeric scaffolds for regenerative medicine

This work combines experimental and computational study of Balb/3T3 clone A31 mouse embryo fibroblasts cell line adhesion and proliferation on fourteen different polymeric surfaces prepared from poly(dioxanone) (PDO), poly(glycolic acid) (PGA), poly(hydroxybutyrate) (PHB), and poly(L-lactic acid) (PLA), and their 1:1 mixtures. The study was done with the aim to explore the attractive interactions between various synthetic biomaterials and simple model of the cell attachment mechanism involving the trans-membrane protein integrin. The considered polymeric biodegradable biomaterials can be used as scaffolds for tissue engineering and regenerative urology. During the growth of new tissue, the polymer scaffold is replaced by the extracellular matrix (ECM) synthetized by the proliferating cells. The adhesion and proliferation experiments were done on thin polymer films produced by solvent casting. The computational approach used 3D molecular models of two layers of ordered parallel polymeric fibres, which formed quasi-planar nanosized models of the scaffold surface. Experimental data showed that PGA based polymer films promote the cell adhesion. Cell proliferation testing, performed by incubating the fibroblast cells with the studied polymer films, disclosed that PLA, PHB/PLA and PHB/PGA systems are able to support proliferation of Balb/3T3 clone A31 cells equal to the plain glass. Relative interaction energies between 3D models of polymeric films and the α₂ I domain of the cell adhesion receptor integrin α₂β₁ computed by molecular mechanics suggest that plain polymers PGA, PDO and mixtures PDO/PGA, PHB/PGA, and especially PGA/PLA display elevated affinity to the cell-attachment protein, which confirms the experimental observations. The combination of experimental and modelling approach can assist rational design of synthetic polymeric biomaterial for scaffolds of artificial human urethra that can be efficiently colonized by cells.

Regenerative medicine for the upper gastrointestinal tract

The main surgical strategy for gastrointestinal tract malignancy is en bloc resection, which consists of not only resection of the involved organs but also simultaneous resection of the surrounding or adjacent mesenteries that contain lymph vessels and nodes. After resection of the diseased organs, the defect of the gastrointestinal conduit is replaced with organs located downstream, such as the stomach and jejunum. However, esophageal and gastric reconstruction using these natural substitutes is associated with a diminished quality of life due to the loss of the reserve function, damage to the antireflux barrier, and dumping syndrome. Thus, replacement of the deficit after resection with the patient's own regenerated tissue to compensate for the lost function and tissue using regenerative medicine will be an ideal treatment. Many researchers have been trying to construct artificial organs through tissue engineering techniques; however, none have yet succeeded in growing a whole organ because of the complicated functions these organs perform, such as the processing and absorption of nutrients. While exciting results have been reported with regard to tissue engineering techniques concerning the upper gastrointestinal tract, such as the esophagus and stomach, most of these achievements have been observed in animal models, and few successful approaches in the clinical setting have been reported for the replacement of mucosal defects. We review the recent progress in regenerative medicine in relation to the upper gastrointestinal tract, such as the esophagus and stomach. We also focus on the functional capacity of regenerated tissue and its role as a culture system to recapitulate the mechanisms underlying infectious disease. With the emergence of technology such as the fabrication of decellularized constructs, organoids and cell sheet medicine, collaboration between gastrointestinal surgery and regenerative medicine is expected to help establish novel therapeutic modalities in the future.

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The recent progress in regenerative medicine in upper gastrointestinal tract.

3D Bioprinting Strategies for the Regeneration of Functional Tubular Tissues and Organs

It is difficult to fabricate tubular-shaped tissues and organs (e.g., trachea, blood vessel, and esophagus tissue) with traditional biofabrication techniques (e.g., electrospinning, cell-sheet engineering, and mold-casting) because these have complicated multiple processes. In addition, the tubular-shaped tissues and organs have their own design with target-specific mechanical and biological properties. Therefore, the customized geometrical and physiological environment is required as one of the most critical factors for functional tissue regeneration. 3D bioprinting technology has been receiving attention for the fabrication of patient-tailored and complex-shaped free-form architecture with high reproducibility and versatility. Printable biocomposite inks that can facilitate to build tissue constructs with polymeric frameworks and biochemical microenvironmental cues are also being actively developed for the reconstruction of functional tissue. In this review, we delineated the state-of-the-art of 3D bioprinting techniques specifically for tubular tissue and organ regeneration. In addition, this review described biocomposite inks, such as natural and synthetic polymers. Several described engineering approaches using 3D bioprinting techniques and biocomposite inks may offer beneficial characteristics for the physiological mimicry of human tubular tissues and organs.

Regeneration of esophagus using a scaffold-free biomimetic structure created with bio-three-dimensional printing

Various strategies have been attempted to replace esophageal defects with natural or artificial substitutes using tissue engineering. However, these methods have not yet reached clinical application because of the high risks related to their immunogenicity or insufficient biocompatibility. In this study, we developed a scaffold-free structure with a mixture of cell types using bio-three-dimensional (3D) printing technology and assessed its characteristics in vitro and in vivo after transplantation into rats. Normal human dermal fibroblasts, human esophageal smooth muscle cells, human bone marrow-derived mesenchymal stem cells, and human umbilical vein endothelial cells were purchased and used as a cell source. After the preparation of multicellular spheroids, esophageal-like tube structures were prepared by bio-3D printing. The structures were matured in a bioreactor and transplanted into 10-12-week-old F344 male rats as esophageal grafts under general anesthesia. Mechanical and histochemical assessment of the structures were performed. Among 4 types of structures evaluated, those with the larger proportion of mesenchymal stem cells tended to show greater strength and expansion on mechanical testing and highly expressed α-smooth muscle actin and vascular endothelial growth factor on immunohistochemistry. Therefore, the structure with the larger proportion of mesenchymal stem cells was selected for transplantation. The scaffold-free structures had sufficient strength for transplantation between the esophagus and stomach using silicon stents. The structures were maintained in vivo for 30 days after transplantation. Smooth muscle cells were maintained, and flat epithelium extended and covered the inner surface of the lumen. Food had also passed through the structure. These results suggested that the esophagus-like scaffold-free tubular structures created using bio-3D printing could hold promise as a substitute for the repair of esophageal defects.

Comparison of polyglycolic acid, polycaprolactone, and collagen as scaffolds for the production of tissue engineered intestine

Cell-seeded scaffolds play critical roles in the production of tissue engineered intestine (TEI), a potential strategy for the treatment of short bowel syndrome. The current study compares polyglycolic acid (PGA), polycaprolactone (PCL), and collagen as scaffolds for TEI production. Tubular PGA scaffolds were prepared from nonwoven BIOFELT^® . Tubular PCL scaffolds were fabricated by electrospinning. Tubular collagen scaffolds were prepared using CollaTape, a wound dressing material. Both PGA and collagen were coated with poly-l-lactic acid (PLLA) to improve scaffold mechanical properties. Pore size, porosity, microstructure, mechanical properties (suture retention strength and ultimate compressive force) were determined. The scaffolds were first seeded with crypt stem cells isolated from 1 to 3 day old rat pups and then implanted into the peritoneal cavity of nude rats. After 4 weeks of in vivo incubation, these cell-seeded scaffolds were harvested for assessment of the TEI produced. Of the three materials compared, PLLA coated tubular PGA scaffolds had the appropriate pore size, mechanical properties and degradation rate leading to the production of TEI with an architecture similar to that of native rat intestine. © 2018 Wiley Periodicals, Inc. J. Biomed. Mater. Res. Part B, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 750-760, 2019.

Angiogenic Self-Assembling Peptide Scaffolds for Functional Tissue Regeneration

Implantation of acellular biomimetic scaffolds with proangiogenic motifs may have exciting clinical utility for the treatment of ischemic pathologies such as myocardial infarction. Although direct delivery of angiogenic proteins is a possible treatment option, smaller synthetic peptide-based nanostructured alternatives are being investigated due to favorable factors, such as sustained efficacy and high-density epitope presentation of functional moieties. These peptides may be implanted in vivo at the site of ischemia, bypassing the first-pass metabolism and enabling long-term retention and sustained efficacy. Mimics of angiogenic proteins show tremendous potential for clinical use. We discuss possible approaches to integrate the functionality of such angiogenic peptide mimics into self-assembled peptide scaffolds for application in functional tissue regeneration.

Biomimetic heterogenous elastic tissue development

There is an unmet need for artificial tissue to address current limitations with donor organs and problems with donor site morbidity. Despite the success with sophisticated tissue engineering endeavours, which employ cells as building blocks, they are limited to dedicated labs suitable for cell culture, with associated high costs and long tissue maturation times before available for clinical use. Direct 3D printing presents rapid, bespoke, acellular solutions for skull and bone repair or replacement, and can potentially address the need for elastic tissue, which is a major constituent of smooth muscle, cartilage, ligaments and connective tissue that support organs. Thermoplastic polyurethanes are one of the most versatile elastomeric polymers. Their segmented block copolymeric nature, comprising of hard and soft segments allows for an almost limitless potential to control physical properties and mechanical behaviour. Here we show direct 3D printing of biocompatible thermoplastic polyurethanes with Fused Deposition Modelling, with a view to presenting cell independent in-situ tissue substitutes. This method can expeditiously and economically produce heterogenous, biomimetic elastic tissue substitutes with controlled porosity to potentially facilitate vascularisation. The flexibility of this application is shown here with tubular constructs as exemplars. We demonstrate how these 3D printed constructs can be post-processed to incorporate bioactive molecules. This efficacious strategy, when combined with the privileges of digital healthcare, can be used to produce bespoke elastic tissue substitutes in-situ, independent of extensive cell culture and may be developed as a point-of-care therapy approach.