Biomanufacturing Seamless Tubular and Hollow Collagen Scaffolds with Unique Design Features and Biomechanical Properties

Effect of Fibrillization pH on Gelation Viscoelasticity and Properties of Biofabricated Dense Collagen Matrices via Gel Aspiration-Ejection

Reconstituted hydrogels based on the self-assembly of acid-solubilized collagen molecules have been extensively used as in vitro models and precursors in biofabrication processes. This study investigated the effect of fibrillization pH-ranging from 4 to 11-on real-time rheological property changes during the gelation of collagen hydrogels and its interplay with the properties of subsequently biofabricated dense collagen matrices generated via automated gel aspiration-ejection (GAE). A contactless, nondestructive technique was used to characterize the temporal progression in shear storage modulus (G', or stiffness) during collagen gelation. There was a relative increase in G' of the hydrogels from 36 to 900 Pa with an increase in gelation pH. Automated GAE, which simultaneously imparts collagen fibrillar compaction and alignment, was then applied to these precursor collagen hydrogels to biofabricate native extracellular matrix-like densified gels. In line with viscoelastic properties, only hydrogels fibrillized in the 6.5 < pH ≤ 10 range could be densified via GAE. There was an increase in both fibrillar density and alignment in the GAE-derived matrices with an increase in gelation pH. These factors, combined with a higher G' in the alkaline precursor hydrogels, led to a significant increase in the micro-compressive modulus of GAE-densified gels of pH 9 and 10. Furthermore, NIH/3T3 fibroblast-seeded GAE-derived matrices densified from gels fibrillized in the pH range of 7 to 10 exhibited low cell mortality with >80% viability. It is anticipated that the results of this study can be potentially applicable to other hydrogel systems, as well as biofabrication techniques involving needles or nozzles, such as injection and bioprinting.

Porous biomaterials for tissue engineering: a review

The field of biomaterials has grown rapidly over the past decades. Within this field, porous biomaterials have played a remarkable role in: (i) enabling the manufacture of complex three-dimensional structures; (ii) recreating mechanical properties close to those of the host tissues; (iii) facilitating interconnected structures for the transport of macromolecules and cells; and (iv) behaving as biocompatible inserts, tailored to either interact or not with the host body. This review outlines a brief history of the development of biomaterials, before discussing current materials proposed for use as porous biomaterials and exploring the state-of-the-art in their manufacture. The wide clinical applications of these materials are extensively discussed, drawing on specific examples of how the porous features of such biomaterials impact their behaviours, as well as the advantages and challenges faced, for each class of the materials.

Human endothelial cells form an endothelium in freestanding collagen hollow filaments fabricated by direct extrusion printing

Fiber-shaped materials have great potential for tissue engineering applications as they provide structural support and spatial patterns within a three-dimensional construct. Here we demonstrate the fabrication of mechanically stable, meter-long collagen hollow filaments by a direct extrusion printing process. The fibres are permeable for oxygen and proteins and allow cultivation of primary human endothelial cells (ECs) at the inner surface under perfused conditions. The cells show typical characteristics of a well-organized EC lining including VE-cadherin expression, cellular response to flow and ECM production. The results demonstrate that the collagen tubes are capable of creating robust soft tissue filaments. The mechanical properties and the biofunctionality of these collagen hollow filaments facilitate the engineering of prevascularised tissue engineering constructs.

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.

Building Scaffolds for Tubular Tissue Engineering

Hollow organs and tissue systems drive various functions in the body. Many of these hollow or tubular systems, such as vasculature, the intestines, and the trachea, are common targets for tissue engineering, given their relevance to numerous diseases and body functions. As the field of tissue engineering has developed, numerous benchtop models have been produced as platforms for basic science and drug testing. Production of tubular scaffolds for different tissue engineering applications possesses many commonalities, such as the necessity for producing an intact tubular opening and for formation of semi-permeable epithelia or endothelia. As such, the field has converged on a series of manufacturing techniques for producing these structures. In this review, we discuss some of the most common tissue engineered applications within the context of tubular tissues and the methods by which these structures can be produced. We provide an overview of the general structure and anatomy for these tissue systems along with a series of general design criteria for tubular tissue engineering. We categorize methods for manufacturing tubular scaffolds as follows: casting, electrospinning, rolling, 3D printing, and decellularization. We discuss state-of-the-art models within the context of vascular, intestinal, and tracheal tissue engineering. Finally, we conclude with a discussion of the future for these fields.

Comparison of the therapeutic effects of adipose‑derived and bone marrow mesenchymal stem cells on erectile dysfunction in diabetic rats

The aim of the present study was to compare the effects of adipose‑derived mesenchymal stem cell (ADSC) and bone marrow mesenchymal stem cell (BMSC) transplantation into the corpora cavernosa of diabetic rats with erectile function. ADSCs and BMSCs were isolated and identified by flow cytometry. Rats with streptozocin‑induced diabetes were screened using apomorphine to obtain a rat model of diabetic erectile dysfunction, followed by transplantation of ADSCs and BMSCs into the corpora cavernosa. Two weeks later, the rats were again injected with apomorphine, the intracavernous pressure (ICP) and mean arterial pressure (MAP) of the penile tissue were measured, and the corpus cavernosum tissues were harvested. Angiogenic endothelial nitric oxide synthase (eNOS) expression was detected by western blotting and immunofluorescence analysis. The blood vessels in the corpus cavernosum were observed following hematoxylin and eosin (H&E) staining, and the expression of collagen was detected by Sirius Red staining. The cellular ultrastructure was examined by transmission electron microscopy. Intracavernous injection of ADSCs significantly increased ICP and ICP/MAP. Western blotting and immunofluorescence results revealed that ADSC treatment improved the expression of eNOS in the penile tissue of diabetic rats. The H&E staining results demonstrated that ADSC treatment promoted revascularization of the corpus cavernosum, and the results of Sirius Red staining revealed that ADSC treatment reduced penile collagen in diabetic rats. Transmission electron microscopy examination revealed that the ultrastructure of the tissues in the ADSC‑treated group was more complete compared with that in the untreated diabetic model group. In conclusion, ADSCs were found to be more effective compared with BMSCs in treating diabetes‑related erectile dysfunction.

Regenerative and engineered options for urethroplasty

Surgical correction of urethral strictures by substitution urethroplasty - the use of grafts or flaps to correct the urethral narrowing - remains one of the most challenging procedures in urology and is frequently associated with complications, restenosis and poor quality of life for the affected individual. Tissue engineering using different cell types and tissue scaffolds offers a promising alternative for tissue repair and replacement. The past 30 years of tissue engineering has resulted in the development of several therapies that are now in use in the clinic, especially in treating cutaneous, bone and cartilage defects. Advances in tissue engineering for urethral replacement have resulted in several clinical applications that have shown promise but have not yet become the standard of care.

Tissue-Engineered Neo-Urinary Conduit from Decellularized Trachea

Decellularized tissues have been increasingly popular for constructing scaffolds for tissue engineering applications due to their beneficial biological compositions and mechanical properties. It is therefore natural to consider decellularized trachea for construction of tissue-engineered trachea, as well as other tubular organs. A Neo-Urinary Conduit (NUC) is such a tubular organ that works as a passage for urine removal in bladder cancer patients who need a urinary diversion after their diseased bladder is removed. In this study, we report our findings on the feasibility of using a decellularized trachea for NUC applications. As a NUC scaffold, decellularized trachea provides benefits of having not only naturally occurring biological components but also having sufficient mechanical properties and structural integrity. We, therefore, decellularized rabbit trachea, evaluated its mechanical performance, and investigated its ability to support in vitro growth of human smooth muscle cells (hSMCs) and human urothelial cells (hUCs). The decellularized trachea had appropriate biomechanical properties with ultimate tensile strength of ∼0.34 MPa in longitudinal direction and ∼1.0 MPa in circumferential direction and resisted a radial burst pressure of >155 mm Hg. Cell morphology study by scanning electron microscopy further showed that hUCs grown on decellularized trachea adopted a typical flatten and interconnected network structure in the lumen of the scaffold, while they formed a round spherical shape and did not spread on the outer surfaces. SMCs, on the other hand, spread well throughout the scaffold. The gene expression analysis by real time quantitative polymerase chain reaction (RT-qPCR) and immunofluorescence studies further confirmed scaffold's ability to support long-term growth of hSMCs. Since uroepithelium has been shown to regenerate itself over time in vivo, these findings suggest that it is possible to construct a NUC from decellularized trachea without any preseeding of UCs. In future, we plan to translate decellularized trachea in a preclinical animal model and evaluate its biological performance.

Facile construction of mechanically tough collagen fibers reinforced by chitin nanofibers as cell alignment templates

Reconstituted collagen fibers with excellent mechanical performance were successfully fabricated with sodium alginate as coagulate and chitin nanofibers as reinforcing filler and applied as a fibroblast alignment templated scaffold.

Urinary Tissue Engineering: Challenges and Opportunities

INTRODUCTION

In this review, we discuss major advancements and common challenges in constructing and regenerating a neo-urinary conduit (NUC). First, we focus on the need for regenerating the urothelium, the hallmark the urine barrier, unique to urinary tissues. Second, we focus on clinically feasible scaffolds based on decellularized matrices and molded collagen that are currently of great research interest.

AIM

To discuss the major advancements in constructing a tissue-engineered NUC (TE-NUC) and the challenges involved in their successful clinical translation.

METHODS

A comprehensive search of peer-reviewed literature from PubMed and Google Scholar on subjects related to urothelium regeneration, decellularized tissue matrices, and collagen scaffolds was conducted.

MAIN OUTCOME MEASURE

We evaluated the main biological and mechanical functions of urinary tissues, the need for TE implants to create a urinary diversion, the reasons for their failures in clinical settings, and the applications of decellularized tissue matrices and collagen-based molded scaffolds in their regeneration.

RESULTS

It is necessary to create a urine barrier that prevents urine leakage into the stroma that can cause failure of the graft. Despite the regeneration potential of the urothelium, the limited supply of healthy urothelial cells in patients with bladder cancer remains a major challenge. In this context, alternative strategies, such as transdifferentiation of cells into urothelium or engineered scaffolds based on decellularized tissues and molded collagen with robust urine barrier properties, are active areas of research.

CONCLUSION

There is an immediate need for developing a functional TE-NUC that can improve the quality of life of patients with bladder cancer. It is possible to achieve a TE-NUC by bioengineering an implant that has appropriate biological and mechanical properties to store and transport urine. We anticipate that future advancements in urothelium regeneration and material design will lead us closer to successful neo-urinary tissue constructs. Singh A, Bivalacqua TJ, Sopko N. Urinary Tissue Engineering: Challenges and Opportunities. Sex Med Rev 2018;6:35-44.