Design of prevascularized three-dimensional cell-dense tissues using a cell sheet stacking manipulation technology

Recent adavances of functional modules for tooth regeneration

Dental diseases, such as dental caries and periodontal disorders, constitute a major global health challenge, affecting millions worldwide and often resulting in tooth loss. Traditional dental treatments, though beneficial, typically cannot fully restore the natural functions and structures of teeth. This limitation has prompted growing interest in innovative strategies for tooth regeneration methods. Among these, the use of dental stem cells to generate functional tooth modules represents an emerging and promising approach in dental tissue engineering. These modules aim to closely replicate the intricate morphology and essential physiological functions of dental tissues. Recent advancements in regenerative research have not only enhanced the assembly techniques for these modules but also highlighted their therapeutic potential in addressing various dental diseases. In this review, we discuss the latest progress in the construction of functional tooth modules, especially on regenerating dental pulp, periodontal tissue, and tooth roots.

Improving the mechanical and biological functions of cell sheet constructs: The interplay of human-derived periodontal ligament stem cells, endothelial cells and plasma rich in growth factors

OBJECTIVE

The aim of this study was to produce and characterize triple-layered cell sheet constructs with varying cell compositions combined or not with the fibrin membrane scaffold obtained by the technology of Plasma Rich in Growth Factors (mPRGF).

MATERIALS AND METHODS

Human primary cultures of periodontal ligament stem cells (hPDLSCs) were isolated, and their stemness nature was evaluated. Three types of triple-layered composite constructs were generated, composed solely of hPDLSCs or combined with human umbilical vein endothelial cells (HUVECs), either as a sandwiched endothelial layer or as coculture sheets of both cell phenotypes. These three triple-layered constructs were also manufactured using mPRGF as cell sheets' support. Necrosis, glucose consumption, secretion of extracellular matrix proteins and synthesis of proangiogenic factors were determined. Histological evaluations and proteomic analyses were also performed.

RESULTS

The inclusion of HUVECs did not clearly improve the properties of the multilayered constructs and yet hindered their optimal conformation. The presence of mPRGF prevented the shrinkage of cell sheets, stimulated the metabolic activity and increased the matrix synthesis. At the proteome level, mPRGF conferred a dramatic advantage to the hPDLSC constructs in their ability to provide a suitable environment for tissue regeneration by inducing the expression of proteins necessary for bone morphogenesis and cellular proliferation.

CONCLUSIONS

hPDLSCs' triple-layer construct onto mPRGF emerges as the optimal structure for its use in regenerative therapeutics.

CLINICAL RELEVANCE

These results suggest the suitability of mPRGF as a promising tool to support cell sheet formation by improving their handling and biological functions.

Advancing organoid design through co-emergence, assembly, and bioengineering

Human adult stem cells and patient-derived induced pluripotent stem cells represent promising tools to understand human biology, development, and disease. Under a permissive environment, stem cell derivatives can self-organize and reconstruct their native milieu, resulting in the creation of organ-like entities known as organoids. Although organoids represent a breakthrough in the stem cell field, there are still considerable shortcomings preventing their widespread use, namely their variability, limited function, and reductionist size. In the past few years, sophisticated methodologies have been proposed to allow the design of organoids with improved biological fidelity and physiological relevance. Here, we summarize these emerging technologies and provide insights into how they can be utilized to fulfill the potential of stem cells.

Engineering of MSCs sheet for the prevention of myocardial ischemia and for left ventricle remodeling

Tissue engineering combines cell biology and material science to construct tissues or organs for disease modeling, drug testing, and regenerative medicine. The cell sheet is a newly developed tissue engineering technology that has brought about scaffold-free tissue and shows great application potential. In this review, we summarized recent progress and future possibilities in preclinical research into and clinical applications of cell sheets fabricated by differing cell types from various sources for cardiac tissue repair, and the manufacturing strategies and promising application potential of 3D cell-dense tissue constructed from cell sheets. Special attention was paid to the mechanisms of mesenchymal stem cell (MSC) sheets in the prevention of myocardial ischemia and left ventricle remodeling. Comparing MSCs sheets with other types of cell sheets and 3D cardiac tissues, engineering tissues' potential safety and effectiveness concerns were also discussed.

Bioengineering of High Cell Density Tissues with Hierarchical Vascular Networks for Ex Vivo Whole Organs

The development of tissue-like structures such as cell sheets, spheroids, and organoids has contributed to progress in regenerative medicine. Simultaneous achievement of scale up and high cell density of these tissues is challenging because sufficient oxygen cannot be supplied to the inside of large, high cell density tissues. Here, in vitro fabrication of vessels to supply oxygen to the inside of millimeter-sized scaffold-free tissues whose cell density is ≈200 million cells mL^-1 , corresponding to those of native tissues, is shown. Hierarchical vascular networks by anastomosis of capillaries and a large vessel are essential for oxygen supply, whereas a large vessel or capillary networks alone make negligible contributions to the supply. The hierarchical vascular networks are formed by a top-down approach, which offers a new option for ex vivo whole organs without decellularization and 3D-bioprinting.

Realizations of vascularized tissues: From in vitro platforms to in vivo grafts

Vascularization is essential for realizing thick and functional tissue constructs that can be utilized for in vitro study platforms and in vivo grafts. The vasculature enables the transport of nutrients, oxygen, and wastes and is also indispensable to organ functional units such as the nephron filtration unit, the blood-air barrier, and the blood-brain barrier. This review aims to discuss the latest progress of organ-like vascularized constructs with specific functionalities and realizations even though they are not yet ready to be used as organ substitutes. First, the human vascular system is briefly introduced and related design considerations for engineering vascularized tissues are discussed. Second, up-to-date creation technologies for vascularized tissues are summarized and classified into the engineering and cellular self-assembly approaches. Third, recent applications ranging from in vitro tissue models, including generic vessel models, tumor models, and different human organ models such as heart, kidneys, liver, lungs, and brain, to prevascularized in vivo grafts for implantation and anastomosis are discussed in detail. The specific design considerations for the aforementioned applications are summarized and future perspectives regarding future clinical applications and commercialization are provided.

Recent Advances in Cell Sheet Engineering: From Fabrication to Clinical Translation

Cell sheet engineering, a scaffold-free tissue fabrication technique, has proven to be an important breakthrough technology in regenerative medicine. Over the past two decades, the field has developed rapidly in terms of investigating fabrication techniques and multipurpose applications in regenerative medicine and biological research. This review highlights the most important achievements in cell sheet engineering to date. We first discuss cell sheet harvesting systems, which have been introduced in temperature-responsive surfaces and other systems to overcome the limitations of conventional cell harvesting methods. In addition, we describe several techniques of cell sheet transfer for preclinical (in vitro and in vivo) and clinical trials. This review also covers cell sheet cryopreservation, which allows short- and long-term storage of cells. Subsequently, we discuss the cell sheet properties of angiogenic cytokines and vasculogenesis. Finally, we discuss updates to various applications, from biological research to clinical translation. We believe that the present review, which shows and compares fundamental technologies and recent advances in cell engineering, can potentially be helpful for new and experienced researchers to promote the further development of tissue engineering in different applications.

Transfer-Tattoo-Like Cell-Sheet Delivery Induced by Interfacial Cell Migration

A direct transfer of a cell sheet from a culture surface to a target tissue is introduced. Commercially available, flexible parylene is used as the culture surface, and it is proposed that the UV-treated parylene offers adequate and intermediate levels of cell adhesiveness for both the stable cell attachment during culture and for the efficient cell transfer to a target surface. The versatility of this cell-transfer process is demonstrated with various cell types, including MRC-5, HDFn, HULEC-5a, MC3T3-E1, A549, C2C12 cells, and MDCK-II cells. The novel cell-sheet engineering is based on a mechanism of interfacial cell migration between two surfaces with different adhesion preferences. Monitoring of cytoskeletal dynamics and drug treatments during the cell-transfer process reveals that the interfacial cell migration occurs by utilizing the existing transmembrane proteins on the cell surface to bind to the targeted surface. The re-establishment and reversal of cell polarity after the transfer process are also identified. Its unique capabilities of 3D multilayer stacking, freeform design, and curved surface application are demonstrated. Finally, the therapeutic potential of the cell-sheet delivery system is demonstrated by applying it to cutaneous wound healing and skin-tissue regeneration in mice models.

Design of Recombinant Spider Silk Proteins for Cell Type Specific Binding

Cytophilic (cell-adhesive) materials are very important for tissue engineering and regenerative medicine. However, for engineering hierarchically organized tissue structures comprising different cell types, cell-specific attachment and guidance are decisive. In this context, materials made of recombinant spider silk proteins are promising scaffolds, since they exhibit high biocompatibility, biodegradability, and the underlying proteins can be genetically functionalized. Here, previously established spider silk variants based on the engineered Araneus diadematus fibroin 4 (eADF4(C16)) are genetically modified with cell adhesive peptide sequences from extracellular matrix proteins, including IKVAV, YIGSR, QHREDGS, and KGD. Interestingly, eADF4(C16)-KGD as one of 18 tested variants is cell-selective for C2C12 mouse myoblasts, one out of 11 tested cell lines. Co-culturing with B50 rat neuronal cells confirms the cell-specificity of eADF4(C16)-KGD material surfaces for C2C12 mouse myoblast adhesion.

Cell Sheet Technology as an Engineering-Based Approach to Bone Regeneration

Bone defects that are congenital or the result of infection, malignancy, or trauma represent a challenge to the global healthcare system. To address this issue, multiple research groups have been developing novel cell sheet technology (CST)-based approaches to promote bone regeneration. These methods hold promise for use in regenerative medicine because they preserve cell-cell contacts, cell-extracellular matrix interactions, and the protein makeup of cell membranes. This review introduces the concept and preparation system of the cell sheet (CS), explores the application of CST in bone regeneration, highlights the current states of the bone regeneration via CST, and offers perspectives on the challenges and future research direction of translating current knowledge from the lab to the clinic.

Macromolecular crowding transforms regenerative medicine by enabling the accelerated development of functional and truly three-dimensional cell assembled micro tissues

Scaffold-free in vitro organogenesis exploits the innate ability of cells to synthesise and deposit their own extracellular matrix to fabricate tissue-like assemblies. Unfortunately, cell-assembled tissue engineered concepts require prolonged ex vivo culture periods of very high cell numbers for the development of a borderline three-dimensional implantable device, which are associated with phenotypic drift and high manufacturing costs, thus, hindering their clinical translation and commercialisation. Herein, we report the accelerated (10 days) development of a truly three-dimensional (338.1 ± 42.9 μm) scaffold-free tissue equivalent that promotes fast wound healing and induces formation of neotissue composed of mature collagen fibres, using human adipose derived stem cells seeded at only 50,000 cells/cm2 on an poly (N-isopropylacrylamide-co-N-tert-butylacrylamide (PNIPAM86-NTBA14) temperature-responsive electrospun scaffold and grown under macromolecular crowding conditions (50 μg/ml carrageenan). Our data pave the path for a new era in scaffold-free regenerative medicine.

Engineering stem cell therapeutics for cardiac repair

Cardiovascular disease is the leading cause of death in the world. Stem cell-based therapies have been widely investigated for cardiac regeneration in patients with heart failure or myocardial infarction (MI) and surged ahead on multiple fronts over the past two decades. To enhance cellular therapy for cardiac regeneration, numerous engineering techniques have been explored to engineer cells, develop novel scaffolds, make constructs, and deliver cells or their derivatives. This review summarizes the state-of-art stem cell-based therapeutics for cardiac regeneration and discusses the emerged bioengineering approaches toward the enhancement of therapeutic efficacy of stem cell therapies in cardiac repair. We cover the topics in stem cell source and engineering, followed by stem cell-based therapies such as cell aggregates and cell sheets, and biomaterial-mediated stem cell therapies such as stem cell delivery with injectable hydrogel, three-dimensional scaffolds, and microneedle patches. Finally, we discuss future directions and challenges of engineering stem cell therapies for clinical translation.

Application of mesenchymal stem cell sheet to treatment of ischemic heart disease

In recent years, mesenchymal stem cells (MSCs) have been used to improve cardiac function and attenuate adverse ventricular remodeling of the ischemic myocardium through paracrine effects and immunoregulation functions. In combination with cell sheet technology, MSCs could be more easily transplanted to the ischemic area. The long-term retention of MSCs in the affected area was realized and significantly improved the curative effect. In this review, we summarized the research and the applications of MSC sheets to the treatment of ischemic heart tissue. At present, many types of MSCs have been considered as multipotent cells in the treatment of heart failure, such as bone marrow-derived mesenchymal stem cells (BM-MSCs), adipose-derived mesenchymal stem cells (AD-MSCs), umbilical cord-derived mesenchymal stem cells (UC-MSCs), and skeletal myoblasts (SMs). Since UC-MSCs have few human leukocyte antigen-II and major histocompatibility complex class I molecules, and are easy to isolate and culture, UC-MSC sheets have been proposed as a candidate for clinical applications to ischemic heart disease.

Vascularization strategies for tissue engineering for tracheal reconstruction

Tissue engineering technology provides effective alternative treatments for tracheal reconstruction. The formation of a functional microvascular network is essential to support cell metabolism and ensure the long-term survival of grafts. Although several tracheal replacement therapy strategies have been developed in the past, the critical significance of the formation of microvascular networks in 3D scaffolds has not attracted sufficient attention. Here, we review key technologies and related factors of microvascular network construction in tissue-engineered trachea and explore optimized preparation processes of vascularized functional tissues for clinical applications.

Neovascularization of engineered tissues for clinical translation: Where we are, where we should be?

One of the key challenges in engineering three-dimensional tissue constructs is the development of a mature microvascular network capable of supplying sufficient oxygen and nutrients to the tissue. Recent angiogenic therapeutic strategies have focused on vascularization of the constructed tissue, and its integration in vitro; these strategies typically combine regenerative cells, growth factors (GFs) with custom-designed biomaterials. However, the field needs to progress in the clinical translation of tissue engineering strategies. The article first presents a detailed description of the steps in neovascularization and the roles of extracellular matrix elements such as GFs in angiogenesis. It then delves into decellularization, cell, and GF-based strategies employed thus far for therapeutic angiogenesis, with a particularly detailed examination of different methods by which GFs are delivered in biomaterial scaffolds. Finally, interdisciplinary approaches involving advancement in biomaterials science and current state of technological development in fabrication techniques are critically evaluated, and a list of remaining challenges is presented that need to be solved for successful translation to the clinics.

3D in vitro models of skeletal muscle: myopshere, myobundle and bioprinted muscle construct

Typical two-dimensional (2D) culture models of skeletal muscle-derived cells cannot fully recapitulate the organization and function of living muscle tissues, restricting their usefulness in in-depth physiological studies. The development of functional 3D culture models offers a major opportunity to mimic the living tissues and to model muscle diseases. In this respect, this new type of in vitro model significantly increases our understanding of the involvement of the different cell types present in the formation of skeletal muscle and their interactions, as well as the modalities of response of a pathological muscle to new therapies. This second point could lead to the identification of effective treatments. Here, we report the significant progresses that have been made the last years to engineer muscle tissue-like structures, providing useful tools to investigate the behavior of resident cells. Specifically, we interest in the development of myopshere- and myobundle-based systems as well as the bioprinting constructs. The electrical/mechanical stimulation protocols and the co-culture systems developed to improve tissue maturation process and functionalities are presented. The formation of these biomimetic engineered muscle tissues represents a new platform to study skeletal muscle function and spatial organization in large number of physiological and pathological contexts.

Cruciate Ligament Cell Sheets Can Be Rapidly Produced on Thermoresponsive poly(glycidyl ether) Coating and Successfully Used for Colonization of Embroidered Scaffolds

Anterior cruciate ligament (ACL) cell sheets combined with biomechanically competent scaffolds might facilitate ACL tissue engineering. Since thermoresponsive polymers allow a rapid enzyme-free detachment of cell sheets, we evaluated the applicability of a thermoresponsive poly(glycidyl ether) (PGE) coating for cruciate ligamentocyte sheet formation and its influence on ligamentocyte phenotype during sheet-mediated colonization of embroidered scaffolds. Ligamentocytes were seeded on surfaces either coated with PGE or without coating. Detached ligamentocyte sheets were cultured separately or wrapped around an embroidered scaffold made of polylactide acid (PLA) and poly(lactic-co-ε-caprolactone) (P(LA-CL)) threads functionalized by gas-phase fluorination and with collagen foam. Ligamentocyte viability, protein and gene expression were determined in sheets detached from surfaces with or without PGE coating, scaffolds seeded with sheets from PGE-coated plates and the respective monolayers. Stable and vital ligamentocyte sheets could be produced within 24 h with both surfaces, but more rapidly with PGE coating. PGE did not affect ligamentocyte phenotype. Scaffolds could be colonized with sheets associated with high cell survival, stable gene expression of ligament-related type I collagen, decorin, tenascin C and Mohawk after 14 d and extracellular matrix (ECM) deposition. PGE coating facilitates ligamentocyte sheet formation, and sheets colonizing the scaffolds displayed a ligament-related phenotype.

Scaffold-free cell-based tissue engineering therapies: advances, shortfalls and forecast

Cell-based scaffold-free therapies seek to develop in vitro organotypic three-dimensional (3D) tissue-like surrogates, capitalising upon the inherent capacity of cells to create tissues with efficiency and sophistication that is still unparalleled by human-made devices. Although automation systems have been realised and (some) success stories have been witnessed over the years in clinical and commercial arenas, in vitro organogenesis is far from becoming a standard way of care. This limited technology transfer is largely attributed to scalability-associated costs, considering that the development of a borderline 3D implantable device requires very high number of functional cells and prolonged ex vivo culture periods. Herein, we critically discuss advancements and shortfalls of scaffold-free cell-based tissue engineering strategies, along with pioneering concepts that have the potential to transform regenerative and reparative medicine.

Liver bioengineering: Recent trends/advances in decellularization and cell sheet technologies towards translation into the clinic

Development of novel technologies provides the best tissue constructs engineering and maximizes their therapeutic effects in regenerative therapy, especially for liver dysfunctions. Among the currently investigated approaches of tissue engineering, scaffold-based and scaffold-free tissues are widely suggested for liver regeneration. Analogs of liver acellular extracellular matrix (ECM) are utilized in native scaffolds to increase the self-repair and healing ability of organs. Native ECM analog could improve liver repairing through providing the supportive framework for cells and signaling molecules, exerting normal biomechanical, biochemical, and physiological signal complexes. Recently, innovative cell sheet technology is introduced as an alternative for conventional tissue engineering with the advantage of fewer scaffold restrictions and cell culture on a Thermo-Responsive Polymer Surface. These sheets release the layered cells through a temperature-controlled procedure without enzymatic digestion, while preserving the cell-ECM contacts and adhesive molecules on cell-cell junctions. In addition, several novelties have been introduced into the cell sheet and decellularization technologies to aid cell growth, instruct differentiation/angiogenesis, and promote cell migration. In this review, recent trends, advancements, and issues linked to translation into clinical practice are dissected and compared regarding the decellularization and cell sheet technologies for liver tissue engineering.

The Application of a Bone Marrow Mesenchymal Stem Cell Membrane in the Vascularization of a Decellularized Tracheal Scaffold

Airway stenosis is a common problem in the neonatal intensive care unit (NICU) and pediatric intensive care unit (PICU). A tissue-engineered trachea is a new therapeutic method and a research hotspot. Successful vascularization is the key to the application of a tissue-engineered trachea. However, successful vascularization studies lack a complete description. In this study, it was assumed that rabbit bone marrow mesenchymal stem cells were obtained and induced by ascorbic acid to detect the tissue structure, ultrastructure, and gene expression of the extracellular matrix. A vascular endothelial cell culture medium was added in vitro to induce the vascularization of the stem cell sheet (SCS), and the immunohistochemistry and gene expression of vascular endothelial cell markers were detected. At the same time, vascular growth-related factors were added and detected during SCS construction. After the SCS and decellularized tracheal (DT) were constructed, a tetrandrine allograft was performed to observe its vascularization potential. We established the architecture and identified rabbit bone marrow mesenchymal stem cell membranes by 14 days of ascorbic acid, studied the role of a vascularized membrane in inducing bone marrow mesenchymal stem cells by in vitro ascorbic acid, and assessed the role of combining the stem cell membranes and noncellular tracheal scaffolds in vivo. Fourteen experiments confirmed that cell membranes promote angiogenesis at gene level. The results of 21-day in vitro experiments showed that the composite tissue-engineered trachea had strong angiogenesis. In vivo experiments show that a composite tissue-engineered trachea has strong potential for angiogenesis. It promotes the understanding of diseases of airway stenosis and tissue-engineered tracheal regeneration in newborns and small infants.

Adipose-derived stem cell sheets combined with β-tricalcium phosphate/collagen-I fiber scaffold improve cell osteogenesis

Transplantation of cell-based material is a promising approach for the treatment of critical bone defects. However, it is still limited by the lack of suitable scaffold material or abundant seeding cell sources. The present study aimed to establish a novel composite of an adipose-derived stem cell (ADSC) sheet and a synthetic porous β-tricalcium phosphate/collagen-I fiber (β-TCP/COL-I) scaffold to enhance osteogenic activity. ADSCs were isolated from 3-week-old female Sprague Dawley rats and the ADSC sheets were prepared in an osteoinductive medium. The study groups included the ADSC sheets/scaffold, scattered ADSCs/scaffold, ADSC sheet alone and scaffold alone. Scanning electron microscopy and energy-dispersive spectrometry were used to observe cell-scaffold interactions and analyze the relative calcium content on the composites' surface. Alizarin red S staining was used to examine the calcium deposition. ELISA and reverse transcription-quantitative PCR were used to detect the expression levels of alkaline phosphatase (ALP), osteocalcin (OCN) and osteopontin (OPN). The results revealed that ADSCs were able to tightly adhere to the β-TCP/COL-I scaffold with no cytotoxicity. The calcifying nodules reaction was positive on ADSC sheets and gradually increased after osteogenic induction. In addition, the β-TCP/COL-I scaffold combined with ADSC sheets was able to significantly enhance the expression levels of ALP, OCN and OPN and increase the superficial relative calcium content compared to scattered ADSCs/scaffold or the ADSC sheet alone (P<0.05). The results indicated that ADSCs possess a strong osteogenic potential, particularly in the cell-sheet form and when compounded with the β-TCP/COL-I scaffold, compared to scattered ADSCs with a β-TCP/COL-I scaffold or an ADSC sheet alone. This novel composite may be a promising candidate for bone engineering.

Design of Temperature-Responsive Cell Culture Surfaces for Cell Sheet Engineering

Temperature-responsive cell culture surfaces, which modulate cell attachment/detachment characteristics with temperature, have been used to fabricate cell sheets. Extensive study on fabrication of cell sheet with the temperature-responsive cell culture surface, manipulation, and transplantation of the cell sheet has established the interdisciplinary field of cell sheet engineering, in which engineering, biological, and medical fields closely collaborate. Such collaboration has pioneered cell sheet engineering, making it a promising and attractive technology in tissue engineering and regenerative medicine. This review introduces concepts of cell sheet engineering, followed by designs for the fabrication of various types of temperature-responsive cell culture surfaces and technologies for cell sheet manipulation. The development of various methods for the fabrication of temperature-responsive cell culture surfaces was also summarized. The availability of cell sheet engineering for the treatment and regeneration of damaged human tissue has also been described, providing examples of the clinical application of cell sheet transplantation in humans.

Tissue Engineering in Musculoskeletal Tissue: A Review of the Literature

Tissue engineering refers to the attempt to create functional human tissue from cells in a laboratory. This is a field that uses living cells, biocompatible materials, suitable biochemical and physical factors, and their combinations to create tissue-like structures. To date, no tissue engineered skeletal muscle implants have been developed for clinical use, but they may represent a valid alternative for the treatment of volumetric muscle loss in the near future. Herein, we reviewed the literature and showed different techniques to produce synthetic tissues with the same architectural, structural and functional properties as native tissues.

Muscle stem cell isolation and in vitro culture for meat production: A methodological review

Cultured muscle tissue-based protein products, also known as cultured meat, are produced through in vitro myogenesis involving muscle stem cell culture and differentiation, and mature muscle cell processing for flavor and texture. This review focuses on the in vitro myogenesis for cultured meat production. The muscle stem cell-based in vitro muscle tissue production consists of a sequential process: (1) muscle sampling for stem cell collection, (2) muscle tissue dissociation and muscle stem cell isolation, (3) primary cell culture, (4) upscaled cell culture, (5) muscle differentiation and maturation, and (6) muscle tissue harvest. Although muscle stem cell research is a well-established field, the majority of these steps remain to be underoptimized to enable the in vitro creation of edible muscle-derived meat products. The profound understanding of the process would help not only cultured meat production but also business sectors that have been seeking new biomaterials for the food industry. In this review, we discuss comprehensively and in detail each step of cutting-edge methods for cultured meat production. This would be meaningful for both academia and industry to prepare for the new era of cellular agriculture.

Selective capture and non-invasive release of cells using a thermoresponsive polymer brush with affinity peptides

Thermoresponsive block copolymer brush with cell affinity peptides was prepared via two steps of ATRP and subsequent click reaction. The prepared polymer brush can purify cells with high selectivity by simply changing temperature.

Strategies for re-vascularization and promotion of angiogenesis in trauma and disease

The maintenance of a healthy vascular system is essential to ensure the proper function of all organs of the human body. While macrovessels have the main role of blood transportation from the heart to all tissues, microvessels, in particular capillaries, are responsible for maintaining tissues' functionality by providing oxygen, nutrients and waste exchanges. Occlusion of blood vessels due to atherosclerotic plaque accumulation remains the leading cause of mortality across the world. Autologous vein and artery grafts bypassing are the current gold standard surgical procedures to substitute primarily obstructed vascular structures. Ischemic scenarios that condition blood supply in downstream tissues may arise from blockage phenomena, as well as from other disease or events leading to trauma. The (i) great demand for new vascular substitutes, arising from both the limited availability of healthy autologous vessels, as well as the shortcomings associated with small-diameter synthetic vascular grafts, and (ii) the challenging induction of the formation of adequate and stable microvasculature are current driving forces for the growing interest in the development of bioinspired strategies to ensure the proper function of vasculature in all its dimensional scales. Here, a critical review of well-established technologies and recent biotechnological advances to substitute or regenerate the vascular system is provided.

Bladder reconstruction using autologous smooth muscle cell sheets grafted on a pre-vascularized capsule

Rationale: Construction of functional vascularized three-dimensional tissues has been a longstanding objective in the field of tissue engineering. The efficacy of using a tissue expander capsule as an induced vascular bed to prefabricate functional vascularized smooth muscle tissue flaps for bladder reconstruction in a rabbit model was tested. Methods: Skin tissue expanders were inserted into the groin to induce vascularized capsule pouch formation. Smooth muscle cells and endothelial progenitor cells were harvested and cocultured to form pre-vascularized smooth muscle cell sheet. Then repeated transplantation of triple-layer cell sheet grafts onto the vascularized capsular tissue was performed at 2-day intervals to prefabricate functional vascularized smooth muscle tissue flaps. Bladder muscular wall defects were created and repaired by six-layer cell sheet graft (sheet only), capsule flap (capsule only) and vascularized capsule prelaminated with smooth muscle cell sheet (sheet plus capsule). The animals were followed for 3 months after implantation and their bladders were explanted serially. Results: Bladder capacity and compliance were maintained in sheet plus capsule group throughout the 3 months. Tissue bath stimulation demonstrated that contractile responses to carbachol and KCl among the three groups revealed a significant difference (p < 0.05). Histologically, inflammation was evident in the capsule only group at 1 month and fibrosis was observed in sheet only group at 3 months. The vessel density in capsule only and sheet plus capsule group were significantly higher than in the sheet only group at each time point (p < 0.05). Comparison of the smooth muscle content among the three groups revealed a significant difference (p < 0.05). Conclusion: These results proved that the capsule may serve as an induced vascular bed for vascularized smooth muscle tissue flap prefabrication. The prefabricated functional vascularized smooth muscle tissue flap has the potential for reliable bladder reconstruction and may create new opportunities for vascularization in 3-D tissue engineering.

Role of Vascular Endothelial Growth Factor and Human Umbilical Vein Endothelial Cells in Designing An In Vitro Vascular-Muscle Cellular Model Using Adipose-Derived Stem Cells

Objective

Researchers have been interested in the creation of a favorable cellular model for use in vascular-muscle tissue engineering. The main objective of this study is to determine the myogenic effects of vascular endothelial growth factor (VEGF) and human umbilical vein endothelial cells (HUVECs) on adipose-derived stem cells (ADSCs) to achieve an in vitro vascular-muscle cellular model.

Materials and Methods

The present experimental research was conducted on two primary groups, namely ADSCs monoculture and ADSCs/HUVECs co-culture that were divided into control, horse serum (HS), and HS/VEGF differentiation subgroups. HUVECs were co-cultured by ADSC in a ratio of 1:1. The myogenic differentiation was evaluated using the reverse transcription-polymerase chain reaction (RT-PCR) and immunofluorescence in different experimental groups. The interaction between ADSCs and HUVECs, as well as the role of ADSCs conditional medium, was investigated for endothelial tube formation assay.

Results

Immunofluorescence staining indicated that Tropomyosin was positive in ADSCs and ADSCs and HUVECs co-culture groups on HS and HS/VEGF culture medium. Furthermore, the MyHC2 gene expression significantly increased in HS and HS/VEGF groups in comparison with the control group (P<0.001). More importantly, there was a significant difference in the mRNA expression of this gene between ADSCs and ADSCs and HUVECs co-culture groups on HS/VEGF culture medium (P<0.05). Current data revealed that the co-culture of ADSCs and HUVECs could develop endothelial network formation in the VEGF-loaded group. Also, the ADSCs-conditioned medium improved the viability and formation of the endothelial tube in the HS and VEGF groups, respectively.

Conclusion

It was concluded that ADSCs/HUVECs co-culture and dual effects of VEGF can lead to the formation of differentiated myoblasts in proximity to endothelial network formations. These in vitro cellular models could be potentially used in vascular-muscle tissue engineering implanted into organ defects where muscle tissue and vascular regeneration were required.

A Gelatin Hydrogel Nonwoven Fabric Facilitates Metabolic Activity of Multilayered Cell Sheets

IMPACT STATEMENT

This study introduces the utility of gelatin hydrogel nonwoven fabrics (GHNFs) for cell sheet engineering. The GHNF had the mechanical property strong enough to hold by forceps even in the swollen condition. The cell sheet harvest and transfer processes were performed simpler and faster than those without using the GHNF. The GHNF facilitates the metabolic activity of three-layered cell sheets, and the cell migration from cell sheets into the GHNF was observed. The GHNF is a promising material used to support cell sheets during the process of assemble formulation and contributes to the improved biological functions of tissue-like cell constructs.

Cellular Based Strategies for Microvascular Engineering

Vascularization is a major hurdle in complex tissue and organ engineering. Tissues greater than 200 μm in diameter cannot rely on simple diffusion to obtain nutrients and remove waste. Therefore, an integrated vascular network is required for clinical translation of engineered tissues. Microvessels have been described as <150 μm in diameter, but clinically they are defined as <1 mm. With new advances in super microsurgery, vessels less than 1 mm can be anastomosed to the recipient circulation. However, this technical advancement still relies on the creation of a stable engineered microcirculation that is amenable to surgical manipulation and is readily perfusable. Microvascular engineering lays on the crossroads of microfabrication, microfluidics, and tissue engineering strategies that utilize various cellular constituents. Early research focused on vascularization by co-culture and cellular interactions, with the addition of angiogenic growth factors to promote vascular growth. Since then, multiple strategies have been utilized taking advantage of innovations in additive manufacturing, biomaterials, and cell biology. However, the anatomy and dynamics of native blood vessels has not been consistently replicated. Inconsistent results can be partially attributed to cell sourcing which remains an enigma for microvascular engineering. Variations of endothelial cells, endothelial progenitor cells, and stem cells have all been used for microvascular network fabrication along with various mural cells. As each source offers advantages and disadvantages, there continues to be a lack of consensus. Furthermore, discord may be attributed to incomplete understanding about cell isolation and characterization without considering the microvascular architecture of the desired tissue/organ.

Magnetic self-assembly of toroidal hepatic microstructures for micro-tissue fabrication

In this study, we developed a procedure for assembling hepatic microstructures into tube shapes using magnetic self-assembly for in vitro 3D micro-tissue fabrication. To this end, biocompatible hydrogels, which have a toroidal shape, were made using the micro-patterned electrodeposition method. Ferrite particles were used to coat the fabricated toroidal hydrogel microcapsules using a poly-L-lysine membrane. The microcapsules were then magnetized with a 3 T magnetic field, and assembled using a magnetic self-assembly process. During electrodeposition, hepatic cells were trapped inside the microcapsules, and they were cultured to construct tissue-like structures. The magnetized toroidal microstructures then automatically assembled to form tube structures. Shaking was used to enhance the assembly process, and the shaking speed was experimentally optimized to achieve the high-speed assembly of longer tube structures. The flow velocity inside the dish during shaking was measured by particle image velocimetry. Hepatic functions were evaluated to check for side-effects of the magnetized ferrite particles on the microstructures. Collectively, our findings indicated that the developed method can achieve the high-speed assembly of a large number of microstructures to form tissue-like hepatic structures.

Detachment of cell sheets from clinically ubiquitous cell culture vessels by ultrasonic vibration

Proteinases that digest the extracellular matrix are usually used to harvest cells from culture vessels in a general culture process, which lowers the initial adhesion rate in regenerative medicine. Cell sheet engineering is one of the most important technologies in this field, especially for transplantation, because fabricated cell sheets have rich extracellular matrixes providing strong initial adhesion. Current cell sheet fabrication relies on temperature-responsive polymer-coated dishes. Cells are cultured on such specialized dishes and subjected to low temperature. Thus, we developed a simple but versatile cell sheet fabrication method using ubiquitous culture dishes/flasks without any coating or temperature modulation. Confluent mouse myoblasts (C2C12 cell line) were exposed to ultrasonic vibration from underneath and detached as cell sheets from entire culture surfaces. Because of the absence of low temperature, cell metabolism was statically increased compared with the conventional method. Furthermore, viability, morphology, protein expression, and mRNA expression were normal. These analyses indicated no side effects of ultrasonic vibration exposure. Therefore, this novel method may become the standard for cell sheet fabrication. Our method can be easily conducted following a general culture procedure with a typical dish/flask, making cell sheets more accessible to medical experts.

Deconstructing, Replicating, and Engineering Tissue Microenvironment for Stem Cell Differentiation

One of the most crucial components of regenerative medicine is the controlled differentiation of embryonic or adult stem cells into the desired cell lineage. Although most of the reported protocols of stem cell differentiation involve the use of soluble growth factors, it is increasingly evident that stem cells also undergo differentiation when cultured in the appropriate microenvironment. When cultured in decellularized tissues, for instance, stem cells can recapitulate the morphogenesis and functional specialization of differentiated cell types with speed and efficiency that often surpass the traditional growth factor-driven protocols. This suggests that the tissue microenvironment (TME) provides stem cells with a holistic "instructive niche" that harbors signals for cellular reprogramming. The translation of this into medical applications requires the decoding of these signals, but this has been hampered by the complexity of TME. This problem is often addressed by a reductionist approach, in which cells are exposed to substrates decorated with simple, empirically designed geometries, textures, and chemical compositions ("bottom-up" approach). Although these studies are invaluable in revealing the basic principles of mechanotransduction mechanisms, their physiological relevance is often uncertain. This review examines the recent progress of an alternative, "top-down" approach, in which the TME is treated as a holistic biological entity. This approach is made possible by recent advances in systems biology and fabrication technologies that enable the isolation, characterization, and reconstitution of TME. It is hoped that these new techniques will elucidate the nature of niche signals so that they can be extracted, replicated, and controlled. This review summarizes these emerging techniques and how the data they generated are changing our view on TME. Impact statement This review summarizes the current state of art of the understanding of instructive niche in the field of tissue microenvironment. Not only did we survey the use of different biochemical preparations as stimuli of stem cell differentiation and summarize the recent effort in dissecting the biochemical composition of these preparations, through the application of extracellular matrix (ECM) arrays and proteomics, but we also introduce the use of open-source, high-content immunohistochemistry projects in contributing to the understanding of tissue-specific composition of ECM. We believe this review would be highly useful for our peer researching in the same field. "Mr. Tulkinghorn is always the same… so oddly out of place and yet so perfectly at home." -Charles Dickens, Bleak House.

Rapid and Detergent-Free Decellularization of Cartilage

The use of decellularized tissues or organs as cell culture scaffolds has proven to be a promising approach for tissue engineering and regenerative medicine, as these decellularized tissues can provide the instructive niche for cell differentiation and functions. Cartilage is a largely avascular tissue with limited regenerative capacity. Lesions caused by arthritis can lead to severe cartilage degeneration. Previous studies have indicated that decellularized cartilage can be used as scaffolds that support the chondrogenic differentiation of adult stem cells. However, these decellularization protocols all require the use of denaturing agents, such as high salt and detergents, that lead to the artifactual disruption of the chemical and physical integrity of the tissue microenvironment. Here, we established a new decellularization method for cartilage, through a combined effect of freezing-thawing, sectioning, and sonication in water. This protocol achieved the complete removal of cells within minutes, instead of hours or days required by existing procedures, and does not use any detergent. The resulting decellularized cartilage preserved the native ultrastructure and biochemical contents, including glycosaminoglycans, which is typically depleted by traditional decellularization methods. Human mesenchymal stem cells could readily adhere onto the decellularized cartilage. Together, this work unveils a simple new method for decellularizing cartilage, which will be useful in studying how tissue microenvironment supports chondrocyte growth and functions. Impact statement In this study, we develop a simple, fast cartilage decellularization method that does not require any detergent, so that the decellularized cartilage chemistry is preserved. Traditional detergent-based decellularization removes the tissue biochemical contents (i.e., glycosaminoglycans). In this new water decellularization protocol, the biochemical contents of cartilage can be preserved. This allows the study of biochemistry and physical content in extracellular matrix as a whole, and this protocol would definitely be useful for studying the effect of tissue microenvironment in supporting chondrocyte growth and functions.

A Surface-Tailoring Method for Rapid Non-Thermosensitive Cell-Sheet Engineering via Functional Polymer Coatings

Cell sheet engineering, a technique utilizing a monolayer cell sheet, has recently emerged as a promising technology for scaffold-free tissue engineering. In contrast to conventional tissue-engineering approaches, the cell sheet technology allows cell harvest as a continuous cell sheet with intact extracellular matrix proteins and cell-cell junction, which facilitates cell transplantation without any other artificial biomaterials. A facile, non-thermoresponsive method is demonstrated for a rapid but highly reliable platform for cell-sheet engineering. The developed method exploits the precise modulation of cell-substrate interactions by controlling the surface energy of the substrate via a series of functional polymer coatings to enable prompt cell sheet harvesting within 100 s. The engineered surface can trigger an intrinsic cellular response upon the depletion of divalent cations, leading to spontaneous cell sheet detachment under physiological conditions (pH 7.4 and 37 °C) in a non-thermoresponsive manner. Additionally, the therapeutic potential of the cell sheet is successfully demonstrated by the transplantation of multilayered cell sheets into mouse models of diabetic wounds and ischemia. These findings highlight the ability of the developed surface for non-thermoresponsive cell sheet engineering to serve as a robust platform for regenerative medicine and provide significant breakthroughs in cell sheet technology.

On-Chip Fabrication of Cell-Attached Microstructures using Photo-Cross-Linkable Biodegradable Hydrogel

We developed a procedure for fabricating movable biological cell structures using biodegradable materials on a microfluidic chip. A photo-cross-linkable biodegradable hydrogel gelatin methacrylate (GelMA) was used to fabricate arbitrary microstructure shapes under a microscope using patterned ultraviolet light. The GelMA microstructures were movable inside the microfluidic channel after applying a hydrophobic coating material. The fabricated microstructures were self-assembled inside the microfluidic chip using our method of fluid forcing. The synthesis procedure of GelMA was optimized by changing the dialysis temperature, which kept the GelMA at a suitable pH for cell culture. RLC-18 rat liver cells (Riken BioResource Research Center, Tsukuba, Japan) were cultured inside the GelMA and on the GelMA microstructures to check cell growth. The cells were then stretched for 1 day in the cell culture and grew well on the GelMA microstructures. However, they did not grow well inside the GelMA microstructures. The GelMA microstructures were partially dissolved after 4 days of cell culture because of their biodegradability after the cells were placed on the microstructures. The results indicated that the proposed procedure used to fabricate cell structures using GelMA can be used as a building block to assemble three-dimensional tissue-like cell structures in vitro inside microfluidic devices.

Wholly vascularized millimeter-sized engineered tissues by cell-sized microscaffolds

The in vitro fabrication of wholly vascularized millimeter-sized engineered tissues is still a key challenge in the tissue engineering field. Recently we reported a unique approach 'sedimentary culture' using a collagen microfiber (CMF) to fabricate large-scale engineered tissues. The millimeter-sized tissues with high extracellular matrix (ECM) density were easily obtained by centrifugation of cells and CMFs and subsequent cultivation because the CMFs acted as a micrometer-sized scaffold. However, cell distribution in the obtained tissues was not homogeneous because of the different sedimentation velocity of the cells and CMFs because of their size difference. Here we report the fabrication of wholly vascularized millimeter-sized engineered tissues using cell-sized CMFs. To avoid dissolving, vacuum drying was performed at 200 °C for 24 h for thermal crosslinking of primary amine groups of type I collagen. The 200- and 20-μm-sized CMFs (CMF-200 and CMF-20) were obtained by homogenization and subsequent sonication of the crosslinked collagen. Interestingly, the CMF-20 indicated a similar sedimentation velocity with cells because of their same size range, thus uniform millimeter-sized tissue with homogeneous cell distribution was fabricated by the sedimentary culture method. To form a whole blood capillary structure in the tissues, fibronectin (FN) was adsorbed on the surface of CMF-20 to stimulate endothelial cell migration. The distribution of the blood capillary network in 1.6-mm-sized tissues was markedly improved by FN-adsorbed CMF-20 (FN-CMF-20). Sedimentary culture using FN-CMF-20 will create new opportunities in tissue engineering for the in vitro fabrication of wholly vascularized millimeter-sized engineered tissues.

Three-dimensional periodontal tissue regeneration using a bone-ligament complex cell sheet

Periodontal tissue is a distinctive tissue structure composed three-dimensionally of cementum, periodontal ligament (PDL) and alveolar bone. Severe periodontal diseases cause fundamental problems for oral function and general health, and conventional dental treatments are insufficient for healing to healthy periodontal tissue. Cell sheet technology has been used in many tissue regenerations, including periodontal tissue, to transplant appropriate stem/progenitor cells for tissue regeneration of a target site as a uniform tissue. However, it is still difficult to construct a three-dimensional structure of complex tissue composed of multiple types of cells, and the transplantation of a single cell sheet cannot sufficiently regenerate a large-scale tissue injury. Here, we fabricated a three-dimensional complex cell sheet composed of a bone-ligament structure by layering PDL cells and osteoblast-like cells on a temperature responsive culture dish. Following ectopic and orthotopic transplantation, only the complex cell sheet group was demonstrated to anatomically regenerate the bone-ligament structure along with the functional connection of PDL-like fibers to the tooth root and alveolar bone. This study represents successful three-dimensional tissue regeneration of a large-scale tissue injury using a bioengineered tissue designed to simulate the anatomical structure.

Advanced Bottom-Up Engineering of Living Architectures

Bottom-up tissue engineering is a promising approach for designing modular biomimetic structures that aim to recapitulate the intricate hierarchy and biofunctionality of native human tissues. In recent years, this field has seen exciting progress driven by an increasing knowledge of biological systems and their rational deconstruction into key core components. Relevant advances in the bottom-up assembly of unitary living blocks toward the creation of higher order bioarchitectures based on multicellular-rich structures or multicomponent cell-biomaterial synergies are described. An up-to-date critical overview of long-term existing and rapidly emerging technologies for integrative bottom-up tissue engineering is provided, including discussion of their practical challenges and required advances. It is envisioned that a combination of cell-biomaterial constructs with bioadaptable features and biospecific 3D designs will contribute to the development of more robust and functional humanized tissues for therapies and disease models, as well as tools for fundamental biological studies.

Cell sheet tissue engineering for scaffold-free three-dimensional (3D) tissue reconstruction

Three-dimensional (3D) reconstruction of highly functional tissues is of great importance in advancing the clinical benefit of tissue engineering and regenerative medicine. In the last quarter century, many studies have found that by engineering a 3D microenvironment that resembles the in vivo tissue condition, cells exhibit behaviors and functions that reflect those of native tissue. Biomaterial scaffolds are a central technology for providing 3D microenvironments in vitro, and, in conjunction with diverse design and cell seeding advents, have produced highly functional and complex 3D tissues. Here, we describe a new approach to creating 3D cell-dense tissue-like constructs without a biomaterial scaffold. Cell sheet technology with cell sheet layering strategies generates highly cell dense, engineered tissue capable of direct crosstalk with the tissue-engraftment surface, in addition to paracrine-mediated signaling. In this chapter, we will introduce methods of reconstructing 3D tissue using cell sheet technology and the advantages of a scaffold-free design.

[Construction of three-dimensional dermoid tissue based on cell sheets technology in vitro]

OBJECTIVE

To explore a new strategy for constructing three-dimensional dermoid tissue in vitro by using cell sheets technology.

METHODS

Rabbit bone marrow mesenchymal stem cells (rBMSCs) were isolated from bone marrow of New Zealand white rabbits and cultured by whole bone marrow adherent method. Human dermal fibroblasts (HDFs) were cultured and passaged in vitro. The 2nd generation rBMSCs and the 3rd generation HDFs were cultured in a culture dish for 2 weeks with cell sheets conditioned medium respectively to obtain a monolayer cell sheets. Human umbilical vein endothelial cells (HUVECs) were inoculated on rBMSCs sheet to construct pre-vascularized cell sheet. During the culture period, the morphological changes of the cell sheet were observed under an inverted phase contrast microscope. At 1, 3, 7, and 14 days, HE staining and CD31 immunofluorescence staining were performed to observe the cell distribution and microvascular network formation. The rBMSCs sheet was used as control. The pre-vascularized cell sheet (experimental group) and rBMSCs sheet (control group) cultured for 7 days were placed in the middle of two HDFs sheets, respectively, to prepare three-dimensional dermoid tissues. After 24 hours of culture, CD31 immunofluorescence staining and collagen type Ⅰ and collagen type Ⅲ immunohistochemical stainings were performed to evaluate cell distribution and collagen expression.

RESULTS

HDFs and rBMSCs sheets were successfully prepared after 2 weeks of cell culture. After inoculation of HUVECs on rBMSCs sheet for 3 days, HUVECs could be seen to rearrange on rBMSCs sheet and forming vacuoles. The reticular structure was visible at 7 days and more obvious at 14 days. The formation of vacuoles between the cell sheets was observed by HE staining, and the vacuoles became more and more obvious, the thickness of the membranes increased significantly with time. CD31 immunofluorescence staining showed the microvascular lumen formation. However, only the thickness of rBMSCs sheet increasing was observed, with no changes in cell morphology or cavitation structure. The three-dimensional dermoid tissue observation showed that the endothelial cells in the experimental group were positive expressions, and the rBMSCs, HDFs, and HUVECs cells were arranged neatly. The endothelial cells were negative expressions and randomly arranged in the control group. The collagen type Ⅰ and collagen type Ⅲ were positive expression in the experimental group and the control group. But compared with control group, experimental group presented a "honeycomb" network connection, where the matrix was distributed regularly, and cells were arranged tightly. The difference in the expression of collagen type Ⅰ and collagen type Ⅲ between the experimental group and the control group was not significant ( P>0.05).

CONCLUSION

Three-dimensional dermoid tissue is successfully constructed by using cell sheet technology. The cell matrix distribution of the pre-vascularized cell sheet constructed by HUVECs and rBMSCs sheet is relatively regular, which has the potential to form tissue engineered dermis.

Skeletal muscle cells derived from mouse skin cultures

We have established a novel, simple, and highly reproducible method to generate skeletal muscle cells from mouse skin. Small pieces of skin from the back of mice were cultured in extracellular material-coated dishes in typical culture medium for about 3 weeks. Myotubes formed after about a week, grew into twitching myotubes, and became twitching myotube clumps after 3 weeks. Skeletal muscle cells are formed spontaneously with no induction. Myotubes were immunologically positive for myosin heavy chains, MyoD, and myogenin. Ultrastructural analysis revealed the presence of the sarcomere structure. Furthermore, PAX7⁺/MyoD^- muscle stem cells proliferated around these myotubes, and MyoD⁺/myogenin⁺/MHC^-- cells were also observed. Moreover, we investigated the formation of skeletal muscle cells from the sialidosis mouse skin, and showed that it is decreased compared to that of the wild type. Our method to generate skeletal muscle cells from skin is thought to be useful for the investigation of muscle cell development and muscle-related disorders.

Enhanced mechanical properties and cell separation with thermal control of PIPAAm-brushed polymer-blend microfibers

Thermoresponsive microfibers with enhanced mechanical properties for temperature-modulated cell separation were developed by electrospinning of blending PVBC and PBMA, and by subsequently modifying the microfibers with PIPAAm via ATRP.

Vascularization strategies for skin tissue engineering

Lack of proper vascularization after skin trauma causes delayed wound healing. This has sparked the development of various tissue engineering strategies to improve vascularization.

Osteochondral tissue regenerated via a strategy by stacking pre-differentiated BMSC sheet on fibrous mesh in a gradient

The reconstruction of osteochondral tissue remains a challenging task in clinical therapy because of its heterogeneous structure. The best way to face the challenge is to develop a biomimetic construct to mimic the multilayered gradient from cartilage, to calcified cartilage and subchondral bone. In this study, bone marrow mesenchymal stromal cells (BMSCs) were cultured on electrospun fibrous meshes and cell sheets were incubated. The fibrous meshes were composed of 50% poly(L-lactide) and 50% gelatin, displaying excellent biocompatibility, cell affinity and degradability. Differentiation of BMSC sheets on fibrous meshes was induced chondrogenically or osteogenically. In particular, the BMSC sheets were able to be efficiently induced differentiating towards calcified cartilage by using a 1:1 (v/v) mixed medium of chondrogenic and osteogenic inductive media. Thus, a gradient 3D construct was built by stacking the differently pre-differentiated cell/mesh complexes layer by layer from top to bottom to mimic the cartilage-to-bone transition. With this gradient construct being implanted in the rabbit knee osteochondral defect, it was confirmed that it could promote the tissue regeneration with intact cartilage layer formation in comparison with the multilayered construct without a gradient. The strategy of using properly pre-differentiated BMSC sheet on fibrous mesh to build the osteochondral interface was thus suggested as being feasible and effective in mimicking its hierarchical complexity, and favored the repairing of injured joint cartilage.

Generation of a large-scale vascular bed for the in vitro creation of three-dimensional cardiac tissue

Introduction

The definitive treatment for severe heart failure is transplantation. However, only a small number of heart transplants are performed each year due to donor shortages. Therefore, novel treatment approaches based on artificial organs or regenerative therapy are being developed as alternatives. We have developed a technology known as cell sheet-based tissue engineering that enables the fabrication of functional three-dimensional (3D) tissue. Here, we report a new technique for engineering human cardiac tissue with perfusable blood vessels. Our method involved the layering of cardiac cell sheets derived from human induced pluripotent stem cells (hiPSCs) on a vascular bed derived from porcine small intestinal tissue.

Methods

For the vascular bed, a segment of porcine small intestine was harvested together with a branch of the superior mesenteric artery and a branch of the superior mesenteric vein. The small intestinal tissue was incised longitudinally, and the mucosa was resected. Human cardiomyocytes derived from hiPSCs were co-cultured with endothelial cells and fibroblasts on a temperature-responsive dish and harvested as a cardiac cell sheet. A triple-layer of cardiac cell sheets was placed onto the vascular bed, and the resulting construct was subjected to perfusion culture in a bioreactor system.

Results

The cardiac tissue on the vascular bed pulsated spontaneously and synchronously after one day of perfusion culture. Electrophysiological recordings revealed regular action potentials and a beating rate of 105 ± 13/min (n = 8). Furthermore, immunostaining experiments detected partial connection of the blood vessels between the vascular bed and cardiac cell sheets.

Conclusions

We succeeded in engineering spontaneously beating 3D cardiac tissue in vitro using human cardiac cell sheets and a vascular bed derived from porcine small intestine. Further development of this method might allow the fabrication of functional cardiac tissue that could be used in the treatment of severe heart failure.

Extracellular Heme Proteins Influence Bovine Myosatellite Cell Proliferation and the Color of Cell-Based Meat

Skeletal muscle-tissue engineering can be applied to produce cell-based meat for human consumption, but growth parameters need to be optimized for efficient production and similarity to traditional meat. The addition of heme proteins to plant-based meat alternatives was recently shown to increase meat-like flavor and natural color. To evaluate whether heme proteins also have a positive effect on cell-based meat production, bovine muscle satellite cells (BSCs) were grown in the presence of hemoglobin (Hb) or myoglobin (Mb) for up to nine days in a fibrin hydrogel along 3D-printed anchor-point constructs to generate bioartificial muscles (BAMs). The influence of heme proteins on cell proliferation, tissue development, and tissue color was analyzed. We found that the proliferation and metabolic activity of BSCs was significantly increased when Mb was added, while Hb had no, or a slightly negative, effect. Hb and, in particular, Mb application led to a very similar color of BAMs compared to cooked beef, which was not noticeable in groups without added heme proteins. Taken together, these results indicate a potential benefit of adding Mb to cell culture media for increased proliferation and adding Mb or Hb for the coloration of cell-based meat.

Fabrication Techniques for Vascular and Vascularized Tissue Engineering

Impaired or damaged blood vessels can occur at all levels in the hierarchy of vascular systems from large vasculatures such as arteries and veins to meso- and microvasculatures such as arterioles, venules, and capillary networks. Vascular tissue engineering has become a promising approach for fabricating small-diameter vascular grafts for occlusive arteries. Vascularized tissue engineering aims to fabricate meso- and microvasculatures for the prevascularization of engineered tissues and organs. The ideal small-diameter vascular graft is biocompatible, bridgeable, and mechanically robust to maintain patency while promoting tissue remodeling. The desirable fabricated meso- and microvasculatures should rapidly integrate with the host blood vessels and allow nutrient and waste exchange throughout the construct after implantation. A number of techniques used, including engineering-based and cell-based approaches, to fabricate these synthetic vasculatures are herein explored, as well as the techniques developed to fabricate hierarchical structures that comprise multiple levels of vasculature.