Reconstruction of functional tissues with cell sheet engineering

A Cell Pre-Wrapping Seeding Technique for Hydrogel-Based Tubular Organ-On-A-Chip

Organ-on-a-chip (OOC) models based on microfluidic technology are increasingly used to obtain mechanistic insight into (patho)physiological processes in humans, and they hold great promise for application in drug development and regenerative medicine. Despite significant progress in OOC development, several limitations of conventional microfluidic devices pose challenges. First, most microfluidic systems have rectangular cross sections and flat walls, and therefore tubular/ curved structures, like blood vessels and nephrons, are not well represented. Second, polymers used as base materials for microfluidic devices are much stiffer than in vivo extracellular matrix (ECM). Finally, in current cell seeding methods, challenges exist regarding precise control over cell seeding location, unreachable spaces due to flow resistances, and restricted dimensions/geometries. To address these limitations, an alternative cell seeding technique and a corresponding workflow is introduced to create circular cross-sectioned tubular OOC models by pre-wrapping cells around sacrificial fiber templates. As a proof of concept, a perfusable renal proximal tubule-on-a-chip is demonstrated with a diameter as small as 50 µm, cellular tubular structures with branches and curvature, and a preliminary vascular-renal tubule interaction model. The cell pre-wrapping seeding technique promises to enable the construction of diverse physiological/pathological models, providing tubular OOC systems for mechanistic investigations and drug development.

Rat Tracheal Cartilage Regeneration Using Mesenchymal Stem Cells Derived From Human iPS Cells

Tracheal cartilage provides structural support to the airways to enable breathing. However, it can become damaged or impaired, sometimes requiring surgical resection and reconstruction. Previously, we clinically applied an artificial trachea composed of a polypropylene mesh and collagen sponge, with a favorable postoperative course. However, the artificial trachea presents a limitation, as the mesh is not biodegradable and cannot be used in pediatric patients. Compared to a polypropylene mesh, regenerated cartilage represents an ideal material for reconstruction of the damaged trachea. The use of mesenchymal stem cells (MSCs) as a source for cartilage regeneration has gained widespread acceptance, but challenges such as the invasiveness of harvesting and limited cell supply persist. Therefore, we focused on the potential of human-induced pluripotent stem cell (hiPSC)-derived mesenchymal stem cells (iMSCs) for tracheal cartilage regeneration. In this study, we aimed to regenerate tracheal cartilage on an artificial trachea as a preliminary step to replace the polypropylene mesh. iMSCs were induced from hiPSCs through neural crest cells and transplanted with a polypropylene mesh covered with a collagen sponge into the damaged tracheal cartilage in immunodeficient rats. Human nuclear antigen (HNA)-positive cells were observed in all six rats at 4 weeks and in six out of seven rats at 12 weeks after transplantation, indicating that transplanted iMSCs survived within the tracheal cartilage defects of rats. The HNA-positive cells coexpressed SOX9, and type II collagen was detected around HNA-positive cells in four of six rats at 4 weeks and in three of seven rats at 12 weeks after transplantation, reflecting cartilage-like tissue regeneration. These results indicate that the transplanted iMSCs could differentiate into chondrogenic cells and promote tracheal cartilage regeneration. iMSC transplantation thus represents a promising approach for human tracheal reconstruction.

Materials Nanoarchitectonics at Dynamic Interfaces: Structure Formation and Functional Manipulation

The next step in nanotechnology is to establish a methodology to assemble new functional materials based on the knowledge of nanotechnology. This task is undertaken by nanoarchitectonics. In nanoarchitectonics, we architect functional material systems from nanounits such as atoms, molecules, and nanomaterials. In terms of the hierarchy of the structure and the harmonization of the function, the material created by nanoarchitectonics has similar characteristics to the organization of the functional structure in biosystems. Looking at actual biofunctional systems, dynamic properties and interfacial environments are key. In other words, nanoarchitectonics at dynamic interfaces is important for the production of bio-like highly functional materials systems. In this review paper, nanoarchitectonics at dynamic interfaces will be discussed, looking at recent typical examples. In particular, the basic topics of "molecular manipulation, arrangement, and assembly" and "material production" will be discussed in the first two sections. Then, in the following section, "fullerene assembly: from zero-dimensional unit to advanced materials", we will discuss how various functional structures can be created from the very basic nanounit, the fullerene. The above examples demonstrate the versatile possibilities of architectonics at dynamic interfaces. In the last section, these tendencies will be summarized, and future directions will be discussed.

Magnetic-Based Strategies for Regenerative Medicine and Tissue Engineering

The fabrication of biological substitutes to repair, replace, or enhance tissue- and organ-level functions is a long-sought goal of tissue engineering (TE). However, the clinical translation of TE is hindered by several challenges, including the lack of suitable mechanical, chemical, and biological properties in one biomaterial, and the inability to generate large, vascularized tissues with a complex structure of native tissues. Over the past decade, a new generation of "smart" materials has revolutionized the conventional medical field, transforming TE into a more accurate and sophisticated concept. At the vanguard of scientific development, magnetic nanoparticles (MNPs) have garnered extensive attention owing to their significant potential in various biomedical applications owing to their inherent properties such as biocompatibility and rapid remote response to magnetic fields. Therefore, to develop functional tissue replacements, magnetic force-based TE (Mag-TE) has emerged as an alternative to conventional TE strategies, allowing for the fabrication and real-time monitoring of tissues engineered in vitro. This review addresses the recent studies on the use of MNPs for TE, emphasizing the in vitro, in vivo, and clinical applications. Future perspectives of Mag-TE in the fields of TE and regenerative medicine are also discussed.

Cryopreserved Adipose-Derived Stem Cell Sheets: An Off-the-Shelf Scaffold for Augmenting Tendon-to-Bone Healing in a Rabbit Model of Chronic Rotator Cuff Tear

BACKGROUND

Adipose-derived stem cell (ADSC) sheets have been shown to promote tendon-to-bone healing. However, conventional laboratory preparation methods for ADSC sheets are time-consuming and risky, which precludes their diverse clinical applications.

PURPOSE

To explore the utility of off-the-shelf cryopreserved ADSC sheets (c-ADSC sheets) for rotator cuff tendon-to-bone healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

The ADSC sheets were cryopreserved and thawed for live/dead double staining, TdT-mediated dUTP Nick-End Labeling (TUNEL) staining, scanning electron microscopy observation, and biomechanical testing. Clone formation, proliferative capacity, and multilineage differentiation of ADSCs within the c-ADSC sheets were assayed to explore the effect of cryopreservation on stem cell properties. A total of 67 rabbits were randomly divided into 4 groups: normal group (without supraspinatus tendon tears; n = 7), control group (repair alone; n = 20), fresh ADSC (f-ADSC) sheet group (repair; n = 20), and c-ADSC sheet group (repair; n = 20). Rabbit bilateral supraspinatus tendon tears were induced to establish a chronic rotator cuff tear model. Gross observation, micro-computed tomography analysis, histological or immunohistochemical tests, and biomechanical tests were conducted at 6 and 12 weeks after repair.

RESULTS

No significant impairment was seen in the cell viability, morphology, and mechanical properties of c-ADSC sheets when compared with f-ADSC sheets. The stem cell properties of ADSC sheets also were preserved by cryopreservation. At 6 and 12 weeks after the repair, the f-ADSC and c-ADSC sheet groups showed superior bone regeneration, higher histological scores, larger fibrocartilage areas, more mature collagen, and better biomechanical results compared with the control group. No obvious difference was seen between the f-ADSC and c-ADSC sheet groups in terms of bone regeneration, histological score, fibrocartilage formation, and biomechanical tests.

CONCLUSION

c-ADSC sheets, an off-the-shelf scaffold with a high potential for clinical translational application, can effectively promote rotator cuff tendon-to-bone healing.

CLINICAL RELEVANCE

Programmed cryopreservation of ADSC sheets is an efficient off-the-shelf scaffold for rotator cuff tendon-to-bone healing.

Unlocking the Mysteries, Bridging the Gap, and Unveiling the Multifaceted Potential of Stem Cell Therapy for Cardiac Tissue Regeneration: A Narrative Review of Current Literature, Ethical Challenges, and Future Perspectives

Revolutionary advancements in regenerative medicine have brought stem cell therapy to the forefront, offering promising prospects for the regeneration of ischemic cardiac tissue. Yet, its full efficacy, safety, and role in treating ischemic heart disease (IHD) remain limited. This literature review explores the intricate mechanisms underlying stem cell therapy. Furthermore, we unravel the innovative approaches employed to bolster stem cell survival, enhance differentiation, and seamlessly integrate them within the ischemic cardiac tissue microenvironment. Our comprehensive analysis uncovers how stem cells enhance cell survival, promote angiogenesis, and modulate the immune response. Stem cell therapy harnesses a multifaceted mode of action, encompassing paracrine effects and direct cell replacement. As our review progresses, we underscore the imperative for standardized protocols, comprehensive preclinical and clinical studies, and careful regulatory considerations. Lastly, we explore the integration of tissue engineering and genetic modifications, envisioning a future where stem cell therapy reigns supreme in regenerative medicine.

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.

Fibrinogen-based cell and spheroid sheets manipulating and delivery for mouse hindlimb ischemia

In this research, we introduced a novel strategy for fabricating cell sheets (CSs) prepared by simply adding a fibrinogen solution to growth medium without using any synthetic polymers or chemical agents. We confirmed that the fibrinogen-based CS could be modified for target tissue regardless of size, shape, and cell types. Also, fibrinogen-based CSs were versatile and could be used to form three-dimensional (3D) CSs such as multi-layered CSs and those mimicking native blood vessels. We also prepared fibrinogen-based spheroid sheets for the treatment of ischemic disease. The fibrinogen-based spheroid sheets had much higherin vitrotubule formation and released more angiogenic factors compared to other types of platform in this research. We transplanted fibrinogen-based spheroid sheets into a mouse hindlimb ischemia model and found that fibrinogen-based spheroid sheets showed significantly improved physiological function and blood perfusion rates compared to the other types of platform in this research.

Potential of Mesenchymal Stem Cell Sheets on Periodontal Regeneration: A Systematic Review of Pre-Clinical Studies

BACKGROUND

Cell sheet technique using mesenchymal stem cells is a high-level strategy in periodontal regenerative medicine. Although recent studies have shown the role of MSCSs in increased dental supporting tissues and bone, there is no systematic review focused specifically on assessing periodontal regeneration in orthotopic animal models.

OBJECTIVE

To evaluate the potential of mesenchymal stem cell sheets (MSCSs) on periodontal regeneration, compared to control, in experimental animal models Methods: Pre-clinical studies in periodontal defects of animal models were considered eligible. The electronic search included the MEDLINE, Web of Science, EMBASE and LILACS databases. The review was conducted according to the Preferred Reporting Item for Systematic Reviews and Meta-Analyses statement guidelines.

RESULTS

A total of 17 of the 3989 studies obtained from the electronic database search were included. MSCSs included dental follicle (DF) MSCSs, periodontal ligament (PL) MSCSs, dental pulp (DP) MSCSs, bone marrow (BM) MSCSs, alveolar periosteal (AP) MSCSs and gingival (G) MSCSs. Regarding cell sheet inducing protocol, most of the studies used ascorbic acid (52.94%). Others used culture dishes grafted with a temperature-responsive polymer (47.06%). Adverse effects were not identified in the majority of studies. Meta-analysis was not considered because of methodological heterogeneities. PDL-MSCSs were superior for periodontal regeneration enhancement compared to the control, but in an induced inflammatory microenvironment, DF-MSCSs were better. Moreover, DF-MSCSs, DP-MSCSs, and BM-MSCSs showed improved results compared to the control.

CONCLUSION

MSCSs can improve periodontal regeneration in animal periodontal defect models.

Molecular Machines and Microrobots: Nanoarchitectonics Developments and On-Water Performances

This review will focus on micromachines and microrobots, which are objects at the micro-level with similar machine functions, as well as nano-level objects such as molecular machines and nanomachines. The paper will initially review recent examples of molecular machines and microrobots that are not limited to interfaces, noting the diversity of their functions. Next, examples of molecular machines and micromachines/micro-robots functioning at the air-water interface will be discussed. The behaviors of molecular machines are influenced significantly by the specific characteristics of the air-water interface. By placing molecular machines at the air-water interface, the scientific horizon and depth of molecular machine research will increase dramatically. On the other hand, for microrobotics, more practical and advanced systems have been reported, such as the development of microrobots and microswimmers for environmental remediations and biomedical applications. The research currently being conducted on the surface of water may provide significant basic knowledge for future practical uses of molecular machines and microrobots.

The Proangiogenic Potential of Rat Adipose-Derived Stromal Cells with and without Cell-Sheet Induction: A Comparative Study

A functional vasculature for survival remains a challenge for tissue regeneration, which is indispensable for oxygen and nutrient supply. Utilizing mesenchymal stromal cells (MSCs) to alleviate tissue ischemia and repair dysfunctional or damaged endothelium is a promising strategy. Compared to other populations of MSCs, adipose-derived stromal cells (ASCs) possess a more significant proangiogenic potential and are abundantly available. Cell sheet technology has recently been widely utilized in bone engineering. Compared to conventional methods of seeding seed cell suspension onto biological scaffolds, cell sheet technology prevents cell loss and preserves the extracellular matrix (ECM). Nevertheless, the proangiogenic potential of ASC sheets remains unknown. In this study, rat ASC sheets were constructed, and their macro- and microstructures were examined. In addition, we investigated the effects of ASCs and ASC sheets on the biological properties and angiogenic capacity of endothelial cells (ECs). The results demonstrated that the ASC sheets gradually thickened as the number of cells and ECM increased over time and that the cells were in an active state of secretion. Similar to ASC-CM, the conditioned medium (CM) of ASC sheets could significantly enhance the proliferative capacity of ECs. ASC sheet-CM has significant advantages over ASC-CM in promoting the migration and angiogenesis of ECs, where the exosomes secreted by ASC sheets play an essential role. Therefore, using ASC sheets for therapeutic tissue and organ regeneration angiogenesis may be a valuable strategy.

Modeling the human heart ex vivo-current possibilities and strive for future applications

The high organ specification of the human heart is inversely proportional to its functional recovery after damage. The discovery of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) has accelerated research in human heart regeneration and physiology. Nevertheless, due to the immaturity of iPSC-CMs, they are far from being an representative model of the adult heart physiology. Therefore, number of laboratories strive to obtain a heart tissues by engineering methods by structuring iPSC-CMs into complex and advanced platforms. By using the iPSC-CMs and arranging them in 3D cultures it is possible to obtain a human heart muscle with physiological capabilities potentially similar to the adult heart, while remaining in vitro. Here, we attempt to describe existing examples of heart muscle either in vitro or ex vivo models and discuss potential options for the further development of such structures. This will be a crucial step for ultimate derivation of complete heart tissue-mimicking organs and their future use in drug development, therapeutic approaches testing, pre-clinical studies, and clinical applications. This review particularly aims to compile available models of advanced human heart tissue for scientists considering which model would best fit their research needs.

Strategies for vascularized skin models in vitro

As the largest organ of the human body, the skin has a complex multi-layered structure. The composition of the skin includes cells, extracellular matrix (ECM), vascular networks, and other appendages. Because of the shortage of donor sites, skin substitutes are of great significance in the field of skin tissue repair. Moreover, skin models for disease research, drug screening, and cosmetic testing fall far short of the demand. Skin tissue engineering has made remarkable progress in developing skin models over the years. However, there are still several problems to be resolved. One of the crucial aspects is the lack of vascular systems for nutrient transport and waste disposal. Here, we will focus on the discussion and analysis of advanced manufacturing strategies for prevascularized skin, such as a scaffold-based method, cell coating technology, cell sheet engineering, skin-on-a-chip, and three-dimensional (3D) bioprinting. These key challenges, which restrict the prevascularized skin and provide perspectives on future directions will also be highlighted.

Cell-Based Microfluidic Device Utilizing Cell Sheet Technology

The development of microelectromechanical systems has resulted in the rapid development of polydimethylpolysiloxane (PDMS) microfluidic devices for drug screening models. Various cell functions, such as the response of endothelial cells to fluids, have been elucidated using microfluidic devices. Additionally, organ-on-a-chip systems that include organs that are important for biological circulation, such as the heart, liver, pancreas, kidneys, and brain, have been developed. These organs realize the biological circulation system in a manner that cannot be reproduced by artificial organs; however, the flow channels between the organs are often artificially created by PDMS. In this study, we developed a microfluidic device consisting only of cells, by combining cell sheet technology with microtitanium wires. Microwires were placed between stacked fibroblast cell sheets, and the cell sheets adhered to each other, after which the microwires were removed leaving a luminal structure with a size approximately equal to the arteriolar size. The lumen structure was constructed using wires with diameters of 50, 100, 150, and 200 μm, which were approximations of the arteriole diameters. Furthermore, using a perfusion device, we successfully perfused the luminal structure created inside the cell sheets. The results revealed that a culture solution can be supplied to a cell sheet with a very high cell density. The biofabrication technology proposed in this study can contribute to the development of organ-on-a-chip systems.

Stem cell therapy applied for digestive anastomosis: Current state and future perspectives

BACKGROUND

Digestive tract resections are usually followed by an anastomosis. Anastomotic leakage, normally due to failed healing, is the most feared complication in digestive surgery because it is associated with high morbidity and mortality. Despite technical and technological advances and focused research, its rates have remained almost unchanged the last decades. In the last two decades, stem cells (SCs) have been shown to enhance healing in animal and human studies; hence, SCs have emerged since 2008 as an alternative to improve anastomoses outcomes.

AIM

To summarise the published knowledge of SC utilisation as a preventative tool for hollow digestive viscera anastomotic or suture leaks.

METHODS

PubMed, Science Direct, Scopus and Cochrane searches were performed using the key words “anastomosis”, “colorectal/colonic anastomoses”, “anastomotic leak”, “stem cells”, “progenitor cells”, “cellular therapy” and “cell therapy” in order to identify relevant articles published in English and Spanish during the years of 2000 to 2021. Studies employing SCs, performing digestive anastomoses in hollow viscera or digestive perforation sutures and monitoring healing were finally included. Reference lists from the selected articles were reviewed to identify additional pertinent articles.

Given the great variability in the study designs, anastomotic models, interventions (SCs, doses and vehicles) and outcome measures, performing a reliable meta-analysis was considered impossible, so we present the studies, their results and limitations.

RESULTS

Eighteen preclinical studies and three review papers were identified; no clinical studies have been published and there are no registered clinical trials. Experimental studies, mainly in rat and porcine models and occasionally in very adverse conditions such as ischaemia or colitis, have been demonstrated SCs as safe and have shown some encouraging morphological, functional and even clinical results. Mesenchymal SCs are mostly employed, and delivery routes are mainly local injections and cell sheets followed by biosutures (sutures coated by SCs) or purely topical. As potential weaknesses, animal models need to be improved to make them more comparable and equivalent to clinical practice, and the SC isolation processes need to be standardised. There is notable heterogeneity in the studies, making them difficult to compare. Further investigations are needed to establish the indications, the administration system, potential adjuvants, the final efficacy and to confirm safety and exclude definitively oncological concerns.

CONCLUSION

The future role of SC therapy to induce healing processes in digestive anastomoses/sutures still needs to be determined and seems to be currently far from clinical use.

Cartilage Regeneration Characteristics of Human and Goat Auricular Chondrocytes

Although cartilage regeneration technology has achieved clinical breakthroughs, whether auricular chondrocytes (AUCs) represent optimal seed cells to achieve stable cartilage regeneration is not clear. In this study, we systematically explore biological behaviors of human- and goat-derived AUCs during in vitro expansion as well as cartilage regeneration in vitro and in vivo. To eliminate material interference, a cell sheet model was used to evaluate the feasibility of dedifferentiated AUCs to re-differentiate and regenerate cartilage in vitro and in vivo. We found that the dedifferentiated AUCs could re-differentiate and regenerate cartilage sheets under the chondrogenic medium system, and the generated chondrocyte sheets gradually matured with increased in vitro culture time (2, 4, and 8 weeks). After the implantation of cartilage sheets with different in vitro culture times in nude mice, optimal neocartilage was formed in the group with 2 weeks in vitro cultivation. After in vivo implantation, ossification only occurred in the group with goat-regenerated cartilage sheet of 8 weeks in vitro cultivation. These results, which were confirmed in human and goat AUCs, suggest that AUCs are ideal seed cells for the clinical translation of cartilage regeneration under the appropriate culture system and culture condition.

There is still plenty of room for layer-by-layer assembly for constructing nanoarchitectonics-based materials and devices

Nanoarchitectonics approaches can produce functional materials from tiny units through combination of various processes including atom/molecular manipulation, chemical conversion, self-assembly/self-organization, microfabrication, and bio-inspired procedures. Existing fabrication approaches can be regarded as fitting into the same concept. In particular, the so-called layer-by-layer (LbL) assembly method has huge potential for preparing applicable materials with a great variety of assembling mechanisms. LbL assembly is a multistep process where different components can be organized in planned sequences while simple alignment options provide access to superstructures, for example helical structures, and anisotropies which are important aspects of nanoarchitectonics. In this article, newly-featured examples are extracted from the literature on LbL assembly discussing trends for composite functional materials according to (i) principles and techniques, (ii) composite materials, and (iii) applications. We present our opinion on the present trends, and the prospects of LbL assembly. While this method has already reached a certain maturity, there is still plenty of room for expanding its usefulness for the fabrication of nanoarchitectonics-based materials and devices.

Enhancing chondrogenic potential via mesenchymal stem cell sheet multilayering

Advanced tissue engineering approaches for direct articular cartilage replacement in vivo employ mesenchymal stem cell (MSC) sources, exploiting innate chondrogenic potential to fabricate hyaline-like constructs in vitro within three-dimensional (3D) culture conditions. Cell sheet technology represents one such advanced 3D scaffold-free cell culture platform, and previous work has shown that 3D MSC sheets are capable of in vitro hyaline-like chondrogenic differentiation. The present study aims to build upon this understanding and elucidate the effects of an established cell sheet manipulation technique, cell sheet multilayering, on fabrication of MSC-derived hyaline-like cartilage 3D layered constructs in vitro. To achieve this goal, multilayered MSC sheets are prepared and assessed for structural and biochemical transitions throughout chondrogenesis. Results support MSC multilayering as a means of increasing construct thickness and 3D cellular interactions related to in vitro chondrogenesis, including N-cadherin, connexin 43, and integrin β-1. Data indicate that increasing construct thickness from 14 μm (1-layer construct) to 25 μm (2-layer construct) increases these cellular interactions and subsequent in vitro MSC chondrogenesis. However, a clear initial thickness threshold (33 μm - 3-layer construct) is evident that decreases the rate and extent of in vitro chondrogenesis, specifically chondrogenic gene expressions (Sox9, aggrecan, type II collagen) and sulfated proteoglycan accumulation in deposited extracellular matrix (ECM). Together, these data support the utility of cell sheet multilayering as a platform for tailoring construct thickness and subsequent MSC chondrogenesis for future articular cartilage regeneration applications.

In Vitro Strategies to Vascularize 3D Physiologically Relevant Models

Vascularization of 3D models represents a major challenge of tissue engineering and a key prerequisite for their clinical and industrial application. The use of prevascularized models built from dedicated materials could solve some of the actual limitations, such as suboptimal integration of the bioconstructs within the host tissue, and would provide more in vivo-like perfusable tissue and organ-specific platforms. In the last decade, the fabrication of vascularized physiologically relevant 3D constructs has been attempted by numerous tissue engineering strategies, which are classified here in microfluidic technology, 3D coculture models, namely, spheroids and organoids, and biofabrication. In this review, the recent advancements in prevascularization techniques and the increasing use of natural and synthetic materials to build physiological organ-specific models are discussed. Current drawbacks of each technology, future perspectives, and translation of vascularized tissue constructs toward clinics, pharmaceutical field, and industry are also presented. By combining complementary strategies, these models are envisioned to be successfully used for regenerative medicine and drug development in a near future.

Dentin-Pulp Complex Tissue Regeneration via Three-Dimensional Cell Sheet Layering

The dentin-pulp complex is a unique structure in teeth that contains both hard and soft tissues. Generally, deep caries and trauma cause damage to the dentin-pulp complex, and if left untreated, this damage will progress to irreversible pulpitis. The aim of this study was to fabricate a layered cell sheet composed of rat dental pulp (DP) cells and odontogenic differentiation of pulp (OD) cells and to investigate the ability to regenerate the dentin-pulp complex in a scaffold tooth. We fabricated two single cell sheets composed of DP cells (DP cell sheet) or OD cells (OD cell sheet) and a layered cell sheet made by layering both cells. The characteristics of the fabricated cell sheets were analyzed using light microscopy, scanning electron microscope (SEM), hematoxylin-eosin (HE) staining, and immunohistochemistry (IHC). Furthermore, the cell sheets were transplanted into the subrenal capsule of immunocompromised mice for 8 weeks. After this, the regenerative capacity to form dentin-like tissue was evaluated using micro-computed tomography (micro-CT), HE staining, and IHC. The findings of SEM and IHC confirmed that layered cell sheets fabricated by stacking OD cells and DP cells maintained their cytological characteristics. Micro-CT of layered cell sheet transplants revealed a mineralized capping of the access cavity in the crown area, similar to that of natural dentin. In contrast, the OD cell sheet group demonstrated the formation of irregular fragments of mineralized tissue in the pulp cavity, and the DP cell sheet did not develop any hard tissue. Moreover, bone volume/tissue volume (BV/TV) showed a significant increase in hard tissue formation in the layered cell sheet group compared with that in the single cell sheet group (p < 0.05). HE staining also showed a combination of soft and hard tissue formation in the layered cell sheet group. Furthermore, IHC confirmed that the dentin-like tissue generated from the layered cell sheet expressed characteristic markers of dentin but not bone equivalent to that of a natural tooth. In conclusion, this study demonstrates the feasibility of regenerating dentin-pulp complex using a bioengineered tissue designed to simulate the anatomical structure. Impact statement The dentin-pulp complex can be destroyed by deep caries and trauma, which may cause pulpitis and progress to irreversible pulpitis, apical periodontitis, and even tooth loss. Current treatments cannot maintain pulp health, and teeth can become brittle. We developed a three-dimensional (3D) layered cell sheet using dental pulp cells and odontogenic differentiation of pulp cells for dentin-pulp complex regeneration. Our layered cell sheet enables the regeneration of an organized 3D dentin-pulp-like structure comparable with that of natural teeth. This layered cell sheet technology may contribute to dentin-pulp complex regeneration and provide a novel method for complex tissue engineering.

Alternative non-oral nutrition in a rat model: a novel modified gastrostomy technique

The gastrostomy technique is essential for esophageal reconstruction using a scaffold. To date, there are no established methods to supply nutrients through a gastrostomy tube in rats. The purpose of this study was to analyze the feasibility of a newly modified gastrostomy technique for non-oral nutrition in an adult rat model. We modified the gastrostomy technique for adult rats in a few different ways. (1) The external opening for food injection was made at the midpoint between the ears to prevent damage due to self-harm behaviour. (2) An imbedded subcutaneous tunnel was created between the internal and external openings of the gastrostomy. We compared the efficacy and safety between groups with a T-tube for biliary drainage (TT group, n=14) and a conventional silicone Foley catheter (FC group, n=7) as optimal gastrostomy tubes for in a rat model. We also evaluated the feasibility of the heparin cap connector at the end of gastrostomy tube to control food supply in the TT group (with a cap, n=7; without a cap, n=7). No mortality was observed in the TT group with a cap, whereas most rats in the FC group died within 2 weeks after the procedure. Weight loss decreased significantly in the TT group with a cap compared with all the other groups. The appearance and attitude scores were significantly better in the TT group with a cap. In addition, histologic analysis showed that the TT group a cap showed a marked decrease over time in tissue fibrosis and macrophages compared with the other experimental groups. Therefore, gastrostomy using a silicone T-tube plugged with a cap proved to be a stable and effective option for non-oral feeding in an adult rat model.

A Near-Infrared-Triggered Dynamic Wrinkling Biointerface for Noninvasive Harvesting of Practical Cell Sheets

Cell sheet engineering represents a new era of precise and efficient regenerative medicine, but its efficacy is limited by the elaborative preparation and the weak mechanics. Herein, a near-infrared (NIR)-triggered dynamic wrinkling biointerface was designed for rapid acquisition of practical cell sheets. The biocompatible NIR can initiate the photothermal-mechanical linkage cascade to efficiently dissolve the collagen supporting layer and release the high-quality cell sheets. The interfacial shear force generates with the dynamic wrinkling, playing an active role in accelerating the cell sheet release. High-quality and self-supporting cell sheets can be harvested within a few minutes, demonstrating a new paradigm of photothermal-mechanical manipulation. The transplantable cell sheets with outstanding physiological and mechanical performances were proven to promote wound healing in skin regeneration. This method may open a completely new front in thermal and mechanical responsive cascade to harvest cell sheets, facilitating their wide applications in regenerative medicine.

A review of regulated self-organizing approaches for tissue regeneration

Tissue and organ regeneration is the dynamic process by which a population of cells rearranges into a specific form with specific functions. Traditional tissue regeneration utilizes tissue grafting, cell implantation, and structured scaffolds to achieve clinical efficacy. However, tissue grafting methods face a shortage of donor tissue, while cell implantation may involve leakage of the implanted cells without a supportive 3D matrix. Cell migration, proliferation, and differentiation in structured scaffolds may disorganize and frustrate the artificially pre-designed structures, and sometimes involve immunogenic reactions. To overcome this limitation, the self-organizing properties and innate regenerative capability of tissue/organism formation in the absence of guidance by structured scaffolds has been investigated. This review emphasizes the growing subfield of the regulated self-organizing approach for neotissue formation and describes advances in the subfield using diverse, cutting-edge, inter-disciplinarity technologies. We cohesively summarize the directed self-organization of cells in the micro-engineered cell-ECM system and 3D/4D cell printing. Mathematical modeling of cellular self-organization is also discussed for providing rational guidance to intractable problems in tissue regeneration. It is envisioned that future self-organization approaches integrating biomathematics, micro-nano engineering, and gene circuits developed from synthetic biology will continue to work in concert with self-organizing morphogenesis to enhance rational control during self-organizing in tissue and organ regeneration.

Assessment of human bioengineered cardiac tissue function in hypoxic and re-oxygenized environments to understand functional recovery in heart failure

Introduction

Myocardial recovery is one of the targets for heart failure treatment. A non-negligible number of heart failure with reduced ejection fraction (EF) patients experience myocardial recovery through treatment. Although myocardial hypoxia has been reported to contribute to the progression of heart failure even in non-ischemic cardiomyopathy, the relationship between contractile recovery and re-oxygenation and its underlying mechanisms remain unclear. The present study investigated the effects of hypoxia/re-oxygenation on bioengineered cardiac cell sheets-tissue function and the underlying mechanisms.

Methods

Bioengineered cardiac cell sheets-tissue was fabricated with human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CM) using temperature-responsive culture dishes. Cardiac tissue functions in the following conditions were evaluated with a contractile force measurement system: continuous normoxia (20% O₂) for 12 days; hypoxia (1% O₂) for 4 days followed by normoxia (20% O₂) for 8 days; or continuous hypoxia (1% O₂) for 8 days. Cell number, sarcomere structure, ATP levels, mRNA expressions and Ca²⁺ transients of hiPSC-CM in those conditions were also assessed.

Results

Hypoxia (4 days) elicited progressive decreases in contractile force, maximum contraction velocity, maximum relaxation velocity, Ca²⁺ transient amplitude and ATP level, but sarcomere structure and cell number were not affected. Re-oxygenation (8 days) after hypoxia (4 days) was associated with progressive increases in contractile force, maximum contraction velocity and relaxation time to the similar extent levels of continuous normoxia group, while maximum relaxation velocity was still significantly low even after re-oxygenation. Ca²⁺ transient magnitude, cell number, sarcomere structure and ATP level after re-oxygenation were similar to those in the continuous normoxia group. Hypoxia/re-oxygenation up-regulated mRNA expression of PLN.

Conclusions

Hypoxia and re-oxygenation condition directly affected human bioengineered cardiac tissue function. Further understanding the molecular mechanisms of functional recovery of cardiac tissue after re-oxygenation might provide us the new insight on heart failure with recovered ejection fraction and preserved ejection fraction.

Cardiac Tissues From Stem Cells: New Routes to Maturation and Cardiac Regeneration

The ability of human pluripotent stem cells to form all cells of the body has provided many opportunities to study disease and produce cells that can be used for therapy in regenerative medicine. Even though beating cardiomyocytes were among the first cell types to be differentiated from human pluripotent stem cell, cardiac applications have advanced more slowly than those, for example, for the brain, eye, and pancreas. This is, in part, because simple 2-dimensional human pluripotent stem cell cardiomyocyte cultures appear to need crucial functional cues normally present in the 3-dimensional heart structure. Recent tissue engineering approaches combined with new insights into the dialogue between noncardiomyocytes and cardiomyocytes have addressed and provided solutions to issues such as cardiomyocyte immaturity and inability to recapitulate adult heart values for features like contraction force, electrophysiology, or metabolism. Three-dimensional bioengineered heart tissues are thus poised to contribute significantly to disease modeling, drug discovery, and safety pharmacology, as well as provide new modalities for heart repair. Here, we review the current status of 3-dimensional engineered heart tissues.

Trends in Articular Cartilage Tissue Engineering: 3D Mesenchymal Stem Cell Sheets as Candidates for Engineered Hyaline-Like Cartilage

Articular cartilage defects represent an inciting factor for future osteoarthritis (OA) and degenerative joint disease progression. Despite multiple clinically available therapies that succeed in providing short term pain reduction and restoration of limited mobility, current treatments do not reliably regenerate native hyaline cartilage or halt cartilage degeneration at these defect sites. Novel therapeutics aimed at addressing limitations of current clinical cartilage regeneration therapies increasingly focus on allogeneic cells, specifically mesenchymal stem cells (MSCs), as potent, banked, and available cell sources that express chondrogenic lineage commitment capabilities. Innovative tissue engineering approaches employing allogeneic MSCs aim to develop three-dimensional (3D), chondrogenically differentiated constructs for direct and immediate replacement of hyaline cartilage, improve local site tissue integration, and optimize treatment outcomes. Among emerging tissue engineering technologies, advancements in cell sheet tissue engineering offer promising capabilities for achieving both in vitro hyaline-like differentiation and effective transplantation, based on controlled 3D cellular interactions and retained cellular adhesion molecules. This review focuses on 3D MSC-based tissue engineering approaches for fabricating “ready-to-use” hyaline-like cartilage constructs for future rapid in vivo regenerative cartilage therapies. We highlight current approaches and future directions regarding development of MSC-derived cartilage therapies, emphasizing cell sheet tissue engineering, with specific focus on regulating 3D cellular interactions for controlled chondrogenic differentiation and post-differentiation transplantation capabilities.

Cell sheet formation enhances the therapeutic effects of human umbilical cord mesenchymal stem cells on myocardial infarction as a bioactive material

Stem cell-based therapy has been used to treat ischaemic heart diseases for two decades. However, optimal cell types and transplantation methods remain unclear. This study evaluated the therapeutic effects of human umbilical cord mesenchymal stem cell (hUCMSC) sheet on myocardial infarction (MI).

Methods

hUCMSCs expressing luciferase were generated by lentiviral transduction for in vivo bio-luminescent imaging tracking of cells. We applied a temperature-responsive cell culture surface-based method to form the hUCMSC sheet. Cell retention was evaluated using an in vivo bio-luminescent imaging tracking system. Unbiased transcriptional profiling of infarcted hearts and further immunohistochemical assessment of monocyte and macrophage subtypes were used to determine the mechanisms underlying the therapeutic effects of the hUCMSC sheet. Echocardiography and pathological analyses of heart sections were performed to evaluate cardiac function, angiogenesis and left ventricular remodelling.

Results

When transplanted to the infarcted mouse hearts, hUCMSC sheet significantly improved the retention and survival compared with cell suspension. At the early stage of MI, hUCMSC sheet modulated inflammation by decreasing Mcp1-positive monocytes and CD68-positive macrophages and increasing Cx3cr1-positive non-classical macrophages, preserving the cardiomyocytes from acute injury. Moreover, the extracellular matrix produced by hUCMSC sheet then served as bioactive scaffold for the host cells to graft and generate new epicardial tissue, providing mechanical support and routes for revascularsation. These effects of hUCMSC sheet treatment significantly improved the cardiac function at days 7 and 28 post-MI.

Conclusions

hUCMSC sheet formation dramatically improved the biological functions of hUCMSCs, mitigating adverse post-MI remodelling by modulating the inflammatory response and providing bioactive scaffold upon transplantation into the heart.

Translational perspective

Due to its excellent availability as well as superior local cellular retention and survival, allogenic transplantation of hUCMSC sheets can more effectively acquire the biological functions of hUCMSCs, such as modulating inflammation and enhancing angiogenesis. Moreover, the hUCMSC sheet method allows the transfer of an intact extracellular matrix without introducing exogenous or synthetic biomaterial, further improving its clinical applicability.

•

Cell sheet formation of hUCMSCs dramatically improves post transplantation cell survival in the infarcted heart.

•

hUCMSC sheet protects cardiomyocytes from infarction by alleviating acute inflammation.

•

The ECM of cell sheet serves as bioactive scaffold to allow the host cells to integrate and form new epicardial tissue.

•

The new epicardial tissue can provide mechanical support and new routes for revascularization.

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.

A nonbiodegradable scaffold-free cell sheet of genome-engineered mesenchymal stem cells inhibits development of acute kidney injury

Cell therapy using genome-engineered stem cells has emerged as a novel strategy for the treatment of kidney diseases. By exploiting genome editing technology, human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) secreting an angiogenic factors or an anti-inflammatory factor were generated for therapeutic application in acute kidney injury. Junction polymerase chain reaction analysis verified zinc finger nucleases-assisted integration of the desired gene into the hUC-MSCs. Flow cytometry and differentiation assays indicated that genome editing did not affect the differentiation potential of these mesenchymal stem cells. Protein measurement in conditioned media with the use of ELISA and immunoblotting revealed the production and secretion of each integrated gene product. For cell therapy in the bilateral ischemia-reperfusion mouse model of acute kidney injury, our innovative scaffold-free cell sheets were established using a non-biodegradable temperature-responsive polymer. One of each type of scaffold-free cell sheets of either the angiogenic factor vascular endothelial grown factor or angiopoietin-1, or the anti-inflammatory factor erythropoietin, or α-melanocyte-stimulating hormone-secreting hUC-MSCs was applied to the decapsulated kidney surface. This resulted in significant amelioration of kidney dysfunction in the mice with acute kidney injury, effects that were superior to intravenous administration of the same genome-engineered hUC-MSCs. Thus, our scaffold-free cell sheets of genome-engineered mesenchymal stem cells provides therapeutic effects by inhibiting acute kidney injury via angiogenesis or anti-inflammation.

Tuning the thermoresponsive properties of PEG-based fluorinated polymers and stimuli responsive drug release for switchable 19F magnetic resonance imaging

Switching on of the 19F MRI signal via stimuli-responsive release of hydrophobic drug from PEG-based partly-fluorinated polymers due to change in thermoresponsive properties.

Novel pre-vascularized tissue-engineered dermis based on stem cell sheet technique used for dermis-defect healing

Insufficient donor dermis and the shortage of three-dimensional vascular networks are the main limitations in the tissue-engineered dermis (TED). To solve these problems, we initially constructed pre-vascularized bone marrow mesenchymal stem cell sheet (PBMCS) and pre-vascularized fibroblasts cell sheet (PFCS) by cell sheet technology, and then superimposed or folded them together to construct a pre-vascularized TED (PTED), aiming to mimic the real dermis structure. The constructed PTED was implanted in nude mice dorsal dermis-defect wound and the wound-healing effect was quantified at Days 1, 7 and 14 via the methods of histochemistry and immunohistochemistry. The results showed that PTED could rapidly promote the wound closure, especially at Day 14, and the wound-healing rate of three-layer PTED could reach 97.2% (P < 0.01), which was faster than the blank control group (89.1%), PBMCS (92.4%), PFCS (93.8%) and six-layer PTED (92.3%). In addition, the vessel density in the PTED group was higher than the other groups on the 14th day. Taken together, it is proved that the PTED, especially three-layer PTED, is more conducive to the full-thickness dermis-defect repair and the construction of the three-dimensional vascular networks, indicating its potential application in dermis-defect repair.

Transparent PDMS Bioreactors for the Fabrication and Analysis of Multi-Layer Pre-vascularized Hydrogels Under Continuous Perfusion

Tissue engineering in combination with stem cell technology has the potential to revolutionize human healthcare. It aims at the generation of artificial tissues that can mimic the original with complex functions for medical applications. However, even the best current designs are limited in size, if the transport of nutrients and oxygen to the cells and the removal of cellular metabolites waste is mainly dependent on passive diffusion. Incorporation of functional biomimetic vasculature within tissue engineered constructs can overcome this shortcoming. Here, we developed a novel strategy using 3D printing and injection molding technology to customize multilayer hydrogel constructs with pre-vascularized structures in transparent Polydimethysiloxane (PDMS) bioreactors. These bioreactors can be directly connected to continuous perfusion systems without complicated construct assembling. Mimicking natural layer-structures of vascular walls, multilayer vessel constructs were fabricated with cell-laden fibrin and collagen gels, respectively. The multilayer design allows functional organization of multiple cell types, i.e., mesenchymal stem cells (MSCs) in outer layer, human umbilical vein endothelial cells (HUVECs) the inner layer and smooth muscle cells in between MSCs and HUVECs layers. Multiplex layers with different cell types showed clear boundaries and growth along the hydrogel layers. This work demonstrates a rapid, cost-effective, and practical method to fabricate customized 3D-multilayer vascular models. It allows precise design of parameters like length, thickness, diameter of lumens and the whole vessel constructs resembling the natural tissue in detail without the need of sophisticated skills or equipment. The ready-to-use bioreactor with hydrogel constructs could be used for biomedical applications including pre-vascularization for transplantable engineered tissue or studies of vascular biology.

Complex-shaped magnetic 3D cell-based structures for tissue engineering

The use of cells as building blocks for tissue engineering purposes has been a matter of research in the recent years. Still, the fabrication of complex-shaped 3D-like constructs using living-based materials is hampered through the difficulty in recapitulating the mechanical properties of the native tissues. In an attempt to develop robust tissue-like constructs, it is herein proposed the fabrication of complex-shaped magnetic cell sheets (CSs) with improved mechanical properties for bone TE. Hence, magnetic CSs with versatile shapes and enhanced mechanical performance are fabricated using a pre-osteoblast cell line (MC3T3-E1) through an universal approach that relies on the design of the substrate, cell density and magnetic force. Results show that such magnetic CSs exhibit a Young's modulus similar to those encountered in the soft tissues. The construction of stratified CSs is also explored using MC3T3-E1 and adipose-derived stromal cells (ASCs). The role of the pre-osteoblast cell line on ASCs osteogenesis is herein investigated for the first time in layered scaffold-free structures. After 21 days, the level of osteogenic markers in the heterotypic CS (MC3T3-E1:ASCs) is significantly higher than in the homotypic one (ASCs:ASCs), even in the absence of osteogenic differentiation factors. These evidences open new prospects for the creation of mechanically robust, complex, higher-ordered and completely functional 3D cell-based materials that better resemble the native environment of in vivo tissues.

Fabrication of hyaline-like cartilage constructs using mesenchymal stem cell sheets

Cell and tissue engineering approaches for articular cartilage regeneration increasingly focus on mesenchymal stem cells (MSCs) as allogeneic cell sources, based on availability and innate chondrogenic potential. Many MSCs exhibit chondrogenic potential as three-dimensional (3D) cultures (i.e. pellets and seeded biomaterial scaffolds) in vitro; however, these constructs present engraftment, biocompatibility, and cell functionality limitations in vivo. Cell sheet technology maintains cell functionality as scaffold-free constructs while enabling direct cell transplantation from in vitro culture to targeted sites in vivo. The present study aims to develop transplantable hyaline-like cartilage constructs by stimulating MSC chondrogenic differentiation as cell sheets. To achieve this goal, 3D MSC sheets are prepared, exploiting spontaneous post-detachment cell sheet contraction, and chondrogenically induced. Results support 3D MSC sheets' chondrogenic differentiation to hyaline cartilage in vitro via post-contraction cytoskeletal reorganization and structural transformations. These 3D cell sheets' initial thickness and cellular densities may also modulate MSC-derived chondrocyte hypertrophy in vitro. Furthermore, chondrogenically differentiated cell sheets adhere directly to cartilage surfaces via retention of adhesion molecules while maintaining the cell sheets' characteristics. Together, these data support the utility of cell sheet technology for fabricating scaffold-free, hyaline-like cartilage constructs from MSCs for future transplantable articular cartilage regeneration therapies.

Thermosensitive "Smart" Surfaces for Biorecognition Based Cell Adhesion and Controlled Detachment

The biorecognition-based control of attachment/detachment of MCF-7 cancer cells from polymer-coated surfaces is demonstrated. A glass surface is coated with a thermoresponsive statistical copolymer of poly(N-isopropylacrylamide-co-acrylamide) [p(NIPAm-co-Am)], which is end-capped with the Gly-Arg-Gly-Asp-Ser (GRGDS) peptide, and the hydrophilic polymer poly(ethylene glycol) (PEG). Below the lower critical solution temperature (LCST) of p(NIPAm-co-Am) (38 °C), the copolymers are in the extended conformation, allowing for accessibility of the GRGDS peptides to membrane-associated integrins thus enabling cell attachment. Above the LCST, the p(NIPAm-co-Am) polymers collapse into globular conformations, resulting in the shielding of the GRGDS peptides into the PEG brush with consequent inaccessibility to cell-surface integrins, causing cell detachment. The surface coating is carried out by a multi-step procedure that included: glass surface amination with 3-aminopropyltriethoxysilane; reaction of mPEG_5kDa -N-hydroxysuccinimide (NHS) and p(NIPam-co-Am)_15.1kDa -bis-NHS with the surface aminopropyl groups and conjugation of GRGDS to the carboxylic acid termini of p(NIPam-co-Am)_15.1kDa -COOH. A range of spectrophotometric, surface, and microscopy assays confirmed the identity of the polymer-coated substrates. Competition studies prove that MCF-7 cancer cells are attached via peptide recognition at the coated surfaces according to the mPEG_5kDa /p(NIPam-co-Am)_15.1kDa -GRGDS molar ratio. These data suggest the system can be exploited to modulate cell integrin/GRGDS binding for controlled cell capture and release.

Enhanced healing of a full-thickness wound by a thermoresponsive dressing utilized for simultaneous transfer and protection of adipose-derived mesenchymal stem cells sheet

To boost the healing process in a full-thickness wound, a simple and efficient strategy based on adipose-derived mesenchymal stem cells (ADSCs) transplantation is described in this work. To increase the chance of ADSCs immobilization in the wound bed and prevent its migration, these cells are fully grown on the surface of a thermoresponsive dressing membrane under in vitro condition. Then, the cells sheet with their secreted extracellular matrix (ECM) is transferred to the damaged skin with the help of this dressing membrane. This membrane remains on wound bed and acts both as a cell sheet transfer vehicle, after external reduction of temperature, and protect wound during the healing process like a common wound dressing. The visual inspection of wounded skin (rat animal model) at selected time intervals shows a higher wound closure rate for ADSCs treated group. For this group of rats, the better quality of reconstructed tissue is approved by results of histological and immunohistochemical analysis since the higher length of the new epidermis, the higher thickness of re-epithelialization layer, a higher level of neovascularization and capillary density, and the least collagen deposition are detected in the healed tissue.

Electrothermal soft manipulator enabling safe transport and handling of thin cell/tissue sheets and bioelectronic devices

"Living" cell sheets or bioelectronic chips have great potentials to improve the quality of diagnostics and therapies. However, handling these thin and delicate materials remains a grand challenge because the external force applied for gripping and releasing can easily deform or damage the materials. This study presents a soft manipulator that can manipulate and transport cell/tissue sheets and ultrathin wearable biosensing devices seamlessly by recapitulating how a cephalopod's suction cup works. The soft manipulator consists of an ultrafast thermo-responsive, microchanneled hydrogel layer with tissue-like softness and an electric heater layer. The electric current to the manipulator drives microchannels of the gel to shrink/expand and results in a pressure change through the microchannels. The manipulator can lift/detach an object within 10 s and can be used repeatedly over 50 times. This soft manipulator would be highly useful for safe and reliable assembly and implantation of therapeutic cell/tissue sheets and biosensing devices.

Tenogenic adipose-derived stem cell sheets with nanoyarn scaffolds for tendon regeneration

Tissue engineering, especially cell sheets-based engineering, offers a promising approach to tendon regeneration; however, obtaining a sufficient source of cells for tissue engineering applications is challenging. Adipose-derived stem cells (ASCs) are essential sources for tissue regeneration and have been shown to have the potential for tenogenic differentiation in vitro via induction by growth differentiation factor 5 (GDF-5). In this study, we explored the feasibility of ASCs cell sheets stimulated by GDF-5 for engineered tendon repair. As shown by quantitative polymerase chain reaction and western blotting, tenogenesis-related markers (Col I&III, TNMD, biglycan, and tenascin C) were significantly increased in GDF-5-induced ASCs cell sheets compared with the uninduced. Moreover, the levels of SMAD2/3 proteins and phospho-SMAD1/5/9 were significantly enhanced, demonstrating that GDF-5 may exert its functions through phosphorylation of SMAD1/5/9. Furthermore, the cell sheets were combined with P(LLA-CL)/Silk fibroin nanoyarn scaffolds to form constructs for tendon tissue engineering. Terminal deoxynucleotidyl transferase dUTP nick end labeling and immunofluorescence assays demonstrated favorable cell viability and tenogenesis-related marker expression in GDF-5-induced constructs. In addition, the constructs showed the potential for tendon repair in rabbit models, as demonstrated by histological, immunohistochemical, and biomechanical analyses. In our study, we successfully produced a new tissue-engineered tendon by the combination of GDF-5-induced ASCs cell sheets and nanoyarn scaffold which is valuable for tendon regeneration.

Adhesion of Epithelial Cells to PNIPAm Treated Surfaces for Temperature-Controlled Cell-Sheet Harvesting

Stimuli responsive polymer coatings are a common motive for designing surfaces for cell biological applications. In the present study, we have characterized temperature dependent adhesive properties of poly(N-isopropylacrylamide) (PNIPAm) microgel coated surfaces (PMS) using various atomic force microscopy based approaches. We imaged and quantified the material properties of PMS upon a temperature switch using quantitative AFM imaging but also employed single-cell force spectroscopy (SCFS) before and after decreasing the temperature to assess the forces and work of initial adhesion between cells and PMS. We performed a detailed analysis of steps in the force-distance curves. Finally, we applied colloid probe atomic force microscopy (CP-AFM) to analyze the adhesive properties of two major components of the extracellular matrix to PMS under temperature control, namely collagen I and fibronectin. In combination with confocal imaging, we could show that these two ECM components differ in their detachment properties from PNIPAm microgel films upon cell harvesting, and thus gained a deeper understanding of cell-sheet maturation and harvesting process and the involved partial ECM dissolution.

100th Anniversary of Macromolecular Science Viewpoint: Poly(N-isopropylacrylamide)-Based Thermally Responsive Micelles

Poly(N-isopropylacrylamide) (PNIPAAm)-based thermally responsive micelles are of great importance as smart materials for a number of applications such as drug delivery and biosensing, owing to their tunable lower critical solution temperature (LCST). Their design and synthesis in the nanoscale size range have been widely studied, and research interest in their structural and physic-chemical properties is continually growing. In this Viewpoint, representative research on the construction of PNIPAAm-based thermally responsive micelles as well as their applications are highlighted and discussed, which would serve as a good start for newcomers in this field and a positive guide for future research.

Silk fibroin-based vascular repairing sheet with angiogenic-promoting activity of SVVYGLR peptide regenerated the damaged vascular in rats

Medical sheets are useful in surgically repair vascular disease. To avoid long-term side effects, they are to be replaced with regenerated tissue after implantation. Silk fibroin is a fibrous protein secreted by silkworm. The advantage of silk fibroin is its biocompatibility and has been used as regenerative artificial materials. The problem of its biodegradability is that the effect is time consuming. In this study, SVVYGLR peptide was used to expect promoting cell migration and accelerating the biodegradation of silk fibroin. Silk fibroin and polyurethane-based medical sheets with or without SVVYGLR peptide were implanted in rat abdominal aorta (silk fibroin/polyurethane/SVVYGLR peptide versus silk fibroin/polyurethane). The result of histological evaluation indicated that the new cell layer created under both sheets was composed of endothelial cells, smooth muscle, and fibroin in both sheets and similar to a native vessel. Both sheets did not show any excessive inflammation or calcification, and moderate biodegradability was observed. The decrease of silk fibroin indicated the biodegradability of all sheets. Silk fibroin/polyurethane/SVVYGLR peptide had many small vessels in the regenerated tissue than silk fibroin/polyurethane. This appearance indicated that SVVYGLR peptide promoted the angiogenesis in the regenerative tissue. This study suggested that SVVYGLR peptide could give the angiogenic-promoting activity to silk fibroin-based vascular repairing sheet.

Scaffold-Free tissue engineering with aligned bone marrow stromal cell sheets to recapitulate the microstructural and biochemical composition of annulus fibrosus

Current tissue engineering strategies through scaffold-based approaches fail to recapitulate the complex three-dimensional microarchitecture and biochemical composition of the native Annulus Fibrosus tissue. Considering limited access to healthy annulus fibrosus cells from patients, this study explored the potential of bone marrow stromal cells (BMSC) to fabricate a scaffold-free multilamellar annulus fibrosus-like tissue by integrating micropatterning technologies into multi-layered BMSC engineering. BMSC sheet with cells and collagen fibres aligned at ~30° with respect to their longitudinal dimension were developed on a microgroove-patterned PDMS substrate. Two sheets were then stacked together in alternating directions to form an angle-ply bilayer tissue, which was rolled up, sliced to form a multi-lamellar angle-ply tissue and cultured in a customized medium. The development of the annulus fibrosus-like tissue was further characterized by histological, gene expression and microscopic and mechanical analysis. We demonstrated that the engineered annulus fibrosus-like tissue with aligned BMSC sheet showed parallel collagen fibrils, biochemical composition and microstructures that resemble the native disk. Furthermore, aligned cell sheet showed enhanced expression of annulus fibrosus associated extracellular matrix markers and higher mechanical strength than that of the non-aligned cell sheet. The present study provides a new strategy in annulus fibrosus tissue engineering methodology to develop a scaffold-free annulus fibrosus-like tissue that resembles the microarchitecture and biochemical attributes of a native tissue. This can potentially lead to a promising avenue for advancing BMSC-mediated annulus fibrosus regeneration towards future clinical applications.

Tissue Engineering and Regenerative Medicine: Achievements, Future, and Sustainability in Asia

Exploring innovative solutions to improve the healthcare of the aging and diseased population continues to be a global challenge. Among a number of strategies toward this goal, tissue engineering and regenerative medicine (TERM) has gradually evolved into a promising approach to meet future needs of patients. TERM has recently received increasing attention in Asia, as evidenced by the markedly increased number of researchers, publications, clinical trials, and translational products. This review aims to give a brief overview of TERM development in Asia over the last decade by highlighting some of the important advances in this field and featuring major achievements of representative research groups. The development of novel biomaterials and enabling technologies, identification of new cell sources, and applications of TERM in various tissues are briefly introduced. Finally, the achievement of TERM in Asia, including important publications, representative discoveries, clinical trials, and examples of commercial products will be introduced. Discussion on current limitations and future directions in this hot topic will also be provided.

Esophageal regenerative therapy using cell sheet technology

We have been conducting research on esophageal regenerative therapy using cell sheet technology. In particular, in the endoscopic field, we have pushed forward clinical research on endoscopic transplantation of cultured autologous oral mucosal epithelial cell sheets to esophageal ulcer after endoscopic submucosal dissection (ESD). We started research in this direction using animal models in 2004 and performed clinical research in 2012 in collaboration with Nagasaki University and Karolinska Institute. Although in full-circumferential cases it was difficult to prevent esophageal stricture after ESD, there were no complications and stricture could be suppressed. The cell sheet technology is still in its infancy. However, we are convinced that it has a high potential for application in various areas of gastrointestinal science. In this review, we focus on the pre-clinical and clinical trial results obtained and on the theoretical aspects of (1) stricture prevention, (2) esophageal tissue engineering research, and (3) endoscopic transplantation, and review the esophageal regenerative therapy by cell sheet technology.

Structure and ingredient-based biomimetic scaffolds combining with autologous bone marrow-derived mesenchymal stem cell sheets for bone-tendon healing

Tendon attaches to bone across a robust fibrocartilaginous tissue termed the bone-tendon interface (BTI), commonly injured in the field of sports medicine and orthopedics with poor prognosis. So far, there is still a lack of effective clinical interventions to achieve functional healing post BTI injury. However, tissue-engineering may be a promising treatment strategy. In this study, a gradient book-type triphasic (bone-fibrocartilage-tendon) scaffold is fabricated based on the heterogeneous structure and ingredient of BTI. After decellularization, the scaffold exhibits no residual cells, while the characteristic extracellular matrix of the original bone, fibrocartilage and tendon is well preserved. Meanwhile, the bone, fibrocartilage and tendon regions of the acellular scaffold are superior in osteogenic, chondrogenic and tenogenic inducibility, respectively. Furthermore, autologous bone marrow mesenchymal stem cell (BMSC) sheets (CS) combined with the acellular scaffolds is transplanted into the lesion site of a rabbit BTI injury model to investigate the therapeutic effects. Our results show that the CS modified scaffold not only successfully achieves triple biomimetic of BTI in structure, ingredient and cell distribution, but also effectively accelerates bone-tendon (B-T) healing. In general, this work demonstrates book-type acellular triphasic scaffold combined with autologous BMSCs sheets is a promising graft for repairing BTI injury.