Cell sheet engineering for regenerative medicine: current challenges and strategies

Transplantation of Neural Progenitor Cells Derived from Stem Cells from Apical Papilla Through Small-Molecule Induction in a Rat Model of Sciatic Nerve Injury

BACKGROUND

Stem cell-based transplantation therapy holds promise for peripheral nerve injury treatment, but adult availability is limited. A cell culture protocol utilizing a small-molecule cocktail effectively reprogrammed stem cells from apical papilla (SCAPs) into neural progenitor cells, subsequently differentiating into neuron-like cells. This study aims to evaluate neural-induced SCAPs, with and without small-molecule cocktail, for sciatic nerve repair potential.

METHODS

A scaffold-free cell sheet technique was used to construct a three-dimensional cell sheet. Subsequently, this cell sheet was carefully rolled into a tube and seamlessly inserted into a collagen conduit, which was then transplanted into a 5 mm sciatic nerve injury rat model. Functional sciatic nerve regeneration was evaluated via toe spread test, walking track analysis and gastrocnemius muscle weight. Additionally, degree of sciatic nerve regeneration was determined based on total amount of myelinated fibers.

RESULTS

Small-molecule cocktail induced SCAPs enhanced motor function recovery, evident in improved sciatic function index and gastrocnemius muscle retention. We also observed better host myelinated fiber retention than undifferentiated SCAPs or neural-induced SCAPs without small-molecule cocktail. However, clusters of neuron-like cell bodies (surrounded by sparse myelinated fibers) were found in all cell sheet-implanted groups in the implantation region. This suggests that while the implanted cells likely survived transplantation, integration was poor and would likely hinder long-term recovery by occupying the space needed for host nerve fibers to project through.

CONCLUSION

Neural-induced SCAPs with small-molecule cocktail demonstrated promising benefits for nerve repair; further research is needed to improve its integration and optimize its potential for long-term recovery.

Rapamycin Inhibits Senescence and Improves Immunomodulatory Function of Mesenchymal Stem Cells Through IL-8 and TGF-β Signaling

Mesenchymal stromal cells (MSCs) grown in high-density monolayers (sheets) are promising vehicles for numerous bioengineering applications. When MSC sheets are maintained in prolonged cultures, they undergo rapid senescence, limiting their downstream efficacy. Although rapamycin is a potential agent that can inhibit senescence in cell cultures, no study has investigated rapamycin's effect on MSCs grown in high-density culture and its effect on downstream target gene expression. In this study, placental-derived MSCs (PMSCs) were seeded at high density to generate PMSC sheets in 24 hours and were then treated with rapamycin or vehicle for up to 7 days. Autophagy activity, cell senescence and apoptosis, cell size and granularity, and senescence-associated cytokines (IL-6 and IL-8) were analyzed. Differential response in gene expression were assessed via microarray analysis. Rapamycin significantly increased PMSC sheet autophagy activity, inhibited cellular senescence, decreased cell size and granularity at all timepoints. Rapamycin also significantly decreased the number of cells in late apoptosis at day 7 of sheet culture, as well as caspase 3/7 activity at all timepoints. Notably, while rapamycin decreased IL-6 secretion, increased IL-8 levels were observed at all timepoints. Microarray analysis further confirmed the upregulation of IL-8 transcription, as well as provided a list of 396 genes with 2-fold differential expression, where transforming growth factor-β (TGF-β) signaling were identified as important upregulated pathways. Rapamycin both decreased senescence and has an immunomodulatory action of PMSCs grown in sheet culture, which will likely improve the chemotaxis of pro-healing cells to sites of tissue repair in future bioengineering applications.

Recent Advances in Cell Sheet-Based Tissue Engineering for Bone Regeneration

In conventional bone tissue engineering, cells are seeded onto scaffolds to create three-dimensional (3D) tissues, but the cells on the scaffolds are unable to effectively perform their physiological functions due to their low density and viability. Cell sheet (CS) engineering is expected to be free from this limitation. CS engineering uses the principles of self-assembly and self-organization of endothelial and mesenchymal stem cells to prepare CSs as building blocks for engineering bone grafts. This process recapitulates the native tissue development, thus attracting significant attention in the field of bone regeneration. However, the method is still in the prebasic experimental stage in bone defect repair. To make the method clinically applicable and valuable in personalized and precision medicine, current research is focused on the preparation of multifunctionalized building blocks using CS technologies, such as 3D layered CSs containing microvascular structures. Considering the great potential of CS engineering in repairing bone defects, in this review, the types of cell technologies are first outlined. We then summarize the various types of CSs as building blocks for engineering bone grafts. Furthermore, the specific applications of CSs in bone repair are discussed. Finally, we present specific suggestions for accelerating the application of CS engineering in the clinical treatment of bone defects.

A new technology for the treatment of premature ovarian insufficiency: Cell sheet

Premature ovarian insufficiency (POI) is defined as the development of hypergonadotropic hypogonadism before the age of 40 with definitive treatment being absent. In the current study, we aim to compare the efficacy of the cell sheet method with an intravenous (IV) application of adipose-derived mesenchymal stem cells (AdMSCs) to the POI with an animal model. In the current prospective study, 6-to-8-week-old Sprague Dawley rats were generated four groups: (i) a control group in which only PBS was administered; (ii) an only-POI group generated by cyclophosphamide; (iii) a POI group treated by way of IV AdMSCs; and (iv) a POI group treated by way of the cell sheet method. Twenty-eight days after an oophorectomy was performed, intracardiac blood was taken. Follicle count, immunohistochemical examination for GDF9, BMP15, and TUNEL were conducted, gene expressions of GDF9 and BMP15 were examined, and E2 was measured in the serum samples. With hematoxylin-eosin, in the third group, multi oocytes follicles were the most remarkable finding. In the fourth group, most of the follicles presented normal morphology. GDF9 involvement was similar between the first and fourth groups. BMP-15 immunoreactivity, in contrast to fourth group, was weak in all stages in the second and third groups. The current attempt represents a pioneer study in the literature in which a cell sheet method is used for the first time in a POI model. These results suggest that the cell sheet method may be a feasible and efficient method for the stem cell treatment of models with POI and could be a new treatment approach in POI.

Research progress of biomimetic materials in oral medicine

Biomimetic materials are able to mimic the structure and functional properties of native tissues especially natural oral tissues. They have attracted growing attention for their potential to achieve configurable and functional reconstruction in oral medicine. Though tremendous progress has been made regarding biomimetic materials, significant challenges still remain in terms of controversy on the mechanism of tooth tissue regeneration, lack of options for manufacturing such materials and insufficiency of in vivo experimental tests in related fields. In this review, the biomimetic materials used in oral medicine are summarized systematically, including tooth defect, tooth loss, periodontal diseases and maxillofacial bone defect. Various theoretical foundations of biomimetic materials research are reviewed, introducing the current and pertinent results. The benefits and limitations of these materials are summed up at the same time. Finally, challenges and potential of this field are discussed. This review provides the framework and support for further research in addition to giving a generally novel and fundamental basis for the utilization of biomimetic materials in the future.

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.

Fibronectin-Enriched Interface Using a Spheroid-Converged Cell Sheet for Effective Wound Healing

Cell sheets and spheroids are cell aggregates with excellent tissue-healing effects. However, their therapeutic outcomes are limited by low cell-loading efficacy and low extracellular matrix (ECM). Preconditioning cells with light illumination has been widely accepted to enhance reactive oxygen species (ROS)-mediated ECM expression and angiogenic factor secretion. However, there are difficulties in controlling the amount of ROS required to induce therapeutic cell signaling. Here, we develop a microstructure (MS) patch that can culture a unique human mesenchymal stem cell complex (hMSCcx), spheroid-attached cell sheets. The spheroid-converged cell sheet structure of hMSCcx shows high ROS tolerance compared to hMSC cell sheets owing to its high antioxidant capacity. The therapeutic angiogenic efficacy of hMSCcx is reinforced by regulating ROS levels without cytotoxicity using light (610 nm wavelength) illumination. The reinforced angiogenic efficacy of illuminated hMSCcx is based on the increased gap junctional interaction by enhanced fibronectin. hMSCcx engraftment is significantly improved in our novel MS patch by means of ROS tolerative structure of hMSCcx, leading to robust wound-healing outcomes in a mouse wound model. This study provides a new method to overcome the limitations of conventional cell sheets and spheroid therapy.

Application of Nanomaterials in Stem Cell-Based Therapeutics for Cardiac Repair and Regeneration

Cardiovascular disease is a leading cause of disability and death worldwide. Although the survival rate of patients with heart diseases can be improved with contemporary pharmacological treatments and surgical procedures, none of these therapies provide a significant improvement in cardiac repair and regeneration. Stem cell-based therapies are a promising approach for functional recovery of damaged myocardium. However, the available stem cells are difficult to differentiate into cardiomyocytes, which result in the extremely low transplantation efficiency. Nanomaterials are widely used to regulate the myocardial differentiation of stem cells, and play a very important role in cardiac tissue engineering. This study discusses the current status and limitations of stem cells and cell-derived exosomes/micro RNAs based cardiac therapy, describes the cardiac repair mechanism of nanomaterials, summarizes the recent advances in nanomaterials used in cardiac repair and regeneration, and evaluates the advantages and disadvantages of the relevant nanomaterials. Besides discussing the potential clinical applications of nanomaterials in cardiac therapy, the perspectives and challenges of nanomaterials used in stem cell-based cardiac repair and regeneration are also considered. Finally, new research directions in this field are proposed, and future research trends are highlighted.

Mesenchymal Stromal/Stem Cell (MSC)-Based Vector Biomaterials for Clinical Tissue Engineering and Inflammation Research: A Narrative Mini Review

Mesenchymal stromal/stem cells (MSCs) have the ability of self-renewal, the potential of multipotent differentiation, and a strong paracrine capacity, which are mainly used in the field of clinical medicine including dentistry and orthopedics. Therefore, tissue engineering research using MSCs as seed cells is a current trending directions. However, the healing effect of direct cell transplantation is unstable, and the paracrine/autocrine effects of MSCs cannot be effectively elicited. Tumorigenicity and heterogeneity are also concerns. The combination of MSCs as seed cells and appropriate vector materials can form a stable cell growth environment, maximize the secretory features of stem cells, and improve the biocompatibility and mechanical properties of vector materials that facilitate the delivery of drugs and various secretory factors. There are numerous studies on tissue engineering and inflammation of various biomaterials, mainly involving bioceramics, alginate, chitosan, hydrogels, cell sheets, nanoparticles, and three-dimensional printing. The combination of bioceramics, hydrogels and cell sheets with stem cells has demonstrated good therapeutic effects in clinical applications. The application of alginate, chitosan, and nanoparticles in animal models has also shown good prospects for clinical applications. Three-dimensional printing technology can circumvent the shortage of biomaterials, greatly improve the properties of vector materials, and facilitate the transplantation of MSCs. The purpose of this narrative review is to briefly discuss the current use of MSC-based carrier biomaterials to provide a useful resource for future tissue engineering and inflammation research using stem cells as seed cells.

Fabrication and Characterization Techniques of In Vitro 3D Tissue Models

The culturing of cells in the laboratory under controlled conditions has always been crucial for the advancement of scientific research. Cell-based assays have played an important role in providing simple, fast, accurate, and cost-effective methods in drug discovery, disease modeling, and tissue engineering while mitigating reliance on cost-intensive and ethically challenging animal studies. The techniques involved in culturing cells are critical as results are based on cellular response to drugs, cellular cues, external stimuli, and human physiology. In order to establish in vitro cultures, cells are either isolated from normal or diseased tissue and allowed to grow in two or three dimensions. Two-dimensional (2D) cell culture methods involve the proliferation of cells on flat rigid surfaces resulting in a monolayer culture, while in three-dimensional (3D) cell cultures, the additional dimension provides a more accurate representation of the tissue milieu. In this review, we discuss the various methods involved in the development of 3D cell culture systems emphasizing the differences between 2D and 3D systems and methods involved in the recapitulation of the organ-specific 3D microenvironment. In addition, we discuss the latest developments in 3D tissue model fabrication techniques, microfluidics-based organ-on-a-chip, and imaging as a characterization technique for 3D tissue models.

Challenges of Periodontal Tissue Engineering: Increasing Biomimicry through 3D Printing and Controlled Dynamic Environment

In recent years, tissue engineering studies have proposed several approaches to regenerate periodontium based on the use of three-dimensional (3D) tissue scaffolds alone or in association with periodontal ligament stem cells (PDLSCs). The rapid evolution of bioprinting has sped up classic regenerative medicine, making the fabrication of multilayered scaffolds-which are essential in targeting the periodontal ligament (PDL)-conceivable. Physiological mechanical loading is fundamental to generate this complex anatomical structure ex vivo. Indeed, loading induces the correct orientation of the fibers forming the PDL and maintains tissue homeostasis, whereas overloading or a failure to adapt to mechanical load can be at least in part responsible for a wrong tissue regeneration using PDLSCs. This review provides a brief overview of the most recent achievements in periodontal tissue engineering, with a particular focus on the use of PDLSCs, which are the best choice for regenerating PDL as well as alveolar bone and cementum. Different scaffolds associated with various manufacturing methods and data derived from the application of different mechanical loading protocols have been analyzed, demonstrating that periodontal tissue engineering represents a proof of concept with high potential for innovative therapies in the near future.

Nanomaterial-based cell sheet technology for regenerative medicine and tissue engineering

Nanomaterial-based cell sheet technology has been reported to be an effective method in regenerative medicine and tissue engineering. Here, we summarized several types of nanomaterials used to harvest cell sheets. Currently, the technology is divided into four categories according to the mechanisms: light-induced cell sheet technology, thermo-responsive cell sheet technology, magnetic-controlled cell sheet technology, and reactive oxygen species (ROS)-induced cell sheet technology. Furthermore, some studies have been conducted to show that nanomaterial-based cell sheets produce satisfying outcomes in the regeneration of bone, skeletal muscle, cardiac tissue, and tendon, as well as angiogenesis and osseointegration. Nevertheless, some shortcomings still exist, such as comprehensive preparation, unclear safety, and cell quality. Thus, future studies should aim to produce more types of nanomaterials to solve this problem.

Scaffold-Free Strategy Using a PEG-Dextran Aqueous Two-Phase-System for Corneal Tissue Repair

Forming thin tissue constructs with minimal extracellular matrix surrounding them is important for tissue engineering applications. Here, we explore and optimize a strategy that enables rapid fabrication of scaffold-free corneal tissue constructs using the liquid-liquid interface of an aqueous two-phase system (ATPS) that is based on biocompatible polymers, dextran and polyethylene glycol. Intact tissue-like constructs, made of corneal epithelial or endothelial cells, can be formed on the interface between the two liquid phases of ATPS within hours and subsequently collected simply by removing the liquid phases. The formed corneal cell constructs express essential physiological markers and have preserved viability and proliferative ability in vitro. The corneal epithelial cell constructs are also able to re-epithelialize the corneal epithelial wound in vitro. The results suggest the promise of our reported strategy in corneal repair.

Human Umbilical Cord Mesenchymal Stem Cells: Current Literature and Role in Periodontal Regeneration

Periodontal disease can cause irreversible damage to tooth-supporting tissues such as the root cementum, periodontal ligament, and alveolar bone, eventually leading to tooth loss. While standard periodontal treatments are usually helpful in reducing disease progression, they cannot repair or replace lost periodontal tissue. Periodontal regeneration has been demonstrated to be beneficial in treating intraosseous and furcation defects to varied degrees. Cell-based treatment for periodontal regeneration will become more efficient and predictable as tissue engineering and progenitor cell biology advance, surpassing the limitations of present therapeutic techniques. Stem cells are undifferentiated cells with the ability to self-renew and differentiate into several cell types when stimulated. Mesenchymal stem cells (MSCs) have been tested for periodontal regeneration in vitro and in humans, with promising results. Human umbilical cord mesenchymal stem cells (UC-MSCs) possess a great regenerative and therapeutic potential. Their added benefits comprise ease of collection, endless source of stem cells, less immunorejection, and affordability. Further, their collection does not include the concerns associated with human embryonic stem cells. The purpose of this review is to address the most recent findings about periodontal regenerative mechanisms, different stem cells accessible for periodontal regeneration, and UC-MSCs and their involvement in periodontal regeneration.

Optimization of a Tricalcium Phosphate-Based Bone Model Using Cell-Sheet Technology to Simulate Bone Disorders

Bone diseases such as osteoporosis, delayed or impaired bone healing, and osteoarthritis still represent a social, financial, and personal burden for affected patients and society. Fully humanized in vitro 3D models of cancellous bone tissue are needed to develop new treatment strategies and meet patient-specific needs. Here, we demonstrate a successful cell-sheet-based process for optimized mesenchymal stromal cell (MSC) seeding on a β-tricalcium phosphate (TCP) scaffold to generate 3D models of cancellous bone tissue. Therefore, we seeded MSCs onto the β-TCP scaffold, induced osteogenic differentiation, and wrapped a single osteogenically induced MSC sheet around the pre-seeded scaffold. Comparing the wrapped with an unwrapped scaffold, we did not detect any differences in cell viability and structural integrity but a higher cell seeding rate with osteoid-like granular structures, an indicator of enhanced calcification. Finally, gene expression analysis showed a reduction in chondrogenic and adipogenic markers, but an increase in osteogenic markers in MSCs seeded on wrapped scaffolds. We conclude from these data that additional wrapping of pre-seeded scaffolds will provide a local niche that enhances osteogenic differentiation while repressing chondrogenic and adipogenic differentiation. This approach will eventually lead to optimized preclinical in vitro 3D models of cancellous bone tissue to develop new treatment strategies.

Photothermal scaffolds/surfaces for regulation of cell behaviors

Regulation of cell behaviors and even cell fates is of great significance in diverse biomedical applications such as cancer treatment, cell-based therapy, and tissue engineering. During the past decades, diverse methods have been developed to regulate cell behaviors such as applying external stimuli, delivering exogenous molecules into cell interior and changing the physicochemical properties of the substrates where cells adhere. Photothermal scaffolds/surfaces refer to a kind of materials embedded or coated with photothermal agents that can absorb light with proper wavelength (usually in near infrared region) and convert light energy to heat; the generated heat shows great potential for regulation of cell behaviors in different ways. In the current review, we summarize the recent research progress, especially over the past decade, of using photothermal scaffolds/surfaces to regulate cell behaviors, which could be further categorized into three types: (i) killing the tumor cells via hyperthermia or thermal ablation, (ii) engineering cells by intracellular delivery of exogenous molecules via photothermal poration of cell membranes, and (iii) releasing a single cell or an intact cell sheet via modulation of surface physicochemical properties in response to heat. In the end, challenges and perspectives in these areas are commented.

Recent Progress in in vitro Models for Atherosclerosis Studies

Atherosclerosis is the primary cause of hardening and narrowing arteries, leading to cardiovascular disease accounting for the high mortality in the United States. For developing effective treatments for atherosclerosis, considerable efforts have been devoted to developing in vitro models. Compared to animal models, in vitro models can provide great opportunities to obtain data more efficiently, economically. Therefore, this review discusses the recent progress in in vitro models for atherosclerosis studies, including traditional two-dimensional (2D) systems cultured on the tissue culture plate, 2D cell sheets, and recently emerged microfluidic chip models with 2D culture. In addition, advanced in vitro three-dimensional models such as spheroids, cell-laden hydrogel constructs, tissue-engineered blood vessels, and vessel-on-a-chip will also be covered. Moreover, the functions of these models are also summarized along with model discussion. Lastly, the future perspectives of this field are discussed.

The Developing Field of Scaffold-Free Tissue Engineering for Articular Cartilage Repair

Articular cartilage is critical for proper joint mobility as it provides a smooth and lubricated surface between articulating bones and allows for transmission of load to underlying bones. Extended wear or injury of this tissue can result in osteoarthritis, a degenerative disease affecting millions across the globe. Because of its low regenerative capacity, articular cartilage cannot heal on its own and effective treatments for injured joint restoration remain a challenge. Strategies in tissue engineering have been demonstrated as potential therapeutic approaches to regenerate and repair damaged articular cartilage. Although many of these strategies rely on the use of an exogenous three-dimensional scaffolds to regenerate cartilage, scaffold-free tissue engineering provides numerous advantages over scaffold-based methods. This review highlights the latest advancements in scaffold-free tissue engineering for cartilage and the potential for clinical translation.

Immunomodulation in the Treatment of Periodontitis: Progress and Perspectives

Periodontitis is one of the most common dental diseases. Compared with healthy periodontal tissues, the immune microenvironment plays the key role in periodontitis by allowing the invasion of pathogens. It is possible that modulating the immune microenvironment can supplement traditional treatments and may even promote periodontal regeneration by using stem cells, bacteria, etc. New anti-inflammatory therapies can enhance the generation of a viable local immune microenvironment and promote cell homing and tissue formation, thereby achieving higher levels of immune regulation and tissue repair. We screened recent studies to summarize the advances of the immunomodulatory treatments for periodontitis in the aspects of drug therapy, microbial therapy, stem cell therapy, gene therapy and other therapies. In addition, we included the changes of immune cells and cytokines in the immune microenvironment of periodontitis in the section of drug therapy so as to make it clearer how the treatments took effects accordingly. In the future, more research needs to be done to improve immunotherapy methods and understand the risks and long-term efficacy of these methods in periodontitis.

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.

Development of alternative gene transfer techniques for ex vivo and in vivo gene therapy in a canine model

INTRODUCTION

Gene therapy have recently attracted much attention as a curative therapeutic option for inherited single gene disorders such as hemophilia. Hemophilia is a hereditary bleeding disorder caused by the deficiency of clotting activity of factor VIII (FVIII) or factor IX (FIX), and gene therapy for hemophilia using viral vector have been vigorously investigated worldwide. Toward further advancement of gene therapy for hemophilia, we have previously developed and validated the efficacy of novel two types of gene transfer technologies using a mouse model of hemophilia A. Here we investigated the efficacy and safety of the technologies in canine model. Especially, validations of technical procedures of the gene transfers for dogs were focused.

METHODS

Green fluorescence protein (GFP) gene were transduced into normal beagle dogs by ex vivo and in vivo gene transfer techniques. For ex vivo gene transfer, blood outgrowth endothelial cells (BOECs) derived from peripheral blood of normal dogs were transduced with GFP gene using lentivirus vector, propagated, fabricated as cell sheets, then implanted onto the omentum of the same dogs. For in vivo gene transfer, normal dogs were subjected to GFP gene transduction with non-viral piggyBac vector by liver-targeted hydrodynamic injections.

RESULTS

No major adverse events were observed during the gene transfers in both gene transfer systems. As for ex vivo gene transfer, histological findings from the omental biopsy performed 4 weeks after implantation revealed the tube formation by implanted GFP-positive BOECs in the sub-adipose tissue layer without any inflammatory findings, and the detected GFP signals were maintained over 6 months. Regarding in vivo gene transfer, analyses of liver biopsy samples revealed more than 90% of liver cells were positive for GFP signals in the injected liver lobes 1 week after gene transfers, then the signals gradually declined overtime.

CONCLUSIONS

Two types of gene transfer techniques were successfully applied to a canine model, and the transduced gene expressions persisted for a long term. Toward clinical application for hemophilia patients, practical assessments of therapeutic efficacy of these techniques will need to be performed using a dog model of hemophilia and FVIII (or FIX) gene.

Chemically Crosslinked Methylcellulose Substrates for Cell Sheet Engineering

Methylcellulose (MC) hydrogels have been successfully proposed in the field of cell sheet engineering (CSE), allowing cell detachment from their surface by lowering the temperature below their transition temperature (Tt). Among the main limitations of pristine MC hydrogels, low physical stability and mechanical performances limit the breadth of their potential applications. In this study, a crosslinking strategy based on citric acid (CA) was used to prepare thermoresponsive MC hydrogels, with different degrees of crosslinking, to exploit their possible use as substrates in CSE. The investigated amounts of CA did not cause any cytotoxic effect while improving the mechanical performance of the hydrogels (+11-fold increase in E, compared to control MC). The possibility to obtain cell sheets (CSs) was then demonstrated using murine fibroblast cell line (L929 cells). Cells adhered on crosslinked MC hydrogels' surface in standard culture conditions and then were harvested at selected time points as single CSs. CS detachment was achieved simply by lowering the external temperature below the Tt of MC. The detached CSs displayed adhesive and proliferative activity when transferred to new plastic culture surfaces, indicating a high potential for regenerative purposes.

Manufacturing of animal products by the assembly of microfabricated tissues

With the current rapidly growing global population, the animal product industry faces challenges which not only demand drastically increased amounts of animal products but also have to limit the emission of greenhouse gases and animal waste. These issues can be solved by the combination of microfabrication and tissue engineering techniques, which utilize the microtissue as a building component for larger tissue assembly to fabricate animal products. Various methods for the assembly of microtissue have been proposed such as spinning, cell layering, and 3D bioprinting to mimic the intricate morphology and function of the in vivo animal tissues. Some of the demonstrations on cultured meat and leather-like materials present promising outlooks on the emerging field of in vitro production of animal products.

Cellular therapy for myocardial ischemia using a temperature-responsive biodegradable injectable polymer system with adipose-derived stem cells

Adipose-derived stem cell (AdSC) has been attracting attention as a convenient stem cell source. Not only AdSC can differentiate into various tissue cells, but it can also accelerate cell proliferation, anti-inflammation, and angiogenesis by secreting paracrine factors. Studies have demonstrated AdSC treatment of ischemic heart. However, an improvement in the remaining live AdSCs administered at the injected site while maintaining paracrine factor secretion is desired to achieve effective regenerative medicine. We previously reported the ABA-type tri-block copolymer of poly(ɛ-caprolactone-co-glycolic acid) and poly(ethylene glycol) (tri-PCG), exhibiting temperature-responsive sol-to-gel transition as biodegradable injectable polymer (IP) systems. Moreover, we recently reported that the biodegradable temperature-triggered chemically cross-linked gelation systems exhibited longer gel state durations using tri-PCG attaching acryloyl groups and a polythiol derivative. In this study, we explored this IP-mediated AdSC delivery system. We investigated the cell viability, mRNA expression, and cytokine secretion of AdSCs cultured in the physical or chemical IP hydrogels. Both of these IP hydrogels retained a certain number of viable cells, and RT-PCR and ELISA analyses revealed that mRNA expression and secretion of vascular endothelial growth factor of the AdSCs cultured in the chemical hydrogel were higher than the physical hydrogel. Moreover, AdSCs injected with the chemical hydrogel into ischemic heart model mice showed longer retention of the cells at the injected site and recovery from the ischemic condition. The results mean that the IP system is a promising candidate for a stem cell delivery system that exhibits the recovery of cardiac function for myocardial infarction treatment.

Recent advances in regenerative medicine strategies for cancer treatment

Cancer stands as one of the most leading causes of death worldwide, while one of the most significant challenges in treating it is revealing novel alternatives to predict, diagnose, and eradicate tumor cell growth. Although various methods, such as surgery, chemotherapy, and radiation therapy, are used today to treat cancer, its mortality rate is still high due to the numerous shortcomings of each approach. Regenerative medicine field, including tissue engineering, cell therapy, gene therapy, participate in cancer treatment and development of cancer models to improve the understanding of cancer biology. The final intention is to convey fundamental and laboratory research to effective clinical treatments, from the bench to the bedside. Proper interpretation of research attempts helps to lessen the burden of treatment and illness for patients. The purpose of this review is to investigate the role of regenerative medicine in accelerating and improving cancer treatment. This study examines the capabilities of regenerative medicine in providing novel cancer treatments and the effectiveness of these treatments to clarify this path as much as possible and promote advanced future research in this field.

Multi-layered in vitro 3D-bone model via combination of osteogenic cell sheets with electrospun membrane interlayer

In this study, it was aimed to present an approach for the development of multi-layered tissue engineering constructs by using cell sheet engineering. Briefly, MC3T3-E1 mouse pre-osteoblast cells were cultured in temperature-responsive plates (Nunc Upcell®) in the presence of osteogenic medium and the resulting cell sheets were laminated with electrospun poly(L-lactic acid) (PLLA) membranes to obtain viable three-dimensional, thick constructs. The constructs prepared without PLLA membranes were used as control. The cell viability and death in the resulting structures were investigated by microscopic and colorimetric methods. The in vitro performance of the structures was discussed comparatively. Alkaline phosphatase (ALP) activity, collagen and sulfated glycosaminoglycan (sGAG) content values were calculated. The presented approach shows potential for engineering applications of complex tissues with at least two or more microenvironments such as osteochondral, corneal or vascular tissues.

Therapeutic applications of dental pulp stem cells in regenerating dental, periodontal and oral-related structures

Dental pulp stem cells (DPSCs) have emerged as a promising tool with great potential for use in tissue regeneration and engineering. Some of the main advantages of these cells are their multifaceted differentiation capacity, along with their high proliferation rate, a relative simplicity of extraction and culture that enables obtaining patient-specific cell lines for their use in autologous cell therapy. PubMed, Scopus and Google Scholar databases were searched for relevant articles related to the use of DPSCs in regeneration of dentin-pulp complex (DPC), periodontal tissues, salivary gland and craniomaxillofacial bone defects. Few studies were found regarding the use of DPSCs for regeneration of DPC. Scaffold-based combined with DPSCs isolated from healthy pulps was the strategy used for DPC regeneration. Studies involved subcutaneous implantation of scaffolds loaded with DPSCs pretreated with odontogenic media, or performed on human tooth root model as a root slice. Most of the studies were related to periodontal tissue regeneration which mainly utilized DPSCs/secretome. For periodontal tissues, DPSCs or their secretome were isolated from healthy or inflamed pulps and they were used either for preclinical or clinical studies. Regarding salivary gland regeneration, the submandibular gland was the only model used for the preclinical studies and DPSCs or their secretome were isolated only from healthy pulps and they were used in preclinical studies. Likewise, DPSCs have been studied for craniomaxillofacial bone defects in the form of mandibular, calvarial and craniofacial bone defects where DPSCs were isolated only from healthy pulps for preclinical and clinical studies. From the previous results, we can conclude that DPSCs is promising candidate for dental and oral tissue regeneration.

Size-controlled human adipose-derived stem cell spheroids hybridized with single-segmented nanofibers and their effect on viability and stem cell differentiation

BACKGROUND

Fabrication of three-dimensional stem cell spheroids have been studied to improve stem cell function, but the hypoxic core and limited penetration of nutrients and signaling cues to the interior of the spheroid were challenges. The incorporation of polymers such as silica and gelatin in spheroids resulted in relatively relaxed assembly of composite spheroids, and enhancing transport of nutrient and biological gas. However, because of the low surface area between cells and since the polymers were heterogeneously distributed throughout the spheroid, these polymers cannot increase the cell to extracellular matrix interactions needed to support differentiation.

METHODS

We developed the stem cell spheroids that incorporate poly(ι-lactic acid) single-segmented fibers synthesized by electrospinning and physical and chemical fragmentation. The proper mixing ratio was 2000 cells/μg fibers (average length of the fibers was 50 μm - 100 μm). The SFs were coated with polydopamine to increase cell binding affinity and to synthesize various-sized spheroids. The function of spheroids was investigated by in vitro analysis depending on their sizes. For statistical analysis, Graphpad Prism 5 software (San Diego, CA, USA) was used to perform one-way analysis of variance ANOVA with Tukey's honest significant difference test and a Student's t-test (for two variables) (P < 0.05).

RESULTS

Spheroids of different sizes were created by modulating the amount of cells and fibers (0.063 mm2-0.322 mm2). The fibers in the spheroid were homogenously distributed and increased cell viability, while cell-only spheroids showed a loss of DNA contents, internal degradation, and many apoptotic signals. Furthermore, we investigated stemness and various functions of various-sized fiber-incorporated spheroids. In conclusion, the spheroid with the largest size showed the greatest release of angiogenic factors (released VEGF: 0.111 ± 0.004 pg/ng DNA), while the smallest size showed greater effects of osteogenic differentiation (mineralized calcium: 18.099 ± 0.271 ng/ng DNA).

CONCLUSION

The spheroids incorporating polydopamine coated single-segmented fibers showed enhanced viability regardless of sizes and increased their functionality by regulating the size of spheroids which may be used for various tissue reconstruction and therapeutic applications.

[Advances in biomimetic modification of materials for oromaxillofacial bone regeneration and dental implant]

Oromaxillofacial hard tissue defects is still a difficult problem in clinical treatment. Regeneration of oromaxillofacial hard tissue based on tissue engineering technology has a good clinical application prospect. The functional modification of scaffolds is one of key factors that influence the outcome of tissue regeneration. The biomimetic design of biomaterials through simulating the natural structure and composition of oromaxillofacial hard tissue has gradually become a research hotspot due to its advantages of simplicity and efficiency. In this article, the biomimetic modification of biomaterials for oromaxillofacial hard tissue regeneration is reviewed, expecting to provide a new idea for the treatment of oromaxillofacial hard tissue defect.

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.

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.

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.

Engineered Cell Sheets for the Effective Delivery of Adipose-Derived Stem Cells for Tendon-to-Bone Healing

BACKGROUND

Efforts are being made to treat rotator cuff tears (RCTs) that exhibit poor healing and high retear rates. Tendon-to-bone healing using mesenchymal stem cells is being explored, but research is needed to establish effective delivery options.

PURPOSE

To evaluate the effects of an adipose-derived stem cell (ADSC) sheet on mesenchymal stem cell delivery for tendon-to-bone healing of a chronic RCT in rats and to demonstrate that ADSC sheets enhance tendon-to-bone healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

Mesenchymal stem cells were obtained from rat adipose tissue, and a cell sheet was prepared using a temperature-responsive dish. To evaluate the efficacy of stem cells produced in a sheet for the lesion, the experiment was conducted with 3 groups: repair group, cell sheet transplantation after repair group, and cell sheet-only group. Histological, biomechanical, and micro-computed tomography (micro-CT) results were compared among the groups.

RESULTS

Hematoxylin and eosin staining for histomorphological analysis revealed that the cell sheet transplantation after repair group (5.75 ± 0.95) showed statistically significant higher scores than the repair (2.75 ± 0.50) and cell sheet-only (3.25 ± 0.50) groups (P < .001). On safranin O staining, the cell sheet transplantation after repair group (0.51 ± 0.04 mm²) had a larger fibrocartilage area than the repair (0.31 ± 0.06 mm²) and cell sheet-only (0.32 ± 0.03 mm²) groups (P = .001). On micro-CT, bone volume/total volume values were significantly higher in the cell sheet transplantation after repair group (23.98% ± 1.75%) than in the other groups (P < .039); there was no significant difference in the other values. On the biomechanical test, the cell sheet transplantation after repair group (4 weeks after repair) showed significantly higher results than the other groups (P < .005).

CONCLUSION

Our study shows that engineered stem cells are a clinically feasible stem cell delivery tool for rotator cuff repair.

CLINICAL RELEVANCE

This laboratory study provides evidence that ADSCs are effective in repairing RCTs, which are common sports injuries.

Scaffold-free, Label-free, and Nozzle-free Magnetic Levitational Bioassembler for Rapid Formative Biofabrication of 3D Tissues and Organs

Scaffolding is the conceptual framework of conventional tissue engineering. Over the past decade, scaffold-free approaches as a potential alternative to classic scaffold-based methods have emerged, and scaffold-free magnetic levitational tissue engineering (magnetic force-based tissue engineering [Mag-TE]) is a type of this novel tissue engineering strategy. However, Mag-TE is often based on the use of potentially toxic magnetic nanoparticles. Scaffold-free and label-free magnetic levitational bioassembly do not employ magnetic nanoparticles and thus, the potential toxicity of magnetic nanoparticles can be avoided. In this short review, we describe the conceptual foundation of scaffold-free, label-free, and nozzle-free formative biofabrication using magnetic fields as “scaffields.” The design and implementation of “Organ.Aut,” the first commercial magnetic levitational bioassembler, and the potential applications of magnetic bioassembler are discussed as well.

π-SACS: pH Induced Self-Assembled Cell Sheets Without the Need for Modified Surfaces

The ability to form tissue-like constructs that have high cell density with proper cell-cell and cell-ECM interactions is critical for many applications including tissue models for drug discovery and tissue regeneration. Newly emerging bioprinting methods sometimes lack the high cellular density needed to provide biophysical cues to orchestrate cellular behavior to recreate tissue architecture and function. Alternate methods using self-assembly can be used to create tissue-like constructs with high cellular density and well-defined microstructure in the form of spheroids, organoids, or cell sheets. Cell sheets have a particularly interesting architecture in the context of tissue regeneration and repair as they can be applied as patches to integrate with surrounding tissues. Until now, the preparation of these sheets has involved culturing on specialized substrates that can be triggered by temperature or phase change (hydrophobic to hydrophilic) to release cells growing on them and form sheets. Here a new technique is proposed that allows delamination of cells and secreted ECM and rapid self-assembly into a cell sheet using a simple pH trigger and without the need to use responsive surfaces or applying external stimuli such as electrical and magnetic fields, only with routine tissue culture plates. This technique can be used with cells that are capable of syncytialization and fusion such as skeletal muscle cells and placenta cells. Using C2C12 myoblast cells we show that the pH trigger induces a rapid delamination of the cells as a continuous layer that self-assembles into a thick dense sheet. The delamination process has little effect on cell viability and maturation and preserves the ECM components that allow sheets to adhere to each other within a short incubation time enabling formation of thicker constructs when multiple sheets are stacked (double- and quadruple-layer constructs are formed here). These thick grafts can be used for regeneration purposes or as in vitro models.

Designer Hydrogel with Intelligently Switchable Stem-Cell Contact for Incubating Cartilaginous Microtissues

Stem-cell-derived organoid can resemble in vivo tissue counterpart and mimic at least one function of tissue or organ, possessing great potential for biomedical application. The present study develops a hydrogel with cell-responsive switch to guide spontaneous and sequential proliferation and aggregation of adipose-derived stem cells (ASCs) without inputting artificial stimulus for in vitro constructing cartilaginous microtissues with enhanced retention of cell-matrix and cell-cell interactions. Polylactic acid (PLA) rods are surface-aminolyzed by cystamine, followed by being involved in the amidation of poly(( l-glutamic acid) and adipic acid dihydrazide (ADH) to form a hydrogel. Along with tubular pore formation in hydrogel after dissolution of PLA rods, aminolyzed PLA molecules with disulfide bonds on rod surfaces are covalently transferred to the tubular pore surfaces of poly(l-glutamic acid)/ADH hydrogel. Because PLA attaches cells, while poly(l-glutamic acid)/ADH hydrogel repels cells, ASCs are found to adhere and proliferate on the tubular pore surfaces of hydrogel first and then cleave disulfide bonds by secreting molecules containing thiol, thus inducing desorption of PLA molecules and leading to their spontaneous detachment and aggregation. Associated with chondrogenic induction by TGF-β1 and IGF-1 in vitro for 28 days, the hydrogel as an all-in-one incubator produces well-engineered columnar cartilage microtissues from ASCs, with the glycosaminoglycans (GAGs) and collagen type II (COL II) deposition achieving 64 and 69% of those in chondrocytes pellet, respectively. The cartilage microtissues further matured in vivo for 8 weeks to exhibit extremely similar histological features and biomechanical performance to native hyaline cartilage. The GAGs and COL II content, as well as compressive modulus of the matured tissue show no significant difference with native cartilage. The designer hydrogel may hold a promise for long-term culture of other types of stem cells and organoids.

Evaluation of Multi-Layered Pancreatic Islets and Adipose-Derived Stem Cell Sheets Transplanted on Various Sites for Diabetes Treatment

Islet cell transplantation is considered an ideal treatment for insulin-deficient diabetes, but implantation sites are limited and show low graft survival. Cell sheet technology and adipose-derived stem cells (ADSCs) can be useful tools for improving islet cell transplantation outcomes since both can increase implantation efficacy and graft survival. Herein, the optimal transplantation site in diabetic mice was investigated using islets and stem cell sheets. We constructed multi-layered cell sheets using rat/human islets and human ADSCs. Cell sheets were fabricated using temperature-responsive culture dishes. Islet/ADSC sheet (AI sheet) group showed higher viability and glucose-stimulated insulin secretion than islet-only group. Compared to islet transplantation alone, subcutaneous AI sheet transplantation showed better blood glucose control and CD31+ vascular traits. Because of the adhesive properties of cell sheets, AI sheets were easily applied on liver and peritoneal surfaces. Liver or peritoneal surface grafts showed better glucose control, weight gain, and intraperitoneal glucose tolerance test (IPGTT) profiles than subcutaneous site grafts using both rat and human islets. Stem cell sheets increased the therapeutic efficacy of islets in vivo because mesenchymal stem cells enhance islet function and induce neovascularization around transplanted islets. The liver and peritoneal surface can be used more effectively than the subcutaneous site in future clinical applications.

Decellularized human corneal stromal cell sheet as a novel matrix for ocular surface reconstruction

The shortage of donor corneas as well as the limitations of tissue substitutes leads to the necessity to develop alternative materials for ocular surface reconstruction. Corneal surface substitutes must fulfill specific requirements such as high transparency, low immunogenicity, and mechanical stability combined with elasticity. This in vitro study evaluates a decellularized matrix secreted from human corneal fibroblasts (HCF) as an alternative material for ocular surface reconstruction. HCF from human donors were cultivated with the supplementation of vitamin C to form a stable and thick matrix. Furthermore, due to enhanced cultivation time, a three-dimensional like multilayered construct which partly mimics the complex structure of the corneal stroma could be generated. The formed human cell-based matrices (so-called cell sheets [CS]) were subsequently decellularized. The complete cell removal, collagen content, ultrastructure, and cell toxicity of the decellularized CS (DCS) as well as biomechanical properties were analyzed. Surgical feasibility was tested on enucleated porcine eyes. After decellularization and sterilization, a transparent, thick, cell free, and sterile tissue substitute resulted, which allowed expansion of limbal epithelial stem cells with no signs of cytotoxicity, and good surgical feasibility. DCS seem to be a promising new corneal tissue substitute derived from human cells without the limitation of donor material; however, future in vivo studies are necessary to further elucidate its potential for ocular surface reconstruction.

Void-free 3D Bioprinting for In-situ Endothelialization and Microfluidic Perfusion

Two major challenges of 3D bioprinting are the retention of structural fidelity and efficient endothelialization for tissue vascularization. We address both of these issues by introducing a versatile 3D bioprinting strategy, in which a templating bioink is deposited layer-by-layer alongside a matrix bioink to establish void-free multimaterial structures. After crosslinking the matrix phase, the templating phase is sacrificed to create a well-defined 3D network of interconnected tubular channels. This void-free 3D printing (VF-3DP) approach circumvents the traditional concerns of structural collapse, deformation and oxygen inhibition, moreover, it can be readily used to print materials that are widely considered "unprintable". By pre-loading endothelial cells into the templating bioink, the inner surface of the channels can be efficiently cellularized with a confluent endothelial layer. This in-situ endothelialization method can be used to produce endothelium with a far greater uniformity than can be achieved using the conventional post-seeding approach. This VF-3DP approach can also be extended beyond tissue fabrication and towards customized hydrogel-based microfluidics and self-supported perfusable hydrogel constructs.

High-Speed Manipulation of Microobjects Using an Automated Two-Fingered Microhand for 3D Microassembly

To assemble microobjects including biological cells quickly and precisely, a fully automated pick-and-place operation is applied. In micromanipulation in liquid, the challenges include strong adhesion forces and high dynamic viscosity. To solve these problems, a reliable manipulation system and special releasing techniques are indispensable. A microhand having dexterous motion is utilized to grasp an object stably, and an automated stage transports the object quickly. To detach the object adhered to one of the end effectors, two releasing methods—local stream and a dynamic releasing—are utilized. A system using vision-based techniques for the recognition of two fingertips and an object, as well automated releasing methods, can increase the manipulation speed to faster than 800 ms/sphere with a 100% success rate (N = 100). To extend this manipulation technique, 2D and 3D assembly that manipulates several objects is attained by compensating the positional error. Finally, we succeed in assembling 80–120 µm of microbeads and spheroids integrated by NIH3T3 cells.

Construction of higher-order cellular microstructures by a self-wrapping co-culture strategy using a redox-responsive hydrogel

In this report, a strategy for constructing three-dimensional (3D) cellular architectures comprising viable cells is presented. The strategy uses a redox-responsive hydrogel that degrades under mild reductive conditions, and a confluent monolayer of cells (i.e., cell sheet) cultured on the hydrogel surface peels off and self-folds to wrap other cells. As a proof-of-concept, the self-folding of fibroblast cell sheet was triggered by immersion in aqueous cysteine, and this folding process was controlled by the cysteine concentration. Such folding enabled the wrapping of human hepatocellular carcinoma (HepG2) spheroids, human umbilical vein endothelial cells and collagen beads, and this process improved cell viability, the secretion of metabolites and the proliferation rate of the HepG2 cells when compared with a two-dimensional culture under the same conditions. A key concept of this study is the ability to interact with other neighbouring cells, providing a new, simple and fast method to generate higher-order cellular aggregates wherein different types of cellular components are added. We designated the method of using a cell sheet to wrap another cellular aggregate the 'cellular Furoshiki'. The simple self-wrapping Furoshiki technique provides an alternative approach to co-culture cells by microplate-based systems, especially for constructing heterogeneous 3D cellular microstructures.