Reconstruction of functional tissues with cell sheet engineering

A Cell-Based Self-Assembly Approach for the Production of Human Osseous Tissues from Adipose-Derived Stromal/Stem Cells

Achieving optimal bone defect repair is a clinical challenge driving intensive research in the field of bone tissue engineering. Many strategies focus on seeding graft materials with progenitor cells prior to in vivo implantation. Given the benefits of closely mimicking tissue structure and function with natural materials, the authors hypothesize that under specific culture conditions, human adipose-derived stem/stromal cells (hASCs) can solely be used to engineer human reconstructed osseous tissues (hROTs) by undergoing osteoblastic differentiation with concomitant extracellular matrix production and mineralization. Therefore, the authors are developing a self-assembly methodology allowing the production of such osseous tissues. Three-dimensional (3D) tissues reconstructed from osteogenically-induced cell sheets contain abundant collagen type I and are 2.7-fold less contractile compared to non-osteogenically induced tissues. In particular, hROT differentiation and mineralization is reflected by a greater amount of homogenously distributed alkaline phosphatase, as well as higher calcium-containing hydroxyapatite (P < 0.0001) and osteocalcin (P < 0.0001) levels compared to non-induced tissues. Taken together, these findings show that hASC-driven tissue engineering leads to hROTs that demonstrate structural and functional characteristics similar to native osseous tissue. These highly biomimetic human osseous tissues will advantageously serve as a platform for molecular studies as well as for future therapeutic in vivo translation.

SiO2/TiO2 Nanocomposite Films on Polystyrene for Light-Induced Cell Detachment Application

Light-induced cell detachment shows much potential in in vitro cell culture and calls for high-performance light-responsive films. In this study, a smooth and dense SiO₂/TiO₂ nanocomposite thin film with thickness of around 250 nm was first fabricated on H₂O₂ treated polystyrene (PS) substrate via a low-temperature sol-gel method. It was observed that the film could well-adhere on the PS surface and the bonding strength became increasingly high with the increase of SiO₂ content. The peeling strength and shear strength reached 3.05 and 30.02 MPa, respectively. It was observed the surface of the film could transform into superhydrophilic upon 20 min illumination of ultraviolet with a wavelength of 365 nm (UV365). In cell culture, cells, i.e., NIH3T3 and MC3T3-E1 cells, cultured on SiO₂/TiO₂ nanocomposite film were easily detached after 10 min of UV365 illumination; the detachment rates reached 90.8% and 88.6%, respectively. Correspondingly, continuous cell sheets with good viability were also easily obtained through the same way. The present work shows that SiO₂/TiO₂ nanocomposite thin film could be easily prepared on polymeric surface at low temperature. The corresponding film exhibits excellent biocompatibility, high bonding strength, and good light responses. It could be a good candidate for the surface of cell culture utensils with light-induced cell detachment property.

Human iPSC-derived cardiomyocytes and tissue engineering strategies for disease modeling and drug screening

Improved methodologies for modeling cardiac disease phenotypes and accurately screening the efficacy and toxicity of potential therapeutic compounds are actively being sought to advance drug development and improve disease modeling capabilities. To that end, much recent effort has been devoted to the development of novel engineered biomimetic cardiac tissue platforms that accurately recapitulate the structure and function of the human myocardium. Within the field of cardiac engineering, induced pluripotent stem cells (iPSCs) are an exciting tool that offer the potential to advance the current state of the art, as they are derived from somatic cells, enabling the development of personalized medical strategies and patient specific disease models. Here we review different aspects of iPSC-based cardiac engineering technologies. We highlight methods for producing iPSC-derived cardiomyocytes (iPSC-CMs) and discuss their application to compound efficacy/toxicity screening and in vitro modeling of prevalent cardiac diseases. Special attention is paid to the application of micro- and nano-engineering techniques for the development of novel iPSC-CM based platforms and their potential to advance current preclinical screening modalities.

PLGA-PTMC-Cultured Bone Mesenchymal Stem Cell Scaffold Enhances Cartilage Regeneration in Tissue-Engineered Tracheal Transplantation

The treatment of long-segment tracheal defect requires the transplantation of effective tracheal substitute, and the tissue-engineered trachea (TET) has been proposed as an ideal tracheal substitute. The major cause of the failure of segmental tracheal defect reconstruction by TET is airway collapse caused by the chondromalacia of TET cartilage. The key to maintain the TET structure is the regeneration of chondrocytes in cartilage, which can secrete plenty of cartilage matrices. To address the problem of the chondromalacia of TET cartilage, this study proposed an improved strategy. We designed a new cell sheet scaffold using the poly(lactic-co-glycolic acid) (PLGA) and poly(trimethylene carbonate) (PTMC) to make a porous membrane for seeding cells, and used the PLGA-PTMC cell-scaffold to pack the decellularized allogeneic trachea to construct a new type of TET. The TET was then implanted in the subcutaneous tissue for vascularization for 2 weeks. Orthotopic transplantation was then performed after implantation. The efficiency of the TET we designed was analyzed by histological examination and biomechanical analyses 4 weeks after surgery. Four weeks after surgery, both the number of chondrocytes and the amount of cartilage matrix were significantly higher than those contained in the traditional stem-cell-based TET. Besides, the coefficient of stiffness of TET was significantly larger than the traditional TET. This study provided a promising approach for the long-term functional reconstruction of long-segment tracheal defect, and the TET we designed had potential application prospects in the field of TET reconstruction.

Composite cell sheet for periodontal regeneration: crosstalk between different types of MSCs in cell sheet facilitates complex periodontal-like tissue regeneration

Background

Tissue-engineering strategies based on mesenchymal stem cells (MSCs) and cell sheets have been widely used for periodontal tissue regeneration. However, given the complexity in periodontal structure, the regeneration methods using a single species of MSC could not fulfill the requirement for periodontal regeneration.

Methods

We researched the interaction between the periodontal ligament stem cells (PDLSCs) and jaw bone marrow-derived mesenchymal stem cells (JBMMSCs), and constructed a composite cell sheet comprising both of the above MSCs to regenerate complex periodontium-like structures in nude mice.

Results

Our results show that by co-culturing PDLSCs and JBMMSCs, the expressions of bone and extracellular matrix (ECM)-related genes and proteins were significantly improved in both MSCs. Further investigations showed that, compared to the cell sheet using PDLSCs or JBMMSCs, the composite stem cell sheet (CSCS), which comprises these two MSCs, expressed higher levels of bone- and ECM-related genes and proteins, and generated a composite structure more similar to the native periodontal tissue physiologically in vivo.

Conclusions

In conclusion, our results demonstrate that the crosstalk between PDLSCs and JBMMSCs in cell sheets facilitate regeneration of complex periodontium-like structures, providing a promising new strategy for physiological and functional regeneration of periodontal tissue.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0417-x) contains supplementary material, which is available to authorized users.

Design and cytocompatibility of chitosan-based thermoresponsive cell culture plates

BACKGROUND

The aim of this study was to develop a novel thermoresponsive material suited for tissue engineering and investigate the growth and harmless detachment of cells cultured on the surface of thermoresponsive tissue culture polystyrene (TCPS).

METHODS

Thermoresponsive N-isopropylacrylamide (NIPAAm) and biocompatible chitosan (CS) were grafted onto the surface of TCPS by ultraviolet (UV)-induced graft polymerization. The chemical composition, surface morphology and thermoresponsiveness of the modified TCPS were investigated by X-ray photoelectron spectroscopy (XPS), atom force microscopy (AFM) and contact angle (CA), respectively. Furthermore, the growth and detachment behaviors of mouse fibroblast cells (L929) on the surface of the modified TCPS were studied by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.

RESULTS

The modified TCPS exhibited good hydrophobic/hydrophilic property alterations in response to temperature. The cytocompatibility of the materials was improved due to the introduction of CS. Cells could be spontaneously detached from the surface without any damage, by controlling environmental temperature. The viability of cells obtained by temperature induction was higher than that obtained by enzymatic digestion.

CONCLUSIONS

This study developed a simple and economical method to fabricate thermoresponsive cell culture dishes and provided new thoughts and experimental bases for exploring novel material applied in tissue engineering.

Recent Advances in Dual Temperature Responsive Block Copolymers and Their Potential as Biomedical Applications

The development of stimuli responsive polymers has progressed significantly with novel preparation techniques, which has allowed access to new materials with unique properties. Dual thermoresponsive (double temperature responsive) block copolymers are particularly of interest as their properties can change depending on the lower critical solution temperature (LCST) or upper critical solution temperature (UCST) of each segment. For instance, these block copolymers can change from being hydrophilic, to amphiphilic or to hydrophobic simply by changing the solution temperature without any additional chemicals and the block copolymers can change from being fully solubilized to self-assembled structures to macroscopic aggregation/precipitation. Based on the unique solution properties, these dual thermo-responsive block copolymers are expected to be suitable for biomedical applications. This review is divided into three parts; LCST-LCST types of block copolymers, UCST-LCST types of block copolymers, and their potential as biomedical applications.

Nanoengineered thermoresponsive magnetic hydrogels for biomedical applications

“Smart” hydrogels are part of an emerging class of biomaterials that respond to multiple external stimuli. A range of thermoresponsive magnetic hydrogels is currently being developed for on‐demand delivery of biomolecules for a range of biomedical applications, including therapeutic drug delivery, bioimaging, and regenerative engineering. In this review article, we explore different types of magnetic nanoparticles and thermoresponsive polymers used to fabricate these smart nanoengineered hydrogels. We highlight some of the emerging applications of these stimuli‐responsive hydrogels for biomedical applications. Finally, we capture the growing trend of these smart nanoengineered hydrogels and will identify promising new research directions.

Effect of Gelatin on Osteogenic Cell Sheet Formation Using Canine Adipose-Derived Mesenchymal Stem Cells

Osteogenically differentiated cell sheet techniques using mesenchymal stem cells (MSCs) are available to stimulate bone regeneration. The advantage of the cell sheet technique is delivering live cells effectively into the focal region. We developed a novel osteogenic cell sheet technique by adding gelatin to osteogenic cell medium. Gelatin-induced osteogenic cell sheets (GCSs) were compared to conventional osteogenic cell sheets (OCSs). Undifferentiated MSCs (UCs) were used as a control. The morphology of these cell sheets was evaluated microscopically and histologically. The time-dependent cell proliferation rate was estimated by DNA quantification. The expression of osteogenic gene markers and the number of calcium depositions were assessed by quantitative real-time polymerase chain reaction and Alizarin red S (ARS) staining, respectively. GCSs were thicker and stronger than OCSs. GCSs showed a significantly higher cell proliferation rate compared to OCSs (p < 0.05). GCSs exhibited significantly higher upregulation of BMP-7 mRNA compared to OCSs (p < 0.05). Both GCSs and OCSs showed negative ARS reactivity on day 10, but only GCSs showed positive ARS reactivity on day 21. With this technique, we observed active cell proliferation with abundant ECM and upregulation of osteogenic bone markers, and our results suggest that GCSs could be promising for therapeutic applications in bone regeneration.

Diffusion-Induced Hydrophilic Conversion of Polydimethylsiloxane/Block-Type Phospholipid Polymer Hybrid Substrate for Temporal Cell-Adhesive Surface

In this study, diffusion-induced hydrophobic-hydrophilic conversion of the surface of the cross-linked polydimethylsiloxane (PDMS) substrate was realized by employing a simple swelling-deswelling process of PDMS substrate in a block-type polymer solution with the aim of development of a temporal cell-adhesive substrate. The ABA block-type polymer composed of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) segment and PDMS segment with over 70% of dimethylsiloxane unit composition could be successfully incorporated in the PDMS substrate during the swelling-deswelling process to prepare the PDMS/phospholipid block copolymer hybrid substrates. During the aging process of the PDMS substrate for 4 days in aqueous medium, its surface property changed gradually from hydrophobic to hydrophilic. X-ray photoelectron spectroscopy and atomic force microscopy data provided strong evidence that the time-dependent hydrophilic conversion of the PDMS/block-type phospholipid polymer hybrid substrate was induced by the diffusion of the hydrophilic PMPC segment in the block-type polymer to be tethered on the substrate. During the hydrophilic conversion process, surface-adsorbed fibronectin was gradually desorbed from the substrate surface, and this resulted in successful detachment of two-dimensional connected cell crowds.

The application of cell sheet engineering in the vascularization of tissue regeneration

Scaffold-free cell sheet engineering (CSE) is a new technology to regenerate injured or damaged tissues, which has shown promising potential in tissue regeneration. CSE uses a thermosensitive surface to form a dense cell sheet that can be detached when temperature decreases. The detached cell sheet can be stacked on top of one another according to the thickness of cell sheet for the specific tissue regeneration application. One of the key challenges of tissue engineering is vascularization. CSE technique provides excellent microenvironment for vascularization since the technique can maintain the intact cell matrix that is crucial for angiogenesis. In this review paper, we will highlight the principle technique of CSE and its application in tissue regeneration.

Effect of different cell sheet ECM microenvironment on the formation of vascular network

The repair and reconstruction of large bone defects remains as a significant clinical challenge mainly due to the insufficient vascularization. The prefabrication of vascular network based on cell sheet technique brings a promising potential for sufficient vascularization due to rich extracellular matrix (ECM) of cell sheets. However, the effect of different cell sheet ECM micro-environment on the formation of a vascular network has not been well understood. Here our goal is to study the effect of different cell sheets on the formation of a vascular network. First we cultured human bone marrow mesenchymal stem cells (hBMSCs) under two culture conditions to obtain osteogenic differentiated cell sheet (ODCS) and undifferentiated cell sheet (UDCS), respectively. Then the human umbilical vein endothelial cells (HUVECs) were seeded onto the surface of the two sheets at different seeding densities to fabricate pre-vascularized cell sheets. Our results indicated that the two sheets facilitated the alignment of HUVECs and promoted the formation of vascular networks. Quantitative analysis showed that the number of networks in ODCS was higher than that in the UDCS. The ECM of the two sheets was remodeled and rearranged during the tubulogenesis process. Furthermore, results showed that the optimal seeding density of HUVECs was 5×10(4)cell/cm(2). In summary, these results suggest that the vascularized ODCS has a promising potential to construct pre-vascularized tissue for bone repair.

In vivo periodontal tissue regeneration by periodontal ligament stem cells and endothelial cells in three-dimensional cell sheet constructs

BACKGROUND AND OBJECTIVE

Chronic periodontitis causes damage to tooth-supporting tissues, resulting in tooth loss in adults. Recently, cell-sheet-based approaches have been studied to overcome the limitations of conventional cytotherapeutic procedures for periodontal regeneration. The purpose of the present study was to investigate the regenerative potential of periodontal ligament stem cells (PDLSCs) and human umbilical vein endothelial cells (HUVECs) in three-dimensional (3D) cell sheet constructs for periodontal regeneration in vivo.

MATERIAL AND METHODS

PDLSCs, HUVECs or co-cultures of both cells were seeded onto temperature-responsive culture dishes, and intact cell sheets were fabricated. Cell sheets were wrapped around the prepared human roots in three different combinations and implanted subcutaneously into immunodeficient mice.

RESULTS

Histological evaluation revealed that after 2, 4 and 8 wk of implantation, periodontal ligament-like tissue arrangements were observed around the implanted roots in experimental groups compared with controls. Vascular lumens were also observed in periodontal compartments of HUVEC-containing groups. Periodontal ligament regeneration, cementogenesis and osteogenesis were evident in the experimental groups at both weeks 4 and 8, as shown by immunostaining for periostin and bone sialoprotein. Human cells in the transplanted cell sheets were stained by immunohistochemistry for the presence of human mitochondria.

CONCLUSIONS

The 3D cell sheet-based approach may be potentially beneficial and is thus encouraged for future regenerative periodontal therapy.

Progress in Corneal Stromal Repair: From Tissue Grafts and Biomaterials to Modular Supramolecular Tissue-Like Assemblies

Corneal injuries and degenerative conditions have major socioeconomic consequences, given that in most cases, they result in blindness. In the quest of the ideal therapy, tissue grafts, biomaterials, and modular engineering approaches are under intense investigation. Herein, advancements and shortfalls are reviewed and future perspectives for these therapeutic strategies discussed.

Extracellular Matrix Revisited: Roles in Tissue Engineering

The extracellular matrix (ECM) is a heterogeneous, connective network composed of fibrous glycoproteins that coordinate in vivo to provide the physical scaffolding, mechanical stability, and biochemical cues necessary for tissue morphogenesis and homeostasis. This review highlights some of the recently raised aspects of the roles of the ECM as related to the fields of biophysics and biomedical engineering. Fundamental aspects of focus include the role of the ECM as a basic cellular structure, for novel spontaneous network formation, as an ideal scaffold in tissue engineering, and its essential contribution to cell sheet technology. As these technologies move from the laboratory to clinical practice, they are bound to shape the vast field of tissue engineering for medical transplantations.

Infused polymers for cell sheet release

Tissue engineering using whole, intact cell sheets has shown promise in many cell-based therapies. However, current systems for the growth and release of these sheets can be expensive to purchase or difficult to fabricate, hindering their widespread use. Here, we describe a new approach to cell sheet release surfaces based on silicone oil-infused polydimethylsiloxane. By coating the surfaces with a layer of fibronectin (FN), we were able to grow mesenchymal stem cells to densities comparable to those of tissue culture polystyrene controls (TCPS). Simple introduction of oil underneath an edge of the sheet caused it to separate from the substrate. Characterization of sheets post-transfer showed that they retain their FN layer and morphology, remain highly viable, and are able to grow and proliferate normally after transfer. We expect that this method of cell sheet growth and detachment may be useful for low-cost, flexible, and customizable production of cellular layers for tissue engineering.

Regeneration of the lung: Lung stem cells and the development of lung mimicking devices

Inspired by the increasing burden of lung associated diseases in society and an growing demand to accommodate patients, great efforts by the scientific community produce an increasing stream of data that are focused on delineating the basic principles of lung development and growth, as well as understanding the biomechanical properties to build artificial lung devices. In addition, the continuing efforts to better define the disease origin, progression and pathology by basic scientists and clinicians contributes to insights in the basic principles of lung biology. However, the use of different model systems, experimental approaches and readout systems may generate somewhat conflicting or contradictory results. In an effort to summarize the latest developments in the lung epithelial stem cell biology, we provide an overview of the current status of the field. We first describe the different stem cells, or progenitor cells, residing in the homeostatic lung. Next, we focus on the plasticity of the different cell types upon several injury-induced activation or repair models, and highlight the regenerative capacity of lung cells. Lastly, we summarize the generation of lung mimics, such as air-liquid interface cultures, organoids and lung on a chip, that are required to test emerging hypotheses. Moreover, the increasing collaboration between distinct specializations will contribute to the eventual development of an artificial lung device capable of assisting reduced lung function and capacity in human patients.

A morphospace for synthetic organs and organoids: the possible and the actual

Efforts in evolutionary developmental biology have shed light on how organs are developed and why evolution has selected some structures instead of others. These advances in the understanding of organogenesis along with the most recent techniques of organotypic cultures, tissue bioprinting and synthetic biology provide the tools to hack the physical and genetic constraints in organ development, thus opening new avenues for research in the form of completely designed or merely altered settings. Here we propose a unifying framework that connects the concept of morphospace (i.e. the space of possible structures) with synthetic biology and tissue engineering. We aim for a synthesis that incorporates our understanding of both evolutionary and architectural constraints and can be used as a guide for exploring alternative design principles to build artificial organs and organoids. We present a three-dimensional morphospace incorporating three key features associated to organ and organoid complexity. The axes of this space include the degree of complexity introduced by developmental mechanisms required to build the structure, its potential to store and react to information and the underlying physical state. We suggest that a large fraction of this space is empty, and that the void might offer clues for alternative ways of designing and even inventing new organs.

Stem Cells for Bone Regeneration: From Cell-Based Therapies to Decellularised Engineered Extracellular Matrices

Currently, autologous bone grafting represents the clinical gold standard in orthopaedic surgery. In certain cases, however, alternative techniques are required. The clinical utility of stem and stromal cells has been demonstrated for the repair and regeneration of craniomaxillofacial and long bone defects although clinical adoption of bone tissue engineering protocols has been very limited. Initial tissue engineering studies focused on the bone marrow as a source of cells for bone regeneration, and while a number of promising results continue to emerge, limitations to this technique have prompted the exploration of alternative cell sources, including adipose and muscle tissue. In this review paper we discuss the advantages and disadvantages of cell sources with a focus on adipose tissue and the bone marrow. Additionally, we highlight the relatively recent paradigm of developmental engineering, which promotes the recapitulation of naturally occurring developmental processes to allow the implant to optimally respond to endogenous cues. Finally we examine efforts to apply lessons from studies into different cell sources and developmental approaches to stimulate bone growth by use of decellularised hypertrophic cartilage templates.

Photovoltaic surfaces enable clonal myoblastic cell release using visible light as external stimulation

Many new biomedical approaches to treating disease require the supply of cells delivered to an injured or diseased organ either individually, collectively as aggregates or sheets, or encapsulated with a scaffold. The collection of cells is accomplished by using enzymatic digestion witch suffer from the need to remove the enzymes after digestion. In addition, enzymatic methods are not applicable for all cells, cell aggregates, cell sheets or 3D structures. The objective of this study was to investigate the release of cultured cells from silicon based Photovoltaic (PV) surfaces using a light source as external stimulation. C2C12 myoblasts were cultured on the negative surface of a PV device and upon confluence they were exposed to light. The amount of released cells was quantified as a function light exposure. It was found that light exposure at 25,000 lux for one hour caused equivalent cell release from the PV surface than trypsination. The released cells are viable and can be re-cultured if needed. This mechanism may offer an alternative method to release excitable cells without using an enzymatic agent. This may be important for cell therapy if larger cell structures such as sheets need to be collected.

Allogeneic Transplantation of Periodontal Ligament-Derived Multipotent Mesenchymal Stromal Cell Sheets in Canine Critical-Size Supra-Alveolar Periodontal Defect Model

Periodontitis is a chronic inflammatory disease that induces the destruction of tooth-supporting tissues, followed by tooth loss. Although several approaches have been applied to periodontal regeneration, complete periodontal regeneration has not been accomplished. Tissue engineering using a combination of cells and scaffolds is considered to be a viable alternative strategy. We have shown that autologous transplantation of periodontal ligament-derived multipotent mesenchymal stromal cell (PDL-MSC) sheets regenerates periodontal tissue in canine models. However, the indications for autologous cell transplantation in clinical situations are limited. Therefore, this study evaluated the safety and efficacy of allogeneic transplantation of PDL-MSC sheets using a canine horizontal periodontal defect model. Canine PDL-MSCs were labeled with enhanced green fluorescent protein (EGFP) and were cultured on temperature-responsive dishes. Three-layered cell sheets were transplanted around denuded root surfaces either autologously or allogeneically. A mixture of β-tricalcium phosphate and collagen gel was placed on the bone defects. Eight weeks after transplantation, dogs were euthanized and subjected to microcomputed tomography and histological analyses. RNA and DNA were extracted from the paraffin sections to verify the presence of EGFP at the transplantation site. Inflammatory markers from peripheral blood sera were quantified using an enzyme-linked immunosorbent assay. Periodontal regeneration was observed in both the autologous and the allogeneic transplantation groups. The allogeneic transplantation group showed particularly significant regeneration of newly formed cementum, which is critical for the periodontal regeneration. Serum levels of inflammatory markers from peripheral blood sera showed little difference between the autologous and allogeneic groups. EGFP amplicons were detectable in the paraffin sections of the allogeneic group. These results suggest that allogeneic PDL-MSC sheets promoted periodontal tissue regeneration without side effects. Therefore, allogeneic transplantation of PDL-MSC sheets has a potential to become an alternative strategy for periodontal regeneration.

Natural and Synthetic Materials for Self-Renewal, Long-Term Maintenance, and Differentiation of Induced Pluripotent Stem Cells

Induced pluripotent stem cells (iPSCs) have attracted considerable attention from the public, clinicians, and scientists since their discovery in 2006, and raised huge expectations for regenerative medicine. One of the distinctive features of iPSCs is their propensity to differentiate into the cells of three germ lines in vitro and in vivo. The human iPSCs can be used to study the mechanisms underlying a disease and to monitor the disease progression, for testing drugs in vitro, and for cell therapy, avoiding many ethical and immunologic concerns. This technology offers the potential to take an individual approach to each patient and allows a more accurate diagnosis and specific treatment. However, there are several obstacles that impede the use of iPSCs. The derivation of fully reprogrammed iPSCs is expensive, time-consuming, and demands meticulous attention to many details. The use of biomaterials could increase the efficacy and safety while decreasing the cost of tissue engineering. The choice of a substrate utilized for iPSC culture is also important because cell-substrate contacts influence cellular behavior such as self-renewal, expansion, and differentiation. This Progress Report aims to summarize the advantages and drawbacks of natural and synthetic biomaterials, and to evaluate their role for maintenance and differentiation of iPSCs.

The likely role of proteolytic enzymes in unwanted differentiation of stem cells in culture

Tissue engineering aims at developing the necessary technological strategies for replacement or regeneration tissues. However, the number of cells required is much greater than the number obtained from a cell source. Expanding the cells' number in cell culture for a long period is required until the necessary amount of cells is obtained. While in culture, cells often go unwanted differentiation. Little attention has been given to the use of proteolytic enzymes in cell passage. Review the importance of extracellular matrix and surface proteins for cell behavior and the possible mechanisms of cellular changes that may occur due to the use of proteolytic enzymes is an essential issue. Possible alternative to replace these enzymes in cell passage has also been developed.

Improved light-induced cell detachment on rutile TiO₂ nanodot films

Anatase TiO2 nanodot films have been found to be able to release cells under light illumination with excellent efficiency and safety. In the present study, we investigated the effects of rutile contents in TiO2 nanodot films on such light induced cell detachment behavior. The results showed that TiO2 nanodot films with different contents of rutile phase have been prepared successfully. The content of rutile phase increased with the increase in calcination temperature. All films possessed good cell adhesion but there was a decrease in cell proliferation with the increasing content of rutile phase. Single cell detachment assay showed that the films with high rutile contents (calcined at 900°C and 1100°C) showed better cell detachment performance. That was ascribed to the changes of the secondary structure of extracellular proteins adsorbed on the nanodot surface after ultraviolet (365 nm, UV365) illumination. In addition, cell sheets detached through UV365 illumination maintained high activity and could be further used in tissue engineering. The present work showed that the existence of rutile phase is helpful in cell detachment behavior and it could be utilized to optimize light-induced cell detachment behavior.

STATEMENT OF SIGNIFICANCE

This work discovers that the presence of rutile phase in TiO2 nanodot films could improve the light-induced cell detachment behavior, although rutile phase is inferior to anatase phase on light induced superhydrophilicity. That strongly supported that the behaviors of adsorbed proteins are crucial in acquiring cell sheet with light illumination. In fact, the state and behavior of adsorbed protein greatly affect the interaction between biomaterials and living cells. Therefore, we consider this work is not only important in harvesting cells or cell sheets through light illumination, but also helpful in further understanding of interaction between biomaterials and cells.

Human turbinate mesenchymal stromal cell sheets with bellows graft for rapid tracheal epithelial regeneration

Rapid functional epithelial regeneration on the luminal surface is essential when using artificial tracheal grafts to repair tracheal defects. In this study, we imposed human turbinate mesenchymal stromal cell (hTMSC) sheets for tracheal epithelial regeneration, and then assessed their potential as a new clinical cell source. In vitro, hTMSCs sheets showed high capacity to differentiate into tracheal epithelium. We fabricated a poly(ε-caprolactone) (PCL) tracheal graft by indirect three-dimensional (3D) printing technique and created a composite construct by transplanting the hTMSC sheets to its luminal surface of the tracheal graft, then applied this tissue-engineered tracheal graft to non-circumferential tracheal reconstruction in a rabbit model. 4 weeks after implantation, the luminal surface of tissue-engineered tracheal graft was covered by a mature and highly-ciliated epithelium, whereas tracheal grafts without hTMSC sheets were covered by only a thin, immature epithelium. Therefore, hTMSC sheets on the luminal surface of a tissue-engineered tracheal graft can accelerate the tracheal epithelial regeneration, and the tissue-engineered tracheal graft with hTMSC sheets provides a useful clinical alternative for tracheal epithelial regeneration.

Osteogenic Ability of Canine Adipose-Derived Mesenchymal Stromal Cell Sheets in Relation to Culture Time

Cell sheets could be used for bone regeneration without requiring a scaffold and can be easily produced from autologous mesenchymal stromal cells (MSCs). We compared the osteogenic potential of MSC-derived cell sheets in relation to culture time. Undifferentiated cell sheets (U-CS) and osteogenic differentiated cell sheets (O-CS) were generated using canine adipose-derived MSCs. Undifferentiated cells (UCs) were used as the control. Osteogenic differentiation was assessed by assaying alkaline phosphatase (ALP) activity. Expression of osteogenesis-related genes was evaluated by reverse transcription-polymerase chain reaction at 4, 7, 14, and 21 days after initiation of culture. The calcium content in cells was measured, and the cells were stained with Alizarin red S (ARS). The mRNA expression of transforming growth factor-β in U-CS and O-CS at day 4 was higher than that in UCs (p < 0.05). The level of bone morphogenetic protein 7 mRNA in O-CS increased significantly at day 4 and was significantly higher than that of U-CS at day 7. The mRNA level of runt-related transcription factor-2 in both sheet types increased significantly at 7 days of culture. The mRNA level of ALP in O-CS and U-CS increased significantly at day 7, and ALP activity was highest at days 7 and 14, respectively (p < 0.05). The mRNA level of osteocalcin in U-CS and O-CS increased significantly at day 21. O-CS and U-CS showed negative ARS staining but their calcium contents increased marginally at day 21. The O-CS cells started to aggregate at days 10-12, and only a partial sheet remained at day 21. The upregulation of expression of genes related to osteogenic differentiation, peak in ALP activity, and morphological changes in cell sheets suggest that the optimal time for application of O-CS and U-CS is between 7 and 10 days and after 14 days of culture, respectively.

Driving cartilage formation in high-density human adipose-derived stem cell aggregate and sheet constructs without exogenous growth factor delivery

An attractive cell source for cartilage tissue engineering, human adipose-derived stem cells (hASCs) can be easily expanded and signaled to differentiate into chondrocytes. This study explores the influence of growth factor distribution and release kinetics on cartilage formation within 3D hASC constructs incorporated with transforming growth factor-β1 (TGF-β1)-loaded gelatin microspheres. The amounts of microspheres, TGF-β1 concentration, and polymer degradation rate were varied within hASC aggregates. Microsphere and TGF-β1 loading concentrations were identified that resulted in glycosaminoglycan (GAG) production comparable to those of control aggregates cultured in TGF-β1-containing medium. Self-assembling hASC sheets were then engineered for the production of larger, more clinically relevant constructs. Chondrogenesis was observed in hASC-only sheets cultured with exogenous TGF-β1 at 3 weeks. Importantly, sheets with incorporated TGF-β1-loaded microspheres achieved GAG production similar to sheets treated with exogenous TGF-β1. Cartilage formation was confirmed histologically via observation of cartilage-like morphology and GAG staining. This is the first demonstration of the self-assembly of hASCs into high-density cell sheets capable of forming cartilage in the presence of exogenous TGF-β1 or with TGF-β1-releasing microspheres. Microsphere incorporation may bypass the need for extended in vitro culture, potentially enabling hASC sheets to be implanted more rapidly into defects to regenerate cartilage in vivo.

Programmed synthesis of three-dimensional tissues

Reconstituting tissues from their cellular building blocks facilitates the modeling of morphogenesis, homeostasis and disease in vitro. Here we describe DNA-programmed assembly of cells (DPAC), a method to reconstitute the multicellular organization of organoid-like tissues having programmed size, shape, composition and spatial heterogeneity. DPAC uses dissociated cells that are chemically functionalized with degradable oligonucleotide 'Velcro', allowing rapid, specific and reversible cell adhesion to other surfaces coated with complementary DNA sequences. DNA-patterned substrates function as removable and adhesive templates, and layer-by-layer DNA-programmed assembly builds arrays of tissues into the third dimension above the template. DNase releases completed arrays of organoid-like microtissues from the template concomitant with full embedding in a variety of extracellular matrix (ECM) gels. DPAC positions subpopulations of cells with single-cell spatial resolution and generates cultures several centimeters long. We used DPAC to explore the impact of ECM composition, heterotypic cell-cell interactions and patterns of signaling heterogeneity on collective cell behaviors.

Applications of regenerative medicine in organ transplantation

A worldwide shortage of organs for clinical implantation establishes the need to bring forward and test new technologies that will help in solving the problem. The concepts of regenerative medicine hold the potential for augmenting organ function or repairing damaged organ or allowing regeneration of deteriorated organs and tissue. Researchers are exploring possible regenerative medicine applications in organ transplantation so that coming together of the two fields can benefit each other. The present review discusses the strategies that are being implemented to regenerate or bio-engineer human organs for clinical purposes. It also highlights the limitations of the regenerative medicine that needs to be addressed to explore full potential of the field. A web-based research on MEDLINE was done using keywords “regenerative medicine,” “tissue-engineering,” “bio-engineered organs,” “decellularized scaffold” and “three-dimensional printing.” This review screened about 170 articles to get the desired knowledge update.

Age-related decline in the matrix contents and functional properties of human periodontal ligament stem cell sheets

In this study, periodontal ligament (PDL) stem cells (PDLSCs) derived from different-aged donors were used to evaluate the effect of aging on cell sheet formation. The activity of PDLSCs was first determined based on their colony-forming ability, surface markers, proliferative/differentiative potentials, senescence-associated β-galactosidase (SA-βG) staining, and expression of pluripotency-associated transcription factors. The ability of these cells to form sheets, based on their extracellular matrix (ECM) contents and their functional properties necessary for osteogenic differentiation, was evaluated to predict the age-related changes in the regenerative capacity of the cell sheets in their further application. It was found that human PDLSCs could be isolated from the PDL tissue of different-aged subjects. However, the ability of the PDLSCs to proliferate and to undergo osteogenic differentiation and their expression of pluripotency-associated transcription factors displayed age-related decreases. In addition, these cells exhibited an age-related increase in SA-βG expression. Aged cells showed an impaired ability to form functional cell sheets, as determined by morphological observations and Ki-67 immunohistochemistry staining. Based on the production of ECM proteins, such as fibronectin, integrin β1, and collagen type I; alkaline phosphatase (ALP) activity; and the expression of osteogenic genes, such as ALP, Runt-related transcription factor 2, and osteocalcin, cell sheets formed by PDLSCs derived from older donors demonstrated a less potent osteogenic capacity compared to those formed by PDLSCs from younger donors. Our data suggest that the age-associated decline in the matrix contents and osteogenic properties of PDLSC sheets should be taken into account in cell sheet engineering research and clinical periodontal regenerative therapy.

Platform technology for scalable assembly of instantaneously functional mosaic tissues

Engineering mature tissues requires a guided assembly of cells into organized three-dimensional (3D) structures with multiple cell types. Guidance is usually achieved by microtopographical scaffold cues or by cell-gel compaction. The assembly of individual units into functional 3D tissues is often time-consuming, relying on cell ingrowth and matrix remodeling, whereas disassembly requires an invasive method that includes either matrix dissolution or mechanical cutting. We invented Tissue-Velcro, a bio-scaffold with a microfabricated hook and loop system. The assembly of Tissue-Velcro preserved the guided cell alignment realized by the topographical features in the 2D scaffold mesh and allowed for the instant establishment of coculture conditions by spatially defined stacking of cardiac cell layers or through endothelial cell coating. The assembled cardiac 3D tissue constructs were immediately functional as measured by their ability to contract in response to electrical field stimulation. Facile, on-demand tissue disassembly was demonstrated while preserving the structure, physical integrity, and beating function of individual layers.

New self-assembling multifunctional templates for the biofabrication and controlled self-release of cultured tissue

The need to source live human tissues for research and clinical applications has been a major driving force for the development of new biomaterials. Ideally, these should elicit the formation of scaffold-free tissues with native-like structure and composition. In this study, we describe a biologically interactive coating that combines the fabrication and subsequent self-release of live purposeful tissues using template-cell-environment feedback. This smart coating was formed from a self-assembling peptide amphiphile comprising a protease-cleavable sequence contiguous with a cell attachment and signaling motif. This multifunctional material was subsequently used not only to instruct human corneal or skin fibroblasts to adhere and deposit discreet multiple layers of native extracellular matrix but also to govern their own self-directed release from the template solely through the action of endogenous metalloproteases. Tissues recovered through this physiologically relevant process were carrier-free and structurally and phenotypically equivalent to their natural counterparts. This technology contributes to a new paradigm in regenerative medicine, whereby materials are able to actively direct and respond to cell behavior. The novel application of such materials as a coating capable of directing the formation and detachment of complex tissues solely under physiological conditions can have broad use for fundamental research and in future cell and tissue therapies.

Towards the design of 3D multiscale instructive tissue engineering constructs: Current approaches and trends

The design of 3D constructs with adequate properties to instruct and guide cells both in vitro and in vivo is one of the major focuses of tissue engineering. Successful tissue regeneration depends on the favorable crosstalk between the supporting structure, the cells and the host tissue so that a balanced matrix production and degradation are achieved. Herein, the major occurring events and players in normal and regenerative tissue are overviewed. These have been inspiring the selection or synthesis of instructive cues to include into the 3D constructs. We further highlight the importance of a multiscale perception of the range of features that can be included on the biomimetic structures. Lastly, we focus on the current and developing tissue-engineering approaches for the preparation of such 3D constructs: top-down, bottom-up and integrative. Bottom-up and integrative approaches present a higher potential for the design of tissue engineering devices with multiscale features and higher biochemical control than top-down strategies, and are the main focus of this review.

Clumps of a mesenchymal stromal cell/extracellular matrix complex can be a novel tissue engineering therapy for bone regeneration

BACKGROUND AIMS

The transplantation of mesenchymal stromal cells (MSCs) to damaged tissue has attracted attention in scientific and medical fields as an effective regenerative therapy. Nevertheless, additional studies are required to develop an MSC transplant method for bone regeneration because the use of an artificial scaffold restricts the number of transplanted cells and their function. Furthermore, regulating the degree of cell differentiation in vitro is desirable for a more effective regenerative therapy. To address these unresolved issues, with the use of a self-produced extracellular matrix (ECM), we developed clumps of an MSC/ECM complex (C-MSCs).

METHODS

MSCs isolated from rat femur were cultured in growth medium supplemented with 50 μg/mL of ascorbic acid for 7 days. To obtain C-MSCs, confluent cells were scratched with the use of a micropipette tip to roll up the cellular sheet, which consisted of ECM produced by the MSCs. The biological properties of C-MSCs were assessed in vitro and their bone regenerative activity was tested by use of a rat calvarial defect model.

RESULTS

Immunofluorescent confocal microscopic analysis revealed that type I collagen formed C-MSCs. Osteopontin messenger RNA expression and amount of calcium content were higher in C-MSCs cultured in osteo-inductive medium than those of untreated C-MSCs. The transplantation of osteogenic-differentiated C-MSCs led to rapid bone regeneration in the rat calvarial defect model.

CONCLUSIONS

These results suggest that the use of C-MSCs refined by self-produced ECM, which contain no artificial scaffold and can be processed in vitro, may represent a novel tissue engineering therapy.

Osteogenic cell sheets reinforced with photofunctionalized micro-thin titanium

Cell sheet technology has been used to deliver cells in single-sheet form with an intact extracellular matrix for soft tissue repair and regeneration. Here, we hypothesized that titanium-reinforced cell sheets could be constructed for bone tissue engineering and regeneration. Fifty-µm-thick titanium plates containing apertures were prepared and roughened by acid etching, some of which were photofunctionalized with 12 min of UV light treatment. Cell sheets were prepared by culturing rat calvarial periosteum-derived cells on temperature-responsive culture dishes and attached to titanium plates. Titanium-reinforced osteogenic cell sheet construction was conditional on various technical and material factors: cell sheets needed to be double-sided and sandwich the titanium plate, and the titanium plates needed to be micro thin and contain apertures to allow close apposition of the two cell sheets. Critically, titanium plates needed to be UV-photofunctionalized to ensure adherence and retention of cell sheets. Single-sided cell sheets or double-sided cell sheets on as-made titanium contracted and deformed within 4 days of incubation. Titanium-reinforced cell sheets on photofunctionalized titanium were structurally stable at least up to 14 days, developed the expected osteogenic phenotypes (ALP production and mineralization), and maintained structural integrity without functional degradation. Successful construction of titanium-reinforced osteogenic cell sheets was associated with increased cell attachment, retention, and expression of vinculin, an adhesion protein by photofunctionalization. This study identified the technical and material requirements for constructing titanium-reinforced osteogenic cell sheets. Future in vivo studies are warranted to test these titanium-reinforced cell sheets as stably transplantable, mechanically durable, and shape controllable osteogenic devices.

Concise review: Engineering myocardial tissue: the convergence of stem cells biology and tissue engineering technology

Advanced heart failure represents a leading public health problem in the developed world. The clinical syndrome results from the loss of viable and/or fully functional myocardial tissue. Designing new approaches to augment the number of functioning human cardiac muscle cells in the failing heart serve as the foundation of modern regenerative cardiovascular medicine. A number of clinical trials have been performed in an attempt to increase the number of functional myocardial cells by the transplantation of a diverse group of stem or progenitor cells. Although there are some encouraging suggestions of a small early therapeutic benefit, to date, no evidence for robust cell or tissue engraftment has been shown, emphasizing the need for new approaches. Clinically meaningful cardiac regeneration requires the identification of the optimum cardiogenic cell types and their assembly into mature myocardial tissue that is functionally and electrically coupled to the native myocardium. We here review recent advances in stem cell biology and tissue engineering and describe how the convergence of these two fields may yield novel approaches for cardiac regeneration.

A novel experimental study on the fabrication and biological characteristics of canine bone marrow mesenchymal stem cells sheet using vitamin C

The aim of this study was to fabricate canine bone marrow mesenchymal stem cell sheet through the use of vitamin C, to identify the biological characteristics of the resulting cell sheets, and to reveal the potential mechanism of cell-sheet promotion by vitamin C. This study used vitamin C to induce bone marrow mesenchymal stem cells to proliferate. The resulting cells secreted large amounts of collagen, thereby shortening the construction time of the cell-sheet layer. In addition to these aims, we identified biological microcharacteristics of the cell sheet through histological observation, transmission electron microscopy, real-time PCR detection, immunohistochemical detection, and osteogenesis-induction experiments on the cell sheet. We were able to stably and rapidly construct bone marrow mesenchymal stem cell sheet, effectively harvest it, and transfer the seed cells for tissue engineering. This study indicates that the use of vitamin C for harvesting mesenchymal stem cell sheets from bone marrow may provide an easy and practical approach for bone tissue regeneration.

Application of regenerative medical technology using tissue-engineered cell sheets for endoscopic submucosal dissection of esophageal neoplasms

We have developed a technique for endoscopic transplantation of cultured autologous oral mucosal epithelial cell sheets to an esophageal ulcer following endoscopic submucosal dissection (ESD). The epithelial cell sheets successfully prevented esophageal stricture after ESD. Key technology is that epithelial cell sheets cultured from oral mucosal tissue and attached proteins can be harvested using cell sheet technology and can be transplanted to a wound site without the use of adhesive material. This regenerative procedure can promote the epithelialization of ulceration safely and effectively. In the near future, the development of advanced endoscopic treatment of regenerative medicine shows promise.

Enzyme-mediated preparation of hydrogels composed of poly(ethylene glycol) and gelatin as cell culture platforms

Horseradish peroxidase-mediated preparation of redox-responsive hydrogels composed of thiolated poly(ethylene glycol) and gelatin allowed the proliferation of cells on the gel and the harvest as a viable cell sheet.

Shape-changing hydrogel surfaces trigger rapid release of patterned tissue modules

The formation and assembly of diverse tissue building blocks is considered a promising bottom-up approach for the construction of complex three-dimensional tissues. Patterned shape-changing materials were investigated as an innovative method to form and harvest free-standing tissue modules with preserved spatial organization and cell-cell connections. Arrays of micro-scale surface-attached hydrogels made of a thermoresponsive polymer were used as cell culture supports to fabricate tissue modules of defined geometric shape. Upon stimulation, these hydrogels swelled anisotropically, resulting in significant expansion of the culture surface and subsequent expulsion of the intact tissue modules. By varying the network crosslink density, the surface strain was modulated and a strain threshold for tissue module release was identified. This mechanical mechanism for rapid tissue module harvest was found to require inter- and intra-cellular tension. These results suggest that the cell-matrix adhesions are disrupted by the incompatibility of surface expansion with tissue module cohesion and stiffness, thus providing a novel method of forming and harvesting tissue building blocks by a mechanism independent of the thermal stimulus that induces the biomaterial shape change.

Construction of three-dimensional vascularized cardiac tissue with cell sheet engineering

Construction of three-dimensional (3D) tissues with pre-isolated cells is a promising achievement for novel medicine and drug-discovery research. Our laboratory constructs 3D tissues with an innovative and unique method for layering multiple cell sheets. Cell sheets maintain a high-efficiently regenerating function, because of the higher cell density and higher transplantation efficiency, compared to other cell-delivery methods. Cell sheets have already been applied in clinical applications for regenerative medicine in treating patients with various diseases. Therefore, in our search to develop a more efficient treatment with cell sheets, we are constructing 3D tissues by layering cell sheets. Native animal tissues and organs have an abundance of capillaries to supply oxygen and nutrients, and to remove waste molecules. In our investigation of vascularized cardiac cell sheets, we have found that endothelial cells within cell sheets spontaneously form blood vessel networks as in vivo capillaries. To construct even thicker 3D tissues by layering multiple cell sheets, it is critical to have a medium or blood flow within the vascular networks of the cell sheets. Therefore, to perfuse medium or blood in the cell sheet vascular network to maintain the viability of all cells, we developed two types of vascular beds; (1) a femoral muscle-based vascular bed, and (2) a synthetic collagen gel-based vascular bed. Both vascular beds successfully provide the critical flow of culture medium, which allows 12-layer cell sheets to survive. Such bioreactor systems, when combined with cell sheet engineering techniques, have produced functional vascularized 3D tissues. Here we explain and discuss the various processes to obtain vascular networks by properly connecting cell sheets and the engineering of 3D tissues.

Modeling human carcinomas: physiologically relevant 3D models to improve anti-cancer drug development

Anti-cancer drug development is inefficient, mostly due to lack of efficacy in human patients. The high fail rate is partly due to the lack of predictive models or the inadequate use of existing preclinical test systems. However, progress has been made and preclinical models were improved or newly developed, which all account for basic features of solid cancers, three-dimensionality and heterotypic cell interaction. Here we give an overview of available in vivo and in vitro models of cancer, which meet the criteria of being 3D and mirroring human tumor-stroma interactions. We only focus on drug response models without touching models for pharmacokinetic and dynamic, toxicity or delivery aspects.

Building a tissue in vitro from the bottom up: implications in regenerative medicine

Tissue engineering aims at creating biological tissues to improve or restore the function of diseased or damaged tissues. To enhance the performance of engineered tissues, it is required to recapitulate in vitro not only the composition but also the structural organization of native tissues. To this end, tissue engineering techniques are beginning to focus on generating micron-sized tissue modules having specific microarchitectural features that can be used alone as living filler in the damaged areas or serve as building blocks to engineer large biological tissues by a bottom-up approach. This work discusses the shortcomings related to traditional "top-down" strategies and the promises of emerging ''bottom-up" approaches in creating engineered biological tissues. We first present an overview of the current tissue-building techniques and their applications, with an analysis of the potentiality and shortcomings of different approaches. We then propose and discuss a novel method for the biofabrication of connective-like micro tissues and how this technique can be translated to cardiac muscle fabrication.