Cell sheet technology: a promising strategy in regenerative medicine

Laminin expression profiles of osteogenic-and chondrogenic-induced dECM sheets

Decellularized extracellular matrix sheets (dECMSs) produced by stem cells have attracted attention because they preserve the natural biological activity of the ECM to direct lineage-specific differentiation with less immunogenicity. As a core ECM protein, laminin modulates cellular phenotype and differentiation. Nevertheless, no studies thus far have explored the distribution and abundance of laminins in diverse dECMSs. Herein, we first compared the differential expression of laminins among dECMSs in osteogenic-induced medium (OI-dECMS), chondrogenic-induced medium (CI-dECMS), and standard medium (dECMS), employing a defined mass spectrometry (MS)-based proteomic analysis. In vitro, dECMSs were verified to be successfully decellularized. Cluster analysis identified a marked fluctuation in the expression of 7 laminins and 17 laminin-associated proteins in OI-dECMS vs dECMS and CI-dECMS vs dECMS. Two significantly changed pathways were selected from the KEGG pathway enrichment analysis: the FAK/ERK pathway and the PI3K/AKT pathway. Moreover, Alkaline Phosphatase (ALP) activity, Alcian blue staining, and RT-qPCR results for recellularization showed that CI-dECMS promotes chondrogenesis while OI-dECMS inhibits osteogenesis compared with dECMS. In vivo experiments were conducted to implant dECMSs in a rat osteochondral defect, demonstrating that dECMS and CI-dECMS promoted bone and cartilage repair. Furthermore, the inhibitory analysis was performed to verify the function of specific laminin isoforms modulating osteogenesis and chondrogenesis, which might be related to FAK/ERK and PI3K/AKT pathways. In summary, this study constructed dECMS, OI-dECMS, and CI-dECMS and uncovered the internal comprehensive molecular regulatory network centralized by laminins, thus proposing a biomimetic substitute for bone and cartilage regeneration.

Scaffold-free 3D culture systems for stem cell-based tissue regeneration

Recent advances in scaffold-free three-dimensional (3D) culture methods have significantly enhanced the potential of stem cell-based therapies in regenerative medicine. This cutting-edge technology circumvents the use of exogenous biomaterial and prevents its associated complications. The 3D culture system preserves crucial intercellular interactions and extracellular matrix support, closely mimicking natural biological niches. Therefore, stem cells cultured in 3D formats exhibit distinct characteristics, showcasing their capabilities in promoting angiogenesis and immunomodulation. This review aims to elucidate foundational technologies and recent breakthroughs in 3D scaffold-free stem cell engineering, offering comprehensive guidance for researchers to advance this technology across various clinical applications. We first introduce the various sources of stem cells and provide a comparative analysis of two-dimensional (2D) and 3D culture systems. Given the advantages of 3D culture systems, we delve into the specific fabrication and harvesting techniques for cell sheets and spheroids. Furthermore, we explore their applications in pre-clinical studies, particularly in large animal models and clinical trials. We also discuss multidisciplinary strategies to overcome existing limitations such as insufficient efficacy, hostile microenvironments, and the need for scalability and standardization of stem cell-based products.

Establishment and identification of bladder cancer cell sheet

Cell sheet technology (CST) has primarily been applied in tissue engineering for repair purposes. Our preliminary research indicates that an in vivo prostate cancer model established using CST outperforms traditional cell suspension methods. However, the potential for CST to be used with bladder cancer cells has not yet been explored. In this study, we investigated the ability of two bladder cancer cell lines, T24 and 5637, to form cell sheets. We found that T24 cells successfully formed cell sheets. We then performed staining to evaluate the integrity, specific markers, and proliferation characteristics of the T24 cell sheets. Our findings demonstrate that bladder cancer cell sheets can be established, providing a valuable tool for both in vivo and in vitro bladder cancer studies and for personalized drug selection for patients.

Simple and Cost-Effective Generation of 3D Cell Sheets and Spheroids Using Curvature-Controlled Paraffin Wax Substrates

The challenges associated with animal testing in pharmaceutical development have driven the search for alternative in vitro models that mimic human tissues more accurately. In this study, we present a simple and cost-effective method for generating 3D cell sheets and spheroids using curvature-controlled paraffin wax films, which are easily accessible laboratory materials that eliminate the need for extracellular matrix (ECM) components or thermo-responsive polymers. By adjusting the curvature of the paraffin wax film, we successfully generated human periodontal ligament fibroblast (HPdLF) cell sheets and bone marrow-derived mesenchymal stem cell (hBMSC) spheroids. Key parameters, such as cell density, substrate curvature, and incubation time, were identified as critical factors for optimizing the formation of these 3D structures. In addition, the use of quantum dots (QDs) for cell tracking enabled long-term visualization and distinction between different cell types within complex tissue-like structures. We further demonstrated that wrapping the hBMSC spheroids with HPdLF cell sheets partially replicated the connective tissue structure of the periodontal ligament surrounding the tooth root. This highlights the potential of this platform for the construction of more sophisticated tissue-mimicking assemblies. In conclusion, curvature-controlled paraffin wax films provide a versatile and practical approach for 3D cell cultures. This simplifies the generation of both cell sheets and spheroids, offering a promising tool for tissue engineering and regenerative medicine applications, where precise cell-to-cell interactions are essential.

Immunomodulatory Behavior of Tendon Magnetic Cell Sheets can be Modulated in Hypoxic Environments under Magnetic Stimulus

Tissue environments play a crucial role in orchestrating cell behavior, guided by a complex interplay of various factors. Long lasting inflammatory signals compromise tendon homeostasis and promote tissue degeneration, while tissue oxygen levels affect local cells' responses with hypoxic environments influencing apoptosis, inflammatory mediators, and matrix production. Recent works have unveiled the therapeutic potential of pulsed electromagnetic field (PEMF) in modulating inflammatory signals expressed by human tendon cells (hTDCs), and in mitigating the hypoxia-induced effects on the regulation of inflammatory cytokines. Thus, we sought to investigate the role of hypoxic environments, namely, 1 and 2% oxygen tension, in the inflammatory profiles of magnetic cell sheets (magCSs) formed by magnetic nanoparticles internalized in contiguous hTDCs with intact cell-cell junctions and deposited matrix. We also aimed to explore the impact of PEMF over hypoxia-treated magCSs, including IL-1β-primed-magCSs, with the objective of harnessing magnetic stimulation to guide abnormal inflammatory cell responses toward efficient treatments supporting tendon regenerative potential. Our findings revealed that low oxygen tensions amplified the expression of hypoxia-associated genes and of inflammatory markers in IL-1β-primed-magCSs with an involvement of the NF-κB signaling pathway. Encouragingly, when PEMF was applied to IL-1β-primed-magCSs under hypoxic conditions, it successfully modulated inflammatory cues by favoring IL-10 and IL-4, via the NF-κB pathway. These results signify the remarkable potential of PEMF in driving proregenerative strategies and opens up new approaches in tendon therapies, highlighting the transformative impact of immunomodulatory magnetic cell sheets.

Characterization of cells in blood evoked from periapical tissues in immature teeth with pulp necrosis and their potential for autologous cell therapy in Regenerative Endodontics

OBJECTIVE

The objectives of this study were to isolate, characterize progenitor cells from blood in the root canals of necrotic immature permanent teeth evoked from periapical tissues and evaluate the applicable potential of these isolated cells in Regenerative Endodontics.

DESIGN

Ten necrotic immature permanent teeth from seven patients were included. Evoked bleeding from periapical tissues was induced after chemical instrumentation of the root canals. Cells were isolated from the canal blood and evaluated for cell surface marker expression, multilineage differentiation potential, proliferation ability, and target protein expression. Cell sheets formed from these cells were transferred into human root segments, and then transplanted into nude mice. Histological examination was performed after eight weeks. Data analysis was conducted using one-way ANOVA followed by Tukey's post-hoc comparison, considering p < 0.05 as statistically significant.

RESULTS

The isolated cells exhibited characteristics typical of fibroblastic cells with colony-forming efficiency, and displayed Ki67 positivity and robust proliferation. Flow cytometry data demonstrated that at passage 3, these cells were positive for CD73, CD90, CD105, CD146, and negative for CD34 and CD45. Vimentin expression indicated a mesenchymal origin. Under differentiation media specific differentiation media, the cells demonstrated osteogenic, adipogenic, and chondrogenic differentiation potential. Subcutaneous root canals with cell sheets of isolated cells in nude mice showed the formation of pulp-like tissues.

CONCLUSIONS

This study confirmed the presence of progenitor cells in root canals following evoked bleeding from periapical tissues of necrotic immature teeth. Isolated cells exhibited similar immunophenotype and regenerative potential with dental mesenchymal stromal cells in regenerative endodontic therapy.

Interactions of Cardiac Proteins with Plasma-Synthesized Polypyrrole (PSPy) to Improve Adult Cardiomyocytes Culture

Plasma-Synthesized Polypyrrole (PSPy) has been reported as a biomaterial suitable for cell growth in vitro and in vivo. An experimental duplicate was carried out that showed the growth of cardiomyocytes with PSPy, following a protocol previously reported by the working group. The cardiomyocytes cultured with the biomaterial retained their native morphological characteristics, a fundamental key to improving cardiac cell therapy procedures. Such observations motivated us to investigate the molecular characteristics of the biomaterial and the type of interactions that could be occurring (mainly electrostatic, hydrogen bonds, and non-polar). Additionally, PSPy has been studied to establish the probable mechanisms of action of the biomaterial, in particular, its action on a group of cell membrane proteins, integrins, which we know participate in the adhesion of cells to the extracellular matrix, in adhesion between cells and as bidirectional signal transducer mechanisms. In this work, we carried out studies of the interactions established between cardiac integrins α2β1 and α5β1 with different PSPy models by molecular docking studies and binding free energies (ΔGb) calculations. The models based on a previously reported PSPy molecule have three variable terminal chemical groups, with the purpose of exploring the differences in the type of interaction that will be established by modifying the position of an amino (-NH2), a hydroxyl (-OH), and a nitrile (C≡N) in (fixed) groups, as well as the length of the terminal chains (a long/short -NH2). A model with short chains for the -OH and -NH2 (lateral) group was the model with the best interactions with cardiac integrins. We experimentally verified the direct interaction of cardiomyocytes with the PSPy biomaterial observed in rat primary cultures, allowing us to validate the favorable interactions predicted by the computational analysis.

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

OBJECTIVE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

CLINICAL RELEVANCE

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

Translational application of human keratinocyte-fibroblast cell sheets for accelerated wound healing in a clinically relevant type 2 diabetic rat model

BACKGROUND AIMS

Despite advancements in wound care, wound healing remains a challenge, especially in individuals with type 2 diabetes. Cell sheet technology has emerged as an efficient and promising therapy for tissue regeneration and wound repair. Among these, bilayered human keratinocyte-fibroblast cell sheets constructed using temperature-responsive culture surfaces have been shown to mimic a normal tissue-like structure and secrete essential cytokines and growth factors that regulate the wound healing process.

METHODS

This study aimed to evaluate the safety and therapeutic potential of human skin cell sheets to treat full-thickness skin defects in a rat model of type 2 diabetes.

RESULTS

Our findings demonstrate that diabetic wounds transplanted with bilayered cell sheets resulted in accelerated re-epithelialization, increased angiogenesis, enhanced macrophage polarization and regeneration of tissue that closely resembled healthy skin. In contrast, the control group that did not receive cell sheet transplantation presented characteristic symptoms of impaired and delayed wound healing associated with type 2 diabetes.

CONCLUSIONS

The secretory cytokines and the upregulation of Nrf2 expression in response to cell sheet transplantation are believed to have played a key role in the improved wound healing observed in diabetic rats. Our study suggests that human keratinocyte-fibroblast cell sheets hold great potential as a therapeutic alternative for diabetic ulcers.

Recent Advances in Alginate-Based Hydrogels for Cell Transplantation Applications

With its exceptional biocompatibility, alginate emerged as a highly promising biomaterial for a large range of applications in regenerative medicine. Whether in the form of microparticles, injectable hydrogels, rigid scaffolds, or bioinks, alginate provides a versatile platform for encapsulating cells and fostering an optimal environment to enhance cell viability. This review aims to highlight recent studies utilizing alginate in diverse formulations for cell transplantation, offering insights into its efficacy in treating various diseases and injuries within the field of regenerative medicine.

Trans-Arterial Stem Cell Injection (TASI): The Role of Interventional Radiology in Regenerative Medicine

Regenerative medicine is taking a step forward in treating multiple diseases. The possibility of renewing damaged tissues with stem cells has become a topic of interest in recent decades. Still a relatively new research topic, many issues in this discipline are being addressed, from cell culturing to the study of different graft materials, and, moreover, cell delivery. For instance, direct intravenous injection has a big downfall regarding its lack of precision and poorly targeted treatment. Trans-arterial and direct percutaneous infusion to the aimed tissue/organ are both considered ideal for reaching the desired region but require image guidance to be performed safely and precisely. In this context, interventional radiology becomes pivotal for providing different cell delivery possibilities in every case. In this review, we analyze different basic stem cell therapy concepts and the current and future role of interventional radiology with a focus on trans-arterial delivery.

Tailoring cell sheets for biomedical applications

Cell sheet technology has emerged as a novel scaffold-free approach for cell-based therapies in regenerative medicine. Techniques for harvesting cell sheets are essential to preserve the integrity of living cell sheets. This review provides an overview of fundamental technologies to fabricate cell sheets and recent advances in cell sheet-based tissue engineering. In addition to the commonly used temperature-responsive systems, we introduce alternative approaches, such as ROS-induced, magnetic-controlled, and light-induced cell sheet technologies. Moreover, we discuss the modification of the cell sheet to improve its function, including stacking, genetic modification, and vascularization. With the significant advances in cell sheet technology, cell sheets have been widely applied in various tissues and organs, including but not limited to the lung, cornea, cartilage, periodontium, heart, and liver. This review further describes both the preclinical and clinical applications of cell sheets. We believe that the progress in cell sheet technology would further propel its biomedical applications.

Cell Sheet Technology: An Emerging Approach for Tendon and Ligament Tissue Engineering

Tendon and ligament injuries account for a substantial proportion of disorders in the musculoskeletal system. While non-operative and operative treatment strategies have advanced, the restoration of native tendon and ligament structures after injury is still challenging due to its innate limited regenerative ability. Cell sheet technology is an innovative tool for tissue fabrication and cell transplantation in regenerative medicine. In this review, we first summarize different harvesting procedures and advantages of cell sheet technology, which preserves intact cell-to-cell connections and extracellular matrix. We then describe the recent progress of cell sheet technology from preclinical studies, focusing on the application of stem cell-derived sheets in treating tendon and ligament injuries, as well as highlighting its effects on mitigating inflammation and promoting tendon/graft-bone interface healing. Finally, we discuss several prerequisites for future clinical translation including the selection of appropriate cell source, optimization of preparation process, establishment of suitable animal model, and the fabrication of vascularized complex tissue. We believe this review could potentially provoke new ideas and drive the development of more functional biomimetic tissues using cell sheet technology to meet the needs of clinical patients.

Fusogenic liposome-coated nanoparticles for rapid internalization into donor corneal endothelial tissue to enable prophylaxis before transplantation

Cold stress (hypothermia) during storage and cytokine stress due to acute allograft rejection adversely affect the donor corneal endothelium in the short term. Pharmacological pre-treatment (before transplantation) of the donor corneal endothelium or cells (propagated in vitro for cell injection therapy) with microtubule stabilizers, cold stress protectants, and other molecules is an attractive strategy to tackle damage caused by hypothermia and cytokine stress. These molecules can be delivered intracellularly to the donor corneal endothelium or cells at controlled rates for desired periods and with one-time administration using nanoparticles. However, the death-to-preservation time of donor corneas of more than 4 to 6 h significantly decreases endothelial cell density and increases the risk of microbial contamination. Therefore, we have developed fusogenic liposome-coated nanoparticles for rapid internalization of nanoparticles into cultured corneal endothelial cells and ex vivo corneal endothelial tissue. Here, we have shown that the fusogenic liposome-coated nanoparticles have the intrinsic ability to efficiently and rapidly internalize into cultured corneal endothelial cells and ex vivo corneal tissue within 3 h by possibly fusing with the cell membrane and bypassing the endocytic pathway. Lactate dehydrogenase assay showed that the internalized fusogenic liposome-coated nanoparticles did not cause cytotoxicity in endothelial cells associated with the ex vivo cornea for at least up to 2 days. Thus, fusogenic liposome-coated nanoparticles have great potential as a platform for engineering cells and endothelial tissue of donor corneas to facilitate prophylactic drug delivery during storage and after transplantation.

Thermoresponsive Smart Copolymer Coatings Based on P(NIPAM-co-HEMA) and P(OEGMA-co-HEMA) Brushes for Regenerative Medicine

The fabrication of multifunctional, thermoresponsive platforms for regenerative medicine based on polymers that can be easily functionalized is one of the most important challenges in modern biomaterials science. In this study, we utilized atom transfer radical polymerization (ATRP) to produce two series of novel smart copolymer brush coatings. These coatings were based on copolymerizing 2-hydroxyethyl methacrylate (HEMA) with either oligo(ethylene glycol) methyl ether methacrylate (OEGMA) or N-isopropylacrylamide (NIPAM). The chemical compositions of the resulting brush coatings, namely, poly(oligo(ethylene glycol) methyl ether methacrylate-co-2-hydroxyethyl methacrylate) (P(OEGMA-co-HEMA)) and poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) (P(NIPAM-co-HEMA)), were predicted using reactive ratios of the monomers. These predictions were then verified using time-of-flight-secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). The thermoresponsiveness of the coatings was examined through water contact angle (CA) measurements at different temperatures, revealing a transition driven by lower critical solution temperature (LCST) or upper critical solution temperature (UCST) or a vanishing transition. The type of transition observed depended on the chemical composition of the coatings. Furthermore, it was demonstrated that the transition temperature of the coatings could be easily adjusted by modifying their composition. The topography of the coatings was characterized using atomic force microscopy (AFM). To assess the biocompatibility of the coatings, dermal fibroblast cultures were employed, and the results indicated that none of the coatings exhibited cytotoxicity. However, the shape and arrangement of the cells were significantly influenced by the chemical structure of the coating. Additionally, the viability of the cells was correlated with the wettability and roughness of the coatings, which determined the initial adhesion of the cells. Lastly, the temperature-induced changes in the properties of the fabricated copolymer coatings effectively controlled cell morphology, adhesion, and spontaneous detachment in a noninvasive, enzyme-free manner that was confirmed using optical microscopy.

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.

From Free Tissue Transfer to Hydrogels: A Brief Review of the Application of the Periosteum in Bone Regeneration

The periosteum is a thin layer of connective tissue covering bone. It is an essential component for bone development and fracture healing. There has been considerable research exploring the application of the periosteum in bone regeneration since the 19th century. An increasing number of studies are focusing on periosteal progenitor cells found within the periosteum and the use of hydrogels as scaffold materials for periosteum engineering and guided bone development. Here, we provide an overview of the research investigating the use of the periosteum for bone repair, with consideration given to the anatomy and function of the periosteum, the importance of the cambium layer, the culture of periosteal progenitor cells, periosteum-induced ossification, periosteal perfusion, periosteum engineering, scaffold vascularization, and hydrogel-based synthetic periostea.

Corneal regeneration strategies: From stem cell therapy to tissue engineered stem cell scaffolds

Corneal epithelial defects and excessive wound healing might lead to severe complications. As stem cells can self-renew infinitely, they are a promising solution for regenerating the corneal epithelium and treating severe corneal epithelial injury. The chemical and biophysical properties of biological scaffolds, such as the amniotic membrane, fibrin, and hydrogels, can provide the necessary signals for stem cell proliferation and differentiation. Multiple researchers have conducted investigations on these scaffolds and evaluated them as potential therapeutic interventions for corneal disorders. These studies have identified various inherent benefits and drawbacks associated with these scaffolds. In this study, we provided a comprehensive overview of the history and use of various stem cells in corneal repair. We mainly discussed biological scaffolds that are used in stem cell transplantation and innovative materials that are under investigation.

Application of mesenchymal stem cell sheet for regeneration of craniomaxillofacial bone defects

Bone defects are among the most common damages in human medicine. Due to limitations and challenges in the area of bone healing, the research field has turned into a hot topic discipline with direct clinical outcomes. Among several available modalities, scaffold-free cell sheet technology has opened novel avenues to yield efficient osteogenesis. It is suggested that the intact matrix secreted from cells can provide a unique microenvironment for the acceleration of osteoangiogenesis. To the best of our knowledge, cell sheet technology (CST) has been investigated in terms of several skeletal defects with promising outcomes. Here, we highlighted some recent advances associated with the application of CST for the recovery of craniomaxillofacial (CMF) in various preclinical settings. The regenerative properties of both single-layer and multilayer CST were assessed regarding fabrication methods and applications. It has been indicated that different forms of cell sheets are available for CMF engineering like those used for other hard tissues. By tackling current challenges, CST is touted as an effective and alternative therapeutic option for CMF bone regeneration.

An efficient method for cell sheet bioengineering from rBMSCs on thermo-responsive PCL-PEG-PCL copolymer

Utilizing both medium enrichment and a thermos-responsive substrate to maintain the cell-to-cell junctions and extracellular matrix (ECM) intact, cell sheet technology has emerged as a ground-breaking approach. Investigating the possibility of using sodium selenite (as medium supplementation) and PCL-PEG-PCL (as vessel coating substrate) in the formation of the sheets from rat bone marrow-derived mesenchymal stem cells (rBMSCs) was the main goal of the present study. To this end, first, Polycaprolactone-co-Poly (ethylene glycol)-co-Polycaprolactone triblock copolymer (PCEC) was prepared by ring-opening copolymerization method and characterized by FTIR, ¹ H NMR, and GPC. The sol-gel-sol phase transition temperature of the PCEC aqueous solutions with various concentrations was either measured. Next, rBMSCs were cultured on the PCEC, and let be expanded in five different media containing vitamin C (50 µg/ml), sodium selenite (0.1 µM), vitamin C and sodium selenite (50 µg/ml + 0.1 µM), Trolox, and routine medium. The proliferation of the cells exposed to each material was evaluated. Produced cell sheets were harvested from the polymer surface by temperature reduction and phenotypically analyzed via an inverted microscope, hematoxylin and eosin (H&E) staining, and field emission scanning electron microscopy (FESEM). Through the molecular level, the expression of the stemness-related genes (Sox2, Oct-4, Nanog), selenium-dependent enzymes (TRX, GPX-1), and aging regulator gene (Sirt1) were measured by q RT-PCR. Senescence in cell sheets was checked by beta-galactosidase assay. The results declared the improved ability of the rBMSCs for osteogenesis and adipogenesis in the presence of antioxidants vitamin C, sodium selenite, and Trolox in growth media. The data indicated that in the presence of vitamin C and sodium selenite, the quality of the cell sheet was risen by reducing the number of senescent cells and high transcription of the stemness genes. Monolayers produced by sodium selenite was in higher-quality than the ones produced by vitamin C.

Synthesis and Characterization of Nanostructured Oxide Layers on Ti-Nb-Zr-Ta and Ti-Nb-Zr-Fe Biomedical Alloys

Nanoporous/nanotubular complex oxide layers were developed on high-fraction β phase quaternary Ti-Nb-Zr-Ta and Ti-Nb-Zr-Fe promising biomedical alloys with a low elasticity modulus. Surface modification was achieved by electrochemical anodization aimed at the synthesis of the morphology of the nanostructures, which exhibited inner diameters of 15–100 nm. SEM, EDS, XRD, and current evolution analyses were performed for the characterization of the oxide layers. By optimizing the process parameters of electrochemical anodization, complex oxide layers with pore/tube openings of 18–92 nm on Ti-10Nb-10Zr-5Ta, 19–89 nm on Ti-20Nb-20Zr-4Ta, and 17–72 nm on Ti-29.3Nb-13.6Zr-1.9Fe alloys were synthesized using 1 M H3PO4 + 0.5 wt% HF aqueous electrolytes and 0.5 wt% NH4F + 2 wt% H20 + ethylene glycol organic electrolytes.

Regeneration Using Adipose-Derived Stem Cell Sheets in a Rabbit Meniscal Defect Model Improves Tensile Strength and Load Distribution Function of the Meniscus at 12 Weeks

PURPOSE

The purpose of this study was to evaluate the mechanical properties, such as the tensile strength and load distribution function, of the meniscus tissue regenerated using adipose-derived stem cell (ADSC) sheets in a rabbit meniscal defect model.

METHODS

ADSC sheets were prepared from adipose tissue of rabbits. The anterior half of the medial meniscus was removed from both knees. One knee was transplanted with an ADSC sheet; the contralateral knee was closed without transplantation. Mechanical tests were performed at 4 and 12 weeks posttransplantation. In the tensile test, tensile force was applied to the entire medial meniscus, including the normal area (n = 10/group). Compression tests were performed on the entire knee, with soft tissues other than the ligament removed. A pressure-sensitive film was inserted under the medial meniscus and a 40-N load was applied (n = 5/group).

RESULTS

In the tensile test, the elastic modulus in ADSC-treated knees was higher at 12 weeks (ADSC: 70.30 ± 18.50 MPa, control: 43.71 ± 7.11 MPa, P = .009). The ultimate tensile strength (UTS) in ADSC-treated knees at 12 weeks was also higher (ADSC: 22.69 ± 5.87 N, control: 15.45 ± 4.08 N, P = .038). In the compression test, the contact area was larger in the ADSC group at 4 weeks (ADSC: 31.60 ± 8.17 mm², control: 20.33 ± 2.86 mm², P = .024) and 12 weeks (ADSC: 41.07 ± 6.09 mm², control: 30.53 ± 5.47 mm², P = .04). Peak pressure was significantly lower in ADSC-treated knees at 12 weeks (ADSC: 11.91 ± 1.03 MPa, control: 15.53 ± 2.3 MPa, P = .002).

CONCLUSIONS

The regenerated meniscus tissue, 12 weeks after transplantation of the ADSC sheets into the meniscal defect area, had high elastic modulus and UTS. In the meniscus-tibia compartment, the contact area was large and the peak pressure was low.

CLINICAL RELEVANCE

ADSC sheets promoted regeneration of meniscus. ADSC sheet transplantation for meniscal defects could be an effective regenerative therapy.

Forskolin enhanced the osteogenic differentiation of human dental pulp stem cells in vitro and in vivo

Background/purpose

Human dental pulp stem cells (hDPSCs) are multipotent adult stem cells that can differentiate into various lineages such as odontoblasts, osteoblasts, and chondrocytes. Regulation of hDPSCs differentiation with small-molecule compounds can be a useful tool for tissue engineering and regenerative therapy. Forskolin is an agonist of adenylate cyclase that promotes cyclic adenosine monophosphate production. However, the role of Forskolin in regulating the osteogenic differentiation of hDPSCs is still unknown.

Materials and methods

A cell counting kit-8 (CCK-8) assay was performed to screen out the safety concentrations of Forskolin. Following, quantitative polymerase chain reaction (qPCR) and alizarin red staining were performed to detect bone-related gene expression and mineralized deposit formation. Furthermore, we prepared cell sheets which were followed by a 3D culture for cell pellet formation. Finally, the hDPSC cell pellets were transplanted into immunodeficient mice.

Results

CCK-8 assay showed 5 μM and 10 μM Forskolin had no significant inhibition on the proliferation of hDPSCs. The qPCR indicated Forskolin (5, 10 μM) enhanced osteogenic differentiation of hDPSCs by upregulating bone-related genes. Alizarin red staining and its quantification analysis demonstrated Forskolin in 5 μM and 10 μM similarly enhanced the mineralized deposit formation of hDPSCs in vitro. After six weeks of transplantation, immunohistochemical stains showed that osteopontin expression and bone formation were significantly boosted in the Forskolin-treated group than in the normal osteogenic inducing group.

Conclusion

Our results indicate Forskolin enhances osteogenic differentiation of hDPSCs in vitro and boosts bone formation in vivo.

Tissue engineering in growth plate cartilage regeneration: Mechanisms to therapeutic strategies

The repair of growth plate injuries is a highly complex process that involves precise spatiotemporal regulation of multiple cell types. While significant progress has been made in understanding the pathological mechanisms underlying growth plate injuries, effectively regulating this process to regenerate the injured growth plate cartilage remains a challenge. Tissue engineering technology has emerged as a promising therapeutic approach for achieving tissue regeneration through the use of functional biological materials, seed cells and biological factors, and it is now widely applied to the regeneration of bone and cartilage. However, due to the unique structure and function of growth plate cartilage, distinct strategies are required for effective regeneration. Thus, this review provides an overview of current research on the application of tissue engineering to promote growth plate regeneration. It aims to elucidates the underlying mechanisms by which tissue engineering promotes growth plate regeneration and to provide novel insights and therapeutic strategies for future research on the regeneration of growth plate.

Global Single-Cell Sequencing Landscape of Adipose Tissue of Different Anatomical Site Origin in Humans

Chronic refractory wounds (CRW) are one of the most serious clinical challenges for surgeons to address. Stromal vascular fraction gels (SVFG), including human adipose stem cells (hASCs), have excellent vascular regenerative and tissue repair properties. Here, we combined single-cell RNA sequencing (scRNA-seq) of leg subcutaneous adipose tissue samples with scRNA-seq data from abdominal subcutaneous adipose tissue, leg subcutaneous adipose tissue, and visceral adipose tissue samples from public databases. The results showed specific differences in cellular levels in adipose tissue from different anatomical site sources. We identified cells including CD4⁺ T cells, hASCs, adipocyte (APC), epithelial (Ep) cells, and preadipocyte. In particular, the dynamics between groups of hASCs, epithelial cells, APCs, and precursor cells in adipose tissue of different anatomical site origins were more significant. Furthermore, our analysis reveals alterations at the cellular level and molecular level, as well as the biological signaling pathways involved in these subpopulations of cells with specific alterations. In particular, certain subpopulations of hASCs have higher cell stemness, which may be related to lipogenic differentiation capacity and may be beneficial in promoting CRW treatment and healing. In general, our study captures a human single-cell transcriptome profile across adipose depots, the cell type identification and analysis of which may help dissect the function and role of cells with specific alterations present in adipose tissue and may provide new ideas and approaches for the treatment of CRW in the clinical setting.

Periodontal ligament stem cell-based bioactive constructs for bone tissue engineering

Objectives: Stem cell-based tissue engineering approaches are promising for bone repair and regeneration. Periodontal ligament stem cells (PDLSCs) are a promising cell source for tissue engineering, especially for maxillofacial bone and periodontal regeneration. Many studies have shown potent results via PDLSCs in bone regeneration. In this review, we describe recent cutting-edge researches on PDLSC-based bone regeneration and periodontal tissue regeneration. Data and sources: An extensive search of the literature for papers related to PDLSCs-based bioactive constructs for bone tissue engineering was made on the databases of PubMed, Medline and Google Scholar. The papers were selected by three independent calibrated reviewers. Results: Multiple types of materials and scaffolds have been combined with PDLSCs, involving xeno genic bone graft, calcium phosphate materials and polymers. These PDLSC-based constructs exhibit the potential for bone and periodontal tissue regeneration. In addition, various osteo inductive agents and strategies have been applied with PDLSCs, including drugs, biologics, gene therapy, physical stimulation, scaffold modification, cell sheets and co-culture. Conclusoin: This review article demonstrates the great potential of PDLSCs-based bioactive constructs as a promising approach for bone and periodontal tissue regeneration.

Structure and Dynamics of Inhomogeneities in Aqueous Solutions of Graft Copolymers of N-Isopropylacrylamide with Lactide (P(NIPAM-graft-PLA)) by Spin Probe EPR Spectroscopy

Coil-to-globule transition and dynamics of inhomogeneities in aqueous solutions of graft copolymers of NIPAM with different content of oligolactide groups were studied using spin probe continuous wave EPR spectroscopy. The technique of the suppressing of TEMPO as spin probe by spin exchange with Cu2+ ions was applied. This approach allowed us to detect individual EPR spectra of the probe in collapsed globules and estimate its magnetic and dynamic parameters reliably. The formation of inhomogeneities at temperatures lower than the volume phase transition temperature measured via transmission, and differential scanning calorimetry was fixed. An increase in oligolactide content in copolymers leads to the formation of looser globules, allowing for the exchange of the probe molecules between the globules and the external solution.

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

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

Biological mechanisms and applied prospects of mesenchymal stem cells in premature ovarian failure

Premature ovarian failure (POF), also known as primary ovarian insufficiency (POI), refers to the loss of ovarian function in women after puberty and before the age of 40 characterized by high serum gonadotropins and low estrogen, irregular menstruation, amenorrhea, and decreased fertility. However, the specific pathogenesis of POF is unexplained, and there is no effective therapy for its damaged ovarian tissue structure and reduced reserve function. Mesenchymal stem cells (MSCs), with multidirectional differentiation potential and self-renewal ability, as well as the cytokines and exosomes they secrete, have been studied and tested to play an active therapeutic role in a variety of degenerative pathologies, and MSCs are the most widely used stem cells in regenerative medicine. MSCs can reverse POI and enhance ovarian reserve function through differentiation into granulosa cells (GCs), immune regulation, secretion of cytokines and other nutritional factors, reduction of GCs apoptosis, and promotion of GCs regeneration. Many studies have proved that MSCs may have a restorative effect on the structure and fertility of injured ovarian tissues and turn to be a useful clinical approach to the treatment of patients with POF in recent years. We intend to use MSCs-based therapy to completely reverse POI in the 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.

Synthesis and characterization of stimuli-responsive hydrogels: evaluation of external stimuli influence on L929 fibroblast viability

In this study, poly(2-hydroxyethyl methacrylate) [p(HEMA)] based hydrogels responsive to the pH, temperature and magnetic field were synthesized. The surface properties of p(HEMA) were improved by designing the stimuli-responsive hydrogels made of MAGA, NIPAAm and methacrylate-decorated magnetite nanoparticles as a function of pH-, thermo- and magnetic responsive cell culture surfaces. These materials were then modified an abundant extracellular matrix component, type I collagen, which has been considered as a biorecognition element to increase the applicability of hydrogels to cell viability. Based on results from scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA), stimuli-responsive hydrogel demonstrated improved non-porous structures and thermal stability with a high degree of cross-linking. Mechanical analyses of the hydrogels also showed that stimuli-responsive hydrogels are more elastomeric due to the polymeric chains and heterogeneous amorphous segments compared to plain hydrogels. Furthermore, surface modification of hydrogels with collagen provided better biocompatibility, which was confirmed with L929 fibroblast cell adhesion. Produced stimuli-responsive hydrogels modulated cellular viability by changing pH and magnetic field.

Trophic and immunomodulatory effects of adipose tissue derived stem cells in a preclinical murine model of endometriosis

Endometriosis, which exhibits enigmatic pathological features such as stromal fibrosis and proliferation of ectopic epithelial cells, is known as a refractory disease. Mesenchymal stem cells modulate the fibrosis in stromal tissues through their trophic and immunomodulatory properties. To investigate the potential of stem cells in treating endometriosis, we examined the secondary morphology and molecular alterations in endometriosis-like lesions after the administration of adipose tissue-derived stem cells (ASCs) to an experimental murine model of endometriosis. The infused ASCs were found integrated in the endometriosis-like lesions. Accompanied by the suppression of stromal fibrosis and proliferation of endometriotic epithelial cells, the infusion of ASCs with stemness potential (early passage of ASCs) suppressed the growth of endometriosis-like lesions and inhibited the expression of pro-inflammatory and pro-fibrotic cytokines, whereas no significant attenuation of endometriosis-like lesions occurred after the infusion of ASCs without stemness potential (late passage of ASCs). Accordingly, the trophic and immunomodulatory properties of ASCs may regulate fibrosis in endometriosis-like lesions, suggesting that regenerative medicine could be recognized as an innovative treatment for patients with endometriosis through the accumulation of evidence of preclinical efficacy.

Droplet-based bioprinting enables the fabrication of cell–hydrogel–microfibre composite tissue precursors

Composites offer the option of coupling the individual benefits of their constituents to achieve unique material properties, which can be of extra value in many tissue engineering applications. Strategies combining hydrogels with fibre-based scaffolds can create tissue constructs with enhanced biological and structural functionality. However, developing efficient and scalable approaches to manufacture such composites is challenging. Here, we use a droplet-based bioprinting system called reactive jet impingement (ReJI) to integrate a cell-laden hydrogel with a microfibrous mesh. This system uses microvalves connected to different bioink reservoirs and directed to continuously jet bioink droplets at one another in mid-air, where the droplets react and form a hydrogel that lands on a microfibrous mesh. Cell–hydrogel–fibre composites are produced by embedding human dermal fibroblasts at two different concentrations (5 × 106 and 30 × 106 cells/mL) in a collagen–alginate–fibrin hydrogel matrix and bioprinted onto a fibre-based substrate. Our results show that both types of cell–hydrogel–microfibre composite maintain high cell viability and promote cell–cell and cell–biomaterial interactions. The lower fibroblast density triggers cell proliferation, whereas the higher fibroblast density facilitates faster cellular organisation and infiltration into the microfibres. Additionally, the fibrous component of the composite is characterised by high swelling properties and the quick release of calcium ions. The data indicate that the created composite constructs offer an efficient way to create highly functional tissue precursors for laminar tissue engineering, particularly for wound healing and skin tissue engineering applications.

Graphic abstract

Insight in Hypoxia-Mimetic Agents as Potential Tools for Mesenchymal Stem Cell Priming in Regenerative Medicine

Hypoxia-mimetic agents are new potential tools in MSC priming instead of hypoxia incubators or chambers. Several pharmaceutical/chemical hypoxia-mimetic agents can be used to induce hypoxia in the tissues: deferoxamine (DFO), dimethyloxaloylglycine (DMOG), 2,4-dinitrophenol (DNP), cobalt chloride (CoCl2), and isoflurane (ISO). Hypoxia-mimetic agents can increase cell proliferation, preserve or enhance differentiation potential, increase migration potential, and induce neovascularization in a concentration- and stem cell source-dependent manner. Moreover, hypoxia-mimetic agents may increase HIF-1α, changing the metabolism and enhancing glycolysis like hypoxia. So, there is clear evidence that treatment with hypoxia-mimetic agents is beneficial in regenerative medicine, preserving stem cell capacities. These agents are not studied so wildly as hypoxia but, considering the low cost and ease of use, are believed to find application as pretreatment of many diseases such as ischemic heart disease and myocardial fibrosis and promote cardiac and cartilage regeneration. The knowledge of MSC priming is critical in evaluating safety procedures and use in clinics. In this review, similarities and differences between hypoxia and hypoxia-mimetic agents in terms of their therapeutic efficiency are considered in detail. The advantages, challenges, and future perspectives in MSC priming with hypoxia mimetic agents are also discussed.

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.

Collagen and nano-hydroxyapatite interactions in alginate-based microcapsule provide an appropriate osteogenic microenvironment for modular bone tissue formation

The addition of nano-hydroxyapatite (nHA) and collagen (Col) to the alginate (Alg) microcapsule hydrogel reduced swelling and degradation ratios while the compressive strength increased compared to Alg, Alg-Col, and Alg-nHA groups. MTT assay and Calcein-AM staining revealed an enhanced MG-63 osteoblasts viability in the Alg-nHA-Col hydrogel compared to the other groups. SEM showed the attachment of MG-63 osteoblasts inside Alg-Col hydrogels. Non-significant differences were found in antioxidant capacity of cells inside the Alg-nHA-Col hydrogel compared to the Alg group. Hematoxylin-Eosin staining showed the distribution of MG-63 osteoblasts inside microspheres. Calcium deposits, alkaline phosphatase (ALP) activity with the increase of intracellular calcium were found in Alg-nHA-Col group. Western blotting showed that levels of osteocalcin, ColA2, Sox-9, and ColA1 also significantly increased compared to the Alg, Alg-Col, Alg-nHA groups. The present study demonstrated that the addition of mineral nHA and protein (Col) into the Alg improves osteogenic potential and provides a 3D platform for modular bone tissue engineering.

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.

Conventional and Recent Trends of Scaffolds Fabrication: A Superior Mode for Tissue Engineering

Tissue regeneration is an auto-healing mechanism, initiating immediately following tissue damage to restore normal tissue structure and function. This falls in line with survival instinct being the most dominant instinct for any living organism. Nevertheless, the process is slow and not feasible in all tissues, which led to the emergence of tissue engineering (TE). TE aims at replacing damaged tissues with new ones. To do so, either new tissue is being cultured in vitro and then implanted, or stimulants are implanted into the target site to enhance endogenous tissue formation. Whichever approach is used, a matrix is used to support tissue growth, known as ‘scaffold’. In this review, an overall look at scaffolds fabrication is discussed, starting with design considerations and different biomaterials used. Following, highlights of conventional and advanced fabrication techniques are attentively presented. The future of scaffolds in TE is ever promising, with the likes of nanotechnology being investigated for scaffold integration. The constant evolvement of organoids and biofluidics with the eventual inclusion of organ-on-a-chip in TE has shown a promising prospect of what the technology might lead to. Perhaps the closest technology to market is 4D scaffolds following the successful implementation of 4D printing in other fields.

Conventional and Recent Trends of Scaffolds Fabrication: A Superior Mode for Tissue Engineering

Tissue regeneration is an auto-healing mechanism, initiating immediately following tissue damage to restore normal tissue structure and function. This falls in line with survival instinct being the most dominant instinct for any living organism. Nevertheless, the process is slow and not feasible in all tissues, which led to the emergence of tissue engineering (TE). TE aims at replacing damaged tissues with new ones. To do so, either new tissue is being cultured in vitro and then implanted, or stimulants are implanted into the target site to enhance endogenous tissue formation. Whichever approach is used, a matrix is used to support tissue growth, known as 'scaffold'. In this review, an overall look at scaffolds fabrication is discussed, starting with design considerations and different biomaterials used. Following, highlights of conventional and advanced fabrication techniques are attentively presented. The future of scaffolds in TE is ever promising, with the likes of nanotechnology being investigated for scaffold integration. The constant evolvement of organoids and biofluidics with the eventual inclusion of organ-on-a-chip in TE has shown a promising prospect of what the technology might lead to. Perhaps the closest technology to market is 4D scaffolds following the successful implementation of 4D printing in other fields.

Cartilage Regeneration Characteristics of Human and Goat Auricular Chondrocytes

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

Detachment of bovine corneal endothelial cell sheets by cooling-induced surface hydration of poly[(R)-3-hydroxybutyrate]-based thermoresponsive copolymer coating

A smart surface was prepared by non-covalently coating of a thermoresponsive copolymer via a simple drop-casting method. The smart surface was conducive to cell culture, from which intact cell sheets could be effectively detached by cooling.

Long term expansion profile of mesenchymal stromal cells at protein nanosheet-stabilised bioemulsions for next generation cell culture microcarriers

Tremendous progress in the identification, isolation and expansion of stem cells has allowed their application in regenerative medicine and tissue engineering, and their use as advanced in vitro models. As a result, stem cell manufacturing increasingly requires scale up, parallelisation and automation. However, solid substrates currently used for the culture of adherent cells are poorly adapted for such applications, owing to their difficult processing from cell products, relatively high costs and their typical reliance on difficult to recycle plastics and microplastics. In this work, we show that bioemulsions formed of microdroplets stabilised by protein nanosheets displaying strong interfacial mechanics are well-suited for the scale up of adherent stem cells such as mesenchymal stromal cells (MSCs). We demonstrate that, over multiple passages (up to passage 10), MSCs retain comparable phenotypes when cultured on such bioemulsions, solid microcarriers (Synthemax II) and classic 2D tissue culture polystyrene. Phenotyping (cell proliferation, morphometry, flow cytometry and differentiation assays) of MSCs cultured for multiple passages on these systems indicate that, although stemness is lost at late passages when cultured on these different substrates, stem cell phenotypes remained comparable between different culture conditions, at any given passage. Hence our study validates the use of bioemulsions for the long term expansion of adherent stem cells and paves the way to the design of novel 3D bioreactors based on microdroplet microcarriers.

Characterization and evaluation of ascorbic acid-induced cell sheet formation in human periodontal ligament stem cells: An in vitro study

OBJECTIVES

Periodontal ligament-derived stem cells (PDLSCs) are regarded as a viable option for periodontal regeneration using cell sheet technology. The objective of the present in vitro study was to characterize human PDLSCs based on their phenotypic and biological properties and to evaluate the ascorbic acid (AA or vitamin C)-induced cell sheet by analyzing the molecular markers.

METHODS

PDLSCs were established from premolars, and their morphology, viability, proliferation, phenotypic marker expression, and ability to differentiate into osteocytes and adipocytes were analyzed. PDLSCs were then induced to form cell sheets using 100 μM AA, and gene expression was examined by real-time polymerase chain reaction.

RESULTS

PDLSCs showed fibroblastic morphology with >95% viability. The cells were highly proliferative and positive for surface antigens CD29, CD73, and CD90 but negative for CD34 and CD45. They were capable of differentiating into osteocytes and adipocytes. Induction with 100 μM AA transformed PDLSCs into two-to three-layered cell sheets. There was no significant upregulation in ALP and RUNX2 expression in the AA-induced cell sheet. However, the expression levels of late osteoblast differentiation marker (bone gamma-carboxy glutamate protein); cementogenic markers (cementum attachment protein and CP23), and genes encoding extracellular matrix (ECM) proteins [collagen type 1 alpha 1 and integrin beta 1) were higher in AA-induced cell sheets by PDLSCs.

CONCLUSIONS

The stimulating effect of AA on cell sheet formation by PDLSCs was confirmed by the expression of typical markers involved in osteogenesis/cementogenesis and ECM secretion, which makes this procedure a prospective option for periodontal tissue regeneration applications.

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

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

Efficient and Consistent Orthotopic Osteosarcoma Model by Cell Sheet Transplantation in the Nude Mice for Drug Testing

Osteosarcoma is a big challenge on clinical treatment. The breakthrough associated with osteosarcoma in basic research and translational research depends on the reliable establishment of an animal model, whereby mice are frequently used. However, a traditional animal modeling technique like tumor cell suspension injection causes batch dynamics and large mice consumption. Here, we suggested a novel approach in establishing an orthotropic osteosarcoma model in nude mice rapidly by cell sheet culture and transplantation. Our findings demonstrated that the 143b osteosarcoma cell sheet orthotopically implanted into the nude mice could form a visible mass within 10 days, whereas it took over 15 days for a similar amount of cell suspension injection to form a visible tumor mass. Living animal imaging results showed that a tumor formation rate was 100% in the cell sheet implantation group, while it was 67% in the cell suspension injection group. The formed tumor masses were highly consistent in both growth rate and tumor size. Massive bone destruction and soft tissue mass formation were observed from the micro CT analysis, suggesting the presence of osteosarcoma. The histopathological analysis demonstrated that the orthotropic osteosarcoma model mimicked the tumor bone growth, bone destruction, and the lung metastasis. These findings imply that such a cell sheet technology could be an appropriate approach to rapidly establish a sustainable orthotropic osteosarcoma model for tumor research and reduce mice consumption.