Matrix control of stem cell fate

Photo-Clickable Triazine-Trione Thermosets as Promising 3D Scaffolds for Tissue Engineering Applications

There is an overwhelming demand for new scaffolding materials for tissue engineering (TE) purposes. Polymeric scaffolds have been explored as TE materials; however, their high glass transition state (Tg) limits their applicability. In this study, a novel materials platform for fabricating TE scaffolds is proposed based on solvent-free two-component heterocyclic triazine-trione (TATO) formulations, which cure at room temperature via thiol-ene/yne photochemistry. Three ester-containing thermosets, TATO-1, TATO-2, and TATO-3, are used for the fabrication of TE scaffolds including rigid discs, elastic films, microporous sponges, and 3D printed objects. After 14 days' incubation the materials covered a wide range of properties, from the soft TATO-2 having a compression modulus of 19.3 MPa and a Tg of 30.4 °C to the hard TATO-3 having a compression modulus of 411 MPa and a Tg of 62.5 °C. All materials exhibit micro- and nano-surface morphologies suited for bone tissue engineering, and in vitro studies found them all to be cytocompatible, supporting fast cell proliferation while minimizing cell apoptosis and necrosis. Moreover, bone marrow-derived mesenchymal stem cells on the surface of the materials are successfully differentiated into osteoblasts, adipocytes, and neuronal cells, underlining the broad potential for the biofabrication of TATO materials for TE clinical applications.

The Effect of Crosslinking Density on Nasal Chondrocytes' Redifferentiation

Hydrogels appear to be an attractive class of biomaterial for cartilage tissue engineering due to their high water content, excellent biocompatibility, tunable stiffness, etc. The crosslinking density of the hydrogel can affect their viscoelastic property, and therefore potentially impact the chondrogenic phenotype of re-differentiated chondrocytes in a 3D microenvironment through physical cues. To understand the effect of crosslinking densities on chondrocytes phenotype and cellular interaction with the hydrogel, this study utilized a clinical grade thiolate hyaluronic acid and thiolate gelatin (HA-Gel) hydrogel, crosslinked with poly(ethylene glycol) diacrylate to create various crosslinking densities. The HA-Gel hydrogels were then mixed with human nasal chondrocytes to generate neocartilage in vitro. The influence of the hydrogel crosslinking density and the viscoelastic property on the cell behaviours on the gene and matrix levels were evaluated using biochemistry assays, histology, quantitative polymerase chain reaction (qPCR) and next-generation sequencing (RNA seq). In general, the differences in the storage modulus of the HA-Gel hydrogel are not enough to alter the cartilaginous gene expression of chondrocytes. However, a positively correlated trend of PPAR-γ gene expression to the crosslinking density was measured by qPCR. The RNA-seq results have shown that 178 genes are significantly negatively correlated and 225 genes are positively correlated to the crosslinking density, which is worth investigating in the future studies.

The Role of Biophysical Factors in Organ Development: Insights from Current Organoid Models

Biophysical factors play a fundamental role in human embryonic development. Traditional in vitro models of organogenesis focused on the biochemical environment and did not consider the effects of mechanical forces on developing tissue. While most human tissue has a Young's modulus in the low kilopascal range, the standard cell culture substrate, plasma-treated polystyrene, has a Young's modulus of 3 gigapascals, making it 10,000-100,000 times stiffer than native tissues. Modern in vitro approaches attempt to recapitulate the biophysical niche of native organs and have yielded more clinically relevant models of human tissues. Since Clevers' conception of intestinal organoids in 2009, the field has expanded rapidly, generating stem-cell derived structures, which are transcriptionally similar to fetal tissues, for nearly every organ system in the human body. For this reason, we conjecture that organoids will make their first clinical impact in fetal regenerative medicine as the structures generated ex vivo will better match native fetal tissues. Moreover, autologously sourced transplanted tissues would be able to grow with the developing embryo in a dynamic, fetal environment. As organoid technologies evolve, the resultant tissues will approach the structure and function of adult human organs and may help bridge the gap between preclinical drug candidates and clinically approved therapeutics. In this review, we discuss roles of tissue stiffness, viscoelasticity, and shear forces in organ formation and disease development, suggesting that these physical parameters should be further integrated into organoid models to improve their physiological relevance and therapeutic applicability. It also points to the mechanotransductive Hippo-YAP/TAZ signaling pathway as a key player in the interplay between extracellular matrix stiffness, cellular mechanics, and biochemical pathways. We conclude by highlighting how frontiers in physics can be applied to biology, for example, how quantum entanglement may be applied to better predict spontaneous DNA mutations. In the future, contemporary physical theories may be leveraged to better understand seemingly stochastic events during organogenesis.

The Plasma Membrane and Mechanoregulation in Cells

Cells inhabit a mechanical microenvironment that they continuously sense and adapt to. The plasma membrane (PM), serving as the boundary of the cell, plays a pivotal role in this process of adaptation. In this Review, we begin by examining well-studied processes where mechanoregulation proves significant. Specifically, we highlight examples from the immune system and stem cells, besides discussing processes involving fibroblasts and other cell types. Subsequently, we discuss the common molecular players that facilitate the sensing of the mechanical signal and transform it into a chemical response covering integrins YAP/TAZ and Piezo. We then review how this understanding of molecular elements is leveraged in drug discovery and tissue engineering alongside a discussion of the methodologies used to measure mechanical properties. Focusing on the processes of endocytosis, we discuss how cells may respond to altered membrane mechanics using endo- and exocytosis. Through the process of depleting/adding the membrane area, these could also impact membrane mechanics. We compare pathways from studies illustrating the involvement of endocytosis in mechanoregulation, including clathrin-mediated endocytosis (CME) and the CLIC/GEEC (CG) pathway as central examples. Lastly, we review studies on cell-cell fusion during myogenesis, the mechanical integrity of muscle fibers, and the reported and anticipated roles of various molecular players and processes like endocytosis, thereby emphasizing the significance of mechanoregulation at the PM.

Optical redox imaging to screen synthetic hydrogels for stem cell-derived cardiomyocyte differentiation and maturation

Significance

Heart disease is the leading cause of death in the United States, yet research is limited by the inability to culture primary cardiac cells. Cardiomyocytes (CMs) derived from human induced pluripotent stem cells (iPSCs) are a promising solution for drug screening and disease modeling.

Aim

Induced pluripotent stem cell-derived CM (iPSC-CM) differentiation and maturation studies typically use heterogeneous substrates for growth and destructive verification methods. Reproducible, tunable substrates and touch-free monitoring are needed to identify ideal conditions to produce homogenous, functional CMs.

Approach

We generated synthetic polyethylene glycol-based hydrogels for iPSC-CM differentiation and maturation. Peptide concentrations, combinations, and gel stiffness were tuned independently. Label-free optical redox imaging (ORI) was performed on a widefield microscope in a 96-well screen of gel formulations. We performed live-cell imaging throughout differentiation and early to late maturation to identify key metabolic shifts.

Results

Label-free ORI confirmed the expected metabolic shifts toward oxidative phosphorylation throughout the differentiation and maturation processes of iPSC-CMs on synthetic hydrogels. Furthermore, ORI distinguished high and low differentiation efficiency cell batches in the cardiac progenitor stage.

Conclusions

We established a workflow for medium throughput screening of synthetic hydrogel conditions with the ability to perform repeated live-cell measurements and confirm expected metabolic shifts. These methods have implications for reproducible iPSC-CM generation in biomanufacturing.

Distinct cytoskeletal regulators of mechanical memory in cardiac fibroblasts and cardiomyocytes

Recognizing that cells "feel" and respond to their mechanical environment, recent studies demonstrate that many cells exhibit a phenomenon of "mechanical memory" in which features induced by prior mechanical cues persist after the mechanical stimulus has ceased. While there is a general recognition that different cell types exhibit different responses to changes in extracellular matrix stiffening, the phenomenon of mechanical memory within myocardial cell types has received little attention to date. To probe the dynamics of mechanical memory in cardiac fibroblasts (CFs) and cardiomyocytes derived from human induced pluripotent stem cells (iPSC-CMs), we employed a magnetorheological elastomer (MRE) cell culture substrate with tunable and reversible stiffness spanning the range from normal to diseased myocardium. In CFs, using increased cell area and increases in α-smooth muscle actin as markers of cellular responses to matrix stiffening, we found that induction of mechanical memory required seven days of stiff priming. Both induction and maintenance of persistent CF activation were blocked with the F-actin inhibitor cytochalasin D, while inhibitors of microtubule detyrosination had no impact on CFs. In iPSC-CMs, mechanical memory was invoked after only 24 h of stiff priming. Moreover, mechanical memory induction and maintenance were microtubule-dependent in CMs with no dependence on F-actin. Overall, these results identify the distinct temporal dynamics of mechanical memory in CFs and iPSC-CMs with different cytoskeletal mediators responsible for inducing and maintaining the stiffness-activated phenotype. Due to its flexibility, this model is broadly applicable to future studies interrogating mechanotransduction and mechanical memory in the heart and might inform strategies for attenuating the impact of load-induced pathology and excess myocardial stiffness.

Emerging factors affecting peri-implant bone metabolism

Implant dentistry has evolved to the point that standard implant osseointegration is predictable. This is attributed in part to the advancements in material sciences that have led toward improvements in implant surface technology and characteristics. Nonetheless, there remain several cases where implant therapy fails (specifically at early time points), most commonly attributed to factors affecting bone metabolism. Among these patients, smokers are known to have impaired bone metabolism and thus be subject to higher risks of early implant failure and/or late complications related to the stability of the peri-implant bone and mucosal tissues. Notably, however, emerging data have unveiled other critical factors affecting osseointegration, namely, those related to the metabolism of bone tissues. The aim of this review is to shed light on the effects of implant-related factors, like implant surface or titanium particle release; surgical-related factors, like osseodensification or implanted biomaterials; various drugs, like selective serotonin reuptake inhibitors, proton pump inhibitors, anti-hypertensives, nonsteroidal anti-inflammatory medication, and statins, and host-related factors, like smoking, diet, and metabolic syndrome on bone metabolism, and aseptic peri-implant bone loss. Despite the infectious nature of peri-implant biological complications, these factors must be surveyed for the effective prevention and management of peri-implantitis.

Biomimetic Conductive Hydrogel Scaffolds with Anisotropy and Electrical Stimulation for In Vivo Skeletal Muscle Reconstruction

The nature of the hydrogel scaffold mimicking extracellular matrix plays a crucial role in tissue engineering like skeletal muscle repair. Herein, an anisotropic and conductive hydrogel scaffold is fabricated using gelatin methacryloyl (GelMA) as the matrix hydrogel and silver nanowire (AgNW) as the conductive dopant, through a directional freezing technique for muscle defect repair. The scaffold has an anisotropic structure composed of a directional longitudinal section and a honeycomb cross-section, with high mechanical strength of 10.5 kPa and excellent conductivity of 0.26 S m-1 . These properties are similar to native muscle extracellular matrix (ECM) and allow for cell orientation under the guidance of contact cues and electrical stimulation synergistically. In vitro experiments show that the scaffold's oriented structure combined with electrical stimulation results in enhanced myotube formation, with a length of up to 863 µm and an orientation rate of 81%. Furthermore, the electrically stimulated scaffold displays a promoted muscle reconstruction ability when transplanted into rats with muscle defects, achieving a muscle mass and strength restoration ratio of 95% and 99%, respectively, compared to normal levels. These findings suggest that the scaffold has great potential in muscle repair applications.

Stretching of porous poly (l-lactide-co-ε-caprolactone) membranes regulates the differentiation of mesenchymal stem cells

Background: Among a variety of biomaterials supporting cell growth for therapeutic applications, poly (l-lactide-co-ε-caprolactone) (PLCL) has been considered as one of the most attractive scaffolds for tissue engineering owing to its superior mechanical strength, biocompatibility, and processibility. Although extensive studies have been conducted on the relationship between the microstructure of polymeric materials and their mechanical properties, the use of the fine-tuned morphology and mechanical strength of PLCL membranes in stem cell differentiation has not yet been studied. Methods: PLCL membranes were crystallized in a combination of diverse solvent-nonsolvent mixtures, including methanol (MeOH), isopropanol (IPA), chloroform (CF), and distilled water (DW), with different solvent polarities. A PLCL membrane with high mechanical strength induced by limited pore formation was placed in a custom bioreactor mimicking the reproducible physiological microenvironment of the vascular system to promote the differentiation of mesenchymal stem cells (MSCs) into smooth muscle cells (SMCs). Results: We developed a simple, cost-effective method for fabricating porosity-controlled PLCL membranes based on the crystallization of copolymer chains in a combination of solvents and non-solvents. We confirmed that an increase in the ratio of the non-solvent increased the chain aggregation of PLCL by slow evaporation, leading to improved mechanical properties of the PLCL membrane. Furthermore, we demonstrated that the cyclic stretching of PLCL membranes induced MSC differentiation into SMCs within 10 days of culture. Conclusion: The combination of solvent and non-solvent casting for PLCL solidification can be used to fabricate mechanically durable polymer membranes for use as mechanosensitive scaffolds for stem cell differentiation.

Biomimetic Nanofibrillar Hydrogel with Cell-Adaptable Network for Enhancing Cellular Mechanotransduction, Metabolic Energetics, and Bone Regeneration

The natural extracellular matrix, with its heterogeneous structure, provides a stable and dynamic biophysical framework and biochemical signals to guide cellular behaviors. It is challenging but highly desirable to develop a synthetic matrix that emulates the heterogeneous fibrous structure with macroscopic stability and microscopical dynamics and contains inductive biochemical signals. Herein, we introduce a peptide fiber-reinforced hydrogel in which the stiff ß-sheet fiber functions as a multivalent cross-linker to enhance the hydrogel's macroscopic stability. The dynamic imine cross-link between the peptide fiber and polymer network endows the hydrogel with a microscopically dynamic network. The obtained fibrillar nanocomposite hydrogel, with its cell-adaptable dynamic network, enhances cell-matrix and cell-cell interactions and therefore significantly promotes the mechanotransduction, metabolic energetics, and osteogenesis of encapsulated stem cells. Furthermore, the hydrogel can codeliver a fiber-attached inductive drug to further enhance osteogenesis and bone regeneration. We believe that our work provides valuable guidance for the design of cell-adaptive and bioactive biomaterials for therapeutic applications.

Modulation of stem cell fate in intestinal homeostasis, injury and repair

The mammalian intestinal epithelium constitutes the largest barrier against the external environment and makes flexible responses to various types of stimuli. Epithelial cells are fast-renewed to counteract constant damage and disrupted barrier function to maintain their integrity. The homeostatic repair and regeneration of the intestinal epithelium are governed by the Lgr5⁺ intestinal stem cells (ISCs) located at the base of crypts, which fuel rapid renewal and give rise to the different epithelial cell types. Protracted biological and physicochemical stress may challenge epithelial integrity and the function of ISCs. The field of ISCs is thus of interest for complete mucosal healing, given its relevance to diseases of intestinal injury and inflammation such as inflammatory bowel diseases. Here, we review the current understanding of the signals and mechanisms that control homeostasis and regeneration of the intestinal epithelium. We focus on recent insights into the intrinsic and extrinsic elements involved in the process of intestinal homeostasis, injury, and repair, which fine-tune the balance between self-renewal and cell fate specification in ISCs. Deciphering the regulatory machinery that modulates stem cell fate would aid in the development of novel therapeutics that facilitate mucosal healing and restore epithelial barrier function.

An interplay of matrix stiffness, dimensionality and adhesivity on cellular behavior

Cell-based assays are essentialin vitrotools for understanding basic cell biology, pathophysiology of diseases and mechanism of drug actions most cancer studies have utilized two-dimensional (2D) cell culture methods, which have their shortcomings including lack of cell- extracellular matrix interactions and three-dimensional (3D) geometry, and inaccurate representation of cell polarity. Hence, 3D matrices are being increasingly used to study the effect of 3D niche on cell behavior. Till date, very few systematic studies have been done to show comparison of cell behavior when seeded on the surface and encapsulated inside the matrix. In this study, we fabricated poly(ethylene glycol) (PEG) and gelatin-based matrices using UV mediated photo-polymerization to establish 2D and 3D cell culture methods using breast cancer MDA-MB-231 cells. We have found that the adhesion and spreading of cells on the gel surface is different from that when embedded in gels. The stiffness of poly (ethylene glycol) diacrylate (PEGDA)-gelatin methacryloyl (GelMA) hydrogels with lower concentration of GelMA is lower than that with higher GelMA; further, those with higher overall concentration of polymers (>5%) retain their mechanical integrity and do not degrade even after 7 d. Physical characterization of these matrices demonstrate their optimal pore size, mechanical stiffness and degradation, which are further tunable for tissue engineering, regenerative medicine, drug delivery and cancer studies. Additionally, these semi-synthetic PEGDA-GelMA matrices are transparent in nature, thereby, allowing easy imaging of cells in 3D. The system developed here can be used for short and long term cell culture and can be potentially explored for cell migration and metastasis studies.

Hydrogels from TEMPO-Oxidized Nanofibrillated Cellulose Support In Vitro Cultivation of Encapsulated Human Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are the most prominent type of adult stem cells for clinical applications. Three-dimensional (3D) cultivation of MSCs in biomimetic hydrogels provides a more physiologically relevant cultivation microenvironment for in vitro testing and modeling, thus overcoming the limitations of traditional planar cultivation methods. Cellulose nanofibers are an excellent candidate biomaterial for synthesis of hydrogels for this application, due to their biocompatibility, tunable properties, availability, and low cost. Herein, we demonstrate the capacity of hydrogels prepared from 2,2,6,6-tetramethylpiperidine-1-oxyl -oxidized and subsequently individualized cellulose-nanofibrils to support physiologically relevant 3D in vitro cultivation of human MSCs at low solid contents (0.2-0.5 wt %). Our results show that MSCs can spread, proliferate, and migrate inside the cellulose hydrogels, while the metabolic activity and proliferative capacity of the cells as well as their morphological characteristics benefit more in the lower bulk cellulose concentration hydrogels.

Hydrogel-based microenvironment engineering of haematopoietic stem cells

Haematopoietic Stem cells (HSCs) have the potential for self-renewal and multilineage differentiation, and their behaviours are finely tuned by the microenvironment. HSC transplantation (HSCT) is widely used in the treatment of haematologic malignancies while limited by the quantity of available HSCs. With the development of tissue engineering, hydrogels have been deployed to mimic the HSC microenvironment in vitro. Engineered hydrogels influence HSC behaviour by regulating mechanical strength, extracellular matrix microstructure, cellular ligands and cytokines, cell-cell interaction, and oxygen concentration, which ultimately facilitate the acquisition of sufficient HSCs. Here, we review recent advances in the application of hydrogel-based microenvironment engineering of HSCs, and provide future perspectives on challenges in basic research and clinical practice.

Biodegradable and Non-Biodegradable Biomaterials and Their Effect on Cell Differentiation

Biomaterials for tissue scaffolds are key components in modern tissue engineering and regenerative medicine. Targeted reconstructive therapies require a proper choice of biomaterial and an adequate choice of cells to be seeded on it. The introduction of stem cells, and the transdifferentiation procedures, into regenerative medicine opened a new era and created new challenges for modern biomaterials. They must not only fulfill the mechanical functions of a scaffold for implanted cells and represent the expected mechanical strength of the artificial tissue, but furthermore, they should also assure their survival and, if possible, affect their desired way of differentiation. This paper aims to review how modern biomaterials, including synthetic (i.e., polylactic acid, polyurethane, polyvinyl alcohol, polyethylene terephthalate, ceramics) and natural (i.e., silk fibroin, decellularized scaffolds), both non-biodegradable and biodegradable, could influence (tissue) stem cells fate, regulate and direct their differentiation into desired target somatic cells.

Mechanotransduction through adhesion molecules: Emerging roles in regulating the stem cell niche

Stem cells have been shown to play an important role in regenerative medicine due to their proliferative and differentiation potential. The challenge, however, lies in regulating and controlling their potential for this purpose. Stem cells are regulated by growth factors as well as an array of biochemical and mechanical signals. While the role of biochemical signals and growth factors in regulating stem cell homeostasis is well explored, the role of mechanical signals has only just started to be investigated. Stem cells interact with their niche or to other stem cells via adhesion molecules that eventually transduce mechanical cues to maintain their homeostatic function. Here, we present a comprehensive review on our current understanding of the influence of the forces perceived by cell adhesion molecules on the regulation of stem cells. Additionally, we provide insights on how this deeper understanding of mechanobiology of stem cells has translated toward therapeutics.

Engineering the viscoelasticity of gelatin methacryloyl (GelMA) hydrogels via small “dynamic bridges” to regulate BMSC behaviors for osteochondral regeneration

The dynamic extracellular matrix (ECM) constantly affects the behaviors of cells. To mimic the dynamics of ECM with controllable stiffness and energy dissipation, this study proposes a strategy in which a small molecule, 3,4-dihydroxybenzaldehyde (DB), was used as fast "dynamic bridges'' to construct viscoelastic gelatin methacryloyl (GelMA)-based hydrogels. The storage modulus and loss modulus of hydrogels were independently adjusted by the covalent crosslinking density and by the number of dynamic bonds. The hydrogels exhibited self-healing property, injectability, excellent adhesion and mechanical properties. Moreover, the in vitro results revealed that the viscous dissipation of hydrogels favored the spreading, proliferation, osteogenesis and chondrogenesis of bone marrow mesenchymal stem cells (BMSCs), but suppressed their adipogenesis. RNA-sequencing and immunofluorescence suggested that the viscous dissipation of hydrogels activated Yes-associated protein (YAP) by stabilizing integrin β1, and further promoted nuclear translocation of smad2/3 and β-catenin to enhance chondrogenesis and osteogenesis. As a result, the viscoelastic GelMA hydrogels with highest loss modulus showed best effect in cartilage and subchondral bone repair. Taken together, findings from this study reveal an effective strategy to fabricate viscoelastic hydrogels for modulating the interactions between cells and dynamic ECM to promote tissue regeneration.

Constructing ECM-like Structure on the Plasma Membrane via Peptide Assembly to Regulate the Cellular Response

This feature article introduces the design of self-assembling peptides that serve as the basic building blocks for the construction of extracellular matrix (ECM)-like structure in the vicinity of the plasma membrane. By covalently conjugating a bioactive motif, such as membrane protein binding ligand or enzymatic responsive building block, with a self-assembling motif, especially the aromatic peptide, a self-assembling peptide that retains bioactivity is obtained. Instructed by the target membrane protein or enzyme, the bioactive peptides self-assemble into ECM-like structure exerting various stimuli to regulate the cellular response via intracellular signaling, especially mechanotransduction. By briefly summarizing the properties and applications (e.g., wound healing, controlling cell motility and cell fate) of these peptides, we intend to illustrate the basic requirements and promises of the peptide assembly as a true bottom-up approach in the construction of artificial ECM.

Electrospun Carbon Nanotube-Based Scaffolds Exhibit High Conductivity and Cytocompatibility for Tissue Engineering Applications

Carbon nanotubes (CNTs) are known for their excellent conductive properties. Here, we present two novel methods, "sandwich" (sCNT) and dual deposition (DD CNT), for incorporating CNTs into electrospun polycaprolactone (PCL) and gelatin scaffolds to increase their conductance. Based on CNT percentage, the DD CNT scaffolds contain significantly higher quantities of CNTs than the sCNT scaffolds. The inclusion of CNTs increased the electrical conductance of scaffolds from 0.0 ± 0.00 kS (non-CNT) to 0.54 ± 0.10 kS (sCNT) and 5.22 ± 0.49 kS (DD CNT) when measured parallel to CNT arrays and to 0.25 ± 0.003 kS (sCNT) and 2.85 ± 1.12 (DD CNT) when measured orthogonally to CNT arrays. The inclusion of CNTs increased fiber diameter and pore size, promoting cellular migration into the scaffolds. CNT inclusion also decreased the degradation rate and increased hydrophobicity of scaffolds. Additionally, CNT inclusion increased Young's modulus and failure load of scaffolds, increasing their mechanical robustness. Murine fibroblasts were maintained on the scaffolds for 30 days, demonstrating high cytocompatibility. The increased conductivity and high cytocompatibility of the CNT-incorporated scaffolds make them appropriate candidates for future use in cardiac and neural tissue engineering.

Highlights on Advancing Frontiers in Tissue Engineering

The field of tissue engineering continues to advance, sometimes in exponential leaps forward, but also sometimes at a rate that does not fulfill the promise that the field imagined a few decades ago. This review is in part a catalog of success in an effort to inform the process of innovation. Tissue engineering has recruited new technologies and developed new methods for engineering tissue constructs that can be used to mitigate or model disease states for study. Key to this antecedent statement is that the scientific effort must be anchored in the needs of a disease state and be working toward a functional product in regenerative medicine. It is this focus on the wildly important ideas coupled with partnered research efforts within both academia and industry that have shown most translational potential. The field continues to thrive and among the most important recent developments are the use of three-dimensional bioprinting, organ-on-a-chip, and induced pluripotent stem cell technologies that warrant special attention. Developments in the aforementioned areas as well as future directions are highlighted in this article. Although several early efforts have not come to fruition, there are good examples of commercial profitability that merit continued investment in tissue engineering. Impact statement Tissue engineering led to the development of new methods for regenerative medicine and disease models. Among the most important recent developments in tissue engineering are the use of three-dimensional bioprinting, organ-on-a-chip, and induced pluripotent stem cell technologies. These technologies and an understanding of them will have impact on the success of tissue engineering and its translation to regenerative medicine. Continued investment in tissue engineering will yield products and therapeutics, with both commercial importance and simultaneous disease mitigation.

A Unified Protocol to Streamline Molecular and Cellular Analysis for Three-Dimensional Cell Cultures

Three-dimensional (3D) cell cultures based on reconstituted basement membrane materials recapitulate features of extracellular matrix (ECM) and tissue stiffness in vivo and provide a physiologically relevant platform to study complex cellular processes, such as stem cell differentiation and tissue morphogenesis, that are otherwise difficult in animal models. The form and composition of 3D matrices in culture can interfere with and pose challenges for different experimental setups and assays, which necessitate alterations to facilitate analysis. Here, we provide a unified protocol for 3D cell cultures with modular workflows that streamline procedures for compatibility with common molecular and cellular assays such as live-cell imaging, immunofluorescence , qPCR, RNAseq, western blotting, and quantitative mass spectrometry.

The Potential Role of Exercise Training and Mechanical Loading on Bone-Associated Skeletal Nerves

The spatial distribution, innervation, and functional role of the bone-associated skeletal nerves have been previously reported in detail. However, studies examining exercise-induced associations between skeletal nerves and bone metabolism are limited. This review introduces a potential relationship between exercise and the skeletal nerves and discusses how it can contribute to exercise-induced bone anabolism. First, the background and current understanding of nerve fiber types and their functions in the skeleton are provided. Next, the influence of exercise and mechanical loading on the skeletal nervous system is elaborated. Effective synthesis of recent studies could serve as an established baseline for the novel discovery of the effects of exercise on skeletal nerve density and bone anabolic activity in the future. Therefore, this review overviews the existing evidence for the neural control of bone metabolism and the potential positive effects of exercise on the peripheral skeletal nervous system. The influence of exercise training models on the relationships of sensory nerve signals with osteoblast-mediated bone formation and the increased bone volume provides the first insight on the potential importance of exercise training in stimulating positive adaptations in the skeletal nerve-bone interaction and its downstream effect on bone metabolism, thereby highlighting its therapeutic potential in a variety of clinical populations.

Diamond Concept as Principle for the Development of Spinal Cord Scaffold: A Literature Review

INTRODUCTION: Spinal cord injury (SCI) has been bringing detrimental impacts on the affected individuals. However, not only that, it also brings a tremendous effect on the socioeconomic and health-care system. Treatment regimen and strategy for SCI patient have been under further research. DISCUSSION: The main obstacles of regeneration on neuronal structure are the neuroinflammatory process and poor debris clearance, causing a longer healing process and an extensive inflammation process due to this particular inflammatory process. To resolve all of the mentioned significant issues in SCIs neuronal regeneration, a comprehensive model is necessary to analyze each step of progressive condition in SCI. In this review, we would like to redefine a comprehensive concept of the “Diamond Concept” from previously used in fracture management to SCI management, which consists of cellular platform, cellular inductivity, cellular conductivity, and material integrity. The scaffolding treatment strategy for SCI has been widely proposed due to its flexibility. It enables the physician to combine another treatment method such as neuroprotective or neuroregenerative or both in one intervention. CONCLUSION: Diamond concept perspective in the implementation of scaffolding could be advantageous to increase the outcome of SCI treatment.

Regulation of stem cell fate using nanostructure-mediated physical signals

One of the major issues in tissue engineering is regulation of stem cell differentiation toward specific lineages. Unlike biological and chemical signals, physical signals with adjustable properties can be applied to stem cells in a timely and localized manner, thus making them a hot topic for research in the fields of biomaterials, tissue engineering, and cell biology. According to the signals sensed by cells, physical signals used for regulating stem cell fate can be classified into six categories: mechanical, light, thermal, electrical, acoustic, and magnetic. In most cases, external macroscopic physical fields cannot be used to modulate stem cell fate, as only the localized physical signals accepted by the surface receptors can regulate stem cell differentiation via nanoscale fibrin polysaccharide fibers. However, surface receptors related to certain kinds of physical signals are still unknown. Recently, significant progress has been made in the development of functional materials for energy conversion. Consequently, localized physical fields can be produced by absorbing energy from an external physical field and subsequently releasing another type of localized energy through functional nanostructures. Based on the above concepts, we propose a methodology that can be utilized for stem cell engineering and for the regulation of stem cell fate via nanostructure-mediated physical signals. In this review, the combined effect of various approaches and mechanisms of physical signals provides a perspective on stem cell fate promotion by nanostructure-mediated physical signals. We expect that this review will aid the development of remote-controlled and wireless platforms to physically guide stem cell differentiation both in vitro and in vivo, using optimized stimulation parameters and mechanistic investigations while driving the progress of research in the fields of materials science, cell biology, and clinical research.

Molecular Mechanisms and Cellular Contribution from Lung Fibrosis to Lung Cancer Development

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, fibrosing interstitial lung disease (ILD) of unknown aetiology, with a median survival of 2-4 years from the time of diagnosis. Although IPF has unknown aetiology by definition, there have been identified several risks factors increasing the probability of the onset and progression of the disease in IPF patients such as cigarette smoking and environmental risk factors associated with domestic and occupational exposure. Among them, cigarette smoking together with concomitant emphysema might predispose IPF patients to lung cancer (LC), mostly to non-small cell lung cancer (NSCLC), increasing the risk of lung cancer development. To this purpose, IPF and LC share several cellular and molecular processes driving the progression of both pathologies such as fibroblast transition proliferation and activation, endoplasmic reticulum stress, oxidative stress, and many genetic and epigenetic markers that predispose IPF patients to LC development. Nintedanib, a tyrosine-kinase inhibitor, was firstly developed as an anticancer drug and then recognized as an anti-fibrotic agent based on the common target molecular pathway. In this review our aim is to describe the updated studies on common cellular and molecular mechanisms between IPF and lung cancer, knowledge of which might help to find novel therapeutic targets for this disease combination.

Osteoblast-derived extracellular matrix coated PLLA/silk fibroin composite nanofibers promote osteogenic differentiation of bone mesenchymal stem cells

Poly-L-lactic acid (PLLA) is one of the most commonly used synthetic materials for regenerative medicine, and silk fibroin (SF) is a natural protein with excellent biocompatibility. Combination of PLLA and SF in a proper proportion by electrospinning may generate composite nanofibers that could meet the requirements of scaffolding in bone tissue engineering. The application of PLLA/SF nanofibrous scaffold for osteogenesis is well established in vitro and in vivo. However, PLLA/SF nanofibrous scaffold does not have an ideal ability to promote cell adhesion, proliferation, and differentiation. Extracellular matrix (ECM) plays a critical role in modulating cellular behavior. However, the role of combination of natural ECM with nanofibrous scaffold in regulating osteogenic differentiation is unclear. In this study, we aimed to develop a novel composite PLLA/SF nanofibrous scaffold coated with osteoblast-derived extracellular matrix (O-ECM/PLLA/SF) and analyze the effects of the modified scaffold on osteogenic differentiation of BMSCs. The surface structural features and compositions of the O-ECM/PLLA/SF scaffold were characterized by SEM and immunofluorescence staining. The capacities of the O-ECM/PLLA/SF scaffold to induce osteogenic differentiation of BMSCs were investigated by alkaline phosphatase (ALP) and alizarin red staining (ARS). The results showed BMSCs cultured on O-ECM/PLLA/SF scaffold significantly increased osteogenic differentiation compared with cells cultured individually on a scaffold or O-ECM. Collectively, these findings indicate that O-ECM-coated nanofibrous scaffold can be a promising strategy for osteogenic differentiation of BMSCs, opening a new possibility of utilizing composite scaffolds for bone tissue engineering.

Effect of Polymeric Matrix Stiffness on Osteogenic Differentiation of Mesenchymal Stem/Progenitor Cells: Concise Review

Mesenchymal stem/progenitor cells (MSCs) have a multi-differentiation potential into specialized cell types, with remarkable regenerative and therapeutic results. Several factors could trigger the differentiation of MSCs into specific lineages, among them the biophysical and chemical characteristics of the extracellular matrix (ECM), including its stiffness, composition, topography, and mechanical properties. MSCs can sense and assess the stiffness of extracellular substrates through the process of mechanotransduction. Through this process, the extracellular matrix can govern and direct MSCs' lineage commitment through complex intracellular pathways. Hence, various biomimetic natural and synthetic polymeric matrices of tunable stiffness were developed and further investigated to mimic the MSCs' native tissues. Customizing scaffold materials to mimic cells' natural environment is of utmost importance during the process of tissue engineering. This review aims to highlight the regulatory role of matrix stiffness in directing the osteogenic differentiation of MSCs, addressing how MSCs sense and respond to their ECM, in addition to listing different polymeric biomaterials and methods used to alter their stiffness to dictate MSCs' differentiation towards the osteogenic lineage.

Critical adhesion areas of cells on micro-nanopatterns

Cell adhesion to extracellular matrices (ECM) is critical to physiological and pathological processes as well as biomedical and biotechnological applications. It has been known that a cell can adhere on an adhesive microisland only over a critical size. But no publication has concerned critical adhesion areas of cells on microislands with nanoarray decoration. Herein, we fabricated a series of micro-nanopatterns with different microisland sizes and arginine-glycine-aspartate (RGD) nanospacings on a nonfouling poly(ethylene glycol) background. Besides reproducing that nanospacing of RGD, a ligand of its receptor integrin (a membrane protein), significantly influences specific cell adhesion on bioactive nanoarrays, we confirmed that the concept of critical adhesion area originally suggested in studies of cells on micropatterns was justified also on the micro-nanopatterns, yet the latter exhibited more characteristic behaviors of cell adhesion. We found increased critical adhesion areas of human mesenchymal stem cells (hMSCs) on nanoarrayed microislands with increased RGD nanospacings. However, the numbers of nanodots with respect to the critical adhesion areas were not a constant. A unified interpretation was then put forward after combining nonspecific background adhesion and specific cell adhesion. We further carried out the asymptotic analysis of a series of micro-nanopatterned surfaces to obtain the effective RGD nanospacing on unpatterned free surfaces with densely grafted RGD, which could be estimated nonzero but has never been revealed previously without the assistance of the micro-nanopatterning techniques and the corresponding analysis.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary materials and methods (details of fabrication of micro-nanopatterns), and supplementary results (selective adhesion or localization of hMSCs on nanoarrayed microislands with non-fouling background, calculation of critical number of integrin-ligand binding N*, etc.) are available in the online version of this article at 10.1007/s12274-021-3711-6.

The Mechanical Interplay Between Differentiating Mesenchymal Stem Cells and Gelatin-Based Substrates Measured by Atomic Force Microscopy

Traditional methods to assess hMSCs differentiation typically require long-term culture until cells show marked expression of histological markers such as lipid accumulation inside the cytoplasm or mineral deposition onto the surrounding matrix. In parallel, stem cell differentiation has been shown to involve the reorganization of the cell’s cytoskeleton shortly after differentiation induced by soluble factors. Given the cytoskeleton’s role in determining the mechanical properties of adherent cells, the mechanical characterization of stem cells could thus be a potential tool to assess cellular commitment at much earlier time points. In this study, we measured the mechanical properties of hMSCs cultured on soft gelatin-based hydrogels at multiple time points after differentiation induction toward adipogenic or osteogenic lineages. Our results show that the mechanical properties of cells (stiffness and viscosity) and the organization of the actin cytoskeleton are highly correlated with lineage commitment. Most importantly, we also found that the mechanical properties and the topography of the gelatin substrate in the vicinity of the cells are also altered as differentiation progresses toward the osteogenic lineage, but not on the adipogenic case. Together, these results confirm the biophysical changes associated with stem cell differentiation and suggest a mechanical interplay between the differentiating stem cells and their surrounding extracellular matrix.

Enhanced mechanosensing of cells in synthetic 3D matrix with controlled biophysical dynamics

3D culture of cells in designer biomaterial matrices provides a biomimetic cellular microenvironment and can yield critical insights into cellular behaviours not available from conventional 2D cultures. Hydrogels with dynamic properties, achieved by incorporating either degradable structural components or reversible dynamic crosslinks, enable efficient cell adaptation of the matrix and support associated cellular functions. Herein we demonstrate that given similar equilibrium binding constants, hydrogels containing dynamic crosslinks with a large dissociation rate constant enable cell force-induced network reorganization, which results in rapid stellate spreading, assembly, mechanosensing, and differentiation of encapsulated stem cells when compared to similar hydrogels containing dynamic crosslinks with a low dissociation rate constant. Furthermore, the static and precise conjugation of cell adhesive ligands to the hydrogel subnetwork connected by such fast-dissociating crosslinks is also required for ultra-rapid stellate spreading (within 18 h post-encapsulation) and enhanced mechanosensing of stem cells in 3D. This work reveals the correlation between microscopic cell behaviours and the molecular level binding kinetics in hydrogel networks. Our findings provide valuable guidance to the design and evaluation of supramolecular biomaterials with cell-adaptable properties for studying cells in 3D cultures.

3D culture systems can provide critical insights into cellular behaviour. Here, the authors study the binding timescale of dynamic crosslinks and the conjugation stability of cell-adhesive ligands in cell–hydrogel network interactions to evaluate the impact on stem cell behaviour, mechanosensing and differentiation.

Microscopic local stiffening in a supramolecular hydrogel network expedites stem cell mechanosensing in 3D and bone regeneration

Dynamic hydrogels cross-linked by weak and reversible physical interactions enhance the 3-dimensional (3D) spreading and mechanosensing abilities of encapsulated cells in a matrix. However, the highly dynamic nature of these physical cross-links also results in low mechanical stiffness in the hydrogel network and high tether compliance of the cell adhesion motifs attached to the network. The resulting low force feedback of the soft hydrogel network impedes the efficient activation of mechanotransduction signalling in the encapsulated cells. Herein, we demonstrate that the chemical incorporation of acryloyl nanoparticle-based cross-linkers creates regionally stiff network structures in the dynamic supramolecular hydrogels without compromising the dynamic properties of the cell-adaptable inter-nanoparticle hydrogel network. The obtained dynamic hydrogels with a heterogeneous hydrogel network topology expedite the development of adhesion structures, 3D spreading, and mechanosensing of the encapsulated stem cells, as evidenced by the upregulated expression of key biomarkers such as vinculin, FAK, and YAP. This enhanced spreading and mechanotransduction promotes the osteogenic differentiation of the encapsulated stem cells. In contrast, doping with physically entrapped nanoparticles or molecular cross-linkers (PEGDA) cannot locally reinforce the dynamic hydrogel network and therefore fails to facilitate cell mechanosensing or differentiation in the 3D hydrogels. We further show that the dynamic hydrogels with a locally stiffened network promote the in situ regeneration of bone defects in an animal model. Our findings provide valuable insights into the design of the supramolecular dynamic hydrogels with biomimetic hierarchical biomechanical structures as the optimized carrier material for stem cell-based therapies.

TMT-based quantitative proteome profiles reveal the memory function of a whole heart decellularized matrix for neural stem cell trans-differentiation into the cardiac lineage

Whole organ or tissue decellularized matrices are a promising scaffold for tissue engineering because they maintain the specific memory of the original organ or tissue. A whole organ or tissue decellularized matrix contains extracellular matrix (ECM) components, and exhibits ultrastructural and mechanical properties, which could significantly regulate the fate of stem cells. To better understand the memory function of whole organ decellularized matrices, we constructed a heart decellularized matrix and seeded cross-embryonic layer stem cells - neural stem cells (NSCs) to repopulate the matrix, engineering cardiac tissue, in which a large number of NSCs differentiated into the neural lineage, but besides that, NSCs showed an obvious tendency of trans-differentiating into cardiac lineage cells. The results demonstrated that the whole heart decellularized microenvironment possesses memory function. To reveal the underlying mechanism, TMT-based quantitative proteomics analysis was used to identify the differently expressed proteins in the whole heart decellularized matrix compared with a brain decellularized matrix. 937 of the proteins changed over 1.5 fold, with 573 of the proteins downregulated and 374 of the proteins upregulated, among which integrin ligands in the ECM serve as key signals in regulating NSC fate. The findings here provide a novel insight into the memory function of tissue-specific microenvironments and pave the way for the therapeutic application of personalized tissues.

Evaluation of the effects of differences in silicone hardness on rat model of lumbar spinal stenosis

Lumbar spinal stenosis (LSS), one of the most commonly reported spinal disorders, can cause loss of sensation and dyskinesia. In currently used animal models of LSS, the spinal cord is covered entirely with a silicone sheet, or block-shaped silicone is inserted directly into the spinal canal after laminectomy. However, the effects of differences between these implant materials have not been studied. We assessed the degree of damage and locomotor function of an LSS model in Sprague-Dawley rats using silicone blocks of varying hardness (70, 80, and 90 kPa) implanted at the L4 level. In sham rats, the spinal cord remained intact; in LSS rats, the spinal cord was increasingly compressed by the mechanical pressure of the silicone blocks as hardness increased. Inflammatory cells were not evident in sham rats, but numerous inflammatory cells were observed around the implanted silicone block in LSS rats. CD68+ cell quantification revealed increases in the inflammatory response in a hardness-dependent manner in LSS rats. Compared with those in sham rats, proinflammatory cytokine levels were significantly elevated in a hardness-dependent manner, and locomotor function was significantly decreased, in LSS rats. Overall, this study showed that hardness could be used as an index to control the severity of nerve injury induced by silicone implants.

Human Periodontal Ligament Stem Cells Transplanted with Nanohydroxyapatite/Chitosan/Gelatin 3D Porous Scaffolds Promote Jaw Bone Regeneration in Swine

Dental-tissue-derived stem cells have been used for tissue engineering owing to their ease of isolation and efficacy in in vitro and in vivo proliferation and differentiation. Nanohydroxyapatite/chitosan/gelatin (nHA/CG) three-dimensional porous scaffolds are promising for bone tissue engineering, especially jaw bone regeneration, because of their structural and functional similarity to natural bone. In our previous study, the efficiency of scaffolds with stem cell complexes in osteogenesis was confirmed in vivo in immunocompromised mice. However, studies on the bone regeneration efficiency of stem cell-seeded nHA/CG scaffolds using large animal jaw bone defect models have not been conducted. This study evaluated the bone regeneration potential of the nHA/CG scaffolds with transplanted human periodontal ligament stem cells (hPDLSCs) in critical-sized jaw bone defects in minipigs. The hPDLSCs isolated from periodontal ligaments of discarded teeth (postorthodontic purposes) were seeded onto the nHA/CG scaffolds. The scaffold was successfully synthesized according to our previous studies. Forty-eight critical-sized jaw bone defects were created in 12 minipigs. The defects were randomly assigned to one of three groups [scaffolds with seeded hPDLSCs (hPDLSCs/nHA/CG), only scaffold (nHA/CG), and a negative control group, ie, no cells and scaffolds implanted into defects] to investigate jaw bone regeneration. The bone regeneration capacities of the three groups were assessed for up to 12 weeks. The results showed that the hPDLSCs adhered well to the nHA/CG scaffold in vitro, and the cell-nHA/CG composites significantly increased new bone formation and generated large bones with normal architectures and vascularization in vivo compared to the nHA/CG and control groups. Immunohistochemistry staining showed that runt-related transcription factor 2 (Runx2) was highly expressed in the bone marrow formed in the hPDLSCs/nHA/CG group. This study provides strong evidence for future clinical applications of the nHA/CG scaffolds transplanted with hPDLSCs to regenerate the bone in large jaw bone defects.

Biomaterial Properties Modulating Bone Regeneration

Biomaterial scaffolds have been gaining momentum in the past several decades for their potential applications in the area of tissue engineering. They function as three-dimensional porous constructs to temporarily support the attachment of cells, subsequently influencing cell behaviors such as proliferation and differentiation to repair or regenerate defective tissues. In addition, scaffolds can also serve as delivery vehicles to achieve sustained release of encapsulated growth factors or therapeutic agents to further modulate the regeneration process. Given the limitations of current bone grafts used clinically in bone repair, alternatives such as biomaterial scaffolds have emerged as potential bone graft substitutes. This review summarizes how physicochemical properties of biomaterial scaffolds can influence cell behavior and its downstream effect, particularly in its application to bone regeneration.

Composite engineered biomaterial adaptable for repair and regeneration of wounds

Ongoing investigations in wound repair bring new opportunities and challenges for creating novel composite engineered biomaterials. Efforts have been directed toward using different combinations of biomaterials with the goal of providing an ideal biomimetic substitute for native tissue. A universal formula using collagen, fibroin and a synthetic polymer is proposed. By modifying the ratio of the building blocks, the composite material can be fabricated to match the mechanical property of different types of tissues and be further tuned to carry desirable physical and biological function. The results should provide composite engineered materials comparable to native tissue in order to repair and regenerate a variety of wounds and tissues.

Supersensitive Layer-by-Layer 3D Cardiac Tissues Fabricated on a Collagen Culture Vessel Using Human-Induced Pluripotent Stem Cells

Background: The fabrication of artificial cardiac tissue is an active area of research due to the shortage of donors for heart transplantation and for drug development. In our previous study, we fabricated vascularized three-dimensional (3D) cardiac tissue by layer-by-layer (LbL) and cell accumulation technique. However, it was not able to develop sufficient function because it was cultured on a hard plastic substrate. Experiment: Herein, we report the fabrication of high-performance 3D cardiac tissue by LbL and cell accumulation technique using a collagen culture vessel. Results: By using a collagen culture vessel, 3D cardiac tissue could be fabricated on a collagen culture vessel and this tissue showed high functionality due to improved interaction with the vessel. In the case of the plastic culture insert, 3D cardiac tissue was found to be peeled off, but this did not occur on the collagen culture vessel. In addition, the 3D cardiac tissue fabricated on a collagen culture vessel showed contraction that was 20 times larger than the tissue fabricated on a plastic culture insert. As a result of evaluation of cardiotoxicity using E-4031, the sensitivity of arrhythmia detection was increased by using collagen culture vessel. Conclusions: These results are expected to contribute to transplantation and drug discovery research as a 3D cardiac tissue model with a function similar to that of the living heart.

Early Committed Clockwise Cell Chirality Upregulates Adipogenic Differentiation of Mesenchymal Stem Cells

Cell chirality is observed with diverse forms and coordinates various left-right (LR) asymmetry in tissue morphogenesis. To give rise to such diversity, cell chirality may be coupled with cell differentiation. Here, using micropatterned human mesenchymal stem cells (hMSCs), an early committed clockwise (CW) cell chirality that can itself upregulate the adipogenic differentiation is reported. hMSC chirality enables a positively tilted chiral orientation on micropatterned stripes. When cultured as single cells on circular micropatterns, an anticlockwise (ACW)-biased nucleus rotation and swirling pattern of actin filament are observed. Interestingly, with adipogenic induction for 3-6 days, such chirality is reversed to negative chiral orientation and CW-biased rotation, which is earlier than the maturation of other differentiation markers, and consistently expressed in terminally differentiated adipocytes. Using latrunculin A (LatA), cytochalasin D (CD), and nocodazole (Noco) that forces a CW-biased actin filament and nucleus rotation resembling the early differentiated chirality upon adipogenic induction, an upregulation of adipogenic differentiation is found. The result demonstrates that the early differentiated chirality may serve as a mechanical precursor to engage the lineage commitment, suggesting a feedback mechanism of chiral actin in regulating cell differentiation and LR morphogenesis.

Tethering, evagination, and vesiculation via cell-cell interactions in microvascular flow

Vesiculation is a ubiquitous process undergone by most cell types and serves a variety of vital cell functions; vesiculation from erythrocytes, in particular, is a well-known example and constitutes a self-protection mechanism against premature clearance, inter alia. Herein, we explore a paradigm that red blood cell derived vesicles may form within the microvascular, in intense shear flow, where cells become adhered to either other cells or the extracellular matrix, by forming tethers or an evagination. Adherence may be enhanced, or caused, by diseased states or chemical anomalies as are discussed herein. The mechanisms for such processes are detailed via numerical simulations that are patterned directly from video-recorded cell microflow within the splenic venous sinus (MacDonald et al. 1987), as included, e.g., as Supplementary Material. The mechanisms uncovered highlight the necessity of accounting for remodeling of the erythrocyte's membrane skeleton and, specifically, for the time scales associated with that process that is an integral part of cell deformation. In this way, the analysis provides pointed, and vital, insights into the notion of what the, often used phrase, cell deformability actually entails in a more holistic manner. The analysis also details what data are required to make further quantitative descriptions possible and suggests experimental pathways for acquiring such.

Molecular and Biomechanical Clues From Cardiac Tissue Decellularized Extracellular Matrix Drive Stromal Cell Plasticity

Decellularized-organ-derived extracellular matrix (dECM) has been used for many years in tissue engineering and regenerative medicine. The manufacturing of hydrogels from dECM allows to make use of the pro-regenerative properties of the ECM and, simultaneously, to shape the material in any necessary way. The objective of the present project was to investigate differences between cardiovascular tissues (left ventricle, mitral valve, and aorta) with respect to generating dECM hydrogels and their interaction with cells in 2D and 3D. The left ventricle, mitral valve, and aorta of porcine hearts were decellularized using a series of detergent treatments (SDS, Triton-X 100 and deoxycholate). Mass spectrometry-based proteomics yielded the ECM proteins composition of the dECM. The dECM was digested with pepsin and resuspended in PBS (pH 7.4). Upon warming to 37°C, the suspension turns into a gel. Hydrogel stiffness was determined for samples with a dECM concentration of 20 mg/mL. Adipose tissue-derived stromal cells (ASC) and a combination of ASC with human pulmonary microvascular endothelial cells (HPMVEC) were cultured, respectively, on and in hydrogels to analyze cellular plasticity in 2D and vascular network formation in 3D. Differentiation of ASC was induced with 10 ng/mL of TGF-β1 and SM22α used as differentiation marker. 3D vascular network formation was evaluated with confocal microscopy after immunofluorescent staining of PECAM-1. In dECM, the most abundant protein was collagen VI for the left ventricle and mitral valve and elastin for the aorta. The stiffness of the hydrogel derived from the aorta (6,998 ± 895 Pa) was significantly higher than those derived from the left ventricle (3,384 ± 698 Pa) and the mitral valve (3,233 ± 323 Pa) (One-way ANOVA, p = 0.0008). Aorta-derived dECM hydrogel drove non-induced (without TGF-β1) differentiation, while hydrogels derived from the left ventricle and mitral valve inhibited TGF-β1-induced differentiation. All hydrogels supported vascular network formation within 7 days of culture, but ventricular dECM hydrogel demonstrated more robust vascular networks, with thicker and longer vascular structures. All the three main cardiovascular tissues, myocardium, valves, and large arteries, could be used to fabricate hydrogels from dECM, and these showed an origin-dependent influence on ASC differentiation and vascular network formation.

Single-cell RNA-seq highlights heterogeneity in human primary Wharton's jelly mesenchymal stem/stromal cells cultured in vitro

BACKGROUND

Mesenchymal stem/stromal cells (MSCs) are multipotent cells with a promising application potential in regenerative medicine and immunomodulation. However, MSCs cultured in vitro exhibit functional heterogeneity. The underlying molecular mechanisms that define MSC heterogeneity remain unclear.

METHODS

We investigated the gene expression profile via single-cell RNA sequencing (scRNA-seq) of human primary Wharton's jelly-derived MSCs (WJMSCs) cultured in vitro from three donors. We also isolated CD142+ and CD142- WJMSCs based on scRNA-seq data and compared their proliferation capacity and "wound healing" potential in vitro. Meanwhile, we analyzed publicly available adipose-derived MSC (ADMSCs) scRNA-seq data and performed transcriptome comparison between WJMSCs and ADMSCs at the single-cell level.

RESULTS

GO enrichment analysis of highly variable genes (HVGs) obtained from WJMSCs revealed that these genes are significantly enriched in extracellular region with binding function, involved in developmental process, signal transduction, cell proliferation, etc. Pathway analysis showed that these HVGs are associated with functional characteristics of classic MSCs, such as inflammation mediated by chemokine and cytokine signaling, integrin signaling, and angiogenesis. After regressing out the batch and cell cycle effects, these HVGs were used for dimension reduction and clustering analysis to identify candidate subpopulations. Differentially expressed gene analysis revealed the existence of several distinct subpopulations of MSCs that exhibit diverse functional characteristics related to proliferation, development, and inflammation response. In line with our data, sorted CD142+ and CD142- WJMSCs showed distinct proliferation capacity as well as "wound healing" potential. Although WJMSCs and ADMSCs were derived from different tissues and were displaying different differentiation potencies, their HVGs were largely overlapped and had similar functional enrichment.

CONCLUSION

HVGs identified in MSCs are associated with classic MSC function. Regarding therapeutic potential, these genes are associated with functional characteristics, on which the MSC clinical application were theoretically based, such as development and inflammation response. Altogether, these HVGs hold the potential to be used as candidate markers for further potency association studies.

Size-Dependent Effects of Suspended Graphene Oxide Nanoparticles on the Cellular Fate of Mouse Neural Stem Cells

PURPOSE

In this study, we aim to explore the effects of graphene oxide (GO), a derivative of graphene, nanoparticles of four different sizes on the cellular fate of mouse neural stem cells (mNSCs).

METHODS

GO NPs were characterized with transmission electron microscopy (TEM), scanning electron micrography (SEM), atomic force microscopy (AFM) and Raman Spectra analysis. The cytotoxic effects of the GO NPs of different sizes on the mNSCs were determined using CCK-8 assay, Annexin V-APC/ 7-AAD staining and EdU staining assays. We investigated the biological and the mechanisms of GO NPs on cells using immunofluorescence analysis and quantitative real-time PCR (qPCR).

RESULTS

The average hydrodynamic sizes of the GO NPs were 417 nm, 663 nm, 1047 nm, and 4651 nm, with a thickness of approximately 22.5 nm, 17.7 nm, 22.4 nm, and 13.4 nm, respectively. GO NPs of all sizes showed low cytotoxicity at a concentration of 20 μg/mL on the mNSCs. Immunostaining demonstrated that treatment with GO NPs, especially the 663 nm ones, enhanced the self-renewal ability of mNSCs in the absence of EGF and bFGF. Under differentiation medium conditions that are free of mitogenic factors, all the GO NPs, particularly the 4651 nm ones, increased the expression level of Tuj1 and GFAP. With regards to the migration ability, we found that 417 nm GO-NP-treated mNSCs migrated over a longer distance than the control group obviously. In addition, higher expression of Rap1, Vinculin and Paxillin was observed in the GO NP-treated groups compared to the control group. mRNA-Sequence analysis and Western blotting results suggested that the 4651 nm GO NPs triggered positive neuronal differentiation through phosphorylation of ERK1/2 by the downregulating of TRPC2.

CONCLUSION

GO NPs play an important role in the applications of inducing self-renewal and differentiation of mNSC, and are promising in the future for further studies.

Pharmacological and Cellular Significance of Triazole-Surrogated Compounds

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Heterocyclic compounds have been at the hierarchy position in academia, and industrial arena, particularly the compounds containing triazole-core are found to be potent with a broad range of biological activities. The resistance of triazole ring towards chemical (acid and base) hydrolysis, oxidative and reductive reaction conditions, metabolic degradation and its higher aromatic stabilization energy makes it a better heterocyclic core as therapeutic agents. These triazole-linked compounds are used for clinical purposes for antifungal, anti-mycobacterium, anticancer, anti-migraine and antidepressant drugs. Triazole scaffolds are also found to act as a spacer for the sake of covalent attachment of the high molecular weight bio-macromolecules with an experimental building blocks to explore structure-function relationships. Herein, several methods and strategies for the synthesis of compounds with 1,2,3-triazole moiety exploring Hüisgen, Meldal and Sharpless 1,3-dipolar cycloaddition reaction between azide and alkyne derivatives have been deliberated for a series of representative compounds. Moreover, this review article highlights in-depth applications of the [3+2]-cycloaddition reaction for the advances of triazole-containing antibacterial as well as metabolic labelling agents for the in vitro and in vivo studies on cellular level.

Mechanics-Controlled Dynamic Cell Niches Guided Osteogenic Differentiation of Stem Cells via Preserved Cellular Mechanical Memory

Stem cells sense and respond to their local dynamic mechanical niches, which further regulate the cellular behaviors. While in naturally, instead of instantly responding to real-time mechanical changes of their surrounding niches, stem cells often present a delayed cellular response over a time scale, namely cellular mechanical memory, which may finally influence their lineage choice. Here, we aim to build a dynamic mechanical niche model with alginate-based hydrogel, therein the dynamic mechanical switching can be easily realized via the introduce or removal of Ca²⁺. The results show that stiffening hydrogel (from soft to stiff) suppresses osteogenic differentiation of human mesenchymal stem cells (hMSCs) early on, though it finally promoted osteogenic differentiation over a long time period. Instead, softening hydrogel (from stiff to soft) still retains the strong osteogenic differentiation in the early days, though it finally showed a lower level of osteogenic differentiation compared with stiff hydrogel. Further, microRNA miR-21 has been found as a long-term mechanical memory sensor of the osteogenic program in hMSCs, as its level remains to match early mechanics of substrate over a period of time. Regulation of miR-21 level is efficient to erase the past mechanical memory and resensitize hMSCs to subsequent substrate mechanics. Our findings highlight cellular mechanical memory effect as a key factor of cell and cellular microenvironment interactions, which has been largely neglected before, and as a crucial design element of biomaterials for cell culture.

Preparation of Biodegradable Polyethylene Glycol Dimethacrylate Hydrogels via Thiol-ene Chemistry

Through the control of the molecular weight, water content and monomer concentration, polyethylene glycol dimethacrylate (PEGDMA) based hydrogels have been adapted for numerous applications, including as structural scaffolds, drug delivery vehicles and cell carriers. However, due to the low biodegradability rates, the use of PEGDMA in tissue engineering has been limited. Thiol-based monomers have been shown to improve the degradation rates of several PEG-based hydrogels, though their impact on several material properties has not been as well defined. In this work, several mercaptopropianoates, as well as mercaptoacetates, were mixed with PEGDMA and copolymerized. Following an initial polymerization check, it was determined that mercaptoacetate-based thiol monomers did not polymerize in the presence of PEGDMA, whereas mercaptopropionates were more successful. The wettability, and the compressive and tensile strength, in addition to the thermal properties, were determined for successfully copolymerized samples via a combination of differential scanning calorimetry, dynamic mechanical analysis, unconfined compression, and goniometry. Further study determined that dipentaerythritol hexa(3-mercaptopropionate) (DiPETMP) successfully enhanced the biodegradability of PEGDMA.