Materials Stiffness-Dependent Redox Metabolic Reprogramming of Mesenchymal Stem Cells for Secretome-Based Therapeutic Angiogenesis

The role of extracellular matrix hydrogels and adipose-derived stromal cells in soft tissue vascularization - A systematic review

Decellularized extracellular matrix (dECM) hydrogels loaded with adipose-derived stromal cells (ASC) or their conditioned medium (ASC CM) present a promising and versatile treatment approach for tissue vascularization and regeneration. These hydrogels are easy to produce, store, personalize, manipulate, and deliver to the target tissue. This literature review aimed to investigate the applications of dECM hydrogels with ASC or ASC CM for in vivo tissue vascularization. Fourteen experimental studies have been reviewed using vessel density as the primary outcome parameter for in vivo vascularization. The studies consistently reported an increased efficacy in augmenting angiogenesis by the ASC or ASC CM-loaded hydrogels compared to untreated controls. However, this systematic review shows the need to standardize procedures and characterization, particularly of the final administered product(s). The findings from these experimental studies highlight the potential of dECM hydrogel with ASC or ASC CM in novel tissue regeneration and regenerative medicine applications.

Matrix stiffness regulates the triad communication of adipocytes/macrophages/endothelial cells through CXCL13

Adipose tissue remodeling and plasticity are dynamically regulated by the coordinated functions of adipocytes, macrophages, and endothelial cells and extracellular matrix (ECM) that provides stiffness networks in adipose tissue component cells. Inflammation and fibrosis are crucial exogenous factors that dysregulate adipose tissue functions and drastically change the mechanical properties of the ECM. Therefore, communication among the ECM and adipose tissue component cells is necessary to understand the multifaceted functions of adipose tissues. To obtain in vivo stiffness, we used genipin as a crosslinker for collagen gels. Meanwhile, we isolated primary adipocytes, macrophages, and endothelial cells from C57BL/6J mice and incubated these cells in the differentiation media on temperature-responsive culture dishes. After the differentiation, these cell sheets were transferred onto genipin-crosslinked collagen gels with varying matrix stiffness. We found that inflammatory gene expressions were induced by hard matrix, whereas antiinflammatory gene expressions were promoted by soft matrix in all three types of cells. Interestingly, the coculture experiments of adipocytes, macrophages, and endothelial cells showed that the effects of soft or hard matrix stiffness stimulation on adipocytes were transmitted to the distant adipose tissue component cells, altering their gene expression profiles under normal matrix conditions. Finally, we identified that a hard matrix induces the secretion of CXCL13 from adipocytes, and CXCL13 is one of the important transmitters for stiffness communication with macrophages and endothelial cells. These findings provide insight into the mechanotransmission into distant cells and the application of stiffness control for chronic inflammation in adipose tissues with metabolic dysregulation.

Mechanical force regulates the paracrine functions of ADSCs to assist skin expansion in rats

BACKGROUND

In the repair of massive tissue defects using expanded large skin flaps, the incidence of complications increases with the size of the expanded area. Currently, stem cell therapy has limitations to solve this problem. We hypothesized that conditioned medium of adipose-derived stem cells (ADSC-CM) collected following mechanical pretreatment can assist skin expansion.

METHODS

Rat aortic endothelial cells and fibroblasts were cultured with ADSC-CM collected under 0%, 10%, 12%, and 15% stretching force. Ten-milliliter cylindrical soft tissue expanders were subcutaneously implanted into the backs of 36 Sprague-Dawley rats. The 0% and 10% stretch groups were injected with ADSC-CM collected under 0% and 10% stretching force, respectively, while the control group was not injected. After 3, 7, 14, and 30 days of expansion, expanded skin tissue was harvested for staining and qPCR analyses.

RESULTS

Endothelial cells had the best lumen formation and highest migration rate, and fibroblasts secreted the most collagen upon culture with ADSC-CM collected under 10% stretching force. The skin expansion rate was significantly increased in the 10% stretch group. After 7 days of expansion, the number of blood vessels in the expanded area, expression of the angiogenesis-associated proteins vascular endothelial growth factor, basic fibroblast growth factor, and hepatocyte growth factor, and collagen deposition were significantly increased in the 10% stretch group.

CONCLUSIONS

The optimal mechanical force upregulates specific paracrine proteins in ADSCs to increase angiogenesis and collagen secretion, and thereby promote skin regeneration and expansion. This study provides a new auxiliary method to expand large skin flaps.

Large Polyacrylamide Hydrogels for Large-Batch Cell Culture and Mechanobiological Studies

The rigidity of a cell's substrate or extracellular matrix plays a vital role in regulating cell and tissue functions. Polyacrylamide (PAAm) hydrogels are one of the most widely used cell culture substrates that provide a physiologically relevant range of stiffness. However, it is still arduous and time-consuming to prepare PAAm substrates in large batches for high-yield or multiscale cell cultures. In this communication, a simple method to prepare PAAm hydrogels with less time cost and easily accessible materials is presented. The hydrogel is mechanically uniform and supports cell culture in a large batch. It is further shown that the stiffness of the hydrogel covers a large range of Young's modulus and is sensed by cells, regulating various cell features including changes in cell morphology, proliferation, and contractility. This method improves the reproducibility of mechanobiology studies and can be easily applied for mechanobiology research requiring large numbers of cells or experimental groups.

Mitochondria: At the crossroads between mechanobiology and cell metabolism

Metabolism and mechanics are two key facets of structural and functional processes in cells, such as growth, proliferation, homeostasis and regeneration. Their reciprocal regulation has been increasingly acknowledged in recent years: external physical and mechanical cues entail metabolic changes, which in return regulate cell mechanosensing and mechanotransduction. Since mitochondria are pivotal regulators of metabolism, we review here the reciprocal links between mitochondrial morphodynamics, mechanics and metabolism. Mitochondria are highly dynamic organelles which sense and integrate mechanical, physical and metabolic cues to adapt their morphology, the organization of their network and their metabolic functions. While some of the links between mitochondrial morphodynamics, mechanics and metabolism are already well established, others are still poorly documented and open new fields of research. First, cell metabolism is known to correlate with mitochondrial morphodynamics. For instance, mitochondrial fission, fusion and cristae remodeling allow the cell to fine-tune its energy production through the contribution of mitochondrial oxidative phosphorylation and cytosolic glycolysis. Second, mechanical cues and alterations in mitochondrial mechanical properties reshape and reorganize the mitochondrial network. Mitochondrial membrane tension emerges as a decisive physical property which regulates mitochondrial morphodynamics. However, the converse link hypothesizing a contribution of morphodynamics to mitochondria mechanics and/or mechanosensitivity has not yet been demonstrated. Third, we highlight that mitochondrial mechanics and metabolism are reciprocally regulated, although little is known about the mechanical adaptation of mitochondria in response to metabolic cues. Deciphering the links between mitochondrial morphodynamics, mechanics and metabolism still presents significant technical and conceptual challenges but is crucial both for a better understanding of mechanobiology and for potential novel therapeutic approaches in diseases such as cancer.

Engineered Nano-Bio Interfaces for Stem Cell Therapy

Engineered nanomaterials (ENMs) with different topographies provide effective nano-bio interfaces for controlling the differentiation of stem cells. The interaction of stem cells with nanoscale topographies and chemical cues in their microenvironment at the nano-bio interface can guide their fate. The use of nanotopographical cues, in particular nanorods, nanopillars, nanogrooves, nanofibers, and nanopits, as well as biochemical forces mediated factors, including growth factors, cytokines, and extracellular matrix proteins, can significantly impact stem cell differentiation. These factors were seen as very effective in determining the proliferation and spreading of stem cells. The specific outgrowth of stem cells can be decided with size variation of topographic nanomaterial along with variation in matrix stiffness and surface structure like a special arrangement. The precision chemistry enabled controlled design, synthesis, and chemical composition of ENMs can regulate stem cell behaviors. The parameters of size such as aspect ratio, diameter, and pore size of nanotopographic structures are the main factors for specific termination of stem cells. Protein corona nanoparticles (NPs) have shown a powerful facet in stem cell therapy, where combining specific proteins could facilitate a certain stem cell differentiation and cellular proliferation. Nano-bio reactions implicate the interaction between biological entities and nanoparticles, which can be used to tailor the stem cells' culmination. The ion release can also be a parameter to enhance cellular proliferation and to commit the early differentiation of stem cells. Further research is needed to fully understand the mechanisms underlying the interactions between engineered nano-bio interfaces and stem cells and to develop optimized regenerative medicine and tissue engineering designs.

Dynamic Stimulations with Bioengineered Extracellular Matrix-Mimicking Hydrogels for Mechano Cell Reprogramming and Therapy

Cells interact with their surrounding environment through a combination of static and dynamic mechanical signals that vary over stimulus types, intensity, space, and time. Compared to static mechanical signals such as stiffness, porosity, and topography, the current understanding on the effects of dynamic mechanical stimulations on cells remains limited, attributing to a lack of access to devices, the complexity of experimental set-up, and data interpretation. Yet, in the pursuit of emerging translational applications (e.g., cell manufacturing for clinical treatment), it is crucial to understand how cells respond to a variety of dynamic forces that are omnipresent in vivo so that they can be exploited to enhance manufacturing and therapeutic outcomes. With a rising appreciation of the extracellular matrix (ECM) as a key regulator of biofunctions, researchers have bioengineered a suite of ECM-mimicking hydrogels, which can be fine-tuned with spatiotemporal mechanical cues to model complex static and dynamic mechanical profiles. This review first discusses how mechanical stimuli may impact different cellular components and the various mechanobiology pathways involved. Then, how hydrogels can be designed to incorporate static and dynamic mechanical parameters to influence cell behaviors are described. The Scopus database is also used to analyze the relative strength in evidence, ranging from strong to weak, based on number of published literatures, associated citations, and treatment significance. Additionally, the impacts of static and dynamic mechanical stimulations on clinically relevant cell types including mesenchymal stem cells, fibroblasts, and immune cells, are evaluated. The aim is to draw attention to the paucity of studies on the effects of dynamic mechanical stimuli on cells, as well as to highlight the potential of using a cocktail of various types and intensities of mechanical stimulations to influence cell fates (similar to the concept of biochemical cocktail to direct cell fate). It is envisioned that this progress report will inspire more exciting translational development of mechanoresponsive hydrogels for biomedical applications.

Mechano-responsive hydrogel for direct stem cell manufacturing to therapy

Bone marrow-derived mesenchymal stem cell (MSC) is one of the most actively studied cell types due to its regenerative potential and immunomodulatory properties. Conventional cell expansion methods using 2D tissue culture plates and 2.5D microcarriers in bioreactors can generate large cell numbers, but they compromise stem cell potency and lack mechanical preconditioning to prepare MSC for physiological loading expected in vivo. To overcome these challenges, in this work, we describe a 3D dynamic hydrogel using magneto-stimulation for direct MSC manufacturing to therapy. With our technology, we found that dynamic mechanical stimulation (DMS) enhanced matrix-integrin β1 interactions which induced MSCs spreading and proliferation. In addition, DMS could modulate MSC biofunctions including directing MSC differentiation into specific lineages and boosting paracrine activities (e.g., growth factor secretion) through YAP nuclear localization and FAK-ERK pathway. With our magnetic hydrogel, complex procedures from MSC manufacturing to final clinical use, can be integrated into one single platform, and we believe this 'all-in-one' technology could offer a paradigm shift to existing standards in MSC therapy.

Integrative Analysis Reveals the Diverse Effects of 3D Stiffness upon Stem Cell Fate

The origin of life and native tissue development are dependent on the heterogeneity of pluripotent stem cells. Bone marrow mesenchymal stem cells (BMMSCs) are located in a complicated niche with variable matrix stiffnesses, resulting in divergent stem cell fates. However, how stiffness drives stem cell fate remains unknown. For this study, we performed whole-gene transcriptomics and precise untargeted metabolomics sequencing to elucidate the complex interaction network of stem cell transcriptional and metabolic signals in extracellular matrices (ECMs) with different stiffnesses, and we propose a potential mechanism involved in stem cell fate decision. In a stiff (39~45 kPa) ECM, biosynthesis of aminoacyl-tRNA was up-regulated, and increased osteogenesis was also observed. In a soft (7~10 kPa) ECM, biosynthesis of unsaturated fatty acids and deposition of glycosaminoglycans were increased, accompanied by enhanced adipogenic/chondrogenic differentiation of BMMSCs. In addition, a panel of genes responding to the stiffness of the ECM were validated in vitro, mapping out the key signaling network that regulates stem cells' fate decisions. This finding of "stiffness-dependent manipulation of stem cell fate" provides a novel molecular biological basis for development of potential therapeutic targets within tissue engineering, from both a cellular metabolic and a biomechanical perspective.

Harnessing cell-material interactions to control stem cell secretion for osteoarthritis treatment

Osteoarthritis (OA) is the most common debilitating joint disease, yet there is no curative treatment for OA to date. Delivering mesenchymal stromal cells (MSCs) as therapeutic cells to mitigate the inflammatory symptoms associated with OA is attracting increasing attention. In principle, MSCs could respond to the pro-inflammatory microenvironment of an OA joint by the secretion of anti-inflammatory, anti-apoptotic, immunomodulatory and pro-regenerative factors, therefore limiting pain, as well as the disease development. However, the microenvironment of MSCs is known to greatly affect their survival and bioactivity, and using tailored biomaterial scaffolds could be key to the success of intra-articular MSC-based therapies. The aim of this review is to identify and discuss essential characteristics of biomaterial scaffolds to best promote MSC secretory functions in the context of OA. First, a brief introduction to the OA physiopathology is provided, followed by an overview of the MSC secretory functions, as well as the current limitations of MSC-based therapy. Then, we review the current knowledge on the effects of cell-material interactions on MSC secretion. These considerations allow us to define rational guidelines for next-generation biomaterial design to improve the MSC-based therapy of OA.

Effect of Extracellular Matrix Stiffness on Candesartan Efficacy in Anti-Fibrosis and Antioxidation

Myocardial fibrosis progression and imbalanced redox state are closely associated with increased extracellular matrix (ECM) stiffness. Candesartan (CAN), an angiotensin II (Ang II) receptor inhibitor, has shown promising anti-fibrosis and antioxidant efficacy in previous cardiovascular disease studies. However, the effect of ECM stiffness on CAN efficacy remains elusive. In this study, we constructed rat models with three different degrees of myocardial fibrosis and treated them with CAN, and then characterized the stiffness, cardiac function, and NADPH oxidase-2 (NOX2) expression of the myocardial tissues. Based on the obtained stiffness of myocardial tissues, we used polyacrylamide (PA) gels with three different stiffness to mimic the ECM stiffness of cardiac fibroblasts (CFs) at the early, middle, and late stages of myocardial fibrosis as the cell culture substrates and then constructed CFs mechanical microenvironment models. We studied the effects of PA gel stiffness on the migration, proliferation, and activation of CFs without and with CAN treatment, and characterized the reactive oxygen species (ROS) and glutathione (GSH) levels of CFs using fluorometry and scanning electrochemical microscopy (SECM). We found that CAN has the best amelioration efficacy in the cardiac function and NOX2 levels in rats with medium-stiffness myocardial tissue, and the most obvious anti-fibrosis and antioxidant efficacy in CFs on the medium-stiffness PA gels. Our work proves the effect of ECM stiffness on CAN efficacy in myocardial anti-fibrosis and antioxidants for the first time, and the results demonstrate that the effect of ECM stiffness on drug efficacy should also be considered in the treatment of cardiovascular diseases.

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

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

Decreased Glycolysis at Menstruation is Associated with Increased Menstrual Blood Loss

Heavy menstrual bleeding (HMB) is common and severely affects the quality of life of the afflicted women. While HMB is known to be caused by impaired endometrial repair after menstruation, its more proximate cause remains unknown. To investigate whether glycolysis plays any role in endometrial repair and thus HMB, we conducted two mouse experiments using a mouse model of simulated menstruation. We performed immunohistochemistry analyses of proteins involved in glycolysis as well as pro- and anti-inflammatory cytokines in endometrium from decidualized and non-decidualized uterine horns. We also assessed the extent of endometrial repair by staging endometrial morphology from decidualization to full repair using histological scoring of uterine sections and quantitated the amount of menstrual blood loss (MBL). In addition, we employed the scratch assay and the CCK-8 assay to evaluate the effect of glycolysis suppression on cellular migration and proliferation, respectively. Finally, we performed an immunohistochemistry analysis of HK2 in endometrium from women with adenomyosis who experienced either moderate/heavy or excessive MBL. We found that endometrial repair coincided with increased glycolysis in endometrium and glycolysis suppression delayed endometrial repair, resulting in increased MBL. Additionally, glycolysis suppression significantly inhibited the proliferative and migratory capability of endometrial cells, and disrupted normal endometrial repair even when hypoxia was maintained. Women with adenomyosis who experienced excessive MBL had significantly lower HK2 staining than those who experienced moderate/heavy MBL. Thus, our study highlights the importance of glycolysis as well as inflammation in optimal endometrial repair, and provides clues for the cause of HMB in women with adenomyosis.

Chorioallantoic Membrane Assay at the Cross-Roads of Adipose-Tissue-Derived Stem Cell Research

With a history of more than 100 years of different applications in various scientific fields, the chicken chorioallantoic membrane (CAM) assay has proven itself to be an exceptional scientific model that meets the requirements of the replacement, reduction, and refinement principle (3R principle). As one of three extraembryonic avian membranes, the CAM is responsible for fetal respiration, metabolism, and protection. The model provides a unique constellation of immunological, vascular, and extracellular properties while being affordable and reliable at the same time. It can be utilized for research purposes in cancer biology, angiogenesis, virology, and toxicology and has recently been used for biochemistry, pharmaceutical research, and stem cell biology. Stem cells and, in particular, mesenchymal stem cells derived from adipose tissue (ADSCs) are emerging subjects for novel therapeutic strategies in the fields of tissue regeneration and personalized medicine. Because of their easy accessibility, differentiation profile, immunomodulatory properties, and cytokine repertoire, ADSCs have already been established for different preclinical applications in the files mentioned above. In this review, we aim to highlight and identify some of the cross-sections for the potential utilization of the CAM model for ADSC studies with a focus on wound healing and tissue engineering, as well as oncological research, e.g., sarcomas. Hereby, the focus lies on the combination of existing evidence and experience of such intersections with a potential utilization of the CAM model for further research on ADSCs.

Effect of Hyaluronic Acid and Mesenchymal Stem Cells Secretome Combination in Promoting Alveolar Regeneration

Pharmacological therapies in lung diseases are nowadays useful in reducing the symptomatology of lung injury. However, they have not yet been translated to effective treatment options able to restore the lung tissue damage. Cell-therapy based on Mesenchymal Stem Cells (MSCs) is an attractive, as well as new therapeutic approach, although some limitations can be ascribed for therapeutic use, such as tumorigenicity and immune rejection. However, MSCs have the capacity to secrete multiple paracrine factors, namely secretome, capable of regulating endothelial and epithelial permeability, decrease inflammation, enhancing tissue repair, and inhibiting bacterial growth. Furthermore, Hyaluronic acid (HA) has been demonstrated to have particularly efficacy in promoting the differentiation of MSCs in Alveolar type II (ATII) cells. In this frame, the combination of HA and secretome to achieve the lung tissue regeneration has been investigated for the first time in this work. Overall results showed how the combination of HA (low and medium molecular weight HA) plus secretome could enhance MSCs differentiation in ATII cells (SPC marker expression of about 5 ng/mL) compared to the only HA or secretome solutions alone (SPC about 3 ng/mL, respectively). Likewise, cell viability and cell rate of migration were reported to be improved for HA and secretome blends, indicating an interesting potentiality of such systems for lung tissue repair. Moreover, an anti-inflammatory profile has been revealed when dealing with HA and secretome mixtures. Therefore, these promising results can allow important advance in the accomplishment of the future therapeutic approach in respiratory diseases, up to date still missing.

Click and bioorthogonal hyaluronic acid hydrogels as an ultra-tunable platform for the investigation of cell-material interactions

The cellular microenvironment plays a major role in the biological functions of cells. Thus, biomaterials, especially hydrogels, which can be design to mimic the cellular microenvironment, are being increasingly used for cell encapsulation, delivery, and 3D culture, with the hope of controlling cell functions. Yet, much remains to be understood about the effects of cell-material interactions, and advanced synthetic strategies need to be developed to independently control the mechanical and biochemical properties of hydrogels. To address this challenge, we designed a new hyaluronic acid (HA)-based hydrogel platform using a click and bioorthogonal strain-promoted azide-alkyne cycloaddition (SPAAC) reaction. This approach facilitates the synthesis of hydrogels that are easy to synthesize and sterilize, have minimal swelling, are stable long term, and are cytocompatible. It provides bioorthogonal HA gels over an uncommonly large range of stiffness (0.5-45 kPa), all forming within 1-15 min. More importantly, our approach offers a versatile one-pot procedure to independently tune the hydrogel composition (e.g., polymer and adhesive peptides). Using this platform, we investigate the independent effects of polymer type, stiffness, and adhesion on the secretory properties of human adipose-derived stromal cells (hASCs) and demonstrate that HA can enhance the secretion of immunomodulatory factors by hASCs.

Squid Suckerin-Spider Silk Fusion Protein Hydrogel for Delivery of Mesenchymal Stem Cell Secretome to Chronic Wounds

Chronic wounds are non-healing wounds characterized by a prolonged inflammation phase. Excessive inflammation leads to elevated protease levels and consequently to a decrease in growth factors at wound sites. Stem cell secretome therapy has been identified as a treatment strategy to modulate the microenvironment of chronic wounds via supplementation with anti-inflammatory/growth factors. However, there is a need to develop better secretome delivery systems that are able to encapsulate the secretome without denaturation, in a sustained manner, and that are fully biocompatible. To address this gap, a recombinant squid suckerin-spider silk fusion protein is developed with cell-adhesion motifs capable of thermal gelation at physiological temperatures to form hydrogels for encapsulation and subsequent release of the stem cell secretome. Freeze-thaw treatment of the protein hydrogel results in a modified porous cryogel that maintains slow degradation and sustained secretome release. Chronic wounds of diabetic mice treated with the secretome-laden cryogel display increased wound closure, presence of endothelial cells, granulation wound tissue thickness, and reduced inflammation with no fibrotic scar formation. Overall, these in vivo indicators of wound healing demonstrate that the fusion protein hydrogel displays remarkable potential as a delivery system for secretome-assisted chronic wound healing.

The progress in titanium alloys used as biomedical implants: From the view of reactive oxygen species

Titanium and Titanium alloys are widely used as biomedical implants in oral and maxillofacial surgery, due to superior mechanical properties and biocompatibility. In specific clinical populations such as the elderly, diabetics and patients with metabolic diseases, the failure rate of medical metal implants is increased significantly, putting them at increased risk of revision surgery. Many studies show that the content of reactive oxygen species (ROS) in the microenvironment of bone tissue surrounding implant materials is increased in patients undergoing revision surgery. In addition, the size and shape of materials, the morphology, wettability, mechanical properties, and other properties play significant roles in the production of ROS. The accumulated ROS break the original balance of oxidation and anti-oxidation, resulting in host oxidative stress. It may accelerate implant degradation mainly by activating inflammatory cells. Peri-implantitis usually leads to a loss of bone mass around the implant, which tends to affect the long-term stability and longevity of implant. Therefore, a great deal of research is urgently needed to focus on developing antibacterial technologies. The addition of active elements to biomedical titanium and titanium alloys greatly reduce the risk of postoperative infection in patients. Besides, innovative technologies are developing new biomaterials surfaces conferring anti-infective properties that rely on the production of ROS. It can be considered that ROS may act as a messenger substance for the communication between the host and the implanted material, which run through the entire wound repair process and play a role that cannot be ignored. It is necessary to understand the interaction between oxidative stress and materials, the effects of oxidative stress products on osseointegration and implant life as well as ROS-induced bactericidal activity. This helps to facilitate the development of a new generation of well-biocompatible implant materials with ROS responsiveness, and ultimately prolong the lifespan of implants.

Zonally Stratified Decalcified Bone Scaffold with Different Stiffness Modified by Fibrinogen for Osteochondral Regeneration of Knee Joint Defect

Articular cartilage is generally known to be a complex tissue with multiple layers. Each layer has different composition, structure, and mechanical properties, making regeneration after knee joint defects a troubling clinical problem. A novel integrated stratified decalcified bone matrix (SDBM) scaffold with different stiffness to mimic the mechanical properties of articular cartilage is presented herein. This SDBM scaffold was modified using fibrinogen (Fg) (Fg + SDBM) to enhance its vascularization ability and improve its repair efficiency for osteochondral defects of knee joints. A Fg + SDBM scaffold with different elastic modulus in each layer (high-stiffness DBM (HDBM) layer, 174.208 ± 44.330 MPa (Fg + HDBM); medium-stiffness DBM (MDBM) layer, 21.214 ± 6.922 MPa (Fg + MDBM); and low-stiffness DBM (LDBM) layer, 0.678 ± 0.269 MPa (Fg + LDBM)) was constructed by controlling the stratified decalcification time with layered embedding paraffin (0, 3, and 5 days). The low- and medium-stiffness layers of the Fg + SDBM scaffold remarkably promoted the cartilage differentiation of bone marrow mesenchymal stem cells in vitro. Subcutaneous transplantation and rabbit knee joint osteochondral defect repair experiments revealed that the low- and medium-stiffness layers of the Fg + SDBM scaffold exhibited wonderful cartilage capacity, whereas the high-stiffness layer of Fg + SDBM scaffold exhibited good osteogenesis ability. Furthermore, this scaffold could promote blood vessel formation in subchondral bone area. This study presents a feasible strategy for osteochondral regeneration of defective knee joints, which is of great clinical value for tissue repair.

Reprogramming stem cells in regenerative medicine

Induced pluripotent stem cells (iPSCs) that are generated from adult somatic cells are induced to express genes that make them pluripotent through reprogramming techniques. With their unlimited proliferative capacity and multifaceted differentiation potential and circumventing the ethical problems encountered in the application of embryonic stem cells (ESC), iPSCs have a broad application in the fields of cell therapy, drug screening, and disease models and may open up new possibilities for regenerative medicine to treat diseases in the future. In this review, we begin with different reprogramming cell technologies to obtain iPSCs, including biotechnological, chemical, and physical modulation techniques, and present their respective strengths, and limitations, as well as the recent progress of research. Secondly, we review recent research advances in iPSC reprogramming-based regenerative therapies. iPSCs are now widely used to study various clinical diseases of hair follicle defects, myocardial infarction, neurological disorders, liver diseases, and spinal cord injuries. This review focuses on the translational clinical research around iPSCs as well as their potential for growth in the medical field. Finally, we summarize the overall review and look at the potential future of iPSCs in the field of cell therapy as well as tissue regeneration engineering and possible problems. We believe that the advancing iPSC research will help drive long-awaited breakthroughs in cellular therapy.

Engineering Hydrogels for Modulation of Material-Cell Interactions

Hydrogels are a recurrent platform for Tissue Engineering (TE) strategies. Their versatility and the variety of available methods for tuning their properties highly contribute to hydrogels' success. As a result, the design of advanced hydrogels has been thoroughly studied, in the quest for better solutions not only for drugs- and cell-based therapies but also for more fundamental studies. The wide variety of sources, crosslinking strategies, and functionalization methods, and mostly the resemblance of hydrogels to the natural extracellular matrix, make this 3D hydrated structures an excellent tool for TE approaches. The state-of-the-art information regarding hydrogel design, processing methods, and the influence of different hydrogel formulations on the final cell-biomaterial interactions are overviewed herein. This article is protected by copyright. All rights reserved.

Versatile polyphenolic platforms in regulating cell biology

Polyphenolic materials are a class of fascinating and versatile bioinspired materials for biointerfacial engineering. In particular, due to the presence of active chemical groups, a series of unique physicochemical properties become accessible and tunable of the as-prepared polyphenolic platforms, which could delicately regulate the cell activities via cell-material contact-dependent interactions. More interestingly, polyphenols could also affect the cell behaviors via cell-material contact-independent manner, which arise due to their intrinsically functional characteristics (e.g., antioxidant and photothermal behaviors). As such, a comprehensive understanding on the relationship between material properties and desired biomedical applications, as well as the underlying mechanism at the cellular and molecular level would provide material design principles and accelerate the lab-to-clinic translation of polyphenolic platforms. In this review, we firstly give a brief overview of cell hallmarks governed by surrounding cues, followed by the introduction of polyphenolic material engineering strategies. Subsequently, a detailed discussion on cell-polyphenols contact-dependent interfacial interaction and contact-independent interaction was also carefully provided. Lastly, their biomedical applications were elaborated. We believe that this review could provide guidances for the rational material design of multifunctional polyphenols and extend their application window.

Secretomes as an emerging class of bioactive ingredients for enhanced cosmeceutical applications

Skin aging is predominantly caused by either intrinsic or extrinsic factors, leading to undesirable skin features. Advancements in both molecular and cellular fields have created possibilities in developing novel stem cell-derived active ingredients for cosmeceutical applications and the beauty industry. Mesenchymal stromal cell (MSC)-derived secretomes or conditioned media hold great promise for advancing skin repair and regeneration due to the presence of varying cytokines. These cytokines signal our cells and trigger biological mechanisms associated with anti-inflammatory, antioxidant, anti-aging, proliferative, and immunomodulatory effects. In this review, we discuss the potential of MSC secretomes as novel biomaterials for skincare and rejuvenation by illustrating their mechanism of action related to wound healing, anti-aging, and whitening properties. The advantages and disadvantages of secretomes are compared to both plant-based and animal-derived extracts. In addition, this paper reviews the current safety standards, regulations, market products and research work related to the cosmeceutical applications of secretomes along with strategies to maintain and improve the therapeutic efficacy and production of secretomes. The future outlook of beauty industry is also presented. Lastly, we highlight significant challenges to be addressed for the clinical realization of MSC secretomes-based skin therapies as well as providing perspectives for the future direction of secretomes.

Polymeric Hydrogels as Mesenchymal Stem Cell Secretome Delivery System in Biomedical Applications

Secretomes of mesenchymal stem cells (MSCs) have been successfully studied in preclinical models for several biomedical applications, including tissue engineering, drug delivery, and cancer therapy. Hydrogels are known to imitate a three-dimensional extracellular matrix to offer a friendly environment for stem cells; therefore, hydrogels can be used as scaffolds for tissue construction, to control the distribution of bioactive compounds in tissues, and as a secretome-producing MSC culture media. The administration of a polymeric hydrogel-based MSC secretome has been shown to overcome the fast clearance of the target tissue. In vitro studies confirm the bioactivity of the secretome encapsulated in the gel, allowing for a controlled and sustained release process. The findings reveal that the feasibility of polymeric hydrogels as MSC -secretome delivery systems had a positive influence on the pace of tissue and organ regeneration, as well as an enhanced secretome production. In this review, we discuss the widely used polymeric hydrogels and their advantages as MSC secretome delivery systems in biomedical applications.

Delivery of Stem Cell Secretome for Therapeutic Applications

Intensive studies on stem cell therapy reveal that benefits of stem cells attribute to the paracrine effects. Hence, direct delivery of stem cell secretome to the injured site shows the comparative therapeutic efficacy of living cells while avoiding the potential limitations. However, conventional systemic administration of stem cell secretome often leads to rapid clearance in vivo. Therefore, a variety of different biomaterials are developed for sustained and controllable delivery of stem cell secretome to improve therapeutic efficiency. In this review, we first introduce current approaches for the preparation and characterization of stem cell secretome as well as strategies to improve their therapeutic efficacy and production. The up-to-date delivery platforms are also summarized, including nanoparticles, injectable hydrogels, microneedles, and scaffold patches. Meanwhile, we discuss the underlying therapeutic mechanism of stem cell secretome for the treatment of various diseases. In the end, future opportunities and challenges are proposed.

Direct reuse of electronic plastic scraps from computer monitor and keyboard to direct stem cell growth and differentiation

Reuse of electronic wastes is a critical aspect for a more sustainable circular economy as it provides the simplest and most direct route to extend the lifespan of non-renewable resources. Herein, the distinctive surface and micro topographical features of computer electronic-plastic (E-plastic) scraps were unconventionally repurposed as a substrate material to guide the growth and differentiation of human adipose-derived mesenchymal stem cells (ADSCs). Specifically, the E-plastics were scavenged from discarded computer components such as light diffuser plate (polyacrylates), prismatic sheet (polyethylene terephthalate), and keyboards (acrylonitrile butadiene styrene) were cleaned, sterilized, and systematically characterized to determine the identity of the plastics, chemical constituents, surface features, and leaching characteristics. Multiparametric analysis revealed that all the E-plastics could preserve stem-cell phenotype and maintain cell growth over 2 weeks, rivalling the performance of commercial tissue-culture treated plates as cell culture plastics. Interestingly, compared to commercial tissue-culture treated plastics and in a competitive adipogenic and osteogenic differentiation environment, ADSCs cultured on the keyboard and light diffuser plastics favoured bone cells formation while the grating-like microstructures of the prismatic sheet promoted fat cells differentiation via the process of contact guidance. Our findings point to the real possibility of utilizing discarded computer plastics as a "waste-to-resource" material to programme stem cell fate without further processing nor biochemical modification, thus providing an innovative second-life option for E-plastics from personal computers.

Mitochondrial fission links ECM mechanotransduction to metabolic redox homeostasis and metastatic chemotherapy resistance

Metastatic breast cancer cells disseminate to organs with a soft microenvironment. Whether and how the mechanical properties of the local tissue influence their response to treatment remains unclear. Here we found that a soft extracellular matrix empowers redox homeostasis. Cells cultured on a soft extracellular matrix display increased peri-mitochondrial F-actin, promoted by Spire1C and Arp2/3 nucleation factors, and increased DRP1- and MIEF1/2-dependent mitochondrial fission. Changes in mitochondrial dynamics lead to increased production of mitochondrial reactive oxygen species and activate the NRF2 antioxidant transcriptional response, including increased cystine uptake and glutathione metabolism. This retrograde response endows cells with resistance to oxidative stress and reactive oxygen species-dependent chemotherapy drugs. This is relevant in a mouse model of metastatic breast cancer cells dormant in the lung soft tissue, where inhibition of DRP1 and NRF2 restored cisplatin sensitivity and prevented disseminated cancer-cell awakening. We propose that targeting this mitochondrial dynamics- and redox-based mechanotransduction pathway could open avenues to prevent metastatic relapse.

A Review on the Design of Hydrogels With Different Stiffness and Their Effects on Tissue Repair

Tissue repair after trauma and infection has always been a difficult problem in regenerative medicine. Hydrogels have become one of the most important scaffolds for tissue engineering due to their biocompatibility, biodegradability and water solubility. Especially, the stiffness of hydrogels is a key factor, which influence the morphology of mesenchymal stem cells (MSCs) and their differentiation. The researches on this point are meaningful to the field of tissue engineering. Herein, this review focus on the design of hydrogels with different stiffness and their effects on the behavior of MSCs. In addition, the effect of hydrogel stiffness on the phenotype of macrophages is introduced, and then the relationship between the phenotype changes of macrophages on inflammatory response and tissue repair is discussed. Finally, the future application of hydrogels with a certain stiffness in regenerative medicine and tissue engineering has been prospected.

Current hydrogel advances in physicochemical and biological response-driven biomedical application diversity

Hydrogel is a type of versatile platform with various biomedical applications after rational structure and functional design that leverages on material engineering to modulate its physicochemical properties (e.g., stiffness, pore size, viscoelasticity, microarchitecture, degradability, ligand presentation, stimulus-responsive properties, etc.) and influence cell signaling cascades and fate. In the past few decades, a plethora of pioneering studies have been implemented to explore the cell-hydrogel matrix interactions and figure out the underlying mechanisms, paving the way to the lab-to-clinic translation of hydrogel-based therapies. In this review, we first introduced the physicochemical properties of hydrogels and their fabrication approaches concisely. Subsequently, the comprehensive description and deep discussion were elucidated, wherein the influences of different hydrogels properties on cell behaviors and cellular signaling events were highlighted. These behaviors or events included integrin clustering, focal adhesion (FA) complex accumulation and activation, cytoskeleton rearrangement, protein cyto-nuclei shuttling and activation (e.g., Yes-associated protein (YAP), catenin, etc.), cellular compartment reorganization, gene expression, and further cell biology modulation (e.g., spreading, migration, proliferation, lineage commitment, etc.). Based on them, current in vitro and in vivo hydrogel applications that mainly covered diseases models, various cell delivery protocols for tissue regeneration and disease therapy, smart drug carrier, bioimaging, biosensor, and conductive wearable/implantable biodevices, etc. were further summarized and discussed. More significantly, the clinical translation potential and trials of hydrogels were presented, accompanied with which the remaining challenges and future perspectives in this field were emphasized. Collectively, the comprehensive and deep insights in this review will shed light on the design principles of new biomedical hydrogels to understand and modulate cellular processes, which are available for providing significant indications for future hydrogel design and serving for a broad range of biomedical applications.

Zyxin Is Involved in Fibroblast Rigidity Sensing and Durotaxis

Focal adhesions (FAs) are specialized structures that enable cells to sense their extracellular matrix rigidity and transmit these signals to the interior of the cells, bringing about actin cytoskeleton reorganization, FA maturation, and cell migration. It is known that cells migrate towards regions of higher substrate rigidity, a phenomenon known as durotaxis. However, the underlying molecular mechanism of durotaxis and how different proteins in the FA are involved remain unclear. Zyxin is a component of the FA that has been implicated in connecting the actin cytoskeleton to the FA. We have found that knocking down zyxin impaired NIH3T3 fibroblast's ability to sense and respond to changes in extracellular matrix in terms of their FA sizes, cell traction stress magnitudes and F-actin organization. Cell migration speed of zyxin knockdown fibroblasts was also independent of the underlying substrate rigidity, unlike wild type fibroblasts which migrated fastest at an intermediate substrate rigidity of 14 kPa. Wild type fibroblasts exhibited durotaxis by migrating toward regions of increasing substrate rigidity on polyacrylamide gels with substrate rigidity gradient, while zyxin knockdown fibroblasts did not exhibit durotaxis. Therefore, we propose zyxin as an essential protein that is required for rigidity sensing and durotaxis through modulating FA sizes, cell traction stress and F-actin organization.

Bioinspired short peptide hydrogel for versatile encapsulation and controlled release of growth factor therapeutics

A short bioinspired octapeptide, GV8, can self-assemble under mild conditions into biodegradable supramolecular physical hydrogels with high storage modulus and good biocompatibility. GV8 hydrogels can encapsulate both single or multiple macromolecular protein-based therapeutics in a simple one-pot formulation manner, making it a promising candidate to address challenges faced by existing synthetic polymer or peptide hydrogels with complex gelation and drug-encapsulation processes. Alongside its versatility, the hydrogel exhibits concentration-dependent storage modulus and controlled drug-release action. We demonstrate that GV8 hydrogels loaded with adipose-derived mesenchymal stem cells (ADMSC) secretome remain mechanically robust, and exhibit promising potential for wound healing applications by preserving secretome activity while maintaining a constant supply of ADMSC secretome to promote epithelial cell migration. Overall, our work highlights the potential of GV8 peptide hydrogel as a versatile and safe carrier for encapsulation and delivery of macromolecular therapeutics. STATEMENT OF SIGNIFICANCE: Supramolecular peptide hydrogels are a popular choice for protein-based macromolecular therapeutics delivery; however, despite the development of abundant hydrogel systems, several challenges limit their adaptability and practical applications. GV8 short peptide hydrogel circumvents these drawbacks and demonstrates the ability to function as a versatile growth factor (GF) encapsulant. It can encapsulate precise concentrations of complex adipose-derived mesenchymal stem cells secretome mixtures with a one-pot formulation approach and perform controlled release of GFs with preserved activity without compromising the self-assembly and mechanical properties of the hydrogel's supramolecular network. The significance of GV8 hydrogel lies in its gelation simplicity and versatility to encapsulate and deliver macromolecular therapeutics, thus representing a promising biomaterial for regenerative medicine applications.

A 3D physio-mimetic interpenetrating network-based platform to decode the pro and anti-tumorigenic properties of cancer-associated fibroblasts

Three-dimensional (3D) biomaterials with physiologically relevant and experimentally tractable biomechanical features are important platforms to advance our understanding of the influence of tissue mechanics in disease progression. Herein, an interpenetrating network (IPN) of collagen and alginate 3D culture system with tunable extracellular microstructure and mechanics is exploited as a tumor stroma proxy to study phenotypic plasticity of colorectal cancer-associated fibroblasts (CAF). In combination with Next Generation Sequencing (NGS) data analysis, we demonstrated that tuning the storage modulus of the IPN hydrogel between 49 and 419 Pa can trigger a reversible switch between an inflammatory (i-state, α-SMA^lowIL-6^high) and myofibroblastic (m-state, α-SMA^highIL-6^low) state in CAF that is dependent on the polymer network confinement effect and ROS-HIF1-α mechanotransduction signaling axis. Secretome from m-state CAF upregulated several epithelial-mesenchymal-transition (EMT) transcripts and induced robust scattering in DLD-1, HCT116, and SW480 human colorectal adenocarcinoma, while the EMT-inducing capacity is muted in i-state CAF, suggestive of an anti-tumorigenic role. Our findings were further validated through Gene Expression Profiling Interactive Analysis (GEPIA), which showed that cytokines secreted at higher levels by i-state CAF are correlated (p < 0.05) with good overall colorectal cancer patient survival. Therefore, 3D network density and spatial cellular confinement are critical biophysical determinants that can profoundly influence CAF states, paracrine signaling, and EMT-inducing potential. STATEMENT OF SIGNIFICANCE: The communication between cancer cells and cancer-associated fibroblasts (CAF) contributes to tumor metastasis. CAF represent a diverse population of cellular subsets that can either promote or restrain tumor progression. However, the origin and cause of CAF heterogeneity remain elusive, limiting CAF-directed therapies for clinical use. We studied the dynamic phenotypes of CAF using a 3D physio-mimetic culture platform consisting of an interpenetrating collagen-alginate network. Combined with transcriptomic stratification and correlative analysis using cancer patient dataset, we showed phenotypic interconversion between inflammatory and myofibroblastic states, with anti- and pro-tumorigenic functions, in human colorectal CAF. This multidisciplinary study reveals the functional diversity of colorectal CAF caused by biophysical cues. The finding will influence the development of new CAF biomarkers and cancer therapies.

Mechano-regulation of vascular network formation without branches in 3D bioprinted cell-laden hydrogel constructs

Restoration of a wound is a common surgical procedure in clinic. Currently, the skin required for clinical use is taken from the patient's own body. However, it can be difficult to obtain enough skin sources for large-sized wounds and thus surgeons have started using commercial skin substitutes. The current commercial skin, which includes epidermis substitute, dermis substitute, and bilateral skin substitute, has been popularized in clinic. However, the application is limited by the occurrence of ischemia necrosis after transplantation. Recent studies suggest the use of pre-vascularized skin substitutes for wound healing is a promising area in the research field of skin tissue engineering. Pre-vascularization can be induced by changes in cultivation periods, exertion of mechanical stimuli, or coculture with endothelial cells and various factors. However, few methods could control the formation of vascular branches in engineering tissue in a self-assembly way. In this study, we use three-dimensional (3D) printing technology to confirm that a mechanical force can control the growth of blood vessels in the direction of mechanical stimulation with no branches, and that Yes-associated protein activity is involved in the regulatory progress. In vivo experiments verified that the blood vessels successfully function for blood circulation, and maintain the same direction. Results provide a theoretical basis for products of pre-vascularized skin tissues and other organs created by 3D bioprinting.

Hydrogel-based therapeutic angiogenesis: An alternative treatment strategy for critical limb ischemia

Critical limb ischemia (CLI) is the most severe clinical manifestation of peripheral arterial disease (PAD), resulting in the total or partial loss of limb function. Although the conventional treatment strategy of CLI (e.g., medical treatment and surgery) can improve blood perfusion and restore limb function, many patients are unsuitable for these strategies and they still face the threats of amputation or death. Therapeutic angiogenesis, as a potential solution for these problems, attempts to manipulate blood vessel growth in vivo for augment perfusion without the help of extra pharmaceutics and surgery. With the rise of interdisciplinary research, regenerative medicine strategies provide new possibilities for treating many clinical diseases. Hydrogel, as an excellent biocompatibility material, is an ideal candidate for delivering bioactive molecules and cells for therapeutic angiogenesis. Besides, hydrogel could precisely deliver, control release, and keep the bioactivity of cargos, making hydrogel-based therapeutic angiogenesis a new strategy for CLI therapy. In this review, we comprehensively discuss the approaches of hydrogel-based strategy for CLI treatment as well as their challenges, and future directions.

Direct and Label-Free Cell Status Monitoring of Spheroids and Microcarriers Using Microfluidic Impedance Cytometry

3D cellular spheroids/microcarriers (100 µm-1 mm) are widely used in biomanufacturing, and non-invasive biosensors are useful to monitor cell quality in bioprocesses. In this work, a novel microfluidic approach for label-free and continuous-flow monitoring of single spheroid/microcarrier (hydrogel and Cytodex) based on electrical impedance spectroscopy using co-planar Field's metal electrodes is reported. Through numerical simulation and experimental validation, two unique impedance signatures (|Z_LF | (60 kHz), |Z_HF | (1 MHz)) which are optimal for spheroid growth and viability monitoring are identified. Using a closed-loop recirculation system, it is demonstrated that |Z_LF | increases with breast cancer (MCF-7) spheroid biomass, while higher opacity (impedance ratio |Z_HF |/|Z_LF |) indicates cell death due to compromised cell membrane. Anti-cancer drug (paclitaxel)-treated spheroids also exhibit lower |Z_LF | with increased cell dissociation. Interestingly, impedance characterization of adipose-derived mesenchymal stem cell differentiation on Cytodex microcarriers reveals that adipogenic cells (higher intracellular lipid content) exhibit higher impedance than osteogenic cells (more conductive due to calcium ions) for both microcarriers and single cell level. Taken together, the developed platform offers great versatility for multi-parametric analysis of spheroids/microcarriers at high throughput (≈1 particle/s), and can be readily integrated into bioreactors for long-term and remote monitoring of biomass and cell quality.

Sustainable aquaculture side-streams derived hybrid biocomposite for bone tissue engineering

Despite being a rich source of bioactive compounds, the current exploitation of aquatic biomass is insufficient. Majority of the aquaculture industry side-streams are currently used for low-value purposes such as animal feed or composting material, with low economical returns. To maximize resource reuse and minimize waste generation, valorization efforts should be augmented with the aim to produce high-value products. Herein, we present a novel aquaculture wastes-derived multi-scale osteoconductive hybrid biocomposite that is composed of chemically crosslinked American bullfrog (Rana catesbeiana) skin-derived type I tropocollagen nanofibrils (~22.3 nm) network and functionalized with micronized (~1.6 μm) single-phase hydroxyapatite (HA) from discarded snakehead (Channa micropeltes) fish scales. The bioengineered construct is biocompatible, highly porous (>90%), and exhibits excellent osteoconductive properties, as indicated by robust adhesion and proliferation of human fetal osteoblastic 1.19 cell line (hFOB 1.19). Furthermore, increased expression level of osteo-related ALPL and BGLAP mRNA transcripts, as well as enhanced osteocalcin immunoreactivity and increasing Alizarin red S staining coverage on the hybrid biocomposite was observed over 21 days of culture. Collectively, the devised "waste-to-resource" platform represents a sustainable waste valorization strategy that is amendable for advanced bone repair and regeneration applications.

Osteogenic and Adipogenic Differentiation of Mesenchymal Stem Cells in Gelatin Solutions of Different Viscosities

Accumulating evidence indicates that stem cell fate can be regulated by mechanical properties of the extracellular matrix. Most studies have focused onthe influence of matrix elasticity and viscoelasticity on stem cell differentiation. However, how matrix viscosity affects stem cell differentiation has been overlooked. In this study, a biphasic gelatin solution/hydrogel system is used for 3D culture of human bone marrow-derived mesenchymal stem cells (MSCs) to investigate the influence of gelatin solution viscosity on simultaneous osteogenic and adipogenic differentiation at the same culture condition. Gelatin solution promotes cell proliferation, while its promotive effect decreases with the increase of viscosity. The influence of viscosity on osteogenic and adipogenic differentiation of MSCs shows opposite trends. A high-viscosity gelatin solution results in an increase of alkaline phosphatase (ALP) activity, calcium deposition, and expression of osteogenesis-related genes. On the other hand, in a low-viscosity gelatin solution, a lot of lipid vacuoles are formed and adipogenesis-related genes are highly expressed. The results indicate high viscosity is beneficial for osteogenic differentiation, while low viscosity is beneficial for adipogenic differentiation. These findings suggest the importance of matrix viscosity on stem cell differentiation in 3D microenvironments.

Mechanotransduction and Stiffness-Sensing: Mechanisms and Opportunities to Control Multiple Molecular Aspects of Cell Phenotype as a Design Cornerstone of Cell-Instructive Biomaterials for Articular Cartilage Repair

Since material stiffness controls many cell functions, we reviewed the currently available knowledge on stiffness sensing and elucidated what is known in the context of clinical and experimental articular cartilage (AC) repair. Remarkably, no stiffness information on the various biomaterials for clinical AC repair was accessible. Using mRNA expression profiles and morphology as surrogate markers of stiffness-related effects, we deduced that the various clinically available biomaterials control chondrocyte (CH) phenotype well, but not to equal extents, and only in non-degenerative settings. Ample evidence demonstrates that multiple molecular aspects of CH and mesenchymal stromal cell (MSC) phenotype are susceptible to material stiffness, because proliferation, migration, lineage determination, shape, cytoskeletal properties, expression profiles, cell surface receptor composition, integrin subunit expression, and nuclear shape and composition of CHs and/or MSCs are stiffness-regulated. Moreover, material stiffness modulates MSC immuno-modulatory and angiogenic properties, transforming growth factor beta 1 (TGF-β1)-induced lineage determination, and CH re-differentiation/de-differentiation, collagen type II fragment production, and TGF-β1- and interleukin 1 beta (IL-1β)-induced changes in cell stiffness and traction force. We then integrated the available molecular signaling data into a stiffness-regulated CH phenotype model. Overall, we recommend using material stiffness for controlling cell phenotype, as this would be a promising design cornerstone for novel future-oriented, cell-instructive biomaterials for clinical high-quality AC repair tissue.

Promotion of Proangiogenic Secretome from Mesenchymal Stromal Cells via Hierarchically Structured Biodegradable Microcarriers

Adipose-derived mesenchymal stromal cells (AdMSC) release numerous soluble factors capable of stimulating angiogenesis. Improved methods for delivering these cells to maximize their potency are now sought that ideally they retain viable cells in the target tissue while promoting the secretion of angiogenic factors. Substrate surface topography is a parameter that can be used to manipulate the behavior of AdMSC but challenges exist with translating this parameter into materials compatible with minimally invasive delivery into tissues for in situ delivery of the angiogenic secretome. The current study investigates three compositions of hierarchically structured, porous biodegradable microcarriers for the culture of AdMSC and the influence of their surface topographies on the angiogenic secretome. All three compositions perform well as cell microcarriers in xeno-free conditions. The attached AdMSC retain their capacity for subsequent trilineage differentiation. The secretome of AdMSC attached to the microcarriers consists of multiple proangiogenic factors, including significantly elevated levels of vascular endothelial growth factor, which stimulates angiogenesis in vitro. The unique properties of hierarchically structured, porous biodegradable microcarriers investigated in this study offer a radically transformative approach for achieving targeted in vivo delivery of AdMSC and enhancing the potency of their proangiogenic activity to induce neovascularization in ischemic tissue.

Mechanical Cues Regulating Proangiogenic Potential of Human Mesenchymal Stem Cells through YAP-Mediated Mechanosensing

Stem cells secrete trophic factors that induce angiogenesis. These soluble factors are promising candidates for stem cell-based therapies, especially for cardiovascular diseases. Mechanical stimuli and biophysical factors presented in the stem cell microenvironment play important roles in guiding their behaviors. However, the complex interplay and precise role of these cues in directing pro-angiogenic signaling remain unclear. Here, a platform is designed using gelatin methacryloyl hydrogels with tunable rigidity and a dynamic mechanical compression bioreactor to evaluate the influence of matrix rigidity and mechanical stimuli on the secretion of pro-angiogenic factors from human mesenchymal stem cells (hMSCs). Cells cultured in matrices mimicking mechanical elasticity of bone tissues in vivo show elevated secretion of vascular endothelial growth factor (VEGF), one of representative signaling proteins promoting angiogenesis, as well as increased vascularization of human umbilical vein endothelial cells (HUVECs) with a supplement of conditioned media from hMSCs cultured across different conditions. When hMSCs are cultured in matrices stimulated with a range of cyclic compressions, increased VEGF secretion is observed with increasing mechanical strains, which is also in line with the enhanced tubulogenesis of HUVECs. Moreover, it is demonstrated that matrix stiffness and cyclic compression modulate secretion of pro-angiogenic molecules from hMSCs through yes-associated protein activity.

Adaptive Liquid Interfacially Assembled Protein Nanosheets for Guiding Mesenchymal Stem Cell Fate

There is a growing interest in the development of dynamic adaptive biomaterials for regulation of cellular functions. However, existing materials are limited to two-state switching of the presentation and removal of cell-adhesive bioactive motifs that cannot emulate the native extracellular matrix (ECM) in vivo with continuously adjustable characteristics. Here, tunable adaptive materials composed of a protein monolayer assembled at a liquid-liquid interface are demonstrated, which adapt dynamically to cell traction forces. An ultrastructure transition from protein monolayer to hierarchical fiber occurs through interfacial jamming. Elongated fibronectin fibers promote formation of elongated focal adhesion structures, increase focal adhesion kinase activation, and enhance neuronal differentiation of stem cells. Cell traction force results in spatial rearrangement of ECM proteins, which feeds back to alter stem cell fate. The reported biomimetic adaptive liquid interface enables dynamic control of stem cell behavior and has potential translational applications.