Premature induction of hypertrophy during in vitro chondrogenesis of human mesenchymal stem cells correlates with calcification and vascular invasion after ectopic transplantation in SCID mice

Effects of Germanium embedded fabric on the chondrogenic differentiation of adipose derived stem cells

Osteoarthritis (OA) is a clinical state which is identified by the degeneration of articular cartilage. OA is a common condition (>500 millions of people affected worldwide), whose frequency is anticipated to continue to rise (> 110 % increase worldwide since 2019). The treatment for early-stage OA is based on a combination of therapeutic approaches, which can include regenerative medicine based on Adipose Derived Stem Cells (ADSCs). Germanium embedded Incrediwear® functional Cred40 fabric has been shown to have positive effects on OA clinically and is envisaged to give encouraging effects also on tissue regeneration. Still, the biological mechanisms underlying this therapeutic modality have not yet been fully defined. We tested the hypothesis that Germanium-embedded Incrediwear® functional Cred40 fabric could enhance chondrogenic differentiation. To this purpose, we applied Incrediwear® to human adipose-derived stem cells (hADSCs) induced to chondrogenic differentiation in vitro. Chondrogenic markers (ACAN, SOX9, RUNX2, COL2A1, COL10A1) were quantified following 21 days of treatment. We also assessed extracellular matrix (ECM) deposition (specifically Collagen and glycosaminoglycans (GAGs)) using Alcian Blue and Sirius Red staining. Here, we provide pilot data to demonstrate that Germanium-embedded Incrediwear® functional Cred40 fabric can enhance hADSCs chondrogenic differentiation and maturity and potentially induce events of cartilage regeneration.

Time- and cell-specific activation of BMP signaling restrains chondrocyte hypertrophy

Stem cell therapies for degenerative cartilage disease are limited by an incomplete understanding of hyaline cartilage formation and maintenance. Human bone marrow stromal cells/skeletal stem cells (hBMSCs/SSCs) produce stable hyaline cartilage when attached to hyaluronic acid-coated fibrin microbeads (HyA-FMBs), yet the mechanism remains unclear. In vitro, hBMSC/SSC/HyA-FMB organoids exhibited reduced BMP signaling early in chondrogenic differentiation, followed by restoration of BMP signaling in chondrogenic IGFBP5 + /MGP + cells. Subsequently, human-induced pluripotent stem cell (hiPSC)-derived sclerotome cells were established (BMP inhibition) and then treated with transforming growth factor β (TGF-β) -/+ BMP2 and growth differentiation factor 5 (GDF5) (BMP signaling activation). TGF-β alone elicited a weak chondrogenic response, but TGF-β/BMP2/GDF5 led to delamination of SOX9 + aggregates (chondrospheroids) with high expression of COL2A1, ACAN, and PRG4 and minimal expression of COL10A1 and ALP in vitro. While transplanted hBMSCs/SSCs/HyA-FMBs did not heal articular cartilage defects in immunocompromised rodents, chondrospheroid-derived cells/HyA-FMBs formed non-hypertrophic cartilage that persisted until at least 5 months in vivo.

Cause and chondroprotective effects of prostaglandin E2 secretion during mesenchymal stromal cell chondrogenesis

Mesenchymal stromal cells (MSCs) that are promising for cartilage tissue engineering secrete high amounts of prostaglandin E2 (PGE2), an immunoactive mediator involved in endochondral bone development. This study aimed to identify drivers of PGE2 and its role in the inadvertent MSC misdifferentiation into hypertrophic chondrocytes. PGE2 release, which rose in the first three weeks of MSC chondrogenesis, was jointly stimulated by endogenous BMP, WNT, and hedgehog activity that supported the exogenous stimulation by TGF-β1 and insulin to overcome the PGE2 inhibition by dexamethasone. Experiments with PGE2 treatment or the inhibitor celecoxib or specific receptor antagonists demonstrated that PGE2, although driven by prohypertrophic signals, exerted broad autocrine antihypertrophic effects. This chondroprotective effect makes PGE2 not only a promising option for future combinatorial approaches to direct MSC tissue engineering approaches into chondral instead of endochondral development but could potentially have implications for the use of COX-2-selective inhibitors in osteoarthritis pain management.

Electrical Stimulation of Mesenchymal Stem Cells as a Tool for Proliferation and Differentiation in Cartilage Tissue Engineering: A Scaffold-Based Approach

Electrical stimulation (ES) is a widely discussed topic in the field of cartilage tissue engineering due to its ability to induce chondrogenic differentiation (CD) and proliferation. It shows promise as a potential therapy for osteoarthritis (OA). In this study, we stimulated mesenchymal stem cells (MSCs) incorporated into collagen hydrogel (CH) scaffolds, consisting of approximately 500,000 cells each, for 1 h per day using a 2.5 Vpp (119 mV/mm) 8 Hz sinusoidal signal. We compared the cell count, morphology, and CD on days 4, 7, and 10. The results indicate proliferation, with an increase ranging from 1.86 to 9.5-fold, particularly on day 7. Additionally, signs of CD were observed. The stimulated cells had a higher volume, while the stimulated scaffolds showed shrinkage. In the ES groups, up-regulation of collagen type 2 and aggrecan was found. In contrast, SOX9 was up-regulated in the control group, and MMP13 showed a strong up-regulation, indicating cell stress. In addition to lower stress levels, the control groups also showed a more spheroidic shape. Overall, scaffold-based ES has the potential to achieve multiple outcomes. However, finding the appropriate stimulation pattern is crucial for achieving successful chondrogenesis.

Craniofacial chondrogenesis in organoids from human stem cell-derived neural crest cells

Knowledge of cell signaling pathways that drive human neural crest differentiation into craniofacial chondrocytes is incomplete, yet essential for using stem cells to regenerate craniomaxillofacial structures. To accelerate translational progress, we developed a differentiation protocol that generated self-organizing craniofacial cartilage organoids from human embryonic stem cell-derived neural crest stem cells. Histological staining of cartilage organoids revealed tissue architecture and staining typical of elastic cartilage. Protein and post-translational modification (PTM) mass spectrometry and snRNA-seq data showed that chondrocyte organoids expressed robust levels of cartilage extracellular matrix (ECM) components: many collagens, aggrecan, perlecan, proteoglycans, and elastic fibers. We identified two populations of chondroprogenitor cells, mesenchyme cells and nascent chondrocytes, and the growth factors involved in paracrine signaling between them. We show that ECM components secreted by chondrocytes not only create a structurally resilient matrix that defines cartilage, but also play a pivotal autocrine cell signaling role in determining chondrocyte fate.

Mesenchymal stromal cell chondrogenesis under ALK1/2/3-specific BMP inhibition: a revision of the prohypertrophic signalling network concept

BACKGROUND

In vitro chondrogenesis of mesenchymal stromal cells (MSCs) driven by the essential chondro-inducer transforming growth factor (TGF)-β is instable and yields undesired hypertrophic cartilage predisposed to bone formation in vivo. TGF-β can non-canonically activate bone morphogenetic protein-associated ALK1/2/3 receptors. These have been accused of driving hypertrophic MSC misdifferentiation, but data remained conflicting. We here tested the antihypertrophic capacity of two highly specific ALK1/2/3 inhibitors - compound A (CompA) and LDN-212854 (LDN21) - in order to reveal potential prohypertrophic contributions of these BMP/non-canonical TGF-β receptors during MSC in vitro chondrogenesis.

METHODS

Standard chondrogenic pellet cultures of human bone marrow-derived MSCs were treated with TGF-β and CompA (500 nM) or LDN21 (500 nM). Daily 6-hour pulses of parathyroid hormone-related peptide (PTHrP[1-34], 2.5 nM, from day 7) served as potent antihypertrophic control treatment. Day 28 samples were subcutaneously implanted into immunodeficient mice.

RESULTS

All groups underwent strong chondrogenesis, but GAG/DNA deposition and ACAN expression were slightly but significantly reduced by ALK inhibition compared to solvent controls along with a mild decrease of the hypertrophy markers IHH-, SPP1-mRNA, and Alkaline phosphatase (ALP) activity. When corrected for the degree of chondrogenesis (COL2A1 expression), only pulsed PTHrP but not ALK1/2/3 inhibition qualified as antihypertrophic treatment. In vivo, all subcutaneous cartilaginous implants mineralized within 8 weeks, but PTHrP pretreated samples formed less bone and attracted significantly less haematopoietic marrow than ALK1/2/3 inhibitor groups.

CONCLUSIONS

Overall, our data show that BMP-ALK1/2/3 inhibition cannot program mesenchymal stromal cells toward stable chondrogenesis. BMP-ALK1/2/3 signalling is no driver of hypertrophic MSC misdifferentiation and BMP receptor induction is not an adverse prohypertrophic side effect of TGF-β that leads to endochondral MSC misdifferentiation. Instead, the prohypertrophic network comprises misregulated PTHrP/hedgehog signalling and WNT activity, and a potential contribution of TGF-β-ALK4/5-mediated SMAD1/5/9 signalling should be further investigated to decide about its postulated prohypertrophic activity. This will help to successfully engineer cartilage replacement tissues from MSCs in vitro and translate these into clinical cartilage regenerative therapies.

Basement membrane extract potentiates the endochondral ossification phenotype of bone marrow-derived mesenchymal stem cell-based cartilage organoids

Endochondral ossification is a developmental process in the skeletal system and bone marrow of vertebrates. During endochondral ossification, primitive cartilaginous anlages derived from mesenchymal stem cells (MSCs) undergo vascular invasion and ossification. In vitro regeneration of endochondral ossification is beneficial for research on the skeletal system and bone marrow development as well as their clinical aspects. However, to achieve the regeneration of endochondral ossification, a stem cell-based artificial cartilage (cartilage organoid, Cart-Org) that possesses an endochondral ossification phenotype is required. Here, we modified a conventional 3D culture method to create stem cell-based Cart-Org by mixing it with a basement membrane extract (BME) and further characterized its chondrogenic and ossification properties. BME enlarged and matured the bone marrow MSC-based Cart-Orgs without any shape abnormalities. Histological analysis using Alcian blue staining showed that the production of cartilaginous extracellular matrices was enhanced in Cart-Org treated with BME. Transcriptome analysis using RNA sequencing revealed that BME altered the gene expression pattern of Cart-Org to a dominant chondrogenic state. BME triggered the activation of the SMAD pathway and inhibition of the NK-κB pathway, which resulted in the upregulation of SOX9, COL2A1, and ACAN in Cart-Org. BME also facilitated the upregulation of genes associated with hypertrophic chondrocytes (IHH, PTH1R, and COL10A1) and ossification (SP7, ALPL, and MMP13). Our findings indicate that BME promotes cartilaginous maturation and further ossification of bone marrow MSC-based Cart-Org, suggesting that Cart-Org treated with BME possesses the phenotype of endochondral ossification.

Regulation of Oxygen Tension as a Strategy to Control Chondrocytic Phenotype for Cartilage Tissue Engineering and Regeneration

Cartilage defects and osteoarthritis are health problems which are major burdens on health care systems globally, especially in aging populations. Cartilage is a vulnerable tissue, which generally faces a progressive degenerative process when injured. This makes it the 11th most common cause of global disability. Conservative methods are used to treat the initial phases of the illness, while orthopedic management is the method used for more progressed phases. These include, for instance, arthroscopic shaving, microfracturing and mosaicplasty, and joint replacement as the final treatment. Cell-based implantation methods have also been developed. Despite reports of successful treatments, they often suffer from the non-optimal nature of chondrocyte phenotype in the repair tissue. Thus, improved strategies to control the phenotype of the regenerating cells are needed. Avascular tissue cartilage relies on diffusion for nutrients acquisition and the removal of metabolic waste products. A low oxygen content is also present in cartilage, and the chondrocytes are, in fact, well adapted to it. Therefore, this raises an idea that the regulation of oxygen tension could be a strategy to control the chondrocyte phenotype expression, important in cartilage tissue for regenerative purposes. This narrative review discusses the aspects related to oxygen tension in the metabolism and regulation of articular and growth plate chondrocytes and progenitor cell phenotypes, and the role of some microenvironmental factors as regulators of chondrocytes.

JD-312 - A novel small molecule that facilitates cartilage repair and alleviates osteoarthritis progression

Background

The chondrogenic differentiation of mesenchymal stem cells (MSCs) to enhance cartilage repair and regeneration is a promising strategy to alleviate osteoarthritis (OA) progression.

Method

The potency of JD-312 in inducing chondrogenic differentiation of MSCs was assessed and verified. The efficacy of JD-312-treated MSCs was evaluated using a Sprague-Dawley rat DMM model. Additionally, the capacity of JD-312 to successfully recruit bone marrow-derived mesenchymal stem cells (BMSCs) for the treatment of OA in vitro was confirmed via intra-articular injection. The repair status of the articular cartilage was analyzed in vivo through histological examination.

Result

In this study, we identify JD-312 as a novel non-toxic small molecule that can promote chondrogenic differentiation in human umbilical cord-derived MSCs (hUCMSCs) and human bone marrow MSCS (hBMSCs) in vitro. We also show that transient differentiation of MSCs with JD-312 prior to in vivo administration remarkably improves the regeneration of cartilage and promotes Col2a1 and Acan expression in rat models of DMM, in comparison to kartogenin (KGN) pre-treatment or MSCs alone. Furthermore, direct intra-articular injection of JD-312 in murine model of OA showed reduced loss of articular cartilage and improved pain parameters. Lastly, we identified that the effects of JD-312 are at least in part mediated via upregulation of genes associated with the focal adhesion, PI3K-Akt signaling and the ECM-receptor interaction pathways, and specifically cartilage oligomeric matrix protein (COMP) may play a vital role.

Conclusion

Our study demonstrated that JD-312 showed encouraging repair effects for OA in vivo.

The translational potential of this article

Together, our findings demonstrate that JD-312 is a promising new therapeutic molecule for cartilage regeneration with clinical potential.

GuiLu-ErXian Glue extract promotes mesenchymal stem cells (MSC)-Induced chondrogenesis via exosomes release and delays aging in the MSC senescence process

ETHNOPHARMACOLOGICAL RELEVANCE

The treatment of osteoarthritis (OA) patients is a challenging problem. Mesenchymal stem cells (MSCs) are multipotent cells and play key roles in regenerative medicine for cartilage degeneration. GuiLu-ErXian Glue (GLEXG) is an herbal remedy widely used in traditional Chinese medicine to treat joint pain and disability in elderly OA patients. However, the mechanisms of how GLEXG affects MSCs-induced chondrogensis remains to be elucidated.

AIM OF THE STUDY

The aim of this study was to investigate the effects of GLEXG on MSC-derived chondrogenesis, both in vitro and in vivo and its potential mechanisms.

METHODS

Using human MSC (hMSCs) as in vitro model, the effects of HPLC-profiled GLEXG water extract on chondrogenic differentiation were investigated by 3D spheroid cultures under chondrogenesis-inducing medium (CIM) condition. The chondrogenesis process was evaluated by measuring the sphere sizes, chondrogenesis-related genes expression by reverse transcription real-time PCR that targeted type II/X collagens, SOX9, aggrecan, and protein expression by immunostaining. Anti-TGF-β1 neutralization antibody was used for mechanistic study. Mono-iodoacetate (MIA) induced OA joint was used to evaluate the effects of GLEXG on in vivo model. MSCs-derived exosomes were purified for proteomics study and senescence process was evaluated by cumulative population doublings and senescence-associated β-Galactosidase staining.

RESULTS

The results showed that GLEXG enhanced hMSCs chondrogenesis and upregulated RNA expression of type II/X collagen, SOX9 and aggrecan at 0.1 μg/mL, 0.3 μg/mL in vitro. In vivo, GLEXG at the dose of 0.3 μg intraarticular (i.a.) injection rescued the MIA-induced cartilage defect. Proteomics and ingenuity pathway analysis obtained from MSCs-released exosomes suggested that senescence pathway was less activated in GLEXG group than in vehicle group. Besides, GLEXG was able to increase cumulative population doubling and delayed hMSCs senescence process after four passages in cultures.

CONCLUSION

we conclude that GLEXG promotes in vitro MSC-induced chondrogenesis possibly via exosomes release and delays aging in the MSC senescence process and that treatment with GLEXG (0.3 μg, i.a.) rescued cartilage defects in rat OA knee model.

Recent advances in 3D bioprinted cartilage-mimicking constructs for applications in tissue engineering

Human cartilage tissue can be categorized into three types: hyaline cartilage, elastic cartilage and fibrocartilage. Each type of cartilage tissue possesses unique properties and functions, which presents a significant challenge for the regeneration and repair of damaged tissue. Bionics is a discipline in which humans study and imitate nature. A bionic strategy based on comprehensive knowledge of the anatomy and histology of human cartilage is expected to contribute to fundamental study of core elements of tissue repair. Moreover, as a novel tissue-engineered technology, 3D bioprinting has the distinctive advantage of the rapid and precise construction of targeted models. Thus, by selecting suitable materials, cells and cytokines, and by leveraging advanced printing technology and bionic concepts, it becomes possible to simultaneously realize multiple beneficial properties and achieve improved tissue repair. This article provides an overview of key elements involved in the combination of 3D bioprinting and bionic strategies, with a particular focus on recent advances in mimicking different types of cartilage tissue.

Preclinical Studies and Clinical Trials on Cell-Based Treatments for Meniscus Regeneration

This study aims at performing a thorough review of cell-based treatment strategies for meniscus regeneration in preclinical and clinical studies. The PubMed, Embase, and Web of Science databases were searched for relevant studies (both preclinical and clinical) published from the time of database construction to December 2022. Data related to cell-based therapies for in situ regeneration of the meniscus were extracted independently by two researchers. Assessment of risk of bias was performed according to the Cochrane Handbook for Systematic Reviews of Interventions. Statistical analyses based on the classification of different treatment strategies were performed. A total of 5730 articles were retrieved, of which 72 preclinical studies and 6 clinical studies were included in this review. Mesenchymal stem cells (MSCs), especially bone marrow MSCs (BMSCs), were the most commonly used cell type. Among preclinical studies, rabbit was the most commonly used animal species, partial meniscectomy was the most commonly adopted injury pattern, and 12 weeks was the most frequently chosen final time point for assessing repair outcomes. A range of natural and synthetic materials were used to aid cell delivery as scaffolds, hydrogels, or other morphologies. In clinical trials, there was large variation in the dose of cells, ranging from 16 × 106 to 150 × 106 cells with an average of 41.52 × 106 cells. The selection of treatment strategy for meniscus repair should be based on the nature of the injury. Cell-based therapies incorporating various "combination" strategies such as co-culture, composite materials, and extra stimulation may offer greater promise than single strategies for effective meniscal tissue regeneration, restoring natural meniscal anisotropy, and eventually achieving clinical translation. Impact Statement This review provides an up-to-date and comprehensive overview of preclinical and clinical studies that tested cell-based treatments for meniscus regeneration. It presents novel perspectives on studies published in the past 30 years, giving consideration to the cell sources and dose selection, delivery methods, extra stimulation, animal models and injury patterns, timing of outcome assessment, and histological and biomechanical outcomes, as well as a summary of findings for individual studies. These unique insights will help to shape future research on the repair of meniscus lesions and inform the clinical translation of new cell-based tissue engineering strategies.

Bioprinting of scaled-up meniscal grafts by spatially patterning phenotypically distinct meniscus progenitor cells within melt electrowritten scaffolds

Meniscus injuries are a common problem in orthopedic medicine and are associated with a significantly increased risk of developing osteoarthritis. While developments have been made in the field of meniscus regeneration, the engineering of cell-laden constructs that mimic the complex structure, composition and biomechanics of the native tissue remains a significant challenge. This can be linked to the use of cells that are not phenotypically representative of the different zones of the meniscus, and an inability to direct the spatial organization of engineered meniscal tissues. In this study we investigated the potential of zone-specific meniscus progenitor cells (MPCs) to generate functional meniscal tissue following their deposition into melt electrowritten (MEW) scaffolds. We first confirmed that fibronectin selected MPCs from the inner and outer regions of the meniscus maintain their differentiation capacity with prolonged monolayer expansion, opening their use within advanced biofabrication strategies. By depositing MPCs within MEW scaffolds with elongated pore shapes, which functioned as physical boundaries to direct cell growth and extracellular matrix production, we were able to bioprint anisotropic fibrocartilaginous tissues with preferentially aligned collagen networks. Furthermore, by using MPCs isolated from the inner (iMPCs) and outer (oMPCs) zone of the meniscus, we were able to bioprint phenotypically distinct constructs mimicking aspects of the native tissue. An iterative MEW process was then implemented to print scaffolds with a similar wedged-shaped profile to that of the native meniscus, into which we deposited iMPCs and oMPCs in a spatially controlled manner. This process allowed us to engineer sulfated glycosaminoglycan and collagen rich constructs mimicking the geometry of the meniscus, with MPCs generating a more fibrocartilage-like tissue compared to the mesenchymal stromal/stem cells. Taken together, these results demonstrate how the convergence of emerging biofabrication platforms with tissue-specific progenitor cells can enable the engineering of complex tissues such as the meniscus.

Converse modulation of Wnt/β-catenin signaling during expansion and differentiation phases of Infrapatellar fat pad-derived MSCs for improved engineering of hyaline cartilage

Mesenchymal stem cells (MSCs) are potential candidates in cell-based therapy for cartilage repair and regeneration. However, during chondrogenic differentiation, MSCs undergo undesirable hypertrophic maturation. This poses a risk of ossification in the neo-tissue formed that eventually impedes the clinical use of MSCs for cartilage repair. TGF-β is a potent growth factor used for chondrogenic differentiation of MSCs, however, its role in hypertrophy remains ambiguous. In the present work, we decipher that TGF-β activates Wnt/β-catenin signaling through SMAD3 and increases the propensity of Infrapatellar fat pad derived MSCs (IFP-MSCs) towards hypertrophy. Notably, inhibiting TGF-β induced Wnt/β-catenin signaling suppresses hypertrophic progression and enhances chondrogenic ability of IFP-MSCs in plasma hydrogels. Additionally, we demonstrate that activating Wnt signaling during expansion phase, promotes proliferation and reduces senescence, while improving stemness of IFP-MSCs. Thus, conversely modulating Wnt signaling in vitro during expansion and differentiation phases generates hyaline-like cartilage with minimal hypertrophy. Importantly, pre-treatment of IFP-MSCs encapsulated in plasma hydrogel with Wnt modulators followed by subcutaneous implantation in nude mice resulted in formation of a cartilage tissue with negligible calcification. Overall, this study provides technological advancement on targeting Wnt/β-catenin pathway in a 3D scaffold, while maintaining the standard chondro-induction protocol to overcome the challenges associated with the clinical use of MSCs to engineer hyaline cartilage.

Bone Regeneration in a Large Animal Model Featuring a Modular Off-the-Shelf Soft Callus Mimetic

Implantation of engineered cartilage with soft callus features triggers remodeling to bone tissue via endochondral bone regeneration (EBR). Thus far, EBR has not progressed to the level of large animals on the axis of clinical translation. Herein, the feasibility of EBR is aimed for a critical-sized defect in a large animal model. Chondrogenesis is first induced in goat-derived multipotent mesenchymal stromal cells (MSCs) by fine-tuning the cellular differentiation process. Through a unique devitalization process, two off-the-shelf constructs aimed to recapitulate the different stages of the transient cartilaginous soft callus template in EBR are generated. To evaluate bone regeneration, the materials are implanted in an adapted bilateral iliac crest defect model in goats, featuring a novel titanium star-shaped spacer. After 3 months, the group at the more advanced differentiation stage shows remarkable regenerative capacity, with comparable amounts of bone regeneration as the autograft group. In contrast, while the biomaterial mimicking the earlier stages of chondrogenesis shows improved regeneration compared to the negative controls, this is subpar compared to the more advanced material. Concluding, EBR is attainable in large animals with a soft callus mimetic material that leads to fast conversion into centimeter-scale bone, which prospects successful implementation in the human clinics.

Complex deformation of cartilage micropellets following mechanical stimulation promotes chondrocyte gene expression

BACKGROUND

Articular cartilage (AC)'s main function is to resist to a stressful mechanical environment, and chondrocytes are responding to mechanical stress for the development and homeostasis of this tissue. However, current knowledge on processes involved in response to mechanical stimulation is still limited. These mechanisms are commonly investigated in engineered cartilage models where the chondrocytes are included in an exogeneous biomaterial different from their natural extracellular matrix. The aim of the present study is to better understand the impact of mechanical stimulation on mesenchymal stromal cells (MSCs)-derived chondrocytes generated in their own extracellular matrix.

METHODS

A fluidic custom-made device was used for the mechanical stimulation of cartilage micropellets obtained from human MSCs by culture in a chondrogenic medium for 21 days. Six micropellets were positioned into the conical wells of the device chamber and stimulated with different signals of positive pressure (amplitude, frequency and duration). A camera was used to record the sinking of each micropellet into their cone, and micropellet deformation was analyzed using a finite element model. Micropellets were harvested at different time points after stimulation for RT-qPCR and histology analysis.

RESULTS

Moderate micropellet deformation was observed during stimulation with square pressure signals as mean von Mises strains between 6.39 and 14.35% were estimated for amplitudes of 1.75-14 kPa superimposed on a base pressure of 50% of the amplitude. The compression, tension and shear observed during deformation did not alter micropellet microstructure as shown by histological staining. A rapid and transient increase in the expression of chondrocyte markers (SOX9, AGG and COL2B) was measured after a single 30-min stimulation with a square pressure signal of 3.5 kPa amplitude superimposed on a minimum pressure of 1.75 kPa, at 1 Hz. A small change of 1% of cyclical deformations when using a square pressure signal instead of a constant pressure signal induced a fold change of 2 to 3 of chondrogenic gene expression. Moreover, the expression of fibrocartilage (COL I) or hypertrophic cartilage (COL X, MMP13 and ADAMTS5) was not significantly regulated, except for COL X.

CONCLUSIONS

Our data demonstrate that the dynamic deformation of cartilage micropellets by fluidic-based compression modulates the expression of chondrocyte genes responsible for the production of a cartilage-like extracellular matrix. This lays the foundations for further investigating the chondrocyte mechanobiology and the cartilage growth under mechanical stimulation.

Suppressing Chondrocyte Hypertrophy to Build Better Cartilage

Current clinical strategies for restoring cartilage defects do not adequately consider taking the necessary steps to prevent the formation of hypertrophic tissue at injury sites. Chondrocyte hypertrophy inevitably causes both macroscopic and microscopic level changes in cartilage, resulting in adverse long-term outcomes following attempted restoration. Repairing/restoring articular cartilage while minimizing the risk of hypertrophic neo tissue formation represents an unmet clinical challenge. Previous investigations have extensively identified and characterized the biological mechanisms that regulate cartilage hypertrophy with preclinical studies now beginning to leverage this knowledge to help build better cartilage. In this comprehensive article, we will provide a summary of these biological mechanisms and systematically review the most cutting-edge strategies for circumventing this pathological hallmark of osteoarthritis.

Inverse Regulation of Cartilage Neogenesis at Physiologically Relevant Calcium Conditions by Human Articular Chondrocytes and Mesenchymal Stromal Cells

Elaborate bioreactor cultivation or expensive growth factor supplementation can enhance extracellular matrix production in engineered neocartilage to provide sufficient mechanical resistance. We here investigated whether raising extracellular calcium levels in chondrogenic cultures to physiologically relevant levels would provide a simple and inexpensive alternative to enhance cartilage neogenesis from human articular chondrocytes (AC) or bone marrow-derived mesenchymal stromal cells (BMSC). Interestingly, AC and BMSC-derived chondrocytes showed an opposite response to a calcium increase from 1.8 mM to 8 mM by which glycosaminoglycan (GAG) and collagen type II production were elevated during BMSC chondrogenesis but depressed in AC, leading to two-fold higher GAG/DNA values in BMSC-based neocartilage compared to the AC group. According to control treatments with Mg²⁺ or sucrose, these effects were specific for CaCl₂ rather than divalent cations or osmolarity. Importantly, undesired pro-hypertrophic traits were not stimulated by calcium treatment. Specific induction of PTHrP mRNA and protein by 8.0mM calcium only in AC, along with negative effects of recombinant PTHrP_1-34 on cartilage matrix production, suggested that the PTHrP pathway contributed to the detrimental effects in AC-based neocartilage. Altogether, raising extracellular calcium levels was discovered as a novel, simple and inexpensive stimulator for BMSC-based cartilage neogenesis without the need for special bioreactors, whereas such conditions should be avoided for AC.

Interferon-Gamma Increases the Immune Modulation of Umbilical Cord-Derived Mesenchymal Stem Cells but Decreases Their Chondrogenic Potential

INTRODUCTION

The pro-inflammatory cytokine interferon-gamma (IFN-γ) is reported to be an agent that boosts the immune modulation of mesenchymal stem cells (MSCs). However, the effects of IFN-γ on the chondrogenic potential of treated MSCs have not been evaluated in depth. This study aimed to evaluate the effects of IFN-γ on the immune modulation and chondrogenic potential of human umbilical cord-derived MSCs (hUC-MSCs).

METHODS

UC-MSCs were isolated and expanded following published protocols. They were characterized as MSCs before their use in further experiments. The UC-MSCs were treated with IFN-γ at 10 ng/mL for 48 h. Changes in phenotype were investigated based on changes in MSC markers, immunomodulatory genes (TGF-β, IL-4, and IDO) for immune modulation, and cartilage-related genes during the induction of differentiation (Col1a2, Col2a1, Sox9, Runx2, and Acan) for chondrogenic potential.

RESULTS

IFN-γ-treated UC-MSCs maintained MSC markers and exhibited decreased expression of transcriptional regulatory factors in chondrogenesis (Sox9 and Runx2) and the extracellular matrix-specific genes Col1a2 and Acan but not Col2a1 compared to non-treated cells (p < 0.05). Furthermore, the immunomodulatory capability of IFN-γ-treated UC-MSCs was clearly revealed through their increased expression of IDO and IL-4 and decreased expression of TGF-β compared to non-treated cells (p < 0.05).

CONCLUSION

This study demonstrated that UC-MSCs treated with IFN-γ at 10 ng/mL had reduced expression of chondrocyte-specific genes; however, they maintained multi-lineage differentiation and exhibited immunomodulatory properties.

In Vitro Mineralisation of Tissue-Engineered Cartilage Reduces Endothelial Cell Migration, Proliferation and Tube Formation

Tissue engineering bone via endochondral ossification requires the generation of a cartilage template which undergoes vascularisation and remodelling. While this is a promising route for bone repair, achieving effective cartilage vascularisation remains a challenge. Here, we investigated how mineralisation of tissue-engineered cartilage affects its pro-angiogenic potential. To generate in vitro mineralised cartilage, human mesenchymal stromal cell (hMSC)-derived chondrogenic pellets were treated with β-glycerophosphate (BGP). After optimising this approach, we characterised the changes in matrix components and pro-angiogenic factors by gene expression analysis, histology and ELISA. Human umbilical vein endothelial cells (HUVECs) were exposed to pellet-derived conditioned media, and migration, proliferation and tube formation were assessed. We established a reliable strategy to induce in vitro cartilage mineralisation, whereby hMSC pellets are chondrogenically primed with TGF-β for 2 weeks and BGP is added from week 2 of culture. Cartilage mineralisation determines loss of glycosaminoglycans, reduced expression but not protein abundance of collagen II and X, and decreased VEGFA production. Finally, the conditioned medium from mineralised pellets showed a reduced ability to stimulate endothelial cell migration, proliferation and tube formation. The pro-angiogenic potential of transient cartilage is thus stage-dependent, and this aspect must be carefully considered in the design of bone tissue engineering strategies.

An assessment of the response of human MSCs to hydrostatic pressure in environments supportive of differential chondrogenesis

Mechanical stimulation can modulate the chondrogenic differentiation of stem/progenitor cells and potentially benefit tissue engineering (TE) of functional articular cartilage (AC). Mechanical cues like hydrostatic pressure (HP) are often applied to cell-laden scaffolds, with little optimization of other key parameters (e.g. cell density, biomaterial properties) known to effect lineage commitment. In this study, we first sought to establish cell seeding densities and fibrin concentrations supportive of robust chondrogenesis of human mesenchymal stem cells (hMSCs). High cell densities (15*10⁶ cells/ml) were more supportive of sGAG deposition on a per cell basis, while collagen deposition was higher at lower seeding densities (5*10⁶ cells/ml). Employment of lower fibrin (2.5 %) concentration hydrogels supported more robust chondrogenesis of hMSCs, with higher collagen type II and lower collagen type X deposition compared to 5 % hydrogels. The application of HP to hMSCs maintained in identified chondro-inductive culture conditions had little effect on overall levels of cartilage-specific matrix production. However, if hMSCs were first temporally primed with TGF-β3 before its withdrawal, they responded to HP by increased sGAG production. The response to HP in higher cell density cultures was also associated with a metabolic shift towards glycolysis, which has been linked with a mature chondrocyte-like phenotype. These results suggest that mechanical stimulation may not be necessary to engineer functional AC grafts using hMSCs if other culture conditions have been optimised. However, such bioreactor systems can potentially be employed to better understand how engineered tissues respond to mechanical loading in vivo once removed from in vitro culture environments.

Regeneration of Humeral Head Using a 3D Bioprinted Anisotropic Scaffold with Dual Modulation of Endochondral Ossification

Tissue engineering is theoretically thought to be a promising method for the reconstruction of biological joints, and thus, offers a potential treatment alternative for advanced osteoarthritis. However, to date, no significant progress is made in the regeneration of large biological joints. In the current study, a biomimetic scaffold for rabbit humeral head regeneration consisting of heterogeneous porous architecture, various bioinks, and different hard supporting materials in the cartilage and bone regions is designed and fabricated in one step using 3D bioprinting technology. Furthermore, orchestrated dynamic mechanical stimulus combined with different biochemical cues (parathyroid hormone [PTH] and chemical component hydroxyapatite [HA] in the outer and inner region, respectively) are used for dual regulation of endochondral ossification. Specifically, dynamic mechanical stimulus combined with growth factor PTH in the outer region inhibits endochondral ossification and results in cartilage regeneration, whereas dynamic mechanical stimulus combined with HA in the inner region promotes endochondral ossification and results in efficient subchondral bone regeneration. The strategy established in this study with the dual modulation of endochondral ossification for 3D bioprinted anisotropic scaffolds represents a versatile and scalable approach for repairing large joints.

Fibronectin matrix assembly and TGFβ1 presentation for chondrogenesis of patient derived pericytes for microtia repair

Tissue engineered cartilage for external ear reconstruction of congenital deformities, such as microtia or resulting from trauma, remains a significant challenge for plastic and reconstructive surgeons. Current strategies involve harvesting autologous costal cartilage or expanding autologous chondrocytes ex vivo. However, these procedures often lead to donor site morbidity and a cell source with limited expansion capacity. Stromal stem cells such as perivascular stem cells (pericytes) offer an attractive alternative cell source, as they can be isolated from many human tissues, readily expanded in vitro and possess chondrogenic differentiation potential. Here, we successfully isolate CD146+ pericytes from the microtia remnant from patients undergoing reconstructive surgery (Microtia pericytes; MPs). Then we investigate their chondrogenic potential using the polymer poly(ethyl acrylate) (PEA) to unfold the extracellular matrix protein fibronectin (FN). FN unfolding exposes key growth factor (GF) and integrin binding sites on the molecule, allowing tethering of the chondrogenic GF transforming growth factor beta 1 (TGFβ1). This system leads to solid-phase, matrix-bound, GF presentation in a more physiological-like manner than that of typical chondrogenic induction media (CM) formulations that tend to lead to off-target effects. This simple and controlled material-based approach demonstrates similar chondrogenic potential to CM, while minimising proclivity toward hypertrophy, without the need for complex induction media formulations.

Hopes and opportunities of stem cells from human exfoliated deciduous teeth (SHED) in cartilage tissue regeneration

Cartilage lesions are common conditions, affecting elderly and non-athletic populations. Despite recent advances, cartilage regeneration remains a major challenge today. The absence of an inflammatory response following damage and the inability of stem cells to penetrate into the healing site due to the absence of blood and lymph vessels are assumed to hinder joint repair. Stem cell-based regeneration and tissue engineering have opened new horizons for treatment. With advances in biological sciences, especially stem cell research, the function of various growth factors in the regulation of cell proliferation and differentiation has been established. Mesenchymal stem cells (MSCs) isolated from different tissues have been shown to increase into therapeutically relevant cell numbers and differentiate into mature chondrocytes. As MSCs can differentiate and become engrafted inside the host, they are considered suitable candidates for cartilage regeneration. Stem cells from human exfoliated deciduous teeth (SHED) provide a novel and non-invasive source of MSCs. Due to their simple isolation, chondrogenic differentiation potential, and minimal immunogenicity, they can be an interesting option for cartilage regeneration. Recent studies have reported that SHED-derived secretome contains biomolecules and compounds that efficiently promote regeneration in damaged tissues, including cartilage. Overall, this review highlighted the advances and challenges of cartilage regeneration using stem cell-based therapies by focusing on SHED.

Curcumin-loaded nanofilm generating avascular niche to stabilize in vivo ectopic chondrogenesis of BMSC

Bone marrow stem cells (BMSCs) engineered cartilage (BEC) represent a promising substitute for cartilage repairment. However, the in vitro-generated BEC was prone to endochondral ossification after in vivo ectopic implantation, significantly hindering its clinical translation. Increasing evidence suggested that vascularization essentially led to endochondral ossification of BEC in the subcutaneous microenvironment. Herein, a potent antiangiogenic agent of curcumin (Cur) was successfully laden into a polycaprolactone (PCL) to prepare a Cur/PCL nanofilm. The in vitro findings of this study showed that after co-culturing with human umbilical vein endothelial cells, Cur was sustained-released from Cur/PCL and suppressed the formation of tubes. Further, the Cur/PCL nanofilm was cytocompatible when recolonized with BMSCs. BMSCs were seeded into a porous polyglycolic acid scaffold and underwent 4 weeks of in vitro chondrogenic culture to successfully produce BEC. Thereafter, the BEC is encapsulated by the Cur/PCL nanofilm and subcutaneously implanted into nude mice for 4 weeks. The localized and sustained Cur release could inhibit vascular invasion via the antagonization of vascular endothelial growth factor signal, and stabilizes the cartilaginous phenotype. The results confirmed that Cur/PCL nanofilms protected BEC from vascularization and endochondral ossification in vivo, thus, indicating that the encapsulation of BEC using an anti-angiogenic nanofilm could be used as a novel strategy for modulating the in vivo ectopic BEC stability to repair cartilage defects.

Cartilage Tissue Engineering: An Introduction

Once damaged, cartilage has limited healing capability. This has led to a huge body of research that aims to repair or regenerate this important tissue. Despite the progress made, significant hurdles still need to be overcome. This chapter highlights some of the progress made, while elaborating on areas that need further research. The concept of translation and the route to clinical translation must be kept in mind if some of the promising preclinical research is to make it to routine clinical application.

Non-hypertrophic chondrogenesis of mesenchymal stem cells through mechano-hypoxia programing

Cartilage tissue engineering aims to generate functional replacements to treat cartilage defects from damage and osteoarthritis. Human bone marrow-derived mesenchymal stem cells (hBM-MSC) are a promising cell source for making cartilage, but current differentiation protocols require the supplementation of growth factors like TGF-β1 or -β3. This can lead to undesirable hypertrophic differentiation of hBM-MSC that progress to bone. We have found previously that exposing engineered human meniscus tissues to physiologically relevant conditions of the knee (mechanical loading and hypoxia; hence, mechano-hypoxia conditioning) increased the gene expression of hyaline cartilage markers, SOX9 and COL2A1, inhibited hypertrophic marker COL10A1, and promoted bulk mechanical property development. Adding further to this protocol, we hypothesize that combined mechano-hypoxia conditioning with TGF-β3 growth factor withdrawal will promote stable, non-hypertrophic chondrogenesis of hBM-MSC embedded in an HA-hydrogel. We found that the combined treatment upregulated many cartilage matrix- and development-related markers while suppressing many hypertrophic- and bone development-related markers. Tissue level assessments with biochemical assays, immunofluorescence, and histochemical staining confirmed the gene expression data. Further, mechanical property development in the dynamic compression treatment shows promise toward generating functional engineered cartilage through more optimized and longer culture conditions. In summary, this study introduced a novel protocol to differentiate hBM-MSC into stable, cartilage-forming cells.

Nanoengineered hydrogels as 3D biomimetic extracellular matrix with injectable and sustained delivery capability for cartilage regeneration

The regeneration of articular cartilage remains a great challenge due to the difficulty in effectively enhancing spontaneous healing. Recently, the combination of implanted stem cells, suitable biomaterials and bioactive molecules has attracted attention for tissue regeneration. In this study, a novel injectable nanocomposite was rationally designed as a sustained release platform for enhanced cartilage regeneration through integration of a chitosan-based hydrogel, articular cartilage stem cells (ACSCs) and mesoporous SiO₂ nanoparticles loaded with anhydroicaritin (AHI). The biocompatible engineered nanocomposite acting as a novel 3D biomimetic extracellular matrix exhibited a remarkable sustained release effect due to the synergistic regulation of the organic hydrogel framework and mesopore channels of inorganic mSiO₂ nanoparticles (mSiO₂ NPs). Histological assessment and biomechanical tests showed that the nanocomposites exhibited superior performance in inducing ACSCs proliferation and differentiation in vitro and promoting extracellular matrix (ECM) production and cartilage regeneration in vivo. Such a novel multifunctional biocompatible platform was demonstrated to significantly enhance cartilage regeneration based on the sustained release of AHI, an efficient bioactive natural small molecule for ACSCs chondrogenesis, within the hybrid matrix of hydrogel and mSiO₂ NPs. Hence, the injectable nanocomposite holds great promise for use as a 3D biomimetic extracellular matrix for tissue regeneration in clinical diagnostics.

•

The anhydroicaritin (AHI) was identified as a bioactive factor for promoting cartilage repair.

•

The hydrogel was designed to achieve sustained AHI release and optimize the microenvironment of cartilage defect sites.

•

The hydrogel exhibited superior advantages for chondrogenic differentiation and cartilage regeneration.

•

The hydrogel holds a great promise for use as functional scaffold for tissue and organ regeneration in the future.

Chondrocyte Hypertrophy in Osteoarthritis: Mechanistic Studies and Models for the Identification of New Therapeutic Strategies

Articular cartilage shows limited self-healing ability owing to its low cellularity and avascularity. Untreated cartilage defects display an increased propensity to degenerate, leading to osteoarthritis (OA). During OA progression, articular chondrocytes are subjected to significant alterations in gene expression and phenotype, including a shift towards a hypertrophic-like state (with the expression of collagen type X, matrix metalloproteinases-13, and alkaline phosphatase) analogous to what eventuates during endochondral ossification. Present OA management strategies focus, however, exclusively on cartilage inflammation and degradation. A better understanding of the hypertrophic chondrocyte phenotype in OA might give new insights into its pathogenesis, suggesting potential disease-modifying therapeutic approaches. Recent developments in the field of cellular/molecular biology and tissue engineering proceeded in the direction of contrasting the onset of this hypertrophic phenotype, but knowledge gaps in the cause-effect of these processes are still present. In this review we will highlight the possible advantages and drawbacks of using this approach as a therapeutic strategy while focusing on the experimental models necessary for a better understanding of the phenomenon. Specifically, we will discuss in brief the cellular signaling pathways associated with the onset of a hypertrophic phenotype in chondrocytes during the progression of OA and will analyze in depth the advantages and disadvantages of various models that have been used to mimic it. Afterwards, we will present the strategies developed and proposed to impede chondrocyte hypertrophy and cartilage matrix mineralization/calcification. Finally, we will examine the future perspectives of OA therapeutic strategies.

Strategies to capitalize on cell spheroid therapeutic potential for tissue repair and disease modeling

Cell therapies offer a tailorable, personalized treatment for use in tissue engineering to address defects arising from trauma, inefficient wound repair, or congenital malformation. However, most cell therapies have achieved limited success to date. Typically injected in solution as monodispersed cells, transplanted cells exhibit rapid cell death or insufficient retention at the site, thereby limiting their intended effects to only a few days. Spheroids, which are dense, three-dimensional (3D) aggregates of cells, enhance the beneficial effects of cell therapies by increasing and prolonging cell-cell and cell-matrix signaling. The use of spheroids is currently under investigation for many cell types. Among cells under evaluation, spheroids formed of mesenchymal stromal cells (MSCs) are particularly promising. MSC spheroids not only exhibit increased cell survival and retained differentiation, but they also secrete a potent secretome that promotes angiogenesis, reduces inflammation, and attracts endogenous host cells to promote tissue regeneration and repair. However, the clinical translation of spheroids has lagged behind promising preclinical outcomes due to hurdles in their formation, instruction, and use that have yet to be overcome. This review will describe the current state of preclinical spheroid research and highlight two key examples of spheroid use in clinically relevant disease modeling. It will highlight techniques used to instruct the phenotype and function of spheroids, describe current limitations to their use, and offer suggestions for the effective translation of cell spheroids for therapeutic treatments.

The Role of Extracellular Matrix and Hydrogels in Mesenchymal Stem Cell Chondrogenesis and Cartilage Regeneration

Diseases associated with articular cartilage disintegration or loss are still therapeutically challenging. The traditional treatment approaches only alleviate the symptoms while potentially causing serious side effects. The limited self-renewal potential of articular cartilage provides opportunities for advanced therapies involving mesenchymal stem cells (MSCs) that are characterized by a remarkable regenerative capacity. The chondrogenic potential of MSCs is known to be regulated by the local environment, including soluble factors and the less discussed extracellular matrix (ECM) components. This review summarizes the process of chondrogenesis, and also the biological properties of the ECM mediated by mechanotransduction as well as canonical and non-canonical signaling. Our focus is also on the influence of the ECM's physical parameters, molecular composition, and chondrogenic factor affinity on the adhesion, survival, and chondrogenic differentiation of MSCs. These basic biological insights are crucial for a more precise fabrication of ECM-mimicking hydrogels to improve cartilage tissue reconstruction. Lastly, we provide an overview of hydrogel classification and characterization. We also include the results from preclinical models combining MSCs with hydrogels for the treatment of cartilage defects, to support clinical application of this construct. Overall, it is believed that the proper combination of MSCs, hydrogels, and chondrogenic factors can lead to complex cartilage regeneration.

Wnt antagonism without TGFβ induces rapid MSC chondrogenesis via increasing AJ interactions and restricting lineage commitment

Human mesenchymal stem cells (MSCs) remain one of the best cell sources for cartilage, a tissue without regenerative capacity. However, MSC chondrogenesis is commonly induced through TGFβ, a pleomorphic growth factor without specificity for this lineage. Using tissue- and induced pluripotent stem cell-derived MSCs, we demonstrate an efficient and precise approach to induce chondrogenesis through Wnt/β-catenin antagonism alone without TGFβ. Compared to TGFβ, Wnt/β-catenin antagonism more rapidly induced MSC chondrogenesis without eliciting off-target lineage specification toward smooth muscle or hypertrophy; this was mediated through increasing N-cadherin levels and β-catenin interactions-key components of the adherens junctions (AJ)-and increasing cytoskeleton-mediated condensation. Validation with transcriptomic analysis of human chondrocytes compared to MSCs and osteoblasts showed significant downregulation of Wnt/β-catenin and TGFβ signaling along with upregulation of α-catenin as an upstream regulator. Our findings underscore the importance of understanding developmental pathways and structural modifications in achieving efficient MSC chondrogenesis for translational application.

Within or Without You? A Perspective Comparing In Situ and Ex Situ Tissue Engineering Strategies for Articular Cartilage Repair

Human articular cartilage has a poor ability to self-repair, meaning small injuries often lead to osteoarthritis, a painful and debilitating condition which is a major contributor to the global burden of disease. Existing clinical strategies generally do not regenerate hyaline type cartilage, motivating research toward tissue engineering solutions. Prospective cartilage tissue engineering therapies can be placed into two broad categories: i) Ex situ strategies, where cartilage tissue constructs are engineered in the lab prior to implantation and ii) in situ strategies, where cells and/or a bioscaffold are delivered to the defect site to stimulate chondral repair directly. While commonalities exist between these two approaches, the core point of distinction-whether chondrogenesis primarily occurs "within" or "without" (outside) the body-can dictate many aspects of the treatment. This difference influences decisions around cell selection, the biomaterials formulation and the surgical implantation procedure, the processes of tissue integration and maturation, as well as, the prospects for regulatory clearance and clinical translation. Here, ex situ and in situ cartilage engineering strategies are compared: Highlighting their respective challenges, opportunities, and prospects on their translational pathways toward long term human cartilage repair.

Functionalized Microscaffold-Hydrogel Composites Accelerating Osteochondral Repair through Endochondral Ossification

Osteochondral regeneration remains a key challenge because of the limited self-healing ability of the bone and its complex structure and composition. Biomaterials based on endochondral ossification (ECO) are considered an attractive candidate to promote bone repair because they can effectively address the difficulties in establishing vascularization and poor bone regeneration via intramembranous ossification (IMO). However, its clinical application is limited by the complex cellular behavior of ECO and the long time required for induction of the cell cycle. Herein, functionalized microscaffold-hydrogel composites are developed to accelerate the developmental bone growth process via recapitulating ECO. The design comprises arginine-glycine-aspartic acid (RGD)-peptide-modified microscaffolds loaded with kartogenin (KGN) and wrapped with a layer of RGD- and QK-peptide-comodified alginate hydrogel. These microscaffolds enhance the proliferation and aggregation behavior of the human bone marrow mesenchymal stem cells (hBMSCs); the controlled release of kartogenin induces the differentiation of hBMSCs into chondrocytes; and the hydrogel grafted with RGD and QK peptide facilitates chondrocyte hypertrophy, which creates a vascularized niche for osteogenesis and finally accelerates osteochondral repair in vivo. The findings provide an efficient bioengineering approach by sequentially modulating cellular ECO behavior for osteochondral defect repair.

Hyaline Cartilage Microtissues Engineered from Adult Dedifferentiated Chondrocytes: Safety and Role of WNT Signaling

The repair of damaged articular cartilage is an unmet medical need. Chondrocyte-based cell therapy has been used to repair cartilage for over 20 years despite current limitations. Chondrocyte dedifferentiation upon expansion in monolayer is well known and is the main obstacle to their use as cell source for cartilage repair. Consequently, current approaches often lead to fibrocartilage, which is biomechanically different from hyaline cartilage and not effective as a long-lasting treatment. Here, we describe an innovative 3-step method to engineer hyaline-like cartilage microtissues, named Cartibeads, from high passage dedifferentiated chondrocytes. We show that WNT5A/5B/7B genes were highly expressed in dedifferentiated chondrocytes and that a decrease of the WNT signaling pathway was instrumental for full re-differentiation of chondrocytes, enabling production of hyaline matrix instead of fibrocartilage matrix. Cartibeads showed hyaline-like characteristics based on GAG quantity and type II collagen expression independently of donor age and cartilage quality. In vivo, Cartibeads were not tumorigenic when transplanted into SCID mice. This simple 3-step method allowed a standardized production of hyaline-like cartilage microtissues from a small cartilage sample, making Cartibeads a promising candidate for the treatment of cartilage lesions.

Chondrogenic differentiation of human bone marrow MSCs in osteochondral implants under kinematic mechanical load is dependent on the underlying osteo component

Chondrogenic models utilizing human mesenchymal stromal cells (hMSCs) are often simplistic, with a single cell type and the absence of mechanical stimulation. Considering the articulating joint as an organ it would be beneficial to include more complex stimulation. Within this study we applied clinically relevant kinematic load to biphasic constructs. In each case, the upper layer consisted of fibrin embedded hMSCs retained within an elastomeric polyurethane (PU) scaffold. These were randomly assigned to five base scaffolds, a cell-free fibrin PU base, viable bone, decellularized bone, 3D printed calcium phosphate or clinically used cement. This allowed the study of cross talk between viable bone and chondrogenically differentiating MSCs, while controlling for the change in stiffness of the base material. Data obtained showed that the bulk stiffness of the construct was not the defining factor in the response obtained, with viable and decellularized bone producing similar results to the softer PU base. However, the stiff synthetic materials led to reduced chondrogenesis and increased calcification in the upper MSC seeded layer. This demonstrates that the underlying base material must be considered when driving chondrogenesis of human cells using a clinically relevant loading protocol. It also indicates that the material used for bony reconstruction of osteochondral defects may influence subsequent chondrogenic potential.

Enhancing cartilage repair with optimized supramolecular hydrogel-based scaffold and pulsed electromagnetic field

Functional tissue engineering strategies provide innovative approach for the repair and regeneration of damaged cartilage. Hydrogel is widely used because it could provide rapid defect filling and proper structure support, and is biocompatible for cell aggregation and matrix deposition. Efforts have been made to seek suitable scaffolds for cartilage tissue engineering. Here Alg-DA/Ac-β-CD/gelatin hydrogel was designed with the features of physical and chemical multiple crosslinking and self-healing properties. Gelation time, swelling ratio, biodegradability and biocompatibility of the hydrogels were systematically characterized, and the injectable self-healing adhesive hydrogel were demonstrated to exhibit ideal properties for cartilage repair. Furthermore, the new hydrogel design introduces a pre-gel state before photo-crosslinking, where increased viscosity and decreased fluidity allow the gel to remain in a semi-solid condition. This granted multiple administration routes to the hydrogels, which brings hydrogels the ability to adapt to complex clinical situations. Pulsed electromagnetic fields (PEMF) have been recognized as a promising solution to various health problems owing to their noninvasive properties and therapeutic potentials. PEMF treatment offers a better clinical outcome with fewer, if any, side effects, and wildly used in musculoskeletal tissue repair. Thereby we propose PEMF as an effective biophysical stimulation to be 4th key element in cartilage tissue engineering. In this study, the as-prepared Alg-DA/Ac-β-CD/gelatin hydrogels were utilized in the rat osteochondral defect model, and the potential application of PEMF in cartilage tissue engineering were investigated. PEMF treatment were proven to enhance the quality of engineered chondrogenic constructs in vitro, and facilitate chondrogenesis and cartilage repair in vivo. All of the results suggested that with the injectable self-healing adhesive hydrogel and PEMF treatment, this newly proposed tissue engineering strategy revealed superior clinical potential for cartilage defect treatment.

•

The supramolecular Alg-DA/Ac-β-CD/gelatin hydrogel with physical and chemical multiple crosslinking was fabricated.

•

The multi-crosslinked structure of the hydrogels endows strong injection, adhesion abilities and mechanical performance.

•

A pre-gel state of the hydrogel grants it more administration routes and ability to adapt to complex clinical scenarios.

•

Pulsed electromagnetic field (PEMF) serves as the 4^th element in mesenchymal stem cell-based cartilage tissue engineering.

•

Bioinformatics analysis reveal that PEMF regulates chondrogenesis and cell hypertrophy via ERK and p38 MAPK pathways.

Stage-Dependent Activity and Pro-Chondrogenic Function of PI3K/AKT during Cartilage Neogenesis from Mesenchymal Stromal Cells

Differentiating mesenchymal stromal cells (MSCs) into articular chondrocytes (ACs) for application in clinical cartilage regeneration requires a profound understanding of signaling pathways regulating stem cell chondrogenesis and hypertrophic degeneration. Classifying endochondral signals into drivers of chondrogenic speed versus hypertrophy, we here focused on insulin/insulin-like growth factor 1 (IGF1)-induced phosphoinositide 3-kinase (PI3K)/AKT signaling. Aware of its proliferative function during early but not late MSC chondrogenesis, we aimed to unravel the late pro-chondrogenic versus pro-hypertrophic PI3K/AKT role. PI3K/AKT activity in human MSC and AC chondrogenic 3D cultures was assessed via Western blot detection of phosphorylated AKT. The effects of PI3K inhibition with LY294002 on chondrogenesis and hypertrophy were assessed via histology, qPCR, the quantification of proteoglycans, and alkaline phosphatase activity. Being repressed by ACs, PI3K/AKT activity transiently rose in differentiating MSCs independent of TGFβ or endogenous BMP/WNT activity and climaxed around day 21. PI3K/AKT inhibition from day 21 on equally reduced chondrocyte and hypertrophy markers. Proving important for TGFβ-induced SMAD2 phosphorylation and SOX9 accumulation, PI3K/AKT activity was here identified as a required stage-dependent driver of chondrogenic speed but not of hypertrophy. Thus, future attempts to improve MSC chondrogenesis will depend on the adequate stimulation and upregulation of PI3K/AKT activity to generate high-quality cartilage from human MSCs.

Preliminary Characterization of the Epigenetic Modulation in the Human Mesenchymal Stem Cells during Chondrogenic Process

Regenerative medicine represents a growing hot topic in biomedical sciences, aiming at setting out novel therapeutic strategies to repair or regenerate damaged tissues and organs. For this perspective, human mesenchymal stem cells (hMSCs) play a key role in tissue regeneration, having the potential to differentiate into many cell types, including chondrocytes. Accordingly, in the last few years, researchers have focused on several in vitro strategies to optimize hMSC differentiation protocols, including those relying on epigenetic manipulations that, in turn, lead to the modulation of gene expression patterns. Therefore, in the present study, we investigated the role of the class II histone deacetylase (HDAC) inhibitor, MC1568, in the hMSCs-derived chondrogenesis. The hMSCs we used for this work were the hMSCs obtained from the amniotic fluid, given their greater differentiation capacity. Our preliminary data documented that MC1568 drove both the improvement and acceleration of hMSCs chondrogenic differentiation in vitro, since the differentiation process in MC1568-treated cells took place in about seven days, much less than that normally observed, namely 21 days. Collectively, these preliminary data might shed light on the validity of such a new differentiative protocol, in order to better assess the potential role of the epigenetic modulation in the process of the hypertrophic cartilage formation, which represents the starting point for endochondral ossification.

The Role of Transforming Growth Factor Beta in Joint Homeostasis and Cartilage Regeneration

Transforming growth factor-beta (TGF-β) is an important regulator of joint homeostasis, of which dysregulation is closely associated with the development of osteoarthritis (OA). In normal conditions, its biological functions in a joint environment are joint protective, but it can be dramatically altered in different contexts, making its therapeutic application a challenge. However, with the deeper insights into the TGF-β functions, it has been proven that TGF-β augments cartilage regeneration by chondrocytes, and differentiates both the precursor cells of chondrocytes and stem cells into cartilage-generating chondrocytes. Following documentation of the therapeutic efficacy of chondrocytes augmented by TGF-β in the last decade, there is an ongoing phase III clinical trial examining the therapeutic efficacy of a mixture of allogeneic chondrocytes and TGF-β-overexpressing cells. To prepare cartilage-restoring chondrocytes from induced pluripotent stem cells (iPSCs), the stem cells are differentiated mainly using TGF-β with some other growth factors. Of note, clinical trials evaluating the therapeutic efficacy of iPSCs for OA are scheduled this year. Mesenchymal stromal stem cells (MSCs) have inherent limitations in that they differentiate into the osteochondral pathway, resulting in the production of poor-quality cartilage. Despite the established essential role of TGF-β in chondrogenic differentiation of MSCs, whether the coordinated use of TGF-β in MSC-based therapy for degenerated cartilage is effective is unknown. We herein reviewed the general characteristics and mechanism of action of TGF-β in a joint environment. Furthermore, we discussed the core interaction of TGF-β with principal cells of OA cell-based therapies, the chondrocytes, MSCs, and iPSCs. Impact Statement Transforming growth factor-beta (TGF-β) has been widely used as a core regulator to improve or formulate therapeutic regenerative cells for degenerative joints. It differentiates stem cells into chondrocytes and improves the chondrogenic potential of differentiated chondrocytes. Herein, we discussed the overall characteristics of TGF-β and reviewed the comprehension and utilization of TGF-β in cell-based therapy for degenerative joint disease.

Efficient engineering of human auricular cartilage through mesenchymal stem cell chaperoning

A major challenge to the clinical translation of tissue-engineered ear scaffolds for ear reconstruction is the limited auricular chondrocyte (hAuC) yield available from patients. Starting with a relatively small number of chondrocytes in culture results in dedifferentiation and loss of phenotype with subsequent expansion. To significantly decrease the number of chondrocytes required for human elastic cartilage engineering, we co-cultured human mesenchymal stem cells (hMSCs) with HAuCs to promote healthy elastic cartilage formation. HAuCs along with human bone marrow-derived hMSCs were encapsulated into 1% Type I collagen at 25 million/mL total cell density with different ratios (HAuCs/hMSCs: 10/90, 25/75, 50/50) and then injected into customized 3D-printed polylactic acid (PLA) ridged external scaffolds, which simulate the shape of the auricular helical rim, and implanted subcutaneously in nude rats for 1, 3 and 6 months. The explanted constructs demonstrated near complete volume preservation and topography maintenance of the ridged "helical" feature after 6 months with all ratios. Cartilaginous appearing tissue formed within scaffolds by 3 months, verified by histologic analysis demonstrating mature elastic cartilage within the constructs with chondrocytes seen in lacunae within a Type II collagen and proteoglycan-enriched matrix, and surrounded by a neoperichondrial external layer. Compressive mechanical properties comparable to human elastic cartilage were achieved after 6 months. Co-implantation of hAuCs and hMSCs in collagen within an external scaffold efficiently produced shaped human elastic cartilage without volume loss even when hAuC comprised only 10% of the implanted cell population, marking a crucial step toward the clinical translation of auricular tissue engineering.

GDF5+ chondroprogenitors derived from human pluripotent stem cells preferentially form permanent chondrocytes

It has been established in the mouse model that during embryogenesis joint cartilage is generated from a specialized progenitor cell type, distinct from that responsible for the formation of growth plate cartilage. We recently found that mesodermal progeny of human pluripotent stem cells gave rise to two types of chondrogenic mesenchymal cells in culture: SOX9+ and GDF5+ cells. The fast-growing SOX9+ cells formed in vitro cartilage that expressed chondrocyte hypertrophy markers and readily underwent mineralization after ectopic transplantation. In contrast, the slowly growing GDF5+ cells derived from SOX9+ cells formed cartilage that tended to express low to undetectable levels of chondrocyte hypertrophy markers, but expressed PRG4, a marker of embryonic articular chondrocytes. The GDF5+-derived cartilage remained largely unmineralized in vivo. Interestingly, chondrocytes derived from the GDF5+ cells seemed to elicit these activities via non-cell-autonomous mechanisms. Genome-wide transcriptomic analyses suggested that GDF5+ cells might contain a teno/ligamento-genic potential, whereas SOX9+ cells resembled neural crest-like progeny-derived chondroprogenitors. Thus, human pluripotent stem cell-derived GDF5+ cells specified to generate permanent-like cartilage seem to emerge coincidentally with the commitment of the SOX9+ progeny to the tendon/ligament lineage.

Bevacizumab-Laden Nanofibers Simulating an Antiangiogenic Niche to Improve the Submuscular Stability of Stem Cell Engineered Cartilage

Bone marrow stem cells (BMSCs) engineered cartilage (BEC) is prone to endochondral ossification in a submuscular environment due to the process of vascular infiltration, which limits its application in repairing tracheal cartilage defects. Bevacizumab, an antitumor drug with pronounced antiangiogenic activity, is successfully laden into a poly(L-lactide-co-caprolactone) system to prepare bevacizumab-laden nanofiber (BevNF) characterized by 5% and 10% bevacizumab concentrations. The in vitro results reveal that a sustained release of bevacizumab can be realized from BevNF, exhibiting inhibitive cytotoxicity toward human umbilical vein endothelial cells whereas non-cytotoxicity toward BMSCs-induced chondrocytes. A model is also established by encapsulating BEC within BevNF, aiming to realize an antiangiogenic niche under conditions of sustained and localized release of bevacizumab to inhibit the process of vascular invasion, resulting in the eventual stabilization of the cartilaginous phenotype and promotion of the process of cartilage maturation in the submuscular environment. These results also confirm that the chondrogenesis stability of BEC increases with an increase in the bevacizumab concentration, and 10% BevNF is sufficient to protect BEC from vascularization. This demonstrates that the use of BevNF can potentially help develop an effective strategy for regulating the submuscular stability of BEC to repair the defects formed in tracheal cartilage.

Cartilage tissue engineering by extrusion bioprinting utilizing porous hyaluronic acid microgel bioinks

3D bioprinting offers an excellent opportunity to provide tissue-engineered cartilage to microtia patients. However, hydrogel-based bioinks are hindered by their dense and cell-restrictive environment, impairing tissue development and ultimately leading to mechanical failure of large scaffoldsin vivo. Granular hydrogels, made of annealed microgels, offer a superior alternative to conventional bioinks, with their improved porosity and modularity. We have evaluated the ability of enzymatically crosslinked hyaluronic acid (HA) microgel bioinks to form mature cartilagein vivo. Microgel bioinks were formed by mechanically sizing bulk HA-tyramine hydrogels through meshes with aperture diameters of 40, 100 or 500µm. Annealing of the microgels was achieved by crosslinking residual tyramines. Secondary crosslinked scaffolds were stable in solution and showed tunable porosity from 9% to 21%. Bioinks showed excellent rheological properties and were used to print different objects. Printing precision was found to be directly correlated to microgel size. As a proof of concept, freeform reversible embedding of suspended hydrogels printing with gelation triggered directly in the bath was performed to demonstrate the versatility of the method. The granular hydrogels support the homogeneous development of mature cartilage-like tissuesin vitrowith mechanical stiffening up to 200 kPa after 63 d. After 6 weeks ofin vivoimplantation, small-diameter microgels formed stable constructs with low immunogenicity and continuous tissue maturation. Conversely, increasing the microgel size resulted in increased inflammatory response, with limited stabilityin vivo. This study reports the development of new microgel bioinks for cartilage tissue biofabrication and offers insights into the foreign body reaction towards porous scaffolds implantation.

Ultra-Low Electromagnetic Fields Application on In Vitro Cartilage Regeneration: A Pilot Study to Improve Treatment of Osteoarticular Diseases

Extremely low-frequency and low-intensity electromagnetic fields show positive effects on the treatment of several osteoarticular diseases, such as osteoarthritis, and are currently applied in the clinical setting with promising results on tissue regeneration. However, the biological mechanisms underlying the beneficial effects triggered by this type of physical stimulation still need to be deciphered. We tested the hypothesis that ultra-low complex electromagnetic fields stimulation using an innovative medical device could enhance chondrogenesis in human adipose-derived stem cells (ADSCs), and analyzed its biological effects. Chondrogenic lineage markers, like ACAN, SOX9, RUNX2, COL2A1, and COL10A1, were evaluated after 21 days of treatment. Thus far, we have provided preliminary evidence that a dedicated pattern of ultra-weak complex electromagnetic sequences emitted by a cutting-edge technology can promote cartilage regeneration, inducing the chondrogenic differentiation and maturity of ADSCs.

In vitro maturation and in vivo stability of bioprinted human nasal cartilage

The removal of skin cancer lesions on the nose often results in the loss of nasal cartilage. The cartilage loss is either surgically replaced with autologous cartilage or synthetic grafts. However, these replacement options come with donor-site morbidity and resorption issues. 3-dimensional (3D) bioprinting technology offers the opportunity to engineer anatomical-shaped autologous nasal cartilage grafts. The 3D bioprinted cartilage grafts need to embody a mechanically competent extracellular matrix (ECM) to allow for surgical suturing and resistance to contraction during scar tissue formation. We investigated the effect of culture period on ECM formation and mechanical properties of 3D bioprinted constructs of human nasal chondrocytes (hNC)-laden type I collagen hydrogel in vitro and in vivo. Tissue-engineered nasal cartilage constructs developed from hNC culture in clinically approved collagen type I and type III semi-permeable membrane scaffold served as control. The resulting 3D bioprinted engineered nasal cartilage constructs were comparable or better than the controls both in vitro and in vivo. This study demonstrates that 3D bioprinted constructs of engineered nasal cartilage are feasible options in nasal cartilage reconstructive surgeries.

Efficacy of treating segmental bone defects through endochondral ossification: 3D printed designs and bone metabolic activities

Three-dimensional printing (3D printing) is a promising technique for producing scaffolds for bone tissue engineering applications. Porous scaffolds can be printed directly, and the design, shape and porosity can be controlled. 3D synthetic biodegradable polymeric scaffolds intended for in situ bone regeneration must meet stringent criteria, primarily appropriate mechanical properties, good 3D design, adequate biocompatibility and the ability to enhance bone formation. In this study, healing of critical-sized (5 ​mm) femur defects of rats was enhanced by implanting two different designs of 3D printed poly(l-lactide-co-ε-caprolactone) (poly(LA-co-CL)) scaffolds seeded with rat bone marrow mesenchymal stem cells (rBMSC), which had been pre-differentiated in vitro into cartilage-forming chondrocytes. Depending on the design, the scaffolds had an interconnected porous structure of 300-500 ​μm and porosity of 50-65%. According to a computational simulation, the internal force distribution was consistent with scaffold designs and comparable between the two designs. Moreover, the defects treated with 3D-printed scaffolds seeded with chondrocyte-like cells exhibited significantly increased bone formation up to 15 weeks compared with empty defects. In all experimental animals, bone metabolic activity was monitored by positron emission tomography 1, 3, 5, 7, 11 and 14 weeks after surgery. This demonstrated a time-dependent relationship between scaffold design and metabolic activity. This confirmed that successful regeneration was highly reproducible. The in vitro and in vivo data indicated that the experimental setups had promising outcomes and could facilitate new bone formation through endochondral ossification.

Acceleration of Bone Regeneration Induced by a Soft-Callus Mimetic Material

Clinical implementation of endochondral bone regeneration (EBR) would benefit from the engineering of devitalized cartilaginous constructs of allogeneic origins. Nevertheless, development of effective devitalization strategies that preserves extracellular matrix (ECM) is still challenging. The aim of this study is to investigate EBR induced by devitalized, soft callus-mimetic spheroids. To challenge the translatability of this approach, the constructs are generated using an allogeneic cell source. Neo-bone formation is evaluated in an immunocompetent rat model, subcutaneously and in a critical size femur defect. Living spheroids are used as controls. Also, the effect of spheroid maturation towards hypertrophy is evaluated. The devitalization procedure successfully induces cell death without affecting ECM composition or bioactivity. In vivo, a larger amount of neo-bone formation is observed for the devitalized chondrogenic group both ectopically and orthotopically. In the femur defect, accelerated bone regeneration is observed in the devitalized chondrogenic group, where defect bridging is observed 4 weeks post-implantation. The authors' results show, for the first time, a dramatic increase in the rate of bone formation induced by devitalized soft callus-mimetics. These findings pave the way for the development of a new generation of allogeneic, "off-the-shelf" products for EBR, which are suitable for the treatment of every patient.