Porcine and fish by-products in particular are rich sources for collagen, which is the main component of the extracellular matrix (ECM). Although there are studies investigating different collagen derived from various tissue sources for the purpose of creating biomaterials, the comparison of biophysical, biochemical and biological properties of type II collagen isolated from cartilaginous tissues has yet to be assessed. In addition, it has been shown from previous studies that sex steroid hormones affect the collagen content in male and female animals, herein, type II collagens from male and female porcine cartilage were assessed in order to investigate gender effects on the property of collagen scaffolds. Moreover, type II collagen has a supportive role in articular cartilage in the knee joint. Therefore, the aim is to assess the properties of type II collagen scaffolds as a function of species, tissue and gender for cartilage regeneration. Type II collagen was extracted from male and female porcine trachea, auricular, articular cartilage and cartilaginous fish through acid-pepsin digestion at 4°C. SDS-PAGE was conducted to confirm the purity of extracted collagen. Collagen sponges were created via freeze-drying. Scaffold structure and pore size were evaluated by scanning electron microscopy (SEM). Thermal stability was assessed by differential scanning calorimetry (DSC). Sponges were seeded with human adipose derived stem cells to assess chondro-inductive potential of collagen sponges after 7, 14 and 21 days of culture. In conclusion, collagen sponges support the proliferation and differentiation of human adipose derived stem cells to different extents

The anterior cruciate ligament (ACL) is the connective tissue located at the end of long bones providing stability to the knee joint. After tear or rupture clinical reconstruction of the tissue remains a challenge due to the particular mechanical properties required for proper functioning of the tissue. The outstanding mechanical properties of the ACL are characterized by a viscoelastic behavior responsible of the dissipation of the loads that are transmitted to the bone. These mechanical properties are the result of a very specialized graded extracellular matrix that transitions smoothly between the heterotypic cells, stiffness and composition of the ACL and the adjacent bone. Thus, mimicking the zonal biochemical composition, cellular phenotype and organization are key to reset the proper functioning of the ACL. We have previously shown how the biochemical composition presented to cells in electrospun scaffolds results in haptokinesis, reverting contact-guidance effects. [1]. Here, we demonstrate that contact guidance can also be disrupted by structural parameters in aligned wavy scaffolds. The presentation of a wavy fiber arrangement affected the cell organization and the deposition of a specific ECM characteristic of fibrocartilage. Cells cultured in wavy scaffolds grew in aggregates, deposited an abundant ECM rich in fibronectin and collagen II, and expressed higher amounts of collagen II, X and tenomodulin as compared to aligned scaffolds. In-vivo implantation in rabbits of triphasic scaffolds accounting for aligned-wavy-aligned zones showed a high cellular infiltration and the formation of an oriented ECM, as compared to traditional aligned scaffolds. [2]

In the native articular cartilage microenvironment, chondrocytes are constantly subjected to dynamic physical stimuli that maintains tissue homeostasis. They produce extra cellular matrix (ECM) components such as collagens (type II mainly, 50-75%), proteoglycans (10-30%) and other type of proteins. 1. . While collagen offers a large resistance in tension, proteoglycans are the responsible of the viscoelastic response under compression due to the negative charge they confer to the ECM allowing it to entrap a large amount of interstitial fluid. In pathologic states (e.g. osteoarthritis), this ECM is degenerated and the negative charge becomes unbalanced, losing the chondroprotective properties and resulting on an overloaded chondrocytes that further degenerate the matrix. Low-Intensity Pulsed Ultrasound Stimulation (LIPUS) has been used to generate acoustic (pressure) waves that create bubbles that collapse with cells, inducing a stimulus that can modulate cell response. 2. This mechanical stimulation promotes the expression of type II collagen, type X collagen, aggrecan and TGF-β, appearing as a great strategy to regenerate cartilage. However, current strategies make use of extrinsic forces to stimulate cartilage formation overlooking the physico-chemical properties of the degenerated cartilage, resulting in an excessive load-transfer to chondrocytes and the consequent hypertrophy and degeneration. Here, interpenetrated networks (IPNs) with different compositions were created using methacrylated gelatin (GelMA), to mimic the collagen, and alginate functionalized with tyramine (Alg-tyr) to mimic glycosaminoglycans and to introduce a negative charge in the model. Within the matrix chondrocytes where encapsulated and stimulated under different conditions to identify the ultrasound parameters that enhance tissue formation. Samples with and without stimulation were compared analysing the expression and deposition of collagen II, aggrecan, collagen X and TGF-β. The results suggested that the chondrogenic marker expression of the samples stimulated for 10 minutes per day for 28 days, was two times higher overall in all of the cases, which was correlated to the tissue formation detected. Acknowledgments: The authors would like to thank the Basque Government for the “Predoctoral Training Program for Non-Doctoral Research Staff 2021-2022” (Grant ref.: PRE_2021_1_0403). This work was supported by the RETOS grant PID2020-114901RA-I00 of the Ministry of Science and Innovation (MICINN)

The biological understanding for the disease progression osteoarthritis (OA) has uncovered specific biomarkers from either synovial fluid, articular chondrocytes or synoviocytes that can be used to diagnose the disease. Examples of these biomarkers include interleukin-1β (IL-1β) or collagen II fragments (1, 2). In parallel, isolation of chondrocytes or bone marrow derived mesenchymal stromal cells (MSCs) has yielded cell-based strategies that have shown long- term beneficial effects in a specific cohort of patients, specifically in traumatic cartilage lesions (2). This latter finding shows that patient stratification of OA is an important tool to both match patients for a specific treatment and to develop novel therapies, especially disease modifying drugs. In order to create disease stage specific therapies, the use of next generation analysis tools such as RNAseq and metabolomics, has the potential to decipher specific cellular and molecular endotypes. Alongside greater understanding of the clinical phenotype (e.g. imaging, pain, co- morbidities), therapies can be designed to alleviate the symptoms of OA at specific points of the disease in patients. This talk will outline the current biological understanding of OA and discuss how patient stratification could assist in the design of innovative therapies for the disease. Acknowledgements: This presentation was supported by the COST action, CA21110 – Building an open European Network on Osteoarthritis Research (NetwOArk)

In a healthy joint, mechanical loading increases matrix synthesis and maintains cell phenotype, while reducing catabolic activities. It activates several pathways, most of them yet largely unknown, with integrins, TGF-β, canonical (Erk 1/2) and stress-activated (JNK) MAPK playing a key role. Degenerative joint diseases are characterized by Wnt upregulation and by the presence of proteolytic fibronectin fragments (FB-fs). Despite they are known to impair some of the aforementioned pathways, little is known on their modulatory effect on cartilage mechanoresponsiveness. This study aims at investigating the effect of mechanical loading in healthy and in vitro diseased cartilage models using pro-hypertrophic Wnt agonist CHIR99021 and the pro-catabolic FB-fs 30 kDa. Human primary chondrocytes from OA patients have been grown in alginate hydrogels for one week, prior to be incubated for 4 days with 3μM CHIR99021 or 1 μM FB-fs. Human cartilage explants isolated from OA patients have incubated 4 days with 3 μM CHIR99021 or 1 μM FB-fs. Both groups have then been mechanically stimulated (unconfined compression, 10% displacement, 1.5 hours, 1 Hz), using a BioDynamic bioreactor 5270 from TA Instruments. Expression of collagen type I, II and X, aggrecan, ALK-1, ALK-5, αV, α5 and β1 integrins, TGF-β1 have been assessed by Real Time-PCR and normalized with the expression of S29. Percentage of phosphorylated Smad2, Smad1 and JNK were determined through western blot. TGF-β1 content was quantified by sandwich ELISA; MMP-13 and GAG by western blot and DMMB assay, respectively. At least three biological replicates were used. ANOVA test was used for parametric analysis; Kruskal-Wallis and Mann-Whitney post hoc test for non-parametric. Preliminary data show that compression increased collagen II expression in control, but not in CHIR99021 and FB-fs pre-treated group (Fig. 1A-B). This was associated with downregulation of β1-integrin expression, which is the main collagen receptor and further regulates collagen II expression, suggesting inhibition of Erk1/2 pathway. A trend of increase expression of collagen type X after mechanical loading was observed in CHIR and FB-fs group. ALK-1 and ALK-5 showed a trend toward stronger upregulation in CHIR99021 group after compression, suggesting the activation of both Smad1/5/8 and Smad 2/3 pathways. To further investigate pathways leading to these different mechano-responses, the phosphorylation levels of Smad1 and Smad2, Erk1/2 and JNK proteins are currently being studied. Preliminary results show that Smad2, Smad1 and JNK protein levels increased in all groups after mechanical loading, independently of an increase in TGF-β1 expression or content. Compression further increased phosphorylation of Smad2, but not of Smad1, in all groups

There are no efficient treatment options for osteoarthritis (OA) that delay further progression. Besides osteoinduction, there is growing evidence of also anti-inflammatory, angiogenetic and neuroprotective effects of biodegradable magnesium-based biomaterials. Their use for the treatment of cartilage lesions in contrast is not well-evaluated yet. Mg-cylinders were analysed in an in vitro and in vivo OA model. In vitro, SCP-1 stem cell line was analysed under inflammatory conditions and Mg-impact. In vivo, small Mg- and WE43 alloy-cylinders (1mm × 0,5mm) were implanted into the subchondral bone of the knee joint of 24 NZW rabbits after establishment of OA. As control, another 12 rabbits received only drill-holes. µCT-scan were performed and assessed for changes in bone volume and density. After euthanasia, cartilage was evaluated macroscopically and histologically after Safranin-O-staining. Furthermore, staining with CD271 directed antibody was performed to assess neuro-reactivity. In vitro, an increased gene expression of extracellular matrix proteins as collagen II or aggrecan even under inflammatory conditions was observed under Mg-impact. In vivo, µCT evaluation revealed twice-elevated values for bone volume in femoral condyles with Mg-cylinders compared to controls while density remained unchanged. Cartilage showed no significant differences between the groups. Mg- and WE-samples showed significantly lower levels of CD271+ cells in the cartilage and bone of the operated joints than in non-operated joints, which was not the case in the Drilling-group. Furthermore, bone in operated knees of Drilling-group showed a strong trend to an increase in CD271+ cells compared to both Cylinder-groups. Counting of CD271+ vessels revealed that this difference was attributable to a higher amount of these vessels. The in vitro results indicate a potential cartilage regenerative activity of the degradable Mg-based material. While so far there was no positive effect on the cartilage itself in vivo, implantation of Mg-cylinders seemed to reduce pain-mediating vessels. Acknowledgements: This work is funded by the German Research Foundation (DFG, project number 404534760). We thank Björn Wiese for production of the cylinders

In the field of tissue engineering (TE), mainly two approaches have been widely studied and utilised throughout the last two decades. Ovsianikov et al. proposed a third strategy for tissue engineering to combine the advantages of the scaffold-based and scaffold-free approach [1]. We utilise the third strategy for TE by fabrication of cell spheroids that are reinforced by microscaffolds, called tissue units (TUs). Aim of the presented study is to differentiate TUs towards a chondrogenic phenotype to show the self-assembly of a millimetre sized cartilage-like tissue in a bottom-up TE approach in vitro. Two-Photon polymerization (2PP) was utilised to fabricate highly porous microscaffolds with a diameter of 300 µm. The biocompatible and biodegradable, resin Degrad INX (supplied from Xpect INX, Ghent, Belgium) was used for 3D-printing. Each microscaffold was seeded with 4000 human adipose derived stem cells (hASCs) in low-adhesive 96-well plates to allow spheroid formation. TUs were differentiated towards the chondrogenic lineage by application of chondrogenic media, subsequently merged in a cylindrical agarose mold, to fuse into a connected tissue with a diameter of ~1.8 mm and a height of 8 mm. The characterization of TUs differentiated towards the chondrogenic phenotype included gene expression and protein analysis. Furthermore, immunohistochemically staining for Collagen II and Alcian blue staining were performed to investigate the matrix deposition and fusion of the self-assembled tissue. Our results suggest that the utilised method could be a promising approach for a variety of tissue engineering approaches, due to the good applicability to a defect side combined with the self-assembly properties of the TUs. Furthermore, the differentiation potential of hASCs is not limited to chondrogenic lineages only, which could pave the way to further TE applications in the future. Acknowledgements:. This research work was financially supported by the European Research Council (Consolidator Grant 772464 A.O.)

Meniscus tears have been treated using partial meniscectomy to relieve pain in patients, although this leads to the onset of early osteoarthritis (OA). Cell-based therapies can help preserve the meniscus, although the presence of inflammatory cytokines compromises clinical outcomes. Anti-inflammatory drugs (e.g. celecoxib), can help to reduce pain in patients and in vitro studies suggest a beneficial effect on cytokine inhibited matrix content. Previously, we have demonstrated that the inhibitory effects of IL-1β can be countered by culture under low oxygen tension or physioxia. The present study sought to understand whether physioxia, celecoxib or combined application can counter the inhibitory effects IL-1β inhibited meniscus cells. Human avascular and vascular meniscus cells (n =3) were isolated and expanded under 20% (hyperoxia) or 2% (physioxia) oxygen. Cells were seeded into collagen scaffolds (Geistlich, Wolhusen) and cultured for 28 days either in the presence of 0.1ng/mL IL-1β, 5µg/mL celecoxib or both under their expansion oxygen conditions. Histological (DMMB, collagen I and collagen II immunostaining), GAG content and gene expression analysis was evaluated for the scaffolds. Under hyperoxia, meniscus cells showed a significant reduction in GAG content in the presence of IL-1β (*p < 0.05). Celecoxib alone did not significantly increase GAG content in IL-1β treated cultures. In contrast, physioxic culture showed a donor dependent increase in GAG content in control, IL-1β and celecoxib treated cultures with corresponding histological staining correlating with these results. Additionally, gene expression showed an upregulation in COL1A1, COL2A1 and ACAN and a downregulation in MMP13 and ADAMTS5 under physioxia for all experimental groups. Physioxia alone had a stronger effect in countering the inhibitory effects of IL-1β treated meniscus cells than celecoxib under hyperoxia. Preconditioning meniscus cells under physioxia prior to implantation has the potential to improve clinical outcomes for cell-based therapies of the meniscus

Cartilage lesions often undergo irreversible progression due to low self-repair capability of this tissue. Tissue engineered approaches based in extrusion bioprinting of constructs loaded with stem cell spheroids may offer valuable alternatives for the treatment of cartilage lesions. Human mesenchymal stromal cell (hMSC) spheroids can be chondrogenically differentiated faster and more efficiently than single cells. This approach allows obtaining larger tissues in a rapid, controlled and reproducible way. However, it is challenging to control tissue architecture, construct stability, and cell viability during maturation. In this study we aimed at the development of a reproducible bioprinting process followed by post-bioprinting chondrogenic differentiation procedure using large quantities of hMSC spheroids encapsulated in a xanthan gum-alginate hydrogel. Multi-layered constructs were bioprinted, ionically crosslinked, and chondrogenically differentiated for 28 days. The expression of glycosaminoglycan, collagen II and IV were observed. After 56 days in culture, the bioprinted constructs were still stable and show satisfactory cell metabolic activity with profuse extracellular matrix production. These results showed a promising procedure to obtain 3D cartilage-like constructs that could be potential use as stable chondral tissue implants for future therapies. Acknowledgments: The National Council for Scientific and Technological Development (CNPq, Brazil – Grants # 314 724/2021-4, 307 829/2018-9, 430 860/2018-8, 142 050/2018-0 and 465 656/2014-5), the Coordination for the Improvement of Higher Educational Personnel (CAPES, Brazil – PrInt 88 887.364849/2019-00 and PrInt 88 887.310405/2018-00), the Fund for Support to Teaching, Research and Extension from the University of Campinas (FAEPEX/UNICAMP, Brazil – Grants # 2921/18, 2324/21), and the European Union's Horizon 2020 JointPromise project – Precision manufacturing of microengineered complex joint implants, under grant agreement 874 837 are acknowledged for the financial support of this study

Silk fibroin (SF) has been used as a scaffold for cartilage tissue engineering. Different silkworms strain produced different protein. Also, molecular weight of SF depends on extraction method. We hypothesised that strain of silkworm and method of SF extraction would effect biological properties of SF scaffold. Therefore, cell viability and chondrogenic gene expression of human chondrogenic progenitor cells (HCPCs) treated with SF from 10 silkworm strains and two common SF extraction methods were investigate in this study. Twenty g of 10 strains silk cocoons were separately degummed in 0.02M Na2CO3 solution and dissolved in 100๐C for 30 minutes. Half of them were then dissolved in CaCl2/Ethanol/H2O [1:2:8 molar ratio] at 70±5๐C (method 1) and other half was dissolved in 46% w/v CaCl2 at 105±5๐C (method 2) for 4 hours. HCPCs were cultured in SF added cultured medial according to strain and extraction method. Cell viability at day 1, 3, and 7, were determined. Expression of collagen I, collagen II, and aggrecan at day 7 and 14, was studied. All experiment were done in triplicated samples. Generally, method 1 SF extraction showed higher cell viability in all strains. Cell viability from Nanglai Saraburi, Laung Saraburi and Nangtui strains were higher than those without SF in every time point while Wanasawan and J108 had higher viability at day 1 and decreased by time. Expression in collagen 1, collagen 2 and aggrecan in method 1 are higher at day 7 and day 14. Collagen 1 expression was highest in Nangnoi Srisaket, followed by Laung Saraburi and Nanglai Saraburi in day 7. Nangnoi Srisaket also had highest expression at day 14, followed by Nanglai Saraburi and Laung Saraburi respectively. Nangseaw had highest collagen 2 expression, follow by Laung Saraburi and Nangnoi Srisaket respectively. Higher aggrecan gene expression of Tubtimsiam, Wanasawan, UB 1 and Nangnoi Srisaket was observed at day 7 and increased expression of all strains at day 14. SF extraction using CaCl2/Ethanol/H2O offered better cell viability and chondrogenic expression. Nangseaw, Laung Saraburi and Nangnoi Srisaket strains expressed more chondrogenic phenotype

Cartilage injuries often represent irreversible tissue damage because cartilage has only a low ability to regenerate. Thus, cartilage loss results in permanent damage, which can become the starting point for osteoarthritis. In the past, bioactive glass scaffolds have been developed for bone replacement and some of these variants have also been colonized with chondrocytes. However, the hydroxylapaptite phase that is usually formed in bioglass scaffolds is not very suitable for cartilage formation (chondrogenesis). This interdisciplinary project was undertaken to develop a novel slowly degrading bioactive glass scaffold tailored for cartilage repair by resembling the native extracellular cartilage matrix (ECM) in structure and surface properties. When colonized with articular chondrocytes, the composition and topology of the scaffolds should support cell adherence, proliferation and ECM synthesis as a prerequisite for chondrogenesis in the scaffold. To study cell growth in the scaffold, the scaffolds were colonized with human mesenchymal stromal cells (hMSCs) and primary porcine articular chondrocytes (pACs) (27,777.8 cells per mm. 3. ) for 7 – 35 d in a rotatory device. Cell survival in the scaffold was determined by vitality assay. Scanning electron microscopy (SEM) visualized cell ultramorphology and direct interaction of hMSCs and pACs with the bioglass surface. Cell proliferation was detected by CyQuant assay. Subsequently, the production of sulphated glycosaminoglycans (sGAGs) typical for chondrogenic differentiation was depicted by Alcian blue staining and quantified by dimethylmethylene blue assay assay. Quantitative real-time polymerase chain reaction (QPCR) revealed gene expression of cartilage-specific aggrecan, Sox9, collagen type II and dedifferentiation-associated collagen type I. To demonstrate the ECM-protein synthesis of the cells, the production of collagen type II and type I was determined by immunolabelling. The bioactive glass scaffold remained stable over the whole observation time and allowed the survival of hMSCs and pACs for 35 days in culture. The SEM analyses revealed an intimate cell-biomaterial interaction for both cell types showing cell spreading, formation of numerous filopodia and ECM deposition. Both cell types revealed initial proliferation, decreasing after 14 days and becoming elevated again after 21 days. hMSCs formed cell clusters, whereas pACs showed an even distribution. Both cell types filled more and more the pores of the scaffold. The relative gene expression of cartilage-specific markers could be proven for hMSCs and pACs. Cell associated sGAGs deposition could be demonstrated by Alcian blue staining and sGAGs were elevated in the beginning and end of the culturing period. While the production of collagen type II could be observed with both cell types, the synthesis of aggrecan could not be detected in scaffolds seeded with hMSCs. hMSCs and pACs adhered, spread and survived on the novel bioactive glass scaffolds and exhibited a chondrocytic phenotype

Mesenchymal Stem Cells (MSCs) are a candidate cell type for treating osteoarthritic focal defects. In vivo, cartilage and bone marrow reside under a low oxygen tension, between 2–7% oxygen or physioxia, that has been shown to enhance MSC chondrogenesis. However, chondrogenesis is inhibited in the presence of IL-1. Here, it was hypothesized that physioxia reduces IL-1 inhibited chondrogenesis. Human MSCs (Mean age, 32 years; n = 9) were split equally for expansion under either 2% (physioxia) or 20% (hyperoxia) oxygen. Chondrogenic pellets (2 × 10. 5. MSCs/pellet) were formed and cultured in the presence of 10 ng/ml TGF-b. 1. and in combination with either 0.1 or 0.5 ng/ml IL-1 under their respective expansion conditions. Pellets were assessed for their wet weight, GAG and collagen II content and evaluated histologically (Collagen X and MMP-13). Statistical analysis was performed using a Two-way ANOVA with Tukey post-hoc test, significant differences stated when p < 0.05. A significant dose-dependent IL-1 inhibition in chondrogenesis was observed for pellet wet weight and GAG content under hyperoxia (p < 0.05). Physioxia alone significantly increased wet weight, GAG and collagen II content (p < 0.05) compared to hyperoxia. A donor-dependant response was observed, whereby 80% of donors responded to physioxia and their analysis showed significant increases in wet weight and GAG content in the presence IL-1(p < 0.05). Furthermore, reduced hypertrophy marker expression (Collagen X and MMP-13) was observed under physioxia in the presence of IL-1. The molecular signalling mechanisms controlling these responses are to be investigated

Introduction and Objective. Current cartilage repair strategies lack adequate tissue integration capacity and often present mechanical failure at the graft-to-host tissue junction. The design of multilayered osteochondral tissue engineering (TE) constructs is an attractive approach to overcome these problems. However, calcium ion-release from resorbable bone-replacement materials was suggested to compromise chondrogenic differentiation of adjacent cartilage tissue and it is unclear whether articular chondrocytes (AC) or mesenchymal stroma cells (MSC) are more sensitive to such conditions. Aim of the study was to compare how elevated calcium levels affect cartilage matrix production during re-differentiation of AC versus chondrogenic differentiation of MSC. The results of this study will help to identify the ideal cell source for growth of neocartilage adjacent to a calcified bone replacement material for design of multilayered osteochondral TE approaches. Materials and Methods. Expanded human AC and MSC (6–12 donors per group) were seeded in collagen type I/III scaffolds and cultured under standard chondrogenic conditions at control (1.8mM) or elevated (8.0mM) CaCl2 for 35 days. Proteoglycan and collagen production were assessed via radiolabel-incorporation, ELISA, qPCR and Western blotting. Differences between groups or cell types were calculated using the non-parametric Wilcoxon or Mann-Whitney U test, respectively, with p < 0.05 considered significant. Results. Elevated calcium significantly reduced GAG synthesis (63% of control, p=0.04) and chondrogenic marker expression of AC, lowering the GAG/DNA content (47% of control, p=0.004) and collagen type II deposition (24% of control, p=0.05) of neocartilage compared to control conditions. Opposite, at elevated calcium levels MSC-derived chondrocytes significantly increased GAG synthesis (130% of control, p=0.02) and collagen type II content (160% of control, p=0.03) of cartilage compared to control tissue. Chondrogenic and hypertrophic marker expression was insensitive to calcium levels in MSC-derived chondrocytes. As a result, maturation under elevated calcium allowed for a significantly higher GAG/DNA content in MSC-derived samples compared to AC constructs, although under control conditions both groups developed similarly. Conclusions. AC and MSC showed an opposite reaction to elevation of calcium levels regarding cartilage matrix production and we propose MSC as a preferred cell source to grow chondrocytes in vicinity to calcified bone replacement materials. Since MSC remained prone to hypertrophy under elevated calcium, trizonal cartilage TE constructs, where an AC-layer is separated from the bone replacement phase by an intermediate layer of MSC appear as an ideal design for multilayered osteochondral TE with respect to calcium sensitivity of cells and protection of the upper cartilage layer from hypertrophy

Introduction. Human Mesenchymal stem cells (hMSCs) are a promising source for articular cartilage repair. Unfortunately, under in vitro conditions, chondrogenically differentiated hMSCs have the tendency to undergo hypertrophy similar to growth plate chondrocytes. Retinoic acid (RA) signalling plays a key role in growth plate hypertrophy. Whilst RA agonists block chondrogenesis and foster hypertrophy during later stages, RAR inverse agonists (IA) enhance chondrogenesis when applied early in culture. Therefore, we hypothesized that treatment with RAR IA will attenuate hypertrophy in chondrogenically differentiated hMSCs. To test this hypothesis, we analysed early (initial chondrogenic differentiation) and late treatment (hypertrophy stage) of hMSCs with an RAR IA. Methods. Pellets of passage 2 hMSCs were formed in V-bottom well plates by centrifugation and pre-differentiated in a chemically defined medium containing 10ng/mL TGFß (CM+) for 14 days. Thereafter, pellets were cultured for an additional 14 days under 6 conditions: CM+, CM- (w/out TGFß), and hypertrophic medium (CM- with 25 ng/ml BMP 4, w/out dexamethasone). Each of these first three conditions was additionally supplemented with the RA receptor (RAR) inverse agonist BMS493 (BMS) at 2μM after 14 days of chondrogenic pre-differentiation. One additional BMP4 group was supplemented with BMS from the beginning of chondrogenic differentiation until day 14. The pellets were assessed for gene expression (Col 2, Col 10, Col 1 and MMP13) and histologically using dimethyl methylene blue (DMMB), alkaline phosphatase staining (ALP) and collagen II and X immunohistochemistry. Results. Hypertrophy was reduced by addition of BMS at day 14 and further reduced by addition from the beginning. BMS treatment resulted in smaller cells under hypertrophic conditions, higher collagen II content in chondrogenic groups and reduction in collagen X production and ALP activity in every condition. Gene expression data for hypertrophic markers, collagen X and MMP13, were upregulated under the influence of BMP4 but a distinct downregulation in MMP13 expression was shown upon addition of BMS during the late stage differentiation and further reduced upon addition during early stage chondrogenesis. Furthermore, Collagen X expression was reduced by early BMS treatment. Discussion. The treatment with the RAR IA, BMS, attenuated hypertrophic changes in chondrogenically differentiated hMSCs as demonstrated by histology, immunohistochemistry and PCR. These findings suggest an additional approach to attenuate hypertrophy in chondrogenically differentiated hMSCs. Current studies are exploring the timing and dose of BMS to most efficaciously prevent hypertrophy

Gene therapy with insulin-like growth factor-1 (IGF-1) increases matrix production and enhances chondrocyte proliferation and survival in vitro. The purpose of this study was to determine whether arthroscopically-grafted chondrocytes genetically modified by an adenovirus vector encoding equine IGF-1 (AdIGF-1) would have a beneficial effect on cartilage healing in an equine femoropatellar joint model. A total of 16 horses underwent arthroscopic repair of a single 15 mm cartilage defect in each femoropatellar joint. One joint received 2 × 10. 7. AdIGF-1 modified chondrocytes and the contralateral joint received 2 × 10. 7. naive (unmodified) chondrocytes. Repairs were analysed at four weeks, nine weeks and eight months after surgery. Morphological and histological appearance, IGF-1 and collagen type II gene expression (polymerase chain reaction, in situ hybridisation and immunohistochemistry), collagen type II content (cyanogen bromide and sodium dodecyl sulphate-polyacrylamide gel electrophoresis), proteoglycan content (dimethylmethylene blue assay), and gene expression for collagen type I, matrix metalloproteinase (MMP)-1, MMP-3, MMP-13, aggrecanase-1, tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) and TIMP-3 were evaluated. Genetic modification of chondrocytes significantly increased IGF-1 mRNA and ligand production in repair tissue for up to nine weeks following transplantation. The gross and histological appearance of IGF-1 modified repair tissue was improved over control defects. Gross filling of defects was significantly improved at four weeks, and a more hyaline-like tissue covered the lesions at eight months. Histological outcome at four and nine weeks post-transplantation revealed greater tissue filling of defects transplanted with genetically modified chondrocytes, whereas repair tissue in control defects was thin and irregular and more fibrous. Collagen type II expression in IGF-1 gene-transduced defects was increased 100-fold at four weeks and correlated with increased collagen type II immunoreaction up to eight months. Genetic modification of chondrocytes with AdIGF-1 prior to transplantation improved early (four to nine weeks), and to a lesser degree long-term, cartilage healing in the equine model. The equine model of cartilage healing closely resembles human clinical cartilage repair. The results of this study suggest that cartilage healing can be enhanced through genetic modification of chondrocytes prior to transplantation

The fibrocartilaginous enthesis displays a complex interface between two mechanically dissimilar tissues, namely tendon and bone. This graded transition zone consists of parallel collagen type I fibres arising from the tendon and inserting into bone across zones of fibrocartilage with aligned collagen type I and collagen type II fibres and mineralised fibrocartilage. Due the high stress concentrations arising at the interface, entheses are prone to traumatic and chronic overuse injuries such as rotator cuff and anterior cruciate ligament (ACL) tears. Treatment strategies range from surgical reattachment for complete tears and conservative treatments (physiotherapy, anti-inflammatory drugs) in chronic inflammatory conditions. Generally, the native tissue architecture is not re-established and mechanically inferior scar tissue is formed. Current interfacial tissue engineering approaches pose scaffold-associated drawbacks and limitations, such as foreign body response. Using a thermo-responsive electrospun scaffold that provides architectural signals similar to native tissues and can be removed prior to implantation, we aim to develop an ECM-rich, cell-based implant for tendon-enthesis regeneration. Alcian blue staining revealed highest sGAG deposition in cell (human adipose derived stem cells) sheets grown on random electrospun fibres and lowest sGAG deposition in collagen type I sponges. Cells did not show an equal distribution throughout the collagen type II scaffolds but tended to form localised aggregates. Thermo-responsive electrospun fibres with random and aligned fibre orientation provided an adequate three-dimensional environment for chondrogenic differentiation of multilayer hADSC-sheets shown by high ECM-production, especially high sGAG deposition. Chondrogenic cell sheets showed increased expression of SOX9, COL2A1, COL1A1, COMP and ACAN after 7 days of chondrogenic induction when compared to pellet culture. Anisotropic fibres enabled the generation of aligned chondrogenic cell sheets, shown by cell and collagen fibre alignment. Thermoresponsive electrospun fibres showed high chondro-inductivity due to their three-dimensionality and therefore pose a promising tool for the generation of scaffold-free multilayer constructs for tendon-enthesis repair within short culture periods. Aligned chondrogenic cell sheets mimic the zonal orientation of the native enthesis as the fibrocartilaginous zone exhibits high collagen alignment

Introduction. Current cell-based treatments and marrow stimulating techniques to repair articular cartilage defects are limited in restoring the tissue in its native composition. Despite progress in cartilage tissue engineering and chondrogenesis in vitro, the main limitation of this approach is the progression towards hypertrophy during prolonged culture in pellets or embedded in biomaterials. The objectives of this study were (A) to compare human bone marrow-derived mesenchymal stromal cells (hMSC) chondrogenesis and hypertrophy in pellet culture from single cells or cell spheroids and (B) to investigate the effect of tyramine-modified hyaluronic acid (THA) and collagen I (Col) content in composite hydrogels on the chondrogenesis and hypertrophy of encapsulated hMSC spheroids. Materials and Methods. Pellet cultures were prepared either from hMSC single cells (250’000 cells/pellet) or hMSC spheroids (282 cells/spheroid) at the same final cell concentration (250’000 cells/pellet = 887 spheroids/pellet). The effect of polymer concentration on encapsulated hMSC spheroids (887 spheroids/hydrogel) was investigated in THA-Col hydrogels (50μl) at the following concentrations (THA-Col mg/ml): Group (1) 12.5–2.5, (2) 16.7–1.7, (3) 12.5–1.7, (4) 16.7–2.5 mg/ml. All samples were cultured for 21 days in standard chondrogenic differentiation medium containing 10ng/ml TGF-β1. Chondrogenic differentiation and hypertrophy of both pellet cultures and hMSCs spheroids encapsulated in THA-Col were analysed using gene expression analysis (Aggrecan (ACAN), COL1A1, COL2A1, COL10A1), dimethylmethylene-Blue assay to quantify glycosaminoglycans (GAGs) retained in the samples and (immuno-) histological staining (Safranin-O, collagen II, aggrecan) on day 1 and day 21 (n=3 donors). Results. The culture of hMSCs in pellets based on single cells or spheroids resulted in an increase in chondrogenic-associated markers COL2A1 (2’900–3’400-fold) and ACAN (45–47-fold) compared to respective samples on day 1 in both groups. GAGs increased in spheroid pellets to 21.2±3.4 mg/ml and in single cell pellets to 20.8±6.6 mg/ml on day 21. Comparing the levels of hypertrophic markers, single cell pellets showed 7-fold and 20-fold higher expression of COL1A1 and COL10A1 than spheroid pellets on day 21. The encapsulation of hMSC spheroids in THA-Col resulted in an upregulation of chondrogenic-associated markers and GAG content in all hydrogels with differences in cell differentiation related to the Col and THA polymer ratio, while level of hypertrophy was comparable in all groups with values similar to the spheroid pellet group. Spheroids embedded in hydrogels with lower THA content (group 1 and 3) resulted in more pronounced chondrogenic phenotype marked by upregulation of COL2A1 (3’200–4’500-fold) and ACAN (152–179-fold) relative to the respective samples on day 1. Spheroids embedded in higher THA content hydrogels (group 2 and 4) showed less pronounced chondrogenesis marked by lower upregulation of COL2A1 (980–1800-fold) and ACAN (25–68-fold, relative to day 1 samples). This was confirmed by quantification of GAGs, increasing from 2.5±1.9 and 2.5±1.7 mg/ml (day 1) to 11.4±2.5 and 9.9±3.8 mg/ml on day 21 for groups 1 and 4, respectively. (Immuno-) histological stainings resulted in a more homogenous staining in lower THA content hydrogels compared to a more local matrix deposition in samples with higher THA content. Conclusion. The reduced level of hypertrophy in hMSC pellets prepared from cell spheroids compared to single cell pellets at same cell count might be related to the packing density of the cells with cells being more densely packed in single cell pellets compared to pellets from spheroids. Investigating the effect of polymer ratios on chondrogenesis, it seems that the THA content is the driving factor influencing hMSC chondrogenesis rather than Col content in THA-Col composites at comparable mechanical properties. This study highlights the feasibility to use hMSC spheroids as alternative approach to study in vitro chondrogenic differentiation and the suitability to investigate the effect of biomaterial composition on chondrogenesis and hMSC hypertrophy

The regenerative capacity of hyaline cartilage is greatly limited. To prevent the onset of osteoarthritis, cartilage defects have to be properly treated. Cartilage, tissue engineered by mean of bioactive glass (BG) scaffolds presents a promising approach. Until now, conventional BGs have been used mostly for bone regeneration, as they are able to form a hydroxyapatite (HA) layer and are therefore, less suited for cartilage reconstruction. The aim of this study is to compare two BGs based on a novel BG composition tailored specifically for cartilage (CAR12N) and patented by us with conventional BG (BG1393) with a similar topology. The highly porous scaffolds consisting of 100% BG (CAR12N, CAR12N with low Ca2+/Mg2+ and BG1393) were characterized and dynamically seeded with primary porcine articular chondrocytes (pACs) or primary human mesenchymal stem cells (hMSCs) for up to 21 days. Subsequently, cell viability, DNA and glycosaminoglycan contents, cartilage-specific gene and protein expression were evaluated. The manufacturing process led to a comparable high (over 80%) porosity in all scaffold variants. Ion release and pH profiles confirmed bioactivity for them. After both, 7 and 21 days, more than 60% of the total surfaces of all three glass scaffold variants was densely colonized by cells with a vitality rate of more than 80%. The GAG content was significantly higher in BG1393 colonized with pACs. In general, the GAG content was higher in pAC colonized scaffolds in comparison to those seeded with hMSCs. The gene expression of cartilage-specific collagen type II, aggrecan, SOX9 and FOXO1 could be detected in all scaffold variants, irrespectively whether seeded with pACs or hMSCs. Cartilage-specific ECM components could also be detected at the protein level. In conclusion, all three BGs allow the maintenance of the chondrogenic phenotype or chondrogenic differentiation of hMSCs and thus, they present a high potential for cartilage regeneration

Mesenchymal stem cells (MSCs) have the potential to repair and regenerate damaged tissues in response to injury, such as fracture or other tissue injury. Bone marrow and adipose tissue are the major sources of MSCs. Previous studies suggested that the regenerative activity of stem cells can be enhanced by exposure to tissue microenvironments. The aim of our project was to investigate whether extracellular matrix (ECM) engineered from human induced pluripotent stem cells-derived mesenchymal-like progenitors (hiPSCs-MPs) can enhance the regenerative potential of human bone marrow mesenchymal stromal cells (hBMSCs). ECM was engineered from hiPSC-MPs. ECM structure and composition were characterized before and after decellularization using immunofluorescence and biochemical assays. hBMSCs were cultured on the engineered ECM, and differentiated into osteogenic, chondrogenic and adipogenic lineages. Growth and differentiation responses were compared to tissue culture plastic controls. Decellularization of ECM resulted in efficient cell elimination, as observed in our previous studies. Cultivation hBMSCs on the ECM in osteogenic medium significantly increased hBMSC growth, collagen deposition and alkaline phosphatase activity. Furthermore, expression of osteogenic genes and matrix mineralization were significantly higher compared to plastic controls. Chondrogenic micromass culture on the ECM significantly increased cell growth and expression of chondrogenic markers, including glycosaminoglycans and collagen type II. Adipogenic differentiation of hBMSCs on the ECM resulted in significantly increased hBMSC growth, but significantly reduced lipid vacuole deposition compared to plastic controls. Together, our studies suggest that BMSCs differentiation into osteogenic and chondrogenic lineages can be enhanced, whereas adipogenic activity is decreased by the culture on engineered ECM. Contribution of specific matrix components and underlying mechanisms need to be further elucidated. Our studies suggest that the three-lineage differentiation of aged BMSCs can be modulated by culture on hiPSC-engineered ECM. Further studies are aimed at scaling-up to three-dimensional ECM constructs for osteochondral tissue regeneration

Low back pain is strongly associated with degeneration of the intervertebral disc (IVD). During degeneration, altered matrix synthesis and increased matrix degradation, together with accompanied cell loss is seen particularly in the nucleus pulposus (NP). It has been proposed that notochordal (NC) cells, embryonic precursors for the cells within the NP, could be utilized for mediating IVD regeneration. However, injectable biomaterials are likely to be required to support their phenotype and viability within the degenerate IVD. Therefore, viability and phenotype of NC cells were analysed and compared within biomaterial carriers subjected to physiological oxygen conditions over a four-week period were investigated. Porcine NC cells were incorporated into three injectable hydrogels: NPgel (a L-pNIPAM-co-DMAc hydrogel), NPgel with decellularized NC-matrix powder (dNCM) and Albugel (an albumin/ hyaluronan hydrogel). The NCs and biomaterials constructs were cultured for up to four weeks under 5% oxygen (n=3 biological repeats). Histological, immunohistochemical and glycosaminoglycans (GAG) analysis were performed to investigate NC viability, phenotype and extracellular matrix synthesis and deposition. Histological analysis revealed that NCs survive in the biomaterials after four weeks and maintained cell clustering in NPgel, Albugel and dNCM/NPgel with maintenance of morphology and low caspase 3 staining. NPgel and Albugel maintained NC cell markers (brachyury and cytokeratin 8/18/19) and extracellular matrix (collagen type II and aggrecan). Whilst Brachyury and Cytokeratin were decreased in dNCM/NPgel biomaterials, Aggrecan and Collagen type II was seen in acellular and NC containing dNCM/NPgel materials. NC containing constructs excreted more GAGs over the four weeks than the acellular controls. NC cells maintain their phenotype and characteristic features in vitro when encapsulated into biomaterials. NC cells and biomaterial construct could potentially become a therapy to treat and regenerate the IVD