Sylvia Nürnberger

NetwOArk is a consortium founded under the framework of the COST Action CA21110 “Building an open European Network on Osteoarthritis research“, aiming to contribute to the progress of osteoarthritis research and translation to clinics, by uniting the relevant stakeholders under one umbrella. These stakeholders are researchers, clinicians, industry and especially also the patients and patient organizations. NetwOArk is convinced that an intensive exchange of all these interest groups is key for successful development and implementation of novel therapies.NetwOArk is structured in four working groups, focusing on patient engagement & information (WG1), translational aspects (WG2), patient stratification (WG3) and the preparation of the future of NetwOArk after ending of the COST Action program (WG4) The four working groups achieved the following goals within the last grant periods:WG 1collected data from almost 600 people on the survey about patients' knowledge of OA and their treatment options.WG 2 organized a series of webinars on translational aspects of drugs and management of osteoarthritis as well as a symposium on integrated care in osteoarthritis management and prepared manuscripts on translational topics such as in vitro and ex vivo models.WG 3 submitted two manuscripts focused on OA stratification terminology from clinical and molecular perspectives.WG 4 founded the European Patient Council (EPC) during a meeting in Umhausen Tyrol/Austria with patient organizations of four countries, extending to 11 countries by the beginning of 2025.Eleven Short Term Scientific Missions (STSM) were awarded to young investigators to conducted research at partner laboratories.All those activities will be followed up in the current and upcoming grant periods and the COST Action CA21110 is still open for potential new members who want to actively contribute to those activities.

Aims: Spontaneous neck fractures are feared complications of cephalomedullary nail removal after successful healing of per- and subtrochanteric fractures. To date, the initial postoperative stability as well as the correct weightbearing regimen remain unclear. The aim of this biomechanical ex vivo study was to evaluate the initial postoperative failure load after hardware removal of specimens, which received cephalomedullary nails during their lifetime.Methods: A total of 20 specimens of voluntary body donors were included in this study. Group 1 (n = 10) consisted of specimens that received cephalomedullary nails during their lifetime due to per- or subtrochanteric fractures. Each individual was matched for age, sex, femur size, and neck-shaft angle (Group 2 = control, n = 10). Biomechanical testing was performed in a single-leg stance setting, and volumetric bone mineral density (vBMD) was measured proximally at the femoral neck and distally at the epicondyles.Results: Groups 1 and 2 differed significantly in terms of failure loads (p = 0.002), fracture types, and ratios of proximal and distal vBMD (p = 0.035). Femora after nail removal were significantly weaker (1,835.0 N vs 4,523.0 N) and showed lower ratios of proximal to distal vBMD (0.74 vs 1.18), which indicated altered stress distributions at the femoral neck in presence of femoral neck screws. They were further characterized by predominantly subcapital buckle-type fractures, while the control Group 2 showed predominantly transcervical fractures.Conclusion: Altered stress distribution in presence of femoral neck screws leads to changes in biomechanical properties of the proximal femur, resulting in potentially unstable situations after nail removal in clinical settings. Elective removal of cephalomedullary nails should be undertaken with caution in view of the potentially increased fracture risk.Cite this article: Bone Joint Res 2025;14(5):365–372.

Decellularized articular cartilage of human origin presents itself as the most homologous filling material for focal cartilage defects. Yet, the full repopulation of the exceptionally dense collagen construct has never been achieved without providing host cells with artificially created migration paths into the matrix. Within this study, we examine the use of a femtosecond laser to engrave fine patterns into human articular cartilage before decellularization and GAG depletion (decell‐deGAG). Scaffolds were tested for decellularization success and mechanical behavior. Seeding tests were performed to assess biocompatibility and examine the performance in a simulated defect environment using an osteochondral plug model in vitro and in vivo in an ectopic nude mouse model. The composition and structure of the newly formed repair tissue and macrophage recruitment were observed via histology. The femtosecond laser was successful in engraving deep, fine structures into the matrix without the thermal damage found with other laser techniques. Engraving was also beneficial for decellularization success. The resulting decell‐deGAG scaffold featured a compressive modulus many times stronger than other biomaterials commonly used for cartilage regeneration and presents a defect filling material that is similar to the tissue it is meant to replace. Moreover, the incisions promoted the repopulation with therapeutically relevant cells. A favorable spatial environment inside the incisions facilitated the formation of repair tissue that mimics hyaline cartilage in composition and collagen orientation. Scaffolds were well‐integrated within simulated defects. Femtosecond laser–engraved cartilage poses an authentic defect filling material with cartilage‐like properties. When used in combination with cell seeding, it promotes the formation of differentiated repair tissue. Thus, the hereby presented biomaterial shows great potential in improving the repair of focal cartilage defects and reducing long‐term graft failures.

The recently developed high-throughput system for cell spheroid generation (SpheroWell) is a promising technology for cost- and time-efficient in vitro analysis of, for example, chondrogenic differentiation. It is a compartmental growth surface where spheroids develop from a cell monolayer by self-assembling and aggregation. In order to automatize the analysis of spheroids, we aimed to develop imaging software and improve the localization of cell compartments and fully formed spheroids. Our workflow provides automated detection and localization of spheroids in different formation stages within Petri dishes based on images created with a low-budget camera imaging setup. This automated detection enables a fast and inexpensive analysis workflow by processing a stack of images within a short period of time, which is essential for the extraction of early readout parameters. Our workflow combines image processing algorithms and deep learning-based image localization/segmentation methods like Mask R-CNN and Unet++. These methods are refined by an evolution strategy for automated grid detection, which is able to improve the overall segmentation and classification quality. Besides the already pre-trained neural networks and predefined image processing parameters, our evolution-based post-processing provides the required adaptability for our workflow to deliver a consistent and reproducible quality. This is especially important due to the use of a low-budget imaging setup with various light conditions. The to-be-detected objects of the three different stages show improved results using our evolutionary post-processing for monolayer and starting aggregation with Dice coefficients of 0.7301 and 0.8562, respectively, compared with the raw scores of 0.2879 and 0.8187. The Dice coefficient of the fully formed spheroids in both cases is 0.8829. With our algorithm, we provide automated analyses of cell spheroid by self-assembling in SpheroWell dishes, even if the images are created using a low-budget camera setup.

Bovine serum albumin (BSA) plays a crucial role in cell culture media, influencing cellular processes such as proliferation and differentiation. Although it is commonly included in chondrogenic differentiation media, its specific function remains unclear. This study explores the effect of different BSA concentrations on the chondrogenic differentiation of human adipose-derived stromal/stem cells (hASCs). hASC pellets from six donors were cultured under chondrogenic conditions with three BSA concentrations. Surprisingly, a lower BSA concentration led to enhanced chondrogenesis. The degree of this effect was donor-dependent, classifying them into two groups: (1) high responders, forming at least 35% larger, differentiated pellets with low BSA in comparison to high BSA; (2) low responders, which benefitted only slightly from low BSA doses with a decrease in pellet size and marginal differentiation, indicative of low intrinsic differentiation potential. In all cases, increased chondrogenesis was accompanied by hypertrophy under low BSA concentrations. To the best of our knowledge, this is the first study showing improved chondrogenicity and the tendency for hypertrophy with low BSA concentration compared to standard levels. Once the tendency for hypertrophy is understood, the determination of BSA concentration might be used to tune hASC chondrogenic or osteogenic differentiation.

Translational models for OA have used a variety of small (mouse, rat) and large (sheep, pig) animal models to evaluate the efficacy of a specific therapy. Clinical trials based on the results of these animal models have yielded mixed results with respect to the treatment of the disease. Due to greater stringency in EU regulations in the use of animal models for research, ex vivo models of OA (e.g. cartilage explants, bioreactors) are being developed to mimic human joint motion as well as the inflammatory milieu (e.g. IL-1β) that can be used to understand efficacy of therapy in a physiological environment. The development of these models can enable therapies to undergo clinical trials in patients without the necessity for long-term animal studies. This presentation will describe the state of the art in this field and will discuss whether there is potential to speed up translation from bench to bedside in the future.

Articular cartilage injuries are currently one of the world's top health concerns owing to its limited capacity of self‐renewal, thus raising to the economic burden in the healthcare system. Cell implantation strategies resorting to a suitable delivery platform hold a great promising approach to increase cell retention to be further supplied in a sufficient amount to the cartilage defects. So far, macromolecular engineering toolboxes for designing cell‐carrier devices with on‐demand cell delivery efficiency are rarely reported. Herein, anisotropically patterned mussel‐inspired membranes, comprising oppositely charged marine‐origin biopolymers (e.g., chitosan and alginate) combined in a multilayered fashion with catechol‐functionalized hyaluronic acid (DOPA‐HA), through electrostatically driven layer‐by‐layer (LbL) assembly approach, are developed. The seamless combination of nanotopography and catechol molecular cues in one single platform significantly augments ASC/TERT1 adhesion at the patterned DOPA‐HA membrane surface. These highest cell density membranes are further applied onto human chondral discs ex vivo models to evaluate their capability to act as cell delivery vehicles. Results show the successful cell migration and retention at cartilage surface, wherein they spread to inhabit both superficial empty lacunae and furrows. Therefore, the present study supplies an important strategy for designing cell delivery vehicles to be applied on cell‐based therapies.

Removing cellular material from a tissue, a process called decellularization, reduces the risk of adverse host reactions, allows for efficient decontamination, and extends the shelf-life of the matrix. It facilitates the use of cartilage tissue as human-derived allograft, thus providing the field of cartilage regeneration with a biomaterial unmatched in its similarity to native cartilage in terms of structure, composition, and mechanical properties. The dense extracellular matrix of articular cartilage requires a particularly thorough process to achieve the removal of cells, cell debris, and reagents used in the process. In our studies (Nürnberger et al., EBioMedicine 64:103196, 2021; Schneider et al., Tissue Eng Part C Methods 22(12):1095–1107, 2016), we have successfully developed a protocol for achieving decellularization via physical, chemical, and enzymatic steps. Combining freeze-thaw cycles for devitalization, hydrochloric acid as decellularization agent and the enzymatic removal of glycosaminoglycans, results in an acellular scaffold that is fully biocompatible and promotes cellular attachment. The structure and sophisticated architecture of collagen type II is left intact. This chapter provides a comprehensive guide to the steps and reagents needed to decellularize articular cartilage. In addition to the standard decell-deGAG protocol, a fast option is given which is suitable for thin specimen. Histological evaluation is presented to illustrate treatment success. Key words Cartilage Decellularization Glycosaminoglycans Hydrochloric acid Decontamination

Cartilage damage typically starts at its surface, either due to wear or trauma. Treatment of these superficial defects is important in preventing degradation and osteoarthritis (OA). Biomaterials currently used for deep cartilage defects lack appropriate properties for this application. Therefore, we investigated photo-crosslinked methacrylamide-modified gelatin (gelMA) as a candidate for treatment of surface defects. It allows for liquid application, filling of surface defects and forming a protective layer after UV-crosslinking, thereby keeping therapeutic cells in place. GelMA and photo-initiator (Li-TPO) concentration were optimized for application as a carrier to create a favourable environment for human articular chondrocytes (hAC). Primary hAC were used in passages 3 and 5, encapsulated into two different gelMA concentrations (7.5 wt% (soft) and 10 wt% (stiff)) and cultivated for 3 weeks with TGF-β3 (0, 1 and 10 ng/mL). Higher TGF-β3 concentrations induced spherical cell morphology independent of gelMA stiffness, while low TGF-β3 concentrations only induced rounded morphology in stiff gelMA. Gene expression did not vary across gel stiffnesses. As a functional model gelMA was loaded with two different cell types (hAC and/or human adipose-derived stem cells (ASC/TERT1) and applied to human osteochondral osteoarthritic plugs. GelMA attached to the cartilage, smoothened the surface and retained cells in place. Resistance against shear forces was tested using a tribometer, simulating normal human gait and revealing maintained cell viability. In conclusion gelMA is a versatile, biocompatible material with good bonding capabilities to cartilage matrix, allowing sealing and smoothening of superficial cartilage defects while simultaneously delivering therapeutic cells for tissue regeneration.

Scaffold-free 3D cell cultures (e.g. pellet cultures) are widely used in medical science, including cartilage regeneration. Their drawbacks are high time/reagent consumption and lack of early readout parameters. While optimisation was achieved by automation or simplified spheroid generation, most culture systems remain expensive or require tedious procedures. The aim of this study was to establish a system for resource efficient spheroid generation with additional early readout parameters. This was achieved by a new approach for spheroid generation via self-assembly from monolayer via compartmentation of cell culture surfaces utilising laser engraving (grid plates). The compartmentation triggered contraction and rolling up of the cell monolayer, finishing in condensation into a spheroid in human adipose-derived stem cell (ASC/TERT1) and human articular chondrocytes (hACs)-ASC/TERT1 co-cultures, when cultivated on grid plates under chondrogenic conditions. Plates with 1 and 3 mm grid size yielded stable diameters (about 140 µ m and 300 µ m, respectively). ASC/TERT1 spheroids fully formed within 3 weeks while co-cultures took 1–2 weeks, forming significantly faster with increasing hAC ratio ( p < 0.05 and 0.01 for 1:1 and 1:4 ASC/TERT1:hAC ratio, respectively). Co-cultures showed slightly lower spheroid diameters, due to earlier spheroid formation and incomplete monolayer formation. However, this was associated with a more homogeneous matrix distribution in the co-culture. Both showed differentiation capacity comparable to standard pellet culture in (immune-)histochemistry and RT-qPCR. To assess usability for cartilage repair, spheroids were embedded into a hydrogel (fibrin), yielding cellular outgrowth and matrix deposition, which was especially pronounced in co-cultures. The herein presented novel cell culture system is not only a promising tool for autonomous spheroid generation with the potential of experimental and clinical application in tissue engineering, but also for the generation of ‘building blocks’ for subsequential biofabrication strategies such as bioprinting.