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• The ultimate way to build organoid tissue for regeneration is to enable the cells to take the initiative to build suitable functions. • Mechanical irritation should be a necessary factor in the construction of musculoskeletal organoids for regeneration. • The construction of the organoids for regeneration should be stimulated by the suitable environment, such as light stimulation for the retinal organoid, sound wave stimulation for cochlear organoid, etc. It has always been a dream to construct tissues and even organs for transplantation to replace those with defects caused by diseases or injuries. Tissue engineering is another milestone in the developmental history of life science after cellular and molecular bioscience. Nevertheless, despite decades of rapid development, tissue-engineered biomaterials have not been widely used clinically. Biomaterials constructed by physical and chemical methods have lots of difficulty in precisely mimicking the macroscopic and microscopic structures of human tissues. The ultimate way to build organoid tissue for regeneration is to enable the cells to take the initiative and build suitable functions. Based on the thoughts of tissue engineering, organoid technology holds great potential as a research tool for a wide range of fields, including developmental biology, disease pathology, cell biology, precision medicine, and drug toxicity and efficacy testing. This technology also holds tremendous potential for regenerative medicine, as organoids present the possibility for autologous and allogeneic cell therapy through the replacement of damaged or diseased tissues with organoid-propagated tissue or stem cell populations. In this review work, we briefly outlook the development history of organoid technology, summarize the current bottlenecks and the underlying reasons, and propose the unified term "function-oriented design in tissue engineering", a new topic that may provide a solution to overcome these bottlenecks. [ABSTRACT FROM AUTHOR]

Neutrophils play a pivotal role in orchestrating the immune system response to biomaterials, the onset and resolution of chronic inflammation, and macrophage polarization. However, the neutrophil response to biomaterials and the consequent impact on tissue engineering approaches is still scarcely understood. Here, we report an in vitroculture model that comprehensively describes the most important neutrophil functions in the light of tissue repair. We isolated human primary neutrophils from peripheral blood and exposed them to a panel of hard, soft, naturally- and synthetically-derived materials. The overall trend showed increased neutrophil survival on naturally derived constructs, together with higher oxidative burst, decreased myeloperoxidase and neutrophil elastase and decreased cytokine secretion compared to neutrophils on synthetic materials. The culture model is a step to better understand the immune modulation elicited by biomaterials. Further studies are needed to correlate the neutrophil response to tissue healing and to elucidate the mechanism triggering the cell response and their consequences in determining inflammation onset and resolution.

Osteomyelitis is an inflammation of the bone and bone marrow that is most commonly caused by a Staphylococcus aureusinfection. Much of our understanding of the underlying pathophysiology of osteomyelitis, from the perspective of both host and pathogen, has been revised in recent years, with notable discoveries including the role played by osteocytes in the recruitment of immune cells, the invasion and persistence of S. aureusin submicron channels of cortical bone, and the diagnostic role of polymorphonuclear cells in implant-associated osteomyelitis. Advanced in vitrocell culture models, such as ex vivoculture models or organoids, have also been developed over the past decade, and have become widespread in many fields, including infectious diseases. These models better mimic the in vivoenvironment, allow the use of human cells, and can reduce our reliance on animals in osteomyelitis research. In this review, we provide an overview of the main pathologic concepts in osteomyelitis, with a focus on the new discoveries in recent years. Furthermore, we outline the value of modern in vitrocell culture techniques, with a focus on their current application to infectious diseases and osteomyelitis in particular.

Aims:To identify differential expression of noncoding RNAs after trypsinization in human mesenchymal stromal cells (hMSCs), focusing on miRNAs, piRNAs and circRNAs. Methods:hMSCs from the bone marrow of three donors were collected for RNA extraction, either lysed directly in monolayer or trypsinized and lysed within 30 min. Total RNA was isolated and sequenced for the evaluation of miRNA and piRNA expression or RNaseR treated and labeled for circRNA array hybridization. RT-qPCR was performed to evaluate the stability of candidate reference genes. Results & conclusions:Alterations in levels of several noncoding RNAs are rapidly induced after trypsinization of hMSCs, affecting critical pathways. This should be carefully considered for a proper experimental design.

Introduction:Mesenchymal stem cells (MSCs) are considered a promising cell source for cartilage repair strategies due to their chondrogenic differentiation potential. However, their in vitrotendency to progress toward hypertrophy limits their clinical use. This unfavorable result may be due to the fact that MSCs used in tissue engineering approaches are all at the same developmental stage, and have lost crucial spatial and temporal signaling cues. In this study, we sought to investigate the effect of a spatial parathyroid hormone-related protein (PTHrP) signaling gradient on the chondrogenic differentiation of MSCs and progression to hypertrophy.Methods:Human bone marrow-derived MSCs were transduced with adenoviral vectors overexpressing PTHrP and seeded into fibrin-poly(ester-urethane) scaffolds. To investigate the effect of a spatial PTHrP signaling gradient, scaffolds were seeded with PTHrP-overexpressing MSCs positioned on top of the scaffold, with untransduced MSCs seeded evenly within. Scaffolds were cultured with or without 2 ng/mL transforming growth factor (TGF)-β1 for 28 days.Results:PTHrP overexpression increased glycosaminoglycan (GAG) production by MSCs irrespective of TGF-β1 treatment, and exerted differential effects on chondrogenic and hypertrophic gene expression when MSCs were cultured in the presence of a PTHrP signaling gradient. Furthermore, PTHrP-overexpressing MSCs were associated with an increase of endogenous TGF-β1 production and reduced total MMP-13 secretion compared to controls.Conclusion:The presence of a spatial PTHrP signaling gradient may support chondrogenic differentiation of MSCs and promote the formation of a more stable cartilage phenotype in tissue engineering applications.

Aging is the most prominent risk factor triggering several degenerative diseases, such as osteoarthritis (OA). Due to its poor self-healing capacity, once injured cartilage needs to be reestablished. This process might be approached through resorting to cell-based therapies and/or tissue engineering. Human mesenchymal stem cells (MSCs) represent a promising approach due to their chondrogenic differentiation potential. Presently, in vitrochondrogenic differentiation of MSCs is limited by two main reasons as follows: aging of MSCs, which determines the loss of cell proliferative and differentiation capacity and MSC-derived chondrocyte hypertrophic differentiation, which limits the use of these cells in cartilage tissue regeneration approach. The effect of aging on MSCs is fundamental for stem cell-based therapy development, especially in older subjects. In the present review we focus on homeostasis alterations occurring in MSC-derived chondrocytes during in vitroaging. Moreover, we deal with potential cell aging regulation approaches, such as cell stimulation through telomerase activators, mechanical strain, and epigenetic regulation. Future investigations in this field might provide new insights into innovative strategies for cartilage regeneration and potentially inspire novel therapeutic approaches for OA treatment.

/objective The use of acellular hydrogels to repair osteochondral defects requires cells to first invade the biomaterial and then to deposit extracellular matrix for tissue regeneration. Due to the diverse physicochemical properties of engineered hydrogels, the specific properties that allow or even improve the behaviour of cells are not yet clear. The aim of this study was to investigate the influence of various physicochemical properties of hydrogels on cell migration and related tissue formation using in vitro, ex vivoand in vivomodels.

The 3D printing process of fused deposition modelling is an attractive fabrication approach to create tissue-engineered bone substitutes to regenerate large mandibular bone defects, but often lacks desired surface porosity for enhanced protein adsorption and cell adhesion. Solvent-based printing leads to the spontaneous formation of micropores on the scaffold’s surface upon solvent removal, without the need for further post processing. Our aim is to create and characterize porous scaffolds using a new formulation composed of mechanically stable poly(lactic-co-glycol acid) and osteoconductive β-tricalcium phosphate with and without the addition of elastic thermoplastic polyurethane prepared by solvent-based 3D-printing technique. Large-scale regenerative scaffolds can be 3D-printed with adequate fidelity and show porosity at multiple levels analysed via micro-computer tomography, scanning electron microscopy and N2sorption. Superior mechanical properties compared to a commercially available calcium phosphate ink are demonstrated in compression and screw pull out tests. Biological assessments including cell activity assay and live-dead staining prove the scaffold’s cytocompatibility. Osteoconductive properties are demonstrated by performing an osteogenic differentiation assay with primary human bone marrow mesenchymal stromal cells. We propose a versatile fabrication process to create porous 3D-printed scaffolds with adequate mechanical stability and osteoconductivity, both important characteristics for segmental mandibular bone reconstruction.

Mesenchymal stem cells (MSCs) are increasingly being used in tissue engineering and cell‐based therapies in all fields ranging from orthopedic to cardiovascular medicine. Despite years of research and numerous clinical trials, MSC therapies are still very much in development and not considered mainstream treatments. The majority of approaches rely on an in vitro cell expansion phase in monolayer to produce large cell numbers prior to implantation. It is clear from the literature that this in vitro expansion phase causes dramatic changes in MSC phenotype which has very significant implications for the development of effective therapies. Previous reviews have sought to better characterize these cells in their native and in vitro environments, described known stem cell interactions within the bone marrow, and discussed the use of innovative culture systems aiming to model the bone marrow stem cell niche. The purpose of this review is to provide an update on our knowledge of MSCs in their native environment, focusing on bone marrow‐derived MSCs. We provide a detailed description of the differences between naive cells and those that have been cultured in vitro and examine the effect of isolation and culture parameters on these phenotypic changes. We explore the concept of “one step” MSC therapy and discuss the potential cellular and clinical benefits. Finally, we describe recent work attempting to model the MSC bone marrow niche, with focus on both basic research and clinical applications and consider the challenges associated with these new generation culture systems. StemCells2014;32:1713–1723

Currently available methods to treat articular cartilage defects still fail to demonstrate satisfactory outcomes for many patients. Functional tissue engineering using human bone marrow-derived mesenchymal stem cells (hMSCs) is a promising alternative approach for the treatment of these defects. This study strived to investigate the combined effect of complex mechanical stimulation and adenoviral-mediated overexpression of bone morphogenetic protein 2 (BMP-2) on hMSC chondrogenesis. hMSCs were encapsulated in a fibrin hydrogel and seeded into biodegradable polyurethane (PU) scaffolds. A novel three-dimensional transduction protocol was used to transduce cells with an adenovirus encoding for BMP-2 (Ad.BMP-2). Control cells were left untransduced. Cells were cultured for 7 or 28 days in a chondropermessive medium, which lacks any exogenous growth factors. Thereby, the in vivosituation is mimicked more precisely. hMSCs in fibrin-PU composite scaffolds were either left as free-swelling controls or mechanically stimulated using a custom-built bioreactor system that is able to generate joint-like forces. Outcome parameters measured were BMP-2 concentration within the culture medium, and biochemical and gene expression analysis. Mechanical stimulation resulted in an upregulation of chondrogenic genes. Further, glycosaminoglycan (GAG)/DNA ratios were elevated in mechanically stimulated groups. Transduction with Ad.BMP-2 led to a pronounced upregulation of the gene aggrecan and an upregulation of Sox9message after 7 days. Furthermore, a synergistic effect in combination with mechanical stimulation on collagen 2 message was detected after 7 days. This synergistic increase was more than 8-fold if compared to the additive effect of the application of each stimulus on its own. However, BMP-2 overexpression consistently resulted in a trend toward decreased GAG/DNA ratios in both mechanical stimulated and unloaded groups.

Objective: To explore the effect of shifting in vitroculture conditions regarding cellular passage and onset of loading within matrix-associated bovine articular chondrocytes cultured under free-swelling and/or dynamical loading conditions on general chondrocyte maturation.Methods: Primary or passage 3 bovine chondrocytes were seeded in fibrin-polyurethane scaffolds. Constructs were cultured either free-swelling for 2 or 4 weeks, under direct mechanical loading for 2 or 4 weeks, or free swelling for 2 weeks followed by 2 weeks of loading. Samples were collected for glycosaminoglycan (GAG) quantification, mRNA expression of chondrogenic genes, immunohistochemistry, and histology.Results: Mechanical loading generally stimulated GAG synthesis, up-regulated chondrogenic genes, and improved the accumulation of matrix in cell-laden constructs when compared with free-swelling controls. Primary chondrocytes underwent more effective cartilage maturation when compared with passaged chondrocytes. Constructs of primary chondrocytes that were initially free-swelling followed by 2 weeks of mechanical load (delayed) had overall highest GAG with strongest responsiveness to load regarding matrix synthesis. Constructs that experienced the delayed loading regime also demonstrated most favorable chondrogenic gene expression profiles in both primary and third passage cells. Furthermore, most intense matrix staining and immunostaining of collagen type II and aggrecan were visualized in these constructs.Conclusions: Primary chondrocytes were more effective than passage 3 chondrocytes when chondrogenesis was concerned. The most efficient chondrogenesis resulted from primary articular chondrocytes, which were initially free-swelling followed by a standardized loading protocol.

Topographical cartilage variation across the knee joint has been previously reported, but there is only limited information on such gene expression profiles. Articular chondrocytes from eight different topographical regions of bovine knee joints were seeded within three-dimensional scaffolds and further cultured under static conditions (unloaded control group) or subjected to an artificial joint environment within a bioreactor (loaded group). Constructs were analyzed for glycosaminoglycan (GAG), DNA, and expression of Collagen-1,-2,-10, Aggrecan, COMP, Sox9, PRG-4, PTHrp, and MMP-1,-3,-13 mRNA after 2 weeks of in vitroculture. Exclusively among loaded constructs the overall GAG production was significantly different between regions. Patella chondrocytes had overall highest, and cells from the femoral notch had overall lowest GAG/DNA under loaded conditions. Gene expression was significantly different between regions for all targets except for Sox9, PRG-4, and PTHrp among controls and with the exception of Aggrecan, Sox9, and PTHrp among loaded samples. Under mechanical stimulation Collagen-1,-2 and Aggrecan was highest at the patello-femoral joint, whereas it was lowest at typical cartilage biopsy regions. There is a clear topographical variation among distinct regions across the knee joint for gene and matrix expression profiles under static and foremost under dynamic conditions.

Articular cartilage injuries and degeneration affect a large proportion of the population in developed countries world wide. Stem cells can be differentiated into chondrocytes by adding transforming growth factor-β1 and dexamethasone to a pellet culture, which are unfeasible for tissue engineering purposes. We attempted to achieve stable chondrogenesis without any requirement for exogenous growth factors. Human mesenchymal stem cells were transduced with an adenoviral vector containing the SRY-related HMG-box gene 9 (SOX9), and were cultured in a three-dimensional (3D) hydrogel scaffold composite. As an additional treatment, mechanical stimulation was applied in a custom-made bioreactor. SOX9increased the expression level of its known target genes, as well as its cofactors: the long form of SOX5and SOX6. However, it was unable to increase the synthesis of sulfated glycosaminoglycans (GAGs). Mechanical stimulation slightly enhanced collagen type X and increased lubricin expression. The combination of SOX9and mechanical load boosted GAG synthesis as shown by 35S incorporation. GAG production rate corresponded well with the amount of (endogenous) transforming growth factor-β1. Finally, cartilage oligomeric matrix protein expression was increased by both treatments. These findings provide insight into the mechanotransduction of mesenchymal stem cells and demonstrate the potential of a transcription factor in stem cell therapy.

In this study, human bone marrow mesenchymal stem cell (hMSC)–seeded fibrin–polyurethane composite scaffolds were subjected to various mechanical load protocols to determine the effect of compression and surface rotation frequency and axial compression magnitude on the induction of chondrocyte-specific gene expression and protein synthesis. After 7 days of preculture and 7 days of load, application of dynamic compression and surface shear 1 h daily enhanced chondrogenesis of hMSCs compared with the nonloaded control samples. Higher load frequency and higher compression amplitude induced higher glycosaminoglycan synthesis, higher chondrocytic gene expression, higher chondrocytic:fibroblastic, chondrocytic:hypertrophic, and chondrocytic:osteoblastic gene expression ratios, as well as higher transforming growth factor β1 (TGFB1) and TGFB3gene expression. The chondrogenesis level of hMSCs was positively related to the TGFB1and TGFB3gene expression level, which was determined by various load regimes. In conclusion, chondrogenesis of human MSCs induced by mechanical stimulation can be further enhanced by modifying frequency and compression.

Mechanical and chemical stimulation have been shown to enhance in vitrochondrogenesis. The aim of this study was to analyze and compare combined physicobiochemical effects. Bovine articular chondrocytes were retrovirally transduced to express bone morphogenetic protein-2 (BMP-2) or left as naïve controls. Cells were seeded in three-dimensional polyurethane scaffolds and further cultured under static conditions or exposed to dynamic compression and shear in a joint-specific bioreactor. Four groups: control (A), load (B), BMP-2-infected (C), and BMP-2-infected plus load (D) were analyzed for DNA and glycosaminoglycan (GAG) content; collagen I, II, and X; aggrecan, (cartilage oligomeric protein (COMP), superficial zone protein, matrix metalloproteinase (MMP)-3; MMP-13 mRNA; histology; and immunohistochemistry at 7, 21, and 35 days post-seeding. Synergistic effects (D) were higher than the sum of the individual treatments (B and C) for GAG/DNA, collagen II, and COMP. Histology revealed a functional organization in D including an intense safranin O staining in C and D superior to that in A and B. Immunostaining for collagen II and aggrecan was detected in C and D and was strongest in D. The results show that both stimuli augment in vitrochondrogenesis better than in controls. Biochemical manipulation proved to be predominantly more effective than load, and synergistic effects were demonstrated.

Fibrin is a hydrogel carrier widely used in cartilage tissue engineering. It is rapidly degraded by plasmin, which is produced by the cells. ɛ-Aminocaproic acid (EACA) can be used to inhibit this enzyme and thus save the fibrin carrier. In this study we investigated the effect of EACA on the transforming growth factor β-1–induced chondrogenic differentiation of human bone marrow–derived mesenchymal stem cells (hMSCs). To assess this, we used the standard pellet culture system, and EACA treatment was compared to an untreated chondrogenic control. To investigate differentiation, real-time RT-PCR was used on chondrocytic marker genes: aggrecan, collagen types II and X, and the SRY-related HMG-box gene 9 (SOX9). Also, specific glycosaminoglycan production was measured. Safranin-O/fast green staining was used to localize proteoglycans and collagens within the pellet. All results concur that EACA did not affect the chondrogenic differentiation process at 5 μM concentration, which is adequate to inhibit fibrin degradation. Therefore, it is a useful plasmin inhibitor for cartilage tissue engineering with hMSCs.

This study investigated whether a three-dimensional (3D) fibrin gel–polyurethane scaffold composite can provide an environment for chondrogenesis of human bone marrow mesenchymal stem cells (hMSCs) that is as supportive as pellet culture, which is an established model for evaluating chondrogenesis. Pellet culture was carried out in serum-free medium in the absence or presence of transforming growth factor beta 1 (TGF-β1) and dexamethasone. hMSCs were seeded into a fibrin gel–biodegradable polyurethane scaffold at cell densities of 2 × 106, 5 × 106, and 10 × 106cells per scaffold and cultured in serum-free medium supplemented with TGF-β1 and dexamethasone. With comparable proteoglycan synthesis and type I and type X collagen gene expression levels, scaffolds seeded with 5 × 106cells expressed higher type II collagen and aggrecan gene transcripts than pellets on day 14. The deposition of proteoglycan and type II collagen was detected on the top layer of scaffolds seeded with 10 × 106cells and was more evenly distributed in the scaffolds seeded with 5 × 106cells. The scaffold composite culture system shows chondrogenesis of hMSCs comparable with that of pellet culture. Initial cell seeding density influences the ability and process of hMSC chondrogenesis. This study founded a basic system for cartilage neo-tissue formation in vitro.

Articular cartilage (AC) is an avascular and flexible connective tissue located on the bone surface in the diarthrodial joints. AC defects are common in the knees of young and physically active individuals. Because of the lack of suitable tissue-engineered artificial matrices, current therapies for AC defects, especially full-thickness AC defects and osteochondral interfaces, fail to replace or regenerate damaged cartilage adequately. With rapid research and development advancements in AC tissue engineering (ACTE), functionalized hydrogels have emerged as promising cartilage matrix substitutes because of their favorable biomechanical properties, water content, swelling ability, cytocompatibility, biodegradability, and lubricating behaviors. They can be rationally designed and conveniently tuned to simulate the extracellular matrix of cartilage. This article briefly introduces the composition, structure, and function of AC and its defects, followed by a comprehensive review of the exquisite (bio)design and (bio)fabrication of functionalized hydrogels for AC repair. Finally, we summarize the challenges encountered in functionalized hydrogel-based strategies for ACTE both in vivoand in vitroand the future directions for clinical translation.

The osteogenic microenvironment of bone-repairing materials plays a key role in accelerating bone regeneration but remains incompletely defined, which significantly limits the application of such bioactive materials. Here, the transcriptional landscapes of different osteogenic microenvironments, including three-dimensional (3D) hydroxyapatite (HA) scaffolds and osteogenic medium (OM), for mesenchymal stromal cells (MSCs) in vitrowere mapped at single-cell resolution. Our findings suggested that an osteogenic process reminiscent of endochondral ossification occurred in HA scaffolds through sequential activation of osteogenic-related signaling pathways, along with inflammation and angiogenesis, but inhibition of adipogenesis and fibrosis. Moreover, we revealed the mechanism during OM-mediated osteogenesis involves the ZBTB16 and WNT signaling pathways. Heterogeneity of MSCs was also demonstrated. In vitroossification of LRRC75A+MSCs was shown to have better utilization of WNT-related ossification process, and PCDH10+MSCs with superiority in hydroxyapatite-related osteogenic process. These findings provided further understanding of the cellular activity modulated by OM conditions and HA scaffolds, providing new insights for the improvement of osteogenic biomaterials. This atlas provides a blueprint for research on MSC heterogeneity and the osteogenic microenvironment of HA scaffolds and a database reference for the application of bioactive materials for bone regeneration.

It has been proven that the mechanical microenvironment can impact the differentiation of mesenchymal stem cells (MSCs). However, the effect of mechanical stimuli in biofabricating hydroxyapatite scaffolds on the inflammatory response of MSCs remains unclear. This study aimed to investigate the effect of mechanical loading on the inflammatory response of MSCs seeded on scaffolds. Cyclic mechanical loading was applied to biofabricate the cell-scaffold composite for 15 min/day over 7, 14, or 21 days. At the predetermined time points, culture supernatant was collected for inflammatory mediator detection, and gene expression was analyzed by qRT-PCR. The results showed that the expression of inflammatory mediators (IL1Band IL8) was downregulated (p < 0.05) and the expression of ALP(p < 0.01) and COL1A1(p < 0.05) was upregulated under mechanical loading. The cell-scaffold composites biofabricated with or without mechanical loading were freeze-dried to prepare extracellular matrix-based scaffolds (ECM-based scaffolds). Murine macrophages were seeded on the ECM-based scaffolds to evaluate their polarization. The ECM-based scaffolds that were biofabricated with mechanical loading before freeze-drying enhanced the expression of M2 polarization-related biomarkers (Arginase 1and Mrc1, p < 0.05) of macrophages in vitro and increased bone volume/total volume ratio in vivo. Overall, these findings demonstrated that mechanical loading could dually modulate the inflammatory responses and osteogenic differentiation of MSCs. Besides, the ECM-based scaffolds that were biofabricated with mechanical loading before freeze-drying facilitated the M2 polarization of macrophages in vitro and bone regeneration in vivo. Mechanical loading may be a promising biofabrication strategy for bone biomaterials.

Clinical treatments for the repair of osteochondral defects (OCD) are merely palliative, not completely curative, and thus enormously unfulfilled challenges. With the in‐depth studies of biology, medicine, materials, and engineering technology, the conception of OCD repair and regeneration should be renewed. During the past decades, many innovative tissue‐engineered approaches for repairing and regenerating damaged osteochondral units have been widely explored. Various scaffold‐free and scaffold‐based strategies, such as monophasic, biphasic, and currently fabricated multiphasic and gradient architectures have been proposed and evaluated. Meanwhile, progenitor cells and tissue‐specific cells have also been intensively investigated in vivo as well as ex vivo. Concerning bioactive factors and drugs, they have been combined with scaffolds and/or living cells, and even released in a spatiotemporally controlled manner. Although tremendous progress has been achieved, further research and development (R&D) is needed to convert preclinical outcomes into clinical applications. Here, the osteochondral unit structure, its defect classifications, and diagnosis are summarized. Commonly used clinical reparative techniques, tissue‐engineered strategies, emerging 3D‐bioprinting technologies, and the status of their clinical applications are discussed. Existing challenges to translation are also discussed and potential solutions for future R&D directions are proposed. Nowadays, many innovative tissue‐engineered approaches emerge for repairing and regenerating osteochondral defects (OCD). Various scaffold‐free and scaffold‐based strategies (e.g., monophasic, biphasic, multi‐phasic, and gradient architectures), engineered cells, bioactive factors, and drugs are widely investigated. Although tremendous progress is achieved, further research and development (R&D) is needed to convert preclinical outcomes into clinical applications.

Staphylococcus aureusis a prominent human pathogen in bone and soft-tissue infections. Pathophysiology involves abscess formation, which consists of central staphylococcal abscess communities (SACs), surrounded by a fibrin pseudocapsule and infiltrating immune cells. Protection against the ingress of immune cells such as neutrophils, or tolerance to antibiotics, remains largely unknown for SACs and is limited by the lack of availability of in vitromodels. We describe a three-dimensional in vitromodel of SACs grown in a human plasma-supplemented collagen gel.

Articular cartilage plays an essential role in joint lubrication and impact absorption. Through this, the mechanical signals are coupled to the tissue's physiological response. Healthy synovial fluid has been shown to reduce and homogenize the shear stress acting on the cartilage surfaces due to its unique shear-thinning viscosity. As cartilage tissues are sensitive to mechanical changes in articulation, it was hypothesized that replacing the traditional culture medium with a healthy non-Newtonian lubricant could enhance tissue development in a cartilage engineering model, where joint-kinematic-mimicking mechanical loading is applied. Different amounts of hyaluronic acid were added to the culture medium to replicate the viscosities of synovial fluid at different health states. Hyaluronic acid supplementation, especially at a physiologically healthy concentration (2.0 mg ml−1), promoted a better preservation of chondrocyte phenotype. The ratio of collagen II to collagen I mRNA was 4.5 times that of the control group, implying better tissue development (however, with no significant difference of measured collagen II content), with a good retention of collagen II and proteoglycan in the mechanically active region. Simulating synovial fluid properties by hyaluronic acid supplementation created a favourable mechanical environment for mechanically loaded constructs. These findings may help in understanding the influence of joint articulation on tissue homeostasis, and moreover, improve methods for functional cartilage tissue engineering.