What is the significance of hyaline cartilage being avascular and aneural

Some recent studies relate osteoarthritis pathogenesis to the re-initiation of the transient chondrocyte phenotype as seen in terminal differentiated growth-plate chondrocytes and the upregulation of collagenase matrix metalloproteinase MMP MMPpromoted methylation in osteoarthritic cartilage, in part, may drive the chondrocyte hypertrophy.

Although osteoarthritis is not classified as an inflammatory joint disease, several inflammatory components e. In addition, nitric oxide NO can be spontaneously produced by osteoarthritis-affected cartilage to cause catabolic effects, including inhibiting PGE2 synthesis as well as activating MMPs. Along with the progressive loss of articular cartilage, osteoarthritis is characterized by increased subchondral bone sclerosis with thickening of cortical plate and formation of osteophytes, which at some stages can be diagnosed as bone bruises and edema via medical imaging.

Like cartilage, the subchondral bone of osteoarthritis patients releases high levels of alkaline phosphatase, osteocalcin, osteopontin, IL-6, IL-8, and progressive ankylosis protein homolog, PG, and insulin growth factor The current gold standard for diagnosing and measuring clinical efficacy in osteoarthritis is radiographic joint space narrowing.

The elevated presence of biochemical biomarkers measured from the serum, urine, and synovia of osteoarthritis patients is often accompanied by cartilage degradation and subchondral bone turnover, such as cartilage oligomeric matrix protein, c -terminal telopeptide of type II collagen, helical fragments Helix-II and Coll , Coll NO2 , amino-terminal type II procollagen propeptide, carboxy-terminal type II procollagen propeptide, chondroitin sulfate epitope CS , HA, n -terminal type I collagen telopeptides, c -terminal type I collagen CTX I or serum CTX I, amino-terminal procollagen propeptide of type I collagen, carboxy-terminal procollagen propeptide of type I collagen, osteocalcin, urinary total pyridinoline, bone sialoprotein, and MMP The aims of osteoarthritis management are to educate patients about the disease, to alleviate pain, and to improve joint function.

Osteoarthritis should be managed on an individual basis and commonly requires a combination of treatment options. The recommended hierarchy of treatments consists of non-pharmacological treatments first, then drugs, and then, if necessary, surgery. The non-pharmacological approach includes education, weight loss e.

Surgery may include arthroscopic debridement and lavage, osteotomy, joint replacement, allografts, autografts, autologous chondrocyte transplantation, and tissue-engineered cartilage transplantation.

The latter has received significant attention and is currently focused on selecting the seed cells e. MSCs and recreating the natural physical environment e. Osteoarthritis in humans has been extensively studied clinically. Since articular cartilage is avascular and aneural, a diagnosis of primary osteoarthritis is not made until a patient experiences pain in the joint, which signals later-stage disease.

The main focus for human osteoarthritis research is to find a way to diagnose the disease early and accurately. The best-known human imaging project during the recent years is the Osteoarthritis Initiative OAI , which is a multi-center observational study of human osteoarthritis sponsored by the National Institutes of Health in the USA. The OAI data are available publically on the internet.

Many correlational studies have been published using various parts of the OAI data. In addition to studies on human osteoarthritis, a large number of different domestic animals have been used in osteoarthritis studies.

This is because no disease can be induced ethically in the human; the only alternative for the entire biomedical community is to study the cellular and animal models of the human disease, in order to gain better insights that could be used to produce guidelines for human treatment.

Primary osteoarthritis progresses slowly over several decades. It is the most common form of osteoarthritis and increases in prevalence and severity with the age in both human and non-human animals.

Post-traumatic osteoarthritis can be reproduced by mechanical insult or by surgery. Since articular cartilage has a limited capacity for repair, the physiological response to the resulting tissue damage rarely restores a normal articular surface.

Similarly, any changes in the cartilage structure caused by abnormal loading in a stable joint, or even by degradative enzymes in the synovium, can lead to the development of osteoarthritis. The assessment of animal models of osteoarthritis traditionally depends on the histological analysis of articular cartilage. Recent advances have seen the emergence of many other effective analyses, such as biomarkers and imaging, for monitoring the progress of osteoarthritis.

Although there is a perceived advantage in using naturally occurring models of osteoarthritis e. Dunkin—Hartley guinea pigs with a slower onset and progression similar to human osteoarthritis, many investigators have utilized fast-advancing animal models first reported by Magnuson in In , Paatsama published a thesis describing the degradation of canine articular cartilage associated with a cranial cruciate ligament rupture.

In addition to cartilaginous changes, Radin and Rose showed alterations in the sub-chondral bone and the calcified zone of cartilage after application of repetitive sub-impact loads to the patellofemoral joint. Responses to traumatic injury were also studied using a direct impact applied to the patella using a "drop tower" type of apparatus in order to produce high-energy damage similar to that seen in human injuries. Intra-articular injections of many proteolytic enzymes such as trypsin, papain, and collagenase have also been used to trigger model osteoarthritis in mice, rats, and rabbits.

However, the mechanisms responsible for cartilage degradation in these models, particularly those in which papain or trypsin was injected, may deviate significantly from those that normally occur in the human disease. Chemically induced osteoarthritis models use intra-articular injection of sodium iodoacetate to study acute cartilage toxicity and degradation and joint pain; however, this has many limitations as a model of osteoarthritis.

However, it does provide an in vivo model of rapid cartilage degradation mirroring some of the events observed in vitro in organ culture screening studies. In contrast to in vivo animal studies concentrating on the outcomes of post-traumatic joints and progression of osteoarthritis, many in vitro models have been used to study the effect of cell death and specific degradative mechanisms in well-defined loading and culture environments.

For example, to investigate the potential use of imaging as a diagnostic tool for osteoarthritis, purified collagenase, trypsin, or chondroitinase ABC , have been used to digest bovine patellar cartilage in order to generate spatial and temporal changes in the cartilage matrix.

Similar changes in structure and collagen network were observed in proteoglycan-depleted tissue and correlated directly with the loss of compressive strength. As an alternative to enzymatic cleavage, many studies have used in vitro explant injury models to study the molecular mechanisms of chondrocyte death and matrix degradation in injured cartilage.

The relatively low compressive moduli and the compression-induced stiffening in the superficial zone are closely related to cell death following a blunt impact or repeated mechanical insults. This was well demonstrated in vitro in a study of chondrocyte necrosis, where chondrocyte death occurred only in the superficial zone when two cartilage disks were positioned articular-surface-to-articular-surface and subjected to 1.

Some aspects of cartilage repair can also be examined in vitro by osteochondral models, such as defects of different depths created using a dermal biopsy punch and a scalpel. Thibault et al. These studies indicated that acute injury in articular cartilage can induce an upregulation of reactive oxygen species and pro-inflammatory cytokines.

These are important areas of research, since the prevention of cell death and the inhibition of matrix-degrading enzymes in the injured joint are significant for the prevention of posttraumatic osteoarthritis. Together, these in vitro explant models provide effective systems to study biomechanical and mechanobiological factors involved in initiating cartilage injury; biochemical factors associated with cell death and matrix degradation; and gene regulation critical for the advance of post-traumatic osteoarthritis.

Yang Xia, Konstantin I. Momot, Zhe Chen, Christopher T. The right human knee is shown. The subchondral bone plate arrowheads form relatively thin strata beneath the hyaline articular cartilage tissue. The section was stained with basic fuchsine and toluidine blue O.

Reproduced from Osteoarthritis Cartilage , 10 , E. Hunziker, T. Quinn, H. The lines represent the orientation of the collagen fibers; the ovals represent the chondrocytes in cartilage not to scale. Reproduced with permission from Poole et al. Helical collagen molecules form from three polypeptide chains, and these associate laterally to form collagen fibrils with a characteristic banded structure.

The sulfate groups are highly negatively charged and cause the aggrecan to spread out. Reproduced with permission from themedicalbiochemistrypage LLC. These repulsive forces cause the aggregate to assume a stiffly extended conformation, occupying a large solution domain. B Applied compressive stress decreases the aggregate solution domain left , which in turn increases the charge density and thus the intermolecular charge repulsive forces right Reproduced with permission from Mow et al. A faster displacement rate creates a higher interstitial pressure peak, while loading slowly could cause the tissue to reach equilibrium without experiencing a spike in interstitial stress.

Arrows and circles indicate tracking of cell nuclei. Reproduced from Osteoarthritis Cartilage , 9 , S. Chen, Y. Falcovitz, R. Schneiderman, A. Maroudas, R. Sah, Depth-dependent compressive properties of normal aged human femoral head articular cartilage: relationship to fixed charge density, —, Copyright with permission from Elsevier.

Within an initial mesenchymal condensation, an unknown trigger stimulates wnt14 expression at the site of incipient joint formation. Gdf5 is thereafter expressed and the cells take on an elongated morphology and significantly reduce SOX9 and collagen type II expression.

Bone morphogenetic protein BMP antagonists chordin and noggin are expressed in the interzone cells and act to stabilize joint-inducing positional cues. The interzone adopts a three-layered structure in the case of long bone elements that undergoes separation or cavitation on mechanically induced synthesis of hyaluronan.

The morphogenesis of the functional joint organ results in articular cartilage lining the ends of skeletal elements, which are bathed in synovial fluid, produced by a synovial membrane, and encased within a fibrous capsule.

Reproduced from Curr. Khan, S. Redman, R. Williams, G. Dowthwaite, S. Oldfield, C. Archer, Copyright with permission from Elsevier. The variations in the cartilage thickness and topographical directions are significant. Reproduced from Arthrosc. A consideration in the orientation of autologous cartilage grafts, —, Copyright with permission from Elsevier. A The non-loaded control; B loaded explants subjected to 1.

Dead cells red were located near the articular surface of loaded explants Reproduced with permission from Chen et al. Gray , P. Williams and L. CDC Morb. Marieb and K. Benjamin and E. Evans , J. Martini , M. Timmons and R. Hall Arthritis Rheum. Young and P. McCutchen Wear , , 5 , 1 —17 CrossRef.

Radin , D. Swann and P. Hills and R. Crawford , J. Klein Proc. Greene , B. Zappone , O. Soderman , D. Topgaard , G. Rata , H. Zeng and J.

Cotran , V. Kumar , T. Collins and S. Tehranzadeh , F. Booya and J. Root , Acta Radiol. Malda , J. Benders , M. Kik , C. Creemers , W. Dhert and P.

Hunziker , T. Quinn and H. Hunziker , R. Schenk and L. Cruz-Orive , J. Bone Jt. Cancedda , F. Descalzi Cancedda and P. Castagnola , Int. Ballock and R. Tam and K.

Cheah , Dev. Snow , L. Riccio , C. Mjaatvedt , S. Hoffman and A. Capehart , Anat. Bush , C. Parisinos and A. Hall , J. Pacifici , E. Koyama and M. Iwamoto , Birth Defects Res.

Weiss , L. Rosenberg and A. Helfet , J. Heinegard and A. Poole , M. Flint and B. Beaumont , J. Poole J. Buckwalter J. Sports Phys. Guilak and V. Mow , J. Enomoto-Iwamoto , M. Iwamoto , K. Nakashima , Y. Mukudai , D. Boettiger , M. Pacifici , K. Kurisu and F. Suzuki , J. Bone Miner.

Loeser , S. Sadiev , L. Tan and M. Wright , P. Jobanputra , C. Bavington , D. Salter and G. Nuki , Clin. Muhammad , Y. Rais , N. Miosge and E. Ornan , Cell. Life Sci. Pritchard and F. Guilak , Arthritis Rheum. Siczkowski and F. Watt , J. Cell Sci. Korver , R. Hauselmann , J. Flechtenmacher , L. Michal , E. Thonar , M. Shinmei , K. Kuettner and M. Aydelotte , Arthritis Rheum. Gauss , H. Benya , S. Padilla and M.

Benya and J. Campagnoli , I. Roberts , S. Kumar , P. Bennett , I. Bellantuono and N. Jiang , B. Jahagirdar , R. Reinhardt , R. Schwartz , C. Keene , X. Ortiz-Gonzalez , M. Reyes , T. Lenvik , T.

Lund , M. Blackstad , J. Aldrich , A. Lisberg , W. Low , D. Largaespada and C. Guillot , C. Gotherstrom , J. Chan , H. Kurata and N. Alsalameh , R. Amin , T. Gemba and M. Lotz , Arthritis Rheum. Fehrer and G. Lepperdinger , Exp. Akesson , L. Markling , A. Kjaeldgaard , S.

Falci and O. Ringden , J. Montjovent , C. Bocelli-Tyndall , C. Scaletta , A. Scherberich , S. Mark , I. Martin , L. Applegate and D. Pioletti , Tissue Eng. Noort , S. Scherjon , C. Kleijburg-van der Keur , A. Kruisselbrink , R. Beekhuizen , R. Willemze , H.

Kanhai and W. Fibbe , Haematologica , , 88 , — Search PubMed. Adult Articular Cartilage , M. Eyre Arthritis Res. Schumacher , K. Mizuno and H. Bachinger , J.

Lodish , A. Berk , C. Kaiser , M. Krieger , A. Bretscher , H. Ploegh , A. Amon and M. Scott , Molecular cell biology , W. Bella , B. Brodsky and H. Kadler , D. Holmes , J. Trotter and J. Chapman , Biochem. Cassimeris , V. Lingappa , G. Plopper and B. Jackson , S. Busch and A. Cardin , Physiol. Gandhi and R. Mancera , Chem. Drug Des. Maroudas Adult Articular Cartilage , M. Ghosh Clin. Iozzo Annu. Watanabe , Y. Yamada and K. Kimata , J. Dudhia Cell. Muir Biochem.

Maroudas Studies in joint disease , A. Maroudas and E. Holborrow, Pitman, Tunbridge Wells, , pp. Handley and D. Shinar and G. Navon , NMR Biomed. Henkelman , X. Huang , Q. Xiang , G. Stanisz , S. Swanson and M. Bronskill , Magn. Ramachandran and R. Grigera and H. Torzilli , E. Askari and J. Jenkins , Biomechanics of Diarthrodial Joints , A. Ratcliffe, S. Woo and V. Mow, Springer, New York, , pp.

Maroudas , E. Wachtel , G. Grushko , E. Katz and P. Weinberg , Biochim. Acta, Gen. Hewitt , H. Kleinman , J. Pennypacker and G. Martin , Proc. Xia Semin. Arthritis Rheum. Cohen , R. Foster and V. Buckwalter and H. Mankin , Instr. Course Lect.

Benninghoff Z. Bowden , E. Wentrup-Byrne , L. Rintoul , T. Bostrom , J. Pope and K. Meachim and R. Stockwell , Adult articular cartilage , M. FreemanPitman Publishing Ltd, London, , pp. Stolz , R. Gottardi , R. Raiteri , S. Miot , I. Polysaccharides: gel forming polysaccharides such as alginic acid and mucopolysaccharides glycosaminoglycans , storage polysaccharides which include starch and glycogen, and structural polysaccharides such as cellulose and chitin.

Protein based polymeric material composed of amino acid groups such as collagen, gelatin, and silk fibroin. Proteins can be classified by their shape, size, solubility, composition, and function. Synthetic polymers have shown potential in tissue engineering due to their improved mechanical and degradation properties with the capacity to be more easily chemically modified or engineered to tune their properties [ , , ].

The hydrolytic and enzymatic degradation of the polymer can be controlled through modification of the polymer [ ]. However, due to lack of biologically functional domains, which can reduce the risk of immune response, synthetic polymers may not facilitate cell phenotype expression or cell attachment as occurs in naturally derived protein-based polymers. Several strategies have been pursued to tackle this limitation, including the blending with bioactive polymers and the functionalisation of polymer backbone with cell-adhesive cues [ , ].

Among synthetic polymers, PCL and poly ethylene glycol PEG have been the most extensively used to create mechanically robust 3D scaffolds with intricate geometries and 3D cell-laden hydrogels, respectively.

PCL has been processed via melt extrusion and melt electrospinning to engineer acellular scaffolds which pores can be eventually filled with cell-laden hydrogels or cell spheroids towards creating biomimetic cartilage tissue constructs [ , , ] In turn, PEG functionalised with a variety of reactive groups has been explored to produce cell-instructive hydrogels with tuneable properties through several crosslinking chemistries, sustaining cartilage formation [ ]. Recent works have explored dynamic covalent chemistries to engineer covalent adaptable networks with controllable viscoelasticity and stress relaxation, recreating such features of the native cartilage.

As an example, Richardson et al. Results suggest that a fine control over the hydrogel viscoelasticity is essential to preserve gel network integrity, while supporting the formation of high-quality neocartilaginous tissue. Decellularised extracellular matrix dECM based biomaterials have also been explored to create 3D constructs.

The native ECM is ideal for tissue engineering as it is identical to the desired matrix structure required and helps controls cell behaviour [ , , , , , ]. Thus the use of dECM is suitable as it is biodegradable, does not produce antagonistic immune responses, provides cues for cell differentiation, and presents bioactive molecules that determine tissue homeostasis and tissue regeneration [ , , ].

The replication of the ECM microenvironment has provided inspiration to use the ECM from articular cartilage as matrix for tissue regeneration [ , ]. Benders et al. Furthermore, bioinks based on dECMs have been developed offering an additional route for their use in tissue engineering applications [ , , ].

The source of dECM, either derived from cartilage tissue or cellular has potentially an impact on cell behaviour with tissue-derived matrices showing greater chondrogenic differentiation whilst cellular-derived matrices facilitated enhanced cell proliferation and chondrogenic potential, although further investigation is required to understand the discrepancies [ ].

Decellularisation protocols from harvesting, decellularisation, and sterilisation to creating the dECM based scaffolds affects the hydration status and 3D configuration of the proteins and ECM, and hence strongly influences biomechanical and biological behaviour properties which may not be suitable anymore [ , ]. Furthermore, concerns remain about potential immunogenicity and poor biomechanical and biological performance. The selection of suitable biomaterials, biofunctionalisation strategies and processing technologies are essential to engineer a cell- and tissue-specific environment that promotes desirable cell behaviour and functional tissue formation Fig.

Each class of biomaterials has their own advantages and disadvantages, thus, there is difficulty in selecting only a specific class of biomaterial for use in osteochondral tissue engineering. Despite the limited long-term evidence of clinical outcomes currently, many ongoing trials and early-stage outcomes are positive and report encouraging results [ 10 , 13 ].

Subsequently, the development of advanced hydrogels which can combine the advantages of both synthetic and natural polymers, for example, in hybrid systems and synthetic self-assembling peptides are promising solutions [ , ]. Engineering biomimetic materials to generate tissue-specific microenvironments. Image from [ ]. The advancement of 3D printing and 3D bioprinting in tissue engineering has allowed the fabrication of scaffolds and biological tissue models that more accurately reflect the complex organisational structure and material properties of tissues and organs [ 14 , ].

The ability to print multiple cells and biocompatible materials with greater design freedom compared with conventional fabrication techniques has enabled the development of 3D structures that resemble the complex 3D biophysical and biochemical environment in tissues. The use of 3D bioprinting within cartilage tissue engineering is becoming widespread as an enabler technology to fabricate complex multi-material structures that mimic, in some extent, the biological and mechanical properties of cartilage tissue [ 15 , ].

Currently, 3D bioprinting predominately uses inkjet, extrusion, and laser-assisted systems to fabricate 3D structures Fig. However, stereolithography based systems are gaining attention due to the development of novel visible light photoinitiators with improved cytocompatibility and advancements in the technology which promises faster fabrication times and increased structure complexity [ , , ].

The development of bioinks has become an essential factor for the success of 3D bioprinting, in particular, biomaterials with controllable mechanical, biological, and biophysical characteristics which can modulate cell behaviour combined with printability Fig. Printing resolution, structure fidelity, material viscoelasticity are crucial parameters in determining the printability of bioinks and its relationship to the final mechanical and biological properties of the structure.

Developing advanced bioinks requires consideration of pre-functionalisation processes to incorporate biological functional groups and crosslinking moieties, the rheological behaviour of the bioink to ensure printability and fidelity, and the crosslinking method to ensure rapid gelation of the hydrogel [ , , , ].

More importantly, such requirements must also have in consideration that cell behaviour and functional properties of the new tissue depend not only on the bioprinting parameters e.

Depending on the biofabrication process and material properties, the bioink polymers will have various chemical and physical characteristics that will determine the corresponding application [ ].

These properties can be determined by rheological characterisation, mechanical assessment and crosslinking properties of the hydrogel [ , ]. Shear-thinning behaviour, a decrease in the viscosity as a function of increasing shear rate, is crucial for bioprinting applications, since the material will flow with an applied force during printing and the lower the applied force the higher the cell viability [ 16 , , ].

The viscoelastic behaviour characterised by the material response during printing needs to be optimised as low viscous materials will deform and collapse during printing, unless a rapid crosslinking process can be initiated. On the contrary high viscosity materials can be difficult to print as they can block the printing nozzle, require high deposition force, and restrict cell attachment and spreading which can negatively impact cell viability [ , ].

Adapted from [ ]. Bioink properties for successful 3D bioprinting require a suitable, a biofabrication window which balances printability and biocompatibility whilst providing a variety of b suitable rheological, mechanical, and biological characteristics. Multiple bioprinting-based strategies have been proposed to generate hierarchical tissue constructs for cartilage applications.

One of the early proposed strategies involved the extrusion bioprinting of cell-laden hydrogel bioinks to directly produce 3D cellularised constructs stimulating cartilage formation [ ]. Despite promising outcomes, a major drawback of hydrogel constructs relies on the disparity of mechanical properties compared to the native cartilage. To overcome this issue, researchers have combined melt extrusion or melt-electrospinning writing of thermoplastic polymers such as PCL with extrusion bioprinting of cell-laden hydrogel bioinks towards the fabrication of reinforced 3D constructs with improved mechanical performance Fig.

This concept was explored by Visser et al. A similar approach was reported by Kang et al. In another study, Mekhileri et al. Bioprinting hybrid cell-laden scaffolds. L: a Schematic of the melt-electrospinning system.

Images adapted from [ ]. L: a Schematic of the multi-printhead 3D bioprinting system and b the basic patterning of cell-laden hydrogels and supporting thermoplastic polymers. R: a 3D bioprinting of cell-laden hydrogels and PCL with integrated microchannels. L: a Representation of the 3D bioprinting and bioassembly system. R top : a Computer-aided-design model and b example of a hybrid biphasic osteochondral construct.

R bottom : a — f Bioassembled micro-tissues and g , h micro-spheres demonstrate chondrogenic markers a — c : safranin-O, d — f : collagen II, and h : aggrecan and cell viability. Images from [ ]. Biochemical, biophysical, and biomechanical stimulation of 3D bioengineered constructs is crucial in the formation and maturation of functional neocartilage tissue Fig.

The stimulation of cells can be achieved at specific stages: cell expansion, differentiation, and the maturation of the tissue construct in vitro. This can be attained through supplementation of the cell culture media, incorporation of biomolecules within the 3D structure, engineering the biophysical ECM environment, and mechanical stimulation of the construct.

Biochemical and biomechanical s timulation combined with appropriate cell sources can be used to engineer cartilage tissue constructs. A key approach to direct cell behaviour and facilitation of neocartilage tissue formation is the use of biological signalling molecules e. Growth factors are proteins that have a key role in cell behaviour and regulate cellular growth, proliferation, differentiation, and migration and are grouped into families with shared amino acid sequences and superfamilies with shared structural folds [ , ].

In articular cartilage tissue engineering, 3D engineered constructs have been used to deliver these biological factors [ , ]. IGF-1 has been reported showing high anabolic effects and decrease in catabolic responses in articular cartilage metabolism in vitro [ , ]. Other studies have reported using different growth factors which were successful in producing several features that resembled typical articular cartilage [ , , ].

Despite the capacity to promote cartilage matrix formation, growth factors have shown some drawbacks with IGF-1 associated with a loss of chondrocyte phenotype and extracellular matrix breakdown [ ]. Furthermore, IGF-1 in human MSCs inhibited collagen II expression and overexpression can induce hypertrophic differentiation and mineralisation [ ]. Biomechanical stimulation is a key factor in the development and homeostasis of functional cartilage tissue [ , , , , ].

The importance of mechanical loading and physical movement on embryonic chondrogenesis has been demonstrated in chicken embryos which when physically impaired exhibited poor development of cartilage tissue [ , , ]. Mechanical loading is required for healthy tissue, however, excessive loading can lead to trauma and disease progression [ ]. Thus, mechanical stimulation of cells and tissue constructs via compression, shear and hydrostatic pressure is important to promote chondrogenic differentiation, maintain a chondrogenic phenotype, and generation of functional tissue in vivo.

The advancement of bioreactors in tissue engineering has enabled the use of mechanical stimulation as a key capability in engineering cartilage tissue formation [ , , ]. Dual compressive and shear mechanical stimulation of human articular chondrocytes encapsulated in gelatin methacrylate and hyaluronic acid methacrylate hydrogels have been demonstrated by Meinert et al.

Cartilage specific marker genes and ECM were upregulated with significant increases in collagen II synthesis. Combining compressive and shear stimulation has been investigated using a multi-axial loading bioreactor which mimics the movement of an articulating joint [ , ].

Vainieri et al. The results showed increased production of chondrogenic specific markers, proteoglycan 4 and cartilage oligomeric matrix protein, and the improved collagen II to I ratio. Alternatively, tensile stimulation of a self-assembled scaffold-free neocartilage construct has shown to increase the tensile strength and modulus of the construct and once implanted in vivo in a mice model had similar mechanical properties and collagen content of native tissue [ ]. The development of improved mechanically stimulating bioreactors and osteochondral models will provide a valuable tool in understanding cartilage development and will aid the screening of biomaterials and tissue engineering strategies.

Major barriers remain in the development of clinically effective therapies for articular cartilage and osteochondral tissue. These challenges stem for the complexity of the native tissue and the difficulty in guiding regenerative processes while halting degenerative pathologies. This section briefly summarises key challenges identified associated with stimulatory factors, tissue inflammation, and implant-native tissue integration. Challenges remain in the use of stimulatory processes to guide cell behaviour and tissue development.

A complete understanding of chondrogenic development is still being unravelled so the entire milieu of factors that influence tissue formation and their functional spatiotemporal presentation to the cells is incomplete. However, tissue engineering strategies will most likely, to be successful, use a combination of growth factors, a controlled biophysical environment, and mechanical stimulation to promote tissue formation with phenotypic stability.

This is supported by the fact that the use of stem cells and chondrocytes, derived or implanted into an osteoarthritic environment, in vitro or in vivo typically results in phenotypic instability and the expression of a hypertrophic chondrocyte phenotype [ 66 , , ]. This can contribute to induce a hypertrophic phenotype in chondrocytes which may have significant implications for the development of functional implanted tissue constructs [ 66 , ].

This will require further understanding of the specific disease state and how different states affect the success of the tissue engineering approach used. The sole use of soluble factors in the maintenance and differentiation of chondrocytes and MSCs in vitro and in vivo seems unlikely to achieve the desired results.

Rather the design of these stimulatory environments including biochemical, physical, and mechanical elements will aim to recapitulate the native environment during all developmental stages of the tissue. A successful strategy will need to determine the combination, dosage, and delivery profile of growth factors, as well as the design of the physical matrix surrounding the cells by controlling parameters such as crosslinking density, ECM protein selection, and oxygen tension.

Finally, determining the timing, type, and loading conditions of mechanical stimulation will be essential in promoting an ECM which is mechanically compliant. However, the complexity of this environment and the actual implementation of a multi-stimulatory strategy is a serious challenge for researchers. The considerable inflammatory environment of osteochondral tissue in a diseased e.

Thus, approaches are necessary to control and understand the inflammatory state which contributes to tissue degradation in osteoarthritic diseases and the influence on implanted tissue constructs. Pro-inflammatory cytokines e. Cartilage degradation products and pro-inflammatory signals act on the synovium inducing further inflammatory processes that enhances the deregulation of typical chondrocyte function.

Integration of tissue constructs with the surrounding native tissue, be that cartilage or subchondral bone, is a key challenge. The issue of integration is a complex problem and can be caused be factors including lack of vascularisation, cell donor age, cell death during surgery and construct implantation, cell phenotype, and stage of tissue maturation of the construct [ ].

This is further compounded by the anti-adhesive properties of proteoglycans and GAGs present in the native matrix which are essential for proper functioning but can prevent integration. To overcome this issue, enzymatic degradation e. Furthermore, the native ECM can impede diffusion of proteins and cells, thus, disrupting the ECM at the site of implantation by using collagenase and hyaluronidase can enhance cell density and integration [ ]. Collagen crosslinking between the native cartilage and tissue construct can be encouraged by minimising complete crosslinking of the construct by blocking the enzyme lysyl oxidase LOX subsequently increasing the availability of collagen precursor crosslinking sites to enhance integration.

Correspondingly, the construct-native tissue interface can be treated with LOX to enhance and mature collagen crosslinking via collagen pyridinoline crosslinks that can anchor and bridge the interface [ , ]. However, implant integration can be influenced by the post-surgery recovery plan, thus appropriate rehabilitation regimes need to be followed. Furthermore, development of surgical procedures to secure implants in place during the integration and maturation phase are required.

For example, Vapniarsky et al. The clinical size and market of cartilage and osteochondral problems is expanding due to the ageing worldwide population and the most common treatment approaches are ineffective at halting the progression of degeneration of the tissue [ 65 , 66 , 69 ].

Thus, tissue engineering strategies are key in solving this pressing clinical problem. The design specification of any biomaterial-based 3D construct must fulfil a stringent criterion requiring suitable biomaterial selection, scaffold architecture, fabrication technique, stimulatory factors, and tissue maturation. Key areas of research include the maintenance of phenotype in the engineered tissue construct and the prevention of hypertrophic or fibrocartilage phenotypes being expressed.

Expansion of therapeutic cells in vitro to sufficient quantities for clinical applications whilst maintaining cell phenotype is a key challenge and research goal. The number of autologous chondrocytes that can be harvested is limited and subsequent passaging rapidly induces phenotypic changes.

Thus, the development of in vitro culturing processes that maintain chondrocyte phenotype and guide chondrogenic development of alternative cell sources. Allogenic cells are an attractive source as articular cartilage is typically considered immune-privileged due to its avascular nature thus allowing the use of allografts. However, this is dependent on implant location within the joint and proximity to the synovium consequently this needs to be taken into consideration when developing tissue engineering therapies [ ].

Another important issue concerns to the development of more effective strategies to promote the integration of tissue constructs with the host healthy tissue in an osteochondral defect, although in total replacement the strategy would primarily to be to anchor the neocartilage to underlying bone. Furthermore, the underlying biological behaviour of the tissue, the early-stage developmental biology, haemostatic processes in adult tissue, and the inflammatory environment in osteoarthritic joints need further understanding.

This knowledge may unlock key aspects of the tissue which may guide tissue engineering strategies. This could require a strategy of multiple stimulatory factors e. Subsequently, future studies should focus on a multi-stimulatory environment, long-term studies to determine phenotypic alterations and tissue formation, and the development of novel bioreactor systems that can more accurately resemble the in vivo environment.

Furthermore, novel approaches utilising gene therapy combined with tissue engineering scaffolds are also a promising approach which may offer a route to solving intractable issues surrounding articular cartilage degeneration [ , ].

Finally, a clear and considered route in the development process of the materials, structures, and strategy should be evaluated prior and during the research phase to expediate clinical and regulatory approval.

This will allow faster and more successful access to animal trials and eventually human clinical trials with the prospect of an efficacious therapy being developed.

Knee Surg Sports Traumatol Arthrosc 18 4 — Google Scholar. Tissue Eng 12 7 — Article Google Scholar. Cartilage 3 3 — Mankin HJ The response of articular cartilage to mechanical injury. JBJS 64 3 — Osteoarth Cartilage 12 12 — Sports Health 1 6 — Biomater Sci 4 5 — Poole C Articular cartilage chondrons: form, function and failure.

J Anat :1— Science — Nat Rev Rheumatol 15 9 — Balakrishnan B, Banerjee R Biopolymer-based hydrogels for cartilage tissue engineering. Chem Rev 8 — Nat Rev Rheumatol Biomaterials — Prog Polym Sci 37 8 — In: Ambrosio L ed Biomedical Composites, 2nd edn.

Woodhead Publishing, Sawston, pp — Nat Biotechnol Adv Healthc Mater. Nat Rev Rheumatol 15 10 — J Anat Br Med Bull 87 1 — Eyre D Articular cartilage and changes in arthritis: collagen of articular cartilage. Arth Res Ther 4 1 Arch Biochem Biophys 2 — Cancedda R Cartilage and bone extracellular matrix. Curr Pharm Des 15 12 — Biomaterials 21 5 — Roughley PJ The structure and function of cartilage proteoglycans.

Eur Cell Mater — FEBS Lett 2 — Osteoarth Cartilage 10 1 — Springer, Berlin, pp — Protein Cell 8 8 — Karl K Matrix loading: assembly of extracellular matrix collagen fibrils during embryogenesis. Birth Defects Res Part C 72 1 :1— MathSciNet Google Scholar. Osteoarth Cartilage 19 12 — Thambyah A, Broom N On how degeneration influences load-bearing in the cartilage—bone system: a microstructural and micromechanical study.

Osteoarth Cartilage 15 12 — Lindahl A From gristle to chondrocyte transplantation: treatment of cartilage injuries. Philos Trans R Soc B Maroudas A, Muir H, Wingham J The correlation of fixed negative charge with glycosaminoglycan content of human articular cartilage.

J Biol Chem 36 — Perrimon N, Bernfield M eds Cellular functions of proteoglycans—an overview. Academic Press, Cambridge. Venn M, Maroudas A Chemical composition and swelling of normal and osteoarthrotic femoral head cartilage.

Chemical composition. Ann Rheum Dis 36 2 — Bone 43 6 — Biochem Pharmacol 83 3 — J Orthop Res 15 4 — Nguyen LH, Kudva AK, Saxena NS, Roy K Engineering articular cartilage with spatially-varying matrix composition and mechanical properties from a single stem cell population using a multi-layered hydrogel. Biomaterials 32 29 — J Anat 3 — Arthroscopy 29 1 — Arthroscopy 29 9 — Arthroscopy 19 5 — Osteoarth Cartilage 14 11 — Cham: Springer International Publishing, pp — Biomaterials 26 17 — Biotechnol Adv 31 5 — Clin Orthop Relat Res — — J Orthop Res 23 2 — Martinez I, Elvenes J, Olsen R, Bertheussen K, Johansen O Redifferentiation of in vitro expanded adult articular chondrocytes by combining the hanging-drop cultivation method with hypoxic environment.

Cell Transplant 17 8 — Osteoarth Cartilage 20 10 — Demange M, Gomoll AH The use of osteochondral allografts in the management of cartilage defects. Curr Rev Musculoskelet Med 5 3 — JBJS 94 11 — Arthroscopy 21 9 — J Orthop Trans — Nat Med 23 6 — The Lancet — Clin Orthop Relat Res — Part 1: the disease and its risk factors. Ann Intern Med 8 — Nat Rev Dis Primers 2 1 Am J Sports Med 33 3 — Oper Tech Orthop 7 4 — Knee Surg Sports Traumatol Arthrosc 16 6 — Curr Rev Musculoskelet Med 8 4 — Osteoarth Cartilage 17 3 — Arthroscopy 22 4 — JBJS 86 3 — Peterson L, Minas T, Brittberg M, Lindahl A Treatment of osteochondritis dissecans of the knee with autologous chondrocyte transplantation: results at two to ten years.

Cartilage 5 3 — Int Orthop 41 4 — Am J Sports Med 47 1 — Cartilage 9 2 — Stem Cells Int Neubauer M, Jeyakumar V, Muellner T, Nehrer S Bone-marrow-aspirate-concentrate for chondral defects: surgical techniques, clinical applications and basic science. Ann Joint Orthop Rev Pavia 8 3 Gobbi A, Whyte GP Long-term clinical outcomes of one-stage cartilage repair in the knee with hyaluronic acid-based scaffold embedded with mesenchymal stem cells sourced from bone marrow aspirate concentrate.

Am J Sports Med 47 7 — Gobbi A, Karnatzikos G, Scotti C, Mahajan V, Mazzucco L, Grigolo B One-step cartilage repair with bone marrow aspirate concentrated cells and collagen matrix in full-thickness knee cartilage lesions: results at 2-year follow-up. Cartilage 2 3 — Heliyon 4 10 :e Osteoarth Cartilage 9 2 — PLoS Med 5 9 :ee. Am J Sports Med 46 10 — Cartilage Tissue Eng Regen Tech.

Biomed Res Int J Orthop Surg Res 12 1 Eur Cells Mater — Curr Mol Biol Rep 2 3 — Animal Biol. Download references. You can also search for this author in PubMed Google Scholar. Correspondence to Jos Malda. Reprints and Permissions. Malda, J. Rethinking articular cartilage regeneration based on a year-old statement. Nat Rev Rheumatol 15, — Download citation. Published : 31 July Issue Date : October Anyone you share the following link with will be able to read this content:.

Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative. Nature Reviews Rheumatology Journal of Materials Science: Materials in Medicine Biomanufacturing Reviews Advanced search. Skip to main content Thank you for visiting nature.

Subjects Cartilage Osteoarthritis Tissue engineering. Access through your institution. Buy or subscribe. Change institution. Rent or Buy article Get time limited or full article access on ReadCube. References 1.