Morphological MRI and T2 mapping of cartilage repair tissue after mosaicplasty with tissue-engineered cartilage in a pig model

The aim of this study was to evaluate the efficacy of mosaicplasty with tissue-engineered cartilage for the treatment of osteochondral defects in a pig model with advanced MR technique. Eight adolescent miniature pigs were used. The right knee underwent mosaicplasty with tissue-engineered cartilage for treatment of focal osteochondral defects, while the left knee was repaired via single mosaicplasty as controls. At 6, 12, 18 and 26 weeks after surgery, repair tissue was evaluated by magnetic resonance imaging （MRI） with the cartilage repair tissue （MOCART） scoring system and T2 mapping. Then, the results of MRI for 26 weeks were compared with findings of macroscopic and histologic studies. The MOCART scores showed that the repaired tissue of the tissue-engineered cartilage group was statistically better than that of controls （P 〈 0.001）. A significant correlation was found between macroscopic and MOCART scores （P 〈 0.001）. Comparable mean T2 values were found between adjacent cartilage and repair tissue in the experimental group （P 〉 0.05）. For zonal T2 value evaluation, there were no significant zonal T2 differences for repair tissue in controls （P 〉 0.05）. For the experimental group, zonal T2 variation was found in repair tissue （P 〈 0.05）. MRI, macroscopy and histology showed better repair results and bony incorporation in mosaicplasty with the tissue-engi- neered cartilage group than those of the single mosaicplasty group. Mosaicplasty with the tissue-engineered cartilage is a promising approach to repair osteochodndral defects. Morphological MRI and T2 mapping provide a non-invasive method for monitoring the maturation and integration of cartilage repair tissue in vivo.

O-alg-THAM/gel hydrogels functionalized with engineered microspheres based on mesenchymal stem cell secretion recruit endogenous stem cells for cartilage repair

Lacking self-repair abilities,injuries to articular cartilage can lead to cartilage degeneration and ultimately result in osteoarthritis.Tissue engineering based on functional bioactive scaffolds are emerging as promising approaches for articular cartilage regeneration and repair.Although the use of cell-laden scaffolds prior to implantation can regenerate and repair cartilage lesions to some extent,these approaches are still restricted by limited cell sources,excessive costs,risks of disease transmission and complex manufacturing practices.Acellular approaches through the recruitment of endogenous cells offer great promise for in situ articular cartilage regeneration.In this study,we propose an endogenous stem cell recruitment strategy for cartilage repair.Based on an injectable,adhesive and self-healable o-alg-THAM/gel hydrogel system as scaffolds and a biophysio-enhanced bioactive microspheres engineered based on hBMSCs secretion during chondrogenic differentiation as bioactive supplement,the as proposed functional material effectively and specifically recruit endogenous stem cells for cartilage repair,providing new insights into in situ articular cartilage regeneration.

“Genetic scissors”CRISPR/Cas9 genome editing cutting-edge biocarrier technology for bone and cartilage repair

CRISPR/Cas9 is a revolutionary genome editing technology with the tremendous advantages such as precisely targeting/shearing ability,low cost and convenient operation,becoming an efficient and indispensable tool in biological research.As a disruptive technique,CRISPR/Cas9 genome editing has a great potential to realize a future breakthrough in the clinical bone and cartilage repairing as well.This review highlights the research status of CRISPR/Cas9 system in bone and cartilage repair,illustrates its mechanism for promoting osteogenesis and chondrogenesis,and explores the development tendency of CRISPR/Cas9 in bone and cartilage repair to overcome the current limitations.

Engineered biochemical cues of regenerative biomaterials to enhance endogenous stem/progenitor cells(ESPCs)-mediated articular cartilage repair

As a highly specialized shock-absorbing connective tissue,articular cartilage(AC)has very limited self-repair capacity after traumatic injuries,posing a heavy socioeconomic burden.Common clinical therapies for small-to medium-size focal AC defects are well-developed endogenous repair and cell-based strategies,including microfracture,mosaicplasty,autologous chondrocyte implantation(ACI),and matrix-induced ACI(MACI).However,these treatments frequently result in mechanically inferior fibrocartilage,low cost-effectiveness,donor site morbidity,and short-term durability.It prompts an urgent need for innovative approaches to pattern a pro-regenerative microenvironment and yield hyaline-like cartilage with similar biomechanical and biochemical properties as healthy native AC.Acellular regenerative biomaterials can create a favorable local environment for AC repair without causing relevant regulatory and scientific concerns from cell-based treatments.A deeper understanding of the mechanism of endogenous cartilage healing is furthering the(bio)design and application of these scaffolds.Currently,the utilization of regenerative biomaterials to magnify the repairing effect of joint-resident endogenous stem/progenitor cells(ESPCs)presents an evolving improvement for cartilage repair.This review starts by briefly summarizing the current understanding of endogenous AC repair and the vital roles of ESPCs and chemoattractants for cartilage regeneration.Then several intrinsic hurdles for regenerative biomaterials-based AC repair are discussed.The recent advances in novel(bio)design and application regarding regenerative biomaterials with favorable biochemical cues to provide an instructive extracellular microenvironment and to guide the ESPCs(e.g.adhesion,migration,proliferation,differentiation,matrix production,and remodeling)for cartilage repair are summarized.Finally,this review outlines the future directions of engineering the next-generation regenerative biomaterials toward ultimate clinical translation.

Recent advances in polymeric biomaterials-based gene delivery for cartilage repair

Untreated articular cartilage damage normally results in osteoarthritis and even disability that affects millions of people.However,both the existing surgical treatment and tissue engineering approaches are unable to regenerate the original structures of articular cartilage durably,and new strategies for integrative cartilage repair are needed.Gene therapy provides local production of therapeutic factors,especially guided by biomaterials can minimize the diffusion and loss of the genes or gene complexes,achieve accurate spatiotemporally release of gene products,thus provideing long-term treatment for cartilage repair.The widespread application of gene therapy requires the development of safe and effective gene delivery vectors and supportive gene-activated matrices.Among them,polymeric biomaterials are particularly attractive due to their tunable physiochemical properties,as well as excellent adaptive performance.This paper reviews the recent advances in polymeric biomaterial-guided gene delivery for cartilage repair,with an emphasis on the important role of polymeric biomaterials in delivery systems.

Ultrasound augmenting injectable chemotaxis hydrogel for articular cartilage repair in osteoarthritis

The increasing incidence of osteoarthritis(OA) seriously affects life quality,posing a huge socioeco nomic burden.Tissue engineering technology has become a hot topic in articular cartilage repair as one of the key treatment methods to alleviate OA.Hydrogel,one of the most commonly used scaffold materials,ca n provide a good extracellular matrix microenvironment fo r seed cells such as bone marrow mesenchymal stem cells(BMSCs),which can promote cartilage regeneration.However,the low homing rate of stem cells severely limits their role in promoting articular cartilage regeneration.Stro mal cell-derived factor-1α(SDF-1α) plays a crucial role in the activatio n,mobilization,homing,and migration of MSCs.He rein,a novel injectable chemotaxis hydrogel,composed of chitosan-based injectable hydrogel and embedding SDF-1α-loaded nanodroplets(PFP@NDs-PEG-SDF-1α) was designed and fabricated.The ultrasound was then used to augment the injectable chemotaxis hydrogel and promote the homing migration of BMSCs for OA cartilage repair.The effect of ultrasound augmenting injectable PFP@NDs-PEG-SDF-1α/hydrogel on the migration of BMSCs was verified in vitro and in vivo,which re markably promotes stem cell homing and the repair of cartilage in the OA model.Therefore,the treatment strategy of ultrasound augmenting injectable chemotaxis hydrogel has a bright potential for OA articular cartilage repair.

Recent strategies of collagen-based biomaterials for cartilage repair: from structure cognition to function endowment

Collagen,characteristic in biomimetic composition and hierarchical structure,boasts a huge potential in repairing cartilage defect due to its extraordinary bioactivities and regulated physicochemical properties,such as low immunogenicity,biocompatibility and controllable degradation,which promotes the cell adhesion,migration and proliferation.Therefore,collagen-based biomaterial has been explored as porous scaffolds or functional coatings in cell-free scaffold and tissue engineering strategy for cartilage repairing.Among those forming technologies,freeze-dry is frequently used with special modifications while 3D-printing and electrospinning serve as the structure-controller in a more precise way.Besides,appropriate cross-linking treatment and incorporation with bioactive substance generally help the collagen-based biomaterials to meet the physicochemical requirement in the defect site and strengthen the repairing performance.Furthermore,comprehensive evaluations on the repair effects of biomaterials are sorted out in terms of in vitro,in vivo and clinical assessments,focusing on the morphology observation,characteristic production and critical gene expression.Finally,the challenge of biomaterial-based therapy for cartilage defect repairing was summarized,which is,the adaption to the highly complex structure and functional difference of cartilage.

Preparation of EGCG decorated,injectable extracellular vesicles for cartilage repair in rat arthritis

Arthritis is a kind of chronic inflammatory autoimmune disease,which can destroy joint cartilage and bone,leading to joint pain,joint swelling,and limited mobility.Traditional therapies have many side effects or focus too much on anti-inflammation while neglecting joint repair.In this experiment,we combined Epigallocatechin gallate(EGCG)with extracellular vesicles derived from macrophages to treat rheumatoid arthritis.Sustained-release resulted in a significant decrease in chondrocyte expression of hypoxia-inducible factor 1-alpha,a decrease in apoptosis-related proteins Cytochrome C,Caspase-3,Caspase-9,and Bax.Molecular biological analysis showed that extracellular vesicles-encapsulated EGCG(EVs-EGCG)more significantly upregulated type II collagen expression by about 1.8-fold than EGCG alone,which was more beneficial for arthritis repair.Animal experiments revealed that these EGCG-coated extracellular vesicles significantly reduced swelling,decreased synovial hyperplasia,repaired cartilage,and attenuated arthritis-related pathology scores in arthritic rats.Measurement data showed that EVs-EGCG treatment reduced joint swelling by approximately 39.5%in rheumatoid rats.In vitro studies have shown that this EVs-EGCG can increase the expression of cartilage type II collagen and reduce apoptosis of chondrocytes.Moreover,it was demonstrated in vivo experiments to reduce cartilage destruction in rheumatoid arthritis rats,providing a solution for the treatment of rheumatoid arthritis.

Functionalized Hydrogels for Articular Cartilage Tissue Engineering

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,espe-cially full-thickness AC defects and osteochondral interfaces,fail to replace or regenerate damaged carti-lage adequately.With rapid research and development advancements in AC tissue engineering(ACTE),functionalized hydrogels have emerged as promising cartilage matrix substitutes because of their favor-able biomechanical properties,water content,swelling ability,cytocompatibility,biodegradability,and lubricating behaviors.They can be rationally designed and conveniently tuned to simulate the extracel-lular 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 func-tionalized hydrogels for AC repair.Finally,we summarize the challenges encountered in functionalized hydrogel-based strategies for ACTE both in vivo and in vitro and the future directions for clinical translation.

Expression of Transforming Growth Factor β_(1) in Mesenchymal Stem Cells: Potential Utility in Molecular Tissue Engineering for Osteochondral Repair

The feasibility of using gene therapy to treat full-thickness articular cartilage defects was investigated with respect to the transfection and expression of exogenous transforming growth factor(TGF)-β_(1)genes in bone marrow-derived mesenchymal stem cells(MSCs)in vitro.The full-length rat TGF-β_(1)cDNA was transfected to MSCs mediated by lipofectamine and then selected with G418,a synthetic neomycin analog.The transient and stable expression of TGF-β_(1)by MSCs was detected by using immunohistochemical staining.The lipofectamine-mediated gene therapy efficiently transfected MSCs in vitro with the TGF-β_(1)gene causing a marked up-regulation in TGF-β_(1)expression as compared with the vector-transfected control groups,and the increased expression persisted for at least 4 weeks after selected with G418.It was suggested that bone marrow-derived MSCs were susceptible to in vitro lipofectamine mediated TGF-β_(1)gene transfer and that transgene expression persisted for at least 4 weeks.Having successfully combined the existing techniques of tissue engineering with the novel possibilities offered by modern gene transfer technology,an innovative concept,i.e.molecular tissue engineering,are put forward for the first time.As a new branch of tissue engineering,it represents both a new area and an important trend in research.Using this technique,we have a new powerful tool with which:(1)to modify the functional biology of articular tissue repair along defined pathways of growth and differentiation and(2)to affect a better repair of full-thickness articular cartilage defects that occur as a result of injury and osteoarthritis.

Effect of low-energy shock waves in microfracture holes in the repair of articular cartilage defects in a rabbit model

Background Microfracture is a type of bone marrow stimulation in arthroscopic cartilage repair. However, the overall concentration of the mesenchymal stem cells is quite low and declines with age, and in the end the lesion is filled by fibrocartilage. The aim of this research was to investigate a novel method of enhancing microfracture by determining whether low-energy shock waves in microfracture holes would facilitate cartilage repair in a rabbit model.Methods Full-thickness cartilage defects were created at the medial femoral condyle of 36 mature New Zealand white rabbits without penetrating subchondral bone. The rabbits were randomly divided into three groups. In experimental group A, low-energy shock-wave therapy was performed in microfracture holes （diameter, 1 mm） at an energy flux density （EFD） of 0.095 m J/mm2 and 200 impulses by DolorClast Master （Electro Medical Systems SA, Switzerland）microprobe （diameter, 0.8 mm）. In experimental group B, microfracture was performed alone. The untreated rabbits served as a control group. At 4, 8, and 12 weeks after the operations, repair tissues at the defects were analyzed stereologically, histologically, and immunohistochemically.Results The defects were filled gradually with repair tissues in experimental groups A and B, and no repair tissues had formed in the control group at 12 weeks. Repair tissues in experimental group A contained more chondrocytes,proteoglycans, and collagen type Ⅱ than those in experimental group B. In experimental group B, fibrous tissues had formed at the defects at 8 and 12 weeks. Histological analysis of experimental group A showed a better Wakitani score （P ＜0.05） than in experimental group B at 8 and 12 weeks after the operation.Conclusions In the repair of full-thickness articular cartilage defects in rabbits, low-energy shock waves in microfracture holes facilitated the production of hyaline-like cartilage repair tissues more than microfracture alone. This model demonstrates a new method of improving microfracture and applying shock waves in vivo. However, longer-term outcomes require further study.

Repairing cartilage defects using chondrocyte and osteoblast composites developed using a bioreactor

Background Articular cartilage injury is a common disease, and the incidence of articular wear, degeneration, trauma and sports injury is increasing, which often lead to disability and reduced quality of life. Unfortunately repair of articular cartilage defects do not always provide satisfactory outcomes. Methods Chondrocyte and osteoblast composites were co-cultured using a bioreactor. The cartilage defects were treated with cell-β-tricalcium phosphate （β-TCP） composites implanted into osteochondral defects in dogs, in vivo, using mosaicplasty, by placing chondrocyte-β-TCP scaffold composites on top of the defect and osteoblast-β-TCP scaffold composites below the defect.Results Electron microscopy revealed that the induced chondrocytes and osteoblast showed fine adhesive progression and proliferation in the β-TCP scaffold. The repaired tissues in the experimental group maintained their thickness to the full depth of the original defects, as compared with the negative control group （q=12.3370, P 〈0.01; q=31.5393, P 〈0.01）. Conclusions Perfusion culture provided sustained nutrient supply and gas exchange into the center of the large scaffold. This perfusion bioreactor enables the chondrocytes and osteoblasts to survive and proliferate in a three-dimensional scaffold.

A versatile 3D-printable hydrogel for antichondrosarcoma,antibacterial,and tissue repair

Following operative treatment of chondrosarcoma,post-surgery tissue reconstruction may be confronted with daunting challenges,including the delayed self-repair of defective tissue,tumor recurrence,and bac-terial infection.To overcome these challenges,a methacrylic anhydride(MA)modified sericin(SerMA)solution mixed with procyanidins(PC)loaded polydopamine(PDA)modified ZIF-8(PC@ZIF-8@PDA)nanoparticles to form a multifunctional PC@ZIF-8@PDA/SerMA hydrogel after exposure under blue light.Hydrogel products with pre-designed shapes were printed out by using the SerMA solution carrying PC@ZIF-8@PDA nanoparticles and chondrocytes,indicating that PC@ZIF-8@PDA/SerMA hydrogels with personalized shapes can be fabricated via 3D printing.Photocrosslinked PC@ZIF-8@PDA/SerMA hydrogel is able to kill chondrosarcoma cells and bacteria,like Staphylococcus aureus(S.aureus),and Escherichia coli(E.coli),by its photothermal activity combined with near-infrared radiation(NIR).The PC@ZIF-8@PDA/SerMA hydrogel exhibited an antioxidative activity and a good biocompatibility and was easily monitored by its florescent and photoacoustic properties.Rabbit articular cartilage defects were efficiently repaired by PC@ZIF-8@PDA/SerMA hydrogels with encapsulated corresponding autologous chondrocytes,and mice skin burning wounds were swiftly regenerated by applying this hydrogel.Hence,the PC@ZIF-8@PDA/SerMA hydrogel can be potentially applied to the clinic treatment of chondrosarcoma and tissue defect repair after chondrosarcoma resection due to its multifunction in the future.

Matrix from urine stem cells boosts tissue-specific stem cell mediated functional cartilage reconstruction

Articular cartilage has a limited capacity to self-heal once damaged.Tissue-specific stem cells are a solution for cartilage regeneration;however,ex vivo expansion resulting in cell senescence remains a challenge as a large quantity of high-quality tissue-specific stem cells are needed for cartilage regeneration.Our previous report demonstrated that decellularized extracellular matrix(dECM)deposited by human synovium-derived stem cells(SDSCs),adipose-derived stem cells(ADSCs),urine-derived stem cells(UDSCs),or dermal fibroblasts(DFs)provided an ex vivo solution to rejuvenate human SDSCs in proliferation and chondrogenic potential,particularly for dECM deposited by UDSCs.To make the cell-derived dECM(C-dECM)approach applicable clinically,in this study,we evaluated ex vivo rejuvenation of rabbit infrapatellar fat pad-derived stem cells(IPFSCs),an easily accessible alternative for SDSCs,by the abovementioned C-dECMs,in vivo application for functional cartilage repair in a rabbit osteochondral defect model,and potential cellular and molecular mechanisms underlying this rejuvenation.We found that C-dECM rejuvenation promoted rabbit IPFSCs’cartilage engineering and functional regeneration in both ex vivo and in vivo models,particularly for the dECM deposited by UDSCs,which was further confirmed by proteomics data.RNA-Seq analysis indicated that both mesenchymal-epithelial transition(MET)and inflammation-mediated macrophage activation and polarization are potentially involved in the C-dECM-mediated promotion of IPFSCs’chondrogenic capacity,which needs further investigation.

Cell-based therapy for management of osteoarthritis

Osteoarthritis(OA)is a most common form of degenerative joint disease,primarily characterized by the degradation of articular cartilage,subchondral sclerosis and inflammation of the synovial membrane.Mesenchymal stem cells(MSCs),a multipotent adult stem cell population,can be isolated from many connective tissue lineages,including those of the diarthrodial joint.Joint-resident MSCs or MSC-like progenitor cells contribute to the maintenance of healthy microenvironment or to the response to trauma.The onset of degenerative changes in the joint related to abnormal condition or depletion of these endogenous MSCs and native host hyaline cartilage cells,leading to limited selfrepair potential of the joint and advance of the degradation.To date,no acknowledged medical treatment strategies,including non-operative and classical surgical techniques,are efficient in restoring normal anatomy and function of hyaline cartilage in OA.This highlights an urgent need for better celled-based therapeutic strategies that supplement these functional cel s exogenously to recover the tissue homeostasis and repair in joint cavity via chondrogenic and anti-in fl ammatory functions.In this review we focus on the role of native MSCs in healthy or OA joint and recent progress in cel-based researches utilizing culture-expanded chondrocytes,pluripotent stem cel s,or MSCs from different sources for treating OA.

Applications of Polypeptide Hydrogels in Cartilage-Regeneration Engineering

Articular cartilage defects are considered to be associated with the development of osteoarthritis.Research on relevant tissue regeneration is important in the treatment of osteoarthritis.The scaffolds applied incartilage regeneration should have good histocompatibility and mechanical properties,as well as no cytotoxicity,and promote the proliferation and differentiation of seed cells.Different combinations of peptide sequences inpolypeptide hydrogels endow them with unique characteristics including excellent biodegradability and accuratesimulation of the extracellular matrix of chondrocytes to maintain the stability of the chondrogenic phenotypeand facilitate articular hyaline cartilage regeneration.Thus,the application of polypeptide hydrogels for cartilage regeneration has a bright future.In this study,the research progress of polypeptide hydrogels used incartilage-regeneration engineering is systematically reviewed.The characteristics,limitations,and prospects ofthese materials are evaluated.

Molecular Tissue Engineering: Applications for Modulation of Mesenchymal Stem Cells Proliferation by Transforming Growth Factor β_1 Gene Transfer

The effect of transforming growth factor β 1 (TGF β 1 ) gene transfection on the proliferation of bone marrow derived mesenchymal stem cells (MSC S ) and the mechanism was investigated to provide basis for accelerating articular cartilage repairing using molecular tissue engineering technology. TGF β 1 gene at different doses was transduced into the rat bone marrow derived MSCs to examine the effects of TGF β 1 gene transfection on MSCs DNA synthesis, cell cycle kinetics and the expression of proliferating cell nuclear antigen (PCNA). The results showed that 3 μl lipofectamine mediated 1 μg TGF β 1 gene transfection could effectively promote the proliferation of MSCs best; Under this condition (DNA/Lipofectamine=1μg/3μl), flow cytometry and immunohistochemical analyses revealed a significant increase in the 3 H incorporation, DNA content in S phase and the expression of PCNA. Transfection of gene encoding TGF β 1 could induce the cells at G0/G1 phase to S1 phase, modulate the replication of DNA through the enhancement of the PCNA expression, increase the content of DNA at S1 phase and promote the proliferation of MSCs. This new molecular tissue engineering approach could be of potential benefit to enhance the repair of damaged articular cartilage, especially those caused by degenerative joint diseases.

Biphasic Mechanical Properties of in vivo Repaired Cartilage

In the fast growing field of scaffold-based tissue engineering, improvement on the mechanical properties of newly formed tissues, e.g. the repaired cartilage, has always been one of the core issues. Studies on the correlations among scaffold composition, in vivo morphological changes of the construct, and the finite deformation behaviors of new tissues （e.g. creep and stress-relaxation, and equilibrium response）, have attracted increasing interests. In this paper, the correlations between the compressive biphasic mechanical properties （i.e., equilibrium elastic modulus E and permeability coefficient k） of 3D printing scaffold （consisting of collagen and fl-tricalcium phosphate） and the proteoglycans （PGs） concentration of the repaired carti- lages after 24 weeks, 36 weeks and 52 weeks of scaffold implantation were investigated. Results indicated that the repaired cartilage covered the entire cartilage surface of large cylindrical osteochondral defects （10 mm in diameter ~ 15 mm in depth） on the canine trochlea grooves after 24 weeks. The equilibrium elastic modulus of the repaired cartilage reached 22.4% at 24 weeks, 70.3% at 36 weeks, and 93.4% at 52 weeks of the native cartilage, respectively. Meanwhile, the permeability coefficient decreased with time and at 52 weeks was still inferior to that of the native cartilage in one order of magnitude. In addition, the amount of glycosaminoglycans （GAGs） of repaired cartilage increased constantly with time, which at 52 weeks approached to nearly 60% of that of native cartilage. 3D printed scaffolds have potential applications in repairing large-scale cartilage defects.

Current research on pharmacologic and regenerative therapies for osteoarthritis

Osteoarthritis（OA）is a degenerative joint disorder commonly encountered in clinical practice,and is the leading cause of disability in elderly people.Due to the poor self-healing capacity of articular cartilage and lack of specific diagnostic biomarkers,OA is a challenging disease with limited treatment options.Traditional pharmacologic therapies such as acetaminophen,non-steroidal anti-inflammatory drugs,and opioids are effective in relieving pain but are incapable of reversing cartilage damage and are frequently associated with adverse events.Current research focuses on the development of new OA drugs（such as sprifermin/recombinant human fibroblast growth factor-18,tanezumab/monoclonal antibody againstβ-nerve growth factor）,which aims for more effectiveness and less incidence of adverse effects than the traditional ones.Furthermore,regenerative therapies（such as autologous chondrocyte implantation（ACI）,new generation of matrix-induced ACI,cell-free scaffolds,induced pluripotent stem cells（iPS cells or iPSCs）,and endogenous cell homing）are also emerging as promising alternatives as they have potential to enhance cartilage repair,and ultimately restore healthy tissue.However,despite currently available therapies and research advances,there remain unmet medical needs in the treatment of OA.This review highlights current research progress on pharmacologic and regenerative therapies for OA including key advances and potential limitations.

Crosstalk between adipose-derived stem cells and chondrocytes:when growth factors matter

Adipose-derived stem cells（ASCs）and mesenchymal stem cells are promising for tissue repair because of their multilineage differentiation capacity.Our previous data confirmed that the implantation of mixed ASCs and chondrocytes into cartilage defects induced desirable in vivo healing outcomes.However,the paracrine action of ASCs on chondrocytes needs to be further elucidated.In this study,we established a co-culture system to achieve cell-to-cell and cell-to-tissue crosstalk and explored the soluble growth factors in both ASCs and chondrocytes supplemented with 1%fetal bovine serum to mimic the physiological microenvironment.In ASCs,we screened for growth factors by semi-quantitative PCR and quantitative real-time PCR and found that the expression of bone morphogenetic protein 2（BMP-2）,vascular endothelial growth factor B（VEGFB）,hypoxia inducible factor-1α（HIF-1α）,fibroblast growth factor-2（FGF-2）,and transforming growth factor-β1 significantly increased after co-culture in comparison with mono-culture.In chondrocytes,VEGFA was significantly enhanced after co-culture.Unexpectedly,the expression of collagen II and aggrecan was significantly down-regulated in the co-culture group compared with the mono-culture group.Meanwhile,among all the growth factors screened,we found that the BMP family members BMP-2,BMP-4,and BMP-5 were down-regulated and that VEGFB,HIF-1α,FGF-2,and PDGF were significantly decreased after co-culture.These results suggest that crosstalk between ASCs and chondrocytes is a pathway through the regulated growth factors that might have potential in cartilage repair and regeneration and could be useful for tissue engineering.