Advanced Strategies for Articular Cartilage Defect Repair

Functionalized hydrogels as smart gene delivery systems to treat musculoskeletal disorders

Despite critical advances in regenerative medicine, the generation of definitive, reliable treatments for musculoskeletal diseases remains challenging. Gene therapy based on the delivery of therapeutic genetic sequences has strong value to offer effective, durable options to decisively manage such disorders. Furthermore, scaffold-mediated gene therapy provides powerful alternatives to overcome hurdles associated with classical gene therapy, allowing for the spatiotemporal delivery of candidate genes to sites of injury. Among the many scaffolds for musculoskeletal research, hydrogels raised increasing attention in addition to other potent systems (solid, hybrid scaffolds) due to their versatility and competence as drug and cell carriers in tissue engineering and wound dressing. Attractive functionalities of hydrogels for musculoskeletal therapy include their injectability, stimuli-responsiveness, self-healing, and nanocomposition that may further allow to upgrade of them as "intelligently" efficient and mechanically strong platforms, rather than as just inert vehicles. Such functionalized hydrogels may also be tuned to successfully transfer therapeutic genes in a minimally invasive manner in order to protect their cargos and allow for their long-term effects. In light of such features, this review focuses on functionalized hydrogels and demonstrates their competence for the treatment of musculoskeletal disorders using gene therapy procedures, from gene therapy principles to hydrogel functionalization methods and applications of hydrogel-mediated gene therapy for musculoskeletal disorders, while remaining challenges are being discussed in the perspective of translation in patients. STATEMENT OF SIGNIFICANCE: Despite advances in regenerative medicine, the generation of definitive, reliable treatments for musculoskeletal diseases remains challenging. Gene therapy has strong value in offering effective, durable options to decisively manage such disorders. Scaffold-mediated gene therapy provides powerful alternatives to overcome hurdles associated with classical gene therapy. Among many scaffolds for musculoskeletal research, hydrogels raised increasing attention. Functionalities including injectability, stimuli-responsiveness, and self-healing, tune them as "intelligently" efficient and mechanically strong platforms, rather than as just inert vehicles. This review introduces functionalized hydrogels for musculoskeletal disorder treatment using gene therapy procedures, from gene therapy principles to functionalized hydrogels and applications of hydrogel-mediated gene therapy for musculoskeletal disorders, while remaining challenges are discussed from the perspective of translation in patients.

Visualization and bibliometric analysis of 3D printing in cartilage regeneration

The self-repair ability of cartilage defects is limited, and 3D printing technology provides hope for the repair and regeneration of cartilage defects. Although 3D printing technology and cartilage repair and regeneration have been studied for decades, there are still few articles specifically describing the relationship between 3D printing and cartilage defect repair and regeneration, and a bibliometric analysis has not been completed. To supplement, sort out and summarize the content in related fields, we analyzed the research status of 3D printing technology and cartilage repair and regeneration from 2002 to 2022. According to the set search strategy, the Web of Science Core Collection was used as the data source, and the literature search was completed on December 6, 2022. CiteSpace V and VOSviewer were used as bibliometric tools to complete the analysis of the research focus and direction of the published literature. Based on the analysis results, we focus on the occurrence and development of this field of combined medical and engineering research. Moreover, the current advantages and limitations of this field as well as future development prospects are discussed in depth. It will help to shape researchers' understanding of 3D printing and cartilage repair and regeneration, inspire researchers' research ideas, guide research directions, and promote related research results to clinical application.

From Interaction to Intervention: How Mesenchymal Stem Cells Affect and Target Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) lacks estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 expressions, making targeted therapies ineffective. Mesenchymal stem cells (MSCs) have emerged as a promising approach for TNBC treatment by modulating the tumor microenvironment (TME) and interacting with cancer cells. This review aims to comprehensively overview the role of MSCs in TNBC treatment, including their mechanisms of action and application strategies. We analyze the interactions between MSC and TNBC cells, including the impact of MSCs on TNBC cell proliferation, migration, invasion, metastasis, angiogenesis, and drug resistance, along with the signaling pathways and molecular mechanisms involved. We also explore the impact of MSCs on other components of the TME, such as immune and stromal cells, and the underlying mechanisms. The review discusses the application strategies of MSCs in TNBC treatment, including their use as cell or drug carriers and the advantages and limitations of different types and sources of MSCs in terms of safety and efficacy. Finally, we discuss the challenges and prospects of MSCs in TNBC treatment and propose potential solutions or improvement methods. Overall, this review provides valuable insights into the potential of MSCs as a novel therapeutic approach for TNBC treatment.

Progressive use of nanocomposite hydrogels materials for regeneration of damaged cartilage and their tribological mechanical properties

Osteoarthritis (OA) is a non-inflammatory deteriorating debilitating state that bring about remarkable health and economic issues globally. Break down/deterioration of the articular cartilage (AC) is one of the pathologic characteristics of osteoarthritis (OA). Nanocomposite hydrogels (NCH) materials are evolving as a potential class of scaffolds for organ regeneration and tissue engineering. In recent years, innovative hydrogels specifically loaded with nanoparticles have been developed and synthesized with the goal of changing conventional cartilage treatments. The detailed development of a tailored nanocomposite hydrogels (NCH) material utilized for tissue engineering is presented in this review study. Also, the mechanical characteristics, particularly the tribological behavior, of these produced NCH have been highlighted. Large amounts of research and data on the hydrogel substance utilized in cartilage healing are summarized in the current review study. When determining future research gaps in the area of hydrogels for cartilage regeneration, such information will provide researchers an advantage to further develop NCH.

In silico evaluation of the mechanical stimulation effect on the regenerative rehabilitation for the articular cartilage local defects

Osteoarthritis is one of the most severe diseases of the human musculoskeletal system, and therefore, for many years, special attention has been paid to the search for effective methods of its treatment. However, even the most modern methods only in a limited number of cases in the early or intermediate stages of osteoarthritis lead to positive treatment results. In the later stages of development, osteoarthritis is practically incurable and most often ends with disability or the need for joint replacement for a large number of people. One of the main reasons hindering the development of osteoarthritis treatment methods is the peculiarities of articular cartilage, in which there is practically no vascular network and tissue homeostasis is carried out mainly due to the diffusion of nutrients present in the synovial fluid. In modern medicine, for the treatment of osteoarthritis, tissue engineering strategies have been developed based on the implantation of scaffolds populated with chondrogenic cells into the area of the defect. In vitro studies have established that these cells are highly mechanosensitive and, under the influence of mechanical stimuli of a certain type and intensity, their ability to proliferate and chondrogenesis increases. This property can be used to improve the efficiency of regenerative rehabilitation technologies based on the synergistic combination of cellular technologies, tissue engineering strategies, and mechanical tissue stimulation. In this work, using a regenerative rehabilitation mathematical model of local articular cartilage defects, numerical experiments were performed, the results of which indicate that the micro-and macro environment of the restored tissue, which changes during mechanical stimulation, has a significant effect on the formation of the extracellular matrix, and, consequently, cartilage tissue generally. The results obtained can be used to plan strategies for mechanical stimulation, based on the analysis of the results of cell proliferation experimental assessment after each stimulation procedure in vivo.

Advances in the Treatment of Partial-Thickness Cartilage Defect

Partial-thickness cartilage defects (PTCDs) of the articular surface is the most common problem in cartilage degeneration, and also one of the main pathogenesis of osteoarthritis (OA). Due to the lack of a clear diagnosis, the symptoms are often more severe when full-thickness cartilage defect (FTCDs) is present. In contrast to FTCDs and osteochondral defects (OCDs), PTCDs does not injure the subchondral bone, there is no blood supply and bone marrow exudation, and the nearby microenvironment is unsuitable for stem cells adhesion, which completely loses the ability of self-repair. Some clinical studies have shown that partial-thickness cartilage defects is as harmful as full-thickness cartilage defects. Due to the poor effect of conservative treatment, the destructive surgical treatment is not suitable for the treatment of partial-thickness cartilage defects, and the current tissue engineering strategies are not effective, so it is urgent to develop novel strategies or treatment methods to repair PTCDs. In recent years, with the interdisciplinary development of bioscience, mechanics, material science and engineering, many discoveries have been made in the repair of PTCDs. This article reviews the current status and research progress in the treatment of PTCDs from the aspects of diagnosis and modeling of PTCDs, drug therapy, tissue transplantation repair technology and tissue engineering ("bottom-up").

Instrumented nanoindentation in musculoskeletal research

Musculoskeletal tissues, such as bone, cartilage, and muscle, are natural composite materials that are constructed with a hierarchical structure ranging from the cell to tissue level. The component differences and structural complexity, together, require comprehensive multiscale mechanical characterization. In this review, we focus on nanoindentation testing, which is used for nanometer to sub-micrometer length scale mechanical characterization. In the following context, we will summarize studies of nanoindentation in musculoskeletal research, examine the critical factors that affect nanoindentation testing results, and briefly summarize other commonly used techniques that can be conjoined with nanoindentation for synchronized imaging and colocalized characterization.

Therapeutic potential of mesenchymal stem cells for refractory inflammatory and immune skin diseases

Inflammatory and immunological skin diseases such as psoriasis, systemic sclerosis, dermatomyositis and atopic dermatitis, whose abnormal skin manifestations not only affected life quality but also caused social discrimination, have been wildly concerned. Complex variables such as hereditary predisposition, racial differences, age and gender can influence the prevalence and therapeutic options. The population of patients with unsatisfactory curative effects under current therapies is growing, it's advisable to seek novel and advanced therapies that are less likely to cause systemic damage. Mesenchymal stem cells (MSCs) have been proven with therapeutic benefits in tissue regeneration, self-renewal and differentiation abilities when treating refractory skin disorders in preclinical and clinical studies. Here we highlighted the immune modulation and inflammation suppression of MSCs in skin diseases, summarized current studies, research progress and related clinical trials, hoping to strengthen the confidence of promising MSCs therapy in future clinical application.

Advances in Biomaterial-Mediated Gene Therapy for Articular Cartilage Repair

Articular cartilage defects caused by various reasons are relatively common in clinical practice, but the lack of efficient therapeutic methods remains a substantial challenge due to limitations in the chondrocytes’ repair abilities. In the search for scientific cartilage repair methods, gene therapy appears to be more effective and promising, especially with acellular biomaterial-assisted procedures. Biomaterial-mediated gene therapy has mainly been divided into non-viral vector and viral vector strategies, where the controlled delivery of gene vectors is contained using biocompatible materials. This review will introduce the common clinical methods of cartilage repair used, the strategies of gene therapy for cartilage injuries, and the latest progress.

Neonatal Enthesis Healing Involves Noninflammatory Acellular Scar Formation through Extracellular Matrix Secretion by Resident Cells

Wound healing typically recruits the immune and vascular systems to restore tissue structure and function. However, injuries to the enthesis, a hypocellular and avascular tissue, often result in fibrotic scar formation and loss of mechanical properties, severely affecting musculoskeletal function and life quality. This raises questions about the healing capabilities of the enthesis. Herein, this study established an injury model to the Achilles entheses of neonatal mice to study the effectiveness of early-age enthesis healing. Histology and immunohistochemistry analyses revealed an atypical process that did not involve inflammation or angiogenesis. Instead, healing was mediated by secretion of collagen types I and II by resident cells, which formed a permanent hypocellular and avascular scar. Transmission electron microscopy showed that the cellular response to injury, including endoplasmic reticulum stress, autophagy, and cell death, varied between the tendon and cartilage ends of the enthesis. Single-molecule in situ hybridization, immunostaining, and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assays verified these differences. Finally, gait analysis showed that these processes effectively restored function of the injured leg. These findings reveal a novel healing mechanism in neonatal entheses, whereby local extracellular matrix secretion by resident cells forms an acellular extracellular matrix deposit without inflammation, allowing gait restoration. These insights into the healing mechanism of a complex transitional tissue may lead to new therapeutic strategies for adult enthesis injuries.

Progress of Polysaccharide-Contained Polyurethanes for Biomedical Applications

Polyurethane (PU) has been widely examined and used for biomedical applications, such as catheters, blood oxygenators, stents, cardiac valves, drug delivery carriers, dialysis devices, wound dressings, adhesives, pacemaker, tissue engineering, and coatings for breast implants due to its mechanical flexibility, high tear strength, biocompatibility, and tailorable foams although bio-acceptability, biodegradability and controlled drug delivery to achieve the desired properties should be considered. Especially, during the last decade, the development of bio-based PUs has raised public awareness because of the concern with global plastic waste for creating more environmentally friended materials. Therefore, it is desirable to discuss polysaccharide (PS)-contained PU for the wound dressing and bone tissue engineering among bio-based PUs because PS has several advantages, such as biocompatibility, reproducibility from the natural resources, degradability, ease of incorporation of bioactive agents, ease of availability and cost-effectiveness, and structural feature of chemical modification to meet the desired needs to overcome the disadvantages of PU itself by containing the PS into the PU.

Application of stem cells and exosomes in the treatment of intracerebral hemorrhage: an update

Non-traumatic intracerebral hemorrhage is a highly destructive intracranial disease with high mortality and morbidity rates. The main risk factors for cerebral hemorrhage include hypertension, amyloidosis, vasculitis, drug abuse, coagulation dysfunction, and genetic factors. Clinically, surviving patients with intracerebral hemorrhage exhibit different degrees of neurological deficits after discharge. In recent years, with the development of regenerative medicine, an increasing number of researchers have begun to pay attention to stem cell and exosome therapy as a new method for the treatment of intracerebral hemorrhage, owing to their intrinsic potential in neuroprotection and neurorestoration. Many animal studies have shown that stem cells can directly or indirectly participate in the treatment of intracerebral hemorrhage through regeneration, differentiation, or secretion. However, considering the uncertainty of its safety and efficacy, clinical studies are still lacking. This article reviews the treatment of intracerebral hemorrhage using stem cells and exosomes from both preclinical and clinical studies and summarizes the possible mechanisms of stem cell therapy. This review aims to provide a reference for future research and new strategies for clinical treatment.

Electrospun halloysite nanotube loaded polyhydroxybutyrate-starch fibers for cartilage tissue engineering

Articular cartilage is a connective load-bearing tissue with a low rate of regeneration due to slow metabolism. Fabricating tissue-like structure modified based on natural features can improve healing process. Fibrous scaffolds based on the composition of hydrophobic polyhydroxybutyrate (PHB) and hydrophilic starch reinforced using halloysite nanotubes (HNTs) with appropriate physico-chemical and biological properties was produced via electrospinning technique for long-term applications like cartilage regeneration. Textural properties were analyzed through SEM imaging that showed incorporating HNTs up to 2 wt% decreased mean fiber diameter to 158 ± 48 nm with larger pore size and appropriate porosity percentage. Moreover, the tensile strength was improved up to 4.21 ± 0.31 MPa after HNTs incorporation support chondrocyte cell growth. Furthermore, incorporating HNTs induced surface hydrophilicity and in vitro degradation. The biological assays both MTT assay and cell attachment of chondrocyte cells on 2 wt% HNTs incorporated into PHB-starch fibers indicated that HNTs incorporation can support cell growth and attachment without any toxicity for biomedical applications. To conclude, the obtained results demonstrated PHB-starch/HNTs fibrous scaffold could be potential for further experimental studies for tissue engineering applications like cartilage.

Stem Cell Therapy in Limb Ischemia: State-of-Art, Perspective, and Possible Impacts of Endometrial-Derived Stem Cells

As an evidence-based performance, the rising incidence of various ischemic disorders has been observed across many nations. As a result, there is a growing need for the development of more effective regenerative approaches that could serve as main therapeutic strategies for the treatment of these diseases. From a cellular perspective, promoted complex inflammatory mechanisms, after inhibition of organ blood flow, can lead to cell death in all tissue types. In this case, using the stem cell technology provides a safe and regenerative approach for ischemic tissue revascularization and functional cell formation. Limb ischemia (LI) is one of the most frequent ischemic disease types and has been shown to have a promising regenerative response through stem cell therapy based on several clinical trials. Bone marrow-derived mononuclear cells (BM-MNCs), peripheral blood CD34-positive mononuclear cells (CD34+ PB-MNCs), mesenchymal stem cells (MSCs), and endothelial stem/progenitor cells (ESPCs) are the main, well-examined stem cell types in these studies. Additionally, our investigations reveal that endometrial tissue can be considered a suitable candidate for isolating new safe, effective, and feasible multipotent stem cells for limb regeneration. In addition to other teams’ results, our in-depth studies on endometrial-derived stem cells (EnSCs) have shown that these cells have translational potential for limb ischemia treatment. The EnSCs are able to generate diverse types of cells which are essential for limb reconstruction, including endothelial cells, smooth muscle cells, muscle cells, and even peripheral nervous system populations. Hence, the main object of this review is to present stem cell technology and evaluate its method of regeneration in ischemic limb tissue.

State of the field: cellular and exosomal therapeutic approaches in vascular regeneration

Pathologies of the vasculature including the microvasculature are often complex in nature, leading to loss of physiological homeostatic regulation of patency and adequate perfusion to match tissue metabolic demands. Microvascular dysfunction is a key underlying element in the majority of pathologies of failing organs and tissues. Contributing pathological factors to this dysfunction include oxidative stress, mitochondrial dysfunction, endoplasmic reticular (ER) stress, endothelial dysfunction, loss of angiogenic potential and vascular density, and greater senescence and apoptosis. In many clinical settings, current pharmacologic strategies use a single or narrow targeted approach to address symptoms of pathology rather than a comprehensive and multifaceted approach to address their root cause. To address this, efforts have been heavily focused on cellular therapies and cell-free therapies (e.g., exosomes) that can tackle the multifaceted etiology of vascular and microvascular dysfunction. In this review, we discuss 1) the state of the field in terms of common therapeutic cell population isolation techniques, their unique characteristics, and their advantages and disadvantages, 2) common molecular mechanisms of cell therapies to restore vascularization and/or vascular function, 3) arguments for and against allogeneic versus autologous applications of cell therapies, 4) emerging strategies to optimize and enhance cell therapies through priming and preconditioning, and, finally, 5) emerging strategies to bolster therapeutic effect. Relevant and recent clinical and animal studies using cellular therapies to restore vascular function or pathologic tissue health by way of improved vascularization are highlighted throughout these sections.

Incorporation of a Collagen-Binding Chondroitin Sulfate Molecule to a Collagen Type I and II Blend Hydrogel for Cartilage Tissue Engineering

Adding chondroitin sulfate (CS) to collagen scaffolds has been shown to improve the outcomes for articular cartilage tissue engineering. Instead of physical entrapment or chemical crosslinking of CS within a scaffold, this study investigated the use of CS with attached collagen-binding peptides (termed CS-SILY). This method better recapitulates the aspects of native cartilage while retaining CS within a collagen type I and II blend (Col I/II) hydrogel. CS retention, average fibril diameter, and mechanical properties were altered by varying the number of SILY peptides attached to the CS backbone. When mesenchymal stromal cells (MSCs) were encapsulated within the scaffolds, the addition of CS-SILY molecules resulted in higher sulfated glycosaminoglycan production, and these results suggest that CS-SILY promotes MSC differentiation into chondrocytes. Taken together, our study shows the promise of adding a CS-SILY molecule to a Col I/II hydrogel with encapsulated MSCs to promote cartilage repair.

Articulation inspired by nature: A review of biomimetic and biologically active 3D printed scaffolds for cartilage tissue engineering

In the human body, articular cartilage facilitates the frictionless movement of synovial joints. However, due to its avascular and aneural nature, it has a limited ability to self-repair when damaged due to injury or wear and tear over time. Current surgical treatment options for cartilage defects often lead to the formation of fibrous, non-durable tissue and thus a new solution is required. Nature is the best innovator and so recent advances in the field of tissue engineering have aimed to recreate the microenvironment of native articular cartilage using biomaterial scaffolds. However, the inability to mirror the complexity of native tissue has hindered the clinical translation of many products thus far. Fortunately, the advent of 3D printing has provided a potential solution. 3D printed scaffolds, fabricated using biomimetic biomaterials, can be designed to mimic the complex zonal architecture and composition of articular cartilage. The bioinks used to fabricate these scaffolds can also be further functionalised with cells and/or bioactive factors or gene therapeutics to mirror the cellular composition of the native tissue. Thus, this review investigates how the architecture and composition of native articular cartilage is inspiring the design of biomimetic bioinks for 3D printing of scaffolds for cartilage repair. Subsequently, we discuss how these 3D printed scaffolds can be further functionalised with cells and bioactive factors, as well as looking at future prospects in this field.

The tissue engineering triad of biomaterials, cells and therapeutics as it applies to the formulation of biomimetic bioinks for cartilage repair. These bioinks can be functionalised with cells or cellular therapeutics to promote cartilage repair.

Main and Minor Types of Collagens in the Articular Cartilage: The Role of Collagens in Repair Tissue Evaluation in Chondral Defects

Several collagen subtypes have been identified in hyaline articular cartilage. The main and most abundant collagens are type II, IX and XI collagens. The minor and less abundant collagens are type III, IV, V, VI, X, XII, XIV, XVI, XXII, and XXVII collagens. All these collagens have been found to play a key role in healthy cartilage, regardless of whether they are more or less abundant. Additionally, an exhaustive evaluation of collagen fibrils in a repaired cartilage tissue after a chondral lesion is necessary to determine the quality of the repaired tissue and even whether or not this repaired tissue is considered hyaline cartilage. Therefore, this review aims to describe in depth all the collagen types found in the normal articular cartilage structure, and based on this, establish the parameters that allow one to consider a repaired cartilage tissue as a hyaline cartilage.

Twenty-Two-Year Outcome of Cartilage Repair Surgery by Perichondrium Transplantation

OBJECTIVE

The main purpose of the present study was to assess the risk for major revision surgery after perichondrium transplantation (PT) at a minimum of 22 years postoperatively and to evaluate the influence of patient characteristics.

DESIGN

Primary outcome was treatment success or failure. Failure of PT was defined as revision surgery in which the transplant was removed, such as (unicondylar) knee arthroplasty or patellectomy. The functioning of nonfailed patients was evaluated using the International Knee Documentation Committee (IKDC) score. In addition, the influence of patient characteristics was evaluated.

RESULTS

Ninety knees in 88 patients, aged 16 to 55 years with symptomatic cartilage defects, were treated by PT. Eighty knees in 78 patients were eligible for analysis and 10 patients were lost to follow-up. Twenty-eight knees in 26 patients had undergone major revision surgery. Previous surgery and a longer time of symptoms prior to PT were significantly associated with an increased risk for failure of cartilage repair. Functioning of the remaining 52 patients and influence of patient characteristics was analyzed using their IKDC score. Their median IKDC score was 39.08, but a relatively young age at transplantation was associated with a higher IKDC score.

CONCLUSIONS

This 22-year follow-up study of PT, with objective outcome parameters next to patient-reported outcome measurements in a unique group of patients, shows that overall 66% was without major revision surgery and patient characteristics also influence long-term outcome of cartilage repair surgery.

Translational Application of 3D Bioprinting for Cartilage Tissue Engineering

Cartilage is an avascular tissue with extremely limited self-regeneration capabilities. At present, there are no existing treatments that effectively stop the deterioration of cartilage or reverse its effects; current treatments merely relieve its symptoms and surgical intervention is required when the condition aggravates. Thus, cartilage damage remains an ongoing challenge in orthopaedics with an urgent need for improved treatment options. In recent years, major advances have been made in the development of three-dimensional (3D) bioprinted constructs for cartilage repair applications. 3D bioprinting is an evolutionary additive manufacturing technique that enables the precisely controlled deposition of a combination of biomaterials, cells, and bioactive molecules, collectively known as bioink, layer-by-layer to produce constructs that simulate the structure and function of native cartilage tissue. This review provides an insight into the current developments in 3D bioprinting for cartilage tissue engineering. The bioink and construct properties required for successful application in cartilage repair applications are highlighted. Furthermore, the potential for translation of 3D bioprinted constructs to the clinic is discussed. Overall, 3D bioprinting demonstrates great potential as a novel technique for the fabrication of tissue engineered constructs for cartilage regeneration, with distinct advantages over conventional techniques.

Bio-3D printing iPSC-derived human chondrocytes for articular cartilage regeneration

Osteoarthritis is a leading cause of pain and joint immobility, the incidence of which is increasing worldwide. Currently, total joint replacement is the only treatment for end-stage disease. Scaffold-based tissue engineering is a promising alternative approach for joint repair but is subject to limitations such as poor cytocompatibility and degradation-associated toxicity. To overcome these limitations, a completely scaffold-free Kenzan method for bio-3D printing was used to fabricate cartilage constructs feasible for repairing large chondral defects. Human induced pluripotent stem cell (iPSC)-derived neural crest cells with high potential to undergo chondrogenesis through mesenchymal stem cell differentiation were used to fabricate the cartilage. Unified, self-sufficient, and functional cartilaginous constructs up to 6 cm²in size were assembled by optimizing fabrication time during chondrogenic induction. Maturation for 3 weeks facilitated the self-organisation of the cells, which improved the construct's mechanical strength (compressive and tensile properties) and induced changes in glycosaminoglycan and type II collagen expression, resulting in improved tissue function. The compressive modulus of the construct reached the native cartilage range of 0.88 MPa in the 5th week of maturation. This paper reports the fabrication of anatomically sized and shaped cartilage constructs, achieved by combining novel iPSCs and bio-3D printers using a Kenzan needle array technology, which may facilitate chondral resurfacing of articular cartilage defects.

PHB/CHIT Scaffold as a Promising Biopolymer in the Treatment of Osteochondral Defects-An Experimental Animal Study

Biopolymer composites allow the creation of an optimal environment for the regeneration of chondral and osteochondral defects of articular cartilage, where natural regeneration potential is limited. In this experimental study, we used the sheep animal model for the creation of knee cartilage defects. In the medial part of the trochlea and on the medial condyle of the femur, we created artificial defects (6 × 3 mm²) with microfractures. In four experimental sheep, both defects were subsequently filled with the porous acellular polyhydroxybutyrate/chitosan (PHB/CHIT)-based implant. Two sheep had untreated defects. We evaluated the quality of the newly formed tissue in the femoral trochlea defect site using imaging (X-ray, Computer Tomography (CT), Magnetic Resonance Imaging (MRI)), macroscopic, and histological methods. Macroscopically, the surface of the treated regenerate corresponded to the niveau of the surrounding cartilage. X-ray examination 6 months after the implantation confirmed the restoration of the contour in the subchondral calcified layer and the advanced rate of bone tissue integration. The CT scan revealed a low regenerative potential in the bone zone of the defect compared to the cartilage zone. The percentage change in cartilage density at the defect site was not significantly different to the reference area (0.06–6.4%). MRI examination revealed that the healing osteochondral defect was comparable to the intact cartilage signal on the surface of the defect. Hyaline-like cartilage was observed in most of the treated animals, except for one, where the defect was repaired with fibrocartilage. Thus, the acellular, chitosan-based biomaterial is a promising biopolymer composite for the treatment of chondral and osteochondral defects of traumatic character. It has potential for further clinical testing in the orthopedic field, primarily with the combination of supporting factors.

Utility of direct 3D co-culture model for chondrogenic differentiation of mesenchymal stem cells on hyaluronan scaffold (Hyaff-11)

This study presents direct 2D and 3D co-culture model of mesenchymal stem cells (MSCs) line with chondrocytes isolated from patients with osteoarthritis (unaffected area). MSCs differentiation into chondrocytes after 14, 17 days was checked by estimation of collagen I, II, X, aggrecan expression using immunohistochemistry. Visualization, localization of cells on Hyaff-11 was performed using enzymatic technique and THUNDER Imaging Systems. Results showed, that MSCs/chondrocytes 3D co-culture induced suitable conditions for chondrocytes grow and MSCs differentiation than 2D monoculture. Despite that differentiated cells on Hyaff-11 expressed collagen X, they showed high collagen II (80%) and aggrecan (60%) expression with simultaneous decrease of collagen I expression (10%). The high concentration of differentiated cells on Hyaff-11, indicate that this structure has an impact on cells cooperation and communication. In conclusion, we suggest that high expression of collagen II and aggrecan in 3D co-culture model, indicate that cooperation between different subpopulations may have synergistic impact on MSCs chondrogenic potential. Revealed the high concentration and localization of cells growing in deeper layers of membrane in 3D co-culture, indicate that induced microenvironmental enhance cell migration within scaffold. Additionally, we suggest that co-culture model might be useful for construction a bioactive structure for cartilage tissue regeneration.

Scaffold-Free Cartilage Construct from Infrapatellar Fat Pad Stem Cells for Cartilage Restoration

Once damaged, the articular cartilage has a very limited intrinsic capacity for self-renewal due to its avascular nature. If left untreated, damaged cartilage can lead to progressive degeneration of bone and eventually causes pain. Infrapatellar fat pad adipose-derived mesenchymal stromal cells (IPFP-ASCs) has a potential role for cartilage restoration. However, the therapeutic role for IPFP-ASCs remains to be evaluated in an appropriate osteochondral defect model. Thus, this study aimed to investigate the potential of using a three-dimensional (3D) cartilage construct of IPFP-ASCs as a promising source of cells to restore articular cartilage and to attenuate pain associated with the cartilage defect in an osteochondral defect model. The chondrogenic differentiation potential of the 3D cartilage construct derived from IPFP-ASCs was determined before implantation and postimplantation by gene expression and immunohistochemistry analysis. Pain-related behavior was also assessed by using a weight-bearing test. A significant pain-associated with the osteochondral defect was observed in this model in all groups postinduction; however, this pain can spontaneously resolve within 3 weeks postimplantation regardless of implantation of IPFP-ASCs constructs. The expression of SOX9 and COL2A1 genes in addition to protein expression were strongly expressed in 3D construct IPFP-ASCs. The existence of mature chondrocytes, along with significant (p < 0.05) positive immunostaining for type II collagen and aggrecan, were identified in the implanted site for up to 12 weeks compared with the untreated group, indicating hyaline cartilage regeneration. Taken together, this study demonstrated the successful outcome of osteochondral regeneration with scaffold-free IPFP-ASCs constructs in an osteochondral defect rat model. It provides novel and interesting insights into the current hypothesis that 3D construct IPFP-ASCs may offer potential benefits as an alternative approach to repair the cartilage defect. Impact statement This study provides evidence of using the human 3D scaffold-free infrapatellar fat pad adipose-derived mesenchymal stromal cells (IPFP-ASCs) construct to restore the full-thickness osteochondral defect in a rat model. This study showed that chondrogenic features of the construct could be retained for up to 12 weeks postimplantation. The results of this proof-of-concept study support that human 3D scaffold-free IPFP-ASCs construct has potential benefits in promoting the hyaline-like native cartilage restoration, which may be beneficial as a tissue-specific stem cell for cell-based cartilage therapy. There are several clinical advantages of IPFP-ASC including ease and minimal invasive harvesting, chondrogenic inducible property, and tissue-specific progenitors in the knee.

Poloxamer: A versatile tri-block copolymer for biomedical applications

Poloxamers, also called Pluronic, belong to a unique class of synthetic tri-block copolymers containing central hydrophobic chains of poly(propylene oxide) sandwiched between two hydrophilic chains of poly(ethylene oxide). Some chemical characteristics of poloxamers such as temperature-dependent self-assembly and thermo-reversible behavior along with biocompatibility and physiochemical properties make poloxamer-based biomaterials promising candidates for biomedical application such as tissue engineering and drug delivery. The microstructure, bioactivity, and mechanical properties of poloxamers can be tailored to mimic the behavior of various types of tissues. Moreover, their amphiphilic nature and the potential to self-assemble into the micelles make them promising drug carriers with the ability to improve the drug availability to make cancer cells more vulnerable to drugs. Poloxamers are also used for the modification of hydrophobic tissue-engineered constructs. This article collects the recent advances in design and application of poloxamer-based biomaterials in tissue engineering, drug/gene delivery, theranostic devices, and bioinks for 3D printing. STATEMENT OF SIGNIFICANCE: Poloxamers, also called Pluronic, belong to a unique class of synthetic tri-block copolymers containing central hydrophobic chains of poly(propylene oxide) sandwiched between two hydrophilic chains of poly(ethylene oxide). The microstructure, bioactivity, and mechanical properties of poloxamers can be tailored to mimic the behavior of various types of tissues. Moreover, their amphiphilic nature and the potential to self-assemble into the micelles make them promising drug carriers with the ability to improve the drug availability to make cancer cells more vulnerable to drugs. However, no reports have systematically reviewed the critical role of poloxamer for biomedical applications. Research on poloxamers is growing today opening new scenarios that expand the potential of these biomaterials from "traditional" treatments to a new era of tissue engineering. To the best of our knowledge, this is the first review article in which such issue is systematically reviewed and critically discussed in the light of the existing literature.

Collagen Type I and II Blend Hydrogel with Autologous Mesenchymal Stem Cells as a Scaffold for Articular Cartilage Defect Repair

Collagen type II is a promising material to repair cartilage defects since it is a major component of articular cartilage and plays a key role in chondrocyte function. This study investigated the chondrogenic differentiation of bone marrow-derived mesenchymal stem cells (MSCs) embedded within a 3:1 collagen type I to II blend (Col I/II) hydrogel or an all collagen type I (Col I) hydrogel. Glycosaminoglycan (GAG) production in Col I/II hydrogels was statistically higher than that in Col I hydrogels or pellet culture, and these results suggested that adding collagen type II promoted GAG production. Col I/II hydrogels had statistically lower alkaline phosphatase (AP) activity than pellets cultured in a chondrogenic medium. The ability of MSCs encapsulated in Col I/II hydrogels to repair cartilage defects was investigated by creating two cartilage defects in the femurs of rabbits. After 13 weeks, histochemical staining suggested that Col I/II blend hydrogels provided favorable conditions for cartilage repair. Histological scoring revealed a statistically higher cartilage repair score for the Col I/II hydrogels compared to either the Col I hydrogels or empty defect controls. Results from this study suggest that there is clinical value in the cartilage repair capabilities of our Col I/II hydrogel with encapsulated MSCs.

Potential of stem cell therapy in intracerebral hemorrhage

Spontaneous intracerebral hemorrhage (ICH) is a common disease associated with high mortality and morbidity. The treatment of patients with ICH includes medical and surgical interventions. New areas of surgical intervention have been focused on the evacuation of hematoma through minimally invasive neurosurgery. In contrast, there have been no significant advances in the development of medical interventions for functional recovery after ICH. Stem cells exert multiple therapeutic functions and have emerged as a promising treatment strategy. Herein, we summarized the pathophysiology of ICH and its treatment targets, and we introduced the therapeutic mechanisms of stem cells (e.g. neutrotrophy and neuroregeneration). Moreover, we reviewed and summarized the experimental designs of the preclinical studies, including the types of cells and the timing and routes of stem cell administration. We further listed and reviewed the completed/published and ongoing clinical trials supporting the safety and efficacy of stem cell therapy in ICH. The limitations of translating preclinical studies into clinical trials and the objectives of future studies were discussed. In conclusion, current literatures showed that stem cell therapy is a promising treatment in ICH and further translation research on judiciously selected group of patients is warranted before it can be extensively applied in clinical practice.

Activation of the SOX-5, SOX-6, and SOX-9 Trio of Transcription Factors Using a Gene-Activated Scaffold Stimulates Mesenchymal Stromal Cell Chondrogenesis and Inhibits Endochondral Ossification

Current treatments for articular cartilage defects relieve symptoms but often only delay cartilage degeneration. Mesenchymal stem cells (MSCs) have shown chondrogenic potential but tend to undergo endochondral ossification when implanted in vivo. Harnessing factors governing joint development to functionalize biomaterial scaffolds, termed developmental engineering, might allow to prime host MSCs to regenerate mature articular cartilage in situ without requiring cell isolation or ex vivo expansion. Therefore, the aim of this study is to develop a gene-activated scaffold capable of delivering developmental cues to host MSCs, thus priming MSCs for articular cartilage differentiation and inhibiting endochondral ossification. It is shown that delivery of the SOX-Trio induced MSCs to over-express COL2A1 and ACAN and deposit a sulfated and collagen type II rich extracellular matrix while hypertrophic gene expression and collagen type X deposition is inhibited. When cell-free SOX-Trio-activated scaffolds are implanted ectopically in vivo, they induced spontaneous chondrogenesis without evidence of hypertrophy. MSCs pre-cultured on SOX-Trio-activated scaffolds prior to implantation differentiate into phenotypically stable chondrocytes as evidenced by a lack of collagen X expression or vascular invasion. This SOX-trio-activated scaffold represents a potent, single treatment, developmentally inspired strategy to prime MSCs in situ for articular cartilage defect repair.

Histological Scoring Systems in the Cartilage Repair of Sheep

Researchers around the world use histological analysis to provide the most detailed morphological information of articular cartilage repair and it predominantly relies on the use of histological scoring systems which are important tools for valid evaluations. Due to hyaline cartilage complex structure and avascular nature, damaged cartilage does not heal spontaneously and it is still a challenge to regenerate and restore its tissue function. The aim of this study was to investigate the quality of regenerated cartilage by using three different histological scoring systems; O’Driscoll, Pineda and Wakitani which are all classic scores described for such animal studies. We used an in vivo ovine model in which a full thickness chondral defect was created and then implanted with the biomaterial (polyhydroxybutyrate/chitosan; PHB/ CHIT). The results of this histological analysis demonstrated that the cartilage repaired tissues received scores indicating that the majority of the regenerated tissue resembled hyaline-like cartilage. After six months of repair the regenerated cartilage showed characteristics like good surface continuity, uniformed stained extracellular matrix, clearly visible zones and cellular proliferation. In conclusion, this study may be used to investigate and improve the regenerative capacity of hyaline cartilage in preclinical models and it also sheds further light on both the evaluation and methods used for the regeneration of damaged cartilage.

Therapeutic "Tool" in Reconstruction and Regeneration of Tissue Engineering for Osteochondral Repair

Repairing osteochondral defects to restore joint function is a major challenge in regenerative medicine. However, with recent advances in tissue engineering, the development of potential treatments is promising. In recent years, in addition to single-layer scaffolds, double-layer or multilayer scaffolds have been prepared to mimic the structure of articular cartilage and subchondral bone for osteochondral repair. Although there are a range of different cells such as umbilical cord stem cells, bone marrow mesenchyml stem cell, and others that can be used, the availability, ease of preparation, and the osteogenic and chondrogenic capacity of these cells are important factors that will influence its selection for tissue engineering. Furthermore, appropriate cell proliferation and differentiation of these cells is also key for the optimal repair of osteochondral defects. The development of bioreactors has enhanced methods to stimulate the proliferation and differentiation of cells. In this review, we summarize the recent advances in tissue engineering, including the development of layered scaffolds, cells, and bioreactors that have changed the approach towards the development of novel treatments for osteochondral repair.

The effect of cartilage extracellular matrix particle size on the chondrogenic differentiation of bone marrow mesenchymal stem cells

Aim: To investigate the effect of cartilage extracellular matrix (ECM) particle size on the chondrogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs). Materials & methods: BMSCs were seeded into the scaffolds fabricated by small particle ECM materials and large particle ECM materials. For the positive control, chondrogenically induced BMSCs were seeded into commercial poly-lactic-glycolic acid scaffolds. Macroscopic observation, histological and immunohistochemical staining, mechanical testing and biochemical analysis were performed to the cell-scaffold constructs. Results: BMSCs in small particle ECM materials and poly-lactic-glycolic acid scaffolds were induced to differentiate into chondrocytes, while BMSCs in the large particle ECM materials scaffold did not differentiate into chondrocytes. Conclusion: The small ECM particle materials improved the induction ability of the cartilage ECM-derived scaffold.

Advances of injectable hydrogel-based scaffolds for cartilage regeneration

Articular cartilage is an important load-bearing tissue distributed on the surface of diarthrodial joints. Due to its avascular, aneural and non-lymphatic features, cartilage has limited self-regenerative properties. To date, the utilization of biomaterials to aid in cartilage regeneration, especially through the use of injectable scaffolds, has attracted considerable attention. Various materials, therapeutics and fabrication approaches have emerged with a focus on manipulating the cartilage microenvironment to induce the formation of cartilaginous structures that have similar properties to the native tissues. In particular, the design and fabrication of injectable hydrogel-based scaffolds have advanced in recent years with the aim of enhancing its therapeutic efficacy and improving its ease of administration. This review summarizes recent progress in these efforts, including the structural improvement of scaffolds, network cross-linking techniques and strategies for controlled release, which present new opportunities for the development of injectable scaffolds for cartilage regeneration.

Biodegradable water-based polyurethane scaffolds with a sequential release function for cell-free cartilage tissue engineering

Three-dimensional (3D) printing technology has rapidly developed as a promising technology for manufacturing tissue engineering scaffolds. Cells used in tissue engineering are subjected to the quality management and risk of contamination, while cell-free scaffolds may not have sufficient therapeutic efficacy. In this study, water-based 3D printing ink containing biodegradable polyurethane (PU), chemokine SDF-1, and Y27632 drug-embedding PU microspheres was printed at low temperature (-40 °C) to fabricate tissue engineering scaffolds with sequential drug release function. The scaffolds containing 200 ng/ml SDF-1 and 22 wt% Y27632-encapsulated microspheres (55 µg/ml Y27632 in microspheres) (abbreviated PU/SDF-1/MS_Y scaffolds) had the optimal performance. The structural design of the scaffolds allowed each of SDF-1 and Y27632 to be released sequentially in vitro and reach the effective concentration (∼100 ng/ml and 3.38 µg/ml, respectively) after the appropriate time (24 h and 62 h, respectively). Human mesenchymal stem cells (hMSCs) seeded in the scaffolds showed significant GAG deposition in 7 days. Besides, the gradual release of SDF-1 from the PU/SDF-1/MS_Y scaffolds could induce the migration of hMSCs. Implantation of the cell-free PU/SDF-1/MS_Y scaffolds in rabbit articular cartilage defects supported the potential of the scaffolds to promote cartilage regeneration. The 3D printed scaffolds with sequential releases of SDF-1 and Y27632 may have potential in cartilage tissue engineering. STATEMENT OF SIGNIFICANCE: The clinical success of tissue engineering depends highly on the quality of externally supplied cells, while cell-free scaffolds may not have sufficient therapeutic efficacy. In this manuscript, water-based 3D printing ink containing biodegradable polyurethane (PU), chemokine SDF-1, and Y27632 drug-embedding PU microspheres was printed at low temperature to fabricate tissue engineering scaffolds with sequential drug release function. The structural design of the scaffolds allowed each of SDF-1 and Y27632 to be released sequentially in vitro. SDF-1 was released earlier from the scaffolds to promote cell migration. The drug Y27632 was released later from the microspheres into the matrix of the scaffolds to induce the chondrogenic differentiation of the attracted cells. Implantation of the cell-free PU/SDF-1/MS_Y scaffolds in rabbit articular cartilage defects supported the potential of the scaffolds to promote cartilage regeneration. We hypothesized that the cell-free scaffolds may improve the clinical applicability and convenience without the use of exogenous cells or growth factor.

In Vitro and In Vivo Comparison of Different Types of Rabbit Mesenchymal Stem Cells for Cartilage Repair

Objective

Systematic studies indicate a growing number of clinical studies that use mesenchymal stem cells (MSCs) for the treatment of cartilage lesions. The current experimental and preclinical study aims to comparatively evaluate the potential of MSCs from a variety of tissues for the treatment of cartilage defect in rabbit’s knee which has not previously been reported.

Materials and Methods

In this experimental study, MSCs isolated from bone marrow (BMMSCs), adipose (AMSCs), and ears (EMSCs) of rabbits and expanded under in vitro culture. The growth rate and differentiation ability of MSCs into chondrocyte and the formation of cartilage pellet were investigated by drawing the growth curve and real-time polymerase chain reaction (RT-PCR), respectively. Then, the critical cartilage defect was created on the articular cartilage (AC) of the rabbit distal femur, and MSCs in collagen carrier were transplanted. The studied groups were as the control (only defect), sham (defect with scaffold), BMMSCs in the scaffold, EMSCs in the scaffold, and EMSCs in the scaffold with cartilage pellets. Histological and the gene expression analysis were performed following the transplantation.

Results

Based on our comparative in vitro investigation, AMSCs possessed the highest growth rate, as well as the lowest chondrogenic differentiation potential. In this context, MSCs of the ear showed a significantly higher growth rate and cartilage differentiation potential than those of bone marrow tissue (P<0.05). According to our in vivo assessments, BMMSC- and EMSC-seeded scaffolds efficiently improved the cartilage defect 4 weeks post-transplantation, while no improvement was observed in the group contained the cartilage pellets.

Conclusion

It seems that the ear contains MSCs that promote cartilage regeneration as much as the conventional MSCs from the bone marrow. Considering a high proliferation rate and easy harvesting of MSCs of the ear, this finding could be of value for the regenerative medicine.

Ageing and Osteoarthritis

The increase in global lifespan has in turn increased the prevalence of osteoarthritis which is now the most common type of arthritis. Cartilage tissue located on articular joints erodes during osteoarthritis which causes pain and may lead to a crippling loss of function in patients. The pathophysiology of osteoarthritis has been understudied and currently no disease modifying treatments exist. The only current end-point treatment remains joint replacement surgery. The primary risk factor for osteoarthritis is age. Clinical and basic research is now focused on understanding the ageing process of cartilage and its role in osteoarthritis. This chapter will outline the physiology of cartilage tissue, the clinical presentation and treatment options for the disease and the cellular ageing processes which are involved in the pathophysiology of the disease.

Role of Mesenchymal Stem Cells Densities When Injected as Suspension in Joints with Osteochondral Defects

OBJECTIVE

The aim of this study was to evaluate an intraarticular injection of different doses of autologous mesenchymal stem cells (MSCs) for improving repair of midterm osteochondral defect.

DESIGN

At 4 weeks postoperative marrow stimulation model bilaterally (3 mm diameter; 4 mm depth) in the medial femoral condyle, autologous MSCs were injected into knee joint. Twenty-four Japanese rabbits aged 6 months were divided randomly into 4 groups ( n = 6 per group): the control group and and MSC groups including 0.125, 1.25, and 6.25 million MSCs. Repaired tissue was assessed macroscopically and histologically at 4 and 12 weeks after intraarticular injection of MSCs.

RESULTS

At 12 weeks, there was no repair tissue in the control group. The gross appearance of the 1.25 and 6.25 million MSC groups revealed complete repair of the defect with white to pink tissue at 12 weeks. An osteochondral repair was histologically significantly better in the 1.25 and 6.25 million MSC groups than in the control and 0.125 million MSC groups at 4 and 12 weeks, due to presence of hyaline-like tissue in the deep layer at 4 weeks, and at 12 weeks hyaline cartilage formation at the periphery and fibrous tissue containing some chondrocytes in the deep layer of the center of the defect. Subchondral bone was restructured in the 1.25 and 6.25 million MSC groups, although it did not resemble the normal bone.

CONCLUSION

An intraarticular injection of 1.25 or 6.25 million MSCs could promote the repair of subchondral bone, even in the case of midterm osteochondral defect.

Human Knee Meniscus Regeneration Strategies: a Review on Recent Advances

PURPOSE OF REVIEW

Lack of vascularity in the human knee meniscus often leads to surgical removal (total or partial meniscectomy) in the case of severe meniscal damage. However, complete recovery is in question after such removal as the meniscus plays an important role in knee stability. Thus, meniscus tissue regeneration strategies are of intense research interest in recent years.

RECENT FINDINGS

The structural complexity and inhomogeneity of the meniscus have been addressed with processing technologies for precisely controlled three dimensional (3D) complex porous scaffold architectures, the use of biomolecules and nanomaterials. The regeneration and replacement of the total meniscus have been studied by the orthopedic and scientific communities via successful pre-clinical trials towards mimicking the biomechanical properties of the human knee meniscus. Researchers have attempted different regeneration strategies which contribute to in vitro regeneration and are capable of repairing meniscal tears to some extent. This review discusses the present state of the art of these meniscus tissue engineering aspects.

Driving mesenchymal stem cell differentiation from self-assembled monolayers

The utilization of self-assembled monolayer (SAM) systems to direct Mesenchymal Stem Cell (MSC) differentiation has been covered in the literature for years, but finding a general consensus pertaining to its exact role over the differentiation of stem cells had been rather challenging. Although there are numerous reports on surface functional moieties activating and inducing differentiation, the results are often different between reports due to the varying surface conditions, such as topography or surface tension. Herein, in view of the complexity of the subject matter, we have sought to catalogue the recent developments around some of the more common functional groups on predominantly hard surfaces and how these chemical groups may influence the overall outcome of the mesenchymal stem cells (MSC) differentiation so as to better establish a clearer underlying relationship between stem cells and their base substratum interactions.

Graphical illustration showing the functional groups that drive MSC differentiation without soluble bioactive cues within the first 14 days.

Erosion of the medial compartment of the canine elbow: occurrence, diagnosis and currently available treatment options

Erosion of the medial compartment of the elbow joint refers to full thickness cartilage loss with exposure of the subchondral bone (modified Outerbridge grades 4–5) of the medial part of the humeral condyle (MHC) and the corresponding ulnar contact area. This finding may appear in the absence of an osteochondral fragment or a cartilage flap, or in combination with fragmentation of the medial coronoid process (MCP) or osteochondritis dissecans (OCD) of the MHC. With regard to the prognosis, it is important to diagnose these severe erosions. Imaging of cartilage lesions by means of radiography, ultrasonography, computed tomography or magnetic resonance imaging is challenging in dogs. In contrast, direct arthroscopic inspection provides detailed information about the cartilage.

The treatment of these severe erosions is difficult because of the limited regenerative capacity of cartilage and presumed mechanical or physical triggering factors. Several conservative and surgical treatment methods have been proposed to treat elbows with severe cartilage defects. However, due to irreversible loss of cartilage, the prognosis in these cases remains guarded.

Biomimetic multidirectional scaffolds for zonal osteochondral tissue engineering via a lyophilization bonding approach

The zonal organization of osteochondral tissue underlies its long term function. Despite this, tissue engineering strategies targeted for osteochondral repair commonly rely on the use of isotropic biomaterials for tissue reconstruction. There exists a need for a new class of highly biomimetic, anisotropic scaffolds that may allow for the engineering of new tissue with zonal properties. To address this need, we report the facile production of monolithic multidirectional collagen-based scaffolds that recapitulate the zonal structure and composition of osteochondral tissue. First, superficial and osseous zone-mimicking scaffolds were fabricated by unidirectional freeze casting collagen-hyaluronic acid and collagen-hydroxyapatite-containing suspensions, respectively. Following their production, a lyophilization bonding process was used to conjoin these scaffolds with a distinct collagen-hyaluronic acid suspension mimicking the composition of the transition zone. Resulting matrices contained a thin, highly aligned superficial zone that interfaced with a cellular transition zone and vertically oriented calcified cartilage and osseous zones. Confocal microscopy confirmed a zone-specific localization of hyaluronic acid, reflecting the depth-dependent increase of glycosaminoglycans in the native tissue. Poorly crystalline, carbonated hydroxyapatite was localized to the calcified cartilage and osseous zones and bordered the transition zone. Compressive testing of hydrated scaffold zones confirmed an increase of stiffness with scaffold depth, where compressive moduli of chondral and osseous zones fell within or near ranges conducive for chondrogenesis or osteogenesis of mesenchymal stem cells. With the combination of these biomimetic architectural and compositional cues, these multidirectional scaffolds hold great promise for the engineering of zonal osteochondral tissue. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 948-958, 2018.

Platelet-rich concentrate in serum-free medium enhances cartilage-specific extracellular matrix synthesis and reduces chondrocyte hypertrophy of human mesenchymal stromal cells encapsulated in alginate

Platelet-rich concentrate (PRC), used in conjunction with other chondroinductive growth factors, have been shown to induce chondrogenesis of human mesenchymal stromal cells (hMSC) in pellet culture. However, pellet culture systems promote cell hypertrophy and the presence of other chondroinductive growth factors in the culture media used in previous studies obscures accurate determination of the effect of platelet itself in inducing chondrogenic differentiation. Hence, this study aimed to investigate the effect of PRC alone in enhancing the chondrogenic differentiation potential of human mesenchymal stromal cells (hMSC) encapsulated in three-dimensional alginate constructs. Cells encapsulated in alginate were cultured in serum-free medium supplemented with only 15% PRC. Scanning electron microscopy was used to determine the cell morphology. Chondrogenic molecular signature of hMSCs was determined by quantitative real-time PCR and verified at protein levels via immunohistochemistry and enzyme-linked immunosorbent assay. Results showed that the cells cultured in the presence of PRC for 24 days maintained a chondrocytic phenotype and demonstrated minimal upregulation of cartilaginous extracellular matrix (ECM) marker genes (SOX9, TNC, COL2, ACAN, COMP) and reduced expression of chondrocyte hypertrophy genes (Col X, Runx2) compared to the standard chondrogenic medium (p < 0.05). PRC group had correspondingly higher levels of glycosaminoglycan and increased concentration of chondrogenic specific proteins (COL2, ACAN, COMP) in the ECM. In conclusion, PRC alone appears to be very potent in inducing chondrogenic differentiation of hMSCs and offers additional benefit of suppressing chondrocyte hypertrophy, rendering it a promising approach for providing abundant pool of chondrogenic MSCs for application in cartilage tissue engineering.