Autologous chondrocyte implantation in a novel alginate-agarose hydrogel: outcome at two years

An overview of nasal cartilage bioprinting: from bench to bedside

Nasal cartilage diseases and injuries are known as significant challenges in reconstructive medicine, affecting a substantial number of individuals worldwide. In recent years, the advent of three-dimensional (3D) bioprinting has emerged as a promising approach for nasal cartilage reconstruction, offering potential breakthroughs in the field of regenerative medicine. This paper provides an overview of the methods and challenges associated with 3D bioprinting technologies in the procedure of reconstructing nasal cartilage tissue. The process of 3D bioprinting entails generating a digital 3D model using biomedical imaging techniques and computer-aided design to integrate both internal and external scaffold features. Then, bioinks which consist of biomaterials, cell types, and bioactive chemicals, are applied to facilitate the precise layer-by-layer bioprinting of tissue-engineered scaffolds. After undergoing in vitro and in vivo experiments, this process results in the development of the physiologically functional integrity of the tissue. The advantages of 3D bioprinting encompass the ability to customize scaffold design, enabling the precise incorporation of pore shape, size, and porosity, as well as the utilization of patient-specific cells to enhance compatibility. However, various challenges should be considered, including the optimization of biomaterials, ensuring adequate cell viability and differentiation, achieving seamless integration with the host tissue, and navigating regulatory attention. Although numerous studies have demonstrated the potential of 3D bioprinting in the rebuilding of such soft tissues, this paper covers various aspects of the bioprinted tissues to provide insights for the future development of repair techniques appropriate for clinical use.

Top 50 Most-Cited Studies about Osteochondritis Dissecans

Purpose

To determine the 50 most frequently cited studies on osteochondritis dissecans (OCD) and to conduct a bibliometric analysis of these studies.

Methods

We performed a search within the Clarivate Web of Science database, identifying articles published before December 2022 that encompass topics related to OCD. The search was conducted using the keywords "Osteochondritis Dissecans OR Osteochondritis OR Dissecans."Search results were then filtered using predetermined guidelines and criteria, and the 50 most-cited articles were selected for analysis. Extracted data included title, journal, design, main topic, joint, citations, year, country of origin, and level of evidence.

Results

The search yielded 3,865 articles. The 50 most-cited articles were published between 1957 and 2018, with the greatest proportion published from 2000 to 2009 (60%). The most frequently studied topic was treatment (68%), followed by etiology (14%) and imaging (8%). The majority of articles had Level IV evidence (36%) and the largest proportion focused on the knee joint (36%), followed by the ankle (32%), and elbow (6%). The mean citation count per article was 287 (range: 157-1,050), with the most-cited articles primarily published from 2000 to 2003. The leading country of origin was the United States, accounting for 19 publications.

Conclusions

Most of the top 50 most-cited articles regarding OCD are about treatment, and the knee is the most-studied joint. The majority of the articles were Level IV evidence and were published in the United States between 2000 and 2009.

Clinical Relevance

The top 50 most-cited studies list will provide researchers, medical students, residents, and fellows with a foundational list of the most important and influential academic contributions regarding osteochondritis dissecans (OCD).

Translation of nanotechnology-based implants for orthopedic applications: current barriers and future perspective

The objective of bioimplant engineering is to develop biologically compatible materials for restoring, preserving, or altering damaged tissues and/or organ functions. The variety of substances used for orthopedic implant applications has been substantially influenced by modern material technology. Therefore, nanomaterials can mimic the surface properties of normal tissues, including surface chemistry, topography, energy, and wettability. Moreover, the new characteristics of nanomaterials promote their application in sustaining the progression of many tissues. The current review establishes a basis for nanotechnology-driven biomaterials by demonstrating the fundamental design problems that influence the success or failure of an orthopedic graft, cell adhesion, proliferation, antimicrobial/antibacterial activity, and differentiation. In this context, extensive research has been conducted on the nano-functionalization of biomaterial surfaces to enhance cell adhesion, differentiation, propagation, and implant population with potent antimicrobial activity. The possible nanomaterials applications (in terms of a functional nanocoating or a nanostructured surface) may resolve a variety of issues (such as bacterial adhesion and corrosion) associated with conventional metallic or non-metallic grafts, primarily for optimizing implant procedures. Future developments in orthopedic biomaterials, such as smart biomaterials, porous structures, and 3D implants, show promise for achieving the necessary characteristics and shape of a stimuli-responsive implant. Ultimately, the major barriers to the commercialization of nanotechnology-derived biomaterials are addressed to help overcome the limitations of current orthopedic biomaterials in terms of critical fundamental factors including cost of therapy, quality, pain relief, and implant life. Despite the recent success of nanotechnology, there are significant hurdles that must be overcome before nanomedicine may be applied to orthopedics. The objective of this review was to provide a thorough examination of recent advancements, their commercialization prospects, as well as the challenges and potential perspectives associated with them. This review aims to assist healthcare providers and researchers in extracting relevant data to develop translational research within the field. In addition, it will assist the readers in comprehending the scope and gaps of nanomedicine's applicability in the orthopedics field.

Neo-cartilage formation using human nondegenerate versus osteoarthritic chondrocyte-derived cartilage organoids in a viscoelastic hydrogel

Current regenerative cartilage therapies are associated with several drawbacks such as dedifferentiation of chondrocytes during expansion and the formation of fibrocartilage. Optimized chondrocyte expansion and tissue formation could lead to better clinical results of these therapies. In this study, a novel chondrocyte suspension expansion protocol that includes the addition of porcine notochordal cell-derived matrix was used to self-assemble human chondrocytes from osteoarthritic (OA) and nondegenerate (ND) origin into cartilage organoids containing collagen type II and proteoglycans. Proliferation rate and viability were similar for OA and ND chondrocytes and organoids formed had a similar histologic appearance and gene expression profile. Organoids were then encapsulated in viscoelastic alginate hydrogels to form larger tissues. Chondrocytes on the outer bounds of the organoids produced a proteoglycan-rich matrix to bridge the space between organoids. In hydrogels containing ND organoids some collagen type I was observed between the organoids. Surrounding the bulk of organoids in the center of the gels, in both OA and ND gels a continuous tissue containing cells, proteoglycans and collagen type II had been produced. No difference was observed in sulphated glycosaminoglycan and hydroxyproline content between gels containing organoids from OA or ND origin after 28 days. It was concluded that OA chondrocytes, which can be harvested from leftover surgery tissue, perform similar to ND chondrocytes in terms of human cartilage organoid formation and matrix production in alginate gels. This opens possibilities for their potential to serve as a platform for cartilage regeneration but also as an in vitro model to study pathways, pathology, or drug development.

Progress and prospect of technical and regulatory challenges on tissue-engineered cartilage as therapeutic combination product

Hyaline cartilage plays a critical role in maintaining joint function and pain. However, the lack of blood supply, nerves, and lymphatic vessels greatly limited the self-repair and regeneration of damaged cartilage, giving rise to various tricky issues in medicine. In the past 30 years, numerous treatment techniques and commercial products have been developed and practiced in the clinic for promoting defected cartilage repair and regeneration. Here, the current therapies and their relevant advantages and disadvantages will be summarized, particularly the tissue engineering strategies. Furthermore, the fabrication of tissue-engineered cartilage under research or in the clinic was discussed based on the traid of tissue engineering, that is the materials, seed cells, and bioactive factors. Finally, the commercialized cartilage repair products were listed and the regulatory issues and challenges of tissue-engineered cartilage repair products and clinical application would be reviewed.

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Tissue engineered cartilage, a promising strategy for articular cartilage repair.

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Nearly 20 engineered cartilage repair products in clinic based on clinical techniques.

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Combination product, the classification of tissue-engineered cartilage.

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Key regulatory compliance issues for combination products.

Therapeutic application of hydrogels for bone-related diseases

Bone-related diseases caused by trauma, infection, and aging affect people’s health and quality of life. The prevalence of bone-related diseases has been increasing yearly in recent years. Mild bone diseases can still be treated with conservative drugs and can be cured confidently. However, serious bone injuries caused by large-scale trauma, fractures, bone tumors, and other diseases are challenging to heal on their own. Open surgery must be used for intervention. The treatment method also faces the problems of a long cycle, high cost, and serious side effects. Studies have found that hydrogels have attracted much attention due to their good biocompatibility and biodegradability and show great potential in treating bone-related diseases. This paper mainly introduces the properties and preparation methods of hydrogels, reviews the application of hydrogels in bone-related diseases (including bone defects, bone fracture, cartilage injuries, and osteosarcoma) in recent years. We also put forward suggestions according to the current development status, pointing out a new direction for developing high-performance hydrogels more suitable for bone-related diseases.

The Use of Autologous Chondrocyte and Mesenchymal Stem Cell Implants for the Treatment of Focal Chondral Defects in Human Knee Joints-A Systematic Review and Meta-Analysis

Focal chondral defects of the knee occur commonly in the young, active population due to trauma. Damage can insidiously spread and lead to osteoarthritis with significant functional and socioeconomic consequences. Implants consisting of autologous chondrocytes or mesenchymal stem cells (MSC) seeded onto scaffolds have been suggested as promising therapies to restore these defects. However, the degree of integration between the implant and native cartilage still requires optimization. A PRISMA systematic review and meta-analysis was conducted using five databases (PubMed, MEDLINE, EMBASE, Web of Science, CINAHL) to identify studies that used autologous chondrocyte implants (ACI) or MSC implant therapies to repair chondral defects of the tibiofemoral joint. Data on the integration of the implant-cartilage interface, as well as outcomes of clinical scoring systems, were extracted. Most eligible studies investigated the use of ACI only. Our meta-analysis showed that, across a total of 200 patients, 64% (95% CI (51%, 75%)) achieved complete integration with native cartilage. In addition, a pooled improvement in the mean MOCART integration score was observed during post-operative follow-up (standardized mean difference: 1.16; 95% CI (0.07, 2.24), p = 0.04). All studies showed an improvement in the clinical scores. The use of a collagen-based scaffold was associated with better integration and clinical outcomes. This review demonstrated that cell-seeded scaffolds can achieve good quality integration in most patients, which improves over time and is associated with clinical improvements. A greater number of studies comparing these techniques to traditional cartilage repair methods, with more inclusion of MSC-seeded scaffolds, should allow for a standardized approach to cartilage regeneration to develop.

The immune microenvironment in cartilage injury and repair

The ability of articular cartilage to repair itself is limited because it lacks blood vessels, nerves, and lymph tissue. Once damaged, it can lead to joint swelling and pain, accelerating the progression of osteoarthritis. To date, complete regeneration of hyaline cartilage exhibiting mechanical properties remains an elusive goal, despite the many available technologies. The inflammatory milieu created by cartilage damage is critical for chondrocyte death and hypertrophy, extracellular matrix breakdown, ectopic bone formation, and progression of cartilage injury to osteoarthritis. In the inflammatory microenvironment, mesenchymal stem cells (MSCs) undergo aberrant differentiation, and chondrocytes begin to convert or dedifferentiate into cells with a fibroblast phenotype, thereby resulting in fibrocartilage with poor mechanical qualities. All these factors suggest that inflammatory problems may be a major stumbling block to cartilage repair. To produce a milieu conducive to cartilage repair, multi-dimensional management of the joint inflammatory microenvironment in place and time is required. Therefore, this calls for elucidation of the immune microenvironment of cartilage repair after injury. This review provides a brief overview of: (1) the pathogenesis of cartilage injury; (2) immune cells in cartilage injury and repair; (3) effects of inflammatory cytokines on cartilage repair; (4) clinical strategies for treating cartilage defects; and (5) strategies for targeted immunoregulation in cartilage repair. STATEMENT OF SIGNIFICANCE: Immune response is increasingly considered the key factor affecting cartilage repair. It has both negative and positive regulatory effects on the process of regeneration and repair. Proinflammatory factors are secreted in large numbers, and necrotic cartilage is removed. During the repair period, immune cells can secrete anti-inflammatory factors and chondrogenic cytokines, which can inhibit inflammation and promote cartilage repair. However, inflammatory factors persist, which accelerate the degradation of the cartilage matrix. Furthermore, in an inflammatory microenvironment, MSCs undergo abnormal differentiation, and chondrocytes begin to transform or dedifferentiate into fibroblast-like cells, forming fibrocartilage with poor mechanical properties. Consequently, cartilage regeneration requires multi-dimensional regulation of the joint inflammatory microenvironment in space and time to make it conducive to cartilage regeneration.

Restoring Carboxylates on Highly Modified Alginates Improves Gelation, Tissue Retention and Systemic Capture

Alginate hydrogels are gaining traction for use in drug delivery, regenerative medicine, and as tissue engineered scaffolds due to their physiological gelation conditions, high tissue biocompatibility, and wide chemical versatility. Traditionally, alginate is decorated at the carboxyl group to carry drug payloads, peptides, or proteins. While low degrees of substitution do not cause noticeable mechanical changes, high degrees of substitution can cause significant losses to alginate properties including complete loss of calcium cross-linking. While most modifications used to decorate alginate deplete the carboxyl groups, we propose that alginate modifications that replenish the carboxyl groups could overcome the loss in gel integrity and mechanics. In this report, we demonstrate that restoring carboxyl groups during functionalization maintains calcium cross-links as well as hydrogel shear-thinning and self-healing properties. In addition, we demonstrate that alginate hydrogels modified to a high degree with azide modifications that restore the carboxyl groups have improved tissue retention at intramuscular injection sites and capture blood-circulating cyclooctynes better than alginate hydrogels modified with azide modifications that deplete the carboxyl groups. Taken together, alginate modifications that restore carboxyl groups could significantly improve alginate hydrogel mechanics for clinical applications. STATEMENT OF SIGNIFICANCE: Chemical modification of hydrogels provides a powerful tool to regulate cellular adhesion, immune response, and biocompatibility with local tissues. Alginate, due to its biocompatibility and easy chemical modification, is being explored for tissue engineering and drug delivery. Unfortunately, modifying alginate to a high degree of substitution consumes carboxyl group, which are necessary for ionic gelation, leading to poor hydrogel crosslinking. We introduce alginate modifications that restore the alginate's carboxyl groups. We demonstrate that modifications that reintroduce carboxyl groups restore gelation and improve gel mechanics and tissue retention. In addition to contributing to a basic science understanding of hydrogel properties, we anticipate our approach will be useful to create tissue engineered scaffolds and drug delivery platforms.

Long-term outcome for repair of osteochondral lesions of the talus by osteochondral autograft: A series of 56 Mosaicplasties®

INTRODUCTION

The present study analyzed results in 56 osteochondral Mosaicplasty® autografts for osteochondral lesion of the talus (OLT) at more than 5 years' follow-up.

HYPOTHESIS

Mosaicplasty® shows long-term efficacy and low morbidity in the treatment of OLT.

PATIENTS AND METHODS

A multicenter retrospective study included patients treated by Mosaicplasty® with more than 5 years' follow-up. Preoperative data were collected from medical files, and all patients were reassessed. AOFAS scores and FAOS were calculated at last follow-up. Imaging comprised standard radiographs and MRI or CT arthrography of the ankle.

RESULTS

Fifty-six patients were included, with a mean age of 34 years (range, 18-60 years). Seventeen involved work accidents. Mean follow-up was 8.5 years (range, 5-20 years). Mean AOFAS score at follow-up was 80.6±19.4 and mean FAOS 77.8±21.5. Work accident, preoperative osteoarthritis and untreated laxity correlated significantly with poorer results. At last follow-up, 22 patients (39%) showed signs of osteoarthritis. There was no morbidity implicating the malleolar osteotomy. There were 11 cases (20%) of persistent patellar syndrome at the donor site.

DISCUSSION

The present results were comparable to those reported elsewhere, showing that functional results of Mosaicplasty® autograft for OLT do not deteriorate over the long term. Work accidents correlated significantly with poorer functional outcome. Any associated instability must always be treated. Malleolar osteotomy provides good exposure without additional morbidity.

LEVEL OF EVIDENCE

IV; retrospective study.

Typical MRI-pattern suggests peak maturation of the ACI graft 2 years after third-generation ACI: a systematic review

PURPOSE

The purpose of the present article was (1) to systematically review the current literature and (2) to collect data regarding the postoperative magnetic resonance imaging (MRI) appearance of third-generation autologous chondrocyte implantation (ACI) grafts and (3) to provide an overview of imaging findings at various postoperative time points.

METHODS

A systematic review of the literature in Medline (Pubmed) and Embase was performed using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Articles which reported the post-operative MRI morphological outcomes following the use of third-generation ACI for treatment of knee cartilage lesions were included. All MRI results were allocated to six different time intervals: ≤ 3 months, > 3-6 months, > 6 months-1 year, > 1 year-2 years, > 2-5 years and > 5 years after surgery.

RESULTS

A total of 22 studies were included and the study populations ranged from 13 to 180 patients adding up to a total of 951 patients. Parameters such as defect fill, border integration, surface contour, graft morphology and integrity of the subchondral lamina all improve gradually with a peak two years following surgery suggesting complete graft maturation at this time point. After this peak, a statistically insignificant decline is noted for most of the parameters. Signal intensity was found to gradually shift from hyperintense to isointense in the first 36 months and to hypointense later on. Contrarily, subchondral bone edema is not only a postoperative feature of the procedure but also can reappear or persist up to ten years after surgery. As graft failures can appear after two years, consequently, the MRI composite score is also affected.

CONCLUSION

Recurring patterns in postoperative MRI appearance were observed in certain parameters including defect filling, graft signal intensity and structure, border integration of the graft while parameters like subchondral bone tend to be unpredictable. Given the heterogenous findings in terms of clinical correlation, and relating that aspect to the patterns found in this review, an MRI is justified at three months, one year, two years and five years after surgery, unless the clinical symptomatology and individual patient needs dictate otherwise.

LEVEL OF EVIDENCE

IV.

Identifying Consensus and Open Questions around Assessing or Predicting the Quality and Success of Cartilage Repair: A Delphi Study

A range of surgical techniques have been developed for the repair or regeneration of lesioned cartilage in the human knee and a corresponding array of scoring systems have been created to assess their outcomes. The published literature displays a wide range of opinions regarding the factors that influence the success of surgical cartilage repair and which parameters are the most useful for measuring the quality of the repair at follow-up. Our objective was to provide some clarity to the field by collating items that were agreed upon by a panel of experts to be important in these areas. A modified, three-round Delphi consensus study was carried out consisting of one idea-generating focus-group and two subsequent, self-completed questionnaire rounds. In each round, items were assessed for their importance and level of consensus against pre-determined threshold levels. In total, 31 items reached consensus, including a hierarchy of tissues in the joint based on their importance in cartilage repair, markers of repair cartilage quality and the implications of environmental and patient-related factors. Items were stratified into those that can be employed for predicting the success of cartilage repair and those that could be used for assessing the structural quality of the resulting repair cartilage. Items that did not reach consensus represent areas where dissent remains and could, therefore, be used to guide future clinical and fundamental scientific research.

Alginate-Agarose Hydrogels Improve the In Vitro Differentiation of Human Dental Pulp Stem Cells in Chondrocytes. A Histological Study

Matrix-assisted autologous chondrocyte implantation (MACI) has shown promising results for cartilage repair, combining cultured chondrocytes and hydrogels, including alginate. The ability of chondrocytes for MACI is limited by different factors including donor site morbidity, dedifferentiation, limited lifespan or poor proliferation in vitro. Mesenchymal stem cells could represent an alternative for cartilage regeneration. In this study, we propose a MACI scaffold consisting of a mixed alginate-agarose hydrogel in combination with human dental pulp stem cells (hDPSCs), suitable for cartilage regeneration. Scaffolds were characterized according to their rheological properties, and their histomorphometric and molecular biology results. Agarose significantly improved the biomechanical behavior of the alginate scaffolds. Large scaffolds were manufactured, and a homogeneous distribution of cells was observed within them. Although primary chondrocytes showed a greater capacity for chondrogenic differentiation, hDPSCs cultured in the scaffolds formed large aggregates of cells, acquired a rounded morphology and expressed high amounts of type II collagen and aggrecan. Cells cultured in the scaffolds expressed not only chondral matrix-related genes, but also remodeling proteins and chondrocyte differentiation factors. The degree of differentiation of cells was proportional to the number and size of the cell aggregates that were formed in the hydrogels.

Clinical evaluation after matrix-associated autologous chondrocyte transplantation : a comparison of four different graft types

Aims

The aim of this retrospective study was to determine if there are differences in short-term clinical outcomes among four different types of matrix-associated autologous chondrocyte transplantation (MACT).

Methods

A total of 88 patients (mean age 34 years (SD 10.03), mean BMI 25 kg/m² (SD 3.51)) with full-thickness chondral lesions of the tibiofemoral joint who underwent MACT were included in this study. Clinical examinations were performed preoperatively and 24 months after transplantation. Clinical outcomes were evaluated using the International Knee Documentation Committee (IKDC) Subjective Knee Form, the Brittberg score, the Tegner Activity Scale, and the visual analogue scale (VAS) for pain. The Kruskal-Wallis test by ranks was used to compare the clinical scores of the different transplant types.

Results

The mean defect size of the tibiofemoral joint compartment was 4.28 cm² (SD 1.70). In total, 11 patients (12.6%) underwent transplantation with Chondro-Gide (matrix-associated autologous chondrocyte implantation (MACI)), 40 patients (46.0%) with Hyalograft C (HYAFF), 21 patients (24.1%) with Cartilage Regeneration System (CaReS), and 15 patients (17.2%) with NOVOCART 3D. The mean IKDC Subjective Knee Form score improved from 35.71 (SD 6.44) preoperatively to 75.26 (SD 18.36) after 24 months postoperatively in the Hyalograft group, from 35.94 (SD 10.29) to 71.57 (SD 16.31) in the Chondro-Gide (MACI) group, from 37.06 (SD 5.42) to 71.49 (SD 6.76) in the NOVOCART 3D group, and from 45.05 (SD 15.83) to 70.33 (SD 19.65) in the CaReS group. Similar improvements were observed in the VAS and Brittberg scores.

Conclusion

Two years postoperatively, there were no significant differences in terms of outcomes. Our data demonstrated that MACT, regardless of the implants used, resulted in good clinical improvement two years after transplantation for localized tibiofemoral defects.

Cite this article: Bone Joint Res 2021;10(7):370–379.

State of the art of clinical applications of Tissue Engineering in 2021

Tissue engineering (TE) was introduced almost 30 years ago as a potential technique for regenerating human tissues. However, despite promising laboratory findings, the complexity of the human body, scientific hurdles, and lack of persistent long-term funding still hamper its translation towards clinical applications. In this report, we compile an inventory of clinically applied TE medical products relevant to surgery. A review of the literature, including articles published within the period from 1991 to 2020, was performed according to the PRISMA protocol, using databanks PubMed, Cochrane Library, Web of Science, and Clinicaltrials.gov. We identified 1039 full-length articles as eligible; due to the scarcity of clinical, randomised, controlled trials and case studies, we extended our search towards a broad surgical spectrum. Forty papers involved clinical TE studies. Amongst these, 7 were related to TE protocols for cartilage applied in the reconstruction of nose, ear, and trachea. Nine papers reported TE protocols for articular cartilage, 9 for urological purposes, 7 described TE strategies for cardiovascular aims, and 8 for dermal applications. However, only two clinical studies reported on three-dimensional (3D) and functional long-lasting TE constructs. The concept of generating 3D TE constructs and organs based on autologous molecules and cells is intriguing and promising. The first translational tissue-engineered products and techniques have been clinically implemented. However, despite the 30 years of research and development in this field, TE is still in its clinical infancy. Multiple experimental, ethical, budgetary, and regulatory difficulties hinder its rapid translation. Nevertheless, the first clinical applications show great promise and indicate that the translation towards clinical medical implementation has finally started.

Modified Alginate-Based Hydrogel as a Carrier of the CB2 Agonist JWH133 for Bone Engineering

Alginate hydrogels have been widely used as excellent scaffold materials for implantation in biological systems because of their good biocompatibility. However, it is difficult to repair bone defects with these materials because of their poor mechanical properties. The aim of the present study was to fabricate a novel degradable alginate/palygorskite (PAL) composite hydrogel with good mechanical properties and investigate its potential for application in bone defect repair. The modified alginate-based hydrogel with increasing PAL content exhibited better mechanical properties than the original alginate hydrogel. In addition, the resulting composite hydrogel was thoroughly characterized by scanning electron microscopy (SEM). With increasing PAL content, the swelling ratio of the hydrogel increased in PBS (pH = 7.4). In vitro cytocompatibility was evaluated using bone marrow-derived mesenchymal stem cells (BMSCs) to confirm that the developed composite hydrogel was cytocompatible after 1, 3, and 7 days. All these results suggest that the developed composite hydrogel has great potential for bone tissue engineering applications. JWH133 is a selective agonist of cannabinoid receptor type 2 (CB2), which exerts dual anti-inflammatory and anti-osteoclastogenic effects. We co-cultured BMSCs with composite hydrogels loaded with JWH133, and analysis of proliferation and osteogenic differentiation indicated that the composite hydrogel loaded with JWH133 may enhance the osteogenic differentiation of rat BMSCs. Furthermore, we found that the composite hydrogel loaded with JWH133 inhibited osteoclast formation and the mRNA expression of osteoclast-specific markers. In summary, the developed composite hydrogel has a high drug-loading capacity, good biocompatibility, and strong potential as a drug carrier for treating osteoporosis by promoting osteoblast and inhibiting osteoclast formation and function.

Recent Progress in 3D Printing of Elastic and High-Strength Hydrogels for the Treatment of Osteochondral and Cartilage Diseases

Despite considerable progress for the regenerative medicine, repair of full-thickness articular cartilage defects and osteochondral interface remains challenging. This low efficiency is largely due to the difficulties in recapitulating the stratified zonal architecture of articular cartilage and engineering complex gradients for bone-soft tissue interface. This has led to increased interest in three-dimensional (3D) printing technologies in the field of musculoskeletal tissue engineering. Printable and biocompatible hydrogels are attractive materials for 3D printing applications because they not only own high tunability and complexity, but also offer favorable biomimetic environments for live cells, such as porous structure, high water content, and bioactive molecule incorporation. However, conventional hydrogels are usually mechanically weak and brittle, which cannot reach the mechanical requirements for repair of articular cartilage defects and osteochondral interface. Therefore, the development of elastic and high-strength hydrogels for 3D printing in the repairment of cartilage defects and osteochondral interface is crucial. In this review, we summarized the recent progress in elastic and high-strength hydrogels for 3D printing and categorized them into six groups, namely ion bonds interactions, nanocomposites integrated in hydrogels, supramolecular guest-host interactions, hydrogen bonds interactions, dynamic covalent bonds interactions, and hydrophobic interactions. These 3D printed elastic and high-strength hydrogels may provide new insights for the treatment of osteochondral and cartilage diseases.

Evolution of hydrogels for cartilage tissue engineering of the knee: A systematic review and meta-analysis of clinical studies

INTRODUCTION

In recent years, studies have boosted our knowledge about the biology and disorders of articular cartilage. In this regard, the design of hydrogel-based scaffolds has advanced to improve cartilage repair. However, the efficacy of knee cartilage repair using hydrogels remains unclear. The aim of systematic review and meta-analysis was to scrutinize the efficiency of hydrogel-based therapy in correcting cartilage defects of knee (femoral condyle, patella, tibia plateau and trochlea).

METHODS

The search was conducted in PubMed to gather articles published from 2004/1/1 to 2019/10/01, addressing the effects of implant of hydrogel on knee joint cartilage regeneration. The Cochrane Collaboration's tool for estimating the risk of bias was applied to check the quality of articles. The clinical data for meta-analysis was recorded using the visual analog scale (VAS), Lysholm score, WOMAC, and IKDC. The guidelines of Cochrane Handbook for Systematic Reviews of Interventions were utilized to conduct the review and meta-analysis in the RevMan 5.3 software.

RESULTS

The search resulted in 50 clinical trials that included 2846 patients, 986 of whom received cell-based hydrogel implants while 1860 patients used hydrogel without cell. There were significant differences comparing the pain scores based on the VAS (MD: -2.97; 95% CI: -3.15 to -2.79, P<0.00001) and WOMAC (MD: -25.22; 95% CI: -31.22 to -19.22, P<0.00001) between pre- and post-treatment with hydrogels. Furthermore, there were significant improvements in the functional scores based on the IKDC total score (MD: 30.67; P<0.00001) and the Lysholm knee scale (MD: 29.26; 95% CI: 26.74 to 31.78, P<0.00001). According to the Lysholm and IKDC score and after cumulative functional analysis, there was a significant improvement in this parameter (MD: 29.25; 95% CI: 27.26 to 31.25, P<0.00001).

CONCLUSIONS

This meta-analysis indicated clinically and statistically significant improvements in the pain score (VAS and WOMAC) and the functional score (IKDC and Lysholm) after the administration of hydrogel compared to pretreatment status. So, the current evidence shows the efficiency of hydrogel-based therapy in correcting and repairing knee cartilage defects.

Implementation of Endogenous and Exogenous Mesenchymal Progenitor Cells for Skeletal Tissue Regeneration and Repair

Harnessing adult mesenchymal stem/progenitor cells to stimulate skeletal tissue repair is a strategy that is being actively investigated. While scientists continue to develop creative and thoughtful ways to utilize these cells for tissue repair, the vast majority of these methodologies can ultimately be categorized into two main approaches: (1) Facilitating the recruitment of endogenous host cells to the injury site; and (2) physically administering into the injury site cells themselves, exogenously, either by autologous or allogeneic implantation. The aim of this paper is to comprehensively review recent key literature on the use of these two approaches in stimulating healing and repair of different skeletal tissues. As expected, each of the two strategies have their own advantages and limitations (which we describe), especially when considering the diverse microenvironments of different skeletal tissues like bone, tendon/ligament, and cartilage/fibrocartilage. This paper also discusses stem/progenitor cells commonly used for repairing different skeletal tissues, and it lists ongoing clinical trials that have risen from the implementation of these cells and strategies. Lastly, we discuss our own thoughts on where the field is headed in the near future.

Click cross-linking improves retention and targeting of refillable alginate depots

Injectable alginate hydrogels have demonstrated utility in tissue engineering and drug delivery applications due in part to their mild gelation conditions, low host responses and chemical versatility. Recently, the potential of these gels has expanded with the introduction of refillable hydrogel depots - alginate gels chemically decorated with click chemistry groups to efficiently capture prodrug refills from the blood. Unfortunately, high degrees of click group substitution on alginate lead to poor viscoelastic properties and loss of ionic cross-linking. In this work, we introduce tetrabicyclononyne (tBCN) agents that covalently cross-link azide-modified alginate hydrogels for tissue engineering and drug delivery application in vivo. Adjusting cross-linker concentration allowed tuning the hydrogel mechanical properties for tissue-specific mechanical strength. The bioorthogonal and specific click reaction creates stable hydrogels with improved in vivo properties, including improved retention at injected sites. Azide-alginate hydrogels cross-linked with tBCN elicited minimal inflammation and maintained structural integrity over several months and efficiently captured therapeutics drug surrogates from the circulation. Taken together, azide-alginate hydrogels cross-linked with tBCN convey the benefits of alginate hydrogels for use in tissue engineering and drug delivery applications of refillable drug delivery depots. STATEMENT OF SIGNIFICANCE: Ionically cross-linked, injectable alginate biomaterials hold promise in many different clinical settings. However, adding new chemical functionality to alginate can disrupt their ionic cross-linking, limiting their utility. We have developed a "click" cross-linking strategy to improve the mechanical properties and tissue function of modified alginate biomaterials and enable them to capture small molecule drugs from the blood. We show that click cross-linked materials remain in place better than ionically cross-linked materials and efficiently capture payloads from the blood. Development of click cross-linking for refillable depots represents a crucial step toward clinical application of this promising drug delivery platform.

Agarose-Based Biomaterials: Opportunities and Challenges in Cartilage Tissue Engineering

The lack of adequate blood/lymphatic vessels as well as low-potential articular cartilage regeneration underlines the necessity to search for alternative biomaterials. Owing to their unique features, such as reversible thermogelling behavior and tissue-like mechanical behavior, agarose-based biomaterials have played a key role in cartilage tissue repair. Accordingly, the need for fabricating novel highly efficient injectable agarose-based biomaterials as hydrogels for restoration of injured cartilage tissue has been recognized. In this review, the resources and conspicuous properties of the agarose-based biomaterials were reviewed. First, different types of signals together with their functionalities in the maintenance of cartilage homeostasis were explained. Then, various cellular signaling pathways and their significant role in cartilage tissue engineering were overviewed. Next, the molecular structure and its gelling behavior have been discussed. Eventually, the latest advancements, the lingering challenges, and future ahead of agarose derivatives from the cartilage regeneration perspective have been discussed.

Pulsed electromagnetic fields promote repair of focal articular cartilage defects with engineered osteochondral constructs

Articular cartilage injuries are a common source of joint pain and dysfunction. We hypothesized that pulsed electromagnetic fields (PEMFs) would improve growth and healing of tissue-engineered cartilage grafts in a direction-dependent manner. PEMF stimulation of engineered cartilage constructs was first evaluated in vitro using passaged adult canine chondrocytes embedded in an agarose hydrogel scaffold. PEMF coils oriented parallel to the articular surface induced superior repair stiffness compared to both perpendicular PEMF (p = .026) and control (p = .012). This was correlated with increased glycosaminoglycan deposition in both parallel and perpendicular PEMF orientations compared to control (p = .010 and .028, respectively). Following in vitro optimization, the potential clinical translation of PEMF was evaluated in a preliminary in vivo preclinical adult canine model. Engineered osteochondral constructs (∅ 6 mm × 6 mm thick, devitalized bone base) were cultured to maturity and implanted into focal defects created in the stifle (knee) joint. To assess expedited early repair, animals were assessed after a 3-month recovery period, with microfracture repairs serving as an additional clinical control. In vivo, PEMF led to a greater likelihood of normal chondrocyte (odds ratio [OR]: 2.5, p = .051) and proteoglycan (OR: 5.0, p = .013) histological scores in engineered constructs. Interestingly, engineered constructs outperformed microfracture in clinical scoring, regardless of PEMF treatment (p < .05). Overall, the studies provided evidence that PEMF stimulation enhanced engineered cartilage growth and repair, demonstrating a potential low-cost, low-risk, noninvasive treatment modality for expediting early cartilage repair.

Advancements and Frontiers in the High Performance of Natural Hydrogels for Cartilage Tissue Engineering

Cartilage injury originating from trauma or osteoarthritis is a common joint disease that can bring about an increasing social and economic burden in modern society. On account of its avascular, neural, and lymphatic characteristics, the poor migration ability of chondrocytes, and a low number of progenitor cells, the self-healing ability of cartilage defects has been significantly limited. Natural hydrogels, occurring abundantly with characteristics such as high water absorption, biodegradation, adjustable porosity, and biocompatibility like that of the natural extracellular matrix (ECM), have been developed into one of the most suitable scaffold biomaterials for the regeneration of cartilage in material science and tissue engineering. Notably, natural hydrogels derived from sources such as animal or human cadaver tissues possess the bionic mechanical behaviors of physiological cartilage that are required for usage as articular cartilage substitutes, by which the enhanced chondrogenic phenotype ability may be achieved by facilely embedding living cells, controlling degradation profiles, and releasing stimulatory growth factors. Hence, we summarize an overview of strategies and developments of the various kinds and functions of natural hydrogels for cartilage tissue engineering in this review. The main concepts and recent essential research found that great challenges like vascularity, clinically relevant size, and mechanical performances were still difficult to overcome because the current limitations of technologies need to be severely addressed in practical settings, particularly in unpredictable preclinical trials and during future forays into cartilage regeneration using natural hydrogel scaffolds with high mechanical properties. Therefore, the grand aim of this current review is to underpin the importance of preparation, modification, and application for the high performance of natural hydrogels for cartilage tissue engineering, which has been achieved by presenting a promising avenue in various fields and postulating real-world respective potentials.

Sustained low-dose dexamethasone delivery via a PLGA microsphere-embedded agarose implant for enhanced osteochondral repair

Articular cartilage defects are a common source of joint pain and dysfunction. We hypothesized that sustained low-dose dexamethasone (DEX) delivery via an acellular osteochondral implant would have a dual pro-anabolic and anti-catabolic effect, both supporting the functional integrity of adjacent graft and host tissue while also attenuating inflammation caused by iatrogenic injury. An acellular agarose hydrogel carrier with embedded DEX-loaded poly(lactic-co-glycolic) acid (PLGA) microspheres (DLMS) was developed to provide sustained release for at least 99 days. The DLMS implant was first evaluated in an in vitro pro-inflammatory model of cartilage degradation. The implant was chondroprotective, as indicated by maintenance of Young's modulus (EY) (p = 0.92) and GAG content (p = 1.0) in the presence of interleukin-1β insult. In a subsequent preliminary in vivo experiment, an osteochondral autograft transfer was performed using a pre-clinical canine model. DLMS implants were press-fit into the autograft donor site and compared to intra-articular DEX injection (INJ) or no DEX (CTL). Functional scores for DLMS animals returned to baseline (p = 0.39), whereas CTL and INJ remained significantly worse at 6 months (p < 0.05). DLMS knees were significantly more likely to have improved OARSI scores for proteoglycan, chondrocyte, and collagen pathology (p < 0.05). However, no significant improvements in synovial fluid cytokine content were observed. In conclusion, utilizing a targeted DLMS implant, we observed in vitro chondroprotection in the presence of IL-1-induced degradation and improved in vivo functional outcomes. These improved outcomes were correlated with superior histological scores but not necessarily a dampened inflammatory response, suggesting a primarily pro-anabolic effect. STATEMENT OF SIGNIFICANCE: Articular cartilage defects are a common source of joint pain and dysfunction. Effective treatment of these injuries may prevent the progression of osteoarthritis and reduce the need for total joint replacement. Dexamethasone, a potent glucocorticoid with concomitant anti-catabolic and pro-anabolic effects on cartilage, may serve as an adjuvant for a variety of repair strategies. Utilizing a dexamethasone-loaded osteochondral implant with controlled release characteristics, we demonstrated in vitro chondroprotection in the presence of IL-1-induced degradation and improved in vivo functional outcomes following osteochondral repair. These improved outcomes were correlated with superior histological cartilage scores and minimal-to-no comorbidity, which is a risk with high dose dexamethasone injections. Using this model of cartilage restoration, we have for the first time shown the application of targeted, low-dose dexamethasone for improved healing in a preclinical model of focal defect repair.

Cell-Free Scaffolds as a Monotherapy for Focal Chondral Knee Defects

Chondral knee defects have a limited ability to be repaired. Current surgical interventions have been unable to regenerate articular cartilage with the mechanical properties of native hyaline cartilage. The use of a scaffold-based approach is a potential solution. Scaffolds are often implanted with cells to stimulate cartilage regeneration, but cell-based therapies are associated with additional regulatory restrictions, an additional surgical procedure for cell harvest, time for cell expansion, and the associated costs. To overcome these disadvantages, cell-free scaffolds can be used in isolation allowing native cells to attach over time. This review discusses the optimal properties of scaffolds used for chondral defects, and the evidence for the use of hydrogel scaffolds and hydrogel-synthetic polymer hybrid scaffolds. Preclinical and clinical studies have shown that cell-free scaffolds can support articular cartilage regeneration and have the potential to treat chondral defects. However, there are very few studies in this area and, despite the many biomaterials tested in cell-based scaffolds, most cell-free studies focused on a specific type I collagen scaffold. Future studies on cell-free scaffolds should adopt the modifications made to cell-based scaffolds and replicate them in the clinical setting. More studies are also needed to understand the underlying mechanism of cell-free scaffolds.

Surgical and tissue engineering strategies for articular cartilage and meniscus repair

Injuries to articular cartilage and menisci can lead to cartilage degeneration that ultimately results in arthritis. Different forms of arthritis affect ~50 million people in the USA alone, and it is therefore crucial to identify methods that will halt or slow the progression to arthritis, starting with the initiating events of cartilage and meniscus defects. The surgical approaches in current use have a limited capacity for tissue regeneration and yield only short-term relief of symptoms. Tissue engineering approaches are emerging as alternatives to current surgical methods for cartilage and meniscus repair. Several cell-based and tissue-engineered products are currently in clinical trials for cartilage lesions and meniscal tears, opening new avenues for cartilage and meniscus regeneration. This Review provides a summary of surgical techniques, including tissue-engineered products, that are currently in clinical use, as well as a discussion of state-of-the-art tissue engineering strategies and technologies that are being developed for use in articular cartilage and meniscus repair and regeneration. The obstacles to clinical translation of these strategies are also included to inform the development of innovative tissue engineering approaches.

Bilayered Scaffold Prepared from a Kartogenin-Loaded Hydrogel and BMP-2-Derived Peptide-Loaded Porous Nanofibrous Scaffold for Osteochondral Defect Repair

Recently, a bilayered scaffold with an anisotropic structure mimicking a native osteochondral tissue shows considerable potential for treating osteochondral defects. Herein, a bilayered scaffold consisting of biomimetic cartilage and a subchondral bone architecture was constructed for repairing osteochondral defect. A hydrogel prepared by the Schiff base reaction of gelatin, silk fibroin, and oxidized dextran was designed as the cartilage layer, while a nanofibrous scaffold with a macroporous structure prepared from the polymer blend of poly(l-lactic acid)/poly(lactic-co-glycolic acid)/poly(ε-caprolactone) using the dual phase separation technique served as a subchondral layer. The subchondral layer was then treated with polydopamine coating for osteogenic factor immobilization. To facilitate the chondrogenic and osteogenic differentiation of bone marrow mesenchymal stem cells on the bilayered scaffold, the cartilage-inducing drug kartogenin (KGN) and osteogenic-inducing factor bone morphogenetic protein 2-derived peptides (P24 peptides) were, respectively, loaded on the subchondral layer. Next, the in vitro release of KGN and P24 peptide from the corresponding layer was monitored, respectively, and the results showed that both the release time of KGN and P24 peptides would last for more than 28 days. The in vitro results indicated that the KGN-loaded cartilage layer and P24 peptides-loaded subchondral layer were capable of supporting cell proliferation, and induced the chondrogenic and osteogenic differentiation, respectively. Furthermore, the in vivo experiments suggested that the bilayered scaffold significantly accelerated the regeneration of the osteochondral tissue in the rabbit knee joint model. Consequently, this bilayered scaffold loaded with KGN and P24 peptides would be a promising candidate for repairing osteochondral defect.

Survival Rates of Various Autologous Chondrocyte Grafts and Concomitant Procedures. A Prospective Single-Center Study over 18 Years

Seven different autologous chondrocyte implantation (ACI) grafts were used consecutively over a period of 18 years for the treatment of cartilage lesions in the knees. The aim was to evaluate this entire ACI patient series for graft-related or unrelated serious adverse events (SAE), graft failures, and to reveal potential risk factors for these incidents. The study group comprised 151 operated patients: classical periosteum-ACI (n = 45); ACI-seeded fibrin-collagen patch, fixed by either periosteum (n = 59), collagen membrane (n = 15), or fibrin glue (n = 6); ACI seeded alginate-agarose hydrogel (n = 14); and biomimetic collagen-hydroxyapatite scaffold injected with the ACI suspension (n = 12). The covariates analyzed as possible predicting factors were: age, gender, BMI, lesion depth, lesion size, lesion location, previous surgeries, and concomitant procedures. The Kaplan-Meier method for estimating survival curves, and Cox's proportional hazards model to test for covariates, were used in the statistical analysis. The patients in this series, follow-up 10.1 (2.1-18.3) years, encountered 11% of graft-related SAE (risk factors: previous cartilage surgery, age over 40 years, BMI over 25 kg/m², and meniscus surgery) and 10% of graft unrelated SAE (risk factors: meniscus surgery and osteotomy). None of these factors was a risk for definitive graft failure. The 10-year graft survival rate was 86%. Females had 2.8 times higher incidence of graft failures than males. There was a tendency toward higher graft failures after a previous cartilage surgery. Different ACI graft types offered safe and durable cartilage repair. Female gender, age over 40 years, increased weight, previous cartilage surgery, and meniscus loss showed increased risk for revision surgery or graft failures.

Characterization of Different Sources of Human MSCs Expanded in Serum-Free Conditions with Quantification of Chondrogenic Induction in 3D

Mesenchymal stem cells (MSCs) represent alternative candidates to chondrocytes for cartilage engineering. However, it remains difficult to identify the ideal source of MSCs for cartilage repair since conditions supporting chondrogenic induction are diverse among published works. In this study, we characterized and evaluated the chondrogenic potential of MSCs from bone marrow (BM), Wharton's jelly (WJ), dental pulp (DP), and adipose tissue (AT) isolated and cultivated under serum-free conditions. BM-, WJ-, DP-, and AT-MSCs did not differ in terms of viability, clonogenicity, and proliferation. By an extensive polychromatic flow cytometry analysis, we found notable differences in markers of the osteochondrogenic lineage between the 4 MSC sources. We then evaluated their chondrogenic potential in a micromass culture model, and only BM-MSCs showed chondrogenic conversion. This chondrogenic differentiation was specifically ascertained by the production of procollagen IIB, the only type II collagen isoform synthesized by well-differentiated chondrocytes. As a pilot study toward cartilage engineering, we encapsulated BM-MSCs in hydrogel and developed an original method to evaluate their chondrogenic conversion by flow cytometry analysis, after release of the cells from the hydrogel. This allowed the simultaneous quantification of procollagen IIB and α10, a subunit of a type II collagen receptor crucial for proper cartilage development. This work represents the first comparison of detailed immunophenotypic analysis and chondrogenic differentiation potential of human BM-, WJ-, DP-, and AT-MSCs performed under the same serum-free conditions, from their isolation to their induction. Our study, achieved in conditions compliant with clinical applications, highlights that BM-MSCs are good candidates for cartilage engineering.

Evaluation of the biocompatibility and stability of allogeneic tissue-engineered cartilage in humanized mice

Articular cartilage (AC) has poor capacities of regeneration and lesions often lead to osteoarthritis. Current AC reconstruction implies autologous chondrocyte implantation which requires tissue sampling and grafting. An alternative approach would be to use scaffolds containing off-the-shelf allogeneic human articular chondrocytes (HACs). To investigate tolerance of allogeneic HACs by the human immune system, we developed a humanized mouse model implanted with allogeneic cartilage constructs generated in vitro. A prerequisite of the study was to identify a scaffold that would not provoke inflammatory reaction in host. Therefore, we first compared the response of hu-mice to two biomaterials used in regenerative medicine, collagen sponge and agarose hydrogel. Four weeks after implantation in hu-mice, acellular collagen sponges, but not acellular agarose hydrogels, showed positive staining for CD3 (T lymphocytes) and CD68 (macrophages), suggesting that collagen scaffold elicits weak inflammatory reaction. These data led us to deepen our evaluation of the biocompatibility of allogeneic tissue-engineered cartilage by using agarose as scaffold. Agarose hydrogels were combined with allogeneic HACs to reconstruct cartilage in vitro. Particular attention was paid to HLA-A2 compatibility between HACs to be grafted and immune human cells of hu-mice: HLA-A2+ or HLA-A2- HACs agarose hydrogels were cultured in the presence of a chondrogenic cocktail and implanted in HLA-A2+ hu-mice. After four weeks implantation and regardless of the HLA-A2 phenotype, chondrocytes were well-differentiated and produced cartilage matrix in agarose. In addition, no sign of T-cell or macrophage infiltration was seen in the cartilaginous constructs and no significant increase in subpopulations of T lymphocytes and monocytes was detected in peripheral blood and spleen. We show for the first time that humanized mouse represents a useful model to investigate human immune responsiveness to tissue-engineered cartilage and our data together indicate that allogeneic cartilage constructs can be suitable for cartilage engineering.

Cellular automata model for human articular chondrocytes migration, proliferation and cell death: An in vitro validation

Articular cartilage is characterized by low cell density of only one cell type, chondrocytes, and has limited self-healing properties. When articular cartilage is affected by traumatic injuries, a therapeutic strategy such as autologous chondrocyte implantation is usually proposed for its treatment. This approach requires in vitro chondrocyte expansion to yield high cell number for cell transplantation. To improve the efficiency of this procedure, it is necessary to assess cell dynamics such as migration, proliferation and cell death during culture. Computational models such as cellular automata can be used to simulate cell dynamics in order to enhance the result of cell culture procedures. This methodology has been implemented for several cell types; however, an experimental validation is required for each one. For this reason, in this research a cellular automata model, based on random-walk theory, was devised in order to predict articular chondrocyte behavior in monolayer culture during cell expansion. Results demonstrated that the cellular automata model corresponded to cell dynamics and computed-accurate quantitative results. Moreover, it was possible to observe that cell dynamics depend on weighted probabilities derived from experimental data and cell behavior varies according to the cell culture period. Thus, depending on whether cells were just seeded or proliferated exponentially, culture time probabilities differed in percentages in the CA model. Furthermore, in the experimental assessment a decreased chondrocyte proliferation was observed along with increased passage number. This approach is expected to having other uses as in enhancing articular cartilage therapies based on tissue engineering and regenerative medicine.

Neither significant osteoarthritic changes nor deteriorating subjective outcomes occur after hybrid fixation of osteochondritis dissecans in the young adult

PURPOSE

The goal of the fixation of painful osteochondritis dissecans of the femoral condyles in adults is to integrate the osteochondral fragment and thus achieve a normal hyaline cartilaginous coverage. The addition of a biological process to primary fixation may result in improved fragment integration (hybrid fixation). Osteochondral plugs may fulfil this role. The aim of this study was to evaluate long-term clinical and radiological results after hybrid fixation of unstable osteochondritis dissecans. The hypothesis was that the rate of secondary osteoarthritis would be low.

METHODS

Nine patients treated by hybrid fixation were retrospectively reviewed at a median follow-up of 10.1 years (range 7-14). The median age at surgery was 21 (range 17-28). Six of them were evaluated as ICRS grade II and three, as ICRS grade III. The mean surface of the lesion was 4.5 cm². All patients were followed up clinically (IKDC, KOOS, Lysholm) and radiologically [Kellgren-Lawrence score (KL)].

RESULTS

During arthroscopic assessment at the time of screw removal (3 months after surgery), the fragments were stable, and autograft plugs were all well integrated. At the most recent follow-up visit, the median IKDC score was 85.8 (range 51.72-100), the KOOS score was 87.7 (52.4-100), and the Lysholm scale score was 89.8 (77-100). In 7 out of 9 patients, radiographs showed a joint space KL grade of 0 or 1.

CONCLUSION

Hybrid fixation for treating osteochondritis dissecans lesions of the femoral condyles using mechanical and biological fixation provides healing of the osteochondral fragments with good long-term outcomes. No significant osteoarthritic change was seen with this technique at a mid-term follow-up.

LEVEL OF EVIDENCE

IV-case series.

Chasing Chimeras - The elusive stable chondrogenic phenotype

The choice of the best-suited cell population for the regeneration of damaged or diseased cartilage depends on the effectiveness of culture conditions (e.g. media supplements, three-dimensional scaffolds, mechanical stimulation, oxygen tension, co-culture systems) to induce stable chondrogenic phenotype. Herein, advances and shortfalls in in vitro, preclinical and clinical setting of various in vitro microenvironment modulators on maintaining chondrocyte phenotype or directing stem cells towards chondrogenic lineage are critically discussed. Chondrocytes possess low isolation efficiency, limited proliferative potential and rapid phenotypic drift in culture. Mesenchymal stem cells are relatively readily available, possess high proliferation potential, exhibit great chondrogenic differentiation capacity, but they tend to acquire a hypertrophic phenotype when exposed to chondrogenic stimuli. Embryonic and induced pluripotent stem cells, despite their promising in vitro and preclinical data, are still under-investigated. Although a stable chondrogenic phenotype remains elusive, recent advances in in vitro microenvironment modulators are likely to develop clinically- and commercially-relevant therapies in the years to come.

Comparative cytocompatibility of multiple candidate cell types to photoencapsulation in PEGNB/PEGDA macroscale or microscale hydrogels

The encapsulation of live cells into photopolymerized hydrogel scaffolds has the potential to augment or repair tissue defects, establish versatile regenerative medicine strategies, and be developed as well-defined, yet tunable microenvironments to study fundamental cellular behavior. However, hydrogel fabrication limitations constrain most studies to macroscale hydrogel scaffolds encapsulating millions of cells. These macroscale materials possess regions of heterogeneous photopolymerization conditions and are therefore poor platforms to identify the response of individual cells to encapsulation. Recently, microfluidic droplet-based hydrogel miniaturization and cell encapsulation offers high-throughput, reproducible, and continuous fabrication. Reports of post-encapsulation cell viability, however, vary widely among specific techniques. Furthermore, different cell types often exhibit different level of tolerance to photoencapsulation-induced toxicity. Accordingly, we evaluate the cellular tolerance of various encapsulation techniques and photopolymerization parameters for four mammalian cell types, with potential applications in tissue regeneration, using polyethylene glycol diacrylate or polyethylene glycol norbornene (PEGNB) hydrogels on micro- and macro-length scales. We found PEGNB provides excellent cellular tolerance and supports long-term cell survival by mitigating the deleterious effects of acrylate photopolymerization, which are exacerbated at diminishing volumes. PEGNB, therefore, is an excellent candidate for hydrogel miniaturization. PEGNB hydrogel properties, however, were found to have variable effects on encapsulating different cell candidates. This study could provide guidance for cell encapsulation practices in tissue engineering and regenerative medicine research.

Challenges in Fabrication of Tissue-Engineered Cartilage with Correct Cellular Colonization and Extracellular Matrix Assembly

A correct articular cartilage ultrastructure regarding its structural components and cellularity is important for appropriate performance of tissue-engineered articular cartilage. Various scaffold-based, as well as scaffold-free, culture models have been under development to manufacture functional cartilage tissue. Even decellularized tissues have been considered as a potential choice for cellular seeding and tissue fabrication. Pore size, interconnectivity, and functionalization of the scaffold architecture can be varied. Increased mechanical function requires a dense scaffold, which also easily restricts cellular access within the scaffold at seeding. High pore size enhances nutrient transport, while small pore size improves cellular interactions and scaffold resorption. In scaffold-free cultures, the cells assemble the tissue completely by themselves; in optimized cultures, they should be able to fabricate native-like tissue. Decellularized cartilage has a native ultrastructure, although it is a challenge to obtain proper cellular colonization during cell seeding. Bioprinting can, in principle, provide the tissue with correct cellularity and extracellular matrix content, although it is still an open question as to how the correct molecular interaction and structure of extracellular matrix could be achieved. These are challenges facing the ongoing efforts to manufacture optimal articular cartilage.

Repair of Damaged Articular Cartilage: Current Approaches and Future Directions

Articular hyaline cartilage is extensively hydrated, but it is neither innervated nor vascularized, and its low cell density allows only extremely limited self-renewal. Most clinical and research efforts currently focus on the restoration of cartilage damaged in connection with osteoarthritis or trauma. Here, we discuss current clinical approaches for repairing cartilage, as well as research approaches which are currently developing, and those under translation into clinical practice. We also describe potential future directions in this area, including tissue engineering based on scaffolding and/or stem cells as well as a combination of gene and cell therapy. Particular focus is placed on cell-based approaches and the potential of recently characterized chondro-progenitors; progress with induced pluripotent stem cells is also discussed. In this context, we also consider the ability of different types of stem cell to restore hyaline cartilage and the importance of mimicking the environment in vivo during cell expansion and differentiation into mature chondrocytes.

Orthopaedic regenerative tissue engineering en route to the holy grail: disequilibrium between the demand and the supply in the operating room

Orthopaedic disorders are very frequent, globally found and often partially unresolved despite the substantial advances in science and medicine. Their surgical intervention is multifarious and the most favourable treatment is chosen by the orthopaedic surgeon on a case-by-case basis depending on a number of factors related with the patient and the lesion. Numerous regenerative tissue engineering strategies have been developed and studied extensively in laboratory through in vitro experiments and preclinical in vivo trials with various established animal models, while a small proportion of them reached the operating room. However, based on the available literature, the current strategies have not yet achieved to fully solve the clinical problems. Thus, the gold standards, if existing, remain unchanged in the clinics, notwithstanding the known limitations and drawbacks. Herein, the involvement of regenerative tissue engineering in the clinical orthopaedics is reviewed. The current challenges are indicated and discussed in order to describe the current disequilibrium between the needs and solutions made available in the operating room. Regenerative tissue engineering is a very dynamic field that has a high growth rate and a great openness and ability to incorporate new technologies with passion to edge towards the Holy Grail that is functional tissue regeneration. Thus, the future of clinical solutions making use of regenerative tissue engineering principles for the management of orthopaedic disorders is firmly supported by the clinical need.

Hybrid fixation in adult osteochondritis dissecans of the knee

Osteochondritis dissecans progresses to osteoarthritis if integration of the fragment is not obtained. The prognosis of osteochondritis dissecans is more severe in adults, as spontaneous integration due to physeal closure does not occur. Hybrid fixation consists in combining screw fixation of the fragment with mosaicplasty through the fragment to promote integration into the native condyle. We describe this technique with reference to 17 patients.

Hydrogel formulations for biologicals: current spotlight from a commercial perspective

Hydrogels are, from a commercial perspective especially because of their ease of production, attractive sustained-release systems for high potent immunoglobulins with short circulation half-lives. Hydrogel formulations can reduce the dosing frequency while maintaining therapeutically relevant drug concentrations locally as well as systemically. However, hydrogels have only limited loading capacities and release hydrophilic immunoglobulins typically within hours or days, whereas weeks or months would be more preferable. Despite an evident medical need, the call for novel depot formulations seems to go unheard. This special report explores sought-after hydrogel properties, discusses arguments for using established versus novel excipients and provides selected examples for hydrogel formulations of biologicals that have proceeded into clinical development.

Theoretically proposed optimal frequency for ultrasound induced cartilage restoration

Background

Matching the frequency of the driving force to that of the system’s natural frequency of vibration results in greater amplitude response. Thus we hypothesize that applying ultrasound at the chondrocyte’s resonant frequency will result in greater deformation than applying similar ultrasound power at a frequency outside of the resonant bandwidth. Based on this resonant hypothesis, our group previously confirmed theoretically and experimentally that ultrasound stimulation of suspended chondrocytes at resonance (5 MHz) maximized gene expression of load inducible genes. However, this study was based on suspended chondrocytes. The resonant frequency of a chondrocyte does not only depend on the cell mass and intracellular stiffness, but also on the mechanical properties of the surrounding medium. An in vivo chondrocyte’s environment differs whether it be a blood clot (following microfracture), a hydrogel or the pericellular and extracellular matrices of the natural cartilage. All have distinct structures and compositions leading to different resonant frequencies. In this study, we present two theoretical models, the first model to understand the effects of the resonant frequency on the cellular deformation and the second to identify the optimal frequency range for clinical applications of ultrasound to enhance cartilage restoration.

Results

We showed that applying low-intensity ultrasound at the resonant frequency induced deformation equivalent to that experimentally calculated in previous studies at higher intensities and a 1 MHz frequency. Additionally, the resonant frequency of an in vivo chondrocyte in healthy conditions, osteoarthritic conditions, embedded in a blood clot and embedded in fibrin ranges from 3.5 − 4.8 MHz.

Conclusion

The main finding of this study is the theoretically proposed optimal frequency for clinical applications of therapeutic ultrasound induced cartilage restoration is 3.5 − 4.8 MHz (the resonant frequencies of in vivo chondrocytes). Application of ultrasound in this frequency range will maximize desired bioeffects.

Synthetic Poly(Vinylalcohol)-Based Membranes for Cartilage Surgery and Repair

Cell-based therapies for cartilage repair are continually being developed to treat osteoarthritis. The cells are either introduced directly by intra-articular injection or via a cell-seeded matrix scaffold. Here, poly(vinylalcohol)-based membranes are developed to be used for mesenchymal stem cell implantation in cartilage repair procedures, having controllable physicochemical properties such as porosity, mechanical strength, and permeability, and a unique self-sealing property. The membranes possess a bilayer structure with a less porous layer providing mechanical strength and selective permeability, exhibit an elastic modulus of between 0.3 and 0.9 MPa, and are permeable to molecules <40 kDa, which is in the range of cartilage permeability. Three different peptide ligands with the sequences Ac-GCGYGRGDSPG, Ac-GCG(OPG)4REGOFG(OPG)4, and Ac-GCG(OPG)7, respectively, are conjugated to the membranes and subject to in vitro cell adhesion and differentiation assays. Col I/Col II gene expression ratios indicated that the collagen-mimetic peptide, Ac-GCG(OPG)7, best supported mesenchymal stem cell differentiation into the chondrogenic lineage. Although low retention of the membrane is observed in vivo in a rabbit knee model, results suggest that the membrane was able to facilitate mesenchymal stem cell implantation and differentiation to chondrocytes. These PVA-based membranes provide a feasible, synthetic, off-the-shelf material for the delivery of stem cells, and can be modified for other surgical applications.

Cell-laden hydrogels for osteochondral and cartilage tissue engineering

Despite tremendous advances in the field of regenerative medicine, it still remains challenging to repair the osteochondral interface and full-thickness articular cartilage defects. This inefficiency largely originates from the lack of appropriate tissue-engineered artificial matrices that can replace the damaged regions and promote tissue regeneration. Hydrogels are emerging as a promising class of biomaterials for both soft and hard tissue regeneration. Many critical properties of hydrogels, such as mechanical stiffness, elasticity, water content, bioactivity, and degradation, can be rationally designed and conveniently tuned by proper selection of the material and chemistry. Particularly, advances in the development of cell-laden hydrogels have opened up new possibilities for cell therapy. In this article, we describe the problems encountered in this field and review recent progress in designing cell-hydrogel hybrid constructs for promoting the reestablishment of osteochondral/cartilage tissues. Our focus centers on the effects of hydrogel type, cell type, and growth factor delivery on achieving efficient chondrogenesis and osteogenesis. We give our perspective on developing next-generation matrices with improved physical and biological properties for osteochondral/cartilage tissue engineering. We also highlight recent advances in biomanufacturing technologies (e.g. molding, bioprinting, and assembly) for fabrication of hydrogel-based osteochondral and cartilage constructs with complex compositions and microarchitectures to mimic their native counterparts.

STATEMENT OF SIGNIFICANCE

Despite tremendous advances in the field of regenerative medicine, it still remains challenging to repair the osteochondral interface and full-thickness articular cartilage defects. This inefficiency largely originates from the lack of appropriate tissue-engineered biomaterials that replace the damaged regions and promote tissue regeneration. Cell-laden hydrogel systems have emerged as a promising tissue-engineering platform to address this issue. In this article, we describe the fundamental problems encountered in this field and review recent progress in designing cell-hydrogel constructs for promoting the reestablishment of osteochondral/cartilage tissues. Our focus centers on the effects of hydrogel composition, cell type, and growth factor delivery on achieving efficient chondrogenesis and osteogenesis. We give our perspective on developing next-generation hydrogel/inorganic particle/stem cell hybrid composites with improved physical and biological properties for osteochondral/cartilage tissue engineering. We also highlight recent advances in biomanufacturing and bioengineering technologies (e.g. 3D bioprinting) for fabrication of hydrogel-based osteochondral and cartilage constructs.

Terapias Celulares y Productos de Ingeniería de Tejidos para el Tratamiento de Lesiones Condrales de Rodilla

El cartílago articular es un tejido vulnerable a las lesiones de diferente etiología; siendo uno de los más afectados,  el cartílago de la rodilla. Aunque la mayoría de los tratamientos convencionales reducen los síntomas, generalmente conducen a la formación de fibrocartílago; el cual, posee características diferentes a las del cartílago hialino de las articulaciones.  Son pocas las aproximaciones terapéuticas que promueven el  reemplazo del tejido dañado por cartílago hialino funcional; las más exitosas son las denominadas terapias avanzadas, que aplican células y  productos de ingeniería de tejidos con el fin de estimular la regeneración del cartílago. La mayoría de ellas se basan en colocar soportes  hechos con biomateriales de diferente origen, que sembrados o no con células exógenas o endógenas, reemplazan al cartílago dañado y promueven su regeneración. Este  trabajo revisa algunas de las aproximaciones terapéuticas enfocadas en la regeneración del cartílago articular de rodilla; así como, los biomateriales más empleados en la elaboración de soportes para terapia celular e ingeniería de tejido cartilaginoso.

Applications of Tissue Engineering in Joint Arthroplasty: Current Concepts Update

Research in tissue engineering has undoubtedly achieved significant milestones in recent years. Although it is being applied in several disciplines, tissue engineering's application is particularly advanced in orthopedic surgery and in degenerative joint diseases. The literature is full of remarkable findings and trials using tissue engineering in articular cartilage disease. With the vast and expanding knowledge, and with the variety of techniques available at hand, the authors aimed to review the current concepts and advances in the use of cell sources in articular cartilage tissue engineering.

Chondrogenic Gene Expression Differences between Chondrocytes from Osteoarthritic and Non-OA Trauma Joints in a 3D Collagen Type I Hydrogel

Objective The purpose of the current study was to compare the donor age variation of chondrocytes from non-OA (osteoarthritic) trauma joints in patients of young to middle age (20.5 ± 3.7, 31.8 ± 1.9, 41.9 ± 4.1 years) embedded in matrix-associated autologous chondrocyte transplantation (MACT) grafts (CaReS). The chondrocyte-specific gene expression of CaReS grafts were then compared to chondrocytes from OA joints (in patients aged 63.8 ± 10 years) embedded in a collagen type I hydrogel. Design OA chondrocytes and articular chondrocyte-laden grafts were cultured over 14 days in chondrogenic growth medium. We performed reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) to evaluate the mRNA expression levels of chondrocyte-specific and hypertrophic markers. Results Gene expression analysis with RT-qPCR revealed no significant difference in chondrocyte-specific genes ( COL2A1, ACAN, SOX9, SOX5, SOX6) among 3 different age group of patients with CaReS grafts. In a comparative analysis of OA chondrocytes to articular chondrocytes, chondrogenic markers ( COL2A1, SOX6) exhibited higher expression in OA chondrocytes ( P < 0.05). Hypertrophic or OA cartilage pathogenesis marker ( MMP3, MMP13) expression was higher and COL1A1 had significantly lower expression ( P < 0.05) in OA chondrocytes than articular chondrocytes when cultivated in collagen type I hydrogels. Conclusion In summary, we identify that donor age variation does not influence the chondrogenic gene expression of the CaReS system. We also identified that freshly isolated OA chondrocytes embedded in collagen type I hydrogels can exhibit chondrogenic gene expression as observed in articular chondrocytes on the CaReS grafts. Transforming OA chondrocytes to articular chondrocytes can be regarded as an alternative option in the MACT technique.

Concise Review: Mesenchymal Stem Cells for Functional Cartilage Tissue Engineering: Taking Cues from Chondrocyte-Based Constructs

Osteoarthritis, the most prevalent form of joint disease, afflicts 9% of the U.S. population over the age of 30 and costs the economy nearly $100 billion annually in healthcare and socioeconomic costs. It is characterized by joint pain and dysfunction, though the pathophysiology remains largely unknown. Due to its avascular nature and limited cellularity, articular cartilage exhibits a poor intrinsic healing response following injury. As such, significant research efforts are aimed at producing engineered cartilage as a cell-based approach for articular cartilage repair. However, the knee joint is mechanically demanding, and during injury, also a milieu of harsh inflammatory agents. The unforgiving mechano-chemical environment requires tissue replacements that are capable of bearing such burdens. The use of mesenchymal stem cells (MSCs) for cartilage tissue engineering has emerged as a promising cell source due to their ease of isolation, capacity to readily expand in culture, and ability to undergo lineage-specific differentiation into chondrocytes. However, to date, very few studies utilizing MSCs have successfully recapitulated the structural and functional properties of native cartilage, exposing the difficult process of uniformly differentiating stem cells into desired cell fates and maintaining the phenotype during in vitro culture and after in vivo implantation. To address these shortcomings, here, we present a concise review on modulating stem cell behavior, tissue development and function using well-developed techniques from chondrocyte-based cartilage tissue engineering. Stem Cells Translational Medicine 2017;6:1295-1303.