Nasal chondrocyte-based engineered autologous cartilage tissue for repair of articular cartilage defects: an observational first-in-human trial

3D Bioprinting of Hyaline Cartilage Using Nasal Chondrocytes

Due to the limited self-repair capacity of the hyaline cartilage, the repair of cartilage remains an unsolved clinical problem. Tissue engineering strategy with 3D bioprinting technique has emerged a new insight by providing patient's personalized cartilage grafts using autologous cells for hyaline cartilage repair and regeneration. In this review, we first summarized the intrinsic property of hyaline cartilage in both maxillofacial and orthopedic regions to establish the requirement for 3D bioprinting cartilage tissue. We then reviewed the literature and provided opinion pieces on the selection of bioprinters, bioink materials, and cell sources. This review aims to identify the current challenges for hyaline cartilage bioprinting and the directions for future clinical development in bioprinted hyaline cartilage.

3D Bioprinting Strategies for Articular Cartilage Tissue Engineering

Articular cartilage is the avascular and aneural tissue which is the primary connective tissue covering the surface of articulating bone. Traumatic damage or degenerative diseases can cause articular cartilage injuries that are common in the population. As a result, the demand for new therapeutic options is continually increasing for older people and traumatic young patients. Many attempts have been made to address these clinical needs to treat articular cartilage injuries, including osteoarthritis (OA); however, regenerating highly qualified cartilage tissue remains a significant obstacle. 3D bioprinting technology combined with tissue engineering principles has been developed to create biological tissue constructs that recapitulate the anatomical, structural, and functional properties of native tissues. In addition, this cutting-edge technology can precisely place multiple cell types in a 3D tissue architecture. Thus, 3D bioprinting has rapidly become the most innovative tool for manufacturing clinically applicable bioengineered tissue constructs. This has led to increased interest in 3D bioprinting in articular cartilage tissue engineering applications. Here, we reviewed current advances in bioprinting for articular cartilage tissue engineering.

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.

Craniofacial chondrogenesis in organoids from human stem cell-derived neural crest cells

Knowledge of cell signaling pathways that drive human neural crest differentiation into craniofacial chondrocytes is incomplete, yet essential for using stem cells to regenerate craniomaxillofacial structures. To accelerate translational progress, we developed a differentiation protocol that generated self-organizing craniofacial cartilage organoids from human embryonic stem cell-derived neural crest stem cells. Histological staining of cartilage organoids revealed tissue architecture and staining typical of elastic cartilage. Protein and post-translational modification (PTM) mass spectrometry and snRNA-seq data showed that chondrocyte organoids expressed robust levels of cartilage extracellular matrix (ECM) components: many collagens, aggrecan, perlecan, proteoglycans, and elastic fibers. We identified two populations of chondroprogenitor cells, mesenchyme cells and nascent chondrocytes, and the growth factors involved in paracrine signaling between them. We show that ECM components secreted by chondrocytes not only create a structurally resilient matrix that defines cartilage, but also play a pivotal autocrine cell signaling role in determining chondrocyte fate.

Bioengineering autologous cartilage grafts for functional posterior lamellar eyelid reconstruction: A preliminary study in rabbits

The reconstruction of posterior lamellar eyelid defects remains a significant challenge in clinical practice due to anatomical complexity, specialized function, and aesthetic concerns. The ideal substitute for the posterior lamellar should replicate the native tarsoconjunctival tissue, providing both mechanical support for the eyelids and a smooth surface for the globe after implantation. In this study, we present an innovative approach utilizing tissue-engineered cartilage (TEC) grafts generated from rabbit auricular chondrocytes and a commercialized type I collagen sponge to reconstruct critical-sized posterior lamellar defects in rabbits. The TEC grafts demonstrated remarkable mechanical strength and maintained a stable cartilaginous phenotype both in vitro and at 6 months post-implantation in immunodeficient mice. When employed as autografts to reconstruct tarsal plate defects in rabbits' upper eyelids, these TEC grafts successfully restored normal eyelid morphology, facilitated smooth eyelid movement, and preserved the histological structure of the conjunctival epithelium. When applied in bilayered tarsoconjunctival defect reconstruction, these TEC grafts not only maintained the normal contour of the upper eyelid but also supported conjunctival epithelial cell migration and growth from the defect margin towards the centre. These findings highlight that auricular chondrocyte-based TEC grafts hold great promise as potential candidates for clinical posterior lamellar reconstruction. STATEMENT OF SIGNIFICANCE: The complex structure and function of the posterior lamellar eyelid continue to be significant challenges for clinical reconstructive surgeries. In this study, we utilized autologous auricular chondrocyte-based TEC grafts for posterior lamellar eyelid reconstruction in a preclinical rabbit model. The TEC grafts exhibited native cartilaginous histomorphology and comparable mechanical strength to those of the native human tarsal plate. In rabbit models with either tarsal plate defects alone or bilayered tarsoconjunctival defects, TEC grafts successfully restored the normal eyelid contour and movement, as well as supported preservation and growth of conjunctival epithelium. This is the first study to demonstrate autologous TEC grafts can be employed for repairing tarsal plate defects, thereby offering an alternative therapeutic approach for treating posterior lamellar defects in clinic settings.

Comparative Analysis of Hyaline Cartilage Characteristics and Chondrocyte Potential for Articular Cartilage Repair

This study aimed to compare the histological, biochemical, and mechanical characteristics of hyaline cartilage in different regions and evaluate the potential of chondrocytes extracted from each region as donor sources for articular cartilage repair. The cartilage tissues of the femoral head and knee joint, ribs, nasal septum, thyroid, and xiphoid process of adult Bama pigs were isolated for histological, biochemical, and mechanical evaluation and analysis. The corresponding chondrocytes were isolated and evaluated for proliferation and redifferentiation capacity, using biochemical and histological analysis and RT-PCR experiments. Compared with articular cartilage, non-articular hyaline cartilage matrix stained more intensely in Safranin-O staining. Glycosaminoglycan and total collagen content were similar among all groups, while the highest content was measured in nasal septal cartilage. Regarding biomechanics, non-articular cartilage is similar to articular cartilage, but the elastic modulus and hardness are significantly higher in the middle region of costal cartilage. The chondrocytes extracted from different regions had no significant difference in morphology. Hyaline cartilage-like pellets were formed in each group after redifferentiation. The RT-PCR results revealed similar expressions of cartilage-related genes across the groups, albeit with lower expression of Col2 in the xiphoid chondrocytes. Conversely, higher expression of Col10 was observed in the chondrocytes from the rib, thyroid, and xiphoid cartilage. This study provides valuable preclinical data for evaluating heterotopic hyaline cartilage and chondrocytes for articular cartilage regeneration. The findings contribute to the selection of chondrocyte origins and advance the clinical translation of technology for cartilage regeneration.

Articular cartilage repair biomaterials: strategies and applications

Articular cartilage injury is a frequent worldwide disease, while effective treatment is urgently needed. Due to lack of blood vessels and nerves, the ability of cartilage to self-repair is limited. Despite the availability of various clinical treatments, unfavorable prognoses and complications remain prevalent. However, the advent of tissue engineering and regenerative medicine has generated considerable interests in using biomaterials for articular cartilage repair. Nevertheless, there remains a notable scarcity of comprehensive reviews that provide an in-depth exploration of the various strategies and applications. Herein, we present an overview of the primary biomaterials and bioactive substances from the tissue engineering perspective to repair articular cartilage. The strategies include regeneration, substitution, and immunization. We comprehensively delineate the influence of mechanically supportive scaffolds on cellular behavior, shedding light on emerging scaffold technologies, including stimuli-responsive smart scaffolds, 3D-printed scaffolds, and cartilage bionic scaffolds. Biologically active substances, including bioactive factors, stem cells, extracellular vesicles (EVs), and cartilage organoids, are elucidated for their roles in regulating the activity of chondrocytes. Furthermore, the composite bioactive scaffolds produced industrially to put into clinical use, are also explicitly presented. This review offers innovative solutions for treating articular cartilage ailments and emphasizes the potential of biomaterials for articular cartilage repair in clinical translation.

Enhanced BMP signaling leads to enlarged nasal cartilage formation in mice

Bone morphogenetic proteins (BMPs) are required for craniofacial bone development. However, it remains elusive how BMP signaling regulates craniofacial cartilage development. To address this question, we utilized a genetic system to enhance BMP signaling via one of BMP type I receptors ALK2 in a chondrocyte-specific manner (hereafter Ca-Alk2:Col2-Cre) in mice. Ca-Alk2:Col2-Cre mice died shortly after birth due to severe craniofacial abnormalities including cleft palate, defective tongue, and shorter mandible formation. Histological analysis revealed that these phenotypes were attributed to the extensive chondrogenesis. Compared with controls, enhanced SOX9 and RUNX2 production were observed in nasal cartilage of Ca-Alk2:Col2-Cre mice. To reveal the mechanisms responsible for enlarged nasal cartilage, we examined Smad-dependent and Smad-independent BMP signaling pathways. While the Smad-independent BMP signaling pathway including p38, ERK, and JNK remained silent, the Smad1/5/9 was highly phosphorylated in Ca-Alk2:Col2-Cre mice. Interestingly, Ca-Alk2:Col2-Cre mice showed enhanced S6 kinase phosphorylation, a readout of mammalian target of rapamycin complex 1 (mTORC1). These findings may suggest that enhanced Smad-dependent BMP signaling positively regulates the mTOR pathway and stimulates chondrocytes toward hypertrophic differentiation, thereby leading to enlarged nasal cartilage formation in mice.

Knee Cartilage Lesion Management-Current Trends in Clinical Practice

Many patients, particularly those aged above 40, experience knee joint pain, which hampers both sports activities and daily living. Treating isolated chondral and osteochondral defects in the knee poses a significant clinical challenge, particularly in younger patients who are not typically recommended partial or total knee arthroplasty as alternatives. Several surgical approaches have been developed to address focal cartilage defects. The treatment strategies are characterized as palliation (e.g., chondroplasty and debridement), repair (e.g., drilling and microfracture), or restoration (e.g., autologous chondrocyte implantation, osteochondral autograft, and osteochondral allograft). This review offers an overview of the commonly employed clinical methods for treating articular cartilage defects, with a specific focus on the clinical trials conducted in the last decade. Our study reveals that, currently, no single technology fully meets the essential requirements for effective cartilage healing while remaining easily applicable during surgical procedures. Nevertheless, numerous methods are available, and the choice of treatment should consider factors such as the location and size of the cartilage lesion, patient preferences, and whether it is chondral or osteochondral in nature. Promising directions for the future include tissue engineering, stem cell therapies, and the development of pre-formed scaffolds from hyaline cartilage, offering hope for improved outcomes.

3D Printed Chondrogenic Functionalized PGS Bioactive Scaffold for Cartilage Regeneration

Tissue engineering is emerging as a promising approach for cartilage regeneration and repair. Endowing scaffolds with cartilaginous bioactivity to obtain bionic microenvironment and regulating the matching of scaffold degradation and regeneration play a crucial role in cartilage regeneration. Poly(glycerol sebacate) (PGS) is a representative thermosetting bioelastomer known for its elasticity, biodegradability, and biocompatibility and is widely used in tissue engineering. However, the modification and drug loading of the PGS scaffold is still a key challenge due to its high temperature curing conditions and limited reactive groups, which seriously hinders its further functional application. Here, a simple versatile new strategy of super swelling-absorption and cross-linked networks locking is presented to successfully create the 3D printed PGS-CS/Gel scaffold for the first time based on FDA-approved PGS, gelatin (Gel) and chondroitin sulfate (CS). The PGS-CS/Gel scaffold exhibits the desirable synergistic properties of well-organized hierarchical structures, excellent elasticity, improved hydrophilicity, and cartilaginous bioactivity, which can promote the adhesion, proliferation, and migration of chondrocytes. Importantly, the rate of cartilage regeneration can be well-matched with degradation of PGS-CS/Gel scaffold, and achieve uniform and mature cartilage tissue without scaffold residual. The bioactive scaffold can successfully repair cartilage in a rabbit trochlear groove defect model indicating a promising prospect of clinical transformation.

Autologous and Allogeneic Cytotherapies for Large Knee (Osteo)Chondral Defects: Manufacturing Process Benchmarking and Parallel Functional Qualification

Cytotherapies are often necessary for the management of symptomatic large knee (osteo)-chondral defects. While autologous chondrocyte implantation (ACI) has been clinically used for 30 years, allogeneic cells (clinical-grade FE002 primary chondroprogenitors) have been investigated in translational settings (Swiss progenitor cell transplantation program). The aim of this study was to comparatively assess autologous and allogeneic approaches (quality, safety, functional attributes) to cell-based knee chondrotherapies developed for clinical use. Protocol benchmarking from a manufacturing process and control viewpoint enabled us to highlight the respective advantages and risks. Safety data (telomerase and soft agarose colony formation assays, high passage cell senescence) and risk analyses were reported for the allogeneic FE002 cellular active substance in preparation for an autologous to allogeneic clinical protocol transposition. Validation results on autologous bioengineered grafts (autologous chondrocyte-bearing Chondro-Gide scaffolds) confirmed significant chondrogenic induction (COL2 and ACAN upregulation, extracellular matrix synthesis) after 2 weeks of co-culture. Allogeneic grafts (bearing FE002 primary chondroprogenitors) displayed comparable endpoint quality and functionality attributes. Parameters of translational relevance (transport medium, finished product suturability) were validated for the allogeneic protocol. Notably, the process-based benchmarking of both approaches highlighted the key advantages of allogeneic FE002 cell-bearing grafts (reduced cellular variability, enhanced process standardization, rationalized logistical and clinical pathways). Overall, this study built on our robust knowledge and local experience with ACI (long-term safety and efficacy), setting an appropriate standard for further clinical investigations into allogeneic progenitor cell-based orthopedic protocols.

Hypoxia Differentially Affects Chondrogenic Differentiation of Progenitor Cells from Different Origins

Background and Objectives

Ear cartilage malformations are commonly encountered problems in reconstructive surgery, since cartilage has low self-regenerating capacity. Malformations that impose psychological and social burden on one's life are currently treated using ear prosthesis, synthetic implants or autologous flaps from rib cartilage. These approaches are challenging because not only they request high surgical expertise, but also they lack flexibility and induce severe donor-site morbidity. Through the last decade, tissue engineering gained attention where it aims at regenerating human tissues or organs in order to restore normal functions. This technique consists of three main elements, cells, growth factors, and above all, a scaffold that supports cells and guides their behavior. Several studies have investigated different scaffolds prepared from both synthetic or natural materials and their effects on cellular differentiation and behavior.

Methods and Results

In this study, we investigated a natural scaffold (alginate) as tridimensional hydrogel seeded with progenitors from different origins such as bone marrow, perichondrium and dental pulp. In contact with the scaffold, these cells remained viable and were able to differentiate into chondrocytes when cultured in vitro. Quantitative and qualitative results show the presence of different chondrogenic markers as well as elastic ones for the purpose of ear cartilage, upon different culture conditions.

Conclusions

We confirmed that auricular perichondrial cells outperform other cells to produce chondrogenic tissue in normal oxygen levels and we report for the first time the effect of hypoxia on these cells. Our results provide updates for cartilage engineering for future clinical applications.

Achieving Nasal Septal Cartilage In Situ Regeneration: Focus on Cartilage Progenitor Cells

The nasal septal cartilage plays an important role in preventing the collapse of the nasal bones and maintaining the appearance of the nose. In the context of inherent difficulties regarding septal cartilage repair and the shortage of cartilage graft resources for regeneration, tissue engineering, especially the in situ strategy based on scaffolds, has become a new prospect and become one of the most promising approaches. Given that it is difficult for chondrocytes to achieve directional migration and secrete matrix components to participate in tissue repair after cartilage injury, cartilage progenitor cells (CPCs), with great migratory ability and stem cell characteristics, have caught the attention of researchers and brought hope for nasal septal cartilage in situ regeneration. In this review, we first summarized the distribution, characteristics, isolation, and culture methods of nasal septal CPCs. Subsequently, we described the roles of migratory CPCs in cartilage regeneration. Finally, we reviewed the existing studies on CPCs-based cartilage tissue engineering and summarized the strategies for promoting the migration and chondrogenesis of CPCs so as to provide ideas for achieving nasal septal cartilage in situ regeneration.

Single-step ultra-purified alginate gel implantation in patients with knee chondral defects

Aims

Implantation of ultra-purified alginate (UPAL) gel is safe and effective in animal osteochondral defect models. This study aimed to examine the applicability of UPAL gel implantation to acellular therapy in humans with cartilage injury.

Methods

A total of 12 patients (12 knees) with symptomatic, post-traumatic, full-thickness cartilage lesions (1.0 to 4.0 cm²) were included in this study. UPAL gel was implanted into chondral defects after performing bone marrow stimulation technique, and assessed for up to three years postoperatively. The primary outcomes were the feasibility and safety of the procedure. The secondary outcomes were self-assessed clinical scores, arthroscopic scores, tissue biopsies, and MRI-based estimations.

Results

No obvious adverse events related to UPAL gel implantation were observed. Self-assessed clinical scores, including pain, symptoms, activities of daily living, sports activity, and quality of life, were improved significantly at three years after surgery. Defect filling was confirmed using second-look arthroscopy at 72 weeks. Significantly improved MRI scores were observed from 12 to 144 weeks postoperatively. Histological examination of biopsy specimens obtained at 72 weeks after implantation revealed an extracellular matrix rich in glycosaminoglycan and type II collagen in the reparative tissue. Histological assessment yielded a mean overall International Cartilage Regeneration & Joint Preservation Society II score of 69.1 points (SD 10.4; 50 to 80).

Conclusion

This study provides evidence supporting the safety of acellular UPAL gel implantation in facilitating cartilage repair. Despite being a single-arm study, it demonstrated the efficacy of UPAL gel implantation, suggesting it is an easy-to-use, one-step method of cartilage tissue repair circumventing the need to harvest donor cells.

Bioinspired gradient scaffolds for osteochondral tissue engineering

Repairing articular osteochondral defects present considerable challenges in self-repair due to the complex tissue structure and low proliferation of chondrocytes. Conventional clinical therapies have not shown significant efficacy, including microfracture, autologous/allograft osteochondral transplantation, and cell-based techniques. Therefore, tissue engineering has been widely explored in repairing osteochondral defects by leveraging the natural regenerative potential of biomaterials to control cell functions. However, osteochondral tissue is a gradient structure with a smooth transition from the cartilage to subchondral bone, involving changes in chondrocyte morphologies and phenotypes, extracellular matrix components, collagen type and orientation, and cytokines. Bioinspired scaffolds have been developed by simulating gradient characteristics in heterogeneous tissues, such as the pores, components, and osteochondrogenesis-inducing factors, to satisfy the anisotropic features of osteochondral matrices. Bioinspired gradient scaffolds repair osteochondral defects by altering the microenvironments of cell growth to induce osteochondrogenesis and promote the formation of osteochondral interfaces compared with homogeneous scaffolds. This review outlines the meaningful strategies for repairing osteochondral defects by tissue engineering based on gradient scaffolds and predicts the pros and cons of prospective translation into clinical practice.

Failure of cartilage regeneration: emerging hypotheses and related therapeutic strategies

Osteoarthritis (OA) is a disabling condition that affects billions of people worldwide and places a considerable burden on patients and on society owing to its prevalence and economic cost. As cartilage injuries are generally associated with the progressive onset of OA, robustly effective approaches for cartilage regeneration are necessary. Despite extensive research, technical development and clinical experimentation, no current surgery-based, material-based, cell-based or drug-based treatment can reliably restore the structure and function of hyaline cartilage. This paucity of effective treatment is partly caused by a lack of fundamental understanding of why articular cartilage fails to spontaneously regenerate. Thus, research studies that investigate the mechanisms behind the cartilage regeneration processes and the failure of these processes are critical to instruct decisions about patient treatment or to support the development of next-generation therapies for cartilage repair and OA prevention. This Review provides a synoptic and structured analysis of the current hypotheses about failure in cartilage regeneration, and the accompanying therapeutic strategies to overcome these hurdles, including some current or potential approaches to OA therapy.

Transit Amplifying Cells (TACs): a still not fully understood cell population

Maintenance of tissue homeostasis and tissue regeneration after an insult are essential functions of adult stem cells (SCs). In adult tissues, SCs proliferate at a very slow rate within "stem cell niches", but, during tissue development and regeneration, before giving rise to differentiated cells, they give rise to multipotent and highly proliferative cells, known as transit-amplifying cells (TACs). Although differences exist in diverse tissues, TACs are not only a transitory phase from SCs to post-mitotic cells, but they also actively control proliferation and number of their ancestor SCs and proliferation and differentiation of their progeny toward tissue specific functional cells. Autocrine signals and negative and positive feedback and feedforward paracrine signals play a major role in these controls. In the present review we will consider the generation and the role played by TACs during development and regeneration of lining epithelia characterized by a high turnover including epidermis and hair follicles, ocular epithelial surfaces, and intestinal mucosa. A comparison between these different tissues will be made. There are some genes and molecular pathways whose expression and activation are common to most TACs regardless their tissue of origin. These include, among others, Wnt, Notch, Hedgehog and BMP pathways. However, the response to these molecular signals can vary in TACs of different tissues. Secondly, we will consider cultured cells derived from tissues of mesodermal origin and widely adopted for cell therapy treatments. These include mesenchymal stem cells and dedifferentiated chondrocytes. The possible correlation between cell dedifferentiation and reversion to a transit amplifying cell stage will be discussed.

Near-infrared light-controlled kartogenin delivery of multifunctional Prussian blue nanocomposites for cartilage defect repair

Articular cartilage injury repair remains a challenge for clinicians and researchers. Mesenchymal stem cells (MSCs) have multiple differentiation potentials and can be induced to differentiate into the chondrogenic lineage for cartilage defect repair; however, the insufficient capacity of chondrogenic differentiation and excess reactive oxygen species (ROS)-mediated oxidative stress, which always lead to differentiation into hypertrophic chondrocytes, still need to be resolved. Accordingly, kartogenin (KGN), which can promote chondrogenic differentiation of MSCs, has shown promise in promoting infected cartilage repair. However, realizing controllable release to prolong its action time and avoid hypertrophic differentiation is critical. We herein developed a mesoporous Prussian blue nanoparticle (mPB)-based near-infrared (NIR) light-responsive controlled nanosystem. KGN was encapsulated in temperature-stimulated responsive phase change materials (PCMs), which were used as excellent gating materials (KGN-PCM@mPBs). In addition, the mPBs could efficiently scavenge ROS by their enzyme-like antioxidative activities. Our study demonstrates that the nanocomposites could efficiently promote chondrogenic differentiation and successfully inhibit the hypertrophic differentiation of MSCs. By intra-articular injection of KGN-PCM@mPBs and NIR-triggered precisely controlled release, satisfactory cartilage repair effects can be achieved in a rat chondral defect model. Thus, this constructed NIR-mediated KGN-PCM@mPB nanoplatform may represent an effective cartilage repair strategy with satisfactory biosafety in clinical applications.

Injectable macro-porous chitosan/polyethylene glycol-silicotungstic acid double-network hydrogels based on "smashed gels recombination" strategy for cartilage tissue engineering

The lack of interconnected macro-porous structure of most injectable hydrogels lead to poor cell and tissue infiltration. Herein, we present the fabrication of injectable macro-porous hydrogels based on "smashed gels recombination" strategy. Chitosan/polyethylene glycol-silicotungstic acid (CS/PEG-SiW) double-network hydrogels were prepared via dual dynamic interactions. The bulk CS/PEG-SiW hydrogels were then smashed into micro-hydrogels with average sizes ranging from 47.6 to 63.8 μm by mechanical fragmentation. The CS/PEG-SiW micro-hydrogels could be continuously injected and rapidly recombined into a stable porous hydrogel based on the dual dynamic interactions between micro-hydrogels. The average pore size of the recombined porous CS/PEG-SiW hydrogels ranged from 52 to 184 μm. The storage modulus, compress modulus and maximum compressive strain of the recombined porous CS/PEG-SiW_1.0 hydrogels reached about 47.2 %, 28.2 % and 127.6 % of the values for their corresponding bulk hydrogels, respectively. The recombined porous hydrogels were cytocompatible and could effectively support proliferation and chondrogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). In a rat cartilage defect model, recombined porous CS/PEG-SiW hydrogels could promote cartilage regeneration. Hematoxylin and eosin (H&E), Safranin-O/Fast green and immunohistochemical staining confirmed the accumulation of glycosaminoglycans (GAG) and type II collagen (Col II) in regenerated cartilage.

Good Manufacturing Practice-compliant change of raw material in the manufacturing process of a clinically used advanced therapy medicinal product-a comparability study

The development of medicinal products often continues throughout the different phases of a clinical study and may require challenging changes in raw and starting materials at later stages. Comparability between the product properties pre- and post-change thus needs to be ensured. Here, we describe and validate the regulatory compliant change of a raw material using the example of a nasal chondrocyte tissue-engineered cartilage (N-TEC) product, initially developed for treatment of confined knee cartilage lesions. Scaling up the size of N-TEC as required for the treatment of larger osteoarthritis defects required the substitution of autologous serum with a clinical-grade human platelet lysate (hPL) to achieve greater cell numbers necessary for the manufacturing of larger size grafts. A risk-based approach was performed to fulfill regulatory requirements and demonstrate comparability of the products manufactured with the standard process (autologous serum) already applied in clinical indications and the modified process (hPL). Critical attributes with regard to quality, purity, efficacy, safety and stability of the product as well as associated test methods and acceptance criteria were defined. Results showed that hPL added during the expansion phase of nasal chondrocytes enhances proliferation rate, population doublings and cell numbers at passage 2 without promoting the overgrowth of potentially contaminant perichondrial cells. N-TEC generated with the modified versus standard process contained similar content of DNA and cartilaginous matrix proteins with even greater expression levels of chondrogenic genes. The increased risk for tumorigenicity potentially associated with the use of hPL was assessed through karyotyping of chondrocytes at passage 4, revealing no chromosomal changes. Moreover, the shelf-life of N-TEC established for the standard process could be confirmed with the modified process. In conclusion, we demonstrated the introduction of hPL in the manufacturing process of a tissue engineered product, already used in a late-stage clinical trial. Based on this study, the national competent authorities in Switzerland and Germany accepted the modified process which is now applied for ongoing clinical tests of N-TEC. The described activities can thus be taken as a paradigm for successful and regulatory compliant demonstration of comparability in advanced therapy medicinal products manufacturing.

Articular Cartilage Repair After Implantation of Hyaline Cartilage Beads Engineered From Adult Dedifferentiated Chondrocytes: Cartibeads Preclinical Efficacy Study in a Large Animal Model

BACKGROUND

Chondrocyte-based cell therapy to repair cartilage has been used for >25 years despite current limitations. This work presents a new treatment option for cartilage lesions.

HYPOTHESIS

High-quality hyaline cartilage microtissues called Cartibeads are capable of treating focal chondral lesions once implanted in the defect, by complete fusion of Cartibeads among themselves and their integration with the surrounding native cartilage and subchondral bone.

STUDY DESIGN

Controlled laboratory study.

METHODS

Cartibeads were first produced from human donors and characterized using histology (safranin O staining of glycosaminoglycan [GAG] and immunohistochemistry of collagen I and II) and GAG dosage. Cartibeads from 6 Göttingen minipigs were engineered and implanted in an autologous condition in the knee (4 or 5 lesions per knee). One group was followed up for 3 months and the other for 6 months. Feasibility and efficacy were measured using histological analysis and macroscopic and microscopic scores.

RESULTS

Cartibeads revealed hyaline features with strong staining of GAG and collagen II. High GAG content was obtained: 24.6-µg/mg tissue (wet weight), 15.52-µg/mg tissue (dry weight), and 35 ± 3-µg GAG/bead (mean ± SD). Histological analysis of Göttingen minipigs showed good integration of Cartibeads grafts at 3 and 6 months after implantation. The Bern Score of the histological assay comparing grafted versus empty lesions was significant at 3 months (grafted, n = 10; nongrafted, n = 4; score, 3.3 and 5.3, respectively) and 6 months (grafted, n = 11; nongrafted, n = 3; score, 1.6 and 5.1).

CONCLUSION

We developed an innovative 3-step method allowing, for the first time, the use of fully dedifferentiated adult chondrocytes with a high number of cell passage (owing to the extensive amplification in culture). Cartibeads engineered from chondrocytes hold potential as an advanced therapy medicinal product for treating cartilage lesions with established efficacy.

CLINICAL RELEVANCE

This successful preclinical study, combined with standardized manufacturing of Cartibeads according to good manufacturing practice guidelines, led to the approval of first-in-human clinical trial by the ethics committee and local medical authority. The generated data highlighted a promising therapy to treat cartilage lesions from a small amount of starting biopsy specimen. With our innovative cell amplification technology, very large lesions can be treated, and older active patients can benefit from it.

Within or Without You? A Perspective Comparing In Situ and Ex Situ Tissue Engineering Strategies for Articular Cartilage Repair

Human articular cartilage has a poor ability to self-repair, meaning small injuries often lead to osteoarthritis, a painful and debilitating condition which is a major contributor to the global burden of disease. Existing clinical strategies generally do not regenerate hyaline type cartilage, motivating research toward tissue engineering solutions. Prospective cartilage tissue engineering therapies can be placed into two broad categories: i) Ex situ strategies, where cartilage tissue constructs are engineered in the lab prior to implantation and ii) in situ strategies, where cells and/or a bioscaffold are delivered to the defect site to stimulate chondral repair directly. While commonalities exist between these two approaches, the core point of distinction-whether chondrogenesis primarily occurs "within" or "without" (outside) the body-can dictate many aspects of the treatment. This difference influences decisions around cell selection, the biomaterials formulation and the surgical implantation procedure, the processes of tissue integration and maturation, as well as, the prospects for regulatory clearance and clinical translation. Here, ex situ and in situ cartilage engineering strategies are compared: Highlighting their respective challenges, opportunities, and prospects on their translational pathways toward long term human cartilage repair.

Cellular therapy and tissue engineering for cartilage repair

Articular cartilage (AC) has limited capacity for repair. The first attempt to repair cartilage using tissue engineering was reported in 1977. Since then, cell-based interventions have entered clinical practice in orthopaedics, and several tissue engineering approaches to repair cartilage are in the translational pipeline towards clinical application. Classically, these involve a scaffold, substrate or matrix to provide structure, and cells such as chondrocytes or mesenchymal stromal cells to generate the tissue. We discuss the advantages and drawbacks of the use of various cell types, natural and synthetic scaffolds, multiphasic or gradient-based scaffolds, and self-organizing or self-assembling scaffold-free systems, for the engineering of cartilage constructs. Several challenges persist including achieving zonal tissue organization and integration with the surrounding tissue upon implantation. Approaches to improve cartilage thickness, organization and mechanical properties include mechanical stimulation, culture under hypoxic conditions, and stimulation with growth factors or other macromolecules. In addition, advanced technologies such as bioreactors, biosensors and 3D bioprinting are actively being explored. Understanding the underlying mechanisms of action of cell therapy and tissue engineering approaches will help improve and refine therapy development. Finally, we discuss recent studies of the intrinsic cellular and molecular mechanisms of cartilage repair that have identified novel signals and targets and are inspiring the development of molecular therapies to enhance the recruitment and cartilage reparative activity of joint-resident stem and progenitor cells. A one-fits-all solution is unrealistic, and identifying patients who will respond to a specific targeted treatment will be critical.

Hyaline Cartilage Microtissues Engineered from Adult Dedifferentiated Chondrocytes: Safety and Role of WNT Signaling

The repair of damaged articular cartilage is an unmet medical need. Chondrocyte-based cell therapy has been used to repair cartilage for over 20 years despite current limitations. Chondrocyte dedifferentiation upon expansion in monolayer is well known and is the main obstacle to their use as cell source for cartilage repair. Consequently, current approaches often lead to fibrocartilage, which is biomechanically different from hyaline cartilage and not effective as a long-lasting treatment. Here, we describe an innovative 3-step method to engineer hyaline-like cartilage microtissues, named Cartibeads, from high passage dedifferentiated chondrocytes. We show that WNT5A/5B/7B genes were highly expressed in dedifferentiated chondrocytes and that a decrease of the WNT signaling pathway was instrumental for full re-differentiation of chondrocytes, enabling production of hyaline matrix instead of fibrocartilage matrix. Cartibeads showed hyaline-like characteristics based on GAG quantity and type II collagen expression independently of donor age and cartilage quality. In vivo, Cartibeads were not tumorigenic when transplanted into SCID mice. This simple 3-step method allowed a standardized production of hyaline-like cartilage microtissues from a small cartilage sample, making Cartibeads a promising candidate for the treatment of cartilage lesions.

Strategies to Convert Cells into Hyaline Cartilage: Magic Spells for Adult Stem Cells

Damaged hyaline cartilage gradually decreases joint function and growing pain significantly reduces the quality of a patient’s life. The clinically approved procedure of autologous chondrocyte implantation (ACI) for treating knee cartilage lesions has several limits, including the absence of healthy articular cartilage tissues for cell isolation and difficulties related to the chondrocyte expansion in vitro. Today, various ACI modifications are being developed using autologous chondrocytes from alternative sources, such as the auricles, nose and ribs. Adult stem cells from different tissues are also of great interest due to their less traumatic material extraction and their innate abilities of active proliferation and chondrogenic differentiation. According to the different adult stem cell types and their origin, various strategies have been proposed for stem cell expansion and initiation of their chondrogenic differentiation. The current review presents the diversity in developing applied techniques based on autologous adult stem cell differentiation to hyaline cartilage tissue and targeted to articular cartilage damage therapy.

Dose-response relationship of in vivo ambulatory load and mechanosensitive cartilage biomarkers—The role of age, tissue health and inflammation: A study protocol

Objective

To describe a study protocol for investigating the in vivo dose-response relationship between ambulatory load magnitude and mechanosensitive blood markers of articular cartilage, the influence of age, cartilage tissue health and presence of inflammation on this relationship, and its ability to predict changes in articular cartilage quality and morphology within 2 years.

Design

Prospective experimental multimodal (clinical, biomechanical, biological) data collection under walking stress and three different load conditions varied in a randomized crossover design.

Experimental protocol

At baseline, equal numbers of healthy and anterior cruciate ligament injured participants aged 20–30 or 40–60 years will be assessed clinically and complete questionnaires regarding their knee health. Biomechanical parameters (joint kinetics, joint kinematics, and surface electromyography) will be recorded while performing different tasks including overground and treadmill walking, single leg balance and hopping tasks. Magnetic resonance images (MRI) of both of knees will be obtained. On separate stress test days, participants will perform a 30-minute walking stress with either reduced (80% body weight (BW)), normal (100%BW) or increased (120%BW) load. Serum blood samples will be taken immediately before, immediately after, 30, 120 and 210 minutes after the walking stress. Concentration of articular cartilage blood biomarkers will be assessed using enzyme linked immunosorbent assays. At 24-month follow-up, participants will be again assessed clinically, undergo an MRI, complete questionnaires, and have a blood sample taken.

Conclusion

The study design provides a standardized set up that allows to better understand the influence of ambulatory load on articular cartilage biomarkers and thereby extend current knowledge on in vivo cartilage metabolism and mechanosensitivity. Further, this study will help to elucidate the prognostic value of the load-induced cartilage biomarker response for early articular cartilage degeneration.

Trial registration

The protocol was approved by the regional ethics committee and has been registered at clinicaltrials.gov (NCT04128566).

Glycosaminoglycan, Antimicrobial Defence Molecule and Cytokine Appearance in Tracheal Hyaline Cartilage of Healthy Humans

Hyaline cartilage is an important tracheal structure, yet little is known about its molecular composition, complicating investigation of pathologies and replacement options. Our aim was to research tracheal hyaline cartilage structure, protective tissue factors and variations in healthy humans. The tissue material was obtained from 10 cadavers obtained from the Riga Stradins University Institute of Anatomy and Anthropology archive. Tissues were stained with Bismarck brown and PAS for glycosaminoglycans, and immunohistochemistry was performed for HBD-2, HBD-3, HBD-4, IL-10 and LL-37. The slides were inspected by light microscopy and Spearman's rank correlation coefficient was calculated. The extracellular matrix was positive across hyaline cartilage for PAS, yet Bismarck brown marked positive proliferation and growth zones. Numerous positive cells for both factors were found in all zones. All of the antimicrobial defence molecules and cytokines were found in a moderate number of cells, except in the mature cell zone with few positive cells. Spearman's rank correlation coefficient revealed strong and moderate correlations between studied factors. Hyaline cartilage is a tracheal defence structure with a moderate number of antimicrobial defence protein and cytokine immunoreactive cells as well as numerous glycosaminoglycan positive cells. The extracellular matrix glycosaminoglycans provide structural scaffolding and intercellular signalling. The correlations between the studied factors confirm the synergistic activity of them.

The Emerging Use of ASC/Scaffold Composites for the Regeneration of Osteochondral Defects

Articular cartilage is composed of chondrocytes surrounded by a porous permeable extracellular matrix. It has a limited spontaneous healing capability post-injury which, if left untreated, can result in severe osteochondral disease. Currently, osteochondral (OC) defects are treated by bone marrow stimulation, artificial joint replacement, or transplantation of bone, cartilage, and periosteum, while autologous osteochondral transplantation is also an option; it carries the risk of donor site damage and is limited only to the treatment of small defects. Allografts may be used for larger defects; however, they have the potential to elicit an immune response. A possible alternative solution to treat osteochondral diseases involves the use of stromal/stem cells. Human adipose-derived stromal/stem cells (ASCs) can differentiate into cartilage and bone cells. The ASC can be combined with both natural and synthetic scaffolds to support cell delivery, growth, proliferation, migration, and differentiation. Combinations of both types of scaffolds along with ASCs and/or growth factors have shown promising results for the treatment of OC defects based on in vitro and in vivo experiments. Indeed, these findings have translated to several active clinical trials testing the use of ASC-scaffold composites on human subjects. The current review critically examines the literature describing ASC-scaffold composites as a potential alternative to conventional therapies for OC tissue regeneration.

In Vitro and Ectopic In Vivo Studies toward the Utilization of Rapidly Isolated Human Nasal Chondrocytes for Single-Stage Arthroscopic Cartilage Regeneration Therapy

Nasal chondrocytes (NCs) have a higher and more reproducible chondrogenic capacity than articular chondrocytes, and the engineered cartilage tissue they generate in vitro has been demonstrated to be safe in clinical applications. Here, we aimed at determining the feasibility for a single-stage application of NCs for cartilage regeneration under minimally invasive settings. In particular, we assessed whether NCs isolated using a short collagenase digestion protocol retain their potential to proliferate and chondro-differentiate within an injectable, swiftly cross-linked and matrix-metalloproteinase (MMP)-degradable polyethylene glycol (PEG) gel enriched with human platelet lysate (hPL). NC-hPL-PEG gels were additionally tested for their capacity to generate cartilage tissue in vivo and to integrate into cartilage/bone compartments of human osteochondral plugs upon ectopic subcutaneous implantation into nude mice. NCs isolated with a rapid protocol and embedded in PEG gels with hPL at low cell density were capable of efficiently proliferating and of generating tissue rich in glycosaminoglycans and collagen II. NC-hPL-PEG gels developed into hyaline-like cartilage tissues upon ectopic in vivo implantation and integrated with surrounding native cartilage and bone tissues. The delivery of NCs in PEG gels containing hPL is a feasible strategy for cartilage repair and now requires further validation in orthotopic in vivo models.

The 50 most-cited clinical articles in cartilage surgery research: a bibliometric analysis

PURPOSE

Articular cartilage lesions remain a challenge for orthopedic surgeons. The identification of the most important articles can help identifying the most influential techniques of the past, the current prevalent focus, and emerging strategies. The aim of this study was to identify milestones and trends in cartilage research.

METHODS

This study is a bibliometric analysis based on published articles. All citation count data included in the "Scopus database" were used to identify eligible studies up to December 2020. The 50 most-cited articles on cartilage surgery were ranked based on the citation count and analyzed regarding citation density and quality (Coleman score and RoB 2.0 tool). A further search was performed to identify the most promising clinical studies among the latest publications on cartilage surgery.

RESULTS

Different kinds of cartilage treatments were investigated in the 50 most-cited clinical articles. Regenerative techniques with chondrocytes were the most reported with a total of 23 articles, followed by microfracture technique in 17 articles and mosaicplasty or osteochondral autograft transplantation (OAT) in 11. Forty-five articles focused on the knee. A higher citation density was found in the most recent articles (p = 0.004). The study of the most promising landmarks of the most recent articles showed new cell-free or tissue engineering-based procedures and an overall increasing quality of the published studies.

CONCLUSION

This bibliometric analysis documented an increasing interest in cartilage surgery, with efforts toward high-quality studies. Over the years, the focus switched from reconstructive toward regenerative techniques, with emerging options including cell-free and tissue-engineering strategies to restore the cartilage surface.

LEVEL OF EVIDENCE

IV.

The Current Status of Clinical Trials on Biologics for Cartilage Repair and Osteoarthritis Treatment: An Analysis of ClinicalTrials.gov Data

OBJECTIVE

Biologics are increasingly used for cartilage repair and osteoarthritis (OA) treatment. This study aimed to provide an overview of the clinical trials conducted on this subject.

DESIGN

Two-word combinations of two sets of key words "cartilage"; "joint"; "osteoarthritis" and "biologics"; "stem cells"; "cell implantation" were used to search the database of ClinicalTrials.gov and supplemented with searches of PubMed and EMbase. The registered trials were analyzed for clinical conditions, completion status, phases, and investigated biologics. Recently completed trials with posted/published results were summarized.

RESULTS

From 2000 to 2022, a total of 365 clinical trials were registered at ClinicalTrials.gov to use biologics for cartilage repair and OA treatment. Since 2006, the number of registered trials accelerated at an annual rate of 16.4%. Of the 265 trials designated with a phase, 72% were early Phase 1, Phase 1, and Phase 2. Chondrocytes and platelet-rich plasma (PRP) were studied in nearly equal number of early- and late-stage trials. Mesenchymal stem/stromal cells (MSCs) were the most commonly investigated biologics (38%) and mostly derived from bone marrow and adipose tissue (70%). In last 5 years, 32 of the 72 completed trials posted/published results, among which seven Phase 3 trials investigated chondrocytes, PRP, bone marrow aspirate concentrate, hyaluronic acid, collagen membrane, and albumin.

CONCLUSIONS

There was a rapid increase in the number of registered clinical trials in recent years, using a variety of biologics for cartilage repair and OA treatment. Majority of the biologics still require late-stage trials to validate their clinical effectiveness.

Pre-culture of human mesenchymal stromal cells in spheroids facilitates chondrogenesis at a low total cell count upon embedding in biomaterials to generate cartilage microtissues

Material-assisted cartilage tissue engineering has limited application in cartilage treatment due to hypertrophic tissue formation and high cell counts required. This study aimed at investigating the potential of human mesenchymal stromal cell (hMSC) spheroids embedded in biomaterials to study the effect of biomaterial composition on cell differentiation. Pre-cultured (3 days, chondrogenic differentiation media) spheroids (250 cells/spheroid) were embedded in tyramine-modified hyaluronic acid (THA) and collagen type I (Col) composite hydrogels (four combinations of THA (12.5 vs 16.7 mg/ml) and Col (2.5 vs 1.7 mg/ml) content) at a cell density of 5 × 10⁶ cells/ml (2 × 10⁴ spheroids/ml). Macropellets derived from single hMSCs (2.5 × 10⁵ cells, ScMP) or hMSC spheroids (2.5 × 10⁵ cells, 10³ spheroids, SpMP) served as control. hMSC differentiation was analyzed using glycosaminoglycan (GAG) quantification, gene expression analysis and (immuno-)histology. Embedding of hMSC spheroids in THA-Col induced chondrogenic differentiation marked by upregulation of aggrecan (ACAN) and COL2A1, and the production of GAGs . Lower THA led to more pronounced chondrogenic phenotype compared to higher THA content. Col content had no significant influence on hMSC chondrogenesis. Pellet cultures showed an upregulation in chondrogenic-associated genes and production of GAGs with less upregulation of hypertrophic-associated genes in SpMP culture compared to ScMP group. This study presents hMSC pre-culture in spheroids as promising approach to study chondrogenic differentiation after biomaterial encapsulation at low total cell count (5 × 10⁶/ml) without compromising chondrogenic matrix production. This approach can be applied to assemble microtissues in biomaterials to generate large cartilage construct. STATEMENT OF SIGNIFICANCE: In vitro studies investigating the chondrogenic potential of biomaterials are limited due to the low cell-cell contact of encapsulated single cells. Here, we introduce the use of pre-cultured hMSC spheroids to study chondrogenesis upon encapsulation in a biomaterial. The use of spheroids takes advantage of the high cell-cell contact within each spheroid being critical in the early chondrogenesis of hMSCs. At a low seeding density of 5·10⁶ cells/ml (2 × 10⁴ spheroids/ml) we demonstrated hMSC chondrogenesis and cartilaginous matrix deposition. Our results indicate that the pre-culture might have a beneficial effect on hypertrophic gene expression without compromising chondrogenic differentiation. This approach has shown potential to assemble microtissues (here spheroids) in biomaterials to generate large cartilage constructs and to study the effect of biomaterial composition on cell alignment and migration.

Retrospective Analysis of Autologous Chondrocyte-Based Cytotherapy Production for Clinical Use: GMP Process-Based Manufacturing Optimization in a Swiss University Hospital

Cultured autologous human articular chondrocyte (HAC) implantation has been extensively investigated for safe and effective promotion of structural and functional restoration of knee cartilage lesions. HAC-based cytotherapeutic products for clinical use must be manufactured under an appropriate quality assurance system and follow good manufacturing practices (GMP). A prospective clinical trial is ongoing in the Lausanne University Hospital, where the HAC manufacturing processes have been implemented internally. Following laboratory development and in-house GMP transposition of HAC cell therapy manufacturing, a total of 47 patients have been treated to date. The main aim of the present study was to retrospectively analyze the available manufacturing records of the produced HAC-based cytotherapeutic products, outlining the inter-individual variability existing among the 47 patients regarding standardized transplant product preparation. These data were used to ameliorate and to ensure the continued high quality of cytotherapeutic care in view of further clinical investigations, based on the synthetic analyses of existing GMP records. Therefore, a renewed risk analysis-based process definition was performed, with specific focus set on process parameters, controls, targets, and acceptance criteria. Overall, high importance of the interdisciplinary collaboration and of the manufacturing process robustness was underlined, considering the high variability (i.e., quantitative, functional) existing between the treated patients and between the derived primary HAC cell types.

In vitro maturation and in vivo stability of bioprinted human nasal cartilage

The removal of skin cancer lesions on the nose often results in the loss of nasal cartilage. The cartilage loss is either surgically replaced with autologous cartilage or synthetic grafts. However, these replacement options come with donor-site morbidity and resorption issues. 3-dimensional (3D) bioprinting technology offers the opportunity to engineer anatomical-shaped autologous nasal cartilage grafts. The 3D bioprinted cartilage grafts need to embody a mechanically competent extracellular matrix (ECM) to allow for surgical suturing and resistance to contraction during scar tissue formation. We investigated the effect of culture period on ECM formation and mechanical properties of 3D bioprinted constructs of human nasal chondrocytes (hNC)-laden type I collagen hydrogel in vitro and in vivo. Tissue-engineered nasal cartilage constructs developed from hNC culture in clinically approved collagen type I and type III semi-permeable membrane scaffold served as control. The resulting 3D bioprinted engineered nasal cartilage constructs were comparable or better than the controls both in vitro and in vivo. This study demonstrates that 3D bioprinted constructs of engineered nasal cartilage are feasible options in nasal cartilage reconstructive surgeries.

Spheroid-Based Tissue Engineering Strategies for Regeneration of the Intervertebral Disc

Degenerative disc disease, a painful pathology of the intervertebral disc (IVD), often causes disability and reduces quality of life. Although regenerative cell-based strategies have shown promise in clinical trials, none have been widely adopted clinically. Recent developments demonstrated that spheroid-based approaches might help overcome challenges associated with cell-based IVD therapies. Spheroids are three-dimensional multicellular aggregates with architecture that enables the cells to differentiate and synthesize endogenous ECM, promotes cell-ECM interactions, enhances adhesion, and protects cells from harsh conditions. Spheroids could be applied in the IVD both in scaffold-free and scaffold-based configurations, possibly providing advantages over cell suspensions. This review highlights areas of future research in spheroid-based regeneration of nucleus pulposus (NP) and annulus fibrosus (AF). We also discuss cell sources and methods for spheroid fabrication and characterization, mechanisms related to spheroid fusion, as well as enhancement of spheroid performance in the context of the IVD microenvironment.

Engineering of Tracheal Grafts Based on Recellularization of Laser-Engraved Human Airway Cartilage Substrates

OBJECTIVE

Implantation of tissue-engineered tracheal grafts represents a visionary strategy for the reconstruction of tracheal wall defects after resections and may develop into a last chance for a number of patients with severe cicatricial stenosis. The use of a decellularized tracheal substrate would offer an ideally stiff graft, but the matrix density would challenge efficient remodeling into a living cartilage. In this study, we hypothesized that the pores of decellularized laser-perforated tracheal cartilage (LPTC) tissues can be colonized by adult nasal chondrocytes (NCs) to produce new cartilage tissue suitable for the repair of tracheal defects.

DESIGN

Human, native tracheal specimens, isolated from cadaveric donors, were exposed to decellularized and laser engraving-controlled superficial perforation (300 μm depth). Human or rabbit NCs were cultured on the LPTCs for 1 week. The resulting revitalized tissues were implanted ectopically in nude mice or orthotopically in tracheal wall defects in rabbits. Tissues were assayed histologically and by microtomography analyses before and after implantation.

RESULTS

NCs were able to efficiently colonize the pores of the LPTCs. The extent of colonization (i.e., percentage of viable cells spanning >300 μm of tissue depth), cell morphology, and cartilage matrix deposition improved once the revitalized constructs were implanted ectopically in nude mice. LPTCs could be successfully grafted onto the tracheal wall of rabbits without any evidence of dislocation or tracheal stenosis, 8 weeks after implantation. Rabbit NCs, within the LPTCs, actively produced new cartilage matrix.

CONCLUSION

Implantation of NC-revitalized LPTCs represents a feasible strategy for the repair of tracheal wall defects.

Application of Biological Composite Materials in the Regeneration of Subchondral Defects and Articular Cartilage in a Synovial Joint: An Experimental Model

Objective: Since the benefits of Nano-material usage have been well documented in orthopedic surgery, this study was conducted to explore the effect of polyvinyl alcohol/nano-hydroxyapatite/polyamide 66 (PVA/n-HA/P66) on repairing of traumatic cartilage defects in rabbit knee joint. Methods: New Zealand white rabbits were used to make a rabbit knee traumatic cartilage defect animal model. All rabbits were randomly located in three groups. Group-A (PVA/n-HA+PA66 implanted in cartilage defects); Group-B (HA nanospheres implanted in cartilage defects)/Gelatin sponge composite scaffold); Group-C (only cartilage defect without implant). The repairment of articular cartilage defects and the general observation were studied by using pathological staining and gene expression of collagen using RT-PCR after 12 weeks. Results: After 12 weeks, we observed a small amount of fibrous tissue growth in group C without soft cell filling. The repaired tissue in group B was stained with immunohistochemical and toluidine blue staining for collagen and type II collagen is positive, but chondrocyte structure is more visible. The relative mRNA expression of type II collagen was higher in group B in comparison to other groups. The results of the Wakitani score were 5.50±2.59 for group A, 8.83±2.79 for group B, 11.50±1.05 for group C. Results showed no significant difference between group B and C; however, significant differences were found in the scoring results between groups A and B, and between-group A and C. Conclusion: This study showed the high effectiveness of PVA/n-HA+PA66 in the treatment of cartilage defects through increasing the expression of type II collagen.

Anti-Inflammatory and Prochondrogenic In Situ-Formed Injectable Hydrogel Crosslinked by Strontium-Doped Bioglass for Cartilage Regeneration

Directed differentiation of bone marrow mesenchymal stem cells (BMSCs) toward chondrogenesis plays a predominant role in cartilage repair. However, the uncontrolled inflammatory response to implants is found to impair the stability of scaffolds and the cartilage regeneration outcome. Herein, we fabricated an injectable hydrogel crosslinked by strontium-doped bioglass (SrBG) to modulate both human BMSC (hBMSC) differentiation and the inflammatory response. The results revealed that the introduction of Sr ions could simultaneously enhance the proliferation of hBMSCs, upregulate cartilage-specific gene expression, and improve the secretion of glycosaminoglycan. Moreover, after cultured with SA/SrBG extracts in vitro, a majority of macrophages were polarized toward the M2 phenotype and subsequently facilitated the chondrogenic differentiation of hBMSCs. Furthermore, after the composite hydrogel was injected into a cartilage defect model, neonatal cartilage-like tissues with a smooth surface and tight integration with original tissues could be found. This study suggests that the synergistic strategy based on an enhanced differentiation ability and a regulated inflammatory response is promising and may lead the way to new anti-inflammatory biomaterials.

Back to the Cradle of Cytotherapy: Integrating a Century of Clinical Research and Biotechnology-Based Manufacturing for Modern Tissue-Specific Cellular Treatments in Switzerland

Empirically studied by Dr. Brown-Séquard in the late 1800s, cytotherapies were later democratized by Dr. Niehans during the twentieth century in Western Switzerland. Many local cultural landmarks around the Léman Riviera are reminiscent of the inception of such cell-based treatments. Despite the discreet extravagance of the remaining heirs of "living cell therapy" and specific enforcements by Swiss health authorities, current interest in modern and scientifically sound cell-based regenerative medicine has never been stronger. Respective progress made in bioengineering and in biotechnology have enabled the clinical implementation of modern cell-based therapeutic treatments within updated medical and regulatory frameworks. Notably, the Swiss progenitor cell transplantation program has enabled the gathering of two decades of clinical experience in Lausanne for the therapeutic management of cutaneous and musculoskeletal affections, using homologous allogeneic cell-based approaches. While striking conceptual similarities exist between the respective works of the fathers of cytotherapy and of modern highly specialized clinicians, major and important iterative updates have been implemented, centered on product quality and risk-analysis-based patient safety insurance. This perspective article highlights some historical similarities and major evolutive differences, particularly regarding product safety and quality issues, characterizing the use of cell-based therapies in Switzerland over the past century. We outline the vast therapeutic potential to be harnessed for the benefit of overall patient health and the importance of specific scientific methodological aspects.

AMIC Technique for the Treatment of Chondral Injuries of the Hand and Wrist

Scaffolds, either alone or combined with cultured chondrocyte cells, are an effective treatment for chondral or osteochondral defects of the knee and ankle joints.

Scaffolds are a more sophisticated solution and have some advantages compared with the isolated use of the more traditional treatments of microfractures or nanofractures.

In addition, scaffolds represent a less complicated technique and a less expensive treatment compared with chondrocyte culture treatments, which are accessible by very few patients.

In the present article, we detail the surgical technique and provide advices and tips for the treatment of ostecochondral hand and wrist lesions using the Chondro-Gide (Geistlich Pharma AG, Wolhausen, Switzerland) scaffold and its patented autologous matrix-induced chondrogenesis (AMIC, Geistlich Pharma AG) technique.

Strategies to Modulate the Redifferentiation of Chondrocytes

Because of the low self-healing capacity of articular cartilage, cartilage injuries and degenerations triggered by various diseases are almost irreversible. Previous studies have suggested that human chondrocytes cultured in vitro tend to dedifferentiate during the cell-amplification phase and lose the physiological properties and functions of the cartilage itself, which is currently a critical limitation in the cultivation of cartilage for tissue engineering. Recently, numerous studies have focused on the modulation of chondrocyte redifferentiation. Researchers discovered the effect of various conditions (extracellular environment, cell sources, growth factors and redifferentiation inducers, and gene silencing and overexpression) on the redifferentiation of chondrocytes during the in vitro expansion of cells, and obtained cartilage tissue cultured in vitro that exhibited physiological characteristics and functions that were similar to those of human cartilage tissue. Encouragingly, several studies reported positive results regarding the modulation of the redifferentiation of chondrocytes in specific conditions. Here, the various factors and conditions that modulate the redifferentiation of chondrocytes, as well as their limitations and potential applications and challenges are reviewed. We expect to inspire research in the field of cartilage repair toward the future treatment of arthropathy.

Sequential Enzymatic Digestion of Different Cartilage Tissues: A Rapid and High-Efficiency Protocol for Chondrocyte Isolation, and Its Application in Cartilage Tissue Engineering

OBJECTIVE

The classic chondrocyte isolation protocol is a 1-step enzymatic digestion protocol in which cartilage samples are digested in collagenase solution for a single, long period. However, this method usually results in incomplete cartilage dissociation and low chondrocyte quality. In this study, we aimed to develop a rapid, high-efficiency, and flexible chondrocyte isolation protocol for cartilage tissue engineering.

DESIGN

Cartilage tissues harvested from rabbit ear, rib, septum, and articulation were minced and subjected to enzymatic digestion using the classic protocol or the newly developed sequential protocol. In the classic protocol, cartilage fragments were subjected to one 12-hour digestion. In the sequential protocol, cartilage fragments were sequentially subjected to 2-hour first digestion, followed by two 3-hour digestions. The collected cells were then subjected to analyses of cell-yield efficiency, viability, proliferation, phenotype, and cartilage matrix synthesis capacity.

RESULTS

Overall, the sequential protocol exhibited higher cell-yield efficiency than the classic protocol for the 4 cartilage types. The cells harvested from the second and third digestions demonstrated higher cell viability, more proliferative activity, a better chondrocyte phenotype, and a higher cartilage-specific matrix synthesis ability than those harvested from the first digestion and after the classic 1-step protocol.

CONCLUSIONS

The sequential protocol is a rapid, flexible, high-efficiency chondrocyte isolation protocol for different cartilage tissues. We recommend using this protocol for chondrocyte isolation, and in particular, the cells obtained after the subsequent 3-hour sequential digestions should be used for chondrocyte-based therapy.

Morphological and Molecular Evaluation of the Tissue Repair following Nasal Septum Biopsy in a Sheep Model

OBJECTIVE

Nasal septal pathologies requiring surgical intervention are common in the population. Additionally, nasal chondrocytes are becoming an important cell source in cartilage tissue engineering strategies for the repair of articular cartilage lesions. These procedures damage the nasal septal cartilage whose healing potential is limited due to its avascular, aneural, and alymphatic nature. Despite the high incidence of various surgical interventions that affect septum cartilage, limited nasal cartilage repair characterizations have been performed to date.

METHODS

To evaluate the healing of the nasal septum cartilage perforation, a septal biopsy was performed in 14 sheep. Two and 6 months later, the tissue formed on the place of perforation was explanted and compared with the native tissue. Tissue morphology, protein and gene expression of explanted tissue was determined using histological, immunohistochemical and real-time quantitative polymerase chain reaction analysis.

RESULTS

Tissue formed on the defect site, 2 and 6 months after the biopsy was characterized as mostly connective tissue with the presence of fibroblastic cells. This newly formed tissue contained no glycosaminoglycans and collagen type II but was positively stained for collagen type I. Cartilage-specific genes COL2, AGG, and COMP were significantly decreased in 2- and 6-month samples compared with the native nasal cartilage. Levels of COL1, COL4, and CRABP1 genes specific for perichondrium and connective tissue were higher in both test group samples in comparison with native cartilage.

CONCLUSIONS

Newly formed tissue was not cartilage but rather fibrous tissue suggesting the role of perichondrium and mucosa in tissue repair after nasal septum injury.

Histological Analysis of Cartilage Defects Repaired with an Autologous Human Stem Cell Construct 48 Weeks Postimplantation Reveals Structural Details Not Detected by T2-Mapping MRI

OBJECTIVE

The aim of this study was to elucidate the efficacy of T2-mapping MRI and correlation with histology for the evaluation of tissue repair quality following the first-in-human implantation of an autologous tissue engineered construct.

DESIGN

We directly compared the results of T2-mapping MRI of cartilage repair tissue with the histology of a biopsy specimen from the corresponding area at 48 weeks postoperatively in 5 patients who underwent the implantation of a scaffold-free tissue-engineered construct generated from autologous synovial mesenchymal stem cells to repair an isolated cartilage lesion. T2 values and histological scores were compared at each of 2 layers of equally divided halves of the repair tissue (upper and lower zones).

RESULTS

Histology showed that the repair tissue in the upper zone was dominated by fibrous tissue and the ratio of hyaline-like matrix increased with the depth of the repair tissue. There were significant differences between upper and lower zones in histological scores. Conversely, there were no detectable statistically significant differences in T2 value detected among zones of the repair tissue, but zonal differences were detected in corresponding healthy cartilage. Accordingly, there were no correlations detected between histological scores and T2 values for each repair cartilage zone.

CONCLUSION

Discrepancies in the findings between T2 mapping and histology suggest that T2 mapping was limited in ability to detect details in the architecture and composition of the repair cartilage.

Costal Chondrocyte-Derived Pellet-Type Autologous Chondrocyte Implantation versus Microfracture for Repair of Articular Cartilage Defects: A Prospective Randomized Trial

OBJECTIVE

To compare the efficacy and safety of costal chondrocyte-derived pellet-type autologous chondrocyte implantation (CCP-ACI) with microfracture (MFx) for repair of articular cartilage defects of the knee.

DESIGN

Thirty subjects with an International Cartilage Repair Society (ICRS) grade 3 to 4 chondral defect (2-10 cm² in area; ≤4 cm³ in volume) were randomized at a ratio of 2:1 (CCP-ACI:MFx). Twenty patients were allocated in the CCP-ACI group and 10 patients in the MFx group. CCP-ACI was performed by harvesting costal cartilage at least 4 weeks before surgery. Implantation was performed without any marrow stimulation. Efficacy and safety were assessed at weeks 8, 24, and 48 after surgery according to the magnetic resonance observation of cartilage repair tissue (MOCART) score and clinical outcomes.

RESULTS

MOCART scores improved from baseline to 24 and 48 weeks postoperatively in both treatment groups. The improvement in MOCART scores in the CCP-ACI group was significantly greater than that in the MFx group at 24 and 48 weeks (39.1 vs 21.8 and 43.0 vs 24.8, respectively). The proportions of complete defect repair and complete integration were significantly higher in the CCP-ACI group than the MFx group at 48 weeks. Improvement in Lysholm score and KOOS subscores, including Function (Sports and Recreational Activity) and knee-related quality of life was significantly greater in the CCP-ACI group than the MFx group at 48 weeks (35.4 vs 31.5, 35.7 vs 28.5, and 27.9 vs 11.6, respectively).

CONCLUSION

Treatment of cartilage defects with CCP-ACI yielded satisfactory cartilage tissue repair outcomes, with good structural integration with native cartilage tissue shown by magnetic resonance imaging at 24 and 48 weeks after surgery.

LEVEL OF EVIDENCE

Level 1: Randomized controlled study.

Articular cartilage and osteochondral tissue engineering techniques: Recent advances and challenges

In spite of the considerable achievements in the field of regenerative medicine in the past several decades, osteochondral defect regeneration remains a challenging issue among diseases in the musculoskeletal system because of the spatial complexity of osteochondral units in composition, structure and functions. In order to repair the hierarchical tissue involving different layers of articular cartilage, cartilage-bone interface and subchondral bone, traditional clinical treatments including palliative and reparative methods have showed certain improvement in pain relief and defect filling. It is the development of tissue engineering that has provided more promising results in regenerating neo-tissues with comparable compositional, structural and functional characteristics to the native osteochondral tissues. Here in this review, some basic knowledge of the osteochondral units including the anatomical structure and composition, the defect classification and clinical treatments will be first introduced. Then we will highlight the recent progress in osteochondral tissue engineering from perspectives of scaffold design, cell encapsulation and signaling factor incorporation including bioreactor application. Clinical products for osteochondral defect repair will be analyzed and summarized later. Moreover, we will discuss the current obstacles and future directions to regenerate the damaged osteochondral tissues.

Early Efficacy of Type I Collagen-Based Matrix-Assisted Autologous Chondrocyte Transplantation for the Treatment of Articular Cartilage Lesions

Background: Articular cartilage is a complex structure that allows for low frictional gliding and effective shock absorption. Various sports injuries and inflammatory conditions can lead to lesions in the articular cartilage, which has limited regenerative potential. Type I collagen combined with autologous chondrocytes in a three-dimensional culture were used to induce the regeneration of single-layer autologous expanded chondrocytes without chondrogenic differentiation. Purpose: To assess the clinical, radiological, and histological changes following collagen-based autologous chondrocyte transplantation (MACT) for chondral knee lesions. Methods: The study prospectively enrolled 20 patients with symptomatic knee chondral lesions (mean size lesion was 2.41 ± 0.43 cm², range: 2.0-3.4 cm²) in the lateral femoral condyle and femoral groove who underwent type I collagen-based MACT between July 2017 and July 2019. knee injury and osteoarthritis outcome score (KOOS) was assessed before the procedure, and periodic clinical follow-up was conducted every 3 months for a maximum of 12 months following the procedure and at 1-year intervals thereafter. Magnetic resonance imaging (MRI) T2 mapping of repaired cartilage was also used for the quantitative analysis of regeneration. In one patient, second-look arthroscopy was performed to assess cartilage regeneration characteristics, and a portion of regenerated cartilage was harvested for histological evaluation 12 months after implantation. Results: At pre-operation and at three, six, 12, and 24 months after the operation, KOOS pain, symptoms, daily life activities, sports and recreation, as well as the quality of life were significantly improved between every two time points. Hematoxylin and eosin (HE) staining indicated that the newly formed cartilage was comprised of naive chondrocytes. Safranin O-fast (S-O) green staining of the regenerated tissue revealed fibroblast-like cells surrounded by glycosaminoglycans. Immunohistochemistry (IHC) analysis indicated that collagen type II was uniformly distributed at the deep zone of articular cartilage and type I collagen mainly depositing in the superficial cartilage layer. The T2 values for repaired tissue gradually decreased, eventually approaching near-average values. Conclusion: The present study demonstrated that type I collagen-based MACT is a clinically effective treatment for improving functionality and pain levels. Histological evidence confirmed hyaline cartilage induction and showed that repaired cartilage tended to emerge from the deep to the superficial layer. The quantitative MRI T2 mapping test indicated that there still was a difference between the transplanted cartilage and the surrounding hyaline cartilage. Taken together, the current method represents an efficient approach for the restoration of knee cartilage lesions.