Search Results (468)

The sequential phases of tissue healing—inflammation, proliferation, and remodeling—demand distinct pharmacokinetic profiles that conventional drug delivery systems fail to provide, creating a “chronotherapy gap” that contributes to chronic wound pathologies. Hydrogels, with their highly tunable network structures, offer a unique platform to program release kinetics in synchrony with these healing timelines. This review systematically examines design strategies for phase-synchronized hydrogel systems, categorized into three hierarchical paradigms: intrinsic network control (crosslinking density, degradation kinetics, and architectural engineering) that pre-programs release profiles; extrinsic/responsive control (endogenous pH/ROS/MMP/glucose and exogenous NIR/ultrasound/electro/magnetic triggers) that enables on-demand phase-shifting; and integrated systems that combine passive spatial compartmentalization with active responsiveness. We survey representative applications across cutaneous wounds, bone defects, cartilage, tendon, myocardial, and neural tissues, highlighting both common design principles and tissue-specific adaptations. Key translational bottlenecks—including in vivo–in vitro discrepancies, cargo stability, sterilization challenges, and regulatory complexity—are critically examined, alongside emerging frontiers such as closed-loop biosensing, artificial intelligence-driven design, and four-dimensional printing. We conclude that the field is evolving from passive drug depots toward active therapeutic synchronizers, where material programming is set to the body’s biological clock, offering a transformative paradigm for regenerative medicine. Full article

The treatment of articular cartilage defects remains a significant clinical challenge due to the tissue’s limited intrinsic repair capacity. This paper presents a review of clinical experiences with the use of Wharton’s jelly-derived mesenchymal stem cells (WJ-MSCs) as a novel therapeutic option for cartilage regeneration. WJ-MSCs offer key advantages, including high proliferative potential, strong immunomodulatory properties, and low immunogenicity, making them suitable for allogeneic applications. This review describes a single-step, dry-arthroscopic technique that was employed for the implantation of WJ-MSCs embedded in a scaffold directly into cartilage defects. Clinical follow-up, supported by MRI evaluation, demonstrated favorable outcomes with evidence of defect filling, improved cartilage surface quality, and sustained functional improvement in patients. These results suggest that WJ-MSC-based therapies, delivered through minimally invasive surgical techniques, represent a safe and effective strategy for cartilage repair, with the potential to become an important alternative to current standard treatments. Recent advances in artificial intelligence (AI) and multimodal bioprinting are opening new perspectives for standardizing regenerative therapies. Machine learning models can predict bioink performance, optimize scaffold design, and integrate real-time imaging feedback such as optical coherence tomography and photoacoustic imaging. These approaches allow closed-loop quality control and the creation of digital twins to ensure biomechanical fidelity of constructs. Incorporating AI-assisted bioprinting with Wharton’s jelly MSCs could accelerate the translation of laboratory findings into reproducible, patient-specific cartilage implants. This manuscript is structured as a translational review of WJ-MSC-based cartilage repair, with AI-assisted bioprinting presented as a prospective future manufacturing direction rather than current clinical practice. Full article

Mechanical stress is thought to be involved in the pathogenesis and pathophysiology of osteoarthritis (OA). However, much remains to be elucidated regarding how chondrocytes sense and respond to mechanical stress (stress sensing and response factors). Additionally, it still remains unclear whether there are defensive responses and mechanisms to protect against pathological agents and mechanical stress in articular cartilage tissue. This study was designed to determine whether repetitive mechanical force, at physiologic levels, affects the expression of factors regulating autophagy such as the autophagy-related proteins ATG5, Beclin-1, and Parkin, and the autophagy process as well as cellular activity in cultured chondrocytes. Three-dimensional cultured tissue was generated from human chondrocytes using a collagen sponge scaffold. After physiological mechanical loading of the 3D cell–collagen sponge construct, comparative analyses of expression levels of ATG5, Beclin-1, and Parkin were performed in human chondrocytes. Chondrocyte activity and Transmission Electron Microscopy (TEM) analysis for detecting autophagy process were also analyzed with or without repetitive compressive loading. In chondrocytes, 60 min or 180 min repetitive compressive loading significantly decreased the expression of ATG5, Beclin-1 and Parkin in comparison with the non-loading group. TEM analysis indicated that, in normal chondrocytes of the non-loading group, the autophagy process was shown to be progressing. In contrast, repetitive loading decreased the number of autophagosomes and autolysosomes in chondrocytes. In addition, numerous degenerated organelles that had not undergone autophagy were observed within the chondrocytes under repetitive loading. The ATG5 and Beclin-1 proteins are known to play crucial roles in regulating cellular autophagy. Furthermore, repetitive mechanical loading caused a decreased expression of Parkin, a mitophagy regulator in chondrocytes. Our results indicate for the first time that a decrease in mitophagy, as well as cellular autophagy, in response to mechanical stress, even at the physiologic level, leads to the accumulation of defective mitochondria and abnormal cellular proteins, resulting in reduced chondrocyte activity and affecting the maintenance of cartilage tissue homeostasis, ultimately contributing to the progression of OA. Full article

Background: The clinical translation of cell-based therapies for knee articular cartilage repair is fundamentally restricted by the severe biological unpredictability of autologous cell sources, inherent manufacturing bottlenecks, and the rapid phenotypic dedifferentiation of cells expanded in conventional 2D monolayers. To overcome these translational hurdles, this study engineered a scaffold-free, 3D formulation of highly characterized allogeneic FE002-Cart chondroprogenitor spheroids. Methods: We systematically investigated the specific microenvironmental cues and Good Manufacturing Practice (GMP) formulation parameters required to direct functional chondrogenesis. The structural and biochemical performance of this allogeneic formulation was benchmarked against multiple primary adult autologous chondrocyte types. Finally, we evaluated the phenotypic resilience of the microtissues in simulated osteoarthritic (OA) environments and investigated both short-term liquid storage and advanced terminal preservation strategies to establish off-the-shelf logistical viability. Results: Precise microenvironmental regulation proved to be a critical biological prerequisite. The synergistic combination of physiological hypoxia (2% O₂) and stringent glucocorticoid limitation (10 nM dexamethasone) induced robust glycosaminoglycan (GAG) deposition and a > 200-fold upregulation of ACAN and COL2, while suppressing the terminal hypertrophic drift observed in adult chondrocytes. Benchmarking revealed that the allogeneic FE002-Cart formulation substantially mitigates the profound morphological and biochemical unpredictability inherent to adult autologous cell sources. Furthermore, the scaffold-free spheroid geometry yielded a 10-fold increase in GAG production per cell compared to traditional matrix-seeded (MACI) platforms. Transitioning to a GMP-compatible manufacturing process revealed extreme cellular sensitivities; excipients within standard pharmaceutical-grade dexamethasone severely aborted chondrogenic differentiation, emphasizing the necessity of rigorous raw-material qualification. Functionally, the 3D architecture acted as a protective physical shield, sustaining high cellular viability when subjected to severe inflammatory stress and 100% OA patient synovial fluid. Logistically, the viable spheroids maintained matrix integrity and inter-spheroid fusion potential for up to 7 days at ambient temperature in transport medium. Finally, advanced spheroid preservation via lyophilization and high-dose gamma irradiation eliminated biological viability but successfully transitioned the microtissues into highly organized, terminally irradiated matrices capable of heterologous in vitro structural merging. Conclusions: These findings define the critical biological thresholds for manufacturing, demonstrate the enhanced in vitro biosynthetic efficiency of 3D allogeneic microtissues compared to specific autologous and matrix-dependent baselines, and establish a highly practical, off-the-shelf logistical framework for the regenerative treatment of large knee chondral defects. Full article

Articular cartilage defects remain a significant clinical challenge due to the limited intrinsic regenerative capacity of cartilage and the inability of many current therapeutic approaches to restore the structure and function of native hyaline tissue. As a result, considerable research efforts have been directed toward the development of tissue-engineering and biomaterial-based strategies capable of promoting more effective regeneration. Among these, hydroxyapatite–hydrogel (HAp–hydrogel) composites have emerged as particularly promising candidates because they combine the biological functionality of HAp with the structural versatility of hydrogel networks. Hydrogels provide a highly hydrated, extracellular matrix-like environment that supports cell survival, facilitates matrix deposition, and enables the localized delivery of therapeutic agents. At the same time, their physicochemical properties can be tailored through a variety of crosslinking approaches and advanced responsive design strategies. The incorporation of HAp, either in nano- or microscale form, contributes to mechanical reinforcement, supports subchondral bone regeneration, and influences cellular behavior through both biochemical and mechanotransductive mechanisms. Beyond promoting chondrogenic differentiation, HAp–hydrogel composites have also been investigated for their capacity to modulate inflammation, stimulate angiogenesis within the subchondral region, provide antibacterial protection, and maintain a microenvironment conducive to tissue repair. This review critically examines recent advances in the development and application of HAp–hydrogel composites for cartilage regeneration, highlighting material design principles, fabrication strategies, healing mechanisms, and the key challenges that continue to influence their clinical translation. Full article

Background: MSC–hydrogel composite systems were developed to overcome the poor cell retention and limited durability of conventional marrow stimulation and suspension-based MSC delivery. A rigorous synthesis of the clinical evidence is lacking. Objectives: To evaluate the safety and efficacy of MSC–hydrogel composite therapy for focal knee cartilage defects and knee osteoarthritis, and to assess the certainty of evidence using the GRADE framework. Methods: PROSPERO-registered systematic review (CRD420261393525), conducted and reported per PRISMA 2020 and SWiM. Five databases (Embase, PubMed/MEDLINE, Cochrane CENTRAL, Scopus, Web of Science) were searched in May 2026 without date, language, or design restrictions. Adults receiving MSCs co-delivered in a hydrogel carrier for knee cartilage pathology were eligible. Risk of bias was assessed using RoB 2 (RCTs) and ROBINS-I (non-randomized studies). Narrative synthesis following Popay et al. was the primary method; GRADE certainty was assessed per outcome domain. Results: Ten studies (N = 521) were identified. Eight studies fulfilled the predefined eligibility criteria for MSC–hydrogel composite interventions and formed the primary evidence synthesis. Two additional studies were retained as contextual comparators because they evaluated either hydrogel-based therapy without MSC administration or MSC therapy without a structured hydrogel carrier. Surgical MSC–hydrogel implantation was associated with improvements in cartilage repair. Intra-articular injection without a hydrogel scaffold produced synovitis reduction but no detectable structural regeneration at six months. No serious treatment-related adverse events were recorded. Risk of bias was serious or critical in seven of nine assessable studies; GRADE certainty was low to very low across all outcome domains. Conclusions: MSC–hydrogel composite implantation may provide favorable safety signals and directionally positive effects on cartilage repair, pain, and function, with seven-year follow-up data suggesting a possible durability advantage over marrow stimulation. However, adverse-event reporting was inconsistent, and certainty of evidence remains low or very low because most studies were non-randomized, single-center, and concentrated around one commercial platform. These findings are relevant to international cartilage-regeneration research because they identify key methodological limitations and trial-design priorities for translating MSC–hydrogel systems across different clinical and regulatory settings. Full article

Purpose: To determine whether specific in vitro biologic characteristics and manufacturing kinetics of cultured human articular chondrocytes (HACs) can serve as predictive biomarkers for patient-reported and structural outcomes following second-generation autologous chondrocyte implantation (ACI) in the knee. Materials and Methods: This prospective cohort study evaluated 67 patients (mean age 25.1 ± 8.3 years) treated with second-generation ACI for large focal cartilage defects (mean size 5.4 ± 2.5 cm²) between 2017 and 2024. HACs were expanded under Good Manufacturing Practice (GMP) conditions using human platelet lysate-supplemented media. Four biological determinants were analyzed: (1) initial chondrocyte yield (ICY) isolated from the cartilage biopsy; (2) chondrogenic activity (relative ACAN and COL2A1 expression); (3) final culture confluence level; and (4) HAC population doubling time (PDT) pre- and post-cryopreservation. Clinical outcomes (KOOS and IKDC) and MRI outcomes (MOCART) were assessed at 2 years (T1) and at a mean final follow-up of 4.2 ± 1.7 years (T2) via univariate and multiple regression analyses. Results: Static biosynthetic markers (ACAN/COL2A1 expression) and final culture confluence did not significantly correlate with longitudinal clinical (KOOS/IKDC) or structural (MOCART) outcomes. Conversely, the retained kinetic parameters served as strong prognostic indicators. Multiple regression revealed that higher ICY values significantly predicted improvements across most KOOS subscales from baseline to T2, including KOOS Symptoms (β = 63.56; p < 0.01), KOOS Pain (β = 88.83; p < 0.001), KOOS ADL (β = 107.84; p < 0.001), and KOOS Sport and Recreation Function (β = 92.3; p < 0.05). Furthermore, a prolonged PDT, indicative of diminished in vitro proliferative vigor, inversely correlated with functional recovery in IKDC (β = −26.12; p < 0.01), KOOS Pain (β = −23.09; p < 0.05), and KOOS ADL (β = −21.71; p < 0.05) scores. Conclusions: The intrinsic proliferative vigor of the HAC cellular payload (shorter PDT) and higher initial cell yields are robust kinetic biomarkers associated with markedly superior mid-term clinical outcomes following second-generation ACI for large focal chondral defects in the knee. In contrast, standard morphological and gene expression metrics failed to predict in vivo functional success. These findings advocate for a risk-based paradigm shift in GMP quality control methodologies, emphasizing dynamic HAC growth kinetics over static cellular features to optimize patient-specific regenerative potential. Full article

Articular cartilage possesses a limited intrinsic repair capacity, and current treatment strategies frequently result in fibrocartilaginous repair tissue with inferior structural and mechanical properties compared with native hyaline cartilage. Increasing evidence indicates that successful restoration of joint function requires regeneration of the entire osteochondral unit and adequate integration between cartilage and subchondral bone. Cartilage tissue engineering has emerged as an effective approach for repairing damaged cartilage. The present study evaluated the long-term performance of electrospun PLA/PCL (70/30) scaffolds coated with iodine-doped polypyrrole (PPy-I), with and without aggrecan incorporation, in a rabbit osteochondral defect model after 12 months of implantation. Two scaffold formulations were evaluated: M1 (PLA-PCL-PPy-I) and M2 (PLA-PCL-PPy-I-AG), each implanted either without cells or after in vitro pre-culture with autologous chondrocytes prior to implantation. Histological analyses were performed to assess tissue organization and osteochondral integration, while indentation testing was used to characterize the mechanical behavior of the regenerated tissues. Experimental force–displacement data were further analyzed using a generalized nonlinear Maxwell viscoelastic model. Histological evaluation revealed that scaffold composition and cellularization influenced the characteristics of the regenerated tissue. The M2 scaffold pre-cultured with autologous chondrocytes exhibited the structural organization most closely resembling native hyaline cartilage, including a tri-zonal architecture and a continuous tidemark indicative of improved osteochondral integration. Mechanical testing demonstrated nonlinear viscoelastic behavior and hysteresis in both regenerated and native tissues. The proposed generalized nonlinear Maxwell viscoelastic model provides a practical framework for the mechanical characterization of regenerated osteochondral tissues using only two effective parameters representing the elastic and viscous response, and may support future studies aimed at estimating their intrinsic mechanical properties. Full article

Osteoarthritis is a leading cause of disability, most commonly affecting the articular cartilage of the knee in older individuals. Younger people are also at risk of developing post-traumatic osteoarthritis, including athletes and those with a history of joint injury. Focal cartilage defects can be treated through clinical interventions such as autologous chondrocyte implantation, where cells from the patient are isolated, cultured, and subsequently reimplanted into the defect site. Despite recent clinical advances, there is a lack of standardisation in the preparation of chondrocytes for cartilage tissue engineering therapies, with considerable variation in culture conditions reported in the literature. A major challenge in cell-based cartilage repair is the dedifferentiation of chondrocytes during monolayer expansion, which leads to a change in phenotype. Native articular chondrocytes exhibit a rounded morphology and express collagen type II and aggrecan, whilst dedifferentiated cells adopt a fibroblastic phenotype, characterised by an elongated morphology and increased expression of collagen type I. This review summarises the key physical, biochemical, and mechanical factors that mitigate chondrocyte dedifferentiation to support the maintenance of a chondrogenic phenotype and preserve the capacity of cells to redifferentiate. A mechanistically informed approach to chondrocyte culture will enhance cartilage tissue engineering therapies. Full article

Background: High tibial osteotomy (HTO) is commonly performed to manage medial compartment knee osteoarthritis by correcting mechanical alignment; however, the role of adjunctive regenerative therapies remains uncertain. Methods: This retrospective study compared leukocyte-rich platelet-rich plasma (LR-PRP) with leukocyte-poor PRP (LP-PRP) in patients undergoing HTO. Forty patients were allocated into three groups: HTO alone (n = 10), HTO with LR-PRP (n = 20), and HTO with LP-PRP (n = 10). Clinical outcomes were assessed preoperatively and at 12 months using the Visual Analog Scale, Oxford Knee Score, and Western Ontario and McMaster Universities Osteoarthritis Index. Cartilage repair appearance was evaluated through second-look arthroscopy using the ICRS grading and Koshino staging systems. Multivariable analysis of covariance (ANCOVA), adjusting for baseline imbalances, was employed to evaluate postoperative outcomes. Results: All groups demonstrated significant improvements in pain and function (p < 0.05), with no significant differences among groups. However, Group B exhibited a greater shift toward lower ICRS grades than Group A (p < 0.05), whereas no significant difference was found between Groups C and A. Arthroscopic findings revealed more complete defect coverage and improved structural integrity in the LR-PRP group. Conclusions: These findings demonstrate a clear discrepancy exists between clinical and structural outcomes; while HTO drives substantial and comparable short-term functional improvements across all cohorts, adjunctive LR-PRP is positively associated with a significantly enhanced arthroscopic cartilage repair appearance compared to LP-PRP or HTO alone. Further prospective studies are needed to validate these findings and elucidate the underlying biological mechanisms. Full article

The treatment of osteochondral defects still poses a challenge, despite the fact that there are currently many methods and various materials designed for the regeneration of these tissues. The aim of our study was to evaluate the biocompatibility and bioactive potential of an innovative biocement enriched with manuka honey and α-tricalcium phosphate in a porcine model, with a focus on subchondral bone regeneration. Osteochondral defects of the medial femoral condyle were treated with the tested biocement in five animals, and five additional animals served as controls (untreated defect). After six months of observation, the regenerative potential of the therapeutic strategy was evaluated macroscopically, using imaging methods (X-ray, CT, and MRI) and histological examination. The studied biomaterial showed no cytotoxicity and proved to be biocompatible. In the in vivo system, based on imaging and histological methods, a typical trabecular organization with cellular elements has been observed in all animals treated with the tested biocement, indicating active remodeling and maturation processes. In animals with untreated defects, incomplete healing of the bone defect occurred, with limited areas of trabecular bone and incomplete boundaries between the cartilage and subchondral bone. Our pilot study, employing a multi-method approach to investigate the in vivo effects of a novel biocement on bone tissue regeneration, may highlight the potential contribution of biomaterials to the development of new therapeutic strategies in the context of osteochondral regeneration. Full article

Articular cartilage repair remains a clinical challenge due to the tissue’s limited regenerative capacity. This study aimed to perform in vivo tracking of human chondrocytes after implantation in femoral trochlear defects. Moreover, we tested the rabbit xenogeneic model to assess the efficacy of human chondrocyte implantation, either in the form of cell suspension or in the form of spheroids, for cartilage regeneration. Chondrocytes were isolated from osteoarthritic human knees, expanded in vitro, and labeled with gold nanoparticles (AuNPs) to enable their in vivo tracking. AuNP labeling did not impair chondrocyte viability and spheroid formation. Knee osteochondral defects were then treated with the labeled cells, either injected intra-articularly as single cells in suspension or aggregated into scaffold-free spheroids and further implanted. Two weeks post-transplantation, macroscopic and histological evaluations were performed to assess cartilage repair and cell engraftment. The presence of labeled cells was detected only in spheroid-treated lesions that exhibited significantly greater tissue filling as reflected by O’Driscoll and ICRS scores. Moreover, localized expression of type II collagen was observed in some of the spheroid-treated defects. In contrast, single cell intra-articular injection resulted in poor cartilage repair and the absence of labeled cells at the defect site. Altogether, our results indicate that human chondrocyte delivery in the form of scaffold-free spheroids in rabbit knees enhances their retention at the defect site and supports early stages of cartilage regeneration. Moreover, our results suggest that the xenogeneic rabbit model could be a useful platform for evaluating human-derived cell therapies. Full article

Osteochondral defects, involving both articular cartilage and subchondral bone, can lead to joint degeneration and osteoarthritis. Recent advances in 3D-printed biphasic scaffolds offer promising opportunities to recreate physiological microenvironments for tissue regeneration. In tissue engineering, these scaffolds can be mechanically stimulated to promote targeted cartilage and bone formation. While computational models have been widely used to study mechanically induced cellular responses in monophasic scaffolds, time-dependent modelling of biphasic osteochondral systems remains relatively scarce. In this study, a fluid–structure interaction (FSI) framework coupled with a mechanoregulatory algorithm was developed to predict mechanically induced early-stage mesenchymal stem cell (MSC) differentiation in biphasic open-porous osteochondral scaffolds comprising chondral and bone layers designed for direct ink writing (DIW). In a second model, an interfacial barrier layer representing the native osteochondral interface was integrated. Dynamic compressive loading (1 Hz, $2.5\%$ strain) was applied. The simulations predicted region-specific differentiation patterns in both the chondral and subchondral bone regions. In the scaffold without a barrier layer, approximately $68.9\%$ of MSCs in the chondral layer and $93.4\%$ of MSCs in the bone layer underwent chondrogenic and osteogenic differentiation, respectively. Incorporation of the barrier layer caused only minor changes, reducing predicted cartilage and bone differentiation by approximately $1.5\%$ and $3.9\%$, respectively. Overall, this study highlights the capability of computational modelling to predict mechanobiological responses in complex osteochondral systems and support scaffold design and effective mechanical stimulation protocols. Full article

The meniscus is a fibrocartilaginous tissue essential for load transmission, shock absorption, joint stability, and cartilage protection in the knee. However, its intrinsic healing capacity is severely limited, particularly in the avascular region and in complex defects, often resulting in persistent symptoms, functional impairment, and progressive joint degeneration. Although current clinical interventions, including meniscal repair, partial meniscectomy, allograft transplantation, and scaffold-assisted meniscal substitution, can provide symptomatic and functional improvement in selected patients, durable structural and functional restoration remains difficult to achieve. Meniscus tissue engineering has therefore emerged as a potential strategy for tissue preservation and functional reconstruction. This review synthesizes recent advances in meniscus tissue-engineered scaffolds, focusing on biomaterial systems, biofabrication strategies, and translational progress. Natural polymers, decellularized extracellular matrix, synthetic polymers, and composite materials are discussed according to their respective roles in biological regulation, mechanical support, structural organization, and clinical feasibility. Emerging biofabrication strategies are further analyzed with respect to geometric reconstruction, zonal organization, fibrous anisotropy, and their implications for scaffold evaluation. Finally, current in vitro, preclinical, and clinical evidence is critically examined to identify the key barriers that still limit long-term regeneration and clinical translation. Full article

Background/Objectives: Total nasal reconstruction has long represented a formidable surgical challenge. To date, no universally accepted, evidence-based protocol for nasal reconstruction exists to guide clinical practice. This study introduces a novel technique for comprehensive, three-layer nasal reconstruction. Specifically, the approach entails (1) reconstruction of the nasal mucosal lining using a free radial forearm flap; (2) provision of robust structural support via an exogenous extended framework; and (3) restoration of the external nasal skin using an expanded forehead flap. Methods: Ten patients underwent reconstruction for full-thickness nasal defects, all achieving successful structural and functional restoration. All surgical procedures were completed successfully, with operative durations ranging from 6.5 to 10.5 h. One patient developed an infection involving the rib cartilage graft. Following thorough debridement, the radial forearm free flap healed uneventfully. A second patient experienced postoperative vascular compromise of the flap. Intraoperative exploration revealed inadequate perfusion; immediate microsurgical revision—including adjustment of recipient vessels and/or re-anastomosis—successfully restored flap viability. Results: Primary wound healing was achieved in all patients within 10–22 days. All patients completed a follow-up of 12–36 months (mean: 21.5 months). Both patients and the surgical team rated postoperative nasal aesthetics as satisfactory. Objective functional assessments—including anterior rhinomanometry and peak nasal inspiratory flow—demonstrated no clinically significant impairment in nasal airflow. Conclusions: This surgical strategy for reconstructing the three-layer nasal architecture in patients with total nasal defects represents a rational and clinically viable approach—offering a valuable reference for rhinoplasty surgeons performing such complex reconstructions. Full article