The basic science of articular cartilage: structure, composition, and function

A MnO2 nanosheets doping double crosslinked hydrogel for cartilage defect repair through alleviating inflammation and guiding chondrogenic differentiation

The inflammatory microenvironment and inferior chondrogenesis are major symptoms after cartilage defect. Although various modifications strategies associated with hydrogels exhibit remarkable capacity of pro-cartilage regeneration, the adverse effect by prolonging inflammation is still formidable to hamper potential biomedical applications of different hydrogel implants. Herein, inspired by the repair microenvironment of articular cartilage defects, an injectable, immunomodulatory, and chondrogenic L-MNS-CMDA hydrogel is prepared through grafting vinyl and catechol groups to chitosan macromolecules using amide reaction, then further loading MnO2 nanosheets (MNS). The double crosslinking of photopolymerization and catechol oxidative polymerization endows L-MNS-CMDA hydrogel with preferable mechanical property, affording a suitable mechanical support for cartilage defect repair. Additionally, the robust tissue adhesion capability stemming from catechol groups guarantees the long-term retention of the hydrogel in the defect site. Meanwhile, L-MNS-CMDA hydrogel decomposes exogenous and intracellular H2O2 into O2 and H2O, to effectively alleviate cellular oxidative stress caused by long-term hypoxia. Under the synergies of catechol groups and MNS, L-MNS-CMDA hydrogel not only inhibits macrophages polarizing into M1 phenotype, but encourages them turn into M2 phenotype, thereby, reconstructing an immunization friendly microenvironment to ultimately enhance cartilage regeneration. Predictably, the hydrogel markedly induces rat bone marrow mesenchymal stem cells differentiating into chondrocytes by expressing abundant glycosaminoglycan and type II collagen. A cartilage defect model of rat knee joint indicates that L-MNS-CMDA hydrogel visually regulate the early inflammatory response of post-implantation, and facilitate cartilage regeneration and recovery of joint function after 12 weeks of post-implantation. All in all, this multifunctional L-MNS-CMDA hydrogel exhibits superior immunomodulatory and chondrogenic properties, holding immense clinical potential in the treatment of cartilage defects.

In situ study on articular cartilage degeneration in simulated microgravity by HOF-ATR-FTIR spectroscopy

Fourier transform infrared spectroscopy (FTIRS) can provide rich information on the composition and content of samples, enabling the detection of subtle changes in tissue composition and structure. This study represents the first application of FTIRS to investigate cartilage under microgravity. Simulated microgravity cartilage model was firstly established by tail-suspension (TS) for 7, 14 and 21 days, which would be compared to control samples. A self-developed hollow optical fiber attenuated total reflection (HOF-ATR) probe coupled with a FTIR spectrometer was used for the spectral acquisition of cartilage samples in situ, and one-way analysis of variance (ANOVA) was employed to analyze the changes in the contents of cartilage matrix at different stages. The results indicate that cartilage degenerates in microgravity, the collagen content gradually decreases with the TS time, and the structure of collagen fibers changes. The trends of proteoglycan content and collagen integrity show an initial decrease followed by an increase, ultimately significantly decreasing. The findings provide the basis for the cartilage degeneration in microgravity with TS time, which must be of real significance for space science and health detection.

The role of mechanosensitive ion channel Piezo1 in knee osteoarthritis inflammation

Mechanosensitive ion channel Piezo1 is known to mediate a variety of inflammatory pathways and is also involved in the occurrence and development of many orthopedic diseases. Although its role in the inflammatory mechanism of knee osteoarthritis (KOA) has been reported, a systematic explanation is yet to be seen. This article aims to summarize the role of inflammatory responses in the pathogenesis of KOA and elucidate the mechanism by which the Piezo1-mediated inflammatory response contributes to the pathogenesis of KOA, providing a theoretical basis for the prevention and treatment of knee osteoarthritis. The results indicate that in the mechanism leading to knee osteoarthritis, Piezo1 can mediate the inflammatory response through chondrocytes and synovial cells, participating in the pathological progression of KOA. Piezo1 has the potential to become a new target for the prevention and treatment of this disease. Additionally, as pain is one of the most severe manifestations in KOA patients, the inflammatory response mediated by Piezo1, which causes the release of inflammatory mediators and pro-inflammatory factors leading to pain, can be further explored.

Reliability and changes in knee cartilage T2 relaxation time from 6 to 24 months after anatomic anterior cruciate ligament reconstruction

The objectives of this study were to evaluate the reliability of cartilage T2 relaxation time measurements and to identify focal changes in T2 relaxation on the affected knee from 6 to 24 months after anatomic anterior cruciate ligament reconstruction (ACLR). Data from 41 patients who received anatomic ACLR were analyzed. A bilateral 3.0-T MRI was acquired 6 and 24 months after ACLR. T2 relaxation time was measured in subregions of the femoral condyle and the tibial plateau. The root-mean-square coefficient of variation (RMSCV) was calculated to evaluate the reliability of T2 relaxation time in the contralateral knee. Subregion changes in the affected knee T2 relaxation time were identified using the contralateral knee as a reference. The superficial and full thickness layers of the central and inner regions showed good reliability. Conversely, the outer regions on the femoral side and regions in the deep layers showed poor reliability. T2 relaxation time increased in only 3 regions on the affected knee when controlling for changes in the contralateral knee, while changes in T2 relaxation time were identified in 14 regions when not using the contralateral knee as a reference. In conclusion, evaluation of cartilage degeneration by T2 relaxation time after ACLR is most reliable for central and inner cartilage regions. Cartilage degeneration occurs in the central and outer regions of the lateral femoral condyle from 6 to 24 months after anatomic ACLR.

Study on ultrasound-enhanced molecular transport in articular cartilage

Local intra-articular administration with minimal side effects and rapid efficacy is a promising strategy for treating osteoarthritis(OA). Most drugs are rapidly cleared from the joint space by capillaries and lymphatic vessels before free diffusion into cartilage. Ultrasound, as a non-invasive therapy, enhances molecular transport within cartilage through the mechanisms of microbubble cavitation and thermal effects. This study investigated the mass transfer behavior of solute molecules with different molecular weights (479 Da, 40 kDa, 150 kDa) within porcine articular cartilage under low-frequency ultrasound conditions of 40 kHz and ultrasound intensities of 0.189 W/cm2 and 0.359 W/cm2. The results revealed that under the conditions of 0.189 W/cm2 ultrasound intensity, the mass transfer concentration of solute molecules were higher compared to passive diffusion, and with an increase in ultrasound intensity to 0.359 W/cm2, the mass transfer effect within the cartilage was further enhanced. Ultrasound promotes molecular transport in different layers of cartilage. Under static conditions, after 2 h of mass transfer, the concentration of small molecules in the superficial layer is lower than that in the middle layer. After applying ultrasound at 0.189 W/cm2, the molecular concentration in the superficial layer significantly increases. Under conditions of 0.359 W/cm2, after 12 h of mass transfer, the concentration of medium and large molecules in the deep layer region increased by more than two times. In addition, this study conducted an assessment of damage to porcine articular cartilage under ultrasound exposure, revealing the significant potential of low-frequency, low-intensity ultrasound in drug delivery and treatment of OA.

Obesity-induced fibrosis in osteoarthritis: Pathogenesis, consequences and novel therapeutic opportunities

Osteoarthritis (OA) is a significant global burden, affecting more than half a billion people across the world. It is characterized by degeneration and loss of articular cartilage, synovial inflammation, and subchondral bone sclerosis, leading to pain and functional impairment. After age, obesity is a major modifiable risk factor for OA, and it has recently been identified as a chronic disease by the World Health Organization (WHO). Obesity is associated with high morbidity and mortality, imposing a significant cost on individuals and society. Obesity increases the risk of knee OA through increased joint loading, altered body composition, and elevated pro-inflammatory adipokines in the systemic circulation. Moreover, obesity triggers fibrotic processes in different organs and tissues, including those involved in OA. Fibrosis in OA refers to the abnormal accumulation of fibrous tissue within and around the joints. It can be driven by increased adiposity, low-grade inflammation, oxidative stress, and metabolic alterations. However, the clinical outcomes of fibrosis in OA are unclear. This review focuses on the link between obesity and OA, explores the mechanism of obesity-driven fibrosis, and examines potential therapeutic opportunities for targeting fibrotic processes in OA.

Particulated Juvenile Articular Cartilage Allograft Transplantation for Patellofemoral Defects Shows Favorable Return-to-Sport Rates and Patient-Reported Outcomes

PURPOSE

To report return-to-sport rates, postoperative patient-reported outcomes (PROs), complication rates, and reoperation rates of a cohort of patients undergoing particulated juvenile articular cartilage (PJAC) allograft transplantation for patellofemoral articular cartilage defects.

METHODS

We performed a single-institution retrospective review of all patients with patellofemoral articular cartilage defects who received PJAC allograft transplantation from 2014 to 2022. Baseline demographic characteristics and surgical data, including concomitant surgical procedures, were collected. Clinical outcomes recorded included return-to-sport rates, complications, reoperations, and the following PRO scores: Kujala knee score, Patient-Reported Outcomes Measurement Information System (PROMIS) Pain Interference score, and PROMIS Physical Function score.

RESULTS

Forty-one knees with a mean age of 23.4 ± 9.7 years and mean follow-up period of 30.3 months (range, 12-107 months) were included. The mean postoperative PROMIS Pain Interference, PROMIS Physical Function, and Kujala knee scores were 47.4 ± 7.7, 52.2 ± 10.8, and 81.7 ± 16.1, respectively, reflecting low residual anterior knee pain and a return to normal function. For patients playing organized sports at the high school and collegiate levels, the overall return-to-sport rate was 100% (17 of 17). During follow-up, complications developed in 12 knees (29.3%), the most common of which was anterior-based knee pain, and 6 knees (14.6%) required a total of 8 reoperations, which occurred from 6 to 32 months postoperatively.

CONCLUSIONS

The 100% return-to-sport rate and satisfactory PRO scores in our study suggest that PJAC allograft transplantation can effectively address patellofemoral cartilage defects in many patients. The complication and reoperation rates of 29.3% and 14.6%, respectively, are consistent with the challenging and heterogeneous etiology and treatment of patellofemoral articular defects.

LEVEL OF EVIDENCE

Level IV, case series.

Unravelling the interplay between ER stress, UPR and the cGAS-STING pathway: Implications for osteoarthritis pathogenesis and treatment strategy

Osteoarthritis (OA) is a debilitating chronic degenerative disease affecting the whole joint organ leading to pain and disability. Cellular stress and injuries trigger inflammation and the onset of pathophysiological changes ensue after irreparable damage and inability to resolve inflammation, impeding the completion of the healing process. Extracellular matrix (ECM) degradation leads to dysregulated joint tissue metabolism. The reparative effort induces the proliferation of hypertrophic chondrocytes and matrix protein synthesis. Aberrant protein synthesis leads to endoplasmic reticulum (ER) stress and chondrocyte apoptosis with consequent cartilage matrix loss. These events in a vicious cycle perpetuate inflammation, hindering the restoration of normal tissue homeostasis. Recent evidence suggests that inflammatory responses and chondrocyte apoptosis could be caused by the activation of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signalling axis in response to DNA damage. It has been reported that there is a crosstalk between ER stress and cGAS-STING signalling in cellular senescence and other diseases. Based on recent evidence, this review discusses the role of ER stress, Unfolded Protein Response (UPR) and cGAS-STING pathway in mediating inflammatory responses in OA.

Engineering considerations in the design of tissue specific bioink for 3D bioprinting applications

Over eight million surgical procedures are conducted annually in the United Stats to address organ failure or tissue losses. In response to this pressing need, recent medical advancements have significantly improved patient outcomes, primarily through innovative reconstructive surgeries utilizing tissue grafting techniques. Despite tremendous efforts, repairing damaged tissues remains a major clinical challenge for bioengineers and clinicians. 3D bioprinting is an additive manufacturing technique that holds significant promise for creating intricately detailed constructs of tissues, thereby bridging the gap between engineered and actual tissue constructs. In contrast to non-biological printing, 3D bioprinting introduces added intricacies, including considerations for material selection, cell types, growth, and differentiation factors. However, technical challenges arise, particularly concerning the delicate nature of living cells in bioink for tissue construction and limited knowledge about the cell fate processes in such a complex biomechanical environment. A bioink must have appropriate viscoelastic and rheological properties to mimic the native tissue microenvironment and attain desired biomechanical properties. Hence, the properties of bioink play a vital role in the success of 3D bioprinted substitutes. This review comprehensively delves into the scientific aspects of tissue-centric or tissue-specific bioinks and sheds light on the current challenges of the translation of bioinks and bioprinting.

Design and Applications of Supramolecular Peptide Hydrogel as Artificial Extracellular Matrix

Supramolecular peptide hydrogels (SPHs) consist of peptides containing hydrogelators and functional epitopes, which can first self-assemble into nanofibers and then physically entangle together to form dynamic three-dimensional networks. Their porous structures, excellent bioactivity, and high dynamicity, similar to an extracellular matrix (ECM), have great potential in artificial ECM. The properties of the hydrogel are largely dependent on peptides. The noncovalent interactions among hydrogelators drive the formation of assemblies and further transition into hydrogels, while bioactive epitopes modulate cell-cell and cell-ECM interactions. Therefore, SPHs can support cell growth, making them ideal biomaterials for ECM mimics. This Review outlines the classical molecular design of SPHs from hydrogelators to functional epitopes and summarizes the recent advancements of SPHs as artificial ECMs in nervous system repair, wound healing, bone and cartilage regeneration, and organoid culture. This emerging SPH platform could provide an alternative strategy for developing more effective biomaterials for tissue engineering.

Nonlinear Stress-Induced Transformations in Collagen Fibrillar Organization, Disorder and Strain Mechanisms in the Bone-Cartilage Unit

By developing a 3D X-ray modeling and spatially correlative imaging method for fibrous collagenous tissues, this study provides a comprehensive mapping of nanoscale deformation in the collagen fibril network across the intact bone-cartilage unit (BCU), whose healthy functioning is critical for joint function and preventing degeneration. Extracting the 3D fibril structure from 2D small-angle X-ray scattering before and during physiological compression reveals of dominant deformation modes, including crystallinity transitions, lateral fibril compression, and reorientation, which vary in a coupled, nonlinear, and correlated manner across the cartilage-bone interface. A distinct intermolecular arrangement of collagen molecules, and enhanced molecular-level disorder, is found in the cartilage (sliding) surface region. Just below, fibrils accommodate tissue strain by reorientation, which transitions molecular-level kinking or loss of crystallinity in the deep zone. Crystalline fibrils laterally shrink far more (20×) than they contract, possibly by water loss from between tropocollagen molecules. With the calcified plate acting as an anchor for surrounding tissue, a qualitative switch occurs in fibrillar deformation between the articular cartilage and calcified regions. These findings significantly advance this understanding of the complex, nonlinear ultrastructural dynamics at this critical interface, and opens avenues for developing targeted diagnostic and therapeutic strategies for musculoskeletal disorders.

Depth-wise multiparametric assessment of articular cartilage layers with single-sided NMR

Articular cartilage (AC) is a specialized connective tissue that covers the ends of long bones and facilitates the load-bearing of joints. It consists of chondrocytes distributed throughout an extracellular matrix and organized into three zones: superficial, middle, and deep. Nuclear magnetic resonance (NMR) techniques can be used to characterize this layered structure. In this study, devoted to a better understanding of the NMR response of this complex tissue, 20 specimens excised from femoral and tibial cartilage of bovine samples were analyzed by the low-field single-sided NMR-MOUSE-PM10. A multiparametric depth-wise analysis was performed to characterize the laminar structure of AC and investigate the origin of the NMR dependence on depth. The depth dependence of the single parameters T1, T2, and D has been described in literature, but their simultaneous measurement has not been fully exploited yet, as well as the extent of their variability. A novel parameter, α, evaluated by applying a double-quantum-like sequence, has been measured. The significant decrease in T1, T2, and D from the middle to the deep zone is consistent with depth-dependent composition and structure changes of the complex matrix of fibers confining and interacting with water. The α parameter appears to be a robust marker of the layered structure with a well-reproducible monotonic trend across the zones. The discrimination of cartilage zones was reinforced by a multivariate principal component analysis statistical analysis. The large number of samples allowed for the identification of the smallest number of parameters or their combination able to classify samples. The first two components clustered the data according to the different zones, highlighting the sensitivity of the NMR parameters to the structural and compositional variations of AC. Using two parameters, the best result was obtained by considering T1 and α. Single-sided NMR devices, portable and low-cost, provide information on NMR parameters related to tissue composition and structure.

Regulation of chondrocyte apoptosis in osteoarthritis by endoplasmic reticulum stress

Osteoarthritis(OA), a common degenerative joint disease, is characterized by the apoptosis of chondrocytes as a primary pathophysiological change, with endoplasmic reticulum stress(ERS) playing a crucial role. It has been demonstrated that an imbalance in endoplasmic reticulum(ER) homeostasis can lead to ERS, activating three cellular adaptive response pathways through the unfolded protein response(UPR) to restore ER homeostasis. Mild ERS exerts a protective effect on cells, while prolonged ERS that disrupts the self-regulatory balance of the endoplasmic reticulum activates apoptotic signaling pathways, leading to chondrocyte apoptosis and hastening OA progression. Hence, controlling the ERS signaling pathway and its apoptotic factors has become a critical focus for preventing and treating OA. This review aims to elucidate the key mechanisms of ERS pathway-induced apoptosis, associated targets, and regulatory pathways, offering valuable insights to enhance the mechanistic understanding of OA. And it also reviews the mechanisms studied for ERS-related drugs or compounds for the treatment of OA.

Measurement of T1ρ dispersion with compressed sensing and magnetization prepared radial balanced steady-state free precession in spontaneous human osteoarthritis

PURPOSE

To assess the potential for accelerating continuous-wave (CW) T1ρ dispersion measurement with compressed sensing approach via studying the effect that the data reduction has on the ability to detect differences between intact and degenerated articular cartilage with different spin-lock amplitudes and to assess quantitative bias due to acceleration.

METHODS

Osteochondral plugs (n = 27, 4 mm diameter) from femur (n = 14) and tibia (n = 13) regions from human cadaver knee joints were obtained from commercial biobank (Science Care, USA) under Ethical permission 134/2015. MRI of specimens was performed at 9.4T with magnetization prepared radial balanced SSFP (bSSFP) readout sequence, and the CWT1ρ relaxation time maps were computed from the measured data. The relaxation time maps were evaluated in the cartilage zones for different acceleration factors. For reference, Osteoarthritis Research Society International (OARSI) grading and biomechanical measurements were performed and correlated with the MRI findings.

RESULTS

Four-fold acceleration of CWT1ρ dispersion measurement by compressed sensing approach was feasible without meaningful loss in the sensitivity to osteoarthritic (OA) changes within the articular cartilage. Differences were significant between intact and OA groups in the superficial and transitional zones, and CWT1ρ correlated moderately with the reference measurements (0.3 < r < 0.7).

CONCLUSION

CWT1ρ was able to differentiate between intact and OA cartilage even with four-fold acceleration. This indicates that acceleration of CWT1ρ dispersion measurement by compressed sensing approach is feasible with negligible loss in the sensitivity to osteoarthritic changes in articular cartilage.

An enzymatically crosslinked collagen type II/hyaluronic acid hybrid hydrogel: A biomimetic cell delivery system for cartilage tissue engineering

This study presents new injectable hydrogels based on hyaluronic acid and collagen type II that mimic the polysaccharide-protein structure of natural cartilage. After collagen isolation from chicken sternal cartilage, tyramine-grafted hyaluronic acid and collagen type II (HA-Tyr and COL-II-Tyr) were synthesized. Hybrid hydrogels were prepared with different ratios of HA-Tyr/COL-II-Tyr using horseradish peroxidase and noncytotoxic concentrations of hydrogen peroxide to encapsulate human bone marrow-derived mesenchymal stromal cells (hBM-MSCs). The findings showed that a higher HA-Tyr content resulted in a higher storage modulus and a lower hydrogel shrinkage, resulting in hydrogel swelling. Incorporating COL-II-Tyr into HA-Tyr hydrogels induced a more favorable microenvironment for hBM-MSCs chondrogenic differentiation. Compared to HA-Tyr alone, the hybrid HA-Tyr/COL-II-Tyr hydrogel promoted enhanced chondrocyte adhesion, spreading, proliferation, and upregulation of cartilage-related gene expression. These results highlight the promising potential of injectable HA-Tyr/COL-II-Tyr hybrid hydrogels to deliver cells for cartilage regeneration.

Fibronectin isoforms promote postnatal skeletal development

Fibronectin (FN) is a ubiquitous extracellular matrix glycoprotein essential for the development of various tissues. Mutations in FN cause a unique form of spondylometaphyseal dysplasia, emphasizing its importance in cartilage and bone development. However, the relevance and functional role of FN during skeletal development has remained elusive. To address these aspects, we have generated conditional knockout mouse models targeting the cellular FN isoform in cartilage (cFNKO), the plasma FN isoform in hepatocytes (pFNKO), and both isoforms together in a double knockout (FNdKO). We used these mice to determine the relevance of the two principal FN isoforms in skeletal development from postnatal day one to the adult stage at two months. We identified a distinct topological FN deposition pattern in the mouse limb during different gestational and postnatal skeletal development phases, with prominent levels at the resting and hypertrophic chondrocyte zones and in the trabecular bone. Cartilage-specific cFN emerged as the predominant isoform in the growth plate, whereas circulating pFN remained excluded from the growth plate and confined to the primary and secondary ossification centers. Deleting either isoform independently (cFNKO or pFNKO) yielded only relatively subtle changes in the analyzed skeletal parameters. However, the double knockout of cFN in the growth plate and pFN in the circulation of the FNdKO mice significantly reduced postnatal body weight, body length, and bone length. Micro-CT analysis of the adult bone microarchitecture in FNdKO mice exposed substantial reductions in trabecular bone parameters and bone mineral density. The mice also showed elevated bone marrow adiposity. Analysis of chondrogenesis in FNdKO mice demonstrated changes in the resting, proliferating and hypertrophic growth plate zones, consistent alterations in chondrogenic markers such as collagen type II and X, decreased apoptosis of hypertrophic chondrocytes, and downregulation of bone formation markers. Transforming growth factor-β1 and downstream phospho-AKT levels were significantly lower in the FNdKO than in the control mice, revealing a crucial FN-mediated regulatory pathway in chondrogenesis and bone formation. In conclusion, the data demonstrate that FN is essential for chondrogenesis and bone development. Even though cFN and pFN act in different regions of the bone, both FN isoforms are required for the regulation of chondrogenesis, cartilage maturation, trabecular bone formation, and overall skeletal growth.

Triamcinolone acetonide has minimal effect on short- and long-term metabolic activities of cartilage

Intra-articular corticosteroid injections, such as triamcinolone acetonide (TA), are commonly used by clinicians to manage joint synovial inflammation. However, due to conflicting evidence in literature, there is a fear among clinicians that the injections may be harmful to otherwise healthy cartilage in young patients. The purpose of this study was to evaluate the effects of TA on young, healthy chondrocytes. Articular cartilage samples were harvested from bovine knee joints (1-2 months old). In both healthy and inflammatory (interleukin-1β) challenged cartilage, samples were treated with TA at doses ranging from 1 nM to 200 μM. Following a short- (2 days) or long-term (10-14 days) treatment, chondrocyte viability, proliferation, and extracellular matrix (ECM) synthesis and degradation were evaluated with a click chemistry-based technique. Chondrocyte viability, proliferation, and anabolic activity were all minimally affected by short-term and long-term TA treatment. After both acute and sustained inflammatory challenges, TA reduced the catabolic activities in cartilage, reducing nascent glycosaminoglycan loss and maintaining cartilage mechanical properties. Overall, at physiologically relevant doses, TA had minimal negative impact on chondrocytes when maintained within their native ECM. Clinical significance: The findings provide new insight for current clinical practices concerning the use of TA in intra-articular injections, especially in young patients, and established a foundation for future investigations into the impact of corticosteroids on joint homeostasis.

Anterior cruciate ligament injury and age affect knee cartilage T2 but not thickness

OBJECTIVE

To investigate the effect of unilateral anterior cruciate ligament (ACL) injury on cartilage thickness and composition, specifically laminar transverse relaxation time (T2) by magnetic resonance imaging (MRI), in younger and older participants and to compare within-person side differences in these parameters between ACL-injured and healthy controls.

DESIGN

Quantitative double-echo steady-state 3 Tesla MRI-sequences were acquired in both knees of 85 participants in four groups: 20-30 years: healthy, HEA20-30, n = 24; ACL-injured, ACL20-30, n = 23; 40-60 years: healthy, HEA40-60, n = 24; ACL-injured, ACL40-60, n = 14 (ACL injury 2-10 years prior to study inclusion). Weight-bearing femorotibial cartilages were manually segmented; cartilage T2 and thickness were computed using custom software. Mean and side differences in subregional cartilage thickness, superficial and deep cartilage T2 were compared within and between groups using non-parametric statistics.

RESULTS

Cartilage thickness did not differ within or between groups. Only the side difference in medial femorotibial cartilage thickness was greater in ACL20-30 than in HEA20-30. Deep zone T2 was longer in the ACL-injured than in the contralateral uninjured knees and than in healthy controls, especially in the lateral compartment. Most ACL-injured participants had side differences in femorotibial deep zone T2 above the threshold derived from controls.

CONCLUSION

In the ACL-injured knee, early compositional differences in femorotibial cartilage (T2) appear to occur in the deep zone and precede cartilage thickness loss. These results suggest that monitoring laminar T2 after ACL injury may be useful in diagnosing and monitoring early articular cartilage changes.

The mechanical properties measurement could be affected by forceps: a technical note on sampling human annulus fibrosus

PURPOSE

To compare the mechanical properties of human annulus fibrosus obtained by forceps versus bistoury and observe whether the measurement could be affected by forceps sampling method.

METHODS

In this study, the mechanical properties of the the extracellular matrix (ECM) of human annulus fibrosus, including elastic modulus and stiffness, were investigated using atomic force microscope (AFM). Tissue was obtained from patients during operation using a bistoury or nucleus pulposus forceps. Tissues obtained with the nucleus pulposus forceps were considered as the forceps group and those obtained with a bistoury were considered as the bistoury group.

RESULTS

There was no significant difference observed between the forceps and bistoury group according to histological staining. The elastic modulus of the forceps group was 0.41 ± 0.08 MPa, and that of bistoury group was 0.53 ± 0.13 MPa, and the difference between the two groups was statistically significant (p < 0.05). The stiffness of the forceps group was 0.024 ± 0.003 N/m, and that of the bistoury group was 0.037 ± 0.003 N/m, and the difference between the two groups was statistically significant (p < 0.05).

CONCLUSION

The results indicate that the forceps sampling method has a substantial negative effect on the micromechanical properties of the ECM of the annulus fibrosus. Bistoury sampling method is recommended as the experimental subject for exploring the micromechanics mechanisms of cervical degenerative disease.

Electrohydrodynamic Direct-Writing Micro/Nanofibrous Architectures: Principle, Materials, and Biomedical Applications

Electrohydrodynamic (EHD) direct-writing has recently gained attention as a highly promising additive manufacturing strategy for fabricating intricate micro/nanoscale architectures. This technique is particularly well-suited for mimicking the extracellular matrix (ECM) present in biological tissue, which serves a vital function in facilitating cell colonization, migration, and growth. The integration of EHD direct-writing with other techniques has been employed to enhance the biological performance of scaffolds, and significant advancements have been made in the development of tailored scaffold architectures and constituents to meet the specific requirements of various biomedical applications. Here, a comprehensive overview of EHD direct-writing is provided, including its underlying principles, demonstrated materials systems, and biomedical applications. A brief chronology of EHD direct-writing is provided, along with an examination of the observed phenomena that occur during the printing process. The impact of biomaterial selection and architectural topographic cues on biological performance is also highlighted. Finally, the major limitations associated with EHD direct-writing are discussed.

Advancements in Engineering Tetrahedral Framework Nucleic Acids for Biomedical Innovations

Tetrahedral framework nucleic acids (tFNAs) are renowned for their controllable self-assembly, exceptional programmability, and excellent biocompatibility, which have led to their widespread application in the biomedical field. Beyond these features, tFNAs demonstrate unique chemical and biological properties including high cellular uptake efficiency, structural bio-stability, and tissue permeability, which are derived from their distinctive 3D structure. To date, an extensive range of tFNA-based nanostructures are intelligently designed and developed for various biomedical applications such as drug delivery, gene therapy, biosensing, and tissue engineering, among other emerging fields. In addition to their role in drug delivery systems, tFNAs also possess intrinsic properties that render them highly effective as therapeutic agents in the treatment of complex diseases, including arthritis, neurodegenerative disorders, and cardiovascular diseases. This dual functionality significantly enhances the utility of tFNAs in biomedical research, presenting valuable opportunities for the development of next-generation medical technologies across diverse therapeutic and diagnostic platforms. Consequently, this review comprehensively introduces the latest advancements of tFNAs in the biomedical field, with a focus on their benefits and applications as drug delivery nanoplatforms, and their inherent capabilities as therapeutic agents. Furthermore, the current limitations, challenges, and future perspectives of tFNAs are explored.

Strategies to engineer articular cartilage with biomimetic zonal features: a review

Articular cartilage (AC) is a highly specialized tissue with restricted ability for self-regeneration, given its avascular and acellular nature. Although a considerable number of surgical treatments is available for the repair, reconstruction, and regeneration of AC defects, most of them do not prioritize the development of engineered cartilage with zonal stratification derived from biomimetic biochemical, biomechanical and topographic cues. In the absence of these zonal elements, engineered cartilage will exhibit increased susceptibility to failure and will neither be able to withstand the mechanical loading to which AC is subjected nor will it integrate well with the surrounding tissue. In this regard, new breakthroughs in the development of hierarchical stratified engineered cartilage are highly sought after. Initially, this review provides a comprehensive analysis of the composition and zonal organization of AC, aiming to enhance our understanding of the significance of the structure of AC for its function. Next, we direct our attention towards the existing in vitro and in vivo studies that introduce zonal elements in engineered cartilage to elicit appropriate AC regeneration by employing tissue engineering strategies. Finally, the advantages, challenges, and future perspectives of these approaches are presented.

Acute responses and recovery in the femoral cartilage morphology following running and cool-down protocols

This study compared the immediate effects of two common post-exercise cool-down methods to a control condition on subsequent morphologic change in femoral cartilage and vascular response in the posterior tibial artery after running. Sixteen healthy young males (23.6 ± 2.2 years, 172.8 ± 4.9 cm, 72.2 ± 7.1 kg) visited the laboratory during three separate sessions and performed 30-min of treadmill running (7.5 km/h for the initial 5-min, followed 8.5 km/h for 25-min). After running, participants experienced one of three 30-min cool-down protocols: active cool-down, cold application, or control (seated rest with their knee fully extended), in a counterbalanced order. Ultrasonographic assessments of femoral cartilage thickness (intercondylar, lateral, and medial) and posterior tibial artery blood flow were compared. To test condition effects over time, two-way analysis of variances and Tukey tests were used (p < 0.05) with Cohen's d effect sizes (ES). There was no condition by time interaction in femoral cartilage thickness (intercondylar: F30,705 = 0.91, p = 0.61; lateral: F30,705 = 1.24, p = 0.18; medial: F30,705 = 0.49, p = 0.99). Regardless of time (condition effect: F2,705 > 3.24, p < 0.04 for all tests), femoral cartilage in the cold application condition was thicker than the control condition (intercondylar: p = 0.01, ES = 0.16; lateral: p < 0.0001, ES = 0.24; medial: p = 0.04. ES = 0.16). Regardless of condition (time effect: F15,705 > 10.31, p < 0.0001 for all tests), femoral cartilage thickness was decreased after running (intercondylar: p < 0.0001, ES = 1.37; lateral: p < 0.0001, ES = 1.58; medial: p < 0.0001, ES = 0.81) and returned to baseline levels within 40-min (intercondylar: p = 0.09; lateral: p = 0.64; medial: p = 0.26). Blood flow volume was different (condition × time: F30,705 = 2.36, p < 0.0001) that running-induced blood flow volume was maintained for 30-min for the active cool-down condition (p < 0.0001, ES = 1.64), whereas it returned to baseline levels within 10-min for other conditions (cold application: p = 0.67; control: p = 0.62). Neither blood flow nor temperature had a significant impact on the recovery in femoral cartilage after running.

Use of Hydrogels in Regenerative Medicine: Focus on Mechanical Properties

Bioengineered materials represent an innovative option to support the regenerative processes of damaged tissues, with the final objective of creating a functional environment closely mimicking the native tissue. Among the different available biomaterials, hydrogels represent the solution of choice for tissue regeneration, thanks to the easy synthesis process and the highly tunable physical and mechanical properties. Moreover, hydrogels are biocompatible and biodegradable, able to integrate in biological environments and to support cellular interactions in order to restore damaged tissues' functionality. This review offers an overview of the current knowledge concerning hydrogel synthesis and characterization and of the recent achievements in their experimental use in supporting skin, bone, cartilage, and muscle regeneration. The currently available in vitro and in vivo results are of great interest, highlighting the need for carefully designed and controlled preclinical studies and clinical trials to support the transition of these innovative biomaterials from the bench to the bedside.

Key roles of the superficial zone in articular cartilage physiology, pathology, and regeneration

ABSTRACT

The superficial zone (SFZ) of articular cartilage is an important interface that isolates deeper zones from the microenvironment of the articular cavity and is directly exposed to various biological and mechanical stimuli. The SFZ is not only a crucial structure for maintaining the normal physiological function of articular cartilage but also the earliest site of osteoarthritis (OA) cartilage degeneration and a major site of cartilage progenitor cells, suggesting that the SFZ might represent a key target for the early diagnosis and treatment of OA. However, to date, SFZ research has not received sufficient attention, accounting for only about 0.58% of cartilage tissue research. The structure, biological composition, function, and related mechanisms of the SFZ in the physiological and pathological processes of articular cartilage remain unclear. This article reviews the key role of the SFZ in articular cartilage physiology and pathology and focuses on the characteristics of SFZ in articular cartilage degeneration and regeneration in OA, aiming to provide researchers with a systematic understanding of the current research status of the SFZ of articular cartilage, hoping that scholars will give more attention to the SFZ of articular cartilage in the future.

In vitro chondrogenic potential of marine biocomposite hydrogel construct for cartilage tissue engineering

Cartilage tissue engineering (CTE) is a field of regenerative medicine focused on constructing ideal substitutes for injured cartilage by effectively combining cells, scaffolds, and stimulatory factors. In vitro CTE employing chondrocytes and biopolymer-based hydrogels has the potential to repair damaged cartilage. In this research, primary chondrocytes were extracted from the rib cartilage of rats and seeded on a hydrogel construct named HACF, which is made from hydroxyapatite, alginate, chitosan, and fucoidan. We then evaluated in vitro chondrogenesis on HACF cartilage construct. The results revealed that the primary chondrocytes were successfully isolated from rat rib cartilage by collagenase D digestion and HACF cartilage construct was effectively synthesized. Chondrocyte viability and its differentiation inside the scaffold HACF were determined by MTT assay, NRU assay, live/dead assay, DAPI nuclear staining, flow cytometry analysis (FCA), mRNA expression studies, and quantification of extracellular matrix components in the HACF scaffold. The findings indicated excellent chondrocyte viability within the HACF scaffold, with no noticeable changes in morphology. Apoptosis was not detected in the chondrocytes cultured on these hydrogels, as confirmed by DAPI staining, live/dead assay, and FCA. This demonstrates that the cells were capable of proliferating, dividing, multiplying, and maintaining their integrity on HACF scaffold. The results also showed more collagen deposition and glycosaminoglycan synthesis showing the good health of chondrocytes on the HACF construct. It indicates that HACF is an ideal scaffold supporting stable cartilage matrix production, highlighting its suitability for cartilage tissue engineering.

Delivery Strategies of Growth Factors in Cartilage Tissue Engineering

Cartilage plays an important role in supporting soft tissues, reducing joint friction, and distributing pressure. However, its self-repair capacity is limited due to the lack of blood vessels, nerves, and lymphatic systems. Tissue engineering offers a potential solution to promote cartilage regeneration by combining scaffolds, seed cells, and growth factors. Among these, growth factors play a critical role in regulating cell proliferation, differentiation, and extracellular matrix remodeling. However, their instability, susceptibility to degradation and potential side effects limit their effectiveness. This article reviews the main growth factors used in cartilage tissue engineering and their delivery strategies, including affinity-based delivery, carrier-assisted delivery, stimuli-responsive delivery, spatial structure-based delivery, and cell system-based delivery. Each method shows unique advantages in enhancing the delivery efficiency and specificity of growth factors but also faces challenges such as cost, biocompatibility, and safety. Future research needs to further optimize these strategies to achieve more efficient, safe, and economical delivery of growth factors, thereby advancing the clinical application of cartilage tissue engineering.

Molecules in Motion: Unravelling the Dynamics of Vascularization Control in Tissue Engineering

Significant progress has been made in tissue engineering (TE), aiming at providing personalized solutions and overcoming the current limitations of traditional tissue and organ transplantation. 3D bioprinting has emerged as a transformative technology in the field, able to mimic key properties of the natural architecture of the native tissues. However, most successes in the area are still limited to avascular or thin tissues due to the difficulties in controlling the vascularization of the engineered tissues. To address this issue, several molecules, biomaterials, and cells with pro- and anti-angiogenic potential have been intensively investigated. Furthermore, different bioreactors capable to provide a dynamic environment for in vitro vascularization control have been also explored. The present review summarizes the main molecules and TE strategies used to promote and inhibit vascularization in TE, as well as the techniques used to deliver them. Additionally, it also discusses the current challenges in 3D bioprinting and in tissue maturation to control in vitro/in vivo vascularization. Currently, this field of investigation is of utmost importance and may open doors for the design and development of more precise and controlled vascularization strategies in TE.

Development and evaluation of 3D composite scaffolds with piezoelectricity and biofactor synergy for enhanced articular cartilage regeneration

The inability of articular cartilage to self-repair following injuries frequently precipitates osteoarthritis, profoundly affecting patients' quality of life. Given the limitations inherent in current clinical interventions, an urgent need exists for more effective cartilage regeneration methodologies. Previous studies have underscored the potential of electrical stimulation in cartilage repair, thus motivating the investigation of innovative strategies. The present study introduces a three-dimensional scaffold fabricated through a composite technique that leverages the synergy between piezoelectricity and biofactors to enhance cartilage repair. This scaffold is composed of polylactic acid (PLLA) and barium titanate (BT) for piezoelectric stimulation and at the bottom with a collagen-coated layer infused with fibroblast growth factor-18 (FGF-18) for biofactor delivery. Designed to emulate the properties of natural cartilage, the scaffold enables controlled generation of piezoelectric charges and the sustained release of biofactors. In vitro tests confirm that the scaffold promotes chondrocyte proliferation, matrix hyperplasia, cellular migration, and the expression of genes associated with cartilage formation. Moreover, in vivo studies on rabbits have illustrated its efficacy in catalyzing the in situ regeneration of articular cartilage defects and remodeling the extracellular matrix. This innovative approach offers significant potential for enhancing cartilage repair and holds profound implications for regenerative medicine.

Electrical stimulation for cartilage tissue engineering - A critical review from an engineer's perspective

Cartilage has a limited intrinsic healing capacity. Hence, cartilage degradation and lesions pose a huge clinical challenge, particularly in an ageing society. Osteoarthritis impacts a significant number of the population and requires the development of repair and tissue engineering methods for hyaline articular cartilage. In this context, electrical stimulation has been investigated for more than 50 years already. Yet, no well-established clinical therapy to treat osteoarthritis by means of electrical stimulation exists. We argue that one reason is the lack of replicability of electrical stimulation devices from a technical perspective together with lacking hypotheses of the biophysical mechanism. Hence, first, the electrical stimulation studies reported in the context of cartilage tissue engineering with a special focus on technical details are summarized. Then, an experimental and numerical approach is discussed to make the electrical stimulation experiments replicable. Finally, biophysical hypotheses have been reviewed on the interaction of electric fields and cells that are relevant for cartilage tissue engineering. With that, the aim is to inspire future research to enable clinical electrical stimulation therapies to fight osteoarthritis.

Postprocedure protocols after intraarticular orthobiologic injections-A scoping review

Osteoarthritis is a chronic degenerative disease affecting 500 million people throughout the world. Although orthobiologics have been proposed as a symptom and disease modifying treatment for osteoarthritis, there is significant heterogeneity in the results of the orthobiologic procedures in the literature. One possible explanation for the heterogeneity is the inconsistent reporting and description of the postorthobiologic protocols. The goal of this scoping review was to identify the current literature on the use of orthobiologics for osteoarthritis and critically evaluate the postorthobiologic protocol within these studies. A total of 200 identified studies met inclusion criteria. In 37.5% of studies, there was no mention of a postorthobiologic protocol. Of the 125 studies that did mention a postorthobiologic protocol, only 38.4% included a rehabilitation protocol, 21.6% included postprocedure weightbearing restrictions, and only 2 (1.6%) mentioned the use of durable medical equipment. Nonsteroidal anti-inflammatory drug restriction was described in 91.2% of study protocols, whereas corticosteroids and immunosuppressants were restricted in 84.8% and 19.2% of protocols, respectively. The results of this scoping review demonstrate the inconsistent reporting of postorthobiologic procedure protocols in the literature, with significant heterogeneity in those that are described. These findings highlight the need for future research and improved reporting of postorthobiologic protocols.

Advancing Cartilage Tissue Engineering: A Review of 3D Bioprinting Approaches and Bioink Properties

Articular cartilage is crucial in human physiology, and its degeneration poses a significant public health challenge. While recent advancements in 3D bioprinting and tissue engineering show promise for cartilage regeneration, there remains a gap between research findings and clinical application. This review critically examines the mechanical and biological properties of hyaline cartilage, along with current 3D manufacturing methods and analysis techniques. Moreover, we provide a quantitative synthesis of bioink properties used in cartilage tissue engineering. After screening 181 initial works, 33 studies using extrusion bioprinting were analyzed and synthesized, presenting results that indicate the main materials, cells, and methods utilized for mechanical and biological evaluation. Altogether, this review motivates the standardization of mechanical analyses and biomaterial assessments of 3D bioprinted constructs to clarify their chondrogenic potential.

Bridging biomimetic and bioenergetics scaffold: Cellulose-graphene oxide-arginine functionalized aerogel for stem cell-mediated cartilage repair

The avascular nature of cartilage tissue limits inherent regenerative capacity to counter any damage and this has become a substantial burden to the health of individuals. As a result, there is a high demand to repair and regenerate cartilage. Existing tissue engineering approaches for cartilage regeneration typically produce either microporous or nano-fibrous scaffolds lacking the desired biological outcome due to lack of biomimetic dual architecture of microporous construct with nano-fibrous interconnected structures like the native cartilage. Most of these scaffolds also fail to suppress ROS generation and provide sustained bioenergetics to cells, resulting in the loss of metabolic activity under avascular microenvironment of cartilage. A dual architecture microporous construct with nano-fibrous interconnected network of cellulose aerogel reinforced with arginine-coated graphene oxide (CNF-GO-Arg aerogel) was developed for cartilage regeneration. The designed dual-architectured CNF-GO-Arg aerogel using dual ice templating assembly demonstrates 80 % strain recovery ability under compression. The release of Arginine from CNF-GO-Arg aerogel supported 41 % reduction in intracellular ROS activity and promoted chondrogenic differentiation of hMSCs by shifting mitochondrial bioenergetics towards oxidative phosphorylation indicated by JC-1 dye staining. Overall developed CNF-GO-Arg aerogel provided multifunctionality via biomimetic morphology, cellular bioenergetics, and suppressed ROS generation to address the need for regeneration of cartilage.

Sex does not influence the long-term outcome of matrix-assisted autologous chondrocyte transplantation

PURPOSE

Regenerative techniques for articular cartilage lesions demonstrated heterogeneous clinical results. Several factors may influence the outcome, with sex being one of the most debated. This study aimed at quantifying the long-term influence of sex on the clinical outcome obtained with a regenerative procedure for knee chondral lesions.

METHODS

Matrix-assisted autologous chondrocyte transplantation (MACT) was used to treat 235 knees which were prospectively evaluated with the International Knee Documentation Committee (IKDC), EuroQol visual analogue scale, and Tegner scores at 14-year mean follow-up. A multilevel analysis was performed with the IKDC subjective scores standardised according to the age/sex category of each patient and/or the selection of a match-paired subgroup to compare homogeneous men and women patients.

RESULTS

At 14 years, men and women showed a failure rate of 10.7% and 28.8%, respectively (p < 0.0005). An overall improvement was observed in both sexes. Women had more patellar lesions and men more condylar lesions (p = 0.001), and the latter also presented a higher preinjury activity level (p < 0.0005). Men had significantly higher IKDC subjective scores at all follow-ups (at 14 years: 77.2 ± 18.9 vs. 62.8 ± 23.1; p < 0.0005). However, the analysis of homogeneous match-paired populations of men and women, with standardised IKDC subjective scores, showed no differences between men and women (at 14 years: -1.6 ± 1.7 vs. -1.9 ± 1.6).

CONCLUSION

Men and women treated with MACT for knee chondral lesions presented a significant improvement and stable long-term results. When both sexes are compared with homogeneous match-paired groups, they have similar results over time. However, women present more often unfavourable lesion patterns, which proved more challenging in terms of long-term outcome after MACT.

LEVEL OF EVIDENCE

Level II.

Multiscale-temporal Feature Extraction and boundary confusion alleviation for VAG-based fine-grained multi-grade osteoarthritis deterioration monitoring

BACKGROUND AND OBJECTIVE

Multi-grade osteoarthritis (OA) deterioration monitoring in the daily paradigm using Vibroarthrography (VAG) is very challenging due to two difficulties: (1) the composition of VAG signals is complex in the daily paradigm where friction is intensified because of weight-bearing movements. (2) VAG signal samples near the decision boundary of adjacent deterioration grades are easy to be misclassified. The majority of existing works only focus on the binary classification of OA, providing inadequate assistance in instructing physicians to develop treatment plans based on the presence or absence of OA. Thus, we propose a novel framework for fine-grained multi-grade OA deterioration monitoring in the daily paradigm.

METHODS

We propose an end-to-end deep learning framework termed Fine-grained Multi-grade OA Deterioration Monitor (FMOADM), which consists of Multiscale-temporal Feature Extraction (MTFE) and Confusion-Free Master-Slave (CF-MS) Classification. Specifically, MTFE is adopted to extract multiscale-temporal discriminative features from the complicated VAG signals. And center loss is introduced by CF-MS to alleviate confusion at the boundary of adjacent deterioration grades in the feature space. Meanwhile, a master-slave structure is proposed for further fine-grained classification, where the master classifier integrates a channel attention mechanism and the slave classifier is designed to update MTFE parameters. As a result, the proposed method ensures fine-grained multi-grade OA monitoring performance via multiscale-temporal discriminative features and boundary confusion alleviation.

RESULTS

Experimental results on the VAG-OA dataset demonstrate that our framework outperforms counterpart methods in the daily paradigm. The proposed framework achieved 78% in precision, obtaining an 8% improvement over the state-of-the-art method.

CONCLUSION

The proposed framework benefits efficient multi-grade OA deterioration monitoring, empowering physicians to develop treatment plans based on fine-grained monitoring results. It takes knee joint health monitoring in daily activities a step further toward feasible.

Boosting chondrocyte bioactivity with ultra-sulfated glycopeptide supramolecular polymers

Although autologous chondrocyte transplantation can be effective in articular cartilage repair, negative side effects limit the utility of the treatment, such as long recovery times, poor engraftment or chondrogenic dedifferentiation, and cell leakage. Peptide-based supramolecular polymers have emerged as promising bioactive systems to promote tissue regeneration through cell signaling and dynamic behavior. We report here on the development of a series of glycopeptide amphiphile supramolecular nanofibers with chondrogenic bioactivity. These supramolecular polymers were found to have the ability to boost TGFβ-1 signaling by displaying galactosamine moieties with differing degrees of sulfation on their surfaces. We were also able to encapsulate chondrocytes with these nanostructures as single cells without affecting viability and proliferation. Among the monomers tested, assemblies of trisulfated glycopeptides led to elevated expression of chondrogenic markers relative to those with lower degrees of sulfation that mimic chondroitin sulfate repeating units. We hypothesize the enhanced bioactivity is rooted in specific interactions of the supramolecular assemblies with TGFβ-1 and its consequence on cell signaling, which may involve elevated levels of supramolecular motion as a result of high charge in trisulfated glycopeptide amphiphiles. Our findings suggest that supramolecular polymers formed by the ultra-sulfated glycopeptide amphiphiles could provide better outcomes in chondrocyte transplantation therapies for cartilage regeneration. STATEMENT OF SIGNIFICANCE: This study prepares glycopeptide amphiphiles conjugated at their termini with chondroitin sulfate mimetic residues with varying degrees of sulfation that self-assemble into supramolecular nanofibers in aqueous solution. These supramolecular polymers encapsulate chondrocytes as single cells through intimate contact with cell surface structures, forming artificial matrix that can localize the growth factor TGFβ-1 in the intercellular environment. A high degree of sulfation on the glycopeptide amphiphile is found to be critical in elevating chondrogenic cellular responses that supersede the efficacy of natural chondroitin sulfate. This work demonstrates that supramolecular assembly of a unique molecular structure designed to mimic chondroitin sulfate successfully boosts chondrocyte bioactivity by single cell encapsulation, suggesting a new avenue implementing chondrocyte transplantation with supramolecular nanomaterials for cartilage regeneration.

Reduced Cell Migration in Human Chondrocyte Sheets Increases Tissue Stiffness and Cartilage Protein Production

BACKGROUND

Chondrogenic differentiation medium (CDM) is usually used to maintain chondrogenic activity during chondrocyte sheet production. However, tissue qualities remain to be determined as to what factors improve cell functions. Moreover, the relationship between CDM and cell migration proteins has not been reported.

METHOD

In this study, the effect of CDM on the behavior of chondrocyte sheets was investigated. Structural analysis, mechanical testing and proteomics were performed to observe tissue qualities. The relationship between CDM and cell migration proteins were investigated using time-lapse observations and bioinformatic analysis.

RESULTS

During 48 h, CDM affected the chondrocyte behaviors by reducing cell migration. Compared to the basal medium, CDM impacted the contraction of monolayered chondrocyte sheets. At day 7, the contracted sheets increased tissue thickness and improved tissue stiffness. Cartilage specific proteins were also upregulated. Remarkedly, the chondrocyte sheets in CDM displayed downregulated proteins related to cell migration. Bioinformatic analysis revealed that TGFβ1 was shown to be associated with cartilage functions and cell migration. Pathway analysis of chondrocyte sheets in CDM also revealed the presence of a TGFβ pathway without activating actin production, which might be involved in synthesizing cartilage-specific proteins. Cell migration pathway showed MAPK signaling in both cultures of the chondrocyte sheets.

CONCLUSION

Reduced cell migration in the chondrocyte sheet affected the tissue quality. Using CDM, TGFβ1 might trigger cartilage protein production through the TGFβ pathway and be involved in cell migration via the MAPK signaling pathway. Understanding cell behaviors and their protein expression would be beneficial for developing high-quality tissue-engineered cartilage.

Advancing Synthetic Hydrogels through Nature-Inspired Materials Chemistry

Synthetic extracellular matrix (ECM) mimics that can recapitulate the complex biochemical and mechanical nature of native tissues are needed for advanced models of development and disease. Biomedical research has heavily relied on the use of animal-derived biomaterials, which is now impeding their translational potential and convoluting the biological insights gleaned from in vitro tissue models. Natural hydrogels have long served as a convenient and effective cell culture tool, but advances in materials chemistry and fabrication techniques now present promising new avenues for creating xenogenic-free ECM substitutes appropriate for organotypic models and microphysiological systems. However, significant challenges remain in creating synthetic matrices that can approximate the structural sophistication, biochemical complexity, and dynamic functionality of native tissues. This review summarizes key properties of the native ECM, and discusses recent approaches used to systematically decouple and tune these properties in synthetic matrices. The importance of dynamic ECM mechanics, such as viscoelasticity and matrix plasticity, is also discussed, particularly within the context of organoid and engineered tissue matrices. Emerging design strategies to mimic these dynamic mechanical properties are reviewed, such as multi-network hydrogels, supramolecular chemistry, and hydrogels assembled from biological monomers.

Advances in the Development of Granular Microporous Injectable Hydrogels with Non-spherical Microgels and Their Applications in Tissue Regeneration

Granular microporous hydrogels are emerging as effective biomaterial scaffolds for tissue engineering due to their improved characteristics compared to traditional nanoporous hydrogels, which better promote cell viability, cell migration, cellular/tissue infiltration, and tissue regeneration. Recent advances have resulted in the development of granular hydrogels made of non-spherical microgels, which compared to those made of spherical microgels have higher macroporosity, more stable mechanical properties, and better ability to guide the alignment and differentiation of cells in anisotropic tissue. The development of these hydrogels as an emerging research area is attracting increasing interest in regenerative medicine. This review first summarizes the fabrication techniques available for non-spherical microgels with different aspect-ratios. Then, it introduces the development of granular microporous hydrogels made of non-spherical microgels, their physicochemical characteristics, and their applications in tissue regeneration. The limitations and future outlook of research on microporous granular hydrogels are also critically discussed.

Collagen as the extracellular matrix biomaterials in the arena of medical sciences

Collagen is a multipurpose material that has several applications in the health care, dental care, and pharmaceutical industries. Crosslinked compacted solids or lattice-like gels can be made from collagen. Biocompatibility, biodegradability, and wound-healing properties make collagen a popular scaffold material for cardiovascular, dentistry, and bone tissue engineering. Due to its essential role in the control of several of these processes, collagen has been employed as a wound-healing adjunct. It forms a major component of the extracellular matrix and regulates wound healing in its fibrillar or soluble forms. Collagen supports cardiovascular and other soft tissues. Oral wounds have been dressed with resorbable forms of collagen for closure of graft and extraction sites, and to aid healing. This present review is concentrated on the use of collagen in bone regeneration, wound healing, cardiovascular tissue engineering, and dentistry.

Assessment of whole cartilage surface damage in an osteoarthritis rat model: The Cartilage Roughness Score (CRS) utilizing microcomputed tomography

OBJECTIVE

This study aims to establish an accurate and robust imaging biomarker for pre-clinical osteoarthritis (OA) research, focusing on early detection of cartilage surface degeneration.

METHOD

Using 50 male Wistar rats, this study aims to observe Collagenase-induced OA (CIOA) progression through microcomputed x-ray tomography (µCT), histopathological analysis, and gait analysis. A novel parameter, Cartilage Roughness Score (CRS), was developed for assessing cartilage structural damage from µCT data and was compared with histological OARSI Cartilage Degeneration Score (OARSI CDS). Additionally, as CRS maps the full surface, it was used to simulate the level of uncertainty in histological sampling.

RESULTS

CRS and OARSI CDS have a linear relationship. CRS for healthy cartilage is 2.75 (95% CI: 1.14-4.36), and with every 1 unit increase in OARSI, CRS is expected to increase by 0.64 (95% CI: 0.35-0.92). Cartilage degeneration due to CIOA was evident in both histopathological scoring and CRS. However, only CRS was sensitive enough to show consistent damage progression from day 10 to day 60. Furthermore, our simulation for histological sampling suggested that up to 16 coronal slices with 200 µm spacing would be needed to accurately represent the full extent of cartilage surface degeneration in a slice-wise manner. Gait analysis showed changes solely at eight days post-collagenase injection, normalizing by day 60.

CONCLUSION

The CRS analysis method emerges as a robust tool for cartilage surface damage assessment. This study demonstrates the potential of automatic 3D analysis over the traditional 2D histological approach when evaluating cartilage surface damage.

Integrative cartilage repair using acellular allografts for engineered structure and surface lubrication in vivo

The repair of articular cartilage after damage is challenging, and decellularized tissue offers a possible treatment option to promote regeneration. Here, we show that acellular osteochondral allografts improve integrative cartilage repair compared to untreated defects after 6 months in an ovine model. Functional measures of intratissue strain/structure assessed by MRI demonstrate similar biomechanics of implants and native cartilage. Compared to native tissue and defects, the structure, composition, and tribology of acellular allografts preserve surface roughness and lubrication, material properties under compression and relaxation, compositional ratios of collagen:glycosaminoglycan and collagen:phosphate, and relative composition of types I/II collagen. While high cellularity was observed in bone regions and integration zones between cartilage-allografts, recellularization of chondral implants was inconsistent, with cell migration typically less than ~750 µm into the dense decellularized tissue, possibly limiting long-term cellular maintenance. Our results demonstrate the structural and biomechanical efficacy of acellular allografts for at least six months in vivo.

A human organoid drug screen identifies α2-adrenergic receptor signaling as a therapeutic target for cartilage regeneration

Directed differentiation of stem cells toward chondrogenesis in vitro and in situ to regenerate cartilage suffers from off-target differentiation and hypertrophic tendency. Here, we generated a cartilaginous organoid system from human expanded pluripotent stem cells (hEPSCs) carrying a COL2A1mCherry and COL10A1eGFP double reporter, enabling real-time monitoring of chondrogenesis and hypertrophy. After screening 2,040 FDA-approved drugs, we found that α-adrenergic receptor (α-AR) antagonists, especially phentolamine, stimulated chondrogenesis but repressed hypertrophy, while α2-AR agonists reduced chondrogenesis and induced hypertrophy. Phentolamine prevented cartilage degeneration in hEPSC cartilaginous organoid and human cartilage explant models and stimulated microfracture-activated endogenous skeletal stem cells toward hyaline-like cartilage regeneration without fibrotic degeneration in situ. Mechanistically, α2-AR signaling induced hypertrophic degeneration via cyclic guanosine monophosphate (cGMP)-dependent secretory leukocyte protease inhibitor (SLPI) production. SLPI-deleted cartilaginous organoid was degeneration resistant, facilitating large cartilage defect healing. Ultimately, targeting α2-AR/SLPI was a promising and clinically feasible strategy to regenerate cartilage via promoting chondrogenesis and repressing hypertrophy.

Loss of collagen content is localized near cartilage lesions on the day of injurious loading and intensified on day 12

Joint injury can lead to articular cartilage damage, excessive inflammation, and post-traumatic osteoarthritis (PTOA). Collagen is an essential component for cartilage function, yet current literature has limited understanding of how biochemical and biomechanical factors contribute to collagen loss in injured cartilage. Our aim was to investigate spatially dependent changes in collagen content and collagen integrity of injured cartilage, with an explant model of early-stage PTOA. We subjected calf knee cartilage explants to combinations of injurious loading (INJ), interleukin-1α-challenge (IL) and physiological cyclic loading (CL). Using Fourier transform infrared microspectroscopy, collagen content (Amide I band) and collagen integrity (Amide II/1338 cm-1 ratio) were estimated on days 0 and 12 post-injury. We found that INJ led to lower collagen content near lesions compared to intact regions on day 0 (p < 0.001). On day 12, near-lesion collagen content was lower compared to day 0 (p < 0.05). Additionally, on day 12, INJ, IL, and INJ + IL groups exhibited lower collagen content along most of tissue depth compared to free-swelling control group (p < 0.05). CL groups showed higher collagen content along most of tissue depth compared to corresponding groups without CL (p < 0.05). Immunohistochemical analysis revealed higher MMP-1 and MMP-3 staining intensities localized within cell lacunae in INJ group compared to CTRL group on day 0. Our results suggest that INJ causes rapid loss of collagen content near lesions, which is intensified on day 12. Additionally, CL could mitigate the loss of collagen content at intact regions after 12 days.

Significance of Necroptosis in Cartilage Degeneration

Cartilage, a critical tissue for joint function, often degenerates due to osteoarthritis (OA), rheumatoid arthritis (RA), and trauma. Recent research underscores necroptosis, a regulated form of necrosis, as a key player in cartilage degradation. Unlike apoptosis, necroptosis triggers robust inflammatory responses, exacerbating tissue damage. Key mediators such as receptor-interacting serine/threonine-protein kinase-1 (RIPK1), receptor-interacting serine/threonine-protein kinase-3(RIPK3), and mixed lineage kinase domain-like (MLKL) are pivotal in this process. Studies reveal necroptosis contributes significantly to OA and RA pathophysiology, where elevated RIPK3 and associated proteins drive cartilage degradation. Targeting necroptotic pathways shows promise; inhibitors like Necrostatin-1 (Nec-1), GSK'872, and Necrosulfonamide (NSA) reduce necroptotic cell death, offering potential therapeutic avenues. Additionally, autophagy's role in mitigating necroptosis-induced damage highlights the need for comprehensive strategies addressing multiple pathways. Despite these insights, further research is essential to fully understand necroptosis' mechanisms and develop effective treatments. This review synthesizes current knowledge on necroptosis in cartilage degeneration, aiming to inform novel therapeutic approaches for OA, RA, and trauma.

Lubricant Strategies in Osteoarthritis Treatment: Transitioning from Natural Lubricants to Drug Delivery Particles with Lubricant Properties

Osteoarthritis (OA) is a debilitating joint disease characterized by cartilage degradation, leading to pain and functional impairment. A key contributor to OA progression is the decline in cartilage lubrication. In physiological conditions, synovial fluid (SF) macromolecules like hyaluronic acid (HA), phospholipids, and lubricin play a crucial role in the boundary lubrication of articular cartilage. In early OA, cartilage damage triggers inflammation, altering SF composition and compromising the lubrication layer. This increases friction between mating interfaces, worsening cartilage degradation and local inflammation. Therefore, early-stage restoration of lubrication (by injecting in the joint different classes of compounds and formulations) could alleviate, and potentially reverse, OA progression. In the light of this, a broad variety of lubricants have been investigated for their ability to reduce friction in OA joints and promote cartilage repair in clinical and preclinical studies. This review examines recent advancements in lubricant-based therapy for OA, focusing on natural, bioinspired, and alternative products. Starting from the currently applied therapy, mainly based on natural lubricants as HA, we will present their modified versions, either in hydrogel form or with specific biomimetic moieties with the aim of reducing their clearance from the joint and of enhancing their lubricating properties. Finally, the most advanced and recent formulation, represented by alternative strategies, will be proposed. Particular emphasis will be placed on those ones involving new types of hydrogels, microparticles, nanoparticles, and liposomes, which are currently under investigation in preclinical studies. The potential application of particles and liposomes could foster the transition from natural lubricants to Drug Delivery Systems (DDSs) with lubricant features; transition which could provide more complete OA treatments, by simultaneously providing lubrication replacement and sustained release of different payloads and active agents directly at the joint level. Within each category, we will examine relevant preclinical studies, highlighting challenges and future prospects.

Application of polydopamine-modified triphasic PLA/PCL-PLGA/Mg(OH)2-velvet antler polypeptides scaffold loaded with fibrocartilage stem cells for the repair of osteochondral defects

Articular cartilage defects often involve damage to both the cartilage and subchondral bone, requiring a scaffold that can meet the unique needs of each tissue type and establish an effective barrier between the bone and cartilage. In this study, we used 3D printing technology to fabricate a tri-phasic scaffold composed of PLA/PCL-PLGA/Mg(OH)₂, which includes a cartilage layer, an osteochondral interface, and a bone layer. The scaffold was filled with Velvet antler polypeptides (VAP), and its characterization was assessed using compression testing, XRD, FTIR, SEM, fluorescence microscopy, and EDS. In vitro investigation demonstrated that the scaffold not only supported osteogenesis but also promoted chondrogenic differentiation of fibrocartilage stem cells (FCSCs). n vivo experiments showed that the tri-phasic PLA/PCL-PLGA/Mg(OH)2-VAP scaffold together with FCSC, when transplanted to animal models, increased the recovery of osteochondral defects. Those results demonstrate the promising future of illustrated tri-phasic PLA/PCL-PLGA/Mg(OH)2-VAP scaffold loaded with FCSCs as a new bone and cartilage tissue engineering approach for osteochondral defects treatment.

Chondroitin Sulfate for Cartilage Regeneration, Administered Topically Using a Nanostructured Formulation

In the pharmaceutical sector, solid lipid nanoparticles (SLN) are vital for drug delivery incorporating a lipid core. Chondroitin sulfate (CHON) is crucial for cartilage health. It is often used in osteoarthritis (OA) treatment. Due to conflicting results from clinical trials on CHON's efficacy in OA treatment, there has been a shift toward exploring effective topical systems utilizing nanotechnology. This study aimed to optimize a solid lipid nanoparticle formulation aiming to enhance CHON permeation for OA therapy. A 3 × 3 × 2 Design of these experiments determined the ideal parameters: a CHON concentration of 0.4 mg/mL, operating at 20,000 rpm speed, and processing for 10 min for SLN production. Transmission electron microscopy analysis confirmed the nanoparticles' spherical morphology, ensuring crucial uniformity for efficient drug delivery. Cell viability assessments showed no significant cytotoxicity within the tested parameters, indicating a safe profile for potential clinical application. The cell internalization assay indicates successful internalization at 1.5 h and 24 h post-treatment. Biopharmaceutical studies supported SLNs, indicating them to be effective CHON carriers through the skin, showcasing improved skin permeation and CHON retention compared to conventional methods. In summary, this study successfully optimized SLN formulation for efficient CHON transport through pig ear skin with no cellular toxicity, highlighting SLNs' potential as promising carriers to enhance CHON delivery in OA treatment and advance nanotechnology-based therapeutic strategies in pharmaceutical formulations.

Harnessing Peptide-Based Hydrogels for Enhanced Cartilage Tissue Engineering

Cartilage tissue engineering remains a formidable challenge due to its complex, avascular structure and limited regenerative capacity. Traditional approaches, such as microfracture, autografts, and stem cell delivery, often fail to restore functional tissue adequately. Recently, there has been a surge in the exploration of new materials that mimic the extracellular microenvironment necessary to guide tissue regeneration. This review investigates the potential of peptide-based hydrogels as an innovative solution for cartilage regeneration. These hydrogels, formed via supramolecular self-assembly, exhibit excellent properties, including biocompatibility, ECM mimicry, and controlled biodegradation, making them highly suitable for cartilage tissue engineering. This review explains the structure of cartilage and the principles of supramolecular and peptide hydrogels. It also delves into their specific properties relevant to cartilage regeneration. Additionally, this review presents recent examples and a comparative analysis of various peptide-based hydrogels used for cartilage regeneration. The review also addresses the translational challenges of these materials, highlighting regulatory hurdles and the complexities of clinical application. This comprehensive investigation provides valuable insights for biomedical researchers, tissue engineers, and clinical professionals aiming to enhance cartilage repair methodologies.

Enhancing Cartilage Repair: Surgical Approaches, Orthobiologics, and the Promise of Exosomes

Treating cartilage damage is challenging as its ability for self-regeneration is limited. Left untreated, it can progress to osteoarthritis (OA), a joint disorder characterized by the deterioration of articular cartilage and other joint tissues. Surgical options, such as microfracture and cell/tissue transplantation, have shown promise as techniques to harness the body's endogenous regenerative capabilities to promote cartilage repair. Nonetheless, these techniques have been scrutinized due to reported inconsistencies in long-term outcomes and the tendency for the defects to regenerate as fibrocartilage instead of the smooth hyaline cartilage native to joint surfaces. Orthobiologics are medical therapies that utilize biologically derived substances to augment musculoskeletal healing. These treatments are rising in popularity because of their potential to enhance surgical standards of care. More recent developments in orthobiologics have focused on the role of exosomes in articular cartilage repair. Exosomes are nano-sized extracellular vesicles containing cargo such as proteins, lipids, and nucleic acids, and are known to facilitate intercellular communication, though their regenerative potential still needs to be fully understood. This review aims to demonstrate the advancements in cartilage regeneration, highlight surgical and biological treatment options, and discuss the recent strides in understanding the precise mechanisms of action involved.