Physical, Mechanical, and Biological Properties of Fibrin Scaffolds for Cartilage Repair

Connecting impaired fibrinolysis and dyslipidemia

A State of the Art lecture entitled "Connecting Fibrinolysis and Dyslipidemia" was presented at the International Society on Thrombosis and Haemostasis Congress 2023. Hemostasis balances the consequences of blood clotting and bleeding. This balance relies on the proper formation of blood clots, as well as the breakdown of blood clots. The primary mechanism that breaks down blood clots is fibrinolysis, where the fibrin net becomes lysed and the blood clot dissolves. Dyslipidemia is a condition where blood lipid and lipoprotein levels are abnormal. Here, we review studies that observed connections between impaired fibrinolysis and dyslipidemia. We also summarize the different correlations between thrombosis and dyslipidemia in different racial and ethnic groups. Finally, we summarize relevant and new findings on this topic presented during the 2023 International Society on Thrombosis and Haemostasis Congress. More studies are needed to investigate the mechanistic connections between impaired fibrinolysis and dyslipidemia and whether these mechanisms differ in racially and ethnically diverse populations.

Advancements in tissue engineering for articular cartilage regeneration

Articular cartilage injury is a prevalent clinical condition resulting from trauma, tumors, infection, osteoarthritis, and other factors. The intrinsic lack of blood vessels, nerves, and lymphatic vessels within cartilage tissue severely limits its self-regenerative capacity after injury. Current treatment options, such as conservative drug therapy and joint replacement, have inherent limitations. Achieving perfect regeneration and repair of articular cartilage remains an ongoing challenge in the field of regenerative medicine. Tissue engineering has emerged as a key focus in articular cartilage injury research, aiming to utilize cultured and expanded tissue cells combined with suitable scaffold materials to create viable, functional tissues. This review article encompasses the latest advancements in seed cells, scaffolds, and cytokines. Additionally, the role of stimulatory factors including cytokines and growth factors, genetic engineering techniques, biophysical stimulation, and bioreactor systems, as well as the role of scaffolding materials including natural scaffolds, synthetic scaffolds, and nanostructured scaffolds in the regeneration of cartilage tissues are discussed. Finally, we also outline the signaling pathways involved in cartilage regeneration. Our review provides valuable insights for scholars to address the complex problem of cartilage regeneration and repair.

PUD@HA/PEEK Scaffold Induces Subchondral Bone Regeneration to Repair Osteochondral Defect in Rabbits

Osteochondral defects (OCDs) pose a significant challenge in clinical practice, and recent advancements in their repair indicate that satisfying subchondral bone repair may be critical for this. Herein, a series of hydroxyapatite/poly(ether ether ketone) (HA/PEEK) scaffolds were fabricated with varying mass percentages (0, 20, 30, and 40%) to induce subchondral bone regeneration. Subsequently, an optimal scaffold with 40% HA/PEEK was selected to establish osteochondral scaffolds with poly(ether urethane) urea-Danshensu (PUD) for repairing the OCD. The material characteristics of HA/PEEK and PUD were investigated using scanning electron microscopy, tensile, swelling, and fatigue tests, and cytological experiments. The effects of serial HA/PEEK scaffolds on subchondral bone repair were then assessed by using microcomputed tomography, hard tissue slicing, and histological staining. Furthermore, the optimal 40% HA/PEEK scaffold was used to develop osteochondral scaffolds with PUD to observe the effect on the OCD repair. HA/PEEK materials exhibited an even HA distribution in PEEK. However, when composited with HA, PEEK exhibited inferior mechanical strength. 40%HA/PEEK scaffolds showed an optimum effect on in vivo subchondral bone repair. Cartilage regeneration on 40%HA/PEEK scaffolds was pronounced. After PUD was introduced onto the HA/PEEK, the PUD@40%HA/PEEK scaffold produced the expected effect on the repair of the OCD in rabbits. Therefore, achieving satisfactory subchondral bone repair can benefit surficial cartilage repair. The PUD@40%HA/PEEK scaffold could induce subchondral bone regeneration to repair the OCD in rabbits and could provide a novel approach for the repair of the OCD in clinical practice.

A review of advanced hydrogels for cartilage tissue engineering

With the increase in weight and age of the population, the consumption of tobacco, inappropriate foods, and the reduction of sports activities in recent years, bone and joint diseases such as osteoarthritis (OA) have become more common in the world. From the past until now, various treatment strategies (e.g., microfracture treatment, Autologous Chondrocyte Implantation (ACI), and Mosaicplasty) have been investigated and studied for the prevention and treatment of this disease. However, these methods face problems such as being invasive, not fully repairing the tissue, and damaging the surrounding tissues. Tissue engineering, including cartilage tissue engineering, is one of the minimally invasive, innovative, and effective methods for the treatment and regeneration of damaged cartilage, which has attracted the attention of scientists in the fields of medicine and biomaterials engineering in the past several years. Hydrogels of different types with diverse properties have become desirable candidates for engineering and treating cartilage tissue. They can cover most of the shortcomings of other treatment methods and cause the least secondary damage to the patient. Besides using hydrogels as an ideal strategy, new drug delivery and treatment methods, such as targeted drug delivery and treatment through mechanical signaling, have been studied as interesting strategies. In this study, we review and discuss various types of hydrogels, biomaterials used for hydrogel manufacturing, cartilage-targeting drug delivery, and mechanosignaling as modern strategies for cartilage treatment.

Spatiotemporal Immunomodulation and Biphasic Osteo-Vascular Aligned Electrospun Membrane for Diabetic Periosteum Regeneration

Under diabetic conditions, blood glucose fluctuations and exacerbated immunopathological inflammatory environments pose significant challenges to periosteal regenerative repair strategies. Responsive immune regulation in damaged tissues is critical for the immune microenvironment, osteogenesis, and angiogenesis stabilization. Considering the high-glucose microenvironment of such acute injury sites, a functional glucose-responsive immunomodulation-assisted periosteal regeneration composite material-PLA（Polylactic Acid）/COLI(Collagen I）/Lipo(Liposome）-APY29 (PCLA)-is constructed. Aside from stimulating osteogenic differentiation, owing to the presence of surface self-assembled type I collagen in the scaffolds, PCLA can directly respond to focal area high-glucose microenvironments. The PCLA scaffolds trigger the release of APY29-loaded liposomes, shifting the macrophages toward the M2 phenotype, inhibiting the release of inflammatory cytokines, improving the bone immune microenvironment, and promoting osteogenic differentiation and angiogenesis. Bioinformatics analyses show that PCLA enhances bone repair by inhibiting the inflammatory signal pathway regulating the polarization direction and promoting osteogenic and angiogenic gene expression. In the calvarial periosteal defect model of diabetic rats, PCLA scaffolds induce M2 macrophage polarization and improve the inflammatory microenvironment, significantly accelerating periosteal repair. Overall, the PCLA scaffold material regulates immunity in fluctuating high-glucose inflammatory microenvironments, achieves relatively stable and favorable osteogenic microenvironments, and facilitates the effective design of functionalized biomaterials for bone regeneration therapy in patients with diabetes.

Increasing Collagen to Bioink Drives Mesenchymal Stromal Cells-Chondrogenesis from Hyaline to Calcified Layers

The bioextrusion of mesenchymal stromal cells (MSCs) directly seeded in a bioink enables the production of three-dimensional (3D) constructs, promoting their chondrogenic differentiation. Our study aimed to evaluate the effect of different type I collagen concentrations in the bioink on MSCs' chondrogenic differentiation. We printed 3D constructs using an alginate, gelatin, and fibrinogen-based bioink cellularized with MSCs, with four different quantities of type I collagen addition (0.0, 0.5, 1.0, and 5.0 mg per bioink syringe). We assessed the influence of the bioprinting process, the bioink composition, and the growth factor (TGF-ꞵ1) on the MSCs' survival rate. We confirmed the biocompatibility of the process and the bioinks' cytocompatibility. We evaluated the chondrogenic effects of TGF-ꞵ1 and collagen addition on the MSCs' chondrogenic properties through macroscopic observation, shrinking ratio, reverse transcription polymerase chain reaction, glycosaminoglycan synthesis, histology, and type II collagen immunohistochemistry. The bioink containing 0.5 mg of collagen produces the richest hyaline-like extracellular matrix, presenting itself as a promising tool to recreate the superficial layer of hyaline cartilage. The bioink containing 5.0 mg of collagen enhances the synthesis of a calcified matrix, making it a good candidate for mimicking the calcified cartilaginous layer. Type I collagen thus allows the dose-dependent design of specific hyaline cartilage layers.

Special Issue "Stem Cell Biology & Regenerative Medicine"

More than 50% of pre-clinical studies fail despite a long and expensive journey of drug discovery using animal models [...].

Human Cartilage Biomechanics: Experimental and Theoretical Approaches towards the Identification of Mechanical Properties in Healthy and Osteoarthritic Conditions

Articular cartilage is a complex connective tissue with the fundamental functions of load bearing, shock absorption and lubrication in joints. However, traumatic events, aging and degenerative pathologies may affect its structural integrity and function, causing pain and long-term disability. Osteoarthritis represents a health issue, which concerns an increasing number of people worldwide. Moreover, it has been observed that this pathology also affects the mechanical behavior of the articular cartilage. To better understand this correlation, the here proposed review analyzes the physiological aspects that influence cartilage microstructure and biomechanics, with a special focus on the pathological changes caused by osteoarthritis. Particularly, the experimental data on human articular cartilage are presented with reference to different techniques adopted for mechanical testing and the related theoretical mechanical models usually applied to articular cartilage are briefly discussed.

Fibrin and Marine-Derived Agaroses for the Generation of Human Bioartificial Tissues: An Ex Vivo and In Vivo Study

Development of an ideal biomaterial for clinical use is one of the main objectives of current research in tissue engineering. Marine-origin polysaccharides, in particular agaroses, have been widely explored as scaffolds for tissue engineering. We previously developed a biomaterial based on a combination of agarose with fibrin, that was successfully translated to clinical practice. However, in search of novel biomaterials with improved physical and biological properties, we have now generated new fibrin-agarose (FA) biomaterials using 5 different types of agaroses at 4 different concentrations. First, we evaluated the cytotoxic effects and the biomechanical properties of these biomaterials. Then, each bioartificial tissue was grafted in vivo and histological, histochemical and immunohistochemical analyses were performed after 30 days. Ex vivo evaluation showed high biocompatibility and differences in their biomechanical properties. In vivo, FA tissues were biocompatible at the systemic and local levels, and histological analyses showed that biointegration was associated to a pro-regenerative process with M2-type CD206-positive macrophages. These results confirm the biocompatibility of FA biomaterials and support their clinical use for the generation of human tissues by tissue engineering, with the possibility of selecting specific agarose types and concentrations for applications requiring precise biomechanical properties and in vivo reabsorption times.

Chondroitin Sulfate-Tyramine-Based Hydrogels for Cartilage Tissue Repair

The degradation of cartilage, due to trauma, mechanical load or diseases, results in abundant loss of extracellular matrix (ECM) integrity and development of osteoarthritis (OA). Chondroitin sulfate (CS) is a member of the highly sulfated glycosaminoglycans (GAGs) and a primary component of cartilage tissue ECM. In this study, we aimed to investigate the effect of mechanical load on the chondrogenic differentiation of bone marrow mesenchymal stem cells (BM-MCSs) encapsulated into CS-tyramine-gelatin (CS-Tyr/Gel) hydrogel in order to evaluate the suitability of this composite for OA cartilage regeneration studies in vitro. The CS-Tyr/Gel/BM-MSCs composite showed excellent biointegration on cartilage explants. The applied mild mechanical load stimulated the chondrogenic differentiation of BM-MSCs in CS-Tyr/Gel hydrogel (immunohistochemical collagen II staining). However, the stronger mechanical load had a negative effect on the human OA cartilage explants evaluated by the higher release of ECM components, such as the cartilage oligomeric matrix protein (COMP) and GAGs, compared to the not-compressed explants. Finally, the application of the CS-Tyr/Gel/BM-MSCs composite on the top of the OA cartilage explants decreased the release of COMP and GAGs from the cartilage explants. Data suggest that the CS-Tyr/Gel/BM-MSCs composite can protect the OA cartilage explants from the damaging effects of external mechanical stimuli. Therefore, it can be used for investigation of OA cartilage regenerative potential and mechanisms under the mechanical load in vitro with further perspectives of therapeutic application in vivo.

Effects of Electrical Stimulation on Articular Cartilage Regeneration with a Focus on Piezoelectric Biomaterials for Articular Cartilage Tissue Repair and Engineering

There is increasing evidence that chondrocytes within articular cartilage are affected by endogenous force-related electrical potentials. Furthermore, electrical stimulation (ES) promotes the proliferation of chondrocytes and the synthesis of extracellular matrix (ECM) molecules, which accelerate the healing of cartilage defects. These findings suggest the potential application of ES in cartilage repair. In this review, we summarize the pathogenesis of articular cartilage injuries and the current clinical strategies for the treatment of articular cartilage injuries. We then focus on the application of ES in the repair of articular cartilage in vivo. The ES-induced chondrogenic differentiation of mesenchymal stem cells (MSCs) and its potential regulatory mechanism are discussed in detail. In addition, we discuss the potential of applying piezoelectric materials in the process of constructing engineering articular cartilage, highlighting the important advances in the unique field of tissue engineering.

Recent advances in tendon tissue engineering strategy

Tendon injuries often result in significant pain and disability and impose severe clinical and financial burdens on our society. Despite considerable achievements in the field of regenerative medicine in the past several decades, effective treatments remain a challenge due to the limited natural healing capacity of tendons caused by poor cell density and vascularization. The development of tissue engineering has provided more promising results in regenerating tendon-like tissues with compositional, structural and functional characteristics comparable to those of native tendon tissues. Tissue engineering is the discipline of regenerative medicine that aims to restore the physiological functions of tissues by using a combination of cells and materials, as well as suitable biochemical and physicochemical factors. In this review, following a discussion of tendon structure, injury and healing, we aim to elucidate the current strategies (biomaterials, scaffold fabrication techniques, cells, biological adjuncts, mechanical loading and bioreactors, and the role of macrophage polarization in tendon regeneration), challenges and future directions in the field of tendon tissue engineering.