Application of Alginate Hydrogels for Next-Generation Articular Cartilage Regeneration

Functionalized hydrogels as smart gene delivery systems to treat musculoskeletal disorders

Despite critical advances in regenerative medicine, the generation of definitive, reliable treatments for musculoskeletal diseases remains challenging. Gene therapy based on the delivery of therapeutic genetic sequences has strong value to offer effective, durable options to decisively manage such disorders. Furthermore, scaffold-mediated gene therapy provides powerful alternatives to overcome hurdles associated with classical gene therapy, allowing for the spatiotemporal delivery of candidate genes to sites of injury. Among the many scaffolds for musculoskeletal research, hydrogels raised increasing attention in addition to other potent systems (solid, hybrid scaffolds) due to their versatility and competence as drug and cell carriers in tissue engineering and wound dressing. Attractive functionalities of hydrogels for musculoskeletal therapy include their injectability, stimuli-responsiveness, self-healing, and nanocomposition that may further allow to upgrade of them as "intelligently" efficient and mechanically strong platforms, rather than as just inert vehicles. Such functionalized hydrogels may also be tuned to successfully transfer therapeutic genes in a minimally invasive manner in order to protect their cargos and allow for their long-term effects. In light of such features, this review focuses on functionalized hydrogels and demonstrates their competence for the treatment of musculoskeletal disorders using gene therapy procedures, from gene therapy principles to hydrogel functionalization methods and applications of hydrogel-mediated gene therapy for musculoskeletal disorders, while remaining challenges are being discussed in the perspective of translation in patients. STATEMENT OF SIGNIFICANCE: Despite advances in regenerative medicine, the generation of definitive, reliable treatments for musculoskeletal diseases remains challenging. Gene therapy has strong value in offering effective, durable options to decisively manage such disorders. Scaffold-mediated gene therapy provides powerful alternatives to overcome hurdles associated with classical gene therapy. Among many scaffolds for musculoskeletal research, hydrogels raised increasing attention. Functionalities including injectability, stimuli-responsiveness, and self-healing, tune them as "intelligently" efficient and mechanically strong platforms, rather than as just inert vehicles. This review introduces functionalized hydrogels for musculoskeletal disorder treatment using gene therapy procedures, from gene therapy principles to functionalized hydrogels and applications of hydrogel-mediated gene therapy for musculoskeletal disorders, while remaining challenges are discussed from the perspective of translation in patients.

Polysaccharide hydrogels for skin wound healing

Advances in the development and utilization of polysaccharide materials are highly promising, offering prominent applications in the field of tissue engineering for addressing diverse clinical needs, including wound healing, bone regeneration, cartilage repair, and treatment of conditions such as arthritis. Novel polysaccharide materials are popular owing to their inherent stability, biocompatibility, and repeatability. This review presents an overview of the biomedical applications of natural polysaccharide hydrogels and their derivatives. Herein, we discuss the latest advancements in the fabrication, physicochemical properties, and biomedical applications of polysaccharide-based hydrogels, including chitosan, hyaluronic acid, alginate, and cellulose. Various processing techniques applicable to polysaccharide materials are explored, such as the transformation of polysaccharide hydrogels into electrospun nanofibers, microneedles, microspheres, and nanogels. Furthermore, the use of polysaccharide hydrogels in the context of wound-healing applications, including hemostatic effects, antimicrobial activities, anti-inflammatory properties, and promotion of angiogenesis, is presented. Finally, we address the challenges encountered in the development of polysaccharide hydrogels and outline the potential prospects in this evolving field.

Collagen and Alginate Hydrogels Support Chondrocytes Redifferentiation In Vitro without Supplementation of Exogenous Growth Factors

Focal cartilage defects are a prevalent knee problem affecting people of all ages. Articular cartilage (AC) possesses limited healing potential, and osteochondral defects can lead to pain and long-term complications such as osteoarthritis. Autologous chondrocyte implantation (ACI) has been a successful surgical approach for repairing osteochondral defects over the past two decades. However, a major drawback of ACI is the dedifferentiation of chondrocytes during their in vitro expansion. In this study, we isolated ovine chondrocytes and cultured them in a two-dimensional environment for ACI procedures. We hypothesized that 3D scaffolds would support the cells' redifferentiation without the need for growth factors so we encapsulated them into soft collagen and alginate (col/alg) hydrogels. Chondrocytes embedded into the hydrogels were viable and proliferated. After 7 days, they regained their original rounded morphology (aspect ratio 1.08) and started to aggregate. Gene expression studies showed an upregulation of COL2A1, FOXO3A, FOXO1, ACAN, and COL6A1 (37, 1.13, 22, 1123, and 1.08-fold change expression, respectively) as early as day one. At 21 days, chondrocytes had extensively colonized the hydrogel, forming large cell clusters. They started to replace the degrading scaffold by depositing collagen II and aggrecan, but with limited collagen type I deposition. This approach allows us to overcome the limitations of current approaches such as the dedifferentiation occurring in 2D in vitro expansion and the necrotic formation in spheroids. Further studies are warranted to assess long-term ECM deposition and integration with native cartilage. Though limitations exist, this study suggests a promising avenue for cartilage repair with col/alg hydrogel scaffolds.

Specific lipid magnetic sphere sorted CD146-positive bone marrow mesenchymal stem cells can better promote articular cartilage damage repair

BACKGROUND

The characteristics and therapeutic potential of subtypes of bone marrow mesenchymal stem cells (BMSCs) are largely unknown. Also, the application of subpopulations of BMSCs in cartilage regeneration remains poorly characterized. The aim of this study was to explore the regenerative capacity of CD146-positive subpopulations of BMSCs for repairing cartilage defects.

METHODS

CD146-positive BMSCs (CD146 + BMSCs) were sorted by self-developed CD146-specific lipid magnetic spheres (CD146-LMS). Cell surface markers, viability, and proliferation were evaluated in vitro. CD146 + BMSCs were subjected to in vitro chondrogenic induction and evaluated for chondrogenic properties by detecting mRNA and protein expression. The role of the CD146 subpopulation of BMSCs in cartilage damage repair was assessed by injecting CD146 + BMSCs complexed with sodium alginate gel in the joints of a mouse cartilage defect model.

RESULTS

The prepared CD146-LMS had an average particle size of 193.7 ± 5.24 nm, an average potential of 41.9 ± 6.21 mv, and a saturation magnetization intensity of 27.2 Am2/kg, which showed good stability and low cytotoxicity. The sorted CD146 + BMSCs highly expressed stem cell and pericyte markers with good cellular activity and cellular value-added capacity. Cartilage markers Sox9, Collagen II, and Aggrecan were expressed at both protein and mRNA levels in CD146 + BMSCs cells after chondrogenic induction in vitro. In a mouse cartilage injury model, CD146 + BMSCs showed better function in promoting the repair of articular cartilage injury.

CONCLUSION

The prepared CD146-LMS was able to sort out CD146 + BMSCs efficiently, and the sorted subpopulation of CD146 + BMSCs had good chondrogenic differentiation potential, which could efficiently promote the repair of articular cartilage injury, suggesting that the sorted CD146 + BMSCs subpopulation is a promising seed cell for cartilage tissue engineering.

Evolution of Hybrid Hydrogels: Next-Generation Biomaterials for Drug Delivery and Tissue Engineering

Hydrogels, being hydrophilic polymer networks capable of absorbing and retaining aqueous fluids, hold significant promise in biomedical applications owing to their high water content, permeability, and structural similarity to the extracellular matrix. Recent chemical advancements have bolstered their versatility, facilitating the integration of the molecules guiding cellular activities and enabling their controlled activation under time constraints. However, conventional synthetic hydrogels suffer from inherent weaknesses such as heterogeneity and network imperfections, which adversely affect their mechanical properties, diffusion rates, and biological activity. In response to these challenges, hybrid hydrogels have emerged, aiming to enhance their strength, drug release efficiency, and therapeutic effectiveness. These hybrid hydrogels, featuring improved formulations, are tailored for controlled drug release and tissue regeneration across both soft and hard tissues. The scientific community has increasingly recognized the versatile characteristics of hybrid hydrogels, particularly in the biomedical sector. This comprehensive review delves into recent advancements in hybrid hydrogel systems, covering the diverse types, modification strategies, and the integration of nano/microstructures. The discussion includes innovative fabrication techniques such as click reactions, 3D printing, and photopatterning alongside the elucidation of the release mechanisms of bioactive molecules. By addressing challenges, the review underscores diverse biomedical applications and envisages a promising future for hybrid hydrogels across various domains in the biomedical field.

Natural based hydrogels promote chondrogenic differentiation of human mesenchymal stem cells

Background: The cartilage tissue lacks blood vessels, which is composed of chondrocytes and ECM. Due to this vessel-less structure, it is difficult to repair cartilage tissue damages. One of the new methods to repair cartilage damage is to use tissue engineering. In the present study, it was attempted to simulate a three-dimensional environment similar to the natural ECM of cartilage tissue by using hydrogels made of natural materials, including Chitosan and different ratios of Alginate. Material and methods: Chitosan, alginate and Chitosan/Alginate hydrogels were fabricated. Fourier Transform Infrared, XRD, swelling ratio, porosity measurement and degradation tests were applied to scaffolds characterization. After that, human adipose derived-mesenchymal stem cells (hADMSCs) were cultured on the hydrogels and then their viability and chondrogenic differentiation capacity were studied. Safranin O and Alcian blue staining, immunofluorescence staining and real time RT-PCR were used as analytical methods for chondrogenic differentiation potential evaluation of hADMSCs when cultured on the hydrogels. Results: The highest degradation rate was detected in Chitosan/Alginate (1:0.5) group The scaffold biocompatibility results revealed that the viability of the cells cultured on the hydrogels groups was not significantly different with the cells cultured in the control group. Safranin O staining, Alcian blue staining, immunofluorescence staining and real time PCR results revealed that the chondrogenic differentiation potential of the hADMSCs when grown on the Chitosan/Alginate hydrogel (1:0.5) was significantly higher than those cell grown on the other groups. Conclusion: Taken together, these results suggest that Chitosan/Alginate hydrogel (1:0.5) could be a promising candidate for cartilage tissue engineering applications.

Polymeric Nanohydrogel in Topical Drug Delivery System

Nanohydrogels (NH) are biodegradable polymers that have been extensively studied and utilized for various biomedical applications. Drugs in a topical medication are absorbed via the skin and carried to the intended location, where they are metabolized and eliminated from the body. With a focus on their pertinent contemporary treatments, this review aims to give a complete overview of recent advances in the creation and application of polymer NH in biomedicine. We will explore the key features that have driven advances in nanotechnology and discuss the significance of nanohydrogel-based formulations as vehicles for delivering therapeutic agents topically. The review will also cover the latest findings and references from the literature to support the advancements in nanotechnological technology related to the preparation and application of NH. In addition, we will also discuss the unique properties and potential applications of NH as drug delivery systems (DDS) for skin applications, underscoring their potential for effective topical therapeutic delivery. The challenge lies in efficiently delivering drugs through the skin's barrier to specific areas with high control. Environmentally sensitive systems, like polymer-based NH, show promise in treating dermatological conditions. Polymers are pivotal in developing these drug delivery systems, with NH offering advantages such as versatile drug loading, controlled release, and enhanced skin penetration.

Recent advances in production of sustainable and biodegradable polymers from agro-food waste: Applications in tissue engineering and regenerative medicines

Agro-food waste is a rich source of biopolymers such as cellulose, chitin, and starch, which have been shown to possess excellent biocompatibility, biodegradability, and low toxicity. These properties make biopolymers from agro-food waste for its application in tissue engineering and regenerative medicine. Thus, this review highlighted the properties, processing methods, and applications of biopolymers derived from various agro-food waste sources. We also highlight recent advances in the development of biopolymers from agro-food waste and their potential for future tissue engineering and regenerative medicine applications, including drug delivery, wound healing, tissue engineering, biodegradable packaging, excipients, dental applications, diagnostic tools, and medical implants. Additionally, it explores the challenges, prospects, and future directions in this rapidly evolving field. The review showed the evolution of production techniques for transforming agro-food waste into valuable biopolymers. However, these biopolymers serving as the cornerstone in scaffold development and drug delivery systems. With their role in wound dressings, cell encapsulation, and regenerative therapies, biopolymers promote efficient wound healing, cell transplantation, and diverse regenerative treatments. Biopolymers support various regenerative treatments, including cartilage and bone regeneration, nerve repair, and organ transplantation. Overall, this review concluded the potential of biopolymers from agro-food waste as a sustainable and cost-effective solution in tissue engineering and regenerative medicine, offering innovative solutions for medical treatments and promoting the advancement of these fields.

Magnetic hydrogel applications in articular cartilage tissue engineering

Articular cartilage defects afflict millions of individuals worldwide, presenting a significant challenge due to the tissue's limited self-repair capability and anisotropic nature. Hydrogel-based biomaterials have emerged as promising candidates for scaffold production in artificial cartilage construction, owing to their water-rich composition, biocompatibility, and tunable properties. Nevertheless, conventional hydrogels typically lack the anisotropic structure inherent to natural cartilage, impeding their clinical and preclinical applications. Recent advancements in tissue engineering (TE) have introduced magnetically responsive hydrogels, a type of intelligent hydrogel that can be remotely controlled using an external magnetic field. These innovative materials offer a means to create the desired anisotropic architecture required for successful cartilage TE. In this review, we first explore conventional techniques employed for cartilage repair and subsequently delve into recent breakthroughs in the application and utilization of magnetic hydrogels across various aspects of articular cartilage TE.

Cartilage tissue healing and regeneration based on biocompatible materials: a systematic review and bibliometric analysis from 1993 to 2022

Cartilage, a type of connective tissue, plays a crucial role in supporting and cushioning the body, and damages or diseases affecting cartilage may result in pain and impaired joint function. In this regard, biocompatible materials are used in cartilage tissue healing and regeneration as scaffolds for new tissue growth, barriers to prevent infection and reduce inflammation, and deliver drugs or growth factors to the injury site. In this article, we perform a comprehensive bibliometric analysis of literature on cartilage tissue healing and regeneration based on biocompatible materials, including an overview of current research, identifying the most influential articles and authors, discussing prevailing topics and trends in this field, and summarizing future research directions.

Blood-Induced Arthropathy: A Major Disabling Complication of Haemophilia

Haemophilic arthropathy (HA) is one of the most serious complications of haemophilia. It starts with joint bleeding, leading to synovitis which, in turn, can cause damage to the cartilage and subchondral bone, eventually inducing degenerative joint disease. Despite significant improvements in haemophilia treatment over the past two decades and recent guidelines from ISTH and WFH recommending FVIII trough levels of at least 3 IU/dL during prophylaxis, patients with haemophilia still develop joint disease. The pathophysiology of HA is complex, involving both inflammatory and degenerative components. Early diagnosis is key for proper management. Imaging can detect joint subclinical changes and influence prophylaxis. Magnetic resonance imagining (MRI) and ultrasound are the most frequently used methods in comprehensive haemophilia care centres. Biomarkers of joint health have been proposed to determine osteochondral joint deterioration, but none of these biomarkers has been validated or used in clinical practice. Early prophylaxis is key in all severe haemophilia patients to prevent arthropathy. Treatment is essentially based on prophylaxis intensification and chronic joint pain management. However, there remain significant gaps in the knowledge of the mechanisms responsible for HA and prognosis-influencing factors. Better understanding in this area could produce more effective interventions likely to ultimately prevent or attenuate the development of HA.

Human Chondrocytes, Metabolism of Articular Cartilage, and Strategies for Application to Tissue Engineering

Hyaline cartilage, which is characterized by the absence of vascularization and innervation, has minimal self-repair potential in case of damage and defect formation in the chondral layer. Chondrocytes are specialized cells that ensure the synthesis of extracellular matrix components, namely type II collagen and aggregen. On their surface, they express integrins CD44, α1β1, α3β1, α5β1, α10β1, αVβ1, αVβ3, and αVβ5, which are also collagen-binding components of the extracellular matrix. This article aims to contribute to solving the problem of the possible repair of chondral defects through unique methods of tissue engineering, as well as the process of pathological events in articular cartilage. In vitro cell culture models used for hyaline cartilage repair could bring about advanced possibilities. Currently, there are several variants of the combination of natural and synthetic polymers and chondrocytes. In a three-dimensional environment, chondrocytes retain their production capacity. In the case of mesenchymal stromal cells, their favorable ability is to differentiate into a chondrogenic lineage in a three-dimensional culture.

Revolutionizing orofacial pain management: the promising potential of stem cell therapy

Orofacial pain remains a significant health issue in the United States. Pain originating from the orofacial region can be composed of a complex array of unique target tissue that contributes to the varying success of pain management. Long-term use of analgesic drugs includes adverse effects such as physical dependence, gastrointestinal bleeding, and incomplete efficacy. The use of mesenchymal stem cells for their pain relieving properties has garnered increased attention. In addition to the preclinical and clinical results showing stem cell analgesia in non-orofacial pain, studies have also shown promising results for orofacial pain treatment. Here we discuss the outcomes of mesenchymal stem cell treatment for pain and compare the properties of stem cells from different tissues of origin. We also discuss the mechanism underlying these analgesic/anti-nociceptive properties, including the role of immune cells and the endogenous opioid system. Lastly, advancements in the methods and procedures to treat patients experiencing orofacial pain with mesenchymal stem cells are also discussed.

Application of 3D- printed hydrogels in wound healing and regenerative medicine

Hydrogels are three-dimensional polymer networks with hydrophilic properties. The modifiable properties of hydrogels and the structure resembling living tissue allow their versatile application. Therefore, increasing attention is focused on the use of hydrogels as bioinks for three-dimensional (3D) printing in tissue engineering. Bioprinting involves the fabrication of complex structures from several types of materials, cells, and bioactive compounds. Stem cells (SC), such as mesenchymal stromal cells (MSCs) are frequently employed in 3D constructs. SCs have desirable biological properties such as the ability to differentiate into various types of tissue and high proliferative capacity. Encapsulating SCs in 3D hydrogel constructs enhances their reparative abilities and improves the likelihood of reaching target tissues. In addition, created constructs can simulate the tissue environment and mimic biological signals. Importantly, the immunogenicity of scaffolds is minimized through the use of patient-specific cells and the biocompatibility and biodegradability of the employed biopolymers. Regenerative medicine is taking advantage of the aforementioned capabilities in regenerating various tissues- muscle, bones, nerves, heart, skin, and cartilage.

Biological Macromolecule-Based Scaffolds for Urethra Reconstruction

Urethral reconstruction strategies are limited with many associated drawbacks. In this context, the main challenge is the unavailability of a suitable tissue that can endure urine exposure. However, most of the used tissues in clinical practices are non-specialized grafts that finally fail to prevent urine leakage. Tissue engineering has offered novel solutions to address this dilemma. In this technology, scaffolding biomaterials characteristics are of prime importance. Biological macromolecules are naturally derived polymers that have been extensively studied for various tissue engineering applications. This review discusses the recent advances, applications, and challenges of biological macromolecule-based scaffolds in urethral reconstruction.

A Critical Review on Classified Excipient Sodium-Alginate-Based Hydrogels: Modification, Characterization, and Application in Soft Tissue Engineering

Alginates are polysaccharides that are produced naturally and can be isolated from brown sea algae and bacteria. Sodium alginate (SA) is utilized extensively in the field of biological soft tissue repair and regeneration owing to its low cost, high biological compatibility, and quick and moderate crosslinking. In addition to their high printability, SA hydrogels have found growing popularity in tissue engineering, particularly due to the advent of 3D bioprinting. There is a developing curiosity in tissue engineering with SA-based composite hydrogels and their potential for further improvement in terms of material modification, the molding process, and their application. This has resulted in numerous productive outcomes. The use of 3D scaffolds for growing cells and tissues in tissue engineering and 3D cell culture is an innovative technique for developing in vitro culture models that mimic the in vivo environment. Especially compared to in vivo models, in vitro models were more ethical and cost-effective, and they stimulate tissue growth. This article discusses the use of sodium alginate (SA) in tissue engineering, focusing on SA modification techniques and providing a comparative examination of the properties of several SA-based hydrogels. This review also covers hydrogel preparation techniques, and a catalogue of patents covering different hydrogel formulations is also discussed. Finally, SA-based hydrogel applications and future research areas concerning SA-based hydrogels in tissue engineering were examined.

Role of nano-hydrogels coated exosomes in bone tissue repair

With the development of nanotechnology, nanomaterials are widely applied in different areas. Some nanomaterials are designed to be biocompatible and can be used in the medical field, playing an important role in disease treatment. Exosomes are nanoscale vesicles with a diameter of 30-200 nm. Studies have shown that exosomes have the effect of angiogenesis, tissue (skin, tendon, cartilage, et al.) repair and reconstruction. Nano-hydrogels are hydrogels with a diameter of 200 nm or less and can be used as the carrier to transport the exosomes into the body. Some orthopedic diseases, such as bone defects and bone infections, are difficult to handle. The emergence of nano-hydrogels coated exosomes may provide a new idea to solve these problems, improving the prognosis of patients. This review summarizes the function of nano-hydrogels coated exosomes in bone tissue repair, intending to illustrate the potential use and application of nano-hydrogels coated exosomes in bone disease.

Dynamic Alginate Hydrogel as an Antioxidative Bioink for Bioprinting

3D bioprinting holds great potential for use in tissue engineering to treat degenerative joint disorders, such as osteoarthritis. However, there is a lack of multifunctional bioinks that can not only support cell growth and differentiation, but also offer protection to cells against injuries caused by the elevated oxidative stress; this conditions is a common characteristic of the microenvironment of the osteoarthritis disease. To mitigate oxidative stress-induced cellular phenotype change and malfunction, an anti-oxidative bioink derived from an alginate dynamic hydrogel was developed in this study. The alginate dynamic hydrogel gelated quickly via the dynamic covalent bond between the phenylboronic acid modified alginate (Alg-PBA) and poly (vinyl alcohol) (PVA). It presented good self-healing and shear-thinning abilities because of the dynamic feature. The dynamic hydrogel supported long-term growth of mouse fibroblasts after stabilization with a secondary ionic crosslinking between introduced calcium ions and the carboxylate group in the alginate backbone. In addition, the dynamic hydrogel showed good printability, resulting in the fabrication of scaffolds with cylindrical and grid structures with good structural fidelity. Encapsulated mouse chondrocytes maintained high viability for at least 7 days in the bioprinted hydrogel after ionic crosslinking. Most importantly, in vitro studies implied that the bioprinted scaffold could reduce the intracellular oxidative stress for embedded chondrocytes under H₂O₂ exposure; it could also protect the chondrocytes from H₂O₂-induced downregulation of extracellular matrix (ECM) relevant anabolic genes (ACAN and COL2) and upregulation of a catabolic gene (MMP13). In summary, the results suggest that the dynamic alginate hydrogel can be applied as a versatile bioink for the fabrication of 3D bioprinted scaffolds with an innate antioxidative ability; this technique is expected to improve the regenerative efficacy of cartilage tissues for the treatment of joint disorders.

Alginate-Based Materials Loaded with Nanoparticles in Wound Healing

Alginate is a naturally derived polysaccharide widely applied in drug delivery, as well as regenerative medicine, tissue engineering and wound care. Due to its excellent biocompatibility, low toxicity, and the ability to absorb a high amount of exudate, it is widely used in modern wound dressings. Numerous studies indicate that alginate applied in wound care can be enhanced with the incorporation of nanoparticles, revealing additional properties beneficial in the healing process. Among the most extensively explored materials, composite dressings with alginate loaded with antimicrobial inorganic nanoparticles can be mentioned. However, other types of nanoparticles with antibiotics, growth factors, and other active ingredients are also investigated. This review article focuses on the most recent findings regarding novel alginate-based materials loaded with nanoparticles and their applicability as wound dressings, with special attention paid to the materials of potential use in the treatment of chronic wounds.

Micromolding-based encapsulation of mesenchymal stromal cells in alginate for intraarticular injection in osteoarthritis

Osteoarthritis (OA) is an inflammatory joint disease that affects cartilage, subchondral bone, and joint tissues. Undifferentiated Mesenchymal Stromal Cells are a promising therapeutic option for OA due to their ability to release anti-inflammatory, immuno-modulatory, and pro-regenerative factors. They can be embedded in hydrogels to prevent their tissue engraftment and subsequent differentiation. In this study, human adipose stromal cells are successfully encapsulated in alginate microgels via a micromolding method. Microencapsulated cells retain their in vitro metabolic activity and bioactivity and can sense and respond to inflammatory stimuli, including synovial fluids from OA patients. After intra-articular injection in a rabbit model of post-traumatic OA, a single dose of microencapsulated human cells exhibit properties matching those of non-encapsulated cells. At 6 and 12 weeks post-injection, we evidenced a tendency toward a decreased OA severity, an increased expression of aggrecan, and a reduced expression of aggrecanase-generated catabolic neoepitope. Thus, these findings establish the feasibility, safety, and efficacy of injecting cells encapsulated in microgels, opening the door to a long-term follow-up in canine OA patients.

Recent progress in polymeric gene vectors: Delivery mechanisms, molecular designs, and applications

Gene therapy and gene delivery have drawn extensive attention in recent years especially when the COVID-19 mRNA vaccines were developed to prevent severe symptoms caused by the corona virus. Delivering genes, such as DNA and RNA into cells, is the crucial step for successful gene therapy and remains a bottleneck. To address this issue, vehicles (vectors) that can load and deliver genes into cells are developed, including viral and non-viral vectors. Although viral gene vectors have considerable transfection efficiency and lipid-based gene vectors become popular since the application of COVID-19 vaccines, their potential issues including immunologic and biological safety concerns limited their applications. Alternatively, polymeric gene vectors are safer, cheaper, and more versatile compared to viral and lipid-based vectors. In recent years, various polymeric gene vectors with well-designed molecules were developed, achieving either high transfection efficiency or showing advantages in certain applications. In this review, we summarize the recent progress in polymeric gene vectors including the transfection mechanisms, molecular designs, and biomedical applications. Commercially available polymeric gene vectors/reagents are also introduced. Researchers in this field have never stopped seeking safe and efficient polymeric gene vectors via rational molecular designs and biomedical evaluations. The achievements in recent years have significantly accelerated the progress of polymeric gene vectors toward clinical applications.

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.

Regeneration of articular cartilage defects: Therapeutic strategies and perspectives

Articular cartilage (AC), a bone-to-bone protective device made of up to 80% water and populated by only one cell type (i.e. chondrocyte), has limited capacity for regeneration and self-repair after being damaged because of its low cell density, alymphatic and avascular nature. Resulting repair of cartilage defects, such as osteoarthritis (OA), is highly challenging in clinical treatment. Fortunately, the development of tissue engineering provides a promising method for growing cells in cartilage regeneration and repair by using hydrogels or the porous scaffolds. In this paper, we review the therapeutic strategies for AC defects, including current treatment methods, engineering/regenerative strategies, recent advances in biomaterials, and present emphasize on the perspectives of gene regulation and therapy of noncoding RNAs (ncRNAs), such as circular RNA (circRNA) and microRNA (miRNA).

Strategy insight: Mechanical properties of biomaterials' influence on hydrogel-mesenchymal stromal cell combination for osteoarthritis therapy

Osteoarthritis (OA) is a kind of degenerative joint disease usually found in older adults and those who have received meniscal surgery, bringing great suffering to a number of patients worldwide. One of the major pathological features of OA is retrograde changes in the articular cartilage. Mesenchymal stromal cells (MSCs) can differentiate into chondrocytes and promote cartilage regeneration, thus having great potential for the treatment of osteoarthritis. However, improving the therapeutic effect of MSCs in the joint cavity is still an open problem. Hydrogel made of different biomaterials has been recognized as an ideal carrier for MSCs in recent years. This review focuses on the influence of the mechanical properties of hydrogels on the efficacy of MSCs in OA treatment and compares artificial materials with articular cartilage, hoping to provide a reference for further development of modified hydrogels to improve the therapeutic effect of MSCs.

Sodium Alginate—Natural Microencapsulation Material of Polymeric Microparticles

From the multitude of materials currently available on the market that can be used in the development of microparticles, sodium alginate has become one of the most studied natural anionic polymers that can be included in controlled-release pharmaceutical systems alongside other polymers due to its low cost, low toxicity, biocompatibility, biodegradability and gelatinous die-forming capacity in the presence of Ca²⁺ ions. In this review, we have shown that through coacervation, the particulate systems for the dispensing of drugs consisting of natural polymers are nontoxic, allowing the repeated administration of medicinal substances and the protection of better the medicinal substances from degradation, which can increase the capture capacity of the drug and extend its release from the pharmaceutical form.

Recent Developments and Current Applications of Organic Nanomaterials in Cartilage Repair

Regeneration of cartilage is difficult due to the unique microstructure, unique multizone organization, and avascular nature of cartilage tissue. The development of nanomaterials and nanofabrication technologies holds great promise for the repair and regeneration of injured or degenerated cartilage tissue. Nanomaterials have structural components smaller than 100 nm in at least one dimension and exhibit unique properties due to their nanoscale structure and high specific surface area. The unique properties of nanomaterials include, but are not limited to, increased chemical reactivity, mechanical strength, degradability, and biocompatibility. As an emerging nanomaterial, organic nanocomposites can mimic natural cartilage in terms of microstructure, physicochemical, mechanical, and biological properties. The integration of organic nanomaterials is expected to develop scaffolds that better mimic the extracellular matrix (ECM) environment of cartilage to enhance scaffold-cell interactions and improve the functionality of engineered tissue constructs. Next-generation hydrogel technology and bioprinting can be used not only for healing cartilage injury areas but also for extensive osteoarthritic degenerative changes within the joint. Although more challenges need to be solved before they can be translated into full-fledged commercial products, nano-organic composites remain very promising candidates for the future development of cartilage tissue engineering.

Three-Dimensional Bioprinting for Cartilage Tissue Engineering: Insights into Naturally-Derived Bioinks from Land and Marine Sources

In regenerative medicine and tissue engineering, the possibility to: (I) customize the shape and size of scaffolds, (II) develop highly mimicked tissues with a precise digital control, (III) manufacture complex structures and (IV) reduce the wastes related to the production process, are the main advantages of additive manufacturing technologies such as three-dimensional (3D) bioprinting. Specifically, this technique, which uses suitable hydrogel-based bioinks, enriched with cells and/or growth factors, has received significant consideration, especially in cartilage tissue engineering (CTE). In this field of interest, it may allow mimicking the complex native zonal hyaline cartilage organization by further enhancing its biological cues. However, there are still some limitations that need to be overcome before 3D bioprinting may be globally used for scaffolds’ development and their clinical translation. One of them is represented by the poor availability of appropriate, biocompatible and eco-friendly biomaterials, which should present a series of specific requirements to be used and transformed into a proper bioink for CTE. In this scenario, considering that, nowadays, the environmental decline is of the highest concerns worldwide, exploring naturally-derived hydrogels has attracted outstanding attention throughout the scientific community. For this reason, a comprehensive review of the naturally-derived hydrogels, commonly employed as bioinks in CTE, was carried out. In particular, the current state of art regarding eco-friendly and natural bioinks’ development for CTE was explored. Overall, this paper gives an overview of 3D bioprinting for CTE to guide future research towards the development of more reliable, customized, eco-friendly and innovative strategies for CTE.

Novel Trends in Hydrogel Development for Biomedical Applications: A Review

Nowadays, there are still numerous challenges for well-known biomedical applications, such as tissue engineering (TE), wound healing and controlled drug delivery, which must be faced and solved. Hydrogels have been proposed as excellent candidates for these applications, as they have promising properties for the mentioned applications, including biocompatibility, biodegradability, great absorption capacity and tunable mechanical properties. However, depending on the material or the manufacturing method, the resulting hydrogel may not be up to the specific task for which it is designed, thus there are different approaches proposed to enhance hydrogel performance for the requirements of the application in question. The main purpose of this review article was to summarize the most recent trends of hydrogel technology, going through the most used polymeric materials and the most popular hydrogel synthesis methods in recent years, including different strategies of enhancing hydrogels’ properties, such as cross-linking and the manufacture of composite hydrogels. In addition, the secondary objective of this review was to briefly discuss other novel applications of hydrogels that have been proposed in the past few years which have drawn a lot of attention.

Printable Hydrogels Based on Alginate and Halloysite Nanotubes

The design of hydrogels for the controlled release of active species is an attractive challenge. In this work, we prepared hybrid hydrogels composed of halloysite nanotubes as the inorganic component, and alginate as the organic counterpart. The reported procedure allowed us to provide the resulting materials with a peculiar wire-like shape. Both optical and scanning electron microscopy were used to characterize the morphological properties of the hydrogel wires, whose diameters were ca. 0.19 and 0.47 mm, respectively. The possibility to be exploited as drug delivery systems was carried out by loading the nanoclay with salicylic acid and by studying the release profiles. Thermogravimetric experiments showed that the amount of encapsulated drug was 4.35 wt%, and the salicylic acid was thermally stabilized after the loading into the nanotubes, as observed by the shift of the degradation peak in the differential thermograms from 193 to 267 °C. The kinetics investigation was conducted using UV–Vis spectrophotometry, and it exhibited the profound effects of both the morphology and dimensions on the release of the drugs. In particular, the release of 50% of the payload occurred in 6 and 10 h for the filiform hydrogels, and it was slower compared to the bare drug-loaded halloysite, which occurred in 2 h. Finally, an induction period of 2 h was observed in the release profile from the thicker sample.

Soft substrates direct stem cell differentiation into the chondrogenic lineage without the use of growth factors

Mesenchymal stem cells (MSCs) hold great promise for the treatment of cartilage related injuries. However, selectively promoting stem cell differentiation in vivo is still challenging. Chondrogenic differentiation of MSCs usually requires the use of growth factors that lead to the overexpression of hypertrophic markers. In this study, for the first time the effect of stiffness on MSC differentiation has been tested without the use of growth factors. Three-dimensional collagen and alginate scaffolds were developed and characterised. Stiffness significantly affected gene expression and ECM deposition. While, all hydrogels supported chondrogenic differentiation and allowed deposition of collagen type II and aggrecan, the 5.75 kPa hydrogel showed limited production of collagen type I compared to the other two formulations. These findings demonstrated for the first time that stiffness can guide MSCs differentiation without the use of growth factors within a tissue engineering scaffold suitable for the treatment of cartilage defects.