Chitosan hydrogel/3D-printed poly(ε-caprolactone) hybrid scaffold containing synovial mesenchymal stem cells for cartilage regeneration based on tetrahedral framework nucleic acid recruitment

Bioprinted biomimetic hydrogel matrices guiding stem cell aggregates for enhanced chondrogenesis and cartilage regeneration

Articular cartilage tissue has limited self-repair capabilities, with damage frequently progressing to irreversible degeneration. Engineered tissues constructed through bioprinting and embedded with stem cell aggregates offer promising therapeutic alternatives. Aggregates of bone marrow mesenchymal stromal cells (BMSCs) demonstrate enhanced and more rapid chondrogenic differentiation than isolated cells, thus facilitating cartilage repair. However, it remains a key challenge to precisely control biochemical microenvironments to regulate cellular adhesion and cohesion within bioprinted matrices simultaneously. Herein, this work reports a bioprintable hydrogel matrix with high cellular adhesion and aggregation properties for cartilage repair. The hydrogel comprises an enhanced cell-adhesive gelatin methacrylate and a cell-cohesive chitosan methacrylate (CHMA), both of which are subjected to photo-initiated crosslinking. By precisely adjusting the CHMA content, the mechanical stability and biochemical cues of the hydrogels are finely tuned to promote cellular aggregation, chondrogenic differentiation and cartilage repair implantation. Multi-layer constructs encapsulated with BMSCs, with high cell viability reaching 91.1%, are bioprinted and photo-crosslinked to support chondrogenic differentiation for 21 days. BMSCs rapidly form aggregates and display efficient chondrogenic differentiation both on the hydrogels and within bioprinted constructs, as evidenced by the upregulated expression of Sox9, Aggrecan and Collagen 2a1 genes, along with high protein levels. Transplantation of these BMSC-laden bioprinted hydrogels into cartilaginous defects demonstrates effective hyaline cartilage repair. Overall, this cell-responsive hydrogel scaffold holds immense promise for applications in cartilage tissue engineering.

Enhancing chondrogenic differentiation of mesenchymal stem cells through synergistic effects of cellulose nanocrystals and plastic compression in collagen-based hydrogel for cartilage formation

Collagen-based (COL) hydrogels could be a promising treatment option for injuries to the articular cartilage (AC) becuase of their similarity to AC native extra extracellular matrix. However, the high hydration of COL hydrogels poses challenges for AC's mechanical properties. To address this, we developed a hydrogel platform that incorporating cellulose nanocrystals (CNCs) within COL and followed by plastic compression (PC) procedure to expel the excessive fluid out. This approach significantly improved the mechanical properties of the hydrogels and enhanced the chondrogenic differentiation of mesenchymal stem cells (MSCs). Radially confined PC resulted in higher collagen fibrillar densities together with reducing fibril-fibril distances. Compressed hydrogels containing CNCs exhibited the highest compressive modulus and toughness. MSCs encapsulated in these hydrogels were initially affected by PC, but their viability improved after 7 days. Furthermore, the morphology of the cells and their secretion of glycosaminoglycans (GAGs) were positively influenced by the compressed COL-CNC hydrogel. Our findings shed light on the combined effects of PC and CNCs in improving the physical and mechanical properties of COL and their role in promoting chondrogenesis.

Micro/nanoengineered agricultural by-products for biomedical and environmental applications

Agriculturally derived by-products generated during the growth cycles of living organisms as secondary products have attracted increasing interest due to their wide range of biomedical and environmental applications. These by-products are considered promising candidates because of their unique characteristics including chemical stability, profound biocompatibility and offering a green approach by producing the least impact on the environment. Recently, micro/nanoengineering based techniques play a significant role in upgrading their utility, by controlling their structural integrity and promoting their functions at a micro and nano scale. Specifically, they can be used for biomedical applications such as tissue regeneration, drug delivery, disease diagnosis, as well as environmental applications such as filtration, bioenergy production, and the detection of environmental pollutants. This review highlights the diverse role of micro/nano-engineering techniques when applied on agricultural by-products with intriguing properties and upscaling their wide range of applications across the biomedical and environmental fields. Finally, we outline the future prospects and remarkable potential that these agricultural by-products hold in establishing a new era in the realms of biomedical science and environmental research.

Effect of tetrahedral framework nucleic acids on the reconstruction of tendon-to-bone injuries after rotator cuff tears

Clinicians and researchers have always faced challenges in performing surgery for rotator cuff tears (RCT) due to the intricate nature of the tendon-bone gradient and the limited long-term effectiveness. At the same time, the occurrence of an inflammatory microenvironment further aggravates tissue damage, which has a negative impact on the regeneration process of mesenchymal stem cells (MSCs) and eventually leads to the production of scar tissue. Tetrahedral framework nucleic acids (tFNAs), novel nanomaterials, have shown great potential in biomedicine due to their strong biocompatibility, excellent cellular internalisation ability, and unparalleled programmability. The objective of this research was to examine if tFNAs have a positive effect on regeneration after RCTs. Experiments conducted in a controlled environment demonstrated that tFNAs hindered the assembly of inflammasomes in macrophages, resulting in a decrease in the release of inflammatory factors. Next, tFNAs were shown to exert a protective effect on the osteogenic and chondrogenic differentiation of bone marrow MSCs under inflammatory conditions. The in vitro results also demonstrated the regulatory effect of tFNAs on tendon-related protein expression levels in tenocytes after inflammatory stimulation. Finally, intra-articular injection of tFNAs into a rat RCT model showed that tFNAs improved tendon-to-bone healing, suggesting that tFNAs may be promising tendon-to-bone protective agents for the treatment of RCTs.

3D Printing of Polysaccharide-Based Hydrogel Scaffolds for Tissue Engineering Applications: A Review

In tissue engineering, 3D printing represents a versatile technology employing inks to construct three-dimensional living structures, mimicking natural biological systems. This technology efficiently translates digital blueprints into highly reproducible 3D objects. Recent advances have expanded 3D printing applications, allowing for the fabrication of diverse anatomical components, including engineered functional tissues and organs. The development of printable inks, which incorporate macromolecules, enzymes, cells, and growth factors, is advancing with the aim of restoring damaged tissues and organs. Polysaccharides, recognized for their intrinsic resemblance to components of the extracellular matrix have garnered significant attention in the field of tissue engineering. This review explores diverse 3D printing techniques, outlining distinctive features that should characterize scaffolds used as ideal matrices in tissue engineering. A detailed investigation into the properties and roles of polysaccharides in tissue engineering is highlighted. The review also culminates in a profound exploration of 3D polysaccharide-based hydrogel applications, focusing on recent breakthroughs in regenerating different tissues such as skin, bone, cartilage, heart, nerve, vasculature, and skeletal muscle. It further addresses challenges and prospective directions in 3D printing hydrogels based on polysaccharides, paving the way for innovative research to fabricate functional tissues, enhancing patient care, and improving quality of life.

Mesenchymal stem cells for cartilage regeneration: Insights into molecular mechanism and therapeutic strategies

The use of mesenchymal stem cells (MSCs) in cartilage regeneration has gained significant attention in regenerative medicine. This paper reviews the molecular mechanisms underlying MSC-based cartilage regeneration and explores various therapeutic strategies to enhance the efficacy of MSCs in this context. MSCs exhibit multipotent capabilities and can differentiate into various cell lineages under specific microenvironmental cues. Chondrogenic differentiation, a complex process involving signaling pathways, transcription factors, and growth factors, plays a pivotal role in the successful regeneration of cartilage tissue. The chondrogenic differentiation of MSCs is tightly regulated by growth factors and signaling pathways such as TGF-β, BMP, Wnt/β-catenin, RhoA/ROCK, NOTCH, and IHH (Indian hedgehog). Understanding the intricate balance between these pathways is crucial for directing lineage-specific differentiation and preventing undesirable chondrocyte hypertrophy. Additionally, paracrine effects of MSCs, mediated by the secretion of bioactive factors, contribute significantly to immunomodulation, recruitment of endogenous stem cells, and maintenance of chondrocyte phenotype. Pre-treatment strategies utilized to potentiate MSCs, such as hypoxic conditions, low-intensity ultrasound, kartogenin treatment, and gene editing, are also discussed for their potential to enhance MSC survival, differentiation, and paracrine effects. In conclusion, this paper provides a comprehensive overview of the molecular mechanisms involved in MSC-based cartilage regeneration and outlines promising therapeutic strategies. The insights presented contribute to the ongoing efforts in optimizing MSC-based therapies for effective cartilage repair.

Research Progress in Hydrogels for Cartilage Organoids

The repair and regeneration of cartilage has always been a hot topic in medical research. Cartilage organoids (CORGs) are special cartilage tissue created using tissue engineering techniques outside the body. These engineered organoids tissues provide models that simulate the complex biological functions of cartilage, opening new possibilities for cartilage regenerative medicine and treatment strategies. However, it is crucial to establish suitable matrix scaffolds for the cultivation of CORGs. In recent years, utilizing hydrogel to culture stem cells and induce their differentiation into chondrocytes has emerged as a promising method for the in vitro construction of CORGs. In this review, the methods for establishing CORGs are summarized and an overview of the advantages and limitations of using matrigel in the cultivation of such organoids is provided. Furthermore, the importance of cartilage tissue ECM and alternative hydrogel substitutes for Matrigel, such as alginate, peptides, silk fibroin, and DNA derivatives is discussed, and the pros and cons of using these hydrogels for the cultivation of CORGs are outlined. Finally, the challenges and future directions in hydrogel research for CORGs are discussed. It is hoped that this article provides valuable references for the design and development of hydrogels for CORGs.

Nanostructured Biopolymer-Based Constructs for Cartilage Regeneration: Fabrication Techniques and Perspectives

The essential functions of cartilage, such as shock absorption and resilience, are hindered by its limited regenerative capacity. Although current therapies alleviate symptoms, novel strategies for cartilage regeneration are desperately needed. Recent developments in three-dimensional (3D) constructs aim to address this challenge by mimicking the intrinsic characteristics of native cartilage using biocompatible materials, with a significant emphasis on both functionality and stability. Through fabrication methods such as 3D printing and electrospinning, researchers are making progress in cartilage regeneration; nevertheless, it is still very difficult to translate these advances into clinical practice. The review emphasizes the importance of integrating various fabrication techniques to create stable 3D constructs. Meticulous design and material selection are required to achieve seamless cartilage integration and durability. The review outlines the need to address these challenges and focuses on the latest developments in the production of hybrid 3D constructs based on biodegradable and biocompatible polymers. Furthermore, the review acknowledges the limitations of current research and provides perspectives on potential avenues for effectively regenerating cartilage defects in the future.

Towards Complex Tissues Replication: Multilayer Scaffold Integrating Biomimetic Nanohydroxyapatite/Chitosan Composites

This study explores an approach to design and prepare a multilayer scaffold mimicking interstratified natural tissue. This multilayer construct, composed of chitosan matrices with graded nanohydroxyapatite concentrations, was achieved through an in situ biomineralization process applied to individual layers. Three distinct precursor concentrations were considered, resulting in 10, 20, and 30 wt% nanohydroxyapatite content in each layer. The resulting chitosan/nanohydroxyapatite (Cs/n-HAp) scaffolds, created via freeze-drying, exhibited nanohydroxyapatite nucleation, homogeneous distribution, improved mechanical properties, and good cytocompatibility. The cytocompatibility analysis revealed that the Cs/n-HAp layers presented cell proliferation similar to the control in pure Cs for the samples with 10% n-HAp, indicating good cytocompatibility at this concentration, while no induction of apoptotic death pathways was demonstrated up to a 20 wt% n-Hap concentration. Successful multilayer assembly of Cs and Cs/n-HAp layers highlighted that the proposed approach represents a promising strategy for mimicking multifaceted tissues, such as osteochondral ones.

The Hippo signalling pathway in bone homeostasis: Under the regulation of mechanics and aging

The Hippo signalling pathway is a conserved kinase cascade that orchestrates diverse cellular processes, such as proliferation, apoptosis, lineage commitment and stemness. With the onset of society ages, research on skeletal aging-mechanics-bone homeostasis has exploded. In recent years, aging and mechanical force in the skeletal system have gained groundbreaking research progress. Under the regulation of mechanics and aging, the Hippo signalling pathway has a crucial role in the development and homeostasis of bone. We synthesize the current knowledge on the role of the Hippo signalling pathway, particularly its downstream effectors yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), in bone homeostasis. We discuss the regulation of the lineage specification and function of different skeletal cell types by the Hippo signalling pathway. The interactions of the Hippo signalling pathway with other pathways, such as Wnt, transforming growth factor beta and nuclear factor kappa-B, are also mentioned because of their importance for modulating bone homeostasis. Furthermore, YAP/TAZ have been extensively studied as mechanotransducers. Due to space limitations, we focus on reviewing how mechanical forces and aging influence cell fate, communications and homeostasis through a dysregulated Hippo signalling pathway.

Strontium/Silicon/Calcium-Releasing Hierarchically Structured 3D-Printed Scaffolds Accelerate Osteochondral Defect Repair

Articular cartilage defects are a global challenge, causing substantial disability. Repairing large defects is problematic, often exceeding cartilage's self-healing capacity and damaging bone structures. To tackle this problem, a scaffold-mediated therapeutic ion delivery system is developed. These scaffolds are constructed from poly(ε-caprolactone) and strontium (Sr)-doped bioactive nanoglasses (SrBGn), creating a unique hierarchical structure featuring macropores from 3D printing, micropores, and nanotopologies due to SrBGn integration. The SrBGn-embedded scaffolds (SrBGn-µCh) release Sr, silicon (Si), and calcium (Ca) ions, which improve chondrocyte activation, adhesion, proliferation, and maturation-related gene expression. This multiple ion delivery significantly affects metabolic activity and maturation of chondrocytes. Importantly, Sr ions may play a role in chondrocyte regulation through the Notch signaling pathway. Notably, the scaffold's structure and topological cues expedite the recruitment, adhesion, spreading, and proliferation of chondrocytes and bone marrow-derived mesenchymal stem cells. Si and Ca ions accelerate osteogenic differentiation and blood vessel formation, while Sr ions enhance the polarization of M2 macrophages. The findings show that SrBGn-µCh scaffolds accelerate osteochondral defect repair by delivering multiple ions and providing structural/topological cues, ultimately supporting host cell functions and defect healing. This scaffold holds great promise for osteochondral repair applications.

Composite Hydrogel Containing Collagen-Modified Polylactic Acid-Hydroxylactic Acid Copolymer Microspheres Loaded with Tetramethylpyrazine Promotes Articular Cartilage Repair

Articular cartilage defects pose a significant challenge due to the limited self-healing ability of cartilage. However, traditional techniques face limitations including autologous chondrocyte expansion issues. This study aims to investigate the effects of the polylactic acid-glycolic acid (PLGA) and collagen-surface modified polylactic acid-glycolic acid (CPLGA) microspheres loaded with tetramethylpyrazine (TMP) on two cell types and the regeneration potential of articular cartilage. CPLGA microspheres are prepared by Steglich reaction and characterized. They evaluated the effect of TMP-loaded microspheres on HUVECs (Human Umbilical Vein Endothelial Cells) and examined the compatibility of blank microspheres with BMSCs (Bone marrow mesenchymal stromal cells) and their potential to promote cartilage differentiation. Subcutaneous implant immune tests and cartilage defect treatment are conducted to assess biocompatibility and cartilage repair potential. The results highlight the efficacy of CPLGA microspheres in promoting tissue regeneration, attributed to improved hydrophilicity and collagen-induced mitigation of degradation. Under hypoxic conditions, both CPLGA and PLGA TMP-loaded microspheres exhibit inhibitory effects on HUVEC proliferation, migration, and angiogenesis. Notably, CPLGA microspheres show enhanced compatibility with BMSCs, facilitating chondrogenic differentiation. Moreover, the CPLGA microsphere-composite hydrogel exhibits potential for cartilage repair by modulating angiogenesis and promoting BMSC differentiation.

Engineering Wet-Resistant and Osteogenic Nanocomposite Adhesive to Control Bleeding and Infection after Median Sternotomy

Median sternotomy surgery stands as one of the prevailing strategies in cardiac surgery. In this study, the cutting-edge bone adhesive is designed, inspired by the impressive adhesive properties found in mussels and sandcastle worms. This work has created an osteogenic nanocomposite coacervate adhesive by integrating a cellulose-polyphosphodopamide interpenetrating network, quaternized chitosan, and zinc, gallium-doped hydroxyapatite nanoparticles. This adhesive is characterized by robust catechol-metal coordination which effectively adheres to both hard and soft tissues with a maximum adhesive strength of 900 ± 38 kPa on the sheep sternum bone, surpassing that of commercial bone adhesives. The release of zinc and gallium cations from nanocomposite adhesives and quaternized chitosan matrix imparts remarkable antibacterial properties and promotes rapid blood coagulation, in vitro and ex vivo. It is also proved that this nanocomposite adhesive exhibits significant in vitro bioactivity, stable degradability, biocompatibility, and osteogenic ability. Furthermore, the capacity of nanocomposite coacervate to adhere to bone tissue and support osteogenesis contributes to the successful healing of a sternum bone defect in a rabbit model in vivo. In summary, these nanocomposite coacervate adhesives with promising characteristics are expected to provide solutions to clinical issues faced during median sternotomy surgery.

Fabrication of gelatin-polyester based biocomposite scaffold via one-step functionalization of melt electrowritten polymer blends in aqueous phase

The rapid manufacturing of biocomposite scaffold made of saturated-Poly(ε-caprolactone) (PCL) and unsaturated Polyester (PE) blends with gelatin and modified gelatin (NCO-Gel) is demonstrated. Polyester blend-based scaffold are fabricated with and without applying potential in the melt electrowriting system. Notably, the applied potential induces phase separation between PCL and PE and drives the formation of PE rich spots at the interface of electrowritten fibers. The objective of the current study is to control the phase separation between saturated and unsaturated polyesters occurring in the melt electro-writing process and utilization of this phenomenon to improve efficiency of biofunctionalization at the interface of scaffold via Aza-Michael addition reaction. Electron-deficient triple bonds of PE spots on the fibers exhibit good potential for the biofunctionalization via the aza-Michael addition reaction. PE spots are found to be pronounced in which blend compositions are PCL-PE as 90:10 and 75:25 %. The biofunctionalization of scaffold is monitored through CN bond formation appeared at 400 eV via X-ray photoelectron spectroscopy (XPS) and XPS chemical mapping. The described biofunctionalization methodology suggest avoiding use of multi-step chemical modification on additive manufacturing products and thereby rapid prototyping of functional polymer blend based scaffolds with enhanced biocompatibility and preserved mechanical properties. Additionally one-step additive manufacturing method eliminates side effects of toxic solvents and long modification steps during scaffold fabrication.

Injectable hydrogels as promising in situ therapeutic platform for cartilage tissue engineering

Injectable hydrogels are gaining prominence as a biocompatible, minimally invasive, and adaptable platform for cartilage tissue engineering. Commencing with their synthesis, this review accentuates the tailored matrix formulations and cross-linking techniques essential for fostering three-dimensional cell culture and melding with complex tissue structures. Subsequently, it spotlights the hydrogels' enhanced properties, highlighting their augmented functionalities and broadened scope in cartilage tissue repair applications. Furthermore, future perspectives are advocated, urging continuous innovation and exploration to surmount existing challenges and harness the full clinical potential of hydrogels in regenerative medicine. Such advancements are crucial for validating the long-term efficacy and safety of hydrogels, positioning them as a promising direction in regenerative medicine to address cartilage-related ailments.

Molecular co-assembled strategy tuning protein conformation for cartilage regeneration

The assembly of oligopeptide and polypeptide molecules can reconstruct various ordered advanced structures through intermolecular interactions to achieve protein-like biofunction. Here, we develop a "molecular velcro"-inspired peptide and gelatin co-assembly strategy, in which amphiphilic supramolecular tripeptides are attached to the molecular chain of gelatin methacryloyl via intra-/intermolecular interactions. We perform molecular docking and dynamics simulations to demonstrate the feasibility of this strategy and reveal the advanced structural transition of the co-assembled hydrogel, which brings more ordered β-sheet content and 10-fold or more compressive strength improvement. We conduct transcriptome analysis to reveal the role of co-assembled hydrogel in promoting cell proliferation and chondrogenic differentiation. Subcutaneous implantation evaluation confirms considerably reduced inflammatory responses and immunogenicity in comparison with type I collagen. We demonstrate that bone mesenchymal stem cells-laden co-assembled hydrogel can be stably fixed in rabbit knee joint defects by photocuring, which significantly facilitates hyaline cartilage regeneration after three months. This co-assembly strategy provides an approach for developing cartilage regenerative biomaterials.

Articular cartilage repair biomaterials: strategies and applications

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

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.

Recent advances of exosomes in soft tissue injuries in sports medicine: A critical review on biological and biomaterial applications

Sports medicine is generally associated with soft tissue injuries including muscle injuries, meniscus and ligament injuries, tendon ruptures, tendinopathy, rotator cuff tears, and tendon-bone healing during injuries. Tendon and ligament injuries are the most common sport injuries accounting for 30-40% of all injuries. Therapies for tendon injuries can be divided into surgical and non-surgical methods. Surgical methods mainly depend on the operative procedures, the surgeons and postoperative interventions. In non-surgical methods, cell therapy with stem cells and cell-free therapy with secretome of stem cell origin are current directions. Exosomes are the main paracrine factors of mesenchymal stem cells (MSCs) containing biological components such as proteins, nucleic acids and lipids. Compared with MSCs, MSC-exosomes (MSC-exos) possess the capacity to escape phagocytosis and achieve long-term circulation. In addition, the functions of exosomes from various cell sources in soft tissue injuries in sports medicine have been gradually revealed in recent years. Along with the biological and biomaterial advances in exosomes, exosomes can be designed as drug carriers with biomaterials and exosome research is providing promising contributions in cell biology. Exosomes with biomaterial have the potential of becoming one of the novel therapeutic modalities in regenerative researches. This review summarizes the derives of exosomes in soft tissue regeneration and focuses on the biological and biomaterial mechanism and advances in exosomal therapy in soft tissue injuries.

Recent advances in 3D bioprinted cartilage-mimicking constructs for applications in tissue engineering

Human cartilage tissue can be categorized into three types: hyaline cartilage, elastic cartilage and fibrocartilage. Each type of cartilage tissue possesses unique properties and functions, which presents a significant challenge for the regeneration and repair of damaged tissue. Bionics is a discipline in which humans study and imitate nature. A bionic strategy based on comprehensive knowledge of the anatomy and histology of human cartilage is expected to contribute to fundamental study of core elements of tissue repair. Moreover, as a novel tissue-engineered technology, 3D bioprinting has the distinctive advantage of the rapid and precise construction of targeted models. Thus, by selecting suitable materials, cells and cytokines, and by leveraging advanced printing technology and bionic concepts, it becomes possible to simultaneously realize multiple beneficial properties and achieve improved tissue repair. This article provides an overview of key elements involved in the combination of 3D bioprinting and bionic strategies, with a particular focus on recent advances in mimicking different types of cartilage tissue.

A Membrane-Targeted Photosensitizer Prevents Drug Resistance and Induces Immune Response in Treating Candidiasis

Candida albicans (C. albicans), a ubiquitous polymorphic fungus in humans, causes different types of candidiasis, including oral candidiasis (OC) and vulvovaginal candidiasis (VVC), which are physically and mentally concerning and financially costly. Thus, developing alternative antifungals that prevent drug resistance and induce immunity to eliminate Candida biofilms is crucial. Herein, a novel membrane-targeted aggregation-induced emission (AIE) photosensitizer (PS), TBTCP-QY, is developed for highly efficient photodynamic therapy (PDT) of candidiasis. TBTCP-QY has a high molar absorption coefficient and an excellent ability to generate 1 O2 and •OH, entering the interior of biofilms due to its high permeability. Furthermore, TBTCP-QY can efficiently inhibit biofilm formation by suppressing the expression of genes related to the adhesion (ALS3, EAP1, and HWP1), invasion (SAP1 and SAP2), and drug resistance (MDR1) of C. albicans, which is also advantageous for eliminating potential fungal resistance to treat clinical infectious diseases. TBTCP-QY-mediated PDT efficiently targets OC and VVC in vivo in a mouse model, induces immune response, relieves inflammation, and accelerates the healing of mucosal defects to combat infections caused by clinically isolated fluconazole-resistant strains. Moreover, TBTCP-QY demonstrates excellent biocompatibility, suggesting its potential applications in the clinical treatment of OC and VVC.

Emerging advances in hydrogel-based therapeutic strategies for tissue regeneration

Significant developments in cell therapy and biomaterial science have broadened the therapeutic landscape of tissue regeneration. Tissue damage is a complex biological process in which different types of cells play a specific role in repairing damaged tissues and growth factors strictly regulate the activity of these cells. Hydrogels have become promising biomaterials for tissue regeneration if appropriate materials are selected and the hydrogel properties are well-regulated. Importantly, they can be used as carriers for living cells and growth factors due to the high water-holding capacity, high permeability, and good biocompatibility of hydrogels. Cell-loaded hydrogels can play an essential role in treating damaged tissues and open new avenues for cell therapy. There is ample evidence substantiating the ability of hydrogels to facilitate the delivery of cells (stem cell, macrophage, chondrocyte, and osteoblast) and growth factors (bone morphogenetic protein, transforming growth factor, vascular endothelial growth factor and fibroblast growth factor). This paper reviewed the latest advances in hydrogels loaded with cells or growth factors to promote the reconstruction of tissues. Furthermore, we discussed the shortcomings of the application of hydrogels in tissue engineering to promote their further development.

3D-printed PCL scaffolds with anatomy-inspired bionic stratified structures for the treatment of growth plate injuries

The growth plate is a cartilaginous tissue with three distinct zones. Resident chondrocytes are highly organized in a columnar structure, which is critical for the longitudinal growth of immature long bones. Once injured, the growth plate may potentially be replaced by bony bar formation and, consequently, cause limb abnormalities in children. It is well-known that the essential step in growth plate repair is the remolding of the organized structure of chondrocytes. To achieve this, we prepared an anatomy-inspired bionic Poly(ε-caprolactone) (PCL) scaffold with a stratified structure using three-dimensional (3D) printing technology. The bionic scaffold is engineered by surface modification of NaOH and collagen Ⅰ (COL Ⅰ) to promote cell adhesion. Moreover, chondrocytes and bone marrow mesenchymal stem cells (BMSCs) are loaded in the most suitable ratio of 1:3 for growth plate reconstruction. Based on the anatomical structure of the growth plate, the bionic scaffold is designed to have three regions, which are the small-, medium-, and large-pore-size regions. These pore sizes are used to induce BMSCs to differentiate into similar structures such as the growth plate. Remarkably, the X-ray and histological results also demonstrate that the cell-loaded stratified scaffold can successfully rebuild the structure of the growth plate and reduce limb abnormalities, including limb length discrepancies and angular deformities in vivo. This study provides a potential method of preparing a bioinspired stratified scaffold for the treatment of growth plate injuries.

Towards Polycaprolactone-Based Scaffolds for Alveolar Bone Tissue Engineering: A Biomimetic Approach in a 3D Printing Technique

The alveolar bone is a unique type of bone, and the goal of bone tissue engineering (BTE) is to develop methods to facilitate its regeneration. Currently, an emerging trend involves the fabrication of polycaprolactone (PCL)-based scaffolds using a three-dimensional (3D) printing technique to enhance an osteoconductive architecture. These scaffolds are further modified with hydroxyapatite (HA), type I collagen (CGI), or chitosan (CS) to impart high osteoinductive potential. In conjunction with cell therapy, these scaffolds may serve as an appealing alternative to bone autografts. This review discusses research gaps in the designing of 3D-printed PCL-based scaffolds from a biomimetic perspective. The article begins with a systematic analysis of biological mineralisation (biomineralisation) and ossification to optimise the scaffold's structural, mechanical, degradation, and surface properties. This scaffold-designing strategy lays the groundwork for developing a research pathway that spans fundamental principles such as molecular dynamics (MD) simulations and fabrication techniques. Ultimately, this paves the way for systematic in vitro and in vivo studies, leading to potential clinical applications.

Current application and modification strategy of marine polysaccharides in tissue regeneration: A review

Marine polysaccharides (MPs) are exceptional bioactive materials that possess unique biochemical mechanisms and pharmacological stability, making them ideal for various tissue engineering applications. Certain MPs, including agarose, alginate, carrageenan, chitosan, and glucan have been successfully employed as biological scaffolds in animal studies. As carriers of signaling molecules, scaffolds can enhance the adhesion, growth, and differentiation of somatic cells, thereby significantly improving the tissue regeneration process. However, the biological benefits of pure MPs composite scaffold are limited. Therefore, physical, chemical, enzyme modification and other methods are employed to expand its efficacy. Chemically, the structural properties of MPs scaffolds can be altered through modifications to functional groups or molecular weight reduction, thereby enhancing their biological activities. Physically, MPs hydrogels and sponges emulate the natural extracellular matrix, creating a more conducive environment for tissue repair. The porosity and high permeability of MPs membranes and nanomaterials expedite wound healing. This review explores the distinctive properties and applications of select MPs in tissue regeneration, highlighting their structural versatility and biological applicability. Additionally, we provide a brief overview of common modification strategies employed for MP scaffolds. In conclusion, MPs have significant potential and are expected to be a novel regenerative material for tissue engineering.

A Metal-Organic Framework-Incorporated Hydrogel for Delivery of Immunomodulatory Neobavaisoflavone to Promote Cartilage Regeneration in Osteoarthritis

The treatment of osteoarthritis (OA)-related cartilage defects is a great clinical challenge due to the complex pathogenesis of OA and poor self-repair ability of cartilage tissue. Combining local and long-term anti-inflammatory therapies to promote cartilage repair is an effective method to treat OA. In this study, a zinc-organic framework-incorporated extracellular matrix (ECM)-mimicking hydrogel platform was constructed for the inflammatory microenvironment-responsive delivery of neobavaisoflavone (NBIF) to promote cartilage regeneration in OA. The NBIF was encapsulated in situ in zeolitic imidazolate frameworks (ZIF-8 MOFs). The NBIF@ZIF-8 MOFs were decorated with polydopamine and incorporated into a methacrylate gelatin/hyaluronic acid hybrid network to form the NBIF@ZIF-8/PHG hydrogel. The hydrogel featured excellent cell/tissue affinity, providing a favorable microenvironment for recruiting cells and cytokines to the defect sites. The hydrogel enabled the on-demand NBIF released in response to a weakly acidic microenvironment at the injured joint site to resolve inflammatory responses during the early stages of OA. Consequently, the cooperativity of the loaded NBIF and hydrogel synergistically modulated the immune response and assisted in cartilage defect repair. In summary, the NBIF@ZIF-8/PHG hydrogel delivery platform represents an effective treatment strategy for OA-related cartilage defects and may attract attentions for applications in other inflammatory diseases.

The potential role of synovial cells in the progression and treatment of osteoarthritis

Osteoarthritis (OA), the commonest arthritis, is characterized by the progressive destruction of cartilage, leading to disability. The Current early clinical treatment strategy for OA often centers on anti-inflammatory or analgesia medication, weight loss, improved muscular function and articular cartilage repair. Although these treatments can relieve symptoms, OA tends to be progressive, and most patients require arthroplasty at the terminal stages of OA. Recent studies have shown a close correlation between joint pain, inflammation, cartilage destruction and synovial cells. Consequently, understanding the potential mechanisms associated with the action of synovial cells in OA could be beneficial for the clinical management of OA. Therefore, this review comprehensively describes the biological functions of synovial cells, the synovium, together with the pathological changes of synovial cells in OA, and the interaction between the cartilage and synovium, which is lacking in the present literature. Additionally, therapeutic approaches based on synovial cells for OA treatment are further discussed from a clinical perspective, highlighting a new direction in the treatment of OA.

3D Printed Chondrogenic Functionalized PGS Bioactive Scaffold for Cartilage Regeneration

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

Advancing drug delivery to articular cartilage: From single to multiple strategies

Articular cartilage (AC) injuries often lead to cartilage degeneration and may ultimately result in osteoarthritis (OA) due to the limited self-repair ability. To date, numerous intra-articular delivery systems carrying various therapeutic agents have been developed to improve therapeutic localization and retention, optimize controlled drug release profiles and target different pathological processes. Due to the complex and multifactorial characteristics of cartilage injury pathology and heterogeneity of the cartilage structure deposited within a dense matrix, delivery systems loaded with a single therapeutic agent are hindered from reaching multiple targets in a spatiotemporal matched manner and thus fail to mimic the natural processes of biosynthesis, compromising the goal of full cartilage regeneration. Emerging evidence highlights the importance of sequential delivery strategies targeting multiple pathological processes. In this review, we first summarize the current status and progress achieved in single-drug delivery strategies for the treatment of AC diseases. Subsequently, we focus mainly on advances in multiple drug delivery applications, including sequential release formulations targeting various pathological processes, synergistic targeting of the same pathological process, the spatial distribution in multiple tissues, and heterogeneous regeneration. We hope that this review will inspire the rational design of intra-articular drug delivery systems (DDSs) in the future.

Sericin nano-gel agglomerates mimicking the pericellular matrix induce the condensation of mesenchymal stem cells and trigger cartilage micro-tissue formation without exogenous stimulation of growth factors in vitro

Mesenchymal stem cells (MSCs) are excellent seed cells for cartilage tissue engineering and regenerative medicine. Though the condensation of MSCs is the first step of their differentiation into chondrocytes in skeletal development, the process is a challenge in cartilage repairing by MSCs. The pericellular matrix (PCM), a distinct region surrounding the chondrocytes, acts as an extracellular linker among cells and forms the microenvironment of chondrocytes. Inspired by this, sericin nano-gel soft-agglomerates were prepared and used as linkers to induce MSCs to assemble into micro-spheres and differentiate into cartilage-like micro-tissues without exogenous stimulation of growth factors. These sericin nano-gel soft-agglomerates are composed of sericin nano-gels prepared by the chelation of metal ions and sericin protein. The MSCs cultured on 2D culture plates self-assembled into cell-microspheres centered by sericin nano-gel agglomerates. The self-assembly progress of MSCs is superior to the traditional centrifugation to achieve MSC condensation due to its facility, friendliness to MSCs and avoidance of the side-effects of growth factors. The analysis of transcriptomic results suggested that sericin nano-gel agglomerates offered a soft mechanical stimulation to MSCs similar to that of the PCM to chondrocytes and triggered some signaling pathways as associated with MSC chondrogenesis. The strategy of utilizing biomaterials to mimic the PCM as a linker and as a mechanical micro-environment and to induce cell aggregation and trigger the differentiation of MSCs can be employed to drive 3D cellular organization and micro-tissue fabrication in vitro. These cartilage micro-masses reported in this study can be potential candidates for cartilage repairing, cellular building blocks for 3D bio-printing and a model for cartilage development and drug screening.

Harnessing knee joint resident mesenchymal stem cells in cartilage tissue engineering

Osteoarthritis (OA) is a widespread clinical disease characterized by cartilage degeneration in middle-aged and elderly people. Currently, there is no effective treatment for OA apart from total joint replacement in advanced stages. Mesenchymal stem cells (MSCs) are a type of adult stem cell with diverse differentiation capabilities and immunomodulatory potentials. MSCs are known to effectively regulate the cartilage microenvironment, promote cartilage regeneration, and alleviate OA symptoms. As a result, they are promising sources of cells for OA therapy. Recent studies have revealed the presence of resident MSCs in synovial fluid, synovial membrane, and articular cartilage, which can be collected as knee joint-derived MSCs (KJD-MSC). Several preclinical and clinical studies have demonstrated that KJD-MSCs have great potential for OA treatment, whether applied alone, in combination with biomaterials, or as exocrine MSCs. In this article, we will review the characteristics of MSCs in the joints, including their cytological characteristics, such as proliferation, cartilage differentiation, and immunomodulatory abilities, as well as the biological function of MSC exosomes. We will also discuss the use of tissue engineering in OA treatment and introduce the concept of a new generation of stem cell-based tissue engineering therapy, including the use of engineering, gene therapy, and gene editing techniques to create KJD-MSCs or KJD-MSC derivative exosomes with improved functionality and targeted delivery. These advances aim to maximize the efficiency of cartilage tissue engineering and provide new strategies to overcome the bottleneck of OA therapy. STATEMENT OF SIGNIFICANCE: This research will provide new insights into the medicinal benefit of Joint resident Mesenchymal Stem Cells (MSCs), specifically on its cartilage tissue engineering ability. Through this review, the community will further realize promoting joint resident mesenchymal stem cells, especially cartilage progenitor/MSC-like progenitor cells (CPSC), as a preventive measure against osteoarthritis and cartilage injury. People and medical institutions may also consider cartilage derived MSC as an alternative approach against cartilage degeneration. Moreover, the discussion presented in this study will convey valuable information for future research that will explore the medicinal benefits of cartilage derived MSC.

Tetrahedral framework nucleic acids enhance the chondrogenic potential of human umbilical cord mesenchymal stem cells via the PI3K/AKT axis

The field of regenerative medicine faces a notable challenge in terms of the regeneration of articular cartilage. Without proper treatment, it can lead to osteoarthritis. Based on the research findings, human umbilical cord mesenchymal stem cells (hUMSCs) are considered an excellent choice for regenerating cartilage. However, there is still a lack of suitable biomaterials to control their ability to self-renew and differentiate. To address this issue, in this study using tetrahedral framework nucleic acids (tFNAs) as a new method in an in vitro culture setting to manage the behaviour of hUMSCs was proposed. Then, the influence of tFNAs on hUMSC proliferation, migration and chondrogenic differentiation was explored by combining bioinformatics methods. In addition, a variety of molecular biology techniques have been used to investigate deep molecular mechanisms. Relevant results demonstrated that tFNAs can affect the transcriptome and multiple signalling pathways of hUMSCs, among which the PI3K/Akt pathway is significantly activated. Furthermore, tFNAs can regulate the expression levels of multiple proteins (GSK3β, RhoA and mTOR) downstream of the PI3K-Akt axis to further enhance cell proliferation, migration and hUMSC chondrogenic differentiation. tFNAs provide new insight into enhancing the chondrogenic potential of hUMSCs, which exhibits promising potential for future utilization within the domains of AC regeneration and clinical treatment.

Harnessing Nucleic Acids Nanotechnology for Bone/Cartilage Regeneration

The effective regeneration of weight-bearing bone defects and critical-sized cartilage defects remains a significant clinical challenge. Traditional treatments such as autologous and allograft bone grafting have not been successful in achieving the desired outcomes, necessitating the need for innovative therapeutic approaches. Nucleic acids have attracted significant attention due to their ability to be designed to form discrete structures and programmed to perform specific functions at the nanoscale. The advantages of nucleic acid nanotechnology offer numerous opportunities for in-cell and in vivo applications, and hold great promise for advancing the field of biomaterials. In this review, the current abilities of nucleic acid nanotechnology to be applied in bone and cartilage regeneration are summarized and insights into the challenges and future directions for the development of this technology are provided.

Enhanced Cartilage and Subchondral Bone Repair Using Carbon Nanotube-Doped Peptide Hydrogel-Polycaprolactone Composite Scaffolds

A carbon nanotube-doped octapeptide self-assembled hydrogel (FEK/C) and a hydrogel-based polycaprolactone PCL composite scaffold (FEK/C3-S) were developed for cartilage and subchondral bone repair. The composite scaffold demonstrated modulated microstructure, mechanical properties, and conductivity by adjusting CNT concentration. In vitro evaluations showed enhanced cell proliferation, adhesion, and migration of articular cartilage cells, osteoblasts, and bone marrow mesenchymal stem cells. The composite scaffold exhibited good biocompatibility, low haemolysis rate, and high protein absorption capacity. It also promoted osteogenesis and chondrogenesis, with increased mineralization, alkaline phosphatase (ALP) activity, and glycosaminoglycan (GAG) secretion. The composite scaffold facilitated accelerated cartilage and subchondral bone regeneration in a rabbit knee joint defect model. Histological analysis revealed improved cartilage tissue formation and increased subchondral bone density. Notably, the FEK/C3-S composite scaffold exhibited the most significant cartilage and subchondral bone formation. The FEK/C3-S composite scaffold holds great promise for cartilage and subchondral bone repair. It offers enhanced mechanical support, conductivity, and bioactivity, leading to improved tissue regeneration. These findings contribute to the advancement of regenerative strategies for challenging musculoskeletal tissue defects.

The Current Progress of Tetrahedral DNA Nanostructure for Antibacterial Application and Bone Tissue Regeneration

Recently, programmable assembly technologies have enabled the application of DNA in the creation of new nanomaterials with unprecedented functionality. One of the most common DNA nanostructures is the tetrahedral DNA nanostructure (TDN), which has attracted great interest worldwide due to its high stability, simple assembly procedure, high predictability, perfect programmability, and excellent biocompatibility. The unique spatial structure of TDN allows it to penetrate cell membranes in abundance and regulate cellular biological properties as a natural genetic material. Previous studies have demonstrated that TDNs can regulate various cellular biological properties, including promoting cells proliferation, migration and differentiation, inhibiting cells apoptosis, as well as possessing anti-inflammation and immunomodulatory capabilities. Furthermore, functional molecules can be easily modified at the vertices of DNA tetrahedron, DNA double helix structure, DNA tetrahedral arms or DNA tetrahedral cage structure, enabling TDN to be used as a nanocarrier for a variety of biological applications, including targeted therapies, molecular diagnosis, biosensing, antibacterial treatment, antitumor strategies, and tissue regeneration. In this review, we mainly focus on the current progress of TDN-based nanomaterials for antimicrobial applications, bone and cartilage tissue repair and regeneration. The synthesis and characterization of TDN, as well as the biological merits are introduced. In addition, the challenges and prospects of TDN-based nanomaterials are also discussed.

Biomaterial-based scaffolds in promotion of cartilage regeneration: Recent advances and emerging applications

Osteoarthritis (OA) poses a significant burden for countless individuals, inflicting relentless pain and impairing their quality of life. Although traditional treatments for OA focus on pain management and surgical interventions, they often fall short of addressing the underlying cause of the disease. Fortunately, emerging biomaterial-based scaffolds offer hope for OA therapy, providing immense promise for cartilage regeneration in OA. These innovative scaffolds are ingeniously designed to provide support and mimic the intricate structure of the natural extracellular matrix, thus stimulating the regeneration of damaged cartilage. In this comprehensive review, we summarize and discuss current landscape of biomaterial-based scaffolds for cartilage regeneration in OA. Furthermore, we delve into the diverse range of biomaterials employed in their construction and explore the cutting-edge techniques utilized in their fabrication. By examining both preclinical and clinical studies, we aim to illuminate the remarkable versatility and untapped potential of biomaterial-based scaffolds in the context of OA.

Thetranslational potential of this article

By thoroughly examining the current state of research and clinical studies, this review provides valuable insights that bridge the gap between scientific knowledge and practical application. This knowledge is crucial for clinicians and researchers who strive to develop innovative treatments that go beyond symptom management and directly target the underlying cause of OA. Through the comprehensive analysis and multidisciplinary approach, the review paves the way for the translation of scientific knowledge into practical applications, ultimately improving the lives of individuals suffering from OA and shaping the future of orthopedic medicine.

Evaluation of the In Vitro Antimicrobial Efficacy against Staphylococcus aureus and epidermidis of a Novel 3D-Printed Degradable Drug Delivery System Based on Polycaprolactone/Chitosan/Vancomycin-Preclinical Study

Acute and chronic bone infections, especially those caused by methicillin-resistant Staphylococcus aureus (MRSA), remains a major complication and therapeutic challenge. It is documented that local administration of vancomycin offers better results than the usual routes of administration (e.g., intravenous) when ischemic areas are present. In this work, we evaluate the antimicrobial efficacy against S. aureus and S. epidermidis of a novel hybrid 3D-printed scaffold based on polycaprolactone (PCL) and a chitosan (CS) hydrogel loaded with different vancomycin (Van) concentrations (1, 5, 10, 20%). Two cold plasma treatments were used to improve the adhesion of CS hydrogels to the PCL scaffolds by decreasing PCL hydrophobicity. Vancomycin release was measured by means of HPLC, and the biological response of ah-BM-MSCs growing in the presence of the scaffolds was evaluated in terms of cytotoxicity, proliferation, and osteogenic differentiation. The PCL/CS/Van scaffolds tested were found to be biocompatible, bioactive, and bactericide, as demonstrated by no cytotoxicity (LDH activity) or functional alteration (ALP activity, alizarin red staining) of the cultured cells and by bacterial inhibition. Our results suggest that the scaffolds developed would be excellent candidates for use in a wide range of biomedical fields such as drug delivery systems or tissue engineering applications.

A lubricant and adhesive hydrogel cross-linked from hyaluronic acid and chitosan for articular cartilage regeneration

Trauma-induced articular cartilage damages are common in clinical practice. Hydrogels have been used to fill the cartilage defects and act as extracellular matrices for cell migration and tissue regeneration. Lubrication and stability of the filler materials are essential to achieve a satisfying healing effect in cartilage regeneration. However, conventional hydrogels failed to provide a lubricous effect, or could not anchor to the wound to maintain a stable curing effect. Herein, we fabricated dually cross-linked hydrogels using oxidized hyaluronic acid (OHA) and N-(2-hydroxypropyl)-3-trimethylammonium chitosan chloride (HTCC) methacrylate (HTCCMA). The OHA/HTCCMA hydrogels, which were dynamically cross-linked and then covalently cross-linked by photo-irradiation, showed appropriate rheological properties and self-healing capability. The hydrogels exhibited moderate and stable tissue adhesion property due to formation of dynamic covalent bonds with the cartilage surface. The coefficient of friction values were 0.065 and 0.078 for the dynamically cross-linked and double-cross-linked hydrogels, respectively, demonstrating superior lubrication. In vitro studies showed that the hydrogels had good antibacterial ability and promoted cell proliferation. In vivo studies confirmed that the hydrogels were biocompatible and biodegradable, and exhibited a robust regenerating ability for articular cartilage. This lubricant-adhesive hydrogel is expected to be promising for the treatment of joint injuries as well as regeneration.

Current advancements in bio-ink technology for cartilage and bone tissue engineering

In tissue engineering, the fate of a particular organ/tissue regeneration and repair mainly depends on three pillars - 3D architecture, cells used, and stimulus provided. 3D cell supportive structure development is one of the crucial pillars necessary for defining organ/tissue geometry and shape. In recent years, the advancements in 3D bio-printing (additive manufacturing) made it possible to develop very precise 3D architectures with the help of industrial software like Computer-Aided Design (CAD). The main requirement for the 3D printing process is the bio-ink, which can act as a source for cell support, proliferation, drug (growth factors, stimulators) delivery, and organ/tissue shape. The selection of the bio-ink depends upon the type of 3D tissue of interest. Printing tissues like bone and cartilage is always challenging because it is difficult to find printable biomaterial that can act as bio-ink and mimic the strength of the natural bone and cartilage tissues. This review describes different biomaterials used to develop bio-inks with different processing variables and cell-seeding densities for bone and cartilage 3D printing applications. The review also discusses the advantages, limitations, and cell bio-ink compatibility in each biomaterial section. The emphasis is given to bio-inks reported for 3D printing cartilage and bone and their applications in orthopedics and orthodontists. The critical/important performance and the architectural morphology requirements of desired bone and cartilage bio-inks were compiled in summary.

3D bioprinted hydrogel/polymer scaffold with factor delivery and mechanical support for growth plate injury repair

Introduction: Growth plate injury is a significant challenge in clinical practice, as it could severely affect the limb development of children, leading to limb deformity. Tissue engineering and 3D bioprinting technology have great potential in the repair and regeneration of injured growth plate, but there are still challenges associated with achieving successful repair outcomes. Methods: In this study, GelMA hydrogel containing PLGA microspheres loaded with chondrogenic factor PTH(1-34) was combined with BMSCs and Polycaprolactone (PCL) to develop the PTH(1-34)@PLGA/BMSCs/GelMA-PCL scaffold using bio-3D printing technology. Results: The scaffold exhibited a three-dimensional interconnected porous network structure, good mechanical properties, biocompatibility, and was suitable for cellchondrogenic differentiation. And a rabbit model of growth plate injury was appliedto validate the effect of scaffold on the repair of injured growth plate. The resultsshowed that the scaffold was more effective than injectable hydrogel in promotingcartilage regeneration and reducing bone bridge formation. Moreover, the addition ofPCL to the scaffold provided good mechanical support, significantly reducing limbdeformities after growth plate injury compared with directly injected hydrogel. Discussion: Accordingly, our study demonstrates the feasibility of using 3D printed scaffolds for treating growth plate injuries and could offer a new strategy for the development of growth plate tissue engineering therapy.

Synthesis, Characterization, Properties, and Biomedical Application of Chitosan-Based Hydrogels

The prospective applications of chitosan-based hydrogels (CBHs), a category of biocompatible and biodegradable materials, in biomedical disciplines such as tissue engineering, wound healing, drug delivery, and biosensing have garnered great interest. The synthesis and characterization processes used to create CBHs play a significant role in determining their characteristics and effectiveness. The qualities of CBHs might be greatly influenced by tailoring the manufacturing method to get certain traits, including porosity, swelling, mechanical strength, and bioactivity. Additionally, characterization methods aid in gaining access to the microstructures and properties of CBHs. Herein, this review provides a comprehensive assessment of the state-of-the-art with a focus on the affiliation between particular properties and domains in biomedicine. Moreover, this review highlights the beneficial properties and wide application of stimuli-responsive CBHs. The main obstacles and prospects for the future of CBH development for biomedical applications are also covered in this review.

Functional hydrogels for the repair and regeneration of tissue defects

Tissue defects can be accompanied by functional impairments that affect the health and quality of life of patients. Hydrogels are three-dimensional (3D) hydrophilic polymer networks that can be used as bionic functional tissues to fill or repair damaged tissue as a promising therapeutic strategy in the field of tissue engineering and regenerative medicine. This paper summarises and discusses four outstanding advantages of hydrogels and their applications and advances in the repair and regeneration of tissue defects. First, hydrogels have physicochemical properties similar to the extracellular matrix of natural tissues, providing a good microenvironment for cell proliferation, migration and differentiation. Second, hydrogels have excellent shape adaptation and tissue adhesion properties, allowing them to be applied to a wide range of irregularly shaped tissue defects and to adhere well to the defect for sustained and efficient repair function. Third, the hydrogel is an intelligent delivery system capable of releasing therapeutic agents on demand. Hydrogels are capable of delivering therapeutic reagents and releasing therapeutic substances with temporal and spatial precision depending on the site and state of the defect. Fourth, hydrogels are self-healing and can maintain their integrity when damaged. We then describe the application and research progress of functional hydrogels in the repair and regeneration of defects in bone, cartilage, skin, muscle and nerve tissues. Finally, we discuss the challenges faced by hydrogels in the field of tissue regeneration and provide an outlook on their future trends.

Advances in mechanically robust and biomimetic polysaccharide-based constructs for cartilage tissue engineering

The purpose of cartilage tissue engineering is to provide artificial constructs with biological functions and mechanical features that resemble native tissue to improve tissue regeneration. Biochemical characteristics of the cartilage extracellular matrix (ECM) microenvironment provide a platform for researchers to develop biomimetic materials for optimal tissue repair. Due to the structural similarity of polysaccharides into physicochemical characteristics of cartilage ECM, these natural polymers capture special attention for developing biomimetic materials. The mechanical properties of constructs play a crucial influence in load-bearing cartilage tissues. Moreover, the addition of appropriate bioactive molecules to these constructs can promote chondrogenesis. Here, we discuss polysaccharide-based constructs that can be used to create substitutes for cartilage regeneration. We intend to focus on newly developed bioinspired materials, fine-tuning the mechanical properties of constructs, the design of carriers loaded by chondroinductive agents, and development of appropriate bioinks as a bioprinting approach for cartilage regeneration.

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

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

Covalently Grafted Biomimetic Matrix Reconstructs the Regenerative Microenvironment of the Porous Gradient Polycaprolactone Scaffold to Accelerate Bone Remodeling

Integrating a biomimetic extracellular matrix to improve the microenvironment of 3D printing scaffolds is an emerging strategy for bone substitute design. Here, a "soft-hard" bone implant (BM-g-DPCL) consisting of a bioactive matrix chemically integrated on a polydopamine (PDA)-coated porous gradient scaffold by polyphenol groups is constructed. The PDA-coated "hard" scaffolds promoted Ca²⁺ chelation and mineral deposition; the "soft" bioactive matrix is beneficial to the migration, proliferation, and osteogenic differentiation of stem cells in vitro, accelerated endogenous stem cell recruitment, and initiated rapid angiogenesis in vivo. The results of the rabbit cranial defect model (Φ = 10 mm) confirmed that BM-g-DPCL promoted the integration between bone tissue and implant and induced the deposition of bone matrix. Proteomics confirmed that cytokine adhesion, biomineralization, rapid vascularization, and extracellular matrix formation are major factors that accelerate bone defect healing. This strategy of highly chemically bonded soft-hard components guided the construction of the bioactive regenerative scaffold.

Cell Encapsulation and 3D Bioprinting for Therapeutic Cell Transplantation

The promise of cell therapy has been augmented by introducing biomaterials, where intricate scaffold shapes are fabricated to accommodate the cells within. In this review, we first discuss cell encapsulation and the promising potential of biomaterials to overcome challenges associated with cell therapy, particularly cellular function and longevity. More specifically, cell therapies in the context of autoimmune disorders, neurodegenerative diseases, and cancer are reviewed from the perspectives of preclinical findings as well as available clinical data. Next, techniques to fabricate cell-biomaterials constructs, focusing on emerging 3D bioprinting technologies, will be reviewed. 3D bioprinting is an advancing field that enables fabricating complex, interconnected, and consistent cell-based constructs capable of scaling up highly reproducible cell-biomaterials platforms with high precision. It is expected that 3D bioprinting devices will expand and become more precise, scalable, and appropriate for clinical manufacturing. Rather than one printer fits all, seeing more application-specific printer types, such as a bioprinter for bone tissue fabrication, which would be different from a bioprinter for skin tissue fabrication, is anticipated in the future.

Chitosan-Based Biomaterials for Tissue Regeneration

Chitosan is a chitin-derived biopolymer that has shown great potential for tissue regeneration and controlled drug delivery. It has numerous qualities that make it attractive for biomedical applications such as biocompatibility, low toxicity, broad-spectrum antimicrobial activity, and many others. Importantly, chitosan can be fabricated into a variety of structures including nanoparticles, scaffolds, hydrogels, and membranes, which can be tailored to deliver a desirable outcome. Composite chitosan-based biomaterials have been demonstrated to stimulate in vivo regeneration and the repair of various tissues and organs, including but not limited to, bone, cartilage, dental, skin, nerve, cardiac, and other tissues. Specifically, de novo tissue formation, resident stem cell differentiation, and extracellular matrix reconstruction were observed in multiple preclinical models of different tissue injuries upon treatment with chitosan-based formulations. Moreover, chitosan structures have been proven to be efficient carriers for medications, genes, and bioactive compounds since they can maintain the sustained release of these therapeutics. In this review, we discuss the most recently published applications of chitosan-based biomaterials for different tissue and organ regeneration as well as the delivery of various therapeutics.

Physico-biological evaluation of 3D printed dECM/TOCN/alginate hydrogel based scaffolds for cartilage tissue regeneration

Cartilage damage is the leading cause of osteoarthritis (OA), especially in an aging society. Mimicking the native cartilage microenvironment for chondrogenic differentiation along with constructing a stable and controlled architectural scaffold is considerably challenging. In this study, three-dimensional (3D) printed scaffolds using tempo-oxidized cellulose nanofiber (TOCN), decellularized extracellular matrix (dECM), and sodium alginate (SA) were fabricated for cartilage tissue regeneration. We prepared three groups (dECM80, dECM50, dECM20) of 3D printable hydrogels with different ratios of TOCN and dECM where SA concentration remained the same. Two-step crosslinking was performed with CaCl₂ solution to achieve the highly stable 3D printed scaffolds. Finally, the fundamental physical characterizations showed that increasing the ratio of TOCN with dECM significantly improved the viscoelastic behaviour, stability, mechanical properties, and printability of the scaffolds. Based on the results, the 3D printed dECM50 scaffolds with controlled and identical pore sizes increased the whole-layer integrity and nutrient supply in each layer of the scaffold. Furthermore, evaluation of in vitro and in vivo biocompatibility of the scaffolds with rBMSCs indicated that dECM50 scaffolds provided a suitable microenvironment for cell proliferation and promoted chondrogenesis by remarkably expressing the cartilage-specific markers. This study demonstrates that 3D printed dECM50 scaffolds provide a favourable and promising microenvironment for cartilage tissue regeneration.

An immunomodulatory polypeptide hydrogel for osteochondral defect repair

Osteochondral injury is a common and frequent orthopedic disease that can lead to more serious degenerative joint disease. Tissue engineering is a promising modality for osteochondral repair, but the implanted scaffolds are often immunogenic and can induce unwanted foreign body reaction (FBR). Here, we prepare a polypept(o)ide-based PAA-RGD hydrogel using a novel thiol/thioester dual-functionalized hyperbranched polypeptide P(EG₃Glu-co-Cys) and maleimide-functionalized polysarcosine under biologically benign conditions. The PAA-RGD hydrogel shows suitable biodegradability, excellent biocompatibility, and low immunogenicity, which together lead to optimal performance for osteochondral repair in New Zealand white rabbits even at the early stage of implantation. Further in vitro and in vivo mechanistic studies corroborate the immunomodulatory role of the PAA-RGD hydrogel, which induces minimum FBR responses and a high level of polarization of macrophages into the immunosuppressive M2 subtypes. These findings demonstrate the promising potential of the PAA-RGD hydrogel for osteochondral regeneration and highlight the importance of immunomodulation. The results may inspire the development of PAA-based materials for not only osteochondral defect repair but also various other tissue engineering and bio-implantation applications.

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A polypept(o)ide-based hydrogel.

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Prominent and early osteochondral repair.

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Minimized immunogenicity.

3D printing of bone and cartilage with polymer materials

Damage and degeneration to bone and articular cartilage are the leading causes of musculoskeletal disability. Commonly used clinical and surgical methods include autologous/allogeneic bone and cartilage transplantation, vascularized bone transplantation, autologous chondrocyte implantation, mosaicplasty, and joint replacement. 3D bio printing technology to construct implants by layer-by-layer printing of biological materials, living cells, and other biologically active substances in vitro, which is expected to replace the repair mentioned above methods. Researchers use cells and biomedical materials as discrete materials. 3D bio printing has largely solved the problem of insufficient organ donors with the ability to prepare different organs and tissue structures. This paper mainly discusses the application of polymer materials, bio printing cell selection, and its application in bone and cartilage repair.