Microcarriers in application for cartilage tissue engineering: Recent progress and challenges

Microfluidic cell carriers for cultured meat

Cultured meat aims to produce meat mass from cell culture instead of conventional livestock slaughtering. Due to anchorage-dependent and 3D culturing manner of cells, cell carriers are critical in cultured meat. Various cell carriers have been used for expansion of seed cells and cultured meat tissue construction, such as commercial microcarriers, electrospray microspheres, and 3D-printed microfibers, but facing suboptimal effect of cell growth and specific differentiation. Compared to traditional methods, microfluidics can purposefully fabricate cell carriers with diverse structures and components, thereby achieving adequate simulation of natural muscle. Research has shown that microfluidic fibrous carriers possessed excellent effect in cultured meat tissue construction. This review overviews application and potential of microfluidic cell carriers in cultured meat. Starting with introduction of materials for carrier construction, we discuss limitations of traditional cell carriers and focus on microfluidic carrier in cultured meat. Finally, we present challenges and perspectives of microfluidics for cultured meat.

Microwaved schiff base dialdehyde cellulose-chitosan hydrogels for sustained drug release with DFT calculations

Dialdehyde cellulose (DAC) prepared from sugarcane bagasse (SC) by an eco-friendly, fast and low-cost microwave method was used for loading and sustained release of 4-aminoacetophenone (4-AAP). DAC was reacted with chitosan (Ch) and 4-AAP via a Schiff base reaction. FTIR analysis confirmed successful Schiff base formation between DAC and Ch, evidenced by the disappearance of the DAC aldehyde peak at 1716 cm⁻1 and the appearance of the imine peak at 1631 cm⁻1, as well as strong hydrogen bonding with incorporated 4-AAP, indicated by a shift in the O-H stretch from 3336 cm⁻1 to 3330 cm⁻1.Swelling studies showed increased water absorption with higher 4-AAP content, with 4-AAP@DAC/Ch2 demonstrating pseudo-second-order kinetics and non-Fickian diffusion. The DFT calculations revealed that the 4-AAP@DAC/Ch hydrogel exhibited enhanced stability and reactivity. A significantly reduced HOMO-LUMO energy gap, coupled with negative Pi values, indicated strong interactions between DAC, chitosan, and 4-AAP. The high adsorption energy further supported the observed slow drug release, validating the experimental findings.

Microfluidics-Based Microcarriers for Live-Cell Delivery

Live-cell therapy has emerged as a revolutionary treatment modality, providing a novel therapeutic avenue for intractable diseases. However, a major challenge in live-cell therapy is to maintain live-cell viability and efficacy during the treatment. Microcarriers are crucial for enhancing cell retention, viability, and functions by providing a protective scaffold and creating a supportive environment for live-cell proliferation and metabolism. For microcarrier construction, the microfluidic technology demonstrates excellent characteristics in terms of controllability over microcarrier size and morphology as well as potential for high-throughput production. To date, multiple live-cell delivery microcarrier types (e.g., microspheres, microfibers, and microneedles) are prepared via microfluidic liquid templates to meet different therapeutic needs. In this review, recent developments in microfluidics-based microcarriers for live-cell delivery are presented. It is focused on categorizing the structural design of microfluidic-derived cell-laden microcarriers, and summarizing various therapeutic applications. Finally, an outlook is provided on the future challenges and opportunities in this field.

A comprehensive review on using injectable chitosan microgels for osteochondral tissue repair

Restoring cartilage to healthy state is challenging due to low cell density and hence low regenerative capacity. The current platforms are not compatible with clinical translation and require dedicated handling of trained personnel. However, by engineering and implanting cell microaggregates in higher concentrations, efficient formation of new cartilage can be achieved, even in the absence of exogenous growth factors. Therefore, one-step surgeries are preferable for novel treatments and we need cell laden microgels allowing the formation of microaggregaets in vivo. Injectability is a key parameter for in situ forming the shape and minimally invasive clinical applications. Hydrogels as bioinks can restore damaged tissues to their primary shape. Chitosan is a polysaccharide derived from chitin with abundant usage in tissue engineering. This review highlights the use of chitosan as an injectable hydrogel for osteochondral defects. Several studies focused on encapsulating mesenchymal stem cells within chitosan hydrogels have been categorized and incorporating microfluidic devices has been identified in the forefront to form microgels. Additionally, the printability is another convenience of chitosan for using in 3D printing for cartilage tissue engineering which is described in this review.

Wild grown Portulaca oleracea as a novel magnetite based carrier with in vitro antioxidant and cytotoxicity potential

The latest research on nanotechnology through the new tailored scaffolds encompassed the therapeutic effects of natural compounds, and the unique properties of metallic nanoparticles offer new possibilities in emerging biomedical fields. Various strategies have been developed to address the limitations of existing therapeutic agents concerning specificity, vectorization, bioavailability, drug resistance, and adverse effects. In this study, the medicinal plant Portulaca oleracea L. and magnetite nanoparticles were used to develop an innovative target carrier system, designed to enhance the cytotoxic effect and overcome the main drawbacks (permeability and localization) of the phytoconstituents. The low-metabolite profile of Romanian wild-grown Portulaca oleracea L. exhibits a diverse range of hundred fifty-five compounds across various chemical categories (amino acids, peptides, fatty acids, flavonoids, alkaloids, terpenoids, phenolic acids, organic acids, esters, sterols, coumarins, nucleosides, lignans, and miscellaneous compounds). Morpho-structural and magnetic properties of the new phytocarrier were investigated using a variety of methods, including XRD, FTIR, Raman, SEM, DLS), and magnetic determinations. The MTT assay was conducted to evaluate in vitro the potential cytotoxicity on normal human dermal fibroblasts (NHDF), as well as on two tumoral cell lines: human osteosarcoma (HOS) and cervical cancer (HeLa). Results indicated that significant inhibition of both cancer cell lines' viability was exerted by the new phytocarrier compared to herbal extract. Furthermore, the results obtained for the total phenolic content and the antioxidant potential screening performed using the FRAP and DPPH assays were superior for the new carrier system. These findings suggest the potential biomedical applications of the developed carrier system and its promising implications for future research and development in the field.

High paracrine activity of hADSCs cartilage microtissues inhibits extracellular matrix degradation and promotes cartilage regeneration

Due to its unique structure, articular cartilage has limited self-repair capacity. Microtissues are tiny tissue clusters that can mimic the function of target organs or tissues. Using cells alone for microtissue construction often results in the formation of necrotic cores. However, the extracellular matrix (ECM) of native cartilage can provide structural support and is an ideal source of microcarriers. Autologous adipose-derived mesenchymal stem cells (ADSCs) and bone marrow mesenchymal stem cells (BMSCs) are widely used in cartilage tissue engineering. In this study, we fabricated microcarriers and compared the behavior of two homologous cell types in the microcarrier environment. The microcarrier environment highlighted the advantages of ADSCs and promoted the proliferation and migration of these cells. Then, ADSCs microtissues (ADSCs-MT) and BMSCs microtissues (BMSCs-MT) were fabricated using a three-dimensional dynamic culture system. In vitro and in vivo experiments verified that the cartilage regeneration ability of ADSCs-MT was significantly superior to that of BMSCs-MT. Transcriptomics revealed that ADSCs-MT showed significantly lower expression levels of ECM degradation, osteogenesis, and fibrocartilage markers. Finally, the protective effect of microtissues on inflammatory chondrocytes was validated. Overall, the ADSCs-MT constructed in this study achieved excellent cartilage regeneration and could be promising for the autologous application of cartilage microtissues.

Magnetically responsive micro-clustered calcium phosphate-reinforced cell-laden microbead sodium alginate hydrogel for accelerated osteogenic tissue regeneration

The rising prevalence of bone injuries has increased the demand for minimally invasive treatments. Microbead hydrogels, renowned for cell encapsulation, provide a versatile substrate for bone tissue regeneration. They deliver bioactive agents, support cell growth, and promote osteogenesis, aiding bone repair and regeneration. In this study, we synthesized superparamagnetic iron oxide nanoparticles (Sp) coated with a calcium phosphate layer (m-Sp), achieving a distinctive flower-like micro-cluster morphology. Subsequently, sodium alginate (SA) microbead hydrogels containing m-Sp (McSa@m-Sp) were fabricated using a dropping gelation strategy. McSa@m-Sp is magnetically targetable, enhance cross-linking, control degradation rates, and provide strong antibacterial activity. Encapsulation studies with MC3T3-E1 cells revealed enhanced viability and proliferation. These studies also indicated significantly elevated alkaline phosphatase (ALP) activity and mineralization in MC3T3-E1 cells, as confirmed by Alizarin Red S (ARS) and Von Kossa staining, along with increased collagen production within the McSa@m-Sp microbead hydrogels. Immunocytochemistry (ICC) and gene expression studies supported the osteoinductive potential of McSa@m-Sp, showing increased expression of osteogenic markers including RUNX-2, collagen-I, osteopontin, and osteocalcin. Thus, McSa@m-Sp microbead hydrogels offer a promising strategy for multifunctional scaffolds in bone tissue engineering.

Sweeten the pill: Multi-faceted polysaccharide-based carriers for colorectal cancer treatment

Colorectal cancer (CRC) ranks as the second deadliest cancer globally and the third most common malignant tumor. While surgery remains the primary treatment for CRC, alternative therapies such as chemotherapy, molecular targeted therapy, and immunotherapy are also commonly used. The significant side effects and toxicity of conventional drugs drive the search for novel targeted therapies, including the design of advanced drug delivery systems. Polysaccharide-based biopolymers, with their low toxicity, non-immunogenic behavior, synergistic interactions with other biopolymers, and tissue and cell compatibility, emerge as excellent drug carriers for this application. This review aims to provide an in-depth overview of recent advancements in developing polysaccharide-based biopolymeric carriers for anticancer compounds in the treatment of CRC. We highlight the multifunctional nature of polysaccharides, showcasing their potential as standalone drug carriers or as integral components of intelligent robotic devices for biomedical therapeutic applications. In addition to exploring the opportunities for using carbohydrate polymers in CRC treatment, we address the challenges and failures that may limit their applicability in biomedical research, as well as summarize the recent preclinical and clinical trials, resulting in several commercialization attempts. This comprehensive overview critically summarizes the potential of polysaccharide-based biomaterials in CRC treatment.

3D printing and computer-aided design techniques for drug delivery scaffolds in tissue engineering

INTRODUCTION

The challenge in tissue engineering lies in replicating the intricate structure of the native extracellular matrix. Recent advancements in AM, notably 3D printing, offer unprecedented capabilities to tailor scaffolds precisely, controlling properties like structure and bioactivity. CAD tools complement this by facilitating design using patient-specific data.

AREA’S COVERED

This review introduces additive manufacturing (AM) and computer-aided design (CAD) as pivotal tools in advancing tissue engineering, particularly cartilage regeneration. This article explores various materials utilized in AM, focusing on polymers and hydrogels for their advantageous properties in tissue engineering applications. Integrating bioactive molecules, including growth factors, into scaffolds to promote tissue regeneration is discussed alongside strategies involving different cell sources, such as stem cells, to enhance tissue development within scaffold matrices.

EXPERT OPINION

Applications of AM and CAD in addressing specific challenges like osteochondral defects and osteoarthritis in cartilage tissue engineering are highlighted. This review consolidates current research findings, offering expert insights into the evolving landscape of AM and CAD technologies in advancing tissue engineering, particularly in cartilage regeneration.

Structure, ingredient, and function-based biomimetic scaffolds for accelerated healing of tendon-bone interface

Background

Tendon-bone interface (TBI) repair is slow and challenging owing to its hierarchical structure, gradient composition, and complex function. In this work, enlightened by the natural characteristics of TBI microstructure and the demands of TBI regeneration, a structure, composition, and function-based scaffold was fabricated. Methods: The biomimetic scaffold was designed based on the "tissue-inducing biomaterials" theory: (1) a porous scaffold was created with poly-lactic-co-glycolic-acid, nano-hydroxyapatite and loaded with BMP2-gelatinmp to simulate the bone (BP); (2) a hydrogel was produced from sodium alginate, type I collagen, and loaded with TGF-β3 to simulate the cartilage (CP); (3) the L-poly-lactic-acid fibers were oriented to simulate the tendon (TP). The morphology of tri-layered constructs, gelation kinetics, degradation rate, release kinetics and mechanical strength of the scaffold were characterized. Then, bone marrow mesenchymal stem cells (MSCs) and tenocytes (TT-D6) were cultured on the scaffold to evaluate its gradient differentiation inductivity. A rat Achilles tendon defect model was established, and BMSCs seeded on scaffolds were implanted into the lesionsite. The tendon-bone lesionsite of calcaneus at 4w and 8w post-operation were obtained for gross observation, radiological evaluation, biomechanical and histological assessment.

Results

The hierarchical microstructures not only endowed the scaffold with gradual composition and mechanical properties for matching the regional biophysical characteristics of TBI but also exhibited gradient differentiation inductivity through providing regional microenvironment for cells. Moreover, the scaffold seeded with cells could effectively accelerate healing in rat Achilles tendon defects, attributable to its enhanced differentiation performance.

Conclusion

The hierarchical scaffolds simulating the structural, compositional, and cellular heterogeneity of natural TBI tissue performed therapeutic effects on promoting regeneration of TBI and enhancing the healing quality of Achilles tendon.

The translational potential of this article

The novel scaffold showed the great efficacy on tendon to bone healing by offering a structural and compositional microenvironment. The results meant that the hierarchical scaffold with BMSCs may have a great potential for clinical application.

Versatile cell cultivation on injectable poly(butylene adipate-co-terephthalate) microcarriers: Impact of surface properties across different cell types

Injectable cell therapies offer several advantages compared with traditional open surgery, including less trauma to the patient, shorter recovery time, and lower risk of infection. However, a significant problem is the difficulty in developing effective cell delivery carriers that are cyto-compatible and maintain cell viability both during and after injection. In the presented study, it was aimed to develop poly(butylene adipate-co-terephthalate) (PBAT) microcarriers using the emulsion preparation-solvent evaporation technique. The optimized diameter of the PBAT microcarriers was determined as 104 ± 15 μm at 700 rpm and there would be no blockage after injection due to the nonswelling feature of microcarriers. Furthermore, the cellular activities of PBAT microcarriers were evaluated in static culture for 7 days using L929 mouse fibroblasts, MC3T3-E1 mouse pre-osteoblasts, and rat adipose-derived mesenchymal cells (AdMSCs). 3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide results and Sscanning electron microscope images showed that PBAT microcarriers increased the adhesion and proliferation properties of pre-osteoblasts and stem cells, while L929 fibroblasts formed aggregates by adhering to certain regions of the microcarrier surface and did not spread on the surface. These results emphasize that PBAT microcarriers can be used as injectable carriers, especially in stem cell therapies, but their surface properties need to be modified for some cells.

Stimuli-responsive microcarriers and their application in tissue repair: A review of magnetic and electroactive microcarrier

Microcarrier applications have made great advances in tissue engineering in recent years, which can load cells, drugs, and bioactive factors. These microcarriers can be minimally injected into the defect to help reconstruct a good microenvironment for tissue repair. In order to achieve more ideal performance and face more complex tissue damage, an increasing amount of effort has been focused on microcarriers that can actively respond to external stimuli. These microcarriers have the functions of directional movement, targeted enrichment, material release control, and providing signals conducive to tissue repair. Given the high controllability and designability of magnetic and electroactive microcarriers, the research progress of these microcarriers is highlighted in this review. Their structure, function and applications, potential tissue repair mechanisms, and challenges are discussed. In summary, through the design with clinical translation ability, meaningful and comprehensive experimental characterization, and in-depth study and application of tissue repair mechanisms, stimuli-responsive microcarriers have great potential in tissue repair.

Gravity-Oriented Microfluidic Device for Biocompatible End-to-End Fabrication of Cell-Laden Microgels

Droplet microfluidics are extensively utilized to generate monodisperse cell-laden microgels in biomedical applications. However, maintaining cell viability is still challenging due to overexposure to harsh conditions in subsequent procedures that recover the microgels from the oil phase. Here, a gravity-oriented microfluidic device for end-to-end fabrication of cell-laden microgels is reported, which integrates dispersion, gelation, and extraction into a continuous workflow. This innovative on-chip extraction, driven by native buoyancy and kinetically facilitated by pseudosurfactant, exhibits 100% retrieval efficiency for microgels with a wide range of sizes and stiffnesses. The viability of encapsulated cells is perfectly maintained at ≈98% with minimal variations within and between batches. The end-to-end fabrication remarkably enhances the biocompatibility and practicality of microfluidics-based cell encapsulation and is promising to be compatible with various applications ranging from single-cell analysis to clinical therapy.

In Situ Remodeling of Efferocytosis via Lesion-Localized Microspheres to Reverse Cartilage Senescence

Efferocytosis, an intrinsic regulatory mechanism to eliminate apoptotic cells, will be suppressed due to the delayed apoptosis process in aging-related diseases, such as osteoarthritis (OA). In this study, cartilage lesion-localized hydrogel microspheres are developed to remodel the in situ efferocytosis to reverse cartilage senescence and recruit endogenous stem cells to accelerate cartilage repair. Specifically, aldehyde- and methacrylic anhydride (MA)-modified hyaluronic acid hydrogel microspheres (AHM), loaded with pro-apoptotic liposomes (liposomes encapsulating ABT263, A-Lipo) and PDGF-BB, namely A-Lipo/PAHM, are prepared by microfluidic and photo-cross-linking techniques. By a degraded porcine cartilage explant OA model, the in situ cartilage lesion location experiment illustrated that aldehyde-functionalized microspheres promote affinity for degraded cartilage. In vitro data showed that A-Lipo induced apoptosis of senescent chondrocytes (Sn-chondrocytes), which can then be phagocytosed by the efferocytosis of macrophages, and remodeling efferocytosis facilitated the protection of normal chondrocytes and maintained the chondrogenic differentiation capacity of MSCs. In vivo experiments confirmed that hydrogel microspheres localized to cartilage lesion reversed cartilage senescence and promoted cartilage repair in OA. It is believed this in situ efferocytosis remodeling strategy can be of great significance for tissue regeneration in aging-related diseases.

Catalpol promotes articular cartilage repair by enhancing the recruitment of endogenous mesenchymal stem cells

Articular cartilage defect is challenged by insufficient regenerative ability of cartilage. Catalpol (CA), the primary active component of Rehmanniae Radix, could exert protective effects against various diseases. However, the impact of CA on the treatment of articular cartilage injuries is still unclear. In this study, full-thickness articular cartilage defect was induced in a mouse model via surgery. The animals were intraperitoneally injected with CA for 4 or 8 weeks. According to the results of macroscopic observation, micro-computed tomography CT (μCT), histological and immunohistochemistry staining, CA treatment could promote mouse cartilage repair, resulting in cartilage regeneration, bone structure improvement and matrix anabolism. Specifically, an increase in the expression of CD90, the marker of mesenchymal stem cells (MSCs), in the cartilage was observed. In addition, we evaluated the migratory and chondrogenic effects of CA on MSCs. Different concentration of CA was added to C3H10 T1/2 cells. The results showed that CA enhanced cell migration and chondrogenesis without affecting proliferation. Collectively, our findings indicate that CA may be effective for the treatment of cartilage defects via stimulation of endogenous MSCs.

Using Decellularized Magnetic Microrobots to Deliver Functional Cells for Cartilage Regeneration

The use of natural cartilage extracellular matrix (ECM) has gained widespread attention in the field of cartilage tissue engineering. However, current approaches for delivering functional scaffolds for osteoarthritis (OA) therapy rely on knee surgery, which is limited by the narrow and complex structure of the articular cavity and carries the risk of injuring surrounding tissues. This work introduces a novel cell microcarrier, magnetized cartilage ECM-derived scaffolds (M-CEDSs), which are derived from decellularized natural porcine cartilage ECM. Human bone marrow mesenchymal stem cells are selected for their therapeutic potential in OA treatments. Owing to their natural composition, M-CEDSs have a biomechanical environment similar to that of human cartilage and can efficiently load functional cells while maintaining high mobility. The cells are released spontaneously at a target location for at least 20 days. Furthermore, cell-seeded M-CEDSs show better knee joint function recovery than control groups 3 weeks after surgery in preclinical experiments, and ex vivo experiments reveal that M-CEDSs can rapidly aggregate inside tissue samples. This work demonstrates the use of decellularized microrobots for cell delivery and their in vivo therapeutic effects in preclinical tests.

Stem Cells Expansion Vector via Bioadhesive Porous Microspheres for Accelerating Articular Cartilage Regeneration

Stem cell tissue engineering is a potential treatment for osteoarthritis. However, the number of stem cells that can be delivered, loss of stem cells during injection, and migration ability of stem cells limit applications of traditional stem cell tissue engineering. Herein, kartogenin (KGN)-loaded poly(lactic-co-glycolic acid) (PLGA) porous microspheres is first engineered via emulsification, and then anchored with chitosan through the amidation reaction to develop a new porous microsphere (PLGA-CS@KGN) as a stem cell expansion vector. Following 3D co-culture of the PLGA-CS@KGN carrier with mesenchymal stem cells (MSCs), the delivery system is injected into the capsule cavity in situ. In vivo and in vitro experiments show that PLGA-CS microspheres have a high cell-carrying capacity up to 1 × 104 mm-3 and provide effective protection of MSCs to promote their controlled release in the osteoarthritis microenvironment. Simultaneously, KGN loaded inside the microspheres effectively cooperated with PLGA-CS to induce MSCs to differentiate into chondrocytes. Overall, these findings indicate that PLGA-CS@KGN microspheres held high cell-loading ability, adapt to the migration and expansion of cells, and promote MSCs to express markers associated with cartilage repair. Thus, PLGA-CS@KGN can be used as a potential stem cell carrier for enhancing stem cell therapy in osteoarthritis treatment.

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.

Recent Developments in Metallic Degradable Micromotors for Biomedical and Environmental Remediation Applications

Synthetic micromotor has gained substantial attention in biomedicine and environmental remediation. Metal-based degradable micromotor composed of magnesium (Mg), zinc (Zn), and iron (Fe) have promise due to their nontoxic fuel-free propulsion, favorable biocompatibility, and safe excretion of degradation products Recent advances in degradable metallic micromotor have shown their fast movement in complex biological media, efficient cargo delivery and favorable biocompatibility. A noteworthy number of degradable metal-based micromotors employ bubble propulsion, utilizing water as fuel to generate hydrogen bubbles. This novel feature has projected degradable metallic micromotors for active in vivo drug delivery applications. In addition, understanding the degradation mechanism of these micromotors is also a key parameter for their design and performance. Its propulsion efficiency and life span govern the overall performance of a degradable metallic micromotor. Here we review the design and recent advancements of metallic degradable micromotors. Furthermore, we describe the controlled degradation, efficient in vivo drug delivery, and built-in acid neutralization capabilities of degradable micromotors with versatile biomedical applications. Moreover, we discuss micromotors' efficacy in detecting and destroying environmental pollutants. Finally, we address the limitations and future research directions of degradable metallic micromotors.

Bioprinting-Enabled Biomaterials: A Cutting-Edge Strategy for Future Osteoarthritis Therapy

Bioprinting is an advanced technology that allows for the precise placement of cells and biomaterials in a controlled manner, making significant contributions in regenerative medicine. Notably, bioprinting-enabled biomaterials have found extensive application as drug delivery systems (DDS) in the treatment of osteoarthritis (OA). Despite the widespread utilization of these biomaterials, there has been limited comprehensive research summarizing the recent advances in this area. Therefore, this review aims to explore the noteworthy developments and challenges associated with utilizing bioprinting-enabled biomaterials as effective DDS for the treatment of OA. To begin, we provide an overview of the complex pathophysiology of OA, highlighting the shortcomings of current treatment modalities. Following this, we conduct a detailed examination of various bioprinting technologies and discuss the wide range of biomaterials employed in DDS applications for OA therapy. Finally, by placing emphasis on their transformative potential, we discuss the incorporation of crucial cellular components such as chondrocytes and mesenchymal stem cells into bioprinted constructs, which play a pivotal role in promoting tissue regeneration and repair.

Microcarriers promote the through interface movement of mouse trophoblast stem cells by regulating stiffness

Mechanical force is crucial in the whole process of embryonic development. However, the role of trophoblast mechanics during embryo implantation has rarely been studied. In this study, we constructed a model to explore the effect of stiffness changes in mouse trophoblast stem cells (mTSCs) on implantation: microcarrier was prepared by sodium alginate using a droplet microfluidics system, and mTSCs were attached to the microcarrier surface with laminin modifications, called T(micro). Compared with the spheroid, formed by the self-assembly of mTSCs (T(sph)), we could regulate the stiffness of the microcarrier, making the Young's modulus of mTSCs (367.70 ± 79.81 Pa) similar to that of the blastocyst trophoblast ectoderm (432.49 ± 151.90 Pa). Moreover, T(micro) contributes to improve the adhesion rate, expansion area and invasion depth of mTSCs. Further, T(micro) was highly expressed in tissue migration-related genes due to the activation of the Rho-associated coiled-coil containing protein kinase (ROCK) pathway at relatively similar modulus of trophoblast. Overall, our study explores the embryo implantation process with a new perspective, and provides theoretical support for understanding the effect of mechanics on embryo implantation.

Photocrosslinked methacrylated natural macromolecular hydrogels for tissue engineering: A review

A hydrogel is a three-dimensional (3D) network structure formed through polymer crosslinking, and these have emerged as a popular research topic in recent years. Hydrogel crosslinking can be classified as physical, chemical, or enzymatic, and photocrosslinking is a branch of chemical crosslinking. Compared with other methods, photocrosslinking can control the hydrogel crosslinking initiation, crosslinking time, and crosslinking strength using light. Owing to these properties, photocrosslinked hydrogels have important research prospects in tissue engineering, in situ gel formation, 3D bioprinting, and drug delivery. Methacrylic anhydride modification is a common method for imparting photocrosslinking properties to polymers, and graft-substituted polymers can be photocrosslinked under UV irradiation. In this review, we first introduce the characteristics of common natural polysaccharide- and protein-based hydrogels and the processes used for methacrylate group modification. Next, we discuss the applications of methacrylated natural hydrogels in tissue engineering. Finally, we summarize and discuss existing methacrylated natural hydrogels in terms of limitations and future developments. We expect that this review will help researchers in this field to better understand the synthesis of methacrylate-modified natural hydrogels and their applications in tissue engineering.

Cartilage Regeneration Units Based on Hydrogel Microcarriers for Injectable Cartilage Regeneration in an Autologous Goat Model

Despite numerous studies on tissue-engineered injectable cartilage, it is still difficult to realize stable cartilage formation in preclinical large animal models because of suboptimal biocompatibility, which hinders further application in clinical settings. In this study, we proposed a novel concept of cartilage regeneration units (CRUs) based on hydrogel microcarriers for injectable cartilage regeneration in goats. To achieve this goal, hyaluronic acid (HA) was chosen as the microparticle to integrate gelatin (GT) chemical modification and a freeze-drying technology to create biocompatible and biodegradable HA-GT microcarriers with suitable mechanical strength, uniform particle size, a high swelling ratio, and cell adhesive ability. CRUs were then prepared by seeding goat autologous chondrocytes on the HA-GT microcarriers and culturing in vitro. Compared with traditional injectable cartilage methods, the proposed method forms relatively mature cartilage microtissue in vitro and improves the utilization rate of the culture space to facilitate nutrient exchange, which is necessary for mature and stable cartilage regeneration. Finally, these precultured CRUs were used to successfully regenerate mature cartilage in nude mice and in the nasal dorsum of autologous goats for cartilage filling. This study provides support for the future clinical application of injectable cartilage.

Volumetric Printing Across Melt Electrowritten Scaffolds Fabricates Multi-Material Living Constructs with Tunable Architecture and Mechanics

Major challenges in biofabrication revolve around capturing the complex, hierarchical composition of native tissues. However, individual 3D printing techniques have limited capacity to produce composite biomaterials with multi-scale resolution. Volumetric bioprinting recently emerged as a paradigm-shift in biofabrication. This ultrafast, light-based technique sculpts cell-laden hydrogel bioresins into 3D structures in a layerless fashion, providing enhanced design freedom over conventional bioprinting. However, it yields prints with low mechanical stability, since soft, cell-friendly hydrogels are used. Herein, the possibility to converge volumetric bioprinting with melt electrowriting, which excels at patterning microfibers, is shown for the fabrication of tubular hydrogel-based composites with enhanced mechanical behavior. Despite including non-transparent melt electrowritten scaffolds in the volumetric printing process, high-resolution bioprinted structures are successfully achieved. Tensile, burst, and bending mechanical properties of printed tubes are tuned altering the electrowritten mesh design, resulting in complex, multi-material tubular constructs with customizable, anisotropic geometries that better mimic intricate biological tubular structures. As a proof-of-concept, engineered tubular structures are obtained by building trilayered cell-laden vessels, and features (valves, branches, fenestrations) that can be rapidly printed using this hybrid approach. This multi-technology convergence offers a new toolbox for manufacturing hierarchical and mechanically tunable multi-material living structures.

Collagen for neural tissue engineering: Materials, strategies, and challenges

Neural tissue engineering (NTE) has made remarkable strides in recent years and holds great promise for treating several devastating neurological disorders. Selecting optimal scaffolding material is crucial for NET design strategies that enable neural and non-neural cell differentiation and axonal growth. Collagen is extensively employed in NTE applications due to the inherent resistance of the nervous system against regeneration, functionalized with neurotrophic factors, antagonists of neural growth inhibitors, and other neural growth-promoting agents. Recent advancements in integrating collagen with manufacturing strategies, such as scaffolding, electrospinning, and 3D bioprinting, provide localized trophic support, guide cell alignment, and protect neural cells from immune activity. This review categorises and analyses collagen-based processing techniques investigated for neural-specific applications, highlighting their strengths and weaknesses in repair, regeneration, and recovery. We also evaluate the potential prospects and challenges of using collagen-based biomaterials in NTE. Overall, this review offers a comprehensive and systematic framework for the rational evaluation and applications of collagen in NTE.

Metabolic regulation by biomaterials in osteoblast

The repair of bone defects resulting from high-energy trauma, infection, or pathological fracture remains a challenge in the field of medicine. The development of biomaterials involved in the metabolic regulation provides a promising solution to this problem and has emerged as a prominent research area in regenerative engineering. While recent research on cell metabolism has advanced our knowledge of metabolic regulation in bone regeneration, the extent to which materials affect intracellular metabolic remains unclear. This review provides a detailed discussion of the mechanisms of bone regeneration, an overview of metabolic regulation in bone regeneration in osteoblasts and biomaterials involved in the metabolic regulation for bone regeneration. Furthermore, it introduces how materials, such as promoting favorable physicochemical characteristics (e.g., bioactivity, appropriate porosity, and superior mechanical properties), incorporating external stimuli (e.g., photothermal, electrical, and magnetic stimulation), and delivering metabolic regulators (e.g., metal ions, bioactive molecules like drugs and peptides, and regulatory metabolites such as alpha ketoglutarate), can affect cell metabolism and lead to changes of cell state. Considering the growing interests in cell metabolic regulation, advanced materials have the potential to help a larger population in overcoming bone defects.

Architecture-Engineered Electrospinning Cascade Regulates Spinal Microenvironment to Promote Nerve Regeneration

The inflammatory cascade after spinal cord injury (SCI) causes necrotizing apoptosis of local stem cells, which limits nerve regeneration. Therefore, coordinating the inflammatory immune response and neural stem cell (NSC) functions is key to promoting the recovery of central nervous system function. In this study, a hydrogel "perfusion" system and electrospinning technology are integrated, and a "concrete" composite support for the repair of nerve injuries is built. The hydrogel's hydrophilic properties activate macrophage integrin receptors to mediate polarization into anti-inflammatory subtypes and cause a 10% increase in polarized M2 macrophages, thus reprogramming the SCI immune microenvironment. Programmed stromal cell-derived factor-1α and brain-derived neurotrophic factor released from the composite increase recruitment and neuronal differentiation of NSCs by approximately four- and twofold, respectively. The fiber system regulates the SCI immune inflammatory microenvironment, recruits endogenous NSCs, promotes local blood vessel germination and maturation, and improves nerve function recovery in a rat SCI model. In conclusion, the engineering fiber composite improves the local inflammatory response. It promotes nerve regeneration through a hydrophilic programmed cytokine-delivery system, which further improves and supplements the immune response mechanism regulated by the inherent properties of the biomaterial. The new fiber composite may serve as a new treatment approach for SCI.

Frontier Review of the Molecular Mechanisms and Current Approaches of Stem Cell-Derived Exosomes

Exosomes are effective therapeutic vehicles that may transport their substances across cells. They are shown to possess the capacity to affect cell proliferation, migration, anti-apoptosis, anti-scarring, and angiogenesis, via the action of transporting molecular components. Possessing immense potential in regenerative medicine, exosomes, especially stem cell-derived exosomes, have the advantages of low immunogenicity, minimal invasiveness, and broad clinical applicability. Exosome biodistribution and pharmacokinetics may be altered, in response to recent advancements in technology, for the purpose of treating particular illnesses. Yet, prior to clinical application, it is crucial to ascertain the ideal dose and any potential negative consequences of an exosome. This review focuses on the therapeutic potential of stem cell-derived exosomes and further illustrates the molecular mechanisms that underpin their potential in musculoskeletal regeneration, wound healing, female infertility, cardiac recovery, immunomodulation, neurological disease, and metabolic regulation. In addition, we provide a summary of the currently effective techniques for isolating exosomes, and describe the innovations in biomaterials that improve the efficacy of exosome-based treatments. Overall, this paper provides an updated overview of the biological factors found in stem cell-derived exosomes, as well as potential targets for future cell-free therapeutic applications.

Biomimetic biphasic scaffolds in osteochondral tissue engineering: Their composition, structure and consequences

Approaches to the design and construction of biomimetic scaffolds for osteochondral tissue, show increasing advances. Considering the limitations of this tissue in terms of repair and regeneration, there is a need to develop appropriately designed scaffolds. A combination of biodegradable polymers especially natural polymers and bioactive ceramics, shows promise in this field. Due to the complicated architecture of this tissue, biphasic and multiphasic scaffolds containing two or more different layers, could mimic the physiology and function of this tissue with a higher degree of similarity. The purpose of this review article is to discuss the approaches focused on the application of biphasic scaffolds for osteochondral tissue engineering, common methods of combining layers and the ultimate consequences of their use in patients were discussed.

Oxygen metabolism-balanced engineered hydrogel microspheres promote the regeneration of the nucleus pulposus by inhibiting acid-sensitive complexes

Intervertebral disc degeneration (IVDD) is commonly caused by imbalanced oxygen metabolism-triggered inflammation. Overcoming the shortcomings of antioxidants in IVDD treatment, including instability and the lack of targeting, remains challenging. Microfluidic and surface modification technologies were combined to graft chitosan nanoparticles encapsulated with strong reductive black phosphorus quantum dots (BPQDs) onto GelMA microspheres via amide bonds to construct oxygen metabolism-balanced engineered hydrogel microspheres (GM@CS-BP), which attenuate extracellular acidosis in nucleus pulposus (NP), block the inflammatory cascade, reduce matrix metalloproteinase expression (MMP), and remodel the extracellular matrix (ECM) in intervertebral discs (IVDs). The GM@CS-BP microspheres reduce H₂O₂ intensity by 229%. Chemical grafting and electrostatic attraction increase the encapsulation rate of BPQDs by 167% and maintain stable release for 21 days, demonstrating the antioxidant properties and sustained modulation of the BPQDs. After the GM@CS-BP treatment, western blotting revealed decreased acid-sensitive ion channel-3 and inflammatory factors. Histological staining in an 8-week IVDD model confirmed the regeneration of NP. GM@CS-BP microspheres therefore maintain a balance between ECM synthesis and degradation by regulating the positive feedback between imbalanced oxygen metabolism in IVDs and inflammation. This study provides an in-depth interpretation of the mechanisms underlying the antioxidation of BPQDs and a new approach for IVDD treatment.

Within or Without You? A Perspective Comparing In Situ and Ex Situ Tissue Engineering Strategies for Articular Cartilage Repair

Human articular cartilage has a poor ability to self-repair, meaning small injuries often lead to osteoarthritis, a painful and debilitating condition which is a major contributor to the global burden of disease. Existing clinical strategies generally do not regenerate hyaline type cartilage, motivating research toward tissue engineering solutions. Prospective cartilage tissue engineering therapies can be placed into two broad categories: i) Ex situ strategies, where cartilage tissue constructs are engineered in the lab prior to implantation and ii) in situ strategies, where cells and/or a bioscaffold are delivered to the defect site to stimulate chondral repair directly. While commonalities exist between these two approaches, the core point of distinction-whether chondrogenesis primarily occurs "within" or "without" (outside) the body-can dictate many aspects of the treatment. This difference influences decisions around cell selection, the biomaterials formulation and the surgical implantation procedure, the processes of tissue integration and maturation, as well as, the prospects for regulatory clearance and clinical translation. Here, ex situ and in situ cartilage engineering strategies are compared: Highlighting their respective challenges, opportunities, and prospects on their translational pathways toward long term human cartilage repair.

Progress in the application of sustained-release drug microspheres in tissue engineering

Sustained-release drug-loaded microspheres provide a long-acting sustained release, with targeted and other effects. There are many types of sustained-release drug microspheres and various preparation methods, and they are easy to operate. For these reasons, they have attracted widespread interest and are widely used in tissue engineering and other fields. In this paper, we provide a systematic review of the application of sustained-release drug microspheres in tissue engineering. First, we introduce this new type of drug delivery system (sustained-release drug carriers), describe the types of sustained-release drug microspheres, and summarize the characteristics of different microspheres. Second, we summarize the preparation methods of sustained-release drug microspheres and summarize the materials required for preparing microspheres. Third, various applications of sustained-release drug microspheres in tissue engineering are summarized. Finally, we summarize the shortcomings and discuss future prospects in the development of sustained-release drug microspheres. The purpose of this paper was to provide a further systematic understanding of the application of sustained-release drug microspheres in tissue engineering for the personnel engaged in related fields and to provide inspiration and new ideas for studies in related fields.

Plant proteins as the functional building block of edible microcarriers for cell-based meat culture application

Edible microcarriers are essential for developing cell-based meat in large-scale cell cultures. As they are required to be embedded in the final products, the microcarriers should be edible, biocompatible, cost-effective, and pathogen-free. The invention of edible animal-free microcarriers would be a breakthrough for cell-based meat culture. We reviewed the fabrication techniques and the materials of microcarriers, and found that plant proteins, having diverse structures and composition, could possess the active domains that are hypnotized to replace the animal-based extracellular matrix (ECM) for meat culture applications. In addition, the bioactive peptides in plants have been reviewed and most of them were resulted from enzyme hydrolysis. Therefore, plant proteins with rich bioactive peptides have the potential in the development microcarriers. Our work provided some new trains of thought for developing plant-based biomaterials as ECM materials and advances the fabrication of microcarriers for meat culture.

3D Bioprinting Technology and Hydrogels Used in the Process

3D bioprinting has gained visibility in regenerative medicine and tissue engineering due to its applicability. Over time, this technology has been optimized and adapted to ensure a better printability of bioinks and biomaterial inks, contributing to developing structures that mimic human anatomy. Therefore, cross-linked polymeric materials, such as hydrogels, have been highly targeted for the elaboration of bioinks, as they guarantee cell proliferation and adhesion. Thus, this short review offers a brief evolution of the 3D bioprinting technology and elucidates the main hydrogels used in the process.

Structural Strength Analyses for Low Brass Filler Biomaterial with Anti-Trauma Effects in Articular Cartilage Scaffold Design

The existing harder biomaterial does not protect the tissue cells with blunt-force trauma effects, making it a poor choice for the articular cartilage scaffold design. Despite the traditional mechanical strengths, this study aims to discover alternative structural strengths for the scaffold supports. The metallic filler polymer reinforced method was used to fabricate the test specimen, either low brass (Cu₈₀Zn₂₀) or titanium dioxide filler, with composition weight percentages (wt.%) of 0, 2, 5, 15, and 30 in polyester urethane adhesive. The specimens were investigated for tensile, flexural, field emission scanning electron microscopy (FESEM), and X-ray diffraction (XRD) tests. The tensile and flexural test results increased with wt.%, but there were higher values for low brass filler specimens. The tensile strength curves were extended to discover an additional tensile strength occurring before 83% wt.%. The higher flexural stress was because of the Cu solvent and Zn solute substituting each other randomly. The FESEM micrograph showed a cubo-octahedron shaped structure that was similar to the AuCu₃ structure class. The XRD pattern showed two prominent peaks of 2θ of 42.6° (110) and 49.7° (200) with d-spacings of 1.138 Å and 1.010 Å, respectively, that indicated the typical face-centred cubic superlattice structure with Cu and Zn atoms. Compared to the copper, zinc, and cart brass, the low brass indicated these superlattice structures had ordered–disordered transitional states. As a result, this additional strength was created by the superlattice structure and ordered–disordered transitional states. This innovative strength has the potential to develop into an anti-trauma biomaterial for osteoarthritic patients.