Sustained Release SDF-1α/TGF-β1-Loaded Silk Fibroin-Porous Gelatin Scaffold Promotes Cartilage Repair

A sequential drug delivery system based on silk fibroin scaffold for effective cartilage repair

Endogenous repair of cartilage defects is a preferential strategy for cartilage repair, but always hindered by insufficient early-stage cells and incomplete cell differentiation at later stages. For in-situ cartilage regeneration, it is crucial to develop a sequential drug release system capable of recruiting endogenous bone marrow mesenchymal stem cells (BMSCs) and promoting their chondrogenic differentiation. Herein, based on our long-term and fruitful research on silk fibroin (SF) porous scaffolds, a cell-free sequential drug delivery SF scaffold was developed. BMSCs affinity peptide PFSSTKT (PFS) was coated on the surface of SF scaffold, in which chondrogenic inducer kartogenin (KGN) and anti-inflammatory factor dexamethasone (DEX) were loaded. PFS was rapidly released within the first 10 days while KGN and DEX could be released over 28 days. The scaffold promoted BMSCs migration and chondrogenic differentiation through the release of PFS and KGN in vitro. Finally, the sequential drug released by the implanted SF scaffolds in rats indeed recruited endogenous BMSCs and significantly promoted the in-situ regeneration of their knee cartilage defects. In summary, this study not only introduces a green and environmentally friendly all silk-based sequential drug delivery system, but also provides an effective tissue engineering functional scaffold for in-situ cartilage regeneration.

Forskolin-loaded carboxymethyl chitosan and silk nonofiber hydrogels composite scaffolds improve skin regeneration

Hydrogel is a kind of carrier of powerful therapeutic bioactive molecules. Here, carboxymethyl chitosan-silk nanofiber (CCSF) composite hydrogels loaded with a small molecule compound, Forskolin, were prepared to achieve sustained release of the small molecule drug for promoting wound healing. In vitro, investigations confirmed that the innovative composite dressing is non-toxic and cyto-compatible. Specifically, it can encourage the proliferation of human umbilical vein endothelial cells (HUVECs) and mouse dermis fibroblasts, and inhibit the accumulation of intracellular reactive oxygen species (ROS) in the cells. The capacity of cell migration in myofibroblasts was restrained, also implying less scarring in vivo. Skin wound regeneration results showed that the Forskolin-loaded compound hydrogel accelerated wound closure, enhanced neovascularization, and promoted hair follicle regeneration. The multiple-material delivery system shows a promising application in skin wound repair.

Preparation of hydrogel microsphere and its application in articular cartilage injury

In recent years, hydrogel microspheres have garnered significant attention due to their unique structure and functionality, demonstrating substantial potential in articular cartilage injury repair. This paper provides a comprehensive overview of current strategies for cartilage injury repair and summarizes the materials and preparation methods of hydrogel microspheres. Furthermore, it highlights the multiple roles of hydrogel microspheres in cartilage repair, including inflammation control, regulation of chondrocyte metabolism, drug and cell delivery, lubrication improvement, and recruitment of endogenous stem cells. Finally, the paper discusses the application prospects of hydrogel microspheres, identifies current limitations and challenges, and offers insights to guide future research and practical applications in cartilage injury repair.

Nerve-Derived Extracellular Matrix Promotes Neural Differentiation of Bone Marrow Stromal Cells and Enhances Interleukin-4 Efficacy for Advanced Nerve Regeneration

Facilitating neuronal differentiation of stem cells and microenvironment remodeling are the key challenges in cell-based transplantation strategies for central nervous system regeneration. Herein, the study harnesses the intrinsic pro-neural differentiation potential of nerve-derived extracellular matrix (NDEM) and its specific affinity for cytokines to develop an NDEM-gelatin methacryloyl(gelMA)-based bifunctional hydrogel delivery system for stem cells and cytokines. This system promotes the neural differentiation of bone marrow stromal cells (BMSCs) and optimizes the therapeutic index of Interleukin-4 (IL-4) for spinal cord injury (SCI) treatment. It is observed that incorporating NDEM into the hydrogel system intrinsically promotes BMSC differentiation into neuron-like cells and effectively regulates IL-4 release kinetics to match the neural reconstructing timeframe. Further analysis reveals that trace amounts of endogenous basic fibroblast growth factor (bFGF) detected in NDEM exhibit a potent effect in promoting neural differentiation. The sustained release of IL-4 from the NDEM significantly encourages macrophage polarization toward the M2 phase, optimizing the transplant microenvironment throughout the reconstruction process. This study demonstrates an NDEM-based optimization strategy for hybrid hydrogel to achieve synchronized delivery of stem cells and cytokines in regenerative medicine applications.

Development of a multi-functional naringin-loaded bioglass/carboxymethyl chitosan/silk fibroin porous scaffold for hemostasis and critical size bone regeneration

Persistent bleeding and limited repair capacity greatly threaten patients with bone destruction. Designing inorganic-organic biomimetic scaffolds with quick hemostasis and osteogenesis functions will solve this problem. A novel degradable and naringin (NG) loaded porous scaffold (SCB-N) based on APTES-modified bioactive glass (ABG), carboxymethyl chitosan and silk fibroin is developed. ABG and NG enhance the strength of the scaffolds. The scaffolds can release NG and bioactive ions (Ca2+ and Si4+), promoting the expression of osteogenesis (OCN, BMP-2), angiogenesis (VEGF), and neurogenesis (TB3, GFAP) genes in bone mesenchymal stem cells (BMSCs) and the related proteins (OCN, BMP-2, VEGF, GFAP). When implanting the scaffolds in rat cranial critical size defects, all scaffolds exhibit good compatibility, and SCB-N2 (with ABG and 1 mg/mL NG) group significantly promotes new bone regeneration and the formation of M2-type macrophages. Transcriptome sequencing results confirmed the osteogenic differentiation of BMSCs stimulated by SCB-N2 scaffolds is mainly regulated through MAPK and Wnt signaling pathways. Moreover, SCB-N2 group demonstrates quick hemostasis in vitro and in vivo due to the high adsorption ability and Ca ions release. The novel bionic scaffolds loaded with ion/traditional Chinese medicine monomer, possess the capabilities of hemostasis, neurovascularization, osteogenesis and immunomodulation, therefore exhibiting potential in bone repair.

An Acellular, Self-Healed Trilayer Cryogel for Osteochondral Regeneration in Rabbits

Osteochondral regeneration remains formidable challenges despite significant advances in microsurgery. Herein, an acellular trilayer cryogel (TC) with injectability, tunable pore sizes (80-200 µm), and appropriate compressive modulus (10.8 kPa) is manufactured from self-healable hydrogel under different gelling times through Schiff reaction between chitosan and difunctionalized polyurethane (DFPU). Bioactive molecules (Y27632 and dexamethasone) are respectively loaded in the top and bottom layers to form the Y27632/dexamethasone-loaded trilayer cryogel (Y/DEX-TC). Mesenchymal stem cells (MSCs) seeded in Y/DEX-TC proliferated ≈350% in vitro and underwent chondrogenesis or osteogenesis in response to the respective release of Y or DEX in 14 days. Acupuncture is administered to animals in an attempt to modulate the innate regulatory system and mobilize endogenous MSCs for osteochondral defect regeneration. In vivo rabbit experiments using Y/DEX-TC combined with acupuncture successfully regulate SDF-1 and TGF-β1 levels, which possibly cause MSC migration toward Y/DEX-TC. The synergistic effect of cryogel and acupuncture on immunomodulation is verified with a ≈7.3-fold enhancement of the M2-/M1-macrophage population ratio by treatment of Y/DEX-TC combining acupuncture, significantly greater than ≈1.5-fold increase by acupuncture or ≈2.2-fold increase by Y/DEX-TC alone. This novel strategy using acellular drug-loaded cryogel and accessible acupuncture shows promise in treating osteochondral defects of joint damage.

An injectable self-lubricating supramolecular polymer hydrogel loaded with platelet lysate to boost osteoarthritis treatment

Globally, osteoarthritis (OA) is the most prevalent joint disease and is characterized by infiltration of M1 macrophages in the synovium, anabolic-catabolic imbalance of the extracellular matrix (ECM), increased articular shear force and overproduction of reactive oxygen species (ROS). Disease-modifying OA drugs are not yet available, and treatments for OA focus solely on reducing pain and inflammation and have limited therapeutic effect. Herein, we developed an injectable self-lubricating poly(N-acryloyl alaninamide) (PNAAA) hydrogel loaded with platelet lysate (PL) (termed "PNAAA@PL") for treating OA. Tribological and drug release tests revealed suitable lubrication properties and sustained release of bioactive factors in PNAAA@PL. In vitro experiments showed that PNAAA@PL alleviated interleukin-1β (IL-1β)-induced anabolic-catabolic imbalance of chondrocytes and repolarized pro-inflammatory M1 macrophages to the anti-inflammatory M2 phenotype via intracellular ROS scavenging. Additionally, the PNAAA@PL hydrogel enhanced the migratory capacity and chemotaxis ability of stem cells, which are essential for chondrogenesis. In vivo, the functionalized PNAAA@PL hydrogel acted like synovial fluid following intra-articular injection into a rat OA model with anterior cruciate ligament transection, ultimately attenuating cartilage degeneration and synovitis. According to molecular mechanism studies, PNAAA@PL repairs cartilage in the OA model by inhibiting the NF-ĸB pathway. Overall, this self-lubricating PNAAA@PL hydrogel offers a comprehensive strategy for preventing OA progression by engineering a biophysiochemical microenvironment to generate high-quality hyaline cartilage.

Tissue engineering strategies hold promise for the repair of articular cartilage injury

Articular cartilage damage and wear can result in cartilage degeneration, ultimately culminating in osteoarthritis. Current surgical interventions offer limited capacity for cartilage tissue regeneration and offer only temporary alleviation of symptoms. Tissue engineering strategies are increasingly recognized as promising modalities for cartilage restoration. Currently, various biological scaffolds utilizing tissue engineering materials are extensively employed in both fundamental and clinical investigations of cartilage repair. In order to optimize the cartilage repair ability of tissue engineering scaffolds, researchers not only optimize the structure and properties of scaffolds from the perspective of materials science and manufacturing technology to enhance their histocompatibility, but also adopt strategies such as loading cells, cytokines, and drugs to promote cartilage formation. This review provides an overview of contemporary tissue engineering strategies employed in cartilage repair, as well as a synthesis of existing preclinical and clinical research. Furthermore, the obstacles faced in the translation of tissue engineering strategies to clinical practice are discussed, offering valuable guidance for researchers seeking to address these challenges.

Drug-Loaded Bioscaffolds for Osteochondral Regeneration

Osteochondral defect is a complex tissue loss disease caused by arthritis, high-energy trauma, and many other reasons. Due to the unique structural characteristics of osteochondral tissue, the repair process is sophisticated and involves the regeneration of both hyaline cartilage and subchondral bone. However, the current clinical treatments often fall short of achieving the desired outcomes. Tissue engineering bioscaffolds, especially those created via three-dimensional (3D) printing, offer promising solutions for osteochondral defects due to their precisely controllable 3D structures. The microstructure of 3D-printed bioscaffolds provides an excellent physical environment for cell adhesion and proliferation, as well as nutrient transport. Traditional 3D-printed bioscaffolds offer mere physical stimulation, while drug-loaded 3D bioscaffolds accelerate the tissue repair process by synergistically combining drug therapy with physical stimulation. In this review, the physiological characteristics of osteochondral tissue and current treatments of osteochondral defect were reviewed. Subsequently, the latest progress in drug-loaded bioscaffolds was discussed and highlighted in terms of classification, characteristics, and applications. The perspectives of scaffold design, drug control release, and biosafety were also discussed. We hope this article will serve as a valuable reference for the design and development of osteochondral regenerative bioscaffolds and pave the way for the use of drug-loaded bioscaffolds in clinical therapy.

Endogenous Tissue Engineering for Chondral and Osteochondral Regeneration: Strategies and Mechanisms

Increasing attention has been paid to the development of effective strategies for articular cartilage (AC) and osteochondral (OC) regeneration due to their limited self-reparative capacities and the shortage of timely and appropriate clinical treatments. Traditional cell-dependent tissue engineering faces various challenges such as restricted cell sources, phenotypic alterations, and immune rejection. In contrast, endogenous tissue engineering represents a promising alternative, leveraging acellular biomaterials to guide endogenous cells to the injury site and stimulate their intrinsic regenerative potential. This review provides a comprehensive overview of recent advancements in endogenous tissue engineering strategies for AC and OC regeneration, with a focus on the tissue engineering triad comprising endogenous stem/progenitor cells (ESPCs), scaffolds, and biomolecules. Multiple types of ESPCs present within the AC and OC microenvironment, including bone marrow-derived mesenchymal stem cells (BMSCs), adipose-derived mesenchymal stem cells (AD-MSCs), synovial membrane-derived mesenchymal stem cells (SM-MSCs), and AC-derived stem/progenitor cells (CSPCs), exhibit the ability to migrate toward injury sites and demonstrate pro-regenerative properties. The fabrication and characteristics of scaffolds in various formats including hydrogels, porous sponges, electrospun fibers, particles, films, multilayer scaffolds, bioceramics, and bioglass, highlighting their suitability for AC and OC repair, are systemically summarized. Furthermore, the review emphasizes the pivotal role of biomolecules in facilitating ESPCs migration, adhesion, chondrogenesis, osteogenesis, as well as regulating inflammation, aging, and hypertrophy-critical processes for endogenous AC and OC regeneration. Insights into the applications of endogenous tissue engineering strategies for in vivo AC and OC regeneration are provided along with a discussion on future perspectives to enhance regenerative outcomes.

High-precision bioactive scaffold with dECM and extracellular vesicles targeting 4E-BP inhibition for cartilage injury repair

The restoration of cartilage injuries remains a formidable challenge in orthopedics, chiefly attributed to the absence of vascularization and innervation in cartilage. Decellularized extracellular matrix (dECM) derived from cartilage, following antigenic removal through decellularization processes, has exhibited remarkable biocompatibility and bioactivity, rendering it a viable candidate for cartilage repair. Additionally, extracellular vesicles (EVs) generated from cartilage have demonstrated a synergistic effect when combined with dECM, potentially mitigating the inhibitory impact on protein synthesis by phosphorylating 4ebp, thereby promoting the synthesis of cartilage-related proteins such as collagen. In pursuit of this objective, we have innovated a novel bioink and repair scaffold characterized by exceptional biocompatibility, bioactivity, and biodegradability, establishing a tissue-specific microenvironment conducive to chondrogenesis. Within rat osteochondral defects, the biologically active scaffold successfully prompted the formation of transparent cartilage, featuring adequate mechanical strength, favorable elasticity, and dECM deposition indicative of cartilage. In summary, this study has effectively engineered a hydrogel bioink tailored for cartilage repair and devised a bioactive cartilage repair scaffold proficient in instigating cell differentiation and fostering cartilage repair.

Sequential release of transforming growth factor β1 and fibroblast growth factor 2 from nanofibrous scaffolds induces cartilage differentiation of mouse adipose-derived stem cells

Once damaged, cartilage has poor intrinsic capacity to repair itself. Current cartilage repair strategies cannot restore the damaged tissue sufficiently. It is hypothesized that biomimetic scaffolds, which can recapitulate important properties of the cartilage extracellular matrix, play a beneficial role in supporting cell behaviors such as growth, cartilage differentiation, and integration with native cartilage, ultimately facilitating tissue recovery. Adipose-derived stem cells regenerated cartilage upon the sequential release of transforming growth factor β1(TGFβ1) and fibroblast growth factor 2(FGF2) using a nanofibrous scaffold, in order to get the recovery of functional cartilage. Experiments in vitro have demonstrated that the release sequence of growth factors FGF2 to TGFβ1 is the most essential to promote adipose-derived stem cells into chondrocytes that then synthesize collagen II. Mouse subcutaneous implantation indicated that the treatment sequence of FGF2 to TGFβ1 was able to significantly induce multiple increase in cartilage regeneration in vivo. This result demonstrates that the group treated with FGF2 to TGFβ1 released from a nanofibrous scaffold provides a good strategy for cartilage regeneration by making a favorable microenvironment for cell growth and cartilage regeneration.

Regulatory effects of stress release from decellularized periosteum on proliferation, migration, and osteogenic differentiation of periosteum-derived cells

Bone injury is often associated with tears in the periosteum and changes in the internal stress microenvironment of the periosteum. In this study, we investigated the biological effects of periosteal prestress release on periosteum-derived cells (PDCs) and the potential mechanisms of endogenous stem cell recruitment. Decellularized periosteum with natural extracellular matrix (ECM) components was obtained by a combination of physical, chemical, and enzymatic decellularization. The decellularized periosteum removed immunogenicity while retaining the natural network structure and composition of the ECM. The Young's modulus has no significant difference between the periosteum before and after decellularization. The extracted PDCs were further composited with the decellularized periosteum and subjected to 20% stress release. It was found that the proliferative capacity of PDCs seeded on decellularized periosteum was significantly enhanced 6 h after stress release of the periosteum. The cell culture supernatant obtained after periosteal prestress release was able to significantly promote the migration ability of PDCs within 24 h. Enzyme-linked immunosorbnent assay (ELISA) experiments showed that the expression of stroma-derived factor-1α (SDF-1α) and vascular endothelial growth factor (VEGF) in the supernatant increased significantly after 3 h and 12 h of stress release, respectively. Furthermore, periosteal stress release promoted the high expression of osteogenic markers osteocalcin (OCN), osteopontin (OPN), and collagen type I of PDCs. The change in stress environment caused by the release of periosteal prestress was sensed by integrin β1, a mechanoreceptor on the membrane of PDCs, which further stimulated the expression of YAP in the nucleus. These investigations provided a novel method to evaluate the importance of mechanical stimulation in periosteum, which is also of great significance for the design and fabrication of artificial periosteum with mechanical regulation function.

Exosomes derived from epidermal growth factor-like domain protein 6-preconditioned mesenchymal stem cells for diabetic wound healing

Diabetic wounds are difficult to repair effectively in the clinic. Tissue engineering based on mesenchymal stem cells (MSCs) showed great therapeutic potential in wound healing. MSCs-derived exosome could reproduce the effect of MSCs by transferring the bioactive substance to the recipient cells. The biological function of exosomes was determined by the state of the derived MSCs. In this study, we cultured hUC-MSCs with EGFL6 and isolated EGFL6-preconditioned exosomes (EGF-Exos), and then investigated the effect of EGF-Exos on wound healing. The results revealed that EGF-Exos promoted the proliferation and migration of HUVECs, had the anti-inflammtory function and improved angiogenesis. Moreover, we fabricated Gelama hydrogel to load EGF-Exos to repair diabetic wounds. In vivo results showed that EGF-Exos contributed to the repair of diabetic wound and provided valuable data for understanding the role of EGF-Exos in diabetic wound healing.

A nanoparticle reinforced microporous methacrylated silk fibroin hydrogel to promote bone regeneration

Natural polymer-based hydrogels have been widely applied in bone tissue engineering due to their excellent biocompatibility and outstanding ability of drug encapsulation. However, they have relatively weak mechanical properties and lack bioactivity. Hence, we developed a bioactive nanoparticle composite hydrogel by incorporating LAPONITE®, which is an osteo-inductive inorganic nanoparticle. The incorporation of the nanoparticle significantly enhanced its mechanical properties. In vitro evaluation indicated that the nanocomposite hydrogel could exhibit good biocompatibility. Besides, the nanocomposite hydrogel was proved to have excellent osteogenic ability with up-regulated expression of osteogenic markers such as type I collagen (COL-I), runt-related transcription factor-2 (Runx-2) and osteocalcin (OCN). Furthermore, the in vivo study confirmed that the composite nanocomposite hydrogel could significantly promote new bone formation, providing a prospective strategy for bone tissue regeneration.

Dual Factor-Loaded Artificial Periosteum Accelerates Bone Regeneration

In the clinic, inactivation of osteosarcoma using microwave ablation would damage the periosteum, resulting in frequent postoperative complications. Therefore, the development of an artificial periosteum is crucial for postoperative healing. In this study, we prepared an artificial periosteum using silk fibroin (SF) loaded with stromal cell-derived factor-1α (SDF-1α) and calcitonin gene-related peptide (CGRP) to accelerate bone remodeling after the microwave ablation of osteosarcoma. The prepared artificial periosteum showed a sustained release of SDF-1α and CGRP after 14 days of immersion. In vitro culture of rat periosteal stem cells (rPDSCs) demonstrated that the artificial periosteum is favorable for cell recruitment, the activity of alkaline phosphatase, and bone-related gene expression. Furthermore, the artificial periosteum improved the tube formation and angiogenesis-related gene expression of human umbilical vein endothelial cells (HUVECs). In an animal study, the periosteum in the femur of a rabbit was inactivated through microwave ablation and then removed. The damaged periosteum was replaced with the as-prepared artificial periosteum and favored bone regeneration. In all, the designed dual-factor-loaded artificial periosteum is a promising strategy to replace the damaged periosteum in the therapy of osteosarcoma for a better bone-rebuilding process.

ICA/SDF-1α/PBMSCs loaded onto alginate and gelatin cross-linked scaffolds promote damaged cartilage repair

A three-dimensional alginate-coated scaffold (GAIS) was constructed in the present study to showcase the multidifferentiation potential of peripheral blood mesenchymal stem cells (PBMSCs) and to investigate the role and mechanism by which Icariin (ICA)/stromal cell-derived factor (SDF-1α)/PBMSCs promote damaged articular repair. In addition, the ability of ICA, in combination with SDF-1α, to promote the migration and proliferation of stem cells was validated through the utilization of CCK-8 and migration experiments. The combination of ICA and SDF-1α inhibited the differentiation of PBMSCs into cartilage, as demonstrated by in vivo experiments and histological staining. Both PCR and western blot experiments showed that GAIS could upregulate the expression of particular genes in chondrocytes. In comparison to scaffolds devoid of alginate (G0), PBMSCs seeded into GAIS scaffolds exhibited a greater rate of proliferation, and the conditioned medium derived from scaffolds containing SDF-1α enhanced the capacity for cell migration. Moreover, after a 12-week treatment period, GAIS, when successfully transplanted into osteochondral defects of mice, was found to promote cartilage regeneration and repair. The findings, therefore, demonstrate that GAIS enhanced the in vitro capabilities of PBMSCs, including proliferation, migration, homing and chondrogenic differentiation. In addition, ICA and SDF-1α effectively collaborated to support cartilage formation in vivo. Thus, the ICA/SDF-1α/PBMSC-loaded biodegradable alginate-gelatin scaffolds showcase considerable potential for use in cartilage repair.

Essential elements for spatiotemporal delivery of growth factors within bio-scaffolds: A comprehensive strategy for enhanced tissue regeneration

The precise delivery of growth factors (GFs) in regenerative medicine is crucial for effective tissue regeneration and wound repair. However, challenges in achieving controlled release, such as limited half-life, potential overdosing risks, and delivery control complexities, currently hinder their clinical implementation. Despite the plethora of studies endeavoring to accomplish effective loading and gradual release of GFs through diverse delivery methods, the nuanced control of spatial and temporal delivery still needs to be elucidated. In response to this pressing clinical imperative, our review predominantly focuses on explaining the prevalent strategies employed for spatiotemporal delivery of GFs over the past five years. This review will systematically summarize critical aspects of spatiotemporal GFs delivery, including judicious bio-scaffold selection, innovative loading techniques, optimization of GFs activity retention, and stimulating responsive release mechanisms. It aims to identify the persisting challenges in spatiotemporal GFs delivery strategies and offer an insightful outlook on their future development. The ultimate objective is to provide an invaluable reference for advancing regenerative medicine and tissue engineering applications.

Advanced Synthetic Scaffolds Based on 1D Inorganic Micro-/Nanomaterials for Bone Regeneration

Inorganic nanoparticulate biomaterials, such as calcium phosphate and bioglass particles, with chemical compositions similar to that of the inorganic component of natural bone, and hence having excellent biocompatibility and bioactivity, are widely used for the fabrication of synthetic bone graft substitutes. Growing evidence suggests that structurally anisotropic, or 1D inorganic micro-/nanobiomaterials are superior to inorganic nanoparticulate biomaterials in the context of mechanical reinforcement and construction of self-supporting 3D network structures. Therefore, in the past decades, efforts have been devoted to developing advanced synthetic scaffolds for bone regeneration using 1D micro-/nanobiomaterials as building blocks. These scaffolds feature extraordinary physical and biological properties, such as enhanced mechanical properties, super elasticity, multiscale hierarchical architecture, extracellular matrix-like fibrous microstructure, and desirable biocompatibility and bioactivity, etc. In this review, an overview of recent progress in the development of advanced scaffolds for bone regeneration is provided based on 1D inorganic micro-/nanobiomaterials with a focus on their structural design, mechanical properties, and bioactivity. The promising perspectives for future research directions are also highlighted.

[Stromal Cell-Derived Factor 1α Inhibits Chondrocyte Apoptosis and Promotes Autophagy Through the Akt Signaling Pathway]

Objective

To investigate the effects of stromal cell-derived factor 1α (SDF-1α) on the apoptosis and autophagy of chondrocytes and the underlying mechanisms.

Methods

Chondrocytes were isolated from the knee joints of neonatal mice. The chondrocytes were then stimulated with 0 (the control group), 50, 100, and 200 ng/mL of SDF-1α. CCK-8 assay was performed to determine the effects of SDF-1α stimulation for 24 h, 48 h, and 72 h on the viability of the chondrocytes. Wound healing assay was conducted to determine the effects of SDF-1α stimulation for 12 h and 24 h on chondrocyte migration. The changes in the expression of Akt signaling pathway proteins in chondrocytes were determined by Western blot assay. Chondrocytes were stimulated with 0 (the control group) and 200 ng/mL of SDF-1α. Flow cytometry was performed to determine the effect of SDF-1α on the apoptosis of chondrocytes. Transmission electron microscope was used to examine the effect of SDF-1α on chondrocyte autophagy. Immunofluorescence staining assays were performed to visualize the differences in p-Akt expression and distribution in chondrocytes treated with SDF-1α.

Results

Compared with the control group, findings for the experimental groups showed that SDF-1α at the concentrations of 50, 100, and 200 ng/mL did not decrease chondrocyte activity at any time point (P<0.01) and it consistently promoted chondrocyte migration at 24 h (P<0.05). Western blot results revealed that, in comparison to the control group, SDF-1α at concentrations of 50, 100, and 200 ng/mL significantly up-regulated the protein expression of p-Akt in chondrocytes, while no significant difference in Akt expression was observed. Flow cytometry demonstrated that SDF-1α could inhibit chondrocyte apoptosis (P<0.05) and transmission electron microscopic observation showed that SDF-1α promoted chondrocyte autophagy (P<0.05). Immunofluorescence staining showed that the expression of p-Akt in chondrocytes was concentrated in the perinuclear area of the cells and this expression was further enhanced in the perinuclear area of the chondrocytes after treatment with SDF-1α.

Conclusion

SDF-1α inhibits chondrocyte apoptosis and promotes chondrocyte migration and autophagy through activating the Akt signaling pathway.

Hypoxic Preconditional Engineering Small Extracellular Vesicles Promoted Intervertebral Disc Regeneration by Activating Mir-7-5p/NF-Κb/Cxcl2 Axis

Chronic low back pain (LBP) caused by intervertebral disc (IVD) degradation is a serious socioeconomic burden that can cause severe disabilities. Addressing the underlying pathogenic mechanisms of IVD degeneration may inspire novel therapeutic strategy for LBP. Herein, hypoxic preconditioning improves both the biological function of MSCs in hostile microenvironments and enhances the production of small extracellular vesicles (sEVs) with desirable therapeutic functions. In vitro results reveal that hypoxic preconditional engineering sEVs (HP-sEVs) alleviate the inflammatory microenvironments of IVD degradation, enhance the proliferation of nucleus pulposus (NP) cells, and promote proteoglycan synthesis and collagen formation. Transcriptomic sequencing reveales the excellent therapeutic effects of HP-sEVs in promoting extracellular matrix regeneration through the delivery of microRNA(miR)-7-5p, which further suppresses p65 production and thus the inhibition of Cxcl2 production. Moreover, in vivo results further confirm the robust therapeutic role of HP-sEVs in promoting IVD regeneration through the same mechanism mediated by miR-7-5p delivery. In conclusion, this study provides a novel therapeutic strategy for treating IVD degradation and is thus valuable for understanding the mechanism-of-action of HP-sEVs in IVD regeneration associated with chronic lower back pain.

Immunity-and-matrix-regulatory cells enhance cartilage regeneration for meniscus injuries: a phase I dose-escalation trial

Immunity-and-matrix-regulatory cells (IMRCs) derived from human embryonic stem cells have unique abilities in modulating immunity and regulating the extracellular matrix, which could be mass-produced with stable biological properties. Despite resemblance to mesenchymal stem cells (MSCs) in terms of self-renew and tri-lineage differentiation, the ability of IMRCs to repair the meniscus and the underlying mechanism remains undetermined. Here, we showed that IMRCs demonstrated stronger immunomodulatory and pro-regenerative potential than umbilical cord MSCs when stimulated by synovial fluid from patients with meniscus injury. Following injection into the knees of rabbits with meniscal injury, IMRCs enhanced endogenous fibrocartilage regeneration. In the dose-escalating phase I clinical trial (NCT03839238) with eighteen patients recruited, we found that intra-articular IMRCs injection in patients was safe over 12 months post-grafting. Furthermore, the effective results of magnetic resonance imaging (MRI) of meniscus repair and knee functional scores suggested that 5 × 107 cells are optimal for meniscus injury treatment. In summary, we present the first report of a phase I clinical trial using IMRCs to treat meniscus injury. Our results demonstrated that intra-articular injection of IMRCs is a safe and effective therapy by providing a permissive niche for cartilage regeneration.

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.

Bioactive Materials for Bone Regeneration: Biomolecules and Delivery Systems

Novel tissue regeneration strategies are constantly being developed worldwide. Research on bone regeneration is noteworthy, as many promising new approaches have been documented with novel strategies currently under investigation. Innovative biomaterials that allow the coordinated and well-controlled repair of bone fractures and bone loss are being designed to reduce the need for autologous or allogeneic bone grafts eventually. The current engineering technologies permit the construction of synthetic, complex, biomimetic biomaterials with properties nearly as good as those of natural bone with good biocompatibility. To ensure that all these requirements meet, bioactive molecules are coupled to structural scaffolding constituents to form a final product with the desired physical, chemical, and biological properties. Bioactive molecules that have been used to promote bone regeneration include protein growth factors, peptides, amino acids, hormones, lipids, and flavonoids. Various strategies have been adapted to investigate the coupling of bioactive molecules with scaffolding materials to sustain activity and allow controlled release. The current manuscript is a thorough survey of the strategies that have been exploited for the delivery of biomolecules for bone regeneration purposes, from choosing the bioactive molecule to selecting the optimal strategy to synthesize the scaffold and assessing the advantages and disadvantages of various delivery strategies.

A cell-free tissue-engineered tracheal substitute with sequential cytokine release maintained airway opening in a rabbit tracheal full circumferential defect model

In this study, a cell-free tissue-engineered tracheal substitute was developed, which is based on a 3D-printed polycaprolactone scaffold coated with a gelatin-methacryloyl (GelMA) hydrogel, with transforming growth factor-β1 (TGF-β) and stromal cell-derived factor-1α (SDF-1) sequentially embedded, to facilitate cell recruitment and differentiation toward chondrocyte-phenotype. TGF-β was loaded onto polydopamine particles, and then encapsulated into the GelMA together with SDF-1, and called G/S/P@T, which was used to coat 3D-printed PCL scaffold to form the tracheal substitute. A rapid release of SDF-1 was observed during the first week, followed by a slow and sustained release of TGF-β for approximately four weeks. The tracheal substitute significantly promoted the recruitment of mesenchymal stromal cells (MSCs) or human bronchial epithelial cells in vitro, and enhanced the ability of MSCs to differentiate towards chondrocyte phenotype. Implantation of the tissue-engineered tracheal substitute with a rabbit tracheal anterior defect model improved regeneration of airway epithelium, recruitment of endogenous MSCs and expression of markers of chondrocytes at the tracheal defect site. Moreover, the tracheal substitute maintained airway opening for 4 weeks in a tracheal full circumferential defect model with airway epithelium coverage at the defect sites without granulation tissue accumulation in the tracheal lumen or underneath. The promising results suggest that this simple, cell-free tissue-engineered tracheal substitute can be used directly after tracheal defect removal and should be further developed towards clinical application.

Engineered biochemical cues of regenerative biomaterials to enhance endogenous stem/progenitor cells (ESPCs)-mediated articular cartilage repair

As a highly specialized shock-absorbing connective tissue, articular cartilage (AC) has very limited self-repair capacity after traumatic injuries, posing a heavy socioeconomic burden. Common clinical therapies for small- to medium-size focal AC defects are well-developed endogenous repair and cell-based strategies, including microfracture, mosaicplasty, autologous chondrocyte implantation (ACI), and matrix-induced ACI (MACI). However, these treatments frequently result in mechanically inferior fibrocartilage, low cost-effectiveness, donor site morbidity, and short-term durability. It prompts an urgent need for innovative approaches to pattern a pro-regenerative microenvironment and yield hyaline-like cartilage with similar biomechanical and biochemical properties as healthy native AC. Acellular regenerative biomaterials can create a favorable local environment for AC repair without causing relevant regulatory and scientific concerns from cell-based treatments. A deeper understanding of the mechanism of endogenous cartilage healing is furthering the (bio)design and application of these scaffolds. Currently, the utilization of regenerative biomaterials to magnify the repairing effect of joint-resident endogenous stem/progenitor cells (ESPCs) presents an evolving improvement for cartilage repair. This review starts by briefly summarizing the current understanding of endogenous AC repair and the vital roles of ESPCs and chemoattractants for cartilage regeneration. Then several intrinsic hurdles for regenerative biomaterials-based AC repair are discussed. The recent advances in novel (bio)design and application regarding regenerative biomaterials with favorable biochemical cues to provide an instructive extracellular microenvironment and to guide the ESPCs (e.g. adhesion, migration, proliferation, differentiation, matrix production, and remodeling) for cartilage repair are summarized. Finally, this review outlines the future directions of engineering the next-generation regenerative biomaterials toward ultimate clinical translation.

Research Progress of Design Drugs and Composite Biomaterials in Bone Tissue Engineering

Bone, like most organs, has the ability to heal naturally and can be repaired slowly when it is slightly injured. However, in the case of bone defects caused by diseases or large shocks, surgical intervention and treatment of bone substitutes are needed, and drugs are actively matched to promote osteogenesis or prevent infection. Oral administration or injection for systemic therapy is a common way of administration in clinic, although it is not suitable for the long treatment cycle of bone tissue, and the drugs cannot exert the greatest effect or even produce toxic and side effects. In order to solve this problem, the structure or carrier simulating natural bone tissue is constructed to control the loading or release of the preparation with osteogenic potential, thus accelerating the repair of bone defect. Bioactive materials provide potential advantages for bone tissue regeneration, such as physical support, cell coverage and growth factors. In this review, we discuss the application of bone scaffolds with different structural characteristics made of polymers, ceramics and other composite materials in bone regeneration engineering and drug release, and look forward to its prospect.

Silk fibroin carriers with sustained release capacity for treating neurological diseases

Neurological diseases such as traumatic brain injury, cerebral ischemia, Parkinson's, and Alzheimer's disease usually occur in the central and peripheral nervous system and result in nervous dysfunction, such as cognitive impairment and motor dysfunction. Long-term clinical intervention is necessary for neurological diseases where neural stem cell transplantation has made substantial progress. However, many risks remain for cell therapy, such as puncture bleeding, postoperative infection, low transplantation success rate, and tumor formation. Sustained drug delivery, which aims to maintain the desired steady-state drug concentrations in plasma or local injection sites, is considered as a feasible option to help overcome side effects and improve the therapeutic efficiency of drugs on neurological diseases. Natural polymers such as silk fibroin have excellent biocompatibility, which can be prepared for various end-use material formats, such as microsphere, gel, coating/film, scaffold/conduit, microneedle, and enables the dynamic release of loaded drugs to achieve a desired therapeutic response. Sustained-release drug delivery systems are based on the mechanism of diffusion and degradation by altering the structures of silk fibroin and drugs, factors, and cells, which can induce nerve recovery and restore the function of the nervous system in a slow and persistent manner. Based on these desirable properties of silk fibroin as a carrier with sustained-release capacity, this paper discusses the role of various forms of silk fibroin-based drug delivery materials in treating neurological diseases in recent years.

Polymeric and Composite Carriers of Protein and Non-Protein Biomolecules for Application in Bone Tissue Engineering

Conventional intake of drugs and active substances is most often based on oral intake of an appropriate dose to achieve the desired effect in the affected area or source of pain. In this case, controlling their distribution in the body is difficult, as the substance also reaches other tissues. This phenomenon results in the occurrence of side effects and the need to increase the concentration of the therapeutic substance to ensure it has the desired effect. The scientific field of tissue engineering proposes a solution to this problem, which creates the possibility of designing intelligent systems for delivering active substances precisely to the site of disease conversion. The following review discusses significant current research strategies as well as examples of polymeric and composite carriers for protein and non-protein biomolecules designed for bone tissue regeneration.

The chemokines CXCL8 and CXCL12: molecular and functional properties, role in disease and efforts towards pharmacological intervention

Chemokines are an indispensable component of our immune system through the regulation of directional migration and activation of leukocytes. CXCL8 is the most potent human neutrophil-attracting chemokine and plays crucial roles in the response to infection and tissue injury. CXCL8 activity inherently depends on interaction with the human CXC chemokine receptors CXCR1 and CXCR2, the atypical chemokine receptor ACKR1, and glycosaminoglycans. Furthermore, (hetero)dimerization and tight regulation of transcription and translation, as well as post-translational modifications further fine-tune the spatial and temporal activity of CXCL8 in the context of inflammatory diseases and cancer. The CXCL8 interaction with receptors and glycosaminoglycans is therefore a promising target for therapy, as illustrated by multiple ongoing clinical trials. CXCL8-mediated neutrophil mobilization to blood is directly opposed by CXCL12, which retains leukocytes in bone marrow. CXCL12 is primarily a homeostatic chemokine that induces migration and activation of hematopoietic progenitor cells, endothelial cells, and several leukocytes through interaction with CXCR4, ACKR1, and ACKR3. Thereby, it is an essential player in the regulation of embryogenesis, hematopoiesis, and angiogenesis. However, CXCL12 can also exert inflammatory functions, as illustrated by its pivotal role in a growing list of pathologies and its synergy with CXCL8 and other chemokines to induce leukocyte chemotaxis. Here, we review the plethora of information on the CXCL8 structure, interaction with receptors and glycosaminoglycans, different levels of activity regulation, role in homeostasis and disease, and therapeutic prospects. Finally, we discuss recent research on CXCL12 biochemistry and biology and its role in pathology and pharmacology.

Preparation and Characterization of Biomimetic Functional Scaffold with Gradient Structure for Osteochondral Defect Repair

Osteochondral (OC) defects cannot adequately repair themselves due to their sophisticated layered structure and lack of blood supply in cartilage. Although therapeutic interventions are reaching an advanced stage, current clinical therapies to repair defects are in their infancy. Among the possible therapies, OC tissue engineering has shown considerable promise, and multiple approaches utilizing scaffolds, cells, and bioactive factors have been pursued. The most recent trend in OC tissue engineering has been to design gradient scaffolds using different materials and construction strategies (such as bi-layered, multi-layered, and continuous gradient structures) to mimic the physiological and mechanical properties of OC tissues while further enabling OC repair. This review focuses specifically on design and construction strategies for gradient scaffolds and their role in the successful engineering of OC tissues. The current dilemmas in the field of OC defect repair and the efforts of tissue engineering to address these challenges were reviewed. In addition, the advantages and limitations of the typical fabrication techniques for gradient scaffolds were discussed, with examples of recent studies summarizing the future prospects for integrated gradient scaffold construction. This updated and enlightening review could provide insights into our current understanding of gradient scaffolds in OC tissue engineering.

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.

Recombinant protein drugs-based intra articular drug delivery systems for osteoarthritis therapy

Osteoarthritis (OA) is the most prevalent chronic degenerative joint disease. It weakens the motor function of patients and imposes a significant economic burden on society. The current medications commonly used in clinical practice do not meet the need for the treatment of OA. Recombinant protein drugs (RPDs) can treat OA by inhibiting inflammatory pathways, regulating catabolism/anabolism, and promoting cartilage repair, thereby showing promise as disease-modifying OA drugs (DMOADs). However, the rapid clearance and short half-life of them in the articular cavity limit their clinical translation. Therefore, the reliable drug delivery systems for extending drug treatment are necessary for the further development. This review introduces RPDs with therapeutic potential for OA, and summarizes their research progress on related drug delivery systems, and make proper discussion on the certain keys for optimal development of this area.

Biomaterials based on hyaluronic acid, collagen and peptides for three-dimensional cell culture and their application in stem cell differentiation

In recent decades, three-dimensional (3D) cell culture technologies have been developed rapidly in the field of tissue engineering and regeneration, and have shown unique advantages and great prospects in the differentiation of stem cells. Herein, the article reviews the progress and advantages of 3D cell culture technologies in the field of stem cell differentiation. Firstly, 3D cell culture technologies are divided into two main categories: scaffoldless and scaffolds. Secondly, the effects of hydrogels scaffolds and porous scaffolds on stem cell differentiation in the scaffold category were mainly reviewed. Among them, hydrogels scaffolds are divided into natural hydrogels and synthetic hydrogels. Natural materials include polysaccharides, proteins, and their derivatives, focusing on hyaluronic acid, collagen and polypeptides. Synthetic materials mainly include polyethylene glycol (PEG), polyacrylic acid (PAA), polyvinyl alcohol (PVA), etc. In addition, since the preparation techniques have a large impact on the properties of porous scaffolds, several techniques for preparing porous scaffolds based on different macromolecular materials are reviewed. Finally, the future prospects and challenges of 3D cell culture in the field of stem cell differentiation are reviewed. This review will provide a useful guideline for the selection of materials and techniques for 3D cell culture in stem cell differentiation.

SDF-1α-Releasing Microspheres Effectively Extend Stem Cell Homing after Myocardial Infarction

Ischemic heart disease (IHD) is one of the main focuses in today's healthcare due to its implications and complications, and it is predicted to be increasing in prevalence due to the ageing population. Although the conventional pharmacological and interventional methods for the treatment of IHD presents with success in the clinical setting, the long-term complications of cardiac insufficiency are on a continual incline as a result of post-infarction remodeling of the cardiac tissue. The migration and involvement of stem cells to the cardiac muscle, followed by differentiation into cardiac myocytes, has been proven to be the natural process, though at a slow rate. SDF-1α is a novel candidate to mobilize stem cells homing to the ischemic heart. Endogenous SDF-1α levels are elevated after myocardial infarction, but their presence gradually decreases after approximately seven days. Additional administration of SDF-1α-releasing microspheres could be a tool for the extension of the time the stem cells are in the cardiac tissue after myocardial infarction. This, in turn, could constitute a novel therapy for more efficient regeneration of the heart muscle after injury. Through this practical study, it has been shown that the controlled release of SDF-1α from biodegradable microspheres into the pericardial sac fourteen days after myocardial infarction increases the concentration of exogenous SDF-1α, which persists in the tissue much longer than the level of endogenous SDF-1α. In addition, administration of SDF-1α-releasing microspheres increased the expression of the factors potentially involved in the involvement and retention of myocardial stem cells, which constitutes vascular endothelial growth factor A (VEGFA), stem cell factor (SCF), and vascular cell adhesion molecules (VCAMs) at the site of damaged tissue. This exhibits the possibility of combating the basic limitations of cell therapy, including ineffective stem cell implantation and the ability to induce the migration of endogenous stem cells to the ischemic cardiac tissue and promote heart repair.

SDF-1α Promotes Chondrocyte Autophagy through CXCR4/mTOR Signaling Axis

SDF-1α, the most common isoform of stromal cell-derived factor 1, has shown vital effects in regulating chondrocyte proliferation, maturation, and chondrogenesis. Autophagy is a highly conserved biological process to help chondrocytes survive in harsh environments. However, the effect of SDF-1α on chondrocyte autophagy is still unknown. This study aims to investigate the effect of SDF-1α on chondrocyte autophagy and the underlying biomechanism. Transmission electron microscope assays and mRFP-GFP-LC3 adenovirus double label transfection assays were performed to detect the autophagic flux of chondrocytes. Western blots and immunofluorescence staining assays were used to detect the expression of autophagy-related proteins in chondrocytes. RNA sequencing and qPCR were conducted to assess changes in autophagy-related mRNA expression. SDF-1α upregulated the number of autophagosomes and autolysosomes in chondrocytes. It also increased the expression of autophagy-related proteins including ULK-1, Beclin-1 and LC3B, and decreased the expression of p62, an autophagy substrate protein. SDF-1α-mediated autophagy of chondrocytes required the participation of receptor CXCR4. Moreover, SDF-1α-enhanced autophagy of chondrocytes was through the inhibition of phosphorylation of mTOR signaling on the upstream of autophagy. Knockdown by siRNA and inhibition by signaling inhibitor further confirmed the importance of the CXCR4/mTOR signaling axis in SDF-1α-induced autophagy of chondrocytes. For the first time, this study elucidated that SDF-1α promotes chondrocyte autophagy through the CXCR4/mTOR signaling axis.

A Cell-Free Silk Fibroin Biomaterial Strategy Promotes In Situ Cartilage Regeneration Via Programmed Releases of Bioactive Molecules

In situ tissue regeneration using cell-free biofunctional scaffolds has been extensively studied as a promising alternative strategy to promote cartilage repair. In this study, a cartilage-biomimetic silk fibroin (SF)-based scaffold with controlled sequential release of two bioactive molecules is developed. Transforming growth factor-β1 (TGF-β1) is initially loaded onto the SF scaffolds by physical absorption, which are then successively functionalized with bone marrow mesenchymal stem cells (BMSCs)-specific-affinity peptide (E7) via gradient degradation coating of Silk fibroin Methacryloyl (SilMA)/Hyaluronic acid Methacryloyl (HAMA). Such SF-based scaffolds exhibit excellent structural stability and catilage-like mechanical properties, thus providing a desirable 3D microenvironment for cartilage reconstruction. Furthermore, rapid initial release of E7 during the first few days, followed by slow and sustained release of TGF-β1 for as long as few weeks, synergistically induced the recruitment of BMSCs and chondrogenic differentiation of them in vitro. Finally, in vivo studies indicate that the implantation of the biofunctional scaffold markedly promote in situ cartilage regeneration in a rabbit cartilage defect model. It is believed that this cartilage-biomimetic biofunctional SF-based scaffold with sequential controlled release of E7 and TGF-β1 may have a promising potential for improved cartilage tissue engineering.

Graphene Hydrogel as a Porous Scaffold for Cartilage Regeneration

Porous scaffolds have widely been exploited in cartilage tissue regeneration. However, it is often difficult to understand how the delicate hierarchical structure of the scaffold material affects the regeneration process. Graphene materials are versatile building blocks for robust and biocompatible porous structures, enabling investigation of structural cues on tissue regeneration otherwise challenging to ascertain. Here, we utilize a graphene hydrogel with stable and tunable structure as a model scaffold to examine the effect of porous structure on matrix remodeling associated with ingrowth of chondrocytes on scaffolds. We observe much-accelerated yet balanced cartilage remodeling correlating the ingrowth of chondrocytes into the graphene scaffold with an open pore structure on the surface. Importantly, such an enhanced remodeling selectively promotes the expression of collagen type II fibrils over proteoglycan aggrecan, hence clearly illustrating that chondrocytes maintain a stable phenotype when they migrate into the scaffold while offering new insights into scaffold design for cartilage repair.

Small Extracellular Vesicles Released from Bioglass/Hydrogel Scaffold Promote Vascularized Bone Regeneration by Transferring miR-23a-3p

BACKGROUND

The treatment of critical-size bone defect is a great difficulty in orthopedics. Osteogenesis and angiogenesis are critical issue during the process of bone repair and remodeling. Mesenchymal stem cells (MSCs)-derived exosomes have the same therapeutic effect to MSCs-based therapies. The effect of human umbilical cord MSCs-derived sEVs (hUC-MSCs-sEVs) on vascularized bone regeneration and the potential mechanism remains to be investigated. Herein, we aimed to explore the therapeutic effect and the mechanism of hUC-MSCs-sEVs on critical-size bone defect.

METHODS

To investigate the potential osteogenesis and angiogenesis effects of sEVs in vitro, we extracted sEVs from hUC-MSCs, and then sEVs were co-incubated with BMSCs and HUVECs. We next investigated the effect and potential mechanism of sEVs on the effects of osteogenesis and angiogenesis. We fabricated 3D-printed bioglass scaffold with Gelma/nanoclay hydrogel coatings to load sEVs (BG-gel-sEVs) to ensure in vivo sustained efficacy of sEVs. Finally, the skull defect model was used to evaluate the capacity of vascularized bone regeneration of the composited scaffolds.

RESULTS

hUC-MSCs-sEVs facilitated calcium deposition and the endothelial network formation, inducing osteogenic differentiation and angiogenesis by delivering miR-23a-3p to activate PTEN/AKT signaling pathway. Additionally, the BG-gel-sEVs composited scaffold achieved vascularized bone regeneration in vivo.

CONCLUSION

This finding illuminated that hUC-MSCs-sEVs promoted osteogenesis and angiogenesis by delivering miR-23a-3p to activate PTEN/AKT signaling pathway, achieving vascularized bone regeneration.

Exosome-based strategy for degenerative disease in orthopedics: Recent progress and perspectives

BACKGROUND

Degenerative diseases in orthopaedics have become a significant global public health issue with the aging of the population worldwide. The traditional medical interventions, including physical therapy, pharmacological therapy and even surgery, hardly work to modify degenerative progression. Stem cell-based therapy is widely accepted to treat degenerative orthopaedic disease effectively but possesses several limitations, such as the need for strict monitoring of production and storage and the potential risks of tumorigenicity and immune rejection in clinical translation. Furthermore, the ethical issues surrounding the acquisition of embryonic stem cells are also broadly concerned. Exosome-based therapy has rapidly grown in popularity in recent years and is regarded as an ideal alternative to stem cell-based therapy, offering a promise to achieve 'cell-free' tissue regeneration.

METHODS

Traditionally, the native exosomes extracted from stem cells are directly injected into the injured site to promote tissue regeneration. Recently, several modified exosome-based strategies were developed to overcome the limitations of native exosomes, which include mainly exogenous molecule loading and exosome delivery through scaffolds. In this paper, a systematic review of the exosome-based strategy for degenerative disease in orthopaedics is presented.

RESULTS

Treatment strategies based on the native exosomes are effective but with several disadvantages such as rapid diffusion and insufficient and fluctuating functional contents. The modified exosome-based strategies can better match the requirements of the regeneration in some complex healing processes.

CONCLUSION

Exosome-based strategies hold promise to manage degenerative disease in orthopaedics prior to patients reaching the advanced stage of disease in the future. The timely summary and highlights offered herein could provide a research perspective to promote the development of exosome-based therapy, facilitating the clinical translation of exosomes in orthopaedics.

TRANSLATIONAL POTENTIAL OF THIS ARTICLE

Exosome-based therapy is superior in anti-senescence and anti-inflammatory effects and possesses lower risks of tumorigenicity and immune rejection relative to stem cell-based therapy. Exosome-based therapy is regarded as an ideal alternative to stem cell-based therapy, offering a promise to achieve 'cell-free' tissue regeneration.

Progress in Osteochondral Regeneration with Engineering Strategies

Osteoarthritis, the main cause of disability worldwide, involves not only cartilage injury but also subchondral bone injury, which brings challenges to clinical repair. Tissue engineering strategies provide a promising solution to this degenerative disease. Articular cartilage connects to subchondral bone through the osteochondral interfacial tissue, which has a complex anatomical architecture, distinct cell distribution and unique biomechanical properties. Forming a continuous and stable osteochondral interface between cartilage tissue and subchondral bone is challenging. Thus, successful osteochondral regeneration with engineering strategies requires intricately coordinated interplay between cells, materials, biological factors, and physical/chemical factors. This review provides an overview of the anatomical composition, microstructure, and biomechanical properties of the osteochondral interface. Additionally, the latest research on the progress related to osteochondral regeneration is reviewed, especially discussing the fabrication of biomimetic scaffolds and the regulation of biological factors for osteochondral defects.

Silk fibroin-based biomaterials for cartilage/osteochondral repair

Osteoarthritis (OA) is a common joint disease with a high disability rate. In addition, OA not only causes great physiological and psychological harm to patients, but also puts great pressure on the social healthcare system. Pathologically, the disintegration of cartilage and the lesions of subchondral bone are related to OA. Currently, tissue engineering, which is expected to overcome the defects of existing treatment methods, had a lot of research in the field of cartilage/osteochondral repair. Silk fibroin (SF), as a natural macromolecular material with good biocompatibility, unique mechanical properties, excellent processability and degradability, holds great potential in the field of tissue engineering. Nowadays, SF had been prepared into various materials to adapt to the demands of cartilage/osteochondral repair. SF-based biomaterials can also be functionally modified to enhance repair performance further. In this review, the preparation methods, types, structures, mechanical properties, and functional modifications of SF-based biomaterials used for cartilage/osteochondral repair are summarized and discussed. We hope that this review will provide a reference for the design and development of SF-based biomaterials in cartilage/osteochondral repair field.

Copper-Lithium-Doped Nanohydroxyapatite Modulates Mesenchymal Stem Cells Homing to Treat Glucocorticoids-Related Osteonecrosis of the Femoral Head

In situ tissue regeneration has been demonstrated to promote bone repair. To identify a better approach for treating osteonecrosis of the femoral head (ONFH), we prepared scaffolds using copper-lithium-doped nanohydroxyapatite (Cu-Li-nHA), which has the potential to modulate mesenchymal stem cells (MSCs) homing. The scaffold was fabricated using the gas foaming method and the migration, angiogenesis, and osteogenesis activities of MSCs were detected using Transwell assays, tube formation assays, alkaline phosphatase and alizarin red S staining, respectively. We then implanted the Cu-Li-nHA scaffold into the femoral heads of ONFH rabbits, and CFSE labeled exogenous MSCs were injected intravenously to verify cell homing. The repair effect was subsequently examined using micro-CT and histological analysis in vivo. The results showed that Cu-Li-nHA significantly promoted MSCs migration and homing by upregulating the HIF-1α/SDF-1 pathway. The Cu-Li-nHA group showed optimal osteogenesis and angiogenesis and greater improvements in new bone formation in ONFH rabbits. To summarize, Cu-Li-nHA promoted homing and induced the osteogenic differentiation of MSCs, thereby enhancing bone regeneration during ONFH repair. Thus, Cu-Li-nHA implantation may serve as a potential therapeutic strategy for ONFH in the future.

Non-Mulberry Silk Fiber-Based Composite Scaffolds Containing Millichannels for Auricular Cartilage Regeneration

Tissue engineering has made significant progress as a cartilage repair alternative. It is crucial to promote cell proliferation and migration within three-dimensional (3D) bulk scaffolds for tissue regeneration through either chemical gradients or physical channels. In this study, by developing optimized silk fiber-based composite scaffolds, millimeter-scaled channels were created in the corresponding scaffolds via facile physical percussive drilling and subsequently utilized for auricular cartilage regeneration. We found that by the introduction of poly-l-lactic acid porous microspheres (PLLA PMs), the channels incorporated into the Antheraea pernyi (Ap) silk fiber-based scaffolds were reinforced, and the mechanical features were well maintained. Moreover, Ap silk fiber-based scaffolds reinforced by PLLA PMs containing channels (CMAF) exhibited excellent chondrocyte proliferation, migration, and synthesis of cartilage-specific extracellular matrix (ECM) in vitro. The biological evaluation in vivo revealed that CMAF had a higher chondrogenic capability for an even deposition of the specific ECM component. This study suggested that multihierarchical CMAF may have potential application for auricular cartilage regeneration.

Material-Assisted Strategies for Osteochondral Defect Repair

The osteochondral (OC) unit plays a pivotal role in joint lubrication and in the transmission of constraints to bones during movement. The OC unit does not spontaneously heal; therefore, OC defects are considered to be one of the major risk factors for developing long-term degenerative joint diseases such as osteoarthritis. Yet, there is currently no curative treatment for OC defects, and OC regeneration remains an unmet medical challenge. In this context, a plethora of tissue engineering strategies have been envisioned over the last two decades, such as combining cells, biological molecules, and/or biomaterials, yet with little evidence of successful clinical transfer to date. This striking observation must be put into perspective with the difficulty in comparing studies to identify overall key elements for success. This systematic review aims to provide a deeper insight into the field of material-assisted strategies for OC regeneration, with particular considerations for the therapeutic potential of the different approaches (with or without cells or biological molecules), and current OC regeneration evaluation methods. After a brief description of the biological complexity of the OC unit, the recent literature is thoroughly analyzed, and the major pitfalls, emerging key elements, and new paths to success are identified and discussed.

Integrated polycaprolactone microsphere-based scaffolds with biomimetic hierarchy and tunable vascularization for osteochondral repair

Osteochondral lesion potentially causes a variety of joint degenerative diseases if it cannot be treated effectively and timely. Microfracture as the conservative surgical choice achieves limited results for the larger defect whereas cartilage patches trigger integrated instability and cartilage fibrosis. To tackle aforementioned issues, here we explore to fabricate an integrated osteochondral scaffold for synergetic regeneration of cartilage and subchondral bone in one system. On the macro level, we fabricated three integrated scaffolds with distinct channel patterns of Non-channel, Consecutive-channel and Inconsecutive-channel via Selective Laser Sintering (SLS). On the micro level, both cartilage zone and subchondral bone zone of integrated scaffold were made of small polycaprolactone (PCL) microspheres and large PCL microspheres, respectively. Our findings showed that Inconsecutive-channel scaffolds possessed integrated hierarchical structure, adaptable compression strength, gradient interconnected porosity. Cartilage zone presented a dense phase for the inhibition of vessel invasion while subchondral bone zone generated a porous phase for the ingrowth of bone and vessel. Both cartilage regeneration and subchondral bone remodeling in the group of Inconsecutive-channel scaffolds have been demonstrated by histological evaluation and immunofluorescence staining in vivo. Consequently, our current work not only achieves an effective and regenerative microsphere scaffold for osteochondral reconstruction, but also provides a feasible methodology to recover injured joint through integrated design with diverse hierarchy. STATEMENT OF SIGNIFICANCE: Recovery of osteochondral lesion highly depends on hierarchical architecture and tunable vascularization in distinct zones. We therefore design a special integrated osteochondral scaffold with inconsecutive channel structure and vascularized modulation. The channel pattern impacts on mechanical strength and the infiltration of bone marrow, and eventually triggers synergetic repair of osteochondral defect. The cartilage zone of integrated scaffolds consisted of small PCL microspheres forms a dense phase for physical restriction of vascularized infiltration whereas the subchondral bone zone made of large PCL microspheres generates porous trabecula-like structure for promoting vascularization. Consequently, the current work indicates both mechanical adaptation and regional vascularized modulation play a pivotal role on osteochondral repair.

Repair of osteochondral defects mediated by double-layer scaffolds with natural osteochondral-biomimetic microenvironment and interface

Tissue engineering provides a new approach for the treatment of osteochondral defects. However, the lack of an ideal double-layer scaffold with osteochondral-biomimetic microenvironment and interface similar to native articular tissue greatly limits clinical translation. Our current study developed a double-layer acellular osteochondral matrix (AOM) scaffold with natural osteochondral-biomimetic microenvironment and interface by integrating ultraviolet (UV) laser and decellularization techniques. The laser parameters were optimized to achieve a proper pore depth close to the osteochondral interface, which guaranteed complete decellularization, sufficient space for cell loading, and relative independence of the chondrogenic and osteogenic microenvironments. Gelatin-methacryloyl (GelMA) hydrogel was further used as the cell carrier to significantly enhance the efficiency and homogeneity of cell loading in the AOM scaffold with large pore structure. Additionally, in vitro results demonstrated that the components of the AOM scaffold could efficiently regulate the chondrogenic/osteogenic differentiations of bone marrow stromal cells (BMSCs) by activating the chondrogenic/osteogenic related pathways. Importantly, the AOM scaffolds combined with BMSC-laden GelMA hydrogel successfully realized tissue-specific repair of the osteochondral defects in a knee joint model of rabbit. The current study developed a novel double-layer osteochondral biomimetic scaffold and feasible strategy, providing strong support for the tissue-specific repair of osteochondral defects and its future clinical translation.

Cartilage Repair Using Clematis Triterpenoid Saponin Delivery Microcarrier, Cultured in a Microgravity Bioreactor Prior to Application in Rabbit Model

Cartilage tissue engineering provides a promising method for the repair of articular cartilage defects, requiring appropriate biological scaffolds and necessary growth factors to enhance the efficiency of cartilage regeneration. Here, a silk fibroin (SF) microcarrier and a clematis triterpenoid saponin delivery SF (CTS-SF) microcarrier were prepared by the high-voltage electrostatic differentiation and lyophilization method, and chondrocytes were carried under the simulated microgravity condition by a rotating cell culture system. SF and CTS-SF microspheres were relatively uniform in size and had a porous structure with good swelling and cytocompatibility. Further, CTS-SF microcarriers could sustainably release CTSs in the monitored 10 days. Compared with the monolayer culture, chondrocytes under the microgravity condition maintained a better chondrogenic phenotype and showed better proliferation ability after culture on microcarriers. Moreover, the sustained release of CTS from CTS-SF microcarriers upregulated transforming growth factor-β, Smad2, and Smad3 signals, contributing to promote chondrogenesis. Hence, the biophysical effects of microgravity and bioactivities of CTS-ST were used for chondrocyte expansion and phenotype maintenance in vitro. With prolonged expansion, SF- and CTS-SF-based microcarrier-cell composites were directly implanted in vivo to repair rabbit articular defects. Gross evaluations, histopathological examinations, and biochemical analysis indicated that SF- and CTS-SF-based composites exhibited cartilage-like tissue repair compared with the nontreated group. Further, CTS-SF-based composites displayed superior hyaline cartilage-like repair that integrated with the surrounding cartilage better and higher cartilage extracellular matrix content. In conclusion, these results provide an alternative preparation method for drug-delivered SF microcarrier and a culture method for maintaining the chondrogenic phenotype of seed cells based on the microgravity environment. CTS showed its bioactive function, and the application of CTS-SF microcarriers can help repair and regenerate cartilage defects.