Engineering pre-vascularized bone-like tissue from human mesenchymal stem cells through simulating endochondral ossification

Modular, Vascularized Hypertrophic Cartilage Constructs for Bone Tissue Engineering Applications

Insufficient vascularization is the main barrier to creating engineered bone grafts for treating large and ischemic defects. Modular tissue engineering approaches have promise in this application because of the ability to combine tissue types and localize microenvironmental cues to drive desired cell function. In direct bone formation approaches, it is challenging to maintain sustained osteogenic activity, since vasculogenic cues can inhibit tissue mineralization. This study harnessed the physiological process of endochondral ossification to create multiphase tissues that allowed concomitant mineralization and vessel formation. Mesenchymal stromal cells in pellet culture were differentiated toward a cartilage phenotype, followed by induction to chondrocyte hypertrophy. Hypertrophic pellets (HPs) exhibited increased alkaline phosphatase activity, calcium deposition, and osteogenic gene expression relative to chondrogenic pellets. In addition, HPs secreted and sequestered angiogenic factors, and supported new blood vessel formation by cocultured endothelial cells and undifferentiated stromal cells. Multiphase constructs created by combining HPs and vascularizing microtissues and maintained in an unsupplemented basal culture medium were shown to support robust vascularization and sustained tissue mineralization. These results demonstrate a promising in vitro strategy to produce multiphase-engineered constructs that concomitantly support the generation of mineralized and vascularized tissue in the absence of exogenous osteogenic or vasculogenic medium supplements.

A hybrid construct with tailored 3D structure for directing pre-vascularization in engineered tissues

Hybrid 3D constructs combining different structural components afford unique opportunities to engineer functional tissues. Creating functional microvascular networks within these constructs is crucial for promoting integration with host vessels and ensuring successful engraftment. Here, we present a hybrid 3D system in which poly (ethylene oxide terephthalate)/poly (butylene terephthalate) fibrous scaffolds are combined with pectin hydrogels to provide internal topography and guide the formation of microvascular beds. The sequence/method of seeding human endothelial cells (EC) and mesenchymal stromal cells (MSC) into the system had a significant impact on microvessel formation. Optimal results were obtained when EC were directly seeded onto the fibrous scaffold, followed by the addition of hydrogel-embedded MSC. This approach facilitated the development of highly oriented microvascular networks along the fibers. These networks were lumenized, supported by a basement membrane, and stabilized by pericyte-like cells, persisting for at least 28 days in vitro. Furthermore, culture under pro-angiogenic and osteoinductive conditions induced MSC osteogenic differentiation without impairing microvessel formation. Upon subcutaneous implantation in mice, the pre-vascularized constructs were infiltrated by host vessels, and human microvessels were still present after 2 weeks. Overall, the proposed hybrid 3D system, combined with an optimized cell-seeding protocol, offers an effective approach for directing the formation of robust and geometrically oriented microvessels, making it promising for tissue engineering applications.

CRISPR innovations in tissue engineering and gene editing

The CRISPR/Cas9 system is a powerful tool for genome editing, utilizing the Cas9 nuclease and programmable single guide RNA (sgRNA). However, the Cas9 nuclease activity can be disabled by mutation, resulting in catalytically deactivated Cas9 (dCas9). By combining the customizable sgRNA with dCas9, researchers can inhibit specific gene expression (CRISPR interference, CRISPRi) or activate the expression of a target gene (CRISPR activation, CRISPRa). In this review, we present the principles and recent advancements of these CRISPR technologies, as well as their delivery vectors. We also explore their applications in stem cell engineering and regenerative medicine, with a focus on in vitro stem cell fate manipulation and in vivo treatments. These include the prevention of retinal and muscular degeneration, neural regeneration, bone regeneration, cartilage tissue engineering, and the treatment of blood, skin, and liver diseases. Furthermore, we discuss the challenges of translating CRISPR technologies into regenerative medicine and provide future perspectives. Overall, this review highlights the potential of CRISPR in advancing regenerative medicine and offers insights into its application in various areas of research and therapy.

Electrostimulation-Based Decellularized Matrix Bladder Patch Promotes Bladder Repair in Rats

Bladder tissue engineering offers significant potential for repairing defects resulting from congenital and acquired conditions. However, the effectiveness of engineered grafts is often constrained by insufficient vascularization and neural regeneration. This study utilized four primary biomaterials─gelatin methacryloyl (GelMA), chitin nanocrystals (ChiNC), titanium carbide (MXene), and adipose-derived stem cells (ADSC)─to formulate two types of bioinks, GCM0.2 and GCM0.2-ADSC, in specified proportions. These bioinks were 3D printed onto bladder acellular matrix (BAM) patches to create BAM-GCM0.2 and BAM-GCM0.2-ADSC patches. The BAM-GCM0.2-ADSC patches underwent electrical stimulation to yield GCM0.2-ADSC-ES bladder patches. Employed for the repair of rat bladder defects, these patches were evaluated against a Control group, which underwent partial cystectomy followed by direct suturing. Our findings indicate that the inclusion of ADSC and electrical stimulation significantly enhances the regeneration of rat bladder smooth muscle (from [24.052 ± 2.782] % to [57.380 ± 4.017] %), blood vessels (from [5.326 ± 0.703] % to [12.723 ± 1.440] %), and nerves (from [0.227 ± 0.017] % to [1.369 ± 0.218] %). This research underscores the superior bladder repair capabilities of the GCM0.2-ADSC-ES patch and opens new pathways for bladder defect repair.

Modular, Vascularized Hypertrophic Cartilage Constructs for Bone Tissue Engineering Applications

Insufficient vascularization is a main barrier to creating engineered bone grafts for treating large and ischemic defects. Modular tissue engineering approaches have promise in this application because of the ability to combine tissue types and to localize microenvironmental cues to drive desired cell function. In direct bone formation approaches, it is challenging to maintain sustained osteogenic activity, since vasculogenic cues can inhibit tissue mineralization. This study harnessed the physiological process of endochondral ossification to create multiphase tissues that allowed concomitant mineralization and vessel formation. Mesenchymal stromal cells in pellet culture were differentiated toward a cartilage phenotype, followed by induction to chondrocyte hypertrophy. Hypertrophic pellets exhibited increased alkaline phosphatase activity, calcium deposition, and osteogenic gene expression relative to chondrogenic pellets. In addition, hypertrophic pellets secreted and sequestered angiogenic factors, and supported new blood vessel formation by co-cultured endothelial cells and undifferentiated stromal cells. Multiphase constructs created by combining hypertrophic pellets and vascularizing microtissues and maintained in unsupplemented basal culture medium were shown to support robust vascularization and sustained tissue mineralization. These results demonstrate a new in vitro strategy to produce multiphase engineered constructs that concomitantly support the generation of mineralize and vascularized tissue in the absence of exogenous osteogenic or vasculogenic medium supplements.

Crosstalk between Wnt and bone morphogenetic protein signaling during osteogenic differentiation

Mesenchymal stem cells (MSCs) originate from many sources, including the bone marrow and adipose tissue, and differentiate into various cell types, such as osteoblasts and adipocytes. Recent studies on MSCs have revealed that many transcription factors and signaling pathways control osteogenic development. Osteogenesis is the process by which new bones are formed; it also aids in bone remodeling. Wnt/β-catenin and bone morphogenetic protein (BMP) signaling pathways are involved in many cellular processes and considered to be essential for life. Wnt/β-catenin and BMPs are important for bone formation in mammalian development and various regulatory activities in the body. Recent studies have indicated that these two signaling pathways contribute to osteogenic differentiation. Active Wnt signaling pathway promotes osteogenesis by activating the downstream targets of the BMP signaling pathway. Here, we briefly review the molecular processes underlying the crosstalk between these two pathways and explain their participation in osteogenic differentiation, emphasizing the canonical pathways. This review also discusses the crosstalk mechanisms of Wnt/BMP signaling with Notch- and extracellular-regulated kinases in osteogenic differentiation and bone development.

Spatiotemporal Modulated Scaffold for Endogenous Bone Regeneration via Harnessing Sequentially Released Guiding Signals

The design of a scaffold that can regulate the sequential differentiation of bone marrow mesenchymal stromal cells (BMSCs) according to the endochondral ossification (ECO) mechanism is highly desirable for effective bone regeneration. In this study, we successfully fabricated a dual-networked composite hydrogel composed of gelatin and hyaluronic acid (termed GCDH-M), which can sequentially release chondroitin sulfate (CS) and magnesium/silicon (Mg/Si) ions to provide spatiotemporal guidance for chondrogenesis, angiogenesis, and osteogenesis. The fast release of CS is from the GCDH hydrogel, and the sustained releases of Mg/Si ions are from poly(lactide-co-glycolide) microspheres embedded in the hydrogel. There is a difference in the release rates between CS and ions, resulting in the ability for the fast release of CS and sustained release of ions. The dual networks between the modified gelatin and hyaluronic acid via covalent bonding and host-guest interactions render the hydrogel with some dynamic feature to meet the differentiation development of BMSCs laden inside the hydrogel, i.e., transforming into a chondrogenic phenotype, further to a hypertrophic phenotype and eventually to an osteogenic phenotype. As evidenced by the results of in vitro and in vivo evaluations, this GCDH-M composite hydrogel was proved to be able to create an optimal microenvironment for embedded BMSCs responding to the sequential guiding signals, which aligns with the rhythm of the ECO process and ultimately boosts bone regeneration. The promising outcome achieved with this innovative hydrogel system sheds light on novel scaffold design targeting bone tissue engineering.

Layered Double Hydroxides: A Novel Promising 2D Nanomaterial for Bone Diseases Treatment

Bone diseases including bone defects, bone infections, osteoarthritis, and bone tumors seriously affect life quality of the patient and bring serious economic burdens to social health management, for which the current clinical treatments bear dissatisfactory therapeutic effects. Biomaterial-based strategies have been widely applied in the treatment of orthopedic diseases but are still plagued by deficient bioreactivity. With the development of nanotechnology, layered double hydroxides (LDHs) with adjustable metal ion composition and alterable interlayer structure possessing charming physicochemical characteristics, versatile bioactive properties, and excellent drug loading and delivery capabilities arise widespread attention and have achieved considerable achievements for bone disease treatment in the last decade. However, to the authors' best knowledge, no review has comprehensively summarized the advances of LDHs in treating bone disease so far. Herein, the advantages of LDHs for orthopedic disorders treatment are outlined and the corresponding state-of-the-art achievements are summarized for the first time. The potential of LDHs-based nanocomposites for extended therapeutics for bone diseases is highlighted and perspectives for LDHs-based scaffold design are proposed for facilitated clinical translation.

A composite, off-the-shelf osteoinductive material for large, vascularized bone flap prefabrication

We previously described an immortalized, genetically-engineered human Mesenchymal stromal cell line to generate BMP2-enriched Chondrogenic Matrices (MB-CM), which after devitalization and storage could efficiently induce ectopic bone tissue by endochondral ossification. In order to increase the efficiency of MB-CM utilization towards engineering scaled-up bone structures, here we hypothesized that MB-CM can retain osteoinductive properties when combined with an osteoconductive material. We first tested different volumetric ratios of MB-CM:SmartBone® (as clinically used, osteoconductive reference material) and assessed the bone formation capacity of the resulting composites following ectopic mouse implantation. After 8 weeks, as little as 25% of MB-CM was sufficient to induce bone formation and fusion across SmartBone® granules, generating large interconnected bony structures. The same composite percentage was then further assessed in a scaled-up model, namely within an axially-vascularized, confined, ectopically prefabricated flap (0.8 cm³) in rats. The material efficiently induced the formation of new bone (31% of the cross-sectional area after 8 weeks), including bone marrow and vascular elements, throughout the flap volume. Our findings outline a strategy for efficient use of MB-CM as part of a composite material, thereby reducing the amount required to fill large spaces and enabling utilization in critically sized grafts, to address challenging clinical scenarios in bone reconstruction. STATEMENT OF SIGNIFICANCE: Most bone repair strategies rely either on osteconductive properties of ceramics and devitalized bone, or osteoinductive properties of growth factors and extracellular matrices (ECM). Here we designed a composite material made of a clinically accepted osteoconductive material and an off-the-shelf tissue engineered human cartilage ECM with strong osteoinductive properties. We showed that low amount of osteoinductive ECM potentiated host cells recruitment to form large vascularized bone structures in two different animal models, one being a challenging prefabricated bone-flap model targeting challenging clinical bone repair. Overall, this study highlights the use of a promising human off-the-shelf material for accelerated healing towards clinical applications.

Close-to-native bone repair via tissue-engineered endochondral ossification approaches

In order to solve the clinical challenges related to bone grafting, several tissue engineering (TE) strategies have been proposed to repair critical-sized defects. Generally, the classical TE approaches are designed to promote bone repair via intramembranous ossification. Although promising, strategies that direct the osteogenic differentiation of mesenchymal stem/stromal cells are usually characterized by a lack of functional vascular supply, often resulting in necrotic cores. A less explored alternative is engineering bone constructs through a cartilage-mediated approach, resembling the embryological process of endochondral ossification. The remodeling of an intermediary hypertrophic cartilaginous template triggers vascular invasion and bone tissue deposition. Thus, employing this knowledge can be a promising direction for the next generation of bone TE constructs. This review highlights the most recent biomimetic strategies for applying endochondral ossification in bone TE while discussing the plethora of cell types, culture conditions, and biomaterials essential to promote a successful bone regeneration process.