Msx1+ stem cells recruited by bioactive tissue engineering graft for bone regeneration

Sequential construction of vascularized and mineralized bone organoids using engineered ECM-DNA-CPO-based bionic matrix for efficient bone regeneration

Given the limitations of allogeneic and artificial bone grafts, bone organoids have attracted extensive attention for their physiological properties that closely resemble natural bone, offering great potential to bone reconstruction for critical-sized bone defects. Although early-stage bone organoids such as osteo-callus organoids and woven bone organoids have been reported, functional bone organoids with vascularization and mineralization are currently unavailable due to the lack of bone-mimicking matrix and dynamic culture systems suitable for the long-term cultivation of mature bone organoids. Herein, a novel engineered bionic matrix hydrogels with multifunctional components and double network structure are developed by incorporating calcium phosphate oligomers (CPO) into a combination of bone-derived decellularized extracellular matrix (ECM) and salmon-derived deoxyribonucleic acid (DNA) via photo-crosslinking and dynamic self-assembly strategies. This kind of bionic matrix hydrogels facilitate recruitment, proliferation, osteogenesis and angiogenesis of bone marrow mesenchymal stromal cells (BMSCs). More importantly, vascularized and mineralized bone organoids are sequentially constructed using BMSCs-loaded engineered bionic matrix hydrogels via in vitro dynamic culture and in vivo heterotopic ossification. Meanwhile, this kind of engineered bionic matrix are capable of achieving efficient bone repair for cranial defect. These findings suggest that engineered bionic matrix hydrogels combined with such dynamic culture system, providing a promising strategy for functional bone organoids construction.

Engineering a stem cell-embedded bilayer hydrogel with biomimetic collagen mineralization for tendon-bone interface healing

The tendon-bone interface effectively transfers mechanical stress for movement, yet its regeneration presents significant clinical challenges due to its hierarchical structure and composition. Biomimetic strategies that replicate the distinctive characteristics have demonstrated potential for enhancing the healing process. However, there remains a challenge in developing a composite that replicates the nanostructure of the tendon-bone interface and embeds living cells. Here, we engineered a nanoscale biomimetic bilayer hydrogel embedded with tendon stem cells for tendon-bone interface healing. Specifically, the biomimetic hydrogel incorporates intra- and extrafibrillar mineralized collagen fibrils as well as non-mineralized collagen fibrils resembling the tendon-bone interface at the nanoscale. Furthermore, biomimetic mineralization with the presence of cells realizes living tendon-bone-like tissue constructs. In the in vivo patella-patellar tendon-interface injury model, the tendon stem cell-laden biomimetic hydrogel promoted tendon-bone interface regeneration, demonstrated by increased fibrocartilage formation, improved motor function, and enhanced biomechanical outcomes. This study highlights the potential of the stem cell-laden biomimetic hydrogel as an effective strategy for tendon-bone interface regeneration, offering a novel approach to engineering complex tissue interfaces.

Living joint prosthesis with in-situ tissue engineering for real-time and long-term osteoarticular reconstruction

The reconstruction of large osteoarticular defects caused by tumor resection or severe trauma remains a clinical challenge. Current metal prostheses exhibit a lack of osteo-chondrogenic functionality and demonstrate poor integration with host tissues. This often results in complications such as abnormal bone absorption and prosthetic loosening, which may necessitate secondary revisions. Here, we propose a paradigm-shifting "living prosthesis" strategy that combines a customized 3D-printed hollow titanium humeral prosthesis with engineered bone marrow condensations presenting bone morphogenetic protein-2 (BMP-2) and transforming growth factor-β3 (TGF-β3) from encapsulated silk fibroin hydrogels. This innovative approach promotes in situ endochondral defect regeneration of the entire humeral head while simultaneously providing immediate mechanical support. In a rabbit model of total humerus resection, the designed "living prosthesis" achieved weight, macroscopic and microscopic morphologies that were comparable to those of undamaged native joints at 2 months post-implantation, with organized osteochondral tissues were regenerated both around and within the prosthesis. Notably, the "living prosthesis" displayed significantly higher osteo-integration than the blank metal prosthesis did, as evidenced by a 3-fold increase in bone ingrowth and a 2-fold increase in mechanical pull-out strength. Furthermore, the "living prosthesis" restored joint cartilage function, with rabbits exhibiting normal gait and weight-bearing capacity. The successful regeneration of fully functional humeral head tissue from a single implanted prosthesis represents technical advance in designing bioactive bone prosthesis, with promising implications for treating extreme-large osteochondral defects.

BMSCs laden gelatin methacrylate (GelMA) hydrogel integrating silk fibroin/hydroxyapatite scaffold with multi-layered-oriented pores for enhanced bone regeneration

Due to the limited regenerative ability of bone tissue, bone injury repair has always been a complicated problem in clinical treatment. Bone tissue engineering based on cell delivery is an effective method to repair bone defects, but it also puts forward strict requirements on the scaffold used in the repair process and the survival rate of cell inoculation. To address this challenge, we constructed a bone mesenchymal stem cells (BMSCs) laden gelatin methacrylate (GelMA) hydrogel to integrate in silk fibroin (SF) /nano-hydroxyapatite (nHAp) scaffold, building a dual architecture to achieve enhanced angiogenesis and bone regeneration. The GelMA hydrogel prepared by visible photo-crosslinking showed good cell loading capacity, and the multi-layered-oriented pores of the scaffold provided a suitable microenvironment for cell proliferation and nutrient exchange. We further explored the effects of this "dual-system" complex on BMSCs and in a critical-sized rat cranial defect model. The results showed that BMSCs@GelMA-SF/nHAp composite scaffold with directional pore structure was more conducive to the repair of skull defects in rats due to the faster rate of vascularization and osteogenesis, indicating the developed gel-scaffold complex would be a promising therapeutic strategy for the repair of bone defects regeneration.

Metabolite-dependent m6A methylation driven by mechanotransduction-metabolism-epitranscriptomics axis promotes bone development and regeneration

Intramembranous ossification, a major bone development process, begins with the condensation of precursor cells through the timely structural adaption of extracellular matrix (ECM) catering to rapid cellular morphological changes. Inspired by this, we design a highly cell-adaptable hydrogel to recapitulate an ECM-dependent mechanotransduction-metabolism-epitranscriptomics axis in mesenchymal stromal cells (MSCs). This hydrogel significantly enhances the E-cadherin-mediated cell-cell interactions of MSCs and promotes glucose uptake and tricarboxylic acid (TCA) cycle activities. We further show that elevated succinate inhibits fat mass and obesity-associated protein (FTO), a N6-methyladenosine (m6A) demethylase, thereby enhancing methyltransferase-like 3 (METTL3)-driven m6A methylation. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) indicates increased m6A methylation of runt-related transcription 2 (Runx2), a key osteogenic signaling factor, promoting osteogenesis of hydrogel-delivered MSCs and bone regeneration in critical-sized bone defects. Our findings reveal the mechanism underlying the critical impact of adaptable ECM structures on tissue development and provide valuable guidance for the design of ECM-mimetic cell carriers to enhance the therapeutic outcomes of regenerative medicine.

3D-Printed Dual-Lineage Inductive Approach for Efficient Osteochondral Regeneration

Osteochondral defect regeneration is challenging due to the mismatch between cartilage and subchondral bone. We developed a functionalized scaffold replicating the natural architecture, biochemical and biomechanical environment of both tissues to promote concurrent regeneration. Our bilayered, zone-specific scaffold combines tailored materials for each tissue type: gelatin methacryloyl (GelMA), modified hyaluronic acid, and umbilical cord-derived extracellular matrix (ECM) for the cartilage layer; GelMA, placenta-derived ECM, and nano amorphous calcium phosphate for the osseous layer. Using 3D digital light-processing printing, we constructed the scaffold with spatially distributed biochemical and biomechanical signaling. This approach created dual chondro-/osteogenic microenvironments facilitating bone marrow mesenchymal stem cell differentiation. In vivo studies demonstrated concurrent regeneration of cartilage and subchondral bone tissues with robust integration. This 3D-printed biomimetic scaffold, featuring dual-lineage inductive properties, shows promising potential for efficient osteochondral regeneration and addresses complex tissue engineering requirements.

Mussel-inspired surface-engineering of 3D printed scaffolds employing bedecked transition metal for accelerated bone tissue regeneration

In modern civilization with fast work culture and uncontrolled lifestyles increase bone-related problems, moreover, lack of auto-regeneration of bone, indulge to formulate a suitable methodology to get rid of this problem. In this article, nanohydroxyapatite (nHA) decorated hierarchical titanium phosphate (TP) was synthesized by solvothermal process and incorporated into newly synthesized tartaric acid-based polyurethane (PU) through in situ technique. The porous 3D scaffold was fabricated by most advanced 3D printing technique with desired porous structure in a controlled manner. The biochemical properties of scaffold's surface were improved via immobilizing polydopamine (PDA) at ambient temperature. Elemental analysis indicated that TP-doped nanohybrid scaffolds experienced higher amount of PDA immobilization as compared to pristine and nHA-doped scaffolds. The unoccupied 'd' orbital of introduced Ti can form a coordinate bond with catechol groups of dopamine (DA) which augments PDA deposition on the scaffold's surface. Furthermore, the higher effective nuclear charge (Z⁎) of tetravalent Ti ion generates an effective dative bond with the urethane groups of PU chain which improves hardness and tensile strength (TS) of produced nanocomposites (PU/TP-nHA) remarkably by 71.3 % and 126 % compared to pristine PU. Ti-doped nanohybrid scaffolds, containing calcium and phosphate components with higher amounts of deposited PDA exhibited improved in vitro osteogenic bioactivity. Moreover, in vivo study expressed superior bone regeneration efficacy of the TP-doped nHA-integrated PU scaffold without showing any organ toxicity. Thus, the optimum level of TP-doped nHA with higher amount of PDA-immobilized PU nanohybrid scaffold would be a suitable bone graft substitute in bone regeneration applications.

Regulating Cell-Material Interfacial Interactions through Selective Cellular Resistance

Regulating the behavior of different types of cells at the material-tissue interface is pivotal for inducing tissue regeneration. Traditional methods enhance target cell activity using specific ligands such as peptides and antibodies, which have stability issues within biological environments. Herein, we show that selective cell resistance can be realized by fine-tuning the material surface chemistry, achieving strong cell selectivity superior to that of extracellular matrix peptides. A certain degree of adsorption resistance differentially affects the adhesion of various types of cells on material surfaces. Taking this principle into account, a polyethylene glycol (PEG) grafted surface was meticulously fine-tuned to selectively support endothelial cells (ECs) while resisting smooth muscle cell attachment. Mechanistic studies identified that the difference in myosin II expression is crucial for cell selectivity. An EC-selective polymer coating for cardiovascular devices was fabricated to promote rapid surface endothelialization and prevent neointimal hyperplasia in vivo.

Curcumin and vitamin D3 release from calcium phosphate enhances bone regeneration

Improving early in vivo osseointegration and removing residual cancer cells after tumor removal requires the development of novel bone implants with osteogenic and anti-cancer properties. Here, curcumin and vitamin D3 (Cur/VitD3) are loaded into calcium phosphate (CaP) matrices to improve in vivo osteogenesis and inhibit the proliferation of human osteosarcoma cells. Patient-specific, 3D-printed tricalcium phosphate (TCP) loaded with Cur/VitD3 increases the viability of in vitro osteoblast cells after 11 days. When delivered in combination, Cur/VitD3 loaded hydroxyapatite (HA)-coated Ti64 implant promotes new bone formation by 2.7-fold compared to the control after 6 weeks. This delivery system also decreases osteosarcoma cell viability relative to the 3D-printed TCP after day 11, indicating its anti-cancer properties. These findings contribute to the understanding of multifunctional CaP bone grafts to improve early osteogenesis after severe bone trauma and suppress the proliferation of osteosarcoma cells after tumor resection surgery.

3D printed scaffolds with multistage osteogenic activity for bone defect repair

The bone defect repair is a complex process including immune regulation, stem cell osteogenic differentiation and extracellular matrix mineralization. Current bone tissue engineering approaches often fail to adapt throughout the above osteogenic process, resulting in suboptimal repair outcomes. To address this problem, a 3D-printed scaffold with multistage osteogenic activity based on shape-memory elastomer and electroactive material is developed. The scaffold exhibits excellent shape memory performance and can trigger shape recovery by physiological temperature. The physiological temperature-triggered shape-memory behavior makes the scaffold promising for minimally invasive implantation. After electric field polarization, the scaffold's surface carries the negative charge, which can activate the PI3K/Akt signaling pathway to promote the polarization of macrophages to M2 phenotype and activate the FAK/ERK signaling pathway to promote osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), indicating that the scaffold can effectively participate in immune microenvironment regulation and stem cell osteogenic differentiation. Additionally, the negative charge on the scaffold's surface can attract calcium and phosphate ions, forming a mineralized matrix and promoting late-stage extracellular matrix mineralization by continuously supplying mineralizing ions such as calcium and phosphate. Overall, this study introduces a 3D-printed scaffold with multistage osteogenic activity, offering a promising strategy for bone defect repair.

Bioinspired artificial antioxidases for efficient redox homeostasis and maxillofacial bone regeneration

Reconstructing large, inflammatory maxillofacial defects using stem cell-based therapy faces challenges from adverse microenvironments, including high levels of reactive oxygen species (ROS), inadequate oxygen, and intensive inflammation. Here, inspired by the reaction mechanisms of intracellular antioxidant defense systems, we propose the de novo design of an artificial antioxidase using Ru-doped layered double hydroxide (Ru-hydroxide) for efficient redox homeostasis and maxillofacial bone regeneration. Our studies demonstrate that Ru-hydroxide consists hydroxyls-synergistic monoatomic Ru centers, which efficiently react with oxygen species and collaborate with hydroxyls for rapid proton and electron transfer, thus exhibiting efficient, broad-spectrum, and robust ROS scavenging performance. Moreover, Ru-hydroxide can effectively sustain stem cell viability and osteogenic differentiation in elevated ROS environments, modulating the inflammatory microenvironment during bone tissue regeneration in male mice. We believe this Ru-hydroxide development offers a promising avenue for designing antioxidase-like materials to treat various inflammation-associated disorders, including arthritis, diabetic wounds, enteritis, and bone fractures.

Black Phosphorus Tagged Responsive Strontium Hydrogel Particles for Bone Defect Repair

Hydrogel-derived implants have proven value in bone tissue regeneration, and current efforts have concentrated on devising strategies for producing functional implants with desired structures and functions to improve therapeutic outcomes. Herein, a novel black phosphorus (BP) tagged responsive strontium (Sr) hydrogel particles are presented for bone defect repair. By applying microfluidic technology, Sr and carboxymethyl chitosan, and BP are integrated into poly(N-isopropyl acrylamide) (pNIPAM) hydrogel matrix to generate such microparticles called pNBCSMs. Upon exposure to near-infrared irradiation, the pNBCSMs experience volume shrinkage and provoke the extrusion of the incorporated Sr, ascribed to the photothermal conversion ability of BP and the thermosensitivity of pNIPAM. In vitro and in vivo experimental results reveal that pNBCSMs subjected to near-infrared light display superior anti-inflammatory, anti-apoptotic, bacterial inhibitory, as well as osteogenesis-promoting effects, thereby effectively improving defective cranial bone repair. These features suggest that the proposed pNBCSMs can be promising candidates for bone repair.

Cordycepin-Loaded Dental Pulp Stem Cell-Derived Exosomes Promote Aged Bone Repair by Rejuvenating Senescent Mesenchymal Stem Cells and Endothelial Cells

Aging impairs bone marrow mesenchymal stem cell (BMSC) functions as well as associated angiogenesis which is critical for bone regeneration and repair. Hence, repairing bone defects in elderly patients poses a formidable challenge in regenerative medicine. Here, the engineered dental pulp stem cell-derived exosomes loaded with the natural derivative of adenosine Cordycepin (CY@D-exos) are fabricated by means of the intermittent ultrasonic shock, which dually rejuvenates both senescent BMSCs and endothelial cells and significantly improve bone regeneration and repair in aged animals. CY@D-exos can efficiently overcome the senescence of aged BMSCs and enhance their osteogenic differentiation by activating NRF2 signaling and maintaining heterochromatin stability. Importantly, CY@D-exos also potently overcomes the senescence of vascular endothelial cells and promotes angiogenesis. In vivo injectable gelatin methacryloyl (GelMA) hydrogels with sustained release of CY@D-exos can accelerate bone injury repair and promote new blood vessel formation in aged animals. Taken together, these results thus demonstrate that cordycepin-loaded dental pulp stem cell-derived exosomes display considerable potential to be developed as a next-generation therapeutic agent for promoting aged bone regeneration and repair.

3D bioprinting of high-performance hydrogel with in-situ birth of stem cell spheroids

Digital light processing (DLP)-based bioprinting technology holds immense promise for the advancement of hydrogel constructs in biomedical applications. However, creating high-performance hydrogel constructs with this method is still a challenge, as it requires balancing the physicochemical properties of the matrix while also retaining the cellular activity of the encapsulated cells. Herein, we propose a facile and practical strategy for the 3D bioprinting of high-performance hydrogel constructs through the in-situ birth of stem cell spheroids. The strategy is achieved by loading the cell/dextran microdroplets within gelatin methacryloyl (GelMA) emulsion, where dextran functions as a decoy to capture and aggregate the cells for bioprinting while GelMA enables the mechanical support without losing the structural complexity and fidelity. Post-bioprinting, the leaching of dextran results in a smooth curved surface that promotes in-situ birth of spheroids within hydrogel constructs. This process significant enhances differentiation potential of encapsulated stem cells. As a proof-of-concept, we encapsulate dental pulp stem cells (DPSCs) within hydrogel constructs, showcasing their regenerative capabilities in dentin and neovascular-like structures in vivo. The strategy in our study enables high-performance hydrogel tissue construct fabrication with DLP-based bioprinting, which is anticipated to pave a promising way for diverse biomedical applications.

Msx1-Modified Rat Bone Marrow Mesenchymal Stem Cell Therapy for Rotator Cuff Repair: A Comprehensive Analysis of Tendon-Bone Healing and Cellular Mechanisms

This study investigates the therapeutic potential of Msx1-overexpressing bone marrow mesenchymal stem cells (BMSCs) in enhancing tendon-bone healing in rotator cuff injuries. BMSCs were genetically modified to overexpress Msx1 and were evaluated in vitro for their proliferation, migration, and differentiation potential. Results demonstrated that Msx1 overexpression significantly increased BMSC proliferation and migration while inhibiting osteogenic and chondrogenic differentiation. In a rat model of acute rotator cuff injury, Msx1-BMSCs embedded in a hydrogel scaffold were implanted at the tendon-bone junction. Micro-CT analysis revealed substantial new bone formation in the Msx1-BMSC group, and histological evaluation showed organized collagen and cartilage structures at the repair site. Biomechanical testing further confirmed enhanced structural strength in the Msx1-BMSC-treated group. These findings suggest that Msx1 modification enhances BMSC-mediated repair by promoting cell proliferation and migration, facilitating tendon-bone integration. This Msx1-based approach presents a promising strategy for advancing regenerative therapies for rotator cuff injuries.

Quercetin-based biomaterials for enhanced bone regeneration and tissue engineering

Quercetin, a natural flavonoid, has been extensively researched for its potential in promoting bone regeneration and tissue engineering. This review aimed to provide a comprehensive overview of the applications of quercetin-based biomaterials in bone regeneration and tissue engineering. The review discusses several studies that have integrated quercetin into biomaterials such as electrospun fibers, hydrogels, microspheres, and nanoparticles. These biomaterials are engineered to imitate the natural extracellular matrix of bone, creating an environment conducive to cell attachment, growth, and differentiation. The investigations presented emphasize the potential of quercetin-derived biomaterials in improving bone regeneration, decreasing oxidative stress and inflammation, and facilitating bone tissue restoration. These biomaterials have demonstrated the ability to facilitate cell encapsulation, maintain consistent quercetin release patterns, and have been applied in a range of uses such as bone grafts, implants, and tissue engineering scaffolds. Biomaterials derived from quercetin are utilized in the treatment of bone-related disorders, including osteoporosis and bone defects. These materials enhance bone regeneration by providing a scaffold for new bone growth, promoting the development of new bone tissue, and improving the mechanical properties of bone tissue.

"Osteo-Organogenesis Niche" Hyaluronic Acid Engineered Materials Directing Re-Osteo-Organogenesis via Manipulating Macrophage CD44-MAPK/ERK-ETV1/5-MRC1 Axis

The strategy of re-organogenesis provides an optimal framework for restoring complex organ structures and functions in adult damage. While the focus has often been on restoring organogenesis stem cells, there is limited investigations of reverting the environmental niche to support this approach. The guiding principle of "Nature selects the fittest to survive" drives the intricate dynamic changes in cellular events within the niche environment, especially through immune surveillance. The extracellular matrix (ECM) serves as the "self-associated molecular patterns" of the niche, containing extensive data on cell-niche reaction data and acting as the active tuner of immune surveillance. In this study, hyaluronic acid (HA) is identified as a unique component of the ECM in cranial osteo-organogenesis. Mechanistically, HA activates the Cluster of Differentiation 44 (CD44)-Mitogen-Activated Protein Kinase (MAPK)/Extracellular Signal-Regulated Kinase (ERK)-Ets Variant 1/5 (ETV1/5)- Mannose Receptor C-Type 1 (MRC1) axis in macrophages, establishing a distinct immune surveillance during osteo-organogenesis. Furthermore, HA is utilized as a novel engineered material for an "Osteo-organogenesis niche", restoring immune surveillance and synergistically regulating stem cells to achieve re-osteo-organogenesis in cranial defects of rats. Taken together, the study unveils a previously unknown strategy for leveraging re-organogenesis by utilizing "organogenesis niche" ECM engineered materials to manipulate immune surveillance, thereby comprehensively regulating stem cells and other tissue cells effectively for re-organogenesis.

Recent Strategies and Advances in Hydrogel-Based Delivery Platforms for Bone Regeneration

Bioactive molecules have shown great promise for effectively regulating various bone formation processes, rendering them attractive therapeutics for bone regeneration. However, the widespread application of bioactive molecules is limited by their low accumulation and short half-lives in vivo. Hydrogels have emerged as ideal carriers to address these challenges, offering the potential to prolong retention times at lesion sites, extend half-lives in vivo and mitigate side effects, avoid burst release, and promote adsorption under physiological conditions. This review systematically summarizes the recent advances in the development of bioactive molecule-loaded hydrogels for bone regeneration, encompassing applications in cranial defect repair, femoral defect repair, periodontal bone regeneration, and bone regeneration with underlying diseases. Additionally, this review discusses the current strategies aimed at improving the release profiles of bioactive molecules through stimuli-responsive delivery, carrier-assisted delivery, and sequential delivery. Finally, this review elucidates the existing challenges and future directions of hydrogel encapsulated bioactive molecules in the field of bone regeneration.

Microenvironment-optimized gastrodin-functionalized scaffolds orchestrate asymmetric division of recruited stem cells in endogenous bone regeneration

The regeneration of osteoporotic bone defects remains challenging as the critical stem cell function is impaired by inflammatory microenvironment. Synthetic materials that intrinsically direct osteo-differentiation versus self-renewal of recruited stem cell represent a promising alternative strategy for endogenous bone formation. Therefore, a microenvironmentally optimized polyurethane (PU) /n-HA scaffold to enable sustained delivery of gastrodin is engineered to study its effect on the osteogenic fate of stem cells. It exhibited interconnected porous networks and an elevated sequential gastrodin release pattern to match immune-osteo cascade concurrent with progressive degradation of materials. In a critical-sized femur defect model of osteoporotic rat, 5% gastrodin-PU/n-HA potently promoted neo-bone regeneration by facilitating M2 macrophage polarization and CD146+ host stem cell recruitment to defective site. The implantation time-dependently increased the bone marrow mesenchymal stem cell (BMSC) population, and further culture of BMSCs showed a robust ability of proliferation, migration, and mitochondrial resurgence. Of note, some of cell pairs produced one stemness daughter cell while the other committed to osteogenic lineage in an asymmetric cell division (ACD) manner, and a much more compelling ACD response was triggered when 5% gastrodin-PU/n-HA implanted. Further investigation revealed that one-sided concentrated presentation of aPKC and β-catenin in dividing cells effectively induced asymmetric distribution, which polarized aPKC biased the response of the daughter cells to Wnt signal. The asymmetric cell division in skeletal stem cells (SSCs) was mechanically comparable to BMSCs and also governed by distinct aPKC and β-catenin biases. Concomitantly, delayed bone loss adjacent to the implant partly alleviated development of osteoporosis. In conclusion, our findings provide insight into the regulation of macrophage polarization combined with osteogenic commitment of recruited stem cells in an ACD manner, advancing scaffold design strategy for endogenous bone regeneration.

Biphasic Calcium Phosphate Ceramic Scaffold Composed of Zinc Doped β-Tricalcium Phosphate and Silicon Doped Hydroxyapatite for Bone Tissue Engineering

The rapid repair of bone defects remains a significant clinical challenge to this day. To address this issue, a 3D-printed biphasic calcium phosphate (BCP) scaffold consisting of 40 wt % hydroxyapatite (HA) and 60 wt % β-tricalcium phosphate (β-TCP) was created. Silicon and zinc were incorporated into HA and β-TCP, respectively, to enhance the angiogenic and osteogenic properties of the BCP scaffold. The physicochemical properties, in vitro cell responses, and bone defect repair efficacy of the modified BCP scaffold were comprehensively investigated. Results showed that the fabricated scaffold possessed a 3D interconnected pore structure. Zinc doping enhanced the sintering of the BCP scaffold, increased its density and strength, but decreased its degradation rate. Conversely, silicon doping had the opposite effect. The modified scaffold was capable of a gradual release of zinc/silicon ions, which promoted the proliferation and differentiation of cells. Specifically, the scaffold doped with zinc significantly promoted the osteogenic differentiation of stem cells. Moreover, co-doping with silicon and zinc synergistically promoted in vitro angiogenesis, with BCP-3 (doped with 2.5 mol % zinc and 4 mol % silicon) exhibiting the best pro-angiogenic activity. BCP-3 significantly induced regeneration of blood vessels and bone tissue in vivo, indicating its potential to accelerate the process of bone defect repair.

Risperidone accelerates bone loss in mice models of schizophrenia by inhibiting osteoblast autophagy

Background

Risperidone (RIS) is the first-line drug in the clinical treatment of schizophrenia, and long-term use may lead to bone loss and even osteoporosis. This study investigated whether the mechanism of RIS-induced bone loss is related to autophagy.

Methods

The schizophrenia mice were established with the administration of MK-801. Then, RIS were injected, or autophagy inducer rapamycin (RAPA) co-injected for 8 weeks. Cognitive performance was determined by the novel object recognition and Open field tests. Bone loss of schizophrenia mice were assessed using microCT, H&E staining, ALP staining, ARS staining and WB, respectively. Autophagy of schizophrenia mice were detected by immunofluorescence, transmission electron microscopy (TEM) and WB, respectively. In addition, osteogenic differentiation of MC3T3-E1 and BMSCs cells were assessed using H&E staining, ALP staining, ARS staining and WB, respectively.

Results

In the present study, we found that RIS treatment can promote bone loss in schizophrenia mice and inhibit osteogenic differentiation of MC3T3-E1 and BMSCs cells. Interesting, the number of autophagosome and autophagy-related protein expression were decreased after RIS treatment. However, the bone loss and inhibition of osteogenic differentiation induced by RIS in schizophrenia mice were reversed by autophagy inducer RAPA.

Conclusion

RIS significantly increased bone loss and inhibited osteogenic differentiation in schizophrenia mice; the underlying mechanism entails suppressing osteoblast autophagy.

An Engineered Hierarchical Hydrogel with Immune Responsiveness and Targeted Mitochondrial Transfer to Augmented Bone Regeneration

Coordinating the immune response and bioenergy metabolism in bone defect environments is essential for promoting bone regeneration. Mitochondria are important organelles that control internal balance and metabolism. Repairing dysfunctional mitochondria has been proposed as a therapeutic approach for disease intervention. Here, an engineered hierarchical hydrogel with immune responsiveness can adapt to the bone regeneration environment and mediate the targeted mitochondria transfer between cells. The continuous supply of mitochondria by macrophages can restore the mitochondrial bioenergy of bone marrow mesenchymal stem cells (BMSC). Fundamentally solving the problem of insufficient energy support of BMSCs caused by local inflammation during bone repair and regeneration. This discovery provides a new therapeutic strategy for promoting bone regeneration and repair, which has research value and practical application prospects in the treatment of various diseases caused by mitochondrial dysfunction.

An Osteoimmunomodulatory Biopatch Potentiates Stem Cell Therapies for Bone Regeneration by Simultaneously Regulating IL-17/Ferroptosis Signaling Pathways

Currently, there are still great challenges in promoting bone defect healing, a common health problem affecting millions of people. Herein an osteoimmunity-regulating biopatch capable of promoting stem cell-based therapies for bone regeneration is developed. A totally biodegradable conjugate is first synthesized, which can self-assemble into bioactive nano micelles (PPT NMs). This nanotherapy effectively improves the osteogenesis of periodontal ligament stem cells (PDLSCs) under pathological conditions, by simultaneously regulating IL-17 signaling and ferroptosis pathways. Incorporation of PPT NMs into biodegradable electrospun nanofibers affords a bioactive patch, which notably improves bone formation in two rat bone defect models. A Janus bio patch is then engineered by integrating the bioactive patch with a stem cell sheet of PDLSCs. The obtained biopatch shows additionally potentiated bone regeneration capacity, by synergistically regulating osteoimmune microenvironment and facilitating stem cell differentiation. Further surface functionalization of the biopatch with tannic acid considerably increases its adhesion to the bone defect, prolongs local retention, and sustains bioactivities, thereby offering much better repair effects in rats with mandibular or cranial bone defects. Moreover, the engineered bioactive patches display good safety. Besides bone defects, this osteoimmunity-regulating biopatch strategy can be applied to promote stem cell therapies for spinal cord injury, wound healing, and skin burns.

Efficient Light-Based Bioprinting via Rutin Nanoparticle Photoinhibitor for Advanced Biomedical Applications

Digital light processing (DLP) bioprinting, known for its high resolution and speed, enables the precise spatial arrangement of biomaterials and has become integral to advancing tissue engineering and regenerative medicine. Nevertheless, inherent light scattering presents significant challenges to the fidelity of the manufactured structures. Herein, we introduce a photoinhibition strategy based on Rutin nanoparticles (Rnps), attenuating the scattering effect through concurrent photoabsorption and free radical reaction. Compared to the widely utilized biocompatible photoabsorber tartrazine (Tar), Rnps-infused bioink enhanced printing speed (1.9×), interlayer homogeneity (58% less overexposure), resolution (38.3% improvement), and print tolerance (3× high-precision range) to minimize trial-and-error. The biocompatible and antioxidative Rnps significantly improved cytocompatibility and exhibited resistance to oxidative stress-induced damage in printed constructs, as demonstrated with human induced pluripotent stem cell-derived endothelial cells (hiPSC-ECs). The related properties of Rnps facilitate the facile fabrication of multimaterial, heterogeneous, and cell-laden biomimetic constructs with intricate structures. The developed photoinhibitor, with its profound adaptability, promises wide biomedical applications tailored to specific biological requirements.

Recent advances of bone tissue engineering: carbohydrate and ceramic materials, fundamental properties and advanced biofabrication strategies ‒ a comprehensive review

Bone is a dynamic tissue that can always regenerate itself through remodeling to maintain biofunctionality. This tissue performs several vital physiological functions. However, bone scaffolds are required for critical-size damages and fractures, and these can be addressed by bone tissue engineering. Bone tissue engineering (BTE) has the potential to develop scaffolds for repairing critical-size damaged bone. BTE is a multidisciplinary engineered scaffold with the desired properties for repairing damaged bone tissue. Herein, we have provided an overview of the common carbohydrate polymers, fundamental structural, physicochemical, and biological properties, and fabrication techniques for bone tissue engineering. We also discussed advanced biofabrication strategies and provided the limitations and prospects by highlighting significant issues in bone tissue engineering. There are several review articles available on bone tissue engineering. However, we have provided a state-of-the-art review article that discussed recent progress and trends within the last 3-5 years by emphasizing challenges and future perspectives.

Multi-site enhancement of osteogenesis: peptide-functionalized GelMA hydrogels with three-dimensional cultures of human dental pulp stem cells

Human dental pulp stem cells (hDPSCs) have demonstrated greater proliferation and osteogenic differentiation potential in certain studies compared to other types of mesenchymal stem cells, making them a promising option for treating craniomaxillofacial bone defects. However, due to low extracting concentration and long amplifying cycles, their access is limited and utilization rates are low. To solve these issues, the principle of bone-forming peptide-1 (BFP1) in situ chemotaxis was utilized for the osteogenic differentiation of hDPSCs to achieve simultaneous and synergistic osteogenesis at multiple sites. BFP1-functionalized gelatin methacryloyl hydrogel provided a 3D culture microenvironment for stem cells. The experimental results showed that the 3D composite hydrogel scaffold constructed in this study increased the cell spread area by four times compared with the conventional GelMA scaffold. Furthermore, the problems of high stem cell dosage and low rate of utilization were alleviated by orchestrating the programmed proliferation and osteogenic differentiation of hDPSCs. In vivo, high-quality repair of critical bone defects was achieved using hDPSCs extracted from a single tooth, and multiple 'bone island'-like structures were successfully observed that rapidly induced robust bone regeneration. In conclusion, this study suggests that this kind of convenient, low-cost, island-like osteogenesis strategy involving a low dose of hDPSCs has great potential for repairing craniomaxillofacial critical-sized bone defects.

METTL3 Modulates Ctsk+ Lineage Supporting Cranial Osteogenesis via Hedgehog

N6-methyladenosine (m6A) modification, a eukaryotic messenger RNA modification catalyzed by methyltransferase-like 3 (METTL3), plays a pivotal role in stem cell fate determination. Calvarial bone development and maintenance are orchestrated by the cranial sutures. Cathepsin K (CTSK)-positive calvarial stem cells (CSCs) contribute to mice calvarial ossification. However, the role of m6A modification in regulating Ctsk+ lineage cells during calvarial development remains elusive. Here, we showed that METTL3 was colocalized with cranial nonosteoclastic Ctsk+ lineage cells, which were also associated with GLI1 expression. During neonatal development, depletion of Mettl3 in the Ctsk+ lineage cells delayed suture formation and decreased mineralization. During adulthood maintenance, loss of Mettl3 in the Ctsk+ lineage cells impaired calvarial bone formation, which was featured by the increased bone porosity, enhanced bone marrow cavity, and decreased number of osteocytes with the less-developed cellular outline. The analysis of methylated RNA immunoprecipitation sequencing and RNA sequencing data indicated that loss of METTL3 reduced Hedgehog (Hh) signaling pathway. Restoration of Hh signaling pathway by crossing Sufufl/+ alleles or by local administration of SAG21 partially rescued the abnormity. Our data indicate that METTL3 modulates Ctsk+ lineage cells supporting calvarial bone formation by regulating the Hh signaling pathway, providing new insights for clinical treatment of skull vault osseous diseases.

Piezocatalytically-induced controllable mineralization scaffold with bone-like microenvironment to achieve endogenous bone regeneration

Orderly hierarchical structure with balanced mechanical, chemical, and electrical properties is the basis of the natural bone microenvironment. Inspired by nature, we developed a piezocatalytically-induced controlled mineralization strategy using piezoelectric polymer poly-L-lactic acid (PLLA) fibers with ordered micro-nano structures to prepare biomimetic tissue engineering scaffolds with a bone-like microenvironment (pcm-PLLA), in which PLLA-mediated piezoelectric catalysis promoted the in-situ polymerization of dopamine and subsequently regulated the controllable growth of hydroxyapatite crystals on the fiber surface. PLLA fibers, as analogs of mineralized collagen fibers, were arranged in an oriented manner, and ultimately formed a bone-like interconnected pore structure; in addition, they also provided bone-like piezoelectric properties. The uniformly sized HA nanocrystals formed by controlled mineralization provided a bone-like mechanical strength and chemical environment. The pcm-PLLA scaffold could rapidly recruit endogenous stem cells, and promote their osteogenic differentiation by activating cell membrane calcium channels and PI3K signaling pathways through ultrasound-responsive piezoelectric signals. In addition, the scaffold also provided a suitable microenvironment to promote macrophage M2 polarization and angiogenesis, thereby enhancing bone regeneration in skull defects of rats. The proposed piezocatalytically-induced controllable mineralization strategy provides a new idea for the development of tissue engineering scaffolds that can be implemented for multimodal physical stimulation therapy.

Cellular Scale Curvature in Bioceramic Scaffolds Enhanced Bone Regeneration by Regulating Skeletal Stem Cells and Vascularization

Critical-sized segmental bone defects cannot heal spontaneously, leading to disability and significant increase in mortality. However, current treatments utilizing bone grafts face a variety of challenges from donor availability to poor osseointegration. Drugs such as growth factors increase cancer risk and are very costly. Here, a porous bioceramic scaffold that promotes bone regeneration via solely mechanobiological design is reported. Two types of scaffolds with high versus low pore curvatures are created using high-precision 3D printing technology to fabricate pore curvatures radius in the 100s of micrometers. While both are able to support bone formation, the high-curvature pores induce higher ectopic bone formation and increased vessel invasion. Scaffolds with high-curvature pores also promote faster regeneration of critical-sized segmental bone defects by activating mechanosensitive pathways. High-curvature pore recruits skeletal stem cells and type H vessels from both the periosteum and the marrow during the early phase of repair. High-curvature pores have increased survival of transplanted GFP-labeled skeletal stem cells (SSCs) and recruit more host SSCs. Taken together, the bioceramic scaffolds with defined micrometer-scale pore curvatures demonstrate a mechanobiological approach for orthopedic scaffold design.

Structure-optimized and microenvironment-inspired nanocomposite biomaterials in bone tissue engineering

Critical-sized bone defects represent a significant clinical challenge due to their inability to undergo spontaneous regeneration, necessitating graft interventions for effective treatment. The development of tissue-engineered scaffolds and regenerative medicine has made bone tissue engineering a highly viable treatment for bone defects. The physical and biological properties of nanocomposite biomaterials, which have optimized structures and the ability to simulate the regenerative microenvironment of bone, are promising for application in the field of tissue engineering. These biomaterials offer distinct advantages over traditional materials by facilitating cellular adhesion and proliferation, maintaining excellent osteoconductivity and biocompatibility, enabling precise control of degradation rates, and enhancing mechanical properties. Importantly, they can simulate the natural structure of bone tissue, including the specific microenvironment, which is crucial for promoting the repair and regeneration of bone defects. This manuscript provides a comprehensive review of the recent research developments and applications of structure-optimized and microenvironment-inspired nanocomposite biomaterials in bone tissue engineering. This review focuses on the properties and advantages these materials offer for bone repair and tissue regeneration, summarizing the latest progress in the application of nanocomposite biomaterials for bone tissue engineering and highlighting the challenges and future perspectives in the field. Through this analysis, the paper aims to underscore the promising potential of nanocomposite biomaterials in bone tissue engineering, contributing to the informed design and strategic planning of next-generation biomaterials for regenerative medicine.

Angiogenesis is uncoupled from osteogenesis during calvarial bone regeneration

Bone regeneration requires a well-orchestrated cellular and molecular response including robust vascularization and recruitment of mesenchymal and osteogenic cells. In femoral fractures, angiogenesis and osteogenesis are closely coupled during the complex healing process. Here, we show with advanced longitudinal intravital multiphoton microscopy that early vascular sprouting is not directly coupled to osteoprogenitor invasion during calvarial bone regeneration. Early osteoprogenitors emerging from the periosteum give rise to bone-forming osteoblasts at the injured calvarial bone edge. Microvessels growing inside the lesions are not associated with osteoprogenitors. Subsequently, osteogenic cells collectively invade the vascularized and perfused lesion as a multicellular layer, thereby advancing regenerative ossification. Vascular sprouting and remodeling result in dynamic blood flow alterations to accommodate the growing bone. Single cell profiling of injured calvarial bones demonstrates mesenchymal stromal cell heterogeneity comparable to femoral fractures with increase in cell types promoting bone regeneration. Expression of angiogenesis and hypoxia-related genes are slightly elevated reflecting ossification of a vascularized lesion site. Endothelial Notch and VEGF signaling alter vascular growth in calvarial bone repair without affecting the ossification progress. Our findings may have clinical implications for bone regeneration and bioengineering approaches.

Extracellular Vesicles in the Repair of Bone and Cartilage Injury: From Macro‐Delivery to Micro‐Modification

Extracellular vesicles (EVs) are intermediaries in intercellular signal transmission and material exchange and have attracted significant attention from researchers in bone and cartilage repair. These nanoscale vesicles hold immense potential in facilitating bone and cartilage repair and regeneration by regulating the microenvironment at an injury site. However, their in vivo utilization is limited by their self‐clearance and random distribution. Therefore, various delivery platforms have been developed to improve EV targeting and retention rates in target organs while achieving a controlled release of EVs. Additionally, engineering modification of EVs has been proposed to effectively enhance EVs' intrinsic targeting and drug‐loading abilities and further improve their therapeutic effects on bone and cartilage injuries. This review aims to introduce the biogenesis of EVs and their regulatory mechanisms in the microenvironment of bone and cartilage injuries and comprehensively discuss the application of EV‐delivery platforms of different materials and various EV engineering modification methods in treating bone and cartilage injuries. The review's findings can help advance EV research and develop new strategies for improving the therapy of bone and cartilage injuries.

Mgp High-Expressing MSCs Orchestrate the Osteoimmune Microenvironment of Collagen/Nanohydroxyapatite-Mediated Bone Regeneration

Activating autologous stem cells after the implantation of biomaterials is an important process to initiate bone regeneration. Although several studies have demonstrated the mechanism of biomaterial-mediated bone regeneration, a comprehensive single-cell level transcriptomic map revealing the influence of biomaterials on regulating the temporal and spatial expression patterns of mesenchymal stem cells (MSCs) is still lacking. Herein, the osteoimmune microenvironment is depicted around the classical collagen/nanohydroxyapatite-based bone repair materials via combining analysis of single-cell RNA sequencing and spatial transcriptomics. A group of functional MSCs with high expression of matrix Gla protein (Mgp) is identified, which may serve as a pioneer subpopulation involved in bone repair. Remarkably, these Mgp high-expressing MSCs (MgphiMSCs) exhibit efficient osteogenic differentiation potential and orchestrate the osteoimmune microenvironment around implanted biomaterials, rewiring the polarization and osteoclastic differentiation of macrophages through the Mdk/Lrp1 ligand-receptor pair. The inhibition of Mdk/Lrp1 activates the pro-inflammatory programs of macrophages and osteoclastogenesis. Meanwhile, multiple immune-cell subsets also exhibit close crosstalk between MgphiMSCs via the secreted phosphoprotein 1 (SPP1) signaling pathway. These cellular profiles and interactions characterized in this study can broaden the understanding of the functional MSC subpopulations at the early stage of biomaterial-mediated bone regeneration and provide the basis for materials-designed strategies that target osteoimmune modulation.

Isolation, identification and osteogenic capability analysis of mesenchymal stem cells derived from different layers of human maxillary sinus membrane

AIM

To discover the populations of mesenchymal stem cells (MSCs) derived from different layers of human maxillary sinus membrane (hMSM) and evaluate their osteogenic capability.

MATERIALS AND METHODS

hMSM was isolated into a monolayer using the combined method of physical separation and enzymatic digestion. The localization of MSCs in hMSM was performed by immunohistological staining and other techniques. Lamina propria layer-derived MSCs (LMSCs) and periosteum layer-derived MSCs (PMSCs) from hMSM were expanded using the explant cell culture method and identified by multilineage differentiation assays, colony formation assay, flow cytometry and so on. The biological characteristics of LMSCs and PMSCs were compared using RNA sequencing, reverse transcription and quantitative polymerase chain reaction, immunofluorescence staining, transwell assay, western blotting and so forth.

RESULTS

LMSCs and PMSCs from hMSMs were both CD73-, CD90- and CD105-positive, and CD34-, CD45- and HLA-DR-negative. LMSCs and PMSCs were identified as CD171+/CD90+ and CD171-/CD90+, respectively. LMSCs displayed stronger proliferation capability than PMSCs, and PMSCs presented stronger osteogenic differentiation capability than LMSCs. Moreover, PMSCs could recruit and promote osteogenic differentiation of LMSCs.

CONCLUSIONS

This study identified and isolated two different types of MSCs from hMSMs. Both MSCs served as good potential candidates for bone regeneration.

Mussel inspired 3D elastomer enabled rapid calvarial bone regeneration through recruiting more osteoprogenitors from the dura mater

Currently, the successful healing of critical-sized calvarial bone defects remains a considerable challenge. The immune response plays a key role in regulating bone regeneration after material grafting. Previous studies mainly focused on the relationship between macrophages and bone marrow mesenchymal stem cells (BMSCs), while dural cells were recently found to play a vital role in the calvarial bone healing. In this study, a series of 3D elastomers with different proportions of polycaprolactone (PCL) and poly(glycerol sebacate) (PGS) were fabricated, which were further supplemented with polydopamine (PDA) coating. The physicochemical properties of the PCL/PGS and PCL/PGS/PDA grafts were measured, and then they were implanted as filling materials for 8 mm calvarial bone defects. The results showed that a matched and effective PDA interface formed on a well-proportioned elastomer, which effectively modulated the polarization of M2 macrophages and promoted the recruitment of dural cells to achieve full-thickness bone repair through both intramembranous and endochondral ossification. Single-cell RNA sequencing analysis revealed the predominance of dural cells during bone healing and their close relationship with macrophages. The findings illustrated that the crosstalk between dural cells and macrophages determined the vertical full-thickness bone repair for the first time, which may be the new target for designing bone grafts for calvarial bone healing.

Novel Nonthermal Atmospheric Plasma Irradiation of Titanium Implants Promotes Osteogenic Effect in Osteoporotic Conditions

Osteoporosis is a metabolic disease characterized by bone density and trabecular bone loss. Bone loss may affect dental implant osseointegration in patients with osteoporosis. To promote implant osseointegration in osteoporotic patients, we further used a nonthermal atmospheric plasma (NTAP) treatment device previously developed by our research group. After the titanium implant (Ti) is placed into the device, the working gas flow and the electrode switches are turned on, and the treatment is completed in 30 s. Previous studies showed that this NTAP device can remove carbon contamination from the implant surface, increase the hydroxyl groups, and improve its wettability to promote osseointegration in normal conditions. In this study, we demonstrated the tremendous osteogenic enhancement effect of NTAP-Ti in osteoporotic conditions in rats for the first time. Compared to Ti, the proliferative potential of osteoporotic bone marrow mesenchymal stem cells on NTAP-Ti increased by 180% at 1 day (P = 0.004), while their osteogenic differentiation increased by 149% at 14 days (P < 0.001). In addition, the results indicated that NTAP-Ti significantly improved osseointegration in osteoporotic rats in vivo. Compared to the Ti, the bone volume fraction (BV/TV) and trabecular number (Tb.N) values of NTAP-Ti in osteoporotic rats, respectively, increased by 18% (P < 0.001) and 25% (P = 0.007) at 6 weeks and the trabecular separation (Tb.Sp) value decreased by 26% (P = 0.02) at 6 weeks. In conclusion, this study proved a novel NTAP irradiation titanium implant that can significantly promote osseointegration in osteoporotic conditions.

Enhanced bone regeneration by osteoinductive and angiogenic zein/whitlockite composite scaffolds loaded with levofloxacin

Promoting angiogenesis following biomaterial implantation is essential to bone tissue regeneration. Herein, the composite scaffolds composed of zein, whitlockite (WH), and levofloxacin (LEVO) were fabricated to augment bone repair by facilitating osteogenesis and angiogenesis. First, three-dimensional composite scaffolds containing zein and WH were prepared using the salt-leaching method. Then, as a model antibiotic drug, the LEVO was loaded into zein/WH scaffolds. Moreover, the addition of WH enhanced the adhesion, differentiation, and mineralization of osteoblasts. The zein/WH/LEVO composite scaffolds not only had significant osteoinductivity but also showed excellent antibacterial properties. The prepared composite scaffolds were then implanted into a calvarial defect model to evaluate their osteogenic induction effects in vivo. Micro-CT observation and histological analysis indicate that the scaffolds can accelerate bone regeneration with the contribution of endogenous cytokines. Based on amounts of data in vitro and in vivo, the scaffolds present profound effects on improving bone regeneration, especially for the favorable osteogenic, intensive angiogenic, and alleviated inflammation abilities. The results showed that the synthesized scaffolds could be a potential material for bone tissue engineering.

Engineered Microchannel Scaffolds with Instructive Niches Reinforce Endogenous Bone Regeneration by Regulating CSF-1/CSF-1R Pathway

Structural and physiological cues provide guidance for the directional migration and spatial organization of endogenous cells. Here, a microchannel scaffold with instructive niches is developed using a circumferential freeze-casting technique with an alkaline salting-out strategy. Thereinto, polydopamine-coated nano-hydroxyapatite is employed as a functional inorganic linker to participate in the entanglement and crystallization of chitosan molecules. This scaffold orchestrates the advantage of an oriented porous structure for rapid cell infiltration and satisfactory immunomodulatory capacity to promote stem cell recruitment, retention, and subsequent osteogenic differentiation. Transcriptomic analysis as well as its in vitro and in vivo verification demonstrates that essential colony-stimulating factor-1 (CSF-1) factor is induced by this scaffold, and effectively bound to the target colony-stimulating factor-1 receptor (CSF-1R) on the macrophage surface to activate the M2 phenotype, achieving substantial endogenous bone regeneration. This strategy provides a simple and efficient approach for engineering inducible bone regenerative biomaterials.

Generation of complex bone marrow organoids from human induced pluripotent stem cells

The human bone marrow (BM) niche sustains hematopoiesis throughout life. We present a method for generating complex BM-like organoids (BMOs) from human induced pluripotent stem cells (iPSCs). BMOs consist of key cell types that self-organize into spatially defined three-dimensional structures mimicking cellular, structural and molecular characteristics of the hematopoietic microenvironment. Functional properties of BMOs include the presence of an in vivo-like vascular network, the presence of multipotent mesenchymal stem/progenitor cells, the support of neutrophil differentiation and responsiveness to inflammatory stimuli. Single-cell RNA sequencing revealed a heterocellular composition including the presence of a hematopoietic stem/progenitor (HSPC) cluster expressing genes of fetal HSCs. BMO-derived HSPCs also exhibited lymphoid potential and a subset demonstrated transient engraftment potential upon xenotransplantation in mice. We show that the BMOs could enable the modeling of hematopoietic developmental aspects and inborn errors of hematopoiesis, as shown for human VPS45 deficiency. Thus, iPSC-derived BMOs serve as a physiologically relevant in vitro model of the human BM microenvironment to study hematopoietic development and BM diseases.

ECM-inspired calcium/zinc laden cellulose scaffold for enhanced bone regeneration

Cellulose-based polymer scaffolds are highly diverse for designing and fabricating artificial bone substitutes. However, realizing the multi-biological functions of cellulose-based scaffolds has long been challenging. In this work, inspired by the structure and function of the extracellular matrix (ECM) of bone, we developed a novel yet feasible strategy to prepare ECM-like scaffolds with hybrid calcium/zinc mineralization. The 3D porous structure was formed via selective oxidation and freeze drying of bacterial cellulose. Following the principle of electrostatic interaction, calcium/zinc hybrid hydroxyapatite nucleated, crystallized, and precipitated on the 3D scaffold in simulated physiological conditions, which was well confirmed by morphology and composition analysis. Compared with alternative scaffold cohorts, this hybrid ion-loaded cellulose scaffold exhibited a pronounced elevation in alkaline phosphatase (ALP) activity, osteogenic gene expression, and cranial defect regeneration. Notably, the hybrid ion-loaded cellulose scaffold effectively fostered an M2 macrophage milieu and had a strong immune effect in vivo. In summary, this study developed a hybrid multifunctional cellulose-based scaffold that appropriately simulates the ECM to regulate immunomodulatory and osteogenic differentiation, setting a measure for artificial bone substitutes.

Conducting biointerface of spider-net-like chitosan-adorned polyurethane/SPIONs@SrO2-fMWCNTs for bone tissue engineering and antibacterial efficacy

In pursuit of enhancing bone cell proliferation, this study delves into the fabrication of porous scaffolds through the integration of nanomaterials. Specifically, we present the development of highly conductive chitosan (CS) nanonets on fibro-porous polyurethane (PU) bio-membranes. These nanofibers comprise functionalized multiwall carbon nanotubes (fMWCNTs), well-dispersed superparamagnetic iron oxide (SPIONs), and strontium oxide (SrO2) nanoparticles. The resulting porous scaffold exhibits remarkable interfacial biocompatibility, antibacterial properties, and load-bearing capability. Through meticulous in vitro investigations, the CS-PU/SPIONs/SrO2-fMWCNTs nanofibrous scaffolds have demonstrated a propensity to promote bone cell regeneration. Notably, the integration of these nanomaterials has been found to upregulate crucial bone-related markers, including ALP, ARS, COL-I, RUNX2, and SPP-I. The evaluation of these markers, conducted through quantitative real-time polymerase chain reaction (qRT-PCR) and immunocytochemistry, substantiates the improved cell survival and enhanced osteogenic differentiation facilitated by the integrated nanomaterials. This comprehensive analysis underscores the efficacy of CS-PU/SPIONs/SrO2-fMWCNTs bioscaffolds in promoting MC3T3-E1 cell regeneration within, thereby holding promise for advancements in bone tissue engineering and regenerative medicine.

Enhanced bone regeneration via endochondral ossification using Exendin-4-modified mesenchymal stem cells

Nonunions and delayed unions pose significant challenges in orthopedic treatment, with current therapies often proving inadequate. Bone tissue engineering (BTE), particularly through endochondral ossification (ECO), emerges as a promising strategy for addressing critical bone defects. This study introduces mesenchymal stem cells overexpressing Exendin-4 (MSC-E4), designed to modulate bone remodeling via their autocrine and paracrine functions. We established a type I collagen (Col-I) sponge-based in vitro model that effectively recapitulates the ECO pathway. MSC-E4 demonstrated superior chondrogenic and hypertrophic differentiation and enhanced the ECO cell fate in single-cell sequencing analysis. Furthermore, MSC-E4 encapsulated in microscaffold, effectively facilitated bone regeneration in a rat calvarial defect model, underscoring its potential as a therapeutic agent for bone regeneration. Our findings advocate for MSC-E4 within a BTE framework as a novel and potent approach for treating significant bone defects, leveraging the intrinsic ECO process.

Biomaterials for Regenerative Cranioplasty: Current State of Clinical Application and Future Challenges

Acquired cranial defects are a prevalent condition in neurosurgery and call for cranioplasty, where the missing or defective cranium is replaced by an implant. Nevertheless, the biomaterials in current clinical applications are hardly exempt from long-term safety and comfort concerns. An appealing solution is regenerative cranioplasty, where biomaterials with/without cells and bioactive molecules are applied to induce the regeneration of the cranium and ultimately repair the cranial defects. This review examines the current state of research, development, and translational application of regenerative cranioplasty biomaterials and discusses the efforts required in future research. The first section briefly introduced the regenerative capacity of the cranium, including the spontaneous bone regeneration bioactivities and the presence of pluripotent skeletal stem cells in the cranial suture. Then, three major types of biomaterials for regenerative cranioplasty, namely the calcium phosphate/titanium (CaP/Ti) composites, mineralised collagen, and 3D-printed polycaprolactone (PCL) composites, are reviewed for their composition, material properties, and findings from clinical trials. The third part discusses perspectives on future research and development of regenerative cranioplasty biomaterials, with a considerable portion based on issues identified in clinical trials. This review aims to facilitate the development of biomaterials that ultimately contribute to a safer and more effective healing of cranial defects.

Osteoinductive Dental Pulp Stem Cell-Derived Extracellular Vesicle-Loaded Multifunctional Hydrogel for Bone Regeneration

Stem cell-derived extracellular vesicles (EVs) show great potential for promoting bone tissue regeneration. However, normal EVs (Nor-EVs) have a limited ability to direct tissue-specific regeneration. Therefore, it is necessary to optimize the osteogenic capacity of EV-based systems for repairing extensive bone defects. Herein, we show that hydrogels loaded with osteoinductive dental pulp stem cell-derived EVs (Ost-EVs) enhanced bone tissue remodeling, resulting in a 2.23 ± 0.25-fold increase in the expression of bone morphogenetic protein 2 (BMP2) compared to the hydrogel control group. Moreover, Ost-EVs led to a higher expression of alkaline phosphatase (ALP) (1.88 ± 0.16 of Ost-EVs relative to Nor-EVs) and the formation of orange-red calcium nodules (1.38 ± 0.10 of Ost-EVs relative to Nor-EVs) in vitro. RNA sequencing revealed that Ost-EVs showed significantly high miR-1246 expression. An ideal hydrogel implant should also adhere to surrounding moist tissues. In this study, we were drawn to mussel-inspired adhesive modification, where the hydrogel carrier was crafted from hyaluronic acid (HA) and polyethylene glycol derivatives, showcasing impressive tissue adhesion, self-healing capabilities, and the ability to promote bone growth. The modified HA (mHA) hydrogel was also responsive to environmental stimuli, making it an effective carrier for delivering EVs. In an ectopic osteogenesis animal model, the Ost-EV/hydrogel system effectively alleviated inflammation, accelerated revascularization, and promoted tissue mineralization. We further used a rat femoral condyle defect model to evaluate the in situ osteogenic ability of the Ost-EVs/hydrogel system. Collectively, our results suggest that Ost-EVs combined with biomaterial-based hydrogels hold promising potential for treating bone defects.

Tolerant and Rapid Endochondral Bone Regeneration Using Framework-Enhanced 3D Biomineralized Matrix Hydrogels

Tissue-engineered bone has emerged as a promising alternative for bone defect repair due to the advantages of regenerative bone healing and physiological functional reconstruction. However, there is very limited breakthrough in achieving favorable bone regeneration due to the harsh osteogenic microenvironment after bone injury, especially the avascular and hypoxic conditions. Inspired by the bone developmental mode of endochondral ossification, a novel strategy is proposed for tolerant and rapid endochondral bone regeneration using framework-enhanced 3D biomineralized matrix hydrogels. First, it is meticulously designed 3D biomimetic hydrogels with both hypoxic and osteoinductive microenvironment, and then integrated 3D-printed polycaprolactone framework to improve their mechanical strength and structural fidelity. The inherent hypoxic 3D matrix microenvironment effectively activates bone marrow mesenchymal stem cells self-regulation for early-stage chondrogenesis via TGFβ/Smad signaling pathway due to the obstacle of aerobic respiration. Meanwhile, the strong biomineralized microenvironment, created by a hybrid formulation of native-constitute osteogenic inorganic salts, can synergistically regulate both bone mineralization and osteoclastic differentiation, and thus accelerate the late-stage bone maturation. Furthermore, both in vivo ectopic osteogenesis and in situ skull defect repair successfully verified the high efficiency and mechanical maintenance of endochondral bone regeneration mode, which offers a promising treatment for craniofacial bone defect repair.

3D Printed SiO2-Tricalcium Phosphate Scaffolds Loaded with Carvacrol Nanoparticles for Bone Tissue Engineering Application

Bone damage resulting from trauma or aging poses challenges in clinical settings that need to be addressed using bone tissue engineering (BTE). Carvacrol (CA) possesses anti-inflammatory, anticancer, and antibacterial properties. Limited solubility and physicochemical stability restrict its biological activity, requiring a stable carrier system for delivery. Here, we investigate the utilization of a three-dimensional printed (3DP) SiO2-doped tricalcium phosphate (TCP) scaffold functionalized with carvacrol-loaded lipid nanoparticles (CA-LNPs) to improve bone health. It exhibits a negative surface charge with an entrapment efficiency of ∼97% and size ∼129 nm with polydispersity index (PDI) and zeta potential values of 0.18 and -16 mV, respectively. CA-LNPs exhibit higher and long-term release over 35 days. The CA-LNP loaded SiO2-doped TCP scaffold demonstrates improved antibacterial properties against Staphylococcus aureus and Pseudomonas aeruginosa by >90% reduction in bacterial growth. Functionalized scaffolds result in 3-fold decrease and 2-fold increase in osteosarcoma and osteoblast cell viability, respectively. These findings highlight the therapeutic potential of the CA-LNP loaded SiO2-doped TCP scaffold for bone defect treatment.

Tricarboxylic Acid Cycle Metabolite-Coordinated Biohydrogels Augment Cranial Bone Regeneration Through Neutrophil-Stimulated Mesenchymal Stem Cell Recruitment and Histone Acetylation-Mediated Osteogenesis

Cranial bone defects remain a major clinical challenge, increasing patients' life burdens. Tricarboxylic acid (TCA) cycle metabolites play crucial roles in facilitating bone tissue regeneration. However, the development of TCA cycle metabolite-modified biomimetic grafts for skull bone regeneration still needs to be improved. The mechanism underlying the release of TCA cycle metabolites from biomaterials in regulating immune responses and mesenchymal stem cell (MSC) fate (migration and differentiation) remains unknown. Herein, this work constructs biomimetic hydrogels composed of gelatin and chitosan networks covalently cross-linked by genipin (CGG hydrogels). A series of TCA cycle metabolite-coordinated CGG hydrogels with strong mechanical and antiswelling performances are subsequently developed. Remarkably, the citrate (Na3Cit, Cit)-coordinated CGG hydrogels (CGG-Cit hydrogels) with the highest mechanical modulus and strength significantly promote skull bone regeneration in rat and murine cranial defects. Mechanistically, using a transgenic mouse model, bulk RNA sequencing, and single-cell RNA sequencing, this work demonstrates that CGG-Cit hydrogels promote Gli1+ MSC migration via neutrophil-secreted oncostatin M. Results also indicate that citrate improves osteogenesis via enhanced histone H3K9 acetylation on osteogenic master genes. Taken together, the immune microenvironment- and MSC fate-regulated CGG-Cit hydrogels represent a highly efficient and facile approach toward skull bone tissue regeneration with great potential for bench-to-bedside translation.

Multifunctional modifications of polyetheretherketone implants for bone repair: A comprehensive review

Polyetheretherketone (PEEK) has emerged as a highly promising orthopedic implantation material due to its elastic modulus which is comparable to that of natural bone. This polymer exhibits impressive properties for bone implantation such as corrosion resistance, fatigue resistance, self-lubrication and chemical stability. Significantly, compared to metal-based implants, PEEK implants have mechanical properties that are closer to natural bone, which can mitigate the "stress shielding" effect in bone implantation. Nevertheless, PEEK is incapable of inducing osteogenesis due to its bio-inert molecular structure, thereby hindering the osseointegration process. To optimize the clinical application of PEEK, researchers have been working on promoting its bioactivity and endowing this polymer with beneficial properties, such as antibacterial, anti-inflammatory, anti-tumor, and angiogenesis-promoting capabilities. Considering the significant growth of research on PEEK implants over the past 5 years, this review aims to present a timely update on PEEK's modification methods. By highlighting the latest advancements in PEEK modification, we hope to provide guidance and inspiration for researchers in developing the next generation bone implants and optimizing their clinical applications.

Cranial Neural Crest Cells Contribution to Craniofacial Bone Development and Regeneration

PURPOSE OF REVIEW

This review aims to summarize (i) the latest evidence on cranial neural crest cells (CNCC) contribution to craniofacial development and ossification; (ii) the recent discoveries on the mechanisms responsible for their plasticity; and (iii) the newest procedures to ameliorate maxillofacial tissue repair.

RECENT FINDINGS

CNCC display a remarkable differentiation potential that exceeds the capacity of their germ layer of origin. The mechanisms by which they expand their plasticity was recently described. Their ability to participate to craniofacial bone development and regeneration open new perspectives for treatments of traumatic craniofacial injuries or congenital syndromes. These conditions can be life-threatening, require invasive maxillofacial surgery and can leave deep sequels on our health or quality of life. With accumulating evidence showing how CNCC-derived stem cells potential can ameliorate craniofacial reconstruction and tissue repair, we believe a deeper understanding of the mechanisms regulating CNCC plasticity is essential to ameliorate endogenous regeneration and improve tissue repair therapies.

A paradigm for high-throughput screening of cell-selective surfaces coupling orthogonal gradients and machine learning-based cell recognition

The combinational density of immobilized functional molecules on biomaterial surfaces directs cell behaviors. However, limited by the low efficiency of traditional low-throughput experimental methods, investigation and optimization of the combinational density remain daunting challenges. Herein, we report a high-throughput screening set-up to study biomaterial surface functionalization by integrating photo-controlled thiol-ene surface chemistry and machine learning-based label-free cell identification and statistics. Through such a strategy, a specific surface combinational density of polyethylene glycol (PEG) and arginine-glutamic acid-aspartic acid-valine peptide (REDV) leads to high endothelial cell (EC) selectivity against smooth muscle cell (SMC) was identified. The composition was translated as a coating formula to modify medical nickel-titanium alloy surfaces, which was then proved to improve EC competitiveness and induce endothelialization. This work provided a high-throughput method to investigate behaviors of co-cultured cells on biomaterial surfaces modified with combinatorial functional molecules.