In Situ Biomimetic Mineralization of Bone-Like Hydroxyapatite in Hydrogel for the Acceleration of Bone Regeneration

Sequential simulation of regeneration-specific microenvironments using scaffolds loaded with nanoplatelet vesicles enhances bone regeneration

Bone regeneration is a complex and coordinated physiological process, and the different stages of this process have corresponding microenvironments to support cell development and physiological activities. However, biological scaffolds that provide different three-dimensional environments during different stages of bone regeneration are lacking. In this study, we report a novel composite scaffold (NPE@DCBM) inspired by the stages of bone regeneration; this scaffold was composed of a fibrin hydrogel loaded with nanoplatelet vesicles (NPVs), designated as NPE, and decellularized cancellous bone matrix (DCBM) microparticles. Initially, the NPE rapidly established a temporary microenvironment conducive to cell migration and angiogenesis. Subsequently, the DCBM simulated the molecular structure of bone and promoted new bone formation. In vitro, the NPVs regulated lipid metabolism in bone marrow mesenchymal stem cells (BMSCs), reprogramed the fate of BMSCs by activating the PI3K/AKT and MAPK/ERK positive feedback pathways, and increased BMSC functions, including proliferation, migration and proangiogenic potential. In vivo, NPV@DCBM accelerated bone tissue regeneration and repair. Initially, the NPE rapidly induced angiogenesis between DCBM microparticles, and subsequently, BMSCs differentiated into osteoblasts with DCBM microparticles at their core. In summary, the design of this composite scaffold that sequentially mimics different bone regeneration microenvironments may provide a promising strategy for bone regeneration, with clinical translational potential.

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.

Facile one-step antibacterial biomineralized scaffolds through regulation of chitosan by imitating bone ingredient bonding to inspire endogenous repair

In situ mineralization based on chitosan (CS) as an organic template achieves uniform distribution of nano-hydroxyapatite (nHAp), and is expected to enhance interface bonding between materials and tissues, therefore promoting endogenous bone repair. However, chitosan-based materials are difficult to provide certain mechanical and antibacterial properties. In this study, Ca2+ and PO43- were used as the precursor of nHAP, Zn2+ as the precursor of nano-ZnO, and synthesized nHAp/ZnO particles in situ on the surface of chitosan to form CS/HAp/ZnO bone repair scaffold. The results indicated that the incorporated Zn2+ was chemically bonded to the system, with formed particles evenly distributed, which achieved more efficient antibacterial activity and osteogenic induction performance in vivo. The material had interconnected pore structure with a porosity of >70 %, which simulates the microenvironment of natural bone. The formed inorganic particles improved the mechanical properties of the chitosan scaffold to match the rate of new bone formation. ZnO endowed scaffolds with antibacterial activity, with antibacterial rate of >95 %. In addition, the material also showed good cell compatibility and biological activity, and promoted the adhesion, migration, proliferation and differentiation of osteoblast-related cells.

Innovative modification strategies and emerging applications of natural hydrogel scaffolds for osteoporotic bone defect regeneration

Osteoporosis, a prevalent systemic metabolic bone disease, is characterized by diminished bone mass, microarchitectural deterioration of bone tissue, and heightened bone fragility. In osteoporotic patients, chronic and progressive bone loss often leads to fractures and, in advanced cases, critical-sized bone defects. While traditional bone repair approaches are constrained by significant limitations, the advent of bioactive scaffolds has transformed the therapeutic paradigm for osteoporotic bone regeneration. Among these innovations, natural polymer-based hydrogel scaffolds have emerged as a particularly promising solution in bone tissue engineering, owing to their superior biocompatibility, tunable biodegradation properties, and exceptional ability to replicate the native extracellular matrix environment. This review systematically explores recent breakthroughs in modification techniques and therapeutic applications of natural hydrogel scaffolds for osteoporotic bone defect repair, while critically analyzing existing clinical challenges and proposing future research trajectories in this rapidly evolving field.

The Phase-Transited Lysozyme Coating Modified Small Intestinal Submucosa Membrane Loaded with Calcium and Zinc Ions for Enhanced Bone Regeneration

Bone defects caused by severe trauma, tumors, infections and diseases remain a global challenge due to limited natural regeneration capacity of bone tissue in large-scale or complex injuries. Guided bone regeneration (GBR) has emerged as a pivotal technique in addressing these issues, relying on barrier membranes to facilitate osteoprogenitor cell infiltration. Current clinical GBR membranes function solely as physical barriers, lacking antibacterial and osteoinductive properties, which underscores the need for advanced alternatives. This study focuses on resorbable GBR membranes made from small intestinal submucosa (SIS), known for biocompatibility and tissue regeneration but hindered by low mechanical strength and rapid degradation. In addition, SIS lacks both antibacterial properties and strong osteogenic capabilities. Enhancements involve crosslinking treatment and dual incorporation of calcium (Ca2+) and zinc (Zn2+), which address the physical property shortcomings and synergistically boost osteoinductivity by activating osteogenic signaling pathways. Additionally, phase-transited lysozyme (PTL) nanofilm technique enables efficient ion loading and controlled release, while offering antibacterial properties. In this study, a multifunctional SIS membrane is constructed by PTL-ions layers, providing a potential solution to the challenge of clinical bone defects.

Controllable Polymerization of Inorganic Ionic Oligomers for Precise Nanostructural Construction in Materials

The rational design of nanostructures is critical for achieving high-performance materials. The close-packing behavior of inorganic ions and their less controllable nucleation process impede the precise nanostructural construction of inorganic ionic compounds. The discovery of inorganic ionic oligomers (stable molecular-scale inorganic ionic compounds) and their polymerization reaction enables the controllable arrangement of inorganic ions for diverse nanostructures. This perspective aims to introduce inorganic ionic oligomers and their currently identified advantages in the precise design of inorganic and organic-inorganic hybrid nanostructures, directing the development of advanced materials with applications across the mechanical, energy, environmental, and biomedical fields. The challenges and opportunities for the controllable polymerization of inorganic ionic oligomers are presented at the end of this perspective. We suggest that inorganic ionic oligomers and their polymerization reaction offer a promising strategy for the preparation of inorganic and organic-inorganic hybrid materials.

Versatile hydrogels prepared by microfluidics technology for bone tissue engineering applications

Bone defects are a prevalent issue resulting from various factors, such as trauma, degenerative diseases, congenital disabilities, and the surgical removal of tumors. Current methods for bone regeneration have limitations. In this context, the fusion of tissue engineering and microfluidics has emerged as a promising strategy in the field of bone regeneration. This study describes the classification of microfluidic devices based on the nature of flow and channel type, as well as the materials and techniques required. An overview of microfluidic methods used to prepare hydrogels and the advantages of using these hydrogels in bone tissue engineering (BTE) combining several basic elements of BTE to highlight its advantages is provided. Furthermore, this work emphasizes the benefits of using hydrogels prepared via microfluidics over conventional hydrogels in BTE because of their controlled release of cargo, they can be used for in situ injection, simplify the steps of single-cell encapsulation and have the advantages of high-throughput and precise preparation. Additionally, organ-on-a-chip models fabricated via microfluidics offer a platform for studying cell and tissue behaviors in an authentic and dynamic environment. Moreover, microfluidic devices can be utilized for noninvasive diagnosis and therapy. Finally, this paper summarizes the preclinical and clinical applications of hydrogels prepared via microfluidics for bone regeneration by focusing on their current developmental status, limitations associated with their application, and future challenges, which underscore their potential impacts on advancing regenerative medicine practices.

Periosteum-bone inspired hierarchical scaffold with endogenous piezoelectricity for neuro-vascularized bone regeneration

The development of scaffolds for repairing critical-sized bone defects heavily relies on establishing a neuro-vascularized network for proper penetration of nerves and blood vessels. Despite significant advancements in using artificial bone-like scaffolds infused with various agents, challenges remain. Natural bone tissue consists of a porous bone matrix surrounded by a neuro-vascularized periosteum, with unique piezoelectric properties essential for bone growth. Drawing inspiration from this assembly, we developed a periosteum-bone-mimicking bilayer scaffold with piezoelectric properties for regeneration of critical-sized bone defects. The periosteum-like layer of this scaffold features a double network hydrogel composed of chelated alginate, gelatin methacrylate, and sintered whitlockite nanoparticles, emulating the viscoelastic and piezoelectric properties of the natural periosteum. The bone-like layer is composed of a porous structure of chitosan and bioactive hydroxyapatite created through a biomineralization process. Unlike conventional bone-like scaffolds, this bioinspired bilayer scaffold significantly enhances osteogenesis, angiogenesis, and neurogenesis combined with low-intensity pulsed ultrasound-assisted piezoelectric stimulation. Such a scheme enhances neuro-vascularized bone regeneration in vivo. The results suggest that the bilayer scaffold could serve as an effective self-powered electrical stimulator to expedite bone regeneration under dynamic physical stimulation.

Biomimetic Mineralized Organic–Inorganic Hybrid Scaffolds From Microfluidic 3D Printing for Bone Repair

Bone defect is a common clinical orthopedic disease. The trend in this field is to develop tissue engineering scaffolds with appropriately designed components and structures for bone repair. Herein, inspired by the organic and inorganic components of bone matrix and the natural biomineralization mechanism, a MgSiO3@Fe3O4 nanoparticle composite polycaprolactone (PCL) hybrid mineralized scaffold for bone repair is developed by microfluidic 3D printing. The incorporation of MgSiO3@Fe3O4 within the PCL scaffold can effectively improve the bioactivity. In addition, a biomimetic mineralized layer is prepared on the surface of the scaffold, which endowed it with unique microstructural characteristics, enhanced cell adhesion and osteogenic activity, and thus improved the bone repair performance. Owing to these advantages, both in vivo and in vitro experiments have demonstrated that the designed scaffold has outstanding biocompatibility and bone repair performance. These features indicate that the organic–inorganic biomineralized hybrid scaffold can be a potential bone graft substitute for clinical bone repair.

Use of Hydrogels in Regenerative Medicine: Focus on Mechanical Properties

Bioengineered materials represent an innovative option to support the regenerative processes of damaged tissues, with the final objective of creating a functional environment closely mimicking the native tissue. Among the different available biomaterials, hydrogels represent the solution of choice for tissue regeneration, thanks to the easy synthesis process and the highly tunable physical and mechanical properties. Moreover, hydrogels are biocompatible and biodegradable, able to integrate in biological environments and to support cellular interactions in order to restore damaged tissues' functionality. This review offers an overview of the current knowledge concerning hydrogel synthesis and characterization and of the recent achievements in their experimental use in supporting skin, bone, cartilage, and muscle regeneration. The currently available in vitro and in vivo results are of great interest, highlighting the need for carefully designed and controlled preclinical studies and clinical trials to support the transition of these innovative biomaterials from the bench to the bedside.

Nanomaterial-integrated injectable hydrogels for craniofacial bone reconstruction

The complex anatomy and biology of craniofacial bones pose difficulties in their effective and precise reconstruction. Injectable hydrogels (IHs) with water-swollen networks are emerging as a shape-adaptive alternative for noninvasively rebuilding craniofacial bones. The advent of versatile nanomaterials (NMs) customizes IHs with strengthened mechanical properties and therapeutically favorable performance, presenting excellent contenders over traditional substitutes. Structurally, NM-reinforced IHs are energy dissipative and covalently crosslinked, providing the mechanics necessary to support craniofacial structures and physiological functions. Biofunctionally, incorporating unique NMs into IH expands a plethora of biological activities, including immunomodulatory, osteogenic, angiogenic, and antibacterial effects, further favoring controllable dynamic tissue regeneration. Mechanistically, NM-engineered IHs optimize the physical traits to direct cell responses, regulate intracellular signaling pathways, and control the release of biomolecules, collectively bestowing structure-induced features and multifunctionality. By encompassing state-of-the-art advances in NM-integrated IHs, this review offers a foundation for future clinical translation of craniofacial bone reconstruction.

Biomimetic Mineralized Hydroxyapatite-Fish-Scale Collagen/Chitosan Nanofibrous Membranes Promote Osteogenesis for Periodontal Tissue Regeneration

Commercial mammalian collagen-based membranes used for guided tissue regeneration (GTR) in periodontal defect repair still face significant challenges, including ethical concerns, cost-effectiveness, and limited capacity for periodontal bone regeneration. Herein, an enhanced biomimetic mineralized hydroxyapatite (HAp)-fish-scale collagen (FCOL)/chitosan (CS) nanofibrous membrane was developed. Specifically, eco-friendly and biocompatible collagen extracted from grass carp fish scales was co-electrospun with CS to produce a biomimetic extracellular matrix membrane. An enhanced biomimetic mineralized HAp coating provided abundant active calcium and phosphate sites, which promoted cell osteogenic differentiation, and showed greater in vivo absorption. In vitro experiments demonstrated that the HAp-FCOL/CS membranes exhibited desirable properties with no cytotoxicity, provided a mimetic microenvironment for stem cell recruitment, and induced periodontal ligament cell osteogenic differentiation. In rat periodontal defects, HAp-FCOL/CS membranes significantly promoted new periodontal bone formation and regeneration. The results of this study indicate that low-cost, eco-friendly, and biomimetic HAp-FCOL/CS membranes could be promising alternatives to GTR membranes for periodontal regeneration in the clinic.

Antibacterial and Osteogenic Dual-Functional Micronano Composite Scaffold Fabricated via Melt Electrowriting and Solution Electrospinning for Bone Tissue Engineering

The utilization of micronano composite scaffolds has been extensively demonstrated to confer the superior advantages in bone repair compared to single nano- or micron-sized scaffolds. Nevertheless, the enhancement of bioactivities within these composite scaffolds remains challenging. In this study, we propose a novel approach to combine melt electrowriting (MEW) and solution electrospinning (SES) techniques for the fabrication of a composite scaffold incorporating hydroxyapatite (HAP), an osteogenic component, and roxithromycin (ROX), an antibacterial active component. Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) confirmed the hierarchical architecture of the nanofiber-microgrid within the scaffold, as well as the successful loading of HAP and ROX. The incorporation of HAP enhanced the water absorption capacity of the composite scaffold, thus promoting cell adhesion and proliferation, as well as osteogenic differentiation. Furthermore, ROX resulted in effective antibacterial capability without any observable cytotoxicity. Finally, the scaffolds were applied to a rat calvarial defect model, and the results demonstrated that the 20% HAP group exhibited superior new bone formation without causing adverse reactions. Therefore, our findings present a promising strategy for designing and fabricating bioactive scaffolds for bone regeneration.

Hydrogel loaded with thiolated chitosan modified taxifolin liposome promotes osteoblast proliferation and regulates Wnt signaling pathway to repair rat skull defects

To alleviate skull defects and enhance the biological activity of taxifolin, this study utilized the thin-film dispersion method to prepare paclitaxel liposomes (TL). Thiolated chitosan (CSSH)-modified TL (CTL) was synthesized through charge interactions. Injectable hydrogels (BLG) were then prepared as hydrogel scaffolds loaded with TAX (TG), TL (TLG), and CTL (CTLG) using a Schiff base reaction involving oxidized dextran and carboxymethyl chitosan. The study investigated the bone reparative properties of CTLG through molecular docking, western blot techniques, and transcriptome analysis. The particle sizes of CTL were measured at 248.90 ± 14.03 nm, respectively, with zeta potentials of +36.68 ± 5.43 mV, respectively. CTLG showed excellent antioxidant capacity in vitro. It also has a good inhibitory effect on Escherichia coli and Staphylococcus aureus, with inhibition rates of 93.88 ± 1.59 % and 88.56 ± 2.83 % respectively. The results of 5-ethynyl-2 '-deoxyuridine staining, alkaline phosphatase staining and alizarin red staining showed that CTLG also had the potential to promote the proliferation and differentiation of mouse embryonic osteoblasts (MC3T3-E1). The study revealed that CTLG enhances the expression of osteogenic proteins by regulating the Wnt signaling pathway, shedding light on the potential application of TAX and bone regeneration mechanisms.

Biomimetic Hydrogel Strategies for Cancer Therapy

Recent developments in biomimetic hydrogel research have expanded the scope of biomedical technologies that can be used to model, diagnose, and treat a wide range of medical conditions. Cancer presents one of the most intractable challenges in this arena due to the surreptitious mechanisms that it employs to evade detection and treatment. In order to address these challenges, biomimetic design principles can be adapted to beat cancer at its own game. Biomimetic design strategies are inspired by natural biological systems and offer promising opportunities for developing life-changing methods to model, detect, diagnose, treat, and cure various types of static and metastatic cancers. In particular, focusing on the cellular and subcellular phenomena that serve as fundamental drivers for the peculiar behavioral traits of cancer can provide rich insights into eradicating cancer in all of its manifestations. This review highlights promising developments in biomimetic nanocomposite hydrogels that contribute to cancer therapies via enhanced drug delivery strategies and modeling cancer mechanobiology phenomena in relation to metastasis and synergistic sensing systems. Creative efforts to amplify biomimetic design research to advance the development of more effective cancer therapies will be discussed in alignment with international collaborative goals to cure cancer.

Soft yet mechanically robust injectable alginate hydrogels with processing versatility based on alginate/hydroxyapatite hybridization

The salient gelling feature of alginate via forming the egg-box structure with calcium ions has received extensive interests for different applications. Owing to the interfacial incompatibility of rigid inorganic solids with soft polymers, the requirement of overall stereocomplexation with calcium released from uniformly distributed solids in alginate remains a challenge. In this study, a novel alginate-incorporated calcium source was proposed to tackle the intractable dispersion for the preparation of injectable alginate hydrogels. Calcium phosphate synthesis in alginate solution yielded CaP-alginate hybrids as a calcium source. The physicochemical characterization confirmed the CaP-alginate hybrid was a nano-scale alginate-hydroxyapatite complex. The colloidally stable CaP-alginate hybrids were uniformly dispersed in alginate solutions even under centrifugation. The calcium-induced gelling of the CaP-alginate hybrids-loaded alginate solutions formed soft yet tough hydrogels including transparent sheets and knittable threads, confirming the homogeneous gelation of the hydrogel. The gelation time, injectability and mechanical properties of the hydrogels could be adjusted by changing preparation parameters. The prepared hydrogels showed uniform porous structure, excellent swelling, wetting properties and cytocompatibility, showing a great potential for applications in different fields. The present strategy with organic/inorganic hybridization could be exemplarily followed in the future development of functional hydrogels especially associated with the interface integration.

An Injectable silk-based hydrogel as a novel biomineralization seedbed for critical-sized bone defect regeneration

The healing process of critical-sized bone defects urges for a suitable biomineralization environment. However, the unsatisfying repair outcome usually results from a disturbed intricate milieu and the lack of in situ mineralization resources. In this work, we have developed a composite hydrogel that mimics the natural bone healing processes and serves as a seedbed for bone regeneration. The oxidized silk fibroin and fibrin are incorporated as rigid geogrids, and amorphous calcium phosphate (ACP) and platelet-rich plasma serve as the fertilizers and loam, respectively. Encouragingly, the seedbed hydrogel demonstrates excellent mechanical and biomineralization properties as a stable scaffold and promotes vascularized bone regeneration in vivo. Additionally, the seedbed serves a succinate-like function via the PI3K-Akt signaling pathway and subsequently orchestrates the mitochondrial calcium uptake, further converting the exogenous ACP into endogenous ACP. Additionally, the seedbed hydrogel realizes the succession of calcium resources and promotes the evolution of the biotemplate from fibrin to collagen. Therefore, our work has established a novel silk-based hydrogel that functions as an in-situ biomineralization seedbed, providing a new insight for critical-sized bone defect regeneration.

Degradable Nanohydroxyapatite-Reinforced Superglue for Rapid Bone Fixation and Promoted Osteogenesis

Bone glue with robust adhesion is crucial for treating complicated bone fractures, but it remains a formidable challenge to develop a "true" bone glue with high adhesion strength, degradability, bioactivity, and satisfactory operation time in clinical scenarios. Herein, inspired by the hydroxyapatite and collagen matrix composition of natural bone, we constructed a nanohydroxyapatite (nHAP) reinforced osteogenic backbone-degradable superglue (O-BDSG) by in situ radical ring-opening polymerization. nHAP significantly enhances adhesive cohesion by synergistically acting as noncovalent connectors between polymer chains and increasing the molecular weight of the polymer matrix. Moreover, nHAP endows the glue with bioactivity to promote osteogenesis. The as-prepared glue presented a 9.79 MPa flexural adhesion strength for bone, 4.7 times that without nHAP, and significantly surpassed commercial cyanoacrylate (0.64 MPa). O-BDSG exhibited degradability with 51% mass loss after 6 months of implantation. In vivo critical defect and tibia fracture models demonstrated the promoted osteogenesis of the O-BDSG, with a regenerated bone volume of 75% and mechanical function restoration to 94% of the native tibia after 8 weeks. The glue can be flexibly adapted to clinical scenarios with a curing time window of about 3 min. This work shows promising prospects for clinical application in orthopedic surgery and may inspire the design and development of bone adhesives.

Biodegradable Nanoflowers with Abaloparatide Spatiotemporal Management of Functional Alveolar Bone Regeneration

Post-extraction alveolar bone atrophy greatly hinders the subsequent orthodontic tooth movement (OTM) or implant placement. In this study, we synthesized biodegradable bifunctional bioactive calcium phosphorus nanoflowers (NFs) loaded with abaloparatide (ABL), namely ABL@NFs, to achieve spatiotemporal management for alveolar bone regeneration. The NFs exhibited a porous hierarchical structure, high drug encapsulation efficacy, and desirable biocompatibility. ABL was initially released to recruit stem cells, followed by sustained release of Ca2+ and PO43- for in situ interface mineralization, establishing an osteogenic "biomineralized environment". ABL@NFs successfully restored morphologically and functionally active alveolar bone without affecting OTM. In conclusion, the ABL@NFs demonstrated promising outcomes for bone regeneration under orthodontic condition, which might provide a desirable reference of man-made "bone powder" in the hard tissue regeneration field.

Enzyme-Mineralized PVASA Hydrogels with Combined Toughness and Strength for Bone Tissue Engineering

Enzymatic mineralization is an advanced mineralization method that is often used to enhance the stiffness and strength of hydrogels, but often accompanied by brittle behavior. Moreover, the hydrogel systems with dense networks currently used for enzymatic mineralization are not ideal materials for bone repair applications. To address these issues, two usual bone repair hydrogels, poly(vinyl alcohol) (PVA) and sodium alginate (SA), were selected to form a double-network structure through repeated freeze-thawing and ionic cross-linking, followed by enzyme mineralization. The results demonstrated that both enzymatic mineralization and double-network structure improved the mechanical and biological properties and even exhibited synergistic effects. The mineralized PVASA hydrogels exhibited superior comprehensive mechanical properties, with a Young's modulus of 1.03 MPa, a storage modulus of 103 kPa, and an equilibrium swelling ratio of 132%. In particular, the PVASA hydrogel did not suffer toughness loss after mineralization, with a high toughness value of 1.86 MJ/m3. The prepared hydrogels also exhibited superior biocompatibility with a cell spreading area about 13 times that of mineralized PVA. It also effectively promoted cellular osteogenic differentiation in vitro and further promoted the formation of new bone in the femur defect region in vivo. Overall, the enzyme-mineralized PVASA hydrogel demonstrated combined strength and toughness and great potential for bone tissue engineering applications.

Bioinspired mineralization of engineered living materials to promote osteogenic differentiation

In this work, Engineered Living Materials (ELMs), based on the combination of genetically-modified bacteria and mineral-reinforced organic matrices, and endowed with self-healing or regenerative properties and adaptation to specific biological environments were developed. Concretely, we produced ELMs combining human mesenchymal stem cells (hMSCs) and Lactococcus lactis (L. lactis), which was specifically programmed to deliver bone morphogenetic protein (BMP-2) upon external stimulation using nisin, into mineralized alginate matrices. The hybrid organic/inorganic matrix was built through a protocol, inspired by bone mineralization, in which alginate (Alg) assembly and apatite (HA) mineralization occurred simultaneously driven by calcium ions. Chemical composition, structure and reologhical properties of the hybrid 3D matrices were dedicately optimized prior the incorportation of the living entities. Then, the same protocol was reproduced in the presence of hMSC and engineered L. lactis that secrete BMP-2 resulting in 3D hybrid living hydrogels. hMSC viability and osteogenic differentiation in the absence and presence of the bacteria were evaluated by live/dead and quantitative real-time polymerase chain reaction (qPCR) and immunofluorescence assays, respectively. Results demonstrate that these 3D engineered living material support osteogenic differentiation of hMSCs due to the synergistic effect between HA and the growth factors BMP-2 delivered by L. lactis.

Calcium sulfate-Cu2+ delivery system improves 3D-Printed calcium silicate artificial bone to repair large bone defects

There are still limitations in artificial bone materials used in clinical practice, such as difficulty in repairing large bone defects, the mismatch between the degradation rate and tissue growth, difficulty in vascularization, an inability to address bone defects of various shapes, and risk of infection. To solve these problems, our group designed stereolithography (SLA) 3D-printed calcium silicate artificial bone improved by a calcium sulfate-Cu2+ delivery system. SLA technology endows the scaffold with a three-dimensional tunnel structure to induce cell migration to the center of the bone defect. The calcium sulfate-Cu2+ delivery system was introduced to enhance the osteogenic activity of calcium silicate. Rapid degradation of calcium sulfate (CS) induces early osteogenesis in the three-dimensional tunnel structure. Calcium silicate (CSi) which degrades slowly provides mechanical support and promotes bone formation in bone defect sites for a long time. The gradient degradation of these two components is perfectly matched to the rate of repair in large bone defects. On the other hand, the calcium sulfate delivery system can regularly release Cu2+ in the temporal and spatial dimensions, exerting a long-lasting antimicrobial effect and promoting vascular growth. This powerful 3D-printed calcium silicate artificial bone which has rich osteogenic activity is a promising material for treating large bone defects and has excellent potential for clinical application.

Morphology-Dependent Immunomodulatory Coating of Hydroxyapatite/PEO for Magnesium-Based Bone Implants

One of the most critical issues concerning orthopedic implants is the risk of chronic inflammation, which poses a threat to the bone healing process. Osteo-immunomodulation plays a pivotal role in implant technology by influencing proinflammatory and anti-inflammatory responses, ultimately promoting bone healing. This study aims to investigate the morphology-dependent osteo-immunomodulatory properties of a hydroxyapatite (HA)/plasma electrolytic oxidation (PEO)-coated WE43 alloy. In this context, following the PEO process with various operational parameters (duty cycles of 50-40, 50-20, 70-40%, and frequencies of 0.5, 0.8, and 1 kHz), a layer of HA was applied as the top coating using a straightforward hot-dip process. The results revealed the formation of the PEO layer with distinct morphologies and pore sizes, depending on the operational parameters. Specifically, a uniform PEO coating with small pore sizes (5.2-5.3 μm) led to the creation of plate-like HA particles, while a random-like HA structure formed on nonuniform surfaces with large pores (7.0-11.1 μm) of PEO. Moreover, it was observed that the plate-like HA coating exhibited higher adhesion strength than the random one (classified as class 2 vs class 3 based on cross-cut standards). Furthermore, electrochemical impedance spectroscopy (EIS) and polarization studies confirmed a substantial increase in the polarization resistance (680 kΩ) and total impedance (48 559.6 Ω) for the plate-like HA/PEO as compared to the substrate (an increase of 1511-fold and 311-fold, respectively) and the random HA/PEO samples (an increase of 85-fold and 18-fold, respectively). In addition, compared to random HA coatings, there was a significant enhancement in the viability (150% control vs 96% control), proliferation, and differentiation of MG63 cells when exposed to plate-like HA coatings. Moreover, surface morphology and chemistry pronouncedly impacted macrophages' viability, morphology, and phenotype. Notably, plate-like HA coatings resulted in a higher upregulation of BMP-2 and TGF-β than proinflammatory cytokines (IL-6 and M-CSF), indicating a polarization of macrophage type 1 (M1) toward type 2 (M2). In summary, the bilayer HA/PEO coating exhibited remarkable osteo-immunomodulatory activity, making it highly appealing for use in bone implant applications.

Hydrogel Tissue Bioengineered Scaffolds in Bone Repair: A Review

Large bone defects due to trauma, infections, and tumors are difficult to heal spontaneously by the body's repair mechanisms and have become a major hindrance to people's daily lives and economic development. However, autologous and allogeneic bone grafts, with their lack of donors, more invasive surgery, immune rejection, and potential viral transmission, hinder the development of bone repair. Hydrogel tissue bioengineered scaffolds have gained widespread attention in the field of bone repair due to their good biocompatibility and three-dimensional network structure that facilitates cell adhesion and proliferation. In addition, loading natural products with nanoparticles and incorporating them into hydrogel tissue bioengineered scaffolds is one of the most effective strategies to promote bone repair due to the good bioactivity and limitations of natural products. Therefore, this paper presents a brief review of the application of hydrogels with different gel-forming properties, hydrogels with different matrices, and nanoparticle-loaded natural products loaded and incorporated into hydrogels for bone defect repair in recent years.

Seamlessly Adhesive Bionic Periosteum Patches Via Filling Microcracks for Defective Bone Healing

Current artificial designs of the periosteum focus on osteogenic or angiogenic properties, while ignoring the filling and integration with bone microcracks, which trigger a prolonged excessive inflammatory reaction and lead to failure of bone regeneration. In this study, seamless adhesive biomimetic periosteum patches (HABP/Sr-PLA) were prepared to fill microcracks in defective bone via interfacial self-assembly induced by Sr ions mediated metal-ligand interactions among pamidronate disodium-modified hyaluronic acid (HAPD), black phosphorus (BP), and hydrophilic polylactic acid (PLA). In vitro, HABP/Sr-PLA exhibited excellent self-healing properties, seamlessly filled bone microcracks, and significantly enhanced osteogenesis and angiogenesis. Furthermore, in a rat cranial defect model, HABP/Sr-PLA was demonstrated to significantly promote the formation of blood vessels and new bone under mild 808 nm photothermal stimulation (42.8 °C), and the highest protein expression of CD31 and OPN was five times higher than that of the control group and other groups. Therefore, the proposed seamless microcrack-filled bionic periosteum patch is a promising clinical strategy for promoting bone repair.

Biologic Mechanisms of Macrophage Phenotypes Responding to Infection and the Novel Therapies to Moderate Inflammation

Pro-inflammatory and anti-inflammatory types are the main phenotypes of the macrophage, which are commonly notified as M1 and M2, respectively. The alteration of macrophage phenotypes and the progression of inflammation are intimately associated; both phenotypes usually coexist throughout the whole inflammation stage, involving the transduction of intracellular signals and the secretion of extracellular cytokines. This paper aims to address the interaction of macrophages and surrounding cells and tissues with inflammation-related diseases and clarify the crosstalk of signal pathways relevant to the phenotypic metamorphosis of macrophages. On these bases, some novel therapeutic methods are proposed for regulating inflammation through monitoring the transition of macrophage phenotypes so as to prevent the negative effects of antibiotic drugs utilized in the long term in the clinic. This information will be quite beneficial for the diagnosis and treatment of inflammation-related diseases like pneumonia and other disorders involving macrophages.