Osteoporotic Bone Recovery by a Highly Bone-Inductive Calcium Phosphate Polymer-Induced Liquid-Precursor

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.

Calcium phosphate nanoclusters modify periodontium remodeling and minimize orthodontic relapse

Orthodontic relapse is one of the most prevalent concerns of orthodontic therapy. Relapse results in patients' teeth reverting towards their pretreatment positions, which increases the susceptibility to functional problems, dental disease, and substantially increases the financial burden for retreatment. This phenomenon is thought to be induced by rapid remodeling of the periodontal ligament (PDL) in the early stages and poor bone quality in the later stages. Current therapies including fixed or removable retainers and fiberotomies have limitations with patient compliance and invasiveness. Approaches using biocompatible biomaterials, such as calcium phosphate polymer-induced liquid precursors (PILP), are an ideal translational approach for minimizing orthodontic relapse. Here, post-orthodontic relapse is reduced after a single injection of high concentration PILP (HC-PILP) nanoclusters by altering PDL remodeling in the early stage of relapse and improving trabecular bone quality in the later stage. HC-PILP nanoclusters are achieved by using high molecular weight poly aspartic acid (PASP, 14 kDa) and poly acrylic acid (PAA, 450 kDa), which resulted in a stable solution of high calcium and phosphate concentrations without premature precipitation. In vitro results show that HC-PILP nanoclusters prevented collagen type-I mineralization, which is essential for the tooth-PDL-bone interphase. In vivo experiments show that the HC-PILP nanoclusters minimize relapse and improve the trabecular bone quality in the late stages of relapse. Interestingly, HC-PILP nanoclusters also altered the remodeling of the PDL collagen during the early stages of relapse. Further in vitro experiments showed that HC-PILP nanoclusters alter the fibrillogenesis of collagen type-I by impacting the protein secondary structure and forming aggregates. These findings propose a new approach for treating orthodontic relapse and provide additional insight into the PILP nanocluster's structure and properties on collagenous structure repair.

Copper doped bioactive glass promotes matrix vesicles-mediated biomineralization via osteoblast mitophagy and mitochondrial dynamics during bone regeneration

Bone defect repair remains a great challenge in the field of orthopedics. Human body essential trace element such as copper is essential for bone regeneration, but how to use it in bone defects and the underlying its mechanisms of promoting bone formation need to be further explored. In this study, by doping copper into mesoporous bioactive glass nanoparticles (Cu-MBGNs), we unveil a previously unidentified role of copper in facilitating osteoblast mitophagy and mitochondrial dynamics, which enhance amorphous calcium phosphate (ACP) release and subsequent biomineralization, ultimately accelerating the process of bone regeneration. Specifically, by constructing conditional knockout mice lacking the autophagy gene Atg5 in osteogenic lineage cells, we first confirmed the role of Cu-MBGNs-promoted bone formation via mediating osteoblast autophagy pathway. Then, the in vitro studies revealed that Cu-MBGNs strengthened mitophagy by inducing ROS production and recruiting PINK1/Parkin, thereby facilitating the efficient release of ACP from mitochondria into matrix vesicles for biomineralization during bone regeneration. Moreover, we found that Cu-MBGNs promoted mitochondrion fission via activating dynamin related protein 1 (Drp1) to reinforce mitophagy pathway. Together, this study highlights the potential of Cu-MBGNs-mediated mitophagy and biomineralization for augmenting bone regeneration, offering a promising avenue for the development of advanced bioactive materials in orthopedic applications.

Bioinspired Materials for Controlling Mineral Adhesion: From Innovation Design to Diverse Applications

The advancement of controllable mineral adhesion materials has significantly impacted various sectors, including industrial production, energy utilization, biomedicine, construction engineering, food safety, and environmental management. Natural biological materials exhibit distinctive and controllable adhesion properties that inspire the design of artificial systems for controlling mineral adhesion. In recent decades, researchers have sought to create bioinspired materials that effectively regulate mineral adhesion, significantly accelerating the development of functional materials across various emerging fields. Herein, we review recent advances in bioinspired materials for controlling mineral adhesion, including bioinspired mineralized materials and bioinspired antiscaling materials. First, a systematic overview of biological materials that exhibit controllable mineral adhesion in nature is provided. Then, the mechanism of mineral adhesion and the latest adhesion characterization between minerals and material surfaces are introduced. Later, the latest advances in bioinspired materials designed for controlling mineral adhesion are presented, ranging from the molecular level to micro/nanostructures, including bioinspired mineralized materials and bioinspired antiscaling materials. Additionally, recent applications of these bioinspired materials in emerging fields are discussed, such as industrial production, energy utilization, biomedicine, construction engineering, and environmental management, highlighting their roles in promoting or inhibiting aspects. Finally, we summarize the ongoing challenges and offer a perspective on the future of this charming field.

Oriented Cortical-Bone-Like Silk Protein Lamellae Effectively Repair Large Segmental Bone Defects in Pigs

Assembling natural proteins into large, strong, bone-mimetic scaffolds for repairing bone defects in large-animal load-bearing sites remain elusive. Here this challenge is tackled by assembling pure silk fibroin (SF) into 3D scaffolds with cortical-bone-like lamellae, superior strength, and biodegradability through freeze-casting. The unique lamellae promote the attachment, migration, and proliferation of tissue-regenerative cells (e.g., mesenchymal stem cells [MSCs] and human umbilical vein endothelial cells) around them, and are capable of developing in vitro into cortical-bone organoids with a high number of MSC-derived osteoblasts. High-SF-content lamellar scaffolds, regardless of MSC inoculation, regenerated more bone than non-lamellar or low-SF-content lamellar scaffolds. They accelerated neovascularization by transforming macrophages from M1 to M2 phenotype, promoting bone regeneration to repair large segmental bone defects (LSBD) in minipigs within three months, even without growth factor supplements. The bone regeneration can be further enhanced by controlling the orientation of the lamella to be parallel to the long axis of bone during implantation. This work demonstrates the power of oriented lamellar bone-like protein scaffolds in repairing LSBD in large animal models.

Osteomimix: A Multidimensional Biomimetic Cascade Strategy for Bone Defect Repair

Despite advancements in biomimetic mineralization techniques, the repair of large-scale bone defects remains a significant challenge. Inspired by the bone formation process, a multidimensional biomimetic cascade strategy is developed by replicating the biomineralization cascade, emulating the hierarchical structure of bone, and biomimicking its biological functions for efficient bone regeneration. This strategy involves the photocrosslinking of sodium methacrylate carboxymethyl cellulose-stabilized amorphous magnesium-calcium phosphate with methacrylate-modified type I collagen to create a self-mineralizing hydrogel. The hydrogel is then integrated with either naturally derived or synthetic oriented bulk scaffolds. The resulting composite, named Osteomimix, provides excellent mechanical support and can be customized for irregular bone defects using CAD/CAM technology. Through in vitro and in vivo studies, this work finds that Osteomimix exhibits spontaneous in situ biomimetic mineralization in a cell-free environment, while modulating immune responses and promoting vascularized bone formation in a cell-dependent manner. Built on bone-specific insights, this strategy achieves biomimicry across temporal, spatial, and functional dimensions, facilitating the seamless integration of artificial constructs with the natural tissue repair dynamics.

Bio-Informed Porous Mineral-Based Composites

Certain biominerals, such as sea sponges and echinoderm skeletons, display a fascinating combination of mechanical properties and adaptability due to the well-defined structures spanning various length scales. These materials often possess high density normalized mechanical properties because they contain well-defined pores. The density-normalized mechanical properties of synthetic minerals are often inferior because the pores are stochastically distributed, resulting in an inhomogeneous stress distribution. The mechanical properties of synthetic materials are limited by the degree of structural and compositional control currently available fabrication methods offer. In the first part of this review, examples of structural elements nature uses to impart exceptional density normalized Young's moduli to its porous biominerals are showcased. The second part highlights recent advancements in the fabrication of bio-informed mineral-based composites possessing pores with diameters that span a wide range of length scales. The influence of the processing of mineral-based composites on their structures and mechanical properties is summarized. Thereby, it is aimed at encouraging further research directed to the sustainable, energy-efficient fabrication of synthetic lightweight yet stiff mineral-based composites.

Biomimetic Extracellular Vesicles Containing Biominerals for Targeted Osteoporosis Therapy

Osteoporosis (OP) is a systemic skeletal disorder characterized by decreased bone mineral density and a heightened risk of fractures. Therapies for OP have primarily focused on balancing bone formation and bone resorption, but enhancing the remineralization of osteoporotic bone is also a key strategy for effective repair. Recent insights into biomineralization mechanisms have highlighted the essential role of mineral-containing extracellular vesicles (EVs) secreted by osteoblasts in promoting bone marrow mesenchymal stromal/stem cell (BMSC) differentiation and initiating matrix mineralization. Drawing from these principles, we developed a biomimetic approach to replicate the structure and function of the osteoblast-derived EVs by engineering biomimetic mitochondrial minerals with bone marrow homing cell membranes (CMs). This bone-targeted biomimetic system exhibits excellent biocompatibility, enhancing osteogenic differentiation and stimulating angiogenesis by regulating cellular energy metabolism. Additionally, the CM-coated structure shows affinity for collagen fibrils, effectively enhancing intrafibrillar collagen mineralization, thereby facilitating osteoporotic bone repair. Overall, the biomimetic system offers a safe and efficient therapeutic alternative, positioning it as a platform for bone tissue engineering and regenerative medicine.

Ultrasound-Triggered Mg2+ Blasting Release Hydrogel Microspheres for Promoting Bone Reconstruction

Mg2+ (Magnesium ion) can affect bone tissue metabolism by regulating related signaling pathways in bone metabolism. However, how to realize precise controlled release of Mg2+ in bone regeneration treatment still presents a challenge. Herein, for the first time, the GelMA-BP (Gelatin Methacryloyl-Bisphosphonate) and the composite nano-bubble system are fused to construct the Mg2+ blasting controlled-release hydrogel microspheres, the stability of the nano-bubbles in the microspheres is enhanced through metal coordination complexation, and the burst of the nano-bubbles is controlled by using ultrasonic cavitation to achieve the precise controlled release of Mg2+, ultimately effectively promoting bone reconstruction. First, GelMA-BP composite is prepared by Schiff base reaction. Second, the nanobubble BP (Bisphosphonate) system is constructed, and Mg2+ is combined with the ligand coordination to prepare the composite nanobubble system. Thirdly, through Mg2+ co-coordination, the ultrasound-triggered Mg2+ blasting controlled release microspheres were prepared to achieve bone repair. Overall, this innovative strategy effectively solves the problem of accurate controlled release of Mg2+, and finally effectively activates in situ bone tissue regeneration.

Constructing the Enamel-Like Dentin Adhesion Interface to Achieve Durable Resin-Dentin Adhesion

Enamel adhesion is acknowledged as durable; however, achieving long-lasting dentin adhesion remains a formidable challenge due to degradation of exposed collagen matrix after acid-etching of dentin. The idea of developing an enamel-like adhesion interface holds great promise in achieving enduring dentin adhesion. In this study, we constructed an enamel-like adhesion interface using a rapid remineralization strategy comprising an acidic primer and a rapid remineralization medium. Specifically, the acidic primer of 10-methacryloyloxydecyl dihydrogen phosphate (MDP) and epigallocatechin-3-gallate (EGCG) nanocomplex (MDP@EGCG primer) was utilized to partially demineralize dentin within 30 s, and the MDP@EGCG nanocomplex showed a strong interaction with exposed collagen, enhancing collagen remineralization properties. Then, the rapid remineralization medium containing polyaspartate (Pasp) stabilized amorphous calcium and phosphorus nanoclusters (rapid Pasp-CaP) was applied to modified dentin collagen for 1 min, which caused rapid collagen remineralization within a clinically acceptable time frame. This strategy successfully generated an inorganic rough and porous adhesive interface resembling etched enamel, fundamentally addressed issues of collagen exposure, and achieved durable dentin adhesion in vitro and in vivo while also ensuring user-friendliness. It exhibited potential in prolonging the lifespan of adhesive restorations in clinical settings. In addition, it holds significant promise in the fields of caries and dentin sensitivity treatment and collagen-based tissue engineering scaffolds.

Engineering biomimetic silk fibroin hydrogel scaffolds with "organic-inorganic assembly" strategy for rapid bone regeneration

Although natural polymers have been widely used in constructing bone scaffolds, it still remains challenging to fabricate natural polymer-derived bone scaffolds with biomimetic mechanical properties as well as outstanding osteogenic properties for large-size and weight-bearing bone defects regeneration. Herein, an "organic-inorganic assembly" strategy is developed to construct silk fibroin (SF)-based bone scaffolds with the aforementioned merits. After secondary structure reshuffling, the 3.3-fold increment of β-sheet structures in SF hydrogel resulted in a 100-fold improvement of mineral-assembly efficacy via influencing the ion adsorption process and providing templates for mineral growth. Notably, abundant minerals were deposited within the hydrogel and also on the surface, which indicated entire mineral-assembly, which ensured the biomimetic mechanical properties of the digital light processing 3D printed SF hydrogel scaffolds with haversian-mimicking structure. In vitro experiments proved that the assembly between the mineral and SF results in rapid adhesion and enhanced osteogenic differentiation of human bone marrow-derived mesenchymal stem cells. In vivo experiments further proved that the mineral-assembled SF hydrogel scaffold could significantly enhance integration and bone regeneration at the weight-bearing site within one month. This SF-based "organic-inorganic assembly" strategy sheds light on constructing cell-free, growth factor-free and natural polymer-derived bone scaffolds with biomimetic 3D structure, mechanical properties and excellent osteogenic properties.

Kneadable dough-type hydrogel transforming from dynamic to rigid network to repair irregular bone defects

Irregular bone defects, characterized by unpredictable size, shape, and depth, pose a major challenge to clinical treatment. Although various bone grafts are available, none can fully meet the repair needs of the defective area. Here, this study fabricates a dough-type hydrogel (DR-Net), in which the first dynamic network is generated by coordination between thiol groups and silver ions, thereby possessing kneadability to adapt to various irregular bone defects. The second rigid covalent network is formed through photocrosslinking, maintaining the osteogenic space under external forces and achieving a better match with the bone regeneration process. In vitro, an irregular alveolar bone defect is established in the fresh porcine mandible, and the dough-type hydrogel exhibits outstanding shape adaptability, perfectly matching the morphology of the bone defect. After photocuring, the storage modulus of the hydrogel increases 8.6 times, from 3.7 kPa (before irradiation) to 32 kPa (after irradiation). Furthermore, this hydrogel enables effective loading of P24 peptide, which potently accelerates bone repair in Sprague-Dawley (SD) rats with critical calvarial defects. Overall, the dough-type hydrogel with kneadability, space-maintaining capability, and osteogenic activity exhibits exceptional potential for clinical translation in treating irregular bone defects.

Small Charged Molecule-Mediated Fibrillar Mineralization: Implications for Ectopic Calcification

Numerous small biomolecules exist in the human body and play roles in various biological and pathological processes. Small molecules are believed not to induce intrafibrillar mineralization alone. They are required to work in synergy with noncollagenous proteins (NCPs) and their analogs, e.g. polyelectrolytes, for inducing intrafibrillar mineralization, as the polymer-induced liquid-like precursor (PILP) process has been well-documented. In this study, we demonstrate that small charged molecules alone, such as sodium tripolyphosphate, sodium citrate, and (3-aminopropyl) triethoxysilane, could directly mediate fibrillar mineralization. We propose that small charged molecules might be immobilized in collagen fibrils to form the polyelectrolyte-like collagen complex (PLCC) via hydrogen bonds. The PLCC could attract CaP precursors along with calcium and phosphate ions for inducing mineralization without any polyelectrolyte additives. The small charged molecule-mediated mineralization process was evidenced by Cryo-TEM, AFM, SEM, FTIR, ICP-OES, etc., as the PLCC exhibited both characteristic features of collagen fibrils and polyelectrolyte with increased charges, hydrophilicity, and density. This might hint at one mechanism of pathological biomineralization, especially for understanding the ectopic calcification process.

Advancing dentin remineralization: Exploring amorphous calcium phosphate and its stabilizers in biomimetic approaches

OBJECTIVE

This review elucidates the mechanisms underpinning intrafibrillar mineralization, examines various amorphous calcium phosphate (ACP) stabilizers employed in dentin's intrafibrillar mineralization, and addresses the challenges encountered in clinical applications of ACP-based bioactive materials.

METHODS

The literature search for this review was conducted using three electronic databases: PubMed, Web of Science, and Google Scholar, with specific keywords. Articles were selected based on inclusion and exclusion criteria, allowing for a detailed examination and summary of current research on dentin remineralization facilitated by ACP under the influence of various types of stabilizers.

RESULTS

This review underscores the latest advancements in the role of ACP in promoting dentin remineralization, particularly intrafibrillar mineralization, under the regulation of various stabilizers. These stabilizers predominantly comprise non-collagenous proteins, their analogs, and polymers. Despite the diversity of stabilizers, the mechanisms they employ to enhance intrafibrillar remineralization are found to be interrelated, indicating multiple driving forces behind this process. However, challenges remain in effectively designing clinically viable products using stabilized ACP and maximizing intrafibrillar mineralization with limited materials in practical applications.

SIGNIFICANCE

The role of ACP in remineralization has gained significant attention in dental research, with substantial progress made in the study of dentin biomimetic mineralization. Given ACP's instability without additives, the presence of ACP stabilizers is crucial for achieving in vitro intrafibrillar mineralization. However, there is a lack of comprehensive and exhaustive reviews on ACP bioactive materials under the regulation of stabilizers. A detailed summary of these stabilizers is also instrumental in better understanding the complex process of intrafibrillar mineralization. Compared to traditional remineralization methods, bioactive materials capable of regulating ACP stability and controlling release demonstrate immense potential in enhancing clinical treatment standards.

Calcium phosphate nanoclusters modify periodontium remodeling and minimize orthodontic relapse

Orthodontic relapse is one of the most prevalent concerns of orthodontic therapy. Relapse results in patients' teeth reverting towards their pretreatment positions, which increases the susceptibility to functional problems, dental disease, and substantially increases the financial burden for retreatment. This phenomenon is thought to be induced by rapid remodeling of the periodontal ligament (PDL) in the early stages and poor bone quality in the later stages. Current therapies, including fixed or removable retainers and fiberotomies, have limitations with patient compliance and invasiveness. Approaches using biocompatible biomaterials, such as calcium phosphate polymer-induced liquid precursors (PILP), is an ideal translational approach for minimizing orthodontic relapse. Here, post-orthodontic relapse is reduced after a single injection of high concentration PILP (HC-PILP) nanoclusters by altering PDL remodeling in the early stage of relapse and improving trabecular bone quality in the later phase. HC-PILP nanoclusters are achieved by using high molecular weight poly aspartic acid (PASP, 14 kDa) and poly acrylic acid (PAA, 450 kDa), which resulted in a stable solution of high calcium and phosphate concentrations without premature precipitation. In vitro results show that HC-PILP nanoclusters prevented collagen type-I mineralization, which is essential for the tooth-periodontal ligament (PDL)-bone interphase. In vivo experiments show that the PILP nanoclusters minimize relapse and improve the trabecular bone quality in the late stages of relapse. Interestingly, PILP nanoclusters also altered the remodeling of the PDL collagen during the early stages of relapse. Further in vitro experiments showed that PILP nanoclusters alter the fibrillogenesis of collagen type-I by impacting the protein secondary structure. These findings propose a novel approach for treating orthodontic relapse and provide additional insight into the PILP nanocluster's structure and properties on collagenous structure repair.

Tissue-Penetrating Ultrasound-Triggered Hydrogel for Promoting Microvascular Network Reconstruction

The microvascular network plays an important role in providing nutrients to the injured tissue and exchanging various metabolites. However, how to achieve efficient penetration of the injured tissue is an important bottleneck restricting the reconstruction of microvascular network. Herein, the hydrogel precursor solution can efficiently penetrate the damaged tissue area, and ultrasound triggers the release of thrombin from liposomes in the solution to hydrolyze fibrinogen, forming a fibrin solid hydrogel network in situ with calcium ions and transglutaminase as catalysts, effectively solving the penetration impedance bottleneck of damaged tissues and ultimately significantly promoting the formation of microvascular networks within tissues. First, the fibrinogen complex solution is effectively permeated into the injured tissue. Second, ultrasound triggered the release of calcium ions and thrombin, activates transglutaminase, and hydrolyzes fibrinogen. Third, fibrin monomers are catalyzed to form fibrin hydrogels in situ in the damaged tissue area. In vitro studies have shown that the fibrinogen complex solution effectively penetrated the artificial bone tissue within 15 s after ultrasonic triggering, and formed a hydrogel after continuous triggering for 30 s. Overall, this innovative strategy effectively solved the problem of penetration resistance of ultrasound-triggered hydrogels in the injured tissues, and finally activates in situ microvascular networks regeneration.

Citrate Improves Biomimetic Mineralization Induced by Polyelectrolyte-Cation Complexes Using PAsp-Ca&Mg Complexes

Magnesium ions are highly enriched in early stage of biological mineralization of hard tissues. Paradoxically, hydroxyapatite (HAp) crystallization is inhibited significantly by high concentration of magnesium ions. The mechanism to regulate magnesium-doped biomimetic mineralization of collagen fibrils has never been fully elucidated. Herein, it is revealed that citrate can bioinspire the magnesium-stabilized mineral precursors to generate magnesium-doped biomimetic mineralization as follows: Citrate can enhance the electronegativity of collagen fibrils by its absorption to fibrils via hydrogen bonds. Afterward, electronegative collagen fibrils can attract highly concentrated electropositive polyaspartic acid-Ca&Mg (PAsp-Ca&Mg) complexes followed by phosphate solution via strong electrostatic attraction. Meanwhile, citrate adsorbed in/on fibrils can eliminate mineralization inhibitory effects of magnesium ions by breaking hydration layer surrounding magnesium ions and thus reduce dehydration energy barrier for rapid fulfillment of biomimetic mineralization. The remineralized demineralized dentin with magnesium-doped HAp possesses antibacterial ability, and the mineralization mediums possess excellent biocompatibility via cytotoxicity and oral mucosa irritation tests. This strategy shall shed light on cationic ions-doped biomimetic mineralization with antibacterial ability via modifying collagen fibrils and eliminating mineralization inhibitory effects of some cationic ions, as well as can excite attention to the neglected multiple regulations of small biomolecules, such as citrate, during biomineralization process.

Low-cost eggshell-fly ash adsorbent for phosphate recovery: A potential slow-release phosphate fertilizer

Fly ash (FA) and eggshells (ES) are common solid wastes with significant potential for the recovery of phosphorus from water. This study focuses on synthesizing a low-cost and environmental-friendly phosphate adsorbent called eggshell-fly ash geopolymer composite (EFG) using eggshells instead of chemicals. The CaO obtained from the high-temperature pyrolysis of eggshells provides active sites for phosphate adsorption, and CO2 serves as a pore-forming agent. The phosphate adsorption performance of EFG varied with the eggshell-fly ash ratios and achieved a maximum of 49.92 mg P/g at an eggshell-fly ash ratio of 40 %. The adsorption process was well described by the pseudo-second-order model and the Langmuir model. EFG also exhibited a good regeneration performance through six-cycle experiments and achieved the highest phosphate desorption at pH 4.0. The results of the column experiment showed that EFG can be used as a filter media for phosphorus removal in a real-scale application with low cost. Soil burial test indicated saturated EFG has a good phosphate slow-release performance (maintained for up to 60 days). Overall, EFG has demonstrated to be a promising adsorbent for phosphorus recovery.

Guidelines derived from biomineralized tissues for design and construction of high-performance biomimetic materials: from weak to strong

Living organisms in nature have undergone continuous evolution over billions of years, resulting in the formation of high-performance fracture-resistant biomineralized tissues such as bones and teeth to fulfill mechanical and biological functions, despite the fact that most inorganic biominerals that constitute biomineralized tissues are weak and brittle. During the long-period evolution process, nature has evolved a number of highly effective and smart strategies to design chemical compositions and structures of biomineralized tissues to enable superior properties and to adapt to surrounding environments. Most biomineralized tissues have hierarchically ordered structures consisting of very small building blocks on the nanometer scale (nanoparticles, nanofibers or nanoflakes) to reduce the inherent weaknesses and brittleness of corresponding inorganic biominerals, to prevent crack initiation and propagation, and to allow high defect tolerance. The bioinspired principles derived from biomineralized tissues are indispensable for designing and constructing high-performance biomimetic materials. In recent years, a large number of high-performance biomimetic materials have been prepared based on these bioinspired principles with a large volume of literature covering this topic. Therefore, a timely and comprehensive review on this hot topic is highly important and contributes to the future development of this rapidly evolving research field. This review article aims to be comprehensive, authoritative, and critical with wide general interest to the science community, summarizing recent advances in revealing the formation processes, composition, and structures of biomineralized tissues, providing in-depth insights into guidelines derived from biomineralized tissues for the design and construction of high-performance biomimetic materials, and discussing recent progress, current research trends, key problems, future main research directions and challenges, and future perspectives in this exciting and rapidly evolving research field.

Construction of Mineralization Nanostructures in Polymers for Mechanical Enhancement and Functionalization

Mineralization capable of growing inorganic nanostructures efficiently, orderly, and spontaneously shows great potential for application in the construction of high-performance organic-inorganic composites. As a thermodynamically spontaneous solid-phase crystallization reaction involving dual organic and inorganic components, mineralization allows for the self-assembly of sophisticated and exclusive nanostructures within a polymer matrix. It results in a diversity of functions such as enhanced strength, toughness, electrical conductivity, selective permeability, and biocompatibility. While there are previous reviews discussing the progress of mineralization reactions, many of them overlook the significant benefits of interfacial regulation and functionalization that come from the incorporation of mineralized structures into polymers. Focusing on different means of assembly of mineralized nanostructures in polymer, the work analyzes their design principles and implementation strategies. Then, their different advantages and disadvantages are analyzed by combining nanostructures with organic substrates as well as involving the basis of different functionalizations. It is anticipated to provide insights and guidance for the future development of mineralized polymer composites and their application designs.

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.

Reversion of ACP Nanoparticles into Prenucleation Clusters via Surfactant for Promoting Biomimetic Mineralization: A Physicochemical Understanding of Biosurfactant Role in Biomineralization Process

Amphiphilic biomolecules are abundant in mineralization front of biological hard tissues, which play a vital role in osteogenesis and dental hard tissue formation. Amphiphilic biomolecules function as biosurfactants, however, their biosurfactant role in biomineralization process has never been investigated. This study, for the first time, demonstrates that aggregated amorphous calcium phosphate (ACP) nanoparticles can be reversed into dispersed ultrasmall prenucleation clusters (PNCs) via breakdown and dispersion of the ACP nanoparticles by a surfactant. The reduced surface energy of ACP@TPGS and the electrostatic interaction between calcium ions and the pair electrons on oxygen atoms of C-O-C of D-α-tocopheryl polyethylene glycol succinate (TPGS) provide driving force for breakdown and dispersion of ACP nanoparticles into ultrasmall PNCs which promote in vitro and in vivo biomimetic mineralization. The ACP@TPGS possesses excellent biocompatibility without any irritations to oral mucosa and dental pulp. This study not only introduces surfactant into biomimetic mineralization field, but also excites attention to the neglected biosurfactant role during biomineralization process.

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

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

Journey of Mineral Precursors in Bone Mineralization: Evolution and Inspiration for Biomimetic Design

Bone mineralization is a ubiquitous process among vertebrates that involves a dynamic physical/chemical interplay between the organic and inorganic components of bone tissues. It is now well documented that carbonated apatite, an inorganic component of bone, is proceeded through transient amorphous mineral precursors that transforms into the crystalline mineral phase. Here, the evolution on mineral precursors from their sources to the terminus in the bone mineralization process is reviewed. How organisms tightly control each step of mineralization to drive the formation, stabilization, and phase transformation of amorphous mineral precursors in the right place, at the right time, and rate are highlighted. The paradigm shifts in biomineralization and biomaterial design strategies are intertwined, which promotes breakthroughs in biomineralization-inspired material. The design principles and implementation methods of mineral precursor-based biomaterials in bone graft materials such as implant coatings, bone cements, hydrogels, and nanoparticles are detailed in the present manuscript. The biologically controlled mineralization mechanisms will hold promise for overcoming the barriers to the application of biomineralization-inspired biomaterials.

Rapid Intrafibrillar Mineralization Strategy Enhances Adhesive-Dentin Interface

Biomimetic mineralization of dentin collagen appears to be a promising strategy to optimize dentin bonding durability. However, traditional postbonding mineralization strategies based on Ca/P ion release still have some drawbacks, such as being time-consuming, having a spatiotemporal mismatch, and having limited intrafibrillar minerals. To tackle these problems, a prebonding rapid intrafibrillar mineralization strategy was developed in the present study. Specifically, polyacrylic acid-stabilized amorphous calcium fluoride (PAA-ACF) was found to induce rapid intrafibrillar mineralization of the single-layer collagen model and dentin collagen at just 1 min and 10 min, as identified by transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. This strategy has also been identified to strengthen the mechanical properties of demineralized dentin within a clinically acceptable timeframe. Significantly, the bonding strength of the PAA-ACF-treated groups outperformed the control group irrespective of aging modes. In addition, the endogenous matrix metalloproteinases as well as exogenous bacterial erosion were inhibited, thus reducing the degradation of dentin collagen. High-quality integration of the hybrid layer and the underlying dentin was also demonstrated. On the basis of the present results, the concept of "prebonding rapid intrafibrillar mineralization" was proposed. This user-friendly scheme introduced PAA-ACF-based intrafibrillar mineralization into dentin bonding for the first time. As multifunctional primers, PAA-ACF precursors have the potential to shed new light on prolonging the service life of adhesive restorations, with promising significance.

ACP-Mediated Phase Transformation for Collagen Mineralization: A New Understanding of the Mechanism

Despite significant efforts utilizing advanced technologies, the contentious debate surrounding the intricate mechanism underlying collagen fibril mineralization, particularly with regard to amorphous precursor infiltration and phase transformation, persists. This work proposes an amorphous calcium phosphate (ACP)-mediated pathway for collagen fibril mineralization and utilizing stochastic optical reconstruction microscopy technology, and has experimentally confirmed for the first time that the ACP nanoparticles can infiltrate inside collagen fibrils. Subsequently, the ACP-mediated phase transformation occurs within collagen fibrils to form HAP crystallites, and significantly enhances the mechanical properties of the mineralized collagen fibrils compared to those achieved by the calcium phosphate ion (CPI)-mediated mineralization and resembles the natural counterpart. Furthermore, demineralized dentin can be effectively remineralized through ACP-mediated mineralization, leading to complete restoration of its mechanical properties. This work provides a new paradigm of collagen mineralization via particle-mediated phase transformation, deepens the understanding of the mechanism behind the mineralization of collagen fibrils, and offers a new strategy for hard tissue repair.

A biomimetic in situ mineralization ECM composite scaffold to promote endogenous bone regeneration

Bone tissue engineering scaffolds constructed from single-component organic materials have inherent limitations. Inspired by the hierarchical structure of physiological natural bone hard tissues, our research explores the construction of organic-inorganic composite scaffold for bone regeneration. In this study, we used a natural and readily obtainable extracellular matrix (ECM) material, i.e., decellularized small intestinal submucosa (SIS), to build the organic component of a phosphorylated hydroxyapatite nanocrystal-containing composite scaffold (nHA@SIS). Guided by polymer-induced liquid-precursor theory, we introduced a soluble inorganic mineralization solution to achieve an inorganic component of nHA@SIS. Using in situ mineralization, we successfully formed inorganic component within SIS and constructed nHA@SIS composite scaffold. We analyzed the physicochemical properties and the osteogenic role of nHA@SIS via a series of in vitro and in vivo studies. Compared with SIS scaffold, the nHA@SIS possessed suitable physicochemical properties, maintained the excellent cell activity of SIS and better guided reorganization of the cell skeleton, thereby achieving superior osteoconductivity and maintaining osteoinductivity at the protein and gene levels. Furthermore, the rat cranial defect area in the nHA@SIS scaffold group was mostly repaired after 12 weeks of implantation, with a larger amount of higher-density new bone tissue being visible at the edge and center than SIS and blank control group. This significantly improved in vivo osteogenic ability indicated the great potential of nHA@SIS for bone tissue engineering applications.

Size- and Dose-Dependent Body-Wide Organ Transcriptomic Responses to Calcium Phosphate Nanomaterials

Nanomaterials are widely used in clinical practice. There are potential risks of body-wide infiltration due to their small size; however, the body-wide reliable risk assessment of nanoparticle infiltration is not fully studied and established. In this study, we demonstrated the size- and dose-dependent body-wide organ transcriptomic responses to calcium phosphate nanomaterials in vivo. In a mice model, a calcium phosphate nanocluster (amorphous calcium phosphate, ACP, ∼1 nm in diameter) and its crystallization product (ACP-M, ∼10 nm in diameter) in a series of doses was administrated systematically; multiorgan transcriptomics were then performed with tissues of heart, liver, spleen, lung, kidney, and brain to investigate the systematic effect of dose and size of nanomaterials on the whole body. The results presented gene expression trajectories correlated with the dose of the nanomaterials and tissue-specific risk effects in all detected tissues. For the dose-dependent tissue-specific risk effects, lung tissue exhibited the most significant risk signatures related to apoptosis, cell proliferation, and cell stress. The spleen showed the second most significant risk signatures associated with immune response and DNA damage. For the size-dependent tissue-specific risk effects, ACP nanomaterials could increase most of the tissue-specific risk effects of nanomaterials in multiple organs than larger calcium phosphate nanoparticles. Finally, we used the size- and dose-dependent body-wide organ transcriptomic responses/risks to nanomaterials as the standards and built up a risk prediction model to evaluate the risk of the local nanomaterials delivery. Thus, our findings could provide a size- and dose- dependent risk assessment scale of nanoparticles in the transcriptomic level. It could be useful for risk assessment of nanomaterials in the future.

Biomimetic Mineralization: From Microscopic to Macroscopic Materials and Their Biomedical Applications

Biomineralization is an attractive pathway to produce mineral-based biomaterials with high performance and hierarchical structures. To date, the biomineralization process and mechanism have been extensively studied, especially for the formation of bone, teeth, and nacre. Inspired by those, abundant biomimetic mineralized materials have been fabricated for biomedical applications. Those bioinspired materials generally exhibit great mechanical properties and biological functions. Nevertheless, substantial gaps remain between biomimetic materials and natural materials, particularly with respect to mechanical properties and mutiscale structures. This Review summarizes the recent progress of micro- and macroscopic biomimetic mineralization from the perspective of materials synthesis and biomedical applications. To begin with, we discuss the progress of biomimetic mineralization at the microscopic level. The mechanical strength, stability, and functionality of the nano- and micromaterials are significantly improved by introducing biominerals, such as DNA nanostructures, nanovaccines, and living cells. Next, numerous biomimetic strategies based on biomineralization at the macroscopic scale are highlighted, including in situ mineralization and bottom-up assembly of mineralized building blocks. Finally, challenges and future perspectives regarding the development of biomimetic mineralization are also presented with the aim of offering insights for the rational design and fabrication of next-generation biomimetic mineralized materials.

Genetic Engineered Ultrasound-Triggered Injectable Hydrogels for Promoting Bone Reconstruction

Genetic engineering technology can achieve specific gene therapy for a variety of diseases, but the current strategy still has some flaws, such as a complex system, single treatment, and large implantation trauma. Herein, the genetic engineering injectable hydrogels were constructed by ultrasonic technology for the first time to realize in vivo ultrasound-triggered in situ cross-linking and cell gene transfection, and finally complete in situ gene therapy to promote bone reconstruction. First, ultrasound-triggered calcium release was used to activate transglutaminase and catalyze the transamidation between fibrinogen. Simultaneously, liposome loaded with Zinc-finger E-box-binding homeobox 1 (ZEB1) gene plasmid (Lip-ZEB1) was combined to construct an ultrasound-triggered in situ cross-linked hydrogels that can deliver Lip-ZEB1. Second, ultrasound-triggered injectable hydrogel introduced ZEB1 gene plasmid into endothelial cell genome through Lip-ZEB1 sustained release, and then acted on the ZEB1/Notch signal pathway of cells, promoting angiogenesis and local bone reconstruction of osteoporosis through genetic engineering. Overall, this strategy provides an advanced gene delivery system through genetic engineered ultrasound-triggered injectable hydrogels.

Fabrication of ACP-CCS-PVA composite membrane for a potential application in guided bone regeneration

The barrier membranes of guided bone regeneration (GBR) have been widely used in clinical medicine to repair bone defects. However, the unmatched mechanical strength, unsuitable degradation rates, and insufficient regeneration potential limit the application of the current barrier membranes. Here, amorphous calcium phosphate-carboxylated chitosan-polyvinyl alcohol (ACP-CCS-PVA) composite membranes are fabricated by freeze-thaw cycles, in which the ATP-stabilized ACP nanoparticles are uniformly distributed throughout the membranes. The mechanical performance and osteogenic properties are significantly improved by the ACP incorporated into the CCS-PVA system, but excess ACP would suppress cell proliferation and osteogenic differentiation. Our work highlights the pivotal role of ACP in GBR and provides insight into the need for biomaterial fabrication to balance mechanical strength and mineral content.

Metal-polyDNA nanoparticles reconstruct osteoporotic microenvironment for enhanced osteoporosis treatment

Current clinical approaches to osteoporosis primarily target osteoclast biology, overlooking the synergistic role of bone cells, immune cells, cytokines, and inorganic components in creating an abnormal osteoporotic microenvironment. Here, metal-polyDNA nanoparticles (Ca-polyCpG MDNs) composed of Ca2+ and ultralong single-stranded CpG sequences were developed to reconstruct the osteoporotic microenvironment and suppress osteoporosis. Ca-polyCpG MDNs can neutralize osteoclast-secreted hydrogen ions, provide calcium repletion, promote remineralization, and repair bone defects. Besides, the immune-adjuvant polyCpG in MDNs could induce the secretion of osteoclastogenesis inhibitor interleukin-12 and reduce the expression of osteoclast function effector protein to inhibit osteoclast differentiation, further reducing osteoclast-mediated bone resorption. PPi4- generated during the rolling circle amplification reaction acts as bisphosphonate analog and enhances bone targeting of Ca-polyCpG MDNs. In ovariectomized mouse and rabbit models, Ca-polyCpG MDNs prevented bone resorption and promoted bone repair by restoring the osteoporotic microenvironment, providing valuable insights into osteoporosis therapy.

Crosslinking Improve Demineralized Dentin Performance and Synergistically Promote Biomimetic Mineralization by CaP_PILP

OBJECTIVE

to explore the effects of optimal crosslinking (chemical treatment) on demineralized dentin matrix and the possible synergism with calcium phosphate polymer-induced liquid precursor (CaP-PILP) bionic remineralization (physical treatment), and offer benefit to the clinic of resin-dentin bonding and dentin hypersensitivity.

METHODS

demineralized dentin was treated with glutaraldehyde (GA), carbodiimide (EDC), and procyanidin (PA) for crosslinking, followed by CaP-PILP biomimetic remineralization. The morphology, surface mechanical and physio-chemical properties, and enzymatic resistance were evaluated regardless of the modification.

RESULTS

the collagen fibers appeared morphologically complete with higher surface microhardness and characteristic peaks of amide I-III bands were visible after GA, PA, and EDC crosslinking. Collagen collapse and dissolution were seen in untreated demineralized dentin with enzyme attack, while the collagen fiber structure remained intact in GA- and PA-treated specimens. The lamellar mineral phase was visible at 2 days and the dentin tubules were almost completely enclosed at 4-6 days after PA crosslinking and mineralization. However, demineralized collagen fibers and open tubules were still visible between the dentinal tubules on day 8 in the control group.

CONCLUSION

the structure integrity, enzyme resistance, and mechanical properties of the collagen fiber network could be significantly preserved by GA and PA crosslinking than EDC and no treatment. While, strongest synergistic effects were observed in PA on bionic remineralization by CaP-PILP, and further significantly improve the quality and shorten the duration of mineralization. These findings would be beneficial for dental clinical practice of resin-dentin bonding and dentin hypersensitivity.

Intrafibrillar Mineralization and Immunomodulatory for Synergetic Enhancement of Bone Regeneration via Calcium Phosphate Nanocluster Scaffold

Inspired by the bionic mineralization theory, organic-inorganic composites with hydroxyapatite nanorods orderly arranged along collagen fibrils have attracted extensive attention. Planted with an ideal bone scaffold will contribute greatly to the osteogenic microenvironment; however, it remains challenging to develop a biomimetic scaffold with the ability to promote intrafibrillar mineralization and simultaneous regulation of immune microenvironment in situ. To overcome these challenges, a scaffold containing ultra-small particle size calcium phosphate nanocluster (UsCCP) is prepared, which can enhance bone regeneration through the synergetic effect of intrafibrillar mineralization and immunomodulatory. By efficient infiltration into collagen fibrils, the UsCCP released from the scaffold achieves intrafibrillar mineralization. It also promotes the M2-type polarization of macrophages, leading to an immune microenvironment with both osteogenic and angiogenic potential. The results confirm that the UsCCP scaffold has both intrafibrillar mineralization and immunomodulatory effects, making it a promising candidate for bone regeneration.

Advances in materials-based therapeutic strategies against osteoporosis

Osteoporosis is caused by the disruption in homeostasis between bone formation and bone resorption. Conventional management of osteoporosis involves systematic drug administration and hormonal therapy. These treatment strategies have limited curative efficacy and multiple adverse effects. Biomaterials-based therapeutic strategies have recently emerged as promising alternatives for the treatment of osteoporosis. The present review summarizes the current status of biomaterials designed for managing osteoporosis. The advantages of biomaterials-based strategies over conventional systematic drug treatment are presented. Different anti-osteoporotic delivery systems are concisely addressed. These materials include injectable hydrogels and nanoparticles, as well as anti-osteoporotic bone tissue engineering materials. Fabrication techniques such as 3D printing, electrostatic spinning and artificial intelligence are appraised in the context of how the use of these adjunctive techniques may improve treatment efficacy. The limitations of existing biomaterials are critically analyzed, together with deliberation of the future directions in biomaterials-based therapies. The latter include discussion on the use of combination strategies to enhance therapeutic efficacy in the osteoporosis niche.

Calcium Phosphate Delivery Systems for Regeneration and Biomineralization of Mineralized Tissues of the Craniofacial Complex

Calcium phosphate (CaP)-based materials have been extensively used for mineralized tissues in the craniofacial complex. Owing to their excellent biocompatibility, biodegradability, and inherent osteoconductive nature, their use as delivery systems for drugs and bioactive factors has several advantages. Of the three mineralized tissues in the craniofacial complex (bone, dentin, and enamel), only bone and dentin have some regenerative properties that can diminish due to disease and severe injuries. Therefore, targeting these regenerative tissues with CaP delivery systems carrying relevant drugs, morphogenic factors, and ions is imperative to improve tissue health in the mineralized tissue engineering field. In this review, the use of CaP-based microparticles, nanoparticles, and polymer-induced liquid precursor (PILPs) amorphous CaP nanodroplets for delivery to craniofacial bone and dentin are discussed. The use of these various form factors to obtain either a high local concentration of cargo at the macroscale and/or to deliver cargos precisely to nanoscale structures is also described. Finally, perspectives on the field using these CaP materials and next steps for the future delivery to the craniofacial complex are presented.

Advances in biomimetic collagen mineralisation and future approaches to bone tissue engineering

With an ageing world population and ~20% of adults in Europe being affected by bone diseases, there is an urgent need to develop advanced regenerative approaches and biomaterials capable to facilitate tissue regeneration while providing an adequate microenvironment for cells to thrive. As the main components of bone are collagen and apatite mineral, scientists in the tissue engineering field have attempted in combining these materials by using different biomimetic approaches to favour bone repair. Still, an ideal bone analogue capable of mimicking the distinct properties (i.e., mechanical properties, degradation rate, porosity, etc.) of cancellous bone is to be developed. This review seeks to sum up the current understanding of bone tissue mineralisation and structure while providing a critical outlook on the existing biomimetic strategies of mineralising collagen for bone tissue engineering applications, highlighting where gaps in knowledge exist.

Progress in bioactive surface coatings on biodegradable Mg alloys: A critical review towards clinical translation

Mg and its alloys evince strong candidature for biodegradable bone implants, cardiovascular stents, and wound closing devices. However, their rapid degradation rate causes premature implant failure, constraining clinical applications. Bio-functional surface coatings have emerged as the most competent strategy to fulfill the diverse clinical requirements, besides yielding effective corrosion resistance. This article reviews the progress of biodegradable and advanced surface coatings on Mg alloys investigated in recent years, aiming to build up a comprehensive knowledge framework of coating techniques, processing parameters, performance measures in terms of corrosion resistance, adhesion strength, and biocompatibility. Recently developed conversion and deposition type surface coatings are thoroughly discussed by reporting their essential therapeutic responses like osteogenesis, angiogenesis, cytocompatibility, hemocompatibility, anti-bacterial, and controlled drug release towards in-vitro and in-vivo study models. The challenges associated with metallic, ceramic and polymeric coatings along with merits and demerits of various coatings have been illustrated. The use of multilayered hybrid coating comprising a unique combination of organic and inorganic components has been emphasized with future perspectives to obtain diverse bio-functionalities in a facile single coating system for orthopedic implant applications.

Biomineralization-inspired sandwich dentin desensitization strategy based on multifunctional nanocomposite with yolk-shell structure

Dentin hypersensitivity (DH) treatment is far from being unequivocal in providing a superior strategy that combines immediate and long-term efficiency of dentinal tubule (DT) occlusion and clinical applicability. In order to achieve this aim, a type of multifunctional yolk-shell nanocomposite with acid resistance, mechanical resistance and biomineralization properties was developed in this study, which consists of a silica/mesoporous titanium-zirconium nanocarrier (STZ) and poly(allylamine hydrochloride) (PAH)-stabilized amorphous calcium phosphate (ACP) liquid precursor. First, the nanocomposite, named as PSTZ, immediately occluded DTs and demonstrated outstanding acid and mechanical resistance. Second, the PSTZ nanocomposite induced intrafibrillar mineralization of single-layer collagen fibrils and remineralization of demineralized dentin matrix. Finally, PSTZ promoted the odontogenic differentiation of dental pulp stem cells by releasing ACP and silicon ions. The reconstruction of the dentin-mimicking hierarchical structure and the introduction of newly formed minerals in the upper, middle and lower segments of DTs, defined as sandwich-like structures, markedly reduced the permeability and achieved superior long-term sealing effects. The nanocomposite material based on mesoporous yolk-shell carriers and liquid-phase mineralized precursors developed in this study represents a versatile biomimetic sandwich desensitization strategy and offers fresh insight into the clinical management of DH.

The synergetic effect of a gold nanocluster-calcium phosphate composite: enhanced photoluminescence intensity and superior bioactivity

Gold nanoclusters (AuNCs) are a unique class of materials that exhibit visible luminescence. Amorphous calcium phosphate (ACP) is a widely used biomaterial for a variety of purposes, such as drug delivery, bone cementing, and implant coatings. In this study, a nanocomposite of AuNCs and ACP is prepared by biomimetic mineralization in a Dulbecco's modified Eagle's medium (DMEM). The strong interaction between AuNCs and Ca²⁺ ions effectively induces aggregation of AuNCs. The as-formed nanocomposite, AuNCs@ACP, emits significantly enhanced luminescence compared to AuNCs alone. The luminescence enhancement mechanism is investigated using synchrotron X-ray absorption fine structure spectroscopy. In addition, the presence of AuNCs stabilizes ACP and also enhances the biocompatibility of ACP in promoting cell proliferation, and the nanocomposites are promising as nanoprobes for cancer therapy and/or bone tissue engineering.

Free or fixed state of nHAP differentially regulates hBMSC morphology and osteogenesis through the valve role of ITGA7

Nano-hydroxyapatite (nHAP) has been widely used in bone repair as an osteo-inductive and naturally-occurring material. However, the optimal applied form of nHAP and the underlying mechanisms involved remain unclear. Herein, to investigate into these, a range of corresponding models were designed, including three applied forms of nHAP (Free, Coating and 3D) that belong to two states (Free or fixed). The results indicate that when fixed nHAP was applied in the 3D form, optimal osteogenesis was induced in human bone marrow stem cells (hBMSCs) with increased bone volume via integrin α7 (ITGA7)-mediated upregulation of the PI3K-AKT signaling pathway, while contrary results were observed with free nHAP. Ectopic osteogenesis experiments in mice subcutaneous transplantation model further confirmed the different tendencies of ITGA7 expression and osteogenesis of hBMSCs in free and fixed states of nHAP. Our results revealed that the two states of nHAP play a different regulatory role in cell morphology and osteogenesis through the valve role of ITGA7, providing cues for better application of nanoparticles and a potential new molecular target in bone tissue engineering.

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Free and fixed states of nHAP differentially regulate cell morphology and osteogenesis of hBMSCs.

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3D fixed nHAP promoted cell volume expansion and osteogenesis, whereas the opposite results were observed in free nHAP.

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ITGA7 plays an important role in osteogenesis under different nHAP applied forms.

Constructions of ROS-responsive titanium-hydroxyapatite implant for mesenchymal stem cell recruitment in peri-implant space and bone formation in osteoporosis microenvironment

To solve the issue of unsatisfactory recruitment of mesenchymal stem cells (MSCs) around implant in osteoporotic fractures, we fabricated a ROS-responsive system on titanium surface through hydroxyapatite coating and biomolecule grafting. The porous hydroxyapatite and phosphorylated osteogenic growth peptides (p-OGP) were introduced onto titanium surface to synergistically improve osteogenic differentiation of MSCs. After the p-OGP-promoted expression of osteogenic related proteins, the calcium and phosphate ions were released through the degradation of hydroxyapatite and integrated into bone tissues to boost the mineralization of bone matrix. The ROS-triggered release of DNA aptamer (Apt) 19S in the osteoporotic microenvironment guides MSC migration to implant site due to its high affinity with alkaline phosphatase on the membrane of MSCs. Once MSCs reached the implant interface, their osteogenic differentiation potential was enhanced by p-OGP and hydroxyapatite to promote bone regeneration. The study here provided a simple and novel strategy to prepare functional titanium implants for osteoporotic bone fracture repair.

Fast Construction of Biomimetic Organic-Inorganic Interface by Crosslinking of Calcium Phosphate Oligomers: A Strategy for Instant Regeneration of Hard Tissue

The organic-inorganic structure in biological hard tissues ensures their marvelous characteristics but these hybrids are easily destroyed by the demineralization of inorganic components, e.g., the damage of dentin. Current clinical materials for hard tissue regeneration commonly act as "fillers" and their therapeutic effect is limited by the failures of biological-linked organic-inorganic interface reconstruction. Herein, a fast in situ crosslinking of calcium phosphate oligomers (CPOs) on collagen matrixes for efficient organic-inorganic interface re-construction, which can result in a biomimetic hybrid, is demonstrated. By using damaged dentin as an example, the inorganic ionic crosslinking can instantly infiltrate into the dentin matrix to rebuild a dense and continuous calcium phosphate-collagen hybrid within only 5 min, where the structurally integrated organic-inorganic interface is identical to natural dentin. As a result, the damaged dentin can be fully recovered to a healthy one, which is superior to any current dentin treatments. The fast construction of biomimetic hybrid by inorganic ionic crosslinking provides a promising strategy for hard tissue repair and follows great potentials of CPOs as advanced biomedical materials in future.

Systemic and single cell level responses to 1 nm size biomaterials demonstrate distinct biological effects revealed by multi-omics atlas

Although ultra-small nanoclusters (USNCs, < 2 nm) have immense application capabilities in biomedicine, the investigation on body-wide organ responses towards USNCs is scant. Here, applying a novel strategy of single-cell mass cytometry combined with Nano Genome Atlas of multi-tissues, we systematically evaluate the interactions between the host and calcium phosphate (CaP) USNCs at the organism level. Combining single-cell mass cytometry, and magnetic luminex assay results, we identify dynamic immune responses to CaP USNCs at the single cell resolution. The innate immune is initially activated and followed by adaptive immune activation, as evidenced by dynamic immune cells proportions. Furthermore, using Nano Genome Atlas of multi-tissues, we uncover CaP USNCs induce stronger activation of the immune responses in the cartilage and subchondral bone among the five local tissues while promote metabolic activities in the liver and kidney. Moreover, based on the immunological response profiles, histological evaluation of major organs and local tissue, and a body-wide transcriptomics, we demonstrate that CaP USNCs are not more hazardous than the Food and Drug Administration-approved CaP nanoparticles after 14 days of injection. Our findings provide valuable information on the future clinical applications of USNCs and introduce an innovative strategy to decipher the whole body response to implants.

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We described a new strategy to facilitate the analysis of body-wide systemic responses of CaP USNCs in vivo.

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At single-cell resolution, we decoded a dynamic immune atlas of CaP USNCs in the blood.

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Based on the body-wide transcriptomics view, the biological effect of CaP USNCs is organ/tissue specific.

In Situ Fluorescence Probing of the Formation of Calcium Phosphate Prenucleation Clusters

Initial-stage prenucleation clusters (PNCs) are critical in calcium phosphate (CaP) biomineralization and thus the formation mechanisms of human bones and teeth. However, several features of PNCs require further examination, e.g., structure, ionic stoichiometry, kinetics, thermodynamics, and nucleation mechanism. In this study, we used poly(acrylic acid) (PAA)-Ca(Eu) complexes with partial Eu³⁺ substitution as pre-PNCs and established a fluorescence method to study PNC formation in situ based on Eu-O charge-transfer transitions. The kinetics and thermodynamics of PNC formation were explored by probing the fluorescence changes of Eu-O charge-transfer transitions during bonding between the pre-PNCs and PO₄^3-. PNC formation was consistent with the pseudo-second-order kinetic and Langmuir isothermal adsorption models. The flexible structures of PNCs aided in regulating the subsequent nucleation and crystallization. This study provides an in situ fluorescence probing method with critical guiding significance in addressing the features of PNC formation, in addition to biomineralization.

A Novel Biodegradable Nanoplatform for Tumor Microenvironments Responsive Bimodal Magnetic Resonance Imaging and Sonodynamic/Ion Interference Cascade Therapy

The unsatisfactory therapeutic effect and long-term adverse effect markedly prevent inorganic nanomaterials from clinical transformation. In light of this, we developed a novel biodegradable theranostic agent (MnCO₃:Ho³⁺@DOX/Ca₃(PO₄)₂@BSA, HMCDB) based on the sonosensitizer manganese carbonate (MnCO₃) coating with calcium phosphate (Ca₃(PO₄)₂) and simultaneously loaded it with the chemotherapeutic drug doxorubicin (DOX). Due to the mild acidity of the tumor microenvironment (TME), the Ca₃(PO₄)₂ shell degraded first, releasing substantial quantities of calcium ions (Ca²⁺) and DOX. Meanwhile, with the ultrasound (US) irradiation, MnCO₃ produced enough reactive oxygen species (ROS) to cause oxidative stress in the cells, resulting in accumulation of Ca²⁺. Consequently, the cascade effect significantly amplified the therapeutic effect. Importantly, the nanocomposite can be completely degraded and cleared from the body, demonstrating that it was a promising theranostic agent for tumor therapy. Furthermore, the doped holmium ions (Ho³⁺) and in situ generation of manganese ions (Mn²⁺) in TME endow the nanoagent with the ability for tumor-specific bimodality T₁/T₂-weighted magnetic resonance imaging (MRI). This novel nanoplatform with low toxicity and biodegradability holds great potential for cancer diagnosis and treatment.

3D-printed NIR-responsive shape memory polyurethane/magnesium scaffolds with tight-contact for robust bone regeneration

Patients with bone defects suffer from a high rate of disability and deformity. Poor contact of grafts with defective bones and insufficient osteogenic activities lead to increased loose risks and unsatisfied repair efficacy. Although self-expanding scaffolds were developed to enhance bone integration, the limitations on the high transition temperature and the unsatisfied bioactivity hindered greatly their clinical application. Herein, we report a near-infrared-responsive and tight-contacting scaffold that comprises of shape memory polyurethane (SMPU) as the thermal-responsive matrix and magnesium (Mg) as the photothermal and bioactive component, which fabricated by the low temperature rapid prototyping (LT-RP) 3D printing technology. As designed, due to synergistic effects of the components and the fabrication approach, the composite scaffold possesses a homogeneously porous structure, significantly improved mechanical properties and stable photothermal effects. The programmed scaffold can be heated to recover under near infrared irradiation in 60s. With 4 wt% Mg, the scaffold has the balanced shape fixity ratio of 93.6% and shape recovery ratio of 95.4%. The compressed composite scaffold could lift a 100 g weight under NIR light, which was more than 1700 times of its own weight. The results of the push-out tests and the finite element analysis (FEA) confirmed the tight-contacting ability of the SMPU/4 wt%Mg scaffold, which had a signficant enhancement compared to the scaffold without shape memory effects. Furthermore, The osteopromotive function of the scaffold has been demonstrated through a series of in vitro and in vivo studies. We envision this scaffold can be a clinically effective strategy for robust bone regeneration.

Hope for bone regeneration: The versatility of iron oxide nanoparticles

Although bone tissue has the ability to heal itself, beyond a certain point, bone defects cannot rebuild themselves, and the challenge is how to promote bone tissue regeneration. Iron oxide nanoparticles (IONPs) are a magnetic material because of their excellent properties, which enable them to play an active role in bone regeneration. This paper reviews the application of IONPs in bone tissue regeneration in recent years, and outlines the mechanisms of IONPs in bone tissue regeneration in detail based on the physicochemical properties, structural characteristics and safety of IONPs. In addition, a bibliometric approach has been used to analyze the hot spots and trends in the field in order to identify future directions. The results demonstrate that IONPs are increasingly being investigated in bone regeneration, from the initial use as magnetic resonance imaging (MRI) contrast agents to later drug delivery vehicles, cell labeling, and now in combination with stem cells (SCs) composite scaffolds. In conclusion, based on the current research and development trends, it is more inclined to be used in bone tissue engineering, scaffolds, and composite scaffolds.

Mineralized Enzyme-Based Biomaterials with Superior Bioactivities for Bone Regeneration

The formation and metabolic balance of bone tissue is a controllable process of biomineralization, which is regulated by various cells, biomolecules, and ions. Enzyme molecules play an important role in this process, and alkaline phosphatase (ALP) is one of the most critical factors. In this study, inspired by the process of bone biomineralization, a biomimetic strategy is achieved for the preparation of mineralized ALP nanoparticles (MALPNs), by taking advantages of the unique reaction between ALP and calcium ions in Dulbecco's modified Eagle's medium. Benefiting from the mild biomineralization reaction, the MALPN system highly maintains the activity of ALP. Furthermore, the in vitro studies show that the MALPN system significantly enhances the proliferation of bone marrow mesenchymal stem cells and upregulates their osteogenic differentiation. When evaluated as synthetic graft materials for bone regeneration, the MALPN-incorporated gelatin methacryloyl graft shows excellent mechanical properties, a sustained release profile of ALP, and high biocompatibility and efficacy in guiding bone regeneration and vascularization for critical-sized rat calvarial defect. Moreover, we also demonstrate that the biomimetic mineralization strategy can be adopted for other proteins such as acid phosphatase, bovine serum albumin, fibrinogen, and gelatin, suggesting its universality for constructing mineralized protein-/enzyme-based bioactive materials for the application of tissue regeneration.

Role of Phosphorus-Containing Molecules on the Formation of Nano-Sized Calcium Phosphate for Bone Therapy

Calcium phosphate (CaP) is the principal inorganic constituent of bone and teeth in vertebrates and has various applications in biomedical areas. Among various types of CaPs, amorphous calcium phosphate (ACP) is considered to have superior bioactivity and biodegradability. With regard to the instability of ACP, the phosphorus-containing molecules are usually adopted to solve this issue, but the specific roles of the molecules in the formation of nano-sized CaP have not been clearly clarified yet. Herein, alendronate, cyclophosphamide, zoledronate, and foscarnet are selected as the model molecules, and theoretical calculations were performed to elucidate the interaction between calcium ions and different model molecules. Subsequently, CaPs were prepared with the addition of the phosphorus-containing molecules. It is found that cyclophosphamide has limited influence on the generation of CaPs due to their weak interaction. During the co-precipitation process of Ca2+ and PO43-, the competitive relation among alendronate, zoledronate, and foscarnet plays critical roles in the produced inorganic-organic complex. Moreover, the biocompatibility of CaPs was also systematically evaluated. The DFT calculation provides a convincing strategy for predicting the structure of CaPs with various additives. This work is promising for designing CaP-based multifunctional drug delivery systems and tissue engineering materials.