Bone hierarchical structure in three dimensions

Synergistic enhancement of desferrioxamine and strontium-doped hydroxyapatite via coaxial electrostatic spinning on osteogenic differentiation

Defective bone repair is a pressing issue in the field of bone regeneration due to donor shortages and the associated complications of bone grafting. Artificial bone repair materials offer more options and are attracting extensive attention from researchers. However, achieving efficient osteogenesis in clinical practice remains a challenge. Here, dual drug-releasing nanofibre membranes (NMs) for bone repair was fabricated by coaxial electrostatic spinning. Strontium-doped hydroxyapatite (SrHA) and desferrioxamine (DFO) were loaded into the shell and core of the NMs for slow and sustained release, respectively. Our results showed that the DFO/SrHA NMs significantly enhanced cell proliferation, angiogenesis and osteogenic differentiation of rat bone mesenchymal stem cells through the synergism of DFO and SrHA. This synergy results from the slow and sustained release of DFO and SrHA via NMs, which maintains the drug concentration in the effective range for a long time, ensuring long-term stable activation of the HIF-1 α and Wnt/β-catenin signalling pathways. Overall, the DFO/SrHA NMs provides a promising strategy for defective bone repair by enhancing osteogenic differentiation.

Facile construction of mechanically robust and highly osteogenic materials for bone regeneration

Hydrogel-based materials exhibit great potential in tissue engineering. However, their mechanical weakness limits applications in hard tissue regeneration, especially under load-bearing conditions. Although various strengthening strategies have been applied, the achieved mechanical response of hydrogels still lags behind the mechanics of natural bone. In this study, we present a novel mineralization approach to fabricate mechanically robust and highly osteogenic mineralized hydrogels. Cross-linking between deprotonated chains of poly(acrylic acid) (PAA) and divalent cations has led to formation of hydrogels with a compressive strength and elastic modulus of 0.3 ± 0.1 kPa and 1.3 ± 0.2 kPa, respectively. Subsequent in situ formation of nano-calcium hydroxide crystals remarkably increased the compressive strength and modulus to 7.9 ± 0.6 MPa and 339.3 ± 31.4 MPa, respectively, surpassing those of trabecular bone. Moreover, the mineralized hydrogels demonstrated remarkable osteogenic potential in vivo, exhibiting immunoregulatory activity, promoting early angiogenesis, and accelerating fracture healing at weeks 4 and 8. The mechanism of osteogenesis was further revealed by transcriptome sequencing, indicating that the mineralized hydrogels regulated the translation of extracellular matrix and biomineralization. Overall, our study presents a pioneering and cost-effective method for fabricating materials with exceptional mechanical strength and strong osteogenic properties, offering a promising avenue for load-bearing bone repair applications of hydrogel-based materials.

The function of citrate in bone: platelet adhesion and mineral nucleation

The mineral component of bone consists of platelets of apatite 2-6 nm thick, which are bound together as stacks of up to 30 platelets located around and between the collagen fibrils. These coherent stacks of platelets, which contribute significantly to the compressive stiffness and strength of bone, are held together by glue. We show that this glue is most likely citrate, 2 wt% of bone. Nuclear magnetic resonance spectroscopy analyses have shown that citrate is attached to calcium atoms in bone, most likely connected to the faces of apatite crystals. Citrate molecules bound on apatite plates also act as the epitaxial site for the growth of additional apatite crystals, forming stacks of mineral plates. The presence of citrate should also contribute to the bonding of minerals to collagen and the resulting mechanical properties of bone. Such insights provide a deeper understanding of bone biology. These findings should also stimulate new studies on the mechanics of bone at the nanoscale aimed to characterize experimentally and computationally the strengths of these two types of interfaces, the mineral-collagen, and mineral-mineral interfaces in the presence of citrate, and their effect on bone's mechanical properties.

Human bone ultrastructure in 3D: Multimodal correlative study combining nanoscale X-ray computed tomography and quantitative polarized Raman spectroscopy

Unique mechanical properties of cortical bone are defined by the arrangement and ratio of its organic and inorganic constituents. This arrangement can be influenced by ageing and disease, urging the understanding of normal and deviant morphological patterns down to the nanoscale level, as much as the exploration of techniques able to grant that knowledge. Here, the ultrastructure and composition of seven samples taken from the femoral neck cortical bone of a single donor (52 y.o. female, no metabolic bone disease) is assessed with emerging characterization techniques. Laboratory-based nanoscale X-ray computed tomography providing ∼50 nm spatial resolution at (16 nm)3 voxel size resolves not only the lacuno-canalicular network but also the mineral ellipsoids associated with mineralized collagen fibrils (MCF). Site-matching 3D data with quantitative polarized Raman spectroscopy provides, in turn, complementary information on relative mineral and organic composition, while both techniques allow to quantify the MCF orientation. Bone matrix composition and lacuna-canalicular network organization are shown to vary between the osteonal and interstitial zones. Both plywood and gradual oscillating motifs of bone lamellation are observed, in line with existing theories. By combining these two methods, future studies can concentrate on other bone ultrastructural units of interest like interlamellar and cement interfaces, the structure of MCF around lacunae and near Haversian channels, as well as the influence of metabolic diseases on bone ultrastructure. STATEMENT OF SIGNIFICANCE: This study provides new insights into bone hierarchical organization, revealing local composition and lacuno-canalicular network organization within osteonal and interstitial bone zones, as well as their mineralized collagen fiber (MCF) orientation within the lamella. Synchrotron-like resolution was achieved on a laboratory-based nano-CT by exposing the volumes of interest from the bulk sample and applying machine learning segmentation algorithms. Site-matched analysis with quantitative Polarized Raman spectroscopy (qPRS) provided indirect access to relative mineral and organic composition variations and local MCF out-of-plane angle, with good agreement between the two methods. The proposed correlative experiment workflow greatly facilitates the characterization of bone ultrastructure and can be applied to other fields dealing with ordered hierarchical materials of similar feature sizes.

Advancing atom probe tomography capabilities to understand bone microstructures at near-atomic scale

Bone structure is generally hierarchically organized into organic (collagen, proteins, ...), inorganic (hydroxyapatite (HAP)) components. However, many fundamental mechanisms of the biomineralization processes such as HAP formation, the influence of trace elements, the mineral-collagen arrangement, etc., are not clearly understood. This is partly due to the analytical challenge of simultaneously characterizing the three-dimensional (3D) structure and chemical composition of biominerals in general at the nanometer scale, which can, in principle be achieved by atom probe tomography (APT). Yet, the hierarchical structures of bone represent a critical hurdle for APT analysis in terms of sample yield and analytical resolution, particularly for trace elements, and organic components from the collagen appear to systematically get lost from the analysis. Here, we applied in-situ metallic coating of APT specimens within the focused ion beam (FIB) used for preparing specimens, and demonstrate that the sample yield and chemical sensitivity are tremendously improved, allowing the analysis of individual collagen fibrils and trace elements such as Mg and Na. We explored a range of measurement parameters with and without coating, in terms of analytical resolution performance and determined the best practice parameters for analyzing bone samples in APT. To decipher the complex mass spectra of the bone specimens, reference spectra from pure HAP and collagen were acquired to unambiguously identify the signals, allowing us to analyze entire collagen fibrils and interfaces at the near-atomic scale. Our results open new possibilities for understanding the hierarchical structure and chemical heterogeneity of bone structures at the near-atomic level and demonstrate the potential of this new method to provide new, unexplored insights into biomineralization processes in the future. STATEMENT OF SIGNIFICANCE: Atom probe tomography (APT) is a relatively new technique for the analysis of bones, teeth or biominerals in general. APT can characterize the microstructure of materials in 3D down to the near-atomic level, combined with a high elemental sensitivity, down to parts per million. APT application to study biomineralization phenomena is plagued by low sample yield and poorer analytical performance compared to metals. Here we have overcome these limitations by in-situ metal coating of APT specimens. This can unlock future APT analysis to gain insights into fundamental biomineralization processes, e.g. collagen/hydroxyapatite interaction, influence of trace elements and a better understanding of bone diseases or bone biomineralization in general.

Nanomaterial-based scaffolds for bone regeneration with piezoelectric properties

For proper cellular growth, to prepare tissue scaffold mimicking the tissue properties is a significant challenge. Bone is a vital organ supporting the whole human body for its function. The efficiencies in its structure for a variety of reasons should properly be remedied. Bone tissue engineering (BTE) is an emerging field addressing to develop or repair bone tissue for its proper function. The bone is naturally a piezoelectric material and generates electrical stimuli because of mechanical stress. Thus, the use of piezoelectric materials to build bone tissue is of great interest in BTE. Both piezoelectric polymers and nanomaterials (NMs) are investigated for this goal. In this review, we give an overview of the recent advances in piezoelectric NMs to construct piezoelectric scaffolds in BTE.

Diverse Bone Matrix and Mineral Alterations in Osteoporosis with Different Causes: A Solid-State NMR Study

Osteoporosis (OP), which is a common skeletal disease with different causes, is prevalent in the aging population. Postmenopause women generally suffer from OP with bone loss due to estrogen deficiency. Diabetes is also associated with OP by complex metabolic mechanisms. Bone qualities of OP caused by aging were compared with those of the ovariectomy (OVX) model and the Type 2 diabetic model using Sprague-Dawley (SD) rats in our study. Combining with micro-computed tomography (μ-CT) and solid-state NMR (SSNMR) methods, this research studied bone changes in SD rats from tissue level to the molecular level. The studies revealed bone loss was most significant for cancellous bones but not for cortical bones in OP rats. However, at the molecular level, the content of HAP in cortical bone increased with aging, contributing to the brittleness of the bone. Triglyceride, as a senescence maker of osteocyte in cortical bone, was also identified to be closely associated with OP in aging and OVX rats but not in diabetic rats. This research suggests that changes of bone quality at the molecular level more objectively reflect the bone tissue reconstruction of OP with various causes rather than mere bone loss revealed by μ-CT analysis.

Bone mineral tessellation: Atomic force microscopy of the volume-filling mineralization pattern in hydrated and dehydrated states

Bone is a specialized hard connective tissue with a hierarchical organization of its components. At the micrometer scale, mineral entities of roughly uniform shape tessellate in 3D within an organized, crosslinked and hydrated scaffold of mostly type I collagen. Here we report on the visualization by atomic force microscopy (AFM) of the volume-filling mineralization pattern of tesselles in lamellar bone, in hydrated and dehydrated conditions (for human, bovine, porcine and ovine bone). Microscale mineral tessellation was clearly visible when bulk lamellar bone was hydrated, whereas dry bone showed submicron nanogranularity instead of tesselle boundaries. Time-lapse AFM experiments of gradual passive dehydration of bone revealed topographical changes for all bone species with the tessellation appearance vanishing after two weeks of dehydration. AFM adhesion forces dropped within the first days of dehydration in all bone species, indicating that surface stickiness is more sensitive to passive dehydration than is stiffness. Irrespective of the bone species, AFM stiffness measurements found that hydrated bone was more compliant than dehydrated bone. AFM Young's modulus measurements of more recently formed osteonal lamellae intersecting with older interstitial lamellae found that the modulus in both hydrated and dehydrated states was lower in the osteonal lamellae. Modelling of water sorption to the surface of stochiometric hydroxyapatite showed that the presence of rigid hydration shells delineates the tesselle boundaries and smoothens the nanogranularity, confirming the AFM observations. This study highlights the importance of regarding water as a fundamental architecting component of bone. STATEMENT OF SIGNIFICANCE: Here we report on visualization of the mineral tessellation pattern in lamellar bone by atomic force microscopy (AFM) in hydrated and dehydrated conditions. We show that lamellar bone (human, bovine, porcine and ovine) contains a universal volume-filling mineral tessellation. The visibility of the tessellation pattern by AFM strongly depends on the state of bone hydration. Modelling water sorption to the surface of stochiometric hydroxyapatite indicated that mechanical and morphological characteristics of lamellar bone (e.g., stiffness, adhesion, contours of tesselle boundaries) can be attributed to the presence of rigid hydration shells. This study highlights the importance of water incorporation as a fundamental component of bone, on par with the mineral and the organic extracellular matrix.

Prediction of the mechanical properties of TPMS structures based on Back propagation neural network

Triply Periodic Minimal Surface (TPMS) has the characteristics of high porosity, a highly interconnected network, and a smooth surface, making it an ideal candidate for bone tissue engineering applications. However, due to the complex relationship between multiple parameters of the TPMS structure and mechanical properties, it is a challenging task to optimize the properties of TPMS structures with different parameters. In this study, a Back-Propagation Neural Network (BPNN) was utilized to construct the relationship between TPMS parameters. Its mechanical performance and the TPMS structure were optimized using the BPNN. Results indicated that after training the correlation coefficient (R) between the BPNN prediction and the experimental results is 0.955475, it shows that our BPNN model has an adequate accuracy in describing the TPMS structures properties. Result of TPMS structure optimization shows that after optimization the yield strength of Hybridized Gyroid-Diamond Structure (HGDS) is 6.20 MPa, which is increased by 102.61% when compared with the original Hybridized Gyroid-Diamond Structure (3.06 MPa). Result of topological morphology indicates the effective bearing area of the optimized model was increased by 12.92% compared with the original model, which ascribe the increase in yield strength of the optimization model.

Revolutionizing tissue regeneration: the art of mimicking diverse collagen-based extracellular matrix hierarchies with decellularized tendon via bioskiving

Precisely simulating the collagen-based extracellular matrix (ECM) hierarchy is essential for advancing tissue regeneration. Although decellularized ECM (dECM) demonstrates considerable potential in fostering tissue regeneration by maintaining the inherent hierarchy, its application remains restricted to homologous tissues due to hierarchical variability. The current challenge involves overcoming obstacles that impede the application of dECM across diverse tissues, with particular emphasis on re-engineering one type of dECM to mimic the complex hierarchies of other tissues. The decellularized tendon, distinguished by its aligned collagen fibers, has garnered substantial interest due to its favorable structural and mechanical properties. Recently, a novel technique termed bioskiving has been developed, which uniquely disassembles macroscale decellularized tendons into microscale collagen sheets via microtome sectioning, thereby preserving micro/nano architecture of fiber alignment without chemical denaturation. These sheets can be further rotationally stacked or rolled to engineer 2D or 3D constructs replicating diverse ECM hierarchies. Bioskiving effectively dismantles the persistent hindrance that traditionally impeded the application of dECM across various tissues. This review offers an in-depth analysis of the fabrication procedure and characterization of constructs produced through bioskiving. It specifically elucidates the applications of constructs across various domains in tissue engineering, demonstrating its potential in overcoming tissue-specific constraints of dECM.

Bioactive Scaffolds with Ordered Micro/Nano-Scale Topological Surface for Vascularized Bone Regeneration

The ordered topological micro/nanostructures of scaffolds play a pivotal role in regulating bone development, remodeling, and regeneration. Nevertheless, achieving the integration of ordered micro/nanostructures into 3D scaffolds remains a formidable challenge. In this context, a brushing-assembly strategy is developed to construct 3D bioactive scaffolds with highly ordered micro/nanostructures. Such an engineered scaffold exhibits a positive regulatory effect on the behavior and fate of bone resident cells, such as mesenchymal stem cells (MSCs) and human umbilical vein endothelial cells (HUVECs), through mechanical stimulation provided by the ordered micro/nanostructures, while also allowing for the precise spatial distribution of multiple cell types through assembly. In vivo experiments demonstrate that scaffolds with ordered nanostructures possess the potential to accelerate vascularized bone regeneration. Overall, this work proposed a universal strategy for the fabrication of bioactive scaffolds with ordered topological micro/nanostructures, bridging the gap between 3D scaffolds and ordered surface microstructures for tissue engineering.

Self-Assembled Multilayered Concentric Supraparticle Architecture

Supraparticles (SPs) with unique properties are emerging as versatile platforms for applications in catalysis, photonics, and medicine. However, the synthesis of novel SPs with complex internal structures remains a challenge. Self-Assembled Multilayered Supraparticles (SAMS) presented here are composed of concentric lamellar spherical structures made from metallic nanoparticles, formed from a synergistic three-way interaction phenomenon between gold nanoparticles, lipidoid, and gelatin, exhibiting interlayer spacing of 3.5  ± 0.2 nm within a self-limited 156.8  ± 56.6 nm diameter. The formation is critically influenced by both physical (including nanoparticle size, lipidoid chain length) and chemical factors (including elemental composition, nanoparticle cap, and organic material), which collectively modulate the surface chemistry and hydrophobicity, affecting interparticle interactions. SAMS can efficiently deliver labile payloads such as siRNA, achieving dose-dependent silencing in vivo, while also showing potential for complex payloads such as mRNA. This work not only advances the field of SP design by introducing a new structure and interaction phenomenon but also demonstrates its potential in nanomedicine.

Transcriptomic Profile of Human Osteoblast-like Cells Grown on Trabecular Titanium

Trabecular titanium implants are widely used in orthopedic surgery and are known to promote osseointegration. In this study, we investigated whether primary human osteoblast-like cells grown inside a 3D trabecular titanium scaffold undergo changes in migration capacity, transcriptomic profile, and cellular phenotype as compared to the same osteoblasts not grown inside the scaffold. Scratch tests have shown that primary human osteoblast-like cells grown inside the 3D trabecular titanium scaffold promote the migration of cells from the external environment into the scaffold. Next generation sequencing analysis demonstrated that primary human osteoblast-like cells grown inside the 3D trabecular titanium scaffold modified the expression of genes involved in cell cycle and extracellular matrix remodeling, while maintaining a normal expression of the specific osteoblast markers, such as osteocalcin and osterix, as well as a comparable mineralization capacity. These data demonstrate that primary human osteoblast-like cells grown inside the titanium scaffold in a 3D environment acquire specific features favoring osseointegration.

Automatic segmentation of cortical bone microstructure: Application and analysis of three proximal femur sites

Osteoporosis is the most common bone metabolic unbalance, leading to fragility fractures, which are known to be associated with structural changes in the bone. Cortical bone accounts for 80 % of the skeleton mass and undergoes remodeling throughout life, leading to changes in its thickness and microstructure. Although many studies quantified the different cortical bone structures using CT techniques (3D), they are often realised on a small number of samples. Therefore, the work presented here proposes a method to quantify cortical bone microstructure using 2D histology, shows its application on a set of 94 samples and compares to 3D methods. Fresh frozen human femur pairs from 47 donors aged between 57 and 96 years were obtained from the Medical University of Vienna. Bone samples were cut from 3 sites: proximal part of the diaphysis, inferior and superior segments of the neck. The samples were stained with toluidine blue and imaged under light microscopy. After manual segmentation of a few regions of interest by multiple operators, a convolutional neural network was trained in combination with a random forest for automatic segmentation. The segmentation analysis compares morphology and structure distribution of Haversian canals, osteocyte lacunae, and cement lines with literature, between anatomical sites, sex, left and right sides, and relation to ageing. Morphological analysis of the segmentation gives results similar to the literature. Comparison between male and female donors shows no significant differences. There is no significant difference between left and right femur on paired samples but significant differences are observed between anatomical locations. The structures' relative amounts do not present significant changes with age but only weak tendencies. Nevertheless, a strong correlation was observed between osteocyte lacunae density and bone areal fraction. This study presents a full process to stain and automatically segment digital cortical bone images. Its application to a large sample set of proximal femora provides strong statistics on the cortical bone structures morphology and distribution. Similarities observed between sides and sexes together with differences observed between sites could indicate that mechanical loading might be a main driver for bone microstructure. Additionally, the relationship between osteocyte lacunae density and bone areal fraction could suggest that bone porosity is regulated by osteocyte survival.

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.

Analysis of cutting forces and microdamage during indentation cutting of bone

In surgery, bone can be cut by applying force to a wedge-shaped blade. The published literature is relatively sparse regarding the biomechanics of this type of indentation cutting, especially regarding the relationships between blade geometry, bone quality, cutting force and microdamage. Microdamage created near the cut surfaces can be beneficial, as a trigger for bone remodelling, but it is known that excessive fracture damage can prolong the healing time. In this research, specimens of compact bovine bone were tested by cutting using wedge blades of different geometries. We labelled and measured microdamage occurring during bone cutting for the first time. We found that there were statistically significant effects arising from the variation in wedge angle, edge radius and blade orientation (with respect to bone's anisotropic structure) on both the magnitude of the cutting force and the extent of the microdamage. Interestingly, we found that the amount of damage occurring during cutting is directly correlated to the cutting force which causes the damage, independent of other factors. This work contributes to a better understanding of the biomechanics of this important surgical cutting process.

The Importance of a Hierarchical Approach in Investigating the Connection Between Peripheral Artery Disease and Risk for Developing Low-Trauma Fractures: A Narrative Literature Review

Considering that skeletal changes are often asymptomatic during routine clinical examination, these disorders are frequently overlooked in patients with peripheral artery disease (PAD). Keeping in mind the inclining prevalence of PAD and bone fragility, especially in older individuals, this narrative literature review aimed to provide a comprehensive overview of skeletal alterations in patients with PAD, focusing on the importance of the multi-scale and multidisciplinary approach in the assessment of the bone hierarchical organization. Several observational studies have shown a connection between PAD and the risk of developing low-trauma fractures, but numerous ambiguities remain to be solved. Recent data indicate that evaluating additional bone properties at various levels of bone hierarchical structure may help in understanding the factors contributing to bone fragility in individuals with PAD. Further research on bone structural alterations (especially on micro- and nano-scale) may enhance the understanding of the complex etiopathogenesis of skeletal disorders in patients with PAD, which may lead to advancements in optimizing the clinical management of these individuals. Since osteoporosis and PAD have numerous overlapping risk factors, it is meaningful to evaluate vascular status in individuals with osteoporosis and examine bone health in individuals with PAD to identify individuals who require treatment for both diseases.

Multi-Physical Lattice Metamaterials Enabled by Additive Manufacturing: Design Principles, Interaction Mechanisms, and Multifunctional Applications

Lattice metamaterials emerge as advanced architected materials with superior physical properties and significant potential for lightweight applications. Recent developments in additive manufacturing (AM) techniques facilitate the manufacturing of lattice metamaterials with intricate microarchitectures and promote their applications in multi-physical scenarios. Previous reviews on lattice metamaterials have largely focused on a specific/single physical field, with limited discussion on their multi-physical properties, interaction mechanisms, and multifunctional applications. Accordingly, this article critically reviews the design principles, structure-mechanism-property relationships, interaction mechanisms, and multifunctional applications of multi-physical lattice metamaterials enabled by AM techniques. First, lattice metamaterials are categorized into homogeneous lattices, inhomogeneous lattices, and other forms, whose design principles and AM processes are critically discussed, including the benefits and drawbacks of different AM techniques for fabricating different types of lattices. Subsequently, the structure-mechanism-property relationships and interaction mechanisms of lattice metamaterials in a range of physical fields, including mechanical, acoustic, electromagnetic/optical, and thermal disciplines, are summarized to reveal critical design principles. Moreover, the multifunctional applications of lattice metamaterials, such as sound absorbers, insulators, and manipulators, sensors, actuators, and soft robots, thermal management, invisible cloaks, and biomedical implants, are enumerated. These design principles and structure-mechanism-property relationships provide effective design guidelines for lattice metamaterials in multifunctional applications.

Understanding the structural biology of osteomalacia through multiscale 3D X-ray and electron tomographic imaging: a review of X-linked hypophosphatemia, the Hyp mouse model, and imaging methods

Biomineralization in bones and teeth is a highly regulated extracellular event. In the skeleton, mineralization at the tissue level is controlled within the collagenous extracellular matrix by both circulating and local factors. While systemic regulation of mineral ion homeostasis has been well-studied over many decades, much less is known about the regulation of mineralization at the local level directly within the extracellular matrix. Some local regulators have been identified, such as tissue-nonspecific alkaline phosphatase (TNAP), phosphate-regulating endopeptidase homolog X-linked (PHEX), pyrophosphate, and osteopontin, and others are currently under investigation. Dysregulation of the actions of enzyme-inhibitor substrate pairs engaged in mineralization (as we describe by the Stenciling Principle for extracellular matrix mineralization) leads to osteomalacic "soft bone" diseases, such as hypophosphatasia (HPP) and X-linked hypophosphatemia (XLH). This review addresses how advances in 3D imaging tools and software now allow contextual and correlative viewing and interpretation of mineralized tissue structure across most length scales. Contextualized and integrated 3D multiscale data obtained from these imaging modalities have afforded an unprecedented structural biology view of bone from the macroscale to the nanoscale. Such correlated volume imaging data is highly quantitative, providing not only an integrated view of the skeleton in health, but also a means to observe alterations that occur in disease. In the context of the many hierarchical levels of skeletal organization, here we summarize structural features of bone over multiple length scales, with a focus on nano- and microscale features as viewed by X-ray and electron tomography imaging methods (submicron μCT and FIB-SEM). We additionally summarize structural changes observed after dysregulation of the mineralization pathway, focusing here on the Hyp mouse model for XLH. More specifically, we summarize how mineral patterns/packs at the microscale (3D crossfibrillar mineral tessellation), and how this is defective in Hyp mouse bone and Hyp enthesis fibrocartilage.

Acoustic Emission in Bone Biomechanics: A Comprehensive Review of Mechanical Properties and Predictive Damage Modeling

This review investigates the application of acoustic emission (AE) techniques in analyzing the mechanical properties and damage prediction of human bone. AE is a non-invasive and non-destructive evaluation method that captures the elastic waves released during microstructural deformations under stress, providing critical insights into bone behavior and failure mechanisms. By analyzing 57 studies, this review synthesizes findings on AE signal characteristics, experimental configurations, and their correlations with bone's mechanical parameters such as yield strength, elastic modulus, and micro-damage evolution. This article highlights AE's potential in early damage detection, differentiation of failure modes, and predictive modeling using stochastic and percolation theories. These models facilitate the prediction of fracture risk and mechanical failure without inducing irreversible damage. This review addresses the strengths and limitations of AE techniques and outlines future directions in biomechanical research.

Bone Regeneration: Mini-Review and Appealing Perspectives

Bone is a natural mineral-organic nanocomposite protecting internal organs and allowing mobility. Through the ages, numerous strategies have been developed for repairing bone defects and fixing fractures. Several generations of bone repair biomaterials have been proposed, either based on metals, ceramics, glasses, or polymers, depending on the clinical need, the maturity of technologies, and knowledge of the natural constitution of the bone tissue to be repaired. The global trend in bone implant research is shifting toward osteointegrative, bioactive and possibly stimuli-responsive biomaterials and, where possible, resorbable implants that actively promote the regeneration of natural bone tissue. In this mini-review, the fundamentals of bone healing materials and clinical challenges are summarized and commented on with regard to progressing scientific discoveries. The main types of bone-healing materials are then reviewed, and their specific relevance to the field is reminded, with the citation of reference works. In the final part, we highlight the promise of hybrid organic-inorganic bioactive materials and the ongoing research activities toward the development of multifunctional or stimuli-responsive implants. This contribution is expected to serve as a commented introduction to the ever-progressing field of bone regeneration and highlight trends of future-oriented research.

A Bio-Inspired Perspective on Materials Sustainability

The article explores materials sustainability through a bio-inspired lens and discusses paradigms that can reshape the understanding of material synthesis, processing, and usage. It addresses various technological fields, from structural engineering to healthcare, and emphasizes natural material cycles as a blueprint for efficient recycling and reuse. The study shows that material functionality depends on both chemical composition and structural modifications, which emphasizes the role of material processing. The article identifies strategies such as mono-materiality and multifunctionality, and explores how responsivity, adaptivity, modularity, and cellularity can simplify material assembly and disassembly. Bioinspired strategies for reusing materials, defect tolerance, maintenance, remodeling, and healing may extend product lifespans. The principles of circularity, longevity, and parsimony are reconsidered in the context of "active materiality", a dynamic bio-inspired paradigm. This concept expands the traditional focus of material science from structure-function relationships to include the development of materials capable of responding or adapting to external stimuli. Concrete examples demonstrate how bio-inspired strategies are being applied in engineering and technology to enhance the sustainability of materials. The article concludes by emphasizing interdisciplinary collaboration as a key factor for developing a sustainable and resilient materials economy in harmony with nature's material cycles.

Biomimetic Mineralized Collagen Scaffolds for Bone Tissue Engineering: Strategies on Elaborate Fabrication for Bioactivity Improvement

Biomimetic mineralized collagen (BMC) scaffolds represent an innovative class of bone-repair biomaterials inspired by the natural biomineralization process in bone tissue. Owing to their favorable biocompatibility and mechanical properties, BMC scaffolds have garnered significant attention in bone tissue engineering. However, most studies have overlooked the importance of bioactivity, resulting in collagen scaffolds with suboptimal osteogenic potential. In this review, the composition of the mineralized extracellular matrix (ECM) in bone tissue is discussed to provide guidance for biomimetic collagen mineralization. Subsequently, according to the detailed fabrication procedure of BMC scaffolds, the substances that can regulate both the fabrication process and biological activities is summarized. Furthermore, a potential strategy for developing BMC scaffolds with superior mechanical properties and biological activities for bone tissue engineering is proposed.

Nanostructured polymer composites for bone and tissue regeneration

Nanostructured polymer composites have gained significant attention in recent years for their remarkable potential in bone and tissue regeneration. Moreover, with the integration of 3D printing technology, these composites hold promise for use in personalized medicine, where patient-specific scaffolds can be tailored to enhance therapeutic outcomes. Therefore, this review article aims to provide a comprehensive overview of the latest advancements in the development and application of nanostructured polymeric composites within the field of tissue engineering and bone regeneration. Here, the potential of biopolymers, natural polymers, and 3D-printed polymers to craft biocompatible, non-toxic, and mechanically robust composites is discussed in brief. Further, the fabrication techniques for 3D scaffolds and various forms of nanocomposites, including nanoparticles, nanocapsules, nanofibers, nanogels, and micelles for bone and tissue regeneration, are listed. Also, particular emphasis is placed on the role of nano-scaffolds and in situ hydrogels in bone and tissue regeneration. Overall, this review provides a concise and authoritative summary of the current state-of-the-art in nanostructured polymer composites for regenerative medicine, highlighting future directions and potential clinical applications.

Cartilage and bone injectable hydrogels: A review of injectability methods and treatment strategies for repair in tissue engineering

Cartilage and bone are crucial tissues causing disability in the elderly population, often requiring prolonged treatment and surgical intervention due to limited regenerative capacity. Injectable hydrogels that closely mimic the extracellular matrix (ECM) of native hard tissue have attracted attention due to their minimally invasive application and ability to conform to irregular defect sites. These hydrogels facilitate key biological processes such as cell migration, chondrogenesis in cartilage repair, osteoinduction, angiogenesis, osteoconduction, and mineralization in bone repair. This review analyzes in-vitro and in-vivo biomedical databases over the past decade to identify advancements in hydrogel formulations, crosslinking mechanisms, and biomaterial selection for cartilage and bone tissue engineering. The review emphasizes the effectiveness of injectable hydrogels as carriers for cells, growth factors, and drugs, offering additional therapeutic benefits. The relevance of these findings is discussed in the context of their potential to serve as a robust alternative to current surgical and non-surgical treatments. This review also examines the advantages of injectable hydrogels, such as ease of administration, reduced patient recovery time, and enhanced bioactivity, thereby emphasizing their potential in clinical applications for cartilage and bone regeneration with emphasis on addressing the shortcomings of current treatments.

Correlative Raman spectroscopy and electron microscopy identifies glycogen rich deposits correlated with local structural defects in long bones of type IV osteogenesis imperfecta patients

Osteogenesis imperfecta (OI) is a genetic bone disease occurring in approximately 1 in 10,000 births, usually as a result of genetic mutation. OI patients suffer from increased fracture risk and - depending on the severity of the disease - deformation of the limbs, which can even lead to perinatal death. Despite extensive studies, the way in which the genetic mutation is translated into structural and compositional anomalies of the tissue is still an open question. Different observations have been reported, ranging from no structural (or chemical) differences to completely chaotic bone structure and composition. Here, we investigated bone samples from two adolescent OI-IV patients, focusing on the bone structure and chemistry in naturally occurring fractures. The exposed fracture plane allows the investigation of the structure and composition of the weakest bone plane. We do so by combining scanning electron microscopy (SEM) imaging with chemical information from Raman microscopy. The exposed fracture planes show different regions within the same tissue, displaying normal osteonal structures next to disorganized osteons and totally disordered structures, while the collagen mineralization in all cases is similar to that of a healthy bone. In addition, we also detected significant amounts of depositions of glycogen-rich, organic, globules of 250-1000 nm in size. These depositions point to a role of cellular disfunction in the disorganization of the collagen in qualitative OI. Overall, our results unite multiple, sometimes contradicting views from the literature on qualitative OI.

A review of the current status and future prospects of the bone remodeling process: Biological and mathematical perspectives

This review dives into the complex dynamics of bone remodeling, combining biological insights with mathematical perspectives to better understand this fundamental aspect of skeletal health. Bone, being a crucial part of our body, constantly renews itself, and with the growing number of individuals facing bone-related issues, research in this field is vital. In this review, we categorized and classified most common mathematical models used to simulate the mechanical behavior of bone under different loading and health conditions, shedding light on the evolving landscape of bone biology. While current models have effectively captured the essence of healthy bone remodeling, the ever-expanding knowledge in bone biology suggests an update in mathematical methods. Knowing the role of the skeleton in whole-body physiology, and looking at the recent discoveries about activities of bone cells emphasize the urgency of refining our mathematical descriptions of the bone remodeling process. The underexplored impact of bone diseases like osteoporosis, Paget's disease, or breast cancer on bone remodeling also points to the need for intensified research into diverse disease types and their unique effects on bone health. By reviewing a range of bone remodeling models, we show the necessity for tailor-made mathematical models to decipher their roots and enhance patient treatment strategies. Collaboration among scientists from various domains is pivotal to surmount these challenges, ensuring improved accuracy and applicability of mathematical models. Ultimately, this effort aims to deepen our understanding of bone remodeling processes and their broader implications for diverse health conditions.

Bone Marrow Stem Cell Population in Single- and Multiple-Level Aspiration

BACKGROUND

Bone marrow aspiration concentrate (BMAC) has garnered increasing interest due to its potential for healing musculoskeletal injuries. While the iliac crest remains a common harvest site, the aspiration technique's efficacy in offering the highest yield and prevalence of mesenchymal stem cells (MSCs) is controversial. This study aimed to compare two different techniques of bone marrow aspiration over the anterior iliac crest from a single level versus multiple levels.

METHODS

Anterior iliac crests were selected in seven adult patients (aged between 31 and 59 years old). Aspiration was achieved using an 11-gauge needle (length: 100 mm; diameter: 2.3 mm) specifically manufactured for bone marrow collection (BD, Becton, Franklin Lakes, NJ, USA) connected to a 10 mL syringe. On one side, 4cc of bone marrow was aspirated at a single level to a depth of 7 cm without changing the needle direction. On the other side, over the same portion of the iliac crest, 1 cc of bone marrow was obtained from multiple levels of different depths during needle retrieval, maintaining a distance of 1 cm and changing the tip direction. The samples were blindly sent to the laboratory without indicating whether they came from an single level or multiple levels. Fluorescence-activated cell sorting (FACS) and osteoblast differentiation were analyzed and compared.

RESULTS

In the FACS analysis, the single level resulted in a higher population of MSCs that were positive for CD105, CD73, and CD90 and negative for CD34, compared to the multiple-level method. In the process of osteoblast differentiation, it was observed that MSCs exhibited more advanced features of enhanced osteoblastic abilities in the single-level method rather than the multiple-level method.

CONCLUSIONS

A single-level aspiration technique at the anterior iliac crest may produce a high-quality bone marrow aspirate. This technique may help obtain specific populations of MSCs with the desired characteristics for use in regenerative therapies for musculoskeletal injuries.

Shape/properties collaborative intelligent manufacturing of artificial bone scaffold: structural design and additive manufacturing process

Artificial bone graft stands out for avoiding limited source of autograft as well as susceptibility to infection of allograft, which makes it a current research hotspot in the field of bone defect repair. However, traditional design and manufacturing method cannot fabricate bone scaffold that well mimics complicated bone-like shape with interconnected porous structure and multiple properties akin to human natural bone. Additive manufacturing, which can achieve implant's tailored external contour and controllable fabrication of internal microporous structure, is able to form almost any shape of designed bone scaffold via layer-by-layer process. As additive manufacturing is promising in building artificial bone scaffold, only combining excellent structural design with appropriate additive manufacturing process can produce bone scaffold with ideal biological and mechanical properties. In this article, we sum up and analyze state of art design and additive manufacturing methods for bone scaffold to realize shape/properties collaborative intelligent manufacturing. Scaffold design can be mainly classified into design based on unit cells and whole structure, while basic additive manufacturing and 3D bioprinting are the recommended suitable additive manufacturing methods for bone scaffold fabrication. The challenges and future perspectives in additive manufactured bone scaffold are also discussed.

Hydroxyapatite/Silk Fibroin Composite Scaffold with a Porous Structure and Mechanical Strength Similar to Cancellous Bone by Electric Field-Induced Gel Technology

Repair and regeneration of bone tissue defects is a multidimensional process that has been highly challenging to date. The artificial bone scaffold materials, which play a core role, still face the conflict that a biofriendly porous structure will reduce the mechanical performance and accelerate degradation. Herein, a multistage porous structured hydroxyapatite (HA)/silk fibroin (SF) composite scaffold (e-HA/SF) was successfully constructed by cleverly utilizing electric field-induced gel technology. The results indicated that the prepared e-HA/SF scaffolds possess biomimetic hierarchical porous structures with a suitable porosity similar to that of cancellous bone. The HA nanocrystals were uniformly encapsulated in the three-dimensional space of the composite scaffold, thus endowing the e-HA/SF composite scaffolds with an enhanced mechanical performance. Notably, the maximum compression stress and Young's modulus of e-HA/SF-2 scaffolds can reach 24.66 ± 0.88 and 28.91 ± 3.19 MPa, respectively, which are equivalent to those of cancellous bone. Such mechanical performance enhancement was previously unattainable through conventional freeze-drying strategies. Moreover, the introduction of bioactive nano-HA can trigger the optimal cell response in both static and dynamic cell culture experiments in vitro. The e-HA/SF composite scaffold developed in this study can better balance the conflict between the porous structure and mechanical and degradation properties of porous scaffolds.

Computed tomography technologies to measure key structural features of polymeric biomedical implants from bench to bedside

Implanted polymeric devices, designed to encourage tissue regeneration, require porosity. However, characterizing porosity, which affects many functional device properties, is non-trivial. Computed tomography (CT) is a quick, versatile, and non-destructive way to gain 3D structural information, yet various CT technologies, such as benchtop, preclinical and clinical systems, all have different capabilities. As system capabilities determine the structural information that can be obtained, seamless monitoring of key device features through all stages of clinical translation must be engineered intentionally. Therefore, in this study we tested feasibility of obtaining structural information in pre-clinical systems and high-resolution micro-CT (μCT) under physiological conditions. To overcome the low CT contrast of polymers in hydrated environments, radiopaque nanoparticle contrast agent was incorporated into porous devices. The size of resolved features in porous structures is highly dependent on the resolution (voxel size) of the scan. As the voxel size of the CT scan increased (lower resolution) from 5 to 50 μm, the measured pore size was overestimated, and percentage porosity was underestimated by nearly 50%. With the homogeneous introduction of nanoparticles, changes to device structure could be quantified in the hydrated state, including at high-resolution. Biopolymers had significant structural changes post-hydration, including a mean increase of 130% in pore wall thickness that could potentially impact biological response. By incorporating imaging capabilities into polymeric devices, CT can be a facile way to monitor devices from initial design stages through to clinical translation.

Evaluating the Anti-Osteoporotic Potential of Mediterranean Medicinal Plants: A Review of Current Evidence

Background: Bones are biological reservoirs for minerals and cells, offering protection to the other organs and contributing to the structural form of the body. Osteoporosis is a prevalent bone condition that significantly impacts people's quality of life. Treatments utilizing natural products and medicinal plants have gained important attention in the management of osteoporosis and its associated implications, such as osteoporotic fractures. Even though thousands of plants grow in the Mediterranean region, the use of medicinal plants as an alternative therapy for osteoporosis is still limited. Methods: This article provides a comprehensive overview of seven Mediterranean medicinal plants that are used in osteoporosis and osteoporotic fractures in in vitro, in vivo, and clinical trials. The mechanism of action of the medicinal plants and their bioactive compounds against diseases are also briefly discussed. Results: The findings clearly indicate the ability of the seven medicinal plants (Ammi majus, Brassica oleracea, Ceratonia siliqua L., Foeniculum vulgare, Glycyrrhiza glabra, Salvia officinalis, and Silybum marianum) as anti-osteoporosis agents. Xanthotoxin, polyphenols, liquiritin, formononetin, silymarin, and silibinin/silybin were the main bioactive compounds that contributed to the action against osteoporosis and osteoporotic fractures. Conclusions: In this review, the Mediterranean medicinal plants prove their ability as an alternative agent for osteoporosis and osteoporotic fractures instead of conventional synthetic therapies. Thus, this can encourage researchers to delve deeper into this field and develop medicinal-plant-based drugs.

Proanthocyanidins modification of the mineralized collagen scaffold based on synchronous self-assembly/mineralization for bone regeneration

Proteoglycans (PG) is crucial for regulating collagen formation and mineralization during bone tissue development. A wide variety of PG-modified collagen scaffolds have been proposed for bone engineering application to promote biological responses and work as artificial matrices that guide tissue regeneration. However, poor performance of theses biomaterials against infections has led to an unmet need for clinical prevention. Therefore, we utilized proanthocyanidins (PA) to simulate the functions of PG, including mediating the collagen assembly and intrafibrillar mineralization, to optimize scaffolds performance. The excellent antibacterial properties of PA can endow the scaffolds with anti-infection effects in the process of tissue regeneration. When PA was added during fibrillogenesis, the collagen fibrils appeared irregular aggregation and the mineralization degree was reduced. In contrast, the addition of PA after collagen self-assembly improved the latter's ability to act as a deposition template and remarkably promoted mineral ions infiltration, thus enhancing intrafibrillar mineralization. The PA-modified scaffold displayed a highly hydrophilicity behaviour and long-term resistance to degradation. The sustained release of PA effectively inhibited the activity of Staphylococcus aureus. The scaffold also showed excellent biocompatibility and improved bone regeneration in calvarial critical-size defect models. The application of PA enables a dual-function scaffold with favourable intrafibrillar mineralization and anti-bacterial properties for bone regeneration.

Bone hierarchical organization through the lens of materials science: Present opportunities and future challenges

Multiscale characterization is essential to better understand the hierarchical architecture of bone and an array of analytical methods contributes to exploring the various structural and compositional aspects. Incorporating X-ray tomography, X-ray scattering, vibrational spectroscopy, and atom probe tomography alongside electron microscopy provides a comprehensive approach, offering insights into the diverse levels of organization within bone. X-ray scattering techniques reveal information about collagen-mineral spatial relationships, while X-ray tomography captures 3D structural details, especially at the microscale. Electron microscopy, such as scanning and transmission electron microscopy, extends resolution to the nanoscale, showcasing intricate features such as collagen fibril organization. Additionally, atom probe tomography achieves sub-nanoscale resolution and high chemical sensitivity, enabling detailed examination of bone composition. Despite various technical challenges, a correlative approach allows for a comprehensive understanding of bone material properties. Real-time investigations through in situ and in operando approaches shed light on the dynamic processes in bone. Recently developed techniques such as liquid, in situ transmission electron microscopy provide insights into calcium phosphate formation and collagen mineralization. Mechanical models developed in the effort to link structure, composition, and function currently remain oversimplified but can be improved. In conclusion, correlative analytical platforms provide a holistic perspective of bone extracellular matrix and are essential for unraveling the intricate interplay between structure and composition within bone.

Multimodal analysis and comparison of stoichiometric and structural characteristics of parosteal and conventional osteosarcoma with massive sclerosis in human bone

Osteosarcoma (OS) is the most common malignant primary bone tumor in humans and occurs in various subtypes. Tumor formation happens through malignant osteoblasts producing immature bone. In the present paper we studied two different subtypes of osteosarcoma, from one individual with conventional OS with massive sclerosis and one individual with parosteal OS, based on a multimodal approach including small angle x-ray scattering (SAXS), wide angle x-ray diffraction (WAXS), backscattered electron imaging (BEI) and Raman spectroscopy. It was found that both tumors showed reduced mineral particle sizes and degree of orientation of the collagen-mineral composite in the affected areas, alongside with a decreased crystallinity. Distinct differences between the tumor material from the two individuals were found in the degree of mineralization. Further differences were observed in the carbonate to phosphate ratio, which is related to the degree of carbonate substitution in bone mineral and indicative of the turnover rate. The contraction of the c-axis of the bone mineral crystals proved to be a further, very sensitive parameter, potentially indicative of malignancy.

Biology of bone mineralization and ectopic calcifications: the same actors for different plays

Bone has several crucial functions. It is essential for locomotion and allows our body to stand erect against gravity. A mismatch between the mechanical stresses applied to it and its mechanical resistance leads to fractures. Bone also has numerous endocrine functions. It acts as a reservoir for minerals such as calcium and phosphorus, making it the target of calciotropic hormones that mobilize these minerals, particularly calcium, according to the body's needs. Additionally, bone secretes hormones, notably fibroblast growth factor 23 (FGF23), which regulates urinary excretion of phosphate and the bioavailability of active vitamin D. Bone mineralization is the process that facilitates the organized deposition of minerals in the bone matrix, providing rigidity and appropriate mechanical resistance. This process is compromised in genetically related bone mineralization disorders, such as those causing hypophosphatemia or hypophosphatasia. Conversely, calcification can be pathological, affecting soft tissues like the blood vessels, as seen in generalized arterial calcification of infancy (GACI) or arterial calcification due to CD73 deficiency (ACDC). The aim of this article is to first present the composition and structure of the mineralized bone matrix, to review the current understanding of the molecular mechanisms of mineralization, and finally to discuss the conditions associated with ectopic calcification and the underlying mechanisms.

Crossing length scales: X-ray approaches to studying the structure of biological materials

Biological materials have outstanding properties. With ease, challenging mechanical, optical or electrical properties are realised from comparatively `humble' building blocks. The key strategy to realise these properties is through extensive hierarchical structuring of the material from the millimetre to the nanometre scale in 3D. Though hierarchical structuring in biological materials has long been recognized, the 3D characterization of such structures remains a challenge. To understand the behaviour of materials, multimodal and multi-scale characterization approaches are needed. In this review, we outline current X-ray analysis approaches using the structures of bone and shells as examples. We show how recent advances have aided our understanding of hierarchical structures and their functions, and how these could be exploited for future research directions. We also discuss current roadblocks including radiation damage, data quantity and sample preparation, as well as strategies to address them.

Electrospun nanofibers: building blocks for the repair of bone tissue

Bone, one of the hardest structures of the body, is the basic constituent of the skeletal system, which gives the shape to the body, provides mechanical support for muscles and soft tissues, and provides movement. Even if there is no damage, bone remodeling is a permanent process to preserve and renew the structural, biochemical, and biomechanical integrity of bone tissue. Apart from the remodeling, bone healing is the highly complicated process of repairing deficiencies of bone tissue by the harmonious operation of osteoblasts, osteocytes, osteoclasts, and bone lining cells. Various materials can be used to both trigger the bone healing process and to provide mechanical support to damaged bone. Nanofiber scaffolds are at the forefront of these types of systems because of their extremely large surface area-to-volume ratio, small pore size, and high porosity. Nanofibers are known to be highly functional systems with the ability to mimic the structure and function of the natural bone matrix, facilitating osteogenesis for cell proliferation and bone regeneration. Electrospinning is an easy and fast method to produce non-woven structures consisting of continuous ultrafine fibers with diameters ranging from micrometers down to nanometers. The simplicity and cost-effectiveness of the electrospinning technique, its ability to use a wide variety of synthetic, natural, and mixed polymers, and the formation of highly porous and continuous fibers are the remarkable features of this method. The importance of nanofiber-based scaffolds in bone tissue regeneration is increasing because of suitable pore size, high porosity, osteoinduction, induction of bone growth with osteoconduction, adaptability to the target area, biodegradation, and appropriate mechanical properties, which are among the main parameters that are important in the design of polymeric bone grafts. The aim of this review is to cast light on the increasing use of nanofiber-based scaffolds in bone tissue regeneration and give an insight about bone regeneration, production techniques of the electrospun nanofibers, and varying formulation parameters in order to reach different drug delivery goals. This review also provides an extensive market research of electrospun nanofibers and an overview on scientific research and patents in the field.

Curved mineral platelets in bone

Bone is a composite material principally made up of a mineral phase (apatite) and collagen fibrils. The mineral component of bone occurs in the form of polycrystalline platelets 2-6 nm in thickness. These platelets are packed and probably glued together in stacks of two or more, ranging up to >30 platelets. Here we show that most of these stacks are curved flat sheets whose cylindrical axes are oriented parallel to the long axes of collagen fibrils. Consequently, the curvature of the platelets is not detectable in TEM sections cut parallel to the collagen fibril axes. The radius of curvature around these axes ranges from about 25 nm (the average radius of the collagen fibrils) to 100's of nm. The shapes of these curved forms contribute to the compressive strength of bone. STATEMENT OF SIGNIFICANCE: Bone, the material of which bones are made, is mainly composed of a protein, collagen, and the mineral apatite (calcium phosphate). The crystals have long been known to be flat plates about 5 nanometers (nm) thick. Here we show that the crystals are bound together in curved platelets with a radius of curvature between 25 and several hundred nm, which weave between fibrils of collagen. Some platelets wrap tightly around fibrils. The platelets form stacks of from two to up to 30. The crystals in the platelets are all oriented parallel to the cylindrical fibrils even though most crystals are not in contact with collagen. These curved structures provide greater strength to bone.

Mesoscale characterization of osseointegration around an additively manufactured genistein-coated implant

Given the hierarchical nature of bone and bone interfaces, osseointegration, namely the formation of a direct bone-implant contact, is best evaluated using a multiscale approach. However, a trade-off exists between field of view and spatial resolution, making it challenging to image large volumes with high resolution. In this study, we combine established electron microscopy techniques to probe bone-implant interfaces at the microscale and nanoscale with plasma focused ion beam-scanning electron microscopy (PFIB-SEM) tomography to evaluate osseointegration at the mesoscale. This characterization workflow is demonstrated for bone response to an additively manufactured Ti-6Al-4V implant which combines engineered porosity to facilitate bone ingrowth and surface functionalization via genistein, a phytoestrogen, to counteract bone loss in osteoporosis. SEM demonstrated new bone formation at the implant site, including in the internal implant pores. At the nanoscale, scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy confirmed the gradual nature of the bone-implant interface. By leveraging mesoscale analysis with PFIB-SEM tomography that captures large volumes of bone-implant interface with nearly nanoscale resolution, the presence of mineral ellipsoids varying in size and orientation was revealed. In addition, a well-developed lacuno-canalicular network and mineralization fronts directed both towards the implant and away from it were highlighted.

DNA preservation in compact and trabecular bone

Significant variation exists in the molecular structure of compact and trabecular bone. In compact bone full dissolution of the bone powder is required to efficiently release the DNA from hydroxyapatite. In trabecular bone where soft tissues are preserved, we assume that full dissolution of the bone powder is not required to release the DNA from collagen. To investigate this issue, research was performed on 45 Second World War diaphysis (compact bone)-epiphysis (trabecular bone) femur pairs, each processed with a full dissolution (FD) and partial dissolution (PD) extraction method. DNA quality and quantity were assessed using qPCR PowerQuant analyses, and autosomal STRs were typed to confirm the authenticity of isolated DNA. Our results support different mechanisms of DNA preservation in compact and trabecular bone because FD method was more efficient than PD method only in compact bone, and no difference in DNA yield was observed in trabecular bone, showing no need for full dissolution of the bone powder when trabecular bone tissue is processed. In addition, a significant difference in DNA yield was observed between compact and trabecular bone when PD was applied, with more DNA extracted from trabecular bone than compact bone. High suitability of trabecular bone processed with PD method is also supported by the similar quantities of DNA isolated by FD method when applied to both compact and trabecular bone. Additionally similar quantities of DNA were isolated when compact bone was extracted with FD method and trabecular bone was extracted with PD method. Processing trabecular bone with PD method in routine identification of skeletonized human remains shortens the extraction procedure and simplifies the grinding process.

A Wood-Derived Periosteum for Spatiotemporal Drug Release: Boosting Bone Repair through Anisotropic Structure and Multiple Functions

Existing artificial periostea face many challenges, including difficult-to-replicate anisotropy in mechanics and structure, poor tissue adhesion, and neglected synergistic angiogenesis and osteogenesis. Here, inspired by natural wood (NW), a wood-derived elastic artificial periosteum is developed to mimic the structure and functions of natural periosteum, which combines an elastic wood (EW) skeleton, a polydopamine (PDA) binder layer, and layer-by-layer (LBL) biofunctional layers. Specifically, EW derived from NW is utilized as the anisotropic skeleton of artificial periosteum to guide cell directional behaviors, moreover, it also shows a similar elastic modulus and flexibility to natural periosteum. To further enhance its synergistic angiogenesis and osteogenesis, surface LBL biofunctional layers are designed to serve as spatiotemporal release platforms to achieve sequential and long-term release of pamidronate disodium (PDS) and deferoxamine (DFO), which are pre-encapsulated in chitosan (CS) and hyaluronic acid (HA) solutions, respectively. Furthermore, the combined effect of PDA coating and LBL biofunctional layers enables the periosteum to tightly adhere to damaged bone tissue. More importantly, this novel artificial periosteum can boost angiogenesis and bone formation in vitro and in vivo. This study opens up a new path for biomimetic design of artificial periosteum, and provides a feasible clinical strategy for bone repair.

Construction of multileveled and oriented micro/nano channels in Mg doped hydroxyapitite bioceramics and their effect on mimicking mechanical property of cortical bone and biological performance of cancellous bone

Drawing on the structure and components of natural bone, this study developed Mg-doped hydroxyapatite (Mg-HA) bioceramics, characterized by multileveled and oriented micro/nano channels. These channels play a critical role in ensuring both mechanical and biological properties, making bioceramics suitable for various bone defects, particularly those bearing loads. Bioceramics feature uniformly distributed nanogrooves along the microchannels. The compressive strength or fracture toughness of the Mg-HA bioceramics with micro/nano channels formed by single carbon nanotube/carbon fiber (CNT/CF) (Mg-HA(05-CNT/CF)) are comparable to those of cortical bone, attributed to a combination of strengthened compact walls and microchannels, along with a toughening mechanism involving crack pinning and deflection at nanogroove intersections. The introduction of uniform nanogrooves also enhanced the porosity by 35.4 %, while maintaining high permeability owing to the capillary action in the oriented channels. This leads to superior degradation properties, protein adsorption, and in vivo osteogenesis compared with bioceramics with only microchannels. Mg-HA(05-CNT/CF) exhibited not only high strength and toughness comparable to cortical bone, but also permeability similar to cancellous bone, enhanced cell activity, and excellent osteogenic properties. This study presents a novel approach to address the global challenge of applying HA-based bioceramics to load-bearing bone defects, potentially revolutionizing their application in tissue engineering.

Multimodal 2D and 3D microscopic mapping of growth cartilage by computational imaging techniques - a short review including new research

Being able to image the microstructure of growth cartilage is important for understanding the onset and progression of diseases such as osteochondrosis and osteoarthritis, as well as for developing new treatments and implants. Studies of cartilage using conventional optical brightfield microscopy rely heavily on histological staining, where the added chemicals provide tissue-specific colours. Other microscopy contrast mechanisms include polarization, phase- and scattering contrast, enabling non-stained or 'label-free' imaging that significantly simplifies the sample preparation, thereby also reducing the risk of artefacts. Traditional high-performance microscopes tend to be both bulky and expensive.Computational imagingdenotes a range of techniques where computers with dedicated algorithms are used as an integral part of the image formation process. Computational imaging offers many advantages like 3D measurements, aberration correction and quantitative phase contrast, often combined with comparably cheap and compact hardware. X-ray microscopy is also progressing rapidly, in certain ways trailing the development of optical microscopy. In this study, we first briefly review the structures of growth cartilage and relevant microscopy characterization techniques, with an emphasis on Fourier ptychographic microscopy (FPM) and advanced x-ray microscopies. We next demonstrate with our own results computational imaging through FPM and compare the images with hematoxylin eosin and saffron (HES)-stained histology. Zernike phase contrast, and the nonlinear optical microscopy techniques of second harmonic generation (SHG) and two-photon excitation fluorescence (TPEF) are explored. Furthermore, X-ray attenuation-, phase- and diffraction-contrast computed tomography (CT) images of the very same sample are presented for comparisons. Future perspectives on the links to artificial intelligence, dynamic studies andin vivopossibilities conclude the article.

The Synergetic Effect of 3D Printing and Electrospinning Techniques in the Fabrication of Bone Scaffolds

The primary goal of bone tissue engineering is to restore and rejuvenate bone defects by using a suitable three-dimensional scaffold, appropriate cells, and growth hormones. Various scaffolding methods are used to fabricate three-dimensional scaffolds, which provide the necessary environment for cell activity and bone formation. Multiple materials may be used to create scaffolds with hierarchical structures that are optimal for cell growth and specialization. This study examines a notion for creating an optimal framework for bone regeneration using a combination of the robocasting method and the electrospinning approach. Research indicates that the integration of these two procedures enhances the benefits of each method and provides a rationale for addressing their shortcomings via this combination. The hybrid approach is anticipated to provide a manufactured scaffold that can effectively replace bone defects while possessing the necessary qualities for bone regeneration.

Cell-induced collagen alignment in a 3D in vitro culture during extracellular matrix production

The bone extracellular matrix consists of a highly organized collagen matrix that is mineralized with carbonated hydroxyapatite. Even though the structure and composition of bone have been studied extensively, the mechanisms underlying collagen matrix organization remain elusive. In this study, we used a 3D cell culture system in which osteogenic cells deposit and orient the collagen matrix that is subsequently mineralized. Using live fluorescence imaging combined with volume electron microscopy, we visualize the organization of the cells and collagen in the cell culture. We show that the osteogenically induced cells are organizing the collagen matrix during development. Based on the observation of tunnel-like structures surrounded by aligned collagen in the center of the culture, we propose that osteoblasts organize the deposited collagen during migration through the culture. Overall, we show that cell-matrix interactions are involved in collagen alignment during early-stage osteogenic differentiation and that the matrix is organized by the osteoblasts in the absence of osteoclast activity.

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.

Hierarchical Scaffold with Directional Microchannels Promotes Cell Ingrowth for Bone Regeneration

Bone regenerative scaffolds with a bionic natural bone hierarchical porous structure provide a suitable microenvironment for cell migration and proliferation. Here, a bionic scaffold (DP-PLGA/HAp) with directional microchannels is prepared by combining 3D printing and directional freezing technology. The 3D printed framework provides structural support for new bone tissue growth, while the directional pore embedded in the scaffolds provides an express lane for cell migration and nutrition transport, facilitating cell growth and differentiation. The hierarchical porous scaffolds achieve rapid infiltration and adhesion of bone marrow mesenchymal stem cells (BMSCs) and improve the expression of osteogenesis-related genes. The rabbit cranial defect experiment presents significant new bone formation, demonstrating that DP-PLGA/HAp offers an effective means to guide cranial bone regeneration. The combination of 3D printing and directional freezing technology might be a promising strategy for developing bone regenerative biomaterials.

Establishment and validation of an efficient method for the 3D culture of osteoclasts in vitro

INTRODUCTION

Osteoclasts (OCs) play a crucial role in maintaining bone health. Changes in OC activity are linked to different bone diseases, making them an intriguing focus for research. However, most studies on OCs have relied on 2D cultures, limiting our understanding of their behavior. Yet, there's a lack of knowledge regarding platforms that effectively support osteoclast formation in 3D cultures.

METHODS

In our investigation, we explored the capacity of collagen and GelMA hydrogels to facilitate osteoclast development in 3D culture settings. We assessed the osteoclast development by using different hydrogels and cell seeding strategies and optimizing cell seeding density and cytokine concentration. The osteoclast development in 3D cultures was further validated by biochemical assays and immunochemical staining.

RESULTS

Our findings revealed that 0.3 % (w/v) collagen was conducive to osteoclast formation in both 2D and 3D cultures, demonstrated by increased multinucleation and higher TRAP activity compared to 0.6 % collagen and 5 % to 10 % (w/v) GelMA hydrogels. Additionally, we devised a "sandwich" technique using collagen substrates and augmented the initial macrophage seeding density and doubling cytokine concentrations, significantly enhancing the efficiency of OC culture in 3D conditions. Notably, we validated osteoclasts derived from macrophages in our 3D cultures express key osteoclast markers like cathepsin K and TRAP.

CONCLUSIONS

To conclude, our study contributes to establishing an effective method for cultivating osteoclasts in 3D environments in vitro. This innovative approach not only promises a more physiologically relevant platform to study osteoclast behavior during bone remodeling but also holds potential for applications in bone tissue engineering.

CLINICAL SIGNIFICANCE

This study introduces an efficient method for cultivating osteoclasts in 3D environments in vitro. It offers a more physiologically relevant platform to investigate osteoclast behavior and holds promise to advance research in bone biology and regenerative dentistry.

A submicron forest-like silicon surface promotes bone regeneration by regulating macrophage polarization

Introduction: Silicon is a major trace element in humans and a prospective supporting biomaterial to bone regeneration. Submicron silicon pillars, as a representative surface topography of silicon-based biomaterials, can regulate macrophage and osteoblastic cell responses. However, the design of submicron silicon pillars for promoting bone regeneration still needs to be optimized. In this study, we proposed a submicron forest-like (Fore) silicon surface (Fore) based on photoetching. The smooth (Smo) silicon surface and photoetched regular (Regu) silicon pillar surface were used for comparison in the bone regeneration evaluation. Methods: Surface parameters were investigated using a field emission scanning electron microscope, atomic force microscope, and contact angle instrument. The regulatory effect of macrophage polarization and succedent osteogenesis was studied using Raw264.7, MC3T3-E1, and rBMSCs. Finally, a mouse calvarial defect model was used for evaluating the promoting effect of bone regeneration on the three surfaces. Results: The results showed that the Fore surface can increase the expression of M2-polarized markers (CD163 and CD206) and decrease the expression of inflammatory cytokines, including interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α). Fore surface can promote the osteogenesis in MC3T3-E1 cells and osteoblastic differentiation of rBMSCs. Furthermore, the volume fraction of new bone and the thickness of trabeculae on the Fore surface were significantly increased, and the expression of RANKL was downregulated. In summary, the upregulation of macrophage M2 polarization on the Fore surface contributed to enhanced osteogenesis in vitro and accelerated bone regeneration in vivo. Discussion: This study strengthens our understanding of the topographic design for developing future silicon-based biomaterials.