Effects of hydroxyapatite surface nano/micro-structure on osteoclast formation and activity

Calcium Phosphate Apatite Filament Co-Wrapped With Perforated Electrospun Sheet of Phosphorylated Chitosan-A Bioinspired Approach Toward Bone Graft Substitute

Bioinspired bone graft substitutes hold incredible opportunities in tissue engineering, potentiating the healing aspect. Here we have fabricated stacks of glutaraldehyde-genipin crosslinked, microporous nanofibrous N-methyl phosphonic chitosan sheets (NMPC) with impregnated eggshell-derived CaP fibers to mimic osteonal architecture. This composite 3D rolled eggshell-derived calcium phosphate (ESCAP) scaffold (RCS), with density and modulus variation from the center to the periphery, has superior mechanical strength. The zwitterionic nature of NMPC, following the surface modulus of the CaP fibers, upgraded the biological performance. The low modulus of the flexible micro-perforated nanofibrous sheet increases along the ceramic phase, which prompts migration and distribution of proliferated MSCs from the outer polymeric surface to the inner ceramic region through micro-perforations. This movement stimulates endochondral ossification, observed by a gradual increment of collagen II expression alongside a decrement of collagen I expression. In vivo assessment of rabbit tibia bone defects revealed prominent healing in the presence of a scaffold by Day 60, accompanied by scaffold resorption. The cellular activity during healing revealed osteoblasts, osteocytes, blood vessels, and chondroblast cells at the boundary of the scaffolds, indicating neotissue and hypertrophic cartilage formation. Thus, the RCS bone grafts promote faster bone healing by osteogenesis and bone remodeling.

Extraction and Characterization of Aceh Bovine Bone-Derived Hydroxyapatite for Applications in Dentistry

OBJECTIVE

 Bone grafts derived from natural hydroxyapatite (HA) are increasingly being explored because they are more economical in terms of production costs compared with commercial HA. HA can be obtained from local cattle slaughter waste in Aceh, Indonesia, which has not been widely studied for its potential for dental applications. This study examines the synthesis and characterization of bovine HA (BHA) derived from Aceh cattle femur through calcination for applications in dentistry.

MATERIALS AND METHODS

 This research began with the cleaning of fresh bones by boiling and soaking them in acetone for 2 hours before 3-hour calcination at varying temperatures. The BHA samples were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction, scanning electron microscopy with energy dispersive X-ray (SEM-EDX), and particle size analyzer (PSA).

STATISTICAL ANALYSIS

 Data were analyzed using SPSS with a one-way analysis of variance to assess the impact of calcination temperature on the yield and particle size of BHA.

RESULTS

 BHA obtained from calcination at 900°C and 1,000°C showed the highest crystallinity, with values above 84%, and uniform particle distribution. PSA and SEM analysis showed that BHA particles were spherical in submicron size, which became smaller and more uniform but agglomeration did not occur significantly between each increase in calcination temperature. FTIR analysis showed the presence of phosphate, carbonate, and hydroxyl functional groups. Elemental composition analysis using EDX confirmed that essential elements such as calcium and phosphorus were distributed consistently at all temperatures with a Ca/P ratio of 1.7 to 2.3.

DISCUSSION

 Based on the characteristics of crystallinity, particle size, and chemical composition of the obtained BHA, it is considered optimal for bioactivity, which allows stimulation of new bone tissue formation and promotes osseointegration while balancing structural stability. This makes BHA derived from Aceh cattle bones a suitable bone filler candidate for treating alveolar bone defects in hard tissue regeneration. These findings highlight the potential use of cattle bone waste as a sustainable source of HA in dental applications.

CONCLUSION

 These findings suggest that Aceh bovine bones are a viable source for producing quality BHA, potentially contributing to more sustainable and ecofriendly biomaterials for dental applications.

Crystallographic plane-induced selective mineralization of nanohydroxyapatite on fibrous-grained titanium promotes osteointegration and biocorrosion resistance

The (002) crystallographic plane-oriented hydroxyapatite (HA) and anatase TiO2 enable favorable hydrophilicity, osteogenesis, and biocorrosion resistance. Thus, the crystallographic plane control in HA coating and crystalline phase control in TiO2 is vital to affect the surface and interface bioactivity and biocorrosion resistance of titanium (Ti) implants. However, a corresponding facile and efficient fabrication method is absent to realize the HA(002) mineralization and anatase TiO2 formation on Ti. Herein, we utilized the predominant Ti(0002) plane of the fibrous-grained titanium (FG Ti) to naturally form anatase TiO2 and further achieve a (002) basal plane oriented nanoHA (nHA) film through an in situ mild hydrothermal growth strategy. The formed FG Ti-nHA(002) remarkably improved hydrophilicity, mineralization, and biocorrosion resistance. Moreover, the nHA(002) film reserved the microgroove-like topological structure on FG Ti. It could enhance osteogenic differentiation through promoted contact guidance, showing one order of magnitude higher expression of osteogenic-related genes. On the other hand, the nHA(002) film restrained the osteoclast activity by blocking actin ring formation. Based on these capacities, FG Ti-nHA(002) improved new bone growth and binding strength in rabbit femur implantation, achieving satisfactory osseointegration within 2 weeks.

Comparative study of bovine and synthetic hydroxyapatite in micro- and nanosized on osteoblasts action and bone growth

Hydroxyapatite (HA) is widely used as a bone graft. However, information on the head-to-head osteoinductivity and in vivo performance of micro- and nanosized natural and synthetic HA is still lacking. Here, we fabricated nanosized bovine HA (nanoBHA) by using a wet ball milling method and compared its in vitro and in vivo performance with microsized BHA, nanosized synthetic HA (nanoHA), and microsized synthetic HA (HA). The results showed that the wet ball milling method successfully reduced the particle size of BHA to 40 nm without changing its natural characteristics. NanoBHA was able to maintain cell viability and induce cell proliferation and calcium deposits. NanoBHA promoted osteogenic differentiation via OPN as a specific regulator, with a 13-fold greater expression level. NanoBHA and HA also activated ERK1/2 indicated corresponding to the proliferation-differentiation and death of cells, respectively. The calvarial bone defect model showed that nanoBHA induced bone growth based on CT images, which is in line with the histological results showing the presence of bone cells and connective tissue at the nanoBHA implantation site. In conclusion, natural HA outperformed synthetic HA. Our findings will attract interest in further research into nanomaterials and their mechanism of action in bone remodeling.

Biomaterial Cues for Regulation of Osteoclast Differentiation and Function in Bone Regeneration

Tissue regeneration involves dynamic dialogue between and among different cells and their surrounding matrices. Bone regeneration is specifically governed by reciprocity between osteoblasts and osteoclasts within the bone microenvironment. Osteoclast-directed resorption and osteoblast-directed formation of bone are essential to bone remodeling, and the crosstalk between these cells is vital to curating a sequence of events that culminate in the creation of bone tissue. Among bone biomaterial strategies, many have investigated the use of different material cues to direct the development and activity of osteoblasts. However, less attention has been given to exploring features that similarly target osteoclast formation and activity, with even fewer strategies demonstrating or integrating biomaterial-directed modulation of osteoblast-osteoclast coupling. This review aims to describe various biomaterial cues demonstrated to influence osteoclastogenesis and osteoclast function, emphasizing those that enhance a material construct's ability to achieve bone healing and regeneration. Additionally discussed are approaches that influence the communication between osteoclasts and osteoblasts, particularly in a manner that takes advantage of their coupling. Deepening our understanding of how biomaterial cues may dictate osteoclast differentiation, function, and influence on the microenvironment may enable the realization of bone-replacement interventions with enhanced integrative and regenerative capacities.

In Vitro Osteo-Immunological Responses of Bioactive Calcium Phosphate-Containing Urethane Dimethacrylate-Based Composites: A Potential Alternative to Poly(methyl methacrylate) Bone Cement

This investigation developed new composite bone cements using urethane dimethacrylate (UDMA), poly(propylene glycol) dimethacrylate (PPGDMA), and hydroxyethyl methacrylate (HEMA), with micrometer-sized aluminosilicate glass filler. Monocalcium phosphate monohydrate (MCPM) and hydroxyapatite (HA) particles were added to enhance biological performance, particularly osteo-immunomodulation. Free radical polymerization was triggered by mixing two pastes containing either benzoyl peroxide (BPO, an initiator) or N-tolyglycine glycidyl methacrylate (NTGGMA, an activator). Increasing butylated hydroxytoluene (BHT, an inhibitor) enabled a suitable delay after mixing at 25 °C for placement. At 37 °C, the delay time was reduced and the final conversion was enhanced. Findings also demonstrated the biocompatibility of the developed bone cement toward osteo-immunological cell lineages, including mesenchymal stem cells (MSCs), fibroblasts, osteoclast precursor RAW 246.7 cells, and peripheral blood mononuclear cells (PBMCs). Notably, the cement with both MCPM and HA combined facilitated sufficient MSC growth, enabling subsequent mineralization while concurrently suppressing the proliferation of fibroblasts, osteoclast progenitors, and PBMCs. Furthermore, composite cement exhibited the capacity to differentially regulate osteoblast differentiation, cell-(in)dependent mineralization, osteoclastogenesis, and PBMC-mediated inflammatory responses at both cellular and molecular levels in vitro. These observations suggested their potential use for bone repair, especially in cases of inflammation-associated bone defects.

Antimicrobial peptide GL13K-Modified titanium in the epigenetic regulation of osteoclast differentiation via H3K27me3

Implant surface designs have advanced to address challenges in oral rehabilitation for healthy and compromised bone. Several studies have analyzed the effects of altering material surfaces on osteogenic differentiation. However, the crucial role of osteoclasts in osseointegration has often been overlooked. Overactive osteoclasts can compromise implant stability. In this study, we employed a silanization method to alter pure titanium to produce a surface loaded with the antimicrobial peptide GL13K that enhanced biocompatibility. Pure titanium (Ti), silanization-modified titanium, and GL13K-modified titanium (GL13K-Ti) were co-cultured with macrophages. Our findings indicated that GL13K-Ti partially inhibited osteoclastogenesis and expression of osteoclast-related genes and proteins by limiting the formation of the actin ring, an important structure for osteoclast bone resorption. Our subsequent experiments confirmed the epigenetic role in regulating this process. GL13K-Ti was found to impact the degree of methylation modifications of H3K27 in the NFATc1 promoter region following RANKL-induced osteoclastic differentiation. In conclusion, our study unveils the potential mechanism of methylation modifications, a type of epigenetic regulatory modality, on osteoclastogenesis and activity on the surface of a material. This presents novel concepts and ideas for further broadening the clinical indications of oral implants and targeting the design of implant surfaces.

In vitro evaluation of bone cell response to novel 3D-printable nanocomposite biomaterials for bone reconstruction

Critically-sized segmental bone defects represent significant challenges requiring grafts for reconstruction. 3D-printed synthetic bone grafts are viable alternatives to structural allografts if engineered to provide appropriate mechanical performance and osteoblast/osteoclast cell responses. Novel 3D-printable nanocomposites containing acrylated epoxidized soybean oil (AESO) or methacrylated AESO (mAESO), polyethylene glycol diacrylate, and nanohydroxyapatite (nHA) were produced using masked stereolithography. The effects of volume fraction of nHA and methacrylation of AESO on interactions of differentiated MC3T3-E1 osteoblast (dMC3T3-OB) and differentiated RAW264.7 osteoclast cells with 3D-printed nanocomposites were evaluated in vitro and compared with a control biomaterial, hydroxyapatite (HA). Higher nHA content and methacrylation significantly improved the mechanical properties. All nanocomposites supported dMC3T3-OB cells' adhesion and proliferation. Higher amounts of nHA enhanced cell adhesion and proliferation. mAESO in the nanocomposites resulted in greater adhesion, proliferation, and activity at day 7 compared with AESO nanocomposites. Excellent osteoclast-like cells survival, defined actin rings, and large multinucleated cells were only observed on the high nHA fraction (30%) mAESO nanocomposite and the HA control. Thus, mAESO-based nanocomposites containing higher amounts of nHA have better interactions with osteoblast-like and osteoclast-like cells, comparable with HA controls, making them a potential future alternative graft material for bone defect repair.

Antitumoral-Embedded Biopolymeric Spheres for Implantable Devices

The bioactive surface modification of implantable devices paves the way towards the personalized healthcare practice by providing a versatile and tunable approach that increase the patient outcome, facilitate the medical procedure, and reduce the indirect or secondary effects. The purpose of our study was to assess the performance of composite coatings based on biopolymeric spheres of poly(lactide-co-glycolide) embedded with hydroxyapatite (HA) and methotrexate (MTX). Bio-simulated tests performed for up to one week evidenced the gradual release of the antitumor drug and the biomineralization potential of PLGA/HA-MTX sphere coatings. The composite materials proved superior biocompatibility and promoted enhanced cell adhesion and proliferation with respect to human preosteoblast and osteosarcoma cell lines when compared to pristine titanium.

Preparation of an injectable and photocurable carboxymethyl cellulose/hydroxyapatite composite and its application in cranial regeneration

Limited bone regeneration, uncontrollable degradation rate, mismatched defect zone and poor operability have plagued the reconstruction of irregular bone defect by tissue-engineered materials. A combination of biomimetic scaffolds with hydroxyapatite has gained great popularity in promoting bone regeneration. Therefore, we designed an injectable, photocurable and in-situ curing hydrogel by methacrylic anhydride -modified carboxymethyl cellulose (CMC-MA) loading with spherical hydroxyapatite (HA) to highly simulate the natural bony matrix and match any shape of damaged tissue. The prepared carboxymethyl cellulose-methacrylate/ hydroxyapatite(CMC-MA/HA) composite presented good rheological behavior, swelling ratio and mechanical property under light illumination. Meanwhile, this composite hydrogel promoted effectively proliferation, supported adhesion and upregulated the osteogenic-related genes expression of MC3T3-E1 cells in vitro, as well as the activity of the osteogenic critical protein, Integrin α1, β1, Myosin 9, Myosin 10, BMP-2 and Smad 1 in Integrin/BMP-2 signal pathway. Together, the composite hydrogels realized promotion of bone regeneration, deformity improvement, and the enhanced new bone strength in skull defect. It also displayed a good histocompatibility and stability of subcutaneous implantation in vivo. Overall, this study laid the groundwork for future research into developing a novel biomaterial and a minimally invasive therapeutic strategies for reconstructing bone defects and contour deficiencies.

Electroactive Biomaterials Regulate the Electrophysiological Microenvironment to Promote Bone and Cartilage Tissue Regeneration

The incidence of large bone and articular cartilage defects caused by traumatic injury is increasing worldwide; the tissue regeneration process for these injuries is lengthy due to limited self‐healing ability. Endogenous bioelectrical phenomenon has been well recognized to play an important role in bone and cartilage homeostasis and regeneration. Studies have reported that electrical stimulation (ES) can effectively regulate various biological processes and holds promise as an external intervention to enhance the synthesis of the extracellular matrix, thereby accelerating the process of bone and cartilage regeneration. Hence, electroactive biomaterials have been considered a biomimetic approach to ensure functional recovery by integrating various physiological signals, including electrical, biochemical, and mechanical signals. This review will discuss the role of endogenous bioelectricity in bone and cartilage tissue, as well as the effects of ES on cellular behaviors. Then, recent advances in electroactive materials and their applications in bone and cartilage tissue regeneration are systematically overviewed, with a focus on their advantages and disadvantages as tissue repair materials and performances in the modulation of cell fate. Finally, the significance of mimicking the electrophysiological microenvironment of target tissue is emphasized and future development challenges of electroactive biomaterials for bone and cartilage repair strategies are proposed.

Three-Dimensional-Printed Spherical Hollow Structural Scaffolds for Guiding Critical-Sized Bone Regeneration

The treatment of bone tissue defects continues to be a complex medical issue. Recently, three-dimensional (3D)-printed scaffold technology for bone tissue engineering (BTE) has emerged as an important therapeutic approach for bone defect repair. Despite the potential of BTE scaffolds to contribute to long-term bone reconstruction, there are certain challenges associated with it including the impediment of bone growth within the scaffolds and vascular infiltration. These difficulties can be resolved by using scaffold structural modification strategies that can effectively guide bone regeneration. This study involved the preparation of biphasic calcium phosphate spherical hollow structural scaffolds (SHSS) with varying pore sizes using 3D printing (photopolymerized via digital light processing). The chemical compositions, microscopic morphologies, mechanical properties, biocompatibilities, osteogenic properties, and impact on repairing critical-sized bone defects of SHSS were assessed through characterization analyses, in vitro cytological assays, and in vivo biological experiments. The results revealed the biomimetic properties of SHSS and their favorable biocompatibility. The scaffolds stimulated cell adhesion, proliferation, differentiation, and migration and facilitated the expression of osteogenic genes and proteins, including Col-1, OCN, and OPN. Furthermore, they could effectively repair a critical-sized bone defect in a rabbit femoral condyle by establishing an osteogenic platform and guiding bone regeneration in the defect region. This innovative strategy presents a novel therapeutic approach for assessing critical-sized bone defects.

Nano-hydroxyapatite structures for bone regenerative medicine: Cell-material interaction

Bone tissue engineering holds great promise for the regeneration of damaged or severe bone defects. However, several challenges hinder its translation into clinical practice. To address these challenges, interdisciplinary efforts and advances in biomaterials, cell biology, and bioengineering are required. In recent years, nano-hydroxyapatite (nHA)-based scaffolds have emerged as a promising approach for the development of bone regenerative agents. The unique similarity of nHA with minerals found in natural bones promotes remineralization and stimulates bone growth, which are crucial factors for efficient bone regeneration. Moreover, nHA exhibits desirable properties, such as strong chemical interactions with bone and facilitation of tissue growth, without inducing inflammation or toxicity. It also promotes osteoblast survival, adhesion, and proliferation, as well as increasing alkaline phosphatase activity, osteogenic differentiation, and bone-specific gene expression. However, it is important to note that the effect of nHA on osteoblast behavior is dose-dependent, with cytotoxic effects observed at higher doses. Additionally, the particle size of nHA plays a crucial role, with smaller particles having a more significant impact. Therefore, in this review, we highlighted the potential of nHA for improving bone regeneration processes and summarized the available data on bone cell response to nHA-based scaffolds. In addition, an attempt is made to portray the current status of bone tissue engineering using nHA/polymer hybrids and some recent scientific research in the field.

Research advances of nanomaterials for the acceleration of fracture healing

The bone fracture cases have been increasing yearly, accompanied by the increased number of patients experiencing non-union or delayed union after their bone fracture. Although clinical materials facilitate fracture healing (e.g., metallic and composite materials), they cannot fulfill the requirements due to the slow degradation rate, limited osteogenic activity, inadequate osseointegration ability, and suboptimal mechanical properties. Since early 2000, nanomaterials successfully mimic the nanoscale features of bones and offer unique properties, receiving extensive attention. This paper reviews the achievements of nanomaterials in treating bone fracture (e.g., the intrinsic properties of nanomaterials, nanomaterials for bone defect filling, and nanoscale drug delivery systems in treating fracture delayed union). Furthermore, we discuss the perspectives on the challenges and future directions of developing nanomaterials to accelerate fracture healing.

Matrix stiffness regulates osteoclast fate through integrin-dependent mechanotransduction

Osteoclasts ubiquitously participate in bone homeostasis, and their aberration leads to bone diseases, such as osteoporosis. Current clinical strategies by biochemical signaling molecules often perturb innate bone metabolism owing to the uncontrolled management of osteoclasts. Thus, an alternative strategy of precise regulation for osteoclast differentiation is urgently needed. To this end, this study proposed an assumption that mechanic stimulation might be a potential strategy. Here, a hydrogel was created to imitate the physiological bone microenvironment, with stiffnesses ranging from 2.43kPa to 68.2kPa. The impact of matrix stiffness on osteoclast behaviors was thoroughly investigated. Results showed that matrix stiffness could be harnessed for directing osteoclast fate in vitro and in vivo. In particular, increased matrix stiffness inhibited the integrin β3-responsive RhoA-ROCK2-YAP-related mechanotransduction and promoted osteoclastogenesis. Notably, preosteoclast development is facilitated by medium-stiffness hydrogel (M-gel) possessing the same stiffness as vessel ranging from 17.5 kPa to 44.6 kPa by partial suppression of mechanotransduction, which subsequently encouraged revascularization and bone regeneration in mice with bone defects. Our works provide an innovative approach for finely regulating osteoclast differentiation by selecting the optimum matrix stiffness and enable us further to develop a matrix stiffness-based strategy for bone tissue engineering.

Monocyte Differentiation on Atomic Layer-Deposited (ALD) Hydroxyapatite Coating on Titanium Substrate

Hydroxyapatite (HA; Ca₁₀(PO₄)₆(OH)₂) coating of bone implants has many beneficial properties as it improves osseointegration and eventually becomes degraded and replaced with new bone. We prepared HA coating on a titanium substrate with atomic layer deposition (ALD) and compared monocyte differentiation and material resorption between ALD-HA and bone. After stimulation with macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor kappa-B ligand (RANKL), human peripheral blood monocytes differentiated into resorbing osteoclasts on bovine bone, but non-resorbing foreign body cells were observed on ALD-HA. The analysis of the topography of ALD-HA and bone showed no differences in wettability (water contact angle on ALD-HA 86.2° vs. 86.7° on the bone), but the surface roughness of ALD-HA (Ra 0.713 µm) was significantly lower compared to bone (Ra 2.30 µm). The cellular reaction observed on ALD-HA might be a consequence of the topographical properties of the coating. The absence of resorptive osteoclasts on ALD-HA might indicate inhibition of their differentiation or the need to modify the coating to induce osteoclast differentiation.

Degradation of 3D-printed magnesium phosphate ceramics in vitro and a prognosis on their bone regeneration potential

Regenerative bone implants promote new bone formation and ideally degrade simultaneously to osteogenesis. Although clinically established calcium phosphate bone grafts provide excellent osseointegration and osteoconductive efficacy, they are limited in terms of bioresorption. Magnesium phosphate (MP) based ceramics are a promising alternative, because they are biocompatible, mechanically extremely stable, and degrade much faster than calcium phosphates under physiological conditions. Bioresorption of an implant material can include both chemical dissolution as well as cellular resorption. We investigated the bioresorption of 3D powder printed struvite and newberyite based MP ceramics in vitro by a direct human osteoclast culture approach. The osteoclast response and cellular resorption was evaluated by means of fluorescence and TRAP staining, determination of osteoclast activities (CA II and TRAP), SEM imaging as well as by quantification of the ion release during cell culture. Furthermore, the bioactivity of the materials was investigated via SBF immersion, whereas hydroxyapatite precipitates were analyzed by SEM and EDX measurements. This bioactive coating was resorbed by osteoclasts. In contrast, only chemical dissolution contributed to bioresorption of MP, while no cellular resorption of the materials was observed. Based on our results, we expect an increased bone regeneration effect of MP compared to calcium phosphate based bone grafts and complete chemical degradation within a maximum of 1.5-3.1 years.

3D-printed hydroxyapatite scaffolds for bone tissue engineering: A systematic review in experimental animal studies

The use of 3D-printed hydroxyapatite (HA) scaffolds for stimulating bone healing has been increasing over the years. Although all the promising effects of these scaffolds, there are still few studies and limited understanding of their interaction with bone tissue and their effects on the process of fracture healing. In this context, this study aimed to perform a systematic literature review examining the effects of different 3D-printed HA scaffolds in bone healing. The search was made according to the preferred reporting items for systematic reviews and meta-analysis (PRISMA) orientations and Medical Subject Headings (MeSH) descriptors "3D printing," "bone," "HA," "repair," and "in vivo." Thirty-six articles were retrieved from PubMed and Scopus databases. After eligibility analyses, 20 papers were included (covering the period of 2016 and 2021). Results demonstrated that all the studies included in this review showed positive outcomes, indicating the efficacy of scaffolds treated groups in the in vivo experiments for promoting bone healing in different animal models. In conclusion, 3D-printed HA scaffolds are excellent candidates as bone grafts due to their bioactivity and good bone interaction.

Nanotopographical cues for regulation of macrophages and osteoclasts: emerging opportunities for osseointegration

Nanotopographical cues of bone implant surface has direct influences on various cell types during the establishment of osseointegration, a prerequisite of implant bear-loading. Given the important roles of monocyte/macrophage lineage cells in bone regeneration and remodeling, the regulation of nanotopographies on macrophages and osteoclasts has arisen considerable attentions recently. However, compared to osteoblastic cells, how nanotopographies regulate macrophages and osteoclasts has not been properly summarized. In this review, the roles and interactions of macrophages, osteoclasts and osteoblasts at different stages of bone healing is firstly presented. Then, the diversity and preparation methods of nanotopographies are summarized. Special attentions are paid to the regulation characterizations of nanotopographies on macrophages polarization and osteoclast differentiation, as well as the focal adhesion-cytoskeleton mediated mechanism. Finally, an outlook is indicated of coordinating nanotopographies, macrophages and osteoclasts to achieve better osseointegration. These comprehensive discussions may not only help to guide the optimization of bone implant surface nanostructures, but also provide an enlightenment to the osteoimmune response to external implant.

Distinct Morphologies of Bone Apatite Clusters in Endochondral and Intramembranous Ossification

Bone apatite crystals grow in clusters, but the microstructure of these clusters is unknown. This study compares the structural and compositional differences between bone apatite clusters formed in intramembranous (IO) and endochondral ossification (EO). Calvaria (IO) and femurs (EO) are isolated from mice at embryonic days (E) 14.5 to 15.5 and post-natal days (P) 6 to 7, respectively. Results show that the initially formed bone apatite clusters in EO (≅1.2 µm² ) are >10 times larger than those in IO (≅0.1 µm² ), without significant changes in ion composition. In IO (E14.5 calvarium), early minerals are formed inside matrix vesicles (MVs). In contrast, in EO (P6 femur epiphysis), no MVs are observed, and chondrocyte-derived plasma membrane nanofragments (PMNFs) are the nucleation site for mineralization. Apatite cluster size difference is linked with the different nucleation sites. Moreover, an alkaline pH and slow P supply into a Ca-rich microenvironment are suggested to facilitate apatite cluster growth, as demonstrated in a biomimetic mineralization system. Together, the results reveal for the first time the distinct and exquisite microstructures of bone apatite clusters in IO and EO, and provide insightful inspirations for the design of more efficient materials for bone tissue engineering and repair.

Enhanced ectopic bone formation by strontium-substituted calcium phosphate ceramics through regulation of osteoclastogenesis and osteoblastogenesis

To explore how strontium influences osteoclastogenesis and osteoblastogenesis during material-induced ectopic bone formation, porous strontium-substituted biphasic calcium phosphate (Sr-BCP) and BCP ceramics with equivalent pore structures and comparable grain size and porosity were prepared. In vitro results showed that compared with BCP, Sr-BCP inhibited the osteoclastic differentiation of osteoclast precursors by delaying cell fusion, down-regulating the expression of osteoclast marker genes, and reducing the activity of osteoclast specific proteins, possibly due to the activated ERK signaling pathway but the suppressed p38, JNK and AKT signaling pathways. Meanwhile, Sr-BCP promoted the osteogenic differentiation of mesenchymal stem cells (MSCs) by up-regulating the osteogenic gene expression. Sr-BCP also mediated the expression of important osteoblast-osteoclast coupling factors, as evidenced by the increased Opg/Rankl ratio in mMSCs, and the reduced Rank expression and enhanced EphrinB2 expression in osteoclast precursors. Similar results were observed in an in vivo study based on a murine intramuscular implantation model. The sign of ectopic bone formation was only seen in Sr-BCP at 8 weeks. Compared to BCP, Sr-BCP obviously hindered the formation of TRAP- and CTSK-positive multinucleated osteoclast-like cells during the early implantation time up to 6 weeks, which is consistent with the in vivo PCR results. This suggested that Sr-BCP could clearly accelerate the ectopic bone formation by promoting osteogenesis but suppressing osteoclastogenesis, which might be closely related to the expression of osteoblast-osteoclast coupling factors regulated by Sr²⁺. These findings may help in the design and fabrication of smart bone substitutes with the desired potential for bone regeneration through modulating both osteoclastic resorption and osteoblastic synthesis.

Osteoclast formation from mouse bone marrow cells on micro/nano-scale patterned surfaces

OBJECTIVES

Osteoclasts can sense the surface topography of materials. However, it is difficult to identify the structural factors that affect osteoclast formation and its function. Furthermore, we hypothesized that the type of osteoclast precursor cells also affects osteoclastogenesis in the materials. In this study, we investigated the effects of defined micro/nanoscale patterns on osteoclastogenesis from bone marrow cells (BMCs).

METHODS

Various cyclo-olefin polymer (COP) patterns were prepared using nanoimprinting. The effects of shape, size, and height of the patterns, and the wettability of the patterned surfaces on osteoclastogenesis from BMCs were evaluated in vitro.

RESULTS

Osteoclast formation was promoted on pillars (diameter, 1 μm or 500 nm; height, 500 nm). Notably, osteoclastogenesis from BMCs was better promoted on hydrophobic pillars than on hydrophilic pillars. In contrast, decreased osteoclast formation was observed on the nanopillars (diameter, 100 nm; height, 200 nm).

CONCLUSIONS

We demonstrated the promotion of osteoclast formation from BMCs on hydrophobic pillars with diameters of 1 μm and 500 nm. Some cellular behaviors in the patterns were dependent on the type of osteoclast precursor cells. The designed patterns are useful for designing the surface of dental implants or bone replacement materials with a controllable balance between osteoblast and osteoclast activities.

Fabrication and Characterization of Submicron-Scale Bovine Hydroxyapatite: A Top-Down Approach for a Natural Biomaterial

Submicron hydroxyapatite has been reported to have beneficial effects in bone tissue engineering. This study aimed to fabricate submicron-scale bovine hydroxyapatite (BHA) using the high-energy dry ball milling method. Bovine cortical bone was pretreated and calcined to produce BHA powder scaled in microns. BHA was used to fabricate submicron BHA with milling treatment for 3, 6, and 9 h and was characterized by using dynamic light scattering, scanning electron microscope connected with energy dispersive X-Ray spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffractometry to obtain its particle size, calcium-to-phosphorus (Ca/P) ratio, functional chemical group, and XRD peaks and crystallinity. Results showed that the particle size of BHA had a wide distribution range, with peaks from ~5 to ~10 µm. Milling treatment for 3, 6, and 9 h successfully gradually reduced the particle size of BHA to a submicron scale. The milled BHA's hydrodynamic size was significantly smaller compared to unmilled BHA. Milling treatment reduced the crystallinity of BHA. However, the treatment did not affect other characteristics; unmilled and milled BHA was shaped hexagonally, had carbonate and phosphate substitution groups, and the Ca/P ratio ranged from 1.48 to 1.68. In conclusion, the fabrication of submicron-scale BHA was successfully conducted using a high-energy dry ball milling method. The milling treatment did not affect the natural characteristics of BHA. Thus, the submicron-scale BHA may be potentially useful as a biomaterial for bone grafts.

Fabrication and biological evaluation of 3D printed calcium phosphate ceramic scaffolds with distinct macroporous geometries through digital light processing technology

Digital light processing (DLP)-based 3D printing technique holds promise in fabricating scaffolds with high precision. Here raw calcium phosphate (CaP) powders were modified by 5.5% monoalcohol ethoxylate phosphate (MAEP) to ensure high solid loading and low viscosity. The rheological tests found that photocurable slurries composed of 50 wt % modified CaP powders and 2 wt % toners were suitable for DLP printing. Based on geometric models designed by CAD system, three printed CaP ceramics with distinct macroporous structures were prepared, including simple cube, octet-truss, and inverse face-centered cube (fcc), which presented the similar phase composition and microstructure, but the different macropore geometries. Inverse-fcc group showed the highest porosity and compressive strength. The in vitro and in vivo biological evaluations were performed to compare the bioactivity of three printed CaP ceramics, and the traditional foamed ceramic was used as control. It suggested that all CaP ceramics exhibited good biocompatibility, as evidence by an even bone-like apatite layer formation on the surface, and the good cell proliferation and spreading. A mouse intramuscular implantation model found that all of CaP ceramics could induce ectopic bone formation, and Foam group had the strongest osteoinduction, followed by Inverse-fcc, while Cube and Octet-truss had the weakest one. It indicated that macropore geometry was of great importance to affect the osteoinductivity of scaffolds, and spherical, concave macropores facilitated osteogenesis. These findings provide a strategy to design and fabricate high-performance orthopedic grafts with proper pore geometry and desired biological performance via DLP-based 3D printing technique.

3D-Printed HA-Based Scaffolds for Bone Regeneration: Microporosity, Osteoconduction and Osteoclastic Resorption

Additive manufacturing enables the realization of the macro- and microarchitecture of bone substitutes. The macroarchitecture is determined by the bone defect and its shape makes the implant patient specific. The preset distribution of the 3D-printed material in the macroarchitecture defines the microarchitecture. At the lower scale, the nanoarchitecture of 3D-printed scaffolds is dependent on the post-processing methodology such as the sintering temperature. However, the role of microarchitecture and nanoarchitecture of scaffolds for osteoconduction is still elusive. To address these aspects in more detail, we produced lithography-based osteoconductive scaffolds from hydroxyapatite (HA) of identical macro- and microarchitecture and varied their nanoarchitecture, such as microporosity, by increasing the maximum sintering temperatures from 1100 to 1400 °C. The different scaffold types were characterized for microporosity, compression strength, and nanoarchitecture. The in vivo results, based on a rabbit calvarial defect model showed that bony ingrowth, as a measure of osteoconduction, was independent from scaffold’s microporosity. The same applies to in vitro osteoclastic resorbability, since on all tested scaffold types, osteoclasts formed on their surfaces and resorption pits upon exposure to mature osteoclasts were visible. Thus, for wide-open porous HA-based scaffolds, a low degree of microporosity and high mechanical strength yield optimal osteoconduction and creeping substitution. Based on our study, non-unions, the major complication during demanding bone regeneration procedures, could be prevented.

Hydroxyapatite-decorated Fmoc-hydrogel as a bone-mimicking substrate for osteoclast differentiation and culture

Hydrogels are water-swollen networks with great potential for tissue engineering applications. However, their use in bone regeneration is often hampered due to a lack of materials' mineralization and poor mechanical properties. Moreover, most studies are focused on osteoblasts (OBs) for bone formation, while osteoclasts (OCs), cells involved in bone resorption, are often overlooked. Yet, the role of OCs is pivotal for bone homeostasis and aberrant OC activity has been reported in several pathological diseases, such as osteoporosis and bone cancer. For these reasons, the aim of this work is to develop customised, reinforced hydrogels to be used as material platform to study cell function, cell-material interactions and ultimately to provide a substrate for OC differentiation and culture. Here, Fmoc-based RGD-functionalised peptide hydrogels have been modified with hydroxyapatite nanopowder (Hap) as nanofiller, to create nanocomposite hydrogels. Atomic force microscopy showed that Hap nanoparticles decorate the peptide nanofibres with a repeating pattern, resulting in stiffer hydrogels with improved mechanical properties compared to Hap- and RGD-free controls. Furthermore, these nanocomposites supported adhesion of Raw 264.7 macrophages and their differentiation in 2D to mature OCs, as defined by the adoption of a typical OC morphology (presence of an actin ring, multinucleation, and ruffled plasma membrane). Finally, after 7 days of culture OCs showed an increased expression of TRAP, a typical OC differentiation marker. Collectively, the results suggest that the Hap/Fmoc-RGD hydrogel has a potential for bone tissue engineering, as a 2D model to study impairment or upregulation of OC differentiation. STATEMENT OF SIGNIFICANCE: Altered osteoclasts (OC) function is one of the major cause of bone fracture in the most commonly skeletal disorders (e.g. osteoporosis). Peptide hydrogels can be used as a platform to mimic the bone microenvironment and provide a tool to assess OC differentiation and function. Moreover, hydrogels can incorporate different nanofillers to yield hybrid biomaterials with enhanced mechanical properties and improved cytocompatibility. Herein, Fmoc-based RGD-functionalised peptide hydrogels were decorated with hydroxyapatite (Hap) nanoparticles to generate a hydrogel with improved rheological properties. Furthermore, they are able to support osteoclastogenesis of Raw264.7 cells in vitro as confirmed by morphology changes and expression of OC-markers. Therefore, this Hap-decorated hydrogel can be used as a template to successfully differentiate OC and potentially study OC dysfunction.

Optimal regenerative repair of large segmental bone defect in a goat model with osteoinductive calcium phosphate bioceramic implants

So far, how to achieve the optimal regenerative repair of large load-bearing bone defects using artificial bone grafts is a huge challenge in clinic. In this study, a strategy of combining osteoinductive biphasic calcium phosphate (BCP) bioceramic scaffolds with intramedullary nail fixation for creating stable osteogenic microenvironment was applied to repair large segmental bone defects (3.0 cm in length) in goat femur model. The material characterization results showed that the BCP scaffold had the initial compressive strength of over 2.0 MPa, and total porosity of 84%. The cell culture experiments demonstrated that the scaffold had the excellent ability to promote the proliferation and osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells (BMSCs). The in vivo results showed that the intramedullary nail fixation maintained the initial stability and structural integrity of the implants at early stage, promoting the osteogenic process both guided and induced by the BCP scaffolds. At 9 months postoperatively, good integration between the implants and host bone was observed, and a large amount of newborn bones formed, accompanying with the degradation of the material. At 18 months postoperatively, almost the complete new bone substitution in the defect area was achieved. The maximum bending strength of the repaired bone defects reached to the 100% of normal femur at 18 months post-surgery. Our results demonstrated the good potential of osteoinductive BCP bioceramics in the regenerative repair of large load-bearing bone defects. The current study could provide an effective method to treat the clinical large segmental bone defects.

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A novel strategy of achieving regenerative repair for large segmental bone defects with osteoinductive calcium phosphate bioceramics was developed successfully.

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The critical-sized goat femur defects (3.0 cm in length) were completely repaired by osteoinductive calcium phosphate bioceramics without using exogenous active factors or cells.

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The current study could provide an effective method to solve the clinical problem about large load-bearing bone defect repair.

Enhanced bone regenerative properties of calcium phosphate ceramic granules in rabbit posterolateral spinal fusion through a reduction of grain size

Osteoinductivity is a crucial factor to determine the success and efficiency of posterolateral spinal fusion (PLF) by employing calcium phosphate (Ca-P) bioceramics. In this study, three kinds of Ca-P ceramics with microscale to nanoscale gain size (BCP-control, BCP-micro and BCP-nano) were prepared and their physicochemical properties were characterized. BCP-nano had the spherical shape and nanoscale gain size, BCP-micro had the spherical shape and microscale gain size, and BCP-control (BAM®) had the irregular shape and microscale gain size. The obtained BCP-nano with specific nanotopography could well regulate in vitro protein adsorption and osteogenic differentiation of MC3T3 cells. In vivo rabbit PLF procedures further confirmed that nanotopography of BCP-nano might be responsible for the stronger bone regenerative ability comparing with BCP-micro and BCP-control. Collectedly, due to nanocrystal similarity with natural bone apatite, BCP-nano has excellent efficacy in guiding bone regeneration of PLF, and holds great potentials to become an alternative to standard bone grafts for future clinical applications.

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The nanocrystal of porous BCP ceramic spheres is similar to natural bone apatite.

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BCP nanoceramics is conducive to protein adsorption and osteogenic differentiation of MC3T3 cells.

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Osteoindutivity of BCP ceramics is a crucial factor to determine the sucess and efficiency of PLF.

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BCP ceramic spheres with nanotopography hold great potential in clinical PLF applications.

In situ construction of a nano-structured akermanite coating for promoting bone formation and osseointegration of Ti-6Al-4V implants in a rabbit osteoporosis model

With the aging population worldwide, osteoporosis, as an age-related bone metabolic disease, is becoming a hot issue in public health. However, it is still a great challenge to realize osteoporotic bone healing due to the alteration of the bone microenvironment in osteoporosis patients. In this study, a nano-structured akermanite (nAK) coating was in situ constructed on Ti-6Al-4V implants to improve osteoporotic bone repair. In vitro studies indicated that both the surface nano-topography and bioactive ions released from the nAK coatings promoted the proliferation, osteogenesis, angiogenesis and inhibited osteoclastogenesis of ovariectomy rabbit-derived bone marrow mesenchymal stem cells (OVX-rBMSCs). Furthermore, the nAK-coated Ti-6Al-4V implants improved new bone formation and osseointegration in an osteoporosis rabbit model in vivo. These results indicated that the AK coating with a nano-structured surface on the Ti-6Al-4V implant could synergistically promote bone formation and osseointegration for osteoporosis patients. This may be a promising strategy to improve the bone regeneration and osseointegration capability of orthopedic implants under osteoporosis conditions.

Hydroxyapatite Nanoparticles in Drug Delivery: Physicochemistry and Applications

Hydroxyapatite (HAP) has been the gold standard in the biomedical field due to its composition and similarity to human bone. Properties such as shape, size, morphology, and ionic substitution can be tailored through the use of different synthesis techniques and compounds. Regardless of the ability to determine its physicochemical properties, a conclusion for the correlation with the biological response it is yet to be found. Hence, a special focus on the most desirable properties for an appropriate biological response needs to be addressed. This review provides an overview of the fundamental properties of hydroxyapatite nanoparticles and the characterization of physicochemical properties involved in their biological response and role as a drug delivery system. A summary of the main chemical properties and applications of hydroxyapatite, the advantages of using nanoparticles, and the influence of shape, size, functional group, morphology, and crystalline phase in the biological response is presented. A special emphasis was placed on the analysis of chemical and physical interactions of the nanoparticles and the cargo, which was explained through the use of spectroscopic and physical techniques such as FTIR, Raman, XRD, SEM, DLS, and BET. We discuss the properties tailored for hydroxyapatite nanoparticles for a specific biomolecule based on the compilation of studies performed on proteins, peptides, drugs, and genetic material.

Signaling Pathway and Transcriptional Regulation in Osteoblasts during Bone Healing: Direct Involvement of Hydroxyapatite as a Biomaterial

Bone defects and periodontal disease are pathological conditions that may become neglected diseases if not treated properly. Hydroxyapatite (HA), along with tricalcium phosphate and bioglass ceramic, is a biomaterial widely applied to orthopedic and dental uses. The in vivo performance of HA is determined by the interaction between HA particles with bone cells, particularly the bone mineralizing cells osteoblasts. It has been reported that HA-induced osteoblastic differentiation by increasing the expression of osteogenic transcription factors. However, the pathway involved and the events that occur in the cell membrane have not been well understood and remain controversial. Advances in gene editing and the discovery of pharmacologic inhibitors assist researchers to better understand osteoblastic differentiation. This review summarizes the involvement of extracellular signal-regulated kinase (ERK), p38, Wnt, and bone morphogenetic protein 2 (BMP2) in osteoblastic cellular regulation induced by HA. These advances enhance the current understanding of the molecular mechanism of HA as a biomaterial. Moreover, they provide a better strategy for the design of HA to be utilized in bone engineering.

[Research progress of nanomaterials in osteomyelitis treatment]

Objective

To review the related studies on the application of nanomaterials in the treatment of osteomyelitis, and to provide new ideas for the research and clinical treatment of osteomyelitis.

Methods

The literature about the treatment of osteomyelitis with nanomaterials at home and abroad in recent years was reviewed and analyzed.

Results

At present, surgical treatment and antibiotic application are the main treatment options for osteomyelitis. But there are many defects such as antibiotic resistance, residual bone defect, and low effective concentration of local drugs. The application of nanomaterials can make up for the above defects. In recent years, nanomaterials play an important role in the treatment of osteomyelitis by filling bone defects, establishing local drug delivery system, and self-antibacterial properties.

Conclusion

It will provide a new idea and an important research direction for the treatment of osteomyelitis to fully study the related characteristics of nanomaterials and select beneficial materials to make drug delivery system or substitute drugs.

Zn-doped mesoporous hydroxyapatites and their antimicrobial properties

Recently, zinc-based materials have gained immense attention as antimicrobial agents. In this study, zinc-doped mesoporous hydroxyapatites (HAps) with various Zn contents were prepared by co-precipitation using a phosphoprotein as the porous template. The use of the phosphoprotein as the porous template resulted in the formation of zinc-doped mesoporous HAps (mHAps) with large pores and specific surface area (182 m² g^-1), as indicated by the nitrogen adsorption/desorption measurements. The formation of the zinc-doped HAps was confirmed by various analytical techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The biomaterials prepared in this study were used as antimicrobial agents against gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria. The Zn2%-mHAp sample showed the maximum bacterial inhibitory concentrations of 50 ± 5% and 77 ± 5% for the Gram-positive and Gram-negative bacteria, respectively. The antibacterial activity of the mHAp samples depended strongly on their Zn²⁺ content. Thus, the use of a biotemplate and Zn²⁺ ions is an efficient approach for the formation of novel HAp-based biomaterials with promising antibacterial properties. This synthesis approach will pave a new pathway for the functionalization of other materials for different biomedical applications.

A biomimetically hierarchical polyetherketoneketone scaffold for osteoporotic bone repair

Osteoporotic fractures are prevalent in society, and their incidence appears to be increasing as the worldwide population ages. However, conventional bone repair materials hardly satisfy the requirements for the repair of pathological fractures. Here, we developed a biomimetic polyetherketoneketone scaffold with a functionalized strontium-doped nanohydroxyapatite coating for osteoporotic bone defect applications. The scaffold has a hierarchically porous architecture and mechanical strength similar to that of osteoporotic trabecular bone. In vitro and in vivo studies demonstrated that the scaffold could promote osteoporotic bone regeneration and delay adjacent bone loss via regulating both osteoblasts and osteoclasts. In addition, the correlations between multiple preimplantation and postimplantation parameters were evaluated to determine the potential predictors of in vivo performance of the material. The current work not only develops a promising candidate for osteoporotic bone repair but also provides a viable approach for designing other functional biomaterials and predicting their translational value.

Design of hydroxyapatite bioceramics with micro-/nano-topographies to regulate the osteogenic activities of bone morphogenetic protein-2 and bone marrow stromal cells

Biomimicking the nanostructure of natural bone apatite to enhance the bioactivity of hydroxyapatite (HA) biomaterials is an eternal topic in the bone regeneration field. In the present study, we designed four kinds of HA bioceramics with micro- to nanosized grains and investigated the effects of bioceramic topographies on the structures of bone morphogenetic protein-2 (BMP-2) and the effects on the responses of bone marrow stromal cells (BMSCs). Compared to the samples with submicron-scale crystalline particles, HA bioceramics with grain sizes of 104.6 ± 27.8 nm exhibited increased roughness, improved hydrophilicity and enhanced mechanical properties. The synergistic effects of these surface characteristics could well maintain the conformation of BMP-2, facilitate cell adhesion and spreading, and activate the osteogenic differentiation of BMSCs. Furthermore, SBF immersion and in vivo canine intramuscular implantation confirmed that the HA bioceramics with nanotopography also processed excellent bone-like apatite forming ability and outstanding osteoinductivity. In summary, these findings suggest that the nanotopography of HA bioceramics is a critical factor to enhance their bioactivity and osteoinductivity.