Microporous calcium phosphate ceramics driving osteogenesis through surface architecture

Effects of void defects on the mechanical properties of biphasic calcium phosphate nanoparticles: A molecular dynamics investigation

Porous biphasic calcium phosphate (BCP) ceramics are widely used in bone tissue engineering, and the mechanical properties of BCP implants must be reliable. However, the effects of pore structure (e.g., shape and size) on the mechanical properties are not well understood. In this study, we used molecular dynamics simulations to investigate the influence of pore shape and size on the mechanical behavior of BCP nanoparticles. BCP void models with cylindrical and cuboid pores ranging from 2 to 16 nm in diameter were constructed, and the elastic moduli were calculated. In addition, uniaxial tensile and compressive tests were performed on the models. We found that the pore size had a more significant impact on the mechanical properties of BCP than pore shape. Further, the elastic moduli decreased nonlinearly with increasing pore size. In addition, the tensile and compressive strength also decreased with the increase in pore size, but the ductility improved. Furthermore, deformation and fracture were more likely to occur near the pores and at the phase interfaces as a result of high atomic local strain in the calcium-deficient hydroxyapatite area. The results of this work reveal the effects of pore parameters on the mechanical properties of porous BCP at the nanometer level, which may aid the design of improved porous and multiphase CaP-based biomaterials for bone regeneration.

Porous BCP ceramics with nanoscale whisker structure accelerate bone regeneration by regulating inflammatory response

Inflammation-induced by biomaterials is a critical event to determine the success and efficiency of tissue repair. Macrophages are a major population that participates the biomaterial induced inflammation. The response of macrophages depends on the characteristics of biomaterials, thus causing a cascade reaction in subsequent biological processes. In this study, porous biphase calcium phosphate (BCP) ceramics with the different surface structures were constructed to compare the effect of surface structure on bone generation potential, and further reveal the inflammation-involved mechanism. Our results demonstrated that macrophages on three ceramics showed distinct morphologies and spreading areas. The nanoscale whisker structure did induce more bone generation in the mice thigh muscle. The in vitro result revealed that nanoscale whisker structure could drive macrophage polarization towards M1-like phenotype, indicated by a higher expression of pro-inflammatory specific markers (iNOS and CCR7), and mass secretion of TNF-α. Further research indicated that additional TNF-α could promote the osteogenic differentiation of mesenchymal stem cells (MSCs). However, excess addition of TNF-α showed an opposite effect on the osteogenic differentiation of MSCs by initiating the NF-κB signaling pathway, which suppresses the osteogenesis process.

Effect of Cell Geometry on the Mechanical Properties of 3D Voronoi Tessellation

Irregular 3D biological scaffolds have been widely observed in nature. Therefore, in the current work, new designs are proposed for lightweight 3D scaffolds based on Voronoi tessellation with high porosity. The proposed designs are inspired by nature, which has undoubtedly proven to be the best designer. Thus, the Rhinoceros 7/Grasshopper software was used to design three geometric models for both normal and elongated Voronoi structures: homogeneous, gradient I, and gradient II. Then, stereolithography (SLA) additive manufacturing was utilized to fabricate biopolymeric materials. Finally, a compression test was carried out to study and compare the mechanical properties of the designed samples. The gradient I cylinder show the highest Young's modulus. For the Homogeneous and gradient II cylinders, elongated Voronoi structures show superior mechanical properties and energy absorption compared to normal Voronoi designs. Hence, these designs are promising topologies for future applications.

Study on βTCP/P(3HB) Scaffolds-Physicochemical Properties and Biological Performance in Low Oxygen Concentration

The search for new materials for bone regenerative purposes is still ongoing. Therefore, we present a series of newly constructed composites based on β tricalcium phosphate (βTCP) and poly(3-hydroxybutyrate) bacteria-derived biopolymer (P(3HB)) in the form of 3D scaffolds with different pore sizes. To improve the polymer attachment to the βTCP surface, the etching of ceramic sinters, using citric acid, was applied. As expected, pre-treatment led to the increase in surface roughness and the creation of micropores facilitating polymer adhesion. In this way, the durability and compressive strength of the ceramic-polymer scaffolds were enhanced. It was confirmed that P(3HB) degrades to 3-hydroxybutyric acid, which broadens applications of developed materials in bone tissue engineering as this compound can potentially nourish surrounding tissues and reduce osteoporosis. Moreover, to the best of our knowledge, it is one of the first studies where the impact of βTCP/P(3HB) scaffolds on mesenchymal stem cells (MSCs), cultured in lowered (5%) oxygen concentration, was assessed. It was decided to use a 5% oxygen concentration in the culture to mimic the conditions that would be found in damaged bone in a living organism during regeneration. Scaffolds enabled cell migration and sufficient flow of the culture medium, ensuring high cell viability. Furthermore, in composites with etched βTCP, the MSCs adhesion was facilitated by hydrophilic ceramic protrusions which reduced hydrophobicity. The developed materials are potential candidates for bone tissue regeneration. Nevertheless, to confirm this hypothesis, in vivo studies should be performed.

Assessment of Cell-Material Interactions in Three Dimensions through Dispersed Coaggregation of Microsized Biomaterials into Tissue Spheroids

In biomaterials R&D, conventional monolayer cell culture on flat/planar material samples, such as films, is still commonly employed at early stages of the assessment of interactions of cells with candidate materials considered for a biomedical application. In this feasibility study, an approach for the assessment of 3D cell-material interactions through dispersed coaggregation of microparticles from biomaterials into tissue spheroids is presented. Biomaterial microparticles can be created comparatively quickly and easily, allow the miniaturization of the assessment platform, and enable an unhindered remodeling of the dynamic cell-biomaterial system at any time. The aggregation of the microsized biomaterials and the cells is supported by low-attachment round-bottom microwells from thin polymer films arranged in densely packed arrays. The study is conducted by the example of MG63 osteoblast-like and human mesenchymal stem/stromal cells, and a small library of model microbiomaterials related to bone repair and regeneration. For the proof of concept, example interactions including cell adhesion to the material, the hybrid spheroids' morphology, size, and shape, material-associated cell death, cell metabolic activity, cell proliferation, and (osteogenic) differentiation are investigated. The cells in the spheroids are shown to respond to differences in the microbiomaterials' properties, their amounts, and the duration of interaction with them.

Preparation and characterization of two novel osteoinductive fishbone-derived biphasic calcium phosphate bone graft substitutes

Many studies have reported on the conversion of natural resources into xenografts with hydroxyapatite (HA) as major component, but the extraction of biphasic calcium phosphate (HA/β-TCP) from animal bones and transformation into bone graft substitutes are rarely reported. In this research, two kinds of fish bones were made into granular porous biphasic calcium phosphate bone graft substitutes with particle sizes between 500 to 1000 μm through a series of preparation procedures (Salmo salar calcined at 900°C named Sa900 and Anoplopoma fimbria calcined at 800°C named An800). The chemical composition was characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The morphology and porous structure of the scaffolds were comparatively analyzed by scanning electron microscopy (SEM) and mercury porosimeter. The specific surface area of materials was measured by the nitrogen adsorption technique based on BET theory. Cytotoxicity and ectopic osteogenesis were also carried out to investigate the biocompatibility and osteoinductive potential of these materials. The results showed that both fishbone-derived scaffolds were composed of HA and β-TCP with different proportions, and numerous interconnected pores with different sizes were observed at the surface of materials. An800 had higher total porosity reaching 74.8% with higher interconnectivity and micropores mostly distributed at 0.27 μm and 0.12 μm, while Sa900 had a higher specific surface area and higher intraparticle porosity with nanopores mostly distributed at 0.07 μm. CCK-8 assays and Live/dead staining demonstrated excellent biocompatibility. Material-induced osteoid formation were observed on the interface of both internal pores and periphery of materials after implantation in muscle pouch of Wistar rats for 8 weeks which indicated some extent of osteoinductive potential of materials. The possible mechanism of material-induced osteogenesis and the effects of chemical composition, surface topography, and spatial structure on osteogenesis were also discussed in this paper.

Sustained local ionic homeostatic imbalance caused by calcification modulates inflammation to trigger heterotopic ossification

Heterotopic ossification (HO) is a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues. Despite being a frequent complication of orthopedic and trauma surgery, brain and spinal injury, the etiology of HO is poorly understood. The aim of this study is to evaluate the hypothesis that a sustained local ionic homeostatic imbalance (SLIHI) created by mineral formation during tissue calcification modulates inflammation to trigger HO. This evaluation also considers the role SLIHI could play for the design of cell-free, drug-free osteoinductive bone graft substitutes. The evaluation contains five main sections. The first section defines relevant concepts in the context of HO and provides a summary of proposed causes of HO. The second section starts with a detailed analysis of the occurrence and involvement of calcification in HO. It is followed by an explanation of the causes of calcification and its consequences. This allows to speculate on the potential chemical modulators of inflammation and triggers of HO. The end of this second section is devoted to in vitro mineralization tests used to predict the ectopic potential of materials. The third section reviews the biological cascade of events occurring during pathological and material-induced HO, and attempts to propose a quantitative timeline of HO formation. The fourth section looks at potential ways to control HO formation, either acting on SLIHI or on inflammation. Chemical, physical, and drug-based approaches are considered. Finally, the evaluation finishes with a critical assessment of the definition of osteoinduction. STATEMENT OF SIGNIFICANCE: The ability to regenerate bone in a spatially controlled and reproducible manner is an essential prerequisite for the treatment of large bone defects. As such, understanding the mechanism leading to heterotopic ossification (HO), a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues, would be very useful. Unfortunately, the mechanism(s) behind HO is(are) poorly understood. The present study reviews the literature on HO and based on it, proposes that HO can be caused by a combination of inflammation and calcification. This mechanism helps to better understand current strategies to prevent and treat HO. It also shows new opportunities to improve the treatment of bone defects in orthopedic and dental procedures.

Effects of ultraviolet irradiation on beta-tricalcium phosphate as a bone graft substitute

Surface modification of various materials using ultraviolet (UV) irradiation improves their wettability. The purpose of this study was to investigate the wettability of a β-tricalcium phosphate (TCP) surface and the composition changes and bioactivity of β-TCP after UV irradiation. We applied 172 nm UV treatment to a β-TCP surface and measured the contact angle before and after UV irradiation. Energy-dispersive X-ray and Fourier transform infrared spectroscopy examinations were performed on the β-TCP disk with or without UV treatment. In an adhesion test of bone marrow cells using β-TCP disks with and without UV irradiation, cell attachment was measured 10, 30, 50, and 70 h after β-TCP insertion. UV-irradiated β-TCP osteogenesis and absorption of bone substitutes were evaluated using hematoxylin and eosin and tartrate-resistant acid phosphatase (TRAP) staining in a rabbit sinus model. The contact angle on the TCP surface decreased from 70° to 10° owing to UV irradiation. Conversely, UV irradiation did not change the composition of carbon, oxygen, and phosphorus. In the cell adhesion test, UV-irradiated β-TCP significantly increased cell adhesion compared with UV-unirradiated β-TCP after 10 to 30 h of culture. In the rabbit sinus model, TRAP staining showed that UV-irradiated β-TCP significantly increased the number of TRAP-positive cells compared with unirradiated β-TCP granules in the central part of β-TCP. Our results indicate that the UV irradiation of β-TCP improves its clinical utility for surgical bone augmentation in the oral and maxillofacial region.

Loading of erythropoietin on biphasic calcium phosphate bioceramics promotes osteogenesis and angiogenesis by regulating EphB4/EphrinB2 molecules

Improving osteogenesis and angiogenesis using different cells and drugs is critical in the field of bone tissue engineering. Recent research has found that erythropoietin (EPO) plays an important role in both osteogenesis and angiogenesis. In this study, we grafted polydopamine and EPO onto the surface of biphasic calcium phosphate. The characterization and release property of the modified bioceramics were assessed. Cell proliferation, expression of osteoblastic and endothelial markers, and EphB4/EphrinB2 molecules were investigated while employing co-cultures of two different cells [rat vein endothelial cells (VECs) and rat bone marrow mesenchymal stromal cells (BMSCs)]. The modified bioceramics were finally implanted into the SD rats' femurs and followed by investigating the bone defect repair efficacy and the expression of EphB4/EphrinB2 molecules in vivo. The results indicated that the modified bioceramics could control the release of EPO continuously. The osteogenesis and angiogenesis were improved along with the increased expression of EphB4/EphrinB2 molecules. The expression of EphB4/EphrinB2 molecules was also significantly increased in vivo and the bone defect was repaired effectively. Overall, our findings demonstrated that EPO loading on biphasic calcium phosphate bioceramics could promote both osteogenesis and angiogenesis. The results suggest that EphB4/EphrinB2 may be crucial in the process. Graphical abstract.

Effect on Rheological Properties and 3D Printability of Biphasic Calcium Phosphate Microporous Particles in Hydrocolloid-Based Hydrogels

The production of patient-specific bone substitutes with an exact fit through 3D printing is emerging as an alternative to autologous bone grafting. To the success of tissue regeneration, the material characteristics such as porosity, stiffness, and surface topography have a strong influence on the cell–material interaction and require significant attention. Printing a soft hydrocolloid-based hydrogel reinforced with irregularly-shaped microporous biphasic calcium phosphate (BCP) particles (150–500 µm) is an alternative strategy for the acquisition of a complex network with good mechanical properties that could fulfill the needs of cell proliferation and regeneration. Three well-known hydrocolloids (sodium alginate, xanthan gum, and gelatin) have been combined with BCP particles to generate stable, homogenous, and printable solid dispersions. Through rheological assessment, it was determined that the crosslinking time, printing process parameters (infill density percentage and infill pattern), as well as BCP particle size and concentration all influence the stiffness of the printed matrices. Additionally, the swelling behavior on fresh and dehydrated 3D-printed structures was investigated, where it was observed that the BCP particle characteristics influenced the constructs’ water absorption, particle diffusion out of the matrix and degradability.

Inductive Materials for Regenerative Engineering

Regenerative engineering has pioneered several novel biomaterials to treat critical-sized bone injuries. However, despite significant improvement in synthetic materials research, some limitations still exist. The constraints correlated with the current grafting methods signify a treatment paradigm shift to osteoinductive regenerative engineering approaches. Because of their intrinsic potential, inductive biomaterials may represent alternative approaches to treating critical bone injuries. Osteoinductive scaffolds stimulate stem cell differentiation into the osteoblastic lineage, enhancing bone regeneration. Inductive biomaterials comprise polymers, calcium phosphate ceramics, metals, and graphene family materials. This review will assess the cellular behavior toward properties of inductive materials.

Repair calvarial defect of osteoporotic rats by berberine functionalized porous calcium phosphate scaffold

In this article, we propose a simple scheme of using berberine (BBR) to modify porous calcium phosphate ceramics (named PCPC). These BBR molecules regulate the crystallization of hydroxyapatite nanorods on PCPC. We found that these nanorods and the adsorbed BBR changed the interface micro-environment of PCPC by SEM images. The microenvironment of PCPC surface is essential for promoting BMSCs’ proliferation and differentiation. These results demonstrated that PCPC/BBR markedly improved the bone regeneration of osteoporosis rats. Moreover, PCPC/BBR had significantly increased the expression levels of ALP, osteocalcin and bone morphogenetic protein2 and RUNX2 in BMSCs originated from osteoporosis rats.

Multiscale porosity in mesoporous bioglass 3D-printed scaffolds for bone regeneration

In order to increase the bone forming ability of MBG-PCL composite scaffold, microporosity was created in the struts of 3D-printed MBG-PCL scaffolds for the manufacturing of a construct with a multiscale porosity consisting of meso- micro- and macropores. 3D-printing imparted macroporosity while the microporosity was created by porogen removal from the struts, and the MBG particles were responsible for the mesoporosity. The scaffolds were 3D-printed using a mixture of PCL, MBG and phosphate buffered saline (PBS) particles, subsequently leached out. Microporous-PCL (pPCL) as a negative control, microporous MBG-PCL (pMBG-PCL) and non-microporous-MBG-PCL (MBG-PCL) were investigated. Scanning electron microscopy, mercury intrusion porosimetry and micro-computed tomography demonstrated that the PBS removal resulted in the formation of micropores inside the struts with porosity of around 30% for both pPCL and pMBG-PCL, with both constructs displaying an overall porosity of 8090%. In contrast, the MBG-PCL group had a microporosity of 6% and an overall porosity of 70%. Early mineralisation was found in the pMBG-PCL post-leaching out and this resulted in the formation a more homogeneous calcium phosphate layer when using a biomimetic mineralisation assay. Mechanical properties ranged from 5 to 25 MPa for microporous and non-microporous specimens, hence microporosity was the determining factor affecting compressive properties. MC3T3-E1 metabolic activity was increased in the pMBG-PCL along with an increased production of RUNX2. Therefore, the microporosity within a 3D-printed bioceramic composite construct may result in additional physical and biological benefits.

Effect of donor age and 3D-cultivation on osteogenic differentiation capacity of adipose-derived mesenchymal stem cells

Background and Purpose: Age and co-morbidities compromise healing tendencies of traumatic fractures in geriatric patients. Non-healing fractures may need regenerative medicine techniques involving autologous mesenchymal stem cells (MSCs). Donor age may affect the viability and differentiation capacity of MSCs. We investigated age-related differences in adipose-derived MSCs (AMSCs) concerning osteogenic potential in 2D and 3D cultivation. Materials and Methods: AMSCs were harvested from young (mean age: 37.5 ± 8.6 years) and old (mean age: 75.8 ± 9.2 years) patients. Cells were induced to osteogenic differentiation and cultivated in 2D and 3D for 14 days. Alkaline phosphatase (ALP) activity, mineralization and gene expression were investigated. Results: ALP activity revealed highest levels in 3D of old AMSCs after 14 days. ALP expression showed significant rises in old vs. young cells in 2D (p = 0.0024). Osteoprotegerin revealed the highest levels in old AMSCs in 2D. Highest osteocalcin levels presented in young cells compared to old cells in 2D (p = 0.0258) and young cells in 3D (p = 0.0014). Conclusion: 3D arrangement of old AMSCs without growth factors is not ensuring superior osteogenesis in vitro. AMSCs, especially cells from older patients, reveal higher osteogenic potential in 2D than in 3D. 3D arrangement favors osteogenic potential of young cells.

Drug-loading three-dimensional scaffolds based on hydroxyapatite-sodium alginate for bone regeneration

Bone tissue engineering is a promising approach for tackling clinical challenges. Osteoprogenitor cells, osteogenic factors, and osteoinductive/osteoconductive scaffolds are employed in bone tissue engineering. However, scaffold materials remain limited due to their source, low biocompatibility, and so on. In this study, a composite hydrogel scaffold composed of hydroxyapatite (HA) and sodium alginate (SA) was manufactured using three-dimensional printing. Naringin (NG) and calcitonin-gene-related peptide (CGRP) were used as osteogenic factors in the fabrication of drug-loaded scaffolds. Investigation using animal experiments, as well as scanning electron microscopy, cell counting kit-8 testing, alkaline phosphatase staining, and alizarin red-D staining of bone marrow mesenchymal stem cell culture showed that the three scaffolds displayed similar physicochemical properties and that the HA/SA/NG and HA/SA/CGRP scaffolds displayed better osteogenesis than that of the HA/SA scaffold. Thus, the HA/SA scaffold could be a biocompatible material with potential applications in bone regeneration. Meanwhile, NG and CGRP doping could result in better and more positive proliferation and differentiation.

Improved Osteogenesis of Selective-Laser-Melted Titanium Alloy by Coating Strontium-Doped Phosphate With High-Efficiency Air-Plasma Treatment

Surface treatment and bioactive metal ion incorporation are effective methods for the modification of titanium alloys to be used as biomaterials. However, few studies have demonstrated the use of air-plasma treatment in orthopedic biomaterial development. Additionally, no study has performed a direct comparison between unmodified titanium alloys and air-plasma-treated alloys with respect to their biocompatibility and osteogenesis. In this study, the biological activities of unmodified titanium alloys, air-plasma-treated titanium alloys, and air-plasma-treated strontium-doped/undoped calcium phosphate (CaP) coatings were compared. The strontium-doped CaP (Sr-CaP) coating on titanium alloys were produced by selective laser melting (SLM) technology as well as micro-arc oxidation (MAO) and air-plasma treatment. The results revealed that rapid air-plasma treatment improved the biocompatibility of titanium alloys and that Sr-CaP coating together with air-plasma treatment significantly enhanced both the biocompatibility and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Overall, this study demonstrated that low temperature air-plasma treatment is a fast and effective surface modification which improves the biocompatibility of titanium alloys. Additionally, air-plasma-treated Sr-CaP coatings have numerous practical applications and may provide researchers with new tools to assist in the development of orthopedic implants.

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

The surface structure of calcium phosphate (CaP) ceramic plays an important role in its osteoinductivity; however, little is known about its effects on osteoclastogenesis. In this study, an intramuscular implantation model suggested a potential relationship between hydroxyapatite (HA)-induced bone formation and osteoclast appearance in the non-osseous site, which might be modulated by scaffold surface structure. Then, three dense HA discs with different grain sizes from biomimetic nanoscale (∼100 nm) to submicron scale (∼500 nm) were fabricated via distinct sintering procedures, and their impacts on osteoclastic differentiation of RAW 264.7 macrophages under RANKL stimulation were further investigated. Our results showed that compared with the ones in the submicron-scale dimension, nano-structured HA discs markedly impaired osteoclastic formation and function, as evidenced by inhibited cell fusion, reduced osteoclast size, less-defined actin ring, increased osteoclast apoptosis, suppressed expression of osteoclast specific genes and proteins, decreased TRAP-positive cells, and hampered resorption activity. This demonstrated that the surface structure of CaP ceramics has a great influence on osteoclastogenesis, which might be further related to its osteoinductive capacity. These findings might not only help us gain insight into biomolecular events during CaP-involved osteoinduction, but also offer a principle for designing orthopaedic implants with an ability of regulating both osteogenesis and osteoclastogenesis to achieve the desired performance.

Effects of micro-porosity and local BMP-2 administration on bioresorption of β-TCP and new bone formation

Background

It has been reported that the microporous structure of calcium phosphate (CaP) ceramics is important to osteoconduction. Bone morphogenetic protein-2 (BMP-2) has been shown to be a promising alternative to bone grafting and a therapeutic agent promoting bone regeneration when delivered locally. The aim of this study was to evaluate the effects of micro-porosity within beta-tricalcium phosphate (β-TCP) cylinders and local BMP-2 administration on β-TCP resorption and new bone formation.

Methods

Bilateral cylindrical bone defects were created in rabbit distal femora, and the defects were filled with β-TCP. Rabbits were divided into 3 groups; defects were filled with a β-TCP cylinder with a total of approximately 60% porosity (Group A: 13.4% micro- and 46.9% macropore, Group B: 38.5% micro- and 20.3% macropore, Group C: the same micro- and macro-porosity as in group B supplemented with BMP-2). Rabbits were sacrificed 4, 8, 12, and 24 weeks postoperatively.

Results

The number of TRAP-positive cells and new bone formation in group B were significantly greater than those in group A at every period. The amount of residual β-TCP in group C was less than that in group B at all time periods, resulting in significantly more new bone formation in group C at 8 and 12 weeks. The number of TRAP-positive cells in group C was maximum at 4 weeks.

Conclusions

These results suggest that the amount of submicron microporous structure and local BMP-2 administration accelerated both osteoclastic resorption of β-TCP and new bone formation, probably through a coupling-like phenomenon between resorption and new bone formation.

In vitro and in vivo assessment of CaP materials for bone regenerative therapy. The role of multinucleated giant cells/osteoclasts in bone regeneration

In this work, bone formation/remodeling/maturation was correlated with the presence of multinucleated giant cells (MGCs)/osteoclasts (tartrate-resistant acid phosphatase [TRAP]-positive cells) on the surface of beta-tricalcium phosphate (β-TCP), sintered deproteinized bovine bone (sDBB), and carbonated deproteinized bovine bone (cDBB) using a maxillary sinus augmentation (MSA) in a New Zealand rabbit model. Microtomographic, histomorphometric, and immunolabeling for TRAP-cells analyses were made at 15, 30, and 60 days after surgery. In all treatments, a faster bone formation/remodeling/maturation and TRAP-positive cells activity occurred in the osteotomy region of the MSA than in the middle and submucosa regions. In the β-TCP, the granules were rapidly reabsorbed by TRAP-positive cells and replaced by bone tissue. β-TCP enabled quick bone regeneration/remodeling and full bone and marrow restoration until 60 days, but with a significant reduction in MSA volume. In cDBB and sDBB, the quantity of TRAP-positive cells was smaller than in β-TCP, and these cells were associated with granule surface preparation for osteoblast-mediated bone formation. After 30 days, more than 80% of granule surfaces were surrounded and integrated by bone tissue without signs of degradation, preserving the MSA volume. Overall, the materials tested in a standardized preclinical model led to different bone formation/remodeling/maturation within the same repair process influenced by different microenvironments and MGCs/osteoclasts. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:282-297, 2020.

3D printing mesoporous bioactive glass/sodium alginate/gelatin sustained release scaffolds for bone repair

Drug delivery and release are a major challenge fabricating bone tissue engineering. In this study, we fabricated new sustained release hydrogel scaffolds composited of mesoporous bioactive glass, sodium alginate and gelatin by a three-dimensional printing technique. Naringin and calcitonin gene-related peptide were used as drugs to prepare drug-loaded scaffolds by direct printing or surface absorption. The physicochemical properties of the scaffolds and the drug release profiles of the two drug-loading models were investigated. We also examined the biocompatibility of the scaffolds, as well as the effect of the released medium on the proliferation and osteogenic differentiation of human osteoblast-like MG-63 cell. The results showed that the scaffolds had a high porosity (approximately 80%) with an interconnected cubic pore structure, rough surface morphology, bioactivity and strong biocompatibility. Furthermore, the naringin or calcitonin gene-related peptide co-printed into the scaffold displayed a steady sustained release behaviour for up to 21 days without an initial burst release, while both naringin and calcitonin gene-related peptide absorbed onto the surface of the scaffold were completely released within two days. MG-63 cells cultured with the extraction containing released drugs displayed promoted cell proliferation and the expression of osteogenesis-related genes more effectively compared with the drug-free extractions. Therefore, these results demonstrate that the developed mesoporous bioactive glass/sodium alginate/gelatin sustained release scaffolds provide a potential application for bone tissue engineering.

Effect of microporosity on scaffolds for bone tissue engineering

Microporosity has a critical role in improving the osteogenesis of scaffolds for bone tissue engineering. Although the exact mechanism, by which it promotes new bone formation, is not well recognized yet, the related hypothesis can be found in many previous studies. This review presents those possible mechanisms about how the microporosity enhances the osteogenic-related functions of cells in vitro and the osteogenic activity of scaffolds in vivo. In summary, the increased specific surface areas by microporosity can offer more protein adsorption sites and accelerate the release of degradation products, which facilitate the interactions between scaffolds and cells. Meanwhile, the unique surface properties of microporous scaffolds have a considerable effect on the protein adsorption. Moreover, capillary force generated by the microporosity can improve the attachment of bone-related cells on the scaffolds surface, and even make the cells achieve penetration into the micropores smaller than them. This review also pays attention to the relationship between the biological and mechanical properties of microporous scaffolds. Although lots of achievements have been obtained, there is still a lot of work to do, some of which has been proposed in the conclusions and perspectives part.

Promoting proliferation and differentiation of BMSCs by green tea polyphenols functionalized porous calcium phosphate

In this article, we proposed a facile protocol to functionalize porous calcium phosphate ceramics (PCPC) using dietary tea polyphenols (TP). TP molecules was attracted and anchored by Ca2+ ions from the surface of CPC. These TP molecules modulated the nucleation and crystallization of calcium phosphate nanorods assemblies on the surface of PCPC. Our results prove that these calcium phosphate nanorods assemblies accompanies functional groups of TP make PCPC/TP effectively promote proliferation and differentiation of bone mesenchymal stem cells (BMSCs). We inferred that these calcium phosphate nanorods assemblies might change the surface microenvironment of PCPC, which is critical to promote the proliferation and differentiation of BMSCs. Compared with naked PCPC, PCPC/TP obviously increased BMP2, ErK/MAPK and JNK/MAPK level and mineralization capacity of cells (ALP level).

Selective effect of hydroxyapatite nanoparticles on osteoporotic and healthy bone formation correlates with intracellular calcium homeostasis regulation

Adequate bone substitutes osseointegration has been difficult to achieve in osteoporosis. Hydroxyapatite of the osteoporotic bone, secreted by pathologic osteoblasts, had a smaller crystal size and lower crystallinity than that of the normal. To date, little is known regarding the interaction of synthetic hydroxyapatite nanoparticles (HANPs) with osteoblasts born in bone rarefaction. The present study investigated the biological effects of HANPs on osteoblastic cells derived from osteoporotic rat bone (OVX-OB), in comparison with the healthy ones (SHM-OB). A selective effect of different concentrations of HANPs on the two cell lines was observed that the osteoporotic osteoblasts had a higher tolerance. Reductions in cell proliferation, ALP activity, collagen secretion and osteoblastic gene expressions were found in the SHM-OB when administered with HANPs concentration higher than 25µg/ml. In contrast, those of the OVX-OB suffered no depression but benefited from 25 to 250µg/ml HANPs in a dose-dependent manner. We demonstrated that the different effects of HANPs on osteoblasts were associated with the intracellular calcium influx into the endoplasmic reticulum. The in vivo bone defect model further confirmed that, with a critical HANPs concentration administration, the osteoporotic rats had more and mechanically matured new bone formation than the non-treated ones, whilst the sham rats healed no better than the natural healing control. Collectively, the observed epigenetic regulation of osteoblastic cell function by HANPs has significant implication on defining design parameters for a potential therapeutic use of nanomaterials.

STATEMENT OF SIGNIFICANCE

In this study, we investigated the biological effects of hydroxyapatite nanoparticles (HANPs) on osteoporotic rat bone and the derived osteoblast. Our findings revealed a previously unrecognized phenomenon that the osteoporotic individuals could benefit from higher concentrations of HANPs, as compared with the healthy individuals. The in vivo bone defect model confirmed that, with a critical HANPs concentration administration, the osteoporotic rats had more mechanically matured new bone formation than the non-treated ones, whilst the sham rats healed no better than the natural healing control. The selective effect of HANPs might be associated with the intracellular calcium influx into the endoplasmic reticulum. Collectively, the observed epigenetic regulation by HANPs has significant implication on defining design parameters for a potential therapeutic use of nanomaterials in a pathological condition.

Hierarchically porous structure, mechanical strength and cell biological behaviors of calcium phosphate composite scaffolds prepared by combination of extrusion and porogen burnout technique and enhanced by gelatin

In this study, hierarchically porous calcium phosphate scaffolds (HTCP) with unidirectional pores, transversely interconnected pores, and micropores were fabricated by the combination of extrusion and porogen burnout technique. Gelatin was incorporated into the HTCP scaffolds by vacuum-impregnation of gelatin solution and subsequent freeze-drying. The phase composition, microstructure, physical and cytobiological properties were analyzed. The results showed that the HTCP scaffolds were composed of β-tricalcium phosphate with minor hydroxyapatite. The HTCP scaffolds had unidirectional pores (~400μm), transversely interconnected pores (~130μm) and micropores (~1μm). The incorporation of gelatin significantly increased the compressive strength, toughness, and cell seeding of the HTCP scaffolds. The composite scaffolds showed excellent cytocompatibility. The hierarchically porous calcium phosphate composite scaffolds may have potential application prospects in bone tissue engineering.

Osteoinductive porous biphasic calcium phosphate ceramic as an alternative to autogenous bone grafting in the treatment of mandibular bone critical-size defects

The bone-induction capacity of a porous biphasic calcium phosphate (pBCP) using heterotopic implantation in mouse (mHI-model) and its efficacy as substitute for autograft in mandibular critical-size defect in rabbit (rabMCSD-model) was investigated. In mHI-model, pBCP was implanted into the thigh muscles and bone formation was histomorphometrically and immunohistochemically evaluated. In rabMCSD-model, 13 mm bone defects were treated with pBCP or autograft and bone repair comparatively evaluated by radiographic and histomorphometric methods. In mHI-model, formed bone and immunolabeling for bone morphogenetic protein-2 and osteopontin were observed in 90% of pBCP implanted samples after 12 weeks. In rabMCSD-model neither statistically significant difference was found in newly formed bone between pBCP and autograft groups at 4 weeks (18.8 ± 5.5% vs 27.1 ± 5.6%), 8 weeks (22.3 ± 2.7% vs 26.2 ± 5.1), and 12 weeks (19.6 ± 4.7% vs 19.6 ± 2.3%). At 12 weeks, the stability and contour of the mandible were restored in both treatments. Near tooth remaining, pBCP particles were covered by small amount of mineralized tissue exhibiting perpendicular attachments of collagen fiber bundles with histological characteristic of acellular cementum. Within the limitations of this study, it was concluded that pBCP is osteoinductive and able to stimulate the new formation of bone and cementum-like tissues in rabMCSD-model, suggesting that it may be an alternative to treatment of large bone defect and in periodontal regenerative therapy. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1546-1557, 2018.

Role of biphasic calcium phosphate ceramic-mediated secretion of signaling molecules by macrophages in migration and osteoblastic differentiation of MSCs

The inflammatory reaction initiates fracture healing and could play a role in the osteoinductive effect of calcium phosphate (CaP) ceramics, which has been widely confirmed; however, the underlying mechanism has not been fully elucidated. In this study, various signaling molecules from macrophages under the stimulation of osteoinductive biphasic calcium phosphate (BCP) ceramic and its degradation products were examined and evaluated for their influence on the migration and osteoblastic differentiation of mesenchymal stem cells (MSCs). The results of cellular experiments confirmed that the gene expression of most inflammatory factors (IL-1, IL-6 and MCP-1) and growth factors (VEGF, PDGF and EGF) by macrophages were up-regulated to varying degrees by BCP ceramic and its degradation products. Cell migration tests demonstrated that the conditioned media (CMs), which contained abundant signaling molecules secreted by macrophages cultured on BCP ceramic and its degradation products, promoted the migration of MSCs. qRT-PCR analysis indicated that CMs promoted the gene expression of osteogenic markers (ALP, COL-I, OSX, BSP and OPN) in MSCs. ALP activity and mineralization staining further confirmed that CMs promoted the osteoblastic differentiation of MSCs. The present study confirmed the correlation between the inflammatory reaction and osteoinductive capacity of BCP ceramic. The ceramic itself and its degradation products can induce macrophages to express and secrete various signaling molecules, which then recruit and promote the MSCs to differentiate into osteoblasts. Compared with BCP conditioned media, degradation particles played a more substantial role in this process. Thus, inflammation initiated by BCP ceramic and its degradation products could be necessary for osteoinduction by the ceramic.

STATEMENT OF SIGNIFICANCE

It is known that the inflammatory reaction initiates fracture healing. The aim of this study was to examine whether osteoinductive BCP ceramics could cause macrophages to change their secretion patterns and whether the secreted cytokines could affect migration and osteoblastic differentiation of MSCs. Moreover, the duration of inflammation could be influenced by the local ionic environment and the degradation products of the implant. Our experimental results revealed the correlation between the inflammatory reaction and osteoinductive capacity of BCP ceramic. The ceramic itself and its degradation products can induce macrophages to express and secrete various signaling molecules, which then recruit and promote the MSCs to differentiate into osteoblasts. Compared with ionic microenvironment, degradation particles played a more substantial role in this process. Therefore, the appropriate inflammation initiated by BCP ceramic and its degradation products could be essential for osteoinduction by the ceramic. We believe that the present study improves the understanding of the effect of biomaterial-mediated inflammation on MSC migration and differentiation and established a preliminary correlation between the immune system and osteoinduction by biomaterials.

Muscle as an osteoinductive niche for local bone formation with the use of a biphasic calcium sulphate/hydroxyapatite biomaterial

Objectives

We have observed clinical cases where bone is formed in the overlaying muscle covering surgically created bone defects treated with a hydroxyapatite/calcium sulphate biomaterial. Our objective was to investigate the osteoinductive potential of the biomaterial and to determine if growth factors secreted from local bone cells induce osteoblastic differentiation of muscle cells.

Materials and Methods

We seeded mouse skeletal muscle cells C2C12 on the hydroxyapatite/calcium sulphate biomaterial and the phenotype of the cells was analysed. To mimic surgical conditions with leakage of extra cellular matrix (ECM) proteins and growth factors, we cultured rat bone cells ROS 17/2.8 in a bioreactor and harvested the secreted proteins. The secretome was added to rat muscle cells L6. The phenotype of the muscle cells after treatment with the media was assessed using immunostaining and light microscopy.

Results

C2C12 cells differentiated into osteoblast-like cells expressing prominent bone markers after seeding on the biomaterial. The conditioned media of the ROS 17/2.8 contained bone morphogenetic protein-2 (BMP-2 8.4 ng/mg, standard deviation (sd) 0.8) and BMP-7 (50.6 ng/mg, sd 2.2). In vitro, this secretome induced differentiation of skeletal muscle cells L6 towards an osteogenic lineage.

Conclusion

Extra cellular matrix proteins and growth factors leaking from a bone cavity, along with a ceramic biomaterial, can synergistically enhance the process of ectopic ossification. The overlaying muscle acts as an osteoinductive niche, and provides the required cells for bone formation.

Cite this article: D. B. Raina, A. Gupta, M. M. Petersen, W. Hettwer, M. McNally, M. Tägil, M-H. Zheng, A. Kumar, L. Lidgren. Muscle as an osteoinductive niche for local bone formation with the use of a biphasic calcium sulphate/hydroxyapatite biomaterial. Bone Joint Res 2016;5:500–511. DOI: 10.1302/2046-3758.510.BJR-2016-0133.R1.

In vitro characterization of an osteoinductive biphasic calcium phosphate in combination with recombinant BMP2

BACKGROUND

The repair of alveolar bone defects with growth factors and bone grafting materials has played a pivotal role in modern dentistry. Recombinant human bone morphogenetic protein-2 (rhBMP2), an osteoinductive growth factor capable of cell recruitment and differentiation towards the osteoblast lineage, has been utilized in combination with various biomaterials to further enhance new bone formation. Recently, a group of novel biphasic calcium phosphate (BCP) bone grafting materials have been demonstrated to possess osteoinductive properties by demonstrating signs of ectopic bone formation. The aim of the present study was to study the effects of rhBMP2 in combination with osteoinductive BCP bone grafts on osteoblast cell behaviour.

METHODS

MC3T3-E1 pre-osteoblasts were seeded on 1) control tissue culture plastic, 2) 10 mg of BCP alone, 3) 100 ng rhBMP2, and 4) 100 ng rhBMP2+ 10 mg of BCP and analyzed for cell recruitment via a Transwell chamber, proliferation via an MTS assay and differentiation as assessed by alkaline phosphatase (ALP) activity, alizarin red staining and real-time PCR for osteoblast differentiation markers including Runx2, collagen1, ALP, and osteocalcin (OCN).

RESULTS

rhBMP2 was able to significantly upregulate cell recruitment whereas the addition of BCP as well as BCP alone had no additional ability to improve osteoblast recruitment. Both BCP and rhBMP2 were able to significantly increase cell proliferation at 3 and 5 days post seeding and cell number was further enhanced when rhBMP2 was combined with BCP. In addition, the combination of rhBMP2 with BCP significantly improved ALP activity at 7 and 14 days post seeding, alizarin red staining at 14 days, and mRNA levels of Runx2, ALP and osteocalcin when compared to cells seeded with rhBMP2 alone or BCP alone.

CONCLUSIONS

The results from the present study demonstrate that 1) the osteoinductive potential of BCP bone particles is equally as osteopromotive as rhBMP2 on in vitro osteoblast differentiation and 2) BCP particles in combination with rhBMP2 is able to further increase the osteopromotive differentiation of osteoblasts in vitro when compared to either rhBMP2 alone or BCP alone. Future animal testing is further required to investigate this combination approach on new bone formation.

Osteogenic gene array of osteoblasts cultured on a novel osteoinductive biphasic calcium phosphate bone grafting material

OBJECTIVES

Recently, novel biphasic calcium phosphate (BCP) scaffolds have emerged as a new class of bone grafts with osteoinductive potential demonstrating the ability to form ectopic bone in extra-skeletal sites. The aim of the present study was to perform an osteogenic gene array to target possible genes responsible for eliciting the changes in cell expression responsible for inducing osteoblast differentiation.

MATERIALS AND METHODS

Human MG63 osteoblast-like cells were seeded for 24 h on tissue culture plastic or osteoinductive BCP particles and analyzed for upregulated genes using an osteogenesis super-array. Osteoblast-related genes including those transcribed during bone mineralization, bone metabolism, cell growth and differentiation, as well as gene products representing extracellular matrix molecules, transcription factors, and cell adhesion molecules were investigated.

RESULTS

An upregulation of genes transcribing biglycan (1.7-fold), bone morphogenetic proteins 1, 2, 4, 6, and 7 (1.5-2.1-fold), various collagen isoforms including 1a1, 1a2, 2a1, and 5a1 (1.73-2.72-fold), colony stimulating factor 2 (2.59-fold), fibroblast growth factor receptor 2 (1.79-fold), fibronectin (2.56-fold), integrin alpha 1, 2, and 3 (1.82-2.24-fold), SOX9 (2.75-fold), transforming growth factor beta receptor 2 (1.72-fold), vitamin D (1.89-fold), and vascular endothelial growth factor A and B (2.00, 1.75-fold) were all significantly (p < 0.05) increased on BCP particles when compared to control tissue culture plastic.

CONCLUSION

In summary, a number of activated genes were involved in bone formation following osteoblast attachment to BCP particles. The involvement of key chondrogenic genes hints that bone grafts capable of spontaneously inducing ectopic bone formation may implicate endochondral ossification. Further investigations in the triggered pathways involved in the process of ectopic bone formation are necessary to understand the key inductive properties of these novel osteoinductive BCP particles.

CLINICAL RELEVANCE

Novel osteoinductive BCP particles demonstrate a wide range of significant increases over several key molecules implicated in osteogenesis that may be implicated in their ability to form ectopic bone formation.

Preclinical testing of drug delivery systems to bone

Bone defects do not heal in 5-10% of the fractures. In order to enhance bone regeneration, drug delivery systems are needed. They comprise a scaffold with or without inducing factors and/or cells. To test these drug delivery systems before application in patients, they finally need to be tested in animal models. The choice of animal model depends on the main research question; is a functional or mechanistic evaluation needed? Furthermore, which type of bone defects are investigated: load-bearing (i.e. orthopedic) or non-load-bearing (i.e. craniomaxillofacial)? This determines the type of model and in which type of animal. The experiments need to be set-up using the 3R principle and must be reported following the ARRIVE guidelines.