Nanocrystalline spherical hydroxyapatite granules for bone repair: in vitro evaluation with osteoblast-like cells and osteoclasts

Bioinks for Space Missions: The Influence of Long-Term Storage of Alginate-Methylcellulose-Based Bioinks on Printability as well as Cell Viability and Function

Bioprinting is considered a key technology for future space missions and is currently being established on the International Space Station (ISS). With the aim to perform bioink production as a critical and resource-consuming preparatory step already on Earth and transport a bioink cartridge "ready to use" to the ISS, the storability of bioinks is investigated. Hydrogel blends based on alginate and methylcellulose are laden with either green microalgae of the species Chlorella vulgaris or with different human cell lines including immortilized human mesenchymal stem cells, SaOS-2 and HepG2, as well as with primary human dental pulp stem cells. The bioinks are filled into printing cartridges and stored at 4°C for up to four weeks. Printability of the bioinks is maintained after storage. Viability and function of the cells embedded in constructs bioprinted from the stored bioinks are investigated during subsequent cultivation: The microalgae survive the storage period very well and show no loss of growth and functionality, however a significant decrease is visible for human cells, varying between the different cell types. The study demonstrates that storage of bioinks is in principle possible and is a promising starting point for future research, making complex printing processes more effective and reproducible.

Bovine hydroxyapatite-based scaffold accelerated the inflammatory phase and bone growth in rats with bone defect

Hydroxyapatite (HA) is a biomaterial widely used to treat bone defect, such as due to traffic accident. The HA scaffold is obtained from synthetic HA or natural sources, such as bovine hydroxyapatite (BHA). This study aims to compare the characteristics and in vivo performance of BHA-based and HA-based scaffolds. For this purpose, the scaffold was formulated with gelatin (GEL) and characterised by SEM-EDX, FTIR and mini autograph. The defect model was carried out on the femur area of Wistar rats classified into three animal groups: defect, HA-GEL and BHA-GEL. Postoperatively (7, 14 and 28 days), the bone was radiologically evaluated, and stained with haematoxylin-eosin, anti-CD80 and anti-CD163. The BHA-GEL scaffold showed a regular surface and spherical particle shape, whereas the HA-GEL scaffold exhibited irregular surface. The BHA-GEL scaffold had higher pore size and compressive strength and lower calcium-to-phosphorus ratio than the HA-GEL scaffold. In vivo study showed that the expression of CD80 in the three experimental groups was not significantly different. However, the expression of CD163 differed significantly between the groups. The BHA-GEL group showed robust expression of CD163 on day 7, which rapidly decreased over time. It also showed increased osteoclasts, osteoblasts and osteocytes cell count that contributed to the integrity of the defect area. In conclusion, the BHA-based scaffold exhibited the desired physical and chemical characteristics that benefit in vivo performance versus the HA-based scaffold. Thus, the BHA-based scaffold may be used as a bone graft.

The antibacterial and angiogenic effect of magnesium oxide in a hydroxyapatite bone substitute

Bone graft infections are serious complications in orthopaedics and the growing resistance to antibiotics is increasing the need for antibacterial strategies. The use of magnesium oxide (MgO) is an interesting alternative since it possesses broad-spectrum antibacterial activity. Additionally, magnesium ions also play a role in bone regeneration, which makes MgO more appealing than other metal oxides. Therefore, a bone substitute composed of hydroxyapatite and MgO (HAp/MgO) spherical granules was developed using different sintering heat-treatment cycles to optimize its features. Depending on the sintering temperature, HAp/MgO spherical granules exhibited distinct surface topographies, mechanical strength and degradation profiles, that influenced the in vitro antibacterial activity and cytocompatibility. A proper balance between antibacterial activity and cytocompatibility was achieved with HAp/MgO spherical granules sintered at 1100 ºC. The presence of MgO in these granules was able to significantly reduce bacterial proliferation and simultaneously provide a suitable environment for osteoblasts growth. The angiogenic and inflammation potentials were also assessed using the in vivo chicken embryo chorioallantoic membrane (CAM) model and the spherical granules containing MgO stimulated angiogenesis without increasing inflammation. The outcomes of this study evidence a dual effect of MgO for bone regenerative applications making this material a promising antibacterial bone substitute.

Dental alloplastic bone substitutes currently available in Korea

As dental implant surgery and bone grafts were widely operated in Korean dentist, many bone substitutes are commercially available, currently. For commercially used in Korea, all bone substitutes are firstly evaluated by the Ministry of Health and Welfare (MOHW) for safety and efficacy of the product. After being priced, classified, and registration by the Health Insurance Review and Assessment Service (HIRA), the post-application management is obligatory for the manufacturer (or representative importer) to receive a certificate of Good Manufacturing Practice by Ministry of Food and Drug Safety. Currently, bone substitutes are broadly classified into C group (bone union and fracture fixation), T group (human tissue), L group (general and dental material) and non-insurance material group in MOHW notification No. 2018-248. Among them, bone substitutes classified as dental materials (L7) are divided as xenograft and alloplastic bone graft. The purpose of this paper is to analyze alloplastic bone substitutes of 37 products in MOHW notification No. 2018-248 and to evaluate the reference level based on the ISI Web of Knowledge, PubMed, EMBASE (1980–2019), Cochrane Database, and Google Scholar using the criteria of registered or trademarked product name.

Organically modified hydroxyapatite (ormoHAP) nanospheres stimulate the differentiation of osteoblast and osteoclast precursors: a co-culture study

Isolated nanospheres consisting of organically modified hydroxyapatite (ormoHAP), prepared by an electric field-assisted ion double migration process, were embedded in foamed gelatin to form a composite scaffold. Degradation rates have been demonstrated to correlate with the crosslinking degree (40%, 80%) as well as with the mineral content of the scaffolds (0%, 20%, 40%). A human co-culture model of osteoblasts and osteoclasts, derived from bone marrow stromal cells and monocytes, respectively, without external addition of the factors RANKL and M-CSF, was run for up to 42 d in order to characterize the action of the ormoHAP-gelatin scaffolds on the co-culture. Examination was performed by quantitative biochemical methods (DNA, LDH, ALP, TRAP5b), gene expression analysis (ALP, BSP II, RANKL, IL-6, VTNR, CTSK, TRAP, OSCAR, CALCR) and confocal laser scanning microscopy (cell nuclei, actin, CD68, TRAP). Results confirm that ormoHAP embedded in the gelatin matrix enhanced TRAP 5b activity. As a feedback, ALP activity and gene expression of BSP II of osteoblasts increased. Finally, a sequence of cell cross-talk actions is suggested, which can explain the behavior of the formed vital co-culture and moreover the influence of the presence and concentration of ormoHAP.

Osteoinductivity of Porous Biphasic Calcium Phosphate Ceramic Spheres with Nanocrystalline and Their Efficacy in Guiding Bone Regeneration

Conventional biphasic calcium phosphate (BCP) bioceramics are facing many challenges to meet the demands of regenerative medicine, and their biological properties are limited to a large extent due to the large grain size in comparison with nanocrystalline of natural bone mineral. Herein, this study aimed to fabricate porous BCP ceramic spheres with nanocrystalline (BCP-N) by combining alginate gelatinizing with microwave hybrid sintering methods and investigated their in vitro and in vivo combinational osteogenesis potential. For comparison, spherical BCP granules with microcrystalline (BCP-G) and commercially irregular BCP granules (BAM, BCP-I) were selected as control. The obtained BCP-N with specific nanotopography could well initiate and regulate in vitro biological response, such as degradation, protein adsorption, bone-like apatite formation, cell behaviors, and osteogenic differentiation. In vivo canine intramuscular implantation and rabbit mandible critical-sized bone defect repair further confirmed that nanotopography in BCP-N might be responsible for the stronger osteoinductivity and bone regenerative ability than BCP-G and BCP-I. Collectedly, due to nanotopographic similarities with nature bone apatite, BCP-N has excellent efficacy in guiding bone regeneration and holds great potential to become a potential alternative to standard bone grafts in bone defect filling applications.

[Efficacy of inactivated autologous porous bone flap and BAM bone-induced artificial bone for repairing skull defect in rats]

OBJECTIVE

To study the effect of BAM bone grafting combined with inactivated autologous porous bone flap in repairing skull defect in rats.

METHODS

Seventy-two Wistar rats with skull defect were randomly divided into control group, inactivated autologous bone flap group (AB group), BAM bone-induced artificial bone material group (BAM group), and inactivated autologous bone flap with BAM bone-induced artificial bone group (BAM+AB group). The bone healing was evaluated with micro-CT and the new bone formation was assessed with histological staining at 1, 2, and 3 months after modeling.

RESULTS

Inactivated porous bone flap combined with BAM bone-induced artificial bone effectively induced vascular and fibrous tissue regeneration and osteogenesis in the cranial defects. With the inactivated porous bone flap as the scaffold, BAM bone-induced artificial bone obviously promoted the restoration of the skull appearance in the rats with cranial defects.

CONCLUSION

Inactivated autologous bone flap group and BAM bone-induced artificial bone material can promote skull healing and restoration of the original skull appearance, and can be used for reconstruction of the local anatomy of the skull surface.

Quantitative stereological analysis of the highly porous hydroxyapatite scaffolds using X-ray CM and SEM

BACKGROUND

Material properties of the scaffolds as well as their microstructure are vital in determining in vivo cellular response. Three-dimensional (3D), highly porous scaffolds are used in tissue engineering to provide a suitable microenvironment and to support regeneration of bone. Both pore sizes and their architecture, in particular interconnection density, impact functionality of scaffold during its biomedical applications.

OBJECTIVE

In this paper a comparative study of the microstructure of highly porous hydroxyapatite scaffolds produced via gelcasting of foamed slurries and replication of polyurethane sponge were carried out.

METHODS

Quantitative stereological analysis of the microstructure was conducted using transmission X-ray computed microtomography (μCT) and scanning electron microscopy (SEM). Application of the X-ray microtomography allowed obtaining the 2D cross-sectional images of examined samples, and then the 3D reflection of individual samples.

RESULTS

In our studies we proved that the distribution of pores in HAp bioceramics can be controlled by selection of the manufacturing method. In the case of material produced by the gelcasting method, the porosity of the samples was about ∼78 vol.%, while for the method of replication of the porous organic matrix it was higher ∼84 vol.%. Application of gelcasting method resulted in bioceramics with the macropores ranging from 95 μm to 158 μm (the modal value of 120 μm). Furthermore, micropores of size 34 μm-60 μm - so called "windows", were observed on spherical macropores surfaces. In the case of replication of polyurethane sponge only macropores from 295 μm to 337 μm (the modal value of 300 μm) were obtained. Application of μCT and SEM give more information than classical mercury intrusion porosimetry in studies of porous bioceramics. Developed materials met the criteria for porous bone substitutes.

CONCLUSIONS

The results of quantitative description of microstructure allowed determining the differences between porous hydroxyapatite bioceramics obtained via replication of porous organic matrix and gelcasting of foamed slurry. The stereological analysis demonstrated, that bioceramics prepared via gelling of foamed slurry has a lower pore size and grains (1.1-1.9 μm) than the material obtained by the method of replication of polyurethane sponge (2.1-2.3 μm). Based on morphological analysis the porosity of tested materials was determined. In the case of material produce by the gelcasting, porosity of the samples was about ∼78 vol.%, while for method of replication of the porous organic matrix the porosity was higher and constituted ∼84 vol.%. Furthermore, evaluated materials varied in porosity and the pore size distribution. It was stated that the method of gelcasting resulted in hydroxyapatite bioceramics with the macropores diameter (95-158 μm), micropores so called "windows" (34-60 μm) - observed on spherical macropores walls and micropores of size 0.6 μm-1.3 μm, which were visible in sintered areas. When the method of replication of polyurethane sponge was applied only macropores from 295 μm to 337 μm were obtained. The comparable values of shape factors such as elongation, curvature of pours boundary and convexity, confirmed that macropores in both studied series had similar shape.

Calcium Phosphate Bioceramics: A Review of Their History, Structure, Properties, Coating Technologies and Biomedical Applications

Calcium phosphate (CaP) bioceramics are widely used in the field of bone regeneration, both in orthopedics and in dentistry, due to their good biocompatibility, osseointegration and osteoconduction. The aim of this article is to review the history, structure, properties and clinical applications of these materials, whether they are in the form of bone cements, paste, scaffolds, or coatings. Major analytical techniques for characterization of CaPs, in vitro and in vivo tests, and the requirements of the US Food and Drug Administration (FDA) and international standards from CaP coatings on orthopedic and dental endosseous implants, are also summarized, along with the possible effect of sterilization on these materials. CaP coating technologies are summarized, with a focus on electrochemical processes. Theories on the formation of transient precursor phases in biomineralization, the dissolution and reprecipitation as bone of CaPs are discussed. A wide variety of CaPs are presented, from the individual phases to nano-CaP, biphasic and triphasic CaP formulations, composite CaP coatings and cements, functionally graded materials (FGMs), and antibacterial CaPs. We conclude by foreseeing the future of CaPs.

Influences of the steam sterilization on the properties of calcium phosphate porous bioceramics

The influences of steam sterilization on the physicochemical properties of calcium phosphate (Ca-P) porous bioceramics, including β-tricalcium phosphate (β-TCP), biphasic calcium phosphate (BCP) and hydroxyapatite (HA) are investigated. After being steam sterilized in an autoclave (121 °C for 40 min), the porous bioceramics are dried and characterized. The steam sterilization has no obvious effects on the phase composition, thermal stability, pH value and dissolubility of β-TCP porous bioceramic, but changes its morphology and mechanical strength. Meanwhile, the steam sterilization leads to the significant changes of the morphology, phase composition, pH value and dissolubility of BCP porous bioceramic. The increase of dissolubility and mechanical strength, the decrease of pH value of the immersed solution and partial oriented growth of crystals are also observed in HA porous bioceramic after steam sterilization. These results indicate that the steam sterilization can result in different influences on the physicochemical properties of β-TCP, BCP and HA porous bioceramics, thus the application of the steam sterilization on the three kinds of Ca-P porous bioceramics should be considered carefully based on the above changed properties.

Radiopacity and cytotoxicity of Portland cement associated with niobium oxide micro and nanoparticles

OBJECTIVE

Mineral Trioxide Aggregate (MTA) is composed of Portland Cement (PC) and bismuth oxide (BO). Replacing BO for niobium oxide (NbO) microparticles (Nbµ) or nanoparticles (Nbη) may improve radiopacity and bioactivity. The aim of this study was to evaluate the radiopacity and cytotoxicity of the materials: (1) PC; (2) White MTA; (3) PC+30% Nbµ; (4) PC+30% Nbη.

MATERIAL AND METHODS

For the radiopacity test, specimens of the different materials were radiographed along an aluminum step-wedge. For cell culture assays, Saos-2 osteoblastic-cells (ATCC HTB-85) were used. Cell viability was evaluated through MTT assay, and bioactivity was assessed by alkaline phosphatase activity assay.

RESULTS

The results demonstrated higher radiopacity for MTA, followed by Nbµ and Nbη, which had similar values. Cell culture analysis showed that PC and PC+NbO associations promoted greater cell viability than MTA.

CONCLUSIONS

It was concluded that the combination of PC+NbO is a potential alternative for composition of MTA.

Antibacterial activity and biocompatibility of three-dimensional nanostructured porous granules of hydroxyapatite and zinc oxide nanoparticles--an in vitro and in vivo study

Ceramic scaffolds are widely studied in the bone tissue engineering field due to their potential in regenerative medicine. However, adhesion of microorganisms on biomaterials with subsequent formation of antibiotic-resistant biofilms is a critical factor in implant-related infections. Therefore, new strategies are needed to address this problem. In the present study, three-dimensional and interconnected porous granules of nanostructured hydroxyapatite (nanoHA) incorporated with different amounts of zinc oxide (ZnO) nanoparticles were produced using a simple polymer sponge replication method. As in vitro experiments, granules were exposed to Staphylococcus aureus and Staphylococcus epidermidis and, after 24 h, the planktonic and sessile populations were assessed. Cytocompatibility towards osteoblast-like cells (MG63 cell line) was also evaluated for a period of 1 and 3 days, through resazurin assay and imaging flow cytometry analysis. As in vivo experiments, nanoHA porous granules with and without ZnO nanoparticles were implanted into the subcutaneous tissue in rats and their inflammatory response after 3, 7 and 30 days was examined, as well as their antibacterial activity after 1 and 3 days of S. aureus inoculation. The developed composites proved to be especially effective at reducing bacterial activity in vitro and in vivo for a weight percentage of 2% ZnO, with a low cell growth inhibition in vitro and no differences in the connective tissue growth and inflammatory response in vivo. Altogether, these results suggest that nanoHA-ZnO porous granules have a great potential to be used in orthopaedic and dental applications as a template for bone regeneration and, simultaneously, to restrain biomaterial-associated infections.

Hydroxyapatite-based materials of marine origin: a bioactivity and sintering study

Single phase hydroxyapatite (HAp) and biphasic material hydroxyapatite/β-tricalcium phosphate (HAp/β-TCP) were obtained from a marine source (Atlantic cod fish bones). Here we report a study on the biological properties of these materials, including cytotoxicity, bioactivity and haemocompatibility. Results showed that the materials are not cytotoxic, neither in their powder nor in pellet form; indeed growth of Saos-2 cells was comparable to that of commercial. The haemolysis rate was lower than 2%; hence the materials can be classified as non-haemolytic. Moreover, when immersed in Simulated Body Fluid (SBF), crystal formation was observed on the surface of both materials. The sintering behaviour of the samples was also studied; both powders showed very high sinterability (density higher than 95% of the theoretical value). Overall, these results confirm the suitability of these materials for biomedical applications.