Meso‐macroporous crack‐free nanohydroxyapatite coatings templated by C 12 E 10 diblock copolymer on Ti6Al4V implant materials toward human osteoblast‐like cells

Enhanced model protein adsorption of nanoparticulate hydroxyapatite thin films on silk sericin and fibroin surfaces

Hydroxyapatite coated metallic implants favorably combine the required biocompatibility with the mechanical properties. As an alternative to the industrial coating method of plasma spraying with inherently potential deleterious effects, sol-gel methods have attracted much attention. In this study, the effects of intermediate silk fibroin and silk sericin layers on the protein adsorption capacity of hydroxyapatite films formed by a particulate sol-gel method were determined experimentally. The preparation of the layered silk protein/hydroxyapatite structures on glass substrates, and the effects of the underlying silk proteins on the topography of the hydroxyapatite coatings were described. The topography of the hydroxyapatite layer fabricated on the silk sericin was such that the hydroxyapatite particles were oriented forming an oriented crystalline surface. The model protein (bovine serum albumin) adsorption increased to 2.62 µg/cm² on the latter surface as compared to 1.37 µg/cm² of hydroxyapatite on glass without an intermediate silk sericin layer. The BSA adsorption on glass (blank), glass/c-HAp, glass/m-HAp, glass/sericin/c-HAp, and glass/sericin/m-HAp substrates, reported as decrease in BSA concentration versus contact time.

Synthesis and characterization of lysozyme-conjugated Ag.ZnO@HA nanocomposite: A redox and pH-responsive antimicrobial agent with photocatalytic activity

Hydroxyapatite (HA) is extensively used for implantable device coating; however, it lacks antibacterial property, leading to potential bacterial infection during orthopedic implantation surgery. Herein, to enhance the antibacterial activity of HA, a redox- and pH-responsive HA nanocomposite with photocatalytic activity was designed. A photosensitive heterostructure, zinc oxide/hydroxyapatite (ZnO.HA), was coated with Ag nanoparticles (AgNPs) with assisted gallic acid using the UV-irradiation method. An antibacterial enzyme, lysozyme, was then conjugated on the surface of the nanocomposite by a cleavable disulfide linker, resulting in a redox-sensitive nanoplatform. In comparison with bare HA, the designed nanocomposites as Lyso.CAGZ@HA displayed much higher antibacterial activity (> 5-fold) toward Escherichia coli (E. coli) owing to the synergistic antibacterial effects of ZnONPs, AgNPs, gallic acid, and lysozyme on the surface of the nanocomposite. However, antibacterial and antifouling effects are much more enhanced in Lyso.CAGZ@HA-treated bacteria as they were subjected to UVA irradiation. Moreover, the cellular uptake of nanocomposite and intracellular glutathione depletion enhanced in the presence of UVA light, resulting in reactive oxygen specious generation enhancement. Further, in vitro cytotoxicity experiments on mammalian cells (human foreskin fibroblast) revealed that nanocomposite has no cytotoxic effects. Hence, this study demonstrated that Lyso.CAGZ@HA could be considered as a potential therapeutic approach against bacterial infectious diseases.

Impact of exogenous metal ions on peri-implant bone metabolism: a review

The development of effective methods to promote the osseointegration of dental implants by surface modification is an area of intense research in dental materials science. Exogenous metal ions present in the implant and surface modifications are closely related to the bone metabolism around the implant. In the complex oral microenvironment, the release of metal ions caused by continuous corrosion of dental implants has an unfavorable impact on the surrounding tissue, and then affects osseointegration, leading to bad results such as loosening and falling off in the late stage of the implant. Besides, these ions can even be distributed in distant tissues and organs. Currently, surface modification techniques are being developed that involve different processing technologies including the introduction of exogenous metal ions with different properties onto the surface of implants to improve performance. However, most metal elements have some level of biological toxicity and can only be used within a safe concentration range to exert the optimum biological effects on recipients. In this paper, we review the adverse effects of metal ions on osseointegration and highlight the emerging applications for metal elements in improving the performance of dental implants.

Induction of osteogenesis in bone tumour cells by purine-conjugated zinc-hydroxyapatite

This study aimed to improve the biocompatibility and osteogenic property of hydroxyapatite (HAP). So HAP nanoparticles were doped with zinc (Zn), and their surface was modified with a purine nucleotide, guanosine 5′-triphosphate (GTP). GTP-loaded nanoparticles (GTP@ZnHAP) were characterised by field emission scanning electron microscopy, Fourier transform infrared, thermogravimetric analysis, zeta potential and ultraviolet–visible spectroscopy. Biological experiments revealed that GTP@ZnHAP nanoparticles were internalised by the cells, inhibiting tumour cell (osteoblast-like cells, Saos-2) expansion with an efficiency more than that observed for ZnHAP nanoparticles and GTP alone. Furthermore, Saos-2 cells were committed to differentiate into the normal osteoblast cells under the influence of GTP@ZnHAP nanoparticles demonstrated by the quantitative assessment of bone-related protein expression (Runx2 and osteocalcin) and cell morphological changes. Moreover, high-performance liquid chromatography analyses disclosed a significant enhancement of intracellular GTP content in GTP@ZnHAP-treated cells, proposing perturbation of intracellular nucleotide equilibrium during the process of osteogenesis induced by GTP@ZnHAP nanoparticles. Overall, GTP@ZnHAP exhibits a better synergistic effect on the modulation of cell growth and induction of osteogenic differentiation in osteosarcoma cells than ZnHAP nanoparticles and GTP alone do. Therefore, GTP@ZnHAP may be regarded as a promising biomaterial for the treatment of bone-related diseases.

Fabrication of nanoparticles for bone regeneration: new insight into applications of nanoemulsion technology

Introducing synthetic bone substitutes into the clinic was a major breakthrough in the regenerative medicine of bone. Despite many advantages of currently available bone implant materials such as biocompatiblity and osteoconductivity, they still suffer from relatively poor bioactivity, osteoinductivity and osteointegration. These properties can be effectively enhanced by functionalization of implant materials with nanoparticles such as osteoinductive hydroxyapatite nanocrystals, resembling inorganic part of the bone, or bioactive polymer nanoparticles providing sustained delivery of pro-osteogenic agents directly at implantation site. One of the most widespread techniques for fabrication of nanoparticles for bone regeneration applications is nanoemulsification. It allows manufacturing of nanoscale particles (<100 nm) that are injectable, 3D-printable, offer high surface-area-to-volume-ratio and minimal mass transport limitations. Nanoparticles obtained by this technique are of particular interest for biomedical engineering due to fabrication procedures requiring low surfactant concentrations, which translates into reduced risk of surfactant-related in vivo adverse effects and improved biocompatibility of the product. This review discusses nanoemulsion technology and its current uses in manufacturing of nanoparticles for bone regeneration applications. In the first section, we introduce basic concepts of nanoemulsification including nanoemulsion formation, properties and preparation methods. In the next sections, we focus on applications of nanoemulsions in fabrication of nanoparticles used for delivery of drugs/biomolecules facilitating osteogenesis and functionalization of bone implants with special emphasis on biomimetic hydroxyapatite nanoparticles, synthetic polymer nanoparticles loaded with bioactive compounds and bone-targeting nanoparticles. We also highlight key challenges in formulation of nanoparticles via nanoemulsification and outline potential further improvements in this field.

Enhanced osteogenesis properties of titanium implant materials by highly uniform mesoporous thin films of hydroxyapatite and titania intermediate layer

Titanium (Ti) has been widely used for medical and dental applications; however, bare Ti cannot be properly connected to a living bone, and hence some modifications are needed for this purpose. The present study describes the synthesis of mesoporous hydroxyapatite thin films (MHF) on titanium implant materials for speeding up and shortening the processes of osteointegration. The uniform MHF was coated on a Ti substrate following the insertion of intermediate titania (TiO₂) film via the sol-gel dip-coating method. The intermediate titania layer improved the bonding strength between the MHF and Ti substrate. MHFs were synthesized using a precursor solution containing phosphoric acid, calcium nitrate tetrahydrate, and a nonionic surfactant (C₁₂E₁₀) as the phosphate source, calcium source, and structure-directing agent, respectively. The effect of calcination temperature on phase composition, morphology, microstructure, roughness, and wettability of the MHFs was investigated using XRD, FE-SEM, COM, AFM, and contact angle measurement. The XRD results revealed the crystalline hydroxyapatite phase, which was improved with an increase in the calcination temperature. Moreover, the FE-SEM images showed the crack-free MHFs, uniform thickness of the layer, and mesoporous surface morphology. In addition, it was found that the roughness and wettability of the samples change upon the alteration of calcination temperature. The biological studies demonstrated that MHFs support the adhesion and proliferation of the mesenchymal stem cells (MSCs) and guid them toward osteogenic differentiation. Therefore, the MHFs prepared in this study may be useful in a wide range of applications, particularly in bone regeneration medicine.