Osseointegration of sputtered SiC-added hydroxyapatite for orthopaedic applications

Over the last few years, a trend in medical applications is to find solutions for metallic implants using coatings that can improve bioactivity and osseointegration. The goal of this study was to obtain and investigate sputtered hydroxyapatite coatings enriched with SiC to enhance the bioactivity and osseointegration of Ti alloys used in orthopaedic applications. The films were characterized in terms of phase composition, roughness, corrosion resistance in a synthetic body fluid (SBF) and in vitro biocompatibility with MG 63 osteoblast-like cells. All of the investigations were conducted using XRD, AFM, cell viability assays and proliferation tests. The results revealed that the addition of SiC had a positive influence on the properties of the sputtered hydroxyapatite. The addition of SiC led to an improvement in coating adhesion and corrosion resistance in an SBF solution over the HAP coating. All of the coatings presented cell viability values over 90%, revealing their suitability for medical applications.     

Preparation of the reticulated hydroxyapatite ceramics using carbon-coated polymeric sponge with elongated pores as a novel template

This paper proposes a novel, simple way to improve the compressive strength of reticulated porous hydroxyapatite (HA) ceramics using carbon-coated polymeric sponges with elongated pores as a novel template. This template allowed samples to have two interconnected pore networks with a preferential orientation, in which an addition pore network was newly formed by removing the carbon-coated polymeric struts, while preserving the pre-existing pore network. The compressive strength of the sample was as high as 2.9 ± 0.3 MPa with a porosity of 76% when tested parallel to the direction of pore elongation. In addition, the in vitro cell test using a pre-osteoblast cell line revealed the samples to have good biocompatibility.     

Highly loaded hydroxyapatite microsphere/ PLA porous scaffolds obtained by fused deposition modelling

The goal of the work was the manufacturing of hydroxyapatite microsphere/polylactic acid (PLA) scaffolds by means of fused deposition modelling (FDM). Micrometer-sized hydroxyapatite spheres synthesized by spray drying (sdHA), were dispersed in PLA by extrusion compounding. Composite filaments were obtained from extrusion which were used in FDM 3D printing for the production of macroporous scaffolds. The sdHA microspheres were used in the composite in order to improve the biomimicry and the bioactivity of the 3D printed scaffold to increase the bone regeneration capacity. Morphological, thermal, physical and mechanical characterizations were performed on the 3D printed composites. Pure PLA scaffolds were 3D printed and used as a reference.Thermal analyses, TGA and DSC evidenced that the glass transition temperature and the degree of crystallinity of PLA were not influenced by the presence of sdHA. Morphological analysis showed a smooth surface of the printed samples when pure PLA was used. A rough surface was found on the PLA/sdHA composites, confirming, the homogeneous dispersion of the ceramic phase in the polymeric matrix. The higher porosity of the composite samples compared to PLA ones, most likely caused a decrease of the mechanical performances of the PLA/sdHA scaffolds. Composite scaffolds displayed stiffness values compatible with that of bone tissue.     

Marine biological waste as a source of hydroxyapatite for bone tissue engineering applications

The demand for bone graft substitutes for orthopedics and dentistry is constantly growing due to the increase of ageing-related diseases. Synthetic hydroxyapatite (HA) is largely used as a bone graft material thanks to its biocompatibility, osteointegration, osteoconductive and osteoinductive properties and similarity to biological apatite, the main mineral component of bones and teeth. Biogenic apatite has gained attention due to its peculiar intrinsic characteristics: multi-doped ion composition and micro- and nano-scale architecture make natural-derived HA particularly promising for biomedical applications.At the same time, the growing interest in green materials is pushing towards the use of more sustainable biomaterials precursors, including re-use materials: marine waste, such as mollusk-shells, shellfish carapaces, cuttlefish bone, and fishbone have become widely studied sources of biogenic HA. Indeed, they are rich in calcium carbonate (CaCO₃), which can be converted into HA by environmentally sustainable processes. This allows the transformation of waste into valuable materials, while paying attention to the issues of sustainability and circular economy.In this review, we listed and discussed the methods to produce HA starting from shell-derived CaCO₃, describing all the steps and synthesis routes proposed for the conversion procedure, with a special focus on the different species of marine shells used. We discussed the use of HA alone or in combination with other materials (natural and synthetic polymers), used to enhance the mechanical and biological properties.We summarized the types of devices obtained by marine-derived HA, including nanorods, particulates and scaffolds and we described their in vitro and in vivo behavior.The up-to-date literature was summarized in tables with a special focus on the in vitro and in vivo biological evaluation of such materials.In conclusion, composite biomaterials based on marine-derived biogenic HA are reported as potential candidates for synthetic bone substitutes highlighting their potential, limitations and future perspectives.     

Subtractive manufacturing of customized hydroxyapatite scaffolds for bone regeneration

An approach to the preparation of customized hydroxyapatite scaffolds for bone regeneration based on subtractive manufacturing has been developed. The developed method is intended as a simple alternative to rapid prototyping based on additive manufacturing methods. The method for the preparation of customized scaffolds consists in computer numerical controlled (CNC) milling of porous hydroxyapatite foam. The machinable foam for customized scaffolds was prepared by direct foaming of a colloidal hydroxyapatite suspension and the foam structure was consolidated by the gelcasting method. The optimal foam after sintering reached a high porosity of 83.3% and the cellular-like structure contained spherical pores with an average diameter of 613 µm, which were connected through windows with an average diameter of 161 µm. The compressive strength of the sintered foam reached an average value of 2 MPa. CNC milling was tested at different stages of the production cycle of the porous foam and after the reinforcing of the foam by impregnation. The best results were obtained by milling the foam presintered at 1100 °C. The milling process was demonstrated and scaffold examples were successfully manufactured.     

Pyrophosphate ions inhibit calcium phosphate cement reaction and enable storage of premixed pastes with a controlled activation by orthophosphate addition

The standard preparation routine of a calcium phosphate cement includes mixing a solid and a liquid component (reactive cement powder and mixing liquid) in an open bowl at the operating theatre. This poses the risk of preparation-related deviations of the resulting properties when the cements are mixed by different persons. Hence, facilitating this mixing procedure is highly desirable. It can be achieved by application of premixed cement pastes: The mixing liquid and a stable suspension of the cement powder are assembled and mixed in a special syringe, minimizing the impact of these preparation-related effects.In this study, a suspension of reactive α-tricalcium phosphate powder in water was stabilized by sodium pyrophosphate decahydrate (PP). Controlled activation of these premixed pastes was then accomplished by adding a concentrated Na₂HPO₄/NaH₂PO₄ (Na₂/Na) solution. Systematic assessment of the activation mechanism, including the effect of the PP concentration and the amount of Na₂/Na added, was performed by isothermal calorimetry, quantitative in-situ X-ray diffraction, rheological characterization and automated Gillmore needle measurements at 37 °C.Premixed pastes with addition of at least 0.05 wt% PP were successfully stabilized for up to 2 weeks at 25 °C, and even 4 weeks at 4 °C. This pre-storage had no significant impact on the setting performance of the pastes. Increasing the PP concentration at constant Na₂/Na amount systematically retarded the setting reaction, while an elevated quantity of Na₂/Na addition at constant PP concentration resulted in an acceleration.Based on these results, a composition stabilized with 0.05 wt% PP and activated with 20.8 vol% Na₂/Na related to the amount of liquid in the premixed pastes appears ideal with respect to the desired setting performance.     

Influence of concentration of hydroxyapatite surface modifier agent on bioactive composite characteristics

The characterization of chitosan – hydroxyapatite (CH – HAp) composite sponges prepared via freeze-drying methodology is reported in this study. Stearic acid (SA), added as a surface modifier of the HAp nanoparticles, induced changes in the TG/DTG results, particle size distribution and particle morphology. Composite sponges prepared with SA coated HAp demonstrated enhanced biocompatibility and structural properties, as compared to the composites prepared with uncoated HAp. SA coating modified the morphology of the composite, promoting a better dispersion of HAp particles within the composite sponges, and better homogeneity of the polymeric cover with HAp particles. The viability of the composites for cell culture applications was analyzed, and the results suggest that the sponges are biocompatible. Therefore, SA proved to be a good candidate for surface coating of HAp nanoparticles prevent agglomerations, and could be used effectively in the preparation of biocompatible composite sponges with chitosan.     

Comparative study of the hydroxyapatite coatings prepared with/without substrate bias

The aim of this paper is to prepare the hydroxyapatite by Ion Beam Assisted Deposition and to investigate in terms of its elemental and phase composition, roughness and in vitro corrosion resistance. The coatings were prepared with and without applying bias on substrate, in order to find the effect of bias on the chemical, structural, morphological and anti-corrosive properties. The biased coatings exhibited Ca/P ratio closer to the value of the stoichiometric HAP (1.67). The phase composition is not affected by the bias evolution. The adhesion of both coatings is still satisfactory for biomedical applications, irrespective of the bias. Hydroxyapatite deposited without bias presented the best corrosion resistance in SBF at 37 °C, probably due to its smooth surface and low porosity. Moreover, this coating proved to have the highest protection ability at the SBF corrosive attack.     

Size and morphology-controlled synthesis of mesoporous hydroxyapatite nanocrystals by microwave-assisted hydrothermal method

We report the rapid microwave-assisted hydrothermal synthesis of mesoporous hydroxyapatite (HAp) nanocrystals with controlled size, morphology, and surface area using various organic modifiers as regulators. The products were analyzed for their crystalline nature, phase purity, morphology, particle size and pore size distribution. Results indicated that ascorbic acid, cetyltrimethyl ammonium bromide (CTAB) and polyvinylpyrrolidone (PVP) play an important role to obtain needle like, rod like and fiber like mesoporous HAp nanocrystals with different specific surface area by controlling growth habit of HAp along c-axis. In addition, the prepared samples were B-type carbonated HAp similar to bone minerals. Therefore, the present approach can be a promising way to obtain precursor for making tissue engineering scaffolds, drug/protein delivery carriers and bone fillers with tunable characteristics.     

Fabrication and characterization of bioactive glass/hydroxyapatite nanocomposite foam by gelcasting method

Bioceramic foams have been applied for drug releasing agents, cell loading, and widely for hard tissue scaffold. The aim of this study was fabrication and characterization of nanostructure bioceramic composite foam (BCF) consisting of hydroxyapatite (HA) and bioactive glass (BG) via gelcasting method for applications in tissue engineering. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analysis techniques were utilized in order to evaluate respectively, phase composition, dimension, morphology, and interconnectivity of pores, and particle size of synthesized HA, BG, and BCF. The results showed that fabrication of the BCF with a particle size in the range 20-42 nm and pore size in the range 100-250 μm was successfully performed. The maximum values of compressive strength and elastic modulus of the BCF were found to be about 1.95 MPa and 204 MPa, respectively, related to a sample sintered at 900 °C for 4 h. The mean values of the true (total) and apparent (interconnected) porosity were calculated in the range 86-91% and 60-71%, respectively. It seems that the measured properties make the BCF a good candidate for tissue engineering applications, preferentially in drug delivery, cell loading, and other nonloading applications.     

Size-controlled synthesis of spinel nickel ferrite nanorods by thermal decomposition of a bimetallic Fe/Ni-MOF

In this work, size-controlled synthesis of nickel ferrite nanoparticles was achieved by the calcination of a bimetallic (Fe/Ni) metal-organic framework (MOF). The bimetallic MOF (Fe₂Ni-MIL-88B) itself was prepared by a two-step route. The first step involved synthesis of the secondary building unit (SBU) by reacting stoichiometric amounts of Ni and Fe precursors with acetic acid. A ligand substitution reaction (terephthalate replaces acetate) in the SBU leads to the formation of the MOF, which was characterized by PXRD, FTIR, SEM and TEM. Afterwards, the MOF was calcined under air atmosphere to obtain nickel ferrite nanorods. PXRD analysis confirmed the spinel structure of the nickel ferrites while electron microscopic analysis (SEM, TEM) revealed their nanorod-like morphology. By increasing the calcination temperature from 600 to 1000 °C, particle size increased from 16 to 32 nm. Oxidation of benzyl alcohol was used as a model test reaction to probe the applicability of spinel nickel ferrite nanorods for catalysis. Interestingly, the largest nanorods exhibited the highest activity (86% conversion), thus demonstrating the potential of spinel ferrites in catalyzing oxidation reactions.     

Structure of the hydroxyapatite plasma-sprayed coatings deposited on pre-heated titanium substrates

Plasma spraying is the most commonly used thermal spray method for the application of hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂) coatings. In the present study, the HA coatings were plasma spraying deposited onto plates of titanium pre-heated to 20 °C, 300 °C and 550 °C. The obtained HA coatings were investigated by means of X-ray diffraction and scanning electron microscopy. It is found that the coatings, in addition to HA, contain the tetracalcium phosphate (TTCP, (Ca₄(PO₄)₂O) phase (~10%) and a small amount of CaO (<2%). Crystal structure of HA in the coatings is revealed to be distorted. The PO4 tetrahedrons are deformed (Baur distortion coefficient D1(TO) ~0.2). The distances Ca1-O1 and Ca1-O2 are changed as compared to these in stoichiometric hydroxyapatite. These distortions are considered as a result of internal stresses, which are demonstrated in the broadening of peaks on X-ray diffraction pattern of HA. Microstructure of coatings consisting of flattened splats was formed by fully molten particles. The axial base texture was developed in the coatings. Ultrastructure is columnar with a preferred orientation of c-axes of the crystals parallel to the normal of plane coating n. The heating of substrate has a marked effect on the ultrastructure of coatings: the domain size increases from 790 to 1100 Å, the strain Δ decreases from 1.6·10^-3 to 1,2·10^–3, TTCP content diminishes from 12% to 7%. These results show that the effects due to heating of the substrate may be associated with partial recovery of HA microstructure.     

Preparation of hydroxyapatite coating on smooth implant surface by electrodeposition

A novel process for the deposition of a hydroxyapatite (HA) coating on a smooth implant surface has been developed. Specimens were firstly subjected to electrodeposition at −1.8 V (versus Ag/AgCl) in a mixed solution of 0.042 M Ca(NO₃)₂·4H₂O and 0.025 M NH₄H₂PO₄ at 85 °C for 5 s, and then post-treated in 1 M NaOH solution for 30 min. The experimental results showed the specimens prepared by the designed process to have better adhesion properties than those prepared by the traditional electrodeposition process.     

Electrophoretic deposition (EPD) of nanohydroxyapatite - nanosilver coatings on Ti13Zr13Nb alloy

Titanium and its alloys are the biomaterials most frequently used in medical engineering, especially as parts of orthopedic and dental implants. The surfaces of titanium and its alloys are usually modified to improve their biocompatibility and bioactivity, for example, in connection with the deposition of hydroxyapatite coatings.The objective of the present research was to elaborate the technology of electrophoretic deposition (EPD) of nanohydroxyapatite (nanoHAp) coatings decorated with silver nanoparticles (nanoAg) and to investigate the mechanical and chemical properties of these coatings as determined by EPD voltage and the presence of nanoAg. The deposition of nanoHAp was carried out at two voltage values, 15 and 30 V. The decoration of nanoHAp coatings with nanoAg was carried out using the EPD process at a voltage value of 60 V and a deposition time of 5 min. The thickness of the undecorated coatings was found to be 2.16 and 5.14 µm for applied EPD voltages of 15- and 30-V, respectively. The release rate of silver nanoparticles into an artificial saliva solution increased with exposure time and EPD voltage. The corrosion current, between 1 and 10 nA/cm², was significantly higher for undecorated nanoHAp coatings and close to that of the substrate for decorated nanoHAp coatings. The hardness of the undecorated nanoHAp coatings obtained at 15 and 30 V of EPD voltage attained 0.2245±0.036 and 0.0661±0.008 GPa, respectively. Resistance to nanoscratching was higher for thicker coatings. The wettability angle was lower for coatings decorated with nanoAg.     

One step method to synthesize flower-like hydroxyapatite architecture using mussel shell bio-waste as a calcium source

Mussel shell, a calcium-rich resource, is found plenty in nature. We have developed a novel and facile method to convert mussel shell bio-waste into hydroxyapatite (HAp) biomaterial using microwave irradiation with the aid of ethylenediaminetetraacetic acid (EDTA) as chelating agent. The obtained HAp had flower-like morphology which can be a potential candidate for developing biomaterial for orthopedic applications. Moreover, the developed method has the potential to recover the bio-waste and reduce environment pollution.     

Sodium dodecyl sulfate mediated microwave synthesis of biocompatible superparamagnetic mesoporous hydroxyapatite nanoparticles using black Chlamys varia seashell as a calcium source for biomedical applications

Designing biocompatible superparamagnetic mesoporous nanoparticles for advanced healthcare applications has received much attention. In this research, we have synthesized intrinsic mesoporous superparamagnetic hydroxyapatite (HAp) nanoparticles using bio-waste of black Chlamys varia seashell as a calcium source by sodium dodecyl sulfate (SDS)–enabled microwave-assisted synthesis approach. The synthesized Fe-doped HAp nanoparticles were characterized using various characterization techniques to know the phase purity and morphological features. The incorporation of Fe greatly affected the morphology of HAp nanoparticles without affecting their crystalline phase. Superparamagnetic behavior was observed with the incorporation of Fe in the HAp nanoparticles. Further, saturation magnetization was enhanced with higher incorporation of Fe ions. The cytotoxicity studies of the synthesized pure and Fe-doped HAp samples conducted using a human osteoblasts cell line (MG63), which indicated that Fe-doped HAp nanoparticles are biocompatible. Further, antibacterial activity analysis also confirmed their excellent antibacterial performance against different pathogens. Hence, SDS-enabled microwave-assisted synthesis approach using seashell as a calcium source would be a better approach for the production of intrinsic mesoporous superparamagnetic HAp nanoparticles for various biomedical applications, such as drug targeting, hyperthermia cancer therapy, and magnetic resonance imaging.     

Incorporation of monovalent cations into diopside to improve biomineralization and cytocompatibility

This paper aims to evaluate the structure, bioactivity, biodegradation and cytocompatibility of diopside (CaMgSi₂O₆) doped with 2?mol% of Li, Na and K separately substituting for 1?mol% of Mg of diopside. An ethanolic, inorganic-salt coprecipitation method, followed by calcination at 900?°C, was used for synthesis. X-ray diffraction showed that the single-phase diopside structure is kept at this level of substitution; however, the crystallinity and lattice volume of diopside were changed depending on the size difference of the replacement components. According to in vitro biological studies, doping of all the alkali ions improves the bioactivity of diopside, with the highest and least effects obtained by K and Na, respectively. The MTT assay of osteoblast-like MG-63 cell cultures indicated that the cell viability and proliferation are improved as a result of using all the dopants, where the most enhancements were found for Na and K. It is eventually concluded that the incorporation of K into diopside ensures the optimal behaviors in terms of bioactivity and biocompatibility in vitro.     

Pore-forming agent induced microstructure evolution of freeze casted hydroxyapatite

There were interconnected small lamellar pores, big spherical pores and ceramic walls in the hydroxyapatite (HAP) ceramics fabricated by a freeze casting/pore-former method. As keeping the content of polymethyl methacrylate (PMMA) constant and decreasing the size of PMMA, the size of spherical pores and length of ceramic wall both decreased, and the compressive strength increased. As keeping the size of PMMA and decreasing the content of PMMA, the open porosity decreased and compressive strength increased. The shapes of pores caused by ice crystals were reticular, lamellar and treelike, in turn. The HAP ceramics with the spherical pores of 150-250 μm, open porosity of 62.13% and compressive strength of 7.01 MPa are prospective to have biomedical application.     

Tribological behaviour of RF-magnetron sputter deposited hydroxyapatite coatings in physiological solution

The aim of the paper is to explore the tribological performance of hydroxyapatite (HA) coatings deposited by radio frequency (RF) magnetron sputtering on AZ31 magnesium alloy (96% Mg, 3% Al, 0.7% Zn, 0.3% Mn) for biomedical applications. In this study, the position of the samples on a substrate holder, relative to a target erosion zone was taken into consideration in order to elucidate its impact on the coating characteristics, such as composition, morphology, surface topography and tribology. Substrate rotation and arc-movement were foreseen in the experimental set-up to increase the uniformity of thin film properties. The deposited HA thin films were revealed to exhibit an increase of the Ca/P ratio from 1.83 to 1.97, a decrease of (002) texture and thickness, as the samples were shifted towards the target erosion zone. By coatings, the roughness of Mg alloy was decreased (R_{a Mg alloy}=31.3 nm; R_{a coating}=29 nm and 21 nm). The coating placed in the centre of the substrate holder showed high hardness and Young's modulus (H =8.3±0.9 GPa; E=89±10 GPa) than the coating prepared under the target erosion zone (H =6.9±1.1 GPa; E=75±6 GPa). The coating deposited under target erosion zone exhibits superior friction behaviour in simulated body fluid environment, with the friction coefficient (μ) of 0.184, while the sample located in the centre of the substrate holder possesses the friction coefficient (0.306) comparable to the AZ31 substrate (0.307). The low wear rate was determined in the case of coating deposited under target erosion zone (4.83×10⁻⁵ mm³ N⁻¹ m⁻¹) than uncoated AZ31 substrate (0.00518 mm³ N⁻¹ m⁻¹) or than coating placed in the centre of the substrate holder (0.00294 mm³ N⁻¹ m⁻¹).     

Synthesis and characterization of chlorinated hydroxyapatite as novel synthetic bone substitute with negative zeta potential

In the present work, chlorine doped hydroxyapatite (ClHA), with varying degrees of ion replacement was successfully synthesized by a simple ball milling technique. The resulting powders were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Field emission scanning electron microscopy and particle size analyzer. The zeta potential of the powders was performed in physiological saline (0.154 M). The results confirmed the formation of apatite as the main phase in all chlorine substituted powders except for some incremental changes in the lattice parameter ‘a’ and unit cell volumes of the resultant powders. However, the crystallinity of the powders declined from 96% to 83%. Fourier transform infrared spectroscopy results confirmed the incorporation of Cl ions in the apatite lattice by the appearance of new bands at 677 cm^-1. FESEM results revealed that the crystallites have grown into grains with no major agglomeration. Vicker hardness test results revealed a hardness value of 2.65 ± 0.258 GPa for ClHA4 dense bodies at a load of 200g. Zeta potential analysis of the powders suggested that ClHA nanopowders can prove to be a potential bone implant material.