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MgF2/MgO composite coatings were prepared on the surface of porous magnesium by chemical vapor deposition (CVD) techniques in a mixed atmosphere of argon and 1,1,1,2‐tetrafluoroethane (HFC‐134a). The morphology, elemental composition and phase composition of the composite coatings were characterized by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X‐ray photoelectron spectroscopy (XPS) and X‐ray diffraction (XRD), and the biocorrosion resistance of the coatings in simulated body fluid (SBF) was investigated by immersion and electrochemical tests. The characterization analysis showed that a dense MgF2/MgO composite coating with some small pores was formed. The content of MgF2 in the coating increased with the increase of HFC‐134a concentration in the mixed atmosphere, reaction time and temperature. The content of MgO decreased with the increase of the concentration of HFC‐134a and reaction time. Immersion tests indicated that MgF2/MgO composite coatings obviously reduced the degradation rate of porous magnesium in simulated body fluid, and the higher the fluorine content in the coating, the smaller the degradation rate of porous magnesium. Electrochemical test demonstrated that MgO/MgF2 coated porous magnesium exhibited a higher biocorrosion resistance than porous magnesium. These results suggest that the MgF2/MgO coated porous magnesium possesses suitable corrosion behavior for the application as biodegradable implant material. [ABSTRACT FROM AUTHOR]

In this study, the electrochemical corrosion properties of high-energy milled Ti6Al4V alloy are investigated. The Ti6Al4V alloy is produced by high-energy milling at different milling times in mechanical milling device as 15–120 min. Produced alloy powders are cold-pressed under 620 MPa pressure and sintered at 1300°C temperature and characterised by scanning electron microscopy (SEM), X-ray diffraction, hardness and density measurements. Corrosion tests are conducted in simulated body fluid at 37°C body temperature. Results showed that the average particle size of the powder is reduced, and the hardness of the alloy is increased with the increasing milling time. It is determined that the corrosion properties of the alloys change by the high-energy milling time, and the corrosion rate increases by the decreasing particle size of the powder. SEM examination of the corroded surfaces after potentiodynamic polarisation tests revealed that pitting formation tendency of the alloys on the alloy surface increases by the increasing high-energy milling time. [ABSTRACT FROM AUTHOR]

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Abstract The presented work aims to evaluate the effect of porosity on the corrosion behaviour of porous iron scaffold for biodegradable implant application. Two different types of iron scaffold samples were prepared using a newly developed process based on the amalgamation of 3D printing and pressureless microwave sintering. Random porous iron scaffold (RPIS) sample having only random microporous structure and topologically ordered porous iron scaffold (TOPIS) sample having designed interconnected macroporous structure were investigated. Dense iron sample was also prepared for comparison purpose. Microstructural and morphological characterization of the prepared iron scaffold samples were performed using scanning electron microscopy and micro-computed tomography. Three different types of pore characteristics namely large sized interconnected micropores, small sized isolated micropores and designed interconnected macropores were obtained and analyzed. The corrosion properties were assessed in simulated body fluid solution at 37 °C using polarization curves and EIS measurements. Corrosion mechanisms were established using suitable circuit models. Impedance results showed that the corrosion of porous iron scaffold samples was mainly governed by the diffusion process. Electrochemical results indicated that an increase in random microporosity and reduction in designed macroporosity resulted in an increased corrosion rate of iron scaffold. Graphical abstract Unlabelled Image Highlights • Porous Fe scaffolds were prepared using a combined process based on 3D printing and pressureless microwave sintering. • Random and topologically ordered Fe scaffolds having 16.83 %-39.60 % and 45.63 %- 80.97 % porosities were prepared. • Topologically ordered porous Fe scaffold sample exhibited 2.25 mmpy corrosion rate as compared to 0.13 mmpy for dense Fe. • Increased random microporosity and reduced macroporosity resulted in an increased corrosion rate of Fe scaffold. • Corrosion mechanism of Fe scaffold using appropriate equivalent circuit models were deduced. [ABSTRACT FROM AUTHOR]

Abstract Nanocomposites of magnetite (Fe 3 O 4) and reduced graphene oxide (rGO) generate heat under an alternating magnetic field and therefore have potential applications as thermoseeds for cancer hyperthermia treatment. However, the properties of such nanocomposites as biomaterials have not been sufficiently well characterized. In this study, the osteoconductivity of Fe 3 O 4 -rGO nanocomposites of various compositions was evaluated in vitro in terms of their apatite-forming ability in simulated body fluid (SBF). Furthermore, the heat generation of the nanocomposites was measured under an alternating magnetic field. The apatite-forming ability in SBF improved as the Fe 3 O 4 content in the nanocomposite was increased. As the Fe 3 O 4 content was increased, the nanocomposite not only rapidly raised the surrounding temperature to approximately 100 °C, but the specific absorption rate also increased. We assumed that the ionic interaction between the Fe 3 O 4 and rGO was enhanced and that Brown relaxation was suppressed as the proportion of rGO in the nanocomposite was increased. Consequently, a high content of Fe 3 O 4 in the nanocomposite was effective for improving both the osteoconductivity and heat generation characteristics for hyperthermia applications. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

The present work deals with a comparative study of ceramic/ceramic composites for the development of scaffolds for biomedical applications. Wollastonite and forsterite were synthesized by a sol–gel combustion method. The influence of constituents and composition on apatite deposition was studied by fabricating wollastonite/forsterite composites. The X-ray diffraction pattern explains the bone like-apatite deposition within early stages of immersion. The atomic force microscopy micrographs revealed that with an increase in wollastonite content in the composites the roughness was enhanced. Dissolution studies further confirmed the rapid consumption of Ca and P ions from the simulated body fluid. Hence, apatite formation was observed to be more on the surface of a composite containing a higher amount of wollastonite. The results suggest that composites have more influence on the biomineralization activity when compared with pure bioceramics. [ABSTRACT FROM AUTHOR]

Torsional fretting corrosion in a physiological medium is one of the main reasons that artificial joints fail. In this study, we carried out experiments on torsional fretting corrosion in Titanium alloys (Ti6Al4V) against Zirconium dioxide (ZrO2) ceramic balls under 37°C in a Hank's simulated body fluid. During the tests, we recorded electrochemical corrosion parameters using an electrochemical analysis system in real-time. We analysed the torsional fretting dynamics behaviours, damage mechanisms, and electrochemical corrosion behaviours in detail using the micro-examinations of a scanning electron microscope (SEM), an energy-dispersive X-ray (EDX), a profilometer, and an X-ray photoelectron spectrometer (XPS). The results showed that the dynamics behaviours strongly depended upon the torsional angular displacement amplitude and the number of cycles. The friction torque increased with increases in the torsional angular displacement amplitude and normal load. We established a running condition fretting map (RCFM), which included three fretting running regimes: a partial slip regime (PSR), a mixed fretting regime (MFR), and a slip regime (SR). We determined that the influences of torsional fretting on electrochemical corrosion behaviours were strongly correlated to the angular displacement amplitude. Under large angular displacement amplitudes, the corrosion of the Ti6Al4V alloys in Hank's simulated body fluids were accelerated by torsional fretting, especially during the initial stage of the test. However, when the angular displacement amplitude was smaller than 1°, the corrosion potentials and corrosion currents were almost invariable during the entire duration of the test. The damage to the Ti6Al4V alloy was the result of wear and corrosion. The wear mechanisms were attributable to delamination and abrasive wear in the three fretting regimes. We observed almost no damage on the contact centre and only slight scratches and wear on the contact edge in the PSR. In MFR testing, the damage zone extended to the contact centre and the sticking zone (which exhibited no damage) contracted to the contact centre with increases in the number of cycles. Ultimately, in MFR and SR testing, the damage mechanisms were primarily the result of abrasive wear, oxidation wear, tribochemical reactions, adhesion wear, and electrochemical corrosion. [ABSTRACT FROM AUTHOR]

The title of this article could sound a bit curious to some readers since a layer of apatite – and not calcium carbonate – is well-known to form on the surface of bioactive glasses upon immersion in simulated body fluids. However, calcium carbonate (commonly reported as calcite crystals) can form on the surface of bioactive glasses as well, instead of or in competition with hydroxyapatite, during in vitro tests. Major factors that govern calcium carbonate formation are a high concentration of Ca2+ ions in the testing solution – and, in this regard, glass composition/texture and type of medium play key roles – along with the volume of solution used during in vitro tests. To date, this phenomenon has received relatively little attention and is still partly unexplored. This article provides a critical overview of the available literature on this topic in order to stimulate constructive discussion among biomaterials scientists and further research for better understanding the mechanisms involved in glass bioactivity. A literature search indicates that a layer of apatite – and not calcium carbonate – is well known to form on the surface of biomaterials during the bioactivity assessment. However, calcium carbonate can form on the surface as well, instead of or in competition with apatite. To date, this phenomenon has received relatively little attention and is still partly unexplored. This review provides a critical overview of the available literature on this topic in order to stimulate constructive discussions that can be further useful for clinical success. [ABSTRACT FROM AUTHOR]

This work reports the surface modification of 3D printed PLA scaffold with chitosan and its hydroxyapatite (HA) forming capability. PLA scaffold was fabricated using a desktop 3D printer followed by the inclusion of chitosan on the surface via surface entrapment. Confocal laser scanning microscopy (CLSM) images showed existence of chitosan entrapment with depth of 24 μm. Immersion of the modified PLA scaffold in simulated body fluid resulted in formation of apatite layers on the surface. Plus the entrapment method does not induce any cytotoxic response towards human fibroblast cell. This method provides a facile approach of obtaining 3D printed scaffold with good bioactivity thus has potential in biomimetic and tissue engineering. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HAp) is a major mineral component of bones which has excellent bioactivity and biocompatibility making it suitable for various biomedical applications. However, the chemical composition of HAp varies from that of native bones in its Ca/P ratio and with respect to other trace elements. Therefore, when compared to HAp the development of bone-like apatite is of great importance for bone and dental applications. Most of the protocols use Tris hydroxyl amino methane for the preparation of SBF which is expensive. In this study, we have made an attempt to synthesize the bone-like apatite in within a shorter duration (6hrs), without adding tris in SBF, while at the same time, using CaCl2 as a calcium precursor and Na2HPO4 as a phosphate precursor. The physiochemical properties of the synthesized bone-like apatite were studied. X-Ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and thermal analysis were used to verify our results. [ABSTRACT FROM AUTHOR]

We synthesized spherical porous hydroxyapatite by a wet method using simulated body fluid and studied its structure. A simulated body fluid with a Ca/P molar ratio of 0.09 was prepared using Dulbecco's PBS, and spherical porous particles with an average particle size of 13 μm were precipitated therein. All spherical particles were covered with submicron plate-like crystals on the surface. Cross-sectional images showed that pores of submicron to 2 μm in size were present at the centre of the spherical particles. In addition, the plate crystals present on the surface were identified as hydroxyapatite (HAp) with the (002) HAp surface in the longitudinal direction and (100) HAp surface in the width direction, extending in the c-axis direction. Here, we discuss the formation mechanism of the spherical porous HAp. [ABSTRACT FROM AUTHOR]

Abstract Porous titanium‑niobium alloys of composition Ti-24Nb, Ti-35Nb and Ti-42Nb were synthesised by electro-deoxidation of sintered oxide discs of mixed TiO 2 and Nb 2 O 5 powders in molten CaCl 2 at 1173 K, and characterised by XRD, SEM, EDX and residual oxygen analysis. At the lower Nb content a dual-phase α/β-alloy was formed consisting of hexagonal close-packed and body-centred cubic Ti-Nb, whereas at the higher Nb contents a single-phase β-alloy was formed of body-centred cubic Ti-Nb. The corrosion behaviour of the alloys prepared was assessed in Hanks' simulated body fluid solution at 310 K over extended periods of time. Potentiodynamic polarisation studies confirmed that the alloys exhibited passivation behaviour, and impedance studies revealed that the passive films formed on the surface of the alloys comprised a bi-layered structure. XPS analysis further proved that this contained hydroxyapatite at the top and native metal oxide underneath. The mechanical properties of the alloys were evaluated, and the elastic moduli and the Vickers hardness were both found to be in the range of that of bone. Overall, Ti-35Nb is proposed to be the best-suited candidate of the materials studied in regard to biomedical applications. Graphical abstract Unlabelled Image Highlights • Porous Ti-Nb alloys were synthesised directly from oxide precursors in molten CaCl 2. • Ti-24Nb alloy was dual-phase α/β, Ti-35Nb and Ti-42Nb alloys were single-phase β. • Polarisation studies in Hanks' simulated body fluid indicated passivation behaviour. • Impedance studies revealed a bi-layered structure of the passivating film. • Young's modulus was in the bone-matching range, strength and hardness were adequate. [ABSTRACT FROM AUTHOR]

Although autoclaving is a common sterilization method for biomedical devices, the ability to induce deposition of apatite particles on hydrothermally treated titanium is still not fully realized. This is because the induction ability is too weak to be evaluated via in vitro apatite formation in Kokubo's simulated body fluid (SBF) by the conventional immersion method, i.e. using samples with open and smooth surface. This study reports on the surface structure of hydrothermally treated titanium and the ability to induce deposition of apatite particles on the surface of parallel confined spaces separated by sub-millimeter gaps in Kokubo's SBF. Thin-film X-ray diffraction and analyses using Fourier transform infra-red (FT-IR) spectroscopy and Raman spectroscopy revealed that a nano-crystalline anatase-type titanium oxide layer was formed on titanium substrates after hydrothermal treatment at 150°C for 2 h. When growth of the titanium oxide layer was moderately suppressed, the hydrothermally treated titanium surface exhibited a characteristic interference color, silver or gold, which does not impair the esthetic appearance of the titanium-based implant. The ability to induce deposition of apatite particles on hydrothermally treated titanium was remarkably amplified by parallel alignment of substrates separated by sub-millimeter gaps. [ABSTRACT FROM AUTHOR]

In this study, a CoCrMo-based metallic alloy was manufactured using a 3D-printing method with metallic powder and a laser-based 3D printer. The obtained material was immersed in a simulated body fluid (SBF) similar to blood plasma and kept 2 months at 37 °C and in relative motion against the SBF in order to mimic the real motion of body fluids against an implant. At determined time intervals (24, 72, 168, 336, and 1344 h), both the metallic sample and SBF were characterized from a physical-chemical point of view in order to assess the alloy’s behaviour in the SBF. Firstly, the CoCrMo based metallic sample was characterized by scanning electron microscopy (SEM) for assessing surface corrosion and X-ray diffraction (XRD) for determining if and/or what kind of spontaneous protective layer was formed on the surface; secondly, the SBF was characterized by pH, electrical conductivity (EC), and inductively coupled plasma mass spectroscopy (ICP-MS) for assessing the metal ion release. We determined that a 3D-printed CoCrMo alloy does not represent a potential biological hazard in terms of the concentration of metal ion releases, since it forms, in a relatively short period of time, a protective CoCr layer on its exposed surface.

In order to develop new effective medical sorbents, the sorption ability of synthetic montmorillonite of various compositions in relation to model protein molecules – oxytocin, albumin and immunoglobulin in a synthetic biological fluid (pH=7.2) was studied. Montmorillonites with varying degrees of isomorphic substitution of aluminium atoms for magnesium atoms in octahedral layers were synthesized under hydrothermal conditions (Na 2x (Al 2(1−x) ,Mg 2x)Si 4 O 10 (OH) 2 .nH 2 O, where x = 0.5, 0.9 and 1). According to the SEM data, the samples had a layered morphology, forming spongy aggregates with secondary pores up to 300–350 nm in diameter. To model the kinetics of protein adsorption on montmorillonites, pseudo-first (PFO) and pseudo-second order (PSO) equations were used, and Langmuir, Freundlich and Temkin models were used to process isotherms. It has been found that the sorption capacity of synthetic montmorillonite in relation to proteins can be 2–4 times higher than that of raw clays, reaching 180, 315 and 900 mg/g for oxytocin, albumin and immunoglobulin, respectively. The existence of a competitive adsorption between proteins and components of simulated body fluid has been detected. The dependence of the adsorption capacity of the samples with respect to proteins of different molecular weights on the chemical composition of the montmorillonite and on the degree of isomorphic substitution of magnesium by aluminium in the octahedral layers has been established. The possibility of developing sorbents for the extracting of proteins from complex mixtures based on synthetic combined montmorillonites has been demonstrated. [Display omitted] • Synthetic clays adsorb proteins to a greater extent than natural clays. • The sorption capacity of montmorillonite depends on its chemical and degree of isomorphic substitutions. • Competitive adsorption of proteins and components of the medium takes place. • Combined synthetic montmorillonites are perspective materials for the effective extraction of proteins from complex mixtures. [ABSTRACT FROM AUTHOR]

Metallic glasses have received attention in the world of materials science and engineering due to their high mechanical and tribological properties. Thin film nanostructured metallic glasses have shown great prospects as surface coatings with increasing applications in biomedical areas for implants and surgical devices. In this work, we deposited titanium- and zirconium-based polymorphous thin film metallic glasses (Ti–Fe–Cu, Zr–Fe–Al, Zr–W–Cu) on medical-grade polished titanium substrate by co-sputtering using a PVD system. The corrosion behaviour of the films was investigated by exposing the samples to sterile simulated body fluid and examined using electrochemistry, microscopy, and spectroscopic analyses. The polymorphic properties of the films after exposure to simulated body fluid were observed by SEM and TEM. SEM analysis shows that the surface morphology of the exposed samples was found to vary significantly compared to their corresponding as-deposited samples. Electrochemical properties (E corr , I corr , and OCV, impedance |Z|) demonstrated that the thin film metallic glasses were found to enhance the corrosion resistance of the substrate. Further investigations of the exposed films by XPS and Raman analyses have revealed that the induced oxide passive layer significantly enhanced the corrosion efficacy of the films on titanium substrate. Among the three samples, Zr–W–Cu coating has shown the highest corrosion protection almost 450 times better than the bare titanium substrate. [Display omitted] • Polymorphous thin film metallic glass mitigates corrosion by formation of oxide layers. • Polymorphous thin film metallic glass coating offers protection from corrosion in the body environment for Ti substrates. • Zr-based (ZrWCu) nanostructured polymorphous thin film metallic glass significantly deters biocorrosion on Ti substrates. [ABSTRACT FROM AUTHOR]

Pure hydroxyapatite, pure titanium, Ti60-HAp (60%Ti), and Ti40-HAp (40%Ti) composite coatings were deposited on 254 SMO steel by Low-Velocity Oxy-fuel (LVOF) spraying. Among the various LVOF sprayed coatings, the Ti40-HAp coating has the highest microhardness and adhesion strength values attributed to its low porosity and low coefficient of thermal expansion. The potentiodynamic polarisation and electrochemical impedance spectroscopy tests also indicated a lower corrosion rate for Ti40-HAp coating in simulated body fluid (SBF). The bacterial adhesion has shown a direct relationship with the surface roughness of the coatings. The bioactivity of the Ti-HAp composite coating was established through an in-vitro bioactivity test. The bioactivity decreased with increasing Ti content in the coating. The formation of rutile TiO 2 and CaTiO 3 phases significantly enhanced the microhardness, adhesion strength and corrosion resistance. • Hydroxyapatite, Ti, Ti60-HAp & Ti40-HAp coatings were deposited on 254 SMO steel by LVOF spraying. • XRD showed CaTiO 3 & TiO 2 phases in Ti-HAp coatings, which enhances adhesion and reduces corrosion. • Reinforcement of Ti in HAp coating increased the microhardness values and reduced the porosities. • A nearly identical bacterial attachment given by Ti-HAp coatings, depending on surface roughness. • An apatite layer was found more pronounced in as-sprayed HAp coating than Ti-HAp coatings. [ABSTRACT FROM AUTHOR]

In this study, nucleation and growth of bone-like hydroxyapatite (HAp) mineral in modified simulated body fluids (m-SBF) were induced on chitosan (CS) substrates, which were prepared by spin coating of chitosan on Ti substrate. The m-SBF showed a two fold increase in the concentrations of calcium and phosphate ions compared to SBF, and the post-NaOH treatment provided stabilization of the coatings. The calcium phosphate/chitosan composite prepared in m-SBF showed homogeneous distribution of approximately 350 nm-sized spherical clusters composed of octacalcium phosphate (OCP; Ca8H2(PO4)6·5H2O) crystalline structure. Chitosan provided a control over the size of calcium phosphate prepared by immersion in m-SBF, and post-NaOH treatment supported the binding of calcium phosphate compound on the Ti surface. Post-NaOH treatment increased hydrophilicity and crystallinity of carbonate apatite, which increased its potential for biomedical application.

Calcium phosphate ceramics consist of materials such as hydroxyapatite, tricalcium phosphate (TCP), calcium phosphate cement (CPC), biphasic calcium phosphate, etc. CPCs have been used for filling bone defects in dentistry and orthopedics. Among these materials, β-tricalcium phosphate is suggested as an ideal candidate for bone graft in hard tissue engineering due to its high biocompatibility, bioactivity and bone bonding. The preparation, as well as the application of this powder material, has been the important topic of research in material science. In this paper, β-tricalcium phosphate (β-TCP), a component that has chemical formulation similar to bone structure, was synthesized by the precipitate method and then calcinated at 1000oC for 5 h. The physico-chemical properties of synthetic material were examined by XRD, FT-IR and SEM methods. In vitro experience was also carried by soaking β-TCP simulated body fluid powder in a different period of time. Obtained results confirmed the quality of β-TCP synthetic material and its bioactivity.

The main goal of this study is to elaborate and evaluate the physicochemical properties of the synthetic biphasic calcium phosphate (BCP) powder: an associate compound of hydroxyapatite (HA): Ca10(PO4)6(OH)2 and beta-tricalcium phosphate (β-TCP): Ca3(PO4)2. The new compound BCP has two advantages: high bioactivity (HA) and fast biodegradation (β-TCP). The obtained powder of BCP was prepared by the precipitate method. XRD analysis confirmed the synthetic material contained both HA and β-TCP crystalline phases. SEM images showed that the small particles of HA attached to bigger particles of β-TCP in the structure morphology of BCP. The in vitro experiment was carried out in static condition by soaking of a series of 50 mg BCP powder in 100 ml of simulated body fluid solution at different period of soaking time. The XRD and SEM methods studied the microstructure and chemical bond after soaking. The obtained results confirmed the bioactivity of synthetic BCP material by the formation of a new apatite layer on its surface.

Statement of Problem: In order to increase the performance of glass ionomer cement, it is reinforced with metal powders, short fibers, bioceramics and other materials. Fluoroapatite(Ca10(PO4)6F2) is found in dental enamel and is usually used in dental materials due to its good chemical and physical properties. Objectives: In this study, the effects of the addition of synthesized fluoroapatite nanoceramic on the compressive strength and bioactivity of glass ionomer cement were investigated. Materials and Methods: The synthesized fluoroapatite nanoceramic particles (~ 70 nm) were incorporated into as-prepared glass ionomer powder and were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Moreover, the compressive strength values of the modified glass ionomer cements with 0, 1, 3 and 5 wt% of fluoroapatite were evaluated. Results: Results showed that glass ionomer cement containing 3 wt%fluoroapatite nanoparticles exhibited the highest compressive strength (102.6± 4) compared to the other groups, including control group. Furthermore, FTIR and SEM investigations indicated that after soaking the glass ionomer cement- 3 wt% fluoroapatite composite in the simulated body fluid solution, the intensity of O-H, P-O and C-O absorption bands increased as a result of the formation of apatite layer on the surface of the sample, and the rather flat and homogeneous surface of the cement became more porous and inhomogeneous. Conclusions: Addition of synthesized nano-fluoroapatite to as-prepared glass ionomer cement enhanced the compressive strength as well as nucleation of the calcium phosphate layer on the surface of the composite. This makes it a good candidate for dentistry and orthopedic applications.

This article reports the mechanical and biocorrosion behaviour of hollow silica nanosphere (SiO2) reinforced (0.5–2 vol.%) magnesium (Mg) syntactic foams. Room temperature tensile properties’ characterization suggests that the increased addition of hollow silica nanospheres resulted in a progressive increase in tensile yield strength (TYS) and ultimate tensile strength (UTS) with Mg-2 vol.% SiO2 exhibiting a maximum TYS of 167 MPa and a UTS of 217 MPa. The degradation behaviour of the developed Mg-SiO2 syntactic foams in four different simulated body fluids (SBFs): artificial blood plasma solution (ABPS), phosphate-buffered saline solution (PBS), artificial saliva solution (ASS) and Hanks’ balanced saline solution (HBSS) was investigated by using potentiodynamic polarization studies. Results indicate that corrosion resistance of the Mg-SiO2 syntactic foam decreases with increasing chloride ion concentration of the SBF. Mg-1.0 vol.% SiO2 displayed the best corrosion response and its corrosion susceptibility pertaining to corrosion rate and polarisation curves in different SBF solutions can be ranked in the following order: ABPS > PBS > HBSS > ASS. The surface microstructure demonstrated the presence of a better passivated layer on the syntactic foams compared to pure Mg. The observed increase in corrosion resistance is correlated with intrinsic changes in microstructure due to the presence of hollow silica nanospheres. Further, the effect of corrosive environment on the degradation behaviour of Mg has been elucidated.

Polymers are widely used in many applications in the field of biomedical engineering. Among eclectic selections of polymers, those with low melting temperature (Tm < 200 °C), such as poly(methyl methacrylate), poly(lactic-co-glycolic acid), or polyethylene, are often used in bone, dental, maxillofacial, and corneal tissue engineering as substrates or scaffolds. These polymers, however, are bioinert, have a lack of reactive surface functional groups, and have poor wettability, affecting their ability to promote cellular functions and biointegration with the surrounding tissue. Improving the biointegration can be achieved by depositing hydroxyapatite (HAp) on the polymeric substrates. Conventional thermal spray and vapor phase coating, including the Food and Drug Administration (FDA)-approved plasma spray technique, is not suitable for application on the low Tm polymers due to the high processing temperature, reaching more than 1000 °C. Two non-thermal HAp coating approaches have been described in the literature, namely, the biomimetic deposition and direct nanoparticle immobilization techniques. In the current review, we elaborate on the unique features of each technique, followed by discussing the advantages and disadvantages of each technique to help readers decide on which method is more suitable for their intended applications. Finally, the future perspectives of the non-thermal HAp coating are given in the conclusion.