Effect of akermanite morphology on precipitation of bone-like apatite

Bioactivity in vivo of ceramic materials has been related to their surface micro-topography and may be estimated by means of simulated body fluid method in vitro. In order to investigate the effect of surface topographies of akermanite ceramics on bioactivity in vitro, akermanite ceramics were synthesized by sol-gel method and different surface topographies of disc-shaped akermanite ceramics were prepared by polishing with different SiC sandpapers. Atomic force microscopy (AFM) was used to evaluate the surface morphology and roughness. The bioactivity in vitro of ceramics with different surface states was evaluated by soaking the ceramics in simulated body fluid (SBF). And the samples after being soaked were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectrometry (EDS). The results showed that the amounts of precipitated apatite on the ceramics with different surface roughness after being soaked in SBF were different and the bioactivity in vitro of ceramic with rough surface was significantly higher than that of ceramic with smooth surface. The study suggested that suitable surface roughness may improve the bioactivity in vitro of akermanite ceramics.     

Biomimetic formation of apatite on the surface of porous gelatin/bioactive glass nanocomposite scaffolds

There have been several attempts to combine bioactive glasses (BaGs) with biodegradable polymers to create a scaffold material with excellent biocompatibility, bioactivity, biodegradability and toughness. In the present study, the nanocomposite scaffolds with compositions based on gelatin (Gel) and BaG nanoparticles in the ternary SiO₂-CaO-P₂O₅ system were prepared. In vitro evaluations of the nanocomposite scaffolds were performed, and for investigating their bioactive capacity these scaffolds were soaked in a simulated body fluid (SBF) at different time intervals. The scaffolds showed significant enhancement in bioactivity within few days of immersion in SBF solution. The apatite formation at the surface of the nanocomposite samples confirmed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray powder diffraction (XRD) analyses. In vitro experiments with osteoblast cells indicated an appropriate penetration of the cells into the scaffold's pores, and also the continuous increase in cell aggregation on the bioactive scaffolds with increase in the incubation time demonstrated the ability of the scaffolds to support cell growth. The SEM observations revealed that the prepared scaffolds were porous with three dimensional (3D) and interconnected microstructure, pore size was 200-500 μm and the porosity was 72-86%. The nanocomposite scaffold made from Gel and BaG nanoparticles could be considered as a highly bioactive and potential bone tissue engineering implant.     

Effects of Mg and Zn on the surface of doped melt-derived glass for biomaterials applications

Bioactive glasses in the system SiO₂-CaO-Na₂O-P₂O₅ were synthesized pure and doped with magnesium or zinc by melt-derived method. The bioactivity was studied during in vitro assays: the ability of hydroxycarbonate apatite (HCA) layer to form on the glass surface was examined after contact with simulated body fluid (SBF). The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) studies were performed before and after immersion in vitro assays. The SBF solutions were also analyzed using inductively coupled plasma-optical emission spectroscopy (ICP-OES).Introduction of magnesium and zinc as trace element induces several modifications on the observed phenomena at the glass surface and in SBF solution after immersion of the samples. The chemical durability of the glasses, the formation of the silica-rich layer and the crystallization of the HCA layer were affected, but not present the same modifications as the introduced doping element.     

Bioactivity of SiO2-CaO-P2O5-Na2O glasses containing zinc-iron oxide

Glasses with composition x(ZnO,Fe₂O₃)(65 − x)SiO₂20(CaO,P₂O₅)15Na₂O (6 ≤ x ≤ 21 mol%) were prepared by melt-quenching technique. Bioactivity of the glasses was investigated in vitro by examining apatite formation on the surface of glasses treated in acellular simulated body fluid (SBF) with ion concentrations nearly equal to those in human blood plasma. Formation of bioactive apatite layer on the samples treated in SBF was confirmed by using Fourier transform infrared reflection (FTIR) spectroscopy, grazing incidence X-ray diffraction (GI-XRD) and scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer. Development of an apatite structure on the surface of the SBF treated glass samples as functions of composition and time could be established using the GI-XRD data. FTIR spectra of the glasses treated in SBF show features at characteristic vibration frequencies of apatite after 1-day of immersion in SBF. SEM observations revealed that the spherical particles formed on the glass surface were made of calcium and phosphorus with the Ca/P molar ratio being close to 1.67, corresponding to the value in crystalline apatite. Increase in bioactivity with increasing zinc-iron oxide content was observed. The results have been used to understand the evolution of the apatite surface layer as a function of glass composition and immersion time in SBF.     

Enhancement of cells proliferation and control of bioactivity of strontium doped glass

Bioactivity and chemical reactivity of bioactive glass offer the ability to bond for soft and hard biological tissues. In this work, synthesis was carried out by using melting and rapid quenching. Strontium was introduced as trace element at different contents in the glass matrix, according to its concentration in the bone matrix. This chemical element presents a high interest in the bone metabolism activity. Investigations were conducted on the surface of biomaterials by using in vitro assay after immersion in SBF. Several physico-chemical methods such as SEM, FTIR, NMR, ICP-OES and MTT test were employed to highlight the effects of the Sr. The in vitro experiments showed that after soaking in SBF, the behaviour of pure glass is different compared to glass doped with Sr. NMR analyses showed in the ²⁹Si MAS-NMR that glass matrix undergoes some changes after in vitro assays particularly the emergence of new components attributed to Q³(OH). The presence of Sr slowed down the bioactivity of glass after immersion in SBF. The non toxic character of compounds was confirmed. Introduction of Sr at 0.1 wt % induce an enhancement of cells at about 14.3%.     

Improving the bioactivity of NiTi shape memory alloy by heat and alkali treatment

TiO₂ films were formed on an NiTi alloy surface by heat treatment in air at 600 °C. Heat treated NiTi shape memory alloys were subsequently alkali treated with 1 M, 3 M and 5 M NaOH solutions respectively, to improve their bioactivity. Then treated NiTi samples were soaked in 1.5SBF to evaluate their in vitro performance. The results showed that the 3 M NaOH treatment is the most appropriate method. A large amount of apatite formed within 1 day's soaking in 1.5SBF, after 7 day's soaking TiO₂/HA composite layer formed on the NiTi surface. SEM, XRD, FT-IR and TEM results showed that the morphology and microstructure are similar to the human bone apatite.     

Bioactive calcium phosphate coating formed on micro-arc oxidized magnesium by chemical deposition

In order to improve the bioactivity of the micro-arc oxidized magnesium, a calcium phosphate coating was formed on the surface of micro-arc oxidized magnesium using a chemical method. The microstructures of the substrate and the calcium phosphate coating before and after the simulated body fluids (SBF) incubation were characterized by X-ray diffraction, Fourier-transformed infrared spectroscopy and scanning electron microscopy. The results showed that the calcified coating was composed of calcium deficient hydroxyapatite (HA) and dicalcium phosphate dihydrate (DCPD). After SBF incubation, some new apatite formation on the calcified coating surface from SBF could be found. The corrosion behaviours of the samples in SBF were also investigated by potentiodynamic polarization curves and immersion tests. The results showed that calcium phosphate coating increased the corrosion potential, and decreased the hydrogen gas release.     

Investigation of the surface reactivity of a sol-gel derived glass in the ternary system SiO2-CaO-P2O5

A new glass formulation, with the molar composition 60% SiO₂-35% CaO-5% P₂O₅, was synthesized using the sol-gel process, for applications as biomaterial in orthopaedic or maxillo facial surgery. Pellets, made of glass powder, were uniaxially compacted and soaked in simulated body fluid (SBF) for up to 7 days at 37 °C to evaluate glass bioactivity. Ionic exchanges at the interface glass-SBF were evaluated by studying evolutions of calcium, phosphorus and silicon concentrations in SBF using ICP-OES. Changes in glass surface, and the formation of crystalline phases were analyzed using XRD, SEM, EDS and FTIR methods.Results form ICP-OES showed a high reactivity of the glass surface with a very high and continuous release of calcium, a limited glass dissolution and an uptake of phosphorous from SBF. Results from both FTIR and XRD analysis indicated that the glass surface was progressively covered by two different phases: CaCO₃ as calcite and a carbonated apatite layer. The formation of these phases, following two different schemas, was observed after 2 h of immersion and confirmed after 7 days. SEM micrographs and EDS analysis demonstrated that the main phase, a carbonated apatite, was present as micro-spheroids and the secondary phase, calcite, was materialized by agglomerates which have diameters up to 10-15 μm. These results are in accordance with a bioactive feature of the glass studied.     

Compositional dependence of in-vitro bioactivity in sodium calcium borate glasses

Borate glasses with composition xCaO (100−x) B₂O₃ (20≤x≤50), where x is in mole percent) and 50CaO·45B₂O₃·5Na₂O have been prepared using conventional melt quench technique. Samples were submerged in simulating body fluid solution (SBF) at 37 °C for various periods of time. After storage the samples were analyzed in order to investigate if a surface layer of hydroxyl carbonate apatite layer (HCA layer/Ca-P layer) had formed. The analysis technique used included Fourier-Transform Infrared Spectroscopy (FTIR). The rate of HCA layer formation on the surface of exposed glass samples is determined by FTIR, percentage weight loss measurements of glass samples in SBF and variation of pH of SBF as a function of time. Increase in calcium content in the glass matrix has shown to decrease the rate of HCA formation on glass surfaces. The borate glass with x=20 has shown HCA layer formation on glass surface within two days of dipping. The bone like apatite formation of glass surface demonstrates the potential of glass for integration with bone.     

Effect of heat treatment on bioactivity of anodic titania films

Anodic oxidation could be employed to produce crystalline titania films on Ti6Al4 V surfaces for inducing apatite formation in simulated body fluid (SBF). In this work, the effect of further heat treatment on the bioactivity of anodic titania films was researched. The surface constitution, morphology, crystal structure and apatite-forming ability of titania films were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicated the apatite formation on the Ti6Al4 V surfaces could be attributed to abundance of Ti-OH groups formed via anodic oxidation, but subsequent heat treatment would decrease the amount of surface hydroxyl (OH) groups and result in the loss of the apatite-forming ability.     

Apatite formation on Poly (vinyl alcohol)-coated Poly (?-caprolactone) films by incubation in simulated body fluids

In this study, biodegradable poly (?-caprolactone) (PCL) films were coated with poly (vinyl alcohol) (PVA) and then incubated in a simulated body fluid 1.5SBF to prepare an apatite (HA)/PCL composite. It was found that the bone-like apatite formability of PCL was enhanced by PVA coating. The changes of surface properties induced by PVA coating were effective for apatite formation. The apatite formability increased with increasing coating amount. After 24 h incubation, apatite was formed on PVA-coated PCL film but hardly any apatite was found on uncoated PCL plate. The surface chemistry of the specimens was examined using XPS, FT-IR-ATR. The apatite formed was characterized by using SEM, TF-XRD, FT-IR, EDS. The apatite formed was similar in morphology and composition to that of natural bone. This indicated that simple PVA coating on PCL substrate could serve as a novel way to accelerated apatite formation via biomimetic method.     

Effects of structure and composition of the CaP composite coatings on apatite formation and bioactivity in simulated body fluid

The surface properties of biomaterials determine the interactions between biomedical devices and the surrounding biological environment. The surface modification of biomaterials is extensively recognized as a key strategy in the design of the next generation of bone implants and tissue engineering. In this study, the highly ordered octacalcium phosphate (OCP) coating and OCP/protein coating with hierarchically porous structure in nano-micro scale were constructed on titanium substrate by electrochemically-induced deposition (ED). The formation behavior of apatite on OCP and OCP/protein coatings immersed in simulated body fluid (SBF) was investigated in physicochemical aspects. It is indicated that soaked in SBF, the OCP and OCP/protein coatings are possible to induce relevant apatite formation on their surface, and the apatite-forming behavior in body environment is depended on the chemical composition and structure of the coatings. The apatite formed on OCP/protein composite coating possesses carbonated structure, needle-like crystals in nano scale, lower Ca/P ratio and higher degree of the preferred c-axis orientation, which are similar to the mineral composition and structure in natural bone, and hence called as bone-like apatite.     

Nanostructured bioactive glass-ceramic coatings deposited by the liquid precursor plasma spraying process

Bioactive glass-ceramic coatings have great potential in dental and orthopedic medical implant applications, due to its excellent bioactivity, biocompatibility and osteoinductivity. However, most of the coating preparation techniques either produce only thin thickness coatings or require tedious preparation steps. In this study, a new attempt was made to deposit bioactive glass-ceramic coatings on titanium substrates by the liquid precursor plasma spraying (LPPS) process. Tetraethyl orthosilicate, triethyl phosphate, calcium nitrate and sodium nitrate solutions were mixed together to form a suspension after hydrolysis, and the liquid suspension was used as the feedstock for plasma spraying of P₂O₅-Na₂O-CaO-SiO₂ bioactive glass-ceramic coatings. The in vitro bioactivities of the as-deposited coatings were evaluated by soaking the samples in simulated body fluid (SBF) for 4 h, 1, 2, 4, 7, 14, and 21 days, respectively. The as-deposited coating and its microstructure evolution behavior under SBF soaking were systematically analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma (ICP), and Fourier transform infrared (FTIR) spectroscopy. The results showed that P₂O₅-Na₂O-CaO-SiO₂ bioactive glass-ceramic coatings with nanostructure had been successfully synthesized by the LPPS technique and the synthesized coatings showed quick formation of a nanostructured HCA layer after being soaked in SBF. Overall, our results indicate that the LPPS process is an effective and simple method to synthesize nanostructured bioactive glass-ceramic coatings with good in vitro bioactivity.     

Influence of surface topography and pore architecture of alkali-treated titanium on in vitro apatite deposition

Alkali-treated titanium surfaces have earlier shown to induce bone-like apatite deposition. In the present study, the effect of surface topography of two-dimensional and pore architecture of three-dimensional alkali-treated titanium substrates on the in vitro bioactivity was investigated. Titanium plates with a surface roughness of R_a = 0.13 μm, 0.56 μm, 0.83 μm, and 3.63 μm were prepared by Al₂O₃ grit-blasting. Simple tetragonal and face-centered Ti6Al4V scaffolds with spatial gaps of 450-1100 μm and 200-700 μm, respectively, were fabricated by a three-dimensional fiber deposition (3DFD) technique. After alkali treatment, the titanium plates with a surface roughness of R_a = 0.56 μm were completely covered with hydroxyapatite globules after 7 days in simulated body fluid (SBF), while the coverage of the samples with other surface roughness values remained incomplete. Similarly, face-centered Ti₆Al₄ scaffolds with spatial gaps of 200-700 μm exhibited a full surface coverage after 21 days in SBF, while simple tetragonal scaffolds with spatial gaps of 450-1100 μm were only covered for 45-65%. This indicates the importance of surface topography and pore architecture for in vitro bioactivity.     

In vitro evaluation of bioactivity of CaO-SiO2-P2O5-Na2O-Fe2O3 glasses

Glasses with compositions 41CaO(52 − x)SiO₂4P₂O₅·xFe₂O₃3Na₂O (2 ≤ x ≤ 10 mol.%) were prepared by melt quenching method. Bioactivity of the different glass compositions was studied in vitro by treating them with simulated body fluid (SBF). The glasses treated for various time periods in SBF were evaluated by examining apatite formation on their surface using grazing incidence X-ray diffraction, Fourier transform infrared reflection spectroscopy, scanning electron microscopy and energy dispersive spectroscopy techniques. Increase in bioactivity with increasing iron oxide content was observed. The results have been used to understand the evolution of the apatite surface layer as a function of immersion time in SBF and glass composition.     

Investigation on bio-mineralization of melt and sol-gel derived bioactive glasses

The bio-mineralization properties of the melt-derived bioactive glass 45S5 and the sol-gel derived bioactive glasses 58S and 77S were investigated and compared using in vitro test combined with BET, XRD, FTIR and SEM techniques. It was found that the surfaces of the three bioactive glasses could be mineralized by immersion in a simulated body fluid (SBF) at 37 °C for several hours. The bio-mineralized products on the surfaces of the bioactive glasses were apatite microcrystals with a low crystallinity, but the composition and morphologies of the apatite microcrystals on three glasses were different.     

Immersion behaviour of calcium polyphosphate in simulated body fluid

This work documents an investigation into the immersion behaviour of calcium polyphosphate (CPP) in simulated body fluid (SBF) for various periods. The results showed that with the increase of soaking time in SBF, a number of tiny particles were observed on the surface of samples by scanning electron microscope (SEM). The results of X-ray diffraction (XRD) indicated that the particles were contributed to apatite. And the changes of PO₄³⁻ and Ca²⁺ concentrations in SBF were detected by phospho-vanado-molybdate method and inductively coupled plasma atomic emission spectroscopy (ICP) methods respectively. The results indicated that the concentrations of PO₄³⁻ and Ca²⁺ in SBF reached the maximum value after 25 days of immersion, and then decreased with further increase of the soaking time. It is suggested that the degradation and ion exchange of CPP samples are dominant during the early stage of soaking, and then the precipitates begin to form and increase gradually as the soaking time increases. This study has demonstrated that apatite could be formed on the surface of CPP samples, and CPP would be used as bone substitution material.     

Biomineralization of electrospun poly(l-lactic acid)/gelatin composite fibrous scaffold by using a supersaturated simulated body fluid with continuous CO2 bubbling

To promote the biomineralization, supersaturated simulated body fluids (SBFs), e.g. five times SBF (5 × SBF), were usually applied. In these SBFs, however, homogeneous nucleation of Ca-P mineralites and deposition unavoidably took place owing to the HCO₃⁻ decomposition and the pH value increment, which made the prediction of bone bioactivity of substrates controversial. In this study, the classically prepared 5 × SBF was continuously bubbled with CO₂ to keep the pH value stable at 6.4 and the solution transparent, and a kind of electrospun poly(l-lactic acid)/gelatin composite fibers was used for the biomineralization study. In such a modified 5 × SBF, heterogenenous nucleation occurred dominantly and thermodynamical unstable brushites (dicalcium phosphate dihydrate, DCPD) were detected shortly on both electrospun PLLA fibers and PLLA/gelatin (1:1 in weight) composite fibers. In comparison with electrospun PLLA fibers, the sheet-like DCPD mineralites transformed into flaky carbonated calcium-deficient hydroxyapatite (CDHA) within 24 h on the PLLA/gelatin composite fibers due to the accelerating effect of gelatin component. The formed apatite coating contained much less Mg²⁺ ions than that deposited in the classical 5 × SBF. The results of this study showed that supersaturated SBFs buffered with gassy CO₂ were expected good choices for the accelerated biomineralization, and for the prediction of the bone bonding bioactivity of substrates.     

The role of target-to-substrate distance on the DC magnetron sputtered zirconia thin films’ bioactivity

Zirconium dioxide thin films were deposited on 316L-stainless steel type substrates using DC unbalanced magnetron sputtering. The process parameter of this work was the target-to-substrate distance (d_t-s), which was varied from 60 to 120 mm. The crystal structure and surface topography of zirconium dioxide thin films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The results demonstrate that all of the ZrO₂ thin films are composed monoclinic phase. The film sputtered at short d_t-s (60 mm) shows a rather heterogeneous, uneven surface. The grain size, roughness, and thickness of thin films were decreased by increasing d_t-s. The bioactivity was assessed by investigating the formation of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) on the thin film surface soaked in simulated body fluids (SBF) for 7 days. XRD and scanning electron microscopy (SEM) were used to verify the formation of apatite layers on the samples. Bone-like apatites were formed on the surface of the ZrO₂ thin film in SBF immersion experiments. A nanocrystalline hydroxyapatite (HA) with a particle size of 2-4 μm was deposited. Higher crystallinity of HA on the surface was observed when the distance d_t-s increased to more than 80 mm. Therefore, it seems that a d_t-s greater than 80 mm is an important sputtering condition for inducing HA on the zirconia film.     

Preparation and characterization of a novel Si-incorporated ceramic film on pure titanium by plasma electrolytic oxidation

A Si-incorporated bioactive ceramic film was prepared on pure titanium by plasma electrolytic oxidation (PEO) in a new bath containing Ca²⁺, H₂PO₄⁻ and SiO₃²⁻. The film was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS). The apatite-induced ability of PEO film was evaluated by soaking in a simulated body fluid (SBF) for various periods. The results showed that Si-incorporated PEO film present a porous microstructure, the pore size is around 1–5 μm. The film mainly consists of anatase and rutile and a small amount of CaHPO₄ and CaO, besides, bioactive compounds such as CaSiO₃ and SiO₂, also exist in the Si-incorporated PEO film. After immersion in SBF for 28 days, not only the surface layer but also the pores inside the Si-incorporated PEO film were completely filled by apatite crystals, whereas on the surface of a benchmark PEO film free of Si just present small piles of apatite crystals. Silicon incorporated into the PEO film provided more heterogeneous nucleation sites for apatite deposition and hence increased remarkably bioactivity of the PEO film.