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Zinc (Zn) alloys provide a new generation for orthopedic applications due to their essential physiological effects and promising degradation properties. However, excessive release of Zn ions (Zn

The effect of nano-scaled Si3N4 particles on the microstructure, mechanical and electrochemical behavior of hopeite (Zn3(PO4)2·4H2O) conversion coating on pure titanium was investigated. Different concentrations of nanoparticles were dispersed into the phosphating bath to incorporate the process of coating deposition. The XRD results demonstrated that nano-Si3N4 were doped into the coatings without any decomposition or reaction with the hopeite phase. A finer and denser microstructure of the composite coating could be obtained at the addition of 0.5 g/L Si3N4 in comparison with the pure hopeite coating. Moreover, the composite coating presented a higher bonding strength and corrosion resistance related to the refinement of microstructure and filling of the embedded nanoparticles. It is suggested that the incorporation of nano-Si3N4 particles in conversion coating is a promising approach for performance optimization.

Strontium (Sr) can be introduced into hydroxyapatite (HA) crystals and stimulate new bone formation. In this study, the single-crystalline Sr-substituted HA microtubes with hexagonal cross-sections are synthesized under the regulation of Sr2+ via the oleic acid-assisted solvothermal method. The morphology of the as-prepared products changes from ultralong flexible nanofibers to hexagonal microtubes with the increasing Sr/(Sr + Ca) ratio. Microtubes can be formed when a small amount of Sr is doped into HA, with the optimal substitution ratio of Sr2+ being ~6%. The inner and outer diameters of the synthetic Sr-substituted HA microtubes are about 1.6 and 2.3 μm, respectively. Moreover, the effects of Sr2+ dopping on the formation process and mechanism of microtubes were discussed.

Flexible hydroxyapatite nanofibers (HANFs) exhibit great potential in various biomedical fields, especially in bone tissue regeneration as a load-bearing implant material. In this study, flexible HANFs have been successfully synthesized through a solvothermal method using different kinds of fatty acids, including linoleic acid, oleic acid, ricinoleic acid, stearic acid, and palmitic acid, as surfactants. The influences of various fatty acids on the composition, thermal stability and microstructure of the products are investigated by XRD, FT-IR, TG, FESEM, EDS and TEM. The as-prepared flexible HANFs with aspect ratios up to >10 000 are composed of multiple short nanofibers with low Ca/P ratios (∼1.3), high crystallinity (>83%) and diameters of ∼10 nm. However, microrods do not exist in the final products by using oleic acid or palmitic acid as surfactants, and products with a higher crystallite size are found when ricinoleic acid or stearic acid is used. The method reported herein may be applicable for the synthesis of HANFs using other fatty acids as surfactants.

An oleic acid-assisted solvothermal method has been utilized to prepare hydroxyapatite (HA) nanofibers with a high flexibility and aspect ratio. Understanding the role of oleic acid in the synthesis of HA may provide effective routes for the design of advanced biomaterials. The concentration of OH− ions ([OH−]) has a great impact on the reaction system, which in turn affects the nucleation and crystal growth of HA. In this work, the effect of oleic acid on the morphology and structure of the as-prepared products under different concentrations of NaOH was investigated by XRD, FTIR and FE-SEM. The formation process of HA was also explored to better explain the role of oleic acid based on structured characteristics and morphology evolution. These results showed that oleic acid molecules absorbed on the surface of HA would effectively induce a one-dimensional crystal growth, even if the crystal growth habit had been changed under different [OH−]. For [OH−] < 1.50 M, [OH−]-responsive oleic acid and its corresponding behavior as a pH buffer can regulate pH at a relatively constant value. Besides, the flexible ultralong HA nanofibers can be formed at [OH−] = 1.25–1.50 M, while the crystallite size and preferred growth along the c-axis were both improved with an increase in [OH−] added.

Using titanium (Ti) for clinical implants often requires surface modification to improve long-term stability and biological activity. However, due to the presence of stable oxide film, modifying the surface of Ti by chemical conversion is difficult. In this research, an electro-assisted method was used to rapidly form chemical transformation coatings on Ti. The effects of Fe2+ and temperature on the phase composition, microstructures, properties, and the formation mechanism of coatings were investigated. The temperature affected the hydrogen evolution by changing the overpotential of hydrogen, thereby affecting the composition of the coatings. The coatings formed at 60 °C were mainly composed of hopeite, whereas those formed at 30 °C mainly composed of elemental zinc (Zn). Fe2+ promoted the reduction of Zn2+ by abnormal co-deposition with Zn2+ and then changed the morphology and properties of the conversion coating.

In the modern construction industry, large gypsum (CaSO4·2H2O) boards are manufactured through a two-step procedure, which features the heating of fine gypsum powders to form the intermediate plast...

Biomimetic deposition of apatite in simulated body fluid (SBF) in vitro has been widely used to evaluate the bioactivity of titanium (Ti) and prepare a functional coating on biomedical metallic substrates. In this study, the deposition behaviors of hydroxyapatite (HA) on Ti samples treated by alkali and heat treatment (AH) in SBFs (1 ×, 2 ×, 3 × SBF) at 37, 47 and 57 °C were researched. The electrochemical results confirmed the characteristic fine and porous network structure on Ti substrate after AH resulted in the decrease of corrosion resistance. SEM images showed that the surface structure and morphology of hydroxyapatite (HA) coatings varied markedly under different soaking conditions. Particularly, high SBF concentrations and immersion temperatures created more homogeneous and dense deposited layers with uniform large spherical HA agglomerates. The results of XRD and FTIR demonstrated that brushite (the precursor of HA) preferentially formed and gradually transformed into HA in SBF with high ion concentration and temperature. Thermodynamic analysis in terms of nucleation and crystal growth mechanism was proposed to fundamentally explain HA deposition process in vitro. This work provides a potential method to rapidly evaluate the bioactivity of Ti-based biomaterials and prepare controlled bioactive coating on the implants.

The synthesis of silver-doped hydroxyapatite (Ag-HA) nanobelts as a HA-based antibacterial bioactive material is of great importance due to their being a potential candidate to curb the infections associated with HA implants along with their advantage as a reinforcement in biomaterials. Here, a facile one-step method for synthesizing Ag-doped hydroxyapatite (AgxHA) [Ca10−xAgx(PO4)6(OH)2] (x = 0, 0.2, 0.5) nanobelts using hydrothermal homogeneous precipitation is demonstrated. The samples were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Their antibacterial properties against Escherichia coli (E. coli) bacteria and cytotoxicity to Swiss embryonic mouse fibroblast (3T3-J2) cells were evaluated with the help of the disc diffusion method and MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) cell viability assay, respectively. Our study indicates that the increased optimum Ag amount in the HA nanobelt has enhanced its antibacterial properties and bioactivity. The flexibility behavior of an individual multi-layered Ag0.2HA nanobelt was observed by in situ TEM. The novel TEM cyclic compression–bending test results indicate that the Ag0.2HA nanobelt can retain its original shape after eight continuous deformation cycles at an extreme angle, revealing its high flexibility. This study provides new insights into the design of bioactive HA nanobelts with antibacterial properties and opens new opportunities for their load-bearing applications.

In this study, the alkali and heat treatment (AH) of titanium (Ti) at different ambient pressures (at atmospheric pressure, 1 Pa and 10−3 Pa) was studied. The results demonstrated that under atmospheric conditions porous layers with rutile/anatase TiO2 formed on the Ti surface, and at 1 Pa and 10−3 Pa more loose surface structures with a large pore size and sodium titanate (Na1.7Ti6O11) were obtained. In particular, after AH at 1 Pa, the surface layer exhibited greater roughness, better wettability and easier hydroxyapatite (HA) deposition in simulated body fluid (SBF) than under other conditions. The electrochemical characterization revealed the porous network structure on the Ti surfaces formed during AH, which resulted in a successive decrease in the corrosion resistance in the SBF with increasing vacuum degrees. This investigation of the AH technique of Ti at different chamber pressures would promote a more potential clinical application of the AH method.

Highly flexible multi-layered hydroxyapatite (HA) nanobelts were successfully grown and compared to nanorods. The nanomechanical behaviour of individual HA nanostructures was visualized using in situ TEM. Compression-induced deformation in HA nanobelts can spontaneously recover at a maximal strain of 99.2%, much larger than the 2.63% failure strain observed for traditional HA nanorods.

Plasma electrolytic oxidation (PEO) is a promising surface treatment technique to enhance the corrosion resistance of Mg alloy. However, the micro-pores and micro-cracks of the PEO coating limit its anti-corrosion protection capability. In this study, a dense Ca3Al2(OH)12 layer was fabricated on the PEO coating surface by hydrothermal treatment (HT), forming a PEO/HT composite coating. Surface morphologies, chemical composition, phase composition and growth process of the PEO/HT composite coating were characterized using Field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectrophotometer (FT-IR). Corrosion resistance of the samples was studied through immersion test, hydrogen evolution test, and electrochemical test. Results demonstrated that the PEO/HT coating possessed a polyhedral structure and the micro-pores and micro-cracks of the PEO coating were sealed. The PEO/HT composite coating showed improved bioactivity in comparison with PEO coating and Mg alloy after immersion in Hanks' solution. Moreover, the Ca3Al2(OH)12 crystals layer improved the corrosion resistance of PEO coating significantly. Furthermore, the growth process of Ca3Al2(OH)12 layer was discussed.

Hydroxyapatite (HA) exhibits excellent biocompatibility, bioactivity, osteoconductivity, non-toxicity and so on, making it a perfect candidate for biomedical applications. However, HA is not qualified to be used in load-bearing sites due to its poor flexural strength and fracture toughness. Design, synthesis and application of fibrous HA is a promising strategy to overcome the inherent brittleness. This review provides a brief description of HA and hydroxyapatite fiber (HAF), then introduces different synthesis methods of HAF and highlights the inherent merits and drawbacks involved in each method. Finally, the future perspectives in this active research area are given. The purpose of this review is to acquaint the reader with this promising new field of biomaterials research and with emphasis on recent techniques to obtain continuous, uniform and long HAF.

Considerable efforts have been devoted to the construction of micro- and nanostructured surfaces to improve the clinical application of Ti-based orthopedic implants. However, the preparation of bioactive microstructures with tunable characteristics remains challenging. Herein, we investigated the structural evolution of oxide layers on Ti6Al4V surfaces by conducting a cold compression and induction heating protocol. We found that the properties of the metallographic microstructures determined the size and structure of oxide crystallites formed via a seeding mechanism: the finer the matrix grains, the smaller the oxide crystallites. In addition, the alloy matrix grain sizes steadily increased with increasing axial compression because of recrystallization during induction heating. The formation of nanoscale rutile (TiO2) crystallites caused an increase of surface roughness and hardness, and considerably improved the bioactivity of Ti6Al4V, as measured by the degree of hydroxyapatite deposition in simulated body fluid in vitro. However, oversized oxide crystallites had a negative effect on the promotion of hydroxyapatite deposition. This important finding offers a feasible method for the controllable in-situ construction of bioactive oxide layers by designing the required matrix microstructures of Ti-based implant materials.

Phosphate chemical conversion coatings have attracted much attention on surface modification of metallic implant, due to their in-situ growth pattern and good mechanical performances. Nevertheless, it is difficult to use this method for preparing a pure hydroxyapatite (HA) coating. In this study, a pure HA coating was prepared on titanium (Ti) in an acidic phosphate aqueous via a simple single-step chemical conversion without alkali post-treatment. The microstructure, chemical composition, electrochemical and mechanical performances of the HA coating were characterized in comparison with those of a precursor dicalcium phosphate (CaP) coating which was alkali post-treated (CaP-OH). Results revealed that the one-step chemically converted HA coating was homogeneously nano-structured with higher phase purity and crystallinity. Moreover, the HA coating was thicker (~6.5 μm) than the CaP-OH one (~40 μm) but with better mechanical properties and corrosion resistance. The results encouraged the direct preparation of crystalline HA coating with superior properties on surface of Ti via a single-step phosphate chemical conversion.

Calcium phosphate coatings have been applied on the surface of Ti implants to realize better osseointegration. The formation of dicalcium phosphate dihydrate (CaHPO 4 ·2H 2 O), mineralogically named brushite on pure Ti substrate has been investigated via chemical conversion method. Coating composition and microstructure have been investigated by X-ray diffractometer, Fourier transform infrared spectrometer and field emission scanning electron microscope. The results reveal that the coatings are composed of high crystalline brushite with minor scholzite (CaZn 2 (PO 4 ) 2 ·2H 2 O). A micro/nano-scaled fibrous morphology can be produced in the acidic chemical conversion bath with pH 5.00. The surface of the fibrous brushite coating exhibits high hydrophilicity and corrosion resistance in the simulated body fluid. The osteoblast cells grow and spread actively on the coated samples and the proliferation numbers and alkaline phosphate activities of the cells improve significantly compared to the uncoated Ti. It is suggested that the micro/nano-fibrous brushite coating can be a potential approach to improve the osteoinductivity and osteoconductivity of Ti implant, due to its similarity in morphology and dimension to inorganic components of biological hard tissues, and favorable responses to the osteoblasts.

Galvanic coupling approach was introduced into chemical conversion of zinc–zinc phosphate composite coatings on Ti-6Al-4V (TC4) to overcome their surface inertness. The phase composition, morphology, electrochemical performance and adhesive strength of the coating were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), electrochemical workstation system and scratch tester, respectively. The results showed that the uniform and fine zinc–zinc phosphate (Zn3(PO4)2·4H2O) composite coatings were prepared on TC4 by galvanic coupling with AZ91D magnesium alloy (MA). The area ratio of TC4 to MA being 1 : 1 in coupling pair presented better corrosion resistance. The scratch test revealed that the coating formed by galvanic coupling at the area ratio of 1 : 2 presented better adhesive strength between coating and substrate.

Chemical surface coatings not only provide a powerful barrier between metallic substrates and their surroundings but also impart desired surface performances to an underlying substrate. Chemical surface coatings not only provide a powerful barrier between metallic substrates and their surroundings but also impart desired surface performances to an underlying substrate. Recently, the increasing public concern with industrial finishing systems has driven many investigations on the functional modification, such as the use of special chemical additives in the treatment bath, pre- and post-processing, of chemical surface coatings. However, these methods are being phased out due to their possible high-cost or harmful effects. Controlled addition of inorganic nanoparticles, without poison and contamination, to the treatment bath has become a good alternative due to the on-demand properties, including enhanced corrosion resistance and mechanical and functional properties, triggered by nanoparticles. This study focuses on the applications of inorganic nanoparticles in various chemical surface coatings such as electroless plating, electroplating, silane, and chemical conversion coatings. The discussed inorganic nanoparticles include TiO2, SiO2, Al2O3, ZrO2, SiC, ZnO, CeO2, MoS2, and diamond and graphite nanoparticles. This review is also concerned with the dispersion methods of inorganic nanoparticles as well as the formation mechanism of nanocomposite coatings.

Hopeite coating on metals by the zinc phosphate chemical conversion (ZPCC) method has attracted more attention for its potential biomedical use. While the deposition ability of HA layer onto hopeite coating has been rarely reported. In this research, the hydroxyapatite (HA) layer is deposited on hopeite coating by biomimetic process. The influence of SBF concentration, immersion time and solid/liquid ratio on the layer characteristics are discussed. SBF concentration and solid/liquid ratio play vital roles in the deposition of HA layer. The deposition of HA layer is defined as three stages, the dissolution of hopeite coating, HA nucleation and growth.

Biomimetic deposition in simulated body fluid (SBF) has been widely used to evaluate the bioactivity of implants and to prepare bioactive coatings. In this research, deposition of hydroxyapatite (HA) was studied during immersion in modified simulated body fluid (3 × SBF) at 57 °C of titanium samples heat-treated in alkaline solution (alkali–heat treatment, AH). SEM results show uniform large spherical agglomerates formed by soaking for only 1 day. In addition, the results of XRD and FTIR indicate that the coating consists of hydroxyapatite (HA) and brushite (CaHPO 4 ·2H 2 O). The large spherical apatite agglomerates were embedded into the whole deposited layer. High temperature and high concentration of SBF can greatly accelerate the deposition and increase the size of HA, even affect the morphology of deposited HA. In addition, the mechanical adhesive strength between the deposited coating and the substrate is relatively high, and slightly enhances with increasing immersion time.

Poly(L-lactic acid) and hydroxyapatie (PLLA/HA) composite scaffolds have good properties and suit to use as bone tissue engineering. In this work, hollow HA microspheres (HAM) with poor crystallinity were fabricated by a flame-drying method. The HAM has the potential to be used to release drugs or proteins in addition to improve osteoconductivity. Different ratios of PLLA/HAM were used to prepare porous composite scaffolds using the thermally induced phase separation technique. The HAMs were randomly incorporated into the PLLA porous scaffolds. As the HAMs ratio was increased, the porous composite scaffolds changed from ladder-like into isotropic structure. In addition, the compressive strength of PLLA/HAMs composite scaffolds improved first and declined with the increasing of HAMs ratio in the scaffolds. In vitro experiment showed that PLLA/HAMs composite scaffolds improved the attachment, migration, and differentiation of osteoblastic cells. These results demonstrated that the PLLA/HAMs composite scaffolds were superior to plain PLLA scaffold for bone tissue engineering.

Hydroxyapatite fiber (HAF) was fabricated via a one-step hydrothermal route by using urea (CA), acetamide (AA) and propanamide (PA) as pH regulators, respectively, and the reaction time was only 0.5 h. The HAF synthesized by CA as the pH regulator was agglomerated with irregular morphology, while using AA or PA as the pH regulator, the HAF was composed of well-dispersed fibers with lengths larger than 200 μm. Two different morphologies form mainly due to the different hydrolysis rates of the pH regulators. Most of the fibers synthesized by the three pH regulators showed curving appearance, implying their outstanding flexibility. The technique in this paper allows the rapid formation of flexible HAF and may have wider applications in the restorations and reinforcement composites.

To enhance the osteointegration and antibacterial property of titanium (Ti) implant, zinc calcium phosphate chemical conversion (Zn-Ca-PCC) was fabricated on pure Ti by phosphate chemical conversion technique. The surface of the coating was verified by combined techniques of scanning electron microscopy, energy-dispersive X-ray spectrometry, atomic force microscopy and water contact angle measurements. Plate-like Zn-Ca-PCC coatings are built up on the surface of Ti. The results obtained from the antibacterial studies suggest that the Zn-Ca-PCC coatings can greatly inhibit the growth of both Gram-positive ( Staphylococcus aureus ) and Gram-negative ( Pseudomonas aeruginosa ) bacteria. Moreover, the in vitro evaluations demonstrate that the adhesion, proliferation and differentiation of osteoblasts on Zn-Ca-PCC coatings were significantly enhanced compared with pure Ti. In conclusion, innovative Zn-Ca-PCC coatings on Ti with excellent antibacterial activity and biocompatibility are promising candidates for orthopedic and dental implants.

MAO/CS composite coatings were generated on Mg-1.75Zn-0.56Ca alloy surface for protection and improving biocompatibility of Mg-Zn-Ca alloy in the physiological environment. The microstructure, surface analysis and corrosion resistance of samples were evaluated by scanning electronic microcopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in SBF solution. In addition, in vitro cell cytotoxicity test was performed by MTT tests. The findings of this work indicated that MAO/CS composite coatings were smooth and defect-free. The MAO/CS coatings retained a low degradation rate and the solution pH value at a moderate level (≤7.5) during immersion test. The corrosion resistance and cell proliferation were greatly enhanced by the composite coating. Furthermore, the different cell cytotoxicity on Mg alloy, MAO and MAO/CS coating was discussed.

Titanium (Ti) and its alloys are believed to be promising scaffold materials for dental and orthopedic implantation due to their ideal mechanical properties and biocompatibility. However, the host immune response always causes implant failures in the clinic. Surface modification of the Ti scaffold is an important factor in this process and has been widely studied to regulate the host immune response and to further promote bone regeneration. In this study, a calcium-strontium-zinc-phosphate (CSZP) coating was fabricated on a Ti implant surface by phosphate chemical conversion (PCC) technique, which modified the surface topography and element constituents. Here, we envisioned an accurate immunomodulation strategy via delivery of interleukin (IL)-4 to promote CSZP-mediated bone regeneration. IL-4 (0 and 40 ng/mL) was used to regulate immune response of macrophages. The mechanical properties, biocompatibility, osteogenesis, and anti-inflammatory properties were evaluated. The results showed that the CSZP coating exhibited a significant enhancement in surface roughness and hydrophilicity, but no obvious changes in proliferation or apoptosis of bone marrow mesenchymal stem cells (BMMSCs) and macrophages. In vitro, the mRNA and protein expression of osteogenic related factors in BMMSCs cultured on a CSZP coating, such as ALP and OCN, were significantly higher than those on bare Ti. In vivo, there was no enhanced bone formation but increased macrophage type 1 (M1) polarization on the CSZP coating. IL-4 could induce M2 polarization and promote osteogenesis of BMMSCs on CSZP in vivo and in vitro. In conclusion, the CSZP coating is an effective scaffold for BMMSCs osteogenesis, and IL-4 presents the additional advantage of modulating the immune response for bone regeneration on the CSZP coating in vivo., Highlights • A chemical conversion calcium-strontium-zinc-phosphate (CSZP) coating is prepared on titanium. • The CSZP coating exhibits micellar lamellar crystal morphology in micro-nano scale. • The CSZP coating has an optimal topography and element composition for osteogenesis. • Interleukin-4 assisted CSZP coating can obtain better osteoimmunomodulation properties.