Alkali-heat Treatment Research Articles

Comparison of the torsional fretting behavior of three porous titanium coatings for biomedical applications

This research evaluated the torsional fretting wear proprieties of three porous bio-coatings modified with anodic oxidation, acid–base treatment, and alkali–heat treatment. Torsional fretting wear tests were carried out under a ball-on-flat contact configuration. Torsional fretting wear mechanisms were investigated by a combination of scanning electron microscope observations, energy dispersive X-ray analysis and X-ray diffraction analysis. Results showed that the torsional fretting wear resistance of anodic oxidation coating was better than that of acid–base coating and alkali–heat coating. Adhesive wear was the main damage mechanism of the three porous titanium coatings in partial slip regime. The combination of abrasive wear, delamination, and material transfer was the main wear mechanism of mixed and gross slip regimes.

Upregulation of cell proliferation via Shc and ERK1/2 MAPK signaling in SaOS-2 osteoblasts grown on magnesium alloy surface coating with tricalcium phosphate.

Magnesium (Mg) alloys have been demonstrated to be viable orthopedic implants because of mechanical and biocompatible properties similar to natural bone. In order to improve its osteogenic properties, a porous β-tricalcium phosphate (β-TCP) was coated on the Mg-3AI-1Zn alloy by alkali-heat treatment technique. The human bone-derived cells (SaOS-2) were cultured on (β-TCP)-Mg-3AI-1Zn in vitro, and the osteoblast response, the morphology and the elements on this alloy surface were investigated. Also, the regulation of key intracellular signalling proteins was investigated in the SaOS-2 cells cultured on alloy surface. The results from scanning electron microscope and immunofluorescence staining demonstrated that (β-TCP)-Mg-3AI-1Zn induced significant osteogenesis. SaOS-2 cell proliferation was improved by β-TCP coating. Moreover, the (β-TCP)-Mg-3AI-1Zn surface induced activation of key intracellular signalling proteins in SaOS-2 cells. We observed an enhanced activation of Src homology and collagen (Shc), a common point of integration between bone morphogenetic protein 2, and the Ras/mitogen-activated protein kinase (MAPK) pathway. ERK1/2 MAP kinase activation was also upregulated, suggesting a role in mediating osteoblastic cell interactions with biomaterials. The signalling pathway involving c-fos (member of the activated protein-1) was also shown to be upregulated in osteoblasts cultured on the (β-TCP)-Mg-3AI-1Zn. These results suggest that β-TCP coating may contribute to successful osteoblast function on Mg alloy surface. (β-TCP)-Mg-3AI-1Zn may upregulate cell proliferation via Shc and ERK1/2 MAPK signaling in SaOS-2 osteoblasts grown on Mg alloy surface.

Periodontal-like gingival connective tissue attachment on titanium surface with nano-ordered spikes and pores created by alkali-heat treatment

ObjectivesEstablishment of periodontal-like connective tissue attachment is one of the outstanding issues in implant dentistry. Organized nanotopographic titanium surface may acquire periodontal-like connective tissue attachment with activation of fibroblastic function. This study aimed to evaluate gingival fibroblastic function and connective tissue attachment on two types of nanotopographic titanium surface created by alkali-heat (AH) treatment. MethodsCommercially pure titanium turned discs with or without acid-etching or two types of AH treatment, underwent scanning electron microscopic evaluation in surface topography. Rat gingival fibroblasts cultured on the discs evaluated in terms of cellular adhesion, collagen synthesis and physicochemical binding strength of deposited collagen on the surfaces. Turned or the AH-treated pure titanium mini-implants were placed on the hard palatal plate of rabbits and underwent histological evaluation at 8 weeks postoperatively. ResultsBoth AH-treated surfaces were characterized by numerous well-organized fine nanospikes with crevasses and nanoholes, and uniform shaggy-like nanotopography with a sponge-like inner network, respectively. These nanotopographic surfaces enhanced cellular adhesion and collagen synthesis and toughened binding strength of deposited collagen sufficiently to resist against experimental overloading and inflammatory conditions by inclusion of collagen fibers into the surface, as compared with turned or acid-etched surfaces. The AH-treated mini-implants yielded inclusion of gingival connective tissue into the nanotopographic surface structure, with collagen fiber directions mimicking periodontal tissue in the transmucosal area. These features were not seen on turned surface implants. SignificanceThe well-organized nanotopographic titanium surface with nanospikes and pores by the AH treatment enhanced gingival fibroblastic collagen synthesis and acquired periodontal-like connective tissue attachment with substantial detachment resistance.

Characterization and Bone Differentiation of Nanoporous Structure Fabricated on Ti6Al4V Alloy

The optimal temperature for the alkaline treatment and subsequent heat treatment is determined to optimize the nanoporous structures formed on Ti6Al4V titanium alloy plates. Surface characterization of the alkali‐heat treated samples was performed by scanning electron microscopy, atomic force microscopy, X‐ray photoelectron spectroscopy, and X‐ray diffraction. The effects of heating temperatures on albumin adhesion, rat bone marrow mesenchymal stem cells (BMMSCs) adhesion, alkaline phosphatase activity, osteocalcin production, calcium deposition, and Runx2 mRNA expression were evaluated. The nanotopography, surface chemistry, and surface roughness were unchanged even after heat treatments at 200, 400, and 600°C. Only the amorphous sodium titanate phase changed, increasing with the temperature of the heat treatments, which played a crucial role in promoting superior cell adhesion on the nanoporous surface compared with the sodium hydrogen titanate obtained by a single alkali treatment. The heat treatment at 800°C did not enhance cell attachment on the surface because the nanostructure was dramatically destroyed with the reappearance of Al and V. This study reveals that nanoporous structures with amorphous sodium titanate were fabricated on Ti6Al4V surface through an amended alkali‐heat treatment process to improve BMMSCs adhesion.

Surface modification of pure titanium by hydroxyapatite-containing composite coatings

Micro-arc oxidation (MAO) is commonly applied to modify the surface of titanium (Ti)-based medical implants with a bioactive and porous Ti oxide (TiO2) coating. The study reports a new method of incorporating hydroxyapatite (HA) within the TiO2 coating by MAO and alkali heat treatment (AHT) in the solution containing Ca ion and P ion. The morphology, composition and phase composition of the coatings were analyzed with scanning electron microscopy with energy-dispersive X-ray spectrometer and X-ray diffraction. Surface topography and roughness of the coatings were investigated by atomic force microscopy operated in the tapping mode. The results showed that TiO2-based coatings were obtained on pure Ti by MAO with an electrolyte containing Ca ion and P ion; the prepared MAO coatings were mainly composed of Ca, P, O and Ti. AHT transformed Ca and P to HA crystals. In conclusion, the TiO2/HA composite coatings can be obtained on the surface of pure Ti by MAO and AHT, and the addition of Ca ion and P ion to the AHT solution contributed to the formation of HA.

Enhanced MC3T3-E1 preosteoblast response and bone formation on the addition of nano-needle and nano-porous features to microtopographical titanium surfaces

Micro/nanotopographical modifications on titanium surfaces constitute a new process to increase osteoblast response to enhance bone formation. In this study, we utilized alkali heat treatment at high (SB-AH1) and low temperatures (SB-AH2) to nano-modify sandblasted titanium with microtopographical surfaces. Then, we evaluated the surface properties, biocompatibility and osteogenic capability of SB-AH1 and SB-AH2 in vitro and in vivo, and compared these with conventional sandblast-acid etching (SLA) and Ti control surfaces. SB-AH1 and SB-AH2 surfaces exhibited micro/nanotopographical modifications of nano-needle structures and nano-porous network layers, respectively, compared with the sole microtopographical surface of macro and micro pits on the SLA surface and the relatively smooth surface on the Ti control. SB-AH1 and SB-AH2 showed different roughness and elemental components, but similar wettability. MC3T3-E1 preosteoblasts anchored closely on the nanostructures of SB-AH1 and SB-AH2 surfaces, and these two surfaces more significantly enhanced cell proliferation and alkaline phosphatase (ALP) activity than others, while the SB-AH2 surface exhibited better cell proliferation and higher ALP activity than SB-AH1. All four groups of titanium domes with self-tapping screws were implanted in rabbit calvarial bone models, and these indicated that SB-AH1 and SB-AH2 surfaces achieved better peri-implant bone formation and implant stability, while the SB-AH2 surface achieved the best percentage of bone-implant contact (BIC%). Our study demonstrated that the micro/nanotopographical surface generated by sandblasting and alkali heat treatment significantly enhanced preosteoblast proliferation, ALP activity and bone formation in vitro and in vivo, and nano-porous network topography may further induce better preosteoblast proliferation, ALP activity and BIC%.

Preparation and Corrosion Resistance of Bionic Coatings on Pure Titanium by Microarc Oxidation and Alkali-heat Treatment

Bionic coatings composed of hydroxyapatite (HA) were prepared on the surface of mi- croarc oxidized pure titanium. Then their morphology, phase composition and corrosion resistance were characterized by SEM, XRD electrochemical workstation respectively. The results show that a porous ceramic TiO2 coating containing Ca and P formed on pure titanium after microarc oxida- tion (MAO) process in calcium acetate-calcium biphosphate electrolyte. After a post alkali-heat (MAOAH) treatment, the holes in the treated coating became smaller and the coating became dens- er. Moreover, scale-like, lamellar- and needle-like HA appeared in the coating. The immersion test revealed an excellent corrosion resistance to the Hank's simulated body fluid (SBF) for both MAO and MAOAH coating. After corrosion test in SBF, a calcium deficient type HA(Ca8.86(PO4)6(H2O2)2) and CaTiO3 were formed in MAO coating. However, anions in SBF reacted with oxides in MAO- AH coating resulting in the increase of the diameter and depth of holes of the coating.

Structure, composition and morphology of bioactive titanate layer on porous titanium surfaces

A bioactive coating was produced on pore surfaces of porous titanium samples by an amendatory alkali-heat treatment method. Porous titanium was prepared by powder metallurgy and its porosity and average size were 45% and 135 μm, respectively. Coating morphology, coating structure and phase constituents were examined by SEM, XPS and XRD. It was found that a micro-network structure with sizes of <200 nm mainly composed of bioactive sodium titanate and rutile phases of TiO2 covered the interior and exterior of porous titanium cells, and redundant Ca ion was detected in the titanate layer. The concentration distribution of Ti, O, Ca and Na in the coating showed a compositional gradient from the intermediate layer toward the outer surface. These compositional gradients indicate that the coating bonded to Ti substrate without a distinct interface. After immersion into the SBF solution for 3 days, a bone-like carbonate–hydroxylapatite showing a good biocompatibility was detected on the coating surface. And the redundant Ca advanced the bioactivity of the coating. Thus, the present modification is expected to allow the use of the bioactive porous titanium as artificial bones even under load-bearing conditions.

Biomimetic Creation of Surfaces on Porous Titanium for Biomedical Applications

Titanium and titanium alloys have been extensively studied for many applications in the area of bone tissue engineering. However, dense titanium is prone to lead into aseptic loosening due to their high elastic modulus compared to natural bone. One way to lower the elastic modulus is to produce a porous structure of the metallic alloy by adjusting its porosity. Another concern is the bioinertness of titanium that have no direct chemical bonding with surrounding tissue. One approach to improve the healing process is the application of a calcium phosphate coating onto the surface of biomedical devices and implants. Biomimetic creation of surface using alkali heat treatment with silica addition was employed in this study. The porosity of the samples ranges from 60% to 70%. It was demonstrated that the biomimetic methods are suitable for inducing apatite on the titanium alloys surface.

Preparation of layered bioceramic hydroxyapatite/sodium titanate coatings on titanium substrates using a hybrid technique of alkali-heat treatment and electrochemical deposition

Bioceramic hydroxyapatite/sodium titanate coating on sandblasted titanium substrate was fabricated by a three-step process. At first, the sandblasted titanium substrate was coated with a flake-like sodium titanate layer by alkali-heat treatment. In the second step, the alkali-heat treated titanium substrate was hydrothermal treated at 180 °C for 4 h with calcium solutions. In the third step, the hydroxyapatite (HA) coating was deposited onto the hydrothermal treated layer via electrochemical deposition method. The surface topography and roughness of the coatings were determined by field emission scanning electron microscope (FESEM) and a mechanical contact profilometer, respectively. The surface compositions were evaluated by X-ray diffraction (XRD), energy-dispersive X-ray spectrum (EDS), and X-ray photoelectron spectroscopy (XPS). The EDS, XPS, and XRD analysis confirm the presence of element Ca, Ca2+, and CaTiO3 on sodium titanate layer after hydrothermal treatment with Ca(NO3)2 solution, respectively. FESEM micrograph shows the rod/needle-shaped crystallites are highly densely packed on the calcium-ion-containing layer with an average size of ~50 nm in diameter. The results indicate that the sodium titanate layer containing Ca2+ ions possesses higher ability to induce HA formation compared with the pure sodium titanate layer. It is revealed that surface composition plays an important role in the electrochemical deposition of HA. The calcium-ion-containing layer probably makes the nucleation of HA easy and effectively promotes orientated growth of HA on flake-like sodium titanate surface. The sodium titanate layer possesses a lower corrosion current density and a higher corrosion potential than sandblasted-Ti substrate. The sodium titanate layer should act as a barrier to the release of metal ions from metallic substrate to physiological solutions and thus reducing the electrochemical reaction rate.

Magnesium metal—A potential biomaterial with antibone cancer properties

Reactive oxygen plays an important role in the pathogenesis of many serious illnesses, including bony cancer. Recently, it has been suggested that hydrogen (H2), a selective antioxidant, can effectively scavenge free radicals. Biomedical magnesium (Mg) used for bone defect repair in the surgery of bony cancer could release H2 because of the degradation, so Mg might have the potential to prevent bony cancer from metastasis and recurrence. In this study, alkali-heat treatment method was employed to modify the surface structure of Mg metal, so as to control the degradation of Mg metal and the H2 releasing rate. Then the released H2 was introduced to the Fenton Reaction system to detect its effect on scavenging free radicals. The modified Mg metal was employed as the substrate for bone cancer cell culture to study the effect of the H2 releasing on scavenging free radicals in the cells. It is found that the H2 released from the Mg degradation could scavenge free radicals both in the Fenton Reaction system and bone cancer cells. The effect on the scavenging free radical is proportional to the rate of H2 releasing. It suggested that Mg might be a potential material with anti-bone cancer properties. It is hopeful to both repair the bone defect and prevent bony cancer from metastasis and recurrence for the bony cancer patients by biomedical Mg metal.

Investigation on Osteoblast Growth on the Modified Surface of Porous Titanium

Three methods have been used to modify the porous titanium surface, which is the alkali heat treatment, alkali heat treatment + SBF solution soak and alkali heat treatment + precalcidied + SBF solution soak. The morphology of different surfaces was observed by scanning electron microscopy (SEM). The MC3T3-E1 osteoblast cell was cultured on the modified and unmodified surface of porous titanium with 3days and 7days, the morphology of osteoblast adhesion and growth on different surface was observed. The results showed that osteoblast adhere on the modified and unmodified surface of the porous titanium. Osteoblast on AHS and HA modified surface can grow and spread, but it cannot grow and spread on unmodified and AH modified surface of the porous titanium. Osteoblast can grow across the different titanium fibers of on HA modified surface of porous titanium. Osteoblast on the HA surface has the very good biological suitability, which is beneficial to the combination of bone tissue and porous titanium.

Mechanical Properties and Bioactive Surface Modification via Alkali-Heat Treatment of Porous Titanium for Biomedical Applications

Porous titanium with relative density from 0.4 to 0.64 was prepared by powder metallurgy. The porous structures were examined by scanning electron microscopy and phase constituents were analysed by X-ray diffraction. Mechanical properties of the porous titanium were investigated using a compressive test. To enhance the bioactivity of the alloy surface, alkali-heat treatment was used to modify the surface. Results indicate that the elastic modulus and plateau stress of the porous titanium samples both as-sintered and alkali and heat treatment decrease with decreasing relative density. And the relationship between relative yield stress and elastic modulus with relative density of porous titanium after alkali and heat treatment are agreement with that of as-sintered porous titanium. After alkali-heat treatment, a bioactive Na2Ti5O11 layer formed on the surface of the pre-treated porous titanium. A reduction in the number and severity of this bioactive deposition was observed with the decrease in relative density of porous titanium because of the increasing surface area. In a word, The mechanical properties of the porous titanium can be tailored to match those of human bone, therefore, these bioactive porous titanium have the potential to be a bioactive implant material.

Mechanical modulation and bioactive surface modification of porous Ti–10Mo alloy for bone implants

The objective of this work was to fabricate a suitable porous Ti–10Mo alloy as the human bone replacement implants. The porous Ti–10Mo alloy was fabricated by mechanical alloying and then consolidated by powder metallurgy technique. NH4HCO3 powder was used as space-holder. It was indicated that the mean pore size, porosity, compressive strength, and elastic modulus of porous Ti–10Mo alloy could be tailored by the amount of NH4HCO3, and then could be matched with those of human bones. Furthermore, porous Ti–10Mo alloy was treated by alkali heat treatment and soaked in the 1.5 times simulated body fluid (1.5SBF). It was observed that the surface and the inside pore wall of porous Ti–10Mo alloy with 25wt.% NH4HCO3 covered with the apatite layer after soaked in 1.5SBF for 28days. These phenomena indicated that the surface modified porous Ti–10Mo alloy exhibited a high potential for bone-bonding, which was expected to be used as bone tissue implant.

Preparation of HA-Coated Mg-4.0Zn-1.0Ca-0.6Zr(wt%) Alloy and its Biodegradation Behaviors

Magnesium and magnesium alloys, as biomaterials, possess many properties that are superior to those of other metals. However, magnesium and magnesium alloys have strong chemical activity and porous and brittle surface oxide film, as degradable implantation materials, their degradation rates are too fast. Hydroxyapatite (HA) has good biocompatibility and biological activity and has become one of the replacement materials of biomedical stiff hemopoietic tissue, but the application of HA biomaterial is hindered because HA is brittle and has low strength. Integrating good mechanical properties of metallic materials with excellent biological performance of HA, the composite obtained by coating HA to the surface of metallic matrix is ideal rehabilitation material of bone tissue. In the present study, a new Mg-4.0Zn-1.0Ca-0.6Zr (wt%) was designed according to the requirements of biocompatibility. The microstructures and the mechanical properties of the new alloy were investigated by experiment. The excellent mechanical properties fully meet the service requirements of human bone tissue for mechanical property. Flat and dense hydroxyapatite coating was prepared on the surface of magnesium alloy matrix by preceding alkali heat treatment, electrodeposition and post alkali heat treatment. The Structure and constituent of HA coating and the biodegradation behavior of HA-coated Mg-4.0Zn-1.0Ca-0.6Zr (wt%) alloy were evaluated. Resuls showed that the degradation rate of HA-coated Mg-4.0Zn-1.0Ca-0.6Zr (wt%) alloy in SBF biomimetic solution decreased obviously and tended to be stable after 10 days. As degradable implantation materials, HA-coated Mg-4.0Zn-1.0Ca-0.6Zr (wt%) alloy fully meets the service requirements of human bone tissue.

Study of Self-Assembled Monolayers of Stearic Acid on Pure Magnesium Surface

In this paper, self-assembled monolayers (SAMs) of stearic acid (SA) surface treatment on pure magnesium were studied to improve bioactivity and corrosion resistance of pure Mg. Three pre-treatment methods (HCl-NaOH treatment, alkali-heat treatment and heat treatment) were used. SAMs treated samples were soaked in simulated body fluid (SBF) and untreated samples were taken as control. The pH variation of SBF solution was examined everyday. The electrochemical property of treated and untreated samples was tested to evaluate the anticorrosion performance of organic surface layer. Scanning electron microscope (SEM), X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) analysis were performed to observe the surface appearance and to identify the composition and phases of samples. The results showed that stearic acid SAMs had successfully been assembled on the surface of the samples, which had a good effect on corrosion resistance of materials and decreased the electric current density of SAM-sample 1% to that untreated sample; SAM inhibited the form of Mg(OH)2 and had a good influence on bioactivities of pure magnesium.

In vitro behavior of human osteoblast-like cells (SaOS2) cultured on surface modified titanium and titanium–zirconium alloy

In this study, titanium (Ti) and titanium–zirconium (TiZr) alloy samples fabricated through powder metallurgy were surface modified by alkali-heat treatment and calcium (Ca)-ion-deposition. The alteration of the surface morphology and the chemistry of the Ti and TiZr after surface modification were examined. The bioactivity of the Ti and TiZr alloys after the surface modification was demonstrated. Subsequently, the cytocompatibility of the surface modified Ti and TiZr was evaluated via in vitro cell culture using human osteoblast-like cells (SaOS2). The cellular attachment, adhesion and proliferation after cell culture for 14 days were characterized by scanning electron microscopy (SEM) and MTT assay. The relationship between surface morphology and chemical composition of the surface modified Ti and TiZr and cellular responses was investigated. Results indicated that the surface-modified Ti and TiZr alloys exhibited excellent in vitro cytocompatibility together with satisfactory bioactivity. Since osteoblast adhesion and proliferation are essential prerequisites for a successful implant in vivo, these results provide evidence that Ti and TiZr alloys after appropriate surface modification are promising biomaterials for hard tissue replacement.

Scanning electron microscopy observation of the growth of osteoblasts on Ti-24Nb-4Zr-8Sn modified by micro-arc oxidation and alkali-heat treatment and implant-bone interface

To observe the efficacy of micro-arc oxidation and alkali-heat treatment (MAH) on Ti-24Nb-4Zr-8Sn (Ti2448). Disks (diameter of 14.5 mm, thickness of 1 mm) and cylinders (diameter of 3 mm, height of 10 mm) were fabricated from Ti2448 alloy. Samples were divided into three groups: polished (Ti2448), micro-arc oxidation(MAO-Ti2448), micro-arc oxidation and alkali-heat treatment (MAH-Ti2448). MC3T3-E1 osteoblastic cells were cultured on the disks and cell morphology was observed with scanning electron microscopy (SEM) aftre 3 days. The cylinder samples were implanted in the tibia of dogs and implant-bone interface was observed with SEM after 3 months. A rough and porous structure was shown in both MAO and MAH group. The MC3T3-E1 cells on the MAH-Ti2448 discs spread fully in intimate contact with the underlying coarse surface through active cytoskeletal extentions. Osseointegration was formed in the implant-bone interface in MAH samples. MAH treatment can provide a more advantageous Ti2448 surface to osteoblastic cells than MAO treatment does, and the former can improve the implant-bone integration.

Fabrication of Bioactive Titanium with Controlled Porous Structure and Cell Culture in Vitro

Abstract One of the direct metal forming techniques, electron beam melting (EBM) process, was used to fabricate Ti6Al4V implants with controllable porous structure. The micro-structural pore characterization, porosity and mechanical properties of the fabricated implants were investigated. Scanning electron microscope (SEM) observation shows that the porous structure of fabricated samples coincide with the designed architecture. It is demonstrated that EBM process can provide accurate control over the internal pore architectures of the implant. The compressive strength of the implant with porosity of 60.1% is 163 MPa. The Young's modulus is 14 GPa, which is similar to that of cortical bone. The surface modification by improved alkali-heat treatment induces apatite formation in simulated body fluid (SBF). In vitro cell culture experiment results reveal that osteoblasts will spread and proliferate on the surface of modified specimens over a culture time of 7 d.

Nanomechanical and nanotribological properties of bioactive titanium surfaces prepared by alkali treatment

Alkali-heat treatment (AHT) is a simple and practical method to make titanium surfaces bioactive. Hydroxyapatite nucleates on Ti when in contact with body fluids due to the presence of a thin sodium titanate film produced by the AHT. This method was proposed more than a decade ago and it has been widely investigated at varied scopes. However, there is still little information about the mechanical properties of this film. In this work, the tribo-mechanical behavior of films produced by alkali treatment (AT) and AHT on Ti is investigated using instrumented indentation technique. The films were also characterized by TF-XRD, SEM, EDS and in vitro bioactivity tests. Analytical methods were employed to obtain the mechanical properties of the film from instrumented indentation data. The heat treatment subsequent to the alkaline processing increased the film elastic modulus from 1.7 GPa to 2.8 GPa, the hardness from 12 MPa to 20 MPa and the critical load for scratch test from 1.5 mN to 5.5 mN. Despite the overall improvement in the film bioactivity and tribo-mechanical behavior, the AHT elastic modulus is only 2% of the pristine Ti whereas hardness is less than 1%. This information must be considered for implant design purposes.