Microstructures and bond strengths of plasma-sprayed hydroxyapatite coatings on porous titanium substrates

Mesoporous Silk-Bioactive Glass Nanocomposites as Drug Eluting Multifunctional Conformal Coatings for Improving Osseointegration and Bactericidal Properties of Metal Implants

Endowing metal implants with multifunctional traits to prevent implant-associated infections and improve osseointegration has become a pivotal facet in orthopedics and dental fixation. Herein, we report the synthesis of mesoporous 70S bioactive glass-silk fibroin nanocomposites inspired by the biomimetic organo-apatites of mineralized collagen. The mesoporous, biomimetic nanocomposites enabled loading of antibiotics (gentamicin and doxycycline) and favored their release in a rapid manner while preserving their bioactivity. Ease in modification of the mesoporous nanocomposites enabled tailoring of 3-(aminopropyl)-triethoxysilane to the silanol network of bioactive glass, which improved the loading capacity of the hydrophobic drug (dexamethasone). The modification favored the slow and sustained release of dexamethasone from the modified mesoporous nanocomposites, which is desired for mediating osteogenesis and immunomodulation. Conformal coatings of these drug-loaded nanocomposites were materialized on stainless-steel implants through a facile electrophoretic deposition (EPD) technique, wherein the deposition yield can be controlled by applied parameters. Antibiotic coatings exhibited antibacterial efficacy with bioactivity retained up to 28 days, while dexamethasone-loaded coatings favored mesenchymal stem cell adhesion and osteoinduction. The immunomodulatory roles were also ascertained, wherein M2 macrophage biasness was favored in dexamethasone-loaded coatings. The versatility of these mesoporous biomimetic nanocomposites guarantee the loading of scenario-specific drugs to aid their local delivery through the conformal EPD coatings developed over metal implants toward improving implant patency.

Electrochemical Deposition of Nanostructured Hydroxyapatite Coating on Titanium with Enhanced Early Stage Osteogenic Activity and Osseointegration

Purpose

The aim of research is to fabricate nanostructured hydroxyapatite (HA) coatings on the titanium via electrochemical deposition (ED). Additionally, the biological properties of the ED-produced HA (EDHA) coatings with a plate-like nanostructure were evaluated in vitro and in vivo by undertaking comparisons with those prepared by acid/alkali (AA) treatment and by plasma spray-produced HA (PSHA) nanotopography-free coatings.

Materials and Methods

Nanoplate-like HA coatings were prepared through ED, and nanotopography-free PSHA coatings were fabricated. The surface morphology, phase composition, roughness, and wettability of these samples were investigated. Furthermore, the growth, proliferation, and osteogenic differentiation of MC3T3-E1 cells cultured on each sample were evaluated via in vitro experiments. Histological assessment and push-out tests for the bone–implant interface were performed to explore the effect of the EDHA coatings on the interfacial osseointegration in vivo.

Results

XRD analysis showed that the strongest intensity for the EDHA coatings was at the (002) plane rather than at the regular (211) plane. Relatively higher surface roughness and greater wettability were observed for the EDHA coatings. Cellular experiments revealed that the plate-like nanostructured EDHA coatings not only possessed an ability, similar to that of PSHA coatings, to promote the adhesion and proliferation of MC3T3-E1 cells but also demonstrated significantly enhanced early or intermediate markers of osteogenic differentiation. Significant osseointegration enhancement in the early stage of implantation period and great bonding strength were observed at the interface of bone and EDHA samples. In comparison, relatively weak osseointegration and bonding strength of the bone–implant interface were observed for the AA treatment.

Conclusion

The biological performance of the plate-like nanostructured EDHA coating, which was comparable with that of the PSHA, improves early-stage osteogenic differentiation and osseointegration abilities and has great potential for enhancing the initial stability and long-term survival of uncemented or 3D porous titanium implants.

ZnO-assisted coating of tetracalcium phosphate/ gelatin on the polyethylene terephthalate woven nets by atomic layer deposition

A new kind of coating consisting of zinc oxide (ZnO)/tetracalcium phosphate (TTCP)/gelatin (Gel) on the PET woven nets is prepared chemically by the method of atomic layer deposition (ALD) and hydrothermal method. The prepared materials are confirmed by XRD and SEM. XRD results show that ZnO and TTCP are well coated on the surface of PET woven nets and ALD-assisted ZnO leads to a surprising coating adhesion of about 8 MPa. Furthermore, SEM results indicate the diameter and morphology of ZnO, TTCP and Gel of PET woven nets. And the water contact angles of PET’s surface are decreased with ZnO, TTCP and Gel of PET woven nets. Moreover, the confocal imaging of NIH3T3 cells shows that the obtained product could promote the cells proliferation, which indicates that the good biocompatibility of the prepared PET/ZnO/TTCP/ Gel woven builds a foundation for their future application. The results aim to obtain an efficient method to modify PET for fabricating an ideal artificial implant meeting the clinical needs, and imply a positive effect in promoting the compatibility of PET for enhancing graft-bone healing after implantation.

X-ray diffraction analysis of hydroxyapatite-coated in different plasma gas atmosphere on Ti and Ti-6Al-4V

Objective:

The aim is to study the effect of plasma working gas on composition, crystallinity, and microstructure of hydroxyapatite (HA) coated on Ti and Ti-6Al-4V metal substrates.

Materials and Methods:

Ti and Ti-6Al-4V metal substrates were coated with HA by plasma spray using four plasma gas atmospheres of argon, argon/hydrogen, nitrogen, and nitrogen/hydrogen. The degree of crystallinity, the phases present, and microstructure of HA coating were characterized using X-ray diffraction and scanning electron microscopy.

Results:

Variation in crystallinity and the microstructure of HA coating on plasma gas atmosphere was observed. Micro-cracks due to thermal stresses and shift in the 2θ angle of HA compared to feedstock was seen.

Conclusion:

Plasma gas atmosphere has a significant influence on composition, crystallinity, and micro-cracks of HA-coated dental implants.

In vitro study of electrodeposited fluoridated hydroxyapatite coating on G-II titanium with a nanostructured TiO2 interlayer

Titanium and its alloys have been widely used as orthopedic and dental implants for several decades due to their superior mechanical properties, corrosion resistance and biocompatibility. Recently, many researches revealed that the hydroxyapatite coatings on biomedical materials can further improve their biocompatibility and bioactivity. However, hydroxyapatite coatings are easily decomposed, weakening the bonding between implants and bone tissues and resulting in a high dissolution rate in the biological environment. Prolonging the lifetime of hydroxyapatite in implants is valuable for improving postoperative quality. Hydroxyapatite is the primary inorganic component of bones and teeth. A suitable amount of fluoride ions would be beneficial for the formation of fluoridated hydroxyapatite, which can enhance bone-cell response and the acid resistance of enamel. In this study, G-II titanium substrate was anodized to form a TiO₂ interlayer with a nanotube structure. An electrolyte composed of fluoride, calcium and phosphorus ions was prepared for electroplating fluoridated hydroxyapatite (FHA) coatings onto anodized G-II titanium substrates at a constant voltage. The obtained coatings were examined for their microstructure, mechanical properties; moreover, the changes of apatite structure, surface morphology and corrosion resistance were further investigated after immersion in simulated body fluid (SBF) for a number of weeks. The results show that FHA coatings have a higher surface roughness and hardness than plain hydroxyapatite. After immersion in SBF, the FHA coatings induced the nucleation and growth of apatite on the surface and increased their crystallinity. In a potentiodynamic polarization test, FHA coatings exhibited a better anti-corrosion ability than bare G-II titanium substrate in SBF. Additionally, the anodized TiO₂ nanotube improved the adhesion and corrosion resistance of FHA as well.

Microstructure and Characteristics of Calcium Phosphate Layers on Bioactive Oxide Surfaces of Air-Sintered Titanium Foams after Immersion in Simulated Body Fluid

We propose a simple and low-cost process for the preparation of porous Ti foams through a sponge replication method using single-step air sintering at various temperatures. In this study, the apatite-forming ability of air-sintered Ti samples after 21 days of immersion in simulated body fluid (SBF) was investigated. The microstructures of the prepared Ca-P deposits were examined by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FTIR) spectroscopy, and cross-sectional transmission electron microscopy (TEM). In contrast to the control sample sintered in vacuum, which was found to have the simple hexagonal α-Ti phase, the air-sintered samples contained only the rutile phase. High intensities of XRD peaks for rutile TiO₂ were obtained with samples sintered at 1000 °C. Moreover, the air-sintered Ti samples had a greater apatite-forming ability than that of the Ti sample sintered in vacuum. Ti samples sintered at 900 and 1000 °C had large aggregated spheroidal particles on their surfaces after immersion in SBF for 21 days. Combined XRD, energy-dispersive X-ray spectroscopy, FTIR spectroscopy, and TEM results suggest that the calcium phosphate deposited on the rutile TiO₂ surfaces consist of carbonated calcium-deficient hydroxyapatite instead of octacalcium phosphate.

Ion-Doped Silicate Bioceramic Coating of Ti-Based Implant

Titanium and its alloy are known as important load-bearing biomaterials. The major drawbacks of these metals are fibrous formation and low corrosion rate after implantation. The surface modification of biomedical implants through various methods such as plasma spray improves their osseointegration and clinical lifetime. Different materials have been already used as coatings on biomedical implant, including calcium phosphates and bioglass. However, these materials have been reported to have limited clinical success. The excellent bioactivity of calcium silicate (Ca-Si) has been also regarded as coating material. However, their high degradation rate and low mechanical strength limit their further coating application. Trace element modification of (Ca-Si) bioceramics is a promising method, which improves their mechanical strength and chemical stability. In this review, the potential of trace element-modified silicate coatings on better bone formation of titanium implant is investigated.

HAp/Ti2Ni coatings of high bonding strength on Ti-6Al-4V prepared by the eutectic melting bonding method

Eutectic melting bonding (EMB) method is a useful technique for fabricating bioactive coatings with relatively high crystallinity and bonding strength with substrate on titanium substrates. Using the EMB method, hydroxyapatite/Ti2Ni coatings were prepared on the surface of Ti-6Al-4V at a relatively low temperature (1,050 °C) in a vacuum furnace. The coatings were then characterized in terms of phase components, microstructure, bonding strength and cytotoxicity. The results showed that the coatings were mainly composed of HAp and Ti2Ni, and the thickness of the coatings was approximately 300 μm. X-ray diffraction analysis showed that the coatings exhibited relatively high crystallinity. The tensile bonding strength between the coatings and the substrates was 69.68±5.15 MPa. The coatings had a porous and rough surface which is suitable for cell attachment and filopodia growth. The cell culture study showed that the number of MG-63 cells increased, and the cell morphology changed with the incubation time. This study showed that the EMB method can be utilized as a potentially powerful method to obtain high quality hydroxyapatite coatings with desired mechanical and biocompatibility properties on Ti-alloy substrates.

Bioactive bredigite coating with improved bonding strength, rapid apatite mineralization and excellent cytocompatibility

Previous studies have shown that bredigite (Ca7MgSi4O16) bioceramics possessed excellent biocompatibility, apatite-mineralization ability and mechanical properties. In this paper, the bredigite coating on Ti-6Al-4 V substrate was prepared by plasma spraying technique. The main compositions of the coating were bredigite crystal phase with small parts of amorphous phases. The bonding strength of the coating to Ti-6Al-4 V substrate reached 49.8 MPa, which was significantly higher than that of hydroxyapatite coating and other silicate-based bioceramic coatings prepared by same method. After immersed in simulated body fluid for 2 days, a distinct apatite layer was deposited on the surface of bredigite coating, indicating that the prepared bredigite coating has excellent apatite-mineralization ability. The prepared bredigite coating supported the attachment and proliferation of rabbit bone marrow stem cells. The proliferation level of bone marrow stem cells was significantly higher than that on the hydroxyapatite coating. Our further study showed that the released SiO44– and Mg2+ ions from bredigite coating as well as the formed nano-apatite layer on the coating surface might mainly contribute to the improvement of cell proliferation. The results indicated that the bredigite coating may be applied on orthopedic implants due to its excellent bonding strength, apatite mineralization and cytocompatibility.

Controlling the degradation rate of AZ91 magnesium alloy via sol-gel derived nanostructured hydroxyapatite coating

Magnesium (Mg) alloys have been introduced as new generation of biodegradable orthopedic materials in recent years since it has been proved that Mg is one of the main minerals required for osseous tissue revival. The main goal of the present study was to establish a desired harmony between the necessities of orthopedic patient body to Mg(2+) ions and degradation rate of the Mg based implants as a new class of biodegradable/bioresorbable materials. This prospect was followed by providing a sol-gel derived nanostructured hydroxyapatite (n-HAp) coating on AZ91 alloy using dip coating technique. Phase structural analysis, morphology study, microstructure characterization, and functional group identification were performed using X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The prepared samples were immersed in simulated body fluid in order to study the formation of apatite-like precipitations, barricade properties of the n-HAp coating, and to estimate the dosage of released Mg(2+) ions within a specified and limited time of implantation. Electrochemical polarization tests were carried out to evaluate and compare the corrosion behavior of the n-HAp coated and uncoated samples. The changes of the in vitro pH values were also evaluated. Results posed the noticeable capability of n-HAp coating on stabilizing alkalization behavior and improving the corrosion resistance of AZ91 alloy. It was concluded that n-HAp coated AZ91 alloy could be a good candidate as a type of biodegradable implant material for biomedical applications.

Hydroxyapatite-anatase-carbon nanotube nanocomposite coatings fabricated by electrophoretic codeposition for biomedical applications

In order to eliminate micro-cracks in the monolithic hydroxyapatite (HA) and composite hydroxyapatite/carbon nanotube (HA/CNT) coatings, novel HA/TiO(2)/CNT nanocomposite coatings on Ti6Al4V were attempted to fabricate by a single-step electrophoretic codeposition process for biomedical applications. The electrophoretically deposited layers with difference contents of HA, TiO(2) (anatase) and CNT nanoparticles were sintered at 800°C for densification with thickness of about 7-10 μm. A dense and crack-free coating was achieved with constituents of 85 wt% HA, 10 wt% TiO(2) and 5 wt% CNT. Open-circuit potential measurements and cyclic potentiodynamic polarization tests were used to investigate the electrochemical corrosion behavior of the coatings in vitro conditions (Hanks' solution at 37°C). The HA/TiO(2)/CNT coatings possess higher corrosion resistance than that of the Ti6Al4V substrate as reflected by nobler open circuit potential and lower corrosion current density. In addition, the surface hardness and adhesion strength of the HA/TiO(2)/CNT coatings are higher than that of the monolithic HA and HA/CNT coatings without compromising their apatite forming ability. The enhanced properties were attributed to the nanostructure of the coatings with the appropriate TiO(2) and CNT contents for eliminating micro-cracks and micro-pores.

A novel nano-porous alumina biomaterial with potential for loading with bioactive materials

Nano-porous alumina, with the potential for being loaded with bioactive materials, has been proposed as a novel material for coating implants. In this study, the shear strength of the interface between such nano-porous anodic aluminium oxide (AAO) coatings and titanium substrates, their biocompatibility, and their potential for pore loading have been investigated. An interface shear strength in excess of 29 MPa was obtained which is comparable with that of conventional plasma sprayed hydroxyapatite implant coatings. The viability and differentiation of MG63 osteoblastic cells co-cultured on the coating was found to be broadly comparable to that of similar cells co-cultured on conventional bioinert implant materials such as titanium and fully dense alumina. Extensive pore loading with silica nano-particles of different sizes and in different combinations was demonstrated throughout the thickness of AAO layers 1 microm and 60 microm thick. This work has demonstrated, that with suitable choice of pore filling materials, this novel coating might simultaneously combat infection, encourage bone regeneration, and secure fixation of the implant to bone.

Plasma-sprayed CaTiSiO5 ceramic coating on Ti-6Al-4V with excellent bonding strength, stability and cellular bioactivity

Novel Ca-Si-Ti-based sphene (CaTiSiO5) ceramics possess excellent chemical stability and cytocompatibility. The aim of this study was to prepare sphene coating on titanium alloy (Ti-6Al-4V) for orthopaedic applications using the plasma spray method. The phase composition, surface and interface microstructure, coating thickness, surface roughness and bonding strength of the plasma-sprayed sphene coating were analysed using X-ray diffraction, scanning electron microscopy, atomic force microscopy and the standard mechanical testing of the American Society for Testing and Materials, respectively. The results indicated that sphene coating was obtained with a uniform and dense microstructure at the interface of the Ti-6Al-4V surface and the thickness and surface roughness of the coating were approximately 150 and 10 microm, respectively. Plasma-sprayed sphene coating on Ti-6Al-4V possessed a significantly improved bonding strength and chemical stability compared with plasma-sprayed hydroxyapatite (HAp) coating. Plasma-sprayed sphene coating supported human osteoblast-like cell (HOB) attachment and significantly enhanced HOB proliferation and differentiation compared with plasma-sprayed HAp coating and uncoated Ti-6Al-4V. Taken together, plasma-sprayed sphene coating on Ti-6Al-4V possessed excellent bonding strength, chemical stability and cellular bioactivity, indicating its potential application for orthopaedic implants.