Homogeneous Apatite Layer Research Articles

DLP Fabrication of Zirconia Scaffolds Coated with HA/β-TCP Layer: Role of Scaffold Architecture on Mechanical and Biological Properties

In order to merge high-mechanical properties and suitable bioactivity in a single scaffold, zirconia porous structures are here coated with a hydroxyapatite layer. The digital light processing (DLP) technique is used to fabricate two types of scaffolds: simple lattice structures, with different sizes between struts (750, 900 and 1050 µm), and more complex trabecular ones, these latter designed to better mimic the bone structure. Mechanical tests performed on samples sintered at 1400 °C provided a linear trend with a decrease in the compressive strength by increasing the porosity amount, achieving compressive strengths ranging between 128–177 MPa for lattice scaffolds and 34 MPa for trabecular ones. Scaffolds were successfully coated by dipping the sintered samples in a hydroxyapatite (HA) alcoholic suspension, after optimizing the HA solid loading at 20 wt%. After calcination at 1300 °C, the coating layer, composed of a mixture of HA and β-TCP (β-TriCalcium Phospate) adhered well to the zirconia substrate. The coated samples showed a proper bioactivity, well pronounced after 14 days of immersion into simulated body fluid (SBF), with a more homogeneous apatite layer formation into the trabecular samples compared to the lattice ones.

Fabrication of highly bioactive zirconia ceramics via grain‐boundary activation for dental implants

AbstractYttria‐stabilized tetragonal zirconia polycrystal (Y‐TZP) ceramics with outstanding mechanical properties and aesthetic origins are expected to be used in dental implant applications. However, tetragonal zirconia ceramics are not bioactive, which affect the osseointegration and reliability as dental implant materials. Herein, in this study, Y‐TZP ceramics were modified by grain‐boundary activation via coating a bioactive glass (BG) sol with different content on the crystal surfaces of zirconia powder and followed by being gelled, dried, granulated, low‐temperature treated, molded and sintered at 1450°C for 3 h in air. The effects of BG content on the morphology, phase compositions, mechanical properties, in vitro mineralization ability and cell biological properties of the bioactivity modified Y‐TZP ceramics were evaluated. The BG additive did not affect the tetragonal–monoclinic phase transformation of ZrO2. However, the addition of BG decreased the flexural strength of the modified Y‐TZP ceramics compared to that of Y‐TZP. The in vitro mineralization results showed that a homogeneous apatite layer was produced on the surface of the Y‐TZP ceramics when they were immersed in the simulated body fluid for 21 days. The cell response results indicated that the bioactive surface modification of Y‐TZP ceramics could promote cell adhesion, propagation and osteogenic differentiation performance. Thus, our research results suggest that the highly bioactive Y‐TZP ceramics could be a potential candidate for dental implant material.

The optimized preparation of HA/L-TiO2/D-TiO2 composite coating on porous titanium and its effect on the behavior osteoblasts.

Various surface bioactivation technology has been confirmed to improve the osteogenic ability of porous titanium (pTi) implants effectively. In this study, a three-layered composite coating, i.e. outer layer of hydroxyapatite (HA), middle layer of loose titanium dioxide (L-TiO2) and inner layer of dense TiO2 (D-TiO2), was fabricated on pTi by a combined processing procedure of pickling, alkali heat (AH), anodic oxidation (AO), electrochemical deposition (ED) and hydrothermal treatment (HT). After soaking in simulated body fluid for 48 h, the surface of the AHAOEDHT-treated pTi was completely covered by a homogeneous apatite layer. Using MC3T3-E1 pro-osteoblasts as cell model, the cell culture revealed that both the pTi without surface treatment and the AHAOEDHT sample could support the attachment, growth and proliferation of the cells. Compared to the pTi sample, the AHAOEDHT one induced higher expressions of osteogenesis-related genes in the cells, including alkaline phosphatase, Type I collagen, osteopontin, osteoclast inhibitor, osteocalcin and zinc finger structure transcription factor. As thus, besides the good corrosion resistance, the HA/L-TiO2/D-TiO2-coated pTi had good osteogenic activity, showing good potential in practical application for bone defect repair.

Development of bioactive and biocompatible ceramic composites based on potassium polytitanate

Bioactive and biocompatible composites were successfully prepared by reactive sintering of mixtures of a crystalline titanate precursor and 45S5 Bioglass?. The polytitanate/glass precursor ratios were 20/80, 40/60, 60/40 or 80/20 (wt.%). The powder mixtures were uniaxially pressed and heat treated at 1000 ?C for 1 h. During sintering, intensive interactions between raw materials occurred. The formed main crystalline phases were: potassium hexatitanate (K2Ti6O13), calcium titanate (CaTiO3), calcium silicate (CaSiO4) and sodium-calcium silicate (Na6Ca3Si6O18). Additionally, a Si-rich glassy phase was also observed. The mechanism of apatite formation indicated that both crystalline and amorphous phases play important roles in this process. A homogeneous apatite layer was formed on Si-OH, Ti-OH-rich interfaces. In vitro bioactivity was assessed using simulated body fluid (SBF K-9). The in vitro cytotoxicity behaviour was evaluated using a human osteoblastlike cells model and compressive strength by ASTM C-773 standard. All the composites demonstrated high bioactivity as cytotoxicity assays indicated a biocompatibility similar to that of the negative control. The samples showed high cell adherence and elongation cell characteristics similar to those observed on biocompatible systems. The compressive strength of the sintered samples decreased as the polytitanate content precursor was increased. The results obtained indicate that these materials are highly promising composites for medical applications.

Morphological, thermal and bioactivity evaluation of electrospun PCL/β-TCP fibers for tissue regeneration

Abstract Electrospinning is a simple and low-cost way to fabricate fibers. Among the various polymers used in electrospinning, polycaprolactone (PCL) stands out due to its excellent biodegradability and biocompatibility. However, PCL has some limitations such as low bioactivity, hydrophobic surface, and long in vivo degradation. Calcium phosphate ceramics have been recognized as an attractive biomaterial. They are bioactive and osteoinductive, and some are even quite biodegradable. Different contents of particles of beta-tricalcium phosphate (β-TCP) were incorporated in polymer matrix to form fibers of PCL/β-TCP composites by electrospinning for possible application in tissue regeneration. The presence of β-TCP particles promoted some changes in the thermal properties of the fibers. The immersion of PCL/β-TCP 8 wt-% fibers in simulated body fluid (SBF) caused the formation of a denser and homogeneous apatite layer on its surface.

Characterizations on Mechanical Properties and In Vitro Bioactivity of Biomedical Ti–Nb–Zr–CPP Composites Fabricated by Spark Plasma Sintering

To alleviate the bio-inert of Ti alloys as hard tissue implants, Ti–35Nb–7Zr–xCPP (calcium pyrophosphate, x = 5, 10, 15, 20 wt%) composites were prepared by mechanical alloying (MA) and following spark plasma sintering (SPS). Mechanical behaviours and in vitro bioactivity of these composites were investigated systematically. Results showed that the composites consisted of β-Ti matrix, α-Ti, and metal–ceramic phases such as CaO, CaTiO3, CaZrO3, and Ti x P y . With increasing CPP content, the composites had higher strength (over 1500 MPa) and higher elastic modulus, but suffered almost zero plastic deformation together with lower relative density. When the CPP contents were 5 and 10 wt%, the compressive elastic moduli were 44 and 48 GPa, respectively, which were close to those of natural bones. However, the compressive elastic modulus of the composites increased significantly when CPP contents exceed 10 wt%, thus deteriorating the mechanical compatibility of the composites owing to more α-Ti and metal–ceramic phases. Besides, the surface of Ti–35Nb–7Zr–10CPP composite was deposited as a homogeneous apatite layer during soaking in simulated body fluid (SBF). It indicates a good bioactivity between the implant materials and living bones.

Flame Spray Projection of a Bioactive Hidroxyapatite Coating on Ti6Al4V for Biomedical Applications

This work consisted in the development and characterization of a bioactive coating on Ti6Al4V samples by flame spray projection. A synthetichidroxyapatite powder was used to form the coatings. Oxygen and acetylene gas were used as combustible, and the metallic substrate was Ti6Al4V with a roughness of 0.4 and 2.3 μm. The time process varied from 5 to 60 seconds. The projection distance was of 22 cm.The spray coatings were mechanical tested; in all cases, the results indicated that the coatings were well adhered to the metallic surfaces and the metallic subtracts did not present any degradation of the mechanical properties. In addition, the coatings were immersed in simulated body fluids for 21 days in physiological conditions to evaluate the bioactivity. The results demonstrated that the coatings are potentially bioactive through the formation of a dense and homogeneous apatite layer similar to the bone. Results of X-ray diffraction exhibited evidence of a hidroxyapatite layer and by energy dispersive spectroscopy, a Ca/P ratio of 1.57 was obtained. This is an indication of that the use of flame spray projection to coat Ti6Al4V substrates do not decompose the original hidroxyapatite powder. Compositional analysis of the remnant fluids, made by inductively coupled plasma spectrometry, showed that nonmetallic ions were present in the coatings.

Construction of micro–nano network structure on titanium surface for improving bioactivity

A novel hierarchical micro–nano structured titania layer was constructed on Ti surface to mimic the multi-level bone structure. The Ti substrate was subjected to a suitable acid etching and subsequent anodization in NaOH electrolyte to form a micro–nano porous titania layer. It was indicated that this microporous/nano-network (micro/nano-network) structured surface presented the enhanced wettability and superhydrophilic property. The polarization curve measurements showed that the as-prepared micro/nano-network structured TiO2 surface was of better corrosion resistance compared to the blank Ti surface, according to its corrosion current decreased, corrosion potential shifted positively and polarization resistance increased in Hank's solution. Meanwhile, the Mott–Schottky plots revealed that less oxygen vacancies existed in the micro/nano-network structured TiO2 film in contrast to the natural oxide film on blank Ti surface. Moreover, it was observed that the micro/nano-network structured surface was completely covered by a homogeneous apatite layer when immersed in simulated body fluid (SBF) for 14 days, exhibiting an excellent ability of biomineration. Furthermore, the superior cell adhesion and viability were discerned on such hierarchically structured surface, through a comparison of MG63 cell behaviors on blank Ti surface, nano-network structured surface and micro/nano-network structured surface. All results suggest our construction of micro–nano porous TiO2 surface is a promising strategy for improving the bioactivity of titanium implants.

The biomimetic apatite-cefalotin coatings on modified titanium

Dental implant failure often occurs due to oral bacterial infection. The aim of this study was to demonstrate that antibiotic efficacy could be enhanced with modified titanium. First, the titanium was modified by anodization and heat-treatment. Then, a biomimetic coating process was completed in two steps. Surface characterization was performed with scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Release of antibiotic was evaluated by UV/VIS spectrometry, and the antibacterial effect was evaluated on Streptococcus mutans. After the second coating step, we observed a thick homogeneous apatite layer that contained the antibiotic, cefalotin. The titanium formed a rutile phase after the heat treatment, and a carbonated apatite phase appeared after biomimetic coating. We found that the modified titanium increased the loading of cefalotin onto the hydroxyapatite coated surface. The results suggested that modified titanium coated with a cefalotin using biomimetic coating method might be useful for preventing local post-surgical implant infections.

Electrophoretic deposition of a bioactive Si, Ca-rich glass coating on 316L stainless steel for biomedical applications

This work consisted in the development and characterization of a vitroceramic coating on 316L stainless steel by means of electrophoretic deposition (EPD). This vitroceramic coating was obtained through a Si-, Ca-rich glass coating crystallization. The electrophoretic deposition tests were performed on 316L stainless steel mechanically polished substrates. The results suggest that the electrophoretic coatings adhered well to the metallic surfaces. The results demonstrate that the crystallized coatings are potentially bioactive, because a dense and homogeneous apatite layer, similar to a bone, makes up.

Electrophoretic deposition of bioactive wollastonite and porcelain–wollastonite coatings on 316L stainless steel

Wollastonite and porcelain–wollastonite coatings on stainless steel were obtained by electrophoretic deposition using acetone as dispersive medium. A direct electric current of 800 V for 3 min was used for obtaining the single wollastonite coating. A well-sintered layer was observed after heat treatment at 1050 °C for 1 h in air. The two-layer coating was obtained by depositing dental porcelain at 400 V for 30 s followed by the deposition of wollastonite at 400 V for 3 min. After forming the two layers, this complex coating was heat treated at 800 °C for 5 min. Under these conditions, strong bonds of both the interface wollastonite–porcelain and that of porcelain–metallic substrate were observed. The in vitro bioactivity assessment of the coatings was performed by immersing the deposited substrates in simulated body fluid (SBF) for 21 days. All the materials showed to be highly bioactive through the formation of a homogeneous apatite layer.

Acceleration of apatite nucleation on microrough bioactive titanium for bone‐replacing implants

The viability of a new two-step method for obtaining bioactive microrough titanium surfaces for bone replacing implants has been evaluated. The method consists of (1) Grit blasting on titanium surface to roughen it; and (2) Thermo-chemical treating to obtain a bioactive surface with bone-bonding ability by means of nucleating and growing an apatite layer on the treated surface of the metal. The aim of this work is to evaluate the effect of surface roughness and chemical composition of the grit-blasting particles on the ability of the surfaces of nucleating and growing a homogeneous apatite layer. The determination and kinetics of the nucleation and growing of the apatite layer on the surfaces has mainly been studied with environmental scanning electron microscopy (ESEM) and grazing-incidence X-ray diffractometry. The results show that Al(2)O(3)-blasted and thermochemically-treated titanium surfaces accelerates nucleation of the apatite, whereas SiC-blasted and thermochemically-treated titanium surfaces inhibits apatite nucleation, compared with the well studied polished and thermochemically-treated titanium surfaces. The acceleration of the apatite nucleation on the Al(2)O(3)-blasted microrough titanium surfaces is because concave parts of the microroughness that are obtained during grit blasting provides to the rough and bioactive surfaces with a chemical- and electrostatic-favored situation for apatite nucleation. This consists of a high density of surface negative charges (also assisted by the nanoroughness of the surface obtained after the thermochemical treatment) and an increased concentration of the Ca(2+)-ions of the fluid, which have a limited mobility at the bottom of the concave parts.

Apatite Formation on Zirconia Based Composites

Bioactive Mg-PSZ composites were developed by using wollastonite ceramics either as a constituent of the composite formulation or as a bioactive bed during the biomimetic treatment in simulated body fluids. The zirconia composites were prepared by uniaxial pressing of powder mixtures and sintered at 1550oC in air. Wollastonite containing zirconia/alumina composites were also sintered at 1350oC. The composites were immersed in SBF for 7 days on a bed of wollastonite powder and then re-immersed in 1.5SBF for 7 days. Tests were also performed with no wollastonite bed. A highly bioactive surface was observed on the Mg-PSZ/CaSiO3 and Mg-PSZ/Al2O3 composites. A homogeneous apatite layer was detected on the Mg-PSZ/CaSiO3 composites immersed for only 7 days in SBF. No apatite was formed on the Mg-PSZ/Al2O3/CaSiO3 composite. During the sintering mechanism at either 1550 or 1350oC small amounts of aluminosilicate phases are formed. These phases inhibited the apatite formation.

Synthesis Routes for Bioactive Sol−Gel Glasses: Alkoxides versus Nitrates

The synthesis of a new bioactive glass with a composition in mol % of 76% SiO2, 23% CaO, and 1% P2O5 was achieved by the sol−gel method with the employment of two different pathways: via inorganic salts (76S) and via metal alkoxides (76SA). The in vitro bioactivity of both glasses was assessed by soaking them in simulated body fluid for different time periods, and the changes in the texture were analyzed. Comparison of glasses synthesized by the two pathways was also carried out. Although both show good bioactivity, glass synthesized via metal alkoxides leads to the formation of a more homogeneous apatite layer on its surface. In addition, this newly formed layer is thicker and more compact for 76SA, and the homogeneous nucleation of the apatite on the surface leads to a better bond between glass and the mentioned newly formed layer.