Thin hydroxyapatite coatings via sol-gel synthesis

Characterization of the 3YSZ/CNT/HAP coating on the Ti6Al4V alloy by electrophoretic deposition

In this article, the effects of the simultaneous addition of the 3 mol % yttria-stabilized zirconia (3YSZ) and carbon nanotubes (CNTs) reinforcements on different properties of the natural hydroxyapatite (HAP) coating were studied. The electrophoretic deposition (EPD) process was implemented to prepare thin coatings on the Ti6Al4V substrate. The coatings were then sintered at 1000 ° C under vacuum for 2 hr and the mechanical properties of them were studied by the nano-indentation method. The microsture and phase content of the coatings were investigated by the scanning electron microscope and X-ray diffraction methods, respectively. The electrochemical properties of the samples were studied by potentiodynamic polarization and electrochemical impedance spectroscopy. The biocompatibility of the coatings was evaluated by the MTT test under standard conditions. It was found that the proper voltage and duration for the deposition of the coatings were 20 V and 4 min, while the longer deposition time of up to 6 min. Was tolerable in the coatings containing 5 wt % of the CNTs. The hardness and Young's modulus of the coatings were improved significantly by the siumultaneous addition of 3YSZ and CNTs, but the effect of nanotubes was more prominent. It was also found that the composite coating had marginally lower biocompatibility, as compared to the natural HAP, which was probably due to their lower roughness. The corrosion resistance of the HAP was not affected by the presence of 3YSZ particles, while the addition of CNTs improved the corrosion resistance of the coatings.

Low-Temperature Hydrothermal Treatment Surface Functionalization of the Ultrafine-Grained TiMo Alloys for Medical Applications

Hydroxyapatite (HAp) is the most widely used material for bio coating. The functional layer can be produced by many methods, however, the most perspective by its utility, easy to scale up, and simplicity aspects remains a hydrothermal treatment approach. In this work, an HAp coating was produced by low-temperature hydrothermal treatment on the ultrafine-grain beta Ti-xMo (x = 23, 27, 35 wt.%) alloys. The proposed surface treatment procedure combines acid etching, alkaline treatment (AT), and finally hydrothermal treatment (HT). The uniqueness of the approach relies on the recognition of the influence of the molar concentration of NaOH (5 M, 7 M, 10 M, 12 M) during the alkaline treatment on the growth of hydroxyapatite crystals. Obtained and modified specimens were examined structurally and microstructurally at every stage of the process. The results show that the layer after AT consist of titanium oxide and phases based on sodium with various phase relations dependent on NaOH concentration and base composition. The AT in 7 M and 10 M enables to obtain the HAp layer, which can be characterized as the most developed in terms of thickness and porosity. Finally, selected coated samples were investigated in terms of surface wettability test managed in time relation, which for the results confirm high hydrophilicity of the surfaces. Conducted research shows that the low-temperature hydrothermal processing could be considered for a possible adaptation in the drug encapsulation and delivery systems.

Sol-Gel Derived Hydroxyapatite Coatings for Titanium Implants: A Review

With the growing demands for bone implant therapy, titanium (Ti) and its alloys are considered as appropriate choices for the load-bearing bone implant substitutes. However, the interaction of bare Ti-based implants with the tissues is critical to the success of the implants for long-term stability. Thus, surface modifications of Ti implants with biocompatible hydroxyapatite (HAp) coatings before implantation is important and gained interest. Sol-gel is a potential technique for deposition the biocompatible HAp and has many advantages over other methods. Therefore, this review strives to provide widespread overview on the recent development of sol-gel HAp deposition on Ti. This study shows that sol-gel technique was able to produce uniform and homogenous HAp coatings and identified the role of surface pretreatment of Ti substrate, optimizing the sol-gel parameters, substitution, and reinforcement of HAp on improving the coating properties. Critical factors that influence on the characteristics of the deposited sol-gel HAp films as corrosion resistance, adhesion to substrate, bioactivity, morphological, and structural properties are discussed. The review also highlights the critical issues, the most significant challenges, and the areas requiring further research.

A comprehensive review of biodegradable synthetic polymer-ceramic composites and their manufacture for biomedical applications

The application of various materials in biomedical procedures has recently experienced rapid growth. One area that is currently receiving significant attention from the scientific community is the treatment of a number of different types of bone-related diseases and disorders by using biodegradable polymer-ceramic composites. Biomaterials, the most common materials used to repair or replace damaged parts of the human body, can be categorized into three major groups: metals, ceramics, and polymers. Composites can be manufactured by combining two or more materials to achieve enhanced biocompatibility and biomechanical properties for specific applications. Biomaterials must display suitable properties for their applications, about strength, durability, and biological influence. Metals and their alloys such as titanium, stainless steel, and cobalt-based alloys have been widely investigated for implant-device applications because of their excellent mechanical properties. However, these materials may also manifest biological issues such as toxicity, poor tissue adhesion and stress shielding effect due to their high elastic modulus. To mitigate these issues, hydroxyapatite (HA) coatings have been used on metals because their chemical composition is similar to that of bone and teeth. Recently, a wide range of synthetic polymers such as poly (l-lactic acid) and poly (l-lactide-co-glycolide) have been studied for different biomedical applications, owing to their promising biocompatibility and biodegradability. This article gives an overview of synthetic polymer-ceramic composites with a particular emphasis on calcium phosphate group and their potential applications in tissue engineering. It is hoped that synthetic polymer-ceramic composites such as PLLA/HA and PCL/HA will provide advantages such as eliminating the stress shielding effect and the consequent need for revision surgery.

Calcium Phosphate Bioceramics: A Review of Their History, Structure, Properties, Coating Technologies and Biomedical Applications

Calcium phosphate (CaP) bioceramics are widely used in the field of bone regeneration, both in orthopedics and in dentistry, due to their good biocompatibility, osseointegration and osteoconduction. The aim of this article is to review the history, structure, properties and clinical applications of these materials, whether they are in the form of bone cements, paste, scaffolds, or coatings. Major analytical techniques for characterization of CaPs, in vitro and in vivo tests, and the requirements of the US Food and Drug Administration (FDA) and international standards from CaP coatings on orthopedic and dental endosseous implants, are also summarized, along with the possible effect of sterilization on these materials. CaP coating technologies are summarized, with a focus on electrochemical processes. Theories on the formation of transient precursor phases in biomineralization, the dissolution and reprecipitation as bone of CaPs are discussed. A wide variety of CaPs are presented, from the individual phases to nano-CaP, biphasic and triphasic CaP formulations, composite CaP coatings and cements, functionally graded materials (FGMs), and antibacterial CaPs. We conclude by foreseeing the future of CaPs.

The Design of Nanostructured Metronidazole-Loaded HPC/Oxide Xerogel Composites: Influence of the Formulation Parameters on In Vitro Characterisation

In this study, oxide and polymer/oxide xerogels with metronidazole were prepared and examined as carriers of drug for the local application to the bone. The nanoporous SiO2-CaO-P2O5 and HPC-SiO2-CaO-P2O5 xerogel materials with different amounts of the polymer [hydroxypropyl cellulose (HPC)] were prepared using the sol-gel technology, and their physicochemical properties were characterised with respect to chemical structure [by Fourier transform infrared spectroscopy (FTIR)], porosity and the specific surface area of solids (BET), crystallinity [by X-ray powder diffraction (XRD)], morphology [by scanning electron microscope (SEM)] and the in vitro release of the metronidazole over time (by UV-vis spectroscopy, in the ultraviolet light region). HPC-modified oxide xerogels as the carriers of drug showed slower release of metronidazole, due to the structure and stronger interactions with drug as compared with the pure oxide xerogel. Kinetic analysis indicated diffusional mechanism of drug release from all xerogel carriers. HPC addition to the oxide material resulted in a decrease in the porosity and improved the bioactive properties of xerogels. Obtained results for xerogel composites suggest that the metronidazole-loaded xerogels could be attractive candidates for local delivery systems particularly to a bone.

Effect of Strontium Enhanced Calcium Phosphate Coating on <i>In Vitro</i> Behavior of Human Mesenchymal Stem Cell (hMSC)

Calcium phosphate is a widely used material as coating for metallic implants. This research describes a biomimetic coating techniques based on deposition of calcium phosphate films on a Ti6Al4V plates that was used to study the effect of strontium additive on the behavior of hMSCs. In this study, strontium additive was homogenously deposited onto calcium phosphate films on a Ti6AlV plates by using a biomimetic techniques. Strontium affected composition and morphology of calcium phosphate deposited on a Ti6Al4V plates to a varying degree, according to concentration of solutions used. The effect of strontium additive on proliferation and differentiation of hMSCs depended on the solution and concentration tested. In general, all individual three coatings showed decreased hMSCs proliferation. Strontium additive demonstrated a significant increase in differentiation into osteogenic lineage when compared with the control and calcium phosphate films without strontium additive. However, no cytotoxic effect of strontium additive in the concentrations tested was detected. The Fourier transform infrared spectra showed that this new coating closely resembles bone mineral. The techniques illustrated in this study mimics bone mineral containing strontium additive, making it constructive for studying basic processes of in vitro bone formation. The results showed in this study can be used for changing bone graft substitutes by addition of strontium additive on implants in order to affect their performance in bone repair and regeneration. Also, the system can aid rapid bone formation around the implant, reducing therewith the patient’s recovery time after surgery.

Hydroxylapatite nanoparticles: fabrication methods and medical applications

Hydroxylapatite (or hydroxyapatite, HAp) exhibits excellent biocompatibility with various kinds of cells and tissues, making it an ideal candidate for tissue engineering, orthopedic and dental applications. Nanosized materials offer improved performances compared with conventional materials due to their large surface-to-volume ratios. This review summarizes existing knowledge and recent progress in fabrication methods of nanosized (or nanostructured) HAp particles, as well as their recent applications in medical and dental fields. In section 1, we provide a brief overview of HAp and nanoparticles. In section 2, fabrication methods of HAp nanoparticles are described based on the particle formation mechanisms. Recent applications of HAp nanoparticles are summarized in section 3. The future perspectives in this active research area are given in section 4.

Synthesis and application of nanostructured calcium phosphate ceramics for bone regeneration

In the past two decades, nanotechnology has entered the field of regenerative medicine, resulting in the development of a novel generation of instructive, nanostructured biomaterials that are able to orchestrate cellular behavior by presenting specific morphological and biological cues. Using nanotechnology, materials containing nanosized features (e.g., pores, patterns, textures, grain sizes) can be obtained that exhibit properties that are considerably altered compared with micron-structured materials. Inspired by the hierarchical nanostructure of bone, the application of nanostructured materials for bone regeneration is gaining increasing interest in the field of biomaterials research. Because crystallographic and chemical studies have shown that synthetic hydroxyapatite closely resembles the inorganic phase found in bone and teeth, synthesis and applications of nanostructured calcium phosphate ceramics have been reviewed. Synthesis techniques for the preparation of calcium phosphate nanoparticles include precipitation, sol-gel, and hydrothermal processes, whereas four main biomedical applications of nanostructured calcium phosphate ceramics in bone regeneration have been addressed in more detail, that is, (1) polymer/calcium phosphate nanocomposites, (2) nanostructured monophasic calcium phosphate bone fillers, (3) nanostructured precursor phases for calcium phosphate cements, and (4) nanostructured calcium phosphate coatings.

Calcium orthophosphate coatings, films and layers

In surgical disciplines, where bones have to be repaired, augmented or improved, bone substitutes are essential. Therefore, an interest has dramatically increased in application of synthetic bone grafts. As various interactions among cells, surrounding tissues and implanted biomaterials always occur at the interfaces, the surface properties of the implants are of the paramount importance in determining both the biological response to implants and the material response to the physiological conditions. Hence, a surface engineering is aimed to modify both the biomaterials, themselves, and biological responses through introducing desirable changes to the surface properties of the implants but still maintaining their bulk mechanical properties. To fulfill these requirements, a special class of artificial bone grafts has been introduced in 1976. It is composed of various mechanically stable (therefore, suitable for load bearing applications) biomaterials and/or bio-devices with calcium orthophosphate coatings, films and layers on their surfaces to both improve interactions with the surrounding tissues and provide an adequate bonding to bones. Many production techniques of calcium orthophosphate coatings, films and layers have been already invented and new promising techniques are continuously investigated. These specialized coatings, films and layers used to improve the surface properties of various types of artificial implants are the topic of this review.

The sol-gel prepared SiO2-CaO-P2O5 composites doped with Metronidazole for application in local delivery systems

The aim of this study was to evaluate the physical properties, chemical structure and bioactivity of sol-gel processed oxide (SiO(2)-CaO-P(2)O(5)) composites used as controlled release materials for Metronidazole-drug applied in periodontal disease treatment. The obtained composite materials were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), the Brunauer-Emmet-Teller (BET) technique and further monitoring in the ultraviolet and visible light regions (UV-Vis) of the in vitro release of the drug over time. Using tetramethoxysilane (TMOS) as a precursor of silica matrix and calcium nitrate tetrahydrate (Ca(NO(3))(2) 4H(2)O), triethyl phosphite (P(OC(2)H(5))(3)) as precursors of CaO and P(2)O(5) respectively, xerogels with different morphology and physical properties were obtained. The applied modifications improved also the bioactivity and changed the profile of the drug release. Based on the presented results of this study, it may be concluded that applied xerogel matrices could be promising candidates for the formulation in local delivery systems.

Antibacterial and osteogenic properties of silver-containing hydroxyapatite coatings produced using a sol gel process

Since bacterial infection is a rising complication following the wide use of implant, there is considerable attention on the effect of implant surface properties on bacterial adhesion. In this study, the effect of silver (Ag) doped hydroxyapatite (HA) coatings on initial antibacterial adhesion and osteoblast cell proliferation and differentiation was investigated. Using a sol-gel process, HA coatings doped with 1 wt % AgNO(3) (AgHA1.0) and 1.5 wt % Ag (AgHA1.5) were prepared. Coated surfaces were characterized using X-ray diffraction (XRD) and contact angles measurements. The initial bacteria adhesion was evaluated using a RP12 strain of Staphylococcus epidermidis (ATCC 35984) and the Cowan I strain of Staphylococcus aureus, whereas osteoblast proliferation and differentiation were evaluated using human embryonic palatal mesenchyme cells (HEPM), an osteoblast precursor cell line. In this study, XRD analysis of all surfaces indicated peaks corresponding to HA. Contact angles for AgHA surfaces were observed to be significantly lower when compared to HA surfaces. In vitro initial bacterial adhesion study indicated a significantly reduced number of S. epidermidis and S. aureus on AgHA surfaces when compared to HA surface. The use of HEPM cells indicated no significant difference in double-stranded DNA (dsDNA) production between all surfaces. Additionally, no differences in alkaline phosphatase specific activity were observed between HA and AgHA1.0 surfaces. Overall, it was concluded that AgHA1.0 has the similar biological activity as HA, with respect to bone cell proliferation and differentiation. In addition, the AgHA1.0 was also concluded to have the ability to minimize the initial bacteria adhesion. (c) 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007.

Dip coated silicon-substituted hydroxyapatite films

Silicon-substituted hydroxyapatites have been deposited onto Ti6Al4V substrates by sol-gel technology. The Ca(10)(PO(4))(6-x-y)(SiO(4))(x)(CO(3))(y)(OH)(2-x+y) coatings obtained, with silicon contents up to x=1 (2.8 wt.%), show a homogeneous and crack-free surface composed of particles smaller than 20 nm. The silicon enters into the apatite structure in the form of SiO(4)(4-) groups that partially substitute the PO(4)(3-) groups. The Si content and the Ca/P molar ratio of the coatings agree with those originally introduced in the sols. Layers with thicknesses around 600 nm show adhesion strengths superior to 20 MPa as determined by a pull-out test. The formation of an apatite layer onto these coatings after immersion in a simulated body fluid is enhanced by the presence of silicon.

Antimicrobial effects and human gingival biocompatibility of hydroxyapatite sol-gel coatings

The sol-gel method was employed to synthesize hydroxyapatite (HAp) coatings modified with Ag or Zn ions onto Ti-6Al-4V substrate. A bacterial strain Streptococcus mutans (S. mutans) and a human gingival fibroblast (HGF-1) cell line were used to investigate the antimicrobial effect and biocompatibility, respectively. HAp coatings containing 100 ppm Ag(+) ions suppressed the growth of S. mutans. An apparent inhibition zone around the HAp coating was further observed at Ag(+) concentration up to 10,000 ppm. However, for coatings containing Zn(2+) ions, a clear inhibition zone was observed at Zn(2+) concentration of 10,000 ppm. Nevertheless, the results of HGF-1 cultivation demonstrated that the Zn(2+)-modified HAp coatings exhibited better attachment and spread of HGF-1 than did the Ag(+)-modified coatings. Zn(2+) modified HAp coatings also increased the plating efficiency of HGF-1 cells. The cytotoxicity associated with the addition of Ag and the cell-conductive capacity associated with the addition of Zn are proportional to the added concentration, from 100 to 10,000 ppm. The dosages of both Ag(+) and Zn(2+) ions that should be added to HAp coatings were considered to prevent infection and improve biocompatibility. The results of this study ensure that HAp coatings modified with a moderate amount of Ag/Zn efficiently resist microorganisms and improve biocompatibility.

Calcium phosphate sol–gel-derived thin films on porous-surfaced implants for enhanced osteoconductivity. Part I: Synthesis and characterization

Thin sol-gel-formed calcium phosphate (Ca-P) films were formed on sintered porous-surfaced implants as an approach to increasing the rate of bone ingrowth. The films were prepared using either an inorganic precursor solution (with calcium nitrate tetrahydrate and ammonium dihydrogen phosphate) or an organic precursor solution (with calcium nitrate tetrahydrate and triethyl phosphite). We report on the formation and characteristics of the films so formed. Film characteristics were assessed by thin film X-ray diffraction, diffuse-reflectance infrared Fourier transform spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. In addition, thin sections were prepared either across or parallel to the Ca-P/Ti6Al4V interface and examined by transmission electron microscopy. Both approaches resulted in the formation of nanocrystalline carbonated hydroxyapatite films but with different Ca/P ratios and structures, the Inorganic Route-formed film having a lower Ca/P ratio (1.46 cf 2.10 for the Organic Route-formed film) and having a more irregular topography. An interfacial reaction product (CaTi(2)O(5)) was identified by selected area electron diffraction with the Inorganic Route-formed film only.

Structural evolution of sol-gel-derived hydroxyapatite

Structural evolution upon transformation of sol to gel, and gel to final ceramic during the synthesis of hydroxyapatite is investigated using Fourier transform infrared (FTIR) analysis, X-ray diffraction (XRD), thermal behavior (DTA and TGA), and electron microscopy examination (SEM/TEM). The sol was first thermally aged at 45 C for various time periods up to 120 min. The colloidal sol, which may have an oligomeric structure, was relatively stable against coagulation. Upon drying, the sol particles consolidated into dry gel through van der Waals attraction, and showed X-ray amorphous phosphate structure. The solid gels showed a particulate microstructure, composed of primary particles of about 8-10 nm in diameter. The amorphous gel transformed into crystalline apatite at temperatures > 300 C. The calcined gels showed a nano-scale microstructure, with grains of 20-50 nm in diameter. Through an appropriate heat treatment between 300 and 400d degrees C. the apatite prepared using current process exhibits a nano-scale, low-crystallinity, carbonated apatitic structure, which closely resembles that of human bone apatite.

Sol-gel hydroxyapatite coatings on stainless steel substrates

Thin film hydroxyapatite deposits onto sandblasted 316L stainless steel substrates were prepared using water-based sol-gel technique recently developed in our lab. The coatings were annealed in air at 375 degrees C, 400 degrees C, and 500 degrees C. Phase formation, surface morphology, interfacial microstructure, and interfacial bonding strength of the coatings were investigated. Apatitic structure developed within the coatings while annealing at temperatures > or = 400 degrees C, while those heat-treated at 375 degrees C showed poor crystallinity. The coatings were dense and firmly attached to the underlying substrates, reaching an average bonding strength (as determined through the pull-out test) of 44 MPa. Nano-porous structure was found for the coatings annealed at 500 degrees C, believed to result from grain growth, and causing a slight decrease in the bonding strength. Surface microcracking, although not extensive, occurred after annealing at temperatures > or = 400 degrees C, and was linked to non-uniform thickness of the coating due to roughness of the substrate. A contraction of the coatings as a result of sintering, and phase transition from amorphous (or poor crystalline) to reasonably good crystalline apatite, may be responsible for the loss of structural integrity of the thicker sections of the coatings. It seems quite promising that a dense and adhesive apatite coating can be achieved through water-based sol gel technology after short-term annealing at around 400 degrees C in air.

Aging effect on the phase evolution of water-based sol-gel hydroxyapatite

In a number of recent reports on the synthesis of sol-gel hydroxyapatite, aging of the precursor solution has been found to be critical in developing an apatitic phase. Critical aging time is required to complete reaction between Ca and P molecular precursors to form a desired intermediate complex that permits a further transformation to apatite phase under appropriate thermal treatment. In this investigation, we employed a water-based sol-gel process recently developed to fabricate hydroxyapatite at relatively low temperatures. The aging effect on apatite formation was systematically studied in terms of aging time and temperature. Experimental results show that the aging time is considerably reduced as aging temperature rises. Long-term thermal aging was unfavorable for apatite formation. The optimal aging parameters for apatite formation were experimentally determined, which was further consolidated into a phase evolution map. Aging kinetic was investigated by monitoring the variation of solution pH, following the determination of an apparent activation energy, which has a value as high as 10.35 kcal/mol, for the chemical reaction occurring upon aging. Optimal solution chemistry was elucidated based on the corresponding phase evolution map.

Water-based sol-gel synthesis of hydroxyapatite: process development

Hydroxyapatite (HA) ceramics were synthesized using a sol-gel route with triethyl phosphite and calcium nitrate as phosphorus and calcium precursors, respectively. Two solvents, water and anhydrous ethanol, were used as diluting media for HA sol preparation. The sols were stable and no gelling occurred in ambient environment for over 5 days. The sols became a white gel only after removal of the solvents at 60 degrees C. X-ray diffraction showed that apatitic structure first appeared at a temperature as low as 350 degrees C. The crystal size and the HA content in both gels increase with increasing calcination temperature. The type of initial diluting media (i.e., water vs. anhydrous ethanol) did not affect the microstructural evolution and crystallinity of the resulting HA ceramic. The ethanol-based sol dip-coated onto a Ti substrate, followed by calcination at 450 degrees C, was found to be porous with pore size ranging from 0.3 to 1 microm. This morphology is beneficial to the circulation of physiological fluid when the coating is used for biomedical applications. The satisfactory adhesion between the coating and substrate suggests its suitability for load-bearing uses.