Thin Layer Of Calcium Phosphate Research Articles

Fluor‑carbonated hydroxyapatite coatings by pulsed laser deposition to promote cell viability and antibacterial properties

Fluorine, an essential element present in bone and dental tissues, promotes mineralization and is directly involved in the bone formation process. The antibacterial effects of fluorine on oral bacteria are also well known. In this study, metallic implants were coated with a thin layer of calcium phosphate enriched with fluorine to improve osteointegration and protect against infections. These coatings were obtained by pulsed laser deposition (PLD) using, as a target, a bioceramic of marine origin, mainly composed of fluorapatite from the enameloid of shark teeth. The compositional dependence of coatings on H2O vapor pressures applied during PLD was analyzed in order to optimize physicochemical properties. Physicochemical characterization to evaluate morphology (SEM), thickness (interferometric profilometry), structure (XRD) and composition (FTIR, XPS) was performed. To evaluate the biological response, both MC3T3-E1 pre-osteoblasts and bacterial strains Staphylococcus aureus and Staphylococcus epidermidis, most responsible for 77% of infections associated with prosthetic implants, were tested. Proper cell proliferation (MTT assay) and ALP synthesis up to 21 days were confirmed. Antibacterial properties were also demonstrated: compared to synthetic hydroxyapatite coatings, there was a significant reduction in colony-forming units (CFUs) for both strains.

Material Analysis and Optical Quality Assessment of Opacified Hydrophilic Acrylic Intraocular Lenses After Pars Plana Vitrectomy

Explanted hydrophilic intraocular lenses (IOLs) with clinically significant opacification after pars plana vitrectomy (PPV) were assessed for material change and optical quality, in an invitro laboratory study. Retrospective observational case series. Ten opacified IOLs after PPV with intraocular gas injection were analyzed in a laboratory setting. Analyses included evaluation of patients' medical history, optical quality assessment, light microscopy, histologic staining, scanning electron microscopy, and energy dispersive x-ray spectroscopy. In all 10 IOLs a thin layer of calcium phosphate that had accumulated underneath either the anterior or posterior optical surface in a central circular area of the IOL optic caused the opacification. The calcifications lead to deterioration of the modulation transfer function (MTF) across all spatial frequencies. PPV with instillation of gas into a pseudophakic eye with an acrylic hydrophilic lens seems to increase the risk for secondary calcification irrespective of the manufacturer. In these cases, IOL exchange is the only treatment option available. Since IOL exchange is associated with a high intraoperative complication rate, our results suggest to consider the risk of IOL calcification when implanting hydrophilic acrylic IOLs.

Hydrophilic intraocular lens opacification after posterior lamellar keratoplasty - a material analysis with special reference to optical quality assessment

BackgroundLaboratory analysis and optical quality assessment of explanted hydrophilic intraocular lenses (IOLs) with clinically significant opacification after posterior lamellar keratoplasty (DMEK and DSAEK).MethodsThirteen opacified IOLs after posterior lamellar keratoplasty, 8 after descemet stripping automated endothelial keratoplasty (DSAEK), 3 after descemet membrane endothelial keratoplasty (DMEK) and 2 after both DSAEK and DMEK were analysed in our laboratory. Analyses included optical bench assessment for optical quality, light microscopy, scanning electron microscopy (SEM) and energy dispersive X-Ray spectroscopy (EDS).ResultsIn all IOLs the opacification was caused by a thin layer of calciumphosphate that had accumulated underneath the anterior optical surface of the IOLs in the area spared by the pupil/anterior capsulorhexis. The calcifications lead to a significant deterioration of the modulation transfer function across all spatial frequencies of the affected IOLs.ConclusionsThe instillation of exogenous material such as air or gas into the anterior chamber increases the risk for opacification of hydrophilic IOLs irrespective of the manufacturer or the exact composition of the hydrophilic lens material. It is recommended to avoid the use of hydrophilic acrylic IOLs in patients with endothelial dystrophy that will likely require procedures involving the intracameral instillation of air or gas, such as DMEK or DS(A)EK.

Calcium phosphates and silicon: exploring methods of incorporation

BackgroundBioinorganics have been explored as additives to ceramic bone graft substitutes with the aim to improve their performance in repair and regeneration of large bone defects. Silicon (Si), an essential trace element involved in the processes related to bone formation and remodeling, was shown not only to enhance osteoblasts proliferation but also to stimulate the differentiation of mesenchymal stem cells (MSCs) and preosteoblasts into the osteogenic lineage. In this study, the added value of Si to calcium phosphate (CaP) coatings was evaluated.MethodsTissue culture plastic well plates were coated with a thin CaP layer to which traces amounts of Si were added, either by adsorption or by incorporation through coprecipitation. The physicochemical and structural properties of the coatings were characterized and the dissolution behavior was evaluated. The adsorption/incorporation of Si was successfully achieved and incorporated ions were released from the CaP coatings. Human MSCs were cultured on the coatings to examine the effects of Si on cell proliferation and osteogenic differentiation. For the statistical analysis, a one-way ANOVA with Bonferroni post-hoc test was performed.ResultsThe results showed that human MSCs (hMSCs) responded to the presence of Si in the CaP coatings, in a dose-dependent manner. An increase in the expression of markers of osteogenic differentiation by human MSCs was observed as a result of the increase in Si concentration.ConclusionsThe incorporation/adsorption of Si into CaP coatings was successfully achieved and hMSCs responded with an increase in osteogenic genes expression with the increase of Si concentration. Furthermore, hMSCs cultured on CaP-I coatings expressed higher levels of ALP and OP, indicating that this may be the preferred method of incorporation of bioinorganics into CaPs.

Preparation of hydroxyapatite layer on Ti-based bulk metallic glasses by acid and alkali pre-treatment

In this paper, a thin calcium phosphate layer was prepared on the surface of Ti40Zr10Cu36Pd14 bulk metallic glasses (BMGs). All samples were dipped in HNO3 aqueous solution and boiled in 1.2 mol·L−1 NaOH aqueous solution. After the two preliminary treatment steps, they were soaked in simulated body fluid (SBF) to form an apatite layer on the surface. After immersion for 12 days, a coating composed mainly of Ca–P particles was rapidly deposited on the surface of Ti40Zr10Cu36Pd14 bulk metallic glasses. The surfaces of chemically treated samples and the samples after immersion in SBF were characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and energy dispersive spectroscopy (EDS). Analysis results indicate that this apatite coating consists of Ca–P particles with different diameters. In addition, the Ca/P ratio of the apatite coatings immersed for 14 days is 1.62, which is close to that of hydroxyapatite (HA).

Multilayered coating on titanium for controlled release of antimicrobial peptides for the prevention of implant-associated infections

Prevention of bacterial colonization and formation of a bacterial biofilm on implant surfaces has been a challenge in orthopaedic surgery. The treatment of implant-associated infections with conventional antibiotics has become more complicated by the emergence of multi-drug resistant bacteria. Antimicrobial eluting coatings on implants is one of the most promising strategies that have been attempted. This study reports a controlled release of an antimicrobial peptide (AMP) from titanium surface through a non-cytotoxic multilayered coating. Three layers of vertically oriented TiO2 nanotubes, a thin layer of calcium phosphate coating and a phospholipid (POPC) film were impregnated with a potent broad-spectrum AMP (HHC-36). The coating with controlled and sustained release of AMP was highly effective against both Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacteria. No cytotoxicity to osteoblast-like cells (MG-63) was observed. Moderate platelet activation and adhesion on the implant surface with no observable activation in solution, and very low red blood cell lysis was observed on the implant. This multi-layer assembly can be a potential approach to locally deliver AMPs to prevent peri-implant infection in orthopaedics without being toxic to host cells.

Enhancement of the capability of hydroxyapatite formation on Zr with anodic ZrO2 nanotubular arrays via an effective dipping pretreatment

Hydroxyapatite (HA) depositions on metallic biomedical implants are widely applied to generate bioactive surfaces in simulated biological environments. Highly ordered anodic ZrO₂ nanotubes have attracted increasing interest for biomedical applications. However, previous reports showed that at least 14-28 days were required to obtain HA coating on ZrO₂ nanotubular arrays under biomimetic condition, thus capability to grow HA coating on ZrO ₂nanotubular at room temperature needs to be enhanced. In the present work, we demonstrate that ZrO₂ nanotubular arrays are suitable for an effective dipping treatment to induce more rapid HA coating. A series of ZrO₂ nanotubular arrays having different dimensions were fabricated in fluoride containing electrolyte. Then, we used a dipping treatment for biomimetic formation of an adhesive HA coating on the nanotubular arrays. The coatings formed rapidly using this procedure under biomimetic conditions and did not require a high-temperature annealing process. The as-formed ZrO₂ nanotubular arrays were treated using several dip-and-dry steps, through which the nanotubular arrays were filled and covered with calcium phosphate (CaP) nucleation sites. The specimens readily grew HA once immersed in the simulated biological fluid after 2 days immersion. The carbonated HA coating had several micron thickness after 8 days of immersion while only a thin layer of CaP were observed on annealed ZrO₂ nanotubes immersed in the same solution for the same duration. Tensile testing showed that bonding strength between HA coating and substrate was 21.6 ± 1.6 MPa. This treatment dramatically improves efficiency for promoting HA formation on anodic ZrO₂ nanotubes at room temperature.

The release of nickel from nickel–titanium (NiTi) is strongly reduced by a sub-micrometer thin layer of calcium phosphate deposited by rf-magnetron sputtering

Thin calcium phosphate coatings were deposited on NiTi substrates (plates) by rf-magnetron sputtering. The release of nickel upon immersion in water or in saline solution (0.9% NaCl in water) was measured by atomic absorption spectroscopy (AAS) for 42 days. The coating was analyzed before and after immersion by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). After an initial burst during the first 7 days that was observed for all samples, the rate of nickel release decreased 0.4-0.5 ng cm(-2) d(-1) for a 0.5 mum-thick calcium phosphate coating (deposited at 290 W). This was much less than the release from uncoated NiTi (3.4-4.4 ng cm(-2) d(-1)). Notably, the nickel release rate was not significantly different in pure water and in aqueous saline solution.

Biomimetic Calcium Phosphate Coatings for Polymeric Artificial Spinal Disc Implants

Discs of poly carbonate urethane (PCU) were coated with a thin layer of calcium phosphate (CaP) by a biomimetic process at temperatures of 28?C and 37?C. The coating morphology was analyzed by SEM. Contact angle analysis was used to assess surface wettability. Human osteoblasts (HOBs) were cultured on uncoated and CaP-coated PCU discs for up to 14 days. Cell metabolism, structure, and morphology were analyzed and compared with the wettability of each sample group. HOBs proliferated and grew on uncoated and CaP-coated samples, but a greater cell metabolism was observed for uncoated samples at early time points in cell culture. A more even dispersion of HOBs across the disc surface, attributable to the increased surface wettability, was seen for CaP-coated samples.

Hydroxyapatite-Coated Polycaprolacton Wide Mesh as a Model of Open Structure for Bone Regeneration

In principle, three-dimensional (3D) osteoconductive grafts with a proper chemical composition, high total porosity, and fully interconnected pores are suitable carriers to provide a proper substrate for in vivo neobone tissue ingrowth. However, most porous materials carry some intrinsic limits because of their internal structure (i.e., limited macroporosity and small pore interconnection size), representing a physical constraint for a massive blood afflux and bone ingrowth and therefore for generating effective osteopermissive grafts. We therefore hypothesized that an unconventional scaffold, based on an "open-structure" concept, should not pose any limit to vascularization of grafts and consequently to the amount of bone growth. Starting from this hypothesis, we have designed and developed a 3D osteoconductive polymeric-based wide-net mesh. Polymer fibers, joining hydroxyapatite beads, were coated with a thin layer of calcium phosphate (Ca-P), coupling the osteoconductivity properties of Ca-P with the handness and bulk properties of polymers. This completely open 3D scaffold prototype was tested both in vitro and in vivo, displaying a promising in vivo blood vessel invasion and bone-forming efficiency.

Effects of soluble cobalt and cobalt incorporated into calcium phosphate layers on osteoclast differentiation and activation

Metal ions originating from mechanical debris and corrosive wear of prosthetic implant alloys accumulate in peri-implant soft tissues, bone mineral, and body fluids. Eventually, metal ions such as cobalt (II) (Co 2+), which is a major component of cobalt–chromium-based implant alloys and a known activator of osteolysis, are incorporated into the mineral phase of bone. We hypothesize that the accumulation of Co 2+ in the mineral could directly activate osteolysis by targeting osteoclasts. To test this hypothesis, we coated tissue culture plastic with a thin layer of calcium phosphate (CaP) containing added traces of Co 2+, thereby mimicking the bone mineral accumulation of Co 2+. Murine bone marrow osteoclasts formed in the presence of M-CSF and RANKL were cultured on these surfaces to examine the effects of Co 2+ on osteoclast formation and resorptive activity. Treatment conditions with Co 2+ involved incorporation into the CaP layer, adsorption to the mineral surface, or addition to culture media. Micromolar concentrations of Co 2+ delivered to developing osteoclast precursors by all 3 routes increased both osteoclast differentiation and resorptive function. Compared to CaP layers without Co 2+, we observed a maximal 75% increase in osteoclast numbers and a 2.3- to 2.7-fold increase in mineral resorption from the tissue culture wells containing 0.1 μ m Co 2+ and 0.1–10 μ m Co 2+, respectively. These concentrations are well within the range found in peri-implant tissues in vivo. This direct effect of Co 2+ on osteoclasts appears to act independently of the particulate phagocytosis/inflammation-mediated pathways, thus enhancing osteolysis and aseptic implant loosening.

The role of calcium gluconate in electrochemical activation of titanium for biomimetic coating of calcium phosphate

Supersaturation of calcium and phosphate in the bath solution and activation of the metal substrate is essential for effective biomimetic growth of apatite on orthopedic implants. In this work, bioactivation of titanium surface was achieved by electrodeposition of a thin layer of calcium phosphate followed by an alkaline treatment to obtain pure hydroxyapatite crystals. The influence of calcium gluconate in the electrolyte solution was evaluated and optimized. Adhesive strength, thickness, structural, and surface characteristics were evaluated. A highly adhesive and uniform layer of hydroxyapatite was formed on titanium surface when the electrodeposition was carried out with an electrolyte solution-containing calcium gluconate. The electrodeposited hydroxyapatite coatings were subjected for biomimetic growth in Kokubo's simulated body fluid (SBF) and Kokubo's modified SBF containing 1.5 times higher concentration of Ca. Biomimetic growth was also improved by the addition of calcium gluconate in the SBF solution.

Effect of calcium phosphate surface coating on bone ingrowth onto porous-surfaced titanium alloy implants in rabbit tibiae

Purpose: The purpose of the present study was to determine whether calcium phosphate coating has a significant impact on bone ingrowth into a porous titanium implant. Materials and Methods: Porous-surfaced titanium alloy Ti-6A1-4V implants were prepared with or without the addition of a thin surface layer of calcium phosphate applied by sol-gel coating. Implants were placed into the tibiae of 16 rabbits. Implanted sites were allowed to heal for 2 weeks, after which specimens were retrieved for morphometric assessment using backscatter scanning electron microscopy. Results: The data collected show that there is more extensive ingrowth into the porous regions of the calcium phosphate–coated implants than into the control implants. The weighted average ingrowth for the calcium phosphate–coated implants was 2.01, whereas that for the noncoated implants was 1.49; the difference is statistically significant (P <.01). Conclusions: The addition of a thin layer of calcium phosphate to these implants appears to promote a more extensive implant-to-bone interface by allowing the neck regions to become intimately ingrown with bone even after only 2 weeks of initial healing. © 2002 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 60:422-425, 2002

The effect of calcium phosphate implant coating on osteoconduction.

The purpose of this study was to determine whether a calcium phosphate (CaP) coating would have a significant impact on osteoconduction. In this investigation, porous-surfaced titanium alloy (Ti-6Al-4V) implants were prepared with or without the addition of a thin surface layer of CaP applied by means of sol-gel coating and implanted into the tibiae of 16 rabbits. Implant sites were allowed to heal for 2 weeks, after which specimens were retrieved for morphometric assessment by using backscatter scanning electron microscopy and the Bioquant Image Analyzer. The absolute contact length was significantly (P <.01) higher for CaP-coated implants (1.18 mm) than for the noncoated implants (0.74 mm), as were the contact length fraction (40.4% vs 27.0%; P <.01) and the straight-line bone growth (1.19 mm vs 1.04 mm; P <.01). On the basis of the findings in this study, the addition of a thin layer of CaP to the implant promotes accelerated bone healing around porous-surfaced implants-even after only 2 weeks of initial healing.

Biomimetic coatings on titanium: a crystal growth study of octacalcium phosphate.

The biomimetic approach allows the coating of metal implants with different calcium-phosphate (Ca-P) phases. Films elaborated at physiological conditions exhibited structures closely resembling those of bone mineral. For instance, octacalcium phosphate (OCP, Ca8(HPO4)2(PO4)4 . 5H2O) crystals have been deposited on titanium through a two-step procedure. After cleaning and etching, Ti6Al4V plates were immersed for 24 h into a simulated body fluid (SBF1). A thin amorphous carbonated Ca-P layer precipitated on the metal substrate. Secondly, these thinly Ca-P coated titanium substrates were immersed for 48 h into another simulated body fluid (SBF2). The thin amorphous carbonated Ca-P layer induced the fast precipitation of a second Ca-P layer of 55 microm in thickness composed of OCP crystals. The measurements of Ca and P concentrations versus soaking time in SBF2 showed that the carbonated Ca-P layer partially dissolved before the deposition of the OCP coating. X-ray diffraction (XRD) revealed that OCP crystals grew epitaxially on the substrate. OCP is known to be one of the precursors during the bone mineralization process, thereby, this new generation of biomimetic coatings are promising for orthopedic surgery.

Biomimetic calcium phosphate coatings on Ti6Al4V: a crystal growth study of octacalcium phosphate and inhibition by Mg 2+ and HCO 3−

The biomimetic approach for coating metal implants allows the deposition of new calcium phosphate (Ca-P) phases. Films elaborated at physiological conditions might have structures closer to bone mineral than hydroxyl-apatite (HA) plasma-sprayed coatings. In this study, different Ca-P coatings have been deposited through a two-step procedure. After cleaning and etching, Ti6Al4V plates were pretreated by soaking in a simulated body fluid (SBF), i.e., a solution containing inorganic components in concentration more or less similar to body fluids: a thin amorphous carbonated Ca-P layer precipitated on the metal substrate. Second, by soaking these thinly coated metal substrates in another SBF, with different concentrations, the thin amorphous carbonated Ca-P layer led to the fast precipitation of a second and thick Ca-P layer. Different SBF solutions were used in order to investigate the influence of magnesium and carbonate ions. From SBF containing only Ca 2+ and HPO 4 2− ions, an octacalcium phosphate layer grew epitaxially on the substrate. When Mg 2+ was added into this SBF, the coating was composed of Ca-deficient apatite crystals, while the addition of HCO 3 − in SBF led to the formation of a B-carbonated apatite layer. Magnesium and carbonate acted as inhibitors of crystal growth. The three phases obtained by our biomimetic process are closer to bone mineral structure than plasma-sprayed HA. Therefore, the obtained results may be particularly relevant for the development of biomimetic Ca-P coatings with optimal bioactivity.

Ion adsorption on titanium surfaces exposed to a physiological solution

Changes in surface properties of titanium platelets exposed to a physiological solution (Hanks' solution) were studied by Auger electron spectroscopy and Attenuated Total Reflection Fourier Transform Infra Red spectroscopy for surface chemical composition analysis and by Scanning Force Microscopy for surface topography measurements. An adsorbed layer of calcium-phosphate was spontaneously formed on the titanium oxide surface and its thickness as well as the Ca/P ratio was found to increase with immersion time. After 71 days of immersion, the Ca/P ratio corresponded to that of brushite or monetite and after 6 months it was close to the value of hydroxyapatite. A higher Ca/P ratio was found for adsorption from solutions where the pH had been increased. After adsorption, the grains of the evaporated titanium substrate appeared slightly smoother because they were covered by a thin layer of calcium phosphate. A comparison between immersion in a Hanks' solution and solutions containing only phosphates or only calcium ions, showed that the presence of phosphates is necessary for the adsorption of Ca-ions.

High-performance liquid chromatographic separation of biomolecules using calcium phosphate supported on macroporous silica microparticles

The preparation of a chromatographic support showing similar selectivity and chemical inertness to hydroxyapatite (HA) and mechanical resistance to the pressures generally used in high-performance liquid chromatography is described. A mixed matrix was formed by covering macroporous silica microparticles with a thin layer of calcium phosphate (CaP—HA). The porous (500, 1000 and 4000 Å) silica microparticles (15 and 10 μm) had been previously inactivated with glycidoxypropyltrimethoxysilane in acidic medium, to convert the silanol groups into hydrophilic groups, producing a biocompatible support with excellent properties in terms of mechanical resistance to high pressure (5000 p.s.i.), selectivity, chemical inertness and efficiency. Columns packed with small particles (5 μm) were run at high pressure and high flow-rates for prolonged periods. Mixed silica WP-DIOL/CaP—HA matrices were used to separate a standard protein mixture antimelanoma monoclonal antibody and some small molecules such as carnitine derivatives and sugars.