Calcium Phosphate Layer Research Articles

Protective layer formation on magnesium in cell culture medium

In the past, different studies showed that hydroxyapatite (HA) or similar calcium phosphates can be precipitated on Mg during immersion in simulated body fluids. However, at the same time, in most cases a dark grey or black layer is built under the white HA crystals. This layer seems to consist as well of calcium phosphates. Until now, neither the morphology nor its influence on Mg corrosion have been investigated in detail. In this work commercially pure magnesium (cp) was immersed in cell culture medium for one, three and five days at room temperature and in the incubator (37°C, 5% CO2). In addition, the influence of proteins on the formation of a corrosion layer was investigated by adding 20% of fetal calf serum (FCS) to the cell culture medium in the incubator. In order to analyze the formed layers, SEM images of cross sections, X-ray Photoelectron Spectroscopy (XPS), X-ray diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDX) and Fourier Transformed Infrared Spectroscopy (FTIR) measurements were carried out. Characterization of the corrosion behavior was achieved by electrochemical impedance spectroscopy (EIS) and by potentio-dynamic polarization in Dulbecco's Modified Eagle's Medium (DMEM) at 37°C.Surface analysis showed that all formed layers consist mainly of amorphous calcium phosphate compounds. For the immersion at room temperature the Ca/P ratio indicates the formation of HA, while in the incubator probably pre-stages to HA are formed. The different immersion conditions lead to a variation in layer thicknesses. However, electrochemical characterization shows that the layer thickness does not influence the corrosion resistance of magnesium. The main influencing factor for the corrosion behavior is the layer morphology. Thus, immersion at room temperature leads to the highest corrosion protection due to the formation of a compact outer layer. Layers formed in the incubator show much worse performances due to completely porous structures. The existence of proteins in DMEM seems to hinder the formation of a corrosion layer. However, protein adsorption leads to similar results as concerns corrosion protection as the formed calcium phosphate layer.

Key parameters for spark plasma sintering of wet-precipitated iodate-substituted hydroxyapatite

A possible strategy for the management of radioactive iodine-129 is to incorporate it under the form of iodate in hydroxyapatite matrices (HA-CaI) intended to be stored in deep geological repositories. To meet disposal requirements, powder materials that were here obtained by a wet-precipitation route required shaping. In this work, we demonstrate that sintering of HA-CaI could be achieved by spark plasma sintering (SPS) at low temperature (T <300°C) without iodine volatilization. Such densification was only possible if a non apatitic hydrated calcium phosphate layer was present at the surface of grains, the content of which directly depended on synthesis conditions. The higher the proportion of hydrated layer, the better uniaxial cold compaction and densification during sintering. For an optimised HA-CaI powder, a relative density of 88% could be reached using a pressure of 100MPa, a dwell temperature of 250°C and a heating rate of 30°Cmin−1.

Calcium phosphate mineralization is widely applied in crustacean mandibles.

Crustaceans, like most mineralized invertebrates, adopted calcium carbonate mineralization for bulk skeleton reinforcement. Here, we show that a major part of the crustacean class Malacostraca (which includes lobsters, crayfishes, prawns and shrimps) shifted toward the formation of calcium phosphate as the main mineral at specified locations of the mandibular teeth. In these structures, calcium phosphate is not merely co-precipitated with the bulk calcium carbonate but rather creates specialized structures in which a layer of calcium phosphate, frequently in the form of crystalline fluorapatite, is mounted over a calcareous “jaw”. From a functional perspective, the co-existence of carbonate and phosphate mineralization demonstrates a biomineralization system that provides a versatile route to control the physico-chemical properties of skeletal elements. This system enables the deposition of amorphous calcium carbonate, amorphous calcium phosphate, calcite and apatite at various skeletal locations, as well as combinations of these minerals, to form graded composites materials. This study demonstrates the widespread occurrence of the dual mineralization strategy in the Malacostraca, suggesting that in terms of evolution, this feature of phosphatic teeth did not evolve independently in the different groups but rather represents an early common trait.

In vitro Degradation of Pure Mg for Esophageal Stent in Artificial Saliva

Magnesium and its alloys as biodegradable implant materials can be potentially used in cardiovascular and orthopedic devices. However, few studies have focused on its application in esophageal stents. In this paper, time-lapse degradation characteristics of pure Mg were analyzed by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, hydrogen evolution, pH and electrochemical measurements after immersion in artificial saliva for different times. Results revealed that a dense degradation product film formed on samples, which mainly consisted of two kinds of layers: one was calcium phosphate compounds with different structures; the other was thin magnesium hydrate layer close to the substrate. Less pH increase and low degradation rate were observed in the first 5 days of immersion, which can be ascribed to the formation of a thicker and denser layer on the sample surface with increasing immersion time. And then there was an increase in degradation rate and pH values; the deposition layer remained almost intact after immersion for 6 and 8 days. After 10 days of immersion, the degradation rate and pH value remained stable, and the calcium phosphate layer was delaminated and the inner magnesium hydrate layer was exposed. This study indicated that pure Mg exhibited desirable degradation resistance in artificial saliva, which provided magnesium-based materials with the potential to be used as esophageal stents.

Effect of air plasma treatment on mechanical properties of bioactive composites for medical application: Composite preparation and characterization

The aim of this study was to fabricate unidirectional bio-glass fibers (BGF) (13-93)-reinforced polylactic acid (PLA) composites with improved mechanical properties for a bone plate to heal the weight-bearing long-bone fractures. Various exposure times of air plasma (30, 60, 90 and 120s) on BGF fibers were studied, and the most suitable conditions were determined for the fabrication of the BGF/PLA composite. Mechanical properties, microscopic characteristics, in vitro degradation and the bioactivity of the BGF/PLA composites were evaluated. Fatigue life of 30s plasma treated composites completed 1 million cycles when actual loading conditions (10–20% body weight) were used. 30s plasma treated specimens showed increase in tensile strength, flexural strength and interlaminar shear strength as 31%, 13.5% and 33%, respectively. The SEM image of fractured surface of 30s plasma treated composite suggested that the failure was shifted to the PLA which is evidence of superior bonding between fiber and PLA matrix. Moreover, a bone-like calcium-phosphate layer was precipitated on the surface of degraded composite that is essential for bone healing.

Combinatorial incorporation of fluoride and cobalt ions into calcium phosphates to stimulate osteogenesis and angiogenesis

Bone healing requires two critical mechanisms, angiogenesis and osteogenesis. In order to improve bone graft substitutes, both mechanisms should be addressed simultaneously. While the individual effects of various bioinorganics have been studied, an understanding of the combinatorial effects is lacking. Cobalt and fluoride ions, in appropriate concentrations, are known to individually favor the vascularization and mineralization processes, respectively. This study investigated the potential of using a combination of fluoride and cobalt ions to simultaneously promote osteogenesis and angiogenesis in human mesenchymal stromal cells (hMSCs). Using a two-step biomimetic method, wells of tissue culture plates were coated with a calcium phosphate (CaP) layer without or with the incorporation of cobalt, fluoride, or both. In parallel, hMSCs were cultured on uncoated well plates, and cultured with cobalt and/or fluoride ions within the media. The results revealed that cobalt ions increased the expression of angiogenic markers, with the effects being stronger when the ions were added as a dissolved salt in cell medium as compared to incorporation into CaP. Cobalt ions generally suppressed the ALP activity, the expression of osteogenic genes, and the level of mineralization, regardless of delivery method. Fluoride ions, individually or in combination with cobalt, significantly increased the expression of many of the selected osteogenic markers, as well as mineral deposition. This study demonstrates an approach to simultaneously target the two essential mechanisms in bone healing: angiogenesis and osteogenesis. The incorporation of cobalt and fluoride into CaPs is a promising method to improve the biological performance of fully synthetic bone graft substitutes.

Electrochemical and morphological investigation of silver and zinc modified calcium phosphate bioceramic coatings on metallic implant materials

In our research nanostructured silver and zinc doped calcium-phosphate (CaP) bioceramic coatings were prepared on commonly used orthopaedic implant materials (Ti6Al4V). The deposition process was carried out by the pulse current technique at 70°C from electrolyte containing the appropriate amount of Ca(NO3)2 and NH4H2PO4 components. During the electrochemical deposition Ag+ and Zn2+ ions were introduced into the solution. The electrochemical behaviour and corrosion rate of the bioceramic coatings were investigated by potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) measurements in conventional Ringer's solution in a three electrode open cell. The coating came into contact with the electrolyte and corrosion occurred during immersion. In order to achieve antimicrobial properties, it is important to maintain a continuous release of silver ions into physiological media, while the bioactive CaP layer enhances the biocompatibility properties of the layer by fostering the bone cell growth. The role of Zn2+ is to shorten wound healing time. Morphology and composition of coatings were studied by Scanning Electron Microscopy, Transmission Electron Microscopy and Energy-dispersive X-ray spectroscopy. Differential thermal analyses (DTA) were performed to determine the thermal stability of the pure and modified CaP bioceramic coatings while the structure and phases of the layers were characterized by X-ray diffraction (XRD) measurements.

Data for accelerated degradation of calcium phosphate surface-coated polycaprolactone and polycaprolactone/bioactive glass composite scaffolds.

Polycaprolactone (PCL)-based composite scaffolds containing 50 wt% of 45S5 bioactive glass (45S5) or strontium-substituted bioactive glass (SrBG) particles were fabricated into scaffolds using melt-extrusion based additive manufacturing technique. Additionally, the PCL scaffolds were surface coated with a layer of calcium phosphate (CaP). For a comparison of the scaffold degradation, the scaffolds were then subjected to in vitro accelerated degradation by immersion in 5 M sodium hydroxide (NaOH) solution for up to 7 days. The scaffold׳s morphology was observed by means of SEM imaging and scaffold mass loss was recorded over the experimental period.

Calcium phosphate/polyelectrolyte multilayer coatings for sequential delivery of multiple growth factors

Event Abstract Back to Event Calcium phosphate/polyelectrolyte multilayer coatings for sequential delivery of multiple growth factors Emily Jacobs1, 2, Marja Hurley3, Gloria Gronowicz3 and Liisa T. Kuhn1, 2 1 UConn, Biomedical Engineering, United States 2 UConn Health, Reconstructive Sciences, United States 3 UConn Health, School of Medicine, United States Introduction: Many of the most promising strategies for regenerative tissue-engineering aim to replicate natural cellular microenvironments using biomimetic, resorbable materials capable of growth factor delivery. Combinations of growth factors synergistically enhance tissue regeneration[1], but require sequential, rather than co-delivery delivery for maximum efficacy. Polyelectrolyte multilayer (PEM) coatings retain growth factor activity, however, staggered, sequential delivery from these coatings requires barrier layers to prevent interlayer diffusion of multiple factors that results in co-delivery. Here we demonstrate that the incorporation of a biomimetic calcium phosphate (bCaP) layer into PEM can prevent interlayer diffusion of biomolecules and enable staggered delivery. This modified PEM system is one of few aqueous, low temperature systems available for sequential, multifactor delivery and has potential to significantly impact the regenerative tissue-engineering field. Methods: bCaP coatings were prepared on sandblasted, 22 mm, treated tissue culture plastic disks, (NUNC, Rochester, NY) using a simulated body fluid method[2]. The PEM coatings (8-30 bilayers) were applied on top of the bCaP layer by automated alternate 10 min dipping into 1 mg/ml poly L glutamic acid (-) or poly-L lysine (+) solutions (Sigma, St. Louis, MO) with saline rinses between. Coatings were characterized with x-ray diffraction and scanning electron microscopy. To demonstrate sequential delivery a combination of a proliferative factor, recombinant human fibroblast growth factor-2 (FGF-2) (150 ng/disk) (R & D Systems, Minneapolis, MN), and a cytotoxic factor antimycin A (AntiA) (213 μg/disk)(Sigma, St. Louis, MO) was used. In vitro cellular activity on the prepared coatings was assessed with MC3T3-E1 mouse calvarial osteoprogenitor cells (ATCC, Manassas, VA) seeded at 10 or 40 x 103 cells/cm2. Proliferative and cytotoxic effects were quantified using the LIVE/DEAD® assay (Invitrogen Life Technologies, Grand Island, NY). Statistical significances were determined by unpaired t-tests and one-way ANOVA with Tukey post-tests. Results: Uniform nanocrystalline coatings of bCaP (Fig. 1A) and bCaP plus 30 bilayers of PEM (CaP-PEM30) (Fig. 1B) on the disks were observed via SEM. MC3T3-E1s cultured directly on adsorbed AntiA with no bCaP or PEM coating (AntiA) resulted in 90% cell death on day 1 (Fig. 2A). MC3T3-E1s cultured on AntiA embedded under 8 bilayers of PEM (AntiA-PEM8) resulted in 47% cell death on day 1 due to diffusion of AntiA through PEM8. MC3T3-E1s cultured on AntiA embedded under bCaP and 8 bilayers of PEM (AntiA-CaP-PEM8) resulted in 15% cell death, significantly better than PEM only (p<0.001). These data demonstrate that the addition of bCaP to PEM coatings inhibits interlayer diffusion. Active FGF-2 was delivered from 30 bilayers of PEM above CaP (CaP-PEM30-FGF2) as demonstrated by a significant increase in MC3T3-E1 proliferation on day 1 as compared to cells cultured on the FGF-2-free control, (Fig. 2B). No growth factor release was detected by ELISA without cells present. Sequential access of cells to FGF-2 followed by AntiA was also demonstrated (Fig. 3A). On day 1, no differences were observed between CaP-PEM30-FGF2 and AntiA-CaP-PEM30-FGF2 indicating access to AntiA was successfully blocked by bCaP. On day 5 however, cell-mediated degradation of PEM30 and bCaP resulted in a significant decrease in LIVE staining between groups (Fig. 3A) indicating AntiA delivery. Conclusions: Addition of a bCaP barrier layer to a PEM delivery system prevents unwanted interlayer diffusion of embedded factors and enables cell-mediated sequential delivery of multiple factors. This technology can be utilized in multiple research applications where a sequential delivery profile activated by cell degradation of matrix is desired. Funding provided from NIH NIDCR R01DE021103

Treating spinal cord injury via sustained drug delivery from calcium phosphate coatings.

Spinal cord injury (SCI) is a devastating trauma that leaves approximately 10,000 to 20,000 people paralyzed every year in the United States. The majority of these cases are young people that will live to almost a full life expectancy, however, their quality of life is significantly reduced. After SCI there is loss of both sensory and motor function below the level of injury. Due to this loss of function SCI patients are often unable to care for themselves and rely on friends and family to serve as their primary caregivers. The Christopher Reeve Foundation found that more than 50 million people each year provide this care in the U.S., the value of which is estimated to be $306 billion annually. Along with the financial burden, SCI patients have emotional stress and continued health care problems throughout their lives most predominately renal complications and pressure sores. These facts demonstrate the overwhelming need to restore function after SCI.

Fast degradation PLLA/apatites composites with high content of mineral phase for bone regeneration.

Event Abstract Back to Event Fast degradation PLLA/apatites composites with high content of mineral phase for bone regeneration. Diego Souza1 and Luiz Henrique Catalani1 1 Instituto de Química - USP, Departamento de Química Fundamental, Brazil Introduction: Since hydroxyapatite (HA) is the main mineral component of bones and teeth, it is widely used as biomaterial[1]. In the last decade, biocomposites of poly(L-lactide) (PLLA) and HA have attracted much attention due its ability to exhibit osteoinductive and osteoconductive properties, biodegradability and adequate mechanical strength[2]. However, its clinical use is limited owing to its slow biodegradation. Moreover, the low miscibility of HA in the polymer phase renders composites of low mineral content. Hence, other fast degradation calcium phosphates (CPs), such as calcium deficient hydroxyapatite (CDHA), β-tricalcium phosphate (β-TCP) and octacalcium phosphate (OCP) have been considered as HA substitute[3]. This work aims at the production fast degradation PLLA composites with high content of alternative CPs as mineral phases, such as CDHA, β-TCP and OCP, as well as to study their bioactivity properties. Results: In order to improve the dispersion of the mineral phase in the polymeric matrix, lauryl chloride was used to functionalize the surface of CPs and improving the interfacial adhesion of the particles. As a result, biocomposites containing up to 40wt% of mineral phase were produced. The bioactivity of the biocomposites was assayed in vitro using a solution of Simulated Blood Fluid (SBF)[4]. After 28 days of immersion in SBF, the formation of an amorphous calcium phosphate layer was observed on the surface of the substrate PLLA/HA; while for the biocomposites containing CDHA or CDHA/ β-TCP (7: 3) the minerals were composed of flake crystals. Increase of bone-like minerals was observed on surface of the substrate PLLA/OCP, these findings indicate that the deposited CP layer coating the surface of electrospun fibers containing OCP was in a more advanced stage of nucleation. Figure 1: SEM images of electrospun PLLA/apatites-laurate 40 wt% after incubation in SBF for 28 days: (a) HA; (b) CDHA; (c) CDHA/TCP (7:3); (d) OCP. The cell viability on all the samples was measured by MTT assay. While pure PLLA presented cell viability around 80%, as compared to control (PS plate) biocomposites containing 40% of funcionalized apatite showed over 100% of cell viability. These results show that these materials are not only atoxic but can help cell proliferation. Figure 2:Viability of NIH/3T3 fibroblasts on PLLA and PLLA/apatites-laurate 40%wt nanofibrous scaffolds. The different biocomposites were tested for adhesion and proliferation assays of NIH/3T3 fibroblasts using MTT assay. The biocomposites showed similar increase in cell proliferation, but after 15 days they promoted higher cell proliferation compared to pure PLLA electrospun fibers. Figure 3: Proliferation of NIH/3T3 fibroblasts on the control PLLA and PLLA/apatites-laurate 40%wt nanofibrous scaffolds as a function of culture time. Conclusions: The bicomposites high mineral phase (up to 40%) were produced. Electrospun mat of PLLA/OCP-laurate 40 wt% presented higher bioactivity in contact with SBF than similar composites containing HAD, HAD/TCP (7:3) or HA. However all CPs biocomposites in this study provided similar increase in cell proliferation, as compared to PLLA. These new materials are proposed as fast degradation CPs biocomposites for bone and teeth applications. FAPESP (Projeto 2011/21442-6); Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq

Topography and nanostructural evaluation of chemically and thermally modified titanium substrates.

In this research, the effects of chemical and thermal treatment on the morphological and compositional aspects of titanium substrates and so, potentially, on development of biomimetic bone like layers formation during simulated body fluid (SBF) soaking was investigated. The HF, HF/HNO3 and NaOH solutions were used for chemical treatment and some of alkali-treated samples followed a heat treatment at 600°C. The treated samples before and after soaking were subjected to material characterization tests using scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). White light interferometry (WLI) was used to determine the roughness parameters such as Ra, Rq, RKu and Rsk. The significance of the obtained data was assessed using ANOVA variance analysis between all samples. It was observed that the reaction at grain boundaries and sodium titanate intermediate layers play a great role in the nucleation of calcium phosphate layers. Based on the obtained results in this work, the calcium phosphate microstructure deposited on titanium substrates was more affected by chemical modification than surface topography.

Bioactive and biocompatible copper containing glass-ceramics with remarkable antibacterial properties and high cell viability designed for future in vivo trials.

In the present study our interest is focused on finding the efficiency of 60SiO2·(32 - x)CaO·8P2O5·xCuO (mol%) glass-ceramics, with 0 ≤ x ≤ 4 mol%, in terms of bioactivity, biocompatibility, antibacterial properties and cell viability in order to determine the most appropriate composition for their further use in in vivo trials. The sol-gel synthesized samples show a preponderantly amorphous structure with a few crystallization centers associated with the formation of an apatite and calcium carbonate crystalline phases. The Fourier Transform Infrared (FT-IR) spectra revealed slightly modified absorption bands due to the addition of copper oxide, while the information derived from the measurements performed by transmission electron microscopy, UV-vis and electron paramagnetic resonance spectroscopy showed the presence of ions and metallic copper species. X-Ray photoelectron spectroscopic analysis indicated the presence of copper metallic species, in a reduced amount, only on the sample surface with the highest Cu content. Regarding in vitro assessment of bioactivity, the results obtained by X-ray diffraction, FT-IR spectroscopy and scanning electron microscopy, demonstrated the formation of a calcium phosphate layer on all investigated sample surfaces. The inhibitory effect of the investigated samples was more significant on the Pseudomonas aeruginosa than the Staphylococcus aureus strain, the sample with the lowest concentration of copper oxide (0.5 mol%) being also the most efficient in both bacterial cultures. This sample also exhibits a very good bactericidal activity, for the other samples it was necessary to use a higher quantity to inhibit and kill the bacterial species. The secondary structure of adsorbed albumin presents few minor changes, indicating the biocompatibility of the glass-ceramics. The cell viability assay shows a good proliferation rate on samples with 0.5 and 1.5 mol% CuO, although all glass-ceramic samples exhibited a good in vivo tolerance.

Effect of inflammatory conditions on bare and coated Ti-6Al-4V surfaces

Event Abstract Back to Event Effect of inflammatory conditions on bare and coated Ti-6Al-4V surfaces Sarah Höhn1 and Sannakaisa Virtanen1 1 University of Erlangen-Nürnberg, Materials Science, Germany Introduction: The calcium-phosphate (Ca-P) formation during long-term immersion in biological environment play an important role for the biocompatibility of the implant. Hence, Ti-6Al-4V was coated with different nano sized structures to evaluate corrosion resistance and Ca-P formation in DMEM under physiological (pH7) and inflammatory con-ditions (pH5 + H2O2). Methods: The samples were pretreated and afterwards coated with TiO2 and incorporated hydroxylapatite nanoparticles, according to Höhn et al[1]. The influence of the coatings on Ca-P formation was investigated with XPS and SEM after immersion in DMEM at pH7 and in comparison under simulated inflammatory conditions at pH5 and in presence of H2O2. The long-term immersion tests at pH5 were performed for 14 days followed by a pH change to pH7 indicating the end of the inflammatory reactions. The effect on corrosion resistance was investigated by electrochemical impedance measurements (EIS). Results: Fig. 1. SEM images of TiO2-NP (~ 30nm; (A)) and HA incorporated TiO2 (~ 700nm (B)) samples and after three months immersion in DMEM at pH5 + H2O2 (C) and (D). Fig. 2. EIS of TiO2-NP (A) and HA incorporated TiO2 coating (B) at pH5 + H2O2 after long-term immersion tests in DMEM. Discussion and Conclusion: The SEM images (Fig. 1) showed that the formation of Ca-P is possible on the different coatings on Ti-6Al-4V in general. However for the pH5 the formation is time-delayed (Fig. 1D). EIS measurements at pH5 showed no effect of the additional Ca-P layer after 14 days immersion. Already after 28d (Fig. 2) and the end of the inflammatory conditions both coatings showed two time constants according to the barrier layer and outer porous layer and thus the Ca-P formation[2]. Compared to the measurements at pH7 the formation is also time-delayed.

Deposition, Heat Treatment And Characterization of Two Layer Bioactive Coatings on Cylindrical PEEK.

Polyether ether ketone (PEEK) rods were coated via ion beam asssited deposition (IBAD) at room temperature. The coating consists of a two-layer design of yttria-stabilized zirconia (YSZ) as a heat-protection layer, and hydroxyapatite (HA) as a top layer to increase bioactivity. A rotating substrate holder was designed to deposit an even coating on the cylindrical surface of PEEK rods; the uniformity is verified by cross-sectional measurements using scanning electron microscopy (SEM). Deposition is followed by heat treatment of the coating using microwave annealing and autoclaving. Transmission electron microscopy (TEM) showed a dense, uniform columnar grain structure in the YSZ layer that is well bonded to the PEEK substrate, while the calcium phosphate layer was amorphous and pore-free in its as-deposited state. Subsequent heat treatment via microwave energy introduced HA crystallization in the calcium phosphate layer and additional autoclaving further expanded the crystallization of the HA layer. Chemical composition evaluation of the coating indicated the Ca/P ratios of the HA layer to be near that of stoichiometric HA, with minor variations through the HA layer thickness. The adhesion strength of as-deposited HA/YSZ coatings on smooth, polished PEEK surfaces was mostly unaffected by microwave heat treatment, but decreased with additional autoclave treatment. Increasing surface roughness showed improvement of bond strength.

Development and characterization of silver and zinc doped bioceramic layer on metallic implant materials for orthopedic application

A successful electrodeposition method for preparing silver and zinc modified bioactive calcium phosphate layers onto surgical grade titanium alloy material (Ti6Al4V) was developed. The coatings were deposited on the Ti6Al4V surface by pulse current at 70°C from an electrolyte containing adequate amounts of calcium nitrate, ammonium dihydrogen phosphate, zinc nitrate and silver nitrate. The corrosion resistivity of the bioceramic coatings was assessed in conventional Ringer׳s solution in a three electrode open cell by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results revealed the pure bioactive calcium phosphate (CaP) coated implant materials to possess the highest resistivity to corrosion, while the silver and zinc doped CaP layer showed at least one order of magnitude lower corrosion resistance. These modified CaP coatings can be further considered as antimicrobial coatings with enhanced biocompatibility. The morphology and structure of the coatings were characterized by Scanning electron microscopy (SEM), Energy-dispersive X-ray Spectroscopy (EDX) and X-ray diffraction (XRD) that confirmed the pulse current deposited CaP layer to consist of a mixture of different calcium phosphate phases such as hydroxyapatite (HAp), monetite (dicalcium phosphate, CaHPO4) as well as other Ca-containing components, portlandite (Ca(OH)2) and parascholzite (CaZn2(PO4)2(H2O)2).

P97: Bioresorbable composites based on hydroxyapatite dispersed in poly-L-lactide matrix

Orthopedic oncologic prostheses are essential in postoperative therapy and improvement of life quality of oncological patients. However, construction and composition of implants has to be improved for better biocompatibility and reduction of inflammatory responses. The materials based on polylactic acid (PLA) and hydroxyapatite (HA) have been suggested as promising solution for implant coating in order to improve reconstruction of bone defects, to reduce risk of inflammation and implant rejection. Objective To obtain the bioresorbable composites using biocompatible poly-L-lactide (PLA) with HA and to evaluate its effect on bone remodeling rate. Materials and methods After dissolution of PLA∗ in chloroform the powder-like HA (d = 20–40 nm) was added under vigorous stirring (PLA: HA = 75:25). The PLA/HA suspension was sonicated (40 kHz) and precipitated in ethanol. Fine fibers (d = 0.1– 0.5 μm, of more than 2 mm length) were formed. The PLA/HA composite fibers were air-dried; they consisted of HA nanoparticles homogeneously distributed in the PLA matrix. The composites ability to participate in bone remodeling was estimated by determination of the polymer matrix dissolution rate and by formation of the CPL on the surface of the composites. Results The degradation rate of the polymer matrix was calculated by measuring concentration of lactic acid (by HPLC method), being released from PLA macromolecules as the result of the hydrolysis in the physiologic solution (pH 7, ω(NaCl) = 0.9%). The PLA degradation rate during the first 4 days of soaking of the substrates (d = 10 mm, S = 190 mm2, m = 0.20 ± 0.01 g) in the solution is rather high (Clactic acid = 10 wt%), while on day 5 it decreases and stays constant during the rest of the time. The HA content increase in the composite results in the enhanced hydrolysis of PLA, caused both by the partial acid-base interaction between PLA and HA, and due to presence of the phase boundaries. Interesting to note that pure PLA (without HA) is hardly hydrolyzed in the physiologic solution even on the 30-th day of the experiment. Formation of calcium phosphate layer (CPL) was done in the SBF media, simulating the mineral constituents of the blood plasma at 37 °C, over 28 days period. The total concentration of Ca2+ and Mg2+ ions in the SBF-solution was determined by daily trilonometry in the ammonia buffer with eriochrome black T as indicator. This investigation clearly shows that the substrates both of HA and PLA/HA promote the CLP formation on their surfaces. On day 14 of the substrates soaking in the SBF solution the increment of Ca2+, Mg2+ ions adsorbed on the HA substrate rose to the value of m (Ca2+ + Mg2+)/VSBF = 0.11 mg/l, while the same value on the composite PLA/HA substrate was 0.06 mg/l. Thus the rate of adsorption of Ca2+ ions on the surface of HA is higher than that on the surface of the PLA/HA substrates. It is the result of the high HA content in the material. Pure PLA does not promote adsorption of Ca2+ and Mg2+ ions from the SBF media. Thus the HA particles incorporated in the PLA matrix may cause fast the CLP formation improving the ossification in the bone reconstruction processes. Biocompatibility and anti-inflammatory activity of PLA, HA and PLA/HA composite was studied in a pilot experiment in the cell-mediated immune response of individual donors in vitro using CD14+ human monocytes. Insignificant pro-inflammatory cytokine secretion of the M1 type (TNFα) is observed in the presence of PLA, while HA and PLA/HA composites don’t contribute to their release. The PLA promotes the release of M2 cytokine CCL18 on day 6 of macrophage culturing suggesting potential anti-inflammatory properties of the material. Conclusion The composite PLA/HA supports active bone-like layer formation on its surface improving ossification in the bone reconstruction process. The pilot experiment suggested that PLA/HA does not cause inflammatory reactions, while PLA can potentially regulate the balance between M1/M2 reaction to suppress unnecessary inflammation. ∗Mol. mass ca 60 kDa, prepared in the Laboratory of Catalytic Research of Tomsk State University. This Research is supported by Tomsk State University Competitiveness Improvement Program . The work was partially supported by the project Russian Foundation for Basic Research RFBR # 15-08-05496_a and EU IMMODGEL project, Grant No. (602694). Work was conducted with the application of the Tomsk regional common use center technical equipment acquired thanks to a grant of the Russian Ministry of the Agreement No. 14.594.21.0001 (RFMEFI59414X0001).

Reaction of calcium and phosphate ions with titanium, zirconium, niobium, and tantalum

To understand the bone formation ability of constituent metal elements of new titanium alloys, titanium, zirconium, niobium, and tantalum, these metals were immersed in various electrolytes containing calcium and/or phosphate ions and characterized using X‐ray photoelectron spectroscopy. In addition, cathodic polarization of the metals in the electrolytes was performed to evaluate the stability of the surface oxide films on the metals in the electrolyte. The calcium phosphate layer formed on Ti in electrolytes containing calcium and phosphate ions is relatively protective against mass transfer throughout the layer. However, the zirconium phosphate layer formed on Zr is much more protective and stable than that on Ti. Therefore, calcium ions were not incorporated. Nb and Ta formed calcium phosphate, but the amount was smaller than that in Ti, because phosphates formed on Nb and Ta are somewhat protective and the incorporation of the calcium ion is inhibited. Titanium played the most important role in forming calcium phosphate, while zirconium inhibited the formation of calcium phosphate on titanium alloys. The control of bone formation is feasible by the design of titanium alloys. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Noble metals role in autocatalytic phosphate coatings on TAV alloys. I.Ag functionalization of autocatalytic phosphate deposition on TAV alloys

The autocatalytic route was created using AgCl similar to PdCl2 to develop calcium phosphate layer on Ti6Al4V (TAV) substrates as previously demonstrated by the present authors. Alkaline (NaOH)-treatment and heat regimes were performed to render the surfaces susceptible to deposition. The anti-bacterial test was achieved for the treated substrates. Further, they were immersed in simulated body fluid (SBF) up to seven days to assess the biochemical stability of deposited coats. Biochemical analyses were performed for SBF left post three and seven days of immersion to evaluate calcium and phosphorus contents. The corresponding formed layers were compared using FESEM, confocal microscopy, TEM and TFXRD, pre- and post-SBF immersion. Results proved that the autocatalytic baths were successful in precipitating Ca–P coatings on the pre-treated substrates after only 2 hours immersion possessing clear inhibition zones of Escherichia coli B210 demonstrating their antibacterial function. A globular phosphatic layer was achieved one-week post immersion in comparison to that of Kokubo's which needed 10–30days. The presence of Ag should have promoted the phosphate formation by reducing its oxidation potential post-SBF immersion.

Composite Calcium Phosphate Coatings on Mg Alloy for Medicine

The high-tech method of creating anticorrosion calcium phosphate coating on the magnesium alloy MA8 (MgMnCe) has been developed. As was demonstrated by the volumetry method the sealing of the layer formed on the surface of Mg alloy using plasma electrolytic oxidation by superdispersed polytetrafluoroethylene substantially reduced the rate of the corrosion process. Here, the surface of the calcium phosphate layer containing hydroxyapatite (Ca/P = 1.61) remains biologically active. Studies of architectonics of the surface of innate immune cells have been performed in vitro.