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Auswahl der wissenschaftlichen Literatur zum Thema „Brushite cements“
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Zeitschriftenartikel zum Thema "Brushite cements"
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No, Young Jung, Ib Holzmeister, Zufu Lu, Shubham Prajapati, Jeffrey Shi, Uwe Gbureck und Hala Zreiqat. „Effect of Baghdadite Substitution on the Physicochemical Properties of Brushite Cements“. Materials 12, Nr. 10 (27.05.2019): 1719. http://dx.doi.org/10.3390/ma12101719.
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Brushite cements have been clinically used for irregular bone defect filling applications, and various strategies have been previously reported to modify and improve their physicochemical properties such as strength and injectability. However, strategies to address other limitations of brushite cements such as low radiopacity or acidity without negatively impacting mechanical strength have not yet been reported. In this study, we report the effect of substituting the beta-tricalcium phosphate reactant in brushite cement with baghdadite (Ca3ZrSi2O9), a bioactive zirconium-doped calcium silicate ceramic, at various concentrations (0, 5, 10, 20, 30, 50, and 100 wt%) on the properties of the final brushite cement product. X-ray diffraction profiles indicate the dissolution of baghdadite during the cement reaction, without affecting the crystal structure of the precipitated brushite. EDX analysis shows that calcium is homogeneously distributed within the cement matrix, while zirconium and silicon form cluster-like aggregates with sizes ranging from few microns to more than 50 µm. X-ray images and µ-CT analysis indicate enhanced radiopacity with increased incorporation of baghdadite into brushite cement, with nearly a doubling of the aluminium equivalent thickness at 50 wt% baghdadite substitution. At the same time, compressive strength of brushite cement increased from 12.9 ± 3.1 MPa to 21.1 ± 4.1 MPa with 10 wt% baghdadite substitution. Culture medium conditioned with powdered brushite cement approached closer to physiological pH values when the cement is incorporated with increasing amounts of baghdadite (pH = 6.47 for pure brushite, pH = 7.02 for brushite with 20 wt% baghdadite substitution). Baghdadite substitution also influenced the ionic content in the culture medium, and subsequently affected the proliferative activity of primary human osteoblasts in vitro. This study indicates that baghdadite is a beneficial additive to enhance the radiopacity, mechanical performance and cytocompatibility of brushite cements.
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Aghyarian, Shant, Lucas C. Rodriguez, Jonathan Chari, Elizabeth Bentley, Victor Kosmopoulos, Isador H. Lieberman und Danieli C. Rodrigues. „Characterization of a new composite PMMA-HA/Brushite bone cement for spinal augmentation“. Journal of Biomaterials Applications 29, Nr. 5 (01.08.2014): 688–98. http://dx.doi.org/10.1177/0885328214544770.
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Calcium phosphate fillers have been shown to increase cement osteoconductivity, but have caused drawbacks in cement properties. Hydroxyapatite and Brushite were introduced in an acrylic two-solution cement at varying concentrations. Novel composite bone cements were developed and characterized using rheology, injectability, and mechanical tests. It was hypothesized that the ample swelling time allowed by the premixed two-solution cement would enable thorough dispersion of the additives in the solutions, resulting in no detrimental effects after polymerization. The addition of Hydroxyapatite and Brushite both caused an increase in cement viscosity; however, these cements exhibited high shear-thinning, which facilitated injection. In gel point studies, the composite cements showed no detectable change in gel point time compared to an all-acrylic control cement. Hydroxyapatite and Brushite composite cements were observed to have high mechanical strengths even at high loads of calcium phosphate fillers. These cements showed an average compressive strength of 85 MPa and flexural strength of 65 MPa. A calcium phosphate-containing cement exhibiting a combination of high viscosity, pseudoplasticity and high mechanical strength can provide the essential bioactivity factor for osseointegration without sacrificing load-bearing capability.
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Lilley, K. J., Uwe Gbureck, Adrian J. Wright, David Farrar und J. E. Barralet. „Investigation into Carboxylic Acids as Cement Reactants“. Key Engineering Materials 309-311 (Mai 2006): 853–56. http://dx.doi.org/10.4028/www.scientific.net/kem.309-311.853.
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Bajpai et al. originally reported the formation of cements by the mixture of carboxylic acids and β-tricalcium phosphate (β-TCP). In the current study, we report and contrast four such cement systems formed from mixing citric, malic, 2-oxoglutaric or phosphoric acid with β-TCP. Cements formed from malic or 2-oxoglutaric appeared to contain crystalline phases and were determined to contain brushite, β-TCP and unreacted acid. In contrast, cement formed with citric acid was poorly crystalline, containing little evidence of brushite formation and was unstable in water and therefore does not appear to be a feasible cement system.
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Altundal, Sahin, Marco Laurenti, Enrique Jose López‐Cabarcos, Jorge Rubio-Retama und Karlis Agris Gross. „Accelerated Transformation of Brushite Cement into Carbonate Apatite in Biomimetic Solution“. Key Engineering Materials 800 (April 2019): 70–74. http://dx.doi.org/10.4028/www.scientific.net/kem.800.70.
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Brushite cement has advantages such as fast setting, high reactivity and good injectability over apatitic cements. To induce the bioactivity of brushite cements, the goal was to convert it into a bone-like low crystalline carbonate apatite. To achieve this induced transformation, potassium and magnesium were used as dopants which were claimed to be effective in the literature. The cements were immersed for 2 periods of time: 1 day and 6 weeks in Tas-Simulated-Body-Fluid (Tas-SBF) due to its excellent biomimetic properties with its adjusted HCO3- and Cl- ionic rates according to human-blood-plasma. 5% of potassium (to calcium sites) seemed to be more effective over magnesium modification. The aim of this study is to define an optimal composition in terms of transforming brushite into apatite.
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Srakaew, N., und Sirirat T. Rattanachan. „Effect of Apatite Wollastonite Glass Ceramic Addition on Brushite Bone Cement Containing Chitosan“. Advanced Materials Research 506 (April 2012): 106–9. http://dx.doi.org/10.4028/www.scientific.net/amr.506.106.
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Apatite wollastonite glass ceramic (AW-GC) (34.2% SiO2, 44.9% CaO, 16.3%P2O5, 4.6% MgO, 0.5% CaF2) was added into a brushite bone cement, which composed of β-tricalcium phosphate (β-Ca3(PO4)2, β-TCP) and monocalcium phosphate monohydrate (Ca (H2PO4)2H2O, MCPM) in powder phases. Cement was prepared using a 3 β-TCP:2 MCPM in weight ratio. To evaluate the effect of AW-GC on the mechanical strength and degradability of brushite bone cement, the powder phases and 1 wt.% of chitosan dissolved in 5 wt.% of citric acid solution were mixed and soaked in simulated body fluid solution at 37 °C for 1, 3, 5,7 and 14 days, respectively. The compressive strength and setting time of AW-GC added in brushite bone cement were studied and compared with pure brushite cement. The pH values increased with addition of AW-GC. Additionally, the obtained brushite bone cements were characterized by XRD, SEM techniques.
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Alkhraisat, Mohammad Hamdan, Jatsue Cabrejos-Azama, Carmen Rueda Rodríguez, Luis Blanco Jerez und Enrique López Cabarcos. „Magnesium substitution in brushite cements“. Materials Science and Engineering: C 33, Nr. 1 (Januar 2013): 475–81. http://dx.doi.org/10.1016/j.msec.2012.09.017.
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Bohner, M., und U. Gbureck. „Thermal reactions of brushite cements“. Journal of Biomedical Materials Research Part B: Applied Biomaterials 84B, Nr. 2 (2008): 375–85. http://dx.doi.org/10.1002/jbm.b.30881.
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Grover, Liam M., Sarika Patel, Y. Hu, Uwe Gbureck und J. E. Barralet. „Modifying Brushite Cement Degradation Using Calcium Alginate Beads“. Key Engineering Materials 361-363 (November 2007): 311–14. http://dx.doi.org/10.4028/www.scientific.net/kem.361-363.311.
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The hydrolysis of brushite in calcium phosphate cements to form hydroxyapatite is known to result in the long term stability of the material in the body. It has previously been established that this hydrolysis reaction can be influenced by implant volume, media refreshment rate and media composition. In this study, the effect of macroporosity on the rate of degradation of the material is investigated. Macroporosity was incorporated into the material using calcium alginate beads mixed into the cement paste. The inclusion of the calcium alginate beads did not influence the degree of conversion of the material and allowed the incorporation of porosity at up to maximum of 57%. The macroporosity weakened the cement matrix (from 46.5 to 3.2 MPa). When aged the brushite in the macroporous cement dissolved completely from the matrix resulting in a weight loss of 60wt% in a period of 28 days. This suggests that the controlled incorporation of calcium alginate beads into brushite cements in vivo can be used to control implant degradation rate.
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Mahmood, S., W. M. Palin, Uwe Gbureck, O. Addison und M. P. Hofmann. „Effect of Mechanical Mixing and Powder to Liquid Ratio on the Strength and Reliability of a Brushite Bone Cement“. Key Engineering Materials 361-363 (November 2007): 307–10. http://dx.doi.org/10.4028/www.scientific.net/kem.361-363.307.
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The effect of mechanical mixing on compressive strength, relative porosity and reliability of strength data of a brushite forming cement at different powder to liquid ratios (PLRs) was investigated. Mean compressive strengths were measured, associated reliability (Weibull moduli) and survival probability distributions of the data sets were analysed. Relative porosities were determined using helium pycnometry. For low PLR (2.2g/ml), no significant differences in compressive strength were observed for either mechanical or hand mixed samples, although reliability of the former was significantly increased. At high PLR (3.4g/ml), mechanically mixed cements exhibited approximately twice the mean compressive strength compared with hand mixing, although Weibull moduli remained statistically similar. At medium PLR (2.8g/ml) strength and reliability of cements were similar and independent of mixing regime. For all PLRs, a significant decrease in porosity of mechanical- compared with hand-mixed cements was observed. Mechanical mixing of a brushite cement can provide lower porosity, increased reliability and higher strength.
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Tamimi, Faleh, Zeeshan Sheikh und Jake Barralet. „Dicalcium phosphate cements: Brushite and monetite“. Acta Biomaterialia 8, Nr. 2 (Februar 2012): 474–87. http://dx.doi.org/10.1016/j.actbio.2011.08.005.
Der volle Inhalt der QuelleDissertationen zum Thema "Brushite cements"
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Ismail, N. A. B. „Development of novel remineralising antimicrobial brushite cements“. Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1448840/.
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Brushite cements have potential as drug carriers and bone filling materials. They can also act as a reservoir for calcium and phosphate ions in remineralisation of hard tissues. Aim and objectives: To optimize brushite cement properties and assess the effect of incorporation of a novel antimicrobial ε-polylysine (PLS) into brushite. Materials and Methods: Powders were mixed with aqueous solutions at a powder to liquid ratio of 3.3:1 or 4:1 to produce cement pastes and start the setting reaction. The powder consisted of 1g of monocalcium phosphate monohydrate (MCPM) and 1.23 g of β -tricalcium phosphate (β-TCP). Two different types of MCPM and different β-TCP particle size range from 4 micron to 34 micron were used. The liquid phase was prepared by dissolving PLS powder in aqueous citric acid 800 mM in incrementally percentages. In control formulations, only citric acid 800 without the PLS was employed. Biaxial flexural strength and modulus were determined using a ball on ring jig. Setting kinetics and chemistry were examined using Fourier transforms infrared spectroscopy (FTIR). Microstructure of brushite cements were examined with scanning electron microscopy (SEM). Results: The largest particle size of â-TCP (34 micron) produced the highest flexural strength of 30 MPa. The handling of brushite cements was better with MCPM 2 (Sigma). This was observed to have much larger flat crystals rather than the more powdered MCPM 1 from Himed. Powder to liquid ratio 4:1 overall increased the strength 5 MPa – 7 MPa compared to powder to liquid ratio 3.3:1. High levels of PLS could be added with only a minor reduction in the strength. Setting time however was delayed and an alternative anhydrous dicalcium phosphate complex formed rather than all brushite which is hydrated dicalcium phosphate. Conclusion: The findings of this research demonstrated that very high levels of PLS could be introduced into brushite cements without serious detrimental effects on mechanical properties. PLS however, did delay the setting time and altered the final chemistry and microstructure of the dicalcium phosphate product.
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Åberg, Jonas. „Premixed Acidic Calcium Phosphate Cements“. Doctoral thesis, Uppsala universitet, Tillämpad materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-168650.
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Calcium phosphate cements are used in medicine to fill bone defects or give support to screws and plates in fracture fixation. The cements are formed via mixing a powder with water and the mixture harden through a dissolution-precipitation reaction. Today the cement mixing is performed in the operating room and consists of several complicated steps that need to be performed under sterile conditions. This renders the mixing a risk factor, potentially leading to harm for the patient e.g. unsatisfactory healing or infection. To reduce this risk, premixed cements have been developed using glycerol as mixing liquid. The premixed cement sets when it is exposed to body liquids. Therefore, premixed cement can be delivered to the operating room in prefilled syringes ready for use, thus eliminating the mixing step. The aim of this thesis is to describe differences between premixed and water-mixed cements and their advantages and drawbacks. The differences will be discussed based on results obtained from bench testing of specific cement properties as function of cement formulations as well as in vitro and in vivo studies. Several cement formulations were evaluated e.g. the influence of powder to liquid ratio (P/L), powder particle size and addition of water on key properties. The results showed that premixed cements have excellent handling properties and have mechanical properties similar to water-based cements. Both P/L and particle size can be used to control these properties. It was shown that small amounts of water improve certain cement properties while dry raw materials were important for long shelf life. To better understand the setting of premixed cements new methods for evaluating working time and setting of premixed cements were developed. In vivo studies showed that the formulations developed in this thesis are biocompatible, resorbable and show good tissue response in bone. This thesis concludes, that the premixed cements are a promising biomaterial with excellent handling properties and good biological response. The most important challenge for the premixed cements, in order to become commercially successful, is to obtain clinically relevant setting time and shelf life simultaneously. An increasing use of premixed cements in the clinics should shorten operation times and reduce infection rates to the benefit of both patients and medical staff.
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Ajaxon, Ingrid. „Can Bone Void Fillers Carry Load? : Behaviour of Calcium Phosphate Cements Under Different Loading Scenarios“. Doctoral thesis, Uppsala universitet, Tillämpad materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-316656.
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Calcium phosphate cements (CPCs) are used as bone void fillers and as complements to hardware in fracture fixation. The aim of this thesis was to investigate the possibilities and limitations of the CPCs’ mechanical properties, and find out if these ceramic bone cements can carry application-specific loads, alone or as part of a construct. Recently developed experimental brushite and apatite cements were found to have a significantly higher strength in compression, tension and flexion compared to the commercially available CPCs chronOS™ Inject and Norian® SRS®. By using a high-resolution measurement technique the elastic moduli of the CPCs were determined and found to be at least twice as high compared to earlier measurements, and closer to cortical bone than trabecular bone. Using the same method, Poisson's ratio for pure CPCs was determined for the first time. A non-destructive porosity measurement method for wet brushite cements was developed, and subsequently used to study the porosity increase during in vitro degradation. The compressive strength of the experimental brushite cement was still higher than that of trabecular bone after 25 weeks of degradation, showing that the cement can carry high loads over a time span sufficiently long for a fracture to heal. This thesis also presents the first ever fatigue results for acidic CPCs, and confirms the importance of testing the materials under cyclic loading as the cements may fail at stress levels much lower than the material’s quasi-static compressive strength. A decrease in fatigue life was found for brushite cements containing higher amounts of monetite. Increasing porosity and testing in a physiological buffer solution (PBS), rather than air, also decreased the fatigue life. However, the experimental brushite cement had a high probability of surviving loads found in the spine when tested in PBS, which has previously never been accomplished for acidic CPCs. In conclusion, available brushite cements may be able to carry the load alone in scenarios where the cortical shell is intact, the loading is mainly compressive, and the expected maximum stress is below 10 MPa. Under such circumstances this CPC may be the preferred choice over less biocompatible and non-degradable materials.
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Jdaini, Jihane. „Potentialités des ciments brushitiques pour le traitement et le conditionnement de déchets radioactifs contaminés par du strontium“. Electronic Thesis or Diss., Montpellier, Ecole nationale supérieure de chimie, 2022. http://www.theses.fr/2022ENCM0024.
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Les opérations d'assainissement d'anciennes installations nucléaires peuvent générer des solutions acides contaminées par du strontium et du césium. Un des moyens de traitement de ces effluents consiste à les faire circuler sur des adsorbants en colonne. S'il existe des matériaux inorganiques permettant le piégeage du césium en milieu acide, aucun adsorbant efficace n'est actuellement disponible dans le cas du strontium. L'enjeu de cette thèse est donc d'élaborer un adsorbant minéral du strontium fonctionnant en milieu acide, mais également compatible avec l'environnement alcalin d'un stockage de déchets nucléaires qui constituera l'exutoire final du piégeur. Certains ciments phosphatés pourraient présenter des atouts pour l'application visée. Leurs performances restent toutefois à déterminer. On cherchera donc dans un premier temps à préciser les contributions des différentes phases qui les composent à la rétention du strontium et on identifiera les mécanismes mis en jeu. A partir des résultats obtenus sur phases pures, on formulera et caractérisera un matériau polyphasique dont l'assemblage minéralogique sera optimisé pour le piégeage. Dans la dernière partie de la thèse, on déterminera l'évolution des propriétés de ce matériau dans l'environnement alcalin d'un stockageDuring the decommissioning of old nuclear facilities, cleaning operations can produce acidic waste streams contaminated by cesium and strontium. One way to treat these effluents is to make them flow through columns filled with sorbents. Inorganic materials have been recently reported for the trapping of cesium in acidic medium. However, a solution is still lacking for strontium. The main objective of this PhD work is thus to design a mineral sorbent of strontium, keeping its efficiency under acidic conditions, and showing a good chemical compatibility with the alkaline environment of a nuclear waste repository, where the sorbent will be finally disposed of. Some phosphate binders may have several assets for the desired application. However, their trapping properties still need to be determined, as well as the consequences of a pH change in their environment. In a first stage, the contributions of the different phases of a phosphate cement paste to strontium retention will be determined, as well as the mechanisms involved. Using the results achieved on pure phases, a polyphasic material, with an optimized phase assemblage for strontium trapping, will then be designed. Finally, the evolution of its properties under the alkaline conditions of a repository will be investigated
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Saadalla, Marco Edward. „A new modified injectable brushite-based calcium phosphate bone cement“. Thesis, Queen Mary, University of London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.498084.
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Mohd, Razi M. R. „Effects of polyacrylic acid on brushite bone cement setting, mechanical properties, degradation and chlorhexidine release“. Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1361005/.
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In the field of Paediatric Dentistry, brushite cement has potential as an endodontic medicament and bone substitute material. Clinical applications however are limited due to their inherent properties, such as rapid setting time and poor mechanical properties. Antimicrobial e.g. chlorhexidine (CHX) could be incorporated into the cement for localised drug release. Aim and objectives: The aim of this study was to assess if partial replacement of citric acid (CA) by polyacrylic acid (PAA) can improve the properties of conventional brushite cements. The objectives were to assess the effects of varying PAA and CHX concentrations in brushite cements on their setting kinetics, final composition, microstructure of the cement, mechanical properties, degradation and CHX release profile. Materials and Methods: The cements consisted of equimolar β- tricalcium phosphate and monocalcium phosphate monohydrate (β-TCP/MCPM) and 6 or 11% (w/w) CHX. The liquid phase consisted of aqueous 800 mM CA and PAA solution at different ratios. Compositions with no CHX and/or PAA were used as control cements. Setting kinetics and final composition were determined using FTIR and Raman spectroscopy respectively. Brushite microstructure was examined using scanning electron microscopy. The cements were tested for microhardness and biaxial flexural strength (BFS). CHX release was quantified with UV spectroscopy and degradation by mass loss. Results: The setting times for compositions with PAA were delayed by up to 12 hours. FTIR indicated formation of dicalcium citrate and polyacrylate complexes could delay brushite formation. High CHX content inhibited the acid retarding effects and complex formation. Raman mapping demonstrated discrete regions of brushite and CHX in all set cements. Microscopically, PAA addition resulted in denser and less porous structure. The BFS ranged from 5.8 ± 1.3 MPa to 11.1 ± 1.2 MPa. CHX incorporation resulted in reduced BFS and modulus whilst PAA addition increased it. The average mass change was significantly different between compositions with and with no chlorhexidine; 12% and 0.2% respectively at the end of study period. The daily degradation rate ranged from 0.1 ± 0.03 wt% to 0.6 ± 0.15 wt%. PAA presence reduced CHX release from more than 90% to less than 20% over 4 weeks. Conclusion: PAA substantially slowed the setting reaction and chlorhexidine release characteristics, altered the final brushite crystal microstructure, increased mechanical properties but did not affect the degradation kinetics.
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Laniesse, Priscillia. „Les ciments brushitiques à base de wollastonite - Réactivité, propriétés et application au traitement et au conditionnement d’effluents contaminés par du strontium“. Thesis, Montpellier, 2019. http://www.theses.fr/2019MONTS017/document.
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Ce travail vise à étudier l’hydratation et les propriétés des ciments brushitiques à base de wollastonite dans la perspective d’une application au traitement et au conditionnement de déchets radioactifs de faible ou moyenne activité acides et/ou contaminés en strontium. Une étude des processus conduisant à la prise et au durcissement d’un ciment commercial est d’abord menée. L’influence de la composition de la solution de gâchage sur les réactions mises en jeu est ensuite précisée. Enfin, une première évaluation du potentiel de ce matériau pour la décontamination ou l’immobilisation d’effluents aqueux contaminés en strontium est réalisée.Les pâtes de ciment brushitique à base de wollastonite sont préparées à partir de wollastonite broyée et d’une solution d’acide phosphorique concentrée contenant des cations métalliques (Zn2+ et Al3+) ainsi que du borax. La wollastonite réagit selon un processus de dissolution/précipitation qui conduit à la formation de brushite, de silice amorphe et d’un aluminophosphate de calcium et de zinc amorphe dont la structure a été caractérisée par RMN-MAS du 31P et 27Al. La précipitation de brushite est précédée par la formation transitoire de phosphate monocalcique monohydraté. La simulation thermodynamique à l’aide d’un code de spéciation géochimique de la réaction de la wollastonite avec une solution d’acide phosphorique reproduit bien la séquence de précipitation des phases cristallines observée expérimentalement.Il apparaît que la concentration optimale de l’acide phosphorique dans la solution de gâchage est comprise entre 9 et 10 mol.L-1. Le bore retarde la prise du ciment tandis que le zinc l’accélère. L’ajout d’aluminium, qui permet la précipitation massive d’aluminophosphate de calcium amorphe, s’avère nécessaire pour obtenir un matériau avec de bonnes performances mécaniques. Une étude de surfaces de réponses par plan d’expériences, suivie d’une optimisation multicritères, a permis d’identifier un domaine de compositions de solutions de gâchage conduisant à un matériau possédant les propriétés recherchées (en terme de temps de prise, auto-échauffement et résistance mécanique) pour une matrice de conditionnement de déchets.Une étude cristallographique montre par ailleurs que la brushite peut incorporer au moins 30 % (mol/mol) de strontium en substitution du calcium dans sa structure. Des essais de piégeage du strontium par une pâte de ciment broyée, menés en suspension diluée, conduisent à une isotherme de sorption de type S, témoignant de l’existence de plusieurs mécanismes de rétention. Enfin, un essai de lixiviation sur un monolithe contenant du strontium révèle le bon confinement de ce dernier, avec un coefficient de rétention Rd plus de 100 fois supérieur à celui obtenu avec une pâte de ciment PortlandThis work aims at studying the hydration process and the properties of wollastonite-based brushite cements. These binders may indeed offer new prospects for the treatment or conditioning of low- or intermediate- level radioactive wastes characterized by a strong acidity and/or a contamination by strontium. First, a study of the hydration process is carried out with a commercial cement. Then, the influence of the mixing solution composition on the setting and hardening process is determined. Finally, a first assessment of the potential of this material for the decontamination and immobilization of strontium-containing aqueous effluents is performed.Wollastonite-based brushite cement pastes are prepared by mixing ground wollastonite and a phosphoric acid solution containing metallic cations (Al3+ and Zn2+) and borax. Wollastonite reacts through a dissolution/precipitation process, which leads to the formation of brushite, amorphous silica and amorphous zinc and calcium aluminophosphate whose structure has been investigated by 31P and 27Al MAS-NMR. The brushite precipitation is preceded by the transient formation of monophosphate calcium monohydrate. The thermodynamic simulation of the wollastonite reaction with a phosphoric acid solution, using a geochemical speciation code, fairly well reproduces the precipitation sequence of crystalline phases observed experimentally.It appears that the optimum phosphoric acid concentration in the mixing solution is comprised between 9 and 10 mol.L-1. Boron retards the cement setting whereas zinc accelerates it. The addition of aluminium, which leads to the massive precipitation of amorphous calcium aluminophosphate, is proved to be necessary to obtain a material with high mechanical strength. Thanks to response surface methodology and multi-criteria optimization, a composition domain of the mixing solution is pointed out, leading to a material with good properties (in terms of setting time, self-heating and mechanical strength) for waste conditioning.A crystallographic study also shows that brushite is able to incorporate at least 30 % (mol/mol) of strontium in substitution for calcium in its structure. Strontium retention tests by a ground cement paste in diluted suspension lead to a type S sorption isotherm, meaning that several retention mechanisms are involved. Finally, a leaching experiment performed on a cement monolith containing strontium shows that this species is well confined within the cement matrix, with a retention coefficient at least two orders of magnitude higher than that of a Portland cement paste
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Ramada, David João Loureiro. „Development and characterization of apatitic and brushitic microneedles for the controlled release of antibiotics“. Master's thesis, Universidade de Aveiro, 2017. http://hdl.handle.net/10773/22570.
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Mestrado em Materiais e Dispositivos BiomédicosAs microagulhas (MN) são microcomponentes inovadores na entrega de fármacos via transdérmica de forma quase impercetível para o paciente. De metais a polímeros, as MN têm sido fabricadas com uma grande variedade de materiais, embora com algumas restrições quanto à resistência mecânica (limitações relacionadas com a perfuração da pele), armazenamento e altos custos de fabrico. Na presente tese, foram utilizados cimentos à base de fosfato tricálcico (TCP) para o fabrico de MN brushíticas e apatíticas via micromoldagem. Foram sintetizados dois pós, -TCP e BTCP (bifásico, -TCP + -TCP). Partindo destes pós, foram preparadas pastas cimentícias na ausência e na presença de fármaco, variando a razão líquido/pó e caracterizadas em termos de tempos de presa inicial e final, parâmetros importantes para o enchimento e desmoldagem dos componentes. Os cimentos resultantes foram caracterizados em termos de porosidade, fases cristalinas, resistência mecânica, microestrutura da superfície e metodologia de secagem. As formulações de cimento que apresentaram os resultados mais promissores para o fabrico de MN foram utilizadas para estudar a taxa de libertação do fármaco. Uma solução aquosa de ácido cítrico com concentração adequada como líquido de presa revelou ser a mais adequada. O antibiótico levofloxacina (LEV) foi utilizado como fármaco modelo. Os resultados obtidos mostraram que a adição de LEV aumenta os tempos de presa iniciais e finais das pastas cimentícias e diminui as propriedades mecânicas dos cimentos. Uma libertação de fármaco de 100% foi alcançada para todas as formulações de cimento testadas após 48 horas de imersão. Do estudo cinético da libertação de fármaco verificou-se que o "Coupled Mechanism" foi o que melhor descreveu o mecanismo de libertação da LEV em todas as formulações de cimentos testadas. Com as pastas cimentícias foi possível obter microagulhas afiadas por enchimento de micromoldes e devidamente desmoldadas. Através da avaliação da sua resistência mecânica é possível prever que as MN obtidas apresentam estrutura e propriedades mecânicas adequadas para a perfuração da pele, uma vez que, é conhecido da literatura que a força necessária para que as agulhas perfurarem a pele humana é à volta de 1-5 N. Das várias agulhas testadas, os valores da força necessária para quebrar a ponta situam-se num intervalo de 57 a 110 N. As MN à base de cimentos de TCP apresentam características adequadas para serem utilizadas como meio de administração de fármacos via transdérmica com futuro em diversas aplicações médicas. O processo de produção utilizado traz imensas vantagens quando comparado com os métodos atuais para a produção de microcomponentes, sendo simples, económico e replicável.
Microneedles (MN) are an up and coming technology offering almost inconspicuous transdermal drug delivery system. From metals to polymers, microneedles have been fabricated with a high variety of materials, although with some constraints regarding mechanical strength (limitations related to skin perforation), storage and high manufacturing costs. In the present thesis, self-setting bioceramics were used to fabricate brushitic and apatitic MN by micro-molding casting. Two precursor powders were synthesized to obtain -TCP and BTCP (biphasic,-TCP+-TCP) as main phases. Cement pastes were prepared in absence and in presence of drug, varying liquid to powder ratio and characterized in terms of initial and final setting times, important parameters for casting and de-molding procedures. The resulting cements were characterized for their porosity, crystalline phases, mechanical strength, surface morphology and drying methodology. The cement formulations that presented the most promising results for MN fabrication (flowability during casting and adequate mechanical properties for de-molding without damage) were used to study drug release rate. A citric acid solution with adequate concentration was the most suitable as setting liquid in both MN types. The antibiotic levofloxacin was used as a model drug. The results show that the addition of levofloxacin increases the setting times of the cement pastes and decreases the mechanical properties of the cements. A 100% drug release was achieved for all the tested cement formulations after 48 hours of immersion time. The drug release kinetics were evaluated being determined that the "coupled mechanism" is the one that best described the release mechanism of cements obtained from both powders. Sharp MN were successfully casted and de-molded. MN tip obtained in this work present adequate mechanical properties for skin perforation without breakage, since according to literature the insertion forces necessary for perforate human skin is around 1-5 N. Among all tested MN, the force necessary to break the tip is in the range 57 to 110 N. From the evaluated work, calcium phosphate cement based MN present adequate characteristics to be used as a promising drug delivery microcomponent for biomedical applications. The fabrication process used (micromolding) has several advantages when compared to the current production MN processes being simple, cost-effective and replicable.
Buchteile zum Thema "Brushite cements"
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Grover, Liam M., Sarika Patel, Y. Hu, Uwe Gbureck und J. E. Barralet. „Modifying Brushite Cement Degradation Using Calcium Alginate Beads“. In Bioceramics 20, 311–14. Stafa: Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-457-x.311.
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Hofmann, M. P., Uwe Gbureck, Liam M. Grover und J. E. Barralet. „Stearate Salts as Brushite Bone Cement Setting Retardants“. In Bioceramics 17, 19–22. Stafa: Trans Tech Publications Ltd., 2005. http://dx.doi.org/10.4028/0-87849-961-x.19.
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Hofmann, M. P., A. M. Young, Showan N. Nazhat, Uwe Gbureck und J. E. Barralet. „Setting Kinetics Observation of a Brushite Cement by FTIR and DSC“. In Bioceramics 18, 837–40. Stafa: Trans Tech Publications Ltd., 2006. http://dx.doi.org/10.4028/0-87849-992-x.837.
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Mahmood, S., W. M. Palin, Uwe Gbureck, O. Addison und M. P. Hofmann. „Effect of Mechanical Mixing and Powder to Liquid Ratio on the Strength and Reliability of a Brushite Bone Cement“. In Bioceramics 20, 307–10. Stafa: Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-457-x.307.
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Ajaxon, Ingrid, und Cecilia Persson. „Mechanical Properties of Brushite Calcium Phosphate Cements“. In Frontiers in Nanobiomedical Research, 285–300. WORLD SCIENTIFIC, 2017. http://dx.doi.org/10.1142/9789813202573_0008.
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Ajaxon, Ingrid, und Cecilia Persson. „Mechanical Properties of Brushite Calcium Phosphate Cements“. In Frontiers in Nanobiomedical Research, 285–300. WORLD SCIENTIFIC, 2017. http://dx.doi.org/10.1142/9789813205573_0008.
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Issa, Khalil, Abdulaziz Alanazi, Khalid A. Aldhafeeri, Ola Alamer und Mazen Alshaaer. „Brushite: Synthesis, Properties, and Biomedical Applications“. In Crystallization and Applications. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.102007.
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In this chapter, besides its biomedical applications, the synthesis and properties of brushite were investigated. Brushite consists of two types of crystals, platy and needle-like, and their formation depends on the pH of the medium during precipitation. Platy crystals are formed in a slightly acidic medium, pH = 5, and needle-like crystals at a higher pH = 6.5–7. In this study, the monoclinic brushite crystals were synthesized using dissolution-precipitation reactions. It is found that the brushite crystal growth occurs mainly along the (020) crystallographic plane. The thermogravimetric analysis confirms the presence of the two structural water molecules, which decompose at a temperature range between 80 and 220°C. Brushite was used in the preparation of tetracalcium phosphate mineral, which is the powder component for calcium phosphate cement (CPC). CPC was subsequently prepared from TTCP and phosphate-based hardening solution. In vitro evaluation of the resultant CPC using Hanks’ Balanced Salt Solution results in the growth of nanofibrous crystals of Calcium-deficient hydroxyapatite (CDHA) layers on the surfaces of the CPC. The cultured CPC exhibits new connective tissues and throughout the CaP matrix.
Konferenzberichte zum Thema "Brushite cements"
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Hindistan, Ozge, Ibrahim Mert, Selen Mandel und A. Cuneyt Tas. „A novel particle morphology for the brushite (CaHPO4·2H2O) powders used in orthopedic cements“. In 2010 15th National Biomedical Engineering Meeting (BIYOMUT 2010). IEEE, 2010. http://dx.doi.org/10.1109/biyomut.2010.5479871.
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Bicakci, Murat, und A. Cuneyt Tas. „Preparation of biphasic brushite-apatite orthopedic cement powders by chemical precipitation“. In 2010 15th National Biomedical Engineering Meeting (BIYOMUT 2010). IEEE, 2010. http://dx.doi.org/10.1109/biyomut.2010.5479869.
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