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Preparation of pHEMA-CP composites with high interfacial adhesionvia template-driven mineralization

Description: We report a template-driven nucleation and mineral growth process for the high-affinity integration of calcium phosphate (CP) with a poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogel scaffold. A mineralization technique was developed that exposes carboxylate groups on the surface of crosslinked pHEMA, promoting high-affinity nucleation and growth of calcium phosphate on the surface along with extensive calcification of the hydrogel interior. External factors such as the heating rate, the agitation of the mineral stock solution and the duration of the process that affect the outcome of the mineralization were investigated. This template-driven mineralization technique provides an efficient approach toward bonelike composites with high mineral-hydrogel interfacial adhesion strength.
Date: December 5, 2002
Creator: Song, Jie; Saiz, Eduardo & Bertozzi, Carolyn R.
Partner: UNT Libraries Government Documents Department

Monte Carlo simulations of phosphate polyhedron connectivity in glasses

Description: Monte Carlo simulations of phosphate tetrahedron connectivity distributions in alkali and alkaline earth phosphate glasses are reported. By utilizing a discrete bond model, the distribution of next-nearest neighbor connectivities between phosphate polyhedron for random, alternating and clustering bonding scenarios was evaluated as a function of the relative bond energy difference. The simulated distributions are compared to experimentally observed connectivities reported for solid-state two-dimensional exchange and double-quantum NMR experiments of phosphate glasses. These Monte Carlo simulations demonstrate that the polyhedron connectivity is best described by a random distribution in lithium phosphate and calcium phosphate glasses.
Date: January 1, 2000
Creator: ALAM,TODD M.
Partner: UNT Libraries Government Documents Department

Monte Carlo Simulations of Phosphate Polyhedron Connectivity in Glasses

Description: Monte Carlo simulations of phosphate tetrahedron connectivity distributions in alkali and alkaline earth phosphate glasses are reported. By utilizing a discrete bond model, the distribution of next-nearest neighbor connectivities between phosphate polyhedron for random, alternating and clustering bonding scenarios was evaluated as a function of the relative bond energy difference. The simulated distributions are compared to experimentally observed connectivities reported for solid-state two-dimensional exchange and double-quantum NMR experiments of phosphate glasses. These Monte Carlo simulations demonstrate that the polyhedron connectivity is best described by a random distribution in lithium phosphate and calcium phosphate glasses.
Date: December 21, 1999
Creator: ALAM,TODD M.
Partner: UNT Libraries Government Documents Department

Biomimetic Nanocomposites of Calcium Phosphate and Self-Assembling Triblock and Pentablock Copolymers

Description: In an effort to mimic the growth of natural bone, self-assembling, micelle and gel-forming copolymers were used as a template for calcium phosphate precipitation. Because of the cationic characteristics imparted by PDEAEM end group additions to commercially available Pluronic{reg_sign} Fl27, a direct ionic attraction mechanism was utilized and a polymer-brushite nanocomposite spheres were produced. Brushite coated spherical micelles with diameters of {approx}40 nm, and agglomerates of these particles (on the order of 0.5 {mu}m) were obtained. Thickness and durability of the calcium phosphate coating, and the extent of agglomeration were studied. The coating has been shown to be robust enough to retain its integrity even below polymer critical micelle concentration and/or temperature. Calcium phosphate-polymer gel nanocomposites were also prepared. Gel samples appeared as a single phase network of agglomerated spherical micelles, and had a final calcium phosphate concentration of up to 15 wt%. Analysis with x-ray diffraction and NMR indicated a disordered brushite phase with the phosphate groups linking inorganic phase to the polymer.
Date: August 9, 2006
Creator: Enlow, Drew Lenzen
Partner: UNT Libraries Government Documents Department

Low temperature solution deposition of calcium phosphate coatings for orthopedic implants

Description: Calcium phosphate coatings were grown from aqueous solution onto a derivatized self-assmebled monolayer (SAM) which was covalently bound to a titanium metal substrate. The SAM molecules provided an idea connection between the metal surface and the calcium phosphate coating. The trichlorosilane terminus of the SAM molecule insured covalent attachment to the surface, while the functionalized ``tail`` induced heterogeneous nucleation of the calcium phosphate coating from supersaturated solutions. This low temperature process allowed for uniform coatings to be produced onto complex-shaped and/or microporous surfaces and provided better control of phase purity.
Date: April 1, 1994
Creator: Campbell, A. A. & Graff, G. L.
Partner: UNT Libraries Government Documents Department

Biomimetic thin film deposition

Description: Biological mineral deposition for the formation of bone, mollusk shell and other hard tissues provides materials scientists with illustrative materials processing strategies. This presentation will review the key features of biomineralization and how these features can be of technical importance. We have adapted existing knowledge of biomineralization to develop a unique method of depositing inorganic thin films and coating. Our approach to thin film deposition is to modify substrate surfaces to imitate the proteins found in nature that are responsible for controlling mineral deposition. These biomimetic surfaces control the nucleation and growth of the mineral from a supersaturated aqueous solution. This has many processing advantages including simple processing equipment, environmentally benign reagents, uniform coating of highly complex shapes, and enhanced adherence of coating. Many different types of metal oxide, hydroxide, sulfide and phosphate materials with useful mechanical, optical, electronic and biomedical properties can be deposited.
Date: September 1, 1995
Creator: Rieke, P.R.; Graff, G.E.; Campbell, A.A.; Bunker, B.C.; Baskaran, S.; Song, L. et al.
Partner: UNT Libraries Government Documents Department

Engineering Titanium for Improved Biological Response

Description: The human body and its aggressive environment challenge the survival of implanted foreign materials. Formidable biocompatibility issues arise from biological, chemical, electrical, and tribological origins. The body's electrolytic solution provides the first point of contact with any kind of implant, and is responsible for transport, healing, integration, or attack. Therefore, determining how to successfully control the integration of a biomaterial should begin with an analysis of the early interfacial dynamics involved. setting, a complicated feedback system of solution chemistry, pH, ions, and solubility exists. The introduction of a fixation device instantly confounds this system. The body is exposed to a range of voltages, and wear can bring about significant shifts in potentials across an implant. In the environment of a new implant the solution pH becomes acidic, ionic concentrations shift, cathodic currents can lead to corrosion, and oxygen levels can be depleted; all of these impact the ability of the implant to retain its protective oxide layer and to present a stable interface for the formation of a biolayer. Titanium has been used in orthopedic and maxilofacial surgery for many years due to its reputation as being biocompatible and its ability to osseointegrate. Osseointegration is defined as direct structural and functional connection between ordered, living bone, and the surface of a load carrying implant. Branemark discovered this phenomenon in the 60's while examining titanium juxtaposed to bone. The mechanism by which titanium and its passivating oxide encourage osseosynthetic activity remains unknown. However in general terms the oxide film serves two purposes: first to provide a kinetic barrier that prevents titanium from corroding and second to provide a substrate that allows the constituents of bone (calcium phosphate crystals, cells, proteins, and collagen) to bond to it. We believe that the electrochemical environment dictates the titanium dioxide surface atomic structure and the ...
Date: January 23, 2002
Creator: Orme, C; Bearinger, J; Dimasi, E & Gilbert, J
Partner: UNT Libraries Government Documents Department

Prototype development and testing of ultrafine grain NZP ceramics. Quarterly progress report {number_sign}4, January 28, 1996--April 27, 1996

Description: Caterpillar Inc. continues to develop a slip casting procedure for CMZP (CaMgZr phosphate) exhaust portliners for diesel engines. ZnO was used as additive. Tubes have been cast and fired and initial properties look excellent. 40 lbs of CMZP powder are being prepared for Caterpillar to complete the slip casting of 90 degree elbows.
Date: May 24, 1996
Creator: Brown, J.J.
Partner: UNT Libraries Government Documents Department

Oxidation resistant coatings for ceramic matrix composite components

Description: Corrosion resistant Ca{sub 0.6}Mg{sub 0.4}Zr{sub 4}(PO{sub 4}){sub 6} (CMZP) and Ca{sub 0.5}Sr{sub 0.5}Zr{sub 4}(PO{sub 4}){sub 6} (CS-50) coatings for fiber-reinforced SiC-matrix composite heat exchanger tubes have been developed. Aqueous slurries of both oxides were prepared with high solids loading. One coating process consisted of dipping the samples in a slip. A tape casting process has also been created that produced relatively thin and dense coatings covering a large area. A processing technique was developed, utilizing a pre-sintering step, which produced coatings with minimal cracking.
Date: November 1, 1998
Creator: Vaubert, V.M.; Stinton, D.P. & Hirschfeld, D.A.
Partner: UNT Libraries Government Documents Department

Electron-irradiation-induced crystallization of amorphous orthophosphates

Description: Amorphous LaPO{sub 4}, EuPO{sub 4}, GdPO{sub 4}, ScPO{sub 4}, and fluorapatite [Ca{sub 5}(PO{sub 4}){sub 3}F] were irradiated by electron beam in a TEM. Irradiations were done at -150 to 300 C, 80 to 200 keV, and current densities from 0.3 to 16 A/cm{sup 2}. In all cases, the materials crystallized to form a randomly oriented polycrystalline assemblage. Crystallization is driven dominantly by inelastic processes, although ballistic collisions with target nuclei can be important above 175 keV, particularly in apatite. Using a high current density, crystallization is so fast that continuous lines of crystallites can be ``drawn`` on the amorphous matrix.
Date: December 1, 1996
Creator: Meldrum, A.; Ewing, R.C. & Boatner, L.A.
Partner: UNT Libraries Government Documents Department

Prototype development and testing of ultrafine grain NZP ceramics. Final report, July 28, 1995--April 27, 1997

Description: The goal of this project was to demonstrate that a new low-expanding ceramic (Ca{sub 0.6},Mg{sub 0.4})Zr{sub 4}(PO{sub 4}){sub 6}, hereafter referred to as CMZP, could be used as an exhaust manifold liner in off-road diesel engines and provide improved engine efficiency (by permitting higher engine operating temperature). This study has successfully demonstrated this improvement and further engine testing (and possible manufacturing) is presently underway at Caterpillar Inc. Laboratories. Basically this program involved two subcontracts: one to Virginia Tech to develop sintering procedures for CMZP, and one to Caterpillar, Inc. to develop slip casting procedures for CMZP. Nearly 100kg of CMZP were prepared by MATVA, Inc. and Virginia Tech for use by Caterpillar. Virginia Tech developed detailed sintering procedures for CMZP and Caterpillar developed slip casting procedures and manufactured several exhaust manifold elbows. These elbows have been cast into prototype cylinder heads and have been shown to be acceptable replacements for metal manifolds. (Caterpillar advises that a new component may require up to 6 years of testing and qualification before acceptance as standard diesel engine part).
Date: August 4, 1997
Creator: Brown, J.J.
Partner: UNT Libraries Government Documents Department

Lost circulation control materials. Progress report

Description: Work in FY 94 continued to investigate the use of calcium phosphate cements as lost circulation control materials for geothermal wells. The calcium phosphate cements were produced by reacting calcium aluminate cement with sodium phosphate compounds. Pumpable formulations with thickening times up to two hours at temperatures between 25 to 90{degrees}C were developed and characterized. The materials showed rapid set behaviour, early strength development, low permeability and acceptable durability in hydrothermal environments. Strengths up to 4 MPa were achieved four hours after mixing and water permeabilities were of the order of 10{sup -9} to 10{sup -7} cm/s at 24 hours. Partial replacement of calcium aluminate cement with ground granulated blast furnace slag was found to reduce the amount of borax retarder required to maintain pumpability at elevated temperatures and pressures.
Date: January 1994
Creator: Allan, M. L. & Kukacka, L. E.
Partner: UNT Libraries Government Documents Department

Powder-based synthesis of nanocrystalline material components for structural application. Final report

Description: Hydroxiapate spray coatings and substrates for implant production as well as multilayered metal ceramic coatings from nanocrystalline materials are a subject of the investigation. The work aims at the improvement of quality of said objects. This study has investigated the processes of hydroxiapatite powder production. Sizes, shapes and relief of initial HA powder surface are analyzed using SEM and TEM. Modes of HA plasma spraying on a substrate from titanium and associated compositions of traditional and nanocrystalline structure are optimized. The quality of the sprayed samples are studied using X-ray phase analysis and metallographic analysis. The results of investigations of bioceramic coating spraying on titanium are theoretically generalized, taking into account obtained experimental data. The results of investigations of ion-beam technology are presented for spraying multilayered coatings consisting of alternating metal-ceramic layers of nanocrystalline structure.
Date: December 1, 1998
Creator: Ilyuschenko, A.F.; Ivashko, V.S. & Okovity, V.A.
Partner: UNT Libraries Government Documents Department

Prototype development and testing of ultrafine grain NZP ceramics. Quarterly technical progress report No. 3, October 28, 1995--January 27, 1996

Description: Caterpillar has been developing advanced low-heat-rejection (LHR) engine designs because by insulating the combustion chamber components for reduced heat rejection, improved fuel economy and emission reduction can be achieved. The insulation eliminates heat loss during the closed portion of the cycle and increases the combustion temperature. Increased combustion temperatures improve emissions by reducing the amount of particulate or smoke. The higher combustion temperatures also provide additional energy to drive a turbocharger that, in turn, improves the overall efficiency of the engine system and results in increased fuel economy.
Date: February 8, 1996
Creator: Brown, J.J.
Partner: UNT Libraries Government Documents Department

The effects of thermal cycling on the physical and mechanical properties of [NZP] ceramics

Description: The [NZP] ceramics, sodium zirconium phosphate and its crystal structure analogs, are noted for their very low thermal expansion characteristics. What has not been widely studied is the effect of thermal cycling on physical and mechanical properties. Two [NZP] compositional series were selected (Ba{sub 1+x}Zr{sub 4}P{sub 6{minus}2x}Si{sub 2x}O{sub 24} and Ca{sub 1{minus}x}Sr{sub x}Zr{sub 4}P{sub 6}O{sub 24}) that exhibit varying bulk thermal expansion from positive to negative and varying degrees of thermal expansion anisotropy. The effect of thermal cycling, to 1,250 C, on the bulk thermal expansion and flexural strength of these ceramics is discussed in relationship to changes in density, thermal expansion anisotropy and microstructure.
Date: December 31, 1994
Creator: Jackson, T.B.; Limaye, S.Y. & Porter, W.D.
Partner: UNT Libraries Government Documents Department

Rapid Determination of 237 Np and Pu Isotopes in Water by Inductively Coupled Plasma Mass Spectrometry and Alpha Spectrometry

Description: A new method that allows rapid preconcentration and separation of plutonium and neptunium in water samples was developed for the measurement of {sup 237}Np and Pu isotopes by inductively-coupled plasma mass spectrometry (ICP-MS) and alpha spectrometry; a hybrid approach. {sup 238}U can interfere with {sup 239}Pu measurement by ICP-MS as {sup 238}UH{sup +} mass overlap and {sup 237}Np via peak tailing. The method provide enhanced removal of uranium by separating Pu and Np initially on TEVA Resin, then moving Pu to DGA resin for additional removal of uranium. The decontamination factor for uranium from Pu is almost 100,000 and the decontamination factor for U from Np is greater than 10,000. This method uses stacked extraction chromatography cartridges and vacuum box technology to facilitate rapid separations. Preconcentration is performed using a streamlined calcium phosphate precipitation method. Purified solutions are split between ICP-MS and alpha spectrometry so that long and short-lived Pu isotopes can be measured successfully. The method allows for simultaneous extraction of 20 samples (including QC samples) in 4 to 6 hours, and can also be used for emergency response. {sup 239}Pu, {sup 242}Pu and {sup 237}Np were measured by ICP-MS, while {sup 236}Pu, {sup 238}Pu, and {sup 239}Pu were measured by alpha spectrometry.
Date: June 23, 2010
Creator: Maxwell, S.; Jones, V.; Culligan, B.; Nichols, S. & Noyes, G.
Partner: UNT Libraries Government Documents Department

Molecular mechanism of crystallization impacting calcium phosphate cements

Description: In summary, SPM data has shown that (1) Mg inhibits growth on all steps but relatively high Mg/Ca ratios are needed. Extracting the mechanism of interaction requires more modeling of the kinetic data, but step morphology is consistent with incorporation. (2) Citrate has several effects depending on the citrate/Ca ratio. At the lowest concentrations, citrate increases the step free energy without altering the step kinetics; at higher concentrations, the polar step is slowed. (3) Oxalate also slows the polar step but additionally stabilizes a new facet, with a [100]{sub Cc} step. (4) Etidronate has the greatest kinetic impact of the molecules studied. At 7{micro}M concentrations, the polar step slows by 60% and a new polar step appears. However, at the same time the [10-1]{sub Cc} increases by 67%. It should be noted that all of these molecules complex calcium and can effect kinetics by altering the solution supersaturation or the Ca to HPO{sub 4}{sup 2-} ratio. For the SPM data shown, this effect was corrected for to distinguish the effect of the molecule at the crystal surface from the effect of the molecule on the solution speciation. The goal of this paper is to draw connections between fundamental studies of atomic step motion and potential strategies for materials processing. It is not our intent to promote the utility of SPM for investigating processes in cement dynamics. The conditions are spectacularly different in many ways. The data shown in this paper are fairly close to equilibrium (S=1.6) whereas the nucleation of cements is initiated at supersaturation ratios in the thousands to millions. Of course, after the initial nucleation phase, the growth will occur at more modest supersaturations and as the cement evolves towards equilibrium certainly some of the growth will occur in regimes such as shown here. In addition to the ...
Date: May 31, 2009
Creator: Giocondi, J L; El-Dasher, B S; Nancollas, G H & Orme, C A
Partner: UNT Libraries Government Documents Department

Resorption Rate Tunable Bioceramic: Si, Zn-Modified Tricalcium Phosphate

Description: This dissertation is organized in an alternate format. Several manuscripts which have already been published or are to be submitted for publication have been included as separate chapters. Chapter 1 is a general introduction which describes the dissertation organization and introduces the human bone and ceramic materials as bone substitute. Chapter 2 is the background and literature review on dissolution behavior of calcium phosphate, and discussion of motivation for this research. Chapter 3 is a manuscript entitled ''Si,Zn-modified tricalcium phosphate: a phase composition and crystal structure study'', which was published in ''Key Engineering Materials'' [1]. Chapter 4 gives more crystal structure details by neutron powder diffraction, which identifies the position for Si and Zn substitution and explains the stabilization mechanism of the structure. A manuscript entitled ''Crystal structure analysis of Si, Zn-modified Tricalcium phosphate by Neutron Powder Diffraction'' will be submitted to Biomaterials [2]. Chapter 5 is a manuscript, entitled ''Dissolution behavior and cytotoxicity test of Si, Zn-modified tricalcium phosphate'', which is to be submitted to Biomaterials [3]. This paper discusses the additives effect on the dissolution behavior of TCP, and cytotoxicity test result is also included. Chapter 6 is the study of hydrolysis process of {alpha}-tricalcium phosphate in the simulated body fluid, and the phase development during drying process is discussed. A manuscript entitled ''Hydrolysis of {alpha}-tricalcium phosphate in simulated body fluid and phase transformation during drying process'' is to be submitted to Biomaterials [4]. Ozan Ugurlu is included as co-authors in these two papers due to his TEM contributions. Appendix A is the general introduction of the materials synthesis, crystal structure and preliminary dissolution result. A manuscript entitled ''Resorption rate tunable bioceramic: Si and Zn-modified tricalcium phosphate'' was published in Ceramic Engineering and Science Proceedings (the 29th International Conference on Advanced Ceramics and Composites - Advances in Bioceramics ...
Date: August 9, 2006
Creator: Wei, Xiang
Partner: UNT Libraries Government Documents Department

Chapter 9: Model Systems for Formation and Dissolution of Calcium Phosphate Minerals

Description: Calcium phosphates are the mineral component of bones and teeth. As such there is great interest in understanding the physical mechanisms that underlie their growth, dissolution, and phase stability. Control is often achieved at the cellular level by the manipulation of solution states and the use of crystal growth modulators such as peptides or other organic molecules. This chapter begins with a discussion of solution speciation in body fluids and relates this to important crystal growth parameters such as the supersaturation, pH, ionic strength and the ratio of calcium to phosphate activities. We then discuss the use of scanning probe microscopy as a tool to measure surface kinetics of mineral surfaces evolving in simplified solutions. The two primary themes that we will touch on are the use of microenvironments that temporally evolve the solution state to control growth and dissolution; and the use of various growth modifiers that interact with the solution species or with mineral surfaces to shift growth away from the lowest energy facetted forms. The study of synthetic minerals in simplified solution lays the foundation for understand mineralization process in more complex environments found in the body.
Date: July 29, 2006
Creator: Orme, C. A. & Giocondi, J. L.
Partner: UNT Libraries Government Documents Department

Studies with Colloids Containing Radioisotopes of Yttrium, Zirconium, Columbium and Lanthaum: 2. The Controlled Selective Localization of Radioisotopes of Yttrium, Zirconium, Columbium in the Bone Marrow, Liver and Spleen

Description: Several workers have shown that certain colloidally dispered materials are removed from the blood stream by the liver and spleen. Jones, Wrobel, and Lyons have utilized suspensions of anhydrous chromic phosphate for the selective irradiation of the liver and spleen with p{sup 32} beta particles. Gersh demonstrated that colloidal calcium phosphate is taken up by the liver and spleen. He stressed the failure of bone marrow phagocytes to take up this colloid in rats and dogs (though he referred to possible uptake in the marrow of rabbits under special conditions), and commented on the relative 'refractoriness' in general of the bono marrow as compared with liver and spleen with respect to the uptake of colloidal dyes from the blood stream. Some histological data indicate that 'Thorotrast' (a colloidal thorium dioxide preparation) is deposited in the bone marrow as well as in the liver and spleen, but no quantitative data as to the relative distribution are available. In the preceding communication the methods for the preparation of colloids incorporating radioisotopes of yttrium, columbium, and zirconium were given. The present studies are concerned with the localization of such colloids primarily in the bone marrow or primarily in the spleen and liver, with an analysis of some of the factors which may be responsible for differences in localization.
Date: April 21, 1948
Creator: Dobson, E.L.; Gofman, J.W.; Jones, H.B.; Kelly, Lola S. & Walker, L.
Partner: UNT Libraries Government Documents Department


Description: A new rapid separation method for radiostrontium in emergency milk samples was developed at the Savannah River Site (SRS) Environmental Bioassay Laboratory (Aiken, SC, USA) that will allow rapid separation and measurement of Sr-90 within 8 hours. The new method uses calcium phosphate precipitation, nitric acid dissolution of the precipitate to coagulate residual fat/proteins and a rapid strontium separation using Sr Resin (Eichrom Technologies, Darien, IL, USA) with vacuum-assisted flow rates. The method is much faster than previous method that use calcination or cation exchange pretreatment, has excellent chemical recovery, and effectively removes beta interferences. When a 100 ml sample aliquot is used, the method has a detection limit of 0.5 Bq/L, well below generic emergency action levels.
Date: July 17, 2008
Creator: Maxwell, S. & Culligan, B.
Partner: UNT Libraries Government Documents Department