Search results for "VATER"
showing 10 items of 56 documents
Risk factors for extrahepatic biliary tract carcinoma in men: medical conditions and lifestyle: results from a European multicentre case-control stud…
2007
OBJECTIVES: To identify risk factors of carcinoma of the extrahepatic biliary tract in men. METHODS: Newly diagnosed and histologically confirmed patients, 35-70 years old, were interviewed between 1995 and 1997 in Denmark, Sweden, France, Germany and Italy. Population controls were frequency-matched by age and region. Adjusted odds ratios and 95%-confidence intervals were estimated by logistic regression. RESULTS: The analysis included 153 patients and 1421 controls. The participation proportion was 71% for patients and 61% for controls. Gallstone disease was corroborated as a risk factor for extrahepatic biliary tract carcinoma in men (odds ratio 2.49; 95% confidence interval 1.32-4.70), …
STRUCTURAL FEATURES AND MECHANICAL PROPERTIES OF PLLA/PEARL POWDER SCAFFOLDS
2013
In order to improve the mechanical properties of scaffolds for bone tissue engineering, the present study aims to bring calcium carbonate (CaCO3) with signaling molecules, namely pearl powder, into poly(L-lactic acid) (PLLA). PLLA/aragonite and PLLA/vaterite scaffolds were successfully fabricated by the freeze-drying method. Both composite scaffolds had a similar porous structure but a different saturated content of pearl powders. For both scaffolds, the porosity decreases and yield strength increases as pearl powder content increases. Introducing pearl powders into PLLA can improve the mechanical properties of the scaffolds. The porous structure plays a crucial role in the yield strength …
Biocalcite, a multifunctional inorganic polymer: Building block for calcareous sponge spicules and bioseed for the synthesis of calcium phosphate-bas…
2014
Calcium carbonate is the material that builds up the spicules of the calcareous sponges. Recent results revealed that the calcium carbonate/biocalcite-based spicular skeleton of these animals is formed through an enzymatic mechanism, such as the skeleton of the siliceous sponges, evolutionarily the oldest animals that consist of biosilica. The enzyme that mediates the calcium carbonate deposition has been identified as a carbonic anhydrase (CA) and has been cloned from the calcareous sponge species Sycon raphanus. Calcium carbonate deposits are also found in vertebrate bones besides the main constituent, calcium phosphate/hydroxyapatite (HA). Evidence has been presented that during the init…
Crystallization of Vaterite Nanowires by the Cooperative Interaction of Tailor-Made Nucleation Surfaces and Polyelectrolytes
2005
The concepts of template-induced crystallization on self-assembled monolayers (SAMs) and the use of polymer additives are combined into a new strategy, where, through the cooperative interaction of a SAM matrix involved in the nucleation process, poly(acrylic acid), a dissolved polyelectrolyte, and the dissolved ions, hierarchically ordered mineral structures are formed. The adsorption of poly(acrylic acid) to the SAM is monitored using a quartz microbalance. Transmission electron microscopy measurements on samples that are taken from polyacrylate solution in short intervals after the start of the reaction reveals that nanometer-sized particles pre-formed in solution are being attached to t…
Transformation of vaterite nanoparticles to hydroxycarbonate apatite in a hydrogel scaffold: relevance to bone formation.
2020
Biomimetic materials have been gaining increasing importance for use as bone biomaterials, because they may provide regenerative alternatives for the use of autologous tissues for bone regeneration. We demonstrate a promising alternative for the use of biomimetic materials based on a biodegradable PEG hydrogel loaded with vaterite nanoparticles as mineral storage. Vaterite, the least stable CaCO3 polymorph, is stable enough to ensure the presence of a potential ion buffer for bone regeneration, but still has sufficient reactivity for the transformation from CaCO3 to hydroxyapatite (HA). A combination of powder X-ray diffraction (PXRD), electron microscopy, and Fourier-transform infrared (FT…
Nanostructure, composition and mechanisms of bivalve shell growth
2008
Abstract Freshwater and marine cultured pearls form via identical processes to the shells of bivalves and can therefore serve as models for the biomineralization of bivalve shells in general. Their nanostructure consists of membrane-coated granules (vesicles) which contain amorphous calcium carbonate (ACC) at the beginning of the biomineralization sequence, preceding the crystallization of aragonite and vaterite. In contrast to the commonly accepted view, crystallization of ACC occurs rapidly and within the granular nano-compartments mediated by organic molecules much earlier than platelet formation. The interlamellar organic sheets in nacre that form the platelet structure of nacre themsel…
Kvaternizēto amonija sāļu noteikšana šķīdumos pēc organomālu apstrādes
2017
Kvaternizēto amonija sāļu noteikšana šķīdumos pēc organomālu apstrādes. Pāls M., zinātniskais vadītājs Dr. ķīm. Nakurte I., Bakalaura darbs, 33 lappuses, 17 attēli, 8 tabulas, 24 literatūras avoti. Latviešu valodā. Literatūras apskatā apkopota informācija par organomāliem un to īpašībām, kā arī organomālu iegūšanas metodēm un to iespējamo pielietojumu. Aprakstīta kvaternizēto amonija sāļu ietekme uz vidi un to noteikšanas metodes. Bakalaura darba praktiskajā daļā veikta AEŠH-MS metodes pielāgošana, lai analizētu kvaternizēto amonija sāļu koncentrāciju dažādos organomālu un organomālus saturošu materiālu skalojumos. Noteikta kvaternizēto amonija sāļu toksicitāte, izmantojot akūtas toksicitāt…
Ar sālsskābi aktivētu Baltijas triasa mālu organofilizācija
2016
Ar sālsskābi aktivētu Baltijas triasa mālu organofilizācija. Ivanova K., zinātniskais vadītājs Dr. ķīm. asoc. prof. Actiņš A., konsultante Mg. ķīm. Karasa J. Maģistra darbs fizikālajā ķīmijā. 57 lappuses, 25 attēli, 16 tabulas, 45 literatūras avoti, 4 pielikumi. Latviešu valodā. Darbā ir veikta Baltijas reģiona triasa smektīta mālu attīrīšana (vienlaicīgi atdzelžošana), izmantojot dažādas koncentrācijas sālsskābes/ūdens/acetona šķīdumus. Kopumā ir izmēģinātas 11 dažādas “atdzelžošanas reaģenta” kombinācijas (variēti gan sālsskābes koncentrācijas, gan mālu skalošanas šķidrums). Visiem attīrītajiem (atdzelžotajiem) mālu paraugiem ir noteiktas sorbcijas kapacitātes vērtības ar klasisko metilēn…
Are morphology and composition of gallstones related? An x-ray diffraction study
1994
Abstract An x-ray diffractometric technique was used to study the crystalline composition of gallstones removed during surgery from 106 patients. Monohydrate cholesterol was found in the stones of 70 (66%) patients, either alone (33%) or in association with calcium salts (33%). The anhydrous form of cholesterol was found in the stones of 28 (26%) patients, either alone (10%) or in association with calcium salts (16%). These salts (vaterite, aragonite, and calcite) were found in 50% of cases in varying amounts (from 12% to 15% of the stone weight). Eight stones contained no cholesterol: 4 showed an amorphous pattern and 4 were composed of calcium carbonate salts. In 7 of 8 patients with bile…
Nucleation and Growth of CaCO3 Mediated by the Egg-White Protein Ovalbumin: A Time-Resolved in situ Study Using Small-Angle Neutron Scattering
2008
Mineralization of calcium carbonate in aqueous solutions starting from its initiation was studied by time-resolved small-angle neutron scattering (SANS). SANS revealed that homogeneous crystallization of CaCO 3 involves an initial formation of thin plate-shaped nuclei which subsequently reassemble to 3-dimensional particles, first of fractal and finally of compact structure. The presence of the egg-white protein ovalbumin leads to a different progression of mineralization through several stages; the first step represents amorphous CaCO 3, whereas the other phases are crystalline. The formation and dissolution of the amorphous phase is accompanied by Ca (2+)-mediated unfolding and cross-link…