The growth of sparingly soluble salts on polymeric substrates

Modification of Surfaces with Vaterite CaCO3 Particles

Former studies have demonstrated a strong interest toward the crystallization of CaCO3 polymorphs in solution. Nowadays, CaCO3 crystallization on solid surfaces is extensively being studied using biomolecules as substrates for the control of the growth aiming at various applications of CaCO3. Calcium carbonate exists in an amorphous state, as three anhydrous polymorphs (aragonite, calcite and vaterite), and as two hydrated polymorphs (monohydrocalcite and ikaite). The vaterite polymorph is considered as one of the most attractive forms due to its large surface area, biocompatibility, mesoporous nature, and other features. Based on physical or chemical immobilization approaches, vaterite can be grown directly on solid surfaces using various (bio)molecules, including synthetic polymers, biomacromolecules such as proteins and peptides, carbohydrates, fibers, extracellular matrix components, and even biological cells such as bacteria. Herein, the progress on the modification of solid surfaces by vaterite CaCO3 crystals is reviewed, focusing on main findings and the mechanism of vaterite growth initiated by various substances mentioned above, as well as the discussion of the applications of such modified surfaces.

Novel composites materials from functionalized polymers and silver coated titanium oxide capable for calcium phosphate induction, control of orthopedic biofilm infections: an "in vitro" study

Three copolymers containing the functional groups P=O, S=O and C=O were prepared, and upon the introduction in calcium phosphate aqueous solutions at physiological conditions, "in vitro" were induced the precipitation of calcium phosphate crystals. The investigation of the crystal growth process was done at constant supersaturation. It is suggested that the negative end of the above functional groups acts as the active site for nucleation of the inorganic phase. In order to obtain the copolymer further antimicrobial activity, titania (TiO(2)) nanocrystals were incorporated in the polymer matrix after silver coverage by UV radiation. The antimicrobial resistance of the composite material (copolymer-titania/Ag) was tested against Staphylococcus epidermidis (SEM), Staphylococcus aureus (SAM), Candida parapsilosis (CAM) and Pseudomonas aeruginosa (PAM), microorganisms, using cut parts of "pi-plate" that covered with the above mentioned composite. The antimicrobial effect increased as the size of the nanocrystals TiO(2)/Ag decreased, the maximum achieved with the third polymer that contained also quartenary ammonium groups.

The effect of Leucine on the crystal growth of calcium phosphate

Crystallization kinetics of hydroxyapatite, HAP, in the presence of Leucine, a natural amino acid with hydrophobic side groups, were investigated at conditions of sustained supersaturation, 37 degrees C, pH 7.40, ionic strength 0.15 M. In the presence of Leucine, the crystal growth rates of HAP decreased markedly. Tauhis action is due to adsorption and subsequent blocking of the active growth sites onto the surface of the HAP crystals. The kinetic results revealed that a Langmuir-type adsorption isotherm is followed and an affinity constants of k(aff )=20.26 x 10(2) L/mol for HAP crystal surface were calculated. The apparent order of the crystal growth reaction was found to be equal to two, suggesting a surface diffusion controlled mechanism.

Growth of calcium hydroxyapatite (Ca-HAp) on cholesterol and cholestanol crystals from a simulated body fluid: A possible insight into the pathological calcifications associated with atherosclerosis

An experimental study into calcium phosphate (CP) nucleation and growth on cholesterol and cholestanol surfaces from a supersaturated simulated body fluid (SBF) is presented with the overall aim of gaining some fundamental insights into the pathological calcifications associated with atherosclerosis. Soaking of pressed cholesterol disks at physiological temperature in SBF solutions was found to lead to CP nucleation and growth if the disks were surface roughened and if an SBF with concentrations of the calcium and hydrogen phosphate ions at 2.25x physiological concentrations was used. The CP phase deposited was shown via SEM micrographs to possess a florette type morphology akin to that observed in earlier reported studies. The use of recrystallised cholesterol and cholestanol microcrystals as substrates for soaking in SBF facilitated the observation of CP deposition. In general, cholesterol recrystallised from polar solvents like 95% ethanol as a cholesterol monohydrate phase which was a better substrate for CP growth than cholesterol recrystallised from more non-polar solvents (e.g., benzene) which produced anhydrous cholesterol phases. CP was also observed to form on recrystallised cholestanol microcrystals, a molecule closely related to cholesterol. Inductively coupled plasma optical emission spectrometry (ICP-OES) data gave confirmation that Ca:P mole ratios of the grown CP were 1.3-1.5 suggesting a mixed phase of octacalcium phosphate (OCP) and Ca-deficient HAp and that the CP coating grows (with time of soaking) on the substrates after nucleation in the SBF growth medium. Infrared (IR) spectra of the extracted coatings from the cholesterol substrates confirmed that the CP phase deposited is a semi crystalline HAp with either carbonate substituted into its structure or else co-deposited as calcium carbonate. Soaking experiments involving modified cholesterol substrates in which the OH group in the molecule was replaced with the oleiyl or phosphonate group showed no CP nucleation and growth. This observation illustrates the importance of the known epitaxial relationship between cholesterol and HAp (which theoretically predicts favourable deposition of one phase upon the other) and the consequences of its destruction (by chemical modification of the cholesterol). In the case of the phosphorylated cholesterol, failure of this substrate to nucleate CP phases may have also been caused by the reduction in concentration of free solution Ca2+ in the SBF medium by complexation with the phosphonate groups on the phosphorylated cholesterol. This would have reduced the ion product of Ca2+ and inorganic phosphate and lowered the degree of supersaturation in the SBF medium.

Water-soluble terpolymer-mediated calcium carbonate crystal modification

The structure of the polymeric substrate plays an important role in the nucleation of calcium carbonate crystals. In this study a synthetic water-soluble poly(acrylamide-co-2-acrylamido-2-methyl-1-propane sodium sufonate-co-n-vinyl pyrrolidone) was found to be a substrate favoring the nucleation of polymorphs of calcium carbonate crystals under specific experimental conditions. Morphological characterization of the polymorphs was done using atomic force microscopy, scanning electron microscopy, energy dispersive spectroscopy, FTIR analysis, and X-ray diffraction. If calcium carbonate is precipitated in the presence of terpolymer, a remarkable increase in nucleation density (number of crystals per unit area) was observed. Stacked crystals of rhombohedral morphology that formed may be due to the presence of sodium sulfonate groups on the terpolymer. However, in the presence of poly-L-aspartic acid, almost all crystals are hollow and have needlelike or plate like morphology was formed. This change in calcium carbonate morphology can be explained by the variation of the polymer conformation, if poly- L-aspartic acid is present.