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Synthetic calcium phosphate (CaP) ceramics and composites are used for medical application because of their outstanding biological performance. Although they are the subject of intensive research, so far no material has been obtained with the unique properties of human bones and teeth. This work review recent author strategies using simulated body fluid media synthesis to obtain novel biomimetic CaPs, as well as the combination of supramolecular self-assembly using non-ionic block copolymers and sol-gel chemistry of alcoxysilanes, to obtain silica-CaP composites with remarkable textural properties applicable to dentistry and orthopedics

The chemical and structural similarity between calcium orthophosphates and biological apatite makes them suitable biomaterials for orthopedic, reconstructive and maxillofacial surgery. Their bioactivity depends on their chemical and phase composition, as well as on their morphology. The behaviour of amorphous calcium phosphate double-doped with Zn2+ and Mg2+ in artificial saliva was monitored in order to elucidate its potential to be used as a component in new hybrid materials for tooth enamel remineralisation. The effect of the composition of artificial saliva (presence of urea, glucose, ascorbic acid and mucin) on the degree of release of Ca2+, Mg2+ and Zn2+ ions from solid to liquid phase was assessed. The concentrations of ions under study in the liquid and solid phases were determined by FAAS (SOLAAR MkII M5-Thermo Electron Co) and TXRF (S2 PICOFOX 400, Bruker) in the presence of mucin and by ICP-OES (PRODIGY 7, Teledyne Leeman Labs, USA) in its absence. It was found that the presence of organic components and especially mucin (high molecular weight, glycosylated protein) several times increases the solubility of amorphous calcium phosphate, respectively the release of Mg2+ and Zn2+ ions, owing to its ability to form complexes with the studied metals. Most intensive is the process of dissolution in the first 6 hours, during which the saliva is enriched with the studied ions, after which their concentration gradually decreases and reaches a constant value. In the absence of mucin, the crystallization processes of pure low- crystalline calcium hydroxyapatite dominate, as the inorganic part of artificial saliva is oversaturated with respect to it.

Essential requirement to calcium phosphate ceramic powders, as regards their use as fillers for bone defects or as ceramics and cements for orthopedics and dentistry, is their uniformity and nanosize. The present study deals with the biomimetic synthesis of ion-modified calcium phosphates with a view to mimic biomineralization processes and to obtain products with a chemical composition close to that of natural enamel, dentin and bone. The reaction medium was a simulated body fluid (SBFс) buffered with glycine (SBFс/GB). The effect of two modifiers of the medium - glycerin (for the system SBFc/GB-GL) and xanthan gum (for the system SBFc/GB-XG) - on the composition and morphology of the obtained precursors was followed. The modifiers were chosen as to prevent the growth of primary nuclei. Glycerin acts as a lubricant of the particles while xanthan gum forms negatively charged hydrogel chains which could increase the nucleation. The precursor preparation procedure includes the method of continuous precipitation at pH 8 with a Ca/P ratio of 1.67 at a standard temperature, under vigorous stirring. Then the suspensions were matured for 24 h and the difference in the crystallinity and habit of the particles was determined. In the non-modified SBFc/GB system the precipitate remains amorphous with a spherical shape of the particles, while in both cases of modification poorly crystalline apatite with particles being extended along one axis was obtained. After few procedures of washing, gelling and lyophilization the precursors were gradually heated at a temperature of 200, 400, 600, 800 and 1000 °C kept constant for 3 hours on each step. The results show that the biomimetic synthesis allows precipitation of amorphous calcium phosphate (ACP) with a Ca/P ratio of 1.4-1.5 incorporating Mg2+, Na+ , K+ , CO3 2- and Clions at levels close to those of natural enamel, dentin and bone with spherical nanoparticles. The precipitation of ACP instead of the thermodynamically stable hydroxyapatite reveals that kinetic factors were decisive for the precipitation processes. Influence of medium modification on the specific surface area of the obtained precipitates was established. For the precursors precipitated in the non-modified SBFc/GBsystem it was 28 m2 /g. Three to four times higher was the specific surface area of precursors precipitated in modified reaction media - 146 m2 /g and 106 m2 /g for SBFc/GB-GL and SBFc/GB-XG systems, respectively. The distribution of the pore volume corresponds to the measured specific surface area. The obtained results are explained in terms of the shape of the precipitated particles and the specific properties of the modifiers. A specific effect of the two modifiers on the particle distribution by size after hightemperature treatment was established, bi-phase ceramic powders consisting of hydroxyapatite and β-tricalcium phosphate being obtained. In the biomimetically unmodified medium (SBFc/GB-system) the particle size is in the range of 0.1 – 1.8 µm, 70 % of which is between 0.4 – 1 µm with a clearly expressed maximum at 0.6 µm. Narrower ranges of particle size variation are found in the modified reaction media (more than 90% of the particles are with a size between 0.1 and 1.2 µm) and the maxima are shifted toward the lower values. Most uniform by size are the particles obtained in the system SBFc/GB-XG, where 70% of them are in the range of 0.25 - 0.55 µm with a maximum at 0.4 µm. The particles obtained in the system SBFc/GB-GL are characterized with two distribution ranges – 40% of them are between 0.05 – 0.2 µm with a clearly expressed maximum (30%) at 0.15 µm while about 55% are between 0.3 – 1 µm showing no maximum but a broad plateau between 0.5 – 0.75 µm

The preparation of synthetic calcium orthophosphates with different composition and nanometric dimensions is of continuous scientific interest due to their chemical and structural similarity to "biological apatite" which makes them suitable for the development of biomaterials for bone regeneration and reconstruction. Despite the large number of scientific studies, it is still a challenge to create one- and / or two-phase calcium phosphate materials, at the same time biocompatible, bioactive and bioresorbable.The aim of the thesis is to investigate the processes of synthesis of ion-modified calcium orthophosphates in the electrolyte medium of a simulated body fluid, as well as their subsequent low- and high-temperature phase transformations to obtain fine powders. It has been thermodynamically predicted and experimentally proven that metastable calcium and magnesium compounds are co-precipitated and recrystallized in the electrolyte medium of a simulated body fluid. It has been shown that amorphous calcium phosphate precipitates at pH 8 and Ca/P = 1.67 while dicalcium phosphate dihydrate precipitates at pH 6 and Ca/P = 1. The dissolution / complexation / crystallization / co-crystallization processes which are taking place determine their transformation into a poorly crystalline bonelike carbonate apatite. The rate of this transformation depends on the type of precursor and on the composition of the simulated body fluid. The conditions for obtaining one- and two-phase calcium, Получаването на синтетични калциеви ортофосфати с различен състав и нанометрични размери са обект на непрекъснат научен интерес поради тяхното химично и структурно сходство с "биологичния апатит", което ги прави подходящи за разработването на биоматериали за костна регенерация и реконструкция. Въпреки големият брой научни изследвания все още предизвикателство е създаването на едно- и/или двуфазни калциевофосфатни материали, едновременно биосъвместими, биоактивни и биорезорбируеми. Цел на дисертационния труд е изследване процесите на синтез на йонномодифицирани калциеви ортофосфати в електролитна среда на симулирана тъкана течност, както и на последващите им ниско и високотемпературни фазови трансформации за получаване на фини прахове. Термодинамично е прогнозирано и експериментално е доказано, че метастабилни калциеви и магнезиеви съединения се съутаяват и рекристализират в електролитна среда на симулирана тъканна течност. Доказано е, че аморфен калциев фосфат се утаява при рН 8 и Са/Р=1.67, а дикалциев фосфат дихидрат при рН 6 и Са/Р=1. Протичането на процеси на разтваряне/комплексообразуване/ кристализация/съкристализация определят тяхтото превръщане в слабо кристален костоподобен карбонат апатит. Скоростта на тази трансформация зависи от вида на прекурсора и от състава на симулираната тъканна течност. Установени са условия за получаване на монофазни и двуфазни калциеви ортофосфати с йонни включвания близки до тези на костната тъкан, както и с повишено съдържание на биол