Investigation of formation processes of porous biocompatible materials based on silicon doped and undoped α-calcium-phosphate and hydroxyapatite

Poslednjih nekoliko decenija, velika pažnja usmerena je na razvoj biomaterijala koji bi imali potencijal da reparišu ili zamene oštećenenih delova koštanog tkiva, pospeše funkcionisanje postojećeg ili ubrzaju stvaranje novog tkiva. Klinička primenana biomaterijala zavisi pre svega od fizičkih i hemijskih svojstava materijala. U savremene sintetičke biomaterijale se ubrajaju ex vivo ćelijama zasejani skafoldi, in vivo resorbilni koštani cementi, prevlake koje pospešuju stvaranje veze između prirodne kosti i implanta, različite forme implantnih proteza i dr. Bioaktivna keramika na bazi kalcijum-fosfata (hidroksiapatit: HA; α-kalcijum-fosfat: α-TCP; β-kalcijum-fosfata; β-(TCP) zauzima značajno mesto zbog strukturne i hemijske sličnosti sa neorganskom komponentom prirodne kosti. Jedno od najvažniji područja inženjerstva koštanog tkiva pretstavlja dizajniranje i procesiranje skafoldnih materijala po strukturi sličim kostima koji bi omogućili vaskularizaciju i urastanje koštanog tkiva. Tokom prve dekade 21. veka velika pažnja je usmerena na razvoj treće generacije bioaktivnih materijala koji bi stimulisali specifičan ćelijski odgovor. Značajnu grupa biomaterija čine materijali na bazi bioaktivnog stakla koji otpuštanjem jona u rastvoru stimulišu faktore rasta koji na kontrolisan način aktiviraju ćelijske funkcije. Cilj ove teze pretstavlja razvoj skafolda na bazi silicijumom dopiranih α-kalcijum-fosfata i hidroksiapatita za supstituciju i reparaciju koštanog tkiva koji bi kontrolisanim otpuštanjem jona silicijuma i kalcijuma i fosfatnih jona povoljno uticali na adheziju i diferencijaciju ćelija i gensku ekspresiju. U tom cilju sa procesiranje skafolda hidrotermalnim postupkom sintetisane su nedopirane i silicijumom dopirane čestice HA različite morfologije (sferne i vlaknaste). Kao polazna jedinjenja za sintezu stehiometrijskog hidroksiapatita (Ca/P = 1,67) i hidroksiapatita sa odnosom Ca/P = 1,50 korišćeni su Ca(NO3)2•4H2O, (NH4)2HPO4•2H2O, Na2EDTA (poslednje jedinjenje je korišćeno za sintezu sfernih čestica) i urea. Silicijumom dopirani hidroksiapatiti su sintetisani za odnos Ca/P = 1,50 korišćenjem tetraetil-ortosilikata (TEOS) kao izvora silicijumovih jona. Dopiranje silicijumom pri odnosu Ca/P = 1,50 je izvšeno u cilju favorizovanja formiranja silicijumom stabilisanog α-TCP i poboljšanja bioaktivnih svojstava u odnosu na stehiometrijski hidroksiapatit. Uticaj stepena supstitucije silicijumom na morfologiju, faznu transformaciju i bioaktivnost sintetisanih sfernih i vlaknastih čestica, kao i skafolda dobijenih od nedopiranih i silicijumom dopiranih čestica analiziran je rendgenskom difrakcijom (XRD), skenirajućom elektronskom mikroskopijom (SEM), transmisionom elektronskom mikroskopijom (TEM), visokorezolucionom transmisionom elektronskom mikroskopijom (HRTEM), energetskom disperzionom rendgenskom fluorescentnom spektroskopijom (EDXRF), infracrvenom spektroskopijom (IC) i u in vitro testovima u kulturi SaOs2, L929 i MRC-5 ćelija. XRD i EDXRF analiza je pokazala različiti nivo supstitucije silicijumom pri istim uslovima sinteze na sfernim i vlaknastim česticama. Takođe, utvrđeno je da dopiranje silicijumom dovodi do snižavanja temperature fazne transformacije HA u α-TCP. Ovaj efekat je izraženiji kod silicijumom dopiranih čestica HA sferne morfologije...During recent decades, a great attention has been focused on research and development of biomaterials that are exploited to replace missing body structures, to enhance functions of existing ones or promote the new tissue formation. The clinical success outcome of biomaterial used in tissue engineering applications depends critically upon physical and chemical properties of tested materials. The synthetic materials, capable of supporting the natural process of bone re-modeling, include the ex vivo generation of cell-scaffold complexes, in vivo resorbable bone cements, coatings that enhance the bonding between natural bone and implant, various forms of implantable prostheses, bone-repair agents etc. Synthetic bioactive ceramics such as certain forms of calcium-phosphate (hydroxyapatite: HA; α-tricalcium phosphate: α-TCP; β-tricalcium phosphate: β-TCP) and combinations of them have been widely studied due to their structural and chemical similarity with the inorganic components of natural bone. One of the most important stages of bone tissue engineering is to design and process scaffold materials aiming to, as high as possible, the in-growth of blood vessels, and to guide the growth of bone in a natural manner mimicking the structure of human compact bone. During the first decade of the twenty-first century third-generation of biomaterials has been designed to stimulate specific cellular responses at the level of molecular biology. Certain formulations of bioactive materials such as bioactive glasses release chemicals in the form of ionic dissolution products, or governing macromolecular growth factors, which at controlled rates, activate the cell functions. The goal of the thesis was to develop three-dimensional scaffolds based on silicon doped HA/α-TCP specifically designed for application in bone tissue engineering where, through controlled release rate of Si, Ca and P, one assure optimal influence at the biological response of material and invoke enhanced cell adhesion, differentiation and gene expression. Therefore, for scaffolds preparations silicon doped and un-doped HA particles were synthesized having different morphologies (spherical and whisker-like) using hydrothermal method. Appropriate quantities of the reactants Ca(NO3)2•4H2O, (NH4)2HPO4•2H2O, Na2EDTA (the last one being used for synthesis of spherical-like particles) and urea were used to prepare stoichiometric hydroxyapatite (Ca/P = 1.67) and hydroxyapatite of Ca/P molar ratio that approaches 1.50. The silicon-substituted apatites were prepared using a Ca/P molar ratio approaching 1.50 by adding two different quantities of tetraethyl orthosilicate (TEOS) as the source of silicon ions. Lower Ca/P ratio and doping with silicon were used in order to enhance formation of silicon-stabilized α-TCP and improve the bioactivity when compared to pure hydroxyapatite. The influence of silicon substitution level in spherical-and whisker-like particles on the morphology, phase transformations and bioactivity of the obtained powders and scaffolds based on these particles was investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive x-ray fluorescence spectroscopy (EDXRF), Fourier transform infrared (FTIR) spectroscopy and in in vitro test performed on SaOs2, L929 and MRC-5 cells. The investigations showed different degree of silicon substitution under the same synthesis conditions on spherical- and whisker-like particles revealed by XRD and EDXRF analyses, where higher content of added silicon enhanced phase transformation from HA to a-TCP at lower temperatures. These transformations are more pronounced on spherical particles..

Comparative analysis of the polarization and morphological characteristics of electrochemically produced powder forms of the intermediate metals

The polarization and morphological characteristics of powder forms of the group of the intermediate metals were examined by the analysis of silver and copper electrodeposition processes at high overpotentials. The pine-like dendrites constructed from the corncob-like forms, which are very similar to each other, were obtained by electrodeposition of these metals at the overpotential belonging to the plateaus of the limiting diffusion current density. A completely different situation was observed by the electrodeposition of silver and copper at the overpotential outside the plateaus of the limiting diffusion current density in the zone with the fast increase in current density with the overpotential. Silver dendrites, which were very similar to silver and copper dendrites obtained inside the plateaus of the limiting diffusion current density, were obtained at the overpotential outside the plateau. Due to the lower overpotential for hydrogen evolution for copper, hydrogen produced during the copper electrodeposition process strongly affected the surface morphology of copper. The same shape polarization curves with completely different surface morphologies of Cu and Ag electrodeposited at overpotentials after the inflection point clearly indicate the importance of morphological analysis in the investigation of polarization characteristics of the electrodeposition systems. The role of hydrogen as a crucial parameter in the continuous change of copper surface morphology from dendrites to honeycomb-like structures was investigated in detail. On the basis of this analysis, the transitional character of the intermediate metals between the normal and inert metals was considered. The typical powder forms characterising electrodeposition of the intermediate metals were also defined and systematized

Porcelain veneers - preparation design: A retrospective review

This paper discusses the preparation of tooth design for porcelain veneers. It follows the literature more than three decades back in the past. From the very beginning, porcelain veneers were placed to no/minimally prepared tooth substance, showing different problems in clinical use. Later, the technique of etching the porcelain and controlling the reduction of tooth structure, presented the great steps forward in porcelain veneers accepting. A special accent concerning the preparative design was placed on variations of incisal edge preparation - the problem, which is still present in current practice. Additionally, the paper emphasizes the extremely demanding protocols in making the porcelain veneers as well as their expanded clinical indications

Morphology transformation induced by calcination: from titania nanotubes to nanoparticles

Titanium dioxide nanotubes (TNT) synthesized via hydrothermal method and calcined at various temperatures, from 200-800 °C are characterized using X-ray diffraction (XRD), UV/Vis spectroscopy and scanning electron microscopy (FESEM). Tubular structure of as prepared TNT was most probably lost after calcination at 200 °C. Elongated forms of titania with different aspect ratios were observed after calcination at all temperatures lower than 800 °C. Calcination at 800 °C induced complete transformation of TNT to nanoparticles. Shape transformation was accompanied with changes in degree of crystallinity and different anatase to rutile crystal phase ratio

Synthesis and structural properties of F-doped LiFePO4/C composite

Olivine type LiFePO4 is used as a cathode material for Li-ion batteries because of its high energy density (with capacity of 170 mAh/g and plateau voltage of 3.5 V vs. Li+ /Li), stability, safety, environmental friendliness and low cost. However, the low intrinsic electronic and ionic conductivity limits its application.Physical chemistry 2012 : 11th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 201

Supplementary data for the article: Izrael Živković, L. T.; Živković, L. S.; Beškoski, V. P.; Gopčević, K. R.; Jokić, B. M.; Radosavljević, D. S.; Karadžić, I. M. The Candida Rugosa Lipase Adsorbed onto Titania as Nano Biocatalyst with Improved Thermostability and Reuse Potential in Aqueous and Organic Media. Journal of Molecular Catalysis B: Enzymatic 2016, 133, S533–S542. https://doi.org/10.1016/j.molcatb.2017.06.001

Supplementary material for: [https://doi.org/10.1016/j.molcatb.2017.06.001]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/315]Related to accepted version: [http://cherry.chem.bg.ac.rs/handle/123456789/3648

Uticaj samodopovanja na elektrohemijsku sintezu i svojstva polianilina

Electrochemical synthesis was used to polymerize aniline and copolymerize aniline and m-aminobenzoic from aqueous acidic electrolyte containing aniline and aniline with different amount of m-aminobenzoic acid. These materials were obtained galvanostatically at graphite electrode at current density of 1.0 mA cm-2 from aqueous electrolyte containing 1.0 mol dm-3 HCl and different amount of monomers. The effect of self-doping due to meta positioned carboxylic group was observed in both synthesis parameters, morphology, degree of oxidation and electrochemical behaviour. The presence of m-aminobenzoic acid led higher copolymerization increasing with the increase of amount of m-aminobenzoic acid if comparing to polymerization potential of aniline. Moreover, the copolymer with equal amount of aniline/m-aminobenzoic acid showed electrochemical activity in neutral electrolyte which might be due to possibility of proton exchange process which can be expelled from the copolymer during oxidation process together by insertion of anions, making this material promising for use in electrochemical biosensors.Elektrohemijski postupak korišćen je za polimerizaciju anilina i kopolimerizaciju anilina i m-aminobenzoeve kiseline iz kiselog vodenog rastvora elektrolita sa različitim molskim odnosima anilina i m-aminobezoeve kiseline. Ovi materijali dobijeni su uslovima konstantne gustine struje od 1,0 mA cm-2 iz kiselog vodenog elektrolita koji je sadržavao 1,0 mol dm-3 HCl, anilin i m-aminobenzoevu kiselinu. Uticaj samo-dopovanja koji je posledica prisustva karboskilne grupe u meta položaju ispoljavao se u različitim parametrima sinteze, morfologiji dobijenih materijala, stepenu oksidacije i elektrohemijskom ponašanju. Prisustvo m-aminobenzoeve kiseline uslovilo je veći potencijal sinteze kopolimera u odnosu na polianilin koji je rastao sa porastom udela m-aminobezoeve kiseline. Kopolimer koji je dobijen iz elektrolita sa jednakim molskim odnosom anilina i m-aminobenzoeve kiseline pokazao je elektrohemijsku aktivnost u neutralnom elektrolitu koja može biti posledica razmene protona što ovaj materijal čini perspektivnim za praktičnu primenu u elektrohemijskim biosenzorima

Properties of Zig-Zag Nickel Nanostructures Obtained by GLAD Technique

Zig-zag structure of the nickel thin film has been obtained using Glancing Angle Deposition (GLAD) technique. Glass substrate was positioned 75 degrees with respect to the substrate normal. The obtained nickel thin film was characterized by X-ray Photoelectron Spectroscopy, Scanning Electron Microscopy and Atomic Force Microscopy. Surface energy of the deposited thin film was determined by measuring the contact angle using the static sessile drop method

Comparative analysis of the polarization and morphological characteristics of electrochemically produced powder forms of the intermediate metals

The polarization and morphological characteristics of powder forms of the group of the intermediate metals were examined by the analysis of silver and copper electrodeposition processes at high overpotentials. The pine-like dendrites constructed from the corncob-like forms, which are very similar to each other, were obtained by electrodeposition of these metals at the overpotential belonging to the plateaus of the limiting diffusion current density. A completely different situation was observed by the electrodeposition of silver and copper at the overpotential outside the plateaus of the limiting diffusion current density in the zone with the fast increase in current density with the overpotential. Silver dendrites, which were very similar to silver and copper dendrites obtained inside the plateaus of the limiting diffusion current density, were obtained at the overpotential outside the plateau. Due to the lower overpotential for hydrogen evolution for copper, hydrogen produced during the copper electrodeposition process strongly affected the surface morphology of copper. The same shape polarization curves with completely different surface morphologies of Cu and Ag electrodeposited at overpotentials after the inflection point clearly indicate the importance of morphological analysis in the investigation of polarization characteristics of the electrodeposition systems. The role of hydrogen as a crucial parameter in the continuous change of copper surface morphology from dendrites to honeycomb-like structures was investigated in detail. On the basis of this analysis, the transitional character of the intermediate metals between the normal and inert metals was considered. The typical powder forms characterising electrodeposition of the intermediate metals were also defined and systematized

The Li2FeSiO4 / c composites obtained from cellulose gel

In this study, monoclinic polymorph of Li2FeSiO4 (space group P21/n) in composite with carbon has been synthesized by sol-gel method followed by rapid heating, short high-temperature delay, and subsequent quenching. Three composites were made with 3, 9 and 14 weight percent of the carbon. The effect of the carbon on structure, morphology and electrochemical performance of the prepared composites has been examined by X-ray diffractometry, scanning electron microscopy and galvanostatic cycling