Proučavanje procesa formiranja poroznih biokompatibilnih materijala na bazi nedopiranih i silicijumom dopiranih αkalcijum-fosfata i hidroksiapatita

Abstract

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...