Synthesis, characterization and degradation of poly(DL-lactide-co-glycolide) nanospheres containing ascorbic acid

Askorbinska kiselina (vitamin C) je izuzetno važan i organizmu neophodan vitamin. Ima ulogu reduktanta slobodnih radikala čime smanjuje oštećenja nastala oksidativnim stresom koji je uzrok ili pratilac mnogih bolesti. U organizmu se ne skladišti i vrlo brzo se iz njega izlučuje. Problem se sastoji u tome da se askorbinska kiselina lako dekonponuje u biološki neaktivna jedinjenja čime je upotreba askorbinske kiseline na polju medicine, farmakologije, kozmetologije veoma limitirana. Kopolimer poli(DL-laktid-ko-glikolid) (DLPLG ) se, pored ostalog, koristi za izradu sistema za kontrolisanu dostavu najrazličitijih klasa medikamenata. Pod medikamentima se podrazumevaju lekovi i druga terapeutska sredstva. Polimerne čestice DLPLG-a dozvoljavaju inkapsulaciju medikamenata unutar polimerne matrice a za njihovo kontrolisano i ravnomerno otpuštanje unutar organizma osnovni je zahtev idealna sferičnost čestica kao i uska raspodela njihovih veličina. Inkapsulacijom askorbinske kiseline u polimernu matricu poli(DL-laktid-ko-glikolida) (DLPLG) bilo bi potencijalno moguće prevazići hemijsku nestabilnost vitamina C kao i postići njegovu višu, efikasniju i ravnomerniju raspodelu u organizmu, tokom dužeg perioda vremena. U ovoj disertaciji je opisano dobijanje poli(DL-laktid-ko-glikolid) nanosfera korišćenjem fizičkohemijske metode rastvarač/nerastvarač i tehnike centrifugalnog procesiranja. Ispitan je uticaj različitih stabilizatora (polivinil alkohola, polivinil pirolidona) na morfološke karakteristike čestica DLPLG-a sa i bez inkapsulirane askorbinske kiseline. U polimernu matricu DLPLG-a su inkapsulirane različite koncentracije askorbinske kiseline homogenizacijom vodene i organske faze. Nanočestice DLPLG-a sa različitim sadržajem askorbinske kiseline imaju različite morfološke karakteristike, različit stepen uniformnosti, sferičnosti, aglomeracije kao i različite veličine. Izračunat je prinos čestica DLPLG-a sa i bez vitamina kao i efikasnost inkapsulacije vitamina u polimernu matricu DLPLG-a. Proces degradacije čestica DLPLG-a bez i sa askorbinskom kiselinom kao i otpuštanje askorbinske kiseline iz polimerne matrice DLPLG-a tokom degradacije je ispitivano u in vitro uslovima u različitim degradacionim medijumima (fiziloškom rastvoru i fosfatnom pufer rastvoru uz prisustvo azida). Karakterizacija uzoraka je radjena metodama infracrvene spektroskopije (IR), ultravioletne spektrofotometrije (UV-VIS), diferencijalne skanirajuće kalorimetrije (DSC), skenirajuće elektronske mikroskopije (SEM) a radjena je i detaljna stereološka analiza.Ascorbic acid (vitamin C) is essential for preserving optimal health and it is used by the body for many purposes. Ascorbic acid acts as a reductant for many free radicals, thereby minimising the damage caused by oxidative stress which is a root cause of, or at least associated with, many diseases. Ascorbic acid is water soluble vitamin, which cannot be synthesised and stored in the body.The problem is that ascorbic acid easily decomposes into biologically inactive compounds making its use very limited in the field of pharmaceuticals, dermatologicals and cosmetics. Copolymer poly(DL-lactide-co-glycolide) (DLPLG) is among other things used for the controlled delivery of the various classes of medicaments. Under medicaments we assume drugs and other therapeutically applications. DLPLG polymer particles allow the encapsulation of the medicament within the polymer matrix, where the principle requirement for the controlled and balanced release of the medicament in the body is its ideal spherical shape and narrow particle size distribution. By encapsulating the ascorbic acid into the polymeric matrix it is assumed that its chemical instability can be overcame as well as higher, more efficient and equally distributed concentration throughout extended period of time can be achieved. This disertation is describing the process of obtaining poly(DL-lactide-co-glycolide) (DLPLG) nanospheres using physico-chemical method with solvent/non-solvent systems where obtained solutions have been centrifuged. The influence of the different stabilizers (polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP)) on the morphological characteristics of DLPLG particles with and without ascorbic acid has been examined. The encapsulation of the ascorbic acid in the polymer matrix is performed by homogenization of water and organic phases. Nanoparticles of the copolymer DLPLG with the different content of the ascorbic acid have different morphological characteristics, i.e. variable degree of uniformity, agglomeration, sizes and spherical shaping. The particle yield of DLPLG with and without ascorbic acid has been calculated as well as the loading efficiency of the ascorbic acid into the polymer matrix DLPLG. The degradation of the nanospheres of DLPLG, DLPLG/ascorbic acid nanoparticles and release rate of the ascorbic acid were studied for eight weeks in different degradation medium (physiological solution (0.9% sodium chloride in water) and phosphate buffered saline). The samples have been characterized by Infrared Spectroscopy (IR), Ultraviolet Spectroscopy (UV), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM) and Stereological analysis