Ventsislava Georgieva

Photoactive chitosan switching on bone-like apatite deposition.

The work was focused on the synthesis and characterization of the chitosan-g-fluorescein (CHFL) conjugate polymer as a biocompatible amphiphilic water-soluble photosensitizer, able to stimulate hydroxyapatite deposition upon visible light irradiation. Fluorescein (FL) grafting to chitosan (CH) chains was confirmed by UV-vis analysis of water solutions of FL and CHFL and by Fourier transform infrared spectroscopy (FTIR-ATR) analysis of CHFL and CH. Smooth CHFL cast films with 4 microm thickness were obtained by solvent casting. Continuous exposure to visible light for 7 days was found to activate the deposition of calcium phosphate crystals from a conventional simulated body fluid (SBF 1.0x) on the surface of CHFL cast films. EDX and FTIR-ATR analyses confirmed the apatite nature of the deposited calcium phosphate crystals. CHFL films preincubated in SBF (1.0x) solution under visible light irradiation and in the dark for 7 days were found to support the in vitro adhesion and proliferation of MG63 osteoblast-like cells (MTT viability test; 1-3 days culture time). On the other hand, the mineralization ability of MG63 osteoblast-like cells was significantly improved on CHFL films preincubated under visible light exposure (alkaline phosphatase activity (ALP) test for 1, 3, 7, and 14 days). The use of photoactive biocompatible conjugate polymer, such as CHFL, may lead to new therapeutic options in the field of bone/dental repair, exploiting the photoexcitation mechanism as a tool for biomineralization.

Temperature‐sensitive polyzwitterionic gels

An abrupt change in the polyzwitterionic swelling ratio as a function of the temperature, sodium chloride concentration and chemical crosslinking density is established. These results are reasonably explained by the model presuming zwitterionic cluster formation in the segments between the chemical junction points. The zwitter-ionic clusters, produced at low chemical crosslinking density only, act as temperature- and salt concentration-dependent physical junction points. An irreversible temperature-stimulated swelling-shrinking behaviour of the polyzwitter-ionic hydrogels (swelling ratio-temperature hysteresis loop) at low chemical cross-linking density is also observed and analysed.

Synthesis and application of vinylpyridine containing ion‐imprinted copolymer gel microbeads for Cu(II) solid‐phase extraction

The influence of polymer matrix on the extraction efficiency for Cu(II) and selectivity against metal ions such as Ni(II), Cd(II), Pb(II) of Cu(II) imprinted copolymer gels was described. The functional monomers investigated include the weakly basic 4-vinylpyridine (4-VP) and its mixure with the acidic and hydrogen binding methacrylic acid. Copolymer gels were prepared by dispersion cross-linking copolymerization using Cu(II)-4-(2-pyridylazo)resorcinol complex, Cu(II), or 4-(2-pyridylazo)resorcinol as templates. The chemical structure and morphology of the Cu(II)-imprinted microbeads are defined using elemental analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. Extraction efficiencies of newly synthesized sorbents were studied by batch procedure. The prepared copolymer gel with 4-VP as monomer and Cu(II)-4-(2-pyridylazo)resorcinol complex has higher capacity and selectivity toward Cu(II) than the copolymer gels prepared using the mixture of methacrylic acid and 4-VP. This new sorbent can be used as an effective SPE material for the highly selective preconcentration and separation of Cu(II) in sea water samples. It shows high mechanical and chemical stability.

Indomethacin Nanoparticles for Applications in Liquid Ocular Formulations / Наночастицы С Индометацином Для Применения В Жидких Лекарственных Формах Для Глаз

Abstract Studies in recent years have consistently shown that polymeric drug nanocarriers can be used in drug release and drug delivery systems to treat eye disorders. To achieve effective control over drug delivery, it is of crucial importance what kind of polymer and which method for drug inclusion in the nanoscale carrier we choose and what conditions are needed for the performance of this process. OBJECTIVE: The aim of this study was to produce poly(vinyl acetate) nanoparticles with indomethacin incorporated in them, assess the effect of time for dialysis of the residual monomer and initiator on the degree of incorporation of indomethacin in the nanoparticles and on the kinetics of its release, to include them in ophtalmic formulations. MATERIALS AND METHODS: Poly(vinyl acetate) nanoparticles with indomethacin were obtained by emulsion radical polymerization of vinyl acetate in the presence of indomethacin (in situ inclusion) and the absence of emulsifier. To release the residual monomer and initiator (ammonium persulfate) the obtained latexes were dialysed for 6, 9, 18 and 23 hours and then the nanoparticles were freeze-dried. Structural analysis was performed by transmission electronic microscopy, infrared spectroscopy, differential thermal analysis and thermogravimetry. Release of indomethacin was observed using ultraviolet spectroscopy. RESULTS: We proved the delayed release of indomethacin from the poly(vinyl acetate) nanocarrier and the lack of chemical interaction between the polymer and indomethacin. After 9-hour dialysis the initiator and the residual vinyl acetate were removed from the nanoparticles, while the entrapped indomethacin kept therapeutic concentrations. CONCLUSIONS: Dialysis for more than 6 and no more than 9 hours is recommended to remove the residual monomer and initiator when preparing indomethacin nanoparticles by in situ radical emulsion polymerization of vinyl acetate, for inclusion in liquid ocular formulations. Резюме ВВЕДЕНИЕ: Проведенные в последние годы исследо- вания показывают, что полимерные наноносители лекарственных веществ могут быть использованы как лекарство-освобождающие и лекарство-достав- ляющие системы при терапии глазных болезней. Выбор полимера и метода включения лекарственного вещества в наноразмерный полимерный носитель как и условия проведения этого процесса имеют решающее значение для эффективного контроля доставки и освобождения лекарственного вещества. ЦЕЛЬ: Настоящая работа ставит себе целью получить поливинилацетатные наночастицы с вклю- ченным в них индометацином и оценить влияние времени для диализа непрореагировавших мономера и инициатора на степень включения индометацина в наночастицы и на кинетику освобождения индо- метацина из них. МАТЕРИАЛ И МЕТОДЫ: Поливинилацетатные на- ночастицы с индометацином получены по методу эмульсионной радикальной полимеризации вини- лацетата в присутствии индометацина (in situ включение) и отсутствии эмульгатора. С целью освобождения от непрореагировавших мономера и инициатора (аммониевый персульфат) полученные латексы подвергнуты диализу в течение 6, 9, 18 и 23 ч., после чего наночастицы лиофилизируют- ся. Их структурный анализ проведен посредством использования трансмиссионной электронной микро- скопии, дифференциальной сканирующей калометрии и инфракрасной спектроскопии. Освобождение индометацина прослежено с помощью ультрафи- олетовой спектроскопии. РЕЗУЛЬТАТЫ: Доказаны замедленное освобождение индометацина из поливинилацетатного наноноси- теля и отсутствие химического взаимодействия между полимером и индометацином. Через 9 ч. диализа инициатор и непрореагировавший винила- цетат отсутствуют в наночастицах, в то время как содержание индометацина в них позволяет достижение терапевтических концентраций. ВЫВОДЫ: Диализ в течение 6 - 9 ч. с целью очищения от непрореагировавших мономера и ини- циатора рекомендуется для получения наночастиц с индометацином через in situ - эмульсионную ра- дикальную полимеризацию винилацетата

Chaperone-Like Effect of Polyzwitterions on the Interaction of C1q with IgG

The amphiphilic polyzwitterion (PZ) poly(ethylene oxide-b-N,N-dimethyl(methacryloyloxyethyl) ammonium propanesulfonate), zwitterionic surfactant (ZS) n-dodecyl- N,N-dimethyl-3-ammonium-1-propanesulfonate, and zwitterionic monomer (ZM) N,Ndimethyl( methacryloyloxyethyl)ammonium propanesulfonate were analyzed for their suggested chaperone-like effect on the interaction of C1q and IgG. Our results proved that the PZ retarded the C1q interaction with IgG, demonstrating a specific protein-folding helper effect. The ZS enhanced this interaction, when the ZS concentration was lower than the critical micelle concentration (CMC), and retarded it, when the ZS concentration was above the CMC. The ZM, with no self-assembling ability, did not influence this interaction. These results support the hypothesis of a hydrophobic interaction between Pts and hydrophobic domains of partly denatured protein molecules. The amphiphilic self-assemblies, formed by polyzwitterionic macromolecules or zwitterionic surfactants, have the ability to transform the hydrophobic domains of the protein molecules into hydrophilic ones, covering them with their hydrophilic parts.

Generalized (Ω) model of radical copolymerization Part 1. Combined Comppen model

The possibility is shown for a considerable generalization of the Comppen model by the regular Markov chain application and the introduction of the comonomer complex dissociation probability (Ω) during the chain propagation step. The generalization is in two directions. The first one is a result of the Ω variation. If Ω= 0 the generalized model coincides with the Comppen model; when Ω=1 it simulates the combined penultimate and complex-dissociation mechanism of chain propagation; at any other Ω values new unknown propagation mechanisms are simulated. The other direction is a result of the possibility to estimate using this model not only monad and triad copolymer composition, as by Comppen model, but the probability for chain formation by the comonomer complex components (P(c)) and lengths and dispersions of the compositional microblocks in the copolymer chain. These magnitudes are estimated for maleic anhydride-styrene copolymers, produced in methyl ethyl ketone at 50°C. The comparison between the experimental and calculated values proves the adequacy of the model.