George Georgiev

Sofia University, California City, California, United States

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Publications (42)72.24 Total impact

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    ABSTRACT: Indomethacin-loaded nanoparticles (IMC-NPs) were obtained by emulsifier-free radical polymerization of vinyl acetate (VAc) in the presence of indomethacin (IMC) in the aqueous solution of Carbopol® (Cbp) or chitozan (CH). The purpose of this study was to investigate the influence of nature and quantity of the added to the reaction system polymer on IMC loading and its kinetic release properties in terms of the future development of topical ophthalmic formulations. CH was chosen as a cationic polysaccharide and Cbp as an anionic crosslinked polymer. TEM and DLS were used to observe the morphology and to determine the average particle size which was in the range of 178.20÷297.90 nm and the polydispersity index (PDI) which was within 0.149÷0.339. A monomodal particle size distribution (PSD) was observed for the CH-coated NPs and bimodal PSD was observed in the models, obtained in the presence of Cbp. FTIR analysis showed that the models were a result of interactions with hydrogen bonds. UV-spectroscopy was used for the determination of IMC inclusion and in vitro release characteristics. The results of release kinetic analyses showed that IMC was released from the investigated models following the first order. The polymer shell (Cbp or CH) around the pVAc– core had an impact on the rate and degree of the released drug.
    American Journal of PharmTech Research ISNN: 2249-3387. 02/2014; 4(1):664-678.
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    ABSTRACT: Objective: To examine indomethacin (IMC) inclusion in in-situ loaded nanoparticles (IMC-NPs) and its in vitro release characteristics varying the polymer composition of the NPs cores and shells. Methods: IMC-NPs were obtained by emulsifier-free radical homo-and co-polymerization of the monomers in the presence of IMC. Poly(vinyl acetate) (pVAc) and a copolymer of vinyl acetate (VAc) with 3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate (DMAPS), (p(VAc-co-DMAPS), were used for the preparation of NPs cores, while biocompatible poly(DMAPS), (pDMAPS), and Carbopol ® (Cbp) were used for the preparation of the NPs shells. TEM and DLS were used to observe the microstructure and determine the particle size. XRD-, FTIR-, UV-spectroscopy and simultaneous DTA-TG analysis were applied for the determination of IMC inclusion and in vitro release characteristics. Results: TEM and DLS determined the particle size which was in range of 128.10÷345.10 nm and its polydispersity index within 0.133÷0.390. A monomodal particle size distribution was observed for the homo-and copolymer uncoated NPs. Bimodal distribution was observed for the coated with pDMAPS and Cbp NPs. Drug loading assessment showed higher values for drug loading, encapsulation efficiency and NPs yield for the uncoated NPs compared to those which were coated with Cbp or pDMAPS. Results of release kinetic analyses showed that IMC was released from investigated patterns following first order kinetics, but their release rate and degree were different. The copolymer NPs (IMC-p(VAc-co-DMAPS)) showed the most rapid release of IMC, while the homopolymer pVAc NPs, coated with Cbp (IMC-p(VAc)+Cbp) -the slowest one. Conclusion: The obtained results prove the possibility to prepare pVAc and p(VAc-co-DMAPS) NPs with in-situ included IMC by emulsifier-free radical homo-and co-polymerization and demonstrate the importance of polymer nature and NPs cores and shells composition for the control of IMC loading and release characteristics.
    International Journal of Pharmacy and Pharmaceutical Sciences 01/2014; 6(1):691-699. · 1.59 Impact Factor
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    ABSTRACT: Copolymer (vinyl acetate (VA)-co-3-dimethyl(methacryloyloxyethyl)ammonium propane sulfonate (DMAPS)) nanoparticles have been synthesized by radical copolymerization in water. It was established that the variation of the initial monomer feed (DMAPS concentration was 10 mol% (copolymer 1) and 90 mol% (copolymer 2)) changes the copolymerization type, nanoparticles morphology, self-organization and size distribution. The shape, average diameter, size distribution and zeta potential of the copolymer nanoparticles are determined by atomic force microscopy (AFM), dynamic light scattering and zeta potential data, respectively. While the copolymer 1 nanoparticles are solid with spherical shape, average diameter 276 nm and zeta potential −25.2 mV, the copolymer 2 nanoparticles have bean-like shapes with an average diameter 49.3 nm and zeta potential −4.4 mV and contain many domains with different density. For the first time the AFM images of the copolymer 2 nanoparticles presented the unique self-organization of the dipole–dipole clusters of DMAPS units. The results indicated that the obtained copolymer nanoparticles with specific structure could be used as drug delivery systems.
    European Polymer Journal 03/2013; 49(3):637–645. · 2.56 Impact Factor
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    ABSTRACT: Radical copolymerization in water was used for obtaining new zwitterionic copolymers, based on vinyl acetate (VA) and 3-dimethyl(methacryloyloxyethyl)ammonium propane sulfonate (DMAPS) (p(VA-co-DMAPS)) with different compositions. Thepresented study involves: (i) synthesis of nanoparticles, based on p(VA-co-DMAPS) with highest and lowest concentration of the zwitterionic monomer DMAPS in the initial monomer feed, by radical copolymerization in water; (ii) the influence of the DMAPS content on size, particles size distribution and the morphology of p(VA-co-DMAPS) nanoparticles.
    Journal of the University of Chemical Technology and Metallurgy. 01/2013; 48(1):12.
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    ABSTRACT: Polydimethylsiloxane (PDMS) finds applications in pharmaceutical and medical devices, due to its biocompatibility and biodurability. This work was aimed at grafting chitosan-Rose Bengal (CH.RB) on PDMS substrates, to reduce the risks of bacterial infection during surgical application. PDMS was activated with argon plasma and functionalised with acrylic acid to introduce carboxyl moieties for further covalent coupling reaction with CH.RB amino groups. The accessible carboxylic groups on the acrylic acid functionalized PDMS (PDMS-pAAc) surface were quantified to be 1.9±0.1 μg/cm2 by Toluidine Blue-O colorimetric method. The appearance of ATR-FTIR absorption peaks at 3100-3700, 1726 and 1633 cm-1 in the PDMS-pAAc ATR-FTIR spectrum suggested the introduction of carboxyl groups, whereas the peaks at 1651 and 1590 cm-1 in the ATR-FTIR spectrum of CH.RB functionalized PDMS (PDMS-pAAc-CH.RB) evidenced the amide bond formation. Analysis of deconvoluted C1s peak in XPS spectra confirmed surface chemical modification at each functionalization step. Surface wettability was affected by surface functionalization: PDMS was hydrophobic (111°), whereas PDMS-pAAc and PDMS-pAAc-CH.RB were hydrophilic (55° and 58° respectively). PDMS-pAAC-CH.RB antibacterial activity was preliminarily investigated using planktonic cells of Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 6538.
    Surface and Coatings Technology 01/2013; · 1.94 Impact Factor
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    ABSTRACT: 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.
    Journal of Separation Science 09/2012; 35(20):2805-12. · 2.59 Impact Factor
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    ABSTRACT: During the last decade the number of investigations on the preparation and application of more effective drug release systems on the basis of nanocarriers from biocompatible and biodegradable polymers are considerably increasing. This is notably in force for practically water insoluble drugs to be applied in liquid forms (eye solutions for an example). The aim of the work presented was the preparation of model poly(vinyl acetate) and poly(styrene) nanosupports for indometacin and their potential inclusion in eye drops. The polymers are synthesized as nanosized latex by a radical polymerization of the monomers in the presence of indometacin. It is proved that the low polymerization temperature and initiator used do not influence indometacin structure and properties. The nanoparticles were characterized by attenuated total reflection Fourier transform infrared spectroscopic analyses, atomic force microscopy, scanning electron microscopy and transmission electron microscopy. The size of the latex particles was around 200 nm, determined by the scan electron microscopy. The indometacin delivery rate from the supports discussed in aqueous solutions was determined at pH 7.4. The change of this rate, in comparison with that for a pure drug substance, was established also as well as its dependence on the nature of the carrier.
    Pharmazie 07/2012; 67(7):601-4. · 0.96 Impact Factor
  • Journal of Controlled Release 11/2010; 148(1):e44-5. · 7.63 Impact Factor
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    ABSTRACT: 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.
    Biomacromolecules 02/2010; 11(2):309-15. · 5.37 Impact Factor
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    ABSTRACT: The design of advanced, nanostructured materials at the molecular level is of tremendous interest for the scientific community because of their potential in several fields, including medicine, biology and tissue engineering. Layer-by-layer (LbL) assembly is a versatile technique for the realization of multilayered films with tailored characteristics at the nanometer scale. Photoactive nanostructured films were prepared by LbL assembly of photozymes: an amphiphilic zwitterionic copolymer, poly(sodium styrene sulphonate-stat-vinyl naphtalene-stat-3-dimethyl(methacryloylethyl) ammonium propane sodium sulfonate) (PSSS-stat-VN-stat-DMPAS; code: ZI), and a cationic polyelectrolyte, chitosan-g-fluorescein (code: CHFL), on a crosslinked gelatin substrate. Although successful LbL assembly of photozymes was proven by the performed characterization, gelatin was not an optimal substrate for the coating, due to its low charge density and amphoteric nature. A regular growth of the layers was found after at least 6 layers were deposited. The macromolecules of the zwitterionic photozyme adopted a coiled micellar conformation in solution which was kept during the assembly. The obtained nanostructured films are promising candidates for carrying out efficient electron transfer process within them, responsible for the anti-microbial activity and the osteointegration ability of the coating.
    Nanotechnology, 2009. IEEE-NANO 2009. 9th IEEE Conference on; 08/2009
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    ABSTRACT: Metal ion-imprinted polymer particles have been prepared by copolymerization of methacrylic acid as monomer, trimethylolpropane trimethacrylate as cross-linking agent and 2,2'-azobisisobutyronitrile as initiator, in the presence of Hg(II)-1-(2-thiazolylazo)-2-naphthol complex. The separation and preconcentration characteristics of the Hg-ion-imprinted microbeads for inorganic mercury have been investigated by batch procedure. The optimal pH value for the quantitative sorption is 7. The adsorbed inorganic mercury is easily eluted by 2 mL 4M HNO(3). The adsorption capacity of the newly synthesized Hg ion-imprinted microbeads is 32.0 micromol g(-1) for dry copolymer. The selectivity of the copolymer toward inorganic mercury (Hg(II)) ion is confirmed through the comparison of the competitive adsorptions of Cd(II), Co(II), Cu(II), Ni(II), Pb(II), Zn(II)) and high values of the selectivity and distribution coefficients have been calculated. Experiments performed for selective determination of inorganic mercury in mineral and sea waters showed that the interfering matrix does not influence the extraction efficiency of Hg ion-imprinted microbeads. The detection limit for inorganic mercury is 0.006 microg L(-1) (3 sigma), determined by cold vapor atomic adsorption spectrometry. The relative standard deviation varied in the range 5-9 % at 0.02-1 microg L(-1) Hg levels. The new Hg-ion-imprinted microbeads have been tested and applied for the speciation of Hg in river and mineral waters: inorganic mercury has been determined selectively in nondigested sample, while total mercury e.g. sum of inorganic and methylmercury, has been determined in digested sample.
    Talanta 05/2009; 78(2):523-9. · 3.50 Impact Factor
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    ABSTRACT: Very stable co-polymer (vinyl acetate (VA)-co-3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate (DMAPS) (p(VA-co-DMAPS)) latexes with different compositions have been synthesized by emulsifier-free emulsion co-polymerization. The dry p(VA-co-DMAPS)s have been used in the preparation of drug tablets for sustained Metoprolol tartrate release. It has been shown that the tablet swelling depends on the mol fraction of DMAPS monomer units (m(DMAPS)), pH and ionic strength (I). An original explanation, based on the swelling behavior of p(VA-co-DMAPS), has been proposed for the "overshooting" phenomenon observed. It assumes the formation of hydrophilic domains with a higher m(DMAPS) in the co-polymer tablets. The formation of dipole-dipole clusters between the DMAPS units at different m(DMAPS) and I are the main cause for the established differences in both the swelling kinetics of the p(VA-co-DMAPS) matrices and Metoprolol tartrate release. The obtained results show that for p(VA-co-DMAPS) matrices-based tablets controlled sustained Metoprolol tartrate release can be realized just by varying two parameters, co-polymer composition and I.
    Journal of Biomaterials Science Polymer Edition 02/2009; 20(2):181-97. · 1.70 Impact Factor
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    ABSTRACT: 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,N-dimethyl(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.
    Zeitschrift fur Naturforschung C 01/2009; 64(1-2):149-54. · 0.60 Impact Factor
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    ABSTRACT: A simple and sensitive method has been developed for the determination of trace elements (Cd, Co, Cu, Ni, Fe and Pb) in sea water and natural waters by electrothermal atomic absorption spectrometry. The method is based on column solid phase extraction of trace elements on a newly synthesized polycarboxylic gel. The sorbent was prepared by dispersion copolymerization of methacrylic acid (as a monomer) and trimethylolpropane trimethacrylate (as a crosslinking agent) in the form of monodisperse microspheres. It exhibits high regeneration ability, chemical and mechanical resistivity. The influence of pH, flow rates and concentration of the eluent on the degree of sorption of trace elements have been evaluated. The maximum static adsorption capacities of the sorbent at the optimal conditions for lead, nickel, cobalt, iron, cadmium and copper are determined. Detection limits achieved for the elements studied for 100mL water sample volume were between 0.005 and 0.05μg L−1. The relative standard deviation varied in the range 5–13% for all elements studied. The validity of the method was checked by an analysis of standard reference material SRLS-3 Riverine Water. Very good agreement between the analytical results and the certified values (t-test at 95% confidence level) was observed. The new polycarboxylic gel was applied to passive sampling procedures due to its high chemical and mechanical stability.
    Microchimica Acta 12/2008; 164(1):55-61. · 3.43 Impact Factor
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    ABSTRACT: The aim of this study was to synthesize stable copolymer (vinyl acetate-co-3-dimethyl[methacryloyloxyethyl] ammonium propane sulfinate) zwitterionic latex with different compositions for the first time by emulsifier-free emulsion copolymerization. Throughout the course of the study, a proposal was made for the explanation of the relationship between the "overshooting" phenomenon (a swelling kinetics with a maximum) and the specific self-association of the zwitterionic copolymers. The zwitterionic monomer unit mole fraction, pH, and ionic strength effects on this relationship, on the swelling kinetics of the zwitterionic copolymers, and on the sustained verapamil hydrochloride release from the model tablets were established by the study's authors.
    Pharmaceutical Development and Technology 01/2008; 13(4):311-21. · 1.33 Impact Factor
  • Macromolecular Reaction Engineering 08/2007; 1(5):553 - 562. · 1.64 Impact Factor
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    ABSTRACT: Ion-imprinted polymer (IIP) particles are prepared by copolymerization of methacrylic acid as monomer, trimethylolpropane trimethacrylate as crosslinking agent and 2,2'-azo-bis-isobutyronitrile as initiator in the presence of Cu(II), a Cu(II)-4-(2-pyridylazo)resorcinol (Cu(II)-PAR) complex, and PAR only. A batch procedure is used for the determination of the characteristics of the Cu(II) solid phase extraction from the IIP produced. The results obtained show that the Cu(II)-PAR IIP has the greatest adsorption capacity (37.4 micromol g(-1) of dry copolymer) among the IIPs investigated. The optimal pH value for the quantitative preconcentration is 7, and full desorption is achieved by 1 M HNO(3). The selectivity coefficients (S(Cu/Me)) for Me=Ni(II), Co(II) are 45.0 and 38.5, respectively. It is established that Cu(II)-PAR IIPs can be used repeatedly without a considerable adsorption capacity loss. The determination of Cu(II) ions in seawater shows that the interfering matrix does not influence the preconcentration and selectivity values of the Cu(II)-PAR IIPs. The detection and quantification limits are 0.001 micromol L(-1) (3sigma) and 0.003 micromol L(-1) (6sigma), respectively.
    Analytica chimica acta 03/2007; 584(1):196-203. · 4.31 Impact Factor
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    ABSTRACT: The N-isopropylacrylamide (NIPAM) and N,N′-dimethyl-(methacryloyloxyethyl) ammonium propane sulfonate (DMAPS) copolymer networks having monomer units with an opposite thermoassembling ability are synthesized and analyzed. The network composition is of crucial importance for their degree of swelling (Q) and Q-Temperature (T) dependences. After the Q normalization these dependences outline two classes of networks which hydrogels expel or imbibe water with T. The boundary network (with 0.39 mole fraction of DMAPS monomer units) defines a critical T (Tcr) at which Q is the same as that at the initial T (To), but with a structure organization, different than that at To. The hydrogels thermoreversibility at the stepped T change, and the salt effect on the Q-T dependences are demonstrated also.
    Macromolecular Symposia 01/2007; 254(1):329-337.
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    ABSTRACT: Nano-nickel (n-Ni) is deposited by a pulsed electrodeposition (PED) in the presence of nonionogenic (poly(ethylene glycol), poly(N-vinylpyrrolidone), starch), anionogenic (gum arabic, sodium alginate), cationic (quaternized guar gum), and polyampholytic (polyzwitterionic) poly(dimethylaminoethylmethacryloylpropanesulfonate) (PDMAEMPS) polymers. It is established that, by PED (40 mA/cm2, ton = 1 ms, toff = 50 ms, 323 K), the size of the nanocrystalline particles produced in the presence of PDMAEMPS is far less (by a factor of 6–10) than those obtained in the presence of other polymer additives. These comparative results emphasize a new possibility of controlling the nanograin size of the electrodeposited metals by PED. The dramatic difference in the size of the nickel particles and the unique ability of the polyzwitterionic (PZI) additives are connected by the specific for the polyzwitterionic macromolecular conformation response to the pulsatile electric potential. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2967–2971, 2006
    Journal of Applied Polymer Science 08/2006; 102(3):2967 - 2971. · 1.40 Impact Factor
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    ABSTRACT: An explanation of the unique nonbiofouling properties of polyzwitterions (PZ) is proposed [in this paper, the term "polyzwitterion" is preferred to "polybetain"]. The existence of an osmotic component of the driving force of the antipolyelectrolyte effect (APE) and the parameters governing this phenomenon are quantitatively established. The correlation between this effect, which is specific of PZ only, and the PZ nonbiofouling properties is grounded.
    Biomacromolecules 05/2006; 7(4):1329-34. · 5.37 Impact Factor

Publication Stats

109 Citations
72.24 Total Impact Points


  • 2001–2013
    • Sofia University
      California City, California, United States
  • 1979–2013
    • Medical University of Sofia
      • • Department of Pharmaceutical Technology and Biopharmacy
      • • Department of Chemistry
      Ulpia Serdica, Sofia-Capital, Bulgaria
  • 2012
    • Sofia University "St. Kliment Ohridski"
      • Faculty of Chemistry and Pharmacy
      Sofia, Oblast Sofiya-Grad, Bulgaria