Violeta Melinte

Synthesis, Evaluation and Preliminary Antibacterial Testing of Hybrid Composites Based on Urethane Oligodimethacrylates and Ag Nanoparticles

A series of urethane dimethacrylates differing structurally by the nature of the spacer (PTHF, PCL, PEG) and the presence or absence of the carboxylic acid groups was synthesized via an isocyanate route frequently encountered in ionomer chemistry. 1H-NMR and FT-IR spectroscopy confirmed the structure of the macromers. Subsequently, the progress of photo-polymerization of all dimethacrylates under UV irradiation was investigated by FT-IR spectroscopy and photo-DSC with respect to conversion and polymerization rate using Irgacure as an initiator. The results of spectroscopic analysis suggested the lower reactivity of some non-carboxylic analogues during the formation of cross-linked polymers, the degree of conversion depending on the structure and viscosity. Photo-polymerization may provide many advantages for incorporating silver nanoparticles (2.5 wt%) into macromers in order to obtain hybrid nanocomposite films with controllable thickness and hydrophobicity. Combined analyses of UV spectroscopy and transmission electron microscopy confirmed the existence of nanosized silver (mean diameter 12 ± 0.7 nm) uniformly distributed in the polymer matrix. Preliminary results concerning the antibacterial activity of some composite films (thickness approx. 24 μm) showed that the obtained nanomaterial could have an excellent bactericidal effect and effectiveness in reducing bacterial growth (Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923).

Photopolymerization experiments and properties of some urethane/urea methacrylates tested in dental composites

Hydrophobic silyl-urea/urethane methacrylates (UHM-1, UHM-2) and a modified BisGMA derivative (BisGMA-UMA) were synthesized and used as photopolymerizable co-monomers in the preparation of dental composites, besides other urethane dimethacrylates containing oligoethylene oxide segments and carboxylic groups. The homo- and copolymerization behaviour of the synthesized monomers were investigated by FTIR spectroscopy using camphorquinone (CQ) and 4-(dimethylamino)-phenylacetic acid (DMPheAA) as a photoinitiating system, as well as by photo-DSC. The first hybrid monomethacrylate, N-(methacryloyloxyethyl-N’-diethoxymethylsilylpropyl)-urea showed the highest value for the maximum polymerization rate (0.117 s−1) followed by BisGMA analogue (0.085 s−1) and N-methacryloyloxyethyl-N’-bis(triethoxysilylpropylcarbamoyloxyethyl)-urea (0.069 s−1), whereas the degree of conversion decreased from 75.1% (UHM-2) to 41.6% (BisGMA-UMA). Polymerization shrinkage (PS) measured by picnometry for the mixture BisGMA-UMA/TEGDMA (4.78 vol.%) was lower than that exhibited of the control organic matrix BisGMA/TEGDMA (6.85 vol.%) at the same dilution. The addition of one of the obtained monomers into a mixture based on urethane oligomers led to a polymerization shrinkage varying between 8.33 and 6.97 vol.%. A number of properties of the composites formulated with our urethane methacrylates, a urethane dimethacrylate, BisGMA, and glass filler (Zr/Sr glass, quartz, and diatomite) were also determined including the surface damage caused by the Vickers indentation to establish their utility in dentistry.

Photopolymerizable phosphate acrylates as comonomers in dental adhesives with or without triclosan monomer units

Phosphate diacrylates (CO-DAP, TMP-DAP) based on castor oil or trimethylolpropane were synthesized and evaluated in dental adhesive formulations in comparison with 3-acryloyloxy-2-hydroxypropyl methacrylate phosphate (AMP-P). In an attempt to promote antibacterial activity, another photopolymerizable monomer (TCS-UMA) containing 5-chloro-2-(2,4-dichlorophenoxy)phenol moiety (triclosan) was prepared and incorporated in adhesive resins. Each of these monomers had a molecular structure confirmed by spectral methods. The photopolymerization rates for monomers (0.063-0.088s(-1)) were lower than those determined in the monomer combinations (0.116-0.158s(-1)) incorporating phosphate diacrylate (11wt.%), BisGMA (33wt.%), TEGDMA (10wt.%), UDMA (10wt.%) and HEMA (15wt.%), the degree of conversion varying between 63.4 and 74.5%. The formed copolymers showed high values for water sorption (18.65-57.02μg/mm(3)) and water solubility (3.51-13.38μg/mm(3)), and the contact angle was dependent on the presence of CO-DAP (θF1: 66.67°), TMP-DAP (θF2: 55.05°) or AMP-P (θF3: 52.90°) in the photocrosslinked specimens compared to the sample without phosphate monomer (θF4: 82.14°). The scanning electron microscopy image of the dentin-resin composite interface after applying our F1 formulation (pH: 4.1) and its light-curing for 20s supports the evidence of the formation of the hybrid layer with the tooth structure created by self-etching approach, with no gaps or cracks in the adhesive. A comparative analysis of the adhesion achieved with commercial adhesive systems (Single Bond Universal, C-Bond) rather indicates similarities than differences between them. The addition of triclosan methacrylate (1wt.%) into the formulation inhibited the bacterial growth of the Streptococcus mutans and Escherichia coli in the direct contact area due to the covalently linked antibacterial monomer.

New acid BisGMA analogs for dental adhesive applications with antimicrobial activity.

OBJECTIVE To achieve bisphenol A glycerolate dimethacrylate (BisGMA) analogs with reduced viscosity to be used in the formulation of dental adhesives containing biocidal components. METHODS A series of low-viscosity BisGMA derivatives (η: 39-12Pas) modified with 30, 60 and, respectively 80mol% carboxylic acid units were synthesized and characterized. Hydrogen bonding interactions in our monomers, the photopolymerization behavior and implicitly the conversion degree (DC) for some experimental adhesive formulations containing acid-modified BisGMA, commercial BisGMA (only in F1-F3), triethyleneglycol dimethacrylate and 2-hydroxyethyl methacrylate were examined by FTIR spectroscopy. The water effects on the photocrosslinked networks together with the flexural strength/modulus were also investigated. The adhesive penetration into the dentin surface was surveyed by SEM analysis, and the antimicrobial activity triggered by the incorporation of 0.5wt% AgNO3, 10wt% zinc methacrylate or 1wt% triclosan methacrylate in selected adhesive formulations on the growth of Streptococcus mutans and Candida albicans strains was evidenced. RESULTS The contribution of the hydrogen bonding interactions was found to be lower in BisGMA derivatives than in non-modified BisGMA, and the DC varied between 56.5 (F6) and 83.7% (F1) compared with a control formulation based on BisGMA:TEGDMA (DC=58.2%). The flexural strength and flexural modulus varied in the range 33.7MPa (F6)-54.4MPa (F8)MPa and 0.64 (F6)-1.43 (F8)GPa, respectively. SEM observation of adhesive-dentin interface revealed the formation of resin tags for the carboxyl-containing adhesive, while for the control adhesive they are hardly formed. Also, the microorganism development was inhibited, the proposed materials displaying antimicrobial activity. SIGNIFICANCE The experimental formulations based on carboxyl-functionalized BisGMA exhibit a similar or even improved behavior over control sample, suggesting their potential applicability as antimicrobial dental adhesives.

Carboxylic polyurethane/organoclay nanocomposites and their properties

New nanocomposite films were prepared from a dispersion of organically modified montmorillonite as the filler and flexible polyurethane as the matrix. The polyurethanes containing a small amount of carboxylic groups were synthesized from 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butanediol (1,4-BD), and poly(tetramethyleneoxide diol) (PTMO) of 1000 average molecular weight, the carboxylic unit being included by means of dimethylol propionic acid (DMPA) or tartaric acid (TA). For comparison, polyurethane without carboxylic moieties was also synthesized. The polymers and their nanocomposites were characterized by 1H-NMR and Fourier transform infrared spectroscopy, thermogravimetric analysis and gel permeation chromatography analysis. Additional information regarding some properties of these materials was obtained from the mechanical evaluation of thin films through stress–strain testing and dynamic mechanical analysis. Moreover, the effects of clay and interlayer ions on the morphology and physical properties of the hybrid nanocomposites were examined using atomic force microscope, X-ray diffractometer and transmission electron microscope.

Tuning the size and the photocatalytic performance of gold nanoparticles in situ generated in photopolymerizable glycomonomers

Polymer nanocomposites containing gold nanoparticles (Au NPs) in situ photogenerated during the UV-curing process were prepared starting from methacrylated glycomonomers with α-D-glucofuranose or D-mannitol structural units, other mono(di)methacrylates and AuCl3. The formation of Au NPs inside the polymer matrix was evidenced through UV-vis, TEM and XRD analyses, the mean size of the spherical particles being around 33 nm. By adding methacrylates functionalized with carboxylic, quaternary ammonium or thiol groups (MA-COOH, MA-N+, MA-SH) in each formulation, the mean size of gold nanoparticles in the hybrid films (purple/dark-blue, red, green) decreased from 6.4 nm to 1.5 nm (for those stabilized by a gold–thiol bond). The catalytic activity was tested for the photodegradation of methylene blue (MB) and methyl orange (MO) in aqueous phase under visible irradiation conditions, and the catalytic performance of the resulting hybrid films was improved by the size decrease of the Au NPs. The hybrid films prepared with 30 wt% MA-SH were more active than the samples with 10 wt% thiol methacrylate. Thus, the percentage degradation with nanosized Au NPs and 30 wt% photopolymerized MA-SH was about 98% in MB and 94% for MO (after 100 min of visible irradiation). Finally it was proved that the hybrid polymeric films can be reused as photocatalysts with high performance for the removal of dyes from contaminated wastewater.

Synthesis of poly(alkenoic acid) with L-leucine residue and methacrylate photopolymerizable groups useful in formulating dental restorative materials.

To develop resin-modified glass ionomer materials, we synthesized methacrylate-functionalized acrylic copolymer (PAlk-LeuM) derived from acrylic acid, itaconic acid and N-acryloyl-L-leucine using (N-methacryloyloxyethylcarbamoyl-N′-4-hydroxybutyl) urea as the modifying agent. The spectroscopic (proton/carbon nuclear magnetic resonance, Fourier transform infrared spectroscopy) characteristics, and the gel permeation chromatography/Brookfield viscosity measurements were analysed and compared with those of the non-modified copolymer (PAlk-Leu). The photocurable copolymer (PAlk-LeuM, ~14 mol% methacrylate groups) and its precursor (PAlk-Leu) were incorporated in dental ionomer compositions besides diglycidyl methacrylate of bisphenol A (Bis-GMA) or an analogue of Bis-GMA (Bis-GMA-1), triethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate. The kinetic data obtained by photo-differential scanning calorimetry showed that both the degree of conversion (60.50–75.62%) and the polymerization rate (0.07–0.14 s−1) depend mainly on the amount of copolymer (40–50 wt.%), and conversions over 70% were attained in the formulations with 40 wt.% PAlk-LeuM. To formulate light-curable cements, each organic composition was mixed with filler (90 wt.% fluoroaluminosilicate/10 wt.% hydroxyapatite) into a 2.7:1 ratio (powder/liquid ratio). The light-cured specimens exhibited flexural strength (FS), compressive strength (CS) and diametral tensile strength (DTS) varying between 28.08 and 64.79 MPa (FS), 103.68–147.13 MPa (CS) and 16.89–31.87 MPa (DTS). The best values for FS, CS and DTS were found for the materials with the lowest amount of PAlk-LeuM. Other properties such as the surface hardness, water sorption/water solubility, surface morphology and fluorescence caused by adding the fluorescein monomer were also evaluated.

Photo-polymers Containing (S)-Phenylalanine and Stilbene Pendants: Synthesis and Properties of Ionic Polyacrylates

Radical co-polymerization of N-acryloyl-(S)-phenylalanine benzyl ester with N,N-dimethylaminoethyl acrylate using microwave-assisted rapid synthesis led to a co-polymer to be subsequently quaternized with 4-chloromethylphenylcarbamoyloxy-methylstilbene. 1H-NMR spectroscopy was employed to determine the molar ratio of monomeric units (1:5.6) and the content of fluorophore (0.15 molar fraction) from the co-polymer. Also, the photophysical properties of the photo-polymer including the fluorescence response toward some amines in DMF solution have been investigated. The effect of monomethyl viologene, 4,4′-bipyridyl, 2,2′-bipyridyl, piperazine and triethylamine, used as quenchers of stilbene fluorescence from co-polymer, was compared with that of ferrocene.

Photocatalysis applications of some hybrid polymeric composites incorporating TiO2 nanoparticles and their combinations with SiO2/Fe2O3

Polymer nanocomposites containing titanium oxide nanoparticles (TiO2 NPs) combined with other inorganic components (Si–O–Si or/and γ-Fe2O3) were prepared by the dispersion of premade NPs (nanocrystalline TiO2, TiO2/SiO2, TiO2/Fe2O3, TiO2/SiO2/Fe2O3) within a photopolymerizable urethane dimethacrylate (polytetrahydrofuran-urethane dimethacrylate, PTHF-UDMA). The physicochemical characterization of nanoparticles and hybrid polymeric composites with 10 wt % NPs (S1–S4) was realized through XRD, TEM and FTIR analyses. The mean size (10–30 nm) and the crystallinity of the NPs varied as a function of the inorganic constituent. The catalytic activity of these hybrid films was tested for the photodegradation of phenol, hydroquinone and dopamine in aqueous solution under UV or visible-light irradiation. The best results were obtained for the films with TiO2/Fe2O3 or TiO2/SiO2/Fe2O3 NPs. The degradation of the mentioned model pollutants varied between 71% and 100% (after 250 min of irradiation) depending on the composition of the hybrid film tested and the light applied (UV–visible light). Also, it was established that such hybrid films can be reused at least for five cycles, without losing too much of the photocatalytic efficiency (ca. 7%). These findings could have implications in the development of new nanocatalysts.

A new fluorinated urethane dimethacrylate with carboxylic groups for use in dental adhesive compositions

A urethane macromer containing hexafluoroisopropylidene, poly(ethylene oxide) and carboxylic moieties (UF-DMA) was synthesized and used in proportions varying between 15 and 35 wt.% (F1-F3) in dental adhesive formulations besides BisGMA, triethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate. The FTIR and (1)H ((13)C) NMR spectra confirmed the chemical structure of the UF-DMA. The experimental adhesives were characterized with regard to the degree of conversion, water sorption/solubility, contact angle, diffusion coefficient, Vickers hardness, and morphology of the crosslinked networks and compared with the specimens containing 10 wt.% hydroxyapatite (HAP) or calcium phosphate (CaP). The conversion degree (after 180 s of irradiation with visible light) ranged from 59.5% (F1) to 74.8% (F3), whereas the water sorption was between 23.15 μg mm(-3) (F1) and 40.52 μg mm(-3) (F3). Upon the addition of HAP or CaP this parameter attained values of 37.82-49.14 μg mm(-3) (F1-F3-HAP) and 34.58-45.56 μg mm(-3), respectively. Also, the formation of resin tags through the infiltration of a dental composition (F3) was visualized by SEM analysis. The results suggest that UF-DMA taken as co-monomer in dental adhesives of acrylic type may provide improved properties in the moist environment of the mouth.