The Influence of Rheological and Wetting Properties of Hydrogel-based Bio-Inks on Extrusion-based Bioprinting

The wall slip and flow behavior of alginate as well as gelatin based hydrogels with respect to the impact of these rheological and wetting properties on extrusion-based bioprinting (EBB) was investigated. Capillary rheometry and printing tests indicate that slip is negligible at high stresses relevant for EBB, i.e., well above the hydrogels yield stress. On the contrary, rotational rheometry performed at low shear stresses revealed that alginate hydrogels present much stronger slip than gelatin gels, irrespective of crosslinker and polymer concentration. This result is presumably due to the formation of a heterogeneous microstructure for alginate gels and has an unfavorable impact on the printing quality with the production of large fluctuations in line width and higher line spread ratio

Development of a Silver Nanoparticle-Based Method for the Antioxidant Capacity Measurement of Polyphenols

A sensitive colorimetric method for the detection of polyphenols (i.e., flavonoids, simple phenolic, and hydroxycinnamic acids) was proposed in this research based on the reduction of Ag+ ions by polyphenols in the presence of citrate-stabilized silver seeds. The color of the stable suspension was controlled by varying the concentration of trisodium citrate, silver nitrate, and silver seeds. The reduction of Ag+ to spherical silver nanoparticles (SNPs) by polyphenols in the presence of trisodium citrate and silver seeds produced a very intense surface plasmon resonance (SPR) absorption band of SNPs at 423 nm. The plasmon absorbance of SNPs allows the quantitative spectrophotometric detection of the polyphenols, and the developed method gave a linear response over a wide concentration range of standard polyphenolic compounds. In contrast to other reported NP-based antioxidant assays, it was established in this work that growth but not nucleation of SNPs gave a linear concentration-dependent response. The trolox equivalent antioxidant capacity (TEAC) values of various (hydrophilic and lipophilic) antioxidants using the developed method were comparable to those of the CUPRAC assay. Common food ingredients like oxalate, citrate, fruit acids, amino acids, and reducing sugars did not interfere with the proposed sensing method. This assay was validated through linearity, additivity, precision and recovery, demonstrating that the assay is reliable and robust. The developed method was used to screen total antioxidant capacity (TAC) of some commercial fruit juices and herbal teas without preliminary treatment, and showed a promising potential for the preparation of antioxidant inventories of a wide range of food plants

Synthesis, characterization and antioxidant capacity of naringenin-oxime

The recognition of the benefits of polyphenolic antioxidants is eliciting increasing interest in the search for new polyphenolic derivatives with improved antioxidant activity. Since naringenin (4'5,7-trihydroxyflavanone) (NG) is one of the most abundant citrus and grapefruit polyphenolics and flavanone oximes were used in the synthesis of anticancer and radioprotector compounds having antiradical activity, the corresponding oxime of NG, naringenin oxime (NG-Ox), was synthesized and investigated. The structure of NG-Ox was characterized by FT-IR, (1)H NMR, elemental analysis, and the synthesized compound was screened for its antioxidant capacity by using the cupric reducing antioxidant capacity (CUPRAC) method. Trolox equivalent antioxidant capacity (TEAC) of NG-Ox was measured to be higher than that of the parent compound, NG. Other parameters of antioxidant activity (scavenging effects on center dot OH, O(2)(center dot-) and H(2)O(2)) of NG-Ox were also determined. (C) 2011 Elsevier B.V. All rights reserved

Selective optical sensing of biothiols with Ellman's reagent: 5,5 '-Dithio-bis(2-nitrobenzoic acid)-modified gold nanoparticles

Development of sensitive and selective methods of determination for biothiols is important because of their significant roles in biological systems. We present a new optical sensor using Ellman's reagent (DTNB)-adsorbed gold nanoparticles (Au-NPs) (DTNB-Au-NP) in a colloidal solution devised to selectively determine biologically important thiols (biothiols) from biological samples and pharmaceuticals. 5,5'-Dithio-bis(2-nitrobenzoic acid) (DTNB), a versatile water-soluble compound for quantitating free sulfhydryl groups in solution, was adsorbed through non-covalent interaction onto Au-NPs, and the absorbance changes associated with the formation of the yellow-colored 5-thio-2-nitrobenzoate (TNB2-) anion as a result of reaction with biothiols was measured at 410 nm. The sensor gave a linear response over a wide concentration range of standard biothiols comprising cysteine, glutathione, homocysteine, cysteamine, dihydrolipoic acid and 1,4-dithioerythritol. The calibration curves of individual biothiols were constructed, and their molar absorptivities and linear concentration ranges determined. The cysteine equivalent thiol content (CETC) values of various biothiols using the DTNB-Au-NP assay were comparable to those of the conventional DTNB assay, showing that the immobilized DTNB reagent retained its reactivity toward thiols. Common biological sample ingredients like amino acids, flavonoids, vitamins, and plasma antioxidants did not interfere with the proposed sensing method. This assay was validated through linearity, additivity, precision and recovery, demonstrating that the assay is reliable and robust. DTNB-adsorbed Au-NPs probes provided higher sensitivity (i.e., lower detection limits) in biothiol determination than conventional DTNB reagent. Under optimized conditions, cysteine (Cys) was quantified by the proposed assay, with a detection limit (LOD) of 0.57 mu M and acceptable linearity ranging from 0.4 to 29.0 mu M (r = 0.998). (C) 2013 Elsevier B. V. All rights reserved

A Novel Differential Pulse Voltammetric (DPV) Method for Measuring the Antioxidant Capacity of Polyphenols-Reducing Cupric Neocuproine Complex

A novel differential pulse voltammetric (DPV) method is presented, using a chromogenic oxidizing reagent, cupric neocuproine complex (Cu(Nc)(2)(2+)), for the assessment of antioxidant capacity of polyphenolic compounds (i.e., flavonoids, simple phenolic acids, and hydroxycinnamic acids), ascorbic acid, and real samples for the first time. The electrochemical behavior of the Cu(Nc)(2)(2+) complex was studied by cyclic voltammetry at a glassy carbon (GC) electrode. The electroanalytical method was based on the reduction of Cu(Nc)(2)(2+) to Cu(Nc)(2)(+) by antioxidants and electrochemical detection of the remaining Cu(II)-Nc (unreacted complex), the difference being correlated to antioxidant capacity of the analytes. The calibration curves of individual compounds comprising polyphenolics and vitamin C were constructed, and their response sensitivities and linear concentration ranges were determined. The reagent on the GC electrode retained its reactivity toward antioxidants, and the measured trolox equivalent antioxidant capacity (TEAC) values of various antioxidants suggested that the reactivity of the Cu(II)-Nc reagent is comparable to that of the solution-based spectrophotometric cupric ion reducing antioxidant capacity (CUPRAC) assay. This electroanalytical method better tolerated sample turbidity and provided higher sensitivity (i.e., lower detection limits) in antioxidant determination than the spectrophotometric assay. The proposed method was successfully applied to the measurement of total antioxidant capacity (TAC) in some herbal tea samples such as green tea, sage, marjoram, and alchemilla. Results demonstrated that the proposed voltammetric method has precision and accuracy comparable to those of the spectrophotometric CUPRAC assay

Novel oxime based flavanone, naringin-oxime: Synthesis, characterization and screening for antioxidant activity

Recent interest in polyphenolic antioxidants due to their involvement in health benefits has led to the investigation of new polyphenolic compounds with enhanced antioxidant activity. Naringin (4 ',5,7-tri-hydroxyflavanone-7-beta-L-rhamnoglucoside-(1,2)-alpha-D-glucopyranoside) is one of the major flavanones in citrus and grapefruit. The present study aimed to synthesize naringin oxime from naringin and to evaluate its antioxidant and anticancer potential using in vitro assay system. The structure of the synthesized compound, naringin oxime, was elucidated by FT-IR, H-1 NMR, elemental analysis and UV-vis spectroscopy. Antioxidant capacity of naringin oxime, as measured by the cupric reducing antioxidant capacity (CUPRAC) method, was found to be higher than that of the parent compound naringin. Other parameters of antioxidant activity (scavenging effects on OH center dot, O-2(center dot-), and H2O2) of naringin and naringin oxime were also determined. (C) 2014 Elsevier Ireland Ltd. All rights reserved

Determination of biothiols by a novel on-line HPLC-DTNB assay with post-column detection

A novel on-line HPLC-DTNB method was developed for the selective determination of biologically important thiols (biothiols) such as L-cysteine (Cys), glutathione (GSH), homocysteine (HCys), N-acetylcysteine (NAC), and 1,4-dithioerythritol (DTE) in pharmaceuticals and tissue homogenates. The biothiols were separated on C18 column using gradient elution, reacted with the postcolumn reagent, DTNB in 0.5% M-beta-CD (w/v) solution at pH 8. to form yellow-colored 5-thio-2-nitrobenzoic acid (TNB), and monitored with a PDA detector (lambda = 410 nm). With the optimized conditions for chromatography and the postcolumn derivatization, 40 nM of NAC, 40 nM of Cys, and 50 nM of GSH can be determined. The relative standard deviations of the recommended method were in the range of 3.2-5.4% for 50 mu M biothiols. The negative peaks of biothiol constituents were monitored by measuring the increase in absorbance due to TNB chromophore. The detection limits of biothiols at 410 nm (in the range of 0.04-0.58 mu M) after post-column derivatization with DTNB + M-beta-CD were much lower than those at 205 nm UV-detection without derivatization, and were distinctly lower than those with post-column DTNB alone. The method is rapid, inexpensive, versatile, nonlaborious, uses stable reagents, and enables the on-line qualitative and quantitative estimation of biothiol constituents of biological fluids and pharmaceuticals. (C) 2012 Elsevier B.V. All rights reserved

Microwave-Assisted Extraction of Polyphenolics from Some Selected Medicinal Herbs Grown in Turkey

The effect of microwave-assisted extraction (MAE) process on the antioxidant capacity/activity of three medicinal herbs from Turkey was investigated by electrochemical differential pulse voltammetric (DPV)CUPric Reducing Antioxidant Capacity (CUPRAC) assay. The optimal extraction time, temperature and solvent type were 6 min, 80 degrees C and 80% (v/v) methanol (MeOH), respectively. Microwave-assisted extracts of herbs (Hypericum scabrum L., Papaver fugax Poiret var. platydiscus Cullen, and Achillea vermicularis Trin.) were screened for total antioxidant capacity (TAC), total phenolic content (TPC) and ROS scavenging activities by employing different in vitro spectrophotometric assays. A positive correlation was observed between TACCUPRAC and TPC (R-2 = 0.972). Similarly, a positive correlation was observed between TAC-CUPRAC and free radical scavenging (FRS) activity (R-2 = 0.977). The order of FRS activities of tested samples was as follows: Hypericum scabrum L. > Achillea vermicularis Trin. > Papaver fugax Poiret var. platydiscus Cullen. These results suggest that these medicinal herbs provide promising antioxidant potentials as potential natural preservative agents in pharmaceutical industries