Effect of Molecular Architecture and Composition on the Aggregation Pathways of POEGMA Random Copolymers in Water.

Understanding of the temperature-induced phase transition of poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) random copolymers with varied composition remains largely incomplete. Upon heating they can form either macroscopically phase-separated aggregates or micelles. We examined the effect of polymer architecture by rationally designing and synthesizing various POEGMA copolymer structures via atom transfer radical polymerization using OEGMA monomers of different EO lengths. Micelle formation occurred for copolymers with a small fraction of long side chains counterbalanced by an appropriate number of short side chains, while macroscopic phase separation occurred for other copolymer compositions. In some copolymer compositions and architectures, micelle formation followed by macroscopic phase separation occurred, and the temperature of these phase transitions could be tailored accordingly. This new strategy allows the control over the microstructure and specific transition temperatures enabling, for instance, the preparation of nanocarriers for encapsulating hydrophobic compounds.

Carbon steel corrosion controlled by vegetable polyol phosphate, in medium containing chloride and glyoxal: influence of phosphate content and CO2.

Glyoxal is a potential sequestrant of H2S in the pre-salt exploration. However, the mixture containing packer fluid and glyoxal is corrosive. The addition of an eco-friendly polyol phosphate acts as corrosion inhibitor of the AISI 1020 in this environment. The objective of the present work was to study the influence of phosphate content in the inhibitor formulation, as well as its action in packer fluid and glyoxal solution in the presence of dissolved CO2, by means of surface analysis and electrochemical measurements. The results demonstrated that the inhibition efficiency increases as the phosphate content increases. In the beginning of the tests, the polarization resistance increases from 2.2 kΩ cm2 (2.5 % phosphate) to 11.2 kΩ cm2 (10 % phosphate). In CO2 - containing medium, 500 ppm dosage of polyol phosphate increases the polarization resistance (from 0.35 kΩ cm2 to 5.9 kΩ cm2) and decreases both the capacitance (from 111.5 µF cm-2 to 10.2 µF cm-2) and the corrosion current (in 67%). Polyol phosphate is effective as corrosion inhibitor in the presence of CO2 due to its adsorption on the metal surface or on the film of the previously formed oxide.

Effect of feeder free poly(lactide-co-glycolide) scaffolds on morphology, proliferation, and pluripotency of mouse embryonic stem cells.

The aim of the study has been to evaluate the morphology, proliferation, and pluripotency maintenance of mouse embryonic stem cells (mESCs) cultivated on poly(lactic-co-glycolic acid) scaffolds. The scaffolds were hydrolyzed with NaOH (treated) and nonhydrolyzed (untreated). Morphological and mechanical characterization of the scaffolds was performed. mESC were evaluated for cell viability, cytotoxicity, expression of pluripotency markers, colony morphology, and overall distribution. The treatment generated a reduction in the hydrophobic characteristics of the scaffolds, leading to a higher wettability compared to the untreated group. The viability, cytotoxicity, number of colonies, and the thickness of the cell layer presented similar results between the scaffold groups. The viability test showed that it was possible to cultivate the mESCs on the scaffolds. The cytotoxicity analysis showed that the PLGA scaffolds were not harmful for the cells. The cells maintained the expression of the pluripotency markers Oct4 and Sox2. The number of colonies and the thickness of the cell layer on the scaffold showed that they were not able to colonize the entire volume of the scaffolds. The area occupied by the mESCs was the same between the treated and untreated groups after 14 days in culture. It is possible to conclude that both conditions are equally suitable for maintaining mESC culture. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 424-432, 2017.

Symmetrical and asymmetrical cyanine dyes. Synthesis, spectral properties, and BSA association study.

New cyanines were prepared by an efficient and practical route with satisfactory overall yield from low-cost starting materials. The photophysical behavior of the cyanines was investigated using UV-vis and steady-state fluorescence in solution, as well as their association with bovine serum albumin (BSA) in phosphate buffer solution (PBS). No cyanine aggregation was observed in organic solvents or in phosphate buffer solution. The alkyl chain length in the quaternized nitrogen was shown to be fundamental for BSA detection in PBS in these dyes.

The effect of sterilization methods on electronspun poly(lactide-co-glycolide) and subsequent adhesion efficiency of mesenchymal stem cells.

The sterilization of scaffolds is an essential step for tissue engineering in vitro and, mainly, clinical biomaterial use. However, this process can cause changes in the structure and surface of the scaffolds. Therefore, the objective of this study was to investigate the effect of sterilization by ethanol, ultraviolet radiation (UVR) or antimicrobial solution (AMS) on poly(lactide-co-glycolide) (PLGA) scaffolds produced by the electrospinning technique. The properties of nanofibers and the cellular adhesion of mesenchymal stem cells to the scaffolds were analyzed after the treatments. All methods generated sterile scaffolds but showed some kind of damage to the scaffolds. Ethanol and AMS caused changes in the morphology and scaffold dimensions, which were not observed when using the UVR method. However, UVR caused a greater reduction in polymeric molecular weight, which increased proportionally with exposure time of treatment. Nanofibers sterilized with AMS for 1 h and 2 h showed greater cellular adhesion than the other methods, demonstrating their potential as a method for sterilizing PLGA nanofibers.

1,3-Diethyl-2-thiobarbituric acid as an alternative coinitiator for acidic photopolymerizable dental materials.

The ethyl-4-dimethylaminobenzoate (EDAB) is widely used as a coinitiator of the camphorquinone (CQ), but in acidic circumstances it might present some instability, reducing the polymerization efficiency of the material. Considering this, new coinitiators are being evaluated. Hence, this study evaluated the kinetic of polymerization (KP), the degree of conversion (DC), and the rate of polymerization (RP ) of experimental resin adhesives containing 1,3-diethyl-2-thiobarbituric acid (TBA) as a coinitiator of the CQ. The experimental monomeric blend was prepared with bisphenol A glycidyl dimethacrylate, 2-hydroxyethyl methacrylate, and acidic monomers. CQ was added at 1 mol % as photoinitiator. Six groups were formulated: four containing concentrations of 0.1, 0.5, 1, and 2 mol % of TBA, one without coinitiator, and the last one containing 1 mol % of EDAB (control group). The KP and the RP were performed using real-time Fourier Transform infrared spectroscopy. The group without coinitiator has not formed a polymer, whereas the addition of TBA resulted in the conversion of monomers in polymer. The DC of the adhesives was as higher as the increase in the TBA content. The group with 2 mol % of TBA presented improved DC and reactivity (RP ) than the other groups and the control one. Hence, the TBA has performed as a coinitiator of the CQ for the radical polymerization of methacrylate resin adhesives and it has improved the DC and the reactivity of the materials. Thus, it is a potential coinitiator for the photopolymerization of dental materials.

AFM characterization of spin coated carboxylated polystyrene nanospheres/xyloglucan layers on mica and silicon.

Self-assembled nano-arrays have a potential application as solid-phase diagnostics in many biomedical devices. The easiness of its production is directly connected to manufacture cost reduction. In this work, we present self-assembled structures starting from spin coated thin films of carboxylated polystyrene (PSC) and xyloglucan (XG) mixtures on both mica and silicon substrates. AFM images showed PSC nanospheres on top of a homogeneous layer of XG, for both substrates. The average nanosphere diameter fluctuated for a constant speed and it was likely to be independent of the component proportions on the mixture within a range of 30-50% (v/v) PSC. It was also observed that the largest diameters were found at the center of the sample and the smallest at the border. The detected nanospheres were also more numerous at the border. This behavior presents a similarity to spin coated colloidal dispersions. We observed that the average nanosphere diameter on mica substrates was bigger than the nanosphere diameters obtained on top of silicon substrates, under the same conditions. This result seems to be possibly connected to different mixture-surface interactions.

Structure of micelles formed by highly asymmetric polystyrene-b-polydimethylsiloxane and polystyrene-b-poly[5-(N,N-diethylamino)isoprene] diblock copolymers.

The internal structure of polystyrene(PS)-shell micelles having core-forming blocks consisting of polydimethylsiloxane (PDMS) or poly[5-(N,N-diethylamino)isoprene] (PAI) was determined in detail by accessing the multilevel structural organization using static and dynamic light scattering and small-angle X-ray scattering techniques. Well-defined PS-b-PDMS and PS-b-PAI diblock copolymers with molar masses in the range of 12.0k-18.2k g/mol were dispersed in cyclohexane, dimethylacetamide, or dimethylformamide. Colloidal nanoparticles exhibiting either swollen core with a large surface area per corona chain that enables the PS chains to assume a random coil conformation with gaussian statistics, or compact core and slightly stretched PS chains in the corona were obtained. Therefore, the results of this study provide an interesting alternative allowing for precise control of the core and corona properties of PS-b-PDMS and PS-b-PAI micelles in selective solvents. Admittedly, such differences in terms of micellar properties can dictate the potential of block copolymer micelles for generating thin films from preformed nano-objects, as well as the capability to function as nanoreactors in organic medium.

Internal structural characterization of triblock copolymer micelles with looped corona chains.

We report the characterization through SAXS measurements of micelles produced from a new series of block copolymers: one diblock and four triblock copolymers bearing short poly[5-(N,N-diethylamino)isoprene] and long polystyrene blocks. Micellar aggregates produced in DMF (selective solvent for polystyrene) from the same set of samples were previously successfully characterized through light scattering measurements. The X-ray scattering profiles of starlike (from the diblock copolymer sample) and flowerlike micelles (from the triblock copolymers samples) could be fitted using the spherical copolymer micelle model proposed by Pedersen and Gerstenberg (Macromolecules 1996, 29, 1363.) where in the case of flowerlike micelles, the particles were understood as formed by hypothetical diblock copolymers having half of the true polymeric molar mass. Using the spherical copolymer micelle model, it could be possible to attest the unswollen nature of the micellar cores. The total micellar size suggested thus that the chains forming the corona are extended which is mainly related to a small core surface area per corona chain entering the core (Ac/n), which also induced a small number of aggregation (N(agg)) of all self-assembled particles. The total micellar size fits well with our previous light scattering measurements.

2-hydroxyethyl methacrylate as an inhibitor of matrix metalloproteinase-2.

This study evaluated the effect of different concentrations of 2-hydroxyethyl methacrylate (HEMA) on the inhibition of matrix metalloproteinase-2 (MMP-2) in vitro. Mouse gingival explants were cultured overnight in Dulbecco's modified Eagle's minimal essential medium, following which the expression of secreted enzymes was analyzed by gelatin zymography and the effects of different amounts of HEMA on enzyme activity were investigated. The gelatinolytic proteinases present in the conditioned media were characterized as being matrix metalloproteinases (MMPs) by means of specific chemical inhibition. The MMPs present in the conditioned media were identified, using immunoprecipitation, as MMP-2. Three major bands were detected in the zymographic assays and were characterized, according to their respective molecular weights, into the following forms of MMP-2: zymogene (72 kDa), intermediate (66 kDa), and active (62 kDa). All forms of MMP-2 were inhibited by HEMA in a dose-dependent manner, implying that MMP-2 may be inhibited by HEMA in vivo.

Aggregation behavior of a new series of ABA triblock copolymers bearing short outer A blocks in B-selective solvent: from free chains to bridged micelles.

A combination of dynamic (DLS) and static (SLS) light scattering measurements was employed to study the self-assembly behavior of a new series of triblock copolymers bearing poly[5-(N,N-diethylamino isoprene)] (PAI) short outer blocks and polystyrene (PS) as the major middle block. Previously, it was verified that PAI outer blocks can be quaternized leading the formation of crew-cut aggregates in water (Riegel, I. C.; Eisenberg, A.; Petzhold, C. L.; Samios, D. Langmuir 2002, 18, 3358). Herein, we focus on the copolymer's ability in the nonquaternized version to undergo self-aggregation in dimethylformamide (DMF), a selective solvent for the middle block. Light scattering measurements showed that formation of well-defined flowerlike micelles is likely to occur. Aggregates with a relatively narrow distribution, small average size, and number of aggregation ranging from 21 to 39 chains/micelle were experimentally observed. The results also suggested that approximately 5-6 polymeric units per each short outer block are needed to induce aggregation. The middle block length governs the size of the micelles and influences the number of aggregation of the resultant particles as well. Furthermore, when the polystyrene middle block was particularly long (degree of polymerization DP > 600), dynamic and static light scattering measurements suggested the formation of bridged micelles in an open structure in concentrations as low as 15 mg mL-1.

Influence of chain extender length of aromatic dimethacrylates on polymer network development.

OBJECTIVE: To investigate the role of chain extender size from Bis-EMA monomers on the polymerization profiles and properties of the crosslinked polymers. Additionally, the influence of Bis-GMA was also evaluated. METHODS: The polymer network from homopolymers Bis-EMA4, Bis-EMA10 and Bis-EMA30 was characterized, as well as copolymers formed among these monomers and Bis-GMA. The degree of conversion from neat and blended monomers as a function of photo-activation time was evaluated by FTIR. Rate of polymerization, network parameter and cross-link density from materials were demonstrated. Water sorption and solubility were determined according to ISO 4049 specification and the data obtained were analyzed by two-way ANOVA/Tukey's test (alpha=0.05). Flexural strength and Young's modulus from polymerized monomers/co-monomers were measured after 24h water storage at 37 degrees C and the results were analyzed by one-way ANOVA/Tukey's test (alpha=0.05). RESULTS: Monomers with larger ethylene oxide units presented the highest values regarding the degree of conversion and cross-link density. The effect of the chain extender length was also observed in water sorption and solubility polymer characteristics, with Bis-EMA4 being the most hydrophobic polymer. Bis-EMA10 and Bis-EMA30 homopolymers were not able to be tested with the three point bending test due to their great flexibility. The addition of Bis-GMA produced stronger and more rigid Bis-EMA polymers (p<0.05). SIGNIFICANCE: Aromatic dimethacrylates with different chain extender lengths can be a useful alternative in controlling the properties of a dental material, adjusting those to specific applications.

Onium salt reduces the inhibitory polymerization effect from an organic solvent in a model dental adhesive resin.

This study evaluated the effect of organic solvent concentration on the polymerization kinetics for a model dental adhesive resin containing a ternary photoinitiator system. A monomer blend based on the bis-GMA, TEGDMA, and HEMA was used as a model dental adhesive resin, which was polymerized using a binary system [camphorquinone (CQ) and ethyl 4-dimethylamine benzoate (EDAB)] and a ternary system [CQ, EDAB, and diphenyliodonium hexafluorphosphate (DPIHFP)]. Additionally, these blends had 0, 10, 20, 30, and 40 wt % ethanol added. Real-time Fourier transform infrared spectroscopy was used to investigate the polymerization reaction over photoactivation time. Data were plotted, and Hill's three-parameter nonlinear regression was performed for curve fitting. The addition of a solvent to the monomer blends decreased the polymerization kinetics, directly affecting the rate of polymerization, delaying vitrification, and attenuating the Trommsdorf effect. The introduction of DPIHFP displayed a strong increase in reaction kinetics, reducing the solvent inhibition effect. After 10 s of photoactivation, the binary system obtained in 0, 10, 20, 30, and 40% of ethanol, a degree of conversion of 44.6, 26.3, 13.4, 1.15, and 0.0%, respectively, whereas when a ternary system was used, the values were 54.6, 40.5, 27.4, 14.5, and 3.4%. An improvement was observed in the polymerization kinetics of a model dental adhesive resin when using a ternary photoinitiation system, making the material less sensitive to the residual presence of a solvent before photoactivation.

Non-destructive method for determination of hydroxyl value of soybean polyol by LS-SVM using HATR/FT-IR.

This paper presents the use of least-squares support vector machine (LS-SVM) for quantitative determination of hydroxyl value (OHV) of hydroxylated soybean oils by horizontal attenuated total reflection Fourier transform infrared (HATR/FT-IR) spectroscopy. A least-squares support vector machine (LS-SVM) calibration model for the prediction of hydroxyl value (OHV) was developed using the range 1805.1-649.9 cm(-1). Validation of the method was carried out by comparing the OHV of a series of hydroxylated soybean oil predicted by the LS-SVM model to the values obtained by the AOCS standard method. A correlation coefficient equal to 0.989 and RMSEP = 4.96 mg of KOH/g was obtained. This study demonstrates a better prediction ability of the LS-SVM technique to determine OHV in hydroxylated soybean oil samples by HATR/FT-IR spectra.