Low-viscosity Solutions Research Articles

Liquidus Tracking: Large scale preservation of encapsulated 3-D cell cultures using a vitrification machine

Currently, cryo-banking of multicellular structures such as organoids, especially in large volumes at clinical scale >1 L, remains elusive for reasons such as insufficient dehydration and cryoprotectant additive (CPA1) penetration, slow cooling and warming rates and devitrification processes. Here we introduce the concept of Liquidus Tracking (LT) using a semi-automated process for liquid volumes of up to 450 ml including 130 ml of alginate encapsulated liver cells (AELC) that archived controlled and reversible vitrification with minimized toxicity.First a CPA solution with optimal properties for LT was developed by employing different small scale test systems. Combining sugars such as glucose and raffinose with Me2SO improved post-exposure (at +0.5 °C) viabilities from 6% ±3.6 for Me2SO alone up to 58% ±6.1 and 65% ±14.2 respectively (p < 0.01). Other permeating CPAs (e.g. ethylene glycol, propylene glycol, methanol) were investigated as partial replacements for Me2SO. A mixture of Me2SO, ethylene glycol and glucose (ratio 4:2:1– termed LTdeg) supported glass-forming tendencies with appropriate low viscosities and toxicities required for LT. When running the full LT process, using Me2SO alone, no viable cells were recovered; using LTdeg, viable recoveries were improved to 40% ±8 (p<0.001%). Further refinements of improved mixing technique further improved recovery after LT. Recoveries of specific liver cell functions such as synthesis of albumin and alpha-fetoprotein (AFP) were retained in post thaw cultures.In summary: By developing a low-toxicity CPA solution of low viscosity (LTdeg) suitable for LT and by improving the stirring system, post-warming viability of AELC of up to 90% and a AFP secretion of 89% were reached. Results show that it may be possible to develop LT as a suitable cryogenic preservation process for different cell therapy products at large scale.

Extraction and Physicochemical Characterization of Mucilage from Opuntia cochenillifera (L.) Miller

The aim of this study was to extract mucilage from O. cochenillifera (L.) cacti and determine its functional and physicochemical properties. The best mucilage yield (31%) was obtained by nonthermal extraction with hydration. The mucilage has appreciable carbohydrate and protein contents. The phytochemical analysis shown the presence of alkaloids and terpenes/steroids. The Fourier transformed infrared (FT-IR) spectrum of the mucilage exhibits typical bands for carbohydrates as O–H, C–H, and –COO−. The mucilage demonstrated water- and oil-holding capacities of 2.78 g water/g dry mucilage and 1.80 g oil/g dry mucilage, respectively, these properties can have a positive effect on the texture of the products when used as a stabilizer. The mildly acidic pH (4.8–5) contributes to its emulsifying capacity. The presence of electrolytes in the mucilage can be of great value in flocculation processes. The mucilage forms low viscosity solutions in the same manner as gum Arabic. Finally, its potential for use as a textile dye remover was evaluated, achieving a 70% removal rate from aqueous solutions. The prepared mucilage exhibits properties that recommend it as a natural material that can be used as an additive in the chemical, food, pharmaceuticals and cosmetics industries, as well as in decontamination processes.

Effect of Polymer Concentration, Rotational Speed, and Solvent Mixture on Fiber Formation Using Forcespinning®

Polycaprolactone (PCL) fibers were produced using Forcespinning® (FS). The effects of PCL concentration, solvent mixture, and the spinneret rotational speed on fiber formation were evaluated. The concentration of the polymer in the solvents was a critical determinant of the solution viscosity. Lower PCL concentrations resulted in low solution viscosities with a correspondingly low fiber production rate with many beads. Bead-free fibers with high production rate and uniform fiber diameter distribution were obtained from the optimum PCL concentration (i.e., 12.5 wt%) with tetrahydrofuran (THF) as the solvent. The addition of N, N-dimethylformamide (DMF) to the THF solvent promoted the gradual formation of beads, split fibers, and generally affected the distribution of fiber diameters. The crystallinity of PCL fibers was also affected by the processing conditions, spinning speed, and solvent mixture.

The Morphology of Electrospun Titanium Dioxide Nanofibers and Its Influencing Factors

Titanium dioxide (TiO2) has high photocatalytic activity and it is extensively applied in solar cell technology and environmental science. Electrospinning is acknowledged as the most versatile technique to fabricate nanofibers such as metal oxide nanofibers. Titanium dioxide nanofibers are generally prepared by electrospinning organic solutions containing alkoxide precursors and a carrier polymer with high voltage supply. The paper discusses on electrospun TiO2 nanofibers including the spin dopes preparation history, influencing factors on fiber morphology and fiber characterizations. In particular, the parameters such as spin dopes viscosity, supplied voltage, feeding rate and effect of temperature that affect the morphology of the nanofibers are emphasized. Based on several studies, smaller diameter of TiO2 nanofibers can be produced with lower viscosity solution, higher voltage and lower feeding rate. The heat treatment of 500 °C reduced the fiber size and produces crystallized anatase TiO2 nanofibers.

Dendritic Polymers for Theranostics.

Dendritic polymers are highly branched polymers with controllable structures, which possess a large population of terminal functional groups, low solution or melt viscosity, and good solubility. Their size, degree of branching and functionality can be adjusted and controlled through the synthetic procedures. These tunable structures correspond to application-related properties, such as biodegradability, biocompatibility, stimuli-responsiveness and self-assembly ability, which are the key points for theranostic applications, including chemotherapeutic theranostics, biotherapeutic theranostics, phototherapeutic theranostics, radiotherapeutic theranostics and combined therapeutic theranostics. Up to now, significant progress has been made for the dendritic polymers in solving some of the fundamental and technical questions toward their theranostic applications. In this review, we briefly summarize how to control the structures of dendritic polymers, the theranostics-related properties derived from their structures and their theranostics-related applications.

Imidazole-catalyzed esterification of cellulose in ionic liquid/molecular solvents: A multi-technique approach to probe effects of the medium

Observed rate constants (kobs) for the imidazole-catalyzed acylation of microcrystalline cellulose by carboxylic acid anhydrides (ethanoic to hexanoic) were calculated from conductivity data. The reaction media consisted of the ionic liquid, IL, 1-allyl-3-methylimidazolium chloride and the molecular solvents, MSs, N,N-dimethylacetamide, DMAc, dimethylsulfoxide, DMSO, and sulfolane, Sulfn. The latter two carry the same dipole (S=O) and have some similar properties. Using FTIR, we showed that the acylating agent is N-acylimidazole. The reaction third order rate constants (k3) depend slightly on [IL] because the reactant is cellulose-IL complex. For ethanoic anhydride, values of k3 decrease in the order: IL-DMSO>IL-DMAc>IL-Sulfn. We analyze this dependence on the nature of the MS by considering the reaction activation parameters; some macroscopic and microscopic properties of the binary solvent mixtures and cellulose solutions therein, and the results of molecular dynamics simulations. Favorable activation enthalpy; lower solution viscosity; larger empirical polarity and basicity, and stronger biopolymer-solvent interactions are responsible for the faster reaction in IL-DMSO, relative to that in IL-Sulfn. The dependence of the values of (k3) on the number of carbon atoms in the acyl moiety showed a complex behavior (decrease from C2 to C4 and then increase), similar to that observed before, probably because of enthalpy/entropy compensation.

Thermal and dielectric properties of electrospun fiber membranes from polyimides with different structural units

ABSTRACTIn this work, electrospinning technique was used to prepare low dielectric constant membranes. First, three kinds of polyimide (PI) fiber membranes were fabricated by electrospinning of poly(amic acid) (PAA) solutions which are from polycondensation of 4,4′‐oxidianiline (ODA) and three dianhydrides, pyromellitic dianhydride (PMDA), 2,2′‐bis(3,4‐dicarboxyphenyl) hexafluropropane dianhydride (6FDA) and 1,2,4,5‐cyclohexanetetracarboxylic dianhydride(HPMDA), followed by imidization at higher temperature. The relationship of the fiber morphology, thermostability and dielectric properties of the membranes with the polymer structure were discussed. Under the same conditions, PAAs with more flexible structure are easier to form low viscosity solution and fabricate high pore fraction membranes which are low dielectric constant materials. Under the coupling effect of fluorine‐containing groups and contribution of pores, the dielectric constant of 6FDA‐containing PI is lowered to 1.21 at 1 KHz with lower dielectric loss which accords with the calculated one. Also the 5% weight loss temperature of the three kinds of PIs is all higher than 400°C. The formed electrospun membranes are thermostable low dielectric constant materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43081.

Revealing New Structural Insights from Surfactant Micelles through DLS, Microrheology and Raman Spectroscopy

The correlation between molecular changes and microstructural evolution of rheological properties has been demonstrated for the first time in a mixed anionic/zwitterionic surfactant-based wormlike micellar system. Utilizing a novel combination of DLS-microrheology and Raman Spectroscopy, the effect of electrostatic screening on these properties of anionic (SLES) and zwitterionic (CapB) surfactant mixtures was studied by modulating the NaCl concentration. As Raman Spectroscopy delivers information about the molecular structure and DLS-microrheology characterizes viscoelastic properties, the combination of data delivered allows for a deeper understanding of the molecular changes underlying the viscoelastic ones. The high frequency viscoelastic response obtained through DLS-microrheology has shown the persistence of the Maxwell fluid response for low viscosity solutions at high NaCl concentrations. The intensity of the Raman band at 170 cm−1 exhibits very strong correlation with the viscosity variation. As this Raman band is assigned to hydrogen bonding, its variation with NaCl concentration additionally indicates differences in water structuring due to potential microstructural differences at low and high NaCl concentrations. The microstructural differences at low and high NaCl concentrations are further corroborated by persistence of a slow mode at the higher NaCl concentrations as seen through DLS measurements. The study illustrates the utility of the combined DLS, DLS-optical microrheology and Raman Spectroscopy in providing new molecular structural insights into the self-assembly process in complex fluids.

B(12)-mediated, long wavelength photopolymerization of hydrogels.

Medical hydrogel applications have expanded rapidly over the past decade. Implantation in patients by noninvasive injection is preferred, but this requires hydrogel solidification from a low viscosity solution to occur in vivo via an applied stimuli. Transdermal photo-cross-linking of acrylated biopolymers with photoinitiators and lights offers a mild, spatiotemporally controlled solidification trigger. However, the current short wavelength initiators limit curing depth and efficacy because they do not absorb within the optical window of tissue (600-900 nm). As a solution to the current wavelength limitations, we report the development of a red light responsive initiator capable of polymerizing a range of acrylated monomers. Photoactivation occurs within a range of skin type models containing high biochromophore concentrations.

Food Colors as Intrinsic Luminescent Sensors in Edible Products

Limited use of luminescence spectroscopy in food and pharmaceutical applications can be related to two main causes: a)the inherent properties of most useful fluorophores (low availability, toxicity, high price and restricted solubility), and b)incomplete photophysical characterization of edible and safe-to-ingest fluorophores.To expand the use of luminescence spectroscopy to monitor quality and safety of edible goods, photophysical properties of five generally-recognized-as-safe(GRAS) food colors that are routinely added to foods or pharmaceuticals were assessed. The sensitivity of the food dyes’ fluorescence emission intensity to the surrounding medium's rigidity and polarity were also determined.Environmental polarity moderately impacted the location of the fluorescence intensity peaks and bathochromic shifts were observed for all dyes as the polarity of the solvents increased. The Stokes shifts,(λem-λexc), were estimated to be 45-90nm depending on the medium and molecular structure of the synthetic color.All these food dyes were practically non emissive in common fluid solvents, which can explain the limited information on their photophysical properties. Excited state tautomerization and/or internal twisting, already reported in synthetic non-edible dyes in low viscosity solutions, can also constitute the predominant non- radiative relaxation pathway of the studied food colors in fluid environments. The medium's rigidity was altered by changing temperature and composition. As the viscosity and consistency index of the surrounding medium increased, the dyes’ fluorescent emission intensity also increased, which suggests the molecular rotor character of these dyes. The maximum fluorescence intensity of each dye vs. viscosity relationship was characterized by a power law model and the sensitivity of each dye to changes in viscosity was evaluated in terms of its parameters.In principle, the large Stokes shift and sensitivity to viscosity supports the potential use of these food colors as probes of microviscosity or molecular crowding in edible goods.

Expanding the Dimensionality of Polymers Populated with Organic Robust Radicals toward Flow Cell Application: Synthesis of TEMPO-Crowded Bottlebrush Polymers Using Anionic Polymerization and ROMP

Poly(norbornene)-g-poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl) (PNB-g-PTMA) was prepared by a grafting-through approach based on anionic polymerization of 4-methacryloyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl using a norbornene-substituted diphenylhexyllithium to yield a norbornene-functionalized macromonomer (NB-PTMA) and subsequent ring-opening metathesis polymerization of NB-PTMA using a Grubbs third-generation catalyst, which avoided critical side reactions involving the nitroxide radical of TEMPO moiety. The anionic polymerization resulted in high yields (>94%), narrow polydispersity indices (<1.20), and radical concentrations (0.95 radicals per monomer unit). The ROMP also resulted in high yields (>98%) and high radical concentrations (0.95 radicals per monomer unit), by virtue of the functional group tolerance of these reactions. Single molecular dimension of PNB-g-PTMA was measured by dynamic light scattering and by atomic force microscopy (AFM), which precisely reflected the bottlebrush structure to reveal the presence of the TEMPO group crowded at the periphery of the molecule. The lengths of PNB-g-PTMA along the macromolecular side chains and the polynorbornene main chain were both approximately equal to the theoretical lengths estimated by the degree of polymerization for each chain. The number-average diameter of PNB-g-PTMA in THF increased with initial NB-PTMA ratio to the Grubbs catalyst. Photo-cross-linked thin layer electrodes of PNB-g-PTMA demonstrated the reversible redox reaction at 0.80 V vs Ag/AgCl corresponding to the TEMPO/TEMPO+ couple and quantitative charging/discharging processes even at 120 C rate (i.e., full charging in 30 s). As a novel application of redox-active polymers, PNB-g-PTMA exhibited 95% efficiency of the theoretical charge capacity in a flow cell system, based on the unique properties of bottlebrush polymers such as the defined molecular dimension and relatively low solution viscosity in comparison with corresponding linear polymers.

Core-Liquid-Induced Transition from Coaxial Electrospray to Electrospinning of Low-Viscosity Poly(lactide-co-glycolide) Sheath Solution

Co-electrospinning has demonstrated that polymer solutions below the entanglement concentration can be made into fibers as an encapsulated core in an electrospinnable sheath solution containing a carrier/template polymer. The carrier polymer may require removal at a later stage. This work shows for the first time that without increasing the polymer concentration/molecular weight or needing a template polymer, simply infusing a liquid in the core nozzle can cause the sheath polymer solution (viscosity <20 mPa s) to electrospin instead of electrospray in a coaxial electrified jet. Different from coelectrospinning, the core liquid can be a common solvent such as water and does not require a readily electrospinnable carrier polymer. The process was not limited to one core liquid system; infusing solvents and nonsolvents with different properties in the core generated either beaded fibers or continuous fibers from the sheath solution. The process of fiber formation instead of particle breakup was attributed to the relaxation time of the elastic polymer sheath solution becoming longer than the growth rate of the Rayleigh instability in the compound jet upon the infusion of a second solvent in the core. Key parameters of the process included high surface tension of the core liquid (e.g., water and glycerol), high interfacial tension between the core and the sheath liquids, and electrohydrodynamic operating parameters such as flow rate and applied voltage. Given that charge was transferred from the sheath solution to the core liquid, differences in the dielectric constant and electrical conductivity of the core liquids showed little influence on the process. Fibers also formed irrespective of the miscibility and solubility of the solvent, though in the case of a nonsolvent, a lower miscibility was desirable to minimize polymer precipitation at the core–sheath interface. The process was investigated using poly(lactide-co-glycolide) as a model system, with polycaprolactone and polymethylsilsesquioxane systems presented as two additional examples. This work documents new roles of solvents in coaxial electrohydrodynamic processes and presents a useful method to obtain micro- and nanofibers from low-viscosity solutions without using a template polymer.

Mediating gel formation from structurally controlled poly(electrolytes) through multiple "head-to-body" electrostatic interactions.

Tuning the chain-end functionality of a short-chain cationic homopolymer, owing to the nature of the initiator used in the atom transfer radical polymerization (ATRP) polymerization step, can be used to mediate the formation of a gel of this poly(electrolyte) in water. While a neutral end group gives a solution of low viscosity, a highly homogeneous gel is obtained with a phosphonate anionic moiety, as characterized by rheometry and diffusion nuclear magnetic resonance (NMR). This novel type of supramolecular control over poly(electrolytic) gel formation could find potential use in a variety of applications in the field of electro-active materials.

Impact of salts on polyacrylamide hydrolysis and gelation: New insights

ABSTRACTPolyacrylamide (PAM) and its derivatives are the most commonly used polymers in the preparation of polymeric gels for water control in petroleum reservoirs. This study involved the use of polyethylenimine (PEI) as a crosslinker for PAM. In this study, we investigated PAM alkaline hydrolysis at high temperatures. The effects of salts [sodium chloride (NaCl) and ammonium chloride (NH4Cl)] on the degree of hydrolysis (DH) of PAM were investigated. These salts were used as retarders to elongate the gelation time of the PAM/PEI system. The data obtained from 13C‐NMR was used to understand the retardation mechanisms by salts. We found that NH4Cl accelerated the extent of hydrolysis more in comparison with NaCl. Moreover, the apparent viscosity of the hydrolyzed samples was measured. PAM hydrolysis in the presence of NH4Cl resulted in a lower solution viscosity than that in the presence of NaCl. Therefore, NH4Cl was more effective in shielding negative charges on the carboxylate groups of the partially hydrolyzed polyacrylamide (PHPA) chain. NaCl and NH4Cl were compatible with the PHPA/PEI system, but sodium carbonate showed a white precipitate. In addition, high‐temperature/high‐pressure elastic modulus data were reported for the first time for this system. Differential scanning calorimetry was coupled with rheology to explain the PAM/PEI crosslinking in the presence of salts. Models were developed to assess the impact of the salts on the PAM DH and the induction period before gelation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41185.

Effect of diffusion on Förster resonance energy transfer in low-viscosity solution

The effect of translational diffusion on Förster resonance energy transfer between rhodamine 6G (the donor) and malachite green (the acceptor) was investigated by examining the donor's fluorescence decay profile. Eight straight-chain alkyl alcohols were used, and the temperature of ethanol was changed to vary the viscosity; the decay profiles were analyzed using the theory developed by Gösele. The critical transfer distance obtained from the decay profile is in good agreement with that evaluated using the spectroscopic quantities, and the diffusion coefficients are consistent with the Stokes-Einstein relation. The fluorescence decay profile was described well by Gösele's theory and the effect of diffusion is clearly verified by the temperature/viscosity dependence of the diffusion constant.

CO2-responsive anionic wormlike micelles based on natural erucic acid

Research interests highlighted in recent years a remarkable growing focus on stimuli-responsive surfactant wormlike micelles, particularly those using carbon dioxide as the trigger. In this article, we report a novel carbon dioxide–responsive wormlike micellar system based on natural erucic fatty acid and examined its solution properties through rheology, Fourier transform infrared spectroscopy and cryo–tranmission electron microscopy. When carbon dioxide is introduced into the erucic acid solution, high-viscelastic wormlike micelles shift to low-viscosity solutions in short-time scale, accompanied by decrease in pH from 11·34 to 8·90, which is accounted for the effect of pH on the existence form of erucic acid in aqueous solutions. Bubbling nitrogen under heating cannot make a converse process since the viscoelastic worms can only be obtained at a high pH. Compared with other carbon dioxide–responsive wormlike micelles, the current one is more readily obtained and more environment-friendly because it can be formed by simply changing pH value of the natural erucic acid solutions without needing complex organic synthesis or addition of hydrotropes.

Occurrence and morphology of bead-on-string structures in centrifugal forcespun PA6 fibers

This research aimed at investigating the morphology and frequency of bead-on-string occurrences on forcespun nano- and sub-micron fibers. The formation of bead-on-string structures was observed on a range of fiber samples forcespun in varied conditions from PA6 solutions of different concentrations. Bead-on-string structures were characterized for morphology using SEM micrographs, and were counted on all samples. Two major factors appeared to affect both the morphology and the bead count, namely spinning solution concentration, i.e. viscosity, and spinning needle gage or diameter. Low viscosity solutions resulted in large numbers of mostly spherical beads. Solutions with higher viscosity appeared to suppress the fluid jet instability thus resulting in significantly fewer beads with exclusively elongated spindle-like shapes. Spinning needle diameter also had a significant impact on beading behavior, with the larger diameter exhibiting higher bead counts. A significant interaction between the two factors was detected and its impact on the competition between the fluid jet visco-elastic relaxation and the Rayleigh instability is discussed.

Insights into organogelation and its kinetics from Hansen solubility parameters. Toward a priori predictions of molecular gelation

Many small molecules can self-assemble by non-covalent interactions into fibrous networks and thereby induce gelation of organic liquids. However, no capability currently exists to predict whether a molecule in a given solvent will form a gel, a low-viscosity solution (sol), or an insoluble precipitate. Gelation has been recognized as a phenomenon that reflects a balance between solubility and insolubility; however, the distinction between these regimes has not been quantified in a systematic fashion. In this work, we focus on a well-known gelator, 1,3:2,4-dibenzylidene sorbitol (DBS), and study its self-assembly in various solvents. From these data, we build a framework for DBS gelation based on Hansen solubility parameters (HSPs). While the HSPs for DBS are not known a priori, the HSPs are available for each solvent and they quantify the solvent's ability to interact via dispersion, dipole-dipole, and hydrogen bonding interactions. Using the three HSPs, we construct three-dimensional plots showing regions of solubility (S), slow gelation (SG), instant gelation (IG), and insolubility (I) for DBS in the different solvents at a given temperature and concentration. Our principal finding is that the above regions radiate out as concentric shells: i.e., a central solubility (S) sphere, followed in order by spheres corresponding to SG, IG, and I regions. The distance (R0) from the origin of the central sphere quantifies the incompatibility between DBS and a solvent-the larger this distance, the more incompatible the pair. The elastic modulus of the final gel increases with R0, while the time required for a super-saturated sol to form a gel decreases with R0. Importantly, if R0 is too small, the gels are weak, but if R0 is too large, insolubility occurs-thus, strong gels fall within an optimal window of incompatibility between the gelator and the solvent. Our approach can be used to design organogels of desired strength and gelation time by judicious choice of a particular solvent or a blend of solvents. The above framework can be readily extended to many other gelators, including those with molecular structures very different from that of DBS. We have developed a MATLAB program that will be freely available (upon request) to the scientific community to replicate and extend this approach to other gelators of interest.

UTILIZATION OF GUM ARABIC FOR INDUSTRIES AND HUMAN HEALTH

Gum Arabic, a natural polysaccharide derived from exudates of Acacia senegal and Acacia seyal trees, is a commonly used food hydrocolloid. The highlight of this study was to review the utilization of gum Arab ic for industries and human health. Gum Arabic has a unique combination of excellent emulsifying properties a nd low solution viscosity. These properties make gum Arabic very useful in several industries but especially in the food industry where it is used as a flavor and stabilize r of citrus oil emulsion concentrates in soft drink s.

Influence of solvents on deposition mechanism of Al-doped ZnO films synthesized by cold wall aerosol-assisted chemical vapor deposition

Using methanol, ethanol, 2-methoxyethanol and isopropanol as solvents in the precursor solutions, respectively, Al-doped ZnO films were synthesized on glass substrates by cold wall aerosol-assisted chemical vapor deposition. The deposition mechanism and the influence of solvents on deposition were discussed, finding that the degree of (0 0 2) orientation growth of the film was significantly influenced by the viscosity of precursor solutions. The deposition velocity decreased as the viscosity of precursor solution increased. Grains tended to uniformly distributed over the substrates for the samples deposited from high-viscosity solutions, while low-viscosity solutions resulted in grain agglomeration. Some droplets generated from 2-methoxyethanol system coagulated due to the greater surface tension. Grains that differ significantly in size were deposited on the film.