Internally self-assembled particles entrapped in thermoreversible hydrogels (original) (raw)
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Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2006
We identified the possible internally self-assembled phases that occur in oil-loaded monoglyceride-based nanoparticles that are dispersed in water. Temperature versus composition of the dispersed phase "T-δ" phase diagrams were constructed at a constant dispersed phase content upon varying the oil/monoglyceride weight ratio at a wide range of temperatures (1-90 • C). We mainly focused on the determination of these phase diagrams by changing the oil type or the monoglyceride purity. They were built when investigating the internal structure of the particles by means of small angle X-ray scattering (SAXS). We show that some internally self-assembled emulsified particles may contain a discontinuous cubic phase (Fd3m symmetry), depending on the oil content. However, the extension of this phase in the diagram strongly depends on the oil. This emulsified liquid crystalline phase is inserted between the inverse hexagonal H 2 phase and the inverse micellar solution L 2 phase, as was previously found in bulk. Moreover, we managed to find the existence of an indirect thermal transformation from hexosomes to emulsified micro-emulsions through micellar cubosomes (emulsified reversed discontinuous micellar cubic phase) within a narrow range of an oil/monoglycerides ratio. This transition via temperature has not been published to our knowledge in these dispersed systems.
Langmuir, 2018
Protein particles were complexed with polysaccharides and the effect on their capacity to stabilize water in water (W/W) emulsions was investigated. Protein microgels were formed by heating aqueous solutions of whey protein isolate. The microgels were subsequently mixed with anionic or cationic polysaccharides: κ-carrageenan (κ-car) or chitosan, respectively. The molar mass and radius of the complexes formed in dilute microgel suspensions (40 mg/L) were characterized by light scattering techniques as a function of the pH and the composition. The structure and stability of complexes formed at a higher microgel concentration (3 g/L) were studied by confocal laser scanning microscopy (CLSM). It was found that small stable complexes can be formed with κ-car between pH 4.3 and pH 5.5 and with chitosan between pH 4.1 and pH 6.5, i.e. both below and above the isoionic point of the microgels (pI = 5.0). Complexation with polysaccharides stabilized aqueous suspensions of microgels in the pH range where they flocculated in the absence of polysaccharides (4.3-5.5). W/W emulsions were produced by mixing dextran and poly(ethylene oxide) (PEO) solutions. Microgels added to these emulsions spontaneously form a layer around the dispersed droplets, which inhibits coalescence to different extents depending on the conditions. The effect of complexation on the structure of the emulsions was investigated as a function of the pH. It is shown that stable liquid like emulsions can be obtained in the pH range where emulsions containing only microgels flocculate.
Design of novel emulsion microgel particles of tuneable size
Food Hydrocolloids, 2017
In this study, we designed a one-step solvent-free route to prepare emulsion microgel 26 particles, i.e., microgel particles containing several sub-micron sized emulsion droplets 27 stabilised by heat-treated whey protein. The heat treatment conditions were optimized 28 using aggregation kinetics via fluorimetry and dynamic light scattering. Emulsions 29 were gelled and microgel particles were formed simultaneously via turbulent mixing 30 with calcium ions using two specific processing routes (Extrusion and T-mixing). By 31 varying the calcium ion concentration and mixing conditions, we identified the optimal 32 parameters to tune the size and structure of the resultant emulsion microgel particles. 33 Microscopy at various length scales (confocal laser scanning microscopy, scanning 34 electron microscopy) and static light scattering measurements revealed a decrease in 35 particle size (100 to 10 µm) with lower turbulent mixing time (ca. 4 ×10-4 s) and lower concentrations of calcium ions (0.1-0.02 M). Larger particle sizes (500-1000 µm) were achieved with an increase in the turbulent mixing time (ca. 2 ×10-2 s) and higher concentrations of calcium ions (1-1.4 M). Using gelation kinetics data (small deformation rheology) and theoretical considerations, creation of smaller sized emulsion microgel particles was explained by the increased flux of calcium ions to the denatured whey protein moieties coating the emulsion droplets, enabling faster gelation of the particle surfaces. These novel emulsion microgel particles of tuneable size formed as a result of complex interplay between calcium ion concentration, heat treatment of whey protein, gelation kinetics and mixing time, may find applications in food, pharmaceutical and personal care industries.
Macromolecular Diffusion in Self-Assembling Biodegradable Thermosensitive Hydrogels
Macromolecules, 2010
Hydrogel formation triggered by a change in temperature is an attractive mechanism for in situ gelling biomaterials for pharmaceutical applications such as the delivery of therapeutic proteins. In this study, hydrogels were prepared from ABA triblock polymers having thermosensitive poly(N-(2-hydroxypropyl)methacrylamide lactate) flanking A-blocks and hydrophilic poly(ethylene glycol) B-blocks. Polymers with fixed length A-blocks (∼22 kDa) but differing PEG-midblock lengths (2, 4, and 10 kDa) were synthesized and dissolved in water with dilute fluorescein isothiocyanate (FITC)-labeled dextrans (70 and 500 kDa). Hydrogels encapsulating the dextrans were formed by raising the temperature. Fluorescence recovery after photobleaching (FRAP) studies showed that diffusion coefficients and mobile fractions of the dextran dyes decreased upon elevating temperatures above 25°C. Confocal laser scanning microscopy and cryo-SEM demonstrated that hydrogel structure depended on PEG block length. Phase separation into polymer-rich and water-rich domains occurred to a larger extent for polymers with small PEG blocks compared to polymers with a larger PEG block. By changing the PEG block length and thereby the hydrogel structure, the mobility of FITC-dextran could be tailored. At physiological pH the hydrogels degraded over time by ester hydrolysis, resulting in increased mobility of the encapsulated dye. Since diffusion can be controlled according to polymer design and concentration, plus temperature, these biocompatible hydrogels are attractive as potential in situ gelling biodegradable materials for macromolecular drug delivery.
The influence of PEG macromonomers on the size and properties of thermosensitive aqueous microgels
Colloid and Polymer Science, 2009
We describe the preparation and thermal response of aqueous microgels based on poly(N-vinyl caprolactam) containing grafted poly(ethylene glycol) (PEG) chains. These microgels were synthesized by free radical copolymerization of vinyl caprolactam and acetoacetoxyethyl methacrylate in the presence of methoxycapped poly(ethylene glycol)methacrylate macromonomers. We show that variation of the amount of PEG macromonomer or the length of the PEG chain provides effective control of the microgel diameter in the range 60-220 nm. The presence of the grafted PEG chains improves the colloidal stability of the microgels. The incorporation of the PEG macromonomers into microgel structure decreases the swelling degree and induces a shift of the volume phase transition to higher temperatures.
Thermoresponsive microgel-based materials
With the continued development of thermoresponsive colloidal hydrogel particles, a number of groups have begun to exploit their properties to create dynamic materials self-assembled from those components. The fundamental details of how those building blocks are assembled, the component functionality, and the geometry or length-scales present in the assemblies contribute to the behavior of the resultant material. In this tutorial review, we examine recent progress in the assembly of responsive hydrogel colloids in two and three dimensions, highlighting their potential applications, especially in the domain of biotechnology.
Self-gelling hydrogels based on oppositely charged dextran microspheres
2005
This paper presents a novel self-gelling hydrogel potentially suitable for controlled drug delivery and tissue engineering. The macroscopic gels are obtained by mixing dispersions of oppositely charged crosslinked dextran microspheres. These microspheres in turn were prepared by crosslinking of dextran derivatized with hydroxyethyl methacrylate emulsified in an aqueous poly(ethylene glycol) solution. Negatively or positively charged microspheres were obtained by addition of methacrylic acid (MAA) or dimethylaminoethyl methacrylate (DMAEMA) to the polymerization mixture. Rheological analysis showed that instantaneous gelation occurred when equal volumes of oppositely charged microspheres, dispersed in buffer solutions of pH 7, were mixed. The shear modulus of the networks could be tailored from 30 to 6500 Pa by varying the water content of the system. Moreover, controlled strain and creep experiments showed that the formed networks were mainly elastic. Importantly for application of these systems, e.g. as controlled matrix of pharmaceutically active proteins, it was demonstrated that the hydrogel system has a reversible yield point, meaning that above a certain applied stress, the system starts to flow, whereas when the stress is removed, gel formation occurred. Further it was shown that the network structure could be broken by either a low pH or a high ionic strength of the medium. This demonstrates that the networks, formed at pH 7 and at low ionic strength, are held together by ionic interactions between the oppositely charged dextran microspheres. This system holds promise as injectable gels that are suitable for drug delivery and tissue engineering applications. r
Novel self-assembling nanogels: Stability and lyophilisation studies
2007
The stability of new supramolecular nanoassemblies (nanogels), based on the association of a hydrophobically modified dextran (MD) and a -cyclodextrin polymer (pCD), has been studied by two complementary methods: (i) size measurements and (ii) turbidity experiments using a Turbiscan optical analyser. Nanogels of about 120-150 nm were obtained whatever the concentration of the two polymer solutions. At low concentrations, the suspensions presented little mean diameter variations upon storage. However, the concentrated ones tended to destabilize and their mean diameter increased upon time. Size measurements and Turbiscan investigations have demonstrated that destabilization in the MD-pCD nanogel suspension was only due to particle aggregation and/or fusion, as no sedimentation or creaming occurred. The destabilization of MD-pCD suspensions led to the formation of a highly viscous phase, as a final state. Moreover, the two methods have shown that aggregation and/or fusion phenomena were more pronounced in the concentrated MD-pCD suspensions than in the diluted ones. The stability of MD-pCD suspensions could be improved by their storage at 4 • C. Finally, freeze-drying was found to be a convenient method for the long-time storage of MD-pCD nanoassemblies.