Glycosaminoglycans (GAGs) are of interest for biomedical applications because of their ability to retain proteins (e.g. growth factors) involved in cell-to-cell signaling processes. In this study, the potential of GAG-based microgels for protein delivery and their protein release kinetics upon encapsulation in hydrogel scaffolds were investigated. Monodisperse hyaluronic acid methacrylate (HAMA) and chondroitin sulfate methacrylate (CSMA) micro-hydrogel spheres (diameters 500-700 μm), were used to study the absorption of a cationic model protein (lysozyme), microgel (de)swelling, intra-gel lysozyme distribution and its diffusion coefficient in the microgels dispersed in buffers (pH 7.4) of varying ionic strengths. Upon incubation in 20 mM buffer, lysozyme was absorbed up to 3 and 4 mg mg⁻¹ dry microspheres for HAMA and CSMA microgels respectively, with loading efficiencies up to 100%. Binding stoichiometries of disaccharide : lysozyme (10.2 : 1 and 7.5 : 1 for HAMA and CSMA, respectively) were similar to those for GAG-lysozyme complex coacervates based on soluble GAGs found in literature. Complex coacervates inside GAG microgels were also formed in buffers of higher ionic strengths as opposed to GAG-lysozyme systems based on soluble GAGs, likely due to increased local anionic charge density in the GAG networks. Binding of cationic lysozyme to the negatively charged microgel networks resulted in deswelling up to a factor 2 in diameter. Lysozyme release from the microgels was dependent on the ionic strength of the buffer and on the number of anionic groups per disaccharide, (1 for HAMA versus 2 for CSMA). Lysozyme diffusion coefficients of 0.027 in HAMA and <0.006 μm² s⁻¹ in CSMA microgels were found in 170 mM buffer (duration of release 14 and 28 days respectively). Fluorescence Recovery After Photobleaching (FRAP) measurements yielded similar trends, although lysozyme diffusion was likely altered due to the negative charges introduced to the protein through the FITC-labeling resulting in weaker protein-matrix interactions. Finally, lysozyme-loaded CSMA microgels were embedded into a thermosensitive hydrogel scaffold. These composite systems showed complete lysozyme release in ∼58 days as opposed to only 3 days for GAG-free scaffolds. In conclusion, covalently crosslinked methacrylated GAG hydrogels have potential as controlled release depots for cationic proteins in tissue engineering applications.

Various mechanisms have been proposed to explain the nonphotochemical laser-induced nucleation (NPLIN). Identifying the dominant mechanism requires addressing a large set of experimental parameters with a statistically significant number of samples, forced by the stochastic nature of nucleation. In this study, with aqueous KCl system, we focus on the nucleation probability as a function of laser wavelength, laser intensity, and sample supersaturation, whereas the influence of filtration and the laser-induced radiation pressure on NPLIN activity is also studied. To account for the nucleation stochasticity, we used 80-100 samples. The NPLIN probability showed an increase with increasing laser intensity. The results are different from the previous report, as a supersaturation independent intensity threshold is not observed. No dependence of the NPLIN probability on the laser wavelength (355, 532, and 1064 nm) was observed. Filtration of samples reduced the nucleation probability suggesting a pronounced role of impurities on NPLIN. The magnitude and the propagation velocity of the laser-induced radiation pressure were quantified using a pressure sensor under laser intensities ranging from 0.5 to 80 MW/cm². No correlation was found between the radiation pressure and NPLIN at our unfocused laser beam intensities ruling out the radiation pressure as a possible cause for nucleation.

Evaporation of sessile droplets containing non-volatile solutes dispersed in a volatile solvent leaves behind ring-like solid stains. As the volatile species evaporates, pinning of the contact line gives rise to capillary flows that transport non-volatile solutes to the contact line. This phenomenon, called the coffee-ring effect, compromises the overall performance of industrially relevant manufacturing processes involving evaporation such as printing, biochemical analysis, manufacturing of nano-structured materials through colloidal and macromolecular patterning. Various approaches have been developed to suppress this phenomenon, which is otherwise difficult to avoid. The coffee-ring effect has also been leveraged to prepare new materials through convection induced assembly. This review underlines not only the strategies developed to suppress the coffee-ring effect but also sheds light on approaches to arrive at novel processes and materials. Working principles and applicability of these strategies are discussed together with a critical comparison.

Nanoemulsions possess powerful nano-scale properties that make them attractive for diverse applications such as drug delivery, food supplements, nanoparticle synthesis and pharmaceutical formulation. However, there is little knowledge in nanoemulsion literature about controlling and predicting droplet size. In this article, we propose a scaling relation to predict the dependence of nanoemulsion droplet size with physical properties such as viscosity of the droplet phase and continuous phase, and process parameters such as input power density. We validate our proposed scaling with a wide range of droplet size data from nanoemulsions prepared with high pressure homogenization and ultrasonication. Our proposed scaling also compares favorably with experimental data from literature. The scaling relation can serve as a guiding principle for rational design of nanoemulsions.

Nanoemulsions are kinetically stable liquid-in-liquid dispersions with droplet sizes on the order of 100 nm. Their small size leads to useful properties such as high surface area per unit volume, robust stability, optically transparent appearance, and tunable rheology. Nanoemulsions are finding application in diverse areas such as drug delivery, food, cosmetics, pharmaceuticals, and material synthesis. Additionally, they serve as model systems to understand nanoscale colloidal dispersions. High and low energy methods are used to prepare nanoemulsions, including high pressure homogenization, ultrasonication, phase inversion temperature and emulsion inversion point, as well as recently developed approaches such as bubble bursting method. In this review article, we summarize the major methods to prepare nanoemulsions, theories to predict droplet size, physical conditions and chemical additives which affect droplet stability, and recent applications.

A controlled synthesis of polymeric particles is becoming increasingly important because of emerging applications ranging from medical diagnostics to self-assembly. Centrifugal synthesis of hydrogel microparticles is a promising method, combining rapid particle synthesis and the ease of manufacturing with readily available laboratory equipment. This method utilizes centrifugal forces to extrude an aqueous polymer solution, sodium alginate (NaALG) through a nozzle. The extruded solution forms droplets that quickly cross-link upon contact with aqueous calcium chloride (CaCl₂) solution to form hydrogel particles. The size distribution of hydrogel particles is dictated by the pinch-off behavior of the extruded solution through a balance of inertial, viscous, and surface tension stresses. We identify the parameters dictating the particle size and provide a numerical correlation predicting the average particle size. Furthermore, we create a phase map identifying different pinch-off regimes (dripping without satellites, dripping with satellites, and jetting), explaining the corresponding particle size distributions, and present scaling arguments predicting the transition between regimes. By shedding light on the underlying physics, this study enables the rational design and operation of particle synthesis by centrifugal forces.