Marius Rutkevičius

Fabrication of environmentally biodegradable lignin nanoparticles.

We developed a method for the fabrication of novel biodegradable nanoparticles (NPs) from lignin which are apparently non-toxic for microalgae and yeast. We compare two alternative methods for the synthesis of lignin NPs which result in particles of very different stability upon change of pH. The first method is based on precipitation of low-sulfonated lignin from an ethylene glycol solution by using diluted acidic aqueous solutions, which yields lignin NPs that are stable over a wide range of pH. The second approach is based on the acidic precipitation of lignin from a high-pH aqueous solution which produces NPs stable only at low pH. Our study reveals that lignin NPs from the ethylene glycol-based precipitation contain densely packed lignin domains which explain the stability of the NPs even at high pH. We characterised the properties of the produced lignin NPs and determined their loading capacities with hydrophilic actives. The results suggest that these NPs are highly porous and consist of smaller lignin domains. Tests with microalgae like Chlamydomonas reinhardtii and yeast incubated in lignin NP dispersions indicated that these NPs lack measurable effect on the viability of these microorganisms. Such biodegradable and environmentally compatible NPs can find applications as drug delivery vehicles, stabilisers of cosmetic and pharmaceutical formulations, or in other areas where they may replace more expensive and potentially toxic nanomaterials.

Fabrication of salt-hydrogel marbles and hollow- shell microcapsules by an aerosol gelation technique

We designed a new method for preparation of liquid marbles by using hydrophilic particles. Salt-hydrogel marbles were prepared by atomising droplets of hydrogel solution in a cold air column followed by rolling of the collected hydrogel microbeads in a bed of micrometre sized salt particles. Evaporation of the water from the resulting salt marbles with a hydrogel core yielded hollow-shell salt microcapsules. The method is not limited to hydrophilic particles and could potentially be also applied to particles of other materials, such as graphite, carbon black, silica and others. The structure and morphology of the salt-hydrogel marbles were analysed by SEM and their particle size distributions were measured. We also tested the dissolution times of the dried salt marbles and compared them with those of table salt samples under the same conditions. The high accessible surface area of the shell of salt microcrystals allows a faster initial release of salt from the hollow-shell salt capsules upon their dissolution in water than from the same amount of table salt. The results suggest that such hollow-shell particles could find applications as a table salt substitute in dry food products and salt seasoning formulations with reduced salt content without the loss of saltiness.

Smart soaps: stimulus responsive soap–hydrogel bead composites for controlled dissolution and release of actives

We designed pressure responsive soap–hydrogel bead composites by incorporating agar hydrogel beads of different size distributions within a molten soap matrix at various volume fractions. Upon cooling, the combined suspension of hydrogel beads into the molten soap was set into a composite of soap matrix. We demonstrate pressure driven syneresis of water from the soap–hydrogel bead composites upon compression. This allowed a release of active components embedded in the hydrogel beads upon application of pressure on these “smart” soap composites. We found that the dissolution rate of these composites generally increases with the volume percentage of hydrogel beads. We achieved a composite dissolution rate approximately 2.8 times higher than the soap control sample without hydrogel beads. However, the composite dissolution rate was independent of the size of the embedded hydrogel beads. We studied the release rates of active components encapsulated within the hydrogel beads used to prepare the composites. It was found that the release rate can be controlled in three different ways: varying the hydrogel beads size, using different concentrations of the gelling polymer used to make the hydrogel and also by co-encapsulating an oppositely charged polyelectrolyte along with the active encapsulated species. We found that the composites compressional strength decreased with an increasing volume percentage of hydrogel beads incorporated within the soap composite. Youngs modulus showed a maximum when 7.5% by volume of hydrogel beads were used for composite preparation. These fast-dissolving soap–hydrogel composites contain significantly less raw materials and would reduce the pollution of waste water with surface active components. We envisage that soap–hydrogel bead composites could improve the sustainability of the soap-producing industry and could find their application within the hotel business, where they could reduce costs and the waste of millions of partially used soap bars discarded on a daily basis.