Camille did 4 months of research internship in Prof Paunov’s group at the University of Hull in 2011 as an exchange student from ENSCR (Rennes, France). She is currently doing a PhD at CNRS, France.  Internship supervisors: Prof Vesselin Paunov (PI) and Marius Rutkevicius

Research project 1:

Fabrication of Environmentally Biodegradable Lignin Nanoparticles

(In collaboration with Velev’s group at NCSU, USA)

We developed a method for the fabrication of novel biodegradable nanoparticles (NPs) from Kraft lignin (Indulin AT) which are apparently non-toxic to microalgae and yeast [1]. We compare two alternative methods for the synthesis of lignin NPs which result in particles of very different stability upon change of pH (Fig. 1). 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  (see Figs. 2 and 3). We characterized 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 (Fig. 4). Such biodegradable and environmentally compatible NPs can find applications as drug delivery vehicles, stabilizers of cosmetic and pharmaceutical formulations, or in other areas where they may replace more expensive and potentially toxic nanomaterials.

Fig. 1 Proposed mechanism for lignin NP formation by A) precipitation of IAT from ethylene glycol with HCl(aq.) and possible subsequent cross-linking and dialysis, and by B) precipitation of IAT from an aqueous solution of high pH to low pH. The lignin NPs produced by route (B) dissolve above pH 5, while the ones produced by route (A) are stable up to pH 10, even without the cross-linking step [1].

Fig. 2 Effect of preparation conditions on the size of lignin NPs: a) size dependence on the percentage of 0.25M HCl used to precipitate 1 wt% lignin solution in ethylene glycol. c) Size dependence on the concentration of lignin in solution (10 vol% 0.25M HCl was used). The particle size measurements are done after the sample was diluted in milli-Q water without further dialysis [1].

Fig. 3 TEM images of lignin NPs obtained by the acid precipitation of 0.56 wt% Indulin AT in ethylene glycol and further dialysis in milli-Q water [1].

Fig. 4 (a) Control sample of yeast cells (Saccharomyces cerevisiae) treated with a physiological solution (0.1M NaCl) and then a solution of fluorescein diacetate (FDA). (b) Yeast cells after being incubated with a dispersion of 50 nm lignin NPs, followed by washing with water and treatment with a FDA solution. Both images (a) and (b) represent a merge of a bright field and fluorescence microscope images of the same sample which allows the observation of both the living cells and the total cell population [1].

References

1. Frangville, C. Rutkevicius, M. Richter, A.P., Velev, O.D. Stoyanov, S.D., Paunov, V.N., “Fabrication of Environmentally Biodegradable Lignin Nanoparticles”, ChemPhysChem, 18 (2012) 4235-4243.