Lignin biomaterial - from enzyme-responsive vehicles to carbon precursor
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Abstract
This thesis presents the first report on enzymatic triggered release of active agents from lignin nanoparticles prepared by a variety of chemistry via the miniemulsion process. The nanoparticles are found very promising as novel drug delivery vehicles in agriculture.
The first approach is to prepare lignin hollow nanocapsules by interfacial polyaddition in inverse miniemulsion. The obtained cross-linked lignin nanocontainers can be loaded with hydrophilic substances which can be released by an enzymatic trigger, namely laccases, present in natural plants. The second strategy for the nanocarrier formation is the modification of lignin by esterification of hydroxyl groups present in lignin with methacrylic anhydride. Then lignin nanocarriers with different morphologies such as solid, core-shell, and porous structure were produced by a combination of miniemulsion polymerization and a solvent evaporation process. A hydrophobic dye is used to investigate the release behavior of the lignin nanocarriers depending on their morphology. To verify the enzymatic response of lignin nanocarriers, the enzyme laccase was used to trigger the release of the dye from the lignin nanocarriers.
Lignin can act as drug delivery vehicles for fungal diseases in plants. For this, biodegradable lignin nanoparticles were loaded with pyroclostrobin, an antifungal drug against a disease of grapevine called Esca; studies in plants were performed by injecting aqueous dispersion of nanoparticles into Esca-infected vitis vinifera (grapevines). This work was carried out in collaboration with Prof. Dr. Eckhard Thines of the Institute of Biotechnology and Drug Research in Kaiserslautern. The enzymes secreted by Esca degraded the lignin nanoparticles and released the drug to cure infected wine plants. All treated plants with the fungicide-filled lignin nanoparticles recovered from the Esca infection.
The effect of biodegradable lignin nanoparticles and non-degradable polystyrene nanoparticles with encapsulated iron oxide on the development of mung beans and their bio-distribution was studied. Magnetic polystyrene nanoparticles influenced the growth of the root and the stem development during seeding, while the lignin particles did not have any visible effect. Both types of nanoparticles could penetrate the epidermis of the root tissue, were accumulated in root cells, and could be transported through the vascular cylinder to leaves. The lignin nanoparticles were further loaded with a model antifungal drug that was distributed within the plant after incubation or injection of the bean with the nanoparticle dispersion.
This thesis shows tremendous potential of lignin nanoparticles in drug delivery for agricultural purposes and also in water purification by carbonization of lignin particles synthesized by the miniemulsion process. The resulting carbon particles exhibited a high surface area and showed efficient adsorption of the methylene blue dye.
These results prove that the abundant biopolymer lignin can be used as an efficient material for the preparation of nanoparticles with variable morphologies that can be applied in agriculture as biodegradable drug carrier or as adsorbent after carbonization.