Lignin-based pH-responsive nanocapsules were successfully fabricated via an interfacial miniemulsion polymerization. Lignin was first grafted with allyl groups through etherification and further dispersed in an oil-in-water (O/W) miniemulsion system via ultrasonication. Then allyl-functionalized lignin was reacted with a thiol-based cross-linking agent in the interfaces of miniemulsion droplets to form nanocapsules via a thiol–ene radical reaction. The FTIR and 1H NMR spectra indicated the successful grafting of allyl groups on lignin. TEM images showed that lignin nanocapsules had particle sizes ranging from 50 to 300 nm. These newly synthesized nanocapsules could be readily loaded with hydrophobic coumarin-6 during the preparation of a miniemulsion system with 0.713 mmol/g entrapment efficiency. Moreover, the release of encapsulated coumarin-6 could be controlled by varying pH in the solution due to the existence of acid-labile β-thiopropionate cross-linkages in the capsule shell. An approximately linear release profile was observed at pH 7.4, whereas the release followed a Korsmeyer–Peppas profile at pH 4. The syntheses of lignin-based nanocapsules not only provide a facile approach to utilize the waste biomaterials from biorefinery industries, but also have great potential for applications in a controllable delivery of hydrophobic molecules such as drugs, essential oils, antioxidants, etc.

Lignin nanotubes (LNTs) synthesized from the aromatic plant cell wall polymer lignin in a sacrificial alumina membrane template have as useful features their flexibility, ease of functionalization due to the availability of many functional groups, label-free detection by autofluorescence, and customizable optical properties. In this report we show that the physicochemical properties of LNTs can be varied over a wide range to match requirements for specific applications by using lignin with different subunit composition, a function of plant species and genotype, and by choosing the lignin isolation method (thioglycolic acid, phosphoric acid, sulfuric acid (Klason), sodium hydroxide lignin), which influences the size and reactivity of the lignin fragments. Cytotoxicity studies with human HeLa cells showed that concentrations of up to 90 mg/mL are tolerated, which is a 10-fold higher concentration than observed for single- or multiwalled carbon nanotubes (CNTs). Confocal microscopy imaging revealed that all LNT formulations enter HeLa cells without auxiliary agents and that LNTs made from NaOH-lignin penetrate the cell nucleus. We further show that DNA can adsorb to LNTs. Consequently, exposure of HeLa cells to LNTs coated with DNA encoding the green fluorescent protein (GFP) leads to transfection and expression of GFP. The highest transfection efficiency was obtained with LNTs made from NaOH-lignin due to a combination of high DNA binding capacity and DNA delivery directly into the nucleus. These combined features of LNTs make LNTs attractive as smart delivery vehicles of DNA without the cytotoxicity associated with CNTs or the immunogenicity of viral vectors.

Limitations of cylindrical carbon nanotubes based on the buckminsterfullerene structure as delivery vehicles for therapeutic agents include their chemical inertness, sharp edges and toxicological concerns. As an alternative, we have developed lignin-based nanotubes synthesized in a sacrificial template of commercially available alumina membranes. Lignin is a complex phenolic plant cell wall polymer that is generated as a waste product from paper mills and biorefineries that process lignocellulosic biomass into fuels and chemicals. We covalently linked isolated lignin to the inner walls of activated alumina membranes and then added layers of dehydrogenation polymer onto this base layer via a peroxidase-catalyzed reaction. By using phenolic monomers displaying different reactivities, we were able to change the thickness of the polymer layer deposited within the pores, resulting in the synthesis of nanotubes with a wall thickness of approximately 15 nm or nanowires with a nominal diameter of 200 nm. These novel nanotubes are flexible and can be bio-functionalized easily and specifically, as shown by in vitro assays with biotin and Concanavalin A. Together with their intrinsic optical properties, which can also be varied as a function of their chemical composition, these lignin-based nanotubes are expected to enable a variety of new applications including as delivery systems that can be easily localized and imaged after uptake by living cells.

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The undergraduate program in the Materials Science and Engineering department at the University of Florida requires its junior students to take the course "Analysis of the Structure of Materials". This course provides students the opportunity to disassemble an engineered product, characterize and analyze the structure of its components, and correlate the structures with properties and processing addressing the criteria most likely used for materials selection by the manufacturers. In addition to the traditional reverse engineering approach, the students must select at least one component and re-create the life cycle of the material/component. The analysis requires collection and analysis of data from emissions, and waste generated from each step of the mining, processing, manufacturing, fabrication, distribution, use, and typical disposal of the product. The students are required to estimate product impacts on the waste stream, environment and society. The final presentation must also include recommendations from the students to create the same product in a more environmentally responsible way.