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1. Preparation and Characterization of Size-Controlled Lignin Nanoparticles with Deep Eutectic Solvents by Nanoprecipitation

   https://doi.org/10.3390/molecules26010218  

   Luo, Tong; Wang, Chao; Ji, Xingxiang; Yang, Guihua; Chen, Jiachuan; Janaswamy, Srinivas; Lyu, Gaojin (January 2021, Molecules)

   null (Ed.)

   Lignin nanomaterials have wide application prospects in the fields of cosmetics delivery, energy storage, and environmental governance. In this study, we developed a simple and sustainable synthesis approach to produce uniform lignin nanoparticles (LNPs) by dissolving industrial lignin in deep eutectic solvents (DESs) followed by a self-assembling process. LNPs with high yield could be obtained through nanoprecipitation. The LNPs were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC). Distinct LNPs could be produced by changing the type of DES, lignin sources, pre-dropping lignin concentration, and the pH of the system. Their diameter is in the range of 20–200 nm and they show excellent dispersibility and superior long-term stability. The method of preparing LNPs from lignin–DES with water as an anti-solvent is simple, rapid, and environmentally friendly. The outcome aids to further the advancement of lignin-based nanotechnology. 

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2. Effects of Sodium Alginate and Calcium Chloride on Fungal Growth and Viability in Biomass-Fungi Composite Materials Used for 3D Printing

   https://doi.org/10.3390/biomimetics9040251  

   Rahman, Al Mazedur; Bedsole, Caleb Oliver; Akib, Yeasir Mohammad; Hamilton, Jillian; Rahman, Taieba Tuba; Shaw, Brian D; Pei, Zhijian (April 2024, Biomimetics)

   To combat climate change, one approach is to manufacture products from biomass-fungi composite materials instead of petroleum-based plastics. These products can be used in packaging, furniture, and construction industries. A 3D printing-based manufacturing method was developed for these biomass-fungi composite materials, eliminating the need for molds, and enabling customized product design. However, previous studies on the 3D printing-based method showed significant shrinkage of printed samples. In this paper, an approach is proposed to reduce the shrinkage by incorporating ionic crosslinking into biomass-fungi composite materials. This paper reports two sets of experiments regarding the effects of sodium alginate (SA) and calcium chloride (CaCl2) on fungal growth and fungal viability. The first set of experiments was conducted using Petri dishes with fungi isolated from colonized biomass-fungi material and different concentrations of SA and CaCl2. Fungal growth was measured by the circumference of fungal colonies. The results showed that concentrations of SA and CaCl2 had significant effects on fungal growth and no fungal growth was observed on Petri dishes with 15% CaCl2. Some of these Petri dishes were also observed under confocal microscopy. The results confirmed the differences obtained by measuring the circumference of fungal colonies. The second set of experiments was conducted using Petri dishes with biomass-fungi mixtures that were treated with different concentrations of SA and exposure times in a CaCl2 (crosslinking) solution. Fungal viability was measured by counting colony-forming units. The results showed that the addition of the SA solution and exposure times in the crosslinking solution had statistically significant effects on fungal viability. The 2SA solution was prepared by dissolving 2 g of SA in 100 mL of water, the 5SA solution was prepared by dissolving 5 g of SA in 100 mL of water, and the crosslinking solution was prepared by dissolving 5 g of CaCl2 in 100 mL of water. The results also showed that fungal viability was not too low in biomass-fungi mixtures that included 2SA solution and were exposed to the crosslinking solution for 1 min. 

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3. Experimental Thermal Conductivity Studies of Agar-Based Aqueous Suspensions with Lignin Magnetic Nanocomposites

   https://doi.org/10.3390/magnetochemistry10020012  

   Gautam, Bishal; Nabat_Al-Ajrash, Saja M; Hasan, Mohammad Jahid; Saini, Abhishek; Watzman, Sarah J; Ureña-Benavides, Esteban; Vasquez-Guardado, Erick S (February 2024, Magnetochemistry)

   Nanoparticle additives increase the thermal conductivity of conventional heat transfer fluids at low concentrations, which leads to improved heat transfer fluids and processes. This study investigates lignin-coated magnetic nanocomposites (lignin@Fe3O4) as a novel bio-based magnetic nanoparticle additive to enhance the thermal conductivity of aqueous-based fluids. Kraft lignin was used to encapsulate the Fe3O4 nanoparticles to prevent agglomeration and oxidation of the magnetic nanoparticles. Lignin@Fe3O4 nanoparticles were prepared using a pH-driven co-precipitation method with a 3:1 lignin to magnetite ratio and characterized by X-ray diffraction, FT-IR, thermogravimetric analysis, and transmission electron microscopy. The magnetic properties were characterized using a vibrating sample magnetometer. Once fully characterized, lignin@Fe3O4 nanoparticles were dispersed in aqueous 0.1% w/v agar–water solutions at five different concentrations, from 0.001% w/v to 0.005% w/v. Thermal conductivity measurements were performed using the transient line heat source method at various temperatures. A maximum enhancement of 10% in thermal conductivity was achieved after adding 0.005% w/v lignin@Fe3O4 to the agar-based aqueous suspension at 45 °C. At room temperature (25 °C), the thermal conductivity of lignin@Fe3O4 and uncoated Fe3O4 agar-based suspensions was characterized at varying magnetic fields from 0 to 0.04 T, which were generated using a permanent magnet. For this analysis, the thermal conductivity of lignin magnetic nanosuspensions initially increased, showing a 5% maximum peak increase after applying a 0.02 T magnetic field, followed by a decreasing thermal conductivity at higher magnetic fields up to 0.04 T. This result is attributed to induced magnetic nanoparticle aggregation under external applied magnetic fields. Overall, this work demonstrates that lignin-coated Fe3O4 nanosuspension at low concentrations slightly increases the thermal conductivity of agar aqueous-based solutions, using a simple permanent magnet at room temperature or by adjusting temperature without any externally applied magnetic field. 

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4. Identifying thermal phase transitions of lignin–solvent mixtures using electrochemical impedance spectroscopy

   https://doi.org/10.1039/C5GC02342D  

   Klett, Adam S.; Gamble, Jordan A.; Thies, Mark C.; Roberts, Mark E. (January 2016, Green Chemistry)

   Lignin is unique among renewable biopolymers in having significant aromatic character, making it potentially attractive for a wide range of uses from coatings to carbon fibers. Recent research has shown that hot acetic acid (AcOH)–water mixtures can be used to recover “ultraclean” lignins of controlled molecular weight from Kraft lignins. A key feature of this discovery is the existence of a region of liquid–liquid equilibrium (LLE), with one phase being rich in the purified lignin and the other rich in solvent. Although visual methods can be used to determine the temperature at which solid lignin melts in the presence of AcOH–water mixtures to form LLE, the phase transition can be seen only at lower AcOH concentrations due to solvent opacity. Thus, an electrochemical impedance spectroscopy (EIS) technique was developed for measuring the phase-transition temperature of a softwood Kraft lignin in AcOH–water mixtures. In electrochemical cells, the resistance to double-layer charging ( i.e. , polarization resistance R p ) is related to the concentration and mobility of free ions in the electrolyte, both of which are affected by the phases present. When the lignin–AcOH–water mixture was heated through the phase transition, R P was found to be a strong function of temperature, with the maximum in R P corresponding to the transition temperature obtained from visual observation. As the system is heated, acetate ions associate with the solid lignin, forming a liquefied, lignin-rich phase. This association increases the overall impedance of the system, as mobile acetate ions are stripped from the solvent phase and thus are no longer available to adsorb on the polarizing electrode surfaces. The maximum in R P occurs once the new lignin-rich phase has completely formed, and no further association of the lignin polymer with AcOH is possible. Except at sub-ambient temperatures, the phase-transition temperature was a strong function of solvent composition, increasing linearly from 18 °C at 70/30 AcOH/water to 97 °C at 10/90 wt% AcOH/water. 

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5. In Vivo Toxicity Assessment of Chitosan-Coated Lignin Nanoparticles in Embryonic Zebrafish (Danio rerio)

   https://doi.org/10.3390/nano11010111  

   Stine, Jared S.; Harper, Bryan J.; Conner, Cathryn G.; Velev, Orlin D.; Harper, Stacey L. (January 2021, Nanomaterials)

   null (Ed.)

   Lignin is the second most abundant biopolymer on Earth after cellulose. Since lignin breaks down in the environment naturally, lignin nanoparticles may serve as biodegradable carriers of biocidal actives with minimal environmental footprint compared to conventional antimicrobial formulations. Here, a lignin nanoparticle (LNP) coated with chitosan was engineered. Previous studies show both lignin and chitosan to exhibit antimicrobial properties. Another study showed that adding a chitosan coating can improve the adsorption of LNPs to biological samples by electrostatic adherence to oppositely charged surfaces. Our objective was to determine if these engineered particles would elicit toxicological responses, utilizing embryonic zebrafish toxicity assays. Zebrafish were exposed to nanoparticles with an intact chorionic membrane and with the chorion enzymatically removed to allow for direct contact of particles with the developing embryo. Both mortality and sublethal endpoints were analyzed. Mortality rates were significantly greater for chitosan-coated LNPs (Ch-LNPs) compared to plain LNPs and control groups. Significant sublethal endpoints were observed in groups exposed to Ch-LNPs with chorionic membranes intact. Our study indicated that engineered Ch-LNP formulations at high concentrations were more toxic than plain LNPs. Further study is warranted to fully understand the mechanisms of Ch-LNP toxicity. 

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