Polyelectrolyte complexes (PECs) are polymeric structures formed by the self-assembly of oppositely charged polymers. Novel biomaterials based on PECs are currently under investigation as drug delivery systems, among other applications. This strategy leverages the ability of PECs to entrap drugs under mild conditions and control their release. In this study, we combined a novel and sustainably produced hemicellulose-rich lignosulphonate polymer (EH, negatively charged) with polyethyleneimine (PEI) or chitosan (CH, positively charged) and agar for the development of drug-releasing PECs. A preliminary screening demonstrated the effect of several parameters (polyelectrolyte ratio, temperature, and type of polycation) on PECs formation. From this, selected formulations were further characterized in terms of thermal properties, surface morphology at the microscale, stability, and ability to load and release methylene blue (MB) as a model drug. EH/PEI complexes had a more pronounced gel-like behaviour compared to the EH/CH complexes. Differential scanning calorimetry (DSC) results supported the establishment of polymeric interactions during complexation. Overall, PECs’ stability was positively affected by low pH, ratios close to 1:1, and the addition of agar. PECs with higher EH content showed a higher MB loading, likely promoted by stronger electrostatic interactions. The EH/CH formulation enriched with agar showed the best sustained release profile of MB during the first 30 h in a pH-dependent environment simulating the gastrointestinal tract. Overall, we defined the conditions to formulate novel PECs based on a sustainable hemicellulose-rich lignosulphonate for potential applications in drug delivery, which promotes the valuable synergy between sustainability and the biomedical field. Graphical abstract: (Figure presented.)

Studies have shown that the size of LNP depends on the molecular weight (M-w) of lignin. There is however need for deeper understanding on the role of molecular structure on LNP formation and its properties, in order to build a solid foundation on structure-property relationships. In this study, we show, for similar M-w lignins, that the size and morphology of LNPs depends on the molecular structure of the lignin macromolecule. More specifically, the molecular structure determined the molecular conformations, which in turn affects the inter-molecular assembly to yield size- and morphological-differences between LNPs. This was supported by density functional theory (DFT) modelling of representative structural motifs of three lignins sourced from Kraft and Organosolv processes. The obtained conformational differences are clearly explained by intra-molecular sandwich and/or T-shaped pi-pi stacking, the stacking type determined by the precise lignin structure. Moreover, the experimentally identified structures were detected in the superficial layer of LNPs in aqueous solution, confirming the theoretically predicted self-assembly patterns. The present work demonstrates that LNP properties can be molecularly tailored, consequently creating an avenue for tailored applications.

The natural polymer, lignin, possesses unique biodegradable and biocompatible properties, making it highly attractive for the generation of nanoparticles for targeted cancer therapy. In this study, we investigated spruce and eucalyptus lignin nanoparticles (designated as S-and E-LNPs, respectively). Both LNP types were generated from high-molecular-weight (M-w) kraft lignin obtained as insoluble residues after a five-step solvent fractionation approach, which included ethyl acetate, ethanol, methanol, and acetone. The resulting S-and E-LNPs ranged in size from 16 to 60 nm with uniform spherical shape regardless of the type of lignin. The preparation of LNPs from an acetone-insoluble lignin fraction is attractive because of the use of high-M-w lignin that is otherwise not suitable for most polymeric applications, its potential scalability, and the consistent size of the LNPs, which was independent of increased lignin concentrations. Due to the potential of LNPs to serve as delivery platforms in liver cancer treatment, we tested, for the first time, the efficacy of newly generated E-LNPs and S-LNPs in two types of primary liver cancer, hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), in vitro. Both S-LNPs and E-LNPs inhibited the proliferation of HCC cells in a dose-dependent manner and did not affect CCA cell line growth. The inhibitory effect toward HCC was more pronounced in the E-LNP-treated group and was comparable to the standard therapy, sorafenib. Also, E-LNPs induced late apoptosis and necroptosis while inhibiting the HCC cell line. This study demonstrated that an elevated number of carbohydrates on the surface of the LNPs, as shown by NMR, seem to play an important role in mediating the interaction between LNPs and eukaryotic cells. The latter effect was most pronounced in E-LNPs. The novel S- and E-LNPs generated in this work are promising materials for biomedicine with advantageous properties such as small particle size and tailored surface functionality, making them an attractive and potentially biodegradable delivery tool for combination therapy in liver cancer, which still has to be verified in vivo using HCC and CCA models.

Nanocellulose membranes based on tunicate-derived cellulose nanofibers, starch, and similar to 5% wood-derived lignin were investigated using three different types of lignin. The addition of lignin into cellulose membranes increased the specific surface area (from 5 to similar to 50 m(2)/g), however the fine porous geometry of the nanocellulose with characteristic pores below 10 nm in diameter remained similar for all membranes. The permeation of H-2, CO2, N-2, and O-2 through the membranes was investigated and a characteristic Knudsen diffusion through the membranes was observed at a rate proportional to the inverse of their molecular sizes. Permeability values, however, varied significantly between samples containing different lignins, ranging from several to thousands of barrers (10(-10) cm(3) (STP) cm cm(-2) s(-1) cmHg(-1) cm), and were related to the observed morphology and lignin distribution inside the membranes. Additionally, the addition of similar to 5% lignin resulted in a significant increase in tensile strength from 3 GPa to similar to 6-7 GPa, but did not change thermal properties (glass transition or thermal stability). Overall, the combination of plant-derived lignin as a filler or binder in cellulose-starch composites with a sea-animal derived nanocellulose presents an interesting new approach for the fabrication of membranes from abundant bio-derived materials. Future studies should focus on the optimization of these types of membranes for the selective and fast transport of gases needed for a variety of industrial separation processes.

Valorization of lignin is still an open question and lignin has therefore remained an underutilized biomaterial. This situation is even more pronounced for hydrolysis lignin, which is characterized by a highly condensed and excessively cross-linked structure. We demonstrate the synthesis of photoactive lignin/Bi4O5Br2/BiOBr bio-inorganic composites consisting of a lignin substrate that is coated by semiconducting nanosheets. The XPS analysis reveals that growing these nanosheets on lignin instead on cellulose prevents the formation of Bi5+ ions at the surface region, yielding thus a modified hetero-junction Bi4O5Br2/BiOBr. The material contains 18.9% of Bi4O5Br2/BiOBr and is effective for the photocatalytic degradation of cationic methylene blue (MB) and zwitterionic rhodamine B (RhB) dyes under light irradiation. Lignin/Bi4O5Br2/BiOBr decreases the dye concentration from 80 mg L-1 to 12.3 mg L-1 for RhB (85%) and from 80 mg L-1 to 4.4 mg L-1 for MB (95%). Complementary to the dye degradation, the lignin as a main component of the composite, was found to be efficient and rapid biosorbent for nickel, lead, and cobalt ions. The low cost, stability and ability to simultaneously photo-oxidize organic dyes and adsorb metal ions, make the photoactive lignin/Bi4O5Br2/BiOBr composite a prospective material for textile wastewaters remediation and metal ions recycling.

The use of lignin from forests as a renewable resource is a greener alternative to the petrochemical industry and accelerates the progress towards the development of more environmentally friendly industrial processes. A better understanding of the complexity of lignin as a raw material is necessary for creating new sustainable value chains, and a deeper understanding of the forces and interactions driving the self-assembly of lignin nanoparticles (LNPs) is required to create new, more advanced lignin nanomaterials. In the current study, “a library” of LNPs made from both softwood (spruce) and hardwood (eucalyptus) lignins was prepared utilizing green solvents-fractionated kraft lignins with narrow structural and molecular weight dispersity, and the LNPs were thoroughly characterized with respect to their size, shape, and surface properties. For both spruce and eucalyptus lignin fractions, the size of the LNPs decreased with increasingMwwith a decreasing number of phenolic hydroxyls and an increasing number of aliphatic hydroxyl units in the lignin fraction. The diameter of the LNP's could be varied between 80 and 500 nm, depending on theMwof the initial lignin and its concentration. The number of methoxy and phenolic groups in the aromatic ring, the aliphatic hydroxyls and β-O-4 bonds in side chains in lignin fractions affect the morphology and surface structure of the LNPs to a significant degree. The LNP's with shapes ranging from doughnut-like structures to filled interconnected spheres were prepared, depending on the type of lignin phenylpropanoid units (botanical origin), concentration, and other properties of the lignin fractions. The identified strong dependence of the properties of the LNPs on the inherent properties of the lignin from which they were derived reveals that it is of crucial importance to select the appropriate starting lignin materials for the controlled design and synthesis of LNPs. This reduces costs for the subsequent purification and further processing of the LNPs, and prevents environmental pollution by minimizing the usage of resources. The obtained knowledge provides a clear guideline for the design of new biomass-based materials.

Polymer hydrogels with lignin in the form of microspheres have been synthesized and their properties were evaluated. Prior to the polymerization, hardwood lignin (Eucalyptus grandis) was modified with methacryloyl chloride, and unmodified lignin (L-N) and its methacrylic derivative (L-M) were polymerized with 2-hydroxyethyl methacrylate (HEMA) and divinylbenzene (DVB) in different ratios using suspension polymerization. The presence of characteristic functional groups in the synthesized hydrogels was confirmed using attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FT-IR) and NMR. Thermal properties were determined by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Swelling was studied in common organic solvents and distilled water. The shapes of the hydrogels were confirmed by scanning electron microscopy (SEM) and optical microscopy. The addition of lignin significantly increased the swelling ability of the hydrogels in water and acetone. The incorporation of methacrylated lignin into the structure of HEMA-DVB hydrogels increased their sorption of Ni(II) ions by 30 % showing that these hydrogels are a promising material for use in nickel removal and recovery, as well as contributing to a better utilization of lignin.

Efficient and sustainable recycling of cobalt(II) is of increasing importance to support technological development in energy storage and electric vehicle industries. A composite material based on membrane-filtered lignin deposited on nanoporous silica microparticles was found to be an effective and sustainable sorbent for cobalt(II) removal. This bio-based sorbent exhibited a high sorption capacity, fast kinetics toward cobalt(II) adsorption, and good reusability. The adsorption capacity was 18 mg Co(II) per gram of dry adsorbent at room temperature (22 degrees C) at near-neutral pH, three times higher than that of the summarized capacity of lignin or silica starting materials. The kinetics study showed that 90 min is sufficient for effective cobalt(II) extraction by the composite sorbent. The pseudo-second-order kinetics and Freundlich isotherm models fitted well with experimentally obtained data and confirmed heterogeneity of adsorption sites. The promising potential of the lignin-silica composites for industrial applications in the cobalt recovering process was confirmed by high values of desorption in mildly acidic solutions.

H-1 liquid-state nuclear magnetic resonance (NMR) spectroscopy was applied for the first time to lignin nanoparticles (LNPs) in an aqueous suspension to study the surface composition of LNPs and to acquire a better understanding of the mechanism of their formation. A series of LNPs were prepared from spruce and eucalyptus kraft lignin fractions with narrow molecular weight distributions and functionalities. An NMR pulse program combining presaturation with excitation sculpting increased the signal resolution, making it possible to observe a superficial layer of LNPs directly in the aqueous suspension, "as prepared". The particle size, charge, and surface morphology were characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS). According to liquid-state NMR, methoxy groups from syringyl and guaiacyl units of lignin are the main groups present on the surface of LNPs. The presence of aliphatic moieties, mainly from side chains of lignin molecules, has also been confirmed. Taking into consideration the chemical composition of the lignin fractions, the structure of lignin NPs as shown by NMR spectroscopy and their size and surface charge, a pattern of lignin self-assembly into LNPs has been suggested.

Recent years have seen the development of technically feasible methods to retrieve kraft lignin from the black liquor as solids or liquids. This opens enormous opportunities to position kraft lignin as a renewable aromatic polymer precursor. However, the heterogeneity of kraft lignin is one major hurdle and manifests in its largely unknown molecular structure, which in recent years has drawn further attention. In this context, we herein studied the detailed structure of Eucalyptus kraft lignin with special emphasis on identifying new linkages signatory to retro-aldol and subsequent radical coupling reactions, which we recently showed to be a key reaction sequence contributing to the structure of spruce kraft lignin. In combination with novel model studies, we unequivocally identified new structures by advanced 2D NMR characterization of Eucalyptus kraft lignin, i.e., 3,5-tetramethoxy-para-diphenol, 3-dimethoxy-para-diphenol and small amounts of 3,5-dimethoxy-benzoquinone. These structures are signatory to retro-aldol followed by radical coupling reactions. The two diphenol structures were further quantified by 1D C-13 NMR at 9% of the interunit linkages in Eucalyptus kraft lignin, which was comparable to the amounts we previously identified in softwood kraft lignin (10%). Radical condensation of kraft lignin to form carbon-carbon bonds therefore does not discriminate between syringyl lignin and guaiacyl lignin units. We rationalize such indiscrimination to emanate from possibilities for radical couplings at unsubstituted C-1 in the formed syringol and guaiacol lignin as a result of the retro-aldol reaction.