Properties and chemical modifications of lignin : Towards lignin-based nanomaterials for biomedical applications

Biorenewable polymers have emerged as an attractive alternative to conventional metallic and organic materials for a variety of different applications. This is mainly because of their biocompatibility, biodegradability and low cost of production. Lignocellulosic biomass is the most promising renewable carbon-containing source on Earth. Depending on the origin and species of the biomass, lignin consists of 20-35% of the lignocellulosic biomass. After it has been extracted, lignin can be modified through diverse chemical reactions. There are different categories of chemical modifications, such as lignin depolymerization or fragmentation, modification by synthesizing new chemically active sites, chemical modification of the hydroxyl groups, and the production of lignin graft copolymers. Lignin can be used for different industrial and biomedical applications, including biofuels, chemicals and polymers, and the development of nanomaterials for drug delivery but these uses depend on the source, chemical modifications and physicochemical properties. We provide an overview on the composition and properties, extraction methods and chemical modifications of lignin in this review. Furthermore, we describe different preparation methods for lignin-based nanomaterials with antioxidant UV-absorbing and antimicrobial properties that can be used as reinforcing agents in nanocomposites, in drug delivery and gene delivery vehicles for biomedical applications. (C) 2017 Elsevier Ltd. All rights reserved.Peer reviewe

Systematic in vitro biocompatibility studies of multimodal cellulose nanocrystal and lignin nanoparticles

Natural biopolymer nanoparticles (NPs), including nanocrystalline cellulose (CNC) and lignin, have shown potential as scaffolds for targeted drug delivery systems due to their wide availability, cost‐efficient preparation, and anticipated biocompatibility. Since both CNC and lignin can potentially cause complications in cell viability assays due to their ability to scatter the emitted light and absorb the assay reagents, we investigated the response of bioluminescent (CellTiter‐Glo®), colorimetric (MTT® and AlamarBlue®) and fluorometric (LIVE/DEAD®) assays for the determination of the biocompatibility of the multimodal CNC and lignin constructs in murine RAW 264.7 macrophages and 4T1 breast adenocarcinoma cell lines. Here, we have developed multimodal CNC and lignin NPs harboring the radiometal chelator DOTA (1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid) and the fluorescent dye Cyanine 5 for the investigation of nanomaterial biodistribution in vivo with nuclear and optical imaging, which were then used as the model CNC and lignin nanosystems in the cell viability assay comparison. CellTiter‐Glo® based on the detection of ATP‐dependent luminescence in viable cells revealed to be the best assay for both nanoconstructs for its robust linear response to increasing NP concentration and lack of interference from either of the NP types. Both multimodal CNC and lignin NPs displayed low cytotoxicity and favorable interactions with the cell lines, suggesting that they are good candidates for nanosystem development for targeted drug delivery in breast cancer and for theranostic applications. Our results provide useful guidance for cell viability assay compatibility for CNC and lignin NPs and facilitate the future translation of the materials for in vivo applications.Peer reviewe

Preparation and characterization of dentin phosphophoryn-derived peptide-functionalized lignin nanoparticles for enhanced cellular uptake

The surface modification of nanoparticles (NPs) using different ligands is a common strategy to increase NP−cell interactions. Here, dentin phosphophoryn‐derived peptide (DSS) lignin nanoparticles (LNPs) are prepared and characterized, the cellular internalization of the DSS‐functionalized LNPs (LNPs‐DSS) into three different cancer cell lines is evaluated, and their efficacy with the widely used iRGD peptide is compared. It is shown that controlled extent of carboxylation of lignin improves the stability at physiological conditions of LNPs formed upon solvent exchange. Functionalization with DSS and iRGD peptides maintains the spherical morphology and moderate polydispersity of LNPs. The LNPs exhibit good cytocompatibility when cultured with PC3‐MM2, MDA‐MB‐231, and A549 in the conventional 2D model and in the 3D cell spheroid morphology. Importantly, the 3D cell models reveal augmented internalization of peptide‐functionalized LNPs and improve antiproliferative effects when the LNPs are loaded with a cytotoxic compound. Overall, LNPs‐DSS show equal or even superior cellular internalization than the LNPs‐iRGD, suggesting that DSS can also be used to enhance the cellular uptake of NPs into different types of cells, and release different cargos intracellularly.Peer reviewe

Antimicrobial Colloidal Silver-Lignin Particles via Ion- and Solvent Exchange

Acid-precipitated lignin nanoparticles with a cationic polymer coating exhibit antibacterial activity when infused with silver. While the use of such particles would be beneficial due to their high antibacterial activity with a low silver content, their production holds steps that are difficult to scale up to inexpensive industrial manufacture. For example, the production of acid-precipitated lignin nanoparticles requires the use of ethylene glycol, which is not easily recycled. Furthermore, the binding of silver to these particles is weak, and thus the particles need to be used rapidly after preparation. Here, we show that with a deprotonation reaction of an organic solution of anhydrous lignin and subsequent ion exchange with silver nitrate and colloid formation by solvent exchange, highly spherical silver carboxylate colloidal lignin particles (AgCLPs) can be prepared. Silver is not released from the particles in deionized water but can be released in physiological conditions, shown by their high antibacterial efficacy with low silver loading. In comparison to lignin nanoparticles with weakly bound silver, AgCLPs have high antibacterial activity even without cationic polyelectrolyte coating, and they retain their antibacterial activity for days. While the rapid depletion of silver from silver-infused lignin nanoparticles can be considered beneficial for some applications, the sustained antibacterial activity of the AgCLPs with ionically bound silver will enable their use in applications where silver nanoparticles have been previously used. Our results demonstrate that CLPs, which can be produced with a closed cycle process on a large scale, can be rapidly and quantitatively functionalized into active materials.Peer reviewe

Photopolymerizable liquid fullerene, phthalocyanine and porphyrin derivatives: synthesis, analysis and photocurrent generation

Photopolymerizable liquid monomers of fullerene, phthalocyanine and porphyrin were synthesized, polymerized and used as photoactive materials in organic solar cell structures. The design of the molecules requires the combination of three major parts: the functional core of the original molecules, alkylic side chains for liquid state and polymerizable end groups. The harsh conditions of the chromophore synthesis require a modular design, where the chromophore core and polymerizable tails are synthesized separately, and combined later by mild acylation. A means of ultra-thin-film polymerization, both photo and thermal, were devised. All of the chromophores could be polymerized as ultrathin films. Because of their high absorbances, it was possible to use UV-Vis spectroscopy to monitor polymerization indirectly; as the films were of only a few monomer units thick, it was possible to dissolve the unreacted monomer residues afterwards and thus determine polymerization degrees as a function of the absorbance of the polymerized film. The molecules were studied extensively to yield the parameters for thin film preparation, photopolymerization, and photocurrent generation. While the monomers were liquid at room temperature, the hardness of the polymers was that of crosslinked epoxy plastics. The porphyrin monomer was used to study photopolymerization kinetics due to its unique self-photoinitiating properties. Polarization modulation IR spectroscopy was used to study real-time photopolymerization of the porphyrin monomer at varying temperatures, yielding rate constants and the activation energy of the reaction. It was the first published study of ultra-thin-film polymerization kinetics. The monomers were polymerized in situ to form bilayers, bulk heterojunctions or hybrids of both, to create a photoactive structure for photocurrent generation. An extensive set of samples was prepared and studied. The monomers employed in this work were optimized for easy photopolymerizability and as such produced unoptimal power conversion efficiency. Nevertheless the basic structure of the polymer lends itself well to modification for improved organic photovoltaic performance

Photopolymerizable liquid fullerene, phthalocyanine and porphyrin derivatives: synthesis, analysis and photocurrent generation

Photopolymerizable liquid monomers of fullerene, phthalocyanine and porphyrin were synthesized, polymerized and used as photoactive materials in organic solar cell structures. The design of the molecules requires the combination of three major parts: the functional core of the original molecules, alkylic side chains for liquid state and polymerizable end groups. The harsh conditions of the chromophore synthesis require a modular design, where the chromophore core and polymerizable tails are synthesized separately, and combined later by mild acylation. A means of ultra-thin-film polymerization, both photo and thermal, were devised. All of the chromophores could be polymerized as ultrathin films. Because of their high absorbances, it was possible to use UV-Vis spectroscopy to monitor polymerization indirectly; as the films were of only a few monomer units thick, it was possible to dissolve the unreacted monomer residues afterwards and thus determine polymerization degrees as a function of the absorbance of the polymerized film. The molecules were studied extensively to yield the parameters for thin film preparation, photopolymerization, and photocurrent generation. While the monomers were liquid at room temperature, the hardness of the polymers was that of crosslinked epoxy plastics. The porphyrin monomer was used to study photopolymerization kinetics due to its unique self-photoinitiating properties. Polarization modulation IR spectroscopy was used to study real-time photopolymerization of the porphyrin monomer at varying temperatures, yielding rate constants and the activation energy of the reaction. It was the first published study of ultra-thin-film polymerization kinetics. The monomers were polymerized in situ to form bilayers, bulk heterojunctions or hybrids of both, to create a photoactive structure for photocurrent generation. An extensive set of samples was prepared and studied. The monomers employed in this work were optimized for easy photopolymerizability and as such produced unoptimal power conversion efficiency. Nevertheless the basic structure of the polymer lends itself well to modification for improved organic photovoltaic performance

Calcium Chelation of Lignin from Pulping Spent Liquor for Water-Resistant Slow-Release Urea Fertilizer Systems

Slow-release fertilizers represent a possible large-scale application for plant polymers. Here we show a facile way to stabilize urea in fertilizer systems by lignin. Chelation of kraft black liquor with calcium acetate at pH 13 precipitated lignin as a calcium complex (Ca-lignin), which offered beneficial effects if compared to those from lignin obtained by precipitation at low pH (Acid-lignin). The reduced affinity of water to Ca-lignin was exploited in the formulation of slow release fertilizers comprising wheat straw sections impregnated with Ca-lignin in molten urea. Compared to the case of Acid-lignin, immersion in water was slowed down more extensively by Ca-lignin. After 24 h incubation at low moisture conditions, the highest proportion of urea retained in the Ca-lignin/straw fertilizer system was 58%. The water resistance of Ca-lignin was explained by a lower aqueous solubility that differed from the typical pH-dependent solubility of Acid-lignin. Electron microscopy, infrared spectroscopy, and accessible surface areas suggested that Ca-lignin consisted of less densely packed molecules organized as calcium-chelated chains. Overall, the controlled water-solubility of lignin precipitated by metal cations is greatly beneficial in fertilizer systems and can open new opportunities in material development (permeable films and others).Peer reviewe

Techno-economic assessment for the large-scale production of colloidal lignin particles

The purpose of this study is to investigate the techno-economic feasibility of an environmentally sustainable and green process for the cost-effective large-scale manufacturing of colloidal lignin particles. The process involves the instantaneous formation of colloidal lignin particles (CLPs) through self-assembly when a concentrated solution of lignin in tetrahydrofuran (THF) and ethanol is introduced into water. The capacity of the plant is assumed to be 50 kt per year of dry colloidal lignin and Aspen plus simulation program is used for the mass and energy balance calculations. The process equipment design and pricing are carried out based on relevant literature and vendor data. Results show that the total investment cost for a plant integrated with an existing pulp mill or bio-refinery is 36 M€ and the annual operating cost is 46 M€. The project lifetime is assumed as 20 years and the cost of production of colloidal lignin is found to be 0.99 € kg−1 (in case of integration) and 1.59 € kg−1 (without integration). The revenue for the process comes mainly from selling the colloidal lignin particles and additional revenue is generated from high pressure and low-pressure steam condensate sold as district heat. The payback period with a CLP selling price of 1.10 € kg−1 is found to be roughly 5 years. A minimum profitability requirement of 10% is considered for the techno-economic analysis and the internal rate of return (IRR) is calculated as 17% making the process viable and profitable. In addition, a sensitivity analysis is carried out to evaluate the effect of raw material price and ethanol recovery on the operating cost. Colloidal lignin has the potential to compete favorably as a renewable replacement for petroleum based feedstock like polyethylene, polypropylene, polyethylene terephthalate (PET) and phenol and can be used in attractive applications like phenol formaldehyde (PF) resins, foams, carbon fillers, bactericides and composites.Peer reviewe