Characterization and In Vitro Cytotoxicity Safety Screening of Fractionated Organosolv Lignin on Diverse Primary Human Cell Types Commonly Used in Tissue Engineering.

There is limited data assessing the cytotoxic effects of organosolv lignin with cells commonly used in tissue engineering. Structural and physico-chemical characterization of fractionated organosolv lignin showed that a decrease of the molecular weight (MW) is accompanied by a less branched conformation of the phenolic biopolymer (higher S/G ratio) and an increased number of aliphatic hydroxyl functionalities. Enabling stronger polymer-solvent interactions, as proven by the Hansen solubility parameter analysis, low MW organosolv lignin (2543 g/mol) is considered to be compatible with common biomaterials. Using low MW lignin, high cell viability (70-100%) was achieved after 2 h, 24 h and 7 days using the following lignin concentrations: MSCs and osteoblasts (0.02 mg/mL), gingival fibroblasts and keratinocytes (0.02 to 0.04 mg/mL), periodontal ligament fibroblasts and chondrocytes (0.02 to 0.08 mg/mL). Cell viability was reduced at higher concentrations, indicating that high concentrations are cytotoxic. Higher cell viability was attained using 30/70 (w/v) NaOH vs. 40/60 (w/v) EtOH as the initial lignin solvent. Hydrogels containing low MW lignin (0.02 to 0.3 mg/mL) in agarose dose-dependently increased chondrocyte attachment (cell viability 84-100%) and hydrogel viscosity and stiffness to 3-11 kPa, similar to the pericellular matrix of chondrocytes. This suggests that low MW organosolv lignin may be used in many tissue engineering fields.

Lignin-Assisted Stabilization of an Oriented Liquid Crystalline Cellulosic Mesophase, Part B: Toward the Molecular Origin and Mechanism.

Lignin valorization has been scarcely considered in the form of liquid crystalline polymer blends. Recently, a stabilizing effect of organosolv lignin (OSL) on the oriented mesophase of hydroxypropyl cellulose (HPC) was observed and related to drastic improvements in tensile properties of the blends. With a view to elucidating this relaxation phenomenon, different molecular weight fractions and derivatives of organosolv lignin are synthesized, blended in solution with the liquid crystalline cellulosic polymer and analyzed in regard to their effect on the microstructural evolution of shear-aligned HPC chains. The rheological and rheo-optical investigations suggest a crucial contribution of the lower molecular weight oligomers and the phenolic hydroxy functionalities to the stabilization of the oriented cellulosic mesophase. The results provide an indication of the molecular origin and mechanism and might be of special interest for the production of anisotropic materials from liquid crystalline cellulosic polymers.

Lignin-Assisted Stabilization of an Oriented Liquid Crystalline Cellulosic Mesophase, Part A: Observation of Microstructural and Mechanical Behavior.

Liquid crystalline polymer blends containing lignin have been scarcely studied in the literature, albeit demonstrating potential for the design of high-performance lignin-based materials. In this study, organosolv lignin is blended in solution with hydroxypropyl cellulose (HPC), a lyotropic cellulose derivative, and its impact on the dynamics of the cellulosic liquid crystalline mesophase is investigated. Rheological measurements and rheo-optical investigations under crossed polarizers reveal that lignin enhances the persistence of the shear-induced orientation of the cellulosic macromolecules. In shear-cast films, the retention of the microstructural organization or band texture entails a drastic increase of the mechanical anisotropy and properties with lignin content. For the origin of the textural stabilization, we propose a specific "jacketing"-like effect of lignin on HPC. This study indicates the possibility of a beneficial impact of lignin on the relaxation behavior of liquid crystalline cellulosic polymers.

Lignin in Bio-Based Liquid Crystalline Network Material with Potential for Direct Ink Writing.

The flow-induced supramolecular arrangement, or band texture, present in water-soluble anisotropic films prepared from blend solutions of hydroxypropyl cellulose and organosolv lignin is locked via esterification with bio-based polycarboxylic acids. Subsequent to shear casting of the blend solutions, the chemical cross-linking with citric acid-based cross-linkers and a dimerized fatty acid yields water-insoluble, anisotropic films prone to swelling in water. The liquid crystalline networks are analyzed by means of polarized optical microscopy, tensile testing, Fourier transform infrared, and swelling experiments. Depending on the cross-linker, the dry "banded" films reach up to 3.5 GPa in tensile modulus, 80 MPa in tensile strength along the shear direction, and 5 MJ/m3 toughness across the shear direction. Films are softened upon water uptake causing a reversible extinguishment of the banded texture without interfering with the specimens' anisotropy. Rheological studies point to the applicability of highly concentrated blend solutions to direct ink writing. The implementation of the findings to the additive manufacturing of cross-linked 3D structures demonstrates the potential of a resource-friendly processing of fully bio-based materials.