Natural Polymers as Sustainable Materials for the 21st Century

Lignin is the second most abundant biopolymer on the planet, yet is also a major waste in paper and pulp industries and biorefinery. Lignocellulosic biorefinery focuses on carbohydrate utilization, leaving lignin as an abundant waste. This waste lignin is often burned to cause carbon emission. Fungible lignin utilization is crucial to sustainability and decarbonization, yet is hindered by the limited understanding of the structure-property relationship of lignin chemistry and product properties. We have advanced such understanding to guide the process and material designs. First, we have discovered that lignin molecular weight, uniformity, linkage profile, and functional groups could impact the lignin biomaterials’ properties. For example, the higher molecular weight, better uniformity, and more linear linkages could improve carbon material properties. The understanding has guided the design of a new type of lignin to achieve the highest reported tensile strength for lignin carbon fiber, empowering lightweight applications for emission reduction. This new type of lignin can also promote the performance of plastic blends. Therefore, based on the fundamental understanding, we have designed processes to transform lignin into a precursor for broad biomaterial applications to promote sustainability and decarbonization. Second, we revealed that lignin processing into smaller molecular weight, monomer-containing, and hydroxyl group-enriched fractions will significantly improve the bioprocessibility. Based on the discovery, we designed a ‘plug-in’ module to transform pretreatment technologies into integrated biorefinery for efficient conversion of both carbohydrates and lignin. In particular, we integrated innovative biorefinery and microbial design to enable cost-effective and efficient lignin conversion into biodegradable plastics. Thirdly, we have developed strategies to integrate the first two approaches to deliver a multi-stream lignocellulosic biorefinery, where different lignin fractions can be used for various high value products to maximize the value proposition and carbon emission reduction. Together, the fundamental understanding of relationship among lignin chemistry, processiblity, and biomaterial properties have enabled us to design the lignin-based biomaterials and lignin processing technologies that can substantially improve the sustainability and economics of modern biorefinery and paper and pulping plants.

Lignocellulose is a supramolecular network formed mainly by the complex polymers cellulose, hemicelluloses, and lignin. Among them, lignin is a ubiquitous and heterogeneous plant cell wall polymer derived mainly from hydroxycinnamyl alcohols via combinatorial radical coupling reactions. Unlike cellulose and hemicelluloses, lignin is an aromatic polymer that contains a variety of ether- and carbon-carbon linkages between monomer-derived units. These properties render the cell wall recalcitrant to chemical depolymerization that is an essential but challenging starting point for entire lignocellulosic industries. Biotechnological efforts to unpack and use these carbon-neutral materials for bioenergy and bioproducts require expensive chemical, physical, or biological processes. Despite the vastly stored carbon in plant biomass, ligninolytic capability on the planet has until now only been understood from an extremely limited range of organisms, other than white rot and brown rot fungi. The evolution of biomass deconstruction in insect-microbial systems has created an intriguing parallel to those of wood decay fungi. Lower termites do have the capability to degrade lignin to a certain degree, as is also seen in brown rot fungi; this approach utilizes wood polysaccharides efficiently while leaving most of the lignin polymer intact although they are able to cleave ether linkages in lignin to gain access to the polysaccharides. As the genome of brown rot fungi, like Rhodonia placenta, encodes no ligninolytic peroxidases, yet they are able to truncate the lignin polymer, the question remains: Do lower termites employ ligninolytic peroxidases or a Fenton system in which electrophilic reactive oxygen species like hydroxyl radicals can cleave lignin? The woodroach, Cryptocercus spp., interestingly displays similar losses in lignin units to those seen in the lower termites. In contrast, the extensive amount of lignin degradation in the more derived Termitidae termites is reminiscent of oxidative attack on the lignin polymer by the white-rot fungi, which produced the first ligninolytic peroxidases to gain stored carbon. These efficient and diverse plant biomass-deconstruction strategies in termites all have the potential to inform industrial saccharification and other biotechnological applications.

Agricultural residues offer promise as a sustainable feedstock for making high-value natural polymers. However, such sources and, unfortunately, environmentally friendly methods to produce functional cellulose are still limited. In this study, we present a simple and scalable process to produce high-quality cellulose from corn cobs, an underused agricultural leftover from corn production. Integrating acetosolv fractionation of the corn cobs followed by alkaline treatment of the crude cellulose pulp yields amorphous cellulose with high purity and at high yields (~75% based on crude cellulose). When compared to commercial microcrystalline cellulose (MCC), the corn cob–derived cellulose (C3) exhibited nearly twice the surface area and pore volume, along with a lower water contact angle, indicating greater hydrophilicity. Remarkably, C3 had roughly four times the water-holding capacity and twice the oil-holding capacity of MCC. Helium pycnometry revealed a higher density for C3 compared to MCC, while low-field NMR data indicated similar water relaxation populations for MCC and C3. X-ray diffraction analysis of C3 showed about a 50% reduction in crystalline index, consistent with the formation of an amorphous structure confirmed by solid-state ¹³C NMR. FTIR and NMR analyses detected no C=C or C=O signals, indicating effective lignin removal. These attributes of C3 are attractive to make functional materials and dietary fibers with significantly more value than the corn cobs. Such product diversification has the potential to improve the economic and environmental profiles of corn-based biorefineries.

Lignin accounts for up to 30% of organic carbon in the biosphere making it a major source of renewable carbon. However, the vast majority of lignin produced in industry is burned as low-value fuel, contributing to carbon emissions at accelerated timescales despite being classified as biogenic carbon. As an alternative to combustion, carbon materials offer an effective pathway for long-term carbon sequestration. Beyond simple carbon sinks, porous carbons can be used in advanced technology to address some of the world’s most pertinent challenges, such as energy storage, water treatment, and CO₂ capture. Owing to its high carbon content, aromatic motifs, and natural tendency to form nanoparticles, lignin is one of the most promising precursors of tunable carbon materials.

Carbons represent a diverse class of materials, highly tunable with respect to their carbon architecture, pore structures and surface chemistries. Often high surface areas with accessible pore structure are targeted for efficient adsorption and mass transport. Chemical activation approaches are effective, but the resulting carbons often have disordered pore structures, and the use of activation chemicals limit scalability. Contemporary approaches focus on producing well-defined pore structures, in this context, lignin nanoparticles offer tunable carbon morphologies, with high surface to volume ratios and predictable packing densities.

Supercapacitors are high power density energy storage devices that store charge at the electrode-electrolyte interface through electrostatic mechanisms. Since the capacitance is proportional to the accessible surface area, carbon materials with high surface areas make excellent supercapacitor electrodes. This work investigates the formation of porous carbon from kraft lignins as electrodes for high-performance supercapacitors. Traditional chemical activation is compared with emerging approaches using lignin nanoparticles. The approaches are evaluated for their impact on the resulting carbon properties and supercapacitor performance. Insights are gained into the advantages of different processing methods for different applications of lignin-based carbon.

Wearable bioelectronic patches are transforming healthcare by enabling continuous monitoring of physiological signals. Nonetheless, existing systems face challenges, including inadequate skin adhesion, gel dehydration, mechanical fragility, and environmental concerns associated with single-use devices. To address these issues, we present a paintable, disposable, and biodegradable ionic-skin hydrogel electrode engineered for clinical-grade electrophysiology and multimodal sensing.

This study was designed to integrate stabilized gallium-based liquid-metal networks into a gelatin-carrageenan biopolymer matrix. Carboxylic acid-functionalized F127 serves as an interfacial stabilizer. This formulation yields a soft, breathable surface that retains moisture and conforms seamlessly to the skin. Functional groups present in the matrix interact with the liquid-metal oxide shell, thereby preventing leakage, preserving metallic pathways, and facilitating self-healing under mechanical strain. Consequently, a hydrogel electrode is developed that integrates triboelectric energy generation with piezoresistive pressure sensing while ensuring long-term hydration and biocompatibility.

Comprehensive evaluations will examine film formation, flow properties, impedance stability, hydration retention, motion durability, and biodegradation. Functional validation involves ECG, EMG, EEG, and pressure-sensing tests, with metrics like impedance drift, SNR, artifact suppression, alpha-band stability, R-wave accuracy, and pressure sensitivity. The F127 scaffold also offers a modular platform for ion recognition, allowing scalable electrochemical sensing without compromising electrophysiological performance.

This study introduces a paintable, environmentally friendly hydrogel patch that can be removed with warm water, thereby ensuring user comfort and reducing environmental impact. By integrating ionic-skin mechanics, liquid-metal conductivity, and molecular stability, the platform facilitates simultaneous monitoring of biopotentials, pressure, and sweat chemistry.

The non-solvent induced phase separation (NIPS) process is commonly used to manufacture films from petroleum-derived polymers using toxic, aprotic solvents, which are under increasing scrutiny due to their negative environmental impacts. In order to decrease our dependence on petroleum-derived polymers, while also increasing our fundamental knowledge in green engineering, this study explores the potential of forming free-standing, antimicrobial films from the natural polymer carboxymethyl cellulose (CMC) using all-aqueous processing. First, turbidity measurements were used to conduct a wide screening of the ability of CMC and the synthetic polycation poly(diallyldimethylammonium chloride) (PDADMAC) in the presence of salt (sodium chloride (NaCl) or potassium bromide (KBr)) and their ability to form polyelectrolyte complexes (PECs). The optimized PEC conditions were corroborated via rheological testing which indicated higher coacervate sensitivity to KBr than to NaCl. Next, the optimized hybrid coacervates were blade-cast into films using aqueous phase separation (APS). Their morphology and mechanical performance were evaluated using scanning electron microscopy (SEM) and tensile testing, respectively. Dense, robust films were formed from the “optimized” coacervates using NaCl or KBr. When high salt concentrations were used, the films morphology changed to a fractured and unstable surface, resulting in a significant decrease in mechanical strength. With the knowledge that our CMC/PDADMAC films were manufactured with an excess of PDADMAC, we hypothesized that their cationic nature would result in strong antimicrobial properties via contact killing. We suggest that these CMC-based films hold potential for the development of packing and coatings via completely aqueous processing of biopolymer-based films for enhanced sustainability.

The development of plant-based meat analogues through high-moisture extrusion (HME) has intensified due to sustainability considerations; however, during HME, proteins are exposed to thermomechanical conditions that may promote oxidative reactions and potentially alter the structuring mechanisms responsible for fibrosity. Recent studies indicate that during extrusion processes lipid and protein oxidation may occur, inducing the formation of carbonyl groups and covalent bonds, which could contribute to the stabilization of the characteristic fibrous structure of meat analogues. In this context, we investigated peroxyl radical (ROO)-mediated oxidative crosslinking, as a chemically relevant model for oxidative processes in food matrices, in faba bean (Vicia faba, FP) and pea (Pisum sativum, PP) proteins and their blends, aiming to elucidate how protein composition modulates the formation of covalent bonds associated with structural protein networks in meat analogues. ROO induced oxidation (AAPH 100 mM) generated comparable levels of hydroperoxides and carbonyl groups across formulations, without detectable changes in the overall secondary structure. However, a marked protein source–dependent behavior was observed: in contrast to PP, whose oxidation led to only minor changes in molecular weight distribution, FP oxidation resulted in pronounced protein crosslinking and the formation of high-molecular-weight aggregates; in blended systems, covalent aggregation progressively decreased as the FP fraction was reduced. LC–MS/MS analysis confirmed the formation of di-tyrosine species in FP, PP, and their blends, whereas di-tryptophan formation was detected exclusively in FP, supporting a differential oxidative crosslinking mechanism associated with the major proteins (legumin ~38 kDa, and vicilin ~47 kDa). Overall, these results demonstrate that the faba bean-to-pea protein ratio allows modulation of the density and nature of oxidative crosslinking under ROO conditions. Given that the formation of anisotropic fibrous structures during HME relies on protein unfolding, alignment, and subsequent stabilization of protein–protein networks, we propose that these covalent linkages may play a structural role in consolidating the protein network during extrusion, thereby influencing final fibrosity. Future studies will correlate di-Tyr/di-Trp formation and covalent aggregation with fibrosity degree, anisotropy, and microstructure in high-moisture extruded products.

Renewable polysaccharides can serve as both the substrate and the functional capture interface in point-of-need diagnostics, enabling water-first fabrication and reducing reliance on persistent petrochemical components. Here, we present a comparative framework that benchmarks polysaccharide nanocrystals as antibody supports for paper-based immunoassays by integrating physicochemical characterization, orthogonal interfacial metrology, and prototype translation. Specifically, we compare cellulose nanocrystals (CNCs), chitin nanocrystals (ChNCs), and CNC/chitosan (CNC/Ch) composites as supports for antibodies targeting human CD66e (CEACAM5), an established biomarker for epithelial cancers.
Nanocrystal platforms were characterized to connect molecular composition and electrostatics to probe presentation and interfacial behavior (morphology, charge, and accessible functional groups). Antibodies were immobilized using carbodiimide/N-hydroxysuccinimide coupling under aqueous conditions, and antigen recognition was quantified in real time using quartz crystal microbalance with dissipation monitoring (QCM-D) and multiparameter surface plasmon resonance (MP-SPR) across a stepwise antigen concentration series to evaluate saturation behavior and concentration-dependent responses. The paired QCM-D/MP-SPR readout is central: it enables mechanistic interpretation of soft biopolymer films where hydration, viscoelasticity, and interfacial restructuring can dominate “apparent mass” signatures, potentially confounding comparisons if a single technique is used.
Across platforms, CNC/Ch composites deliver superior antibody immobilization efficiency and stronger antigen-binding responses than CNC or ChNC supports, consistent with synergistic cationic chitosan–high-surface-area CNC interfaces that increase effective capture density while maintaining practical processing. To demonstrate translational relevance, these renewable capture layers are deployed on additive-free paper and paired with gold-nanoparticle labels in a simple colorimetric prototype compatible with replicate testing and short assay times. Building on our broader detection portfolio (including rapid dipstick-style assays on cellulose-based interfaces), this work provides green-chemistry-aligned design rules for renewable immunoassays that are scalable, fieldable, and grounded in interfacial structure–function relationships.