Protein nanofibrils and their use as building blocks of sustainable materials

The development towards a sustainable society requires a radical change of many of the materials we currently use. Besides the replacement of plastics, derived from petrochemical sources, with renewable alternatives, we will also need functional materials for applications in areas ranging from green energy and environmental remediation to smart foods. Proteins could, with their intriguing ability of self-assembly into various forms, play important roles in all these fields. To achieve that, the code for how to assemble hierarchically ordered structures similar to the protein materials found in nature must be cracked. During the last decade it has been demonstrated that amyloid-like protein nanofibrils (PNFs) could be a steppingstone for this task. PNFs are formed by self-assembly in water from a range of proteins, including plant resources and industrial side streams. The nanofibrils display distinct functional features and can be further assembled into larger structures. PNFs thus provide a framework for creating ordered, functional structures from the atomic level up to the macroscale. This review address how industrial scale protein resources could be transformed into PNFs and further assembled into materials with specific mechanical and functional properties. We describe what is required from a protein to form PNFs and how the structural properties at different length scales determine the material properties. We also discuss potential chemical routes to modify the properties of the fibrils and to assemble them into macroscopic structures.Funding Agencies|FormasSwedish Research Council Formas [2019-00679, 2017-00396]; VRSwedish Research Council [2020-03329]</p

Preparation of functionalized protein materials assisted by mechanochemistry

Herein, we investigate the suitability of hen egg-white lysozyme (HEWL) as a protein matrix for dispersal of various hydrophobic dyes. Moreover, we investigate the use of a mixer mill for grinding operation as an alternative to hand grinding by mortar and pestle. HEWL and various dyes are mixed by mechanochemistry, and the resulting composite material is dissolved in aqueous acid. The samples are then exposed to conditions promoting self-assembly of HEWL into protein nanofibrils (PNFs). The effect of PNF formation on dye photophysics is investigated by spectroscopic examination by absorption and luminescence spectroscopy, and product morphology is examined by scanning electron microscopy. The self-assembly process results in protein nanofibrils functionalized with luminescent dyes. Such structures may find future applications in various devices for light emission. In addition, we demonstrate that the anticancer drug camptothecin can be incorporated into protein nanofibrils giving materials that can find application as drug delivery agents.Funding Agencies|China Scholarship Council; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009-00971]</p

Water Processable Bioplastic Films from Functionalized Protein Fibrils

A combination of mechanochemistry and aqueous self-assembly is employed to prepare protein nanofibrils (PNFs) functionalized with perylene diimide (PDI) dyes. These materials are then mixed with poly(vinyl alcohol) (PVA) and casted into bioplastic films. The functionalization process not only results in luminescent hybrid materials, but the presence of the dye modifies the physical properties of the PNFs. Films formed from PNFs functionalized with PDIs display anisotropic organization, which enables emission of polarized light. Crucially, the presence of PDI dyes improves the stability of PNF-PVA films in water and moreover the films are processable when wet. By applying water, films can be glued together or self-healed by applying water. Mechanochemical methodology can thus be employed for modifying properties of protein materials. This represents a new highly flexible and novel strategy for tuning both properties and functionality of protein materials.Funding Agencies|Formas [2019-00679]; China Scholarship Council</p

Protein-based luminescent aerogels with elastic properties

Gelatin is a famous gel-forming proteinaceous material with excellent hydrogelation properties. Herein, we report that protein nanofibrils (PNFs) can be employed to form hybrids with gelatin that can be converted to aerogels with attractive mechanical properties. Moreover, we are able to influence the gelation behavior of PNFs by mechanochemical processing. A combination of mechanochemistry and aqueous self-assembly is employed to prepare PNFs functionalized with hydrophobic dyes. These materials are then mixed with gelatin and converted into aerogels by freeze drying. We find that PNFs functionalized with PNFs lead to the formation of aerogels with more robust mechanical properties. Mechanochemical methodology as a green and scalable method can thus be employed for influencing the properties of protein-based aerogels. This represents a new and highly flexible and novel strategy for tuning both properties and functionality of protein materials. This work opens a simple and feasible way to produce nontoxic and biodegradable aerogel materials with favorable mechanical strength.Funding Agencies|China Scholarship Council</p

Protein-Based Flexible Conductive Aerogels for Piezoresistive Pressure Sensors

Gelatin is an excellent gelling agent and is widely employed for hydrogel formation. Because of the poor mechanical properties of gelatin when dry, gelatin-aerogels are comparatively rare. Herein we demonstrate that protein nanofibrils can be employed to improve the mechanical properties of gelatin aerogels, and the materials can moreover be functionalized with a an electrically conductive polyelectrolyte resulting in formation of an elastic electrically conductive aerogel that can be employed as a piezoresistive pressure sensor. The aerogel sensor shows a good linear relationship in a wide pressure range (1.8-300 kPa) with a sensitivity of 1.8 kPa(-1). This work presents a convenient way to produce electrically conductive elastic aerogels from low-cost protein precursors

Mechanochemical Preparation and Self-Assembly of Protein : Dye Hybrids for White Luminescence

Protein nanofibrils (PNFs) functionalized with multiple dyes are prepared by a combination of mechanochemistry and liquid-phase self-assembly. The three employed dyes are Fluorescent Brightener 378 (F378), 2-butyl-6-(butylamino)-1H-benzo[de]isoquinoline-1,3(2H)-dione (Fluorol 555), and Nile red (NR). F378 acts as the donor with Fluorol 555 as the acceptor. F555 in turn acts as the donor and NR as the acceptor. This enables a FRET cascade that enables conversion of UV light to white light. The efficiency of FRET can be influenced by the details of the self-assembly process. If proteins milled with different dyes are mixed prior to self-assembly, nanofibrils are formed containing all three dyes, thus favoring FRET processes. By tuning the ratio of the three luminescent dyes, PNF dispersions are obtained that display bright white light emission. Moreover, the PNF dispersions can be converted into white luminescent films and gels where the PNFs may help to organize dye molecules. Additionally, the PNF materials can be employed as coatings on commercial LEDs, enabling emission of white light.Funding Agencies|China Scholarship Council (CSC)China Scholarship Council; COST (European Cooperation in Science and Technology)European Cooperation in Science and Technology (COST); COST ActionEuropean Cooperation in Science and Technology (COST) [CA18112]</p

Ionovoltaic electricity generation over graphene-nanoplatelets: protein-nanofibril hybrid materials

Continuous harvesting of electricity from the ambient environment has attracted great attention as a facile approach to green and sustainable energy. Natural water evaporation-driven electricity generators with active materials from economical and environment-friendly sources are highly sought after. Herein, we present devices made from a combination of protein nanofibrils (PNFs) and low-cost graphene nanoplatelets (GNPs) that can be employed for electricity generation, simply by partly inserting the device into evaporating standing water. The origin of the electricity generation can be explained by the ionovoltaic effect where ionic motion, driven by evaporating water, leads to movement of charge carriers in the electrically conductive GNP-phase. Moreover, the device performance can be improved by adding a small amount of salt to the active layer. A device, composed of GNP:PNF:AlCl3, produces a sustained voltage of about 0.48 V, and a current of 89 nA. Furthermore, the device can tolerate saline water, with only a modest decrease of voltage, which provides potential for harvesting electricity from both evaporating saline water and fresh water.Funding Agencies|Formas [2019-00679]; China Scholarship Council</p

Scalable lignin/graphite electrodes formed by mechanochemistry

Lignin is a promising candidate for energy storage because of its abundance, wide geographic distribution, and low cost as it is mainly available as a low value product from processing of wood into paper pulp. Lignin contains large amounts of potential quinone groups, which can be oxidized and reduced in a two electron process. This redox reaction makes lignin suitable for charge storage. However, lignin is insulating and therefore conductive materials are necessary in lignin electrodes, for whom the cost of the conductive materials hinders the scalable application. Among the organic conductive materials, graphite is one of the cheapest and is easily acquired from nature. In this work, we combine graphite and lignosulfonate (LS) and fabricate LS/graphite organic electrodes under a solvent-free mechanical milling method, without additives. The graphite is sheared into small particles with a size range from 50 nm to 2000 nm. Few-layer graphene is formed during the ball milling process. The LS/graphite hybrid material electrodes with primary stoichiometry of 4/1 (w/w) gives a conductivity of 280 S m(-1) and discharge capacity of 35 mA h g(-1). It is a promising material for the scalable production of LS organic electrodes.Funding Agencies|Knut and Alice Wallenberg foundation (KAW)Knut &amp; Alice Wallenberg Foundation; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; China Scholarship Council (CSC)China Scholarship Council</p

Biocarbon Meets Carbon-Humic Acid/Graphite Electrodes Formed by Mechanochemistry

Humic acid (HA) is a biopolymer formed from degraded plants, making it a ubiquitous, renewable, sustainable, and low cost source of biocarbon materials. HA contains abundant functional groups, such as carboxyl-, phenolic/alcoholic hydroxyl-, ketone-, and quinone/hydroquinone (Q/QH(2))-groups. The presence of Q/QH(2) groups makes HA redox active and, accordingly, HA is a candidate material for energy storage. However, as HA is an electronic insulator, it is essential to combine it with conductive materials in order to enable fabrication of HA electrodes. One of the lowest cost types of conductive materials that can be considered is carbon-based conductors such as graphite. Herein, we develop a facile method allowing the biocarbon to meet carbon; HA (in the form of a sodium salt) is mixed with graphite by a solvent-free mechanochemical method involving ball milling. Few-layer graphene sheets are formed and the HA/graphite mixtures can be used to fabricate HA/graphite hybrid material electrodes. These electrodes exhibit a conductivity of up to 160 Sm-1 and a discharge capacity as large as 20 mAhg(-1). Our study demonstrates a novel methodology enabling scalable fabrication of low cost and sustainable organic electrodes for application as supercapacitors.Funding Agencies|Knut and Alice Wallenberg foundation (KAW), through a Wallenberg Scholar grant; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; China Scholarship Council (CSC)China Scholarship Council</p