for tissue and cells to grow on. Such scaffolds can be derived from protein or carbohydrate biopolymers, including silk, collagen, fibrin, chitosan, alginate, and agarose. Biocompatibility and the ability to contribute to biological functions with the cells are necessary properties. Chapter 11 highlights bio‐based feedstock that can be used in scaffold manufacturing for tissue engineering.
Carbohydrate‐based materials play an essential role in cellular recognition processes. Carbohydrate‐protein interactions can be probed by synthetic glycomaterials to diagnose viral and bacterial infections. In Chapter 10, bio‐based glycomaterials and carbohydrate‐functionalized materials are discussed including their application in drug/gene delivery, wound healing, biorecognition, and sensing.
Chitosan and chitin/glucan complexes have been used in a wide range of applications such as anticancer, antibacterial, antioxidant as well as gene delivery due to their unique biochemical properties (Chapter 9). The major limitation of these biopolymers is their insolubility in water and, as such, steps have been taken to improve their solubility by various modification methods. Other applications of chitosan include fertilizers (Chapter 16) and antibacterial food packaging (Chapter 15). For food‐packaging applications, chitosan is limited by its low mechanical strength, rigid structure, and low thermal stability, which can be overcome by blending chitosan with other (bio)polymers (Chapter 15).
Due to their safety and biocompatibility, polysaccharide‐based materials find applications in the food industry as emulsion stabilizers. Starch modified with octenyl succinic anhydride (OSA) generates an amphiphilic character of the starch, making it an effective stabilizer of oil‐in‐water emulsions. Gums such as gum acacia, gum tragacanth, xanthan gum, and guar gum are used as surfactants to stabilize emulsions and liposomes in the food industry, as well as the formation of coacervates. Additionally, cellulose nanocrystals find applications in food applications in the stabilization of Pickering emulsions (Chapter 14).
Polysaccharides have a high abundance of functional groups, e.g. hydroxyl groups of cellulose, amine of chitosan, and carboxylic acid of alginate. These functional groups have a good affinity for complexation of metal ions through mechanisms such as reduction, chelation, and complexation. The polysaccharides alone are poor sorbents due to their low stability and need to be improved by chemical (e.g. introduction of other functional groups) as well as physical modification (e.g. forming composites with other polymers as well as inorganic materials). The use of bio‐based composites for the recovery of precious and heavy metals is discussed in detail in Chapter 7.
In electrochemical storage devices, synthetic binders such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) are traditionally used, which suffer from environmental and safety issues. As a green and renewable replacement, various biopolymer‐based binders have been used in either pristine or modified forms. For example, cellulose and its modified forms such as CMC, EC, and CA, but also chitosan, alginate, and gums have shown great potential as environmentally friendly binders (Chapter 5). Biopolymers such as chitosan, cellulose, and carrageenan can also be used as components of proton exchange membranes in fuel cells. Especially, chitosan is a highly promising biopolymer for fuel cell applications due to its low cost, environmental friendliness, hydrophilicity, ease of modification, and low methanol permeability (Chapter 5).
As mentioned in Section 1.1, a major challenge in the use of biomass feedstocks is the complex processing to obtain sufficient purity and quantity for the use in high‐performance products. Deep eutectic solvents (DES) comprise a class of solvents formed by eutectic mixtures of Lewis or Brønsted acids and bases, with physical properties similar to ionic liquids but different chemical properties [10]. These green solvents have the advantage over traditional ionic liquids since they are derived from biological resources and can be designed to have low toxicity and good biocompatibility. Chapter 6 of this book highlights a versatile approach of how biocompatible DES can be used as synthetic modifiers to achieve materials with a wide range of properties.
1.2.1.2 Other Biopolymers
Lignin is a three‐dimensional biopolymer composed of coniferyl alcohol, sinapyl alcohol, and p‐coumaryl alcohol monomers, but its specific structure and composition depend on the biomass [11]. A large number of hydroxyl groups in lignin provide a template for modification with specific functional groups. The ease and variability of lignin modification enable tailoring of the lignin structure to recover precious metals and rare earth metals (Chapter 7). Lignin has been used in fertilizer formulations, with the addition of plasticizers to improve the film‐forming properties (Chapter 16). Other applications of lignin are as binders in Li‐ion batteries (Chapter 5).
1.2.1.3 Proteins and Amino Acids
Proteins are biomolecules that are composed of amino acids and can be divided into plant‐based (e.g. soy protein, zein, and gliadin) and animal‐based proteins (e.g. gelatin, casein, and whey proteins). Plant proteins such as zein (extracted from maize) and gliadin (a component of gluten, extracted from wheat) are applied in the food industry as stabilizers of Pickering emulsions. However, pure protein emulsions are sensitive to changes in pH, which can be overcome by the formation of polymer‐biopolymer complexes. Zein nanoparticles can also be used to protect a hydrophobic core (such as vitamins) against oxidation and hydrolysis. Soy protein isolate, whey protein isolate, and casein are used in the formation of coacervates to encapsulate lipophilic‐active ingredients (Chapter 14). Gelatin, a natural water‐soluble protein obtained from collagen, is used in food‐packaging applications (Chapter 15).
Amino acids, the building blocks of proteins, and aliphatic diacids, like fumaric, glutaric, azelaic, and itaconic acids, have been used for the synthesis of MOFs with good water sorption and heat transfer applications (Chapter 12).
1.2.1.4 Active Biological Compounds
Apart from biopolymers and proteins, bio‐based resources may contain various active compounds that possess unique properties. Such high‐value chemicals may include fragrances, flavoring agents, and nutraceuticals like vitamins and antioxidants, and are generally extracted first before further processing of the biomass [12]. Naturally occurring fat‐soluble (A, D, E, and K) and water‐soluble vitamins (B and C) find applications in food. Here the key challenge is to retain the stability of the vitamins during storage and processing, which can be done by encapsulating the vitamin into delivery vesicles such as liposomes or coacervates (Chapter 14). Lecithins (such as phosphatidylcholine) and saponins (such as Quillaja saponins) are molecules with amphiphilic properties, which are used as natural surfactants to
