Keratin Associations with Synthetic, Biosynthetic and Natural Polymers: An Extensive Review

Abstract

Among the biopolymers from animal sources, keratin is one the most abundant, with a major contribution from side stream products from cattle, ovine and poultry industry, offering many opportunities to produce cost-effective and sustainable advanced materials. Although many reviews have discussed the application of keratin in polymer-based biomaterials, little attention has been paid to its potential in association with other polymer matrices. Thus, herein, we present an extensive literature review summarizing keratin’s compatibility with other synthetic, biosynthetic and natural polymers, and its effect on the materials’ final properties in a myriad of applications. First, we revise the historical context of keratin use, describe its structure, chemical toolset and methods of extraction, overview and differentiate keratins obtained from different sources, highlight the main areas where keratin associations have been applied, and describe the possibilities offered by its chemical toolset. Finally, we contextualize keratin’s potential for addressing current issues in materials sciences, focusing on the effect of keratin when associated to other polymers’ matrices from biomedical to engineering applications, and beyond.

Properties and Degradation of Novel Fully Biodegradable PLA/PHB Blends Filled with Keratin

“…Besides the sample with the highest keratin loading, a decrease in both elongation at break and tensile strength with an increased keratin loading was observed without significant changes in the stress–strain slope. Many authors reported [ 50 ] higher keratin loading (larger than 10 wt %) leading to significant deterioration of tensile properties, due to worse compatibility and disintegration into the material.…”

Hydrogels and Dentin–Pulp Complex Regeneration: From the Benchtop to Clinical Translation

“…Hard keratin is formed from tightly packed filaments in the cysteine-rich proteins matrix, while soft keratin is composed of loosely packed filaments [ 144 , 146 ]. Keratin is considered as one of the most abundant natural polymers [ 147 ]. It is usually extracted under low pH in the presence of reducing agents to give rise to keratein, or of oxidizing, agents giving rise to keratose [ 145 , 148 ].…”

Biopolymer-Waste Fiber Reinforcement for Earthen Materials: Capillary, Mechanical, Impact, and Abrasion Performance

“…Specifically, the chemical composition of these CFs presents cysteine (7.8 mol %), glycine (13.7 mol %), proline (9.8 mol %), serine (14.1 mol %), hydrophobic residues, and β-pleated sheets [ 2 , 3 , 4 , 7 ]. The type of keratin found in CFs (β-keratin) [ 22 , 23 , 24 , 25 ] exhibits a pleated sheet structure, as shown in Figure 1 , consisting of β-strands connected laterally (either parallel or non-parallel) through hydrogen intermolecular bonds (see the red circle in Figure 1 ) [ 22 ]. This pleated sheet structure is stable due to two main factors: (i) The hydrogen bond between β-strands allows the generation of a sheet and (ii) the planar peptide bond induces a folded sheet [ 22 ].…”

“…These BPFs have been morphologically, physically, and chemically characterized in several studies, whose results have highlighted their very low density (approximately 0.8 g/cm 3 ) and good thermal and sound-damping performance, among other properties [ 9 , 26 ]. In addition, these BPFs have been studied as fiber-reinforcement for generic composite materials (e.g., [ 6 , 8 , 19 , 24 , 27 , 28 , 29 , 30 ]) and also as fiber-reinforcement for cement-based and plastic-based construction composite materials (e.g., [ 7 , 11 , 19 , 22 , 27 , 28 ]). Nevertheless, the use of these BPFs as fiber-reinforcement for non-synthetic construction materials has been included in very few studies, which have mainly been focused on the use of BPFs as reinforcement in soil remediation applications [ 13 , 29 , 30 ].…”