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Fabrication of feather keratin bio-based materials: Thermoplastics and tissue engineered scaffolds
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- Author / Creator
- Esparza, Yussef O
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Chicken feathers are an abundant by-product from poultry industry. Feathers are composed of around 90% keratin, a valuable protein bioresource that have great potential for non-food applications. Keratin is characterized by a high content of cysteine residues forming disulfide bonds. This feature makes keratin an interesting biopolymer for the fabrication of mechanically resistant materials, including thermoplastics and tissue engineered scaffolds. Therefore, the overall objectives of the thesis are 1) to fabricate and improve mechanical properties of chicken feather thermoplastics; 2) to study and characterize the self-assembly of feather keratin hydrogels and their physical and biological properties; 3) to compare hydrogel properties of hair, wool and feather keratins; and 4) to evaluate the feasibility of electrospinning of feather keratin for the fabrication of nanofibrous scaffolds. Chicken feathers were mixed with glycerol/propylene glycol plasticizers and thermally processed into plastic films. The tensile mechanical properties of films were evaluated. Incorporation of up to 2% graphite oxide nanoparticles resulted in enhanced tensile strength and Young modulus of plastic films, which were attributed to keratin intercalation into graphene oxide nanosheets and interaction between oxygen functionalities of graphite oxide with amino acid side groups of keratin, and plasticizers. Chicken feather keratin was also studied for developing scaffolds for potential application in tissue engineering. Keratin from chicken feathers was solubilized in a solution containing urea, thiourea, and sodium metabisulfite. Keratin hydrogels were spontaneously formed during controlled dialysis of extracted keratin solution. Keratin gelation and stability of gels was mainly controlled by the extent of disulfide bond re-formation. Gelation at neutral pH proceeded slowly towards the formation of transparent gels, whereas rapid gelation occurred at pHs of 3 and 9 due to isoelectric aggregation and increased rate of disulfide exchange reactions, respectively. Hydrogels had similar viscoelastic properties of adipose and dermal tissue. Increasing keratin concentration resulted in increased storage modulus of hydrogels; however, swelling capacity and porosity decreased with increased concentration. Hydrogel scaffolds supported the growth of human dermal fibroblasts (HDFa) over a period of 21 days. Cells infiltration was affected by the dense arrangement of keratin and lower porosity in hydrogels prepared at (10 and 12.5%), where the growth of cells was limited to the surface of scaffolds. Keratin from different sources was compared for their hydrogel properties. Keratin from hair, wool and feathers were characterized by their molecular weight, amino acid composition, and thermal and conformational properties. Hydrogels from feather keratin demonstrated substantially higher storage modulus (~10 times higher) than others. However, higher swelling capacity (>3000%) was determined in hair and wool over feather keratin (1500%) hydrogels. The smaller molecular weight and -sheet structure of feather keratin facilitated the self-assembly of rigid hydrogels. Whereas, higher molecular weight stretchable -helix keratins in hair and wool resulted in weaker hydrogels. Fibroblasts showed the highest proliferation rate on feather keratin hydrogel scaffolds, which was attributed to their superior viscoelastic properties. In the last part of the thesis, the potential of forming keratin nanofibers through electrospinning was evaluated. Electrospun keratin nanofiber were fabricated with non-toxic solvents and crosslinking reagents. Keratin was solubilized at room temperature in a 1 M NaOH solution. Poly(vinyl alcohol) (PVA)/citric acid aqueous solution was used as an aid for electrospinning. Solutions containing 10, 20, and 30% keratin/PVA mass ratio were successfully electrospun. The diameter of nanofibers decreased from 565 ± 154 nm in PVA to 274 ± 42nm in 20% keratin electrospun mats, which was attributed to a reduction in the viscosity of the solutions. Further decrease in viscosity with 30% keratin resulted in beads-on-fiber. The resultant nanofibrous mats were thermally cross-linked by esterification of PVA hydroxyl groups with carbonyl groups in citric acid. The incorporation of keratin in PVA nanofiber was confirmed by FTIR and XPS results. Proliferation of fibroblasts after 14 days was higher in scaffolds containing 20% keratin, which was attributed to the superior biological properties of keratin and higher surface area to volume ratio compared to 30% keratin. Feather keratin is a valuable bioresource for material applications. Feather plastics can be evaluated for applications including agricultural films. Keratin hydrogel and electrospun mat scaffolds support the proliferation of fibroblasts, making them potential materials for in vivo studies in skin tissue engineering.
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- Graduation date
- Fall 2017
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.