Drawing inspiration from the field of designer self-assembling materials, this work is aimed to focus on the self-assembling nature of extracted peptides. Hair keratin, a proteinacious reject in tanning industry has been chosen since they have been extracted and used for wide range of applications. Keratin source was subjected to five hydrolysis treatments (viz., sulphitolysis, β-mercaptoethanol, ionic liquid, thioglycolic acid and alkali) and assayed for functional groups. This was followed by the prediction of secondary structure using circular dichroism, determining the microstructural level to which the extracted peptide has self-assembled. Sulphitolysis and thioglycolic acid based hydrolysates exist in monomeric conformation, whereas β-mercaptoethanol based hydrolysate exhibited dimeric conformation. The subsequent part of the study is to incorporate these peptides into the nanofibers to study the structural implication of keratin peptides on its characteristics. Accordingly, the peptides were electrospun with PVA and subjected to morphological, mechanical, thermal and biological characterizations. Monomeric nanofiber mat has high tensile strength of around 5.5 MPa and offered lower mass transport resistance, whereas dimeric mat has high Tm of around 290 °C and was more biocompatible. These results help in understanding the extraction-structure-function aspect of the hydrolysates stressing the role of extraction methods on the choice of application.
Keratin is unique due to its high cysteine content. This renders it with exceptional structural stability in native form, whereas in extracted form it makes them highly reactive. Hence keratin possesses higher capacity to assemble without stimulus, thus necessitating the study. The choice of extraction was limited to sulphitolysis and β-mercaptoethanol (M-KH) based procedures, as these extracts exist in different structural levels evidenced through Circular Dichroic studies. Thermally induced irreversible structural transition of M-KH from α-helix to β-sheet has resulted in lowering moisture loss peak of β-mercaptoethanol extract based mat (PVA-M-T) to 80.4 °C compared to 120.6 °C of neat PVA fibers and 92 °C of sulphitloysis extract based mat. This signals presence of increased free water content in PVA-M-T after crosslinking. This helped PVA-M-T retain sufficient elongation at break values (∼ 31 %) without compromising its strength (∼ 8.5 MPa). Also PVA-M-T with increased β-sheet content along with cell binding sequences (RGD, LDV and EDS) resulted in better protein-protein recognition and association thus favouring increased bioactivity.
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