In Situ Fibril Formation of κ‑Casein
by External Stimuli within Multilayer Thin Films
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Abstract
We
have developed the in situ fibrillation of κ-casein, employed
as amyloid precursor, within multilayer films consisting of κ-casein
and poly(acrylic acid) (PAA) prepared by the layer-by-layer (LbL)
deposition. The fibrillation of κ-casein within the multilayered
films is strongly dependent on the extent of intermolecular interactions
between κ-casein and PAA. When films constructed initially at
pH 3 were heat treated at the same pH, κ-casein did not transform
into fibrils. However, when the films were subjected to heat treatment
at pH 5, κ-casein was transformed into fibrils within multilayer
films due to weakened intermolecular interactions between κ-casein
and PAA. We also noted that the multilayer film was swollen at pH
5 by the charge imbalance within the film, which we believe gives
enough mobility for κ-caseins to form fibrils with adjacent
κ-caseins within the multilayer. The fibrils were found to be
uniformly distributed across the entire film thickness, and the aspect
ratio as well as the number density of fibrils increased as a function
of incubation time. The present study reveals a strategy to realize
in situ nanocomposites within LbL multilayer films simply by triggering
the formation of protein fibrils by controlling the intermolecular
interactions between amyloid precursors and polyelectrolytes (PEs)