Silk fibroin films were modified with zwitterionic and hydrophilic brush-like polymers via surface-initiated ATRP, resulting in surfaces that reduced protein adsorption and cell attachment.
The
use of the traditional growing-from approach to prepare surface-initiated
polymer brushes is widespread as it produces polymer brushes with
higher grafting densities than grafting-to methods. In this article,
we present an investigation of a passing-though approach that supplies
the monomer from below the initiator-functionalized surface, inverting
the concentration gradient found in the traditional growing-from technique
that has been shown to increase the D̵ of brushes.
Using Fourier transform infrared (FTIR) spectroscopy mapping combined
with substrate masking, we show that the brushes incorporate only
monomer diffusing from below and not from the surrounding solution.
Further, we characterize these brushes with contact angle analysis,
FTIR, and atomic force microscopy and compare them to brushes synthesized
by the traditional growing-from approach. Finally, we demonstrate
that several properties of the zwitterionic polymer brush prepared
by our passing-through method, for example, wettability, grafting
density, uniformity, salt permeation retardation, and fouling resistance,
are superior to those of brushes prepared by the growing-from technique.
Passing-through polymerization is a technique for growing
surface-initiated
polymer brushes where monomers are supplied to the growing chains
by diffusing through the initiator-functionalized surface. This inverts
the monomer concentration gradient relative to conventional grafting-from
mechanisms, allowing for the synthesis of thicker and more densely
packed brushes. Here we use a combination of coarse-grained computer
simulations and experimental techniques to demonstrate how this approach
can be implemented, with swellable network-like substrates supplying
monomers to the functionalized surface as they diffuse out of the
swollen network. Compared to grafting-from polymer brushes, this method
shows a higher contact angle and a greater brush mass. Additionally,
we observed that the passing-through approach could lead to strain-induced
crystallization in the brush layer or wrinkling of the brush surface,
which we used to estimate the brush thickness. The developed method
opens a path for large-scale synthesis of the brush-modified elastic
substrates.
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