1 research outputs found
Controlling the Cell-Adhesion Properties of Poly(acrylic acid)/Polyacrylamide Hydrogen-Bonded Multilayers
A thorough understanding of thermal effects on the physicochemical
properties of layer-by-layer (LbL) assembled multilayers is crucial
in utilizing these films in a variety of applications. In this work,
we investigate the effect of thermal treatment on cross-linking and
swelling of a hydrogen-bonded multilayer film made of polyÂ(acrylic
acid) (PAA) and polyacrylamide (PAAm), which has been shown to exhibit
excellent long-term cell adhesion resistance. We observe that the
apparent swelling of PAA/PAAm multilayers treated at 90 and 180 °C
in a physiologically relevant condition is similar; however, these
two multilayers with different thermal history exhibit completely
different cell adhesion properties when assessed with human mesenchymal
stem cells (hMSCs). While the 90 °C treated samples show excellent
cell adhesion resistance, those treated at 180 °C are highly
cell adhesive. A combination of characterization techniques including
thermogravimetric analysis (TGA) and Fourier-transform infrared (FT-IR)
spectroscopy reveals that complete cross-linking between PAA and PAAm
chains occurs above 150 °C. PAA/PAAm multilayer films incubated
at temperatures below 150 °C have a very low degree of cross-linking.
Thus, when these less-cross-linked films are exposed to aqueous solutions
of pH 4 or higher, a significant loss of the constituent materials
is observed. This lightly cross-linked hydrogel-like network in phosphate
buffered saline (PBS) has a water content of ∼94 vol %, making
the surface cell-adhesion resistant. In constrast, PAA/PAAm films
incubated at 180 °C consist of ∼72 vol % water in PBS
and exhibit cell-adhesive properties. The shear modulus of 180 °C
treated films measured by quartz crystal microbalance with dissipation
(QCM-D) monitoring is 6.0 MPa, which is 2 orders of magnitude higher
than that of lightly cross-linked 90 °C treated films (0.02 MPa),
suggesting that mechanical compliance plays a significant role in
influencing the cell adhesion behaviors. This work emphasizes the
importance of thermal treatment conditions, which potentially can
be used as a postassembly route to gradually modify and control the
properties of LbL multilayers over a wide range for specific applications