  The presented study highlights the efficiency of employing a KrF excimer
laser to create diverse types of periodic nanostructures (LIPSS - laser induced
periodic surface structures) on polyether ether ketone (PEEK) and polyethylene
naphthalate (PEN) substrates. By exposing the polymer films below their
ablation threshold to laser fluence ranging from 4 to 16 mJcm-2 at 6,000
pulses, we studied both single-phase exposure at beam incidence angles of 0deg
and 45deg, and two-phase exposure. Atomic force microscopy analysis revealed
that the laser-treated samples contained distinctive periodic patterns such as
waves, globules, and pod-like structures each exhibiting unique surface
roughness. Moreover, using analytical methods like EDS and XPS shed light on
the changes in the atomic composition, specifically focusing on the C and O
elements, as a result of laser exposure. Notably, in almost all cases, we
observed an increase in oxygen percentage on the sample surfaces. This increase
not only led to a decrease in the contact angle with water but also lowered the
zeta potential value, thus showing that the modified samples have enhanced
hydrophilicity of the surface and altered electrostatic properties. Last but
not least, the samples were assessed for biocompatibility; we studied the
interaction of the prepared replicates with mouse myoblasts (C2C12). The impact
of globular/dot structures on the cell growth in comparison to pristine or
linear LIPSS-patterned surfaces was determined. The linear pattern (LIPSS)
induced the myoblast cell alignment along the pattern direction, while
dot/globular pattern even enhanced the cytocompatibility compared to LIPSS
samples.
