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Thermally induced wrinkling of poly-L-lactic acid with palladium nanolayers

Poly-L-lactic acid has lately attracted a lot of scientific interest as this material is capable of forming complex nanostructures by self organization due to wrinkling instability. This process is induced thermally on samples which were plasma-treated, sputtered with metal layers or both and therefore it offers many parameters for tweaking to achieve desired material properties. This paper focuses on poly-L-lactic acid samples coated with palladium nanolayers. After annealing these samples develop sharp wrinkles with size directly dependent on thickness of sputtered metal layer as observed by means of atomic force microscopy. Sheet resistance was also measured and has shown significant changes of electrical properties dependent both on palladium layer thickness and thermal treatment. X-ray photoelectron spectroscopy has shown that annealing does not change metal concentration on the surface of the sample it only causes rearrangement of the palladium. These data were important for choosing viable candidates for biocompatibility tests that are also presented in the paper. Annealed samples with thin palladium layers have shown significant improvement over polystyrene mock and even significant improvement of adhesion and short term proliferation (up to 60 hours) over pristine poly-L-lactic acid.