Responsive coatings from naturally occurring pectin polysaccharides

Pectin polysaccharides have significant potential as all-natural, non-toxic green coatings that exhibit thermally-cued swelling behavior. Herein, ultra-thin coatings of highly-esterified pectin polysaccharides were cross linked with calcium chloride (CaCl2) and their swelling in water was investigated with ellipsometry. At low temperatures, the coatings swell to 2-3 times their dry layer thickness. As the temperature is increased, the coatings show a pronounced decrease in swollen thickness, reminiscent of the hydrophilic-hydrophobic transition observed in lower critical solution temperature (LCST) polymers. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy establishes that this transition is driven by dehydration of the esterified galacturonic acid residues along the pectin backbone. By adjusting both the CaCl2 concentration used to crosslink the pectin coatings as well as pH of swelling medium, the pectin coatings could be judiciously tuned for a desired swelling response as a function of temperature. Due to their non-toxic and responsive nature, it was further tdemonstrated that such coatings could be used in applications to control cell adhesion.