(417c) Stimuli-Responsive Thin Coatings Made from Natural Pectins

Pectins have been widely used in pharmaceutical formulations and the food and beverage industries due to their non-toxic nature and low production costs. They exhibit significant potential as “green” coatings with prospective applications in controlled release of drugs, tissue engineering scaffolds, and membranes for mass-separation of organic compounds. We have fabricated ultra-thin layers of cross-linked natural (high-methoxyl) pectin polysaccharides which exhibit tunable thermo- and pH-response behaviors.

Thin films were fabricated by spin-casting solutions of natural pectin followed by cross-linking upon exposure to solutions of calcium chloride (CaCl₂) in ethanol. Ethanol is a poor solvent for pectin thus did not disrupt the coating while allowing for Ca²⁺ ions to diffuse into the layers. Coatings were cross-linked over a range of CaCl₂ concentrations to obtain networks at different extents of cross-linking.

ATR-FTIR assessed the chemical properties of pectin coatings and their modifications upon crosslinking. The pH- and thermal-responsive behaviors of networks were evaluated by characterizing the swelling behaviors using ellipsometry.

Our findings showed that the swelling capacity of the coatings was dependent on the degree of cross-linking. Moreover, the swelling of the natural coatings showed an active function of temperature. At temperatures below approximately 35 ËšC the coatings were hydrophilic. As the temperature was increased, the pectin layers underwent a volume-phase transition, similar to a hydrophilic/hydrophobic shift found in lower critical solution temperature polymers. The ATR-FTIR revealed that the thermo-dependent change was driven by dehydration of the carbomethoxy groups along the backbone of the pectin chains.

The coatings of cross-linked pectin networks demonstrated a swelling behavior which could be tuned by adjusting temperature, degree of cross-linking, and pH of the surroundings to induce the desired response. Our findings provide an improved understanding of the chemical properties and the gelling behavior of thin films of pectins which can be employed for establishing responsive surfaces with tunable response suitable for the pharmaceutical and biotechnology industries.