(430g) Responsive Coatings from Low-Methoxyl Opuntia Ficus-indica Cactus Intended for Controlled Release Applications

Pectin extracted from cactus mucilage provide promising potential to be used as an alternative to commercial sources of pectin to fabricate ‘‘smart’’ responsive coatings implemented in controlled release applications. The structural and molecular properties of pectin vary widely based on their extraction source, encouraging the exploration of diverse sources of pectin to achieve versatile functionalities. Here, we investigated the mucilage of Opuntia ficus-indica cactus as an underexplored source of highly purified pectin. Opuntia ficus-indica belongs to the cactaceae family, and is grown in dry regions. Mucilage extracted from Opuntia ficus-indica is a heteropolysaccharide composed of a backbone chain structure of α-D-galacturonic acid. The carboxyl groups present in a polygalacturonic acid chain can be cross-linked in the presence of divalent ions to render hydrogel networks with conformations responsive to internal and external variables.

Herein, ultra-thin coatings of Opuntia ficus-indica cactus pectin were fabricated as surface-attached hydrogel networks by spin-casting solutions of pectin followed by Ca²⁺ induced cross-linking. The pH- and thermal-responsive behaviors of cactus pectin networks were assessed by characterizing the swelling behaviors using ellipsometry. The coatings displayed a remarkable capacity to sensitively interact with Ca²⁺ ions due to the presence of a large number of carboxyl groups. Additionally, the coatings demonstrated responsiveness to the pH and to a lesser extent temperature variations.

Promising properties including inherent biocompatibility and biodegradability, high molecular weight, along with responsive behavior indicate the potential utility of coatings of cactus pectin in controlled release applications.