Dilute acid polymerizes degassed, aqueous acrylamide with concomitant gelation, without the need for added free radical initiator or cross-linking agent. This reaction is accelerated by sonication or UV irradiation, but inhibited by adventitious oxygen or the addition of a free radical inhibitor, suggesting an acid-accelerated free radical process. The resulting hydrogels are thixotropic in nature and partially disrupted by the addition of chaotropic agents, indicating the importance of hydrogen bonding to the 3D network. This discovery was made while trying to prepare pectin-polyacrylamide hydrogels. We observed that pectin initiated the gelation of acrylamide, but only if the aqueous pectin samples had a pH lower than ca. 5.
Natural polysaccharide pectin has for the first time been grafted with polyhydroxybutyrate (PHB) via ring-opening polymerization of β-butyrolactone. This copolymer, pectin-polyhydroxybutyrate (pec-PHB), was blended with PHB in various proportions and electrospun to produce nanofibers that exhibited uniform and bead-free nanostructures, suggesting the miscibility of PHB and pec-PHB. These nanofiber blends exhibited reduced fiber diameters from 499 to 336-426 nm and water contact angles from 123.8 to 88.2° on incorporation of pec-PHB. They also displayed 39-335% enhancement of elongation at break relative to pristine PHB nanofibers. pec-PHB nanofibers were found to be noncytotoxic and biocompatible. Human retinal pigmented epithelium (ARPE-19) cells were seeded onto pristine PHB and pec-PHB nanofibers as scaffold and showed good proliferation. Higher proportions of pec-PHB (pec-PHB10 and pec-PHB20) yielded higher densities of cells with similar characteristics to normal RPE cells. We propose, therefore, that nanofibers of pec-PHB have significant potential as retinal tissue engineering scaffold materials.