title: Systematic study of alginate-based microcapsules by micropipette aspiration and confocal fluorescence microscopy.
abstract: Micropipette aspiration and confocal fluorescence microscopy were used to study the structure and mechanical properties of calcium alginate hydrogel beads (A beads), as well as A beads that were additionally coated with poly-L-lysine (P) and sodium alginate (A) to form, respectively, AP and APA hydrogels. A beads were found to continue curing for up to 500 h during storage in saline, due to residual calcium chloride carried over from the gelling bath. In subsequent saline washes, micropipette aspiration proved to be a sensitive indicator of gel weakening and calcium loss. Aspiration tests were used to compare capsule stiffness before and after citrate extraction of calcium. They showed that the initial gel strength is largely due to the calcium alginate gel cores, while the long term strength is solely due to the poly-L-lysine-alginate polyelectrolyte complex (PEC) shells. Confocal fluorescence microscopy showed that calcium chloride exposure after PLL deposition led to PLL redistribution into the hydrogel bead, resulting in thicker but more diffuse and weaker PEC shells. Adding a final alginate coating to form APA capsules did not significantly change the PEC membrane thickness and stiffness, but did speed the loss of calcium from the bead core.
authors.affiliation: Department of Chemistry and Chemical Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1,Canada.
authors.forename: Rachelle M
authors.initials: RM
authors.lastname: Kleinberger
authors.forename: Nicholas A D
authors.initials: NA
authors.lastname: Burke
authors.forename: Kari
authors.initials: K
authors.lastname: Dalnoki-Veress
authors.forename: Harald D H
authors.initials: HD
authors.lastname: Stöver
mesh_terms: D000464:Alginates / Q000737:chemistry*; D002214:Capsules; D019343:Citric Acid / Q000737:chemistry; D005782:Gels / Q000737:chemistry; D020723:Glucuronic Acid / Q000737:chemistry; D006603:Hexuronic Acids / Q000737:chemistry; D018613:Microscopy, Confocal / Q000379:methods*; D008856:Microscopy, Fluorescence / Q000379:methods*; D010316:Particle Size; D011107:Polylysine / Q000031:analogs & derivatives / Q000737:chemistry; D011312:Pressure; D013696:Temperature; D013997:Time Factors
chemical_list: D000464:Alginates; D002214:Capsules; D005782:Gels; D006603:Hexuronic Acids; C051546:alginate-polylysine-alginate; D011107:Polylysine; D019343:Citric Acid; D020723:Glucuronic Acid
keywords: A; AP; APA; Alginate capsules; G; M; MW; Mechanical properties; Membrane thickness; Micropipette aspiration; PEC; PLL; Poly-l-lysine; alginate; alginate/poly-l-lysine; alginate/poly-l-lysine/alginate; guluronic acid; mannuronic acid; molecular weight; poly-l-lysine; polyelectrolyte complex