Considerations in binding diblock copolymers on hydrophilic alginate beads for providing an immunoprotective membrane.
Bottom Line: In the present study, we describe the stepwise considerations for successful application of diblock copolymer of polyethylene glycol (PEG) and poly-L-lysine (PLL) on the surface of alginate beads.Shorter PLL blocks resulted in less stable capsules.Our results show that we can successfully apply block copolymers on the surface of hydrophilic alginate beads without interfering with the physicochemical properties.
Affiliation: Department of Polymer Chemistry, Zernike Institute for Advanced Materials, University of Groningen, 9747, AG Groningen, the Netherlands; Departments of Pathology and Laboratory Medicine, Section of Medical Biology, Division of Immunoendocrinology, University of Groningen, Hanzeplein 1, 9700, RB Groningen, The Netherlands.Show MeSH
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Mentions: This study was undertaken as a first effort to overcome the complexity of the encapsulation procedure by proposing a simple one step procedure to create in a nonlaborious way a reproducible surface. As most studies with block copolymers have been performed with hydrophobic materials, we could not rely on published protocols.51,52 Instead we had to test new procedures to demonstrate the efficacy of the membrane formation. As PLL has a high affinity for alginate, we applied this macromolecule as an anchoring block in our design. PEG blocks stay on the surface and form a polymer layer. This process was found to be highly dependent on the molecular weight of PLL. To understand this we have to elaborate on the binding process on bead surfaces (Fig. 7). After gelification of alginate beads in calcium, we apply a washing step in buffer with low calcium and containing high sodium.17,53,54 This step is required to extract some calcium from the surface of the beads, which will subsequently be substituted by sodium.17,53,54 Sodium will be electrostatically bound to the carboxyl groups of alginate. It has a lower affinity for the alginate than PLL. The PLL that is subsequently added is binding to constitutive alginate molecules in a highly cooperative manner to form a strong, rigid membrane. The degree of cross-linking determines the mechanical stability and permeability of the membrane.8,12,26,27
Affiliation: Department of Polymer Chemistry, Zernike Institute for Advanced Materials, University of Groningen, 9747, AG Groningen, the Netherlands; Departments of Pathology and Laboratory Medicine, Section of Medical Biology, Division of Immunoendocrinology, University of Groningen, Hanzeplein 1, 9700, RB Groningen, The Netherlands.