Polymers for Reversible Cell Encapsulation

Abstract

<p>Cell encapsulation aims to introduce immune-isolated living cells into patients to treat endocrine disorders. The conventional microcapsule structure is the alginate/PLL/alginate capsule (APA), which can provide a fairly biocompatible, semi-permeable shell for cells, but with insufficient chemical-mechanical stability. Clinical applications of APA capsules are still far off due to PLL protein absorption, alginate cytotoxicity and weakening the interpenetrated porous structure through the sodium/calcium ion exchange.</p> <p>In this study, a reactive polyanion (poly (methacrylic acid-<em>co</em>-2[methacryloyloxy] ethyl acetoacetate), 70:30, A 70) was prepared by free radical polymerization in ethanol. A70 was combined with sodium alginate solution, and gelled in calcium chloride to provide crosslinked shell around PLL-coated CaAlg capsules, and to reinforce the CaAlg core by forming covalent bonds with PLL that diffused to the capsule interior.</p> <p>This system benefits from a rapid non-toxic crosslinking reaction at physiological conditions. The mechanism and rate of covalent bond formation and cleavage were studied with the help of model reactions and UV/Vis and ¹H-NMR. We also studied the ability of polyanion, A70, to reinforce the CaAlg core by forming covalent bonds with indiffused PLL. The PLL diffusion depth, the mobility of A70 inside the CaAlg gel, the encapsulation process and microcapsule structure were studied in detail. Network degradation was also studied using gel dissolution for the capsules stored at 37°C, and correlated with studies of chemical hydrolysis of the network forming polyanion.</p> <p>Overall, this thesis introduces a simple, fast and accurate method to study the polyelectrolyte ability to form enamine bonds, and the stability of resulting crosslink bond in aqueous solution via small molecule models with an acceptable match to real microcapsules. According to these results the synthetic polyanion, A70, showed significant potential for applications that require protection of cells for the time needed to develop their own extracellular matrix, and as such can certainly find valuable uses in the field of cell encapsulation.</p>