Alginate hydrogel compositions

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15-16. (canceled)

18-21. (canceled)

24-26. (canceled)

A method of preparing a hydrogel composition comprising an alginate matrix covalently crosslinked in the periphery of the alginate matrix to a multi-armed water soluble polymer, the method comprising:

• reacting an aqueous mixture comprising an alginate matrix having from about 3 mol % to about 50 mol % of a second functional group (“ALG-B”) with a multi-armed water soluble polymer comprising a first functional group at a terminus of one or more of its polymer arms (“POLY-A”) at a temperature ranging from about 0° C. to 60° C., wherein the first and second functional groups are selectively chemically reactive under mild reaction conditions to form covalent links, C, to thereby provide a hydrogel composition comprising a first product, a semi-permeable alginate matrix covalently crosslinked in its periphery to the multi-armed water soluble polymer.

30-52. (canceled)

A semi-permeable hydrogel composition comprising an alginate matrix covalently crosslinked in the periphery of the alginate matrix to a multi-armed water soluble polymer, wherein the multi-armed water soluble polymer penetrates the periphery of the alginate matrix and the periphery of the alginate matrix is interlocked with and covalently crosslinked to the multi-armed water soluble polymer, wherein the hydrogel composition is stable for at least 30 days at 40° C. in 1 mM phosphate buffered saline, wherein the composition is characterized by a first tan delta value determined at the time the composition is subjected to storage at 40° C. in 1 mM phosphate buffered saline (day 0), and a second tan delta value determined after the composition has been stored for 30 days at 40° C. in 1 mM phosphate buffered saline;

• and wherein the first tan delta value and the second tan delta value are the same or differ by no more than about 0.05.