Saturated n-alkyl fatty acid chlorides (CH3(CH2)(n)COCl where n = 0, 2, 4, 6, 8, 10, 12, and 14) were covalently attached to pH-sensitive hydrogel objects (mugels) within microfluidic systems using an in situ process. Staining with a lipophilic dye indicated that the resulting fatty acid layer was confined to the periphery of the mugel. The barrier properties of these fatty acid coatings were investigated by determining the half-life of mugel expansion after exposure to a buffer solution that triggers swelling of unmodified mugels. For n = 0, the half-life values were similar to those for unmodified mugels, indicating that no significant ion gradient was established. Considerably longer half-lives were observed for mugels modified with n-alkyl fatty acid layers with n greater than or equal to 2 carbons, as these mugels significantly retarded ion penetration. However, the half-lives of mugel expansion did not increase as the fatty acid chain lengthened, suggesting that the utilization of a hydrogel substrate involves additional factors (e.g. pinhole defects) that influence the permeability of the fatty acid coatings to a greater degree than the alkyl chain length.