pH-responsive Ca-alginate-based capsule membranes with grafted poly(methacrylic acid) brushes for controllable enzyme reaction

Highlight
• pH-responsive capsule membranes are prepared via surface grafting.
• Capsule membranes are composed of Ca-alginate substrate and grafted PMAA brushes.
• The pH-responsive Ca-alginate capsule membranes are biocompatible with enzyme.
• Diffusional permeability across capsule membrane exhibits pH-responsive property.
• Enzymatic reaction in capsules is effectively controlled by ambient pH condition.

A novel biocompatible pH-responsive Ca-alginate-based capsule membrane with grafted PMAA brushes for controllable enzyme reaction has been designed and prepared by combining co-extrusion minifluidic approach, biosilicification method and UV-irradiation-induced grafting technique. The proposed capsule membrane is composed of an inner Ca-alginate soft layer and an outer silica rigid surface layer with grafted PMAA brushes, in which the former offers the biocompatible carrier for the enzyme and the latter provides the pH-responsive switching function caused by swelling/shrinking behaviors of the grafted PMAA brushes at different pH values. When the environmental pH is lower than the value of pKaPMAA, the grafted PMAA brushes shrink and then the resistance for trans-membrane mass-transfer is large; as a result, the enzymatic reaction in the capsule is in the inactive state due to the low permeability of substrates and reactants across the membrane. On the contrary, when the ambient pH is higher than the value of pKaPMAA, the grafted PMAA brushes swell and the resistance for trans-membrane mass-transfer is low; consequently, the enzymatic reaction in the capsule is in the active state due to the high permeability of substrates and reactants across the membrane. The proposed Ca-alginate-based capsule membranes with grafted PMAA brushes exhibit both good biocompatibility with enzyme and excellent pH-responsive performance for controllable enzyme reaction.

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