Calcium alginate (Ca-alginate) capsule membranes are widely used in biological and medical fields due to their notable advantages such as good biocompatibility

and mild gelation conditions. Thin capsule membranes are desired to reduce the resistance to the mass transfer across the membranes

and to accelerate the exchange of solutes between the internal space of the capsule and the external environment. Therefore

fabrication and functionalization of Ca-alginate capsules with ultrathin membranes have attracted much attention recently. This paper reviews recent progress in fabrication and functionalization of Ca-alginate capsules with ultrathin membranes

and the controllable fabrication of Ca-alginate capsules with ultrathin membranes via a co-extrusion approach

organic/inorganic hybrid processing via adsorption of protamine molecules and biosilicification as well as functional modification of the Ca-alginate capsules with ultrathin membranes are highlighted. The thicknesses of the resultant Ca-alginate capsule membranes range from 0.6 to 150 μm

and the permeability performance of the capsule membranes could be controllably adjusted. The strategy reported in this paper provides a novel approach to fabricate novel structures of capsule membranes for various applications

particularly as a new tool for screening microorganism survival and growth in three-dimensional environments. Protamine is used to inspire and template silica formation onto the surfaces of the Ca-alginate capsules

which provides a facile and efficient method to prepare the organic/inorganic hybrid capsules with ultrathin membranes. The Ca-alginate/protamine/silica capsules efficiently inhibit the swelling of Ca-alginate capsules

and thus are promising carriers for encapsulation of cells and enzymes. In addition

Ca-alginate capsules membranes blended with poly(N-isopropylacrylamide) (PNIPAM) nanogels exhibit desirable thermo-responsive gating characteristics. pH-Responsive switching functions can be endowed by the electrostatic interactions between Ca-alginate networks and protamine molecules

or by the swelling/shrinking behaviors of the grafted poly(methacrylic acid) (PMAA) brushes on the capsule membranes. These functional capsules with ultrathin membranes have many potential applications in various fields such as enzyme catalytic reactions

immobilizations of cells and foods

and controlled release of chemicals.