Immunoisolating semi-permeable membranes for cell encapsulation: Focus on hydrogels

Cell-based medicine has recently emerged as a promising cure for patients suffering from various diseases anddisorders that cannot be cured/treated using technologies currently available. Encapsulation within semipermeablemembranes offers transplanted cell protection from the surrounding host environment to achievesuccessful therapeutic function following in vivo implantation. Apart from the immunoisolation requirements,the encapsulating material must allow for cell survival and differentiation while maintaining its physicomechanicalproperties throughout the required implantation period. Here we review the progress made in thedevelopment of cell encapsulation technologies from the mass transport side, highlighting the essentialrequirements of materials comprising immunoisolating membranes. The review will focus on hydrogels, themost common polymers used in cell encapsulation, and discuss the advantages of these materials and thechallenges faced in the modification of their immunoisolating and permeability characteristics in order tooptimize their function.