Mechanical stability, uniformity of size, complete encapsulation of cells and optimal microenvironment are major challenges in the design and development of microcapsules for cell immobilisation purposes. In this work, a novel microcapsule chemistry based on polyelectrolyte complexation between alginate and poly(methylene-co-guanidine) (PMCG) is presented. We have characterised the effect of PMCG concentration and time of exposure on microcapsule diameter and membrane thickness, selecting a PMCG concentration of 0.5% (v/v) and an exposure time of 1 min as optimal parameters for a correct coating. Afterwards, the mechanically most resistant alginate-PMCG-alginate (A-PMCG-A) microcapsule type was chosen according to two different stability studies. Beads with a solid core and an inhomogeneous internal configuration resulted in stronger microcapsules. Further, the selected A-PMCG-A beads presented both an increased stability compared to classical Ca(2+)/alginate and alginate-poly-L-lysine-alginate (APA) microcapsules, and had an adequate microenvironment for cell viability. This new chemistry allows the controlled adjustment of microcapsule size and wall thickness, offering new alternatives for cell transplantation.