Regarding the HPAN_PEI immobilized biocatalysts, it can be observed that the immobilization yield is boosted when the TA immobilization was performed at pH 5.5 (HeWT_HPAN1b and TsRTA_HPAN1b) rather than 8 (HeWT_HPAN1a and TsRTA_HPAN1a). This can be explained by the fact the PEI is more positively charged at low pH and is thus able to electrostatically attract a larger amount of TA at its surface. Accordingly, the observed activity is higher. Importantly, the specific activity (activity normalized by the amount of immobilized TA on the membrane) was the same, which indicates that, on average, the intrinsic activity of each additional immobilized transaminases was maintained. However, leaching after catalytic test was important, highlighting the need of post-treatment strategies to improve the anchoring of the immobilized TAs at the membrane surface. Inspired by Shi et al. , we attempted to entrap the immobilized TA into a polymeric matrix formed by sodium alginate (SA, see Figure ; bottom). This biopolymer is able to electrostatically interact with the PEI layer, bringing additional negative charges that can in principle help stabilizing the enzyme. This post-treatment was found to preserve the enzyme loading and the specific activity, and concomitantly to reduce enzyme leaching (Table , compare HeWT_HPAN2b and TsRTA_HPAN2b to HeWT_HPAN1b and TsRTA_HPAN1b, respectively).