The highlight in the sandwiched-LBL

The highlight in the sandwiched-LBL(S-LBL) is the facile embedding of polyphenol EGCG into the polyelectrolytes,so as to weaken the activity loss caused by the pre-grafting of EGCG to the back bone of bioactive polyelectrolytes. The EGCG embedding was carried under pH 6.5,though the assembly time is short, part of the natural EGCG might also suffer self-oxidation. To verify the existence of EGCG in the S-LBL coating,the UV–vis absorption spectrum was conducted and the results were shown in Fig.2A. The wide adsorption band between 275 and 325 nm in the (PEI/EGCG/HEP)10 sandwiched coating indicated the presence of natural EGCG and partial slightly oxidized EGCG, which was consistent with the previous reports[34]. Natural EGCG ensured the LBL coating as an enhanced reservoir for loading dexamethasone. Oxidized EGCG could produce a little amount of o-quinones which would form covalent bonding with PEI via Schiff base or Michael addition reaction, which then further formed the namely ‘weak inter molecular cross linking’between adjacent PEI,using EGCG as the weak cross-linker.