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The aim of this work was to develop a nanolayered pH sensitive coating method whereby proteins are coated at a suitable pH on the surface of chemically modified biomedical/bioanalytical microdevices and protein release is triggered by a pH-shift upon contact with the physiological environment. In this work such a coating was developed and was applied onto microneedles. First, the surface of microneedle arrays was modified with basic groups with a surface pK a below physiological pH. This modification was a multistep procedure: first the surface was hydroxylated in a piranha mixture, then 3-aminopropyltriethoxysilane was coupled (yielding a "pH independent" surface with a positive charge over a broad pH range), next 4-pyridinecarboxaldehyde was coupled to the obtained surface amine groups and finally the imine bond was reduced by sodium cyanoborohydride. The obtained pH-sensitive pyridinemodified microneedles were coated with ovalbumin at surface pK a > pH > pI of the protein; thus the surface of the microneedles is positively charged and the protein is negatively charged. The coating efficiency of ovalbumin was 95% for the amine-modified (pH independent) and the pyridine-modified (pH sensitive) surfaces, whereas a non-modified surface had a coating efficiency of only 2%. After the protein-coated microneedle arrays were pierced into the skin, having a pH > surface pK a of the microneedle arrays, 70% of the protein was released within 1 minute, whereas the protein release from pH independent microneedle arrays was only 5%. In conclusion, we developed a procedure to efficiently coat microneedle arrays with proteins that are released upon piercing into human skin.

Worldwide, enteric infections rank third among all causes of disease burdens, and vaccines able to induce a strong and long-lasting intestinal immune responses are needed. Parenteral immunization generally do not generate intestinal IgA. Recently, however, injections of retinoic acid (RA) dissolved in oil, administered multiple times before vaccination to precondition the vaccine-draining lymph nodes, enabled a parenteral vaccine strategy to induce intestinal IgA. As multiple injections of RA before vaccination is not an attractive strategy for clinical practice, we aimed to develop a "one injection" vaccine formulation that upon parenteral administration induced intestinal IgA. Our vaccine formulation contained two liposomal delivery systems. One delivery system, based on 1,2-distearoyl-sn-glycero-3-phosphocholine stabilized with PEG, was designed to exhibit fast drainage of RA to local lymph nodes to precondition these for a mucosal immune response before being subjected to the vaccine antigen. The other delivery system, based on the cationic liposomal adjuvant CAF01 stabilized with cholesterol, was optimized for prolonged delivery of the antigen by migratory antigen-presenting cells to the preconditioned lymph node. Combined we call the adjuvant CAF23. We show that CAF23, administered by the subcutaneous route induces an antigen specific intestinal IgA response, making it a promising candidate adjuvant for vaccines against enteric diseases.