Master's Defense: Madalena Campos dos Reis Branco

Influence of pH on diphtheria anatoxin incorporation into SBA-15.

Oral vaccines are preferred to intramuscular injections used today for diphtheria vaccine, due to ease of administration, non-invasiveness and convenience, since they are cheaper and require less technical skills. However, oral vaccines require the use of delivery vehicles for the passage through the gastrointestinal tract to protect the antigen from physiological barriers. To stimulate an immune response we need a specific amount of anatoxin, which needs to be incorporated into that carrier to get in contact with our immune system. 

Previous studies have already reported on the efficiency of using SBA-15 as a nanocarrier for diphtheria. Nevertheless, finding optimal encapsulation conditions is essential to enable maximal protein uptake, while minimizing aggregation. Since the incorporation of DT into SBA-15 is performed in aqueous medium, the process is highly affected by electrostatic and hydrophilic interactions, therefore it is relevant to find the optimal environmental condition, considering pH, ionic strength and concentrations. The main goal of this project was to experimentally find the optimal pH and protein concentration for encapsulation. 

To measure the protein uptake, we used UV-vis spectroscopy and thermal gravimetric analysis coupled to a Fourier transform infrared spectroscopy and mass spectrometry (TGA-FTIR-MS). The last technique is also used for chemical characterization of the samples. 

From the analysis of diphtheria anatoxin incorporated into SBA-15, at different pHs and concentrations, we concluded that thermal degradation profiles and water dynamics are different, depending on pH, but overall all samples displayed a similar behavior. We observed higher adsorption and earlier protein degradation for lower pHs. We hypothesize that pH 2.9 is the best pH, since it allows for higher adsorption levels, but more experiments should be performed, in order to understand if it is the ideal pH for encapsulation.