Wettability regulation, preparation process optimization and performance characterization of pollen drug delivery systems

To investigate the transformation of wettability of phosphoric acid-treated pollen after treatment with different reagents, to optimize the preparation of the wettability-transformed pollen sporopollenin carrier system to find the optimal alkali treatment conditions, and to characterize its structure and surface morphology, we first analyzed the wettability of the original pollen and the acid-dissolved pollen, measured the water contact angle of the acid-dissolved pollen treated with each reagent with the help of a contact angle tester, conducted a one-way test on the alkali treatment conditions that could transform the wettability of the pollen, explored the influence of the optimization of the conditions for the preparation of the hydrophilic pollen sporopollenin carriers by using a response surface methodology and the glycerol absorption time as the response value, and carried out a validation and verification test on the process parameters. The process parameters were verified and validation tests were conducted, and finally the sporopollenin was characterized by FTIR and SEM. The contact angle test showed that the water contact angle of pollen after acid digestion was 135.1°, which was changed to 16° after NaOH treatment, and the contact angle of glycerol was changed from 140.8° to 9.6°. The best alkali treatment process was obtained through the optimization of one-factor test and response surface method, and the final optimization conditions were obtained according to the actual experimental process: the volume of NaOH was 105 mL, i.e., 15 times the volume of pollen, and the concentration of NaOH was 1.5 mol·L^-1. The stirring time was 18 h, and the stirring temperature was 85 ℃. Under these conditions, three parallel experiments were carried out to verify the wettability of Codonopsis pollen and Lotus pollen respectively, in which the average value of Codonopsis pollen results was 58 s, and the average value of Lotus pollen results was 49 s, and the RSD was less than 5%. The wettability study revealed that pollen sporopollenin changed from hydrophobicity to hydrophilicity after NaOH treatment, and according to the results of response surface optimization, the prepared alkali-treated pollen sporopollenin showed a significantly shorter time for complete glycerol absorption and a better hydrophilicity with a water contact angle of close to 0°, which is a reproducible process and a stable and reliable preparative process, and theoretically, will be more conducive to the loading of hydrophilic drugs.