To begin, mix components A and B of polydimethylsiloxane, or PDMS, in a ratio of 10 to one. After stirring the mixture well, pour the mixture into a master mold. Place the PDMS mold under a pressure of one pound per square inch for 15 minutes to remove air bubbles.
Cure the PDMS mold at 60 degrees Celsius for two hours. De-mold to obtain the production mold of the microneedle. Then, clean the production mold with ultra pure water before use.
Quantify the protein content of the prepared exosome solution using a BCA assay kit. Add an appropriate amount of DPBS to the exosome solution. Now, prepare a solution of 200 milligrams per milliliter of trehalose using DPBS as the solvent.
Stir for 20 minutes to ensure full dissolution. Next, prepare a solution of hyaluronic acid and polyvinylpyrrolidone, or PVP, using DPBS and ethanol as the solvent, respectively. Stir overnight to ensure full dissolution.
Mix the exosome solution and trehalose solution in an equal ratio. Add an equal volume of hyaluronic acid solution and mix thoroughly to obtain the tip solution. Using a plasma cleaner, process the surface of the PDMS mold for 30 seconds at a low grade to enhance its hydrophilicity.
Add 40 microliters of the tip solution to the PDMS mold. Centrifuge at 3, 000G for three minutes at room temperature to ensure the liquid fills the needle layer of the mold. Remove excess liquid from the mold and dry at room temperature in a vacuum drying oven for one day.
Then, add 200 microliters of PVP solution to the PDMS mold. Centrifuge at 3, 000G for three minutes at room temperature to ensure the liquid fills the mold's backing layer. After drying the mold for one day, de-mold to obtain the exosome-loaded microneedle's patch.
