To begin, place mini pumps on a clean, sterile countertop. With the thumb and forefinger, gently pinch the cap that matches the pump body and hold the pump body with the other hand. Use the thin tube attached to the cap to poke the filling port of the pump several times.
Now take a needle that matches the pump and the one milliliter syringe. Attach the needle to the syringe tightly. Slowly draw up the final solution of letrozole into the syringe.
Next, carefully pinch a mini pump with one hand so that it stands upright. With the other hand, insert the one milliliter syringe into the bottom of the pump. Slowly inject the letrozole solution into the pump.
When the pump is full, withdraw the syringe. Carefully insert the cap into the pump body and tighten it. Wipe away any spillage that occurs.
With the outlet of the filled pump facing outwards, immerse the pump into sterile saline in a prepared centrifuge tube. Cap the tube and place it on the tube rack. Place the tubes in a thermostat at 37 degrees Celsius for 48 hours.