I think our blender pens are the best and I use mine a lot so when the blender pen becomes empty, this is what you can do. Instead of buying a new set of blender pens, you can use this blender pen refill recipe.
Blender Pen Refill Recipe
2 tablespoons and 2 teaspoons of glycerin
5 tablespoons of distilled water
1 teaspoon of rubbing alcohol
Put the ingredients in a small jar and just let the tip of the pen soak up the liquid for about half an hour. Then soak the other end of the pen.