A Lubricious Coating That Has Dry Lubricity
Here is another question that comes up sometimes: Do you have a coating that is lubricious when dry?
More often than not, these questions come from non-medical professionals who want to use the coating for a piece of machinery, rather than a biomaterial which interacts with a living system. In other cases, the device is for a machine that is used as part of a medical device that has moving parts.
The easiest answer to this question is "no", because hydrophilic coatings accomplish their mechanism through formation of hydrogels on a microscopic level, which closely associate electrostatically with water and lower friction.
The more precise answer is actually a question: What do you mean by lubricious? How slippery is slippery enough? Ok, that is two questions.
Let's put things into perspective and talk about coefficient of friction on a surface. The coefficient of friction of teflon is about 0.2 to 0.3. The coefficient of friction of ice is about 0.01 to about 0.1. The coefficient of friction for most hydrophilic coatings for medical devices ranges from 0.01 to about 0.1 also. Some hydrophobic coatings like Parylene have coefficients of friction ranging from 0.25 to about 0.4.
If you want a coating that has a coefficient of friction in the 0.01 to 0.05 range while dry, you are basically out of luck. You may want to try a lubricant like silicone oil. On the other hand, if friction in the range of 0.2 to 0.3 is ok for you, then you want teflon or parylene. The drawback there is that these are hydropobic not hydrophilic.
In some cases, there are hydrophilic silicones that can have coefficients of friction around 0.2.