Masking method for coating a microneedle array

1. A method of coating a microneedle array comprising:

providing a microneedle array having a substrate and at least one needle;

providing a removable masking layer on the microneedle array such that the substrate is at least partially covered by the masking layer and the at least one needle remains at least partially exposed; and

applying a coating material to at least a portion of the exposed portion of the microneedle array.

2. A method according to claim 1 wherein the masking layer is a fluid.

3. A method according to claim 2 wherein the coating material is applied from a coating solution comprising a carrier fluid and further comprising the step of evaporating the carrier fluid thereby providing a dried coating.

4. A method according to claim 3 wherein the density of the masking layer fluid is higher than the density of the carrier fluid.

5. A method according to claim 3 wherein the volatility of the masking layer fluid is lower than that of the carrier fluid.

6. A method according to claim 3 wherein the carrier fluid is substantially immiscible with the masking layer fluid.

7. A method according to claim 3 further comprising the step of allowing the masking layer fluid to evaporate.

8. A method according to claim 7 wherein the carrier fluid is allowed to completely evaporate prior to complete evaporation of the masking layer fluid.

9. A method according to claim 2 wherein the masking layer fluid is a fluorinated liquid.

10. A method according to claim 1 wherein the microneedle array comprises a plurality of needles.

11. A method according to claim 10 wherein more than 50% by weight of the coating material applied to the microneedle array is present on the needles.

12. A method according to claim 1 wherein the masking layer is a solid or a semi-solid that may be transformed into a liquid.

13. A method according to claim 12 wherein the transformation of the masking layer is caused by a change in temperature, electric field, or pH.

14. A method according to claim 3 wherein the coating solution comprises a therapeutically active substance.

15. A method according to claim 14 wherein more than 50% by weight of the therapeutically active substance applied to the microneedle array is present on the needles.

16. A method according to claim 3 wherein the coating solution comprises water.

17. A method according to claim 3 wherein the coating solution comprises a vaccine, vaccine adjuvant, or mixture thereof.

18. A method according to claim 1 wherein the coating material is preferentially deposited onto the microneedles.

19. A method according to claim 1 wherein the coating material is preferentially deposited on or near the tips of the microneedles.

20. A method according to claim 1 wherein the removable masking layer is initially applied to the microneedle array such that no microneedle is exposed and the masking layer is subsequently allowed to partially evaporate thereby providing at least one partially exposed needle.

21. A method according to claim 20 whereby the coating material is initially applied to the masking layer and application of the coating material to at least a portion of the exposed portion of the microneedle array occurs as the masking layer evaporates.

22. A method according to claim 1 wherein the coating material comprises a carrier fluid.

23. A method according to claim 3 wherein the coating solution comprises a suspension of dispersed particles.

24. A method according to claim 1 wherein at least a portion of the surface of the microneedles is plasma treated prior to the step of providing the removable masking layer on the microneedle array.

25. A method according to claim 24 wherein the plasma comprises oxygen or nitrogen.

26. A method according to claim 1 wherein a solid coating is provided on at least a portion of the surface of the microneedles prior to the step of providing the removable masking layer on the microneedle array.

27. A method according to claim 26 wherein the solid coating comprises polyvinylpyrrolidone, polyvinyl alcohol, potassium citrate, or a diamond-like glass.

28. A method according claim 1 wherein a solvent is applied to the masking layer prior to the step of applying the coating material to at least a portion of the exposed portion of the microneedle array.