Microprojection applicators and methods of use

1. An applicator, comprising:

a rigid planar plate member with an upper surface on a first side of the plate member and a lower surface on a second side of the plate member, the plate member having at least one opening therethrough;

a blocking element in contact with the upper surface of the plate member and being capable of moving between a first position and a second position;

a plunger having a proximal end, a distal end on which at least one microprojection is retained, and a shaft extending therebetween, at least a portion of the proximal end rests directly on and is at least partially retained by the blocking element in its first position; wherein, the plunger is slidably accommodated within the opening of the plate member;

an energy-storing element positioned between the lower surface of the plate member and the distal end of the plunger; and

an actuating member having an external surface for application of a force, and having at least one surface in mechanical communication with the blocking element, wherein the actuating member moves the blocking element from its first position to its second position when a force is applied to the external surface of the actuating member, thereby to effect release of the plunger and the energy-storing element.

2. The applicator of claim 1 , further comprising:

at least one microprojection positioned on a bottom surface of the plunger distal end.

3. The applicator of claim 2 , wherein the at least one microprojection is a microprojection array comprising a plurality of microprojections, a hypodermic needle or a trocar.

4. The applicator of claim 3 , wherein the plurality of microprojections are dissolvable or erodible microprojections.

5. The applicator of claim 2 , wherein the at least one microprojection includes at least one therapeutic agent selected from a drug, a small molecule, a protein, a peptide, or a vaccine.

6. The applicator of claim 2 , further comprising:

a backing member positioned on a distal surface of the plunger distal end, wherein the at least one microprojection is positioned on a distal surface of the backing member;

the backing member being detachable from the plunger distal end.

7. The applicator of claim 3 , wherein at least a portion of the plurality of microprojections are detachable from the microprojection array.

8. The applicator of claim 1 , further comprising:

at least one flexure element in mechanical communication with the blocking element, wherein the at least one flexure element directs the blocking element into the plunger in the blocking member's first position.

9. The applicator of claim 1 , wherein the actuating member causes the blocking element to have a displacement selected from a linear displacement and a rotational displacement.

10. The applicator of claim 1 , wherein the energy-storing element is an elastic energy element.

11. The applicator of claim 10 , wherein the elastic energy element is selected from a compression spring, a coil spring, or a wave spring.

12. The applicator of claim 1 , wherein the proximal end of the plunger is dimensioned to be retained by the blocking element in its first position by a ledge at least partially circumscribing the plunger shaft.

13. The applicator of claim 1 , wherein at least one of the plate member, the blocking member, or the plunger are formed from a material with an elastic modulus between about 0.5 to 500 KSI.

14. The applicator of claim 1 , wherein at least one of the plate member, the plunger, or the blocking member is formed from a metal.

15. The applicator of claim 14 , wherein the metal is selected from stainless steel, carbon steel, titanium, and alloys thereof.

16. The applicator of claim 1 , further comprising a housing member with an opening through which the external surface of the actuating member can be accessed.

17. The applicator of claim 16 , wherein the housing includes a surface on which an adhesive is applied to secure the housing to a subject.

18. The applicator of claim 1 , wherein the plunger shaft has a length and the energy-storing element is selected to provide a force on the plunger that causes the plunger to travel a distance longer than the length of the shaft.

19. The applicator of claim 1 , further comprising:

a damper positioned between the energy-storing element and a proximal surface of the plunger distal end.

20. A method of delivering a therapeutic agent to a subject, comprising:

applying to a skin site of the subject, a microprojection array affixed to the distal end of the plunger of the applicator according to claim 1 ;

contacting the external surface of the actuating member to actuate the actuating member from a first position to a second position in mechanical communication with the blocking element;

moving the blocking element from its first position in contact with the proximal end of the plunger to its second position, whereby the plunger is released from contact with the blocking member;

releasing the energy-storing element thereby to deploy the plunger into contact with a subject's skin; and

delivering the therapeutic agent from the microprojection array to the subject.

21. The method of claim 20 , further comprising:

adhering the applicator to the subject's skin.

22. The method of claim 20 , wherein moving the blocking element effects movement of the plunger from a retracted position to a deployed position.

23. The method of claim 20 , further comprising;

detaching a backing member from the plunger such that the backing member and the microprojection array are retained on the subject's skin when the applicator is removed from the subject's skin.