A process for making a microneedle array master comprises: (a) providing a photoreactive composition, the photoreactive composition comprising: (1) at least one reactive species that is capable of undergoing an acid- or radical-initiated chemical reaction, and (2) at least one multiphoton photoinitiator system and (b) imagewise exposing at least a portion of the composition to light sufficient to cause simultaneous absorption of at least two photons, thereby inducing at least one acid- or radical-initiated chemical reaction where the composition is exposed to the light, the imagewise exposing being carried out in a pattern that is effective to define at least the surface of a plurality of microneedles. The microneedles may be solid and the outer surface of the microneedles may be characterized by at least one concave area. The master may be used to fabricate a tool for replication.
