Devices for intradermal vaccination.

New insights in vaccine development, the need for safe, economic and efficient vaccine administration and the increasing mechanistic knowledge of immune responses induced by targeting the intradermal layers of the skin have all driven the engineering of devices for intradermal vaccination. In this review we highlight different delivery devices that make the epidermal and dermal layers of the skin accessible for vaccine administration. Depending on the device the desired vaccine can be applied either as a liquid formulation or as solid, powdered vaccine particles. The process of intradermal injection employs micron-sized needles that are inserted 1.5mm perpendicularly into the skin, and which inject approximately 100-200μl of a liquid vaccine formulation into the dermal skin layers. Tattoo devices, on the other hand, can be used to deliver liquid vaccine formulations into the dermal layer of the skin by the use of oscillating needles. Microneedle arrays are made of vaccine-coated solid microneedles or biodegradable microneedles. These are inserted into the dermal layers of the skin where either the vaccine coating is dissolved, or the microneedle itself dissolves in place. Jet-injectors operate by generating a high pressured stream, which flushes the liquid vaccine formulation into the deeper skin layers. Delivery devices using liquid vaccine formulations are advantageous, as established vaccine formulations can be used as provided without the need for reformulation. However, approaches that deliver vaccines in a solid form may also prove to be promising. One such method is the ballistic approach, in which solid vaccine particles or vaccine-coated gold particles are accelerated towards the skin by needle-free devices, so that the particles are deposited in the epidermal and dermal layers of the skin. These various delivery devices are explored in this review with regard to their delivery mechanism and ease of handling, their efficacy in clinical trials and their suitability for practical use.