Ex-vivo studies of intradermal jet injection

Intradermal delivery of vaccines are typically sought after due to a confluence of enhanced immune response and dose-sparing potential. For a typical fractional dose (0.1 ml) of liquid vaccine injected into the intradermal region of the skin, the primary indicator of successful injection is a raised `wheal' or skin `bleb'. This is commonly characterized as a circular region raised a few millimeters above the normal skin level with a blanched appearance. However, based purely from visual inspection of the skin, there is little information available on how to estimate the actual volume that has been correctly deposited into the ID region. Herein, we present a systematic study of skin bleb growth and ultimate bleb sizes from an ex-vivo study employing needle-free jet injection. The main focus is on correlation of the delivered volume, measured by mass diference on a fine resolution balance, and the geometrical dimensions of the skin bleb such as top-view diameter, diameter viewed from below the dermis, and the cross-section. In addition, we provide some unique observations on the growth dynamics of the skin blebs from the jet injection method.