The HP D300 digital dispenser allows ultra-low volume (pL-nL droplets) delivery of DMSO solubilized (or suspended) test materials. Defined volumes of the stock solution can be delivered directly into medium & cell containing multi-well plates or tissue inserts, to achieve exposures over a predetermined dose range. The dispensing of patterns of droplets using volumes of only nL to µL allows exposure of the apical surface of tissues cultured at ALI. Ciliated cultures quickly mix the test materials in the mucus layer to achieve a homogenous exposure to the epithelium.