To make these particles, Edwards sprayed a solution of drug into droplets and dried the droplets very quickly with hot air at precise temperature and velocity to control evaporation of the suspension. To make a porous particle, both the time required for a droplet to dry and the time required for a solute or a nanoparticle to diffuse from the edge of the droplet to its center need to be considered. As the droplet evaporates and particles accumulate on the surface, capillary forces push them together and lock them in place. At the end of the process, a shell is formed. Any remaining solution escapes by evaporating through the shell, which is punctured during this process. When porous particles containing drugs were applied in vivo the results were striking. Large porous particles of insulin stayed active in rat lungs for 96 hours, 15 times longer than the longest-acting aerosol on the market. They also found that porous particles embedded with testosterone effectively raised blood hormone levels for extended periods. In the case of estradiol (a potent female sex hormone) delivered as an aerosol into the lungs of rats, bioavailability approached 87%, a much higher percentage than previously achieved. Such enhanced efficiencies permit prescribed medicines to be taken at less frequent intervals and at lower doses, thereby improving convenience. Future applications may include not only obvious pulmonary disorders such as asthma, but also inhalant delivery of insulin, testosterone, estradiols, and monoclonal antibodies for treating viral diseases.