UC San Diego

Porous silicon has been investigated as a novel material for biomedical applications since the early 1990s. Owing to its low toxicity profile and unique properties, it has been utilized in a variety of manners, including biomedical imaging and sustained delivery applications discussed within. In the first portion of this dissertation, quantum confined domains of silicon were used as ratiometric fluorescent probes, in which the long-lived excited states were harnessed to generate wavelength-dependent quenching motifs. To further evaluate the performance of porous silicon as a biomedical imaging agent, it was then compared and contrasted against a series of luminescent silicon nanocrystals to probe which unique properties are intrinsic to all silicon nanocrystals and which are imbued during the fabrication process. Finally, porous silicon microparticles were used to sustain the delivery of hormonal progestins to develop injectable contraceptives with the goal of reducing maternal mortality rates in sub-Saharan Africa. Owing to the anisotropic dissolution of porous silicon, hydrophobic progestin molecules were able to be released from the porous particle host in a highly linear fashion and for longer periods of time than the unprotected controls. The progestins were incorporated into the porous particle via a technique known as melt casting, in which molten drug infiltrates and then recrystallizes within the porous structure. Strategies for melt casting thermally instable drugs were also explored. Particles containing segesterone acetate were found to be non-toxic and well tolerated in a cohort of adult female Sprague-Dawley rats over an extended period of time.