No abstract

Responsive polymeric biomaterials can be triggered to degrade using localized environments found in vivo. A limited number of biomaterials provide precise control over the rate of degradation, the release rate of entrapped cargo, and yield a material that is intrinsically non-toxic. Here we design non-toxic acid-sensitive biomaterials based on silyl ether chemistry. A host of silyl ether cross-linkers were synthesized and molded into relevant medical devices including Trojan horse particles, sutures, and stents. The resulting devices were engineered to degrade under acidic conditions known to exist in tumor tissue, inflammatory tissue, and within diseased cells. The implementation of silyl ether chemistry gave precise control over the rate of degradation, and depending upon the steric bulk around the silicon atom, afforded devices that could degrade over the course of hours, days, weeks, or months. These novel materials could be useful for numerous biomedical applications including drug-delivery, tissue repair, and general surgery.

Asymmetric bifunctional silyl ether (ABS) prodrugs of chemotherapeutics were synthesized and incorporated within 200 nm x 200 nm particles. ABS prodrugs of gemcitabine were selected as model compounds because of the difficulty to encapsulate a water soluble drug within a hydrogel. The resulting drug delivery systems were degraded under acidic conditions and were found to release only the parent or active drug. Furthermore, changing the steric bulk of the alkyl substituents on the silicon atom could regulate the rate of drug release and therefore the intracellular toxicity of the gemcitabine-loaded particles. This yielded a family of novel nanoparticles that could be tuned to release drug over the course of hours, days, or months.

The incorporation of multiple p-carborane cages within an aliphatic polyester dendrimer was accomplished through the preparation of a bifunctional carborane synthon. A p-carborane derivative having an acid and a protected alcohol functionality was found to efficiently couple to peripheral hydroxyl groups of low-generation dendrimers under standard esterification conditions. Deprotection of carborane hydroxyl groups allowed for further dendronization through a divergent approach using the highly reactive anhydride of benzylidene-protected 2,2-bis(hydroxymethyl)propanoic acid. This approach was used to prepare fourth- and fifth-generation dendrimers that contain 4, 8, and 16 carborane cages within their interior. Upon peripheral deprotection to liberate a polyhydroxylated dendrimer exterior, these structures exhibited aqueous solubility as long as a minimum of eight hydroxyl groups per carborane were present. Several of the water-soluble structures were found to exhibit a lower critical solution temperature. Additionally, irradiation of these materials with thermal neutrons resulted in emission of gamma radiation that is indicative of boron neutron capture events occurring within the carborane-containing dendrimers.