Gold Nanoparticles as Radiographic Contrast Agents for Noninvasive Monitoring of Scaffold Degradation and Detection of Breast Microcalcifications

Noninvasive monitoring of tissue remodeling or disease progression is critical for predicting early outcomes and providing opportunity for intervention. In tissue engineering, scaffold degradation kinetics are critical to tissue regeneration and/or drug release, but characterization is limited by destructive test methods or two-dimensional imaging. In breast cancer, microcalcifications are important biomarkers but radiographic detection is often masked by dense breast tissue. X-ray imaging modalities, such as computed tomography and mammography, are widely available and offer noninvasive, three-dimensional diagnostic imaging at high spatiotemporal resolution, but imaging contrast in soft tissues is poor. Gold nanoparticles (Au NPs) have been investigated as biocompatible X-ray contrast agents. Therefore, the overall objective of this dissertation was to investigate the use of Au NPs as an X-ray contrast agent for noninvasive monitoring of scaffold degradation and detection of breast microcalcifications.

Au NPs were covalently linked to collagen scaffold fibrils such that Au NP release was only possible upon enzymatic degradation of collagen. Scaffolds containing ≥ 60 mM exhibited sufficient contrast to measure scaffold degradation. Collagen scaffold degradation kinetics were measured during in vitro enzymatic degradation and validated by concurrent measurements with gravimetric analysis and optical spectroscopy. Thus, Au NPs enabled nondestructive, longitudinal, and volumetric measurement of collagen scaffold degradation by contrast-enhanced computed tomography.

Bisphosphonate (BP)-functionalized Au NPs were investigated for targeting and providing contrast-enhanced mammographic detection of hydroxyapatite (HA) breast microcalcifications. Mammographic phantoms were designed to exhibit variable breast tissue density with embedded model HA microcalcifications and were shown to recapitulate the clinical problem of dense tissue masking the detection of microcalcifications. BP-Au NPs enabled contrast-enhanced mammographic detection of microcalcifications that were otherwise indistinguishable from the background tissue density.

BP-Au NPs were subsequently investigated for therapeutic potential to inhibit HA-mediated cellular mitogenesis and migration. BP-Au NPs were targeted to HA crystals of varying shape and size in vitro. BP-Au NPs inhibited HA-mediated mitogenesis and cellular migration in Hs578T cells exposed to plate-like HA crystals, as measured by BrdU immunolabeling and scratch assays, respectively. However, BP-Au NPs did not exhibit an inhibitory effect for HA whiskers, HA nanoparticles, and nanoporous HA.Therefore, further research is required to confirm a relationship between HA microcalcifications and mitogenesis, and possible inhibition by BP-Au NPs.