Bio-Inspired Degradable Polyethylenimine/Calcium Phosphate Micro-/Nano-Composites for Transient Ultrasound and Photoluminescence Imaging

Inorganic nanomaterials hold immense potential in theranostics, but their translation is limited by the toxicity resulting from non-degradability. Bulk phosphate-based glasses offer great biodegradability, biocompatibility, and ease in incorporating imaging dyes and drugs. However, the facile and mild solution-based synthesis of micro-/nanoparticles of this material is yet to be explored. Inspired by the biosilicification process in the diatom, we created polyethylenimine (PEI)/phosphate aggregates via the hydrogen bonding between amine (PEI) and hydroxyl (phosphate) groups, which was proved by dynamic light scattering and 1H solution nuclear magnetic resonance. The sol-gel reaction between the calcium precursor and PEI/phosphate aggregates yielded degradable PEI/ calcium phosphate (PEI/CP) micro-/nano-composites with versatile sizes (396 +/- 128 nm to 63 +/- 8 mu m) and morphologies (hexagonal micro-disc, micro-flower, micro-leaf, nano-butterfly, and nano-ribbon). The PEI/CP composition and chemical structure were examined. PEI/CP has negligible cell cytotoxicity and degrades within 24 h. In vitro studies showed the promise for PEI/CP in transient ultrasound and photoluminescence imaging.