[n]Cycloparaphenylenes as Compatible Fluorophores for Melt Electrowriting

Abstract: Fluorescent probes are an indispensable tool in the realm of bioimaging technologies, providing valuable insights into the assessment of biomaterial integrity and structural properties. However, incorporating fluorophores into scaffolds made from melt electrowriting (MEW) poses a challenge due to the sustained, elevated temperatures that this processing technique requires. In this context, we report that [n]cycloparaphenylenes ([n]CPPs) serve as excellent fluorophores for MEW processing with the additional benefit of customizable emissions profiles with the same excitation wavelength. We use three fluorescent blends with distinct [n]CPPs with emission wavelengths of either 466 nm, 494 nm, or 533 nm, identifying 0.01 wt.% as the preferred concentration. We discover that [n]CPPs disperse well within poly(ε-caprolactone) (PCL) and maintain their fluorescence even after a week of continuous heating at 80°C. The [n]CPP-PCL blends show no cytotoxicity and support counterstaining with commonly used DAPI (Ex/Em: 359nm/457nm), rhodamine- (Ex/Em: 542/565 nm), and fluorescein-tagged (Ex/Em: 490/515 nm) phalloidin stains. Using different color [n]CPP-PCL blends, we sequentially deposit different MEW fibers into a semi-woven scaffold and onto a solution electrospun membrane containing [8]CPP as a contrasting substrate for the [10]CPP MEW fibers. In general, [n]CPPs are potent fluorophores for MEW, providing new imaging options for this technology. Introduction