Experimental and Computational Investigation of Clustering Behavior of Cyclodextrin–Perfluorocarbon Inclusion Complexes as Effective Histotripsy Agents

Abstract

Recently developed nanocones (NCs), which are inclusion complexes that are made up of cyclodextrins (CDs) and perfluorocarbons (PFCs), have shown promising results in nanoparticle-mediated histotripsy (NMH) applications due to stable inclusion complexation, PFC quantification, simple synthesis, and processing. FDA-approved βCD and its modified versions such as low-degree methylated βCD have been previously demonstrated as prime examples of structures capable of accommodating PFC molecules. However, the complex formation potential of different CDs with various cavity sizes in the presence of PFC molecules, and their consequent aggregation, needs to be explored. In the present study, the complexation and aggregation potential of some natural CDs and their respective derivatives either exposed to perfluoropentane (PFP) or perfluorohexane (PFH) were studied in the wet lab. Computational studies were also performed to account for the limitations faced in PFC quantification because of the low optical density of PFCs within the CD complex and to discover the best candidate for NMH applications. All results revealed that only βCD and γCD (except HMγCD) derivatives form an inclusion complex with PFCs and only LMβCD, βCD, and γCD form nanocone clusters (NCCs), which precipitate and can be collected for use. Furthermore, the data collectively show that βCD and PFCs have the best complexation due to stable complex formation, ease of production, and product recovery, especially with PFH as a more suitable candidate due to its high boiling point, which allows workability during synthesis. Although simulations suggest that highly stable inclusion complexes exist, such as HPβCD, the cluster formation resulting in precipitation is hindered due to the high solubility of CDs in water, resulting in intangible yields to work with even after employing general laboratory recovery methods. Conclusively, histotripsy cavitation experiments successfully showed a decreased cavitation threshold among optimal NCC candidates that were identified, supporting their use in NMH.

Bioconjugated β-Cyclodextrin–Perfluorohexane Nanocone Clusters as Functional Nanoparticles for Nanoparticle-Mediated Histotripsy

“…The particle size and ζ-potential of NCC derivatives were determined in double-distilled water by dynamic light scattering (DLS) using a Malvern Zetasizer Nano ZSP. The PFH amount in the NCCs was detected using a gas chromatography (GC) Agilent Technologies 7820A GC system, using a previously published method . Fourier transform infrared (FTIR) spectra were recorded on an Agilent Technologies Cary 630 FTIR instrument using attenuated total reflectance (ATR) mode, over the range 4000–400 cm –1 .…”

“…The size of the hydrophobic cavity of cyclodextrin derivatives and the localization of PFC in this cavity dictates the stability of the complex and determines further cluster formation. If the formed inclusion complex provides a chance for guest PFC to interact with free PFC, a more compact and stable NCC can form . It was also shown that the water solubility of the CD derivatives, as well as how the CD derivative interacts with PFC, determines whether the formed NCC can be obtained as a precipitate for further use.…”

“…It was also shown that the water solubility of the CD derivatives, as well as how the CD derivative interacts with PFC, determines whether the formed NCC can be obtained as a precipitate for further use. For instance, hydroxypropylated β-cyclodextrin (HPβCD) derivatives can make an inclusion complex with PFC derivatives, but PFC in the cavity does not interact with free PFC due to the elongated cavity’s loose interaction between the core and the surrounding inclusion complexes . Moreover, HPβCD was shown to have the best water solubility, which lowers the precipitation potential of any formed clustering.…”

“…Given the fact that PFC derivatives used for this application are volatile, it is extremely difficult to obtain NCCs including PFC as an ultrasound active part without direct precipitation. Although the aforementioned studies show that β-cyclodextrin (βCD), low-degree methylated β-cyclodextrin (LMβCD), and γ-cyclodextrin (γCD) can form NCCs as a precipitate for further use, only βCD and LMβCD-NCC showed good potential for NMH, with βCD ultimately selected for further use because it is the most commonly used CD derivative, commercially available, FDA-approved, and would not require any further modification . It was also reported that both perfluoropentane (PFP, b.p.…”

“…29 °C) and perfluorohexane (PFH, b.p. 56 °C) could be used as PFCs to enable an acoustically active liquid for effective NMH cavitation. , However, histotripsy cavitation experiments also showed that PFH-containing NCCs produced a more compact, well-defined histotripsy bubble cloud, indicating that PFH NCCs are a better reagent for nanoparticles designed for NMH …”