Star-Pseudopolyrotaxane Organized in Nanoplatelets for Poly(ε-caprolactone)-Based Nanofibrous Scaffolds with Enhanced Surface Reactivity

Abstract

Herein, it is demonstrated that star pseudopolyrotaxanes (star-pPRs) obtained from the inclusion complexation of α-cyclodextrin (CD) and four-branched star poly(ε-caprolactone) (star-PCL) organize into nanoplatelets in dimethyl sulfoxide at 35 °C. This peculiar property, not observed for linear pseudopolyrotaxanes, allows the processing of star-pPRs while preserving their supramolecular assembly. Thus, original PCL:star-pPR core:shell nanofibers are elaborated by coaxial electrospinning. The star-pPR shell ensures the presence of available CD hydroxyl functions on the fiber surface allowing its postfunctionalization. As proof of concept, fluorescein isothiocyanate is grafted. Moreover, the morphology of the fibers is maintained due to the star-pPR shell that acts as a shield, preventing the fiber dissolution during chemical modification. The proposed strategy is simple and avoids the synthesis of polyrotaxanes, i.e., pPR end-capping to prevent the CD dethreading. As PCL is widely used for biomedical applications, this strategy paves the way for simple functionalization with any bioactive molecules.

Aliphatic Polyester Nanofibers Functionalized with Cyclodextrins and Cyclodextrin-Guest Inclusion Complexes

“…This is typically accomplished by a variety of post-modification reactions on hydroxyl groups, facilitating intermolecular interactions, such as ionic interactions [100,101] and click chemistries [102], potentially resulting in the immobilization of bioactive molecules. Although our studies did not focus on further development of the functionalized PCL, Elisseeff [103] and Schlatter [104,105] have reported various bioactive molecule immobilization on PCL-α-CD-IC nanofibers.…”

“…We overcame this difficulty by electrospinning pseudorotaxanes (PpR) from CFM and improved solution conductivity with the addition of BTEAC salt. Another easier method was reported by Schlatter’s research group, who reported on the fabrication of core–shell nanofibers comprised of four branched star-PpR or mikto-arm PpR for shell and neat PCL for core regions, respectively [104,105]. Small angle neutron scattering measurements (SANS) showed temperature-dependent shell stability/core instability of PpR in DMSO, based on which stable PpR solution was prepared for electrospinning (35 °C) (Figure 10A).…”

“…Small angle neutron scattering measurements (SANS) showed temperature-dependent shell stability/core instability of PpR in DMSO, based on which stable PpR solution was prepared for electrospinning (35 °C) (Figure 10A). WAXD analyses of PCL/PpR nanofibers (10:2 and 10:3 ratios) showed a 2θ = 20° peak, indicating the presence of intact rotaxane crystals in the coaxial spun nanofibers [104]. The intact PpR was further taken advantage of by immobilizing fluorescein isothiocyanate (FITC) onto star PpR via immersing the scaffolds in acetonitrile, a water (1:1) solution containing FITC [104].…”

“…WAXD analyses of PCL/PpR nanofibers (10:2 and 10:3 ratios) showed a 2θ = 20° peak, indicating the presence of intact rotaxane crystals in the coaxial spun nanofibers [104]. The intact PpR was further taken advantage of by immobilizing fluorescein isothiocyanate (FITC) onto star PpR via immersing the scaffolds in acetonitrile, a water (1:1) solution containing FITC [104]. Interestingly, confocal microscopy experiments showed fluorescence in core–shell fibers containing star-PpR in the shell region (Figure 10B,C), whereas in the core–shell nanofibers containing linear PpR, such a fluorescent effect was not observed due to the dethreading and subsequent leaching of CDs [104].…”

Electrospun Fibers of Cyclodextrins and Poly(cyclodextrins)

“…The polypseudorotaxanes adopted a nanoplatelet arrangement, which was maintained after electrospinning. The core-shell structure ensured that the hydroxyl groups of αCD were available on the fibers surface for subsequent immobilization of active substances [ 103 ].…”