Synthesis, Characterization, and Potential Application of Cyclodextrin-Based Polyrotaxanes for Reinforced Atelocollagen Threads

Abstract

Preparing strong and flexible atelocollagen-based materials for biomedical applications is still a challenging task. To address this challenge, this study describes the synthesis and characterization of water-soluble polyrotaxanes (PRs) with different coverage ratios and molecular weights of axle polymers, and their potential applications for PR-reinforced atelocollagen threads (PRATs). A novel method was established for the syntheses of PRs with relatively low coverage ratio at the sub-gram scale, in which the aldehyde groups were employed as crosslinking sites for preparing the PRATs via reductive amination. The aldehyde groups were successfully quantified by ¹H nuclear magnetic resonance spectroscopy using 1,1-dimethylhydrazine as an aldehyde marker. Fourier-transform infrared and thermogravimetric analysis measurements supported the characterization of the PRs. Interestingly, tensile testing demonstrated that coverage ratio affected the mechanical properties of the PRATs more strongly than molecular weight. The insights obtained in this study would facilitate the development of soft materials based on atelocollagens and PRs.

Keywords: atelocollagen thread; crosslinking; cyclodextrins; polyrotaxane; slide-ring features.

Figure 1

Schematic illustrations of PRs for PRATs.

Scheme 1

Synthetic scheme for PluPRβCD1.

Scheme 2

Synthetic scheme for PegPRαCD1.

Figure 2

¹H NMR spectra of (a) Peg_10kPRαCD1-DMHZ and (b) Plu_9kPRβCD1-DMHZ (400 MHz, 318 K, DMSO-d₆).

Figure 3

FT–IR spectra of (a) PegPRαCD2, (b) PegPRαCD1, (c) PluPRβCD2, and (d) PluPRβCD1.

Figure 4

TGA curves: (a) Peg–NH₂, αCD, αCD–CHO, PegPRαCD3, PegPRαCD2, and PegPRαCD1; (b) Plu–COOH, βCD, βCD–CHO, PluPRβCD3, PluPRβCD2, and PluPRβCD1. The samples were heated to 700 °C at a heating rate of 10 °C/min.

Figure 5

Tensile testing of AtCol alone and PRATs. (a) Representative photograph of the tensile testing setup. (b) Representative stress–strain curves. Bar graphs of the (c) fracture stress, (d) toughness, (e) Young’s modulus, and (f) fracture strain. Fracture stress was calculated by dividing the fracture test force (N) by the cross-sectional area (ca. 0.03 mm²). Young’s modulus was determined from the slope of the initial linear region (~6% strain) of the stress–strain curve. * p < 0.01, ** p < 0.05 (Tukey’s test).