Production and Mechanical Characterisation of TEMPO-Oxidised Cellulose Nanofibrils/β-Cyclodextrin Films and Cryogels

Abstract

Wood-based TEMPO-oxidised cellulose nanofibrils (toCNF) are promising materials for biomedical applications. Cyclodextrins have ability to form inclusion complexes with hydrophobic molecules and are considered as a method to bring new functionalities to these materials. Water sorption and mechanical properties are also key properties for biomedical applications such as drug delivery and tissue engineering. In this work, we report the modification with β-cyclodextrin (βCD) of toCNF samples with different carboxyl contents viz. 756 ± 4 µmol/g and 1048 ± 32 µmol/g. The modification was carried out at neutral and acidic pH (2.5) to study the effect of dissociation of the carboxylic acid group. Films processed by casting/evaporation at 40 °C and cryogels processed by freeze-drying were prepared from βCD modified toCNF suspensions and compared with reference samples of unmodified toCNF. The impact of modification on water sorption and mechanical properties was assessed. It was shown that the water sorption behaviour for films is driven by adsorption, with a clear impact of the chemical makeup of the fibres (charge content, pH, and adsorption of cyclodextrin). Modified toCNF cryogels (acidic pH and addition of cyclodextrins) displayed lower mechanical properties linked to the modification of the cell wall porosity structure. Esterification between βCD and toCNF under acidic conditions was performed by freeze-drying, and such cryogels exhibited a lower decrease in mechanical properties in the swollen state. These results are promising for the development of scaffold and films with controlled mechanical properties and added value due to the ability of cyclodextrin to form an inclusion complex with active principle ingredient (API) or growth factor (GF) for biomedical applications.

Keywords: cryogels; films; nanocellulose; β-cyclodextrin.

Figure 1

Atomic force microscopy (AFM) images of L-toCNF (left) and H-toCNF (right). toCNFs: TEMPO-oxidised cellulose nanofibrils. L and H are low and high contents, respectively.

Figure 2

Water sorption as a function of time of conditioning at 25 °C 90% relative humidity (RH) for L-toCNF (left) and H-toCNF (right).

Figure 3

SEM images of the cross-section of films casted from suspensions H1 (a), H2 (b), H3 (c), and H4 (d).

Figure 4

Water sorption for toCNF cryogels in immersion.

Figure 5

SEM images of the cross-section of toCNF cryogel.

Figure 6

Relative density dependence of the compression modulus, normalised compression modulus, and maximum stress at 70% deformation for L-toCNF and H-toCNF cryogels.

Figure 7

SEM images for toCNF cryogels. From Top to bottom: cryogels from suspensions 1/2/3/4.

Figure 8

Representative compression curves for H-toCNF cryogels.

Figure 9

Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra for toCNF cryogels.

Figure 10

Representative compression curves for dry and swollen H-toCNF cryogels.