Biomimetic composite scaffold from an in situ hydroxyapatite coating on cellulose nanocrystals

Abstract

A novel nanocomposite scaffold was developed by homogeneous deposition of hydroxyapatite (HAP) on a cellulose nanocrystals (CNCs) matrix suspended in a simulated body fluid (SBF). By adjusting the pH of the SBF, the HAP content in the nanocomposite could be controlled between 15 wt% and 47 wt%. Physical and chemical characteristics of the nanocomposites were analyzed by SEM, FTIR, XRD, SAED, and TEM, which confirmed the successful incorporation of HAP onto the CNCs. The nanocomposites were then freeze-casted into porous scaffolds by different solidification technologies (i.e., directional freezing (DF), plunging in liquid N₂ (PL) or in a -20 °C freezer (FZ)) followed by lyophilization. Compression testing of the HAP/CNCs foams indicated that DF caused significant improvement in mechanical properties due to the specific orientation and anisotropic porous structure compared to conventional freezing methods such as PL and FZ. Moreover, the scaffold with high HAP content exhibited improved mechanical and thermal properties, which holds potential for application in bone tissue engineering.

Fig. 1. The SEM images of CNCs before and after hydroxyapatite (HAP) coating. (a) Pure CNCs; (b) at SBF of pH 6.0; (c) at SBF pH 7.4; (d) at SBF pH 8.5.

Fig. 2. FTIR (a), XRD (b) and SAED (c) analysis of the CNCs and HAP coated CNCs.

Fig. 3. Micrographs of CNCs before (a) and after (b) HAP coating, scale bars 100 nm. The relationship between the HAP content and the pH values (c).

Fig. 4. SEM images of the longitudinal side views of the freeze-casted porous foams. (a–c) Directionally frozen; (d–f) frozen by plunging into liquid N₂. (a and d) Pure CNCs; (b and e) prepared at pH 7.4; (c and f) prepared at pH 8.5.

Fig. 5. TGA-DTG curves of the CNCs/HAP scaffolds.