Ovalbumin-Based Scaffolds Reinforced with Cellulose Nanocrystals for Bone Tissue Engineering

In the field of tissue engineering, a major area of study is developing bone scaffolds that will provide support for osteoblasts. Despite many advances in recent years there is still a significant need for new bio-based 3-D porous scaffolds that possess sufficient initial mechanical properties to prevent immediate failure upon implantation. Ovalbumin (OVA), a glycoprotein from chicken egg whites, has been use to fabricate biodegradable, porous hydrogel bone scaffolds that promote osteoblast attachment and proliferation.

Although ovalbumin scaffolds encourage bioactivity and are naturally resorbed into the body after bone regeneration, they are also very fragile. Extremely stiff cellulose nanocrystals (CNCs), derived from wood pulp, can be utilized to reinforce these scaffolds while improving biocompatibility. When chemically modified to incorporate surface amine groups, cellulose nanocrystals become capable of covalently crosslinking with the OVA matrix for improved mechanical resilience.

Three concentrations (2, 5, 10 wt. %) of CNCs were incorporated and crosslinked to form nanocomposite scaffolds then were compared to pure OVA scaffolds. After fabrication, pore size morphology was compared between each CNC loading using SEM. The images revealed that the 10 wt. % CNC concentration doubled the pore compared to pure OVA scaffolds. Under high magnification, the CNCs were incorporated into the pore walls, providing a contoured surface. AFM was applied to analyze the topography of OVA with CNCs present. The surfaces laden with CNCs had a higher mean surface roughness, but was insufficient to impact cell behavior.

Compression testing was carried out on both Instron and DMA machines to demonstrate any reinforcing effect provided by the CNCs. While the compressive modulus remained constant, the elastic limit and strain increased with CNC loading, indicating a change in the resilience of the reinforced scaffolds. With a MTT Assay, it was shown that MC3T3-E1 preosteoblasts significantly increase in metabolic activity on 2 wt. % films and scaffolds, an indication of proliferation. All scaffolds had a net increase in metabolic activity suggesting overall biocompatibility for OVA scaffolds and those incorporating CNCs. Overall, the 5 wt. % scaffolds had the highest mechanical strength and had a positive cell response.