Plasma-treated bacterial nanocellulose-lignin composites for biomedical applications

Bacterial nanocellulose (BC) as a bioimplant possesses several limitations, encompassing absence of bioactivity, and unsatisfactory mechanical properties. Envisaging antimicrobial activity, enhanced cytocompatibility and mitigation of the inflammatory response, surface characteristics such as hydrophilicity and rugosity were tailored. Different strategies comprising treatments with Kraft lignin (KL), glycerin (GLY), and dielectric barrier discharge (DBD) plasma were evaluated. DBD plasma treatments at different energy dosages (5, 10, and 15 kW/min/m²) increased the metabolic activity of L-929 fibroblasts, corroborating BC biomedical potential. Higher DBD plasma dosages promoted surface etching, producing a denser micro-hole structure and higher surface roughness (21.45 nm), as confirmed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Considering that no significant differences in metabolic activity were observed across the DBD plasma dosages, the lowest dosage (5 kW/min/m²) was selected for further functionalisation of both untreated and DBD-treated samples, which were either never-dried or dried, with 3 wt% of KL and/or GLY. Analysis of morphological, chemical, mechanical, and biological properties were performed. The antibacterial activity was slightly improved, especially in the dried KL/GLY composites, resulting in a 76 % reduction in bacterial growth against Pseudomonas aeruginosa. Furthermore, KL imparted antioxidant properties, with increased effects in the dried plasma-post-treated systems, reaching up to 50 % inhibition of the 2,2-diphenyl-1-picryl-hydrazyl radical (DPPH•). Mechanical properties benefited from the presence of GLY, resulting in increased flexibility and decreased stiffness, with the lowest Young's modulus of 4.12 MPa (never-dried KL/GLY). In addition, combining KL/GLY and DBD plasma-induced surface modification also enhanced tensile strength to 105 MPa. Overall, the DBD plasma-assisted functionalisation of BC with KL/GLY improved implant biocompatibility, antibacterial efficacy, and antioxidant potential, emphasising its potential as a multifunctional biomaterial for biomedical applications.