# Cellulose Nanofibers and Other Biopolymers for Biomedical Applications. A Review
## 4 Outline of Biomedical Applications
### Tissue Engineering
CNF obtained by TEMPO-mediated oxidation or acetylation process exhibited favourable fidelity under wet and dry cases, remarkable stability, and good biocompatibility with cardiac myoblast cells [123]. Hepatic tissue engineering aims to construct functional hepatic organs for organ transplantation. CNF hydrogels promote the 3D hepatocyte culture and induce the formation of hepatocyte HepaRG and HepG2 cells. Bioinks of CNC/Alginate were used to mimic hepatic structure by three-dimensional bioprinting, obtaining great shape fidelity with minimal cell mortality [124; 125]. The excellent optical, mechanical, barrier and compatibility properties of nanocellulose allow to use it in ophthalmic tissue engineering. CNC and CNF were used as a matrix to produce hyperelastic hydrogels in combination with PVA matrix obtaining exceptionally high-water content and similar mechanical properties to native tissues [126]. In addition, other biopolymers have been used to produce materials for tissue engineering. A silk/collagen/hyaluronic acid composite scaffold was produced incorporating pilose antler polypeptides. It was shown to have repaired cartilage defects in rabbit studies in 13 weeks [127]. Similarly, silk fibroin and melanin scaffolds seeded with human neuroblastoma cells (SH-SY5Y) have demonstrated the potential for nerve regeneration as they successfully promoted neuronal growth along the axis of the scaffold [128]. These scaffolds can also be applied to stimulate bone growth. Figure 12 shows an example of scaffolds prepared using silk fibroin via electrospinning. Porous hydroxyapatite scaffolds for bone tissue engineering were successfully prepared using 3D gel-printing technology [129]. Tissue engineered heart valves are also being developed using biopolymers to eventually replace mechanical counterparts as they hold advantages in terms of durability, the abilities to grow, repair and remodel cardiac tissue [130]. Xylan/poly(vinyl alcohol) (PVA) based nanofibrous scaffolds cross-linked with glutaraldehyde vapours have been investigated as a support for cell adhesion and proliferation in cardiac tissue engineering [132]. Similarly, Xlyan-based hydrogels have been synthesized and tested for use for cell encapsulation and in vivo delivery. Mesenchymal stem cells were encapsulated in the hydrogel for one week and were shown to have retained their adipogenic differentiation capacity within the gel [133]. The addition of lignin and xylan to cellulose-based hydrogels has been shown to improve the mechanical strength and stiffness, whilst lignin imparted antimicrobial properties to the film [134]. Alginate/lginin aerogels have been shown to be non-cytotoxic and feature good cell adhesion [110]. Lignin derived nanoparticles have been reported to show gram-negative and gram-positive biocidal activity at significantly lower silver concentrations compared to conventional reagents, such as silver nanoparticles or silver nitrate, while leaving an inactive biodegradable particle after the release, and thus, having a smaller environmental impact [111].