## 3 Results and Discussion
### Characterization of BNC/\(\kappa\)-Car Composites
#### 3.2.5 Mechanical Strength  
Tissue engineering applications commonly encompass the use of scaffolds to provide a suitable microenvironment for the incorporation of cells to regenerate damaged tissues or organs. Scaffolds should exhibit high mechanical strength to maintain integrity until new tissue regeneration. It is especially important in case of cartilage tissue replacements. As the load bearing material, cartilage functions in a challenging mechanical environment. Bacterial nanocellulose is known as a mechanically stable biomaterial with hydrogel-like characteristic [53]. Interestingly, incorporation of \(\kappa\)-Car into BNC additionally improved the tensile strength of BNC/\(\kappa\)-Car composites at \(\kappa\)-Car concentrations up to 2% (Table 3). Also, the elongation at break was affected by the incorporation of \(\kappa\)-Car. In the case of the second method of BNC/\(\kappa\)-Car production, the fracture strain was increased to 163 and 180% compared to the native BNC for BNC/\(\kappa\)-Car\({}_{2.0}\) and BNC/\(\kappa\)-Car\({}_{4.0}\), respectively. The Young's modulus of the native articular cartilage is about 10 MPa [54,55]. All the composites obtained in this study, with an exception of BNC/\(\kappa\)-Car\({}_{4.0}\), were characterized by the higher tensile modulus values ranging from 12.32 to 16.35 MPa, in contrast to pure BNC, whose Young's modulus was below 9 MPa. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**Tensile Strength**} & \multicolumn{2}{c}{**Compression**} \\ \cline{2-5}  & **Stress (MPa)** & **Elongation (\%)** & **Young’s Modulus (MPa)** & **Young’s Modulus (MPa)** \\ \hline
**BNC** & 2.01 \({}^{\text{c}}\)\(\pm\) 0.24 & 28.16 \({}^{\text{c}}\)\(\pm\) 1.80 & 8.96 \({}^{\text{c}}\)\(\pm\) 1.28 & 7.44 \({}^{\text{c}}\)\(\pm\) 0.81 \\
**BNC/\(\kappa\)-Car\({}_{0.2}\)** & 2.22 \({}^{\text{c}}\)\(\pm\) 0.31 & 21.89 \({}^{\text{d}}\)\(\pm\) 1.07 & 12.82 \({}^{\text{b}}\)\(\pm\) 1.57 & 7.48 \({}^{\text{c}}\)\(\pm\) 0.70 \\
**BNC/\(\kappa\)-Car\({}_{0.5}\)** & 2.73 \({}^{\text{b}}\)\(\pm\) 0.42 & 23.22 \({}^{\text{d}}\)\(\pm\) 1.14 & 16.35 \({}^{\text{a}}\)\(\pm\) 2.34 & 5.63 \({}^{\text{d}}\)\(\pm\) 0.40 \\
**BNC/\(\kappa\)-Car\({}_{0.8}\)** & 2.95 \({}^{\text{b}}\)\(\pm\) 0.26 & 31.71 \({}^{\text{c}}\)\(\pm\) 2.97 & 12.32 \({}^{\text{b}}\)\(\pm\) 1.11 & 4.90 \({}^{\text{d}}\)\(\pm\) 0.38 \\
**BNC/\(\kappa\)-Car\({}_{2.0}\)** & 4.86 \({}^{\text{a}}\)\(\pm\) 0.58 & 45.79 \({}^{\text{b}}\)\(\pm\) 5.79 & 12.64 \({}^{\text{b}}\)\(\pm\) 1.27 & 14.31 \({}^{\text{b}}\)\(\pm\) 1.55 \\
**BNC/\(\kappa\)-Car\({}_{4.0}\)** & 3.10 \({}^{\text{b}}\)\(\pm\) 0.46 & 50.50 \({}^{\text{a}}\)\(\pm\) 4.53 & 7.46 \({}^{\text{c}}\)\(\pm\) 0.90 & 16.21 \({}^{\text{a}}\)\(\pm\) 1.60 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Mechanical strength of BNC/\(\kappa\)-Car composites (The data are presented as the means \(\pm\) SD from at least twelve independent experiments; the means that are marked with different letters are significantly different). Figure 7: Water retention ratio of BNC and BNC/\(\kappa\)-Car composites. (The data are presented as the means \(\pm\) SD from at least three independent experiments). As components of cartilage tissue, the chondrocytes are adapted to function under elevated pressure, and mechanical compression is thought to stimulate the proliferation and differentiation of these cells [56; 57]. Therefore, the compression modulus is the key parameter, which determines the utility of scaffolds in tissue engineering. The study of [PERSON] et al. showed that exposition of chondrocytes seeded in a three-dimensional agarose scaffold on the static or pulsing hydrostatic pressure of 5 MPa for 4 h resulted in the increasing of GAG synthesis and a four-fold higher level of aggrecan mRNA [56]. In the case of BNC and BNC-based composites, the compression properties depend on the arrangement and thickness of fibers as well as the porosity and crystallinity of membranes.