## 2 Results and Discussion  
### Elasticity and Adhesive Behavior of Collagen Fiber  
Figure 1 shows typical force-distance curves of collagen fibers recorded at overlap and gap zones in native and treated states, respectively, with a \(\sim\)20 nm indentation. Parameters used were \(\mu\) = 0.5 by assuming the isometric changes in fibrils, and R \(\approx\) 20 nm, K\({}_{\rm C}\) = 3.1 N/m (provided by manufacturer). The Young's modulus of the overlap region is 1.1 \(\pm\) 0.2 GPa (\(n\) = 40) and the gap region is 1.2 \(\pm\) 0.2 GPa (\(n\) = 40). These measurements align with those previously determined using the nanoindentation technique (Table 1). The differences between the Young's moduli of the gap and overlap regions of the native collagen are small (<0.15 GPa). There were no significant differences observed with longer incubations with anti-collagen antibodies. Significant differences are observed in the compression elasticity measurements made in the overlap regions, particularly with antibody incubation time (Table 2). The decreasing trend in error in calculation with increased incubation time indicates a gradual and uniform distribution of antibody with time in the overlap region. There were no significant differences observed in the adhesion force in the gap region, even with longer antibody incubations (Table 3). Although a general increase in adhesion force is observed, the changes are small, especially relative to that observed in the overlap region. This indicates that the binding density of the antibody in the gap region was small and the increase in adhesion could be a result of instability and random attraction of some antibody molecules to/within the gap region. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Young’s Modulus (GPa)** & **Source Tissue** \\ \hline \multirow{2}{*}{Results reported here} & 1.1 \(\pm\) 0.2 (overlap) & \multirow{2}{*}{Rat tail tendon} \\  & 1.2 \(\pm\) 0.2 (gap) & \\ \hline [PERSON] et al., 2006 [16] & 1–2 & Inner dermis of sea cucumber \\ \hline [PERSON] et al., 2007 [17] & \(\sim\)1.2 & \multirow{2}{*}{Calf skin} \\ \hline [PERSON] et al., 2007 [18] & 1.9 \(\pm\) 0.5 & Bovine achilles tendon \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Young’s Modulus of the collagen determined by AFM nanoindentation, in comparison to the results reported here. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Incubation Time** & \(n\) & \begin{tabular}{c} **Adhesion Force** \\ **(nN)** \\ \end{tabular} & \begin{tabular}{c} **Percentage Error** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **Percentage Change** \\ **from Native (\%)** \\ \end{tabular} \\ \hline \begin{tabular}{c} Native \\ (0 min) \\ \end{tabular} & 40 & \(4.5\pm 0.6\) & 13.3 & - \\ \hline \begin{tabular}{c} 20 min \\ \end{tabular} & 40 & \(5.3\pm 0.8\) & 15.1 & 17.8 \\ \hline \
\begin{tabular}{c} 1 h \\ \end{tabular} & 40 & \(6.7\pm 0.5\) & 7.5 & 48.9 \\ \hline
\begin{tabular}{c} 2 h \\ \end{tabular} & 40 & \(8.2\pm 0.4\) & 4.9 & 82.2 \\ \hline \end{tabular}
\end{table} 
Table 2: Adhesion force measurements form the overlap region after antibody treatment. Figure 1: Elasticity and adhesive behavior of collagen fiber determined by atomic force microscopy (AFM) nanoindentation. **(A)** The region of interest with gap and overlap (OL) were marked where nanoindentation was performed; **(B)** Typical force-distance curves of collagen fibers recorded at overlap and gap zones in native and treated states, respectively, with a \(\sim\)20 nm indentation. The plot is also annotated with the process of indentation (i–v) from the AFM tip approaching the sample through to indenting and releasing after adhesion.