25% GP. For each sample, the relaxation data in the x-and y-direction are averaged. Stresses were normalized to the … To study the dilution calculator effect of crosslinking on the stress relaxation behavior of collagen matrices, in Figures 6A and and7A7A we plotted the normalized biaxial stress relaxation curves. Stresses were normalized to the initial stresses at time t = 0. To eliminate the effect of initial stress levels on the rate of stress relaxation, samples with different crosslinking were tested at the initial stresses of 12 �� 0.2 kPa and 85 �� 2 kPa for collagen gel and thin film, respectively.30 For collagen thin film in Figure 7A, the rate of stress relaxation is almost independent on crosslinking. For collagen gel in Figure 6A, however, the rate of stress-relaxation shows obvious inverse dependency on crosslinking.

More crosslinked collagen gel relaxes slower than the less crosslinked ones, which suggests that less crosslinked collagen gels are more viscous. The effect of crosslinking on the stress relaxation behavior of collagen matrices can also be seen from the relaxation time spectrum in Figures 6B and and7B.7B. For both collagen matrices, the relaxation times at each peak are similar for different crosslinking. For collagen gel, there is a decrease in peak intensity for higher GP concentration in general, although the last peak shows the most prominent decrease in intensity. However collagen thin film shows little variation of peak intensity as the GP concentration changes. Discussion Hydration level is important to many connective tissues in order to maintain their normal biomechanical functions.

31-33 The dehydration process may change the structure of collagen network by deducing the space between molecules as well as affecting the inter-and intra-molecular chemical bonds.34 Our macroscopic mechanical testing results show that the stiffness of collagen thin film is about one order of magnitude higher than the hydrated collagen gel (Fig. 1). McDaniel et al. (2007) found that the contact stiffness of collagen fibrils increases an order of magnitude when dehydrated. The changes of hydrogen bonds and network structure during dehydration were believed to cause the increased stiffness. Infrared reflection spectroscopy showed a strengthening and shortening of hydrogen bonds within the triple helix during the dehydration process.

35 Using Raman spectroscopy, Leikin et al.36 demonstrated the structural role for hydration layers in keeping the spacing between collagen fibrils. The tighter packing of fibrils during dehydration resulted Cilengitide in enhanced mechanical rigidity. Also, molecular dynamics simulations of a collagen like peptide showed that the number of intra-molecular hydrogen bonds increased due to the absence of water and the molecule tended to be stiffer.34 Both experimental and modeling efforts have been made to determine the mechanisms by which strain is dispersed within the tissue.