Biomedical Engineering Reference
In-Depth Information
The collagen fibrils were observed by high-resolution scanning electron microscopy (SEM).
The preparation of the specimen was performed according to a previous report [16, 24].
Figure 6 shows the well-developed networks of nano-fibrils on the BC gel and e-BC gel. The
width of the fibrils on the BC-gel was in the range of 50-100 nm (Fig. 6a). However, a wider
(width; >200 nm) and winding fibril-like structure was observed on the e-BC gel (Fig. 6b),
indicating that the fibril structure of collagen was deformed through the heat treatment. The
wide and winding fibril-like structure of the e-BC gel should be directly derived from the
collagen nano-fibrils of the original BC gel through swelling of the fibrils by comparison of
both surface structures.
Fig. 6. SEM images of BC gels (a) and e-BC gels (c). Bars: 1 μm.
4.
Mechanical properties of e-BC gel
The mechanical properties of the e-BC gel were evaluated by tensile tests. The original BC
gel rarely had elasticity and stretchability similar to the usual collagen materials. However,
the e-BC gel showed rubberlike elasticity and high stretchability. Figure 7 shows the stress-
strain curves to the breaking point obtained in the strain rate of 0.1 mm/s (n = 5). Salmon-
derived elastic collagen gels (e-SC gel) were used as controls [24]. The mean values ±
standard deviation (SD) of elongation at the break of the e-BC gel and e-SC gel were 201 ±
47% and 260 ± 59%, respectively (Fig. 7c). At the early stage of loading, stress was almost
linearly increased depending on the strain. Above a strain of ca. 100%, an increase in strain
hardening was observed. There was no significant difference in elongation between the two
e-gels. According to the report by Koide and Daito [31], collagen films reinforced by
traditional cross-linking reagents, glutaraldehyde and tannic acid, showed only small
elongation at the breaking point (6.6% and 12.4%, respectively). Weadock et al. showed
small ultimate strains (approximately 40% and 30%) of collagen fibers cross-linked by UV
irradiation and dehydrothermal treatment, respectively [36]. Even a purified skin with an
intact fibrous collagen network gives elongation at a breaking point of 125% [36]. Recently, it
was reported that a chemically cross-linked collagen-elastin-glycosaminoglycan scaffold,
which are the contents analogous to the actual tissue/organs, demonstrated good
stretchability (150% strain) [37]. To the best of our knowledge, this is the first report of a
material from bovine collagen with elongation at a breaking point over 200%. Although the
mechanism of the high stretchability was not well understood, the denaturation of the
