TY - JOUR
T1 - In vitro fracture testing of submicron diameter collagen fibril specimens
AU - Shen, Zhilei Liu
AU - Dodge, Mohammad Reza
AU - Kahn, Harold
AU - Ballarini, Roberto
AU - Eppell, Steven J.
N1 - Funding Information:
We performed in vitro fracture tests on type I collagen fibril specimens isolated from sea cucumber dermis using MEMS devices. We obtained stress-strain curves from 13 specimens with diameters in the range of 205–905 nm, which to our knowledge are the first measurements of in vitro fracture behavior of these biologically ubiquitous submicron-size objects. Three types of different mechanical behavior were observed, including 1. A relatively linear region all the way to brittle fracture. 2. Multiple linear regions before brittle fracture. 3. Multiple linear regions followed by a stepwise graceful fracture region. A majority (11 out of 13) of the specimens showed brittle failure, while the two largest specimens showed graceful failure which may be a result of multiple fibrils. After excluding the two largest specimens, we found an elastic modulus of 470 ± 410 MPa, a fracture strength of 230 ± 160 MPa, a fracture strain of 80% ± 44%, and a toughness of 140 ± 180 × 10 6 J/m 3 in vitro. The collagen fibril specimens displayed statistically significantly lower elastic modulus in vitro than in air. However, there are no statistically significant differences in the other mechanical properties such as the fracture strength, the fracture strain, and the toughness when comparing the in vitro study to the in air study. Both the fracture strength and fracture strain obtained in vitro and in air are significantly larger than those obtained in vacuo, indicating the difference rises from the lack of intrafibrillar water molecules produced by vacuum drying. Some mechanical properties of collagen fibrils, such as the fracture strength and fracture strain, were significantly different from those obtained at the fibril bundle, fascicle, and tissue levels, confirming the importance of obtaining these properties at the fibrillar level for multiscale hierarchical modeling. Future work could include a study of the effect of cross-link density, genetic variation, and mineralization on the mechanical properties of collagen fibrils. We thank Prof. John A. Trotter of the University of New Mexico for providing the collagen fibrils, Prof. Ioannis Chasiotis and Dr. Mohammad Naraghi of the University of Illinois at Urbana-Champaign for help on DIC, and Prof. Markus J. Buehler of the Massachusetts Institute of Technology for enlightening conversation. This work was funded by National Science Foundation grant No. 0532320 and National Institutes of Health grant No. 1 R21 EB004985-01A1. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Science Foundation or the National Institute of Health. This investigation was conducted in a facility constructed with support from Research Facilities Improvement Program grant No. C06 RR12463-01 from the National Center for Research Resources, National Institutes of Health. Z.L.S. was supported by an Innovation Incentive Fellowship grant from the Ohio Board of Regents. R.B. acknowledges the support by National Science Foundation grant NSF CMMI 0800896.
PY - 2010
Y1 - 2010
N2 - Mechanical testing of collagenous tissues at different length scales will provide improved understanding of the mechanical behavior of structures such as skin, tendon, and bone, and also guide the development of multiscale mechanical models. Using a microelectromechanical-systems (MEMS) platform, stress-strain response curves up to failure of type I collagen fibril specimens isolated from the dermis of sea cucumbers were obtained in vitro. A majority of the fibril specimens showed brittle fracture. Some displayed linear behavior up to failure, while others displayed some nonlinearity. The fibril specimens showed an elastic modulus of 470 ± 410 MPa, a fracture strength of 230 ± 160 MPa, and a fracture strain of 80% ± 44%. The fibril specimens displayed significantly lower elastic modulus in vitro than previously measured in air. Fracture strength/strain obtained in vitro and in air are both significantly larger than those obtained in vacuo, indicating that the difference arises from the lack of intrafibrillar water molecules produced by vacuum drying. Furthermore, fracture strength/strain of fibril specimens were different from those reported for collagenous tissues of higher hierarchical levels, indicating the importance of obtaining these properties at the fibrillar level for multiscale modeling.
AB - Mechanical testing of collagenous tissues at different length scales will provide improved understanding of the mechanical behavior of structures such as skin, tendon, and bone, and also guide the development of multiscale mechanical models. Using a microelectromechanical-systems (MEMS) platform, stress-strain response curves up to failure of type I collagen fibril specimens isolated from the dermis of sea cucumbers were obtained in vitro. A majority of the fibril specimens showed brittle fracture. Some displayed linear behavior up to failure, while others displayed some nonlinearity. The fibril specimens showed an elastic modulus of 470 ± 410 MPa, a fracture strength of 230 ± 160 MPa, and a fracture strain of 80% ± 44%. The fibril specimens displayed significantly lower elastic modulus in vitro than previously measured in air. Fracture strength/strain obtained in vitro and in air are both significantly larger than those obtained in vacuo, indicating that the difference arises from the lack of intrafibrillar water molecules produced by vacuum drying. Furthermore, fracture strength/strain of fibril specimens were different from those reported for collagenous tissues of higher hierarchical levels, indicating the importance of obtaining these properties at the fibrillar level for multiscale modeling.
UR - https://www.scopus.com/pages/publications/77957325775
U2 - 10.1016/j.bpj.2010.07.021
DO - 10.1016/j.bpj.2010.07.021
M3 - Article
AN - SCOPUS:77957325775
SN - 0006-3495
VL - 99
SP - 1986
EP - 1995
JO - Biophysical Journal
JF - Biophysical Journal
IS - 6
ER -