Molecular-level changes in collagen due to in vitro tensile overload in a tendon model

Soft tissue injuries, such as common ligament sprains and tendon strains, are poorly understood at the molecular level. This thesis reports the first in-depth investigation of molecular-level changes in fibrous collagen due to in vitro tensile overload. A conceptual model is presented that provides a mechanistic explanation of how and why molecular collagen changes upon tensile overload of a tendon.

Using an assortment of biochemical and biophysical techniques, hypotheses based on the model were tested, confirmed and the model was substantiated. In vitro tensile overload of a newly characterized bovine tail tendon (BTT) model resulted in a 3- to 4-fold increase in proteolysis of collagen by (acetyl)trypsin. This was mirrored by a decrease in thermal stability of approximately 3°C (measured with differential scanning calorimetry). Interestingly, the data also indicated no significant change in molecular conformation (denaturation) due to tensile overload. These new results can be explained by an increase in the gyration of the collagen molecules' intrahelical hydroxyproline-free thermally labile domains caused by disruption of the fibrillar lattice structure. A novel application of hydrothermal isometric tension (HIT) testing showed that complete tissue rupture was not required to decrease the thermal stability and additional overloading cycles furthered the effect. In addition, increased covalent crosslinking density and stability inhibited the decrease in thermal stability by inhibiting lattice structure deformation.

This thesis represents an original and significant contribution to fundamental (bio)materials science concerning the most important structural biopolymer, fibrous collagen. It also has both important clinical and biomedical implications in treatment of injuries and tissue engineering respectively.