Stability and mechanical performance of collagen films under different environmental conditions

Protein-based biomaterials are becoming increasingly popular for biomedical applications as they can replicate both chemical and mechanical properties of native tissues. Type I collagen is widely available and used for such applications, particularly as 2D structures (films and membranes). The degradation mechanism and mechanical performance of collagen films are investigated in this study for long-term exposure to three different environments – ambient laboratory conditions (Type A), water immersion (in-aqua) (Type B) and rehydration (replenishment of water lost in dehydration) (Type C) conditions. Specimens exposed to Type A conditions showed an increased stiffness with reduction in the ductility over the exposure period (1 year) due to the loss of physically bonded water without any change of chemical and structural properties. Another group of specimens were exposed to Type B conditions for a period of only 14 days due to quick deterioration in both the global (tensile) and local (nanoindentation) modulus. The decrease in the dimensions of the exposed specimens, their weight loss over time and changes in surface morphology through erosion and formation of micro-pores indicate that degradation might have occurred via surface erosion mechanisms. Interestingly, the chemical functional groups and triple-helix conformation of the exposed specimens remained intact over the exposure time. An increase of about 53% in the global modulus occurred on day 3 of in-aqua exposure (compared to day 1) due to rearrangement of the collagen nano-fibrils. Type C conditions were implemented by exposing the specimens in-aqua for a specific time and then dehydrating them. Such specimens exhibited poorer mechanical properties compared to the freshly manufactured ones.