Mechanical properties of collagen fibrils on thin films by Atomic Force Microscopy nanoindentation

Atomic Force Microscopy (AFM) is a powerful tool as far as surface characterization is concerned, due to its ability to relate high resolution imaging with mechanical properties. Furthermore biological samples, such as collagen, can be studied by AFM with a non-destructive manner. Collagen is the most abundant protein in mammals and because of its unique properties is widely used as biomaterial. Due to the human skin chronic exposure to sun light and since UV-rays are used in sterilizing and cross linking methods of collagen based biomaterials, the investigation of the influence of UV light on collagen, is crucial. The purpose of this paper was to investigate the topographic features and the mechanical properties of collagen fibrils prior and post ultraviolet (UV) by using the AFM indentation method. Hence, load-displacement curves were obtained on collagen fibrils in order to calculate the Young modulus for each case. Each curve presented, was the average of 10 curves. The results showed that Young modulus value increased after 4 hours of UV irradiation from 0.5 GPa to 1.53 GPa. After 8 hours of UV irradiation the Young modulus value was calculated equal to 3.2 GPa. These experiments yielded a clear stiffening of collagen fibrils as a result of UV exposure. Moreover, after 8 hours of UV exposure, collagen fibrillar structure started to deform and the characteristic D-band of collagen fibrils deteriorated. The investigation of the alterations of the modulus under UV irradiation, will contribute to the clarification of the impact that different physical and chemical parameters have on the mechanical properties of collagen-based materials. In addition, this will enable the design and development of biomaterials with improved properties.