The effects of UV irradiation on collagen D-band revealed by atomic force microscopy

Abstract

The objective of this paper was to investigate the influence of UV irradiation on collagen D-band periodicity by using the AFM imaging and nanoindentation methods. It is well known than UV irradiation is one of the main factors inducing destabilization of collagen molecules. Due to the human's skin chronic exposure to sun light, the research concerning the influence of UV radiation on collagen is of great interest. The impact of UV irradiation on collagen can be studied in nanoscale using Atomic Force Microscopy (AFM). AFM is a powerful tool as far as surface characterization is concerned, due to its ability to relate high resolution imaging with mechanical properties. Hence, high resolution images of individual collagen fibrils and load-displacement curves on the overlapping and gap regions, under various time intervals of UV exposure, were obtained. The results demonstrated that the UV rays affect the height level differences between the overlapping and gap regions. Under various time intervals of UV exposure, the height difference between overlaps and gaps reduced from ~3.7 nm to ~0.8 nm and the fibril diameters showed an average of 8-10% reduction. In addition, the irradiation influenced the mechanical properties of collagen fibrils. The Young's modulus values were reduced per 66% (overlaps) and 61% (gaps) compared to their initial values. The observed alterations on the structural and the mechanical properties of collagen fibrils are probably a consequence of the polypeptide chain scission due to the impact of the UV irradiation.

Effects of UV on apoptotic factors in lens epithelial cells of an animal model

“…One of the factors that can easily cause LEC damage is UV. Numerous studies have shown (14–16) that UV radiation is closely related to the occurrence of cataract. LEC apoptosis is the initiation of cataract, in which p53 has a strong ability to regulate cell growth (17).…”

Hertz model or Oliver & Pharr analysis? Tutorial regarding AFM nanoindentation experiments on biological samples

“…As it has been previously reported for spherical indenters, if the indenter's radius is at least ten times smaller from each horizontal dimension of the sample, then the sample can be considered as an elastic half space [13]. In addition, the maximum indentation depth should not exceed the 5%-10% of the sample's thickness in order to avoid measuring the sample's substrate properties (Buckle's rule) [12].…”

“…AFM nanoindentation experiments on biological samples 2.1.1. Loading and unloading curves In a typical AFM nanoindentation experiment the AFM tip indents the sample of interest and a loaddisplacement curve is recorded [9,12]. The same procedure is also performed on a hard reference sample [9,12].…”

“…Loading and unloading curves In a typical AFM nanoindentation experiment the AFM tip indents the sample of interest and a loaddisplacement curve is recorded [9,12]. The same procedure is also performed on a hard reference sample [9,12]. As a result, the indentation values are calculated by the difference in the piezo-displacement between the hard and the soft sample for the same applied load [9].…”

Unraveling the role of Calcium ions in the mechanical properties of individual collagen fibrils

“…Atomic force microscopy (AFM) based nanoindentation has been well established as a powerful technique for the investigation of the mechanics at the nanoscale level916171819. To have a better understanding of the effect of abnormal calcium homeostasis on soft tissues’ mechanics, we attempted to employ AFM-based nanoindentation to study the mechanical behavior of type II collagen fibril extracted from AC.…”