Study of Nano-Mechanics of Collagen I Triple-helices by Computerized Processing of AFM Images

Abstract

We used atomic force microscope (AFM) to acquire high-resolution images of collagen type I triple-helices under ambient conditions in tapping mode. Angles between consecutive fixed-length segments were measured and analyzed to yield persistence length and elastic constant. Changing the segment length allowed exploring the mechanics at various scales. Understanding the mechanical properties of collagen molecules could serve to elucidate mechanisms of complex mechanical properties of interest in nanomedicine and nanotechnology.

Nanomechanics of Biomaterials – from Cells to Shells

“…For instance, we adsorbed collagen molecules on a freshly cleaved mica substrate to immobilize them for AFM imaging. [38] In this case, salts in the prep solution must be selectively rinsed away to avoid their interference. A challenge here is to find binding conditions whereby the salts are removed but the molecule of interest is retained.…”

“…[3a] The imaging function can be used to visualize the indentation impression, locate a specific nano-sized feature for testing, and even to deduce the modulus of fibrilar structures from their radius of curvature. [38] AFM measurements are possible not only in ambient and vacuum conditions, but also in liquid, allowing operation under physiologically relevant conditions. [27,39] The accessible forces are limited to a small range governed by the cantilever stiffness, which should be comparable to the stiffness of the contact (dependent on sample modulus and size of contact determined by tip shape and indentation depth), to enable sufficient cantilever deflection along with a significant depth of indentation into the sample.…”

“…Force vs. distance curves can be recorded at a specific point to monitor inter‐ and intramolecular interaction forces and also for characterizing the sample mechanical properties, such as elasticity, viscoelasticity, and adhesion, which can be mapped at high spatial resolution simultaneously with the topographical imaging [3a] . The imaging function can be used to visualize the indentation impression, locate a specific nano‐sized feature for testing, and even to deduce the modulus of fibrilar structures from their radius of curvature [38] . AFM measurements are possible not only in ambient and vacuum conditions, but also in liquid, allowing operation under physiologically relevant conditions [27,39] …”

“…This is less of an issue when the sample is studied in dehydrated state as the drying process immobilizes the sample on the surface. For instance, we adsorbed collagen molecules on a freshly cleaved mica substrate to immobilize them for AFM imaging [38] . In this case, salts in the prep solution must be selectively rinsed away to avoid their interference.…”

Επίδραση Οπτικής Ακτινοβολίας Στην Τοπολογία Κολλαγόνου Με Χρήση Απεικονιστικής Μικροσκοπίας Ατομικής Δύναμης Και Σάρωσης Ηλεκτρονίων

“…Αυτό εξηγήθηκε με το ότι δεν ήταν ολόκληρο το μόριο τεντωμένο κατά την διαδικασία μέτρησης της δύναμης και το γεγονός αυτό μπορεί να σχετιστεί με την απουσία ισοσθενούς δεσίματος μεταξύ του προβολού, του δείγματος και του υποστρώματος στην συγκεκριμένη πειραματική διαδικασία. Επίσης, πρόσφατα, oι Bitler et al χρησιμοποίησαν το AFM σε tapping mode για να διερευνήσουν τις μηχανικές ιδιότητες στο μονομερές κολλαγόνο (τροποκολλαγόνο), στις τριπλές έλικες δηλαδή του κολλαγόνου τύπου Ι[249]. Σε αυτή την εργασία μετρήθηκαν γωνίες και αποστάσεις μεταξύ σταθερών τμημάτων της τριπλής έλικας και αναλύθηκαν ώστε να υπολογιστούν οι μηχανικές ιδιότητες για συγκεκριμένα μεμονωμένα τμήματα της τριπλής έλικας.…”