Tuning the Elastic Modulus of Hydrated Collagen Fibrils

Abstract

Systematic variation of solution conditions reveals that the elastic modulus (E) of individual collagen fibrils can be varied over a range of 2-200 MPa. Nanoindentation of reconstituted bovine Achilles tendon fibrils by atomic force microscopy (AFM) under different aqueous and ethanol environments was carried out. Titration of monovalent salts up to a concentration of 1 M at pH 7 causes E to increase from 2 to 5 MPa. This stiffening effect is more pronounced at lower pH where, at pH 5, e.g., there is an approximately 7-fold increase in modulus on addition of 1 M KCl. An even larger increase in modulus, up to approximately 200 MPa, can be achieved by using increasing concentrations of ethanol. Taken together, these results indicate that there are a number of intermolecular forces between tropocollagen monomers that govern the elastic response. These include hydration forces and hydrogen bonding, ion pairs, and possibly the hydrophobic effect. Tuning of the relative strengths of these forces allows rational tuning of the elastic modulus of the fibrils.

Finite Element Analysis on Nanomechanical Sensing of Cellular Forces

“…Since the Young's moduli of gelatin and collagen vary ranging from 10 3 to 10 10 Pa depending on molecular weight and structure, they are applicable to coatings with high affinity for cells. [23][24][25] However, it should be noted that signals may be reduced as a result of stress relaxation for very soft materials since the effect of viscoelastic properties is not taken into account in the present simulation. …”

White Paper: Collagen fibrils imaging in air and in liquid

“…In addition, the modulus of the fully hydrated collagen in liquid signifi cantly dropped to only 4-12 MPa, reasonable numbers for liquid collagen samples based on previous reports. 8 The individual fi brils and small segments became hard to visualize compared to those in air. One possible reason is that the FMR cantilever is too stiff for soft collagen fi brils in liquid.…”

Combining nano-physical and computational investigations to understand the nature of “aging” in dermal collagen

“…The variation in fibrillar Young's modulus independent of age followed trends in the literature, which found a significant increase in fibril modulus upon dehydration. 36 In the case of hydrated fibrils, the mean hydrated fibril modulus of the young volunteer was E y-hyd = (1.24±0.09) MPa N fibrils =63 ( Figure 5B) and for the old volunteer E o-hyd = (0.89±0.05) MPa N fibrils =64 ( Figure 5C). In the case of air-dried, dehydrated fibrils, the mean fibril modulus for young volunteers was found to be E y-dehyd = (6.84±0.64) GPa N fibrils =128 ( Figure 5D), and for old volunteers E o-dehyd = (4.03±0.38) GPa N fibrils =126 Figure 5 Nanoindentation of collagen fibrils.…”

“…The measurement of collagen mechanical properties by AFM 34 has been shown to change depending on the level of fibrillar hydration. 35,36 To evaluate the impact of hydration on the mechanical properties of collagen, two sets of measurements were carried out on the same sections: first, in a dehydrated environment, followed by a repeat of the same measurements after 10 minutes rehydration in phosphate-buffered saline (PBS). The variation in fibrillar Young's modulus independent of age followed trends in the literature, which found a significant increase in fibril modulus upon dehydration.…”