  Collagen is a key structural protein in the human body, which undergoes
mineralization during the formation of hard tissues. Earlier studies have
described the mechanical behavior of bone at different scales highlighting
material features across hierarchical structures. Here we present a study that
aims to understand the mechanical properties of mineralized collagen fibrils
upon tensile/compressive transient loads, investigating how the kinetic energy
propagates and it is dissipated at the molecular scale, thus filling a gap of
knowledge in this area. These specific features are the mechanisms that Nature
has developed to passively dissipate stress and prevent structural failures. In
addition to the mechanical properties of the mineralized fibrils, we observe
distinct nanomechanical behaviors for the two regions (i.e., overlap and gap)
of the D-period to highlight the effect of the mineralization. We notice
decreasing trends for both wave speeds and Young s moduli over input velocity
with a marked strengthening effect in the gap region due to the accumulation of
the hydroxyapatite. In contrast, the dissipative behavior is not affected by
either loading conditions or the mineral percentage, showing a stronger
dampening effect upon faster inputs compatible to the bone behavior at the
macroscale. Our results improve the understanding of mineralized collagen
composites unveiling the energy dissipative behavior of such materials. This
impacts, besides the physiology, the design and characterization of new
bioinspired composites for replacement devices (e.g., prostheses for sound
transmission or conduction) and for optimized structures able to bear transient
loads, e.g., impact, fatigue, in structural applications.
