Protein Crystals: Molecular to Continuum Level Models Based on Crystal Plasticity Theory - Multiscale Modeling in Biomechanics and Mechanobiology - page 13

scale, how molecular properties, and range of material scales and hierarchies con-
tribute to the biological function that leads to the unique properties of the specific
protein material at the mesoscale, which spans from nanometers to micrometers
on length scale and nanoseconds to microseconds on timescale, and what role they
play in the physiological and pathological phenomena, remains an active frontier of
research. This type of bottom-up hierarchical approach toward understanding behav-
ior of protein material holds great potential for fundamental contributions to biology
and medicine as well as for the synthesis of self-assembled engineered materials.
The hierarchical structure of protein in the formof self-assembled three-dimensio-
nal molecular crystals enables dissipation of mechanical energy through crystallo-
graphic slip, that is sliding of molecules against each other, and, hence, delays the
catastrophic failure. For example, the staggered arrangement of protein molecules
into fibrils plays a key part in increasing the toughness of various collagen materials
such as bone [ 3 - 5 ]. The plastic deformation may also induce refolding of protein
into a new three-dimensional folded structure. This unfolding may occur locally and
involve only certain domains of the protein that may lead to deformation hotspots.
Protein folding is critical to biological functions, and misfolding lead to diseases
and disorders such as Alzheimer's disease, Parkinson's disease, Type II diabetes,
and several types of cancer [ 6 , 7 ]. Hence, it may be of interest to relate the response
of deformation of distinct domain of the protein to their biological function. This
may also be used to advance our understanding of diseases and potentially lead to
development of new therapeutic drugs. Further, an improved understanding of how
the deformation mechanisms at the multiple scales contributes to the mechanical
stability of the protein material in diseases could bring about new strategies for the
treatment through selective breakdown of foreign material deposits in diseased tis-
sues in case of Alzheimer's disease, Parkinson's disease, and Type II diabetes [ 8 - 11 ].
Also, detailed understanding of mechanical stability, adhesion properties of the pro-
tein crystals due to change in amino acid sequence and solvent effects may help
to contribute to advance the understand the molecular origin of sickle cell anemia,
or Alzheimer's disease. Aside from therapeutics, it may also help in the develop-
ment of biomimetic materials and devices for a range of engineering and medical
applications including regenerative medicine, electronic materials, biotechnology,
nanotechnology, and drug delivery.
However, the mechanical properties and stability of many protein materials under
different conditions has not been extensively studied. A little is known about their
molecular deformation mechanisms, and influence of the nanoscale processes on the
mechanical properties. Therefore, further research is needed to explore the funda-
mental design principles for the development of suchmaterials with optimal function-
ality and stability. Goal is to understand the relationship between fine scale primary
structure and processes and macroscale response of the protein molecular crystals.
In this chapter, we study the bulk mechanical properties of the of protein crys-
tal such that it accounts for the properties of the molecular crystal along with the
phenomena occurring at the lower scale. Like most crystalline solids, the mechan-
ical properties of protein materials are strongly influenced by defects such as dis-
locations through slip-induced plastic deformation [ 12 ], which is captured using