BIOE 3200 - Fall 2015
Hard and Soft Tissue Biomechanics
BIOE 3200 Fall 2015
BIOE 3200 - Fall 2015
Identify tissue structures and components that contribute and/or explain viscoelastic properties for different biologic materials◦ These slides focus on bone◦ In class we will focus on ligament
Learning Objective:
σ= f(ε, ἐ); E = f(ε, ἐ) Strain rate in daily activities
increases as activity becomes more strenuous◦ Slow walking ~ 0.001/sec◦ Brisk walking ~ 0.01/sec
For typical daily activities, E changes by ~15%
◦ Slow running ~ 0.03/sec◦ Fast running ~ 0.06/sec
We can estimate the % change in bone strength for brisk walking versus slow walking
BIOE 3200 - Fall 2015
Cortical bone: strain rate sensitivity
Loaded slower
Loaded faster
BIOE 3200 - Fall 2015
Graph of bone strain over time for adult human cortical bone in tension shows…◦ Bone will continue to deform if
under constant stress for an extended period of time
◦ If loaded for long enough time, cortical bone will break at a stress well below yield and ultimate strengths.
◦ Creep without fracture: permanent deformation (viscoplastic behavior)
Creep: cortical bone continues to deform under constant stress.
BIOE 3200 - Fall 2015
As loading rate increases by 6 orders of magnitude:◦ Modulus (E) increases
by a factor of 2 ◦ Strength (σ) increases
by a factors of 3
Ultimate strength of cortical bone is more sensitive to strain rate than modulus.
BIOE 3200 - Fall 2015
Mechanical Properties of Cortical and Trabecular Bone
BIOE 3200 - Fall 2015
Mechanical properties of trabecular bone depend on apparent density
BIOE 3200 - Fall 2015
Effects of Age on Mechanical Properties of Bone
From Orthopaedic Biomechanics, Bartel, Davy and Keaveny (2006).
BIOE 3200 - Fall 2015
Quick review: Composition and Structure of Bone
Bone tissue:◦ Mineral phase (70% by
weight) Calcium phosphate
(hydroxyapatite) Calcium carbonate
◦ Organic matrix (20% by weight) with cells embedded Type I collagen (90%) Other glycoproteins
and glycosaminoglycans (10%)
◦ Water (10% by weight)
BIOE 3200 - Fall 2015
Question: What are combined effects of
viscoelastic behavior and age on bone?Consider effects of factors such as strain rate, structure, and level of osteoporosis for, say, a 90 year old compared to a 20 year old.
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