Exploring Engineering
Chapter 14
Bioengineering
Topics to be Covered
 What is bioengineering?
Impact damage to the human body
 Fracture criterion
 Injury potential
 Gadd Severity Impact Parameter
 Examples
What is Bioengineering?
Bioengineering applies engineering
methods and techniques to problems in
biology and medicine.
Biology
Tissue Engineering
Neural Implants
DNA Expression Arrays
Medicine
Engineering
Pumps
Pacemakers
Prosthetics
Neural Engineering


Neural Engineers use modeling and analysis to
understand and control the nervous system.
Advances in neuroscience and microfabrication
have opened the doors to exciting applications
in neuroprosthetics, biosensors and hybrid
biocomputers.
Fluorescent Stained Myocyte
Microfabrication Surface
Cell and Tissue Engineering


Cell and Tissue Engineering allows one to repair or
replace the function of natural tissue with
bioengineered substitutes.
Principles of engineering, chemistry, and biology are
combined to create tissue substitutes from living cells
and synthetic materials.
New Companies: Advanced Tissue
Sciences, Inc. Organogenesis
Tissue Engineered Skin
Bioinformatics & Genomics

Bioinformatics combines computer science with
biomedicine to develop tools for identifying and
understanding the genetic blueprint of life.

Genome Annotation (DNA sequence identification of
genes)
 Discover genetic basis for disease (cancer, diabetes)
 Develop new diagnostic devices (cDNA chip)
cDNA Array
Future of Bioengineering

Human Genome Sequence
 Heart Cell Regeneration
 Pre-implantation Genetic Diagnosis
 Bioinformatics
 Bio-Molecular Modeling
 Genetic Engineering of Animals
 Genetic Engineering of Proteins, Drugs
 Cell and Tissue Engineering
 Neural Engineering
 Biomaterials
Accelerations That Kill

High speed doesn't itself produce harmful injuries,
but high acceleration or deceleration can be fatal.
The common term "g" is a measure of acceleration.
Everything is said to feel normal at 1 g, twice as
heavy at 2g, and weightless at 0 g.

One standard for sudden impact acceleration on a
human that would cause severe injury or death is
about 65 g's.

Military aircraft are so fast and nimble that evasive
maneuvers can add 9 times the acceleration of
gravity (or 9g's) to the weight of a pilot's body. It can
cause fatigue, blackout, or death as gravity drives
blood and oxygen from the brain, lungs, and heart.
Planes, Cars and Coasters



Aircraft, car crashes, and roller coaster rides are
common examples of high g situations. Roller
coasters undergo a maximum of 3 to 4 g's for brief
periods. Military pilots may be exposed to 9 g's for
short periods of time.
An acceleration of 4 to 6 g's is held for more than a
few seconds could result in blackout or death. The
car crash of Princess Diana of Wales in 1997
produced between 70 - 100 g's.
In 1985 Sammy Miller set the fastest 1/4 mile time to
date of 3.58 seconds at 386 mph in his Vanishing
Point rocket car. His average acceleration over the
quarter-mile was 4.6 g’s.
Car Racing

The British Ultima GTR accelerates from 0 to 60. mph
in 2.6 secs, and from 0 to 100. mph in 5.30 secs.
 The average acceleration is aavg.= ΔV/Δt so,
ΔV = [60 - 0 miles/hr](5280 ft/mile)(1 hr/3600 s) = 88 ft/s
So aavg:0-60 = (88 ft/s)/(2.6 s) = 33.8 ft/s2
and since g = 32.2 ft/s2 in the English unit system,
aavg:0-60 = 33.8/32.2 = 1.05 g, and
aavg:0-100 = 147/5.30 = 27.7 ÷ 32.2 = 0.86 g
 This car also brakes from 100. to 0 mph in 3.60
seconds, which produces a deceleration (negative
acceleration) of
aavg:0-100 = (0 – 147)/3.60 = - 40.7 ÷ 32.2 = -1.26 g
Rocket Cars


Phenomenal times of 0-60 mph in 0.2 seconds and 0100 mph in 0.3 seconds are normal for rocket cars.
They produce accelerations of 14 - 15 g’s.
Sammy Miller’s rocket car had around 25,000 hp and
did 0-60 in 0.16 seconds (17 g’s). He had to lie
almost flat on his back in the car; otherwise, the
incredible acceleration would have caused him to
black out. He said that every time he raced the car
his nose and ears bled.
The Fastest Ever

The fastest ever quarter mile was run by Kitty O’Neil
in the ‘The Conklin Comet’ at El Mirage in California
in 1977. She achieved 412 mph with an elapsed time
of 3.235 secs. The car is a hydrogen peroxide fuelled
rocket dragster with a engine producing 7,500lbs of
thrust.
Danica Patrick
Makes IndyCar History

Danica Patrick became the first female winner
in IndyCar history April 20, 2008, taking the
Indy Japan 300.

Patrick finished 5.8594 seconds ahead of polesitter Helio Castroneves on the 1.5-mile Twin
Ring Motegi oval after leader Scott Dixon pitted
with five laps left and Dan Wheldon and Tony
Kanaan came in a lap later.

The 26-year-old Patrick won in her 50th career
IndyCar start, taking the lead from Castroneves
on the 198th lap in the 200-lap race.

At the 2005 Indy 500, she nearly won the pole
and became the first female driver to lead the
race en route to a fourth-place finish. It was the
best finish by a woman at Indy, and helped her
take rookie of the year honors.
Forensic Engineering

Forensic engineering is the investigation of materials, products,
structures or components that fail or do not operate/function as
intended, causing personal injury or damage to property.
 The consequences of failure are dealt by the law of product liability.
The subject is applied most commonly in civil law cases, although may
be of use in criminal law cases.
 Generally the purpose of a forensic engineering investigation is to
locate cause or causes of failure with a view to improve performance or
life of a component, or to assist a court in determining the facts of an
accident.
 It can also involve investigation of intellectual property claims,
especially patents.
The Human Nervous System
Brain Injuries Due
to Whiplash
Stress-Speed-StoppingDistance-Area (SSSA) Criterion



Suppose a body of mass m is subjected to a
deceleration of ‘a’. Then the force experienced by the
body = mV2/2DS. (Stopping distance = DS)
Now suppose that this force is experienced as the
contact of an area A of the head or body with a surface.
Then the stress can be calculated as follows.
Stress,  = mv2/2ADS
This useful relationship may be called the stressspeed-stopping-distance-area (SSSA) criterion. It
states that, technically, it’s not enough to say that
“speed kills”. What kills is the combination of high
speeds, short stopping distances, and small contact
areas!
v=
Note: a = v/t then F = ma = mv/t. Since
the area under the V – t plot is Ds, then
Ds = ½ Vt, and t = 2Ds/V and  F =
mV2/2Ds
Area = Ds
V

0
ts
t
t
How Many g’s?

The human body should not be subjected to more
than 30. g’s. Above 30. g’s the damaging effects of
acceleration or deceleration on the human body can
range from loss of consciousness to ruptured blood
vessels to concussion to the breaking of the bone
and to trauma or death.

The 30 g criterion serves as an initial rule of thumb
for the design of safety devices.

However, very high decelerations, measured in
hundreds of g’s, can be survived - if the exposure is
short enough. Deceleration at moderate g levels, on
the other hand, can prove fatal if the exposure is long
enough.
Injury Criterion
An unconscious 8 weeks old infant was admitted
to a hospital and found to have bilateral, subdural
and retinal hemorrhages. He died the following
day.
The parents explanation for the infant’s injuries
was that the infant had been in a baby-rocker and
that they had seen the rocker being rocked
vigorously by their 14 months old daughter on two
separate occasions.
A biomechanical analysis of the infant in the babyrocker was used to estimate the maximum forces
generated. These forces were then compared
with those necessary to cause the subdural
hemorrhage.
Conclusions

An instrumented infant dummy placed in a child
rocker was subjected to a series of rocking impulses,
applied by both a young child and an adult. A range
of physical parameters was recorded and calculated.

Head injury models were derived from dummy
simulations based on animal experiments and
mathematical modeling, accident investigation and
reconstruction, adult volunteer and cadaver studies.

The experiments do not support the account offered
by the parents that the injuries suffered by the infant
were sustained in the baby-rocker in the manner
described.
Mathematical Model:
The Gadd Severity Index (GSI)
The Gadd Severity Index was developed with data from tests on
human cadavers, and supported with real accident data.
GSI = a2.5tS
where tS is the duration of the impact in seconds, and a is the
deceleration in g’s. A human head can sustain values as high
as 1,000 without serious injury as long as the peak value does
not last for more than 10 or 15 milliseconds. For comparison, a
hammer hitting a nail into wood gives a value of about 3,000, a
baseball hitting a concrete wall is about 10,000, and a hammer
hitting a concrete wall is about 3,600,000.
Average acceleration, g
1,000
Experimental
Points
300
GSI is the
equation of
this line
100
30
10
3
1
.001
.01
.1
1
10
Duration, s
100
1000
Text Example 1
A car traveling at 30. miles per hour runs into a sturdy stone wall.
Assume the car is a totally rigid body that neither compresses nor
crumples during the collision. The wall “gives” a distance of DS = 0.03
meters in the direction of the collision as the car is being brought to a
stop. Assuming constant deceleration, calculate the deceleration.
t=0
V = 30 mph 0.5 m
0.
5
m
V = 0 mph
t ==t s
0.47 m
After impact, seconds later
Just before impact
v=
V
=13.4 m/s
Speed
Initial state–
Area = Stopping distance
DS = 0 .03 m
0
tss
t
Text Example 1 Continued
Need: Deceleration = ____ m/s2
Know - How: First sketch the situation to clarify what is occurring
at the impact. Then use speed - time graph to model the collision.
The slope of speed - time graph is acceleration.
Solve: We first need to calculate the stopping time, ts , to decelerate
from 30. mph (13.4 m/s) to 0. From Chapter 10, if deceleration is
constant, we know that distance equals the area under the V – t
graph or DS = 0.03 [m]
= ½  13.4[m/s]  ts [s] where ts is the stopping time.
Therefore ts = 0.06/13.4 = 0.0045 s.
Also the deceleration rate is the slope od the V-t graph,
V/t = (0 - 13.4)/ (0.0045 - 0) = -2980 = -3,000 m/s2
(about 306 g’s)
Text Example 2

The car and its belted driver of Example 1 suffers the
same constant deceleration of 306 g (or ~3,000
m/s2). What is the force he or she experiences
during the collision if their mass is 75 kg? Assume
the car is a totally rigid body that neither compresses
nor crumples during the collision.
DS
30 mph
Text Example 2 Continued
Need: Force stopping 75 kg driver on sudden impact in SI.
Force = _____ N
Know: The driver’s weight is 75 [kg]  9.8 [m/s2] = 735 N
and deceleration rate is 306 g.
How: F = ma = mg  a/g
Solve: F = 735  306 = 2.24  105 N (or ~50,000 lbf!).
Even though the driver is belted in position, this is a very
substantial force. What are the effects on human tissue of
such large forces?
Structure of the Body’s Long Bones
Dense outer bone
layer
Femur
Marrow
channel
Sectional
view
Compact and
spongy bone
(made up of
osteoblasts,
collagen, and
calcium phosphate)
Bone Mechanical Properties
125
 MPa
100
Longitudinal
75
Transverse
50
25
0
5
10
15 20
e  10-3
25
Seat Belts & Crumple Zones
30 mph
30 mph
A
30
30mph
mph
30 mph
B
V=0
v= 0
C
The purpose of a seat belt is to attach the driver to a rigid
internal passenger shell while the rest of the car shortens
by crumpling. A seat belt is most effective when a car
significantly crumples during a collision.
Crumple Zone
The crumple zone is the area of a
car designed to absorb energy
upon impact. Engineers
deliberately place weak spots in a
car's structure to enable the metal
work to collapse in a controlled
manner to direct energy from the
impact from the passenger area,
and channeled to the floor,
bulkhead, roof, or hood. Energy
from the impact is converted into
heat and sound (loud noise).
Crumple Zone
Crash bunny
Late night!
Exercise
A car is traveling 30. mph hits a wall. The car
has a crumple zone of zero and the passenger is
not wearing a seat belt. The passenger’s head
hits the windshield, and is stopped in the
distance of 0.10 m. The area of contact of the
head and the windshield is 0.010 m2.
1) Provide a graph of V - t and F - t of the skull
with the windshield.
2) If the compressive strength of bone is 3.0  106
N/m2, will the collision break the skull?
Exercise 1 Solution

Need: V - t graph of the collision and F = _____ N
 Know: v = 30. mph = 13.4 m/s; Ds = 0.10 m and
A (contact) = 0.010 m2. Skull mass = 5.0 kg.
 How: V-t graph area relates to Ds and hence the time of impact.
This gives the deceleration and thus the acting force.
 Solve: Ds = ½ V0 × ts; hence ts = 2 × 0.10/13.4 [m][s/m] = 0.0149 s.
(Constant) deceleration rate = V0/ts = 13.4/0.0149 [m/s][1/s] = 899 m/s2.
Force on head at contact is m × a = 5.0 × 899 [kg][m/s2] = 4490
= 4,500 N and lasting 0.015 s.
13.4m/s
V
0
Force, N
Ds= ½ V0 × ts
4,500
= 0.10 m
ts t
0
t, s
ts = .015 s
Exercise 2 Solution

Need: Max allowable stress on skull exceeded = _____ (yes/no)

Know: Contact area = 0.010 m2 and force is 4,500 N.
Compressive Strength of head bone = 3.0 × 106 N/m2.

How: Compute force per unit area (which is the same as the
energy per unit volume) of collision, and compare to
compressive strength of head bone.

Solve: Force = 4,500 N, so Force/Area = stress = 4,500 /0.01
[N][1/m2] = 4.5 × 105 N/m2 (which is less than the compressive
strength of bone, so no, the skull will not be broken, but other
very serious injuries may still occur within the head or neck).
Another Exercise
A rear facing child safety seat holds a child of mass 12 kg rigidly
within the interior of a car. The area of contact between the seat and
the child is 0.10 m2. The car undergoes a 30. mph collision. The car’s
crumple zone causes the distance traveled by the rigid interior to be 1.0
m. Give the stress experienced by the child’s body in terms of a
fraction of the breaking strength of bone assuming an infant’s bone
breaks at a stress of 10. MN/m2.
Child
Exercise Solution




Need: Stress experienced by child’s body = ____ ÷ breaking stress
of bone.
Know: Impact at 30. mph = 13.4 m/s; deceleration distance = 1.0 m and
contact area = 0.10 m2. Breaking stress in infant’s bone = 10. MN/m2.
How: Find duration of accident tf from V – t diagram. Find deceleration
from V0 and tf. Find force from F = ma and find stress from force/area.
Compare to breaking stress of 10. MN/m2.
Solve: From V – t diagram, 1.0 m = ½ ×13.4 × tf [m/s][s]
so that tf = 2.0/13.4 = 0.15 s.
Hence deceleration rate for infant = 13.4/0.15 = 90. m/s2.
Force on baby = 12. × 90. [kg][ m/s2] = 1.08 × 103 N.
Stress = 1.08 × 103/0.10 = 1.08 × 104 N/m2.
As fraction of breaking stress, 1.08 × 104/ 10. × 106 = 1.08 × 10-3
Bones should hold and infant should be safe.
One More Exercise
A car strikes a wall traveling 30. mph. The driver’s cervical spine
(basically the neck) first stretches forward relative to the rest of the body by
0.01 m, and then recoils backward by 0.02 m, as shown below. Assume the
spine can be modeled by a material of a modulus E = 10. GPa and a
strength of 1.00  102 MPa. Will the maximum stress on the cervical spine
during this “whiplash” portion of the accident exceed the strength of the
spine? The length of the cervical spine is 0.15 m.
V = 30. mph
T1
Before stopping
V=0
V < 30. mph
T2
While stopping
T3
After stopping
Exercise Solution

Need: Stress on cervical spine = _____ (greater than/equal to/less
than) tensile strength of spine?

Know: V0 = 30. mph = 13.4 m/s; cervical spine length = 0.15 m.
During stopping period, T2, spine stretches forward 0.01 m and on
stopping at T3 backwards by 0.02 m. Elastic constants are E = 10. GPa
and “transverse” strength of 1.00 × 102 MPa for this failure mode.

How: Compute stress on spine from its strain. Compare to its strength.

Solve: Maximum stretch of cervical spine = 0.02 m.
Maximum strain of spine = 0.02/0.15 [m][1/m] = 0.133
Stress on cervical spine = modulus × strain = 1010 × 0.133 = 1.3 × 109
N/m2.
Compare maximum stress on spine to tensile strength of spine:
1.3 × 109 N/m2 (max stress) > 108 N/m2 (strength)
Stress on cervical spine is greater than its tensile strength.
Summary

Bioengineering is name of a group of applied
sciences applied to the human body
 A subset of these measured the body’s
response to sudden accelerations and
particularly to sudden decelerations
 Under accident conditions decelerations of
hundreds of gs can be survived for short times
and is described by the Gadd Severity Index.
 Bone can be modeled the same way as other
materials, i.e., stress, strain and moduli
 Crush zones + passenger restraints protect
people because the stopping distance educes
other wise fatal decelerations.