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T.E.A.K. - Bioengineering
Mechanics of a Joint Lesson Plan
TEAK
BIOENGINEERING
Biomedical Engineering Kit
Biomechanics of a Joint Activity
1
T.E.A.K. - Bioengineering
Biomechanical Joint
Instructor Preparation Guide:
Page 2
Biomechanics of a Joint
Bioengineering Overview
Bioengineering is the use of engineering principles to tackle challenges in the fields of
biology and medicine. Bioengineering applies engineering design principles to model living
systems.
Biomechanics Overview
Biomechanics is the application of mechanical principles to living organisms.
Mechanical engineers apply their engineering principles and knowledge of physics and
mechanics to simulate living things. Areas of biomechanics that will be covered in this lesson
include prosthesis, robotics, and materials. Prostheses help people with disabilities perform
tasks that they could not do naturally. Advances in robotics are helping doctors perform
surgeries that take a great deal of precision and control. The materials needed for these
applications of biomechanics must be selected based on the many different functions and
environments a system will be used in.
Figure 1 – X-Ray of a Human Elbow
Figure 2 – Robotic Hand with Air Muscles
T.E.A.K. - Bioengineering
Biomechanical Joint
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Mechanical Advantage
Mechanical advantage is a factor by which a
simple machine can multiply an input force to
overcome a resistance. Many human joints
can move in multiple directions, but for this
activity we will be focusing on a simple, one
direction of motion joint similar to the elbow.
In some cases a human can lift more than 50
lbs alone using just the bicep muscle, even
though the mechanical advantage is the least
favorable. The three orders of mechanical
advantages for a lever are shown on the right.
The first order has a mechanical advantage of
one, where the output force equals the input
force. The second order has a mechanical
advantage greater than one, and the third
order has a mechanical advantage less than
one.
Load
Fulcrum
Effort
Effort
Fulcrum
Load
MA = Output Force ÷ Input Force
The students will be able to experiment with
how the mechanical advantage would change
if the bicep muscle were located along
different points of the forearm. They will be
asked to test the different connection points
and determine the pros and cons of each
scenario. The students will also use different
methods to apply a force. This will allow them
to act as engineers who are trying to solve a
problem by maximizing the effectiveness of a
system.
Effort
Resistance
Fulcrum
Air Muscles
Air muscles are operated by compressed air. They are very lightweight because their
main element is a thin membrane, usually made of latex or silicone. This allows them to be
directly connected to the structure they power, which is an advantage when considering the
replacement of a defective muscle. Since the membrane is connected to rigid endpoints, which
T.E.A.K. - Bioengineering
Biomechanical Joint
Page 4
introduces tension concentrations and possible membrane ruptures, muscles may need to be
replaced on a regular basis. Another advantage of air muscles is their inherent compliant
behavior: when a force is exerted on the air muscle, it "gives in" without increasing the force in
the actuation. This is an important feature when the air muscle is used as an actuator in a robot
that interacts with a human or when delicate operations have to be carried out. In air muscles,
the force is not only dependent on air pressure but also on each muscle’s inflation. This is one
of the major disadvantages, because the mathematical model that supports the air muscle
functionality is a non-linear system which makes them more difficult to control precisely.
However, the relationship between force and extension in air muscles mirrors what is seen in
the length-tension relationship in biological muscle systems. Another disadvantage is that gas is
compressible, so an air muscle that uses long tubes must have a control system that can deal
with a delay between the movement control signal and the effective muscle action. An air
muscle actuator system needs electric valves and a compressed air generator, both of which
are neither light nor small.
Resources


www.wikipedia.com
http://www.new-sng.com/giveahand.cfm
Image Resources

Figure 2:
http://en.wikipedia.org/wiki/File:Coude_fp.PNG
Date: February 3rd, 2009

Time: 1:00 PM
Figure 1: http://images.google.com/imgres?imgurl=http://hackedgadgets.com/wpcontent/shadow_robot_company_hand_c5_claw_back.jpg&imgrefurl=http://hackedgadg
ets.com/2007/07/25/tactile-robotic-hand-with-air-muscles/&usg=__ST4nIlh4pIeu-wbURJhDx-N8Aw=&h=1600&w=1200&sz=197&hl=en&start=1&um=1&tbnid=Es5fnVfFMUMKM:&tbnh=150&tbnw=113&prev=/images%3Fq%3DRobotic%2BHand%26um
%3D1%26hl%3Den
Date: February 3rd, 2009
Time: 12:00 PM
T.E.A.K. - Bioengineering
Biomechanical Joint
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Activity Preparation Guide - Biomechanical Joint
Overview
This kit contains discussions and an activity to help students to gain a better
understanding of how engineers solve complex technical problems and design medical
instrumentation. It demonstrates some of the issues faced by engineers who design and
develop mechanical prosthetics, and allows students to work through these issues to construct
and test a simple biomechanical elbow joint.
Learning Objectives
By the end of this lesson, students should be able to:
• Explain what bioengineering is
• Solve an engineering problem
• Weigh pros and cons in order to determine the best design
• Describe what an air muscle is and how it works
Engineering Connection
Engineers work with doctors to create solutions to problems that arise within surgical
and medical environments. Due to advancements in surgical operations and in the field of
robotics in general, the need for robotic devices that can mimic human joint motion has been
increasing over the years. By studying human joint motion, engineers are able to optimize the
range of motion a typical person possesses and then apply that range of motion through a
mechanical system to carry out a function with great precision and accuracy.
Activity Description
Biomechanics of a Joint Activity: 30 Minutes
During this activity, the students will work in teams to figure out the best way to move a
biomechanical elbow. They will learn about mechanical advantage, and then use what they
learned by trying different attachment positions for the muscle. After they have tested all of the
potential solutions and analyzed the data, they will make their decision as to which system
design creates the best solution.
Student Engineering Team Roles
Mechanical Engineer – Responsible for setting up the mechanical joint
Design Engineer – Responsible for modifying the design features
Test Engineer – Responsible for making the mechanical joint move
Data Engineer – Responsible for collecting and recording data
Extension Activity:
Air Muscle Activity: 10 Minutes
During this activity, the students will learn about the parts that make up an air muscle.
They will then get to see an air muscle power the mechanical joint from the above activity. The
students will use what they learned and observed about the air muscle to compare and contrast
it with a real human muscle.
T.E.A.K. - Bioengineering
Biomechanical Joint
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New York State Learning Standards
New York State Health Learning Standards
a.) Standard 3: Resource Management
- Students: Distinguish between invalid and valid health information, products,
and services.
- Students: Analyze how the media and technology influence the selection of
health information, products, and services.
New York State Technology Learning Standards
a.) Standard 1: Engineering Design
-Students will use mathematical analysis, scientific inquiry, and engineering
design, as appropriate, to pose questions, seek answers and develop solutions.
- Students:
· Activate devices
· Recognize why an object or choice is not working properly
· Recognize how a defective simple object or device might be fixed
· Under supervision, manipulate components of a simple, malfunctioning
device to improve its performance
· Design a structure or environment (e.g., a neighborhood) using
modeling materials such as LEGO Duplo blocks, model vehicles, model
structures, etc.)
b.) Standard 5: Technological Systems
- Students will apply technological knowledge and skills to design, construct, use,
and evaluate products and systems to satisfy human and environmental needs.
- Students:
· Identify and operate familiar systems
· Assemble simple systems
New York State Science Learning Standards
a.) Intermediate Standard 1: Analysis, Inquiry, and Design.
- T1.1: Identify needs and opportunities for technical solutions to from an
investigation of situations of general or social interest.
- T1.1a: Identify a scientific or human need that is subject to a technological
solution which applies scientific principles.
- T1.3a: Identify alternative solutions base on the constraints of the design.
b.) Intermediate Standard 6: Interconnectedness
- 1.4: Describe how the output of one part of a system can become the input to
other parts.
- 4.1: Describe how feedback mechanisms are use in both designed and natural
systems to keep changes within desired limits.
- 6.1: Determine the criteria and constraints and make trade-offs to determine the
best decision.
Resources
1.) http://www.emsc.nysed.gov/ciai/cores.htm
2.) http://accelerateu.org/standards/index.cfm?page=Explore
3.) http://www.albanyinstitute.org/Education/standards.pdf
Note: Many of these resources were used in assisting the creation of the following Lesson Plan and we want to thank
and reference them for their valuable instruction.
T.E.A.K. - Bioengineering
Biomechanical Joint
Biomechanics of a Joint
Duration
50-55 Minutes
Concepts covered:
Bioengineering
Biomechanics
Mechanical Advantage
Medical Applications
Page 7
T.E.A.K. - Bioengineering
Biomechanical Joint
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Bioengineering Discussion: 5 Minutes
Background Information:
Bioengineering is the application of engineering principles to address challenges
in the fields of biology and medicine. Bioengineering is the application of the principles
of engineering design to the full spectrum of living systems.
Group Discussion:
Bioengineering Background
(Pose the following questions to the group and let the discussion flow naturally… try to
give positive feedback to each child that contributes to the conversation)
What do you think bio (biology) means?



The study of life and a branch of the natural sciences that studies living
organisms and how they interact with each other and their environment.
The study of the environment.
The study of living organisms and living systems.
What do you think engineering is? What do you think it means to be an engineer?

A technical profession that applies skills in:
o Math
o Science
o Technology
o Materials
o Anatomy
o Environmental Studies
Discuss with the students what bioengineering is and the broad scope of areas that
bioengineering includes. For this discussion, provide students with examples of
bioengineered products and applications.


Bioengineering applies engineering principles in the fields of medicine, biology,
robotics, and any other living system.
Examples of products that have been bioengineered are:
o Prosthetic Joints
o Artificial Limbs
o Hearing Aids
o Artificial Organs – Heart, Lungs, Etc.
o Dialysis Machines.
o Contact Lenses.
T.E.A.K. - Bioengineering
Biomechanical Joint
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Biomechanics of a Joint Activity Introduction: 10 Minutes
Background Information:
This kit contains discussions and an activity to help students to gain a
better understanding of how engineers solve complex technical problems and design
medical instrumentation. It demonstrates some of the issues faced by engineers who
design and develop mechanical prosthetics, and allows students work through these
issues to construct and test a simple biomechanical elbow joint.
Simplified Definitions:

Mechanical Advantage – A factor by which a mechanism multiplies the force.
The force you get out divided by the force you put in.

Lever – A simple machine used to lift weight.

Biomechanics – Taking knowledge of mechanical systems and applying them to
living organisms. EX: Prosthetic joint, robotics
Group Discussion:
Mechanical Elbow
(Pose the following questions to the group and let the discussion flow naturally…
try to give positive feedback to each child that contributes to the conversation)
Can you think of an example of a lever?
(There may be more correct answers than the ones listed.)
 Seesaw
 Wheel barrow
 Wrench
 Bicycle Hand Brake
 Your arm!
Do you think these levers make it harder or easier to do work?
 Easier, because of mechanical advantage.
Discuss the 3 orders of levers and draw diagrams on the board.
 First Order Lever
o The fulcrum is between the effort and the load. Mechanical advantage = 1
o EX: See saw, scissors
 Second Order Lever
o The load is between the fulcrum and the effort. MA is greater than 1
o EX: Wheelbarrow
 Third Order Lever
o The effort is between the fulcrum and the load. MA is less than 1
o EX: Shovel, your arm!
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Biomechanical Joint
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If someone needed a mechanical limb (such as an arm), what kind of simple
machine should they use?
 A lever
Why would someone need a mechanical limb?
 To replace a lost or missing limb.
 To perform a task that a person cannot do on their own.
 Increase strength or motion of a human limb.
What do engineers need to know to create a mechanical body part?
(There may be more correct answers than the ones listed.)
 Range of motion
 Strength
 Size
 Purpose
Biomechanical Joint Activity – 30 Minutes
Learning Objectives
By the end of this exercise, students should be able to:
1. Work as a team to build an apparatus.
2. Follow a procedure to test predictions.
3. Analyze data that has been collected.
Materials (per group)
-
1 Activity Worksheet
1 Mechanical Joint with Quick Release Pin
1 Clamp
1 Clip
1 Ruler
1 Protractor
1 Bag of Team Roles
Roles
ME
Mechanical Engineer – Responsible for setting up the mechanical joint with the
assistance of other team members.
DE
Design Engineer – Responsible for modifying the design features with the
assistance of other team members.
TE
Test Engineer – Responsible for making the mechanical joint move with the
assistance of other team members.
DataE Data Engineer – Responsible for collecting and recording data with the
assistance of other team members.
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Biomechanical Joint
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Procedure
1. Have the students get into 5 groups.
2. Draw the First, Second, and Third Order levers from the mechanical advantage
schematic on the board and explain what they mean.
(Should have already been done!!)
3. Hand out one activity worksheet to each group.
4. Instruct students to discuss the first three questions with their group and come up
with answers.
5. Discuss the questions/answers with the class. Tell them that they will be able to
test their hypothesis (what they think will happen) with the mechanical joint
activity.
6. Hand out the joint activity kit.
**Make sure that the students understand that the activity will be done as a group. Each
step of the activity will start with verbal instructions and then the students will get to do
that part. The instructor should walk between groups to check that everyone
understands the instructions and that they are doing the activity correctly. After each
step is completed, students should raise their hands to let the instructor know that their
group is ready to move on. Demos may be helpful for the assembly and first test.
ALL
Take the ALL parts out of the plastic container, and put the container on the floor.
Open the bag of team roles. Place the role tags upside down on the table.
Everyone pick a tag and read your team role and the role description.
ME
Attach the clamp to the side of a desk/table. To attach the mechanical arm to the
clamp, take the end with the black pulley wheel and put it through the clamp from
the bottom (so that the wheel ends up on the top with the arm/joint hanging
below it). Tighten the clamp onto the arm so that it holds it securely.
DE
Take the quick release pin and put it through the hole in position A (the hole
closest to the hinge) on the mechanical arm. Make sure that you put the pin
through from the top, so that the lanyard will be in the right position. Lay the
lanyard over the pulley.
TE
Make sure that the lanyard is pulled taught, but that the arm is still hanging
vertically. Attach the clip to the lanyard on the side of the lanyard that you are
pulling, and make sure that it starts off touching the pulley.
ME
Take the protractor out. Hold the protractor next to the arm so that the flat side is
parallel to the arm. When the TE starts to pull the arm, you will need to watch the
protractor and stop the TE when the arm is at a 90 angle.
TE
Start to pull the string and raise the arm until the ME tells you to stop.
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Biomechanical Joint
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DataE Use the ruler to measure from the black pulley to the clip on the lanyard. Write
down the length of the lanyard that was used in the appropriate box.
ALL
Repeat the procedure for the other 3 positions.
TE
Take out the hanging weight. Hang it from the hook on the end of the arm.
DE
Move the quick release pin back to position A.
ALL
Take turns moving the arm from its resting position (hanging vertically) to the
farthest position it will move. Think about how hard it is to lift the arm/weight.
DE
Move the quick release pin to each of the other 3 positions. (Leave the weight in
the same spot.)
ALL
Take turns lifting the weight with the lanyard in each of the other 3 positions.
Discuss how hard it was to lift the arm/weight in each position. Rank the positions
on how easy/hard it was to lift the arm and weight assembly. Write the word hard
in the box for the position that was the hardest to lift, and the word easy in the
box for the position that was the easiest to lift. Draw an arrow from easy to hard.
Then have them pick 2 positions and fill out the pros and cons of each muscle
setup in the charts provided. They will use the tables to help them pick out the
mechanical joint design they think is best.
DataE Write down the hardest and easiest lifting positions that your group decided on.
ME
Take the mechanical arm out of the clamp and remove the clamp from the
desk/table. Put all parts back into the container.
ALL
Answer the questions on the bottom of the activity handout.
**While the students are working on the concluding questions, collect all the activity kits
and check them for parts.
End Biomechanical Joint Activity
T.E.A.K. - Bioengineering
Biomechanical Joint
Lesson Extension Activity
Duration
20-25 Minutes
Concepts Covered:
Air Muscles
Page 13
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Biomechanical Joint
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Air Muscles Introduction: 5 Minutes
Background Information:
Air muscles are operated by compressed air. They are very lightweight because their
main element is a thin membrane, usually made of latex or silicone. This allows them to
be directly connected to the structure they power.
Simplified Definition:

Air Muscle – A man-made “muscle” that uses air pumped into tubing to mimic
the actions of human muscles. It works like a Chinese finger trap.
Group Discussion: 5 Minutes
(Pose the following questions to the group and let the discussion flow naturally…
try to give positive feedback to each child that contributes to the conversation)
What muscles could air muscles replace?

Any muscle
What are some things that could go wrong with an air muscle?




Hose comes unattached
Clamp loosens
Hook pulls out
Air connections breaks
Would you want to have a human bicep muscle or an air muscle bicep? Why?


Whatever they think will be correct.
Some possible answers:
o Human biceps can lift more than an air muscle
o Human biceps don’t need an air source to make them move
o Human biceps don’t have parts that need replacement
o Human biceps can fix themselves
T.E.A.K. - Bioengineering
Biomechanical Joint
Page 15
Air Muscle Activity – 10 Minutes
Learning Objectives
By the end of this exercise, students should be able to:
 Describe what an air muscle is and how it works
 Determine similarities/differences between an air muscle and a human muscle
Materials
-
1 Mechanical Joint with Parts
1 Clamp
1 Ruler
1 Protractor
1 Air Muscle
Procedure
1. Borrow the clamp/mechanical joint setup from one group’s activity kit and mount
it in a central location.
2. Make sure that the air muscle is securely fastened to the bike pump connection.
Don’t over-tighten the connection!!!
3. Attach the air muscle to the mechanical joint in the A position using a quick
release pin. The eye bolt on the air muscle should attach to the pin.
4. Have all the students gather around so that they can see, but make sure that
they aren’t too close.
5. Inflate the air muscle by pumping the bike pump. Have the students pay attention
to how much the air muscle inflates, how much the arm moves, and how much
effort it took to pump the air.
6. Repeat step 5 as needed.
End Air Muscle Activity
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Biomechanical Joint
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Concluding Discussion: 5 Minutes
Did the air muscle move as far as you expected it to?

Whatever they think will be correct.
What part(s) of the air muscle could be changed to allow it to move farther?


Longer tube/mesh
Thicker tube
Do you think an air muscle is a good replacement for a human muscle?
Why or why not?



Whatever they think will be correct.
Some possible yes reasons
o Allows for the same movements as a human muscle
o Parts can be replaced if they break
o Makes robotic arms more realistic
Some possible no reasons
o More bulky than human muscles
o Parts can break
Mechanical Joint Activity Handout
Warm-up Questions (Circle one answer for each question)
Which type of lever will require the most muscle force to lift the load?
1st Order Lever
2nd Order Lever
3rd Order Lever
Which type of lever will require the least muscle force to lift the load?
1st Order Lever
2nd Order Lever
3rd Order Lever
Data Tables
Position
A
B
C
D
Length of Rope Used
(inches)
Easy to hard
Position _____
Pros
Position _____
Cons
Pros
Follow-up Questions
Which position is most like a human arm?
Which position do you think is the best for a mechanical joint? Why?
HINT: Use the pros and cons from the tables from above.
What problems would exist if your bicep were actually attached at your wrist?
Cons
Mechanical Joint Activity Handout (Answers)
Use the three types of levers drawn on the board to answer the questions.
Which type of lever will require the most muscle force to lift the load?
1st Order Lever
2nd Order Lever
3rd Order Lever
Which type of lever will require the least muscle force to lift the load?
1st Order Lever
2nd Order Lever
3rd Order Lever
Data Tables
Position
A
B
C
D
Length of Rope
Used (inches)
~3
~4.5
~6
~7.5
Position A
Position D
Pros
Cons
Pros
Cons
Muscle close to the
upper arm
Hard to lift heavy
weight
Can lift heavier weights
Muscle is attached at the
wrist
Muscle doesn’t get in
the way
Smaller range of
motion
Forearm has better range
of motion
Muscle gets in the way
…
…
…
…
** Can choose any 2 positions
Follow-up Questions
Which position is most like a human arm?
 Position A
Which position do you think is the best for a mechanical joint? Why?
HINT: Use the pros and cons from the tables from above.
 Can be whatever they think is right
 Make sure they have explained using pros vs. cons
What problems would exist if your bicep were actually attached at your wrist?
 The muscle would get in the way of your everyday life
 Your arm would not be able to travel as far