HSC Senior Science – Medical Technology: Bionics
9.3.3
The wide range of movements, continual absorption of shocks and diseases make the skeletal
system vulnerable to damage but new technologies are allowing the replacement of some
damaged structures.
9.3.3.A
Identify the role of the skeletal system particularly in relation to maintaining an upright stance
and protecting vital organs.
The skeleton has FIVE main functions:1)
2)
3)
4)
5)
PROTECTS vital organs such as the brain, heart and the lungs.
SUPPORTS the body. It gives us the body shape we have.
ALLOWS MOVEMENT of the body because muscles are attached to bones.
MAKES blood cells.
STORES important minerals such as calcium.
9.3.3.B
Describe the different types of synovial joints as
–
ball and socket
–
hinge
–
double hinge
–
sliding
–
pivot
and identify their location.
Synovial joint is a joint enclosed in a capsule and lubricated by fluid. Cartilage covers the end
of the bones.
A synovial joint has the following features:•
•
•
•
•
•
•
Joint capsule – surrounds the joint completely.
Joint cavity – surrounded by the joint capsule.
Synovial fluid – is secreted by the synovial membrane.
Bones – come together to form the joint.
Cartilage – covers the bone ends.
Ligaments – connect the bones at the joint.
Tendons – attach muscle to bone.
Types of synovial joints:•
•
Ball and socket joints: One rounded head bone fits into a cup shaped bone.
Movement in almost any direction – side to side, back and forth, rotation. Examples
include hip and shoulder.
Hinge joints: One bone curves out and fits a second bone that curves in. movement in
one plane-backward and forward. Examples include elbow, knee, ankle, and finger
joints.
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HSC Senior Science – Medical Technology: Bionics
•
•
•
Double hinge joints: General term for Condylorid Joints and Saddle Joints.
Movements in two planes that together allow some rotation at the joint. Examples
include wrist and thumb.
Sliding joints: Both bones are slightly curved and bones slide over each other.
Movement in all directions but not rotational. Examples include Metacarpals in wrist
and Vertebrae.
Pivot joints: A bony projection on one bone fits in a ring shaped bony structure on
the other bone. Movement is rotational. Examples include elbow, first and second
cervical vertebrae.
A typical ball and socket joint: Shoulder – the round ball-shaped end of the humerus fits into
the cup-shaped socket formed by the top of the scapula.
9.3.3.C
Describe the role of cartilage and synovial fluid in the operation of joints.
•
•
Synovial Fluid: Lubricates the joint e.g. ball in socket joint in knee.
Cartilage: Connective tissue between bones and joints.
9.3.3.D
Identify the properties of silicone that make it suitable for use in bionics.
The silicone is flexible, elastic, impervious to water, insoluble in water, inert, biocompatible,
permeable to oxygen, absorbs impacts, durable, easy to shape, has a similar density to human
tissue and forms a smooth, low friction surface.
9.3.3.E
Explain why silicone joints would be suitable substitutes for small joints in the fingers and toes
that bear little force.
The areas of the skeleton where silicone would provide a suitable substitute is coating the
bones that form joints in the fingers and toes.
Silicone is a suitable substitute in this area because it can be used to make replacements are as
strong and flexible as natural joints; it’s also biocompatible so will not be rejected, allows the
flow of oxygen, is inert to living fluids and insoluble in them. However, it won’t be suitable
for use in a weight-bearing joint as it doesn’t provide enough support.
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HSC Senior Science – Medical Technology: Bionics
9.3.3.F
Describe the properties that make ultrahigh molecular weight polyethylene (UHMWPE) a
suitable alternative to cartilage surrounding a ball and socket joint in terms of its
–
biocompatability with surrounding tissue
–
low friction
–
durability
Case Study 1
Over a period of 17 years, in a 60 year old patient, the shaft of a hip implant will be exposed
to approximately 34,000,000 impacts, each with a force of 200 kilograms weight if the
person is moving slowly and 600 kilograms weight if running.
Question: Outline the implications of this for hip implants.
Answer: They must be made of a material which is strong enough to withstand these impacts
and a similar density to human tissue, e.g. metal alloys such as those containing titanium.
Case Study 2
One problem with the use of metal alloys in implants is that corrosion by surrounding fluids
may occur, and, with constant friction, small particles wear off and accumulate in surrounding
tissues and the blood. These can cause allergic reactions in some people.
Question: How do bionic engineers address this problem?
Answer: Coat the surface of implants with a smooth, inert substance such as UHMWPE. Also
alloys may be heated at high temperatures and pressure in argon to change their properties
and make them more resistant to wear.
UHMWPE stands for ultra high molecular weight polyethylene. Polyethylene is a polymer
made from thousands of ethylene units joined together.
The part of a joint sometimes replaced with UHMWPE is cartilage surrounding the bones in a
joint.
The table below identifies properties of UHMWPE and reasons for its suitability as a
replacement for cartilage in joints.
Properties of UHMWPE
Biocompatible with human tissues
Reasons for suitability
Won’t be rejected or won’t react with living
tissues.
Won’t cause problems as it will have similar
weight to living structure it replaces.
Lasts a long time so constant replacement
isn’t necessary.
Reduces friction in the joint.
Will maintain its shape.
Stretches with joint movement when
necessary and will help absorb impacts.
Similar density to living tissues
Durable
Low friction
Hard, strong and resists deformity
Highly elastic
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HSC Senior Science – Medical Technology: Bionics
9.3.3.G
Explain why artificial joints have the articulating ends covered in polyethylene.
Polyethylene is smoother so reduces friction between the articulating surfaces. It’s easier to
compress so it helps to absorb the shock of impacts as the person moves. If metal parts rub
together, small particles of metal accumulate in the joint and cause problems.
9.3.3.H
Describe the properties of materials such as ‘superalloy’ that make a ball and stem for the
bone components of a large joint including:
– high strength
– low weight
– good compatibility with body tissue
– inertness
The properties of the ‘superalloy’ used to make a ball and stem for the bone components of a
large joint is high strength, low weight, good compatibility with body tissue, resists corrosion,
doesn’t absorb water and low friction.
The need for these properties in materials used to manufacture components of a replacement
for a large joint such as a hip joint is that high strength is needed to be able to support
weight, but the artificial hip joint must be as light as normal body parts so that the person can
move around. The joint replacement must be biocompatible and chemically unreactive so
that it’s safe and durable in the body. This means that it shouldn’t corrode or absorb water.
The alloys that could be suitable for use in artificial joints is that stainless steel was used in
early joints, but this has been replaced by more corrosion-resistant alloys such as titanium
alloys and cobalt-chromium-molybdenum alloys. Carbon-reinforced polymers are also used.
All of these substances are strong, low weight, inert and they’re compatible with living tissue.
9.3.3.I
Identify that artificial implants can be either cemented or uncemented into place.
The ways in which artificial implants can be fixed in place is cementing implants in place or
using uncemented implants.
9.3.3.J
Describe the properties of the cement that is used in implants and discuss how an uncemented
implant forms a bond with bone.
The properties of the cement that’s used in implants is the cement is a chemical called methyl
methacrylate. This is mixed with a catalyst which makes the cement form long polymer
chains into the surrounding bone tissue. This makes a strong bond between the
replacement part and the surrounding bone.
An uncemented implants forms a bond with bone is that implants which aren’t to be
cemented in place are made with microscopic pores so the body’s own tissue can grow
into and around the implant and hold it in place. Mostly used with younger patients with
strong growth of bone tissue.
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HSC Senior Science – Medical Technology: Bionics
The advantages of using cemented and uncemented implants is that cemented implants
doesn’t tend to last long as uncemented. However, recovery after the operation is much
quicker when using cemented implants.
9.3.3.i
Perform a first-hand investigation to remove calcium compounds from chicken bones to
examine the flexible nature of bones.
Aim: To observe how the flexibility of bone changes as the calcium content is changed.
Hypothesis: I predict that the chicken in white vinegar solution will perhaps become flexible
and soft, while the more calcium it has, the more solid it will become after a couple of
days.
Materials: 2 chicken wing bones, 2x 100ml measuring cylinder, 2x 250ml beaker, 100ml white
vinegar, 100ml plain water, glad wrap and 2x elastic bands.
Method:1) Collect all equipment.
2) Place an 8cm chicken bone in a beaker each.
3) Using a measuring cylinder, fill 100ml of plain water and pour it into a beaker.
4) Repeat Step 3 but fill 100ml of white vinegar and pour it into another beaker.
5) Put on glad wrap on all beakers securing with an elastic band on each. Leave for 2
days and note the changes.
Results:Strength of the bone (description)
Solution
Trial 1
Trial 2
Trial 3
Average
Plain water
Strong
Strong
Strong
Strong
White vinegar
Slightly bendy
Slightly bendy
Slightly bendy
Slightly bendy
Discussion:Positives
Negatives
Improvements
Reliability The results were all
Only 3 trials were
Do more trials.
conducted.
consistent for each
solution used.
Accuracy
Used a measuring
Limited range of
Take more time to
cylinder.
measuring equipment
prepare the
was used.
experiment and use a
variety range of
measuring equipment.
Validity
Dependent variable
The chicken bones
Use identical chicken
bones.
(strength of the bone), weren’t identical.
independent variable
(the solutions used),
controlled variables
(same equipment and
same time left to sit
for a couple of days).
Conclusion: The results show that the hypothesis was correct as the chicken bone placed in
white vinegar solution has become slightly bendy as it lost calcium.
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HSC Senior Science – Medical Technology: Bionics
9.3.3.ii
Perform an investigation to examine the relationship between cartilage, muscle, tendon and
bone in an animal limb.
Example: Chicken wing.
The table shows the properties that a Year 12 student has observed for each of the following
components of a chicken wing.
Part of a chicken wing
Observed properties
Cartilage
Smooth, shiny white covering over the ends of bones at the
joints.
Tendon
Bone
Thin, white, strong strap joining muscle to bone.
Strong, flexible.
Muscle
Soft bundles of tissue parallel to bones.
9.3.3.iii
Perform an investigation to demonstrate the different types of joints and the range of
movements they allow.
During this topic, students examined a human skeleton and compared the types of joints
present and the range of movement allowed by each.
The following table shows some joints they would have observed, identified their type and
compared their movement.
Joint
Shoulder
Elbow
Skull
Fingers
Type of Joint
Ball and socket
Hinge
Fixed
Hinge
Movement
Freer movement in a circular motion.
To-and-fro, like a door hinge, in only one plane.
No movement.
To-and-fro, like a door hinge, in only one plane.
9.3.3.iv
Process secondary information to compare the shock absorbing abilities of different parts of
bones.
Aim: To examine a bone and compare the shock absorbing abilities of different parts of the
bone.
Materials: Large bone, sawn open lengthwise.
Method:1.
2.
Observe the bone provided by your teacher.
Draw a neat, labelled diagram of the bone using a pencil.
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HSC Senior Science – Medical Technology: Bionics
Results:-
Discussion: Cartilage is considered to be the most elastic. The following parts of a bone in
decreasing order of shock absorbing ability are: cartilage, spongy bone, compact bone and
bone marrow.
Conclusion: A bone was examined and the different parts abilities to absorb shocks were
compared.
9.3.3.v
Plan, choose equipment or resources for and perform a first-hand investigation to
demonstrate properties of silicone such as acid resistance, flexibility and imperviousness to
water that make it suitable for use in bionics.
Part 1
Scenario: Some Year 12 students obtained a tube of silicone sealant from the hardware section
of a store. They allowed sections of this to dry and then tested it for acid resistance.
Question: Describe how they could carry out this test and the results they would expect.
Answer: Place equal-sized pieces of silicone in acid and water. Leave for a few days and
observe. They would expect that neither the pieces in water nor the pieces in acid would
show signs of dissolving or pitting. This would show that silicone is insoluble in water and
resistant to acid attack.
Part 2
Scenario: The students then coated a sugar cube with silicone and placed it in water.
Question (a): Identify what they would use as a control.
Answer to question (a): Sugar cube without silicone coating placed in water – use the same
quantities and conditions, e.g. same temperature.
Question (b): Outline the results you would expect after 24 hours and a conclusion you could
draw from these results.
Answer to question (b): The sugar cub without the silicone would dissolve. If you cut the
other cube open, you would find that no water has reached the sugar. The conclusion would
be that silicone is impervious to water.
Part 3
Question: Describe how you tested the flexibility of silicone.
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HSC Senior Science – Medical Technology: Bionics
Answer: Obtain strips of silicone and try to bend it. The silicone bends easily so is flexible.
9.3.3.vi
Analyse secondary information to compare the strength of UHMWPE and ‘superalloy’ metal.
A superalloy is made from a mixture of metals. Superalloys are strong, durable, inert to
chemicals, biocompatible, and relatively lightweight. Examples are cobalt-chromium,
molybdenum alloy and titanium alloys.
The following table compares some mechanical characteristics of THREE types of alloys:
stainless steel, cobalt-chromium alloys and titanium alloys.
Characteristics
Stainless steel alloy
Stiffness
Strength
Corrosion resistance
Biocompatibility
Cobalt-chromium
alloy
Medium
Medium
Medium
Medium
High
Medium
Low
Low
Titanium alloy
Low
High
High
High
The suitability of the THREE types of alloys for use as orthopaedic alloys is that orthopaedic
alloys need to be very strong, not too stiff, strongly resistant to corrosion and biocompatible.
The alloys which best fits this description is the titanium alloy, so it would be the most
suitable.
The following table shows some physical characteristics of substances used in orthopaedic
implants.
Characteristics
Density (g cm-3)
Tensile strength
(mPa)
Elongation @
break (%)
Steel
8.0
515
Chromium/molybdenum/nickel
Titanium
alloy
alloy
8.3
4.5
1311
234
0.93
48
40
20
350
54
UHMWPE
The following graph on the next page compares the density of these THREE substances.
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HSC Senior Science – Medical Technology: Bionics
Density of orthopaedic implants
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Density (g/cm-3)
8
7
6
5
4
3
2
1
0
Steel
Cr/Mo/Ni alloy
Titanium alloy
UHMWPE
Types of implants
The implications, for the production of implants, of the relatively low density of UHMWPE
compared to the alloys is that UHMWPE is very light, lighter than water, and weights much
less than the same quantity of steel. This means the person receiving the implant has less
weight to carry than if other materials were used.
Question: Use data in the table to compare the strength of the substances listed.
Answer: The table only provides information on tensile strength. Of the substances listed in
the table, the Cr/Mo/Ni alloy is the strongest (1311 mPa), then steel (515 mPa) and Ti alloy
(234 mPa), with UHMWPE having the lowest strength (48 mPa).
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