Slide 1

Report
Modern Materials I - Polymers and Biomaterials
• Penn State has a rich tradition in
materials research.
• First school to offer a materials
curriculum in 1960.
• Developed the first
interdisciplinary materials
laboratory in 1962.
• Penn State is ranked #1 in the
US in materials research
Materials You Know
Ceramics (inorganic, nonmetalic solids)
Material: Zeolites for water
softening.
Na+ ions in aluminosilicate
cages are easily exchanged
for Ca2+
Sodium Zeolite A
Polymers
Material: Kevlar for bullet
proof vests.
Hydrogen bonding between
polymer chains produces a
strong material.
Kevlar
Materials You Know
Semiconductors
Material: Light Emitting
Diodes in traffic lights.
A diode is a semiconducor device
that only allows current to flow in one
direction only.
LEDs are diodes
The chemical makeup of the LED
determines the wavelength (color) of
the photon.
Materials You Know
Mr. McGuire: Are you listening?
Ben: Yes I am.
Mr. McGuire: “Plastics.”
Ben: Exactly how do you mean?
Mr. McGuire: There's a great future in plastics. Think
about it. Will you think about it?
Ben: Yes I will.
The Graduate 1967
POLYMERS
Monomer = repeating unit
Polymer = macromolecule made by joining monomers
Polymer Synthesis
Condensation polymers
polymers form by eliminating a small molecule (H2O,
HCl, CO2) from monomers
Examples: Biological Polymers
Proteins
DNA
carbohydrates
Addition polymers
Monomer contains a double bond
Polymers form by addition reaction
Condensation Reactions
2 molecules join by eliminating a small molecule
(such as water)
Esters and Amides are formed by condensation reactions:
carboxylic +
alcohol  ester + water
acid
O
O
+ HOR’ 
+ H2O
C
C
R
OR'
R
OH
carboxylic + amine
acid
O
+ H N H
C
R
OH
R

amide
+ water
O

R
C
NHR'
+ H2O
Structure of Proteins
Secondary structure of
proteins is maintained
by H-bonding
Tertiary structure (protein
folding) is even more
complex. This structure
is important in protein
activity.
DNA
monomer
ADDITION POLYMERS
ethylene
TFE
styrene
Poly(ethylene)
(lunch bags)
Teflon
Poly(styrene)
(styrofoam)
Cross-Linking
Bonds formed between polymer
chains make the polymer stiffer.
• Natural rubber is too soft and chemically
reactive to make a useful material.
• By vulcanizing the rubber (crosslinking the
chains with sulfur) useful materials are made.
S8
heat
isoprene
Natural rubber
(gummy)
Cross-linked rubber
(tough elastomer)
Poly(vinylalcohol): An Addition Polymer
H
H
C=C
vinyl alcohol
H
OH
CH
(
CH
2
catalyst
heat
OH
OH
CH
)
CH x
2
poly(vinyl alcohol)
x = 10 3- 104
linear chain polymer
cross linker: borax (B O 2- )
4 7
Resulting material is viscoelastic
Properties of Polymers
•Polymer chains tend to be flexible and easily entangled or
folded. Crystalline alignment of chains makes a polymer
stiffer.
•Stretching or extruding a polymer can increase
crystallinity.
•Degree of crystallinity determined by chemical structure
and polymer chain length:
low density polyethylene (LDPE) has an average
molecular weight of 104 amu (used in plastic wrap)
high density polyethylene (HDPE) has an average
molecular weight of 106 amu (used in milk cartons).
Biomaterials
Characteristics of Biomaterials
Biomaterials are any materials that have
biomedical applications.
For example, the materials that are used to fill
teeth are biomaterials.
The biomaterials must be biocompatible:
The body’s immune system must not attack the
biomaterial.
Biomaterials
Biomaterials
Characteristics of Biomaterials
Physical requirements:
Biomaterials must be created for a specific
environment.
Artificial heart valves must open and close 70
to 80 times per minute.
Chemical requirements:
Biomaterials must be of medical grade.
Polymers are very important biomaterials: beware
of fillers, stabilizers, etc.
Biomaterials
Polymeric Biomaterials
The degree to which the body tolerates
foreign materials depends on the nature
of the atomic groups in the material.
Naturally occurring biomaterials are
polymers of sugars (polysaccharides),
nucleotides (RNA, DNA) and amino acids
(proteins, enzymes, etc.).
Biomaterials
Types of Polymers
Plastic: materials that can be formed into shapes.
Thermoplastic: materials that can be shaped more than
once. (Used as replacements for blood vessels.)
Thermosetting: materials that can only be shaped once
(Used in dental devices, and orthopedics such as hip
replacements.)
Elastomer: material that is elastic. If moderately deformed,
the elastomer will return to its original shape.
Used as catheters, and for covering leads on implanted
electronics, like pacemakers.
Biomaterials
Examples of Biomaterial Applications
Heart Replacement and Repairs:
A heart that fails completely must be replaced by a donor
organ.
About 60,000 people in the US suffer heart failure and only
2,500 donor hearts are available.
About 250,000 heart valve replacements are made each year.
About 45 % of these valve replacements occur with a
mechanical valve.
Biomaterials
Examples of Biomaterial Applications
The replacement valve must be smooth to prevent
the destruction of blood vessels.
The valve must also be anchored to the inside of
the heart.
Polyethylene terephthalate, called Dacron™, is
used in the artificial heart valves.
Dacron™ is used because tissue will grow through
a polymer mesh.
Biomaterials
Examples of Biomaterial Applications
Vascular grafts:
A vascular graft is the replacement for a piece of
blood vessel.
Dacron™ is used for large arteries.
Polytetrafluoroethylene,
-[(CF2CF2)n-]-, is used for smaller vascular grafts.
Biomaterials
Examples of Biomaterial Applications
Artificial Tissue:
Artificial skin, which is grown in the laboratory, is
used to treat patients with extensive skin loss.
The challenge with growing artificial skin is getting
the cells to align properly.
Therefore a scaffold must be used for the cells.
The most successful scaffold is lactic acid-glycolic
acid copolymer.
Biomaterials
Examples of Biomaterial Applications
Hip Replacements:
About 200,000 hip replacements are performed each year.
A metal ball, a cobalt chromium alloy, is often used in a hip
replacement.
This alloy is attached to a titanium alloy and cemented
using a tough thermoset polymer.
The acetabulum, which accommodates the femur, is lined
with a polyethylene layer.

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