BIOMATERIALSstorage.googleapis.com/wzukusers/user...Lecture 2: Properties of Materials Sept. 11,...
Transcript of BIOMATERIALSstorage.googleapis.com/wzukusers/user...Lecture 2: Properties of Materials Sept. 11,...
Ming Li, Ph.D.
Professor of Materials Science and Engineering
Central South University
E-mail:[email protected]
Office: Room 308, Chemistry Building, Main Campus
BIOMATERIALS
Lecture 2: Properties of Materials
Sept. 11, 2019
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Last Lecture
• Introduction and overview
• Basic concepts and course requirements
• Covered topics
• History of biomaterials
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Contents
• Nature of matter and materials
• Bulk properties of materials
• Surface properties of materials
• Surface analysis techniques
• Role of water
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1. Nature of Matter and Materials
❑ Biomaterials are materials
❑ The key to understanding matter is to understand
attractive and interactive forces between atoms
What holds those atoms and molecules together to make a
strong nylon fiber or a cell membrane, or a hard, brittle
hydroxyapatite ceramic, or a sheet of gold, or a drop of
water?
In the early 18th century, Isaac Newton was pondering this
issue: “There are therefore Agents in Nature able to make
the Particles of Bodies stick together by very strong
Attractions.”
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1. Nature of Matter and Materials
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• Atom-atom interactions through electron cloud coupling
• Electrostatic interaction
• Hydrogen bond• Metallic bonding
• Covalent bonding
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Molecules
Supramolecules,
assemblies or
organs
Atoms
Hierarchical structure of Materials
Collagen protein
1. Nature of Matter and Materials
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2. Bulk Properties of Materials
❑ Physical properties
density, electrical, magnetic, optical, …
❑ Mechanical properties
Tensile strength, ductility, brittleness,
elasticity, plasticity, toughness, hardness, …
❑ Chemical properties
corrosion resistance, …
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Mechanical Properties of Materials
• elastic and shear modulus (E, G)
• strength (σy), ultimate tensile strength
(σB) and fracture strength (σf)
• ductility (δ)
• fracture toughness (KIC)
• fatigue strength (σNf)
• creep strength (σc)
2. Bulk Properties of Materials
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Load, stress and strain: deformation
𝜎𝑛 =𝐹
𝐴1
𝜀𝑛 =𝐼2 − 𝐼1𝐼1
=∆𝐼
𝐼1
nominal stress:
nominal strain:
true stress:
true strain:
𝜎𝑡 =𝐹
𝐴2
= 𝜎𝑛 𝜀𝑛 + 1
𝜀𝑡 1→2 = 𝑙𝑛𝐼2𝐼1= 𝑙𝑛 𝜀𝑛 + 1
2. Bulk Properties of Materials
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Typical nominal stress vs. nominal strain
2. Bulk Properties of Materials
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nominal stress vs. nominal strain
2. Bulk Properties of Materials
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1. Which is much stiffer?
Same stiffness - same slope
2. Which is stronger?
Red - holds a higher stress
before failure
3. Which is brittle?
Both are brittle because they only
exhibit elastic deformation. Red has
a higher strain-to-failure or total
elongation, but both are brittle strain
materials
2. Bulk Properties of Materials
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1. Which is much stiffer?
Green is much stiffer because it
has a steeper slope, therefore a
higher elastic modulus.
2. Which is stronger?
both have the same strength
because they hold the same
stress at failure.
3. Which is ductile?
Neither, both are brittle (only
elastic deformation)
2. Bulk Properties of Materials
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3. Surface Properties of Materials
Five Points About Surfaces
1. Surfaces have unique reactivity
2. The surface is inevitably different from the bulk
3. The mass of material that makes up the surface zone
is very small
4. Surfaces readily contaminate
5. Surface molecules can exhibit considerable mobility.
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❑ Reversal surface
structure when
transferred from air
to water
❑ Surface reactivity:
• Bonding orbitals of
atoms on the surface
• surface adsorption on
the medical device
surface
3. Surface Properties of Materials
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Surface characteristics
Rough, stepped
or smoothVarious surface
chemistries
Structurally or
compositionally
inhomogeneous
Depth
inhomogeneous
or overlayered
thin film
Highly crystalline or
disordered
Unreconstructed or
reconstructed surface
3. Surface Properties of Materials
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4. Surface Analysis Techniques
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Contact Angle
Contact angles directly measure surface wettability, and indirectly
probe surface energy, roughness, heterogeneity, contamination,
and molecular mobility.
𝛾𝑠𝑣 = 𝛾𝑠𝑙 + 𝛾𝑙𝑣 cos 𝜃
4. Surface Analysis Techniques
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4. Surface Analysis Techniques: Contact Angle
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Also called Electron Spectroscopy for Chemical Analysis (ESCA)
X-ray photoelectron spectroscopy
(XPS)
BE = ℎ𝑣 − KE
Binding
energyEnergy
of X-rays
Kinetic
energy
XPS analyzes to approximately 10 nm and gives information on
elements present, their concentrations and their bonding
environments.
4. Surface Analysis Techniques
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4. Surface Analysis Techniques: XPS
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Survey scan Detailed scan
C1s
4. Surface Analysis Techniques: XPS
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Secondary Ion Mass Spectrometry
(SIMS)
Static SIMS provides qualitative information on the atomic and
molecular composition in the outermost 1–2 nm of surface
with high analytical sensitivity and excellent x,y spatial
resolution.
4. Surface Analysis Techniques
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Other Surface Analysis Techniques
SEM provides a high resolution image of the surface. On
insulating materials, metallic coating is required and the image is
actually of the coating surface, not the underlying material.
• Scanning electron microscopy (SEM):
4. Surface Analysis Techniques
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• Attenuated total reflectance infrared (ATR-IR) spectrometry:
ATR-IR permits detailed molecular analysis of the outermost
1–5 microns of a sample.
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Raman spectroscopy and surface-enhanced Raman
spectroscopy will be introduced later
• Scanning Tunneling Microscopy (STM), Atomic Force
Microscopy (AFM), and the Scanning Probe Microscopies
(SPM).
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5. Role of Water
In the world there is nothing more submissive and weak
than water. Yet for attacking that which is hard and strong
nothing can surpass it.
Lao Tzu
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Five water molecule interactions
1. free water (similar to bulk water) (c)
2. tightly-bound water (more structured
and with limited mobility) (a)
3. intermediate water (b)
5. Role of Water
free water
tightly-
bound
water
intermediate
water
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Water: significance for biomaterials
When a protein or a cell approaches a biomaterial, it interacts
with the surface water first.
Lipid molecules with polar head
groups (white) and hydrophobic tails
(brown), when placed in water,
organize themselves to minimize
surface area contact between the
hydrophobic tail (typically comprised
of methylene units, -CH2-) and water.
This minimization of contact area,
depending on precise conditions,
can lead to micelles, liposomes or
bilayer sheets.
5. Role of Water
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Role of water molecules at the biointerface of
medical polymers
(a) Bio/blood-compatible
polymers.
(b) Non-bio/blood-compatible
polymers.
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Reading materials:
Book: Biomaterials Science: An Introduction to Materials in
Medicine (3rd Edition, 2013)
• Properties of Materials
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Lecture 3: Metals as Biomaterials
On Monday, Sept. 16 , 2019
Next Lecture