Công nghệ vật liệu trong y sinh học biom aterials

Biomaterials

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Lecture

Lecturer: TA THI PHUONG HOA

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Teaching Assistant: DINH THI NHUNG

Advanced Program Biomedical Engineering – HUST, Vietnam

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About Materials

“Understanding the history of materials
means understanding the history of
mankind and civilization”
civilization”

“Who can master the materials, can
master the future”
future”

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Part 1: Material Science & Engineering
Chap. 1. Properties of materials
- The structure of solids
- Mechanical properties of materials
- Surface properties of materials
- Role of water in biomaterials
Chap. 2. Classes of materials used in medicine

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- Polymer
- Silicone
- Medical fibers & biotextiles
- Hydrogels

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- Applications of “Smart Polymers” as biomaterials

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- Bioresorbable and bioerodible materials
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Part 1: Material Science & Engineering

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Chap. 2.(cont.)
- Natural materials
- Metals
- Ceramics, glasses, and glass-ceramics
- Composite
- Nonfouling (Anti-fouling) surfaces
- Surface modification of materials used in medicine
- Textured and porous materials
- Surface-immobilized Biomolecules

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The structure of solids

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Chap.1. Properties of materials-

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The periodic table

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Chap.1. Properties of materials- The structure of solids

1.1. Structure of solids
Which states of materials do you know? The differences of them?

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What determine the properties of material?
What are solids?
- Their constituent atoms are held together by strong interatomic
forces
- Structure, physical properties: depend on the nature and

strength of the interatomic bonds
- Strong bonds: ionic, covalent and metallic
Structure of solids: on many levels of scale
- Atomic or molecular: 0.1- 1 nm
- Nanoscale or ultrastructural: 1 nm- 1 µm
- Microstructural: 1 µm- 1 mm
- Macrostructural: > 1mm

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Chap.1. Properties of materials-

The structure of solids

Atomic bonding: primary interatomic bonds and secondary bonds
Primary interatomic bonds (strong bonds)
Ionic bonding:
* Formed by exchanging electrons between metallic and nonmetallic
atoms
- Electron donor atoms (metallic) transfer one or more electron to an
electron acceptor (nonmetallic) to form cation and anion

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- Cations and anions strongly attract each other by Coulomb effect
- The attraction of cations and anions constitutes IB (Hummel, 1997)
• Ionic solid structures are limited in their atomic arrangement

• Bonding energy: relative large, between 600- 1500 kJ/mol (3-8 eV/atom),
leads to relative high melting temperature

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• Poor electrical conductor, relative low chemical reactivity

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• Examples: NaCl, MgO

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The structure of solids

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Chap.1. Properties of materials-

Loosely bound electrons are
tightly held in the locality of the
ionic bonding

Fig. 1. Schematic
representation of ionic
bonding in sodium chloride
(NaCl)

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Chap.1. Properties of materials-

The structure of solids

Covalent bonding:
- Elements between metals and nonmetals (equal tendency to donate and

accept electrons), many nonmetals, molecule containing dissimilar atoms
- Bonding by sharing valence electron to form stable electron structure
(all valence electrons in pair localized at valence bonding)
- Bonding is highly directional and strong, may be very strong (diamond),
• Materials as poor electric conductors

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• Examples: H2, Cl2; Si, C; CH4, H2O

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The structure of solids

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Chap.1. Properties of materials-

Fig. 2: Schematic representation of covalent bonding in a molecule of methane (CH4)
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Chap.1. Properties of materials-

The structure of solids

Metallic bonding:
- Three-dimensional pattern with valence electrons migrating within
atoms (Fig.3)
- Bonding may be week or strong, energies range from 68kJ/mol (0.7
eV/atom) for mercury to 850 kJ/mol (8.8 eV/atom) for tungsten
- Material may be very strong (cobalt) and have very high melting point

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- Good electrical and thermal conductor

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The structure of solids

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Chap.1. Properties of materials-

Valence electrons can move freely
within atoms (sea of valence electrons)

Fig. 3. Schematic illutration of

metallic bonding

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Chap.1. Properties of materials-

The structure of solids

Secondary bonds (week bonds)
Van der Waals (physical bonds)

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Fig.4. Van der Waals bonding
between two dipoles

- Forces arise when electrons are not distributed equally among ions
that can form dipoles

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- Much weaker than hydrogen bonds, effect is over a short distance

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Chap.1. Properties of materials-

The structure of solids

Hydrogen bonds

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- Hydrogen bonds can arise when the hydrogen atom is covalently
bonded to an electronegative atom so that it becomes a positive ion
- The electrostatic force between them can be substancial
- Bonding mechanisms are now discussed briefly

Fig.5. Hydrogen bonding in hydrogen fluoride (HF)

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Chap.1. Properties of materials-

The structure of solids

Atomic structure
• Crystal
- A solid whose atoms and ions are arranged in an orderly repeating
pattern in three dimensions
- Atoms can be very closely packed
- Number of primary bond is maximized

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- Energy of aggregate is minimized
• Crystal structure

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- Unit cell have all the geometric properties of whole crystal

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Chap.1. Properties of materials-

The structure of solids

Materials, their chemical bonds and atom structure

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Table 1: Strength of different chemical bonds as reflected in their heat of vaporization

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The structure of solids

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Chap.1. Properties of materials-

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Fig. 6. Some materials exhibit nearly ideal covalent, metallic or ionic
bonding, but most materials exhibit a hybrid bond types
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The structure of solids

* Metals

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Chap.1. Properties of materials-

A: Face-centered cubic (FCC)
B: Full size atom
C: Hexagonal close-packed (HCP)
D: Body-centered cubic (BCC)

Fig.7. Typical metal crystal structure (unit cells)

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Chap.1. Properties of materials-

The structure of solids

* Crystal structure of carbon

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Tab. 2: Related physical properties of diamond and graphite

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The structure of solids

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Chap.1. Properties of materials-

cubic

hexagonal

Fig.8: Crystal structure of carbon; A: diamond, B: graphite

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Chap.1. Properties of materials-

The structure of solids

• Ceramics
- Various combinations of ionic and covalent bonding
- Tightly packed structure
- Carbon: often included with ceramics
• Polymer
- Thermoplastics

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- Thermoset: three dimensions

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Chap.1. Properties of materials- Mechanical properties

Mechanical properties of materials

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Properties of solids?

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Important properties for biomaterials: mechanical and chemical

StressStress- Strain behavior
For materials that undergo a mechanical deformation:
- Normalized load:

Stress = Force/cross-section area (N/m2)

- Normalized deformation: Strain = Change in length/Original length
- Tension & compression (load is perpendicular to loading direction)
- Shear (load is parallel to the area supporting it & dimension change
is perpendicular to the reference dimension

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Chap.1. Properties of materials- Mechanical properties

Shear stress and shear strain

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Tensile stress & tensile strain

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Chap.1. Properties of materials- Mechanical properties

Elastic behavior

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- In tensile test
- Extension: proportional to the load (Hook law-1687)

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Chap.1. Properties of materials- Mechanical properties

Elastic constants

 = E ε , tension and compression
=G,

-E & G: proportionality constants

shear

- Tensile constant E: tensile modulus (Young’s modulus)

- E and G represent inherent properties of materials
- Strong bonds: high moduli, small strain

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- Week bonds: low moduli

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- G: shear modulus

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Chap.1. Properties of materials- Mechanical properties

Stress versus strain for elastic solids
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Chap.1. Properties of materials- Mechanical properties

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Tab.3. Mechanical properties of some important implant materials and tissues

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Chap.1. Properties of materials- Mechanical properties

Isotropy

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Isotropy: properties are same in all direction

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E & G: needed to fully characterize the stiffness of an isotropic material
Single crystal: anisotropic
Polycrystalline materials: on average isotropic

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Chap.1. Properties of materials- Mechanical properties

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Mechanical testing

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Chap.1. Properties of materials-

The structure of solids

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Mechanical properties derivable from a tensile test

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Chap.1. Properties of materials- Mechanical properties
Plastic deformation

-Only metals exhibit true plastic deformation
-Ceramic and many polymer do not undergo

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Stress versus strain for a ductile material

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-Important for shaping metals and alloys

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Chap.1. Properties of materials- Mechanical properties

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Creep and viscous flow

A: Elongation vs time at constant load (creep)

B: Load vs time at constant elongation

A: Dash pot or cyclinder and piston model of viscous flow
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B: Dash pot and spring model

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Chap.1. Properties of materials- Mechanical properties
Toughness
-The ability of a material to plastically deform under the influence of
the complex stress field at the tip of a crack
- Brittle fracture (glass, ceramics, graphite, very hard alloys, some
polymer like PMMA-bone cement
- Elastic fracture
- Fracture toughness test:

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. Single Edge Notched Bend (SENB) Test, ISO 13586: 2000 (E),
. GIC & KIC: Fracture toughness

. KIC: Critical Stress Intensity Factor; I (mode I): loading is applied
perdendicular to the crack path

KIC= (EGIC)1/2

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Sample: L = 78 mm, w = 16mm; B = 4mm, a = 8mm

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Chap.1. Properties of materials- Mechanical properties

Fatigue

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- Is process by which structure fail as a result of cyclic stresses
(usually less than ultimate tensile stress)
- Important for dynamic loaded structure
- Fatigue strength is sensitive to environment, temperature, corrosion,
deterioration and cyclic rate

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Chap.1. Properties of materials- Mechanical properties

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A: Stress versus time in a fatigue test

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B: Fatigue stress versus cycles to failure

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Chap.1. Properties of materials- Surface properties

Surface properties of materials

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•Surface properties are very important for biomaterials

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•Surface: boundary between different phases

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Chap.1. Properties of materials- Surface properties

Surface tension
* Surface energy

dG = dw - dA

w: work done on the surface area change dA
: surface energy of the material

• Contact angle
• Surface structure (surface area and surface chemistry decide surface energy)

Surface tension of some materials
Substances

Temperature, oC

0.465
0.452
0.758
1.103
1.128

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Surface tension, N/m

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Mercury
Lead
Zinc
Copper
Gold

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• Surface energy: very important for wettability and adhesion (adsortion & chemisorbtion)

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Chap.1. Properties of materials-

Surface properties

Several methods to determine the contact angle of solid and liquid
Wilhelmy plate method with Tensiometer

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Sessile drop method with goniometer

Micro balance

F (µN)
Wilhelmy equation

γsv
Drop on flat substrate

θ contact

vapour

angle

γsl

cos 

F
p lv

γlv

liquid

Drop on fibre
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Chap.1. Properties of materials- Surface properties
- Roughness is a very important factor for surface energy (due to surface area)

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A: Rough, step, smooth; B: composed of different chemistries;C: inhomogeneous in plane

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D: inhomogeneous in with depth; E: highly crystalline or disordered; F:Crystalline surface with many organisations

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Chap.1. Properties of materials- Surface properties

- Surface chemistry is also very important for surface tension (due to chemical
composition, especially functional groups at the surface)

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- Hydrophilic groups

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- Hydrophobic groups

Evaluation of a surface:
-Measurement of contact angle (general surface energy)
-Study morphology of the surface: SEM…
-Study surface roughness: AFM, SEM
-Study the surface chemistry: IR (FTIR), XPS, Raman Spectroscopy, SIMS

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Chap.1. Properties of materials- Surface properties

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Common methods for evaluation the surface properties of biomaterials

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