Biomaterials Flashcards
What is Biomaterials?
A material intended to interface with biological systems to evaluate, treat, augment, or replace any tissue, organ, or function of the body.
What is an important attribute that a biomaterial should have from the point-of-view: A manufacturer, a clinician, and a patient.
Biocompatibility, and covered by insurance is shared by all point-of-views.
Definition of Biocompatibility?
The ability of a material to perform with an appropriate host response.
Examples of Biocompatibility?
Resistant to blood clotting, resistant of infection, “uncomplicated” healing”, ** must do patient no harm**
Key considerations of Biocompatibility?
- Application (*e.g. implanted vs. non-implanted, needs will differ per application)
- Material (Properties: mechanical (bulk property), surface, chemical etc.)
- Processing (smooth vs rough)
- Time/”Life” (degradable cs. non-degradable)
Testing Biomaterials
- Application Specific
- Tissue Specific
Dominated by Surface Characterization though, because this is where the most interaction occurs with biological systems
Types of Chemical Bonds (Primary Bonds)
- Covalent
- Ionic
- Metallic
- Ionic/Covalent Mixed
Types of Chemical Bonds (Secondary Bonds)
- Polar Bonds
2. Non-Polar
What is a covalent bond?
Share electrons to achieve octet rule.
Mostly occurs in polymers and other organics
Poor Thermal and electrical conductivity
Single bond allows rotation of atoms and thus result sin felixible and deformable material.
What is an Ionic bond?
Transfer of electrons that generate ions
Bonding due to electrostatic attraction
Atoms arrange in crystal lattice
Mostly found in ceramics
High strength and stiffness but brittle due to atoms inability to move in response to external forces.
Electrons not available for charge transfer = Bad conductors
What is a metallic bond?
Metals atoms are good donors of electrons. Tightly packed positive ions surrounded by electrons.
Good charge transfer
What determines whether two elements will bond covalently, ionically or netallically?
Electronegativity: the measure of how strongly an atom wants electrons.
What is a dipole?
A molecule with a spatial separation between the negative and positive charge (ex. H2O)
Which of the following materials would you expect to be strongest?
A. Iron
B. Diamond
C. Magnesium
D. Ice
A. iron
Which of the following materials would you expect to have the highest thermal conductivity? A. Iron B. Diamond C. Magnesium D. Ice
A Iron
What are material properties?
Are quantifiable attributes of a material that do not depend on the amount of the material present.
What is the most basic mechanical test procedure for measuring load-deformation?
Uniaxial Tensile Testing
What do you measure in tensile test?
- Amount of elongation
2. Amount of force required o produce deformation
Process of Uniaxial Tensile Test?
- Test specimen loaded and fixated to bottem clamp first then top.
- Top clamp moves away from the bottom and measures the force required
- Force vs. deformation data produced.
Is force vs. deformation a mechanical property?
No. This relationship depends on the size of specimen, That’s why there are standards.
Engineering Stress Equation?
Stress = Force/Area
Engineering Strain
Strain = change of length/ original length
When calculating the yield strength what is the offset percantage from Young’s modulus?
0.2%
What measurement(s) do you need to take before testing?
Thickness, Width of Gage, Length of gage
How do you find toughness in the Stress-Strain curve?
The whole area under the curve.q
How do you find resilience in the stress-strain curve?
The area under the the linear region of the stress-strain curve.
Which of the following would be considered be made from a biomaterial according to the modern definition for biomaterials?
(a) Pacemaker for the heart
(b) walking stick
(c) stethoscope
(d) bascular graft
(e) totthbrush
(f) suture
(a) pacemaker for the heart
(d) Vascular graft
(f) suture
Of ceramics, polymers, and metal, which have low resistance to crack propagation and fracture?
Ceramics = lowest resistance to crack propagation due to inability to undergo ductile deformation. High stresses at crack-tips can exceed the failure strength of the material and cause local failure that will cause the crack to grow (propagate).
If you had to produce an arterial artery, what are the essential properties you will incorporate in your design? Which type of material would you first consider? why?
The artificial artery properties:
Leak proof - prevent blood loss
Flexible - be easily positioned
elastic (resilient) - for changes in blood pressure without undergoing failure
non-thrombogenic - don’t caude blood clots
non-immunogenic - not elicit an immune or adverse response
Material - Polymer
Why are the surface properties of a biomaterial important?
The majority of body-device interactions occur on the surface of the material. The surface properties dictate much of how a biomaterial behaves in relation to the body.
Cold welding
Joining of two pieces of metal join without fusion/heating at the interface of the two parts to be welded.
What makes cold welding possible w/ metal?
In the absence of a reactive atmosphere (mostly Oxygen), metals will not undergo surface oxidation. In addition, the electron-cloud config. of metals have no bonding directionality, and so when placed in perfect contact with another piece, the atoms have no way of knowing that they are separate pieces and thus will bond.
Do you expect other material, such as ceramics or polymers to be able to be cold welded?
I do not expect this. Ceramics have ionic bonds which are the most stable config, to minimise surface energy
What is preventing two separate pieces of gold from instantly bonding when touched together?
Oxygen will almost always react with the surface of any material even gold. So when the thin oxide layer is rubbed out this only creates more surface area to react and only a small portion cold welds.
Behaviour of material in the linear (elastic) region?
Stress = E* Strain
Just like hooke’s Law.
Elastic modulus is the constant that characterizes the elastic properties
What is yield stress?
The stress which causes the onset of permanent deformation.
What is the proportional limit?
The highest stress at which stress is linearly proportional to the strain. Like a spring.
What is the maximum stress that material can undergo before fracture called?
Ultimate stress (strength)
What is it called when the stress levels continues to increase after the yield stress is reached?
Strain Hardening
What is strain hardening?
This resistance is caused by the decreased mobility of atomic planes within the material due to the interaction of multiple dislocations.
Why does the stress drop after ultimate strength has been reached?
The material’s cross-section decreases called “Necking.” As area decreases, the force required to produce constant deformation rate also decreases
What is uniform plastic deformation?
Occurs before ultimate strength point reaches. The entire specimen stretches.
What is Local plastic deformation?
Occurs after ultimate strength point. Preferential stretching near necking region.
What is Strain Energy Density?
The amount of work required to deform a material per unit volume.
What are the types of material fractures?
Brittle and Ductile fractures
What kind of loads can a material undergo?
Tensile Compression Bending Twisting Shearing
What is fracture?
When the cohesive strength between adjoining atoms is exceeded by applied stress.
Poisson’s effect?
When the under tension the material contracts. Generally speaking.
Define failure.
Definition of of failure depends on design contraints.
