Material Science: Mechanical Properties Quiz
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Questions and Answers

Which strength measures a material's ability to withstand bending loads?

  • Fracture Toughness
  • Compressive Strength
  • Elastic Modulus
  • Flexural Strength (correct)

Fracture Toughness is a measure of a material's ability to resist crack propagation.

True (A)

What is the term used to describe the maximum stress a material can withstand while being compressed?

Compressive Strength

The ratio of stress to strain in the elastic deformation region is known as ______.

<p>Elastic Modulus</p> Signup and view all the answers

Match the following terms with their definitions:

<p>Compressive Strength = Maximum stress while being compressed Flexural Strength = Ability to withstand bending Fracture Toughness = Resistance to crack growth Elastic Modulus = Ratio of stress to strain during elasticity</p> Signup and view all the answers

Which property makes zirconia a desirable material for orthopaedic implants?

<p>High bending strength (C)</p> Signup and view all the answers

Alumina is known for its high wear properties and biocompatibility.

<p>True (A)</p> Signup and view all the answers

What type of carbon is widely utilized for implant fabrication?

<p>Pyrolitic carbon</p> Signup and view all the answers

Zirconia has a melting temperature that is significantly higher than that of __________.

<p>alumina</p> Signup and view all the answers

Match the following materials with their key characteristics:

<p>Alumina = High hardness and low friction Zirconia = Higher strength than alumina Carbon = Allotropic forms such as diamond and graphite Pyrolitic carbon = Widely used for implants</p> Signup and view all the answers

Which material has bending strength and fracture toughness that is 2-3 times greater than alumina?

<p>Zirconia (B)</p> Signup and view all the answers

Elastic modulus is also referred to as bending strength.

<p>False (B)</p> Signup and view all the answers

Fracture toughness measures the energy required to __________ a crack.

<p>grow</p> Signup and view all the answers

What is the primary characteristic of non-inert bioceramics?

<p>They are chemically broken down by the body. (D)</p> Signup and view all the answers

Bioactive glass is an example of a natural resorbable bioceramic.

<p>False (B)</p> Signup and view all the answers

What is one synthetic example of a resorbable bioceramic?

<p>Hydroxyapatite</p> Signup and view all the answers

Hydroxyapatite has a similar mineral composition to that of ________.

<p>bone</p> Signup and view all the answers

Which of the following is a natural bioceramic?

<p>Biocoral (B)</p> Signup and view all the answers

What is the chemical formula of Hydroxyapatite?

<p>Ca10(PO4)6(OH)2</p> Signup and view all the answers

Match the following materials with their type:

<p>Hydroxyapatite = Synthetic Biocoral = Natural Bioactive glass = Synthetic Calcium phosphate = Synthetic</p> Signup and view all the answers

The __________ in resorbable bioceramics must be processed through normal metabolic pathways.

<p>chemicals</p> Signup and view all the answers

What is the elastic modulus of enamel?

<p>74 GPa (C)</p> Signup and view all the answers

Dentin has a higher elastic modulus than compact bone.

<p>True (A)</p> Signup and view all the answers

What are the primary components of hard tissues such as bone and dental enamel?

<p>Hydroxyapatite, protein, other organic materials, and water</p> Signup and view all the answers

Biocoral is transformed into hydroxyapatite by a chemical exchange reaction with __________ under hydrothermal conditions.

<p>di-ammonium phosphate</p> Signup and view all the answers

Match the following materials with their elastic modulus values:

<p>Enamel = 74 GPa Dentin = 21 GPa Compact Bone = 12-18 GPa Polycrystalline Hydroxyapatite = 40-117 GPa</p> Signup and view all the answers

Which factor influences the degradation rate of ceramics by increasing surface area interaction with the environment?

<p>Material surface area to volume ratio (A)</p> Signup and view all the answers

Single crystal ceramics degrade more quickly than polycrystalline ceramics due to having more grain boundaries.

<p>False (B)</p> Signup and view all the answers

What effect does a high amount of water have on the degradation rate of ceramics?

<p>Increases the degradation rate</p> Signup and view all the answers

Ceramic degradation is encouraged in areas with high mechanical __________.

<p>stress</p> Signup and view all the answers

Match the following factors with their effect on degradation rate:

<p>Amount of media = Increased degradation with high water availability Material surface area to volume ratio = Faster degradation with high porosity Mechanical environment = Encouraged degradation under high stress Grain boundaries = Increased degradation in polycrystalline ceramics</p> Signup and view all the answers

What is the purpose of controlled crystallization?

<p>To produce crystals of small uniform size (B)</p> Signup and view all the answers

A composition of 60% SiO2 in bioactive glass is considered very bioactive.

<p>False (B)</p> Signup and view all the answers

What film layer must be formed simultaneously for bioglass to bond with bone?

<p>calcium phosphate and SiOâ‚‚-rich film layer</p> Signup and view all the answers

Bioglass has a composition of 45 wt% SiOâ‚‚, 24.5 wt% CaO, 24.5 wt% Naâ‚‚O, and ______________.

<p>6.0 wt% Pâ‚‚Oâ‚…</p> Signup and view all the answers

Match the following ceramics with their primary applications:

<p>Alumina = Used in joint replacements and dental implants Zirconia = Used in dental implants and prosthetics Hydroxyapatite = Used in human cortical bone Bioglass = Promotes bone regeneration and bonding</p> Signup and view all the answers

What effect can small changes in the composition of a biomaterial have?

<p>They affect whether it is bioinert, resorbable, or bioactive (C)</p> Signup and view all the answers

Bioactive ceramics have minimal biological interaction.

<p>False (B)</p> Signup and view all the answers

Identify one type of glass ceramic besides Bioglass.

<p>Ceravital®</p> Signup and view all the answers

Bioglass can bond with bone in approximately __________ days.

<p>30</p> Signup and view all the answers

Which property is NOT characteristic of bioactive ceramics?

<p>No degradation over time (D)</p> Signup and view all the answers

Inert ceramics have high biocompatibility but minimal biological interaction.

<p>True (A)</p> Signup and view all the answers

What is the tensile strength range of alumina?

<p>300-1000 MPa</p> Signup and view all the answers

Bioactive glasses with less than __________% SiOâ‚‚ are considered very bioactive.

<p>45</p> Signup and view all the answers

Match the following properties with their values for bioceramics:

<p>Tensile Strength = 50-150 MPa (Hydroxyapatite) Compressive Strength = 100-200 MPa (Bioglass) Fracture Toughness = 0.5-2 MPa·m^0.5 (Bioglass) Elastic Modulus = 10-40 GPa (Hydroxyapatite)</p> Signup and view all the answers

Flashcards

Flexural Strength

A material's ability to resist bending.

Fracture Toughness

A material's resistance to crack propagation.

Elastic Modulus

Ratio of stress to strain in elastic deformation.

Alumina

Bioceramic with high hardness, low friction, and low wear.

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Zirconia

Bioceramic with high melting temp + chemical stability, better mechanical properties than alumina.

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Pyrolitic Carbon

Type of carbon used in implant fabrication.

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High Melting Temperature

Characteristic of a material that can withstand high temperatures without melting.

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Biocompatibility

The ability of a material to coexist peacefully with living tissue without causing harm.

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What are non-inert bioceramics?

Bioceramics that are broken down by the body and replaced by natural tissue.

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What are some examples of synthetic resorbable bioceramics?

Calcium Phosphate, Hydroxyapatite, Bioactive Glass.

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What are some examples of natural resorbable bioceramics?

Biocoral.

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What is the most important calcium compound in the body?

Hydroxyapatite is the mineral phase found in bone and teeth.

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What does Hydroxyapatite do in the body?

Hydroxyapatite acts as reinforcement in hard tissues like bone and teeth, giving them their strength.

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What is the chemical formula of Hydroxyapatite?

Ca10(PO4)6(OH)2

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What is the Hydrothermal Technique?

A method used to create synthetic Hydroxyapatite.

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What is the Ca/P ratio in Hydroxyapatite?

The ratio of Calcium to Phosphorus in Hydroxyapatite is 5:3

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Hydroxyapatite's Elastic Modulus

Hydroxyapatite's elastic modulus is a measure of its stiffness and resistance to deformation. It ranges from 40 to 117 GPa, making it a strong material.

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Hydroxyapatite in Hard Tissues

Hydroxyapatite is the primary mineral component of hard tissues like bone, dentin, and enamel, providing their structural strength and rigidity.

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Enamel's Stiffness

Enamel, the outermost layer of teeth, has the highest elastic modulus (74 GPa) of all the hard tissues due to its high mineral content, making it very resistant to deformation.

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Dentin's Mineral Content

Dentin, found beneath enamel, is less stiff than enamel with an elastic modulus of 21 GPa, as it contains less mineral, and more organic material, making it less rigid.

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Bone's Mineral Content

Compact bone has an elastic modulus of 12-18 GPa, containing less mineral than enamel and dentin, contributing to its lower stiffness.

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Compressive Strength

The maximum stress a material can withstand under compression before it breaks.

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What are the important properties for load-bearing materials?

Load-bearing materials need high compressive strength, flexural strength, and fracture toughness. They should also have a good elastic modulus for efficient deformation under stress.

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Controlled Crystallization

A process that involves specific compositions, heat-treatment, and controlled nucleation to grow crystals of small, uniform size.

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Bioactive Bioceramics

Ceramics that actively interact with the body, promoting bonding and integration with surrounding tissues.

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What defines bioactive bioceramics?

Bioactive bioceramics contain specific compositions like Bioglass® and Ceravital®. These compositions allow direct bonding with bone.

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Bioglass® Composition

The composition of Bioglass® is 45% SiO₂, 24.5% CaO, 24.5% Na₂O, and 6.0% P₂O₅, making it a bioactive material.

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Why is Bioglass® bioactive?

Bioglass® forms a calcium phosphate and SiO2-rich film layer on its surface, allowing it to directly bond with bone in approximately 30 days.

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Bioactive Glass and SiO2 Content

A higher SiO2 content in bioactive glass makes it more chemically stable but less bioactive. Conversely, a lower SiO2 content promotes bioactivity.

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Inert Ceramics

Bioceramics that have minimal biological interaction with the body, showing little to no reaction over time.

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Non-Inert Ceramics

Bioceramics that can degrade or cause a reaction over time, eventually being replaced by natural tissue.

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Biocompatibility of Bioceramics

Bioceramics can have varying levels of biocompatibility, based on their composition. Inert ceramics have high biocompatibility due to minimal tissue interaction.

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Degradation of Bioceramics

Inert ceramics don't degrade, non-inert ceramics degrade over time, and bioactive ceramics can undergo controlled degradation.

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Tensile Strength in Bioceramics

The maximum stress a bioceramic can withstand before breaking when pulled or stretched.

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Compressive Strength in Bioceramics

Indicates the amount of pressure a bioceramic can withstand before crushing or breaking.

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Flexural Strength in Bioceramics

The ability of a bioceramic to resist bending or flexing before breaking.

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Fracture Toughness in Bioceramics

The ability of a bioceramic to resist the propagation of cracks and to prevent catastrophic failure.

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Elastic Modulus of Bioceramics

The stiffness of the material, represented as the ratio of stress to strain in elastic deformation.

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Grain Boundaries and Degradation

Polycrystalline ceramics, having many smaller crystals with grain boundaries, degrade faster than single crystal ceramics due to the presence of these boundaries. The grain boundaries provide more surfaces for interaction with the surrounding environment, leading to increased dissolution.

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Water's Effect on Degradation

The amount of water available significantly impacts degradation rate. High amounts of water accelerate degradation, while low amounts slow it down.

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Surface Area and Degradation

Highly porous ceramics degrade more quickly than ceramics with fewer pores. The increased surface area in porous materials provides more points for interaction with the surrounding environment, leading to increased dissolution.

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Mechanical Stress and Degradation

Ceramic degradation is encouraged in areas with high mechanical stress, either due to implant site location, presence of stress raisers in the device, or the production of wear particles. This stress can lead to an inflammatory response, lowering pH, and further accelerating degradation.

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How does implant site location affect degradation?

The location of an implant within the body can affect the mechanical stress it experiences. Highly stressed areas can accelerate degradation due to the increased forces and friction.

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Study Notes

Ceramic Materials

  • Ceramics are inorganic, non-metallic solids, typically oxides, nitrides, or carbides.
  • They are hardened by high-temperature shaping.
  • Ceramics are hard, brittle, and resistant to high compression stress.
  • They are good insulators (electrically and thermally).
  • Many ceramics appear aesthetically pleasing and are transparent to light.

Outline of Ceramic Materials

  • Introduction
  • Desired properties of bioceramics
  • Types of bioceramics
  • Degradation of ceramic

Desired Properties of Bioceramics

  • Biocompatibility: Must be compatible with biological systems.
  • Appropriate mechanical properties: Suitable for specific application.
  • Degradation/Stability: Degradable or stable for the implanted time.
  • Bioactivity: Actively interacts with the host tissues for their lifetime.
  • Non-toxic: Should not cause harm to the body system.
  • Non-carcinogenic: Should not cause cancer.
  • Non-allergic: Must not cause allergic reactions.
  • Non-inflammatory: Should not lead to inflammation.

Types of Bioceramics

  • Inert (Non-Absorbable) Bioceramics: Maintain their properties in the host. Examples include Alumina, Zirconia, and Carbon
    • Alumina: High hardness, low wear, inert. Used in orthopedic implants, femoral heads, and coatings. The main source is bauxite and corundum. It has high compressive strength, is chemically inert, and has good wear resistance.
    • Zirconia: Obtained from zircon. Has high bending strength and toughness compared to alumina, excellent biocompatibility, and also used in orthopedic implants.
    • Carbon: Generally used as a surface coating.
  • Non-Inert (Resorbable) Bioceramics: Degrade in the body or absorbed by the tissues over time. Synthesised or natural. Examples include calcium phosphate and Biocoral.
    • Calcium Phosphate: Used to create artificial bone. Examples include hydroxyapatite (HA) and tricalcium phosphate.
    • Biocoral: A natural material transformed into HA. Ideal for repairing traumatized bone and correcting bone defects.
  • Surface Reactive/ Bioactive Bioceramics: Interact directly chemically with the body's tissues or surrounding bone. Examples: Glass ceramics, hydroxyapatite.
    • Glass Ceramics: Crystalline materials from controlled crystallization of an amorphous glass. Specific compositions and controlled nucleation are needed to achieve controlled crystallization and small, uniform crystal growth. Used as a replacement for metallic implants.
    • Hydroxyapatite: Similar composition to hard tissues like bone, dentin, and enamel. Has excellent biocompatibility and forms a direct chemical bond with hard tissues.

Degradation of Ceramics

  • Biodegradable ceramics: Degrade in the body.

  • Uncontrolled degradation: Causes wear and inflammatory responses, leading to implant loosening.

    • Mechanical environment
    • Ceramic porosity (stress raiser)

  • Controlled degradation: Desirable in tissue engineering and drug delivery. Ideal for temporary applications.

Factors Affecting Degradation Rate

  • Amount of crystallinity: More tightly packed crystalline material less susceptible to dissolution.
  • Amount of media (water): High water→ Higher degradation rate.
  • Material surface area to volume ratio: Highly porous material degrades faster.
  • Mechanical environment: High stress areas encourage faster degradation.

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Description

Test your knowledge on the mechanical properties of materials, including strength measures, fracture toughness, and elastic modulus. This quiz covers key concepts that are crucial for understanding material behavior under various loads, especially in the context of engineering and biomedical applications.

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