MNB.2 Mechanical Properties of Bone Tissue Flashcards

Comprehensive practice flashcards covering the mechanical properties of bone tissue, including matrix composition, stress/strain relationships, and biomechanical design.

What are the five primary functions of bone?

1. Support, 2. Protection of Organs, 3. Leverage, 4. Storage and release of minerals and lipids, 5. Blood cell production.

Where are red and white blood cells produced?

Red and white blood cells are produced in the red marrow.

Why do mechanical properties of bone vary at different length scales?

Bone is a hierarchical structure, meaning properties at the nano scale (collagen and mineral) are different from properties measured at the macroscale (compact or trabecular bone).

What percentage of bone weight is composed of Inorganic Material?

$$60\%$$

What are the primary components of the inorganic matrix in bone?

Calcium phosphate (in the form of insoluble hydroxyapatite crystals), calcium carbonate, fluoride, sulphate, potassium, and magnesium.

What percentage of bone weight is composed of Organic Material?

$$~35\%$$

What are the components of the organic matrix of bone?

Primarily collagen, glycoproteins, proteoglycans, and glycosaminoglycans (GAGs).

What is the function of proteoglycans in the bone matrix?

They provide hydration and swelling pressure to withstand compression.

What is the role of glycosaminoglycans (GAGs) in bone?

They regulate collagen formation and mineralisation.

What percentage of bone weight is water?

$$~5\%$$

Identify the four types of cells mentioned in the bone matrix composition.

Osteoblasts, osteoclasts, osteocytes, and bone lining cells.

What is the most abundant structural protein in the human body?

Type I collagen.

Which mechanical properties does collagen provide to bone?

Flexibility and the ability to resist pulling and stretching forces (tensile forces).

How does the organization of collagen fibers in concentric lamellae contribute to bone strength?

Alternating collagen fiber orientation creates a fiber reinforced composite.

What mechanical properties does hydroxyapatite provide to bone?

Stiffness and resistance to pressing and squeezing forces (compressive forces).

What is considered the elementary building block of bone?

The structure of mineralised fibrils.

When does a material behave elastically?

When it can return to its original shape after the applied force is removed.

What is the definition of Stress ($\sigma$)?

Stress is the force per unit area, calculated as $\sigma = \frac{F}{A}$, where $F$ is force and $A$ is cross-sectional area.

What are the units for Stress?

$N/m^2$ or $Pa$

How many ways can materials be stressed depending on force direction?

Five ways.

What is the definition of Strain ($\epsilon$)?

Strain is the fractional change in length of the material, defined as $\epsilon = \frac{\Delta L}{L}$.

What are the units for strain?

Strain has no units (it is dimensionless).

What is Young’s Modulus ($E$)?

Young’s Modulus is the ratio of Stress to Strain within the linear region where the material obeys Hooke’s Law.

What does a high Young’s Modulus indicate about a material?

A high Young’s Modulus indicates a stiff material.

How is Young’s Modulus determined from a stress-strain graph?

It is the slope of the stress-strain graph in the linear region (up to point A).

What happens to the relationship between stress and strain between points A and B on the stress-strain graph?

Stress and strain are not linearly proportional, although deformation is still elastic.

What is Point B on the stress-strain relationship graph called?

The elastic limit or yield point.

What type of deformation occurs beyond point B (the yield point)?

Plastic Deformation, where the material is permanently deformed.

What does Point C represent on the stress-strain graph?

The maximum permissible stress.

What does Point D represent on the stress-strain graph?

The fracture point (ultimate yield).

What is compact bone (cortical bone)?

Solid bone that forms the solid outer shell and shaft (diaphysis) of long bones.

What is trabecular bone (cancellous or spongy bone)?

A network of trabecular struts commonly found at the ends (epiphyses) of long bones.

Is bone stronger under compression or tension?

Bone is stronger under compression.

What is the typical range of bone strength in compression?

$$70\times 280\,MPa$$

What is anisotropy in the context of bone?

It means the mechanical properties of bone vary depending on the direction (orientation) in which the bone is tested.

Which is stronger under compression: a straight solid column or a curved hollow bone?

A straight, solid column of bone is stronger.

What are the three evolutionary advantages of curved bones?

1. Predictable deformation direction when loaded, 2. Bends more as load increases, 3. Offers greater resistance to bending.

What happens to the opposite surfaces of a bone during bending?

One surface experiences compression (shortens) and the opposite surface experiences tension (lengthens).

What is the 'Neutral Surface' (or Neutral Axis) during bending?

A surface at the center of the material that undergoes no change in length and experiences no resisting forces.

Where do the greatest resisting forces occur during bending?

At the outer surfaces (most extreme top and bottom fibers).

To maximize resistance to bending, how should material be distributed relative to the neutral surface?

Material should be distributed as far as possible from the neutral surface.

What is the mechanical trade-off if a hollow bone cylinder is too thin?

It will buckle under compressive forces.

What is the structural role of the diaphysis in the femur?

The hollow cylinder of compact bone in the diaphysis provides structural support.

What is the mechanical role of trabecular bone in the epiphysis of the femur?

It acts as a shock absorber.

How is the design of the femur optimized?

It offers strength and flexibility with optimized resistance to compression and bending in a lightweight hollow tube.

State the formula for Weight (Force) related to mass.

$$Force = Weight = mg$$

Convert $3\,cm^2$ to $m^2$.

$$3\times (10^{-2})^2 = 3\times 10^{-4}\,m^2$$

If Young’s modulus is $1.8\times 10^{11}\,Pa$, the mass is $80\,kg$, and length is $0.5\,m$, what is the stress applied to a $3\times 10^{-4}\,m^2$ area?

$$\sigma = \frac{80\times 9.8}{3\times 10^{-4}} = 2.61\times 10^6\,Pa$$

Using the tibia problem data ($L = 0.5\,m$, $A = 3\times 10^{-4}\,m^2$, $m = 80\,kg$, $E = 1.8\times 10^{11}\,Pa$), what is the change in length ($\Delta L$)?

$$\Delta L = 7.26\times 10^{-6}\,m$$

What determines the magnitude of deformation besides the size of the force?

The area over which the force is applied (force per unit area).