Lecture 15 - Balancing Bone Resorption/Deposition

Question 1

Cell Response to Mechanical Force

Answer 1

• Cells can put force on material

- Cells can sense mechanical environment of material and respond accordingly

Question 2

Bone Remodeling/Homeostasis

Answer 2

• Bone is dynamic/active tissue
• Small-scale changes in bone architecture occur continually
• Activation, Resorption, Reversal Phase, Formation, Resting Phase

Question 3

Activation

Answer 3

• Detection of initiating signal by osteocytes (mechanical load, hormones)
• Damage to matrix or immobilization cause osteocyte apoptosis (death)
• Increase osteoclastogenisis (making more osteoclast and therefore more bone resorption)

Question 4

Osteocytes

Answer 4

• Live in holes/pools of liquid

- Want coordinated response to loads (touching)

Question 5

Resorption

Answer 5

• Osteoblasts respond to signals from osteocytes (recruit osteoclast precursors)
• Cytokines released induce osteoclast formation from precursors and increase osteoclast activity

Question 6

Osteoclasts

Answer 6

• Seal to bone
• Digest mineral component below
• Phagocytose remnants
• Concentrate/don’t allow remnants to destroy surrounding enviroment

Question 7

Reversal

Answer 7

• Undigested, demineralized collagen removed (osteoblast precursors start to adhere)

Question 8

Formation

Answer 8

Mechanical stimulation and endocrine signaling:
- Osteocytes normally produce sclerostin (prevents Wnt signaling that makes bone)
- Mechanical strain blocks production of sclerostin (allows Wnt signalling-bone formation)
Osteoblast pregenitors return
- Differentiate and secrete molecules that will become bone

Question 9

Key Signals in Bone Remodeling

Answer 9

• Mechanical strain (promotes bone formation)

- Lack of mechanical forces (increased osteoclastogenisis which is responsible for resorption)

Question 10

Stress Shielding

Answer 10

• Taking load in material and shielding natural tissue (bone) around
• Areas not feeling load trigger bone resorption
• Reducing bone density weakens bone, leading to fracture/failure

Question 11

Types of Biomedical Ti

Answer 11

• CP Ti
• Alpha + Beta Ti
• Beta-Ti

Question 12

CP Ti

Answer 12

• Alpha-HCP

- 105 GPa

Question 13

Alpha + Beta Ti

Answer 13

• Alpha-HCP
• Beta-BCC
• 115 GPa

Question 14

Beta-Ti

Answer 14

• Add alloying additions to stabilize beta phase and cool rapidly
• High strength beta alloys have chemistry closer to alpha+beta boundary
• Stable beta alloys have chemistry closer to low modulus/stiff/strength
• Use less cytotoxic components