Bioactive Ceramics 1

Question 1

What is the composition of bone?

Answer 1

• 70% mineral phase that is 95% hydroxyapatite
• 30% organic phase that is 98% matrix (95% collagen, 5% non collagenous proteins) and 2% cells (osteoblasts, osteocytes, osteclasts)

Question 2

What type of biomaterials-tissue interaction exists for bioactive ceramics?

Answer 2

Bioactive fixation (chemical bonding)

Question 3

What dictates whether or not a CaP is resorbable?

Answer 3

the phases

Question 4

What does the stability of the CaP phases depend on

Answer 4

Temperature and water contact, during processing or within the use environment

Question 5

What are the stable phases of CaP in contact with body fluids at body temperature

Answer 5

Below pH of 4.2, DCPD or brushite

Above pH of 4.2, hydroxyapatite

Question 6

True or false

A lower calcium to phosphate ratio leaves to higher degradation rate.

Answer 6

True!

Question 7

What ratio of Ca/P is suitable for implantation

Answer 7

Ca/P > 1

Question 8

What must be taken into account when creating resorbable bioceramics?

Answer 8

• Care must be taken to match the rate of resorption with that of the expected bone tissue renegeration
• resorption relies on cell mediated mechanisms
• in vivo, resorption occurs through the contribution of cell action (phagocytosis)
• affected by implant surface area. Porous implants are more degradable than dense implants

Question 9

What factors cause resorption of CaPs?

Answer 9

1. Physico-chemical dissolution, which depends on the solubility product of the material and the local pH of its environment. New surfaces may be formed
2. Physical disintegration into small particles due to preferential chemical attack of grain boundaries
3. Biological factors (ie phagocytes) which case a decrease in local pH concentrations.

Question 10

What are the general principles of ceramic dissolution? Which structures are more soluble than others?

Answer 10

For the same composition, ranked solubility:

• amorphous forms > polycrystalline grains > single crystals
• hydrated forms > non-hydrated
• porous or fine particulate materials > solid nonporous form of equal weight
• small particles (<25um) > solid bodies

Question 11

What are biphasic calcium phosphates (BCPS) and what dictates the rate of solubility?

Answer 11

a combination of either a- or B-TCP with HA to combine the solubility of TCP with the stability of HA. The ratio of TCP/HA dictates solubility.

Question 12

how is the CaP ratio calculated (what is the equation)?

Answer 12

Ca/P = (3x+10(100-x)M(of b-TCP)/M(of Ha))/(2x+6(100-x)M(of b-TCP)/M(of Ha))
where x is the weight % of the TCP phase, and M are the molar weights