Bioactive glasses part 2

Question 1

Time dependence of bioglass bioactive fixation bond strength

Answer 1

Internal bond strength increases over time
Very strong bond
Stronk
Up to 75 MPa

Question 2

Time dependence of healed certical bone bond strength

Answer 2

Medium internal bond strength
:P
Range between 25-35 MPa approximately

Question 3

Time dependence of biological fixation bond strength

Answer 3

Increases to about 25 MPA in 13 weeks, then goes down

Question 4

Time dependence for morphological fixation bond strength

Answer 4

Increases up to around 7 MPa in 9 weeks, goes down

Question 5

Bioglass-implant bone interface composition vs. interface distance

Answer 5

Closer to interface (bulk bioglass, silicon-rich layer): Predominant Si, then Ca, then P.
Further from interface (Calcium Phosphate, Bone):
Predominant Ca, P, then Si

Question 6

Comparison of interfacial thickness of bio ceramics in bone

Answer 6

WIP :P

Question 7

Soft tissue interface Thickness vs. Time

Answer 7

Increased thickness over time to about 300 micrometers

Increase, then small plateau, then increase again

Question 8

Bone bioglass interface thickness vs. time

Answer 8

Increased thickness over time to 175 micrometers over time

Question 9

Youngs modulus of soft tissue vs depth

Answer 9

Near start of interface, high strength of bioglass of 34 GPa
Then Sio-rich part of bonding gel-layer greatly decreases strength to almost 0 GPa
Stays at 0 GPa for HCA and adherent soft tissue
Strength at cancellous bone increases up to 5 GPa

Question 10

Youngs modulus of bone-bioglass interface

Answer 10

Near start of interface, high strength of bioglass of 34 GPa
Decreases to close to 0 Gpa for Sio-rich part of Bonding Gel-Layer
At HCA part for Bonding Gel-Layer, strength starts increasing
Cortical Bone will be at 25 Gpa, and Cancellous bone will be at 15 Gpa

Question 11

Composition of silicate-based bioglasses

Answer 11

Tetrahedra of four oxygen atoms and a silicon atom in the centre.
Each oxygen is shared by two tetrahedra thus giving a bulk composition of SiO2
This silicate networks acts as a network former

Question 12

Network former of silicate

Answer 12

Can incorporate many atoms

Can be made with different compositions and properties

Question 13

Network Modifiers

Answer 13

Disrupt the glass network and impact the melting temperature and chemical durability
Change the ratio of bridging versus non bridging oxygens in the glass network.
Ex: CaO and Na2O

Question 14

What can you predict with network connectivity?

Answer 14

The bioactivity of glasses

Question 15

Network connectivity

Answer 15

Measure of bridging oxygen bonds per network former.

Question 16

Scale of network connectivity

Answer 16

Scale of 0 to 4.
4 indicates a fully connected, chemically most stable network.
Glasses with an NC between 2 and 2.6 have generally been regarded as bioactive.

Question 17

Equation to calculate NC

Answer 17

NC = (4[SiO2]-2[M12O+M11O] + 6[P2O5])/[SiO2]

M12O and M11O are the molar fractions of the mono and divalent modifier oxides in the glass

Question 18

Bioactivity index (Ib) definition

Answer 18

Expresses rate of formation of hard tissue at the implant interface
level of reactivity can be related to time for more than 50% of the interface to be bonded

Question 19

Bioactivity index

Answer 19

IB  = 100/(t_{0.5bb})
t_{0.5bb} = time required for one half of the interface to be bonded to bone, in vivo

Question 20

Why is 50% bonding criterion for IB imposed?

Answer 20

Interface between bone implant is irregular
All bioactive implants require an incubation period before bone bonding, the length of which varies depending on implant composition

Question 21

What happens if you increase the surface area of a bioactive implant

Answer 21

The bioactivity will increase as well

Small particles behave as partially resorbable

Question 22

What is the thickness of the bonding zone between a bioactive implant and bone proportional to?

Answer 22

It is proportional to its Ib (bioactive index)

Question 23

What is the failure strength of a bio actively fixed bond inversely proportional to?

Answer 23

The thickness of the interfacial zone

Question 24

Which bioglass has a high Ib and bonding layer of 200 micrometers, but also low bond shear strength?

Answer 24

Bioglass 45S5

Question 25

Which ceramic has an intermediate IB that has an interface of 10-20 mm and a high bond shear strength?

Answer 25

A-W glass ceramic

Question 26

At what Ib is interfacial bonding optimal?

Answer 26

At Ib = 4

Question 27

Interfacial bond strength growth over time for A-W Glass ceramic, Bioactive glass, and Alumina

Answer 27

Greatest at first for bioactive glass, then A-W glass ceramic takes over after around 8 weeks
Alumina has lowest interfacial bond strength

Question 28

Morphological factors affecting interfacial strength of bonding

Answer 28

• Change in interfacial area with time
• Progressive mineralization of interfacial tissues, resulting in the increase of the modulus of the interfacial bond
• Shear strength/unit of bonded area

Question 29

What is A-W glass ceramic mostly made of?

Answer 29

SiO2 and CaO

Question 30

What is KGS ceravital mostly made of?

Answer 30

SiO2 and CaO

Question 31

What is KGC Ceravital mostly made of?

Answer 31

SiO2, CaO, and Ca(PO3)2

Question 32

Ceravital Glass Ceramics

Answer 32

Low-alkali glass-ceramics
Used as middle ear implant
Mixtures are melted, cooled, then annealed
They also undergo nucleation and crystallization
Uniformly distributed crystallites of about 0.4 micrometers
Strength in range of 100-200 MPa

Question 33

What compromise must be done for ceravital glass-ceramics?

Answer 33

Compromise is required between biocompatibility and mechanical properties (strength and brittleness)

Question 34

A-W Glass-Ceramics

Answer 34

Ca-phosphate glass-ceramic composed of apatite and wollastonite (CaO, SiO2) crystals and a residual silica glassy matrix.
Commercially known as Cerabone, it is bone bonding and used in vertebral surgery.