Bioactive glasses part 2 Flashcards
Time dependence of bioglass bioactive fixation bond strength
Internal bond strength increases over time
Very strong bond
Stronk
Up to 75 MPa
Time dependence of healed certical bone bond strength
Medium internal bond strength
:P
Range between 25-35 MPa approximately
Time dependence of biological fixation bond strength
Increases to about 25 MPA in 13 weeks, then goes down
Time dependence for morphological fixation bond strength
Increases up to around 7 MPa in 9 weeks, goes down
Bioglass-implant bone interface composition vs. interface distance
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
Comparison of interfacial thickness of bio ceramics in bone
WIP :P
Soft tissue interface Thickness vs. Time
Increased thickness over time to about 300 micrometers
Increase, then small plateau, then increase again
Bone bioglass interface thickness vs. time
Increased thickness over time to 175 micrometers over time
Youngs modulus of soft tissue vs depth
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
Youngs modulus of bone-bioglass interface
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
Composition of silicate-based bioglasses
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
Network former of silicate
Can incorporate many atoms
Can be made with different compositions and properties
Network Modifiers
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
What can you predict with network connectivity?
The bioactivity of glasses
Network connectivity
Measure of bridging oxygen bonds per network former.
Scale of network connectivity
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.
Equation to calculate NC
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
Bioactivity index (Ib) definition
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
Bioactivity index
IB = 100/(t_{0.5bb})
t_{0.5bb} = time required for one half of the interface to be bonded to bone, in vivoWhy is 50% bonding criterion for IB imposed?
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
What happens if you increase the surface area of a bioactive implant
The bioactivity will increase as well
Small particles behave as partially resorbable
What is the thickness of the bonding zone between a bioactive implant and bone proportional to?
It is proportional to its Ib (bioactive index)
What is the failure strength of a bio actively fixed bond inversely proportional to?
The thickness of the interfacial zone
Which bioglass has a high Ib and bonding layer of 200 micrometers, but also low bond shear strength?
Bioglass 45S5
Which ceramic has an intermediate IB that has an interface of 10-20 mm and a high bond shear strength?
A-W glass ceramic
At what Ib is interfacial bonding optimal?
At Ib = 4
Interfacial bond strength growth over time for A-W Glass ceramic, Bioactive glass, and Alumina
Greatest at first for bioactive glass, then A-W glass ceramic takes over after around 8 weeks
Alumina has lowest interfacial bond strength
Morphological factors affecting interfacial strength of bonding
- 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
What is A-W glass ceramic mostly made of?
SiO2 and CaO
What is KGS ceravital mostly made of?
SiO2 and CaO
What is KGC Ceravital mostly made of?
SiO2, CaO, and Ca(PO3)2
Ceravital Glass Ceramics
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
What compromise must be done for ceravital glass-ceramics?
Compromise is required between biocompatibility and mechanical properties (strength and brittleness)
A-W Glass-Ceramics
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.
