preparation techniques solid freeform fabrication foams method starch consolidation (*) ...
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Preparation Techniques
Solid Freeform Fabrication
Foams Method
Starch consolidation (*)
Gel-casting
Dual phase mixing
Burn-out of organic phases (*)
Polymeric sponge method (*)
* Used at our Dept.
Starch as pore former
Insoluble in water at low T, but swelling occurs
One of the polymers of glucose…
o Starch form a gel in contact with water and turn a ceramic suspension into a rigid body
o After burn-out of starch and sintering of the ceramic matrix, a material is obtained with porosity corresponding to the swollen starch particles
Polveri ceramiche
(m)
H2O distillata
Preparazione sospensione
Miscelazione e riscaldamento
Amido (m)
Gelificazione
Posizionamento in stampo
Consolidamento
Burn-out
Sinterizzazione
OVERALL SCHEME OF PREPARATION
Starting material (SCNM)50%SiO2 - 16% CaO - 25% Na2O - 9% MgO
Powders sieved
< 106mm
a) b)
c)
Several types of starch
a)
mais potato
rice25% weight
15 % starch
Poor porosity
30% starch
Bad sintering
Average Porosity 100 mm
Total porosity 40%vol.
Res. Compression 6 MPa
A GOOD MATERIAL HAS…
SNCM polvere
SNCM 15 gg SBF
SNCM 1 mese SBF
Confronto tra SNCM tal quale, dopo 15 gg SBF e dopo 1 mese SBF
2 weaks in SBF
Comparison between original material and after soaking in SBF
Development of HAp4 weaks in SBF
Preparation Techniques
Solid Freeform Fabrication
Foams Method
Starch consolidation (*)
Gel-casting
Dual phase mixing
Burn-out of organic phases (*)
Polymeric sponge method (*)
* Used at our Dept.
An ORGANIC COMPONENT occluded
into the matrix leaves POROSITY in the
ceramics when burnt away.
Polymers used: PMMA, PE and PEG.
The organic component must be
homogeneously dispersed and removed
without damaging the ceramic structure
Starting materials
Glass powders SCK (SiO2-CaO-K2O)
Polyethylene with suitable size
METHOD Mixing glass powder and polyethylene
Uniaxial compression
Thermal Treatament
Disks and bars
Uniaxial pressing
PE1: 100-300m
PE2: 300-600m
Two types of PE with different grain saize
Conditions of Treatment
950°C 3h
Differential thermal analysis: 3 crystallization peaks: at 950°C only one left
Vetroceramic material (amorphous matrix + one or more dispersed
crystalline phases)
NEEDS
Maximize % vol. porosity
Sufficient dimensions of pores
Satisfactory mechanical properties
Establish highest tolerable PE content
MERCURY POROSIMETRY
Mercury does not wet the solid
PROCEDUREOutgassing of the sample and filling with Hg.o Initial pressure due to the height of the column o Increase in pressure causes Hg intrusion into smaller and smaller
pores o Max achievable pressure dictates smallest measurable diametero Results: total pore volume, Plot of pore distribution
Washburn equation: inverse relationship between pressure and pore radius
= surface tension of mercury
θ = contact angle between Hg and the sample
Porosimetry results for (PE1-50)
Small pores between 1 - 6m
Large pores round 85 m
Samples Pore volume %
PE1-50 (1) 62.4
PE1-50 (2) 62.6
PE1-50 (3) 65.4
Good reproducibility
Pore volume larger than that of PE: additional porosity due
to evolution of gases during burning out
Total pore volume for three samples from the same batch
Other means to study porosity: analysis of SEM images
SEM back-scattering
Different coloration according to pore size
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50-100 100-200 200-300 300-650
Dimensioni pori [micron]
Nu
me
ro p
ori
Distribution of pores according to size.
Big pores (useful for vascularization) and small pores (useful in cellular adhesion)
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50-100 100-200 200-300 300-650
Dimensioni pori [micron]
% A
rea
po
ri
Volume of pores as a function of size
Good interconnection
of porosity
Trabecular
porosity
Behavior of scaffolds in SBF
48h in SBF High bioactivity
7 days in SBF
2 weaks in SBF
Samples
Soaking time in SBF
Weight loss %
Weight loss/Area (mg/cm2)
SCK glass
1 week 1.8 ± 0.1 4.3 ± 0.3
SCK glass
3 months 3.1 ± 0.3 7.6 ± 0.3
SCK vc 1 weak 0.7 ± 0.2 1.6 ± 0.3
SCK vc 3 months / /
Glass material more soluble than corresponding vetroceramic
Samples
Soaking time in
SBF
Weight loss %
Weight loss/ Area (mg/cm2)
PE1-50 2 weaks 8.5 ± 0.4 12.1 ± 0.2
PE2-50 2 weaks 7.6 ± 0.2 9.1 ± 0.2
PE2-50 3 months 30.7 ± 0.4 53.4 ± 3.1
Scaffold, with very high surface, has a weight loss much more pronounced! (30% after 3 months)
Processes: • release of cations (K+) • capture of H+ from solution Increase in pH (up to 9: non compatible with a successful implant).
Vetroceramic: good adhesion of osteoblasts
after 6h
Cellular death after 4 days, due to an increase in pH!)
POSSIBLE SOLUTION
Pre-treatment in SBF before implant to quench the pH change
ADVANTAGES
o Avoid cellular death
o Implant a material with HAp microcrystals
already present: better osteointegration
Proliferation on scaffold after pre-treatment in SBF: marked increase in cellular response
The end