preparation techniques
DESCRIPTION
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. One of the polymers of glucose…. Starch as pore former - PowerPoint PPT PresentationTRANSCRIPT
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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.
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Starch as pore former
Insoluble in water at low T, but swelling occurs
One of the polymers of glucose…
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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
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Polveri ceramiche
(m)
H2O distillata
Preparazione sospensione
Miscelazione e riscaldamento
Amido (m)
Gelificazione
Posizionamento in stampo
Consolidamento
Burn-out
Sinterizzazione
OVERALL SCHEME OF PREPARATION
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Starting material (SCNM)50%SiO2 - 16% CaO - 25% Na2O - 9% MgO
Powders sieved
< 106mm
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a) b)
c)
Several types of starch
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a)
mais potato
rice25% weight
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15 % starch
Poor porosity
30% starch
Bad sintering
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Average Porosity 100 mm
Total porosity 40%vol.
Res. Compression 6 MPa
A GOOD MATERIAL HAS…
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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
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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.
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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
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Starting materials
Glass powders SCK (SiO2-CaO-K2O)
Polyethylene with suitable size
METHOD Mixing glass powder and polyethylene
Uniaxial compression
Thermal Treatament
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Disks and bars
Uniaxial pressing
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PE1: 100-300m
PE2: 300-600m
Two types of PE with different grain saize
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Conditions of Treatment
950°C 3h
Differential thermal analysis: 3 crystallization peaks: at 950°C only one left
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Vetroceramic material (amorphous matrix + one or more dispersed
crystalline phases)
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NEEDS
Maximize % vol. porosity
Sufficient dimensions of pores
Satisfactory mechanical properties
Establish highest tolerable PE content
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MERCURY POROSIMETRY
Mercury does not wet the solid
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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
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Washburn equation: inverse relationship between pressure and pore radius
= surface tension of mercury
θ = contact angle between Hg and the sample
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Porosimetry results for (PE1-50)
Small pores between 1 - 6m
Large pores round 85 m
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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
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Other means to study porosity: analysis of SEM images
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SEM back-scattering
Different coloration according to pore size
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30
11
34
0
5
10
15
20
25
30
35
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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7
119
73
0
10
20
30
40
50
60
70
80
50-100 100-200 200-300 300-650
Dimensioni pori [micron]
% A
rea
po
ri
Volume of pores as a function of size
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Good interconnection
of porosity
Trabecular
porosity
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Behavior of scaffolds in SBF
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48h in SBF High bioactivity
7 days in SBF
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2 weaks in SBF
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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
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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)
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Processes: • release of cations (K+) • capture of H+ from solution Increase in pH (up to 9: non compatible with a successful implant).
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Vetroceramic: good adhesion of osteoblasts
after 6h
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Cellular death after 4 days, due to an increase in pH!)
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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
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Proliferation on scaffold after pre-treatment in SBF: marked increase in cellular response
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The end