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Preparation Techniques  Solid Freeform Fabrication  Foams Method  Starch consolidation (*)  Gel-casting  Dual phase mixing  Burn-out of organic phases.

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Presentation on theme: "Preparation Techniques  Solid Freeform Fabrication  Foams Method  Starch consolidation (*)  Gel-casting  Dual phase mixing  Burn-out of organic phases."— Presentation transcript:

1 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.

2  Starch as pore former  Insoluble in water at low T, but swelling occurs One of the polymers of glucose…

3 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

4 Polveri ceramiche (m) H 2 O distillata Preparazione sospensione Miscelazione e riscaldamento Amido (m) Gelificazione Posizionamento in stampo Consolidamento Burn-out Sinterizzazione OVERALL SCHEME OF PREPARATION

5 Starting material (SCNM) 50%SiO % CaO - 25% Na 2 O - 9% MgO Powders sieved < 106mm

6 a) b) c) Several types of starch

7 a) mais potato rice 25% weight

8 15 % starch Poor porosity 30% starch Bad sintering

9  Average Porosity 100 mm  Total porosity 40%vol.  Res. Compression 6 MPa A GOOD MATERIAL HAS…

10 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 HAp 4 weaks in SBF

11 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.

12 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

13 Starting materials  Glass powders SCK (SiO 2 -CaO-K 2 O)  Polyethylene with suitable size METHOD  Mixing glass powder and polyethylene  Uniaxial compression  Thermal Treatament

14 Disks and bars Uniaxial pressing

15 PE1:  m PE2:  m Two types of PE with different grain saize

16 Conditions of Treatment 950°C 3h Differential thermal analysis: 3 crystallization peaks: at 950°C only one left

17 Vetroceramic material (amorphous matrix + one or more dispersed crystalline phases)

18 NEEDS  Maximize % vol. porosity  Sufficient dimensions of pores  Satisfactory mechanical properties  Establish highest tolerable PE content

19 MERCURY POROSIMETRY Mercury does not wet the solid

20 PROCEDURE Outgassing 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 diameter o Results: total pore volume, Plot of pore distribution

21 Washburn equation: inverse relationship between pressure and pore radius  = surface tension of mercury θ = contact angle between Hg and the sample

22 Porosimetry results for (PE1-50) Small pores between  m Large pores round 85  m

23 SamplesPore 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

24 Other means to study porosity: analysis of SEM images

25 SEM back-scattering Different coloration according to pore size

26 Dimensioni pori [micron] Numero pori Distribution of pores according to size. Big pores (useful for vascularization) and small pores (useful in cellular adhesion)

27 Volume of pores as a function of size

28 Good interconnection of porosity Trabecular porosity

29 Behavior of scaffolds in SBF

30 48h in SBF High bioactivity 7 days in SBF

31 2 weaks in SBF

32 Samples Soaking time in SBF Weight loss % Weight loss/Area (mg/cm 2 ) SCK glass1 week1.8 ± ± 0.3 SCK glass3 months3.1 ± ± 0.3 SCK vc1 weak0.7 ± ± 0.3 SCK vc3 months// Glass material more soluble than corresponding vetroceramic

33 Samples Soaking time in SBF Weight loss % Weight loss/ Area (mg/cm 2 ) PE1-502 weaks 8.5 ± ± 0.2 PE2-502 weaks 7.6 ± ± 0.2 PE2-503 months 30.7 ± ± 3.1 Scaffold, with very high surface, has a weight loss much more pronounced! (30% after 3 months)

34 Processes: release of cations (K + ) capture of H + from solution Increase in pH (up to 9: non compatible with a successful implant).

35 Vetroceramic: good adhesion of osteoblasts after 6h

36 Cellular death after 4 days, due to an increase in pH!)

37 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

38 Proliferation on scaffold after pre-treatment in SBF: marked increase in cellular response

39 The end


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