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

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)

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

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