MACROPOROUS SCAFFOLDS FOR

BONE REPLACEMENT

SCAFFOLD is, as in house building, a structure meant to

support the growing edifice: bone regeneration

Simulates the features of trabecular (cancellous, spongy) bone

Cancellous Bone

Porous and interconnected structure:

Resistance to compression 2-12 MPa, porosity 60-70% vol.

Requirements for a SCAFFOLD

Pore Dimension > 100µm-150µm Pore volume Percentage > 50% vol. High interconnection degree Suitable mechanical properties Workability Bioactivity Good surface-cell interaction (to favor cell

proliferation and growth)

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.

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.

Solid Freeform Fabrication: a very expensive technique for reproducing 3D objects

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.

Several ways of introducing porosity into the systems:

• from suspensions

• from sol-gel

Several ways of introducing porosity into the systems:

• from suspensions

• from sol-gel

Foams with H2O2

glass powder suspensions are foamed with a dilute solution of H2O2 at 60°C. The release of O2 generates the porous structure, then the substrate is sintered

Navarro, Biomaterials 25 (2004) 4233–4241

phosphate glass P2O5–CaO– Na2O–TiO2

Scaffold 3D

40% H2O2

60% H2O2

Foams with in situ polymerization

Sepulveda, J Eur Cer Soc 1999

Different Microstructures as a function of foaming degree

Garrn J Eur Cer Soc 24(2004)579-587

Other possibility: Albumin as foam former in water sospension

Anfiphylic proprieties, (both polar and

apolar aminoacids)

albumin

Several ways of introducing porosity into the systems:

• from suspensions

• from sol-gel

FOAMING SOL-GEL

Jones, J mat Sci 38(2003)3783-3790

Sol-gel glasses: more expensive, but more bioactive and bio-reabsorbable because of a mesotexture (pores 2-50 nm)

Reactionso Hydrolysis of reactanto alcohol condensationo Water condensation

Factors pH Temperature and duration of reaction Concentration of reagents Ratio H2O/Si Ageing Drying

General scheme for sol-gel procedure

Sol-gel method

Solution: dispersion at the molecular level

Sol: suspension of microscopic particles (colloids). Light scattering (Tyndall effect)

Gel: a suspension keeping its form. Reticulation among particles

Gels come from sols

Use of alcoxides R-O-Me

TEOS: tetraetoxysilane (C2H5O)4Si, ma also Me = Ti, etc.

Steps:1. hydrolysis2. monomer condensation3. formation of particles (sol)4. agglomeration of particles to form the gel

Hydrolysis (EtO)4Si + 4 H2O H4SiO4 + 4 EtOH

acid (and base) catalyzed: H- protonation of TEOS I (EtO)3Si- O-Et + H+ (EtO)3Si- O-Et + - attack of water on Si atom (as shown by

measurements with H218O)

- release of EtOH with formation of + (EtO)3Si-O-H I H- distacco di H+ che ritorna in circolo

Silicic acid condenses to silica

To obtain massive sol-gel glasses

600°C 700°C

800°C 1000°C

Mesopores distribution as obtained from nitrogen adsorption (BJH method)

Macropores as obtained from

mercury porosimeter (described below)

Sintering: from glass to vetroceramics

Wollastonite present

8h 3 days

Different bioactivity of samples sintered at different temperatures:

Low-tp samples favor the formation of HAp

Compression behavior of scaffoldsI Linear region (max resistance)

II Collapse of the pores

III Res. to compression of the solid