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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 scaffolds
I Linear region (max resistance)
II Collapse of the pores
III Res. to compression of the solid