MACROPOROUS SCAFFOLDS FOR BONE REPLACEMENT

1. MACROPOROUS SCAFFOLDS FOR BONE REPLACEMENT

2. SCAFFOLD is, as in house building, a structure meant to support the growing edifice: bone regeneration Simulates the features of trabecular (cancellous, spongy) bone

3. Cancellous Bone Porous and interconnected structure: Resistance to compression 2-12 MPa, porosity 60-70% vol.

4. 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)

5. 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.

6. 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.

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

9. 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.

10. Several ways of introducing porosity into the systems: • from suspensions • from sol-gel

11. Several ways of introducing porosity into the systems: • from suspensions • from sol-gel

12. 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

13. 40% H2O2 60% H2O2

14. Foams with in situ polymerization Sepulveda, J Eur Cer Soc 1999

15. Different Microstructures as a function of foaming degree

16. 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

17. Several ways of introducing porosity into the systems: • from suspensions • from sol-gel

18. Jones, J mat Sci 38(2003)3783-3790 FOAMING SOL-GEL Sol-gel glasses: more expensive, but more bioactive and bio-reabsorbable because of a mesotexture (pores 2-50 nm) • Reactions • Hydrolysis of reactant • alcohol condensation • Water condensation • Factors • pH • Temperature and duration of reaction • Concentration of reagents • Ratio H2O/Si • Ageing • Drying

19. General scheme for sol-gel procedure

20. 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

21. Use of alcoxides R-O-Me • TEOS: tetraetoxysilane (C2H5O)4Si, ma also Me = Ti, etc. • Steps: • hydrolysis • monomer condensation • formation of particles (sol) • agglomeration of particles to form the gel

22. 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

24. Silicic acid condenses to silica

25. To obtain massive sol-gel glasses

28. 600°C 700°C 800°C 1000°C

29. Mesopores distribution as obtained from nitrogen adsorption (BJH method) Macropores as obtained from mercury porosimeter (described below)

30. Sintering: from glass to vetroceramics Wollastonite present

31. 3 days 8h Different bioactivity of samples sintered at different temperatures: Low-tp samples favor the formation of HAp

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