a) Abstract:

Development of nano-macroporous glass bone scaffolds by sol-gel processing

During my staying at LehighUniversity (Jan-March 2006), my work consisted of the development of sol-gel derived bioactive silica-based glasses, in which the pore structure is optimized for enhanced bone restoration performance. These materials, with potential applications as glass bone scaffolds, exhibit a nano-macro bimodal pore size distribution, including pores of both 100’s of micrometers and 10’s of nanometers in size. Macropores in excess of 100 m are required for bone cell in-growth, vascularization and nutrient delivery to the centre of the regenerating tissue on implantation, whereas nanopores are thought to be useful for the rapid crystallization of hydroxycarbonate apatite (HCA) and cell adhesion. Interconnected macropores (10-200 m) have been achieved by polymerization-induced (spinodal) phase separation parallel to the sol-gel transition, when a water soluble polymer was added to the sol-gel solution. On the other hand, the nanopore (10-40 nm) structure of such macroporous gel skeletons could be easily tailored by solvent exchange procedures which increase the size of the original micropores inherent to the inorganic sol-gel process. The morphology and texture of the glass monoliths were observed by high resolution scanning electron microscopy (SEM). Specific surface areas, pore volumes and pore size distributions were determined by nitrogen adsorption techniques and mercury intrusion porosimetry.

b) a bullet list of major findings and or what has been accomplished to date

  • Bioactive nano-macroporous glass scaffolds of silica-based composition were successfully produced by the sol-gel method.
  • A polymerization-induced phase separation(of the spinodal type) was found to act as a precursor for macroporosity (interconnected pores of 10-200 m in size).
  • The nanopore structure of the gel skeletons can be easily tailored by the solvent exchange procedures, in basic conditions, giving rise to pores of 10-40 nm in size.
  • Nanopores size was found to increase with:

- solvent exchange: the concentration of ammonia (NH4OH) and time of immersion in ammonia.

- presence of urea or other pore expander additive

- decrease of heat treatment temperature.

  • By stirring vigorously the sol, prior to sol-gel transition, the foaming of the sol is induced. In this case both phenomena, foaming and polymerization-induced phase separation, occur, resulting in a pore network with macropores in excess of 600 m connected by pore windows with diameters in excess of 100 m. The gel skeleton (wall of the pores) is found to contain pores of 1-10 m and nanopores of 10-40 nm, if solvent exchange procedure is done.

c) listing of any publications or presentations based on this work or any collaborations resulting from contact made through the IMI interactions

An abstract, for oral presentation, was submitted to the 8th European Society of Glass Conference (ESG2006) to be held in Sunderland, UK, in September.

d) list of any patents awarded, applications or pending related to work supported by IMI

We are filing a patent application on “Nano-macroporous glass bone scaffolds prepared by sol-gel processing”

e) any awards or honor you have received in the last year regardless of whether resulting from IMI sponsored research (we want to list the accomplishments of our scholars)

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Figure 1.SEM micrographs of 70%SiO2-30%CaO and 77%SiO2-19%CaO-4%P2O5(mol%) bioactive glasses, heat treated at 700C, showing hierarchical interconnected pore morphology. For the first case, SiO2-CaO composition,the specific surface areais 173 m2g-1, the total pore volume is 0.7 cm3g-1 and the totalporosity is ca. 65 vol%, whereas for SiO2-CaO-P2O5 composition,the specific surface areais 208 m2g-1 and the total pore volume is 0.65 cm3g-1.

Figure 3. Pore size distribution curve of 70%SiO2-30%CaO bioactive glass obtained from Hg porosimetry (Porosity=67.2%, bulk density=0.513 and apparent density =1.567).

Figure 2. Pore size distribution curves calculated by the BJH method using the adsorption branches of nitrogen adsorption isotherms.