of the patterned features can be achieved simply by changing the aspect of the
lithographic stamp, allowing flexibility in the directed growth of hydroxyapatite
upon porous silicon. Additional collaboration between Canham and Coffer has resulted in the preparation of transition metal complex-doped hydroxyapatite/silicon
systems that are potentially capable of in vivo delivery of anti-tumor agents and
nucleotide partners [72, 73]. Immersion of porous silicon substrates in SBF containing Ru(II) species produced calcium phosphate films doped with metal complex, confirmed by photoluminescence spectroscopy and fluorescence microscopy.
Diffusion of the metal complex from the hydroxyapatite matrix was observed upon
heating to 130
C, releasing submicromolar concentrations of Ru(II) as determined
by spectrophotometry. Incorporation of anti-cancer agents such as cis-platin and
related Pt(II) complexes into hydroxyapatite films was also accomplished, shown
through SIMS and EDS. Increasing the concentration of Pt(II) in the SBF medium
resulted in higher dopant levels; however, the thickness of hydroxyapatite deposits
decreased on average, suggesting that the metal complex may inhibit diffusion and
nucleation of the solvated apatite precursors upon the silicon surface. At equivalent
concentrations, doping of hydroxyapatite/porous silicon with the more steric carboplatin species was less efficient than cis-platin, further supporting a complexinhibitive mechanism. Diffusion rates of Pt(II) complexes to the surrounding medium upon thermal annealing were discovered to depend largely upon the initial
loading concentrations and comparatively little upon the ligands. These results
indicate that a variety of platinum- and other metal-based drugs and biomolecules
could be dispensed from these hydroxyapatite–silicon structures, limited primarily
by the amount of compound that can be precipitated within the calcium films.
Future work is expected to focus upon the development of these undoped and
metal complex-doped hydroxyapatite–silicon composites, as well as biodegradable
porous silicon itself, for connective tissue grafts and drug delivery implants.
The bioactivity of porous silicon toward living cellular systems is also under
investigation. Efforts have been made by Bayliss, Buckberry, and their collaboFig. 16.8. Images of patterned silicon
substrates. (a) SEM image of 100 mm wide
SiO 2 mesas on silicon. (b) Optical image of
(a) after anodic etching of the silicon surface.
(c) Optical image of (b) after cathodization in
SBF for 30 min. (Reprinted with permission
from [71]. Copyright 2002 Wiley-VCH. J. L.
Coffer is thanked for permission to reprint this
figure.)
16.4 Chemical Applications Based on Porous Silicon 529
lithographic stamp, allowing flexibility in the directed growth of hydroxyapatite
upon porous silicon. Additional collaboration between Canham and Coffer has resulted in the preparation of transition metal complex-doped hydroxyapatite/silicon
systems that are potentially capable of in vivo delivery of anti-tumor agents and
nucleotide partners [72, 73]. Immersion of porous silicon substrates in SBF containing Ru(II) species produced calcium phosphate films doped with metal complex, confirmed by photoluminescence spectroscopy and fluorescence microscopy.
Diffusion of the metal complex from the hydroxyapatite matrix was observed upon
heating to 130
C, releasing submicromolar concentrations of Ru(II) as determined
by spectrophotometry. Incorporation of anti-cancer agents such as cis-platin and
related Pt(II) complexes into hydroxyapatite films was also accomplished, shown
through SIMS and EDS. Increasing the concentration of Pt(II) in the SBF medium
resulted in higher dopant levels; however, the thickness of hydroxyapatite deposits
decreased on average, suggesting that the metal complex may inhibit diffusion and
nucleation of the solvated apatite precursors upon the silicon surface. At equivalent
concentrations, doping of hydroxyapatite/porous silicon with the more steric carboplatin species was less efficient than cis-platin, further supporting a complexinhibitive mechanism. Diffusion rates of Pt(II) complexes to the surrounding medium upon thermal annealing were discovered to depend largely upon the initial
loading concentrations and comparatively little upon the ligands. These results
indicate that a variety of platinum- and other metal-based drugs and biomolecules
could be dispensed from these hydroxyapatite–silicon structures, limited primarily
by the amount of compound that can be precipitated within the calcium films.
Future work is expected to focus upon the development of these undoped and
metal complex-doped hydroxyapatite–silicon composites, as well as biodegradable
porous silicon itself, for connective tissue grafts and drug delivery implants.
The bioactivity of porous silicon toward living cellular systems is also under
investigation. Efforts have been made by Bayliss, Buckberry, and their collaboFig. 16.8. Images of patterned silicon
substrates. (a) SEM image of 100 mm wide
SiO 2 mesas on silicon. (b) Optical image of
(a) after anodic etching of the silicon surface.
(c) Optical image of (b) after cathodization in
SBF for 30 min. (Reprinted with permission
from [71]. Copyright 2002 Wiley-VCH. J. L.
Coffer is thanked for permission to reprint this
figure.)
16.4 Chemical Applications Based on Porous Silicon 529