Influence of Surface Chemistry on Ibuprofen Adsorption and Confinement in Mesoporous Silicon Microparticles

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Abstract
The effect of adsorption and confinement on ibuprofen were studied by immersion loading the molecules into mesoporous silicon (PSi) microparticles. The PSi microparticles were modified into thermally oxidized (TOPSi) and thermally hydrocarbonized (THCPSi), in order to evaluate the effects of the loading solvent and surface chemistry on the obtainable drug payloads. The payloads, location, and the molecular state of the adsorbed drug were evaluated using thermal analysis. The results showed that after ~800 mg/cm3 (wdrug/Vpores) of drug had adsorbed into the mesopores, depending on the solvent used in the immersion, the drug began to rapidly recrystallize on the external surface of the particles. Moderate concentrations, however, enabled payloads of 800‒850 mg/cm3 without excessive surface crystallization, and thus, there was no need for rinsing the samples to remove the external crystallized portion. The results showed that the confined ibuprofen forms nanocrystals inside the mesopores after ca. 200 mg/cm3 payloads were obtained, accounting for half of the adsorbed drug amount. The presence of both crystalline and non-crystalline phase was further characterized with variable temperature solid-state nuclear magnetic resonance (NMR) measurements. The interactions between the drug molecules and the pore walls of TOPSi and THCPSi were observed with Fourier transform infrared (FTIR) and 1H NMR spectroscopies, and confirmed the hydrogen bonding between the silanol groups of TOPSi and the adsorbed ibuprofen, but having only limited effect on the overall state of the confined drug. In vitro drug permeation studies in Caco-2 and Caco-2/HT29 co-cultures showed the adsorption into hydrophilic or hydrophobic PSi microparticles had no significant effects on the ibuprofen permeation, whether the drug was partially nanocrystalline or completely in liquid-like state.
Funding Information
  • European Commission (310892)
  • Suomen Akatemia (252215, 277190, 281300)

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