Abstract
Ureasil-Poly(ethylene oxide) (u-PEO500) and ureasil-Poly(propylene oxide) (u-PPO400) films, unloaded and loaded with dexamethasone acetate (DMA), have been investigated by carrying out atomic force microscopy (AFM), ultrasonic force microscopy (UFM), contact-angle, and drug release experiments. In addition, X-ray diffraction, small angle X-ray scattering, and infrared spectroscopy have provided essential information to understand the films’ structural organization. Our results reveal that while in u-PEO500 DMA occupies sites near the ether oxygen and remains absent from the film surface, in u-PPO400 new crystalline phases are formed when DMA is loaded, which show up as ~30–100 nm in diameter rounded clusters aligned along a well-defined direction, presumably related to the one defined by the characteristic polymer ropes distinguished on the surface of the unloaded u-PPO film; occasionally, larger needle-shaped DMA crystals are also observed. UFM reveals that in the unloaded u-PPO matrix the polymer ropes are made up of strands, which in turn consist of aligned ~180 nm in diameter stiffer rounded clusters possibly formed by siloxane-node aggregates; the new crystalline phases may grow in-between the strands when the drug is loaded. The results illustrate the potential of AFM-based procedures, in combination with additional physico-chemical techniques, to picture the nanostructural arrangements in polymer matrices intended for drug delivery.
Highlights
Introduction published maps and institutional affilUreasil-polyether hybrid films provide an extremely versatile matrix—platform for many different applications, including controlled drug delivery [1,2,3]
The precursor was dissolved in water and ethanol in an appropriate vessel, and HCl was added as a catalyst to subject the precursor to the sol-gel hydrolysis and condensation reactions, in the proportion 500 μL ethanol, 25 μL water, and 25 μL HCl catalyst to 0.75 mg of ureasil-polyether hybrid precursor
The u-PEO500 and u-PPO400 films were immersed in 900 mL of medium (phosphate buffer 7.2 pH with 0.5% of procetyl AWS® (CRODA, Rawcliffe Bridge, UK)) to guarantee the sink condition at 37 ± 0.5 ◦ C and were stirred with a USP dissolution apparatus 2 at a speed of 50 rpm
Summary
The ureasil-polyether hybrid materials were synthesized by the well-known sol-gel process. A modified alkoxide, 3-(isocyanatopropyl)-triethoxysilane (IsoTrEOS) (Sigma-Aldrich, São Paolo, Brasil 95% purity, CAS #24801-88-5) in a polymer/alkoxide molar ratio of 1:2 was added to this solution, and the resulting solution was maintained at reflux for 24 h at 60 ◦ C to promote the formation of the hybrid precursor (EtO) Si(CH2 ) NHC(=O)NHCHCH3 CH2 -(polyether)-CH2 CH3 CHNH(O=)NHC(CH2 ) Si(OEt). The precursor was dissolved in water and ethanol in an appropriate vessel, and HCl was added as a catalyst to subject the precursor to the sol-gel hydrolysis and condensation reactions, in the proportion 500 μL ethanol, 25 μL water, and 25 μL HCl catalyst to 0.75 mg of ureasil-polyether hybrid precursor. Brasil, CAS: 1177-87-3) in 3% wt/wt proportion to the precursor in our case was dissolved in the ethanol/water solution, and the precursor and the HCl catalyst were added to induce the reactions.
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