SBA-15 silica was prepared according to Zhao [14] using commercial triblock copolymer Pluronic P123—PEO20- PPO70-PEO20 [poly(ethylene glycol)-block-poly (propylene glycol)-block-poly(ethylene glycol)] (Sigma-Aldrich) as a templating agent. The P123 copolymer was dissolved in a mixture of distilled water and HCl under stirring, followed by the addition of tetraethyl orthosilicate (TEOS). The mixture was maintained at 35˚C for 24 h, and then for an additional 24 h at 100˚C under static conditions in a Teflon-lined autoclave. The obtained material was filtered and dried at 40˚C and the surfactant was removed by calcination (550˚C for 5 h).

The hybrid was prepared using the following procedure [28]: 0.5 g of calcined SBA-15 was added to a 3.5 mL solution of 0.245 g of monomer (N-isopropylacrylamide—N-iPAAm) and 0.005 g of crosslinking agent (N,N,N’, N’-methylene-bisacrylamide—MBA). The mixture was transferred to an INNOVA 4200 (150 rpm) shaker, and the mixture was continuously purged with nitrogen. The solution was then allowed to polymerize for 24 h in a water bath at 10˚C. The obtained hybrid material was dried at 60˚C for 24 h and subsequently washed to remove the excess of monomers, crosslinking agent, initiator, and accelerator. In the washing stage, the material was disaggregated, suspended in water, and continually stirred. The hybrid was then collected by centrifugation at 3600 rpm for 3 min and dried at 60˚C for 24 h [29].

The FTIR measurements were conducted with an ABB Bomen model MB102 spectrophotometer within the range of 4000 - 400 cm^–1. The FTIR spectra were recorded at room temperature using KBr pellets and a resolution of 4 cm^–1 and 64 scans/min. SEM characterization was performed in a scanning electron microscope (Quanta 200 FEG-FEI) operating at 30 kV. The small-angle XRD patterns were obtained using an Ultima IV ® (Rigaku Inc.) 3 kW generator rotating equipment anode X-ray diffraction equipped with a copper anode (λ = 1.54 Ǻ). The generator was operated at 40 kV and 30 mA. The incident X-ray was set at a wavelength of 1.488 Å, while the angle scattering 2θ ranged from 0˚ to 5˚.

SBA-15 and [SBA-15/P(N-iPAAm)] were loaded with Metaiodobenzylguanidine (MIBG) as follows: 0.2 g of the powder sample was added to 25 mL of an MIBG solution (800 µg·mL^–1) and shaken for 48 h at 25˚C (200 rpm). A 1:10 weight ratio of the MIBG/solid sample was used. Powder MIBG-loaded samples were recovered by filtration, washed with distilled water, and left to dry for 24 h at 60˚C. The in vitro release profile was obtained by soaking the samples (50 mg) in 30 mL of a simulated body fluid (SBF) [30] for 24hs at room temperature. The UV spectrometry procedure (Shimadzu UV-VIS V-V 2550) was used to monitor the amount of MIBG that had been loaded and released as a function of time. The solutions were continuously stirred, and the concentration of MIBG in SBF was determined by the intensity of the absorption band at 230 nm.

The cytotoxicity of SBA-15 and [SBA-15/P(N-iPAAm)] were evaluated by means of MTT ((3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay in human lung fibroblast cells (MRC-5), obtained from the radiobiology laboratory from the Center for the Development of Nuclear Technology (CDTN/CNEN).

The cells (1500 cells/well) were subjected to treatment for 48 hours, under increasing concentrations of SBA-15 and [SBA-15/P(N-iPAAm)] (0.1 to 200 μg·mL^–1). Eight replicates were investigated for statistical evaluation. The determination of the absorbance at 570 nm of the formed product is a measure of metabolic cell viability, and both quantities are directly proportional.

All experiments were performed in triplicate and expressed as the mean ± standard deviation, unless otherwise stated. The specific activity data were compared by means of the Student’s t-test, using the prism 4.0 software, considering a 95% confidence interval.

Figure 1 shows the FTIR spectra of all studied samples. The spectra of pure SBA-15 and the hybrid sample exhibited different absorption bands. The SBA-15 spectrum was dominated by nO-H modes, presenting a broad and intense band at 3440 cm^–1 assigned to hydroxyl groups. A broad and very intense band in the range 1000 - 1200 cm^-1, corresponding to nSi-O-Si modes of the SBA-15 siliceous matrix, was also present. The band at 960 cm^–1 could be assigned to δ (HOH) physisorbed water and the Si-O stretching vibration of surface Si-OH groups. In hybrid systems, the bands corresponding to the nC-H modes of P(N-iPAAm) are commonly observed between 2972 and 2875 cm^–1; the bands attributed to the isopropyl group were located at 1386 and 1368 cm^–1; the band corresponding to the bending vibration of CH₃ was located at 1456 cm^–1; while the bands arising from C=O stretching and N-H bending vibrations were observed at 1645 and 1550 cm^–1, respectively.

The monomer characteristic bands (nC=C 1620 cm^–1; dCH₂ = 1409 cm^–1; dH₂C=C- 1305 and 1325 cm^–1; dvinyl group at 990 and 916 cm^–1) were not present in the hybrid sample spectra, as can be seen in the scale-expanded FTIR spectrum in the 1800 - 900 cm^–1 region (Figure 2). These results prove the presence of P(N-iPAAm) in SBA- 15 pores with no other significant synthesis components (monomer, initiator, or accelerator) and demonstrate the successful conversion of the monomers into polymer [29].

Figure 3 shows SEM images of the SBA-15 and [SBA-15/P(N-iPAAm)] samples. SBA-15 consists of many rope-like domains with average sizes of 1.7 μm aggregated into wheat-like macrostructures, Figure 3(a). A