RESUMO
Layer-by-layer films composed of polysaccharides and poly(amidoamine) dendrimer bearing phenylboronic acid (PBA-PAMAM) were prepared to study the deposition behavior of the films and their stability in buffer solutions and in sugar solutions. Alginic acid (AGA) and carboxymethylcellulose (CMC) were employed as counter-polymers in constructing LbL films. AGA/PBA-PAMAM films were successfully prepared at pH 6.0-9.0, whereas the preparation of CMC/PBA-PAMAM film was unsuccessful at pH 8.0 and 9.0. The results show that the LbL films formed mainly through electrostatic affinity between PBA-PAMAM and polysaccharides, while, for AGA/PBA-PAMAM films, the participation of boronate ester bonds in the films was suggested. AGA/PBA-PAMAM films were stable in the solutions of pH 6.0-9.0. In contrast, CMC/PBA-PAMAM films decomposed at pH 7.5-9.0. The AGA/PBA-PAMAM films decomposed in response to 5-30 mM fructose at pH 7.5, while the films were stable in glucose solutions. Thus, AGA is useful as a counter-polymer for constructing PBA-PAMAM films that are stable at physiological pH and decompose in response to fructose.
RESUMO
Layer-by-layer (LbL) multilayer films were prepared using phenylboronic acid-modified poly(amidoamine) dendrimers and poly(vinyl alcohol) (PVA) in order to investigate the glucose sensitivity of the films. We used dendrimer derivatives modified with 3-carboxyphenylboronic acid (3CPBA-D) and 3-carboxy-5-nitrophenylboronic acid (3C5NPBA-D) to evaluate the effect of electron-withdrawing nitro groups on glucose sensitivity. PVA/3CPBA-D and PVA/3C5NPBA-D films were prepared on the surface of a quartz slide from PVA and 3CPBA-D or 3C5NPBA-D solutions at pH 7.0, 8.0, and 9.0 through boronate ester bonds. The dendrimer-based LbL films were stable at pH 7.0-9.0, whereas they decomposed in acidic media because of the instability of the boronate ester linkages. The pH threshold of decomposition was at pH 6.0-7.0 for both films. The PVA/3C5NPBA-D film was more stable than the PVA/3CPBA-D film in this range. Both films decomposed in response to glucose under physiological conditions (pH 7.4 buffer solution containing 150 mM NaCl at 37 °C), and the decomposition depended on the glucose concentration. The PVA/3C5NPBA-D film was more sensitive to glucose than the PVA/3CPBA-D film, probably due to the higher binding affinity of 3C5NPBA-D to glucose under physiological conditions. The higher response of the PVA/3C5NPBA-D film was explained by the electron-withdrawing effect of the nitro substituent on the phenylboronic acid ring. The results suggest that dendrimer-based LbL films could be used for glucose-triggered release systems.
