pH-responsive layer-by-layer films of zwitterionic block copolymer micelles

Abstract

We report a strategy to incorporate micelles of poly[3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate]-block-poly[2-(diisopropylamino)ethyl methacrylate] (bPDMA-b-PDPA) into electrostatic layer-by-layer (LbL) films. We obtained micelles with pH-responsive PDPA-cores and zwitterionic bPDMA-coronae at pH 8.5 through pH-induced self-assembly of bPDMA-b-PDPA in aqueous solution. To incorporate bPDMA-b-PDPA micelles into LbL films, we first obtained a net electrical charge on bPDMA-coronae. Negative charges of the zwitterionic units were screened through complexation of bPDMA-b-PDPA micelles and poly(allylamine hydrochloride) (PAH). Positively charged micellar complexes were then self-assembled at the surface using poly(sodium 4-styrenesulfonate) (PSS). The pH-stability of the multilayers was examined by exposing the films to decreasing pH values. Despite the disintegration of micellar complexes below pH 7, no change in film thickness was recorded between pH 8.5 and 3.5. Only $20% of the film released at pH < 3.5. Moreover, we demonstrated that when multilayers were exposed to decreasing pH at a temperature below the upper critical solution temperature (UCST) of betainized coronal chains, the film thickness increased by 20% between pH 4.5 and 3. This is probably due to phase separation of the corona block and formation of voids within the film, probably entrapping water molecules within the multilayers. Decreasing temperature also shifted the critical disintegration pH (onset of multilayer dissolution) to a slightly lower pH. By taking advantage of the pH-responsive cores, we showed that multilayers were capable of releasing functional molecules under moderately acidic conditions. Important biological properties of polybetaines, higher loading capacity of zwitterionic block copolymer micelles than linear polybetaines and pH-response of the multilayers at physiologically related pH values make such films promising for biomedical applications.

Preparation of Layer‐by‐Layer Films with Remarkably Different pH‐Stability and Release Properties Using Dual Responsive Block Copolymer Micelles

“…In addition, owing to their hydrophobic micellar cores, BCMs increase the loading capacity of LbL films for drug molecules with low water solubility. Multilayers containing stimuli‐responsive BCMs have been reported earlier . In this study, we report on preparation of LbL films containing PDMA‐ b ‐PDEA micelles and the effect of film deposition pH and temperature on the properties of the micellar multilayers.…”

“…Multilayers containing stimuli-responsive BCMs have been reported earlier. [24][25][26][27][28][29][30][31][32][33][34] In this study, we report on preparation of LbL films containing PDMA-b-PDEA micelles and the effect of film deposition pH and temperature on the properties of the micellar multilayers. We found that only 0.5 unit difference in film deposition pH or 5 °C difference in film deposition temperature can lead to multilayer films with drastically different pH-stability and release properties from surface.…”

Stimuli-Responsive Polymers Providing New Opportunities for Various Applications

“…The related aggregate structures can reversibly dissolve, swell or shrink depending on the pH of the medium (Figure 4d) [27][28][29][30][31]. When these polymers are used in various surface applications such as films, layerby-layer (LbL) technology, membranes, brushes, many behaviors such as ion selective permeability, surface charge change, wettability, change in pore size and thickening/thinning of the polymer layer are encountered [32][33][34][35][36][37][38][39]. When these polymers are involved in surface applications such as membranes, numerous behaviors such as ion selective permeation and change in pore size are encountered (Figure 4f) [39][40][41][42].…”

Multi-responsive hydrogels for drug delivery and tissue engineering applications

“…LbL assembly of microgel [ 56 ] or micellar [ 57 ] structures has also been demonstrated in the literature as a method to control responsive properties of the material. By varying the composition of the microgels, Clark and Lyon showed that the temperature response of the LbL-assembled film of P(NIPAAm- co-N -isopropyl methacrylamide) microgels with a polycationic layer could be tuned not only by the composition of the microgels, but also by the ratio of different microgel compositions assembled in the film [ 56 ].…”

“…Similarly, Yusan et al [ 57 ] found that the upper critical solution temperature (UCST) response of the zwitterionic poly[3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate] (β-PDMA)-coronae of micelles assembled via LbL deposition into a multilayer film altered the effect of decreasing pH on the film thickness. The increase in thickness of the film at a temperature below the UCST was attributed to the phase separation of the β-PDMA chains, resulting in voids within the multilayers that increased the imbibition of water and volume of the film.…”