Asymmetric Modification of Carbon Nanotube Arrays with Thermoresponsive Hydrogel for Controlled Delivery

Abstract

In this work, bipolar electrochemistry is used to perform wireless indirect electrodeposition of two different polymer coatings on both sides of carbon nanotube arrays. Using a thermoresponsive hydrogel on one side and an inert insoluble polymer on the other side, it is possible to generate, in a single step, a nanoporous reservoir with Janus character closed on one side by a thermoresponsive membrane. The thermoresponsive polymer, poly­(N-isopropylacrylamide) (pNIPAM), is generated by the local reduction of persulfate ions, which initiates radical polymerization of NIPAM. Electrophoretic paint (EP) is chosen as an inert polymer. It is deposited by precipitation because of a local decrease in pH during water oxidation. Both polymers can be deposited simultaneously on opposite sides of the bipolar electrode during the application of the electric field, yielding a double-modified Janus object. Moreover, the length and thickness of the polymer layers can be controlled by varying the electric field and the deposition time. This concept is applied to vertically aligned carbon nanotube arrays (VACNTs), trapped inside an anodic aluminum oxide membrane, which can further be used as a smart reservoir for chemical storage and release. A fluorescent dye is loaded in the VACNTs and its release is studied as a function of temperature. Low temperature, when the hydrogel layer is in the swollen state, allows diffusion of the molecule. Dye release occurs on the hydrogel-modified side of the VACNTs. At high temperatures, when the hydrogel layer is in the collapsed state, dye release is blocked because of the impermeability of the pNIPAM layer. This concept paves the way toward the design of advanced devices in the fields of drug storage and directed delivery.

Recent Progress of Fabrication, Characterization, and Applications of Anodic Aluminum Oxide (AAO) Membrane: A Review

“…Fluorescein molecules were stored in nanocontainers, and unidirectional release from the containers below 32°C was observed. The functionalized VACNTS embedded in AAO pores has the potential to be used as drug containers and temperature-dependent controlled drug delivery [157]. Chitosan functionalized AAO membrane for the formation of drug release system with the schematic and experimental setup is provided in Fig.…”

“…Enhanced degradation and diffusion rate of polymer molecules result in a much slower release under static conditions [158]. Various applications of AAO membrane in drug delivery systems are given in Table 6 [100,151,[154][155][156][157][158][159][160][161][162][163][164][165][166][167][168].…”

Bipolar Electrochemistry

“…The reduction of the persulfate generates a radical anion that initiates the polymerization. In a single step, a nanoporous reservoir can be generated, because on one side the thermoresponsive membrane allows the uptake and delivery of molecules, while the opposite side remains closed by the electrophoretic paint (Figure 3a) (99).…”

Temperature-Sensitive Janus Particles PEG/SiO2/PNIPAM-PEA: Applications in Foam Stabilization and Defoaming

“…Another technique employs electro- chemical methods by leveraging the partitioning characteristics of electrodes to deposit thermosensitive and nonthermosensitive materials on opposing sides, resulting in Janus particles displaying thermosensitivity on one side. 29 Zigah and coworkers 30 utilized wireless indirect electrodeposition to apply distinct polymer coatings on both sides of a carbon nanotube array, employing a thermally responsive polymer (PNIPAM) to generate Janus particles that demonstrated temperatureresponsive behavior. However, it is worth noting that although these methods have yielded promising results in the production of Janus particles with thermosensitive attributes, there still remain challenges and limitations.…”