For environmentally-switchable adhesive systems to be reused repeatedly, the adhesive strength must not deteriorate after each adhesion cycle. An important criterion to achieve this goal is that the integrity of the interface must be retained after each adhesion cycle. Furthermore, in order to have practical benefits, reversing the adhesion must be a relatively rapid process. Here, a double-network hydrogel of poly(methacrylic acid) and poly[oligo(ethylene glycol)methyl ether methacrylate] is shown to undergo adhesive failure during pH-switchable adhesion with a grafted (brush) layer of polycationic poly[2-(diethyl amino)ethyl methacrylate], and can be reused at least seven times. The surfaces are attached at pH 6 and detached at pH 1. A single-network hydrogel of poly(methacrylic acid), also exhibits pH-switchable adhesion with poly[2-(diethyl amino)ethyl methacrylate] but cohesive failure leads to an accumulation of the hydrogel on the brush surface and the hydrogel can only be reused at different parts of that surface. Even without an environmental stimulus (i.e. attaching and detaching at pH 6), the double-network hydrogel can be used up to three times at the same point on the brush surface. The single-network hydrogel cannot be reused under such circumstances. Finally, the time taken for the reuse of the double-network hydrogel is relatively rapid, taking no more than an hour to reverse the adhesion.

This study investigated a process for removing paracetamol (PCM) from aqueous solutions using mesoporous silica nanoparticles (MSNs) grafted with pH-responsive poly(2-(tert-butylamino)ethyl methacrylate) brushes (PTBAEMA) via the surface-initiated atom transfer radical polymerisation technique on the inner and outer surface of the solid particles. The successful incorporation of PTBAEMA on the surface of MSNs was confirmed using XPS technique by a strong absorption peak at ~1750 cm⁻¹, which was assigned to – C = O stretching vibrations. The adsorption efficiency of MSN-PTBAEMA for PCM was studied as a function of different pH levels. The obtained results showed that the extraction efficiency of MSN-PTBAEMA for PCM was found to be about 92% higher when pH was in a range between 5 and 7. However, the adsorption efficiency of PTBAEMA-MSNs decreased to ~74% and ~38.6% at pH 9 with a PCM concentration of 100 ppm and 300 ppm, respectively. The maximum adsorption capacity of MSN-PTBAEMA for PCM was recorded at 237 mg/g. The Freundlich isotherms model was applied to the obtained adsorption data and suggested that a multilayer adsorption mechanism occurred on the surface of the adsorbent. In addition, the adsorption kinetics data was found to be best fitted with the pseudo second-order model, comparing to the pseudo first-order model. The obtained results confirmed that MSN-PTBAEMA could be effectively applied for the removal of PCM from the aqueous environments.

Mesoporous silica nanoparticles (MSNs) are considered a highly promising candidate for novel the drug delivery systems (DDSs) due to the possibility of controlling their functionalizable pores, their large pore volume, high loading cavities and biocompatibility. MSNs functionalized with stimuli-responsive polymers have been demonstrated to represent a controllable and smart drug delivery application able to release drugs in response to certain stimuli, including pH, temperature, light, enzyme or redox. The surface of the MSNs is coated with stimuli-responsive polymer brushes so as to increase the stability and extend the release period of the loaded drug. This minireview highlights the latest research developments of polymer-brush-grafted MSNs and their potential biomedical applications in this area.

In this paper, a new pH-responsive nanosystem based on mesoporous silica nanoparticles (MSNs) was developed for cancer therapy. Poly(2-(diethylamino) ethyl methacrylate) (PDEAEMA) was grafted on their outer surface and acts as a gatekeeper, followed by subsequent modification of the polymer by cysteine (MSN-PDEAEMA-Cys) and poly(oligo(ethylene glycol) methyl ether methacrylate) (MSN-PDEAEMA-Cys-POEGMEMA). The physicochemical properties of these nanocarriers were characterized using scanning and transmission electron microscopies (SEM and TEM), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and dynamic light scattering (DLS). The synthesized nanoparticles were well-dispersed with a diameter of ca. 200 nm. The obtained XPS results confirm the successful modification of MSN-PDEAEMA with Cys and POEGMEMA by increasing the peak intensity of C–O and C=O groups at 286.5 and 288.5 eV, respectively. An anti-cancer drug, doxorubicin (DOX), was encapsulated into the fabricated nanoplatform. The DOX release amount at physiological pH of 7.4 was limited (10%), while an accumulation drug release of ca. 35% was accomplished after 30 h in acidic media. The MTT cell line was used to assess the cytotoxicity of the unloaded and DOX-loaded fabricated nanoplatforms. Upon loading of DOX on these nanomaterials, they showed significant toxicity to human liver cancer cells. These results suggest that the prepared nano-structured materials showed good biocompatibility as well, and they can serve as nanocarriers for the delivery of anti-cancer drugs.