Mesoporous Silica Micromotors with a Reversible Temperature Regulated On–Off Polyphosphazene Switch

Abstract

The incorporation of an extraneous on–off braking system is necessary for the effective motion control of the next generation of micrometer‐sized motors. Here, the design and synthesis of micromotors is reported based on mesoporous silica particles containing bipyridine groups, introduced by cocondensation, for entrapping catalytic cobalt(II) ions within the mesochannels, and functionalized on the surface with silane‐derived temperature responsive bottle‐brush polyphosphazene. Switching the polymers in a narrow temperature window of 25–30 °C between the swollen and collapsed state, allows the access for the fuel H2O2 contained in the dispersion medium to cobalt(II) bipyridinato catalyst sites. The decomposition of hydrogen peroxide is monitored by optical microscopy, and effectively operated by reversibly closing or opening the pores by the grafted gate‐like polyphosphazene, to control on demand the oxygen bubble generation. This design represents one of the few examples using temperature as a trigger for the reversible on–off external switching of mesoporous silica micromotors.

Reversible Speed Regulation of Self‐Propelled Janus Micromotors via Thermoresponsive Bottle‐Brush Polymers

“…Upon reducing the temperature to 15 °C, a pronounced decrease in velocity was observed. The reason for this is thought to be the partial solvation and then, expansion of the PPz1 upon passing below its LCST thus hindering the flow of H 2 O 2 into the particles [14b] . Note the LCST of the silanized PPz1 on the surface is around 15 °C, higher than the free PPz1, an effect observed in other similar reported works [14] .…”

Dual stimuli-responsive polyphosphazene-based molecular gates for controlled drug delivery in lung cancer cells

“…As expected, the surface properties of the undecorated MSN0 commonly covered by -OH groups was highly negative (À48 mV) and in agreement with this type of nanoparticles. 19 Similarly, the nanoparticles loaded with azide exhibited a positive increase of the z-potential which may be due to the effective graing step. Surprisingly, aer the polymer graing step the surface charge was not signicantly affected.…”

“…That was in agreement to the expected overall increase of the hydrophilicity of the polymer due to protonation of the N atoms from the PPz backbone at acidic pHs. 19…”

“…15 Due to a widely observed phenomenon for amphiphilic polymers, 16,17 thermoresponsive polymers commonly possess a lower critical solution temperature (LCST) in aqueous solutions, above which the macromolecules collapse, followed oen by agglomeration and/or gelation. 17 On surfaces the macromolecules collapse, 18 for example to control fuel access to micromotors 19 or to modulate cell adhesion and detachment, facilitating fabrication of cell sheets. 20 In this work, we use Jeffamine-functionalized bottle-brush polyphosphazenes which are reported to have LCSTs which can be tuned to biologically relevant temperatures.…”

Visible Light Photocleavable Ruthenium-Based Molecular Gates to Reversibly Control Release from Mesoporous Silica Nanoparticles

“…Molecules can be attached to the surface as pore-blockers or “molecular gates” capable of controlling the access or transfer of mass from the inner pores upon the application of certain stimuli [ 3 ]. This closing–opening mechanism is a unique and special feature of these “gate-like” systems that have driven them, in the recent years, towards new designs in controlled-release drug delivery systems [ 4 ], development of selective optical chemosensing materials [ 2 ] and, very recently, for the preparation of responsive micromotors [ 5 ].…”