Scalable Chemical Synthesis Route to Manufacture pH-Responsive Janus CaCO₃ Micromotors

Abstract

A cost-effective scalable chemical route to produce pH-responsive active colloids (ACs) is developed here. For the first time, calcium carbonate particles are half-coated with a silica layer via Pickering emulsion methodology. This methodology allows to create anisotropy on the particles’ surfaces and benefit from the decomposition of the calcium carbonate in acidic media to generate self-propulsion. The coupling between the self-diffusiophoretic motion of these ACs and acid concentrations is experimentally investigated in Newtonian media via optical microscopy. With increasing hydrogen-ion concentrations, the pH-responsive colloids experience higher mean-square displacements because of self-propulsion velocities and enhanced long-time diffusivities. Because they are biocompatible and environmentally friendly, these ACs constitute a platform for advanced diagnostics, targeted drug delivery, and water/soil remediation.

Engineering Active Micro and Nanomotors

“…Consequently, particles experience a net thrust, for example through bubble propulsion, along the direction from the exposed side toward the covered side and become motile (see one example in Figure 2c). Many different fuel-reactant systems have been employed for this type of Janus particles including Mg-water [29,[87][88][89], Zn-water [90], Al-water [23,28], gallium-water [28], CaCO 3 -acid [91] and poly (2-ethyl cyanoacrylate)-water [92] etc. Such micromotors have good tolerance to ionic conditions and thus work in a broad range of solutions.…”

Enzymatic/Magnetic Hybrid Micromotors for Synergistic Anticancer Therapy

“…Notably, as well as being both biocompatible and porous, CaCO 3 particles are sensitive to acidic environments and thus can undergo pH-sensitive degradation and drug release in tumors owing to acidosis . Numerous studies have investigated CaCO 3 -based MNMs. − Baylis et al propelled CaCO 3 -based micromotors against the blood flow using bubbles generated by acidic breakdown as a strong driving force . Guix et al fabricated CaCO 3 micromotors for drug delivery, which show enhanced diffusion in the ultralight acidic environment generated by cancer cells .…”

Edible CaCO3 nanoparticles stabilized Pickering emulsion as calcium‐fortified formulation

“…In the recent decade, there has been growing research interest in assembling particles using ''generally regarded as safe'' (GRAS) inorganic materials, such as hydroxyapatite, calcium phosphate, tri-calcium phosphate, and calcium carbonate, to maximize emulsion stabilization and minimize side effects [10][11][12][13]. Among the vast variety of materials, food-grade calcium carbonate (CaCO 3 ) has gained attention as a Pickering emulsifier, particularly in the food, pharmacy, and medical industries [14], as it is of substantial importance for three main reasons: (1) CaCO 3 is a recognized food additive and pharmaceutical ingredient that is advantageous for its low-cost and availability in large quantities [3]; (2) CaCO 3 particles can impart acid-responsive properties into the Pickering emulsion it stabilizes by virtue of its acid-soluble nature [15]; (3) functional properties (calcium fortification and acid neutralization capacity) can also be added to the Pickering emulsion after converting CaCO 3 particles into absorbable calcium ions once exposed to gastric acid [16]. Until now, CaCO 3 -based oil-in-water and water-in-oil Pickering emulsions have been reported [3,[17][18][19].…”