Micro- and nano-motors: the New Generation of Drug Carriers

Abstract

Micro-and nano-motors are emerging as novel drug delivery platforms, offering advantages such as rapid drug transport, high tissue penetration and motion controllability. They can be propelled and/or guided by endogenous (i.e., chemotaxis) or exogenous stimuli (e.g., ultrasound, magnetic fields, light) toward the area of interest. Moreover, such stimuli can be used to trigger the release of a therapeutic payload when the motor reaches certain location in order to improve the drug targeting. In this review article, we highlight medically oriented micro-/nano-motors, in particular the ones created for targeted drug delivery, and discuss their current limitations and possibilities toward in vivo applications. Drug-delivery systems have greatly evolved since 1952, when the first sustained release systems were introduced (see the graphical abstract) [1]. In the 1980s, self-regulated drug release carriers as well as the first drug delivery nanostructures were developed. From then on, research in this field has been focused on improving the targeting and systemic circulation of those carriers as well as to study different nanoparticle-based drug formulations, topics which have been widely reviewed in the literature [2][3][4][5][6][7]. Several nanocarriers (between 5 and 200 nm diameter) have been explored for therapy (e.g. inorganic, polymeric, liposomes, nanocrystals, nanotubes and dendrimers) [8], many of them already approved by the Food and Drug Administration (FDA) to treat, for example, neurovascular diseases, neurological cancers and neurodegenerative maladies [9]. The study of their pharmacokinetics has led to the creation of new carriers with reduced drug dose and protection from efflux or degradation [10]. Most of these nanocarriers include sophisticated surface biofunctionalization and coatings like polyethylene glycol (PEG) [11] or biomimetic modifications, [12] to increase their specificity and circulation time [13]. However, challenges still remain for those carriers such as the improvement of their targeting (currently only about 0.7% -median -of the administrated nanoparticle dose is found to be delivered to a solid tumor [14]), their penetration ability, drug loading capacity and delivery on the subcellular level. Other type of drug carriers are the cellular ones, which have many advantages such Graphical abstract:

Mobile Microrobots for Active Therapeutic Delivery

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A Review on Artificial Micro/Nanomotors for Cancer-Targeted Delivery, Diagnosis, and Therapy

“…In order to deliver the drug precisely to the target disease site, the drug carrier needs to have some unique capabilities, including propulsion, cargo and release, and penetration. Given these challenges in drug delivery systems, the advent of micro/ nanomotors offers a new and attractive option for drug delivery, thereby increasing the therapeutic effect and reducing the systemic side effects of highly toxic drugs [54][55][56]. Here, the self-propelled micro/nanomotors provide the carriers with continuous driving power to help them transport across biological tissues.…”

Self‐Propelled PLGA Micromotor with Chemotactic Response to Inflammation

“…[12] Hydrogen peroxide (H 2 O 2 ) is the precursor for the production of most ROS and is therefore found at elevated levels in inflamed tissue, up to 50-100 × 10 −6 m. [13] In the last decade, several groups have developed various autonomous micromotors responsive to the presence of H 2 O 2 to achieve a relevant biological mission. [14] The first example was micromotors used for the transport and release drugs, which demonstrate the catalytic nanowire shuttles are capable of picking up drug-loaded particles or liposomes and transporting them in a predetermined route. [15] Another typical attempt is to produce Janus multilayer capsule motor with partially coated dendritic platinum nanoparticles.…”