Designing Covalent Organic Framework‐Based Light‐Driven Microswimmers toward Therapeutic Applications

Abstract

While micromachines with tailored functionalities enable therapeutic applications in biological environments, their controlled motion and targeted drug delivery in biological media require sophisticated designs for practical applications. Covalent organic frameworks (COFs), a new generation of crystalline and nanoporous polymers, offer new perspectives for light-driven microswimmers in heterogeneous biological environments including intraocular fluids, thus setting the stage for biomedical applications such as retinal drug delivery. Two different types of COFs, uniformly spherical TABP-PDA-COF sub-micrometer particles and texturally nanoporous, micrometer-sized TpAzo-COF particles are described and compared as lightdriven microrobots. They can be used as highly efficient visible-light-driven drug carriers in aqueous ionic and cellular media. Their absorption ranging down to red light enables phototaxis even in deeper and viscous biological media, while the organic nature of COFs ensures their biocompatibility. Their inherently porous structures with ≈2.6 and ≈3.4 nm pores, and large surface areas allow for targeted and efficient drug loading even for insoluble drugs, which can be released on demand. Additionally, indocyanine green (ICG) dye loading in the pores enables photoacoustic imaging, optical coherence tomography, and hyperthermia in operando conditions. This real-time visualization of the drug-loaded COF microswimmers enables unique insights into the action of photoactive porous drug carriers for therapeutic applications.

In vivoapplications of micro/nanorobots

“…12,65 On the other hand, ultraviolet (UV) light can cause severe side effects, while visible (Vis) light has poor penetration depth into the tissue. 66,67 In general, nearinfrared (NIR) light can provide both safety and considerable penetration depth to enable the configurable locomotion of micro/nanorobots in vivo. [68][69][70]…”

Broad‐Wavelength Light‐Driven High‐Speed Hybrid Crystal Actuators Actuated Inside Tissue‐Like Phantoms

“…Different concentrations (10−200 μg mL −1 ) of two different materials were incubated with fibroblast cells, and their viability was investigated for up to 72 h. After 72 h incubation with Ti 3 C 2 T x and enol-1, the viability of fibroblasts was more than 95% in all treated groups, implying that the hybrid crystal actuators are biocompatible and safe to use in biological environments. Lastly, to evaluate the stability of agar-encapsulated Ti 3 C 2 T x /enol-1 crystals in biological environments, we immersed the agar phantom-encapsulated hybrid crystals in two biological media, namely, Dulbecco's phosphatebuffered saline (DPBS) and Dulbecco's modified eagle's medium (DMEM) [51,52] and monitored any changes that occurred in the samples. DPBS closely mimics the pH, osmolality, and ion concentrations of the human body, while DMEM is a widely used basal medium to support the growth of a variety of cells.…”

Photochargeable Semiconductors: in “Dark Photocatalysis” and Beyond

“…PHIs and other layered organic polymers like covalent organic frameworks have recently stimulated great interest to develop light-driven microswimmers, because of their high interlayer ion-storing capacity. [162] To date, the work by Sridhar et al is the only report of a photochargeable nanomotor. As for many other applications of photochargeable semiconductors, the charge/discharge time ratio is a key figure of merit.…”