Requirement and Development of Hydrogel Micromotors towards Biomedical Applications

Abstract

<jats:p>With controllable size, biocompatibility, porosity, injectability, responsivity, diffusion time, reaction, separation, permeation, and release of molecular species, hydrogel microparticles achieve multiple advantages over bulk hydrogels for specific biomedical procedures. Moreover, so far studies mostly concentrate on local responses of hydrogels to chemical and/or external stimuli, which significantly limit the scope of their applications. Tetherless micromotors are autonomous microdevices capable of converting local chemical energy or the energy of external fields into motive forces for self-propelled or externally powered/controlled motion. If hydrogels can be integrated with micromotors, their applicability can be significantly extended and can lead to fully controllable responsive chemomechanical biomicromachines. However, to achieve these challenging goals, biocompatibility, biodegradability, and motive mechanisms of hydrogel micromotors need to be simultaneously integrated. This review summarizes recent achievements in the field of micromotors and hydrogels and proposes next steps required for the development of hydrogel micromotors, which become increasingly important for <jats:italic>in vivo</jats:italic> and <jats:italic>in vitro</jats:italic> bioapplications.</jats:p>

Micro‐Bio‐Chemo‐Mechanical‐Systems: Micromotors, Microfluidics, and Nanozymes for Biomedical Applications

“…[ 47 ] First, the size of the micromotors is optimized to overcome Brownian diffusion. A growing body of literature has examined different shapes, sizes, materials of micromotors, [ 48 ] compositions, [ 31 ] and concentrations. [ 49 ] Mechanisms of catalytic reactions have been elucidated to achieve higher motive forces, ultra‐fast propulsion, [ 50 ] ultraprecise positioning, [ 51 ] develop accurate control methods, and test swarming/collective behaviors of micromotors.…”

“…Moreover, since conventional optical microscopy (widely used in nano-/micro motors research) cannot be used to imaging micromachines in the human body-powerful super-resolution deep tissue biomedical imaging methods (e.g., ultrasound) are desperately needed. There are multiple excellent reviews already available for each of our discussed emerging topics: nanozymes, [14,30] nano-/micromotors, [2,31] and microfluidics. [32][33][34][35] By cultivating interdisciplinarity as a habit of mind, our review discusses integration or interconnectedness of these emerging topics by focusing on i) generation of new ideas, ii) discussions across disciplinary boundaries (overlap of emerging topics allows looking at the problem from a variety of viewpoints-the same questions can be asked in different ways), and iii) solutions to complex problems, which are beyond the scope of a single discipline.…”

Engineering Polysaccharides for Tissue Repair and Regeneration

“…Granular hydrogel is formed by the packing of microgels other than the crosslinking of molecules (Figure 6H), [ 157,158 ] and the discrete microgel packing gives rise to an inherent micro pore structure. [ 159 ] This structure allows porosity and degradability to be independent from each other, thus facilitating cell migration, vascularization and matrix deposition. [ 160,161 ] Granular hydrogels have thus drawn increasing interest in 3D printing and biofabrication for tissue engineering.…”

A Journey of Nanomotors for Targeted Cancer Therapy: Principles, Challenges, and a Critical Review of the State‐of‐the‐Art

“…To close this section, and to direct readers to sources of information beyond this current review, we list the following excellent review articles on nanomotors for biomedical applications, on the topics of 1) overall overviews, [36,[72][73][74][75] 2) drug delivery/cargo transportation, [32,34,38,40,[76][77][78][79][80][81] 3) diagnosis, [82] 4) sensing, [77][78][79]83] 5) in vivo applications, [34,[84][85][86] 6) surface coating, [87] 7) cancer therapy, [33,37,88,89] 8) biocompatibility, [66] 9) biological barriers/complex environment/entering a cell [39,[90][91][92] and 10) imaging, [90,93,94] as well as on particular types of nanomotors for biomedical application, such as those made of hydrogel [95] or those powered by magnetic fields. [96] This list of review articles-a total of 35 and counting-is by no means comprehensive, and only covers the period of 2013-2020 (see the book by Prof. Joseph Wang [7] for pre-2013 reviews).…”