Engineered Microgels—Their Manufacturing and Biomedical Applications

Abstract

Microgels are hydrogel particles with diameters in the micrometer scale that can be fabricated in different shapes and sizes. Microgels are increasingly used for biomedical applications and for biofabrication due to their interesting features, such as injectability, modularity, porosity and tunability in respect to size, shape and mechanical properties. Fabrication methods of microgels are divided into two categories, following a top-down or bottom-up approach. Each approach has its own advantages and disadvantages and requires certain sets of materials and equipments. In this review, we discuss fabrication methods of both top-down and bottom-up approaches and point to their advantages as well as their limitations, with more focus on the bottom-up approaches. In addition, the use of microgels for a variety of biomedical applications will be discussed, including microgels for the delivery of therapeutic agents and microgels as cell carriers for the fabrication of 3D bioprinted cell-laden constructs. Microgels made from well-defined synthetic materials with a focus on rationally designed ultrashort peptides are also discussed, because they have been demonstrated to serve as an attractive alternative to much less defined naturally derived materials. Here, we will emphasize the potential and properties of ultrashort self-assembling peptides related to microgels.

Self-Crosslinked Ellipsoidal Poly(Tannic Acid) Particles for Bio-Medical Applications

“…As microgels are versatile and have a broad range of applications covering food, cosmetic, energy, sensor, and medical fields, a facile and rapid synthesis without using many chemicals makes them more significant in these applications [ 38 , 39 , 40 ]. The tunable small sizes and functionality of microgels dignifies the value-added potentials in human-related in vivo applications [ 41 , 42 ].…”

Engineering Biological Tissues from the Bottom-Up: Recent Advances and Future Prospects

“…In this method, an emulsion will form with the mixture of two incompatible liquids (Figure 2A). The first step of this method is to stir the multiphase mixture to produce small droplets of hydrogel precursors (Figure 2B), whose size is controlled by the degree of mechanical agitation, viscosity of each phase, and the presence of surfactant [23]. Additionally, the spherical microgels are then formed by various cross-linking mechanisms, which can be used for immunoisolation, carriers in bioreactors, or analysis of stem cell biology applications by adding cells in the water phase.…”

“…The top priority of bottom-up tissue engineering is to construct functional module units, which are usually composed of microscale cell-carrying hydrogels (such as polyethylene glycol, collagen, polyethylene glycol diacrylate, and gelatin-methacrylic anhydride [9,[21][22][23]). At present, there are six methods commonly used to prepare cell microgel modules, including emulsification, microchannels, microfluidic technology, bioprinting technology, and the liquid bridge manufacturing module units method [24] (Table 1).…”

“…Finally, cell-loaded microgel modules can be obtained. (Reproduced with permission from the Reference [23]).…”

Self-Assembling Peptides and Carbon Nanomaterials Join Forces for Innovative Biomedical Applications

“…Several reviews have appeared in the last year on self-assembling short peptides for biomedical applications [ 24 , 25 ], especially drug delivery [ 26 , 27 ] and tissue engineering [ 28 ], also owing to their ability to mimic the extracellular matrix [ 29 ]. More specifically, their use has been reviewed as microgels [ 30 ], antimicrobials [ 31 ], for angiogenesis [ 32 ], in gene therapy [ 33 ], to treat metabolic syndromes [ 34 ] and gastrointestinal diseases [ 35 ], to regenerate bone [ 36 ] and conductive tissues [ 37 ] such as nerves [ 38 ], to develop bioelectronics [ 39 ] and vaccines [ 40 ]. Therefore, in this review we will not analyze in detail these highly promising systems.…”