Electrochemical Glue for Binding Chitosan–Alginate Hydrogel Fibers for Cell Culture

Three-dimensional organs and tissues can be constructed using hydrogels as support matrices for cells. For the assembly of these gels, chemical and physical reactions that induce gluing should be induced locally in target areas without causing cell damage. Herein, we present a novel electrochemical strategy for gluing hydrogel fibers. In this strategy, a microelectrode electrochemically generated HClO or Ca2+, and these chemicals were used to crosslink chitosan–alginate fibers fabricated using interfacial polyelectrolyte complexation. Further, human umbilical vein endothelial cells were incorporated into the fibers, and two such fibers were glued together to construct “+”-shaped hydrogels. After gluing, the hydrogels were embedded in Matrigel and cultured for several days. The cells spread and proliferated along the fibers, indicating that the electrochemical glue was not toxic toward the cells. This is the first report on the use of electrochemical glue for the assembly of hydrogel pieces containing cells. Based on our results, the electrochemical gluing method has promising applications in tissue engineering and the development of organs on a chip.

Biofabrication of controllable alginate hydrogel cell scaffolds based on bipolar electrochemistry

Bipolar electrochemistry successfully realized the electrodeposition of calcium alginate hydrogels in specific target areas in tissue engineering. However, the shape and quantity of three-dimensional cannot be accurately controlled. We presented a novel growth model for fabricating hydrogels based on bipolar electrochemical by patterned bipolar electrodes using photolithography. This work highlights pattern customization and quantitative control of hydrogels in cell culture platforms. Furthermore, alginate hydrogels with different heights can be controlled by adjusting the key parameters of the growth model. This strategy exhibits promising potential for cell-oriented scaffolds in tissue engineering.

Recent advances in bio-orthogonal and dynamic crosslinking of biomimetic hydrogels

In recent years, dynamic, 'click' hydrogels have been applied in numerous biomedical applications. Owing to the mild, cytocompatible, and highly specific reaction kinetics, a multitude of orthogonal handles have been developed for fabricating dynamic hydrogels to facilitate '4D' cell culture. The high degree of tunability in crosslinking reactions of orthogonal 'click' chemistry has enabled a bottom-up approach to install specific biomimicry in an artificial extracellular matrix. In addition to click chemistry, highly specific enzymatic reactions are also increasingly used for network crosslinking and for spatiotemporal control of hydrogel properties. On the other hand, covalent adaptable chemistry has been used to recapitulate the viscoelastic component of biological tissues and for formulating self-healing and shear-thinning hydrogels. The common feature of these three classes of chemistry (i.e., orthogonal click chemistry, enzymatic reactions, and covalent adaptable chemistry) is that they can be carried out under ambient and aqueous conditions, a prerequisite for maintaining cell viability for in situ cell encapsulation and post-gelation modification of network properties. Due to their orthogonality, different chemistries can also be applied sequentially to provide additional biochemical and mechanical control to guide cell behavior. Herein, we review recent advances in the use of orthogonal click chemistry, enzymatic reactions, and covalent adaptable chemistry for the development of dynamically tunable and biomimetic hydrogels.

Fabrication of three-dimensional calcium alginate hydrogels using sacrificial templates of sugar

Hydrogels are receiving increasing attention in bioapplications. Among hydrogels, calcium alginate (Ca-alginate) hydrogels are widely used for their biocompatibility, low toxicity, low cost, and rapid fabrication by simple mixing of Ca²⁺ and sodium alginate (Na-alginate). For bioapplications using hydrogels, it is necessary to construct designed hydrogel structures. Although several methods have been proposed for fabricating designed hydrogels, a simple and low-cost method is desirable. Therefore, we developed a new method using sacrificial templates of sugar structures to fabricate three-dimensional (3D) designed Ca-alginate hydrogels. In this method, Na-alginate solution is mixed with molten sugar, and the resulting highly viscous material used to mold 3D sugar structures as sacrificial templates. Since sugar constructs are easily handled compared to hydrogels, sugar templates are useful for preparing 3D constructs. Finally, the sugar and Na-alginate structure is immersed in a CaCl₂ solution to simultaneously dissolve the template and form the Ca-alginate hydrogel. The resulting hydrogel takes the shape of the sugar template. By stacking and fusing various sugar structures, such as fibers and blocks, 3D designed Ca-alginate hydrogels can be successfully fabricated. This simple and low-cost method shows excellent potential for application to a variety of bioapplications.

In situ condensation of an anti-cancer drug into fibrin gel enabling effective inhibition of tumor cell growth

We show herein the highly effective inhibition of tumor cell growth using a gel consisting of a fibrin polymer formed with the in situ condensation of a camptothecin (CPT) derivative as an anti-cancer drug, which is efficiently conveyed with a carrier aptamer from a solution to the gel in a phenomenon, called selective oligonucleotide entrapment in fibrin polymers (SOEF).