Dual-functional alginate crosslinker: Independent control of crosslinking density and cell adhesive properties of hydrogels via separate conjugation pathways

Alginate is an abundant natural polysaccharide widely utilized in various biomedical applications. Alginate also possesses numerous hydroxyl and carboxylate functional groups that allow chemical modifications to introduce different functionalities. However, it is difficult to apply various chemical reactions to alginate due to limited solubility in organic solvents. Herein, functional moieties for radical polymerization and cell adhesion were separately conjugated to hydroxyl and carboxylate groups of alginate, respectively, in order to independently control the crosslinking density and cell adhesive properties of hydrogels. Sodium counterions of alginate are first substituted with tetrabutylammonium ions to facilitate the dissolution in an organic solvent, followed by in situ conjugations of (1) cell adhesion molecules (CAM) via carbodiimide-mediated amide formation and (2) methacrylate via ring-opening nucleophilic reaction. The resulting CAM-linked methacrylic alginate was able to not only crosslink different monomers to form hydrogels with varying mechanical properties, but also induce stable cell adhesion to the hydrogels

Mechanotopography-Driven Design of Dispersible Nanofiber-Laden Hydrogels as a 3D Tissue Fibrosis Platform

Fibrosis is one of the most frequent occurrences during one???s lifetime, identified by various physiological changes including, most notably, excessive deposition of extracellular matrix (ECM). Despite its physiological importance, it is still a significant challenge to conduct systematic investigation of tissue fibrosis, mainly due to the lack of in vitro 3D tissue model that can accurately portray the characteristic features of fibrotic events. Herein, a hybrid hydrogel system incorporating dispersible nanofibers is developed to emulate highly collagenous deposits formed within a fibrotic tissue leading to altered mechanotopographical properties. Micrometer-length, aqueous-stable nanofibers consisting of crosslinked gelatin network embedded with graphene oxide (GO) or reduced graphene (rGO) are infused into hydrogel, resulting in controllable mechanotopographical properties while maintaining permeability sufficiently enough for various cellular activities. Ultimately, the ability to induce fibrotic behavior of fibroblasts cultured in these mechanotopography-controlled, nanofiber-laden hydrogels is investigated in detail

Anisotropic Nanofiber-Laden Hydrogel as Guidance to 3D Cell Orientation

Along with continuous research in biotechnology, there is a growing demand for cell culture platforms that can provide a more biological microenvironment to induce complex cell behavior. The extracellular matrix (ECM) controls chemical signals and stores cytokines and nutrients beyond the structural support of tissue. It also serves to control the physical signals mediated by the integrins and has structural diversity. On the other hand, in conventional plastic substrates such as flasks and well plates, cells are attached to the surface and cultured so the behavior of cells can be explored only by the response to chemical signals such as growth factors. To mimic various biological tissues, an extracellular matrix environment suitable for each cell activity must be served. The three-dimensional hydrogel culture system can control mechanical properties within a physiological range by controlling crosslinking density of polymer. Hydrogel can also provide a microenvironment that mimics natural surroundings for cell growth. However, overall hydrogel structures were difficult to control the fine physical properties of the cell niche. The limitation of controlling the local environment around cells can be studied by introducing other nanomaterials within hydrogels. Electrospun nanofibers are widely used as scaffolds in tissue engineering that they are easy to fabricate and can simulate the structure of natural proteins derived from ECM. The other advantage of introducing nanofibers is that the porosity of the hydrogel can be maintained and the stiffness of the local area is controlled by the fiber density. Moreover, nanofibers can recreate the topographical heterogeneity of ECM architectures. In particular, aligned structures of connective tissue can be easily found across soft tissue, skeletal muscle, heart tissue, and cancer tumor. From a microscopic point of view, the aligned structure affects angiogenesis, ECM reconstruction, and, electrical signal propagation in neurons. From a macroscopic point of view, it supports tendon loading, transmits muscle force, and is used to determine the malignant prognosis of tumors. However, the traditional strategy to control the direction of cell migration is to give a chemical or physical cell adhesion gradient that would change cellular fates. Moreover, mimicking anisotropy in a three-dimensional structure still has been a challenge. Hence, this research demonstrates to regulate the orientation of cells along gelatin nanofibers aligned under an external magnetic field. This work establishes a new multifunctional scaffold strategy that mimics the aligned three-dimensional fiber structure of various nature tissues with independent control of physical and chemical properties

Independent control of crosslinking density and cell adhesive properties of hydrogels via alginate crosslinker developed by separate conjugation pathways

Alginate is an abundant natural polysaccharide widely utilized in various biomedical applications. Alginate also possesses numerous hydroxyl and carboxylate functional groups that allow chemical modifications to introduce different functionalities. However, it is difficult to apply various chemical reactions to alginate due to its severely limited solubility in organic solvents. Herein, functional moieties responsible for radical polymerization (methacrylate) and cell adhesion (e.g. RGD peptide, gelatin) were separately conjugated to hydroxyl and carboxylate groups of alginate, respectively, in order to independently control the crosslinking density and cell adhesive properties of hydrogels. Sodium ions of alginate in the original form are first substituted with tetrabutylammonium ions to facilitate the dissolution in an organic solvent (i.e. dimethyl sulfoxide), followed by in situ conjugations of (1) cell adhesion molecules (CAM) via carbodiimide-mediated amide formation and (2) methacrylate via ring-opening nucleophilic reaction. The resulting CAM-linked methacrylic alginate (MAlg) was able to not only crosslink different monomers to form hydrogels with varying mechanical properties controlled by the concentration and the degree of methacrylate substitution, but also induce stable cell adhesion to the hydrogels

Mechanotopography-Driven Design of Dispersible Nanofiber-Laden Hydrogel as a 3D Cell Culture Platform for Investigating Tissue Fibrosis

Fibrosis is one of the most frequent occurrences during one's lifetime, identified by various physiological changes including, most notably, excessive deposition of extracellular matrix (ECM). Despite its physiological importance, it is still a significant challenge to conduct a systematic investigation of tissue fibrosis, mainly due to the lack of in vitro 3D tissue model that can accurately portray the characteristic features of fibrotic events. Herein, a hybrid hydrogel system incorporating dispersible nanofibers is developed to emulate highly collagenous deposits formed within a fibrotic tissue leading to altered mechanotopographical properties. Micrometer-length, aqueous-stable nanofibers consisting of crosslinked gelatin network embedded with graphene oxide (GO) or reduced graphene (rGO) are infused into hydrogel, resulting in controllable mechanotopographical properties while maintaining permeability sufficiently enough for various cellular activities. Ultimately, the ability to induce fibrotic behavior of fibroblasts cultured in these mechanotopography-controlled, nanofiber-laden hydrogels is investigated in detail

Emerging Technology of Nanofiber-Composite Hydrogels for Biomedical Applications

Hydrogels and nanofibers have been firmly established as go-to materials for various biomedical applications. They have been mostly utilized separately, rarely together, because of their distinctive attributes and shortcomings. However, the potential benefits of integrating nanofibers with hydrogels to synergistically combine their functionalities while attenuating their drawbacks are increasingly recognized. Compared to other nanocomposite materials, incorporating nanofibers into hydrogel has the distinct advantage of emulating the hierarchical structure of natural extracellular environment needed for cell and tissue culture. The most important technological aspect of developing "nanofiber-composite hydrogel" is generating nanofibers made of various polymers that are cross-linked and short enough to maintain stable dispersion in hydrated environment. In this review, recent research efforts to develop nanofiber-composite hydrogels are presented, with added emphasis on nanofiber processing techniques. Several notable examples of implementing nanofiber-composite hydrogels for biomedical applications are also introduced

Synergistic control of mechanics and microarchitecture of 3D bioactive hydrogel platform to promote the regenerative potential of engineered hepatic tissue

Culturing autologous cells with therapeutic potential derived from a patient within a bioactive scaffold to induce functioning tissue formation is considered the ideal methodology towards realizing patient-specific regenerative medicine. Hydrogels are often employed as the scaffold material for this purpose mainly for their tunable mechanical and diffusional properties as well as presenting cell-responsive moieties. Herein, a two-fold strategy was employed to control the physicomechanical properties and microarchitecture of hydrogels to maximize the efficacy of engineered hepatic tissues. First, a hydrophilic polymeric crosslinker with a tunable degree of reactive functional groups was employed to control the mechanical properties in a wide range while minimizing the change in diffusional properties. Second, photolithography technique was utilized to introduce microchannels into hydrogels to overcome the critical diffusional limit of bulk hydrogels. Encapsulating hepatic progenitor cells derived via direct reprogramming of tissue-harvested fibroblasts, the application of this strategy to control the mechanics, diffusion, and architecture of hydrogels in a combinatorial manner could allow the optimization of their hepatic functions. The regenerative capacity of this engineered hepatic tissue was further demonstrated using an in vivo acute liver injury model

Synergistic control of mechanics and microarchitecture of 3D bioactive hydrogels for hepatic tissue engineering

Culturing autologous cells with therapeutic potential derived from a patient within a bioactive scaffold to induce functioning tissue formation is considered the ideal methodology towards realizing patient-specific regenerative medicine. Hydrogels are often employed as the scaffold material for this purpose mainly for their tunable mechanical and diffusional properties as well as presenting cell-responsive moieties. Herein, a two-fold strategy was employed to control the physicomechanical properties and microarchitecture of hydrogels to maximize the efficacy of engineered hepatic tissues. First, a hydrophilic polymeric crosslinker with a tunable degree of reactive functional groups was employed to control the mechanical properties in a wide range while minimizing the change in diffusional properties. Second, photolithography technique was utilized to introduce microchannels into hydrogels to overcome the critical diffusional limit of bulk hydrogels. Encapsulating hepatic progenitor cells derived via direct reprogramming of tissue-harvested fibroblasts, the application of this strategy to control the mechanics, diffusion, and architecture of hydrogels in a combinatorial manner could allow the optimization of their hepatic functions. The regenerative capacity of this engineered hepatic tissue was further demonstrated using an in vivo acute liver injury model

Multiscale Engineering of Nanofiber-Aerogel Composite Nanogenerator with Tunable Triboelectric Performance Based on Multifunctional Polysuccinimide

Multiscale polymer engineering, involving chemical modification to control their triboelectric polarities as well as physicomechanical modification to maximize charge transfer and structural durability, is paramount to developing a high-performance triboelectric nanogenerator (TENG). This report introduces a highly efficient and comprehensive strategy to engineer high-performance TENG based on multifunctional polysuccinimide (PSI). With the ability of PSI to undergo facile nucleophilic addition with amines, sodium sulfate and quaternary ammonium chlorides having opposite charged groups are conjugated to PSI in varying densities. The resulting Sulfo-PSI and TMAC-PSI, respectively, processed into nanofibrous films, demonstrate highly enhanced and variable triboelectric properties based on the charge type and density. To further enhance the mechanical toughness and biocompatibility necessary for wearable applications, these PSI nanofibers are processed into alginate aerogel (AG). The sustained triboelectric performance of this nanofiber-AG TENG as a wearable energy harvester and biosensor is examined and validated in detail