The Combined Effects of Co-Culture and Substrate Mechanics on 3D Tumor Spheroid Formation within Microgels Prepared via Flow-Focusing Microfluidic Fabrication

Tumor spheroids are considered a valuable three dimensional (3D) tissue model to study various aspects of tumor physiology for biomedical applications such as tissue engineering and drug screening as well as basic scientific endeavors, as several cell types can efficiently form spheroids by themselves in both suspension and adherent cell cultures. However, it is more desirable to utilize a 3D scaffold with tunable properties to create more physiologically relevant tumor spheroids as well as optimize their formation. In this study, bioactive spherical microgels supporting 3D cell culture are fabricated by a flow-focusing microfluidic device. Uniform-sized aqueous droplets of gel precursor solution dispersed with cells generated by the microfluidic device are photocrosslinked to fabricate cell-laden microgels. Their mechanical properties are controlled by the concentration of gel-forming polymer. Using breast adenocarcinoma cells, MCF-7, the effect of mechanical properties of microgels on their proliferation and the eventual spheroid formation was explored. Furthermore, the tumor cells are co-cultured with macrophages of fibroblasts, which are known to play a prominent role in tumor physiology, within the microgels to explore their role in spheroid formation. Taken together, the results from this study provide the design strategy for creating tumor spheroids utilizing mechanically-tunable microgels as 3D cell culture platform

Comprehensive Enhancement of Mechanical, Water-Repellent and Antimicrobial Properties of Regenerated Seaweed and Plant-Based Paper with Chitosan Coating

Regenerated papers made from discarded natural sources, such as seaweeds or non-wood plants, are viewed as promising eco-friendly alternatives relative to conventional wood-based paper. However, due to its limited mechanical strength and higher water absorption than compared to traditional wood paper, it often results in premature structural disintegration. In order to overcome this limitation, this research introduces an efficient and comprehensive strategy of coating seaweed and plant papers with varying concentrations and molecular weights of chitosan. Increased concentration and molecular weight resulted in a greater amount of chitosan deposition, while the highest molecular weight also shows increased dissolution of soluble components of the paper. Since plants and seaweeds contain high anionic polysaccharide contents, the cationic chitosan shows high binding affinity towards paper. The resulting chitosan-coated papers demonstrate significant enhancements in water repellency and mechanical properties. In addition, the chitosan-coated papers also show significant bacterial inhibition effects due to the natural anti-microbial activity of chitosan

Design of multi-functional hydrogel for cell therapies

Hydrogels are being actively investigated as encapsulation devices for cell transplantation therapies, as they provide structural stability and protection against harsh chemical and mechanical stimuli, and host immune system. In addition, chemical moieties, mechanical stiffness, and minerals presented in hydrogels act as insoluble signals to regulate a variety of cellular function. However, the conventional hydrogel design is plagued by complex dependencies between hydrogel properties; stiffness, permeability, density of cell adhesion molecules, and mineralization capacity. The objective of this research is to decouple or tune the intricate dependencies between these hydrogel properties, in order to better understand and regulate cellular activities in a 3D matrix. The hydrogel system is created by the assembly of three functional modules that contribute to the overall hydrogel properties: (1) The dependency between stiffness and permeability was tuned by incorporating pendant polymeric chains into a poly(ethylene glycol)-based hydrogel system; (2) Incorporation of alginate into a hydrogel system by co-polymerization allowed the control of hydrogel stiffness without affecting permeability; (3) The hydrogel was modified with cell adhesion proteins independent of other hydrogel properties using an amine-reactive polyaspartamide linker enabling single-step protein conjugation. Furthermore, mineralization capacity of the hydrogel was controlled independently by modulating hydrophobicity, charge density, and porosity. The efficacy of the hydrogel system developed in this research was evaluated by encapsulating two different cell types, fibroblasts and mesenchymal stem cells, and exploring the effects of hydrogel properties on the viability and growth factor expression of the encapsulated cells

Graphene-Polymer Nanocomposite Materials for Biomedical Applications

Polymer-based materials, such as fibers, hydrogels, and elastomers, are widely used in biomedical applications for their compatibility with living organisms. However, due to their limited range of physical and chemical properties, it becomes necessary to augment their functions by appropriate modifications. Incorporating nanostructures having unique and favorable properties into a polymer-based material would be a highly strategy for this purpose. In this work, we developed a nanocomposite hydrogel system by covalently incorporating graphene oxide (GO) into gelatin-based hydrogels. GO is a 2D carbon nanomaterial well known for its electronic properties and mechanical strength. Mechanical strength of the resulting nanocomposite hydrogel was significantly enhanced as compared to gelatin-only hydrogel which showed low mechanical stability. In addition, covalent incorporation proved to be a much more effective method than physical incorporation. This was due to the fact that GO was highly susceptible to aggregation by ??-?? stacking and depletion forces especially and was not stably dispersed especially in high polymer concentrations. By modifying the surface of GO with methacrylic groups, GO was able to undergo copolymerization with gel-forming polymer chains, resulting in covalent incorporation of GO into the hydrogel. In addition, 3D in vitro cell culture study demonstrated the biocompatibility of GO-linked hydrogel, which atest to their potential applications in biomedical engineering

Decoupled control of degradation and mechanical properties of in situ forming and fast dissolving polyaspartamide hydrogels

Hydrogels are widely used in various biomedical applications such as scaffolds for cell and tissue culture, drug delivery systems, and biosensor platforms. Most hydrogels are created by crosslinking monomers or macromers via chemical reactions that require toxic initiation process. Therefore, the reactions that can proceed without initiators and are mild enough to minimize toxic effects, while still allowing hydrogel formation under aqueous conditions, are highly desired. Herein, a polyaspartamide-based crosslinker system that can undergo ???in situ??? forming chemical reactions to form hydrogels is presented. Polyaspartamide crosslinkers presenting amino functional groups with varying lengths and degrees of substitutions are efficiently synthesized by nucleophilic reactions with polysuccinimide. These crosslinkers are reacted with gel-forming polymers via Michael addition or Schiff base formation under physiological and biocompatible conditions (e.g. neutral pH, room temperature, no initiators). In addition, modulating the graft parameters allows the control of mechanical and degradational properties of resulting hydrogels in a wide range. Their biomedical potential as an injectable delivery system is demonstrated using ex vivo tissue model, in which the injection of precursor solution and subsequent hydrogel formation within the tissue are demonstrated

Multi-functional polymer systems for biomedical applications

Polymer-based materials are increasingly utilized as platforms for investigating and optimizing biological interactions for biomedical applications, such as tissue engineering, drug delivery and biosensors. Most conventional polymers adopted for this purpose serve as mechanical support and lack functional diversity to account for the complexity of biological systems. Herein, multifunctional polymer systems, based on polyaspartamide and hyperbranched hyperbranched polyglycerol, are introduced. Their ability to acquire multifunctionality through simple chemical modifications allowed efficient modulation of physicomechanical and bioactive properties of soft biomaterials. In addition, they could also be integrated with other polymers to develop hybridized materials with advanced functions. The biomedical potential of these polymers was demonstrated as bioinks for 3D bioprinting and injectable and biodegradable drug delivery systems

Nanofiber-laden Hydrogels For Biomedical Applications

Hydrogels are widely used in biomedical engineering, most notably as drug delivery systems, cell culture scaffolds and biosensors. Mechanical properties of hydrogels are generally controlled by the crosslinking density of the polymeric network. But this inevitably leads to significant changes in their permeability. To resolve this issue, the strategy of incorporating short nanofibers into the hydrogels is employed. This allowed the control of mechanics only with a small amount of nanofibers without changing the polymer concentration. Furthermore, new functionalities could be introduced to the hydrogels by incorporating nanofibers prepared using various types of functional polymers

Multifunctional heteroscaled hydrogels integrated with dispersible hybrid nanofibers

Hydrogels are widely used as scaffolds for cell and tissue culture applications. However, it is challenging to culture cells in 3D hydrogels at higher mechanical stiffness, as diminished permeability leads to limited diffusion of nutrients and available space for sufficient cellular activities. Herein, a novel strategy of incorporating short, aqueous-dispersible nanofibers into hydrogel is presented. Infusing nanofibers into hydrogel without changing the crosslinking density allowed the control of hydrogel mechanics, while limiting the change in permeability. Furthermore, nanofibers with a conductive polymer helped impart electrical conductivity to the hydrogel, allowing more efficient propagation of externally-applied electrical signals through the hydrogels. The resulting multifunctional nanofiber-infused hydrogels, with controllable mechanical and electrical properties, were utilized as a 3D cell culture platform to study the effects of various microenvironmental conditions

Nanofiber-laden hydrogels for biomedical applications

Hydrogels are widely used in biomedical engineering, most notably as drug delivery systems, cell culture scaffolds and biosensors. Mechanical properties of hydrogels are generally controlled by the crosslinking density of the polymeric network. But this inevitably leads to significant changes in their permeability. To resolve this issue, the strategy of incorporating short nanofibers into the hydrogels is employed. This allowed the control of mechanics only with a small amount of nanofibers without changing the polymer concentration. Furthermore, new functionalities could be introduced to the hydrogels by incorporating nanofibers prepared using various types of functional polymers

Synergistic control of mechanics and microarchitecture of 3d hydrogel for engineering hepatic tissue

Culturing autologous cells with therapeutic potential derived from a patient within a bioactive scaffold to induce high 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 applications of this strategy to control the mechanics, diffusion, and architecture of hydrogels in a combinatorial manner could maximize their hepatic functions. The regenerative capacity of this engineered hepatic tissue was further demonstrated using an in vivo acute liver injury model