Aqueous Suspensions of Cellulose Oligomer Nanoribbons for Growth and Natural Filtration-Based Separation of Cancer Spheroids.

In vitro growth of cancer spheroids (CSs) and the subsequent separation of CSs from a 2D or 3D cell culture system are important for fundamental cancer studies and cancer drug screening. Although biopolymer-based or synthetic hydrogels are suitable candidates to be used as 3D cell culture scaffolds, alternatives with better processing capabilities are still required to set up cell culture microenvironment. In this study, we show that aqueous suspensions of crystalline nanoribbons composed of cellulose oligomers have a potential for CS growth and separation. The nanoribbon suspensions in serum-containing cell culture media fixed single cancer cells and CSs with large sizes in a 3D space, leading to suspension cultures for CS growth corresponding to culture time. Well-grown CSs were easily separated from the suspensions by natural filtration using a mesh filter with a suitable pore size. Cell viability tests revealed negligible cytotoxicity of the nanoribbons. In addition, physical damages to CSs by the separation procedures were negligible. Stable suspensions of biocompatible nanomaterials will thus provide novel microenvironments for growth and separation of diverse cell aggregates.

Antibacterial Synthetic Nanocelluloses Synergizing with a Metal-Chelating Agent.

Antibacterial materials composed of biodegradable and biocompatible constituents that are produced via eco-friendly synthetic strategies will become an attractive alternative to antibiotics to combat antibiotic-resistant bacteria. In this study, we demonstrated the antibacterial properties of nanosheet-shaped crystalline assemblies of enzymatically synthesized aminated cellulose oligomers (namely, surface-aminated synthetic nanocelluloses) and their synergy with a metal-chelating antibacterial agent, ethylenediaminetetraacetic acid (EDTA). Growth curves and colony counting assays revealed that the surface-aminated cellulose assemblies had an antibacterial effect against Gram-negative Escherichia coli (E. coli). The cationic assemblies appeared to destabilize the cell wall of E. coli through electrostatic interactions with anionic lipopolysaccharide (LPS) molecules on the outer membrane. The antibacterial properties were significantly enhanced by the concurrent use of EDTA, which potentially removed metal ions from LPS molecules, resulting in synergistic bactericidal effects. No antibacterial activity of the surface-aminated cellulose assemblies was observed against Gram-positive Staphylococcus aureus even in the presence of EDTA, further supporting the contribution of electrostatic interactions between the cationic assemblies and anionic LPS to the activity against Gram-negative bacteria. Analysis using quartz crystal microbalance with dissipation monitoring revealed the attractive interaction of the surface-aminated cellulose assembly with LPS Ra monolayers artificially produced on the device substrate.

Alkyl chain length-dependent protein nonadsorption and adsorption properties of crystalline alkyl ß-celluloside assemblies.

Cellulose-based crystalline assemblies artificially constructed in a bottom-up manner are attracting increasing attention as chemically stable and functionally designable nano- to macroscale materials. However, basic knowledge of how such crystalline assemblies interact with biomolecules and how to control them via molecular design is still limited. In this study, we investigated the protein adsorption properties of crystalline lamella assemblies composed of alkyl ß-cellulosides (namely, ethyl, n-butyl, and n-hexyl ß-cellulosides) or plain cellulose, which all have an antiparallel molecular arrangement. It was found that the adsorption of proteins was observed only for the n-hexyl ß-celluloside assembly, while it was hardly observed for other assemblies. The n-hexyl groups appeared to be ordinarily embedded in the assembly surface in an aqueous phase, while, when in contact with proteins, n-hexyl groups appeared to be tethered to promote protein adsorption. All-atom molecular dynamics simulations supported the contradictory protein adsorption properties. The basic knowledge obtained herein is highly valuable for controlling the interactions of cellulose-based synthetic assemblies with proteins for designing new biological applications.