Reversible coating of cells with synthetic polymers for mechanochemical regulation of cell adhesion

The chemical control of cell–cell interactions using synthetic materials is useful for a wide range of biomedical applications. Herein, we report a method to regulate cell adhesion and dispersion by introducing repulsive forces to live cell membranes. To induce repulsion, we tethered amphiphilic polymers, such as cholesterol-modified polyethylene glycol (PEG-CLS) to cell membranes. These amphiphilic polymers both bind to and dissociate rapidly from membranes and thus, enable the reversible coating of cells by mixing and washout without requiring genetic manipulation or chemical synthesis in the cells. We found that the repulsive forces introduced by these tethered polymers can induce cell detachment from a substrate and allow cell dispersion in a suspension, modulate the speed of cell migration, and improve the separation of cells from tissues. Our analyses showed that coating the cells with tethered polymers most likely generated two distinct repulsive forces, lateral tension and steric repulsion, on the surface, which can be tuned by altering the polymer size and density. We also modeled how these two forces can be generated in kinetically distinctive manners to explain the various responses of cells to the coating. Collectively, our observations and analyses show how we can mechanochemically regulate cell adhesion and dispersion and may contribute to the optimization of chemical coating strategies for regulating various types of cell–cell interacting systems.

Conformation and Dynamics of Long-Chain End-Tethered Polymers in Microchannels

Polyelectrolytes constitute an important group of materials, used for such different purposes as the stabilization of emulsions and suspensions or oil recovery. They are also studied and utilized in the field of microfluidics. With respect to the latter, a part of the interest in polyelectrolytes inside microchannels stems from genetic analysis, considering that deoxyribonucleic acid (DNA) molecules are polyelectrolytes. This review summarizes the single-molecule experimental and molecular dynamics simulation-based studies of end-tethered polyelectrolytes, especially addressing their relaxation dynamics and deformation characteristics under various external forces in micro-confined environments. In most of these studies, DNA is considered as a model polyelectrolyte. Apart from summarizing the results obtained in that area, the most important experimental and simulation techniques are explained.

Relaxation of surface-tethered polymers under moderate confinement

In moderate confinement between parallel planes, the longest relaxation time of surface-tethered polymers increases with decreasing channel height.

Stretching of surface-tethered polymers in pressure-driven flow under confinement

Stretching of a surface tethered polymer chain in pressure-driven flow under confinement is governed mainly by the wall shear stress and the chain contour length.

Thermal and Spectral Analysis of Novel Amide-Tethered Polymers from Poly(allylamine)

Post-polymerization modification of poly(allylamine hydrochloride) was applied to synthesize a library of amide-linked polyelectrolytes with tethered aliphatic, aromatic, and cubyl moieties. The efficacy of amidation was determined to be between 12 and 98 %, depending on the electronics, sterics, and solubility of the amide linkage. 13C solid-state NMR was used to further validate their structure. Thermogravimetric analysis and differential scanning calorimetry analysis indicated that none of the new polymers displayed a classic melt/freeze profile, but all displayed onset decomposition temperatures smaller than 215°C. We anticipate that the structure–property relationships observed in the resulting library of graft-modified polymers can facilitate better understanding of how to design polyelectrolytes for the construction of well-defined multilayer systems.