Bottlebrush Bridge between Soft Gels and Firm Tissues.

Softness and firmness are seemingly incompatible traits that synergize to create the unique soft-yet-firm tactility of living tissues pursued in soft robotics, wearable electronics, and plastic surgery. This dichotomy is particularly pronounced in tissues such as fat that are known to be both ultrasoft and ultrafirm. However, synthetically replicating this mechanical response remains elusive since ubiquitously employed soft gels are unable to concurrently reproduce tissue firmness. We have addressed the tissue challenge through the self-assembly of linear-bottlebrush-linear (LBL) block copolymers into thermoplastic elastomers. This hybrid molecular architecture delivers a hierarchical network organization with a cascade of deformation mechanisms responsible for initially low moduli followed by intense strain-stiffening. By bridging the firmness gap between gels and tissues, we have replicated the mechanics of fat, fetal membrane, spinal cord, and brain tissues. These solvent-free, nonleachable, and tissue-mimetic elastomers also show enhanced biocompatibility as demonstrated by cell proliferation studies, all of which are vital for the safety and longevity of future biomedical devices.

Strained Bottlebrushes in Super-Soft Physical Networks.

ABA triblock copolymers composed of a poly(dimethylsiloxane) (PDMS) bottlebrush central block and linear poly(methyl methacrylate) (PMMA) terminal blocks self-assemble into a physical network of PDMS bottlebrush strands connected by PMMA spherical domains. A combination of small- and ultrasmall-angle X-ray scattering techniques was used to concurrently examine dimensions of PMMA spherical domains and PDMS bottlebrush strands both in the bulk and at the PMMA-PDMS interface. In agreement with scaling model predictions, the degrees of polymerization of the bottlebrush backbone (nbb) and PMMA block (nA) correlate with the measured PMMA domain size and area per molecule at the PMMA-PDMS interface as DA ∝ (nbbnA)1/3 and S ∝ nA2/3nbb-1/3, respectively. In the bulk, bottlebrush strands are extended due to steric repulsion between the side chains and unfavorable interactions between the different blocks. At the PMMA-PDMS interface with large curvature, packing constraints require additional bottlebrush backbone extension and alignment of side chains along the backbone in the direction perpendicular to the interface.

Adsorption behavior of optical brightening agent on microfibrillated cellulose studied through inverse liquid chromatography: The need to correct for axial dispersion effect.

Inverse liquid chromatography is a technique for studying solid/liquid interaction and most specifically for the determination of solute adsorption isotherm. For the first time, the adsorption behaviour of microfibrillated cellulose was assessed using inverse liquid chromatography. We showed that microfibrillated cellulose could adsorb 17 mg/g of tetrasulfonated optical brightening agent in typical papermaking conditions. The adsorbed amount of hexasulfonated optical brightening agent was lower (7 mg/g). The packing of the column with microfibrillated cellulose caused important axial dispersion (Da = 5e-7 m²/s). Simulation of transport phenomena in the column showed that neglecting axial dispersion in the analysis of the chromatogram caused significant error (8%) in the determination of maximum adsorbed amount. We showed that conventional chromatogram analysis technique such as elution by characteristic point could not be used to fit our data. Using a bi-Langmuir isotherm model improved the fitting, but did not take into account axial dispersion, thus provided adsorption parameters which may have no physical significance. Using an inverse method with a single Langmuir isotherm, and fitting the transport equation to the chromatogram was shown to provide a satisfactory fitting to the chromatogram data. In general, the inverse method could be recommended to analyse inverse liquid chromatography data for column packing with significant axial dispersion (Da > 1e-7 m²/s).