Infiltration of Proteins in Cholesteric Cellulose Structures.

Livia K Bast,Blaise L Tardy,Konrad W Klockars,Orlando J Rojas,Nico Bruns,Luiz G Greca

doi:10.1021/acs.biomac.1c00183

Abstract

Cellulose nanocrystals (CNCs) can spontaneously self-assemble into chiral nematic (cn) structures, similar to natural cholesteric organizations. The latter display highly dissipative fracture propagation mechanisms given their “brick” (particles) and “mortar” (soft matrix) architecture. Unfortunately, CNCs in liquid media have strong supramolecular interactions with most macromolecules, leading to aggregated suspensions. Herein, we describe a method to prepare nanocomposite materials from chiral nematic CNCs (cn-CNCs) with strongly interacting secondary components. Films of cn-CNCs were infiltrated at various loadings with strongly interacting silk proteins and bovine serum albumin. For comparison and to determine the molecular weight range of macromolecules that can infiltrate cn-CNC films, they were also infiltrated with a range of poly(ethylene glycol) polymers that do not interact strongly with CNCs. The extent and impact of infiltration were evaluated by studying the optical reflection properties of the resulting hybrid materials (UV–vis spectroscopy), while fracture dissipation mechanisms were observed via electron microscopy. We propose that infiltration of cn-CNCs enables the introduction of virtually any secondary phase for nanocomposite formation that is otherwise not possible using simple mixing or other conventional approaches.

Highlights

Nature produces hierarchical structures, from the molecular scale to the macroscale
Under the illumination proteins) were infiltrated into chiral nematic cellulose nanocrystals (CNCs) (cn-CNCs) films prepared through conditions used for the transmission mode imaging, the photoevaporation-induced self-assembly (EISA)
We investigate the infiltration of macromolecules into cn-CNC films to open the pathway to high-performance composites similar to those observed in nature

Summary

Introduction

From the molecular scale to the macroscale. The combination of soft and hard matrices at the nano- and microscales is ubiquitous in natural materials and the evolutionary convergent solution to attain strong and tough materials. Typical examples are bones,[1,2] seashells, and crustaceans.[3] The latter consist of fibrils arranged in layers stacked in a helix Such chiral nematic (cn) structures (Bouligand, plywood, helicoidal, or cholesteric structures) are observed in many organisms.[3−6] Within each layer, the fibrils are ordered in parallel, but their direction rotates by a fixed angle between the layers (Figure 1).[5,7] Several synthetic materials have been made using nanocompositing routes to create cn composites with higher strength and toughness than the individual parts they form.[5,8,9] In the past decade, cellulose nanomaterials, extracted from the cell walls of plant fibers, have been investigated in such contexts.[10] This is because such fibers are inherently stiff and strong. CNCs are insoluble in most conventional solvents; they have a high thermal decomposition temperature (>200 °C), and their

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