Project Outputs

Visual Appearance of Chiral Nematic Cellulose‐Based Photonic Films: Angular and Polarization Independent Color Response with a Twist

Advanced Materials, 31:52, DOI:
Chun Lam Clement Chan, Mélanie M. Bay, Gianni Jacucci, Roberto Vadrucci, Cyan A. Williams, Gea T. van de Kerkhof, Richard M. Parker, Kevin Vynck, Bruno Frka‐Petesic and Silvia Vignolini

Hydroxypropyl cellulose (HPC) is a biocompatible cellulose derivative capable of self‐assembling into a lyotropic chiral nematic phase in aqueous solution. This liquid crystalline phase reflects right‐handed circular polarized light of a specific color as a function of the HPC weight fraction. Here, it is demonstrated that, by introducing a crosslinking agent, it is possible to drastically alter the visual appearance of the HPC mesophase in terms of the reflected color, the scattering distribution, and the polarization response, resulting in an exceptional matte appearance in solid‐state films. By exploiting the interplay between order and disorder, a robust and simple methodology toward the preparation of polarization and angular independent color is developed, which constitutes an important step toward the development of real‐world photonic colorants.

Replicating the complexity of natural surfaces: Technique validation and applications for biomimetics, ecology and evolution

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences, 377:2138, DOI:
Charchit Kumar , Alejandro Palacios , Venkata A. Surapaneni, Georg Bold, Marc Thielen, Erik Licht, Timothy E. Higham, Thomas Speck and Vincent Le Houérou

The surfaces of animals, plants and abiotic structures are not only important for organismal survival, but they have also inspired countless biomimetic and industrial applications. Additionally, the surfaces of animals and plants exhibit an unprecedented level of diversity, and animals often move on the surface of plants. Replicating these surfaces offers a number of advantages, such as preserving a surface that is likely to degrade over time, controlling for non-structural aspects of surfaces, such as compliance and chemistry, and being able to produce large areas of a small surface. In this paper, we compare three replication techniques among a number of species of plants, a technical surface and a rock. We then use two model parameters (cross-covariance function ratio and relative topography difference) to develop a unique method for quantitatively evaluating the quality of the replication. Finally, we outline future directions that can employ highly accurate surface replications, including ecological and evolutionary studies, biomechanical experiments, industrial applications and improving haptic properties of bioinspired surfaces. The recent advances associated with surface replication and imaging technology have formed a foundation on which to incorporate surface information into biological sciences and to improve industrial and biomimetic applications. This article is part of the theme issue ‘Bioinspired materials and surfaces for green science and technology’.

Effects of Silk Degumming Process on Physicochemical, Tensile, and Optical Properties of Regenerated Silk Fibroin

Macromolecular Materials and Engineering, 303:12, DOI:
Kira Nultsch, Livia K. Bast, Muriel Näf, Salima El Yakhlifi, Nico Bruns, Oliver Germershaus

Sericin removal from silk (degumming) affects material characteristics of silk fibroin (SF). Sodium carbonate is most commonly used for degumming, but numerous alternative methods are available. Herein, a systematic comparison of degumming methods is provided. Sodium carbonate, sodium oleate, trypsin, and ionic liquid are used, and materials are characterized regarding mass loss, SF content, molecular integrity of SF, refractive index, and tensile properties. Complete degumming is achieved within 30 min of using sodium carbonate, but results in significant reduction of molecular weight, shift toward less acidic charge variants, and reduction of yield‐ and rupture force. Sodium oleate and trypsin are inefficient and negatively affect tensile properties, while ionic liquid shows good efficiency and marginal degradation of SF but also reduced yield‐ and rupture force. Refractive index is not affected by degumming. These results allow rational selection of the degumming method and tuning of SF properties for biomedical applications.

advanced materials special issue

Special Issue: Bio-Inspired Materials

Bioinspiration is a powerful concept to develop novel functional materials. This Special Issue, edited by Silvia Vignolini and Nico Bruns, presents bioinspired materials across all length scales, such as wood‐based water‐purification systems, mussel‐protein‐inspired glues, diatoms that encapsulate drugs, fiber‐reinforced composites that indicate damage by bleeding, helical cellulose nanocrystals for optical applications, pigments and coatings that mimic the structural color of insects and plants, architecture inspired by the moving parts of plants, and many more.

Self‐Reporting Fiber‐Reinforced Composites That Mimic the Ability of Biological Materials to Sense and Report Damage

Advanced Materials, 30:19, DOI:
Omar Rifaie‐Graham, Edward A. Apebende, Livia K. Bast and Nico Bruns

Sensing of damage, deformation, and mechanical forces is of vital importance in many applications of fiber‐reinforced polymer composites, as it allows the structural health and integrity of composite components to be monitored and microdamage to be detected before it leads to catastrophic material failure. Bioinspired and biomimetic approaches to self‐sensing and self‐reporting materials are reviewed. Examples include bruising coatings and bleeding composites based on dye‐filled microcapsules, hollow fibers, and vascular networks. Force‐induced changes in color, fluorescence, or luminescence are achieved by mechanochromic epoxy resins, or by mechanophores and force‐responsive proteins located at the interface of glass/carbon fibers and polymers. Composites can also feel strain, stress, and damage through embedded optical and electrical sensors, such as fiber Bragg grating sensors, or by resistance measurements of dispersed carbon fibers and carbon nanotubes. Bioinspired composites with the ability to show autonomously if and where they have been damaged lead to a multitude of opportunities for aerospace, automotive, civil engineering, and wind‐turbine applications. They range from safety features for the detection of barely visible impact damage, to the real‐time monitoring of deformation of load‐bearing components.