As contamination and environmental degradation increase nowadays, there is a huge demand for new eco-friendly materials. Despite its use for thousands of years, cellulose and its derivatives have gained renewed interest as favourable alternatives to conventional plastics, due to their abundance and lower environmental impact. We report the fabrication of photonic and plasmonic structures by moulding hydroxypropyl cellulose into sub-micrometric periodic lattices, using soft lithography. This is an alternative way to achieve structural colour in this material which is usually obtained exploiting its chiral nematic phase. Cellulose based photonic crystals are biocompatible and can be dissolved in water or not depending on the derivative employed. Patterned cellulose membranes exhibit tuneable colours and may be used to boost the photoluminescence of a host organic dye. Furthermore, we show how metal coating these cellulose photonic architectures leads to plasmonic crystals with excellent optical properties acting as disposable surface enhanced Raman spectroscopy substrates.

516 wileyonlinelibrary.com COMMUNICATION www.MaterialsViews.com www.advopticalmat.depreparation of compression sensitive inverse opals which allow the mechanical tuning of the photonic stopgap position. [ 18 ] Elastomers have also played a fundamental role for studying color tunable photonic crystals (PCs), [ 19,20 ] whose lattice parameter might be controlled by deformation (mechanochromic effect) or elastomer swelling. [ 21 ] An equivalent approach was proposed for the development of tunable phononic crystals. [ 22 ] Another active area of research concerns fl exible systems implemented, for instance, as UV-fi lters [ 23 ] and light emitting diodes or displays. [ 24 ] The present work addresses the fabrication of periodic nanofeatures with SME by using a replica molding approach for imprinting a 2D photonic nanostructure on the surface of a shape-memory elastomer. Structural and optical characterization of the as-produced system allowed to demonstrate its shape-memory functionality for confi guring the lattice parameter or erasing the nanopattern. This property might be very attractive, for example, for the development of reusable or self-healing photonic elements with adaptive properties.Polydiolcitrates (PDCs), fi rst described by Ameer and colleagues in 2004, [ 25 ] have been recently identifi ed as thermoresponsive elastomers presenting SME. [ 26 ] However, as far as we know, their applicability in the accomplishment of photonic nanostructured systems has not been reported in the literature yet. The synthesized polyester networks were obtained upon:(1) increase of the mol ratio of hydroxyl to carboxyl groups in the reaction mixture (4:3 in hydroxyl-dominant PDCs versus 1:1 in the original ones) and (2) the use of a more hydrophobic diol (e.g., 1,12-dodecanediol, DD). These polymers include covalent netpoints responsible for the permanent shape and hydrophobic micro-domains (either pre-polymer or DD-rich domains) physically cross-linked by intermolecular hydrophobic interactions as switch structures to fi x the temporary shape. To investigate the SME of these polymers for potential photonic applications, we followed the general procedure depicted in Figure 1 . The fi rst step consisted of the synthesis of the pre-polymer solution composed of DD and citric acid. 1 H nuclear magnetic resonance ( 1 H-NMR) confi rmed the mol ratio expected for both components (1.5) and the beginning of the condensation reaction (e.g., multiplicity of peaks at 2.6-2.9 ppm) (see Supporting Information (SI), Figure S7). Nanopatterning of the elastomer surface was achieved by using an approach inspired in soft-lithography [ 27 ] and, more specifi cally, in replica molding (Figure 1 a). [ 28,29 ] Briefl y, the pre-polymer solution was spread over the template, in our case a colloidal monolayer composed of polystyrene (PS) spheres of 870 nm in diameter ( d ). After curing at 90 °C for 12 h, the resulting cross-linked poly mer (PDDC-HD) was peeled off from the monolayer. When evaluating the cross-linking degree of the so-produced elast...

Bio-polymer based composites enable to combine different functionalities using renewable materials and cost-effective routes. Here we fabricate novel thermoresponsive photonic films combining cellulose nanocrystals (CNCs) with a polydiolcitrate elastomer exhibiting shape memory properties. In this composite, CNCs provide an intense structural coloration and improve the overall mechanical cohesion, while the elastomer drastically reduces the intrinsic brittleness of the photonic cellulose film and enables the shape memory effect. The fabricated samples are characterized by polarized optical microscopy, scanning electron microscopy and thermomechanical programming. The obtained results demonstrate that this hybrid material retains its chiral nematic structure and performs shape recovery in thermomechanical experiments thus widening the functionality of the independent components. Keywords cellulose nanocrystals; cholesteric; polydiolcitrates; shape memory; biomimetic Plastics are key materials in many aspects of daily life, ranging from packaging, to construction, to medical applications. The replacement of conventional plastics with biocompatible and biodegradable ones enables to exploit the versatility of polymeric materials with the advantage of using sustainable fabrication approaches. Within this context, photonic materials produced by self-assembly of biopolymers are receiving growing interest in the materials community.1-3 Many photonic structures with diverse optical responses have been produced using a large variety of biomaterials and fabrication methods. *Corresponding Authors: C.L.: c.lopez@csic.es; S.V.: sv319@cam.ac.uk. 1 Institut de Ciència de Materials de Barcelona, Consejo Superior de Investigaciones Científicas, Carrer dels Til·lers S/N, Campus de la UAB, 08193 Bellaterra, Barcelona, Spain. Author ContributionsThe manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Europe PMC Funders Group Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts 4-6 However, there are limitations on the different functionalities that can be achieved using only sustainable and biocompatible polymers. As an example, cellulose-based photonic structures can provide strong, intense colorations but they are generally very brittle.7 The addition of organic and inorganic matrices to such cellulose structures improves their mechanical properties but either comports the loss of the photonic effect or reduces the fully biocompatibility of the final composite.8Here we present a hybrid cellulose-based photonic structure exhibiting shape memory, fabricated by combining cellulose nanocrystals (CNCs) photonic films with a polydiolcitrate elastomer.9 In particular, we directly impregnate and embed colored CNC films with hydroxyl-dominant poly(dodecanediol-co-citrate) (PDDC-HD).10 The CNCs contribute both to the structural coloration of the film and to its overall mechanical cohesion, while the PDDC-HD provides both flexibil...