www.afm-journal.de www.MaterialsViews.com Thanh-Dinh Nguyen, Bernardo U Peres, Ricardo M Carvalho, and Mark J MacLachlan* FULL PAPER Photonic Hydrogels from Chiral Nematic Mesoporous Chitosan Nanofibril Assemblies wavelength that depends on the repeating distance, or pitch, of the helicoidal arrangement.[6] The organization of chitin in the Bouligand structure is a solid-state manifestation of optically active chiral nematic (cholesteric) lyotropic liquid crystals (LCs).[7] Cellulose nanocrystals (CNCs) and other cellulose derivatives, such as hydroxypropyl cellulose, can also organize into a lyotropic chiral nematic LC phase above a critical concentration.[8] The LC order of CNCs is preserved upon evaporation of solvent to yield left-handed chiral nematic CNC films that are iridescent.[9] The coloration of the films can be tuned by changing the pitch of CNC assemblies upon drying in response to certain stimuli.[10] Recently, we produced photonic chiral nematic mesoporous cellulose films from the self-assembly of a CNC dispersion with melamineurea-formaldehyde resins and subsequent alkali treatment.[11] These cellulosic nanocrystal films are responsive photonic materials whose reflected colors change upon swelling The exoskeletons of crustaceans are mainly composed of chitin, minerals, and protein Interestingly, chitin is arranged into a Bouligand structure within the exoskeleton,[5] but most likely arthropods first evolved the Bouligand-type organization for structural reinforcement rather than for coloration As crustacean shells are a waste by-product from seafood processing, it is attractive to use the crustacean exoskeletons for the development of new advanced materials Recently, we exploited the Bouligand structure of chitin in endocuticles of crab shells[12] directly as a template to produce photonic silica/chitin composites by hydrolyzing tetramethoxysilane within pores of the chiral nematic mesoporous chitin network innate to the crab cuticles Calcination of these composites under different conditions recovered mesoporous solid replicas (silica and N-doped carbon) that retained the Bouligand-twisted organization and high surface area of the cuticle nanofibrils.[12] Similar to the chiral nematic phase of CNCs, the twisted mesoporous chitinous cuticles could be useful for constructing hierarchical photonic nanomaterials.[13] Smart photonic hydrogels that can respond to external stimuli with a change in color have received a great deal of attention because they are useful for optical sensing.[14] Chiral nematic structures with photonic properties can be an intriguing platform to transfer into a hydrogel.[15] Stimuliresponsive photonic hydrogels were previously formed by polymerizing suitable monomers (e.g., acrylamide, acrylic Iridescence in animals and plants often arises from structural coloration, which involves hierarchical organization of minerals and biopolymers over length scales of the visible spectrum, leading to diffraction of light In this work, discarded crustacean shells that are not known for their structural colors are used to produce photonic nanostructures of large, freestanding chiral nematic mesoporous chitosan membranes with tunable iridescent color Bioinspired by colorful nanostructures in nature, photonic hydrogels with Bouligand-type organization are fabricated from the twisted mesoporous membranes, where the chitosan nanofibrils are a novel precursor for surface acetylation and are also a biotemplate for polymerizing methyl methacrylate The colors of the hydrogels can be tailored by swelling as they show large volume changes in response to changes in solvent environment Introduction More than two billion years of evolution have led to remarkable natural materials, such as bone and nacre, with complex 3D hierarchical structures.[1] Diverse and beautiful examples of iridescent colors in plants, insects, and other animals originate from hierarchical nanostructured organization of substances, often carbohydrates, which interact with light to create vibrant colors These structural colors have evolved by natural selection for warding off predators, attracting mates, and mimicry.[2] Examples of structural colors include the blue feathers of peacocks, the metallic hues of dragonfly bodies and beetle elytra, and the blue wings of the morpho butterfly.[3] The remarkable natural architectures responsible for the coloration of these organisms and others are inspiring scientists to create new photonic materials.[4] Within the exoskeleton of many arthropods, for example, chitin fibrils organize into a left-handed helical “twisted plywood” arrangement that is known as a Bouligand structure.[5] This long-range twisted order leads these structures to selectively reflect circularly polarized light with a Dr T.-D Nguyen, Prof M J MacLachlan Department of Chemistry University of British Columbia 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada E-mail: mmaclach@chem.ubc.ca B U Peres, Prof R M Carvalho Department of Oral Biological and Medical Sciences Faculty of Dentistry University of British Columbia 2199 Wesbrook Mall, Vancouver, British Columbia V6T 1Z3, Canada DOI: 10.1002/adfm.201505032 Adv Funct Mater 2016, 26, 2875–2881 © 2016 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim wileyonlinelibrary.com 2875 www.afm-journal.de FULL PAPER www.MaterialsViews.com acid) during the self-assembly of CNCs into a chiral nematic phase.[16] There are many reports of biocompatible chitosan-based hydrogels,[17] but introducing the chiral nematic order into photonic chitosan hydrogels has been virtually unexplored Here we report, for the first time, the preparation and investigations of photonic hydrogels with tunable polarized color from chiral nematic mesoporous chitosan (CNMC) nanofibrils derived from shells and endocuticles of crustaceans Results and Discussion Visibly, the original shells and endocuticles of shrimps not generally appear iridescent (Figure S1a, Supporting Information) Until now the chirality and coloration of shrimp shells are unknown and this is not surprising since they have an inhomogeneous layered structure of chitin fibrils (Figure S2, Supporting Information) Protein and minerals (mostly calcium carbonate) were removed from the shrimp shells by sequentially treating them with dilute alkali and acid solutions to obtain white chitin membranes Even after purification, chitin membranes obtained Figure Photonic mesoporous chitosan nanofibrils with chiral nematic structure prepared show neither structural colors nor chiroptical from shrimp shells a) Photograph of dried membranes of iridescent CNMC obtained by treating the shrimp shells twice with 50 wt% NaOH(aq) solution at 90 °C for h b) Solid-state properties (Figure S1b, Supporting Informa- 13C CP/MAS NMR spectra of the purified chitin shrimp shells before (red line) and after (blue tion) We were thus surprised to find that line) repeated alkali treatment c) POM image of the dried CNMC viewed under crossed polarhot alkali treatment of the purified shrimp izers at the top surface of the film d) Photographs of dried CNMC observed under left-handed shells affords photonic materials resembling (left) and right-handed (right) circularly polarized filters e) CD spectra of dried (blue) and wet crab endocuticles.[12] The coloration of the (red) CNMC deacetylated chitin membranes was evolved main structure of the shrimp shells, but considerably decreased by repeatedly treating the purified shrimp shells several times the crystallinity of the chitin fibrils This is consistent with the with hot concentrated alkali solution Interestingly, flexible alkali-treated crab endocuticles previously reported.[12] These membranes obtained after drying are more transparent, appear violet-green iridescent in color, and retain the original shapes results confirm that the materials obtained from the alkali treatof the shrimp shells with ≈100–150 µm thickness (Figure 1a) ment of the purified shrimp shells are chitosan, the highly deaThe purified shrimp shells before and after alkali treatment cetylated form of chitin The alkali-treated membranes show were analyzed using a variety of techniques Elemental analyses lower crystallinity and more transparency than pristine chitin confirm that the elemental C:N ratio in chitin decreases from Reduced interchain hydrogen bonding between the chitosan 6.86 to 5.25 (wt/wt%) after alkali treatment, giving a ratio that polymers may lead the originally inhomogeneous layered is close to the theoretical C:N ratio of 5.14 in chitosan Solidnanofibrils to significantly relax upon swelling into a structure state 13C cross-polarization/magic-angle spinning (CP/MAS) with improved order and photonic properties Mesoporosity was obtained within the colorful chitosan NMR spectroscopy (Figure 1b) shows that the pristine chitin membranes after removal of calcium minerals from the shrimp has peaks at 163.5 and 13.5 ppm assigned to C7 carbonyl shells, which makes them swell reversibly (Figure S4, Supand C8 methyl carbons, respectively; peaks at 46–96 ppm are porting Information) Polarized optical microscopy (POM) assigned to the resonances of C1-C6 on the N-acetyl-D-glucosaimages (Figure 1c) of the chitosan membranes show strong mine unit of chitin.[18] The sharp peaks of the acetyl groups birefringence with some regions showing fingerprint textures mostly disappear in the chitin samples after alkali treatment, composed of adjacent lines; the images look similar to those demonstrating that chitin was strongly deacetylated by hot conof chiral nematic mesoporous cellulose films.[11] The iridescent centrated alkali solution to yield chitosan.[18] Powder X-ray diffraction (PXRD) patterns (Figure S3b, Supporting Information) violet-green colors of the membrane are clearly observed under of the alkali-treated chitin show diffraction peaks at the same a left-handed circularly-polarized filter and turn to a dull shade positions as for pristine chitin, but with decreased diffraction when viewed under a right-handed circularly-polarized filter intensity, confirming that the alkali treatment preserved the (Figure 1d) Circular dichroism (CD) spectra (Figure 1e) of the 2876 wileyonlinelibrary.com © 2016 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim Adv Funct Mater 2016, 26, 2875–2881 www.afm-journal.de www.MaterialsViews.com Adv Funct Mater 2016, 26, 2875–2881 © 2016 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim wileyonlinelibrary.com FULL PAPER heating of the alkali treatment enhances the green-blue polarized colors of CNMC and consequently enhances the optical reflectance (Figure S6c,d, Supporting Information) Similar to the 13C CP/MAS NMR spectroscopy of the shrimp shell-derived chitosan membranes, the resonances of C7 carbonyl and C8 methyl carbons in N-acetylD-glucosamine unit are dramatically diminished after alkali treatment of the chitinous crab endocuticles (Figure S7, Supporting Information).[18] Furthermore, the peak reflected wavelength of the pristine CNMC red shifted from ≈550 nm to ≈770 nm when aging the membrane in acid (pH 1.0) for d (Figure S8, Supporting Information) Treating CNMC with dilute acid may disrupt interchain hydrogen bonding between nanofibrils, leading to swelling and an increase in the pitch, and thus a red shift of the iridescence CNMC swells rapidly upon immersion in solvents of different polarity, resulting in a red shift of the reflectance peak as the helical pitch lengthens (Figure S9, Figure SEM images of CNMC prepared from the chitin shrimp shells viewed along a) cutting Supporting Information) Soaking CNMC in edges and b–d) fracture cross-sections with different magnifications, and e) Schematic of chiral water causes a large color change compared nematic mesoporous chitosan nanofibril structure to soaking in anhydrous ethanol, where the colors are mostly unchanged By soaking CNMC in water/ethanol, the reflected colors span from the UV dried membrane show a very intense positive signal at ≈550 nm to near-IR (infrared) regions The mesoporosity, lower crystalthat red shifts to ≈650 nm upon swelling of the sample in linity, and surface amphiphilicity likely result in fast swelling of water The position and shape of the CD spectrum of the chithe chitosan membranes in water within tens of seconds (see tosan sample not change significantly when rotating the video in Supporting Information), which is comparable to that membrane, indicating that that the signal is not dominated by of photonic mesoporous cellulosic films.[11] linear birefringence (Figure S5, Supporting Information) Scanning electron microscopy (SEM) images (Figure 2) of the chiPhotonic hydrogels based on natural polymers are of partosan membranes viewed along cross-sections show a repeating ticular interest for applications in optical sensors for biomedilayered structure of the nanofibrils organized with a countercine.[14] As shown above, CNMC may be used directly as a clockwise direction over micrometer distances Together, these swellable biomaterial with tunable chiroptical properties To results clearly confirm that the chitosan nanofibrils organize further demonstrate the use of CNMC as a bioinspired platinto a left-handed chiral nematic structure in the membrane form to develop photonic hydrogels, we investigated the surthat selectively reflects left-handed circularly polarized light face acetylation of chitosan and the use of chitosan to template to create the iridescent colors Based on qualitative electronpoly(methylmethacrylate) (PMMA) photonic hydrogels with microscopic observations, we suggest that the Bouligand-type chiral nematic ordering (The photonic membranes prepared organization of the chitosan nanofibrils in the shrimp shells is from both the crab endocuticles and shrimp shells can be used slightly lower order than that in the crab shells.[12] This leads for these experiments.) Photonic hydrogels were directly prepared from CNMC by the CNMC to appear less iridescent and to show less intense controlled N-terminal acetylation and subsequent swelling in reflectance peaks by UV–vis and CD spectroscopy From a water Acetylation was carried out by simply treating CNMC survey of the literature, most previous efforts to observe chiropwith pure acetic anhydride, giving partial acetamide groups tical phenomena in regular shrimps have failed;[5b,c,d] this is the on the chitosan fibrils The mesoporous membranes retain first demonstration of freestanding chiral nematic mesoporous the original shapes and structural colors upon acetylation chitosan membranes with tunable photonic properties from (Figure 3a, left) The acetylated chitosan hydrogels (ACH) swell common shrimp shells with a simultaneous change in the pitch of the chiral nematic We previously reported iridescent CNMC prepared from crab structure and the reflected color Interestingly, we found endocuticles,[12] but we found that the manual delamination that ACH strongly absorbs water and undergoes substantial of layers from inner sides of the shells leads to tearing of the swelling with a several-fold increase in thickness to form transendocuticles into small pieces We now successfully obtained parent hydrogels within several minutes (Figure 3a-right and the endocuticles with intact shapes of large-sized exoskeletons Figure S10a of Supporting Information) This response is much by peeling off outer sides of the crab shells (Figure S6a, Supmore dramatic than the pristine CNMC that only shows modest porting Information) Also, we additionally found that extended 2877 www.afm-journal.de FULL PAPER www.MaterialsViews.com Figure Photonic hydrogels by swelling of the acetylated chitosan nanofibrils a) Photographs of swelling behavior of ACH (prepared from crab endocuticles) in water b) POM image of ACH after swelling viewed under crossed polarizers at a transverse cross-section of the film c) SEM image viewed along a cross-section of the dried ACH d) CD and UV–vis spectra of ACH upon swelling in water Because the CD spectrometer could not measure beyond 900 nm (blue lines), the UV–vis spectrometer was used to confirm the reflection peaks of ACH in the swollen states at longer wavelengths (red lines) e) Microtensile load-displacement curves for CNMC (red) and ACH dried (blue) and swollen (black) in water Stress-strain curves were calculated based on the original cross-sectional area of each tested specimen and assuming a gauge length of 20 mm swelling in water The acetylation-induced swelling offers a simple way to directly use the chitosan membranes for fabricating photonic hydrogels Elemental analyses show that the elemental C:N ratio in CNMC increases from 5.83 to 5.92 (wt/ wt%) after acetylation of chitosan IR spectra (Figure S11, Supporting Information) of the acetylated CNMC show an increase in the absorption intensity of the amide and alkyl stretching bands, indicating that acetic anhydride predominantly reacetylated the primary amino groups of chitosan PXRD patterns (Figure S12, Supporting Information) of the deswollen acetylated chitosan confirm the retention of α-chitin structure with slightly lower crystallinity than the pristine chitin The swollen acetylated chitosan hydrogels retain optically anisotropic properties when viewed under crossed polarizers and show a striated texture with a distance between lines corresponding to one half-pitch (Figure 3b) CD spectral measurements confirm that ACH before swelling shows a positive signal at ≈550 nm, the same wavelength as the peak reflection of CNMC, indicating the intact retention of the chiral nematic structure during acetylation (Figure 3d) CD spectroscopy of the hydrogels confirms the selective reflection of left-handed circularly polarized light, and the wavelength of the reflectance peak red shifts as the material is swollen in water The fully swollen hydrogels appear colorless and transparent as a result of extending the peak reflection into the near-IR region at ≈1200 nm (Figure 3d) Upon deswelling of ACH, the positive CD signal blue shifts to ≈680 nm (Figure S14a, Supporting Information), confirming that the left-handed twisted order of the chitosan nanofibrils was preserved in the deswollen 2878 wileyonlinelibrary.com hydrogel structure The acetylation likely results in reduction of hydrogen bonding and crystallinity of the chitosan fibrils, leading to large swelling of the acetylated membranes in water This is the cause of a drastic change in the pitch to induce the reversible shift of the reflection of the swollen structure of the acetylated chitosan hydrogels (Figure S14a, Supporting Information) Tensile mechanical testing (Figure 3e) showed a mean ultimate tensile strength (UTS) and elongation at break (EB) of 23.6 ± 3.0 MPa and ± 0.7% for the dried ACH; and of 22.8 ± 1.2 MPa and ± 0.2% for CNMC, respectively While both structures showed a typical viscoelastic behavior, there was a clearly distinct strain-dependent shift of moduli between them ACH presented a higher modulus at low strain (0%–3%), while CNMC presented a higher modulus only after reaching 6% strain The combined information on the UTS and EB indicates that ACH is a stronger and more brittle material at low strain, but CNMC is in an overall stronger and tougher material at high strain These differences could be attributed to the reduced hydrogen bonding between crystalline fibers resulting from the surface acetylation of chitosan Upon swelling in water from dryness, the UTS of ACH dropped to 3.1 ± 0.7 MPa at a strain of ± 0.3% After reaching this maximum stress, the material did not sharply break, but seemed to gradually disintegrate as if the fibers were deforming permanently and breaking nonuniformly as the strain increased This behavior resembles a gel-like structure and reflects the reduced internal cohesive structure that is now filled with water The mesoporous structure of the twisted chitosan nanofibrils makes the large-sized membrane useful as a template for the © 2016 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim Adv Funct Mater 2016, 26, 2875–2881 www.afm-journal.de www.MaterialsViews.com FULL PAPER Figure Biomimetic templating of twisted mesoporous chitosan nanofibrils with methyl methacrylate into photonic hydrogels a) Photographs of swelling response of PCH (prepared from crab endocuticles) at pH 1.4 b) POM image of PCH after swelling viewed under crossed polarizers at the top surface of the film c) SEM image viewed at cutting edges of the dried PCH d) CD and UV–vis spectra of PCH upon swelling in acidic media at pH 1.4 As the CD spectrometer that was used could not measure beyond 900 nm (blue lines), the reflection peaks of PCH in the swollen states beyond this range were confirmed with complementary UV–vis spectroscopy (red lines) e) Microtensile load-displacement curves for PCH dried (red) and swollen (blue) in acidic media at pH 1.4 Stress-strain curves calculated were based on the original cross-sectional area of each tested specimen and assuming a gauge length of 20 mm construction of photonic materials We improved the responsive swelling and mechanical properties of CNMC by incorporating PMMA into the mesopores of the chitosan nanofibril networks PMMA was prepared by photo-induced polymerization of methyl methacrylate monomer within the pores of CNMC in the presence of a 2,2-diethoxyacetophenone photoinitiator PMMA/chitosan composite with slightly red shifted colors is a true replica of the biotemplate and is more transparent and flexible than the pristine and acetylated CNMC (Figure 4a, top) The PMMA/chitosan composites strongly swell into hydrogels in acidic media over a wide range of pH from to (Figure 4a-bottom and Figure S10b of Supporting Information) The photonic hydrogels show a change in color from green to red and transparent during swelling with a several-fold increase in thickness within several minutes, while retaining their original shapes and enhancing the flexibility relative to CNMC Elemental analyses confirmed 44.74 wt% carbon in the PMMA/ chitosan composite in comparison to 41.13 wt% carbon in the pristine CNMC, consistent with the incorporation of PMMA into the chitosan film From these analysis results, the content of PMMA in the PMMA/chitosan composites was found to be ≈8 wt%, in agreement with that determined from the dissolution of the chitosan template by immersing the composites in an aqueous solution of vol% acetic acid at room temperature for 24 h IR spectra (Figure S13, Supporting Information) of PMMA/chitosan show amide I and II bands at 1560–1660 cm−1, a C O stretching band at 1025 cm−1 characteristic of chitosan, and a peak at 1720 cm−1 assigned to the ester carbonyl vibration of PMMA This provides substantial evidence of grafting PMMA on chitosan fibrils without altering the original chitosan Adv Funct Mater 2016, 26, 2875–2881 structure The acidic pH-dependent response of the PMMA/ chitosan hydrogels (PCH) may result from the protonation of the primary amino groups, which favors large expansion of the hydrogel volume PCH responds much faster to acidic pH than to basic pH because the chitosan template strongly swells in dilute acid solution but not in base POM images (Figure 4b) of the swollen PCH hydrogels show optical birefringence Optical spectroscopy shows photonic response of the reversible swelling of PCH in acidic media CD spectra of the PMMA/chitosan composites before swelling show a positive signal at ≈650 nm that is slightly red-shifted relative to CNMC, which likely results from the expansion of the helical structure by incorporating PMMA within the pores of the chitosan nanofibril membrane (Figure 4d) The selective reflection of left-handed circularly polarized light from films of PCH was confirmed by CD spectroscopy, which shows a peak with positive ellipticity that red shifts upon the swelling of the material (Figure 4d) When fully swollen, PCH shows a reflectance peak at ≈1200 nm and appears colorless and transparent as the reflection has moved into the near-IR region (Figure 4d) Upon deswelling, PCH shows a slightly blue-shifted CD signal with positive ellipticity at ≈720 nm (Figure S14b, Supporting Information), indicating that the hydrogels preserved the lefthanded twisted organization of the chitosan template upon drying of water from acidic media The reversible shift of the reflection originates from a drastic change in the pitch of the highly swollen structure of PCH The peak reflections of the deswollen PCH slightly red shift relative to the pristine CNMC before swelling, which is likely attributed to relaxation of the organized nanofibril structure after deswelling PCH shows © 2016 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim wileyonlinelibrary.com 2879 www.afm-journal.de FULL PAPER www.MaterialsViews.com reversible color changes and its chiroptical properties change negligibly upon redrying and reswelling in acidic media (Figure S14b, Supporting Information) Tensile mechanical testing (Figure 4e) shows that the dried PMMA/chitosan composites have a mean UTS of 27.2 ± 2.1 MPa at a strain of 13 ± 0.1% that are much higher than those of CNMC (22.8 ± 1.2 MPa, ± 0.2%, see Figure 3e) Significantly lower UTS was observed for the PMMA/chitosan composites (2.2 ± 0.5 MPa) after swelling in acidic media Elongation at break was also reduced after swelling to ± 0.3% (Figure 4e) Although these values are lower than the dried specimens, the UTS is relatively higher than that obtained with the swollen acetylated chitosan hydrogels without PMMA (see Figure 3e) The enhanced properties, including toughness, of PCH are mainly attributed to the combination of chitosan with polymer Retention of the chiral nematic organization of these hydrogels was confirmed by SEM (Figures 3c and 4c; Figures S15 and S16 of Supporting Information) ACH and PCH both show a repeating layered structure with nanofibrils rotating in a counter-clockwise direction at fracture cross-sections, which is characteristic of left-handed chiral nematic order These geometrical nanostructured features resemble those of CNMC, confirming the preservation of the Bouligand-type organization of the hydrogels upon acetylation and PMMA polymerization These observations also indicate that the chitosan acetylation predominantly occurred on the nanofibril surfaces while PMMA homogeneously formed around the nanofibrils The interlayer separations measured from cross-sections perpendicular to the top surfaces of these deswollen hydrogels are slightly higher than those of CNMC, which are consistent with their relative reflectance peaks The twisted layered structure of these hydrogels resembles that of the mesoporous cellulosic films[11] and the shells of Jewel beetles[6a] and Pollia fruits.[6b] Hydrogels prepared from chitosan[19a] and templating of PMMA by chitosan butterfly wings[19b] were previously demonstrated, but they not have chiral nematic order and exhibit only modest swelling Photonic biological structures are frequently sought by observing the visible coloration reflected on the organism’s outer shells.[6] By starting from the popular crustacean exoskeletons without structural coloration, we exploited both their endocuticles and shells to produce iridescent, freestanding photonic mesoporous chitosan membranes and hydrogels with chiral nematic structures Conclusions In summary, we have used discarded crustacean exoskeletons and shells to develop tunable photonic nanomaterials The Bouligand structure of chitin that is hidden in the crustacean exoskeletons was exploited by deacetylation of the purified endocuticles and shells of the crustaceans to improve long-range order of the Bouligand-type arrangement of chitosan nanofibrils and obtain large, intact mesoporous photonic membranes We demonstrated proof-of-concept for using the mesoporous chitosan nanofibrils as a novel precursor for acetylation and also as a platform for templating poly(methylmethacrylate) to produce photonic hydrogels Upon swelling, these hydrogels 2880 wileyonlinelibrary.com undergo large volume expansion that is responsible for their tunable chiroptical properties The introduction of the photonic properties in various types of sustainable nanomaterials may open new possibilities for optical sensing and templating Experimental Section Preparation of Chiral Nematic Mesoporous Chitosan Nanofibrils: Shrimp shells (12 g) were treated with NaOH(aq) (250 mL, wt%) at 90 °C for h to decompose protein and then treated with HCl(aq) (250 mL, 0.1 M) at room temperature for h to remove calcium minerals The purified chitin shells were collected and rinsed with copious water Elemental analysis: 6.19% N, 42.49% C, 6.47% H To gain a photonic structure, the resultant white chitin shells (3.5 g) were treated with a concentrated NaOH(aq) solution (50 mL, 50 wt%) at 90 °C for h and this deacetylation of chitin nanofibrils was repeated at least twice to enhance the structural coloration The resulting shells were washed thoroughly with water and allowed to dry at ambient conditions to obtain highly flexible, transparent chitosan membranes that appear iridescent, retain the original shapes of the shrimp shells, and lose ≈13 wt% compared to the purified chitin shells Elemental analysis: 6.93% N, 36.39% C, 6.82% H Note that we found that this photonic transformation can be extended to the most popular crab species except the king crabs possibly due to rigid structures of their outer shells To produce intact shapes of the chitosan endocuticles of large king crab exoskeletons, the chitin endocuticle membranes were manually delaminated by carefully peeling off the outer sides of the alkali-treated shells to obtain intact endocuticles The pure chitin membranes were obtained by treating the separated cuticles with a dilute HCl(aq) solution (500 mL, 0.1 M) to completely remove calcium minerals at room temperature within h followed by washing with copious water We also found that the photonic twisted cuticles can be obtained from different species of the crabs, but the chiral nematic order of the nanofibrils organized in the king crabs is better than that of other ones The purified chitin crab endocuticles (7 g) were then treated with a concentrated NaOH(aq) solution (100 mL, 50 wt%) at 90 °C with various periods of time up to h for controlled deacetylation of N-acetyl groups The reaction products (CNMC) were washed with copious water to obtain intact chitosan membranes with enhanced transparency, flexibility, and coloration The CNMC samples were used to investigate the tunable coloration by swelling the membranes in different solvents and acidic media Fabrication of Photonic Hydrogels: The CNMC samples prepared from the endocuticles and shells of the crustaceans were used to investigate the production of photonic hydrogels For the preparation of ACH, the dried CNMC membranes as a starting material (300 mg) were immersed in 20 mL pure acetic anhydride at room temperature The surface acetylation of chitosan was carried out for 30 and then the resulting membranes were collected from the reaction mixture by filtration The acetylated chitosan membranes were dabbed with tissue paper to remove the absorbed acetic anhydride and then immersed in water to swell into hydrogels Elemental analysis of the dried acetylated chitosan: 7.04% N, 41.64% C, 7.13% H For the preparation of PCH, the dried CNMC membranes (300 mg) were immersed in 15 mL dimethylformamide solution containing mL methyl methacrylate (MMA) and 80 µL 2,2-diethoxyacetophenone photoinitiator The reaction mixture was exposed to UV light (from an W, 300 nm UV-B light source) at ambient conditions to polymerize MMA onto the chitosan nanofibril template The photo-induced polymerization was conducted within h to sufficiently incorporate PMMA into the mesoporous membranes to obtain flexible, homogeneous PMMA/chitosan composites Extending the photopolymerization time beyond h resulted in overall coating of PMMA on the film surfaces of the chitosan template to form less flexible, thicker composite membranes The resulting PMMA/chitosan composites were then taken out from the reaction mixture and dabbed © 2016 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim Adv Funct Mater 2016, 26, 2875–2881 www.afm-journal.de www.MaterialsViews.com [8] Supporting Information Supporting Information is available from the Wiley Online Library or from the author Acknowledgements The authors thank the Natural Sciences and Engineering Research Council (NSERC) for funding (Discovery Grant) and a postdoctoral fellowship for T.-D.N R.M.C thanks UBC Dentistry for start-up funds [9] Received: November 23, 2015 Revised: February 4, 2016 Published online: March 15, 2016 [10] [1] a) J W Schopf, A B Kudryaytsev, M R Walter, M J V Kranendonk, K H Williford, R Kozdon, J W Valley, V A Gallardo, C Espinoza, D T Flannery, Proc Natl Acad Sci USA 2015, 112, 2087; 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hydrogels with chiral nematic structures Conclusions In summary, we have used discarded crustacean exoskeletons and shells to develop tunable photonic