Chitin Fibers Research Articles

Creation of 3D chitin/chitosan composite scaffold from naturally pre-structured verongiid sponge skeleton

This study represents the first creation and characterization of a 3D chitin/chitosan composite scaffold derived from the naturally pre-structured skeleton of the cultivated marine demosponge Aplysina aerophoba, aiming to preserve the intricate architecture of the unique tube-like chitin while incorporating chitosan layers. Advanced staining methods, including the use of iodine and Cibacron Brilliant Red (CBR), were employed to distinguish these polysaccharides. ATR-FTIR spectroscopy confirmed the system's structural integrity and identified the optimal chitin/chitosan balance, achieved after 60-minute treatment in 38 % NaOH at 95 °C. Fluorescent microscopy using fluorescein isothiocyanate (FITC) effectively confirmed the presence of chitosan layers in the created chitin/chitosan scaffolds. Scanning electron microscopy analysis further elucidated significant morphological distinctions, where chitin fibers displayed a smooth, uniform surface, contrasting with the ragged and irregular texture of chitosan-containing fibers, indicating significant surface modifications. Zeta potential measurements confirmed the partial transformation of chitin into chitosan. The dual-layer configuration, consisting of a resilient chitin core and a versatile chitosan exterior, not only provides structural support, but also enhances the scaffold's functionality for potential technological and biomedical applications. The preferential metallization of the chitosan phase by copper nanoparticles in the created 3D chitin/chitosan composite opens the way to the potential use of such scaffolds in catalysis.

Evaluating the strategies to improve strength and water-resistance of chitin nanofibril assembled structures: Molecule-bridging, heat-treatment and deacidifying

Chitin nanofibril (ChiNF) is a promising building block used to fabricate chitin fibers, films or gels via self-assembly from its aqueous suspension. Although mechanical strengthening of its assembled structures has made great advances, the unsatisfactory water-resistance is still a crucial obstacle to practical application and even rarely referred to. Herein, ChiNF was prepared via deacetylation-ultrasonication treatment and the strategies of molecule-bridging, heat-treatment and deacidifying that aiming to improve the strength and water-resistance of its assembled films were evaluated. Molecule-bridging, including tannic acid (TA) or/and chitosan (CS), improved the mechanical properties to some extent, but had no obvious positive effects on water-resistance; heat-treatment was a useful route to enhance both strength and water-resistance; interestingly, deacidifying was more efficient than heat-treatment with respect to improving strength and water-resistance, implying the presence of acid was the major reason for deteriorating assembled structures. Combining molecule-bridging, deacidifying and heat-treatment produced a strong ChiNF-TA/CS cast film with excellent water-resistance. Different from the commonly-used approach of vacuum filtration, these strategies are very suitable for large-scale production of the ChiNF-based self-supported films or coatings via solution casting. Furthermore, the reverse dialysis deacidification simultaneously produced highly concentrated suspensions suitable for dry-spinning, and thus strong chitin macrofibers were successfully fabricated.

Innovative bamboo-plastic composites interfacial compatibility design approach: Self-assembled crosslinked structure of polydopamine with acylated chitin fibers

Achieving interfacial compatibility through sustainable methods is a key objective in natural fiber-plastic composites research, aimed at optimizing mechanical performance. This study introduced an innovative organic bamboo-plastic composite (BPC) interfacial layer, incorporating O-acylated chitin fibers densely coated with polydopamine (PDA) via a mild and facile self-assembly method. Chitin nanofibers were acylated with dodecenylsuccinic anhydride in a deep eutectic solvent in a one-pot process. The resulting BPCs exhibited significantly enhanced mechanical properties, with tensile strength, flexural strength, modulus, and impact strength increased by 73.64 %, 39.19 %, 15.42 %, and 63.57 %, respectively, compared to untreated BPCs. This improvement highlights the effectiveness of tailoring cross-linked networks across heterogeneous interfaces in providing strength, dissipating strain, and promoting interfacial compatibility. Furthermore, these modified BPCs demonstrated enhanced thermal stability, crystallization behavior, and moderate hydrophobicity. This surface treatment strategy offers a distinctive approach to producing high-performance, eco-friendly BPCs, also facilitating the processing and utilization of marine biological resources on a wide scale.

Hierarchically porous and flexible chitin-fiber/melamine-sponge composite filter with high-loading of PdAu nanoparticles for effective hydrodechlorination of chlorophenols

Hydrodechlorination has emerged as a promising technique for detoxifying chlorophenols (CPs) in wastewater, but it suffers from sluggish reaction kinetics and limited durability due to the lack of effective and stable catalysts. Herein, a composite filter consisting of melamine-sponge (MS), chitin fiber (CF) and ultrafine PdAu nanoparticles (PdAu/CF-MS) has been designed for continuous hydrodechlorination of CPs by using formic acid as a H-donor and sodium formate as a promoter. Benefitting from the dense active sites, rich porosity, and synergetic interaction of Pd/Au, the PdAu/CF-MS filter exhibits excellent hydrodechlorination performance (∼ 100 % conversion) towards 4-chlorophenol (1 mM, fluxes below 6100 mL·h−1·g−1) and outstanding durability (over 500 h at 61 mL·h−1·g−1), surpassing most reported counterparts (usually deactivated within 200 h or several cycles). Moreover, other CPs can also be effectively dechlorinated by the PdAu/CF-MS filter. The catalytic system proposed herein will provide a promising candidate for the detoxification of wastewater containing toxic CPs.

Study of the influence of macro-structure and micro-structure on the mechanical properties of stag beetle upper jaw

Macrostructural control of stress distribution and microstructural influence on crack propagation is one of the strategies for obtaining high mechanical properties in stag beetle upper jaws. The maximum bending fracture force of the stag beetle upper jaw is approximately 154, 000 times the weight of the upper jaw. Here, we explore the macro and micro-structural characteristics of two stag beetle upper jaws and reveal the resulting differences in mechanical properties and enhancement mechanisms. At the macroscopic level, the elliptic and triangular cross-sections of the upper jaw of the two species of stag beetles have significant effects on the formation of cracks. The crack generated by the upper jaws with a triangular section grows slowly and deflects easily. At the microscopic level, the upper jaw of the two species is a chitin cross-layered structure, but the difference between the two adjacent fiber layers at 45° and 50° leads to different deflection paths of the cracks on the exoskeleton. The mechanical properties of the upper jaw of the two species of stag beetle were significantly different due to the interaction of macro-structure and micro-structure. In addition, a series of bionic samples with different cross-section geometries and different fiber cross angles were designed, and mechanical tests were carried out according to the macro-structure and micro-structure characteristics of the stag beetle upper jaw. The effects of cross-section geometry and fiber cross angle on the mechanical properties of bionic samples are compared and analyzed. This study provides new ideas for designing and optimizing highly loaded components in engineering. Statement of significanceThe upper jaw of the stag beetle is composed of a complex arrangement of chitin and protein fibers, providing both rigidity and flexibility. This structure is designed to withstand various mechanical stresses, including impacts and bending forces, encountered during its burrowing activities and interactions with its environment. The study of the upper jaw of the stag beetle can provide an efficient structural design for engineering components that are subjected to high loads. Understanding the relationship between structure and mechanical properties in the stag beetle upper jaw holds significant implications for biomimetic design and engineering.

Functional role of carbohydrate-binding modules in multi-modular chitinase OfChtII

The primary distinction between insect and bacterial chitin degradation systems lies in the presence of a multi-modular endo-acting chitinase ChtII, in contrast to a processive exo-acting chitinase. Although the essential role of ChtII during insect development and its synergistic action with processive chitinase during chitin degradation have been established, the mechanistic understanding of how it deconstructs chitin remains largely elusive. Here OfChtII from the insect Ostrinia furnacalis was investigated employing comprehensive approaches encompassing biochemical and microscopic analyses. The results demonstrated that OfChtII truncations with more carbohydrate-binding modules (CBMs) exhibited enhanced hydrolysis activity, effectively yielding a greater proportion of fibrillary fractions from the compacted chitin substrate. At the single-molecule level, the CBMs in these OfChtII truncations have been shown to primarily facilitate chitin substrate association rather than dissociation. Furthermore, a greater number of CBMs was demonstrated to be essential for the enzyme to effectively bind to chitin substrates with high crystallinity. Through real-time imaging by high-speed atomic force microscopy, the OfChtII-B4C1 truncation with three CBMs was observed to shear chitin fibers, thereby generating fibrillary fragments and deconstructing the compacted chitin structure. This work pioneers in revealing the nanoscale mechanism of endo-acting multi-modular chitinase involved in chitin degradation, which provides an important reference for the rational design of chitinases or other glycoside hydrolases.

Characterization of an RR-2 cuticle protein DcCP8 and its potential application based on SPc nanoparticle-wrapped dsRNA in Diaphorina citri.

The insect cuticle consists of chitin fibers and a protein matrix, which plays an important role in protecting the body from invasion of various pathogens and prevents water loss. Periodic synthesis and degradation of the cuticle is required for the growth and development of insects. Key genes involved in cuticle formation have long been considered a potential target for pest control. In this study, a member of the RR-2 subfamily of cuticular protein 8 (DcCP8) was identified from the Diaphorina citri genome database. Immunofluorescence analysis suggested that DcCP8 was mainly located in the Diaphorina citri exocuticle and can be induced to up-regulate 12 h following 20-hydroxyecdysone (20E) treatment. Silencing of DcCP8 by RNA interference (RNAi) significantly disrupted the metamorphosis to the adult stage, and improved the permeability of the cuticle. Transmission electron microscopy (TEM) analysis revealed that the synthesis of the exocuticle was impressed after silencing of DcCP8. Furthermore, the recombinant DcCP8 protein exhibited chitin-binding properties in vitro, down-regulation of DcCP8 significantly inhibited expression levels of chitin metabolism-related genes. Additionally, a sprayable RNAi method targeting DcCP8 based on star polycation (SPc) nanoparticles-wrapped double-stranded RNA (dsRNA) significantly increased Diaphorina citri mortality. Transcriptome sequencing further confirmed that genes associated with the endocytic pathway and immune response were up-regulated in Diaphorina citri after SPc treatment. The current study indicated that DcCP8 is critical for the formation of Diaphorina citri exocuticles, and lays a foundation for Diaphorina citri control based on large-scale dsRNA nanoparticles. © 2024 Society of Chemical Industry.

Preparation of chitin twisted fiber and its functional applications

Chitin has garnered significant attention due to its renewable, biocompatibility and biodegradability, while its practical application seriously hindered as the functionality of chitin itself can no longer meet people's increasing requirements for materials. Here, an effective method is successfully built for high-performance chitin fibers fabrication through a multi-step strategy that involved chemical pre-crosslinking, followed by wet-twisting and wet-stretching techniques, combined with physical cross-linking. The as-prepared chitin fiber exhibited a smooth surface, adjustable diameter, and mechanical strong properties (144.6 MPa). More importantly, functional chitin fiber with magnetic or conductive abilities can be easily obtained by spraying Fe3O4 particles or Ag nanowire on the chemical pre-crosslinking chitin gel film before stretching and twisting. The doped functional inorganic particles exist in a continuous ribbon structure in the fiber reduced the decrease in material strength caused by uneven particles dispersion, resulting 88.4 % of stress and 91.6 % of strain retention. This work not only bestow invaluable insights into the fabrication of functional chitin fibers but also provide a novel approach to solve the problem of poor compatibility between organic and inorganic composite materials.

Crustacean-inspired chitin-based flexible buffer layer with a helical cross-linked network for bamboo fiber/poly(3-hydroxybutyrate) biocomposites

Marine biological resources, serving as a renewable and sustainable reservoir, holds significant import for the utilization of composite material. Hence, we produced bamboo fiber/poly(3-hydroxybutyrate) (BF/PHB) biocomposites with exceptional performance and economic viability, drawing inspiration from the resilience of crustacean shells. Polyaminoethyl modified chitin (PAECT) was synthesized using the alkali freeze-thaw method and introduced into the interface between BF and PHB to improve interfacial adhesion. The resulting chitin fibers, characterized by their intertwined helical chains, constructed a flexible mesh structure on the BF surface through an electrostatic self-assembly approach. The interwoven PAECT filaments infiltrated the dual-phase structure, acting as a promoter of interfacial compatibility, while the flexible chitin network provided a greater capacity for deformation accommodation. Consequently, both impact and tensile strength of the BF/PHB composites were notably enhanced. Additionally, this flexible layer ameliorated the thermal stability and crystalline properties of the composites. This investigation aimed to leverage the distinctive helical configuration of chitin to facilitate the advancement of bio-reinforced composites.

Fabrication of all-chitin composite films

The aim of this study is to propose a first concept for the procedure to prepare an all-chitin composite. The fabrication of all-chitin composite films was investigated for the first time via the mixing of low-crystalline matrix dispersions with high-crystalline fiber dispersions. Self-assembled chitin nanofiber (ChNF) films, prepared from a chitin ion gel, were treated with aqueous NaOH for deacetylation, followed by treatment with different types of aqueous acids via ultrasonication to produce dispersions. When the treatment was carried out with 1.0 mol/L aqueous acetic acid, we obtained a scaled-down ChNF (high-crystalline chitin fiber) dispersion, as previously reported. The crystallinity was reduced by treatment with 1.0 mol/L aqueous trifluoroacetic acid for 10 min at room temperature via ultrasonication and subsequent treatment for 24 h at 50 °C with stirring to produce a low-crystalline chitin matrix dispersion. The resulting two dispersions were mixed, and treated by suction filtration and drying to produce all-chitin composite films. The mechanical properties of the obtained composite films with appropriate weight ratios of the two components were superior to those of the high-crystalline scaled-down ChNF film. All-chitin complexes are expected to be used in the future as sustainable materials for a variety of applications.

Properties and Soil Degradation Characteristics of Chitin‐Reinforced Poly(butylene succinate)/Hydroxyapatite Composites

AbstractPoly(butylene succinate) (PBS) is a biodegradable polymer; however, a prolonged soil degradation rate of PBS limits its wide range of applications. Here, the impact of incorporating chitin in mechanical and thermal properties and soil degradation characteristics of PBS/hydroxyapatite (HAP) composites is investigated. Chitin is one of the most abundant natural polymers extensively used for various applications and has a fast soil degradation characteristic. Therefore, ternary PBS composites are melt‐processed in a twin‐screw extruder with a fixed amount of HAP (1.5 wt%) and two different loadings of chitin (1.5 and 3 wt%). Morphological characterization using transmission electron microscopy shows a homogeneous distribution of both fillers in a PBS composite containing 1.5 wt% chitin. In contrast, an optical microscopy study of the same composite at the melt state shows defibrillation and breakage of the chitin fibers during the extrusion. Incorporation of chitin decreases the elongation at break of the PBS/HAP composite, which is likely a consequence of chitin fiber morphology. However, the soil degradation characteristics and melt strength of PBS/HAP composites are improved in the presence of chitin fibers. In summary, chitin is shown to have the potential as an additive to obtain environmentally benign PBS composites for a wide range of applications.

Multifunctional composite membranes for interfacial solar steam and electricity generation

Emerging water purification technology, known as interfacial solar steam generation (ISSG), has been rapidly developing in recent years. ISSG offers a promising solution to address both freshwater shortage and energy demand by simultaneously producing freshwater and electricity. This is achieved through the combination of microporous films and highly efficient photothermal materials. In this study, we have developed a composite film using a 2D material, reduced graphene oxide (rGO), and a combination of 1D materials, chitin fiber@multi-walled carbon nanotube (Chiber@CNT). Through a hybrid dimensional design, these materials’ advantages are integrated, resulting in a composite film with a distinct laminar porous structure and excellent broadband absorption. Notably, under 1 kW·m−2 sunlight irradiation, the composite film achieves a water evaporation flux of 2.10 kg·m−2·h−1 with a photothermal conversion efficiency of 75.79%. In addition, by utilizing an energy-harvesting strategy based on natural water evaporation in porous nanomaterials for power generation, the composite film successfully enables the simultaneous production of freshwater and electricity. Its output voltage reaches 0.39 V in a 3.5 wt% NaCl solution. Furthermore, the film’s output voltage varies with the concentration of NaCl, increasing from 0.26 V (in deionized water) to 0.45 V (in the saturated NaCl solution). Molecular dynamic simulation results indicate that the enhanced power generation can be attributed to the difference in interatomic interaction strength between ions and hydrophilic functional groups in chitin fiber (Chiber). This finding provides a deep physical mechanism and opens up possibilities for the film’s application in highly concentrated salt solutions.

Screening diatom strains belonging to Cyclotella genus for chitin nanofiber production under photobioreactor conditions: Chitin productivity and characterization of physicochemical properties

Diatom species belonging to Cyclotella and Thalassiosira genera have the unique and industrially relevant ability to biosynthesize and extrude pure chitin nanofibers. The current understanding of diatom-based chitin production is narrowed by the complete reliance on the performance of a single strain. This study aims to facilitate the development of a wider understanding for enhanced industrial utility. For this purpose, six Cyclotella strains were cultivated under standardized process conditions of a bubble column photobioreactor, and the resulting productions were characterized in terms of rate and physicochemical properties. A two-stage cultivation protocol was followed where the cells were cultivated under silicon replete and then following its complete consumption under silicon deplete conditions. All the strains produced chitin fibers of β-form with relatively constant average diameters, ranging from 48 to 58 nm. Chitin production rates and final concentrations as well as fiber number densities and length distributions were highly strain-dependent. Dissolved silicon availability controlled chitin biosynthesis: following its depletion, the productivity of all the strains increased drastically. Two strains of marine origin, C. cryptica CCMP 332 and C. cryptica CCMP 333, generated the most favorable outcomes for commercial-scale production and had final concentrations of 272 ± 9 mg/L and 316 ± 12 mg/L, and maximum production rates of 48 ± 2 mg/L-day and 51 ± 2 mg/L-day, respectively. The superior performance of these strains was due to (i) the extrusion of more fibers per fiber port, in the case of C. cryptica CCMP 333 as many as 20.7 ± 1.0. indicating free fiber accumulation in suspension, and (ii) the biosynthesis of longer fibers, mean fiber lengths varied from 15 to 20 μm during cultivation. This study demonstrates the importance of species selection and silicon availability for diatom-based chitin production in terms of rate, final concentration, and nanofiber fiber length distributions.

Self-Healing Properties of Fibers Constructed from Mushroom-Derived Chitinous Polymers

Chitinous polymers were extracted from common Agaricus bisporus mushrooms through simple processes, which are successfully formed into continuous fibers with a custom-built laboratory-scale fiber spinning setup. The spun fibers are composed of numerous chitin fibrils embedded within the glucan matrix, and their fiber diameters are controlled by the needle gauges. All the mushroom chitin fibers exhibited self-healing properties upon exposure to a small amount (<10 μL) of water within 30 s. The macroscopically damaged mushroom chitin fibers with a microblade can repair their original shape and tensile properties effectively, as evidenced by high self-healing efficiency for the tensile strength (up to 119%) and breaking strain (up to 132%). Interestingly, no solvents, such as ethanol or acetone, other than water induced the self-healing. This indicates that swelling and deswelling of mushroom chitin fibers may have led to the intermeshing of chitin fibrils and glucan across the damaged fiber interfaces, resulting in powerful self-healing action. Simple preparation of chitin fibers provides sustainable manufacturing opportunities for real-world applications in various technical areas, as we demonstrated the repeatable self-healing performance on a large scale in the form of fibers and woven structures.

Structural and functional analyses of chitinolytic enzymes in the nacreous layer of Pinctada fucata

In this study, chitinolytic activity was confirmed in the protein extracted from the inner nacreous layer of Pinctada fucata shells. Allosamidin, a specific inhibitor of family 18 chitinase, was injected into pearl oysters, and an abnormal organic membrane was observed in the nacreous layer. When shell-notched individuals were injected with allosamidin, the organic fibers in the regenerated site were thicker than those without allosamidin treatment. To identify chitinases in the nacreous layer, proteins extracted from the nacreous layer were analyzed using LC-MS/MS. Two chitinases (PfCN1 and PfCN2) were identified, and their different spatial expression patterns were observed in mantle tissue. To understand the function of chitinolytic enzymes in nacre formation, we designed an in vivo gene knockdown experiment using PfCN1 and PfCN2 dsRNA, and in vitro calcium carbonate crystallization experiments using chitinolytic enzymes. In the knockdown experiment, abnormal aragonite tablets and organic films were observed in the nacreous layer. In the crystallization experiment, we found that the thickness of the chitin film decreased and the space between the chitin fibers increased when calcium carbonate was formed on the chitin film on the glass substrate with chitin-degrading enzyme treatment. These reactions induce the growth of calcium carbonate crystals through the chitin film. The penetration of chitin film by calcium carbonate is similar to that of mineral bridges that connect the nacre tablets vertically. These results showed the novel function of chitinolytic enzymes that will give a comprehension of nacre formation.

Acceleration of bone repair in critical-size defect using angiopoietin-2 associated with novel carbon nanotubes scaffold via mitophagy-pyroptosis pathway.

To investigate the curative effect of Ang-2 combined with novel carbon nanotubes (CNTs) scaffold critical-size bone defect in rabbits. CNTs with good properties were first prepared by freeze-drying method. The mechanical properties and surface hydrophilicity of scaffolds were improved by adjusting the addition ratio of polylactic acid (LPA) and chitin fibers (CHI). After purification and functionalization of CNTs, CNTs/PLA/CHI three-dimensional porous scaffolds were prepared for animal experiments. Subsequently, the CNTs/PLA/CHI scaffolds were implanted into the rabbit critical-sized radius defect model to evaluate the osteogenic properties in vivo. Adult male New Zealand white rabbits were randomly allocated into three groups. Group A was the control group, and both groups B and C underwent radial bone defect surgery and implanted CNTs/PLA/CHI scaffolds. Animals in group C received a daily local injection of 1 mL of 400 ng/mL Ang-2 dissolved in physiological saline in the bone defect area for up to 14 days after surgery, while group B received the same amount of physiological saline. Scanning electron microscope results showed that the porosity of the CNTs/PLA/CHI three-dimensional porous scaffolds was as high as 80%. The surface contact angle was 35° to 55°, and the hydrophilicity was suitable for cell adhesion and growth. The CNTs/PLA/CHI three-dimensional porous scaffolds had excellent biological properties. The general observation and X-ray imaging after 12 weeks together indicated that the CNTs/PLA/CHI scaffolds could accelerate bone repair with the combination of endogenous angiogenic factor Ang-2. The results of western blotting and histology revealed that the expression of mitophagy proteins LC3, Beclin-1, PINK1 and Parkin was elevated in the new bone, and the expression of pyroptosis proteins Nod-like receptor protein NLRP3, caspase-1 and Gasdermin D (GSDMD) was decreased. Ang-2 associated with CNTs/PLA/CHI scaffolds accelerated bone regeneration through autophagy-pyroptosis pathway.

Nutrient Composition and Growth of Yellow Mealworm (Tenebrio molitor) at Different Ages and Stages of the Life Cycle

The nutrient composition of yellow mealworm (YM) Tenebrio molitor varies based on the stages of the life cycle, the rearing conditions, and the feeding substrate. This study monitored the growth of yellow mealworm larvae at 8, 10, and 12 weeks of age, separating samples into large-sized and small-sized insects. During the experiment, we measured the nutrient composition: dry matter (DM), crude protein (CP), crude fat (CF), crude fibre, chitin, crude ash, and nitrogen free extract (NFE) of YM at different age groups and sizes. We measured the nutrient composition of the pre-moult, moult, cuticle, and pupae as well. The results show that there is no significant difference between the compositions of the different age groups, but larger-sized individuals had a higher DM and crude fibre and lower chitin and NFE than the smaller sizes. The pre-moult and moult stages showed no significant difference in nutrient composition. Although the cuticle had a high DM (97.5%), that did not cause any significant difference between the DM of the moult and pre-moult, because it is only a negligible part of the total wet weight. With the increased DM, the crude protein content and the chitin content, fibre, ash content, and NFE increased, while the fat content decreased. The DM, CF, and chitin contents of pupae are significantly lower than those of the pre-moult and moult stages. Our results show that it is the size and not the age that has a positive effect on the nutrient composition of YM.

Preparation and properties of chitin/silk fibroin biocompatible composite fibers

In the present world chitin is used enormously in various fields, such as biopharmaceuticals, medical and clinical bioproducts, food packaging, etc. However, its development has been curbed by the impaired performance and cumbersome dissolution process when chitin materials are dissolved and regenerated by physical or chemical methods. To further obtain the regenerated chitin fiber material with improved performance, silk fibroin was introduced into the chitin matrix material, and chitin/silk fibroin biocompatible composite fibers were obtained by formic acid/calcium chloride/ethanol ternary system and top-down wet spinning technology. The produced composite fibers outperformed previously reported chitin-silk composites in terms of the tensile strength (160 MPa) and failure strain (25%). The fibers also performed good cell compatibility and strong cellular affinity for non-toxicity. The cell viabilities of the fibers were about 20% greater than those of silk fiber after three days of co-culture with NIH-3T3. Furthermore, no hemolysis occurs in the presence of chitin/silk fibers, demonstrating their superior hemocompatibility. The fibers had a hemolysis index as low as 1%, which is far lower than the acceptable level of 5%. The material offers prospective opportunities for biomaterial applications in anticoagulation, absorbable surgical sutures, etc.

Fiber arrangement endow compression resistance of the mantis shrimp hammer-like appendage

For engineering materials, it is important to search for strategies to enhance certain combinations of mechanical properties, because many performances, such as strength and toughness, are mutually exclusive. Effective strategies have evolved in the biological tissues of many plants and animals to construct composite materials with unique combinations of mechanical properties. One impressive example is found in the hammer-like appendages of mantis shrimp, which are exceptionally resistant to crushing because they must withstand the reaction forces created when attacking prey. In this paper, quasi-static compression tests, advanced microscopic observation, and spectroscopic analysis were employed to identify a series of characteristic changes, including changes in mineral composition and arrangement of chitin fibers, and the resulting toughening mechanisms are also examined. The combination of experiments and finite element analysis revealed that by combining different fiber arrangements and components in adjacent macroscopic layers, longitudinal stress could be shifted to the lateral direction, hence efficiently enhancing longitudinal compression resistance while avoiding catastrophic failure. Overall, these findings further the understanding of the fiber structure and toughening mechanism of appendages, which may serve as a foundation for the development of tough bioinspired composites.

Fibrous anisotropy and mineral gradients within the radula stylus of chiton: Controlled stiffness and damage tolerance in a flexible biological composite

Over hundreds of millions of years, organisms have evolved architected structures via precise control over hierarchically assembled components, including the integration of dissimilar materials. One such example is found in the radula system of chitons, intertidal mollusks that feed on algae growing on the rock. Their radula consists of multiple rows of ultrahard teeth, each integrated with a foldable belt-like substrate via a stiff, yet flexible stylus, which is essential for efficient rasping during the feeding process. Here, we investigate the nano and micro-scale components and architectures as well as regional mechanical properties of the stylus, and their subsequent role during the rasping of Cryptochiton stelleri. Three important factors were determined to contribute to the regio-specific stiffness of the stylus: the presence of mineral components, highly oriented chitinous fibers, and a chemically cross-linked protein matrix. All these factors are varied throughout the stylus. There is a high mineral content on the trailing edge close to the tooth and a cross-linked matrix on the leading edge, both with orientational specific oriented chitin fibers that provide force transduction to the tooth. Conversely, there is a significant lack of mineral or cross-linked matrix in the proximal end as well as a low degree of fiber orientation, resulting in a flexible region that can accommodate torsion and flexure during rasping. Understanding the graded composite structure of the stylus and applying this unique design to various engineering fields such as soft robotics, biotechnology, and the medical industry, can inspire the production of high-performance materials.