Biological Composites Research Articles

Building Blocks of the Protective Suberin Plant Polymer Self-Assemble into Lamellar Structures with Antibacterial Potential.

The protection of terrestrial plants from desiccation, mechanical injury, and pathogenic invasion is achieved by waxes and cutin polyesters on leaf and fruit surfaces as well as suberin polymers that are embedded in the cell walls of roots, but the physicochemical principles governing the organization of these biological composites remain incompletely understood. Despite the well-established enzymatic mediation of suberin formation in the skins of potato tubers, cork oak trees, and internal plant tissues, the additional possibility of self-assembly in this system was suggested by our serendipitous finding that solvent extracts from potato phellem tissues form suspended fibers and needles in the absence of such catalysts over a period of several weeks. In the current study, we investigated self-assembly for three-component model chemical mixtures comprised of a hydroxyfatty acid, glycerol, and either of two hydroxycinnamic acids that together typify the building blocks of potato suberin biopolymers. We demonstrate that these mixtures spontaneously form lamellar structures that are reminiscent of suberized plant tissues, incorporate all constituents into self-assemblies, can form covalently bound ester structures, and display antibacterial activity. These findings provide new perspectives on the self-association and reactivity of these classes of organic compounds, insights into agriculturally important suberin formation in food crops, and a starting point for engineering sustainable materials with antimicrobial capabilities.

Interfacial energy dissipation in bio-inspired graphene nanocomposites

Bio-inspired nanocomposites have been fabricated by self-assembly using graphene oxide (GO) based fillers, and their interfacial energy dissipation during cyclic deformation has been studied. The GO flakes were washed with a base solution to remove some functional groups and this base-washed GO (BwGO) obtained was also employed as a comparison to study the effect of functional groups on the interface. Raman spectroscopy was used to monitor the deformation of the fillers and to determine their stress-strain curve in the nanocomposites. The area of the hysteresis loop between the loading and unloading curves was used to calculate the interfacial energy dissipation during cyclic deformation. The presence of functional groups on GO reduced the interfacial energy dissipation in the elastic regime. The energy dissipation starts to increase with strain, and eventually when the applied strain is beyond the elastic regime, the functional groups ‘toughen’ the interface by requiring higher energy to break and also roughening the interface, similar to the behaviour of the biological composites. This work has shed light on the fabrication of bio-inspired nanocomposites and the evaluation and application of the graphene-based fillers where energy dissipation is needed, for example, in composites toughening and the damping of elastomers.

Structural Design Variations in Beetle Elytra (Adv. Funct. Mater. 50/2021)

Biological Composites In article number 2106468, David Kisailus and co-workers study the structure–mechanical property relationships in the protective exoskeletal elytra of flying and terrestrial beetles. Comparison of elytra from two divergent species reveals variations in cuticle density, cuticle thickness, fiber arrangement, and degree of cross-linking resulting in variations in stiffness and fracture behavior. Z-pinning fibers also prevent delamination and improve and enhance toughness.

Advances in anti-adversity of biological composites based on metal-organic frameworks

Metal-organic frameworks (MOFs) are formed by self-assembly of metal ions or clusters with organic ligands, and are widely used in the fields of catalysis, sensing, energy and biomedicine. Recently, biological composites based on MOFs have attracted increasing attention. MOFs can be used as a platform for encapsulating bioactive substances due to the advantages such as large pore capacity, large specific surface area and diverse structure composition. These features can protect bioactive substances from adverse conditions, e.g. high temperature, high pressure, and organic solvents, thus improving the anti-adversity of bioactive substances. This review summarizes the advances of using MOFs as protective coatings to improve the anti-adversity of different bioactive substances, and introduces the synthesis strategy of MOFs-based biological composites, with the aim to promote the practical application of MOFs-based biological composites.

Role of interphase layers in mechanical properties of nacreous structures

An exceptional combination of mechanical properties such as high stiffness, high strength, and high toughness makes nacre one of the most remarkable natural materials. It has been shown that these outstanding properties arise from the multilayered brick-and-mortar structure of the nacre and the vital nanoscale features in its structure. Moreover, problem-solving strategies of naturally growing composites such as nacre give us a unique vision to design, optimize and fabricate simultaneously tough, stiff, and strong composites. It is widely known that nature’s biologically evolved, complex and effective functionally graded interfaces essentially enable the exceptional mechanical properties of biological composites. Particularly in nacre, the organic–inorganic interface referred hereto as interphase , in which the confined protein layer behaves stiffer and stronger in the proximity of the calcium carbonate minerals platelets, provides a key role in its toughness that is orders of magnitude higher than aragonite platelets as its main constituent. Hence, understanding the role of the interphase properties in the toughening mechanisms is paramount in the design and synthesis of high-performing bioinspired materials. In this study, a micromechanical model of the “Brick-Mortar” and “Brick-Bridge-Mortar” composites is presented focusing on the role of interphase properties on strengthening and toughening mechanisms. Shear-lag theory is employed on a simplified two-dimensional unit-cell of a multilayered composite. The computed closed-form solutions for the displacements as a function of constituent properties are used to calculate elastic modulus , strength, and work-of-fracture for a wide range of multilayered materials . Our results show that the properties of the soft phase in mineral bridges proximity can have a significant effect on the mechanical properties. The detailed relationships presented can help identify the future directions for advanced material design and development.

Decorated silver nanoparticles on biodegradable magnetic chitosan/starch composite: Investigation of its cytotoxicity, antioxidant and anti-human breast cancer properties

Nanotechnology is the field to yield modern systems, tools, and materials by controlling at the atomic and molecular levels using the features that appear on those surfaces. Applications for nanotechnology in medical diagnostics, food, medicine, biotechnology, environment, energy, chemistry, physics, etc, introduce this technology as an interdisciplinary and cross-sectoral context. In the current years, conjugated bio-nanomaterials involving magnetic core are a promising platform in new generation biological composites. In this regard, we report herein a novel Ag NPs supported chitosan-starch composite functionalized Fe3O4, a dual core-shell type nanoparticle (Fe3O4@CS-Starch/Ag). In the oncological part of the recent study, the treated cells with Fe3O4@CS-Starch/Ag nanocomposite were assessed by MTT assay for 48 h about the cytotoxicity and anti-breast carcinoma properties on normal (HUVEC) and breast carcinoma cell lines i.e. Hs 578Bst, Hs 319. T, UACC-3133, UACC-732, and MDA-MB-453. The post-synthetically modified biogenic material was analyzed in detail over several physicochemical methods like, field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), energy dispersive X-ray analysis (EDX) elemental mapping, transmission electron microscopy (TEM), vibrating-sample magnetometer (VSM), X-ray diffraction analysis (XRD), and inductively coupled plasma-atomic emission spectrometry (ICP-AES) analysis. The viability of breast carcinoma cell lines reduced dose-dependently in Fe3O4@CS-Starch/Ag nanocomposite. The IC50 of Fe3O4@CS-Starch/Ag nanocomposite was 183, 207, 194, 279, and 252 µg/mL against Hs 578Bst, Hs 319. T, UACC-3133, UACC-732, and MDA-MB-453 cell lines, respectively.

Hierarchical crack buffering triples ductility in eutectic herringbone high-entropy alloys.

In human-made malleable materials, microdamage such as cracking usually limits material lifetime. Some biological composites, such as bone, have hierarchical microstructures that tolerate cracks but cannot withstand high elongation. We demonstrate a directionally solidified eutectic high-entropy alloy (EHEA) that successfully reconciles crack tolerance and high elongation. The solidified alloy has a hierarchically organized herringbone structure that enables bionic-inspired hierarchical crack buffering. This effect guides stable, persistent crystallographic nucleation and growth of multiple microcracks in abundant poor-deformability microstructures. Hierarchical buffering by adjacent dynamic strain-hardened features helps the cracks to avoid catastrophic growth and percolation. Our self-buffering herringbone material yields an ultrahigh uniform tensile elongation (~50%), three times that of conventional nonbuffering EHEAs, without sacrificing strength.

Structural Design Variations in Beetle Elytra

AbstractBeetles typically use their protective wing coverings or elytra to shield their membranous hindwings from the environment. Elytra in some terrestrial species have evolved a greater protective role capable of shielding the organism from powerful antagonistic predators. The structure–function relationships of these biological composites identify how architectural and chemical variations of the cuticle are tuned to create light‐weight, impact resistant composites. Specifically, the elytral structures of a tree dwelling beetle capable of flight, Trypoxylus dichotomus, and a terrestrial beetle incapable of flight, Phloeodes diabolicus, are compared to understand how their varied environmental needs forged the elytra to facilitate fight or resist fatal predator strikes. Mechanical and microstructural analysis reveals P. diabolicus has a harder, stiffer elytra that incorporate through‐thickness fibers to resist greater mechanical stresses imposed by bending and puncture. Conversely, the elytra of T. dichotomus have a compliant structure with large voids that facilitates localized deformation. Variations in flexural strength and puncture resistance remain attributed to P. diabolicus possessing a thicker cuticle with a greater degree of cross‐linking and an increased amount of endocuticular layers. These findings may provide useful insight into the design and manufacturing of composite materials for use in light‐weight or energy‐absorbing applications.

The microstructure, mechanical properties, corrosion performance and biocompatibility of hydroxyapatite reinforced ZK61 magnesium-matrix biological composite

Magnesium (Mg)-based composites, as biomaterials, have attracted widespread attention due to their adjustable mechanical properties like elastic modulus, ductility, ultimate tensile strength, and corrosion resistance. In this study, hydroxyapatite (HA) reinforced ZK61 Mg-matrix composites were prepared by powder metallurgy and hot extrusion methods. The influence of the content of HA (10 wt%, 20 wt%, and 30 wt%) on the microstructure, density, mechanical properties, corrosion property and biocompatibility were investigated. The results showed that the density and yield strength of the composites match those of natural bone. Moreover, the composite with 10 % HA (ZK61-10HA) exhibited the best corrosion resistance, as determined by the electrochemical measurement and immersion test in simulated body fluid (SBF) at 37 °C. In addition, the ZK61-10HA composite significantly enhanced the cell viability (≥78 %) compared with ZK61 alloy in vitro testing. It is demonstrated that the mechanical properties, corrosion resistance and biocompatibility of Mg alloy can be effectively controlled by adjusting the content of HA, which suggested that the ZK61-HA composites were promising candidates for degradable implant materials.

Biomechanical strategies to reach a compromise between stiffness and flexibility in hind femora of desert locusts

Insect cuticle can reach a wide range of material properties, which is thought to be the result of adaptations to applied mechanical stresses. Biomechanical mechanisms behind these property variations remain largely unknown. To fill this gap, here we performed a comprehensive study by simultaneous investigation of the microstructure, sclerotization and the elasticity modulus of the specialized cuticle of the femora of desert locusts. We hypothesized that, considering their different roles in jumping, the femora of fore-, mid- and hind legs should be equipped with cuticles that have different mechanical properties. Surprisingly, our results showed that the hind femur, which typically bears higher stresses, has a lower elasticity modulus than the fore and mid femora in the longitudinal direction. This is likely due to the lower sclerotization and different microstructure of the hind femur cuticle. This allows for some deformability in the femur wall and is likely to reduce the risk of mechanical failure. In contrast to both other femora, the hind femur is also equipped with a set of sclerotized ridges that are likely to provide it with the required stiffness to withstand the mechanical loads during walking and jumping. This paper is one of only a few comprehensive studies on insect cuticle, which advances the current understanding of the relationship between the structure, material property and function in this complex biological composite. Statement of significanceInsect cuticle is a biological composite with strong anisotropy and wide ranges of material properties. Using an example of the femoral cuticle of desert locusts, we measured the elasticity modulus, microstructure and sclerotization level of the cuticle. Our results show that, although the hind femur withstands most of the stress during locomotion, it has a lower elasticity modulus than the fore and mid femora. This is likely to be a functional adaption to jumping, in order to allow small deformations of the femur wall and reduce the risk of material failure. Our results deepen the current understanding of the structure-material-function relationship in the complex insect cuticle.

Assessing the Interfacial Dynamic Modulus of Biological Composites.

Biological composites (biocomposites) possess ultra-thin, irregular-shaped, energy dissipating interfacial regions that grant them crucial mechanical capabilities. Identifying the dynamic (viscoelastic) modulus of these interfacial regions is considered to be the key toward understanding the underlying structure–function relationships in various load-bearing biological materials including mollusk shells, arthropod cuticles, and plant parts. However, due to the submicron dimensions and the confined locations of these interfacial regions within the biocomposite, assessing their mechanical characteristics directly with experiments is nearly impossible. Here, we employ composite-mechanics modeling, analytical formulations, and numerical simulations to establish a theoretical framework that links the interfacial dynamic modulus of a biocomposite to the extrinsic characteristics of a larger-scale biocomposite segment. Accordingly, we introduce a methodology that enables back-calculating (via simple linear scaling) of the interfacial dynamic modulus of biocomposites from their far-field dynamic mechanical analysis. We demonstrate its usage on zigzag-shaped interfaces that are abundant in biocomposites. Our theoretical framework and methodological approach are applicable to the vast range of biocomposites in natural materials; its essence can be directly employed or generally adapted into analogous composite systems, such as architected nanocomposites, biomedical composites, and bioinspired materials.

Couple effect of surface energy and strain gradient on the mechanical behaviors of the biological staggered composites

Biological staggered composites, which are hierarchy spanning from nano scale to macro scale, boast remarkable mechanical properties. In this paper, a trans-scale shear-lag model is established based on the strain gradient theory and the Gurtin-Murdoch model, which provides a chance to glimpse how the micro-nano structures of the biological composite determine its macroscopic mechanical behavior. With the trans-scale shear-lag model, we found that the deformation, stress distribution and overall effective modulus have strong size effects, which are related to the thickness of the ‘matrix’ and ‘platelet’ of the biological staggered composites. Based on the analysis, two normalized numbers d/l and Es/(hEp) are proposed to describe the size effects caused by the thickness of the matrix and platelet, respectively. Besides, the predicted effective moduli of the biological staggered structure composites are compared with the experiments to verify our trans-scale shear-lag model. Our research sheds light on the understanding of the mechanical behaviors of the staggered biological composites and provides theoretical guidance for the design of high-performance bionic composite materials.

Transparent materials with stiff and tough hierarchical structures

Materials that are transparent in the visible spectrum are useful in applications that range broadly from displays in portable devices to large-area panels and windows used in the construction industry. The high strength and hardness of silica-based glasses make them most suitable choice in many of these applications. However, such properties come at the cost of the low fracture resistance and low damage tolerance of glasses, which result in brittle and unpredictable failure with potentially dangerous and harmful outcomes. Strong and fracture resistant transparent materials are therefore in high demand in several structural applications. Inspired by the hierarchical structure of biological composites, researchers have been able to fabricate synthetic materials that combine high strength and toughness. Nevertheless, reconciling these mechanical properties with optical transparency does not constitute a trivial task. In this review article, we describe and discuss some of the most promising biologically templated and biologically inspired composite materials that have been proposed to combine optical transparency, strength and fracture toughness. The replication of some of the hierarchical features of biological materials within their structure allows these composites to take advantage of synergistic toughening mechanisms that act at different length scales and provide high resistance against fracture. Understanding how they are fabricated and which mechanisms contribute to their toughness is key to draw guidelines for the synthesis of future transparent, strong and tough composites that are safer and more reliable than state-of-the-art silica-based glasses.

Multi-scale design of the chela of the hermit crab Coenobita brevimanus

The chela of the hermit crab protects its body against the attack from predators. Yet, a deep understanding of this mechanical defense is still lacking. Here, we investigate the chela of hermit crab, Coenobita brevimanus, and establish the relationships between the microstructures, chemical compositions and mechanical properties to gain insights into its biomechanical functions. We find that the chela is a multi-layered shell composed of five different layers with distinct features of the microstructures and chemical compositions, conferring different mechanical properties. Especially, an increase of the calcium carbonate content towards the layer furthest from the exterior, unlike the chemical gradients of many crustacean exoskeletons, provides a strong resistance to deformation. Nanoindentation measurements reveal that the overall gradient of the elastic modulus and hardness in the cross-section displays a sandwich profile, i.e., a soft core clamped by two stiff surface layers. Further mechanics modeling demonstrates that the high curvature and stiff innermost sublayer enhance the structural rigidity of the chela. In conjunction with the experimental observations, dynamic finite element analysis maps the time-spatial distribution of principal stress and indicates that fiber bridging might be the major mechanism against crack propagation at microscale. The lessons gained from the study of this multiphase biological composite could provide important insights into the design and fabrication of bioinspired materials for structural applications. Statement of significanceMultiple hierarchical structures have been discovered in a variety of exoskeletons. They are naturally designed to maintain the structural integrity and act as a protective layer for the animals. However, each kind of the hierarchical structures has its unique topology, chemical gradients as well as mechanical properties. We find that the chela is multi-layered shell composed of five different layers with distinct features of the microstructures and chemical compositions, conferring different mechanical properties. Especially, a large amount of helicoidal organic fibrils form highly organized 3D woven matrix in the innermost layer, providing a strong mechanical resistance to avoid catastrophic failure. The overall gradient of the elastic modulus and hardness in the cross-section display a sandwich profile, effectively minimizing the stress concentration and deformation. The lessons gained from the multiscale design strategy of the chela provide important insights into the design and fabrication of bioinspired materials.

Gradients of Mechanical Properties in Taenioglossan Radular Teeth is Linked with Specific Function and Ecological Niche

Biological composites usually display graded heterogeneities in structure and mechanical properties, enabling proper functioning. The radula, one important molluscan autapomorphy and the organ for food processing, is well examined in the light of its morphology, but the mechanical properties that enable an efficient acting of the radular teeth on the ingesta with a simultaneous reduction of structural failure are not known for the vast majority of gastropods. In this case study, we employed nanoindentation technique, to measure mechanical properties (hardness and Young’s modulus) on three distinct localities of an individual radular tooth in taenioglossan radular teeth of African paludomid gastropods with distinct ecological niches (preferred feeding substrate). A gradual distribution of measured properties along the teeth was found in species foraging on solid or mixed feeding substrates, but soft substrate feeders exhibit teeth almost homogeneous in their biomechanical properties. We hypothesize, that large-scale gradients are not abundant in all biological materials and that the presence of functional gradients is rather directly linked with their specific function and in general with the species ecology.

Sawtooth patterns in flexural force curves of structural biological materials are not signatures of toughness enhancement: Part I

Layered architectures are prevalent in tough biological composites, such as nacre and bone. Another example of a biological composite with layered architecture is the skeletal elements—called spicules—from the sponge Euplectella aspergillum. Based on the similarities between the architectures, it has been speculated that the spicules are also tough. Such speculation is in part supported by a sequence of sudden force drops (sawtooth patterns) that are observed in the spicules' force-displacement curves from flexural tests, which are thought to reflect the operation of fracture toughness enhancing mechanisms. In this study, we performed three-point bending tests on the spicules, which also yielded the aforementioned sawtooth patterns. However, based on the analysis of the micrographs obtained during the tests, we found that the sawtooth patterns were in fact a consequence of slip events in the flexural tests. This is put into perspective by our recent study, in which we showed that the spicules' layered architecture contributes minimally to their toughness, and that the toughness enhancement in them is meager in comparison to what is observed in bone and nacre [Monn MA, Vijaykumar K, Kochiyama S, Kesari H (2020): Nat Commun 11:373]. Our past and current results underline the importance of inferring a material's fracture toughness through direct measurements, rather than relying on visual similarities in architectures or force-displacement curve patterns. Our results also suggest that since the spicules do not possess remarkable toughness, re-examining the mechanical function of the spicule's intricate architecture could lead to the discovery of new engineering design principles.

FM-FRP: new materiality in FRP as architectured matter with textile attributes

FRP material properties offer unique opportunities for architecture, but their mould-based standard forming processes stand in contrast to contemporary practices, aiming for variation and surface articulation. Fabric materiality FRP (FM-FRP) is an alternative approach to the design and fabrication of architectural FRP that enhances the textile qualities of the fibre material in the composite. Through integration of key textile attributes and a set methodology, two FM-FRP material systems are developed. Released from the necessity of moulds, design principles of biological composites can be integrated into synthetic FRP shaping processes and resilient properties show. A new materiality of FRP emerges, blurring boundaries between material and structure. Functionality is achieved by the intricate spatial distribution of voids and matter, resulting in highly porous volumetric FRP material. Taking-up on the approach and terminology of material-science, a new understanding of FM-FRP as architectured material is suggested. It opens a new path for its development towards enhanced functionalities, to enable future more sustainable application for the architectural field.

Growing phenotype-controlled phononic materials from plant cells scaffolds

Biological composites offer self-healing properties, biocompatibility, high responsivity to external stimuli, and multifunctionality, due, in part, to their complex, hierarchical microstructure. Such materials can be inexpensively grown, and self-assembled from the bottom up, enabling democratized, sustainable manufacturing routes for micro- and nano-devices. While biological composites have been shown to incorporate rich photonic structures, their phononic properties have hitherto remained unexplored. In this study, we demonstrate that biological composites in the form of micron-thick decellularized onion cell scaffolds behave as an organic phononic material, with the presence of band gaps forbidding the propagation of elastic waves in select frequency ranges. We show that the onion cells' phononic properties can be phenotypically tuned, and anticipate these findings will yield new biologically-derived, green, and genetically tailorable phononic materials.

Study on Mechanical and Thermal Performance of Building Energy-saving Wall with Insulation Materials

Sodium alginate and natural fiber were used as modifiers to prepare sodium alginate natural fiber type biological composites. The mechanical properties were characterized by universal testing machine, and the thermal properties were analyzed by conductivity, The effects of wood fiber and straw fiber content on the comprehensive properties of biological composite materials were evaluated by relevant instruments, and the feasibility of biological composite materials as building energy-saving wall insulation materials was evaluated. The results show that the flexural strength, compressive strength and elastic modulus of the composites increase with the increase of wood fiber content. When the wood fiber content is 100%, the mechanical properties of the sample are the best, the flexural strength is 0.573 MPa, and the compressive strength is 1.410 MPa. The results showed that wood fiber and sodium alginate binder were closely combined and had good wettability. The thermal conductivity of biological composite is 0.078-0.089w / (m · K), which means it has good thermal insula tion performance and can be used as thermal insulation material for building energy-saving wall. The results show that the properties of the composite can be improved by adding a higher proportion of wood fiber and a certain amount of glyoxal crosslinking agent.

In-situ quantification of microscopic contributions of individual cells to macroscopic wood deformation with synchrotron computed tomography

Wood-based composites hold the promise of sustainable construction. Understanding the influence on wood cellular microstructure in the macroscopic mechanical behavior is key for engineering high-performance composites. In this work, we report a novel Individual Cell Tracking (ICT) approach for in-situ quantification of nanometer-scale deformations of individual wood cells during mechanical loading of macroscopic millimeter-scale wood samples. Softwood samples containing > 104 cells were subjected to controlled radial tensile and longitudinal compressive load in a synchrotron radiation micro-computed tomography (SRµCT) setup. Tracheid and wood ray cells were automatically segmented, and their geometric variations were tracked during load. Finally, interactions between microstructure deformations (lumen geometry, cell wall thickness), cellular arrangement (annual growth rings, anisotropy, wood ray presence) with the macroscopic deformation response were investigated. The results provide cellular insight into macroscopic relations, such as anisotropic Poisson effects, and allow direct observation of previously suspected wood ray reinforcing effects. The method is also appropriate for investigation of non-linear deformation effects, such as buckling and deformation recovery after failure, and gives insight into less studied aspects, such as changes in lumen diameter and cell wall thickness during uniaxial load. ICT provides an experimental tool for direct validation of hierarchical mechanical models on real biological composites.