Amplification in toughness and balance with stiffness and strength are fundamental characteristics of biological structural composites, and a long sought-after objective for engineering design. Nature achieves these properties through a combination of multiscale key features. Yet, emulating all these features into synthetic de novo materials is rather challenging. Here, we fine-tune manual lamination, to implement a newly designed bone-inspired structure into fiber-reinforced composites. An integrated approach, combining numerical simulations, ad hoc manufacturing techniques, and testing, yields a novel composite with enhanced fracture toughness and balance with stiffness and strength, offering an optimal lightweight material solution with better performance than conventional materials such as metals and alloys. The results also show how the new design significantly boosts the fracture toughness compared to a classic laminated composite, made of the same building blocks, also offering an optimal tradeoff with stiffness and strength. The predominant mechanism, responsible for the enhancement of fracture toughness in the new material, is the continuous deviation of the crack from a straight path, promoting large energy dissipation and preventing a catastrophic failure. The new insights resulting from this study can guide the design of de novo fiber-reinforced composites toward better mechanical performance to reach the level of synergy of their natural counterparts.

8In the setting of emerging approaches for material design, we investigate the use of 9 extended finite element method (XFEM) to predict the behavior of a newly designed bone-10 inspired fiber-reinforced composite and to elucidate the role of the characteristic 11 microstructural features and interfaces on the overall fracture behavior. The outcome of the 12 simulations, showing a good agreement with the experimental results, reveals the 13 fundamental role played by the heterogeneous microstructure in altering the stress field, 14 reducing the stress concentration at the crack tip, and the crucial role of the interface region 15 (i.e. cement line) in fostering the activation of characteristic toughening mechanisms, thus 16 increasing the overall flaw tolerance of the composite.17 18 Keywords: 19 B. Fracture 20 C. Numerical analysis; Computational modeling; 21 XFEM (Extended Finite Element Method) 22 23 24 M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 2 2 of ideal design, being simultaneously lightweight, stiff, strong and tough. Examples are 3 bone, which provides supports to many animal bodies, nacre and seashells, working as 4 natural body armors and providing protection from external predators' attacks, bamboo, 5 whose gradient structure guarantees an augmented flexural rigidity, enabling protection 6 from crosswind and gravity. Ancient but ever-intriguing, these materials are paradigms of 7 natural structural composites, made of few universal constituents and achieving -through a 8 sophisticated design -a unique combination of mechanical properties, bypassing the trade-9 off faced by synthetic engineering materials [1]. Traditional structural materials, indeed, 10 continuously face a typical engineering issue of satisfying both strength and toughness 11 requirements. For instance, ceramics provide high strength with a low toughness, whereas 12 steel and metals have high toughness and a limited strength. Composites often represent a 13 good compromise, being lightweight and stiff and offering a good balance with strength-14 toughness [2]. In particular, fiber-reinforced composites, which present the highest 15 stiffness-to-weight and strength-to-weight ratio, represent an attractive solution for 16 structural applications where the weight is a crucial aspect (e.g. automotive and aerospace) 17 [3-5]. However, they often fail in a brittle way. Enhancing the fracture toughness, by 18 promoting larger energy release before failure, will increase the intrinsic safety of such 19 materials, also fostering their adoption for diverse structural applications. 20 Drawing inspiration from nature can offer a path towards enhancing their resistance 21 to fracture. Bone, in particular, may represent an excellent biomimetic model for novel 22 composite design. Bone is a lightweight strong and tough natural composite made of 23 M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 3 hydroxyapatite mineral crystals, providing stiffness and strength, interspersed into an 1 organic matrix (mainly made of collagen) th...

Biofouling refers to the adverse attachment and colonization of fouling organisms, including macromolecules, bacteria, and sessile invertebrates, on the surfaces of materials submerged in aquatic environments. Almost all structures working in watery surroundings, from marine infrastructures to healthcare facilities, are affected by this sticky problem, resulting in massive direct and indirect economic loss and enormous cost every year in protective maintenance and remedial cleaning. Traditional approaches to preventing marine biofouling primarily rely on the application of biocide-contained paints, which certainly impose adverse effects on the ocean environment and marine ecology. Biomimicry offers an efficient shortcut to developing environmentally friendly antifouling techniques and has yielded encouraging and promising results. The antifouling strategies learned from nature can be broadly classified into two categories according to the nature of the cues applied for biofouling control. One is the chemical antifouling techniques, which are dedicated to extracting the effective antifoulant compounds from marine organisms and synthesizing chemicals mimicking natural antifoulants. In contrast, the physical biomimetic (BM) antifouling practices focus on the emulation and optimization of the physical cues such as micro and nanoscale surface topographies learned from naturally occurring surfaces for better antifouling efficacy. In this review, a synopsis of the techniques for manufacturing the BM and bioinspired (BI) antifouling surface topographies is introduced, followed by the bioassay to assess the antifouling performance of the structured surfaces. Then, the BM and BI surface topographies that were reported to possess enhanced antifouling competence are introduced, followed by a summary of theoretical modeling. The whole paper is concluded by summarizing the studies' deficiencies so far and outlooking the research directions in the future.

Surface topography has been demonstrated as an effective nonchemical strategy for controlling the fouling resistance of a surface, but its impact on optical transparency remains a barrier to the application of this strategy in optical materials. To reconcile the conflicting effects of surface topography on optical transparency and fouling resistance, here we study the optical properties and antifouling performance of nanowrinkled surfaces inspired by the corneal surface of zebrafish (Danio rerio). Experimental and numerical analyses demonstrate that a good compromise between optical transparency and antifouling efficacy can be achieved by wavy nanowrinkles with a characteristic wavelength of 800 nm and an amplitude of 100 nm. In particular, the optimal wrinkled surface under study can reduce biofouling by up to 96% in a single-species (Pseudoalteromonas sp.) bacterial settlement assay in the laboratory and 89% in a field test while keeping the total transmittance above 0.98 and haze below 0.04 underwater. Moreover, our nanowrinkled surface also exhibits excellent resistance against contamination by inorganic particles. This work provides a nonchemical strategy for achieving the coexistence of optical transparency and fouling resistance on one single material, which implies significant application potential in various optical devices and systems, such as antibacterial contact lenses and self-cleaning solar panels.

The attachment efficiency of biofouling organisms on a solid surface depends on a variety of factors including species of the fouler, nutrition abundance, salinity, temperature, flow rate, surface morphology and mechanical properties of the solid to be attached and so on.So far, extensive research has been carried out to investigate the effects of these factors on the attachment behavior for various fouling species. However, the obtained results are normally species-dependent and seemly scattering. There is no universal rule that can be applied to predict the attachment efficiency under given conditions. To solve this problem, in this paper we carry out a meta-analysis on the effects of 10 selected factors on the attachment efficiency, resulting in a universal quantitative correlation between the attachment density and the selected factors. This obtained correlation is experimentally validated by an attachment test of tubeworms (Hydroides elegans) on PDMS surfaces with controllable stiffness. Our results provide a practical approach to quantitatively predict the attachment efficiency of fouling organisms and should be of great value to the design of anti-biofouling materials and structures.

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