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1. Optimal and continuous multilattice embedding

   https://doi.org/10.1126/sciadv.abf4838  

   Sanders, E. D. ; Pereira, A. ; Paulino, G. H. ( April 2021 , Science Advances)

   Because of increased geometric freedom at a widening range of length scales and access to a growing material space, additive manufacturing has spurred renewed interest in topology optimization of parts with spatially varying material properties and structural hierarchy. Simultaneously, a surge of micro/nanoarchitected materials have been demonstrated. Nevertheless, multiscale design and micro/nanoscale additive manufacturing have yet to be sufficiently integrated to achieve free-form, multiscale, biomimetic structures. We unify design and manufacturing of spatially varying, hierarchical structures through a multimicrostructure topology optimization formulation with continuous multimicrostructure embedding. The approach leads to an optimized layout of multiple microstructural materials within an optimized macrostructure geometry, manufactured with continuously graded interfaces. To make the process modular and controllable and to avoid prohibitively expensive surface representations, we embed the microstructures directly into the 3D printer slices. The ideas provide a critical, interdisciplinary link at the convergence of material and structure in optimal design and manufacturing. 

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2. Review on 3D Printing of Bioinspired Structures for Surface/Interface Applications

   https://doi.org/10.1002/adfm.202309323  

   He, Qingqing ; Tang, Tengteng ; Zeng, Yushun ; Iradukunda, Nadine ; Bethers, Brandon ; Li, Xiangjia ; Yang, Yang ( December 2023 , Advanced Functional Materials)

   Natural organisms have evolved a series of versatile functional biomaterials and structures to cope with survival crises in their living environment, exhibiting outstanding properties such as superhydrophobicity, anisotropy, and mechanical reinforcement, which have provided abundant inspiration for the design and fabrication of next‐generation multi‐functional devices. However, the lack of available materials and limitations of traditional manufacturing methods for complex multiscale structures have hindered the progress in bio‐inspired manufacturing of functional structures. As a revolutionary emerging manufacturing technology, additive manufacturing (i.e., 3D printing) offers high design flexibility and manufacturing freedom, providing the potential for the fabrication of intricate, multiscale, hierarchical, and multi‐material structures. Herein, a comprehensive review of current 3D printing of surface/interface structures, covering the applied materials, designs, and functional applications is provided. Several bio‐inspired surface structures that have been created using 3D printing technology are highlighted and categorized based on their specific properties and applications, some properties can be applied to multiple applications. The optimized designs of these 3D‐printed bio‐inspired surfaces offer a promising prospect of low‐cost, high efficiency, and excellent performance. Finally, challenges and opportunities in field of fabricating functional surface/interface with more versatile functional material, refined structural design, and better cost‐effective are discussed.

    

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3. An Investigation of Integrated Multiscale Three-Dimensional Printing for Hierarchical Structures Fabrication

   https://doi.org/10.1115/1.4054317  

   Li, Xiangjia ; Baldacchini, Tommaso ; Chen, Yong ( December 2021 , Journal of Micro- and Nano-Manufacturing)

   Abstract Nature provides us with a large number of functional material systems consisting of hierarchical structures, where significant variations in dimensions are present. Such hierarchical structures are difficult to build by traditional manufacturing processes due to manufacturing limitations. Nowadays, three-dimensional (3D) objects with complex structures can be built by gradually accumulating in a layer-based additive manufacturing (AM); however, the hierarchical structure measured from macroscale to nanoscale sizes still raises significant challenges to the AM processes, whose manufacturing capability is intrinsically specified within a certain scope. It is desired to develop a multiscale AM process to narrow this gap between scales of feature in hierarchical structures. This research aims to investigate an integration approach to fabricating hierarchical objects that have macro-, micro-, and nano-scales features in an object. Firstly, the process setup and the integrated process of two-photon polymerization (TPP), immersed surface accumulation (ISA), and mask image projection-based stereolithography (MIP-SL) were introduced to address the multiscale fabrication challenge. Then, special hierarchical design and process planning toward integrating multiple printing processes are demonstrated. Lastly, we present two test cases built by our hierarchical printing method to validate the feasibility and efficiency of the proposed multiscale hierarchical printing approach. The results demonstrated the capability of the developed multiscale 3D printing process and showed its future potential in various novel applications, such as optics, microfluidics, cell culture, as well as interface technology. 

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4. Hybrid Loss for Hierarchical Multi–label Classification Network

   https://doi.org/10.1109/BigData59044.2023.10386341  

   Qi, Wenting ; Chelmis, Charalampos ( December 2023 , IEEE International Conference on Big Data)

   Machine learning models for hierarchical multilabel classification (HMC) typically achieve low accuracy. This is because such models need not only predict multiple labels for each data instance, but also ensure that predicted labels conform to a given hierarchical structure. Existing state-of the-art strategies for HMC decouple the learning process from ensuring that predicted labels reside in a path of the hierarchy, thus inevitably degrading the overall classification accuracy. To address this limitation, we propose a novel loss function, which enables a model to encode both a global perspective of the class hierarchy, as well local class-relationships in adjacent hierarchical levels, to ensure that predictions align with the class hierarchy, both during training and testing. We demonstrate the superiority of the proposed approach against multiple state-of-the-art methods for HMC on 20 real-world datasets. 

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5. 3D Printed Bioinspired Hierarchical Surface Structure With Tunable Wettability

   https://doi.org/10.1115/1.4064051  

   Rahman, M. M. ; Joyee, Erina Baynojir ( December 2022 , Journal of Micro- and Nano-Manufacturing)

   Nature has examples of impressive surfaces and interfaces with diverse wettability stemming from superhydrophilicity to superhydrophobicity. The multiscale surface structures found in biological systems generally have high geometric complexity, which makes it challenging to replicate their characteristics, especially using traditional fabrication techniques. It is even more challenging to fabricate such complex microstructures with tunable wettability. In this paper, we propose a method to tune the wettability of a microscale surface by changing the geometrical parameters of embedded microstructures in the surface. By taking inspiration from an insect (springtails), we designed micropillar arrays with different roughness by adjusting geometric parameters such as reentrant angle, pitch distance, and the number of spikes and pillars. This study shows that, by changing geometrical parameters in microscale, the apparent contact angle, and hence the surface wettability can be calibrated. The microscale pillars were fabricated using a precise microdirect light processing (μDLP) three-dimensional (3D) printer. Different printing parameters were studied to optimize the geometric parameters to fabricate 3D hierarchical structures with high accuracy and resolution. The largest apparent contact angle in our experiments is up to 160 deg, with pillars of 0.17 mm height and 0.5 mm diameter, 55 deg reentrant angle, and a spacing of 0.36 mm between pillars. The lowest contact angle is ∼35 deg by reducing the pillar size and spacing. By controlling the size of different features of the pillar, pillar number, and layout of the mushroom-shaped micropillars, the wettability of the surface is possible to be tuned from a highly nonwetting liquid/material combination to highly wetting material. Such wettability tuning capability expands the design space for many biomedical and thermofluidic applications.

    

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