Collaborative Research: Revealing Strengthening and Toughening Mechanisms in Coconut Endocarp through Integrated Multiscale Modeling and Characterization

非技术概述：椰子的硬壳，称为内果皮，是一种轻质材料，具有令人印象深刻的强度、韧性和硬度。与许多生物材料一样，这种出色的行为是由于高度复杂的结构。在放大倍数下研究时，内果皮在每个放大倍数下显示不同的结构。在最大的层面上，可以看到一个多孔的网络，由一束束的中空通道组成。更大的放大显示出一种渐变的细胞结构，在椰子的内部发现了较大的细胞，向外发现了较小的细胞。细胞本身的特征是由许多层组成的壁，每一层都由微小的纤维组成。全面了解所有这些因素是如何共同作用使椰子如此坚韧是一个巨大的挑战，特别是因为它们的大小不同。该项目将开发新的计算机模拟技术，能够以相应的大小同时处理这些不同的元素。该项目还将开发新的实验技术，以直接测量和可视化椰子内果皮中的不同元素如何相互作用，以测试和校准计算机模型。这种计算和实验相结合的方法将为椰子的结构如何产生出色的性能提供前所未有的见解。然后，这些见解和方法可以用来设计受椰子启发的轻量级应用程序，这些应用程序既强大又坚固，例如用于改进头盔。该项目将为本科生提供研究机会。例如，暑期将为本科生提供计算和实验系列培训。代表不足的学生，包括女学生和少数族裔学生，将参加这一研究项目。该项目还将为残疾学生提供远程计算建模的机会。将为初中生和高中生提供演讲和研讨会演讲，以吸引他们参与生物材料研究。技术摘要：椰子内果皮实质上比木材更坚固，尽管它们有相同的主要成分：纤维素、半纤维素和木质素。这种令人印象深刻的机械性能的关键是一种复杂的结构，在分子尺度和宏观尺度之间具有多个层次的结构层次。该项目的目标是通过整合新的计算和实验技术的多尺度努力，对内果皮的结构/性质关系进行严格的理解。一个并行的原子-连续(CAC)计算工具将被开发出来，以自然地跨越该材料系统的所有相关长度尺度。这种方法将克服当前计算方法的局限性，在这些方法中，不同的长度尺度是用概念上不同的模型来处理的，需要进行接口。CAC方法将首次用于分层材料，代表着材料科学改变游戏规则的发展。实验工作将反映计算工作，并提供所有长度尺度的特征。扫描探针技术将不仅在表征内果皮纳米和微米级成分的结构和力学性能方面发挥关键作用，而且还将在表征它们的界面相互作用方面发挥关键作用。其结果将是一个强大的模型，它可以在多个长度尺度上进行校准和验证。这个模型可以作为一个基础，以椰子内果壳为灵感，建立具有突出机械性能的合成细胞轻质材料的自下而上的分层设计指南。该项目由材料研究部门的生物材料计划(BMAT)和既定的刺激竞争研究计划(EPSCoR)联合资助。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical Summary:The hard shell of the coconut, called endocarp, is a lightweight material with impressive strength, toughness, and hardness. As with many biological materials, this outstanding behavior is due to a highly complex structure. When studied at increasing magnifications, the endocarp reveals different structures at each magnification level. At the largest level, a porous network can be seen, consisting of bundles of hollow channels. Larger magnifications reveal a graded cellular structure, where larger cells are found toward the inside of the coconut, and smaller cells toward the outside. The cells themselves feature walls consisting of many layers, and each of these layers consists of tiny fibrils. Understanding comprehensively how all of these elements work together to make the coconut so strong and tough is a significant challenge, especially because of their disparity in size. This project will develop novel computer simulation techniques with the capability of treating these different elements simultaneously at the relevant sizes. This project will also develop new experimental techniques to measure and visualize directly how the different elements inside the coconut endocarp interact, to test and calibrate the computer models. This integrated computational and experimental approach will provide unprecedented insights into how the coconut’s structure gives rise to its outstanding performance. These insights and methods can then be used to engineer coconut-inspired lightweight applications that are strong and tough, for instance to improve helmets. This project will provide research opportunities to undergraduate students. For instance, computational and experimental training series will be offered to undergraduate students during the summer. Underrepresented students including female and minority students will participate in this research project. This project will also provide opportunities to students with disabilities to work on computational modeling remotely. Presentations and seminar talks will be offered to middle and high school students to attract them to participate into biomaterial research. Technical Summary:Coconut endocarp is substantially stronger and stiffer than wood, despite sharing the same major ingredients: cellulose, hemi-cellulose, and lignin. The key to this impressive mechanical performance is a sophisticated structure with many levels of structural hierarchy between the molecular scale and the macroscale. This project’s goal is to develop a rigorous understanding of the endocarp’s structure/property relationships by means of a multi-scale effort integrating novel computational and experimental techniques. A concurrent atomic-continuum (CAC) computational tool will be developed to span all relevant length scales of this materials system naturally. This approach will overcome limitations of current computational approaches, where different length scales are treated with conceptually different models that need to be interfaced. The CAC approach will be used on hierarchical materials for the first time, representing a game changing development for the materials sciences. The experimental efforts will mirror the computational work and provide characterization across all length scales. Scanning probe techniques will play a crucial role in characterizing not only the structure and mechanical properties of nano- and microscale constituents of the endocarp, but also their interfacial interactions. The outcome will be a powerful model that is calibrated and verified across multiple length scales. This model can serve as a basis to establish guidelines for bottom-up hierarchical design of synthetic cellular lightweight materials with outstanding mechanical performance, inspired by the coconut endocarp.This project is jointly funded by the Biomaterials progam (BMAT) in the division of materials research (DMR) and the Established Program to Stimulate Competitive Research (EPSCoR).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.