A ZINC-HISTIDINE, IRON PHOSPHATE, AND ZINC HYDROXIDE BIO-COMPOSITE IN CUTTING AND PUNCTURING TOOLS

非技术摘要蚂蚁和蝎子这样的小动物是如何如此容易地刺穿人类皮肤的，而人类即使拥有强大的颌部肌肉，也很难咬破类似的皮肤？答案是，肌肉较小的生物体使用非常锋利的嘴部、刺痛和爪子来集中他们的微小力量。但是，锋利的工具很容易损坏，如果生物体不够强壮，不能用钝化的工具切割，损坏和磨损可能是致命的。由于这种压力，特殊材料可能已经进化出来，帮助小型生物制造锋利的工具并保持它们的锋利。人类可以从这些材料中学习，并利用这些知识来改进人造材料。最近在蝎子嘴爪中发现了这种材料的一个很好的候选者。这种材料可以最大限度地减少甚至“治愈”切割刃的损伤和磨损。这笔赠款将确认并进一步研究这种蝎子材料的组成，方法是使用原子探测断层扫描技术几乎逐个原子地分解这种材料。这种材料被认为含有两种不同的矿物--磷酸铁和氢氧化锌，以及一种含有约10%锌的蛋白质成分。新材料的硬度和其他机械性能将使用可以测量微小样品这些性能的技术进行研究。此外，将使用集成到电子显微镜中的测试设备来研究切割过程中锋利边缘的行为，并用爪子切割和穿孔。蝎子的材料由锌-组氨酸交联物加强，这种交联物就像加固建筑物的横梁，但这些交联物有时会在切割压力下断裂。大量额外锌的一个可能原因是为了快速修复断裂的锌-组氨酸交联链。此外，氢氧化锌可以填充和粘结正在形成的裂缝的两侧。电子显微镜将使切割过程中的磨损、损伤和自我修复可视化，测试机将测量重复刺穿所需的力。蝎子的材料将被与人造刀片和尖端等其他材料进行比较，研究人员将通过检查蝎子在不同发育阶段的情况来研究蝎子是如何制造这种材料的。除了对材料技术和材料科学的潜在贡献外，该项目还将进一步了解材料在生物学中的重要性，架起材料科学和生物生物学领域的桥梁。一名研究生和数十名本科生也将通过这个项目接受研究培训。技术概述小动物经常使用非常锋利的嘴部、刺和爪子来克服力量限制。但是，锋利的工具很容易损坏，如果生物体依赖锋利的工具进行防御或获取食物，损坏和磨损可能是致命的。该项目将研究最近在蝎子嘴爪中发现的一种复杂的生物材料，这种材料可能已经进化到产生尖锐的结构，同时将损伤和磨损降至最低，并可能得到“修复”。原子探针断层扫描将被用来证实和扩展初步发现，这表明该材料含有两种不同的生物矿物质，磷酸铁和氢氧化锌，以及一种富含组氨酸的蛋白质，它在~10%的浓度下与锌结合。将使用纳米压痕来测量硬度、弹性模数和阻尼值(损耗正切)，并在扫描电子显微镜内安装穿孔/切割测试仪，以便直观地了解材料在穿孔/切割过程中的磨损情况，以及爪尖和爪缘是否具有自我愈合性能。自我修复假说是，断裂的锌-组氨酸键以类似于最近在贻贝丝线上发现的微小规模的锌-组氨酸键修复的方式重新建立。为了研究自我愈合，穿刺机中的重复穿刺率和纳米压痕器的重复压痕率将有所不同。氢氧化锌的存在的一个可能的解释是，它为这种自我修复机制提供了现成的锌，帮助迅速重新建立联系。许多锌-组氨酸键的周期性断裂和重新建立可以作为一种减震机制，吸收原本可能会断裂的能量。最后，蝎子将在发育的不同阶段接受检查，以开始了解它们是如何产生这种复杂的材料的。除了启发新材料技术和材料科学的潜力外，该项目还将进一步了解材料在生物学中的重要性，通过将材料特性的差异转化为所需力量和肌肉质量的差异，将材料科学和生物生物学领域联系起来。一名研究生和数十名本科生也将通过这个项目接受研究培训。这一奖项反映了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 summaryHow do small animals like ants and scorpions so easily puncture human skin, while humans would have a difficult time biting through similar skin, even with their vastly stronger jaw muscles? The answer is that organisms with small muscles focus their tiny forces using very sharp mouth parts, stings and claws. But, sharp tools are easily damaged, and if an organism is not strong enough to cut with blunted tools, damage and wear may be fatal. Because of this pressure, special materials may have evolved to help small organisms make sharp tools and keep them sharp. Humans may learn from these materials, and use this knowledge to improve human-made materials. A good candidate for such a material was recently discovered in scorpion mouth claws. This material may minimize and even “heal” damage and wear of the cutting edges. This grant will confirm and further study the composition of this scorpion material by disassembling the material nearly atom-by-atom using Atom Probe Tomography. The material is thought to contain two different minerals, iron phosphate, and zinc hydroxide, as well as a protein component that contains about 10% zinc. The hardness and other mechanical properties of the new material will be investigated using techniques that can measure these properties for tiny samples. In addition, the behavior of the sharp edges during cutting will be studied using a testing device that is integrated into an electron microscope and cuts and punctures with the claws. The scorpion material is strengthened by zinc-histidine cross links, which act like cross beams strengthening a building, but these cross links are sometimes broken under the pressures of cutting. One possible reason for the large quantities of extra zinc is to quickly repair broken zinc-histidine cross links. In addition, the zinc hydroxide may fill in and bond opposite sides of developing cracks. The electron microscope will allow visualization of wear, damage and self-healing during cutting, and the testing machine will measure the forces required for repeated puncture. The scorpion material will be compared to other materials like human-made blades and tips, and the researchers will investigate how the scorpions make the material by examining scorpions at various stages of development. In addition to potential contributions to materials technology and materials science, this project will further the understanding of the importance of materials in biology, bridging the fields of material science and organismal biology. A graduate student and dozens of undergraduates will also receive research training through this project.Technical summarySmall animals often overcome force limitations using very sharp mouth parts, stings and claws. But, sharp tools are easily damaged, and if an organism relies on sharp tools for defense or food acquisition, damage and wear may be fatal. The project will investigate a recently discovered complex biomaterial in scorpion mouth claws that may have evolved to produce sharp structures while minimizing and possibly “healing” damage and wear. Atom Probe Tomography will be used to confirm and extend the preliminary findings, which suggested that the material contains two different biominerals, iron phosphate, and zinc hydroxide, as well as a histidine - rich protein that binds Zn in ~10% concentrations. Nanoindentation will be used to measure hardness, modulus of elasticity and damping (loss tangent), and a puncture/cutting tester will be installed inside a Scanning Electron Microscope in order to visualize how the material wears during the puncture/cutting process, and whether the claw tips and edges have self-healing properties. The self-healing hypothesis is that broken zinc-histidine bonds re-establish in a manner similar to the minute-scale healing of zinc-histidine bonds recently discovered in mussel byssal threads. The rate of repeated punctures in the puncture testing machine, and repeated indentations with the nanoindenter, will be varied in order to investigate self-healing. One possible explanation for the presence of zinc hydroxide is that it acts as a ready supply of zinc for this self-healing mechanism, helping bonds re-establish quickly. A cyclical breaking and re-establishing of many zinc-histidine bonds could act as a damping mechanism, absorbing energy that might otherwise be available for fracture. Finally, scorpions will be examined at various stages of development in order to begin to understand how they produce this complex material. In addition to the potential of inspiring new materials technology and materials science, this project will further the understanding of the importance of materials in biology, bridging the fields of materials science and organismal biology by translating material property differences into differences in required force and muscle mass. A graduate student and dozens of undergraduates will also receive research training through this project.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.