Collaborative Research: Ontogeny, Mechanics and Function of the Tessellated Skeleton of Cartilaginous Fishes

这项研究项目是对软骨骨骼矿化部分的结构和功能进行多层次、跨学科的研究。软骨通常被认为是一种关节材料，是骨元素之间的承重面，或者是鼻子和耳朵的轮廓填充物。然而，鲨鱼和它们的近亲使用软骨作为它们的骨骼材料。这种形式的软骨是轻微矿化的，表面覆盖着一层小的、离散的块状物，完全覆盖在表面。有两个因素使这种“镶嵌”的软骨格外有趣：1)鲨鱼放弃了骨骼，转而选择这种软骨，这样我们就可以在矿化过程中看到早期骨形成的发育和生化痕迹；2)因为鲨鱼和人类一样，不能修复它们的软骨，所以在动物的一生中，它必须特别抵抗疲劳损伤。了解这种抗疲劳性的基础可能会发现一种新的生物材料，这种材料既僵硬，又能很好地分散能量。初步数据显示，镶嵌软骨和骨骼的矿化过程有许多不同。镶嵌软骨的钙化细胞不会像在骨骼中那样扩大和死亡，细胞也不会被组织成文件夹，但就像在骨骼中一样，在矿化前沿的边缘有一个明显的有组织的胶原纤维区域。这可能标志着发育水平上的相似性。研究人员将用组织学技术调查这些相似之处的程度，以探索发育中的骨骼的独特生化信号。他们还将使用低温扫描电子显微镜来检查发育中的矿化组织中细胞的形状和排列。这一微观和发育研究将得到对镶嵌骨架的力学研究的补充。整个骨骼元素将用能够测量活组织中阻尼的周长计进行测试，以验证该组织非常善于消耗应变能量的假设。这些研究将通过基于模型的研究来加强，研究矿化块大小和未矿化软骨硬度对减震质量的影响。一台快速打样机将被用来打印出不同块大小和形状的模型，然后在传统的材料测试系统上进行检查。这些实验将由加州大学欧文分校、乔治华盛顿大学、德国斯图加特的马克斯·普朗克研究所和墨西哥拉巴斯的跨学科海洋科学研究所的实验室合作进行。进行这项研究的科学家包括研究生和本科生，包括发育生物学家、生物机械学家、机械工程师和表面生物学家。该小组的几名成员是代表不足的少数群体，包括一名首席调查员和四名研究生。

This research project is a multi-level, interdisciplinary investigation of the structure and function of the mineralized portion of the cartilaginous skeleton. Cartilage is usually perceived as an articular material, a bearing surface between bony elements, or as contour-filler in the nose and ears. However, sharks and their relatives use cartilage as their skeletal material. This form of cartilage is lightly mineralized, with a surface coating of small, discrete blocks that completely cover the surface. Two factors make this 'tessellated' form of cartilage particularly interesting: 1) sharks abandoned a bony skeleton in favor of this cartilage so we may see the developmental and biochemical traces of early bone formation in the mineralization processes; and 2) since sharks, like human, cannot heal their cartilage it must be particularly resistant to fatigue damage over the life of the animal. Understanding the basis for this fatigue resistance may uncover a new class of biological materials that are both stiff and able to dissipate energy well. Preliminary data shows many differences between the mineralization process in tessellated cartilage and bone. The calcifying cells of tessellated cartilage do not enlarge and die as they do in bone, nor are the cells organized into files, but just as in bone there is a distinct region of organized collagen fibers on the edges of the mineralizing front. This may signal similarities at the developmental level. The researchers will investigate the extent of these similarities with histological techniques that probe for distinctive biochemical signals of developing bone. They will also use cryogenic scanning electron microscopy to examine the shape and arrangement of the cells in the developing mineralizing tissue. This microscopic and developmental investigation will be complemented by a study of the mechanics of the tessellated skeleton. Whole skeletal elements will be tested with a Periometer capable of measuring damping in living tissue to test the hypothesis that this tissue is very good at dissipating strain energy. These studies will be augmented with model-based investigations of the effect of mineralized block size and unmineralized cartilage stiffness on the damping qualities. A rapid prototyper will be used to 'print out' models with different block sizes and shapes, which will then be examined on a conventional material testing system. These experiments will be carried out by a collaboration between labs at the University of California - Irvine, George Washington University, the Max Planck Institute in Stuttgart, Germany and the Institute for Interdisciplinary Marine Sciences in La Paz, Mexico. The scientists, including graduate and undergraduate students, performing the research include developmental biologists, biomechanists, mechanical engineers and surface biologists. Several members of the group are under-represented minorities including one of the principal investigators and four of the graduate students.