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首页> 外文学位 >In search of a countermeasure for astronauts' bone loss: Microstructural imaging and fluid transport in the lacunar-canalicular network of compact bone.
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In search of a countermeasure for astronauts' bone loss: Microstructural imaging and fluid transport in the lacunar-canalicular network of compact bone.

机译：寻找宇航员骨质流失的对策：致密骨的腔-小管网络中的微结构成像和液体运输。

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摘要

Astronauts lose 1-2% of bone minerals per month in microgravity, due to disuse-induced osteoporosis. Under earth's gravity, cyclic loading in weight-bearing bones causes nutrients, waste, as well as bio-signaling molecules to circulate between the blood capillary and lacunar-canalicular network (LCN); in weightlessness the loading is absent. This solute transport is thought to be essential for osteocyte survival. Buried in hard, calcified tissue, the LCN structure is difficult to study by conventional biochemical and bioimaging methods, which makes it difficult to obtain knowledge of LCN dimensions and track its interstitial fluid flow. We applied AFM, SEM and confocal microscopy to the analysis of the LCN in transverse, radial and longitudinal orientations of demineralized bovine tibia. Bovine compact bone has been reported to closely resemble human bone microstructure. A novel AFM sample preparation technique (epoxy embedded demineralized and then ultratomed bone sections) allowed detailed analysis of LCN components. Results from this imaging study show that lamellae of an osteon were found to consist of alternating high and low bands, canaliculi appear to follow the surface contour of the lamella bands, the canalicular porosity in the LCN is 0.051 +/- 0.018, and the integrity of the LCN is preserved after demineralization. An AFM compression study of the high and low bands in demineralized bone suggests that collagen fibril density is homogenous throughout the lamellae. Over the last four decades rat has been a popular animal model for NASA's biomedical study of astronauts' mineral loss. However, it remains unclear how accurately rat bone simulates human's in its structure and microfluidics. AFM and SEM analysis compared bovine and rat demineralized compact bones and revealed that significant structural differences exist. Knowledge gained from this study will aid in the evaluation of rat as an animal model for our research toward a countermeasure against astronauts' bone loss and osteoporosis. Further, fluorescence recovery after photobleaching (FRAP) technique was used to track diffusional flow in the LCN with a Rhodamine B tracer. Demineralized bovine compact bone was cryotome sectioned to 20 mum in the transverse orientation, tracer saturated and analyzed by FRAP under confocal microscopy. Together with a mathematical model for tracer diffusion, the effective diffusivity of 4.0 +/- 2.0 cm2/cm and a tortuosity of 3.8 +/- 0.8 are reported in the LCN. The tortuosity is consistent with reported literature values measured by other tracer types. The time required for nutrient recovery in the LCN after periods devoid of cyclic loading is an important parameter for optimization of the astronaut's exercise program. A preliminary diffusion-based model of an osteon under cyclic load was developed and can be used to approximate nutrient recovery times in the LCN under normal physical stimulation i.e. running, walking or standing. Parameters such as LCN dimensions, microstructure assembly, and tortuosity obtained by this work brings us closer to understanding the governing mechanisms leading to bone resorption and further the development of a countermeasure against astronaut's bone loss.
机译：由于停用引起的骨质疏松症，宇航员每月在微重力中损失1-2％的骨矿物质。在地球的重力作用下，承重骨骼中的周期性载荷会导致营养，废物以及生物信号分子在毛细血管和腔－小管网络（LCN）之间循环。在失重状态下，没有负载。这种溶质运输被认为对骨细胞的生存至关重要。埋在坚硬的钙化组织中的LCN结构很难通过常规的生化和生物成像方法研究，这使得难以获得LCN尺寸的知识并跟踪其间质液流动。我们将AFM，SEM和共聚焦显微镜应用于脱盐牛胫骨横向，径向和纵向的LCN分析。据报道，牛致密骨与人类骨骼的微观结构非常相似。一种新颖的AFM样品制备技术（环氧树脂嵌入的脱矿物质，然后是超薄的骨切片）可以对LCN成分进行详细分析。这项成像研究的结果表明，发现骨质骨的薄片由交替的高低带组成，小管似乎遵循薄片带的表面轮廓，LCN中的小管孔隙度为0.051 +/- 0.018，完整性脱盐后保留LCN的一部分。对脱矿质骨中高带和低带的AFM压缩研究表明，整个薄片中的胶原原纤维密度是均匀的。在过去的四十年中，老鼠一直是NASA关于宇航员矿物质流失的生物医学研究的流行动物模型。然而，尚不清楚大鼠骨骼在结构和微流控学方面模拟人类的精确程度。原子力显微镜和扫描电镜分析比较了牛和大鼠的脱矿质致密骨，发现存在明显的结构差异。从这项研究中获得的知识将有助于将大鼠作为动物模型进行评估，作为我们针对宇航员的骨质流失和骨质疏松症的对策的研究。此外，光漂白后的荧光恢复（FRAP）技术用于用罗丹明B示踪剂跟踪LCN中的扩散流。将脱钙的牛致密骨冷冻切片机横向切成20毫米，示踪剂饱和，并在共聚焦显微镜下用FRAP分析。连同示踪剂扩散的数学模型，在LCN中报告了4.0 +/- 2.0 cm2 / cm的有效扩散率和3.8 +/- 0.8的曲折度。曲折度与其他示踪剂类型测得的文献报道值一致。在没有周期性负荷之后，LCN中营养物恢复所需的时间是优化宇航员锻炼计划的重要参数。建立了在循环载荷下基于骨的初步扩散模型，该模型可用于在正常的物理刺激（即跑步，步行或站立）下估算LCN中的养分恢复时间。通过这项工作获得的参数（例如LCN尺寸，微结构组装和曲折度）使我们更加了解导致骨吸收的控制机制，并进一步发展了针对宇航员骨丢失的对策。

著录项

  • 作者

    Lin, Yekaterina Aleksandrovna.;

  • 作者单位

    Florida Institute of Technology.;

  • 授予单位 Florida Institute of Technology.;
  • 学科 Engineering Biomedical.;Engineering Chemical.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 139 p.
  • 总页数 139
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 农学（农艺学）;
  • 关键词

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