CAREER: Driving Hierarchical Collagen Fiber Maturation with Mechanobiology

这个学院早期职业发展（Career）奖将研究发育的机械力量如何引导细胞产生胶原纤维。具体来说，这项工作将研究如何使纤维具有与天然胶原纤维相同的组织和强度。胶原纤维是全身组织力量的主要来源，特别是在肌腱、韧带和半月板中。然而，这些纤维在受伤后不会再生。工程组织替代品不包括这些纤维，这使得修复选择不充分。天然胶原纤维主要在出生后形成，机械线索引导细胞将小原纤维组装成更大的纤维和束。这些机械线索对纤维的形成至关重要，但它们各自的作用尚不清楚。这项工作将探索发育缓慢拉伸和肌肉激发的循环负荷如何驱动细胞产生分层组织的胶原纤维。此外，这项研究将阐明控制纤维形成的机制。还将开发基于骨科和组织工程的多层次教育计划，旨在招募和留住STEM中代表性不足的少数民族和女性。具体来说，本科生将参与研究机会和跨学科课程，初中和高中学生将通过实践研究和国家生物力学日计划参与，当地初中和高中教师将接受基于探究的课程技术培训，以促进整个弗吉尼亚中部地区STEM的保留。本研究的具体目标是探索发育启发的机械负荷如何驱动韧带成纤维细胞产生具有天然组织和强度的工程韧带。核心假设是，拉伸应变反映了发育的缓慢伸长和快速的循环肌肉活动，将以大小和持续时间依赖的方式单独和协同地驱动天然样分层胶原组织和基质成熟，从而产生显着更强的功能替代品。使用一种新型的培养系统，该系统支持迄今为止最大、最有组织的分层纤维的细胞发育，本研究将研究1)模拟出生后生长速度的慢应变（0.1-1毫米/天）和2)模拟肌肉活动的快速间歇循环拉伸应变（1-2毫米/秒）如何单独和3)共同驱动分层胶原纤维成熟。具体来说，胶原组织在纤维，纤维和束水平，基质组成和组织力学性能将与每种类型的应变进行评估。缓慢的生长伸长和快速的循环肌肉活动发生在应变速率的数量级上，很可能对细胞产生非常不同的影响。了解这些负荷的不同影响不仅有助于设计功能替代，而且对于制定康复方案以恢复损伤后的功能也是不可或缺的。未来的工作可以利用这些结果来驱动损伤后胶原纤维的再生。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This Faculty Early Career Development (CAREER) award will examine how the mechanical forces of development guide cells to produce collagen fibers. Specifically, this work will study how fibers are made to have the same organization and strength as native collagen fibers. Collagen fibers are the primary source of strength in tissues throughout the body, particularly in tendons, ligaments, and menisci. However these fibers are not recreated after injury. Engineered tissue replacements do not include these fibers, which makes repair options inadequate. Native collagen fibers are primarily formed postnatally when mechanical cues guide cells to assemble small fibrils into larger fibers and fascicles. These mechanical cues are critical to fiber formation, however their individual contributions are unknown. This work will explore how developmental slow stretch and muscle-inspired cyclic loading drive cells to produce hierarchically organized collagen fibers. Additionally, this research will shed light on the mechanics that govern fiber formation. A multi-level educational program based in orthopaedics and tissue engineering will be developed as well, aimed at recruiting and retaining underrepresented minorities and women in STEM. Specifically, undergraduates will participate in research opportunities and interdisciplinary courses, middle and high school students will be engaged through hands-on research and National Biomechanics Day programming, and local middle and high school teachers will be trained in inquiry-based curriculum techniques to promote enhanced retention of STEM throughout the central Virginia area. The specific goal of this research is to explore how developmentally-inspired mechanical loads drive ligament fibroblasts to produce engineered ligament with native organization and strength. The central hypothesize is that tensile strains, which mirror developmental slow elongation and rapid cyclic muscle activity, will individually and synergistically drive native-like hierarchical collagen organization and matrix maturation, in a magnitude- and duration-dependent fashion, resulting in significantly stronger, functional replacements. Using a novel culture system, which supports cellular development of the largest, most organized hierarchical fibers to date, this research will investigate how 1) slow strains (0.1-1 mm/day) that mimic postnatal growth rates, and 2) rapid intermittent cyclic tensile strains (1-2 mm/sec) that mimic muscular activity, individually and 3) in combination drive hierarchical collagen fiber maturation. Specifically, collagen organization at the fibril, fiber, and fascicle level, matrix composition, and tissue mechanical properties will be evaluated with each type of strain. Slow growth elongation and rapid cyclic muscle activity occur at strain rates orders of magnitude apart, most likely producing very different effects on cells. Understanding the different effects of these loads will not only help to engineer functional replacements, but will be integral in developing rehabilitation protocols to restore function after injury. Future work can use these results to drive regeneration of collagen fibers after injury.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.