Polymerized Estrogen Microfibers in Injectable Hydrogels for Astrocyte-Mediated Neurite Guidance and Protection

摘要包括脑和脊髓在内的中枢神经系统（CNS）是人体内复杂的信息传输高速公路。中枢神经系统在生命的许多不同过程中起着至关重要的作用，但它也是一个非常脆弱的软组织。脑或脊柱的创伤性损伤可导致肿胀、炎症和疤痕，几乎所有患者都无法完全恢复功能。有许多药物可用于治疗这类损伤，但不幸的是，结果仍然相当糟糕——部分原因是对损伤的反应很复杂，而且很难准确地在需要的时间和地点提供药物。因此，迫切需要新的科学和工程方法来研究如何提高受损中枢神经系统的药物疗效。在这个项目中，该团队正在构建一种新材料，这种材料是由药物分子串在一起形成长长的链，称为“聚合物”。这些聚合药物可以作为一种结构植入物，支持大脑和脊髓神经元等细胞的生长，同时在植入部位局部逐渐释放少量药物分子。具体来说，他们使用了最近发明的雌激素聚合物，雌激素是一种主要的女性性激素，已知可以促进脊髓损伤后的再生作用。该团队将研究这些材料的结构与中枢神经系统中至关重要的细胞（包括神经元和其他帮助控制神经元行为的细胞）对它们的反应之间的基本科学关系。研究人员将研究两种材料配方：一种是一组微观纤维，它模仿了经常引导体内细胞生长的纤维蛋白；另一种是一种柔软的水凝胶材料，它基本上就像医药上的凝胶。他们假设，将这两种含药物的材料结合在一起，形成一个单一的混合管道，将有助于我们了解如何诱导受损中枢神经系统中的细胞，以避免疤痕和炎症，促进健康组织的愈合和再生。从这项工作中收集的信息有一天可能会为脊髓损伤和创伤性脑损伤的新治疗方法铺平道路。该团队还将通过参加路易斯·斯托克斯少数民族研究联盟（LSAMP）和国家化学日，扩大STEM外展活动的参与。该团队将让本科生参与科学写作，比如创建和编辑维基百科页面，以及向开源期刊Wiki提交内容。j .科学。技术摘要：中枢神经系统的挫伤引起急性创伤、炎症和肿胀，随后是复杂的慢性继发性损伤级联，最终阻碍了功能的完全恢复。雌性主要性激素17β-雌二醇（E2）在啮齿类动物模型中已被证明可以促进功能恢复，但需要反复全身给药。该团队建议开发新型植入式生物材料，该材料由聚合的17β-雌二醇（E2）前体药物组成，其配方为定向电纺丝微纤维，嵌入可注射水凝胶基质中。这些材料通过水解缓慢降解，局部释放E2。纤维是由原-17β-雌二醇的线性共聚物和柔性链连接单元制成的。该水凝胶由4臂星形聚乙二醇与末端憎水的E2形成，在水溶液中与聚（β-环糊精）形成瞬态非共价交联。化学上，这些聚合雌激素支架通过水解缓慢降解，在支架部位局部释放低（纳摩尔）剂量的E2，持续极长时间（数月至数年），并且能够以微创方式应用。定向微纤维被提出模拟纤维蛋白的近似力学特性，并将促进机械接触引导线索，以控制体外星形胶质细胞和神经元的形态，表型和蛋白质表达。纤维周围的可注射水凝胶基质旨在机械地匹配中枢神经系统中非常柔软的组织的硬度。本研究项目的中心目标是将材料特性与细胞反应联系起来。该团队将合成一个具有系统调谐化学结构的聚合E2变体库。疏水性和链柔韧性会发生变化，进而影响其力学性能、表面拓扑结构以及降解和药物释放的速率和机制。然后将这些材料与星形胶质细胞和神经元一起培养，以评估它们的特性对观察到的细胞行为的影响。最终目标是了解如何协调细胞对生物材料的反应，从而促进再生表型，并可能提高功能恢复的可能性。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。

Non-Technical AbstractThe central nervous system (CNS), including the brain and the spinal cord, is a complex superhighway of information transport within the human body. The CNS is vital to conducting the many varied processes of life, but it is also a remarkably fragile, soft tissue. Traumatic injuries to the brain or spine can lead to swelling, inflammation, and scarring that prevent full functional recovery in nearly all patients. Many drugs are available to treat such injuries, but unfortunately the outcomes are still quite poor – in part because of the complexity of the response to the injury and difficulty in delivering the medicine precisely where and when it is needed. There is hence an urgent impetus for novel science and engineering approaches to figure out how to improve drug efficacy within the injured CNS. In this project, the team are building new materials that are composed of drug molecules strung together in long chains called “polymers”. These polymerized drugs can act as a structural implant for supporting the growth of cells such as neurons from the brain and spinal cord, while gradually releasing small amounts of drug molecules locally at the site of implantation. Specifically, they are using recently invented polymers of estrogen, the major female sex hormone, which is known to promote regenerative effects in the spinal cord post injury. The team will examine the fundamental scientific relationships between the structure of these materials and how critically important cells from the central nervous system respond to them, including neurons and other cells that assist in controlling neuron behavior. Two material formulations will be studied: one is an array of microscopic fibers, which mimics the fibrillar proteins that often guide cell growth in the body and the other is a soft hydrogel material, which is basically like the pharmaceutical equivalent of jello. They hypothesized that combining these two drug-containing materials together into a single hybrid conduit will help us understand how to coax cells in the injured CNS to avoid scarring and inflammation and promote healing and regeneration of healthy tissue. The information gleaned from this work could someday pave the way for new therapeutic approaches to spinal cord injury and traumatic brain injury. The team will also broaden participation in STEM outreach activities through participation with the Louis Stokes Alliances for Minority Research (LSAMP) and the National Chemistry Day. The team will engage undergraduates in science writing such as creating and editing Wikipedia pages and submissions to the open source journal, Wiki. J. Sci.Technical Abstract Contusive injuries to the central nervous system provoke acute trauma, inflammation, and swelling, followed by a complex and chronic secondary injury cascade which ultimately prevents full functional recovery. The major female sex hormone 17β-estradiol (E2) has been shown to promote functional recovery in rodent models, but requires repeated systemic administration. The team proposes to develop novel implantable biomaterials composed of polymerized pro-drugs of 17β-estradiol (E2), formulated as oriented electrospun microfibers embedded in a matrix of injectable hydrogel. These materials degrade slowly by hydrolysis to release E2 locally. The fibers are made from a linear copolymer of pro-17β-estradiol and a flexible chain linker unit. The hydrogel is formed from 4-arm star polyethylene glycol with terminal units of hydrophobic E2, which forms transient non-covalent crosslinks with poly(β-cyclodextrin) in aqueous solution. Chemically, these polymerized estrogen scaffolds slowly degrade by hydrolysis to release low (nanomolar) doses of E2 locally at the site of the scaffold, sustained for exceptionally long periods of time (months to years), and with the ability to be applied in a minimally invasive manner. The oriented microfibers are proposed to mimic the approximate mechanical properties of fibrillar proteins and will promote mechanical contact guidance cues for controlling the morphology, phenotype, and protein expression in astrocytes and neurons in vitro. The injectable hydrogel matrix surrounding the fibers is intended to mechanically match the stiffness of very soft tissue in the central nervous system. The central goal of this research project is to relate the material properties to the cell response. The team will synthesize a library of polymerized E2 variants with systematically tuned chemical structures. The hydrophobicity and chain flexibility will be varied, which in turn will influence mechanical properties, surface topology and the rate and mechanism of degradation and drug release. These materials will then be incubated with astrocytes and neurons to assess the impact of their properties on the cell behavior observed. The ultimate goal is to understand how to orchestrate cell response to biomaterials that can promote regenerative phenotypes and possibly improve the likelihood of functional recovery.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.