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

中枢神经系统（CNS），包括大脑和脊髓，是人体内复杂的信息传输高速公路。中枢神经系统对于生命的许多不同过程至关重要，但它也是一种非常脆弱的软组织。 脑或脊柱的创伤性损伤可导致肿胀、炎症和瘢痕形成，几乎所有患者都无法完全恢复功能。许多药物可用于治疗此类损伤，但不幸的是，结果仍然相当差-部分原因是对损伤的反应复杂，并且难以在需要的地方和时间精确提供药物。因此，迫切需要新的科学和工程方法来找出如何提高受损CNS内的药物疗效。在这个项目中，该团队正在构建由药物分子组成的新材料，这些药物分子以长链形式连接在一起，称为“聚合物”。这些聚合的药物可以作为结构植入物，用于支持来自脑和脊髓的细胞如神经元的生长，同时在植入部位局部逐渐释放少量药物分子。具体来说，他们正在使用最近发明的雌激素聚合物，雌激素是主要的女性性激素，已知它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如何对它们做出反应之间的基本科学关系，包括神经元和其他帮助控制神经元行为的细胞。将研究两种材料配方：一种是微观纤维阵列，它模仿通常引导体内细胞生长的纤维状蛋白质，另一种是柔软的水凝胶材料，它基本上就像果冻的药物等价物。他们假设，将这两种含药物的材料结合在一起成为一个单一的混合管道将有助于我们了解如何诱导受损CNS中的细胞，以避免疤痕和炎症，并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。该团队还将通过参与路易斯·斯托克斯少数民族研究联盟（LSAMP）和国家化学日，扩大对STEM外联活动的参与。该团队将让本科生参与科学写作，例如创建和编辑维基百科页面以及向开源期刊Wiki提交材料。J. Sci.Technical Abstract中枢神经系统的挫伤引起急性创伤、炎症和肿胀，随后是复杂和慢性的继发性损伤级联，其最终阻止完全功能恢复。主要的雌性性激素17β-雌二醇（E2）已被证明可促进啮齿动物模型的功能恢复，但需要重复全身给药。该团队提出开发由17β-雌二醇（E2）的聚合前药组成的新型可植入生物材料，配制为嵌入可注射水凝胶基质中的定向电纺微纤维。这些材料通过水解缓慢降解，局部释放E2。该纤维由前-17 β-雌二醇和柔性链连接单元的线性共聚物制成。该水凝胶由具有疏水E2末端单元的4-臂星星聚乙二醇形成，其在水溶液中与聚（β-环糊精）形成瞬时非共价交联。在化学上，这些聚合的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，持续非常长的时间（数月至数年），并且能够以微创方式应用。定向的微纤维被提出来模仿纤维状蛋白的近似机械性质，并且将促进用于控制体外星形胶质细胞和神经元中的形态、表型和蛋白表达的机械接触引导线索。 纤维周围的可注射水凝胶基质旨在机械匹配中枢神经系统中非常软的组织的硬度。该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整化学结构的聚合E2变体库。疏水性和链柔性将变化，这反过来将影响机械性能、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孵育，以评估其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NSF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.