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

非技术摘要中枢神经系统(CNS)，包括大脑和脊髓，是人体内信息传输的复杂高速公路。中枢神经系统对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会导致肿胀、炎症和疤痕形成，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种损伤，但不幸的是，结果仍然相当糟糕--部分原因是对损伤的反应复杂，而且难以准确地在需要的地方和时间提供药物。因此，迫切需要新的科学和工程方法来解决如何在受损的中枢神经系统内提高药物疗效的问题。在这个项目中，该团队正在建造一种新材料，这种材料是由药物分子串在一起的长链组成的，这种物质被称为“聚合物”。这些聚合药物可以作为结构性植入物，支持来自大脑和脊髓的神经元等细胞的生长，同时在植入点局部逐渐释放少量药物分子。具体地说，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，众所周知，它可以促进脊髓损伤后的再生效果。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：一种是微小纤维阵列，它模仿经常引导体内细胞生长的纤维蛋白；另一种是柔软的水凝胶材料，基本上就像药用的果冻。他们假设，将这两种含药材料结合到一个单一的杂交管道中，将有助于我们了解如何诱使受损中枢神经系统中的细胞避免疤痕和炎症，并促进健康组织的愈合和再生。从这项工作中收集到的信息有朝一日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。该小组还将通过参加路易斯·斯托克斯少数群体研究联盟(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，如创建和编辑维基百科页面，以及向开源期刊维基提交材料。结论中枢神经系统损伤会引起急性创伤、炎症和肿胀，继而发生复杂和慢性的继发性损伤，最终阻碍功能的完全恢复。主要的雌性激素17雌二醇(17β-estadiol，E2)已被证明能促进啮齿动物模型的功能恢复，但需要反复全身给药。该团队建议开发由17β-雌二醇(E2)的聚合前体药物组成的新型可植入生物材料，其配方为定向电纺微纤维嵌入可注射水凝胶基质中。这些物质通过水解在局部释放E2来缓慢降解。纤维由PRO-17β-雌二醇线性共聚物和柔性链连接单元制成。该水凝胶是由4臂星形聚乙二醇链末端含有疏水性的E2，在水溶液中与聚(β-环糊精)形成瞬时的非共价交联物。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剂量(纳摩尔)的E2，持续非常长的时间(几个月到几年)，并能够以最小侵入性的方式应用。定向微纤维被认为是模拟纤维蛋白的近似力学性质，并将促进机械接触指导线索，以控制在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软组织的硬度。这项研究项目的中心目标是将材料特性与细胞响应联系起来。该团队将合成一个具有系统调整化学结构的聚合E2变异体文库。疏水性和链的柔韧性会发生变化，这反过来会影响力学性能、表面拓扑结构以及降解和药物释放的速度和机制。然后将这些材料与星形胶质细胞和神经元孵育，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，以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智力优势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.