Immobilizing Gradients of Neurotrophic Factors On An Aligned Biomaterial Scaffold

描述(申请人提供)：用于促进脊髓损伤(SCI)后神经元再生和指导轴突生长的生物材料是治疗这种毁灭性疾病的一个非常有前途的领域。特别是，一种模仿脊髓高度排列性质的材料将在引导轴突再生方面特别有效 受伤地点。许多研究表明，梯度生长因子NGF(对感觉神经元)和NT-3或BDNF(对运动神经元)在刺激和指导脊髓损伤后轴突再生方面都是有效的。拟议的工作概述了一种战略，即用这些生长因子的梯度来功能化高度排列的生物材料水凝胶，以便引导和 促进轴突再生。这种生物材料将由多肽两亲性(PA)分子组成，这些分子自组装成纳米纤维，并可用于形成可生物降解的水凝胶，纤维在宏观距离上排列。申请人的初步工作表明，无论大小和电荷如何，排列的PAGE可以有效地捕获一些蛋白质数周，包括溶菌酶(它的大小和电荷与大多数神经营养因子相同)。此外，通过使用简单的基于扩散的方法，可以沿着排列的轴线构建稳定的蛋白质梯度，该方法允许在生物材料凝胶化之前直接产生梯度。在这项工作的基础上，将研究凝胶保持和创造稳定生长因子梯度的能力。将详细研究这种凝胶在先前显示的促进生物活性的浓度范围内固定明确梯度的神经营养素的能力。在凝胶构建之后，神经元将被结合到材料中，以确定其在促进和指导轴突生长方面的有效性。背根神经节神经元(对NGF反应)和皮质脊髓运动神经元(对NT-3反应)都将被结合到带有适当神经营养因子梯度的PA凝胶中。将确定轴突的长度和数量，以及它们的方向性和生长速度，并将调整梯度参数以优化这些轴突生长的测量。如果成功，这项拟议的工作将创造出第一种生物兼容、可降解和易于注射的生物材料，这种材料在高度排列和细胞黏附的支架上具有生长因子的长期梯度。从长远来看，无论是急性或慢性脊髓损伤后，这种材料都可以在损伤部位注射和凝胶化，以刺激轴突生长和功能连接，逆转或至少减轻损伤的影响。

DESCRIPTION (provided by applicant): Biomaterials for promoting neuron regeneration and directing axon growth following spinal cord injury (SCI) represent a highly promising field for treatment of this devastating condition. In particular, a material that mimics the highly aligned nature of the spinal cord will be particularly effective at directing axon regeneration through the site of injury. A number of studies have shown the effectiveness of gradients of growth factors NGF (for sensory neurons) and NT-3 or BDNF (for motor neurons), at both stimulating and directing axon regrowth following SCI. The proposed work outlines a strategy for functionalizing a highly aligned biomaterial hydrogel with gradients of these growth factors in order to direct and promote axon regeneration. The biomaterial will be composed of peptide amphiphile (PA) molecules that self-assemble into nanofibers and can be used to form a biodegradable hydrogel with the fibers aligned over macroscopic distances. Preliminary work by the applicant has demonstrated that aligned PAgels can efficiently entrap a number of proteins for several weeks, regardless of size and charge, including lysozyme (which has the same size and charge as most neurotrophins). In addition, a stable gradient of protein can be constructed along the aligned axis by using a simple diffusion-based method that allows for direct generation of the gradient immediately prior to biomaterial gelation. Building on this work, the ability of the gel t retain and create a stable gradient of growth factors will be investigated. The gel's ability to immobilize well-defined gradients of neurotrophins, in concentration ranges previously shown to promote bioactivity, will be investigated in detail. Following construction of the gel, neurons wil be incorporated into the material in order to determine its effectiveness at promoting and directing axon growth. Both dorsal root ganglia neurons (which respond to NGF), and corticospinal motor neurons (which respond to NT-3) will be incorporated into PA gels bearing the appropriate neurotrophin gradients. The length and number of axons, as well as their directionality and rate of growth will be determined, and the gradient parameters will be tuned to optimize these measures of axon growth. If successful, the work proposed will create the first biocompatible, degradable, and easily injectable biomaterial that possesses a long-lived gradient of growth factors on a highly aligned and cell-adhesive scaffold. In the long term, this material could be injected and gelled in the injury site following either acute or chronic SCI in order to stimulate axon growth and functional connectivity, reversing or at least mitigating the effects of the injury.