Interphases for Tougher Composites

描述(申请人提供)：流行病学研究表明，牙科复合修复体失败的主要原因有两个：一是聚合体收缩引起的反复腐烂；二是材料断裂。收缩问题主要是通过改变基质聚合物体系来解决的。断裂仍然是一个令人担忧的问题，因为目前可用于临床的牙科复合材料是脆性的，而且文献调查表明，断裂韧性值在过去20多年中没有显著变化(增加)；KIC保持在大约1.75 MPa.m1/2以下。脆性材料容易发生灾难性破坏，增加韧性仍然是材料研究的主要目标。对天然生物复合材料的研究已经确定了几种增韧策略，这些策略有可能显著延长复合材料的寿命，并说明了它们的用途，但在合成复合材料中没有得到充分利用。我们特别感兴趣的是珍珠层蛋白通过牺牲键机制表现出的能量吸收，这有助于珍珠层韧性。我们提出了以下具体目标：目标1：合成类似珍珠层蛋白的2-肽，它将共价连接无机和有机复合成分。目的2：研究球形颗粒/纤维复合模型复合材料的吸能界面增韧假说，即使复合材料的形态和排列不能完全模拟天然复合材料的结构。无论如何，对非珍珠质复合材料的大量研究表明，延性中间相在增韧方面是有效的。如果该策略被证明是成功的，该方案可以简单地通过改变2-肽链的活性En基团来应用于各种填料和基质聚合物组合物。 与公共健康相关：这项拟议的研究旨在开发更坚韧、更持久的复合材料，可用于修复缺失的牙齿或牙齿结构。这里将采用的策略是合成模仿珍珠层中发现的蛋白质的2-氨基酸聚合物，然后使用这些类肽聚合物作为偶联剂将基质聚合物粘合到增强填料颗粒上。人们期望这些2-肽具有珍珠层蛋白的能量吸收和增韧特性。这里提出的研究将检验这样一种假设，即更坚韧的复合材料将来自2-肽共价并弹性地横跨填料-基质界面，与硅烷和甲基丙烯酸端相连。将控制的变量包括链长和附着密度，以及填料形态；纤维增强将作为珍珠层堆积结构的近似值包括在内。如果这一假设被证明是正确的，这项研究将在偶联剂设计方面取得重大进展，该设计将适用于广泛的复合材料基质材料和填料组合物。

DESCRIPTION (provided by applicant): Epidemiological studies indicate that dental composite restorations fail for two main reasons: because of recurrent decay caused by polymerization shrinkage, and because of material fracture. The problem of shrinkage is being addressed primarily by changing the matrix polymer systems. Fracture continues to be a concern, as the dental composites currently available for clinical use are brittle, and literature surveys indicate that fracture toughness values have not changed (increased) significantly over the past 20+ years; KIc remains below approximately 1.75 MPa.m1/2. Brittle materials are prone to catastrophic failure, and increasing toughness remains a major goal of materials research. Studies of naturally-occurring bio-composites have identified several toughening strategies which have the potential to significantly increase composite lifetimes and also the indications for their use, but which are not adequately exploited in synthetic composites. Of particular interest to us is the energy absorption exhibited by nacre proteins by virtue of the sacrificial bond mechanism, which contributes to nacre toughness. We propose the following specific aims: Aim 1: Synthesize 2- peptides analogous to nacre proteins that will covalently bridge inorganic and organic composite components. Aim 2: Compound spherical particle- and fiber-reinforced model composites to test the hypothesis that energy absorbing interphases can toughen composites even if the filler morphology and arrangement does not exactly simulate natural composite architectures. In any case, numerous studies of non-nacreous composites have shown ductile interphases to be effective in toughening. If the strategy proves successful, the scheme can be applied to a variety of filler and matrix polymer compositions simply by changing the reactive en groups of the 2-peptide chain. PUBLIC HEALTH RELEVANCE: The proposed research is intended to lead to the development of tougher and longer-lasting composites that could be used to restore missing teeth or tooth structure. The strategies that will be pursued here is to synthesize 2-amino acid polymers that mimic proteins found in nacre, then use these peptide-like polymers as coupling agents to bond matrix polymers to reinforcing filler particles. The expectation is that these 2-peptides will possess the energy-absorbing and toughening properties of nacre proteins. Studies proposed here will test the hypothesis that tougher composites will derive from 2-peptides covalently and elastically spanning the filler-matrix interface, attached with silane and methacrylic ends. Variables that will be controlled include chain length and attachment density, and filler morphology; fiber reinforcement will be included as an approximation of the stacked architecture of nacre. If the hypothesis is proven true, this research will provide a significant advance in coupling agent design that will be applicable to a wide range of composite matrix materials and filler compositions.