RUI: Crystallization of Biologically-Relevant Poly(ethylene oxide)-b-poly(epsilon-caprolactone) Copolymers During Film Preparation

【非技术】生物医学工业中使用的材料根据其结构与所需性能之间的关系找到用途。在高分子材料（塑料）中，相关性能通常包括强度、柔韧性、在体内分解的能力等。两种这样的聚合物材料，PEO和PCL，已经在生物医学领域找到了各种用途，例如植入物涂层和药物输送系统。当这两种材料结合使用时，应用范围增加了。要设计特定的产品，必须知道如何在这种组合材料（PEO-PCL）中开发特定的结构。这项研究的目的是了解这些结构是如何发展的，以及如何控制由此产生的性质的可变性。通过改变处理这些材料的溶液的温度和特性，人们能够获得所需的性能，包括但不限于强度、柔韧性和分解率。聚合物是唯一适合于各种应用的，因为它们的性质可以跨越很大的范围，这取决于它们的化学和结构。例如，塑料根据其结构可以是刚性和脆性的，也可以是柔性和柔软的。了解PEO-PCL结构的发展应该会增加这种廉价、广泛流行和坚固的材料的可能用途。此外，本研究结果可应用于其他生物医学、商品或可持续塑料的结构和性能研究。第二，但同样重要的是，这项工作的目标是培养学生在高分子和材料科学的广泛学科，并为他们在技术相关领域的职业生涯做好准备。技术摘要结构表征是预测或调整材料宏观性能的关键组成部分。在二嵌段共聚物中，结构涉及两种组分之间的相分离以及一种或两种组分可能的结晶。聚（环氧乙烷）-嵌段聚（己内酯）（PEO-b-PCL）共聚物在几个方面是独特的。首先，它们都可以在相似的转变温度下结晶。其次，它们在生物医学领域都很流行，因为它们具有生物相容性，而且PCL是可生物降解的。最后，通过将亲水性PEO和疏水性PCL结合成嵌段共聚物，材料是两亲性的，允许将疏水药物运输到体内。正是这些特性使这些材料在植入物涂层和药物输送系统中具有吸引力。对于这些应用，控制强度、弹性和降解率以及其他性能的能力是很重要的。这些性质取决于材料如何从溶液中相分离和结晶。由于相分离是由结晶驱动的，因此本研究的重点是了解结晶机理，然后通过改变工艺条件（如温度、铸造溶剂、分子量）来控制材料的结晶度。使用FTIR和DSC分析，将监测由不同溶剂铸造和/或在不同等温温度下退火的具有相似重量分数或很大重量分数的样品中的PEO和PCL块的结晶情况。因为转变温度是相似的，热力学和动力学的考虑可以更容易地通过改变这些参数来操纵。目标是确定每种条件如何影响结晶机制，整体结晶度以及生物医学领域感兴趣的后续特性。

NON-TECHNICAL ABSTRACTMaterials used in the biomedical industry find utility based on the relationship between their structure and the properties needed. Among polymer materials (plastics) the relevant properties often include strength, flexibility, the ability to break down in the body, etc. Two such polymer materials, PEO and PCL, already find a variety of uses in the biomedical field, e.g. in implant coatings and medication-delivery systems. The range of applications increases when these two materials are combined. To engineer a specific product, one must know how to develop specific structures in this combined material (PEO-PCL). This research aims to understand how these structures develop and how to control the variability of the resultant properties. By varying the temperature and characteristics of the solution from which these materials are processed, one is able to obtain desired properties including, but not limited to, strength, flexibility, and breakdown rate. Polymers are uniquely suited for a variety of applications because their properties may span a large range depending on their chemistry and structure. For example, plastics can be rigid and brittle or flexible and soft depending on their structure. Understanding the development of PEO-PCL structures should lead to an increase in possible uses for this inexpensive, widely prevalent, and robust material. Moreover, the results of this study could be applied to the study of the structures and properties of other biomedical, commodity, or sustainable plastics. A second, but no less important, goal of this work is to train students in the broad disciplines of polymer and materials sciences and prepare them for careers in technology-related areas.TECHNICAL ABSTRACTStructural characterization is a critical component in predicting or tailoring the macroscopic properties of a material. In diblock copolymers, the structure involves phase separation between the two components and possible crystallization of one or both of the components. Poly(ethylene oxide)-block-poly(caprolactone) (PEO-b-PCL) copolymers are unique in several ways. First, they are both crystallizable with similar transition temperatures. Second, they are both prevalent in the biomedical field since they are biocompatible and since PCL is biodegradable. Lastly, by combining hydrophilic PEO and hydrophobic PCL into a block copolymer, the material is amphiphilic allowing for transport of hydrophobic drugs into the body. It is all of these traits that make these materials attractive for use in implant coatings and drug delivery systems. For these applications, the ability to manipulate the strength, elasticity, and degradation rate, amongst other properties, is important. These properties depend on how the material phase-separates and crystallizes from solution. Since phase separation is driven by crystallization, the focus of this research is to understand the crystallization mechanism and then control the crystallinity of the material by changing processing conditions such as temperature, casting solvent, and molecular weight. Using FTIR and DSC analyses, the crystallization of PEO and PCL blocks in samples with similar weight fractions or largely different weight fractions, cast from different solvents and/or annealed at different isothermal temperatures, will be monitored. Because the transition temperatures are similar, thermodynamic and kinetic considerations can be manipulated more easily by changes in these parameters. The goal is to pinpoint how each condition influences the crystallization mechanism, the overall crystallinity, and subsequent properties of interest in the biomedical field.