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

生物医药工业中使用的非技术材料基于其结构和所需性能之间的关系找到用途。在聚合物材料(塑料)中，相关的性能通常包括强度、弹性、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，例如在植入物涂层和药物输送系统中。当这两种材料结合在一起时，应用范围就会扩大。要设计一种特定的产品，必须知道如何在这种组合材料(PEO-PCL)中开发特定的结构。这项研究旨在了解这些结构是如何发展的，以及如何控制所产生的属性的可变性。通过改变加工这些材料的溶液的温度和特性，能够获得所需的性能，包括但不限于强度、柔韧性和崩解率。聚合物特别适合于各种应用，因为它们的性质可能跨越很大范围，这取决于它们的化学和结构。例如，塑料可以是刚性和脆性的，也可以是柔性的和柔软的，这取决于它们的结构。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，本研究的结果还可应用于其他生物医学、商品或可持续塑料的结构和性能的研究。这项工作的第二个但同样重要的目标是培训学生在聚合物和材料科学的广泛学科中，并为他们在与技术相关的领域的职业生涯做好准备。技术摘要结构表征是预测或定制材料宏观性能的关键组成部分。在两嵌段共聚物中，这种结构涉及两个组分之间的相分离以及可能的一个或两个组分的结晶。聚环氧乙烷-嵌段-聚己内酯(PEO-b-PCL)共聚物在几个方面都是独一无二的。首先，它们都是可结晶的，具有相似的转变温度。其次，它们在生物医学领域都很流行，因为它们是生物相容的，而且PCL是可生物降解的。最后，通过将亲水的PEO和疏水的PCL结合成嵌段共聚物，该材料是两亲性的，允许疏水药物进入体内。正是这些特点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，能够控制强度、弹性和降解率以及其他性能非常重要。这些性质取决于材料从溶液中分离和结晶的方式。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，然后通过改变温度、浇注溶剂和相对分子质量等工艺条件来控制材料的结晶度。利用FTIR和DSC分析，将监测重量分数相近或重量分数相差较大的样品中PEO和PCL块的结晶情况，这些样品从不同的溶剂浇注和/或在不同的等温温度下热处理。由于转变温度相似，热力学和动力学方面的考虑可以更容易地通过这些参数的变化来处理。其目标是查明每种条件如何影响结晶机制、整体结晶度以及随后在生物医学领域感兴趣的性质。

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.