Surface chemical reactivity of diamond-like carbon films

由于其优异的性能，类金刚石（DLC）薄膜在机械工程和生物材料等各个领域都有广泛的应用。世界范围内对DLC薄膜的研究活动已经使人们对其整体微观结构和性能，以及表面自由能、润湿和粘附性能等物理表面特性有了深刻的认识和理解。另一方面，关于DLC薄膜表面的化学性质，特别是它们的化学反应性的知识还很不发达。在文献报道的一些研究中，XPS分析与标准化学衍生结合使用，以获得有关环境条件下老化过程中表面化学的时间发展的信息，通常导致氧摄取（自氧化）和含氧亲电官能团的形成。然而，从这些报道中，我们无法得出DLC表面与有机分子，特别是携带亲核官能团的生物分子在光滑条件下发生反应的能力。因此，该提案的主要目标是实质性地推进表面化学的知识和理解，特别是老化的无氢和氢化DLC膜，a-C和a-C:H。浸没- irras （ImIRRAS）和XPS的强大组合，加上非标准化学衍生化技术，将提供迄今为止尚未获得的有关自氧化机制本身以及新出现的反应基团的信息。这些官能团在DLC表面与生物分子（主要是蛋白质）相互作用的生物医学应用中具有重要意义。由于反应性官能团的尺寸通常为3 - 10nm，因此它们的密度非常小，低至0.01 nm2，就足以结合单层。初步研究表明，imiras可以量化这种低密度。这也适用于在氧化过程中假定为中心中间体的羟基。该项目的结果将具有根本性的兴趣，填补了DLC薄膜知识的空白。了解DLC薄膜的老化对于更全面地理解其物理化学表面性质是很重要的。然而，可以推测，DLC的表面官能团也因其作为血液相容涂层的优异性能而发挥了重要作用。因此，本项目将探索表面化学反应性与允许血液相容性第一等级的几个特性之间的关系：使用原位FTIR-ATR光谱，a- c:H或a- c上反应基团的存在将与表面吸附或固定蛋白质的能力相关，这些蛋白质对表面的血液相容性起主要作用。这些研究将通过血小板沉积调查和凝血试验加以补充。

Owing to their outstanding properties, diamond-like carbon (DLC) films have found applications in fields as diverse as mechanical engineering on the one hand and biomaterials on the other. Worldwide research activities on DLC films have resulted in profound knowledge and understanding of its bulk microstructure and properties, as well as physical surface characteristics such as surface free energy, wetting and adhesion properties. Knowledge about the chemical nature of DLC film surfaces and especially about their chemical reactivity, on the other hand, is very poorly developed. In a few studies reported in literature, XPS analyses were used in conjunction with standard chemical derivatization in order to gain information about the temporal development of surface chemistry during aging under ambient conditions, generally resulting in oxygen uptake (autoxidation) and formation of oxygen-containing electrophilic functional groups. From these reports, however, no conclusions can be drawn about the ability of DLC surfaces to react under smooth conditions with organic molecules, especially biomolecules carrying nucleophilic functional groups. For this reason the main objective of the proposal is to advance substantially the knowledge and understanding of surface chemistry in general and reactivity specifically on aging hydrogen-free and hydrogenated DLC films, a-C and a-C:H, respectively. A powerful combination of immersion-IRRAS (ImIRRAS) and XPS, together with non-standard chemical derivatization techniques, will provide so far unavailable information regarding the autoxidation mechanism itself as well as the emerging reactive groups. These functional groups are of importance in biomedical applications where DLC surfaces interact with biomolecules, primarily proteins. Due to their size of typically 3 to 10 nm, very small densities of reactive functional groups, down to 0.01 nm2, may suffice to bind a monolayer. Preliminary studies have shown that ImIRRAS can quantify such low densities. This holds also true for hydroperoxy groups, presumed central intermediates in the oxidation process. Results of the project will be of fundamental interest, filling a gap in the knowledge about DLC films. Understanding the aging of DLC films is important for a more general comprehension of their physico-chemical surface properties. Presumably, however, surface functional groups of DLC also play an important role for its outstanding properties as a hemocompatible coating. Therefore the relation between surface chemical reactivity and several properties allowing a first rating of blood compatibility will be explored in this project: Using FTIR-ATR spectroscopy in situ, the presence of reactive groups on a-C:H or a-C will be correlated with the ability of the surfaces to adsorb or immobilize proteins playing a major role for the hemocompatibility of a surface. These studies will be complemented by investigations of platelet deposition and by blood clotting tests.