Towards Anti-Microbial Multifunctional Stainless Steel Surfaces: Active-Screen Plasma Surface Alloying with C, N, Ag and Cu

多年来，奥氏体不锈钢一直是医疗(如外科和牙科工具和医院工作表面)、家用(如厨房用具和食品加工设备)和一般工程的重要选择材料。然而，术后感染、患者在住院期间的交叉感染(例如MRSA)和与细菌(例如大肠杆菌)有关的食物中毒是越来越令人关注的领域。事实上，NHS没有走上实现MRSA目标的轨道，另一种细菌，艰难梭菌，在医院流行。银(Ag)和铜(Cu)在人类医疗保健和医学中的使用历史悠久，因为银/铜对细菌的毒性就像铅对人类的毒性一样。由于其广谱的抗菌活性和极低的人体毒性，银已被发现在医学上有多种应用，包括含银的PMMA骨水泥、含银的留置导管和含银的聚合物伤口敷料。虽然已经尝试用掺银聚合物涂层来覆盖不锈钢，但聚合物涂层的耐久性太差，不适合摩擦学应用，而且涂层不锈钢中银的高度不受控制的释放可能会潜在地导致细胞毒性。显然，从科学和技术的角度来看，开发具有高耐磨性、持久的抗菌效果和最小的银/铜浸出的多功能不锈钢表面是一项及时的任务。这种创新的表面可以通过开发一种新的表面工程技术来实现，该技术既基于最近发展起来的有源屏等离子体技术，又基于对亚稳态过饱和膨胀奥氏体即S相的详细的科学理解。有源屏等离子体技术将用于不锈钢中间隙元素(如C、N)和替代元素(如Ag、Cu)的合金化；而极硬的S相的形成将使替代合金元素如银和铜扩散到奥氏体不锈钢表面，形成可持续的低浓度的银/铜储存库，从而缓慢、可控和持续地释放银/铜，从而延长抗菌效果。本研究旨在开发具有增强的摩擦学、腐蚀和持久抗菌性能的新型不锈钢表面，从而延长产品寿命，预防医院感染和食源性疾病。为此，将用间隙元素C和N(形成坚硬耐用的C/N S相)和替代元素Ag和Cu(以赋予抗微生物效果)进行一系列活性屏蔽等离子表面合金化处理。将研究银/铜与S相之间的相互作用，以增进科学认识，并将进行系统的材料表征，以建立工艺开发所需的科学和技术数据库。

Austenitic stainless steel has been an important material of choice for many years for medical (such as surgical and dental tools and hospital work surfaces), domestic (such as kitchen-ware and food processing equipment) and general engineering. However, post operative infections, cross-infection of patients during hospitalisation (e.g. MRSA) and bacterial (e.g. E-coli) related food poisoning are areas of increasing concern. Indeed, the NHS is not on track to meet its MRSA target and another bug, Clostridium difficile, is endemic in hospitals. Silver (Ag) and Copper (Cu) have a long history of use in human healthcare and medicine because Ag/Cu is poisonous to bacteria just as lead is to human beings. Due to its desirable combination of broad-spectrum antimicrobial activities and remarkably low human toxicity, Ag has been found several medical applications including Ag-containing PMMA bone cement, Ag-implanted indwelling catheters and Ag-impregnated polymer wound dressings. Although attempts have been made to coat stainless steels with a Ag-doped polymer coating, the durability of the polymer coating is too poor for tribological applications and the high uncontrolled release of silver from the coated stainless steel may potentially cause cytotoxicity. Clearly, it is a timely task from both a scientific and a technological view-point to develop multi-functional stainless steel surfaces with high wear resistance, long-lasting antimicrobial effects and minimal leaching of Ag/Cu. Such innovative surfaces could be achieved by developing a novel surface engineering technology based both on recently developed active screen plasma technology and a detailed scientific understanding of metastable supersaturated expanded austenite, i.e. S-phase. The active screen plasma technology will be used to alloy stainless steels with both interstitial (e.g. C and N) and substitutional (e.g. Ag and CU) elements; and the formation of a very hard S-phase with an extremely expanded lattice would make it possible for such substitutional alloying elements as Ag and Cu to diffuse into austenitic stainless steels surfaces to form a sustainable low concentration Ag/Cu reservoir for slow, controlled and continual release of Ag/Cu for prolonged antimicrobial effect.The proposed research seeks to develop novel stainless steels surfaces with enhanced combined tribological, corrosion and long-lasting anti-microbial properties, thus extending product lifetime and preventing hospital-acquired infection and food-borne diseases. To this end, a series of active screen plasma surface alloying treatments will be conducted with both interstitial elements C and N (to form hard and durable C/N S-phase) and substitutional elements Ag and Cu (to confer the anti-microbial effect). The interaction between Ag/Cu and the S-phase will be investigated to advance scientific understanding, and systematic materials characterisation will be conducted to build up the necessary scientific and technical database for process development.