Automated Patterning of Bioactive Deposits on Advanced Biomaterials for Orthopaedic Applications

模板辅助电流体动力雾化（TAEA）喷涂图案化是一种新颖的，最近获得专利的方法，它允许在平坦的金属基底上生产互锁的生物活性涂层。图案几何形状可以通过简单地改变模板几何形状和尺寸来改变。该方法基于经受电场的流动液体/悬浮液的稳定喷射，并且在环境温度和压力下进行。使用所施加的电压、流率和流动喷嘴与基板之间的工作（收集）距离来控制该快速过程是容易的。由于生物活性涂层与先前通过TAEA沉积的图案化缓冲层涂层互锁，因此这种生物活性图案化方法还可以使涂层具有更好的附着力。此外，细胞实体对TAEA图案化生物活性沉积物的生物反应已被证明更有利。当考虑到常规等离子体喷涂（其通常用于在金属基底上仅简单地覆盖涂覆生物活性材料）在极高温度（高约三个数量级）下进行并且难以控制（尤其是当涉及到薄涂层的制备时）的事实时，这些因素相比非常有利。据业内人士称，由于等离子喷涂涉及的故障和停机时间造成的经济损失非常严重，该行业正在寻求发现和实施替代方案。该项目旨在研究TAEA生物活性图案在曲面上的使用，以便该工艺是制备临床插入物和植入物的理想方法，特别是对于骨科行业，这是工业项目合作伙伴的业务。这将确保该过程可以在具有平坦和弯曲表面的许多真实的植入物中实施。该项目工作致力于系统地研究TAEA喷涂生物活性纳米结构羟基磷灰石到弯曲的生物相容性基材上，如骨科钛合金，从良好表征的悬浮液和溶液开始-粘度，表面张力和电导率影响稳定的喷射。将制备不同直径的凸形和凹形钛合金基底，以及各种合适的弯曲铜网模板，这些模板允许沉积不同的图案-内衬、六边形和正方形。平面TAEA和曲面TAEA之间的一个关键区别是喷涂时遇到的不同工作距离。这可能导致涂层厚度不均匀和不均匀。为了解决这一问题，将安装一个自动化输送系统，使基板能够被固定和移入移出和/或旋转，该策略的设计，建造和实施将是该项目的关键部分。本文主要用电子显微镜研究了所制备的曲面TAEA涂层的微观结构。涂层的附着力和机械性能将使用划痕和纳米压痕技术进行全面评估;评估附着力，硬度/划痕硬度和产生的载荷位移数据，从中估计弹性模量和屈服强度。还将尝试使用涂层上可能存在的任何压痕裂纹来计算断裂韧性和残余应力。还将对涂层进行细胞培养试验，以确定生物活性。本论文还将研究另外两个方面的问题：第一，尝试使用一种改进的、简单的在线热处理方法来强化基底上的二氧化钛缓冲层。其次，我们将尝试做同轴（共流）TAEA，这将为复合聚合物-陶瓷生物活性沉积物或掺杂有其他成分如抗生素和生长因子的生物活性沉积物铺平道路。

Template-assisted electrohydrodynamic atomisation (TAEA) spray-patterning is a novel, recently patented, method which allows the production of interlocked bioactive coatings on flat metallic substrates. The pattern geometry can be varied by simply changing the template geometry and dimensions. The process is based on stable jetting of a flowing liquid/suspension subjected to an electric field and is carried out at the ambient temperature and pressure. It is easy to control this rapid process using the applied voltage, the flow rate and the working (collection) distance between the flow nozzle and the substrate. Because of the interlocking of the bioactive coating with a patterned buffer layer coating, previously deposited via TAEA, this method of bioactive patterning also allows better adhesion of the coating. Also, the biological response to TAEA patterned bioactive deposits by cellular entities has proven to be more favourable. These factors compare very favourably when considering the fact that conventional plasma spraying, which is usually used to just plainly cover-coat bioactive materials on metallic substrates, is carried out at extremely high temperatures (about three orders of magnitude higher) and is difficult to control especially when it comes to the preparation of thin coatings. According to industry sources, economic loss due to malfunction and shutdown time involved with plasma spraying is very significant and the industry is looking to uncover and implement alternatives. This project proposed is concerned with investigating the use of TAEA bioactive patterning on curved surfaces in order that the process is ideal for the preparation of clinical inserts and implants, especially for the orthopaedics sector which is the business of the industrial project partner. This will ensure that the process can be implemented in many real implants which have both flat and curved surfaces. The project work endeavours to systematically investigate TAEA spraying of bioactive nanostructured hydroxyapatite onto curved biometallic substrates, such as orthopaedic titanium alloys, starting from well-characterised suspensions and solutions - the viscosity, surface tension and electrical conductivity of which affect stable jetting. Convex and concave titanium alloy substrates of different diameter will be prepared, together with a variety of fitting curved copper mesh-templates which allow different patterns to be deposited - lined, hexagonal and square. One key difference between flat and curved surface TAEA will be the varying working distance encountered as spraying takes place. This can result in uneven coating thicknesses and inhomogeneties. In order to counteract this, an automated conveyer system which will enable the substrate to be held and moved in and out and/or rotated will be put in place, and the design, construction and implementation of this strategy will be a key part of the project. The microstructures of the curved surface TAEA coatings produced will be studied mainly by electron microscopy. Adhesion and mechanical properties of the coatings will be fully assessed using scratch- and nano-indentation techniques; evaluating adhesion, hardness/scratch hardness and the generation of load-displacement data from which the elastic modulus and the yield strength will be estimated. An attempt will also be made to calculate fracture toughness and residual stresses using any indentation cracks which might be present on the coatings. The coatings will also be subjected to cell culture tests in order to ascertain bioactivity. Two other aspects will also be investigated: Firstly, using an improved and simpler on-line heat treatment to consolidate the titania buffer layer on the substrate will be tried out. Secondly, we shall attempt to do co-axial (co-flow) TAEA which will pave the way for composite polymer-ceramic bioactive deposits or bioactive deposits doped with other ingredients like antibiotics and growth factors.