Automated Patterning of Bioactive Deposits on Advanced Biomaterials for Orthopaedic Applications

模板辅助电流体雾化(TAEA)喷雾图案化是一种新的、最近获得专利的方法，它允许在平板金属衬底上生产互锁的生物活性涂层。只需更改模板几何形状和尺寸即可改变图案几何形状。该过程基于在电场作用下流动的液体/悬浮液的稳定喷射，并在环境温度和压力下进行。通过施加电压、流速和流动喷嘴与衬底之间的工作(收集)距离，可以很容易地控制这一快速过程。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的互锁，这种生物活性图案化方法还允许涂层更好的附着力。此外，细胞实体对TAEA图案化生物活性沉积物的生物反应被证明是更有利的。考虑到通常只在金属基材上覆盖生物活性材料的常规等离子喷涂是在极高的温度(大约高出三个数量级)下进行的，并且很难控制，特别是在制备薄涂层时，这些因素非常有利。据业内消息人士称，等离子喷涂故障和停机时间造成的经济损失非常大，该行业正在寻求发现和实施替代方案。该项目旨在研究在曲面上使用TAEA生物活性图案，以使该工艺适用于临床植入物和植入物的制备，特别是作为工业项目合作伙伴业务的整形外科部门。这将确保该工艺可以在许多具有平面和曲面的真实植入物中实施。该项目致力于系统地研究生物活性纳米结构羟基磷灰石在弯曲的生物金属基材(如整形外科钛合金)上的喷涂，从特性良好的悬浮液和溶液开始--其粘度、表面张力和导电性会影响稳定的喷射。将制备不同直径的凸形和凹形钛合金基板，以及各种适合的弧形铜网模板，允许沉积不同的图案-衬里、六角形和正方形。平面和曲面TAEA之间的一个关键区别是在进行喷涂时会遇到不同的工作距离。这可能会导致涂层厚度不均匀和不均匀。为了抵消这一点，将建立一个自动输送系统，使基材能够保持和移入移出和/或旋转，这一战略的设计、施工和实施将是该项目的关键部分。表面涂层的微观结构将主要用电子显微镜进行研究。将使用划痕和纳米压痕技术来全面评估涂层的附着力和机械性能；评估附着力、硬度/划痕硬度，并生成载荷-位移数据，根据该数据可以估计弹性模数和屈服强度。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。涂层还将接受细胞培养测试，以确定生物活性。还将研究另外两个方面：第一，尝试使用一种改进的、更简单的在线热处理方法来加固衬底上的二氧化钛缓冲层。其次，我们将尝试做同轴(同流)TAEA，这将为复合聚合物-陶瓷生物活性沉积或掺杂抗生素和生长因子等其他成分的生物活性沉积铺平道路。

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.