Exploring the biomedical significance of time-dependent design enabled by additive manufacturing

增材制造（AM）具有在创建几何形状的同时创建组件材料的独特能力，这是传统减材制造技术无法实现的。因此，这为改变材料的生产方式提供了机会，因此在构建组件时改变了固有的材料特性。这种在制造过程中的时间依赖性设计，也称为增材制造的时间设计（TDfAM），有时也称为4D打印，有可能为设计师提供新的设计自由度;能够在同质部件中引入材料或表面特性的异质性。AM还可以制造否则无法制造的几何形状，例如：晶格。这是AM能够通过使用不同的晶格拓扑来为设计者提供对材料特性的增加的控制的另一种方式。晶格晶胞拓扑结构不仅影响诸如相对密度和整体刚度的特性，而且不同晶格拓扑结构的规格提供了对表面积与体积比的增加的控制，如果考虑退化，这是一个重要特性。因此，将不同的晶格设计与生物可吸收材料相结合，可以在降解过程中随着时间的推移导致刚度的不同变化，从而导致在使用过程中随时间而变化的设计。这种类型的附加控制和随时间而变化的特性可以在需要随时间而变化的领域中看到许多应用，但手动驱动这种变化是困难的或不可能的，例如在生物医学植入物中。在骨折固定的情况下，最佳刚度要求随时间而变化：骨折后立即需要稳定性，但大约6周后，骨折块间的运动决定了愈合的效果。在这种情况下，改变固定的顺应性可以通过使骨折部位周围随时间变化的微动来提供增强的愈合。使用当前的方法，不可能在不需要多次手术的情况下满足这种随着时间的推移而变化和矛盾的设计要求，这将比其价值更具有创伤性。设计一个固定解决方案与定制的时间依赖性的刚度，满足不同的刚度requires.In该项目中，这是通过设计和建模的晶格结构增材制造的生物可吸收材料，如锌，专门着眼于骨折固定在胫骨高位截骨术的应用作为一个案例研究。该项目通过实验研究了TDfAM（构建过程中工艺参数的变化）可以为生物医学背景下的设计师提供的对材料和表面特性的潜在额外控制;还研究了生物可吸收晶格作为车辆，通过使用设计，有限元建模和计算验证，实现骨折固定内刚度的时间依赖性设计。

Additive manufacture (AM) has the unique ability of creating the component material simultaneously with the geometry, something which is not possible with traditional subtractive manufacturing techniques. As such, this opens up the opportunity to vary how the material is produced, and therefore the intrinsic material properties, as the component is being built. This form of time-dependent design during manufacture, otherwise known as Temporal Design for Additive Manufacture (TDfAM) or sometimes called 4D printing, has the potential to afford a designer a new dimension of design freedom; being able to introduce heterogeneity of material or surface properties within a homogenous part.AM also enables the manufacture of geometries that would otherwise be impossible to manufacture, for example: lattices. This is another way in which AM has the ability to afford a designer increased control over material properties, through the use of different lattice topologies. Not only does a lattice unit cell topology influence characteristics such as relative density and overall stiffness, but specification of different lattice topologies gives increased control over surface area to volume ratio, an important characteristic if considering degradation. As such, combining different lattice designs with bioresorbable materials can result in different variations in stiffness over time during degradation, resulting in a design that is time dependent during service.This type of additional control and variation in properties over time could see many applications in areas where a time dependent response is required but manually actuating such a variation is difficult or impossible, such as in biomedical implants. In the case of fracture fixation, the optimum stiffness requirement varies over time: stability is required immediately after fracture but after approximately 6 weeks, interfragmentary motion governs the efficacy of healing. In this instance, changing the compliance of the fixation could offer enhanced healing, by enabling micromotion around the fracture site which changes over time. Using current methods, it is not possible to satisfy this changing and contradictory design requirement over time without the need for multiple surgeries, which would be more traumatic than its worth. Designing a fixation solution with tailored time-dependent stiffness that satisfies the varying stiffness requirements would solve these issues.In this project this is achieved through the design and modelling of lattice structures additively manufactured from bioresorbable materials, such as zinc, looking specifically at the application of fracture fixation in a high tibial osteotomy as a case study. This project experimentally investigates the potential additional control over material and surface characteristics that TDfAM (variation of process parameters during the build) can afford a designer in a biomedical context; and also investigates bioresorbable lattices as a vehicle to enable time dependent design of stiffness within fracture fixation, through the use of design, finite element modelling and computational validation.