Functionally graded materials (FGMs) are desirable in a variety of applications. Due to a lack of understanding of design and manufacturing methods, it remains a challenge to engineer FGMs. Gradient patterns and performance shown in biological materials present motifs for designing FGMs. The bottom-up characteristic of additive manufacturing (AM) enables unparalleled control over material and structure, making AM a perfect candidate for FGMs. The integration of the two provides an unprecedented opportunity for developing next generation advanced materials. In this review, we firstly detail the biological gradient materials/structures in terms of their functions. Subsequently, the art-of-the-state AM methods for fabricating FGMs are reviewed, with a focus on the technology types of AM that can prepare biomimetic material and structural FGMs, especially emphasizing the multiform gradients induced by processing parameters. Then, the performance and application cases of FGMs created by AM are summarized. Finally, an outlook for further developments of AM technologies towards FGMs is provided. 

Graded biological materials and additive manufacturing technologies for producing bioinspired graded materials: An overview

Enhancement of wastewater treatment performance using 3D printed structures: A major focus on material composition, performance, challenges, and sustainable assessment.

This article investigates the state-of-the-art of polyjet 3D printing of polymers and multi-material structures, with an emphasis on its applications in a range of industrial domains, including aerospace, architecture, toy fabrication, and medical field. While significant research and development in the field of additively manufactured (AM) multi-material and reinforced composite structures have been carried out during the previous decade, the need of the hour is to utilize a single manufacturing platform which would not only help to govern the composition, shape, and characteristics of multi-material 3D printed objects at the microscopic level but would also help industries to replace the conventional AM manufacturing methods and optimize their mechanical performance. Significant advancements in polyjet 3D printing of fiber-reinforced and functionally graded structures with numerous modifications in material composition are reviewed, which may revolutionize the industrial sector. Numerous polyjet printing parameters such as accuracy, printing speed, photo-curing effect, build orientation, layer thickness, print angles, and post-processing are comprehensively discussed, and best outputs to optimize the mechanical performance and enhance the accuracy of the polyjet 3D printing products are highlighted. FEA (finite element analysis) models and analytical relations for multi-material 3D printed structures are presented to predict and enhance the overall performance of polyjet fabrication. Along with the benefits of polyjet manufacturing, a few of the limitations and challenges of polyjet AM are addressed which would benefit the reader to conduct further research in this field and enhance fabrication quality significantly. Vivid comparisons with other multi-material AM fabrication techniques such as FDM, SLA, and SLS with their brief discussion, merits, and demerits are done.

A review on polyjet 3D printing of polymers and multi-material structures

Biodegradable polymer vascular stents (BPVSs) have been widely used in percutaneous coronary interventions for the treatment of coronary artery diseases. The development of BPVSs is an integrated process that combines material design/selection, manufacturing, and performance characterization. Three-dimensional (3D) printing technology is a powerful tool for polymer stent fabrication. Current review studies have focused primarily on the material and structural design of polymer stents but have failed to comprehensively discuss different 3D printing approaches and stent characterization techniques. In this paper, we address these shortcomings by discussing 3D printing methods and their application in BPVSs. First, some commonly used 3D printing methods (including material extrusion, vat polymerization, and powder bed fusion) and potential 3D printing strategies (including material jetting and binder jetting) for fabricating BPVSs are discussed; furthermore, the main post-treatments are summarized. Then, techniques to characterize the morphology, mechanical properties, and biological properties of the printed BPVSs are introduced. Subsequently, representative commercial BPVSs and lab-grade BPVSs are compared. Finally, based on the limitations of stent printing and characterization processes, future perspectives are proposed, which may help develop new techniques to fabricate more customized stents and accurately evaluate their performance. 

3D Printing of Biodegradable Polymer Vascular Stents: A Review

Additive manufacturing is defined as a process based on the superposition of layers of materials in order to obtain 3D parts; however, the process does not allow achieve the adequate and necessary surface finishing. In addition, with the development of new materials with superior properties, some of them acquire high hardness and strength, consequently decreasing their ability to be machined. To overcome this shortcoming, a new technology assembling additive and subtractive processes, was developed and implemented. In this process, the additive methods are integrated into a single machine with subtractive processes, often called hybrid manufacturing. The additive manufacturing process is used to produce the part with high efficiency and flexibility, whilst machining is then triggered to give a good surface finishing and dimensional accuracy. With this, and without the need to transport the part from one machine to another, the manufacturing time of the part is reduced, as well as the production costs, since the waste of material is minimized, with the additive–subtractive integration. This work aimed to carry out an extensive literature review regarding additive manufacturing methods, such as binder blasting, directed energy deposition, material extrusion, material jetting, powder bed fusion, sheet laminating and vat polymerization, as well as machining processes, studying the additive-subtractive integration, in order to analyze recent developments in this area, the techniques used, and the results obtained. To perform this review, ScienceDirect, Web of Knowledge and Google Scholar were used as the main source of information because they are powerful search engines in science information. Specialized books have been also used, as well as several websites. The main keywords used in searching information were: “CNC machining”, “hybrid machining”, “hybrid manufacturing”, “additive manufacturing”, “high-speed machining” and “post-processing”. The conjunction of these keywords was crucial to filter the huge information currently available about additive manufacturing. The search was mainly focused on publications of the current century. The work intends to provide structured information on the research carried out about each one of the two considered processes (additive manufacturing and machining), and on how these developments can be taken into consideration in studies about hybrid machining, helping researchers to increase their knowledge in this field in a faster way. An outlook about the integration of these processes is also performed. Additionally, a SWOT analysis is also provided for additive manufacturing, machining and hybrid manufacturing processes, observing the aspects inherent to these technologies.

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Shubhang Tyagi

Papers

Review on mechanical characterization of 3D printed parts created using material jetting process

An overview on parametric study of photochemical machining process and its applications