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The purpose of this paper is to extend existing knowledge of 4D printing, in line with Khoo et al. (2015) who defined the production of 4D printing using a single material, and 4D printing of multiple materials. It is proposed that 4D printing can be achieved through the use of functionally graded materials (FGMs) that involve gradational mixing of materials and are produced using an additive manufacturing (AM) technique to achieve a single component.

The latest state-of-the-art literature was extensively reviewed, covering aspects of materials, processes, computer-aided design (CAD), applications and made recommendations for future work.

This paper clarifies that functionally graded additive manufacturing (FGAM) is defined as a single AM process that includes the gradational mixing of materials to fabricate freeform geometries with variable properties within one component. The paper also covers aspects of materials, processes, CAD, applications and makes recommendations for future work.

This paper examines the relationship between FGAM and 4D printing and defines FGAM as a single AM process involving gradational mixing of materials to fabricate freeform geometries with variable properties within one component. FGAM requires better computational tools for modelling, simulation and fabrication because current CAD systems are incapable of supporting the FGAM workflow.

It is also identified that other factors, such as strength, type of materials, etc., must be taken into account when selecting an appropriate process for FGAM. More research needs to be conducted on improving the performance of FGAM processes through extensive characterisation of FGMs to generate a comprehensive database and to develop a predictive model for proper process control. It is expected that future work will focus on both material characterisation as well as seamless FGAM control processes.

This paper examines the relationship between FGAM and 4D printing and defines FGAM as a single AM process that includes gradational mixing of materials to fabricate freeform geometries with variable properties within one component.

The purpose of this article is to reviews state-of-the-art developments in four-dimensional (4D) printing, discuss what it is, investigate new applications that have been discovered and suggest its future impact.

The article clarifies the definition of 4D printing and describes notable examples covering material science, equipment and applications.

This article highlights an emerging technology cycle where 4D printing research has gained traction within additive manufacturing. The use of stimuli-responsive materials can be programmed and printed to enable pre-determined reactions when subject to external stimuli.

This article reviews state-of-the-art developments in 4D printing, discusses what it is, investigates new applications that have been discovered and suggests its future impact.

A review on additive manufacturing (AM) of shape memory polymer composites (SMPCs) is put forward to highlight the progress made up to date, conduct a critical review and show the limitations and possible improvements in the different research areas within the different AM techniques. The purpose of this study is to identify academic and industrial opportunities.

This paper introduces the reader to three-dimensional (3 D) and four-dimensional printing of shape memory polymers (SMPs). Specifically, this review centres on manufacturing technologies based on material extrusion, photopolymerization, powder-based and lamination manufacturing processes. AM of SMPC was classified according to the nature of the filler material: particle dispersed, i.e. carbon, metallic and ceramic and long fibre reinforced materials, i.e. carbon fibres. This paper makes a distinction for multi-material printing with SMPs, as multi-functionality and exciting applications can be proposed through this method. Manufacturing strategies and technologies for SMPC are addressed in this review and opportunities in the research are highlighted.

This paper denotes the existing limitations in the current AM technologies and proposes several directions that will contribute to better use and improvements in the production of additive manufactured SMPC. With advances in AM technologies, gradient changes in material properties can open diverse applications of SMPC. Because of multi-material printing, co-manufacturing sensors to 3D printed smart structures can bring this technology a step closer to obtain full control of the shape memory effect and its characteristics. This paper discusses the novel developments in device and functional part design using SMPC, which should be aided with simple first stage design models followed by complex simulations for iterative and optimized design. A change in paradigm for designing complex structures is still to be made from engineers to exploit the full potential of additive manufactured SMPC structures.

Advances in AM have opened the gateway to the potential design and fabrication of functional parts with SMPs and their composites. There have been many publications and reviews conducted in this area; yet, many mainly focus on SMPs and reserve a small section to SMPC. This paper presents a comprehensive review directed solely on the AM of SMPC while highlighting the research opportunities.

Soft robotics is currently a rapidly growing new field of robotics whereby the robots are fundamentally soft and elastically deformable. Fabrication of soft robots is currently challenging and highly time- and labor-intensive. Recent advancements in three-dimensional (3D) printing of soft materials and multi-materials have become the key to enable direct manufacturing of soft robots with sophisticated designs and functions. Hence, this paper aims to review the current 3D printing processes and materials for soft robotics applications, as well as the potentials of 3D printing technologies on 3D printed soft robotics.

The paper reviews the polymer 3D printing techniques and materials that have been used for the development of soft robotics. Current challenges to adopting 3D printing for soft robotics are also discussed. Next, the potentials of 3D printing technologies and the future outlooks of 3D printed soft robotics are presented.

This paper reviews five different 3D printing techniques and commonly used materials. The advantages and disadvantages of each technique for the soft robotic application are evaluated. The typical designs and geometries used by each technique are also summarized. There is an increasing trend of printing shape memory polymers, as well as multiple materials simultaneously using direct ink writing and material jetting techniques to produce robotics with varying stiffness values that range from intrinsically soft and highly compliant to rigid polymers. Although the recent work is done is still limited to experimentation and prototyping of 3D printed soft robotics, additive manufacturing could ultimately be used for the end-use and production of soft robotics.

The paper provides the current trend of how 3D printing techniques and materials are used particularly in the soft robotics application. The potentials of 3D printing technology on the soft robotic applications and the future outlooks of 3D printed soft robotics are also presented.

This paper aims to present a hybrid machine learning algorithm for additive manufacturing (AM) design feature recommendation during the conceptual design phase.

In the proposed hybrid machine learning algorithm, hierarchical clustering is performed on coded AM design features and target components, resulting in a dendrogram. Existing industrial application examples are used to train a supervised classifier that determines the final sub-cluster within the dendrogram containing the recommended AM design features.

Through a case study of designing additive manufactured R/C car components, the proposed hybrid machine learning method was proven useful in providing feasible conceptual design solutions for inexperienced designers by recommending appropriate AM design features.

The proposed method helps inexperienced designers who are newly exposed to AM capabilities explore and utilize AM design knowledge computationally.

The purpose of this paper is to compare four different additive manufacturing (AM) processes to assess their suitability in the context of upper extremity splinting.

This paper describes the design characteristics and subsequent fabrication of six different wrist splints using four different AM processes: laser sintering (LS), fused deposition modelling (FDM), stereolithography (SLA) and polyjet material jetting via Objet Connex. The suitability of each process was then compared against competing designs and processes from traditional splinting. The splints were created using a digital design workflow that combined recognised clinical best practice with design for AM principles.

Research concluded that, based on currently available technology, FDM was considered the least suitable AM process for upper extremity splinting. LS, SLA and material jetting show promise for future applications, but further research and development into AM processes, materials and splint design optimisation is required if the full potential is to be realised.

Unlike previous work that has applied AM processes to replicate traditional splint designs, the splints described are based on a digital design for AM workflow, incorporating novel features and physical properties not previously possible in clinical splinting. The benefits of AM for customised splint fabrication have been summarised. A range of AM processes have also been evaluated for splinting, exposing the limitations of existing technology, demonstrating novel and advantageous design features and opportunities for future research.

The purpose of this paper is to investigate the performance of post-disaster housing reconstruction projects, propose the conceptual living-transforming disaster relief shelter (LTFDR-shelter) approach where temporary shelter is incrementally transformed into a more permanent dwelling by using living technologies and investigate its applicability to provide sustainable post-disaster housing following natural-hazard-induced disasters.

A questionnaire survey with 120 household recipients of three Sri Lankan post-disaster housing projects was employed to explore how the post-disaster housing projects have performed against the occupants' expectations. Furthermore, the new proposed LTFDR-shelter conceptual approach's applicability to address the existing issues found in the study was investigated.

The paper evaluates and identifies the physical and technical, and socio-economic performance issues of post-disaster housing and discusses the applicability of the proposed LTFDR-shelter conceptual approach as an efficient tool to adequately improve the identified factors integrating three phases of relief, rehabilitation and reconstruction employing living technology.

Although the study's scope was limited to the occupant view of the performance of post-disaster housing in Sri Lanka, the findings and conceptual LTFDR-shelter approach could be of particular relevance to other developing countries affected by similar disasters. Further research is recommended to investigate and develop this concept in depth.

This study lays the conceptual foundation for a new theoretical approach in post-disaster housing, which encourages more interdisciplinary collaborations and empirical investigations that potentially enhance post-disaster housing performance and facilitates the application of living technology in the built environment.

This study aims to cover the overall gamut of rapid prototyping processes and biomaterials used for the fabrication of occlusal splints in a comprehensive manner and elucidate the characteristics of the materials, which are essential in determining their clinical efficacy when exposed to oral surroundings.

A collective analysis of published articles covering the use of rapid prototyping technologies in the fabrication of occlusal splints, including manufacturing workflow description and essential properties (mechanical- and thermal-based) evaluation of biocompatible splinting materials, was performed.

Without advances in rapid prototyping processes and materials engineering, occlusal splints would tend to underperform clinically due to biomechanical limitations.

Three-dimensional printing can improve the process capabilities for commercial customization of biomechanically efficient occlusal splints.

Rapid technological advancement in dentistry with the extensive utilization of rapid prototyping processes, intra-oral scanners and novel biomaterial seems to be the potential breakthrough in the fabrication of customized occlusal splints which have endorsed occlusal splint therapy (OST) as a cornerstone of orthodontic treatment.

This paper aims to present an optimal prototyping technology for the manufacture of occlusal splints.

To carry out this study, a comparative technique was used to analyze models obtained by different prototyping techniques. Subsequently, further tests were carried out with respect to the manufacturing of splints by means of thermoforming in a vacuum. This involved an analysis of the most important variables such as prototype material, geometric accuracy, surface finish and costs.

It was found that there is a group of prototyping technologies that are suitable for the manufacture of the models used in the thermoforming of correction splints, the most appropriate technologies being based on ink jet printing (IJP-Objet), ultraviolet photo polymerization and fused deposition modelling due to the fact that they offer an optimal relationship between the cost and the quality of the model required for thermoforming.

The application of rapid prototyping techniques in medicine makes the production of physical models from three-dimensional medical image processing and their subsequent use in different specialties possible. It also makes preoperative planning processes, the production of prostheses and the preparation of surgical templates possible, thereby offering a higher quality of diagnosis, safer surgery and cost and time savings compared to conventional manufacturing technologies.

This paper suggests that there exists a group of prototyping technologies for the manufacture of splints that offer advantages over existing technologies. The results also suggest that, in many cases, the most expensive technology is not the most appropriate: there are other options that provide an optimal model in terms of the cost and the quality needed for thermoforming.