3D printing of smart materials: A review on recent progresses in 4D printing

ABSTRACT

Additive manufacturing (AM), commonly known as three-dimensional (3D) printing or rapid prototyping, has been introduced since the late 1980s. Although a considerable amount of progress has been made in this field, there is still a lot of research work to be done in order to overcome the various challenges remained. Recently, one of the actively researched areas lies in the additive manufacturing of smart materials and structures. Smart materials are those materials that have the ability to change their shape or properties under the influence of external stimuli. With the introduction of smart materials, the AM-fabricated components are able to alter their shape or properties over time (the 4th dimension) as a response to the applied external stimuli. Hence, this gives rise to a new term called ‘4D printing’ to include the structural reconfiguration over time. In this paper, recent major progresses in 4D printing are reviewed, including 3D printing of enhanced smart nanocomposites, shape memory alloys, shape memory polymers, actuators for soft robotics, self-evolving structures, anti-counterfeiting system, active origami and controlled sequential folding, and some results from our ongoing research. In addition, some research activities on 4D bio-printing are included, followed by discussions on the challenges, applications, research directions and future trends of 4D printing.     

Role of porosity defects in metal 3D printing: Formation mechanisms,impacts on properties and mitigation strategies

Metal 3D printing (3DP), a state-of-the-art manufacturing technology that brings the potential to fabricate complex structures at low cost and reduced energy consumption, has been extensively adopted in various industries. However, the porosity defects inherited from the printing process can significantly impede the mechanical properties and weaken the performance of as-printed components, potentially challenging this approach's reliability and reproducibility. The advancement of detection techniques currently opens up a more intuitive and deeper study of porosity defects. Given that, this review systematically states the 'restriction role' of porosity defects in metal 3DP by generalizing the detailed information on porosity defects, including their characterizations, formation and migration mechanisms, and their impacts on the performance of printed parts. Furthermore, feasible porosity mitigation measures are discussed to inspire more advanced methodologies for the next generation of metal 3DP.     

A Review of 3D Printing Technology for Medical Applications

Donor shortages for organ transplantations are a major clinical challenge worldwide. Potential risks that are inevitably encountered with traditional methods include complications, secondary injuries, and limited source donors. Three-dimensional (3D) printing technology holds the potential to solve these limitations; it can be used to rapidly manufacture personalized tissue engineering scaffolds, repair tissue defects in situ with cells, and even directly print tissue and organs. Such printed implants and organs not only perfectly match the patient’s damaged tissue, but can also have engineered material microstructures and cell arrangements to promote cell growth and differentiation. Thus, such implants allow the desired tissue repair to be achieved, and could eventually solve the donor-shortage problem. This review summarizes relevant studies and recent progress on four levels, introduces different types of biomedical materials, and discusses existing problems and development issues with 3D printing that are related to materials and to the construction of extracellular matrix in vitro for medical applications.     

Hydrothermal synthesis of zirconia-based nanocomposite powder reinforced by graphene and its application for bone scaffold with 3D printing

Hydrothermal method is a cheap and green approach for the synthesis of composite powders. In this study, the zirconia (ZrO₂)-based nanocomposite powder was reinforced with reduced graphene oxide (ZrO₂/RGO) and was synthesized in a one-pot as a precursor for bone scaffold applications. Moreover, for the stimulation of osseointegration in bone scaffolds, Hydroxyapatite (HA) was used in 10 wt%. In this regard, the two types of ZrO₂/RGO and ZrO₂/RGO/HA precursors were applied for the fabrication of bone scaffolds via 3D printing and finally, the mechanical and biological properties of scaffolds were evaluated. For characterization, the X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), compress strength, and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide as MTT assay protocol were performed. The results demonstrated that the ZrO₂/RGO scaffolds with a tolerance of compressive stress of 240.11 MPa depicted better mechanical properties compared with ZrO₂/RGO/HA with the compress strength of 141.66 MPa. Moreover, after 7 days of bone scaffolds immersion in simulated body fluid (SBF) the growth of compressive strength began while after 28 days reached 260.15 MPa for ZrO₂/RGO and 192.31 for ZrO₂/RGO/HA. Finally, the cellular response of the scaffolds indicated the lack of cellular toxicity of the scaffolds during MTT assay.     

Aesthetic reconstruction of microtia: a review of current techniques and new 3D printing approaches

Three dimensional (3D) printing and biofabrication technologies are revolutionising medicine with low-cost and novel treatments for complex medical conditions. These approaches differ from traditional treatments by using 3D scanning, computer modelling and 3D printing to automate the production of patient-specific tissue replacement or prostheses using a wide range of materials. One area impacted by this technology is the treatment of congenital maxillofacial conditions such as microtia, a condition affecting the intrauterine development of the auricle (external ear) and with a prevalence of 2.06 cases for every 10,000 births. While not life-threatening, microtia significantly impacts the emotional and psychological well-being of the affected child and their parents. Current treatments include the use of prosthetic ears or surgical methods such as autografting rib cartilage or alloplastic implants. Although current options have shown documented success, they are highly dependent on the surgeon’s skill and it has been demonstrated that poor quality solutions can further exacerbate negative psychosocial impacts. As such, higher quality, lower cost and more customised options would be welcomed by patients and parents alike. Recent advances in 3D scanning, modelling and printing techniques could significantly benefit the treatment and reconstructive options for children with microtia, leading to improved quality of life.     

挤出方式对黏弹性浆料3D打印出料可控性的影响EI北大核心CSCD

基于挤出工艺的陶瓷3D打印技术应用过程中,不同挤出方式对出料速率可控性存在重要影响,从而导致打印样件在表面质量及打印成功率方面存在明显差异。针对这一问题,研究选择柱塞和螺杆两种挤出方式,在Bingham黏弹性流体浆料及0.6 mm喷嘴直径的基本条件下,结合现场实验数据和模拟仿真得出的出料速率变化曲线,对柱塞与螺杆两种挤出方式的3D打印效果进行对比分析。结果表明:螺杆挤出方式在0.03 s内,出料速率已降至原始出料速率的30%以下,而柱塞挤出方式达到该出料速率所需的时间为2.4 s,在停止供料的0.27 s内柱塞挤出方式的出料量是螺杆挤出方式出料量的3倍。通过流场分析发现黏弹性浆料条件下两种挤出装置的驱动原理不同是造成该差异的主要原因。     

光固化3D打印陶瓷浆料及流变性研究进展EI北大核心CSCD

基于光固化技术原理的陶瓷3D打印因可制备尺寸精度高、表面光洁度好、显微结构均匀和力学性能优异的复杂结构陶瓷零件而备受关注,是实现高性能陶瓷零件增材制造的重要技术手段之一。该技术的核心是制备同时具有高固含量和良好打印适性要求的陶瓷浆料,其组成对固化效果和打印进程有着至关重要的影响。本文综述了立体光固化(stereolithography,SL)和数字光处理(digital light processing,DLP)两种主流光固化3D打印方法用于光固化陶瓷打印的技术方案和工作原理,比较了两者的优缺点。围绕近年来在陶瓷浆料领域的研究工作,讨论了单体/低聚物和稀释剂、分散剂、陶瓷颗粒物理性质以及固含量等对黏度、剪切稀化/增稠行为、黏弹性、屈服应力等流变行为的影响,并提出了光固化3D打印陶瓷浆料的主要发展趋势和面临的挑战,为构建高固含量光固化3D打印陶瓷浆料提供了一般性指导原则。     

3D打印技术探究

3D打印技术是将三维数字模型分解成若干层平面切片,然后由3D打印机把粉末状、液状或丝状可粘合材料按切片图形逐层叠加,最终堆积成完整物体的技术。文章对3D打印的技术原理、步骤、常用材料、主要技术、发展及建议进行了深层次的探讨。与传统制造技术相比,3D打印技术有很多优势,目前已广泛应用于建筑、工业设计等领域。该技术将会带来全球制造业经济的重大变革。     

3D printing technology and its impact on Chinese manufacturing

For both developed and developing countries, manufacturing plays a crucial role in international competition. There is a growing consensus that 3D printing (3DP) technologies will revolutionise the development of global manufacturing. Although considerable research has previously been conducted to define the technological and economic benefits of 3DP on global manufacturing, minimal research has linked 3DP with Chinese manufacturing (CM). Therefore, to address this research gap and to investigate 3DP’s potential impact on alleviating CM’s development issues, this paper explores the definition, characteristics and mainstream technologies of 3DP, presents the current situation and the main problems of CM, and analyses the potential impact of 3DP on the development of CM. Then, this study introduces the current 3DP promotion and industrialisation situation in China as well as the issues with promoting 3DP in CM.     

Review: Recent advancement and research possibilities in 4D printing technology

The development of smart materials has provided a new technology in the field of 3D printing which is termed as 4D printing technology. Such development has allowed the researchers to design a material and component which can respond to external stimuli. The present review focuses on an overview of the advancement in 3D printing technology and 4D printing technology and possibilities for further development. Apart from 3 dimensions of 3D printing, 4D printing uses time as fourth dimension to create or modify shape when exposed to stimuli. The parameters which change with time include temperature, water, light, humidity, pH etc. The invention of smart materials, development in fabrication process and deformation model, advancement in printing methods have led to development of 4D printing technology. The ability of smart material to change the shape and design according to their environment and as per the application have enhanced degree of freedom of parts during application. The effect of major components including smart materials, printing methods and stimuli on 4D printing technology have been reviewed. Some recent discoveries have shown promising results but still need to overcome certain impediments.     

Additive manufacturing of concrete in construction: potentials and challenges of 3D concrete printing

Additive manufacturing is gaining ground in the construction industry. The potential to improve on current construction methods is significant. One of such methods being explored currently, both in academia and in construction practice, is the additive manufacturing of concrete (AMoC). Albeit a steadily growing number of researchers and private enterprises active in this field, AMoC is still in its infancy. Different variants in this family of manufacturing methods are being developed and improved continuously. Fundamental scientific understanding of the relations between design, material, process, and product is being explored. The collective body of work in that area is still very limited. After sketching the potential of AMoC for construction, this paper introduces the variants of AMoC under development around the globe and goes on to describe one of these in detail, the 3D Concrete Printing (3DCP) facility of the Eindhoven University of Technology. It is compared to other AMoC methods as well as to 3D printing in general. Subsequently, the paper will address the characteristics of 3DCP product geometry and structure, and discuss issues on parameter relations and experimental research. Finally, it will present the primary obstacles that stand between the potential of 3DCP and large-scale application in practice, and discuss the expected evolution of AMoC in general.     

Biocompatibility of ceramic scaffolds for bone replacement made by 3D printing

Bone replacement materials used in tissue engineering require a high degree of safety and biological compatibility. For these reasons synthetic bone replacement materials based on calcium‐phosphates are being used more widely. To mimic natural bone, rapid prototyping processes and especially 3D printing are favourable. Using 3D printing, complex 3 dimensional structures can be made easily. In this study we successfully performed biocompatibility tests with a Hydroxyapatite test structure (HA‐S) made by 3D printing. Cytotoxicity tests were carried out according to DIN ISO 10993‐5 in static and dynamic cultivation setups. To estimate cell proliferation and analyze morphology, histological evaluation was done. In summary, good cell viability as well as good proliferation behaviour were found. Moreover, these results show that the 3D printing process in combination with the suitable material presented in this study is well suited for fabricating scaffolds for TE in the required accuracy and biological compatibility.     

聚乳酸/聚乙二醇/羟基磷灰石多孔骨支架的3D打印制备及其生物相容性

聚乳酸(PLA)是一种应用广泛的生物高分子材料,但在应用过程中存在韧性、亲水性、生物活性差等缺点。用聚乙二醇(PEG)和羟基磷灰石(HA)对PLA进行改性。通过熔融共混制备不同质量比的PLA/PEG/HA复合3D打印线材,并通过分析PLA/PEG/HA线材的力学性能、结晶性能、热性能、流变性能等,筛选更适合熔融沉积成型(FDM)的3D打印成型线材,进而利用3D打印制备精度高的力学性能试样及生物相容性好、细胞可增殖和分化的生物多孔支架。结果表明:PEG的添加提高了PLA的韧性,降低了PLA的熔点。HA的添加则提高PLA/PEG/HA复合材料的弹性模量和冷结晶温度,同时HA也可以改善复合材料的加工性能。SEM与荧光标记结果表明多孔支架与细胞具有良好的生物相容性。生物支架对体外细胞的成功培养,为进一步发掘生物多孔支架在动物体内、生物医学及定制化应用方面提供了潜在可能。     

3D printing of tuneable agglomerates: Strain distribution and effect of internal flaws

The current study presents a novel and reliable method for producing 3D printed agglomerates with different colour distributions and material properties with 2-fold aims: providing feasible and accurate control on compression of agglomerates under different compression angles, and better tracking of individual particle position after agglomerate breakage. Multi-coloured agglomerates in cubic tetrahedral and random sphere shapes were printed with both rigid and soft bonds. The printed agglomerates were analysed thoroughly of their surface and structural properties including surface roughness and printing accuracy. The agglomerate breakage behaviours under static compression were analysed as a function of bond strength, loading rate and loading directions, with strain distribution plotted over the random sphere agglomerate structure. In addition, agglomerate structures with designed internal macro-voids in different positions and sizes were also created for breakage study, in an effort to better understand parameters governing the mechanical properties of agglomerates with cavities and voids which is inevitable in particle industry but poorly understood at present.     

A review on powder-based additive manufacturing for tissue engineering: selective laser sintering and inkjet 3D printing

Abstract

Since most starting materials for tissue engineering are in powder form, using powder-based additive manufacturing methods is attractive and practical. The principal point of employing additive manufacturing (AM) systems is to fabricate parts with arbitrary geometrical complexity with relatively minimal tooling cost and time. Selective laser sintering (SLS) and inkjet 3D printing (3DP) are two powerful and versatile AM techniques which are applicable to powder-based material systems. Hence, the latest state of knowledge available on the use of AM powder-based techniques in tissue engineering and their effect on mechanical and biological properties of fabricated tissues and scaffolds must be updated. Determining the effective setup of parameters, developing improved biocompatible/bioactive materials, and improving the mechanical/biological properties of laser sintered and 3D printed tissues are the three main concerns which have been investigated in this article.     

A review on powder-based additive manufacturing for tissue engineering: selective laser sintering and inkjet 3D printing

Since most starting materials for tissue engineering are in powder form, using powder-based additive manufacturing methods is attractive and practical. The principal point of employing additive manufacturing (AM) systems is to fabricate parts with arbitrary geometrical complexity with relatively minimal tooling cost and time. Selective laser sintering (SLS) and inkjet 3D printing (3DP) are two powerful and versatile AM techniques which are applicable to powder-based material systems. Hence, the latest state of knowledge available on the use of AM powder-based techniques in tissue engineering and their effect on mechanical and biological properties of fabricated tissues and scaffolds must be updated. Determining the effective setup of parameters, developing improved biocompatible/bioactive materials, and improving the mechanical/biological properties of laser sintered and 3D printed tissues are the three main concerns which have been investigated in this article.     

磁控触变流体的3D打印工艺研究

针对现有磁控智能流体无法应用于3D打印的问题,本文制备了一种在磁场调控下能够实现溶胶-凝胶可逆转变的新型磁控触变流体,并对其打印工艺进行了研究。采用全系统损耗润滑油、有机膨润土和Fe₃O₄颗粒制备了不同配比的打印样品,搭建了直写式3D打印实验平台,研究其可打印性。流变学实验表明:磁控触变流体有机膨润土含量越高,触变性越强,剪切变稀越明显;磁场强度越强,屈服应力越高,储存模量越高。3种挤出方式下的打印实验结果表明,采用匀料恢复挤出方式打印的结构具备最高分辨率和最大高度。磁控触变流体在根据其流变特性设计的挤出装置下具有良好可打印性,为该材料应用于柔性传感、软体机器人个性化复杂结构设计与驱动、微流控检测等领域奠定了基础。     

3D printing with particles as feedstock materials

3D printing has been applied in numerous research fields ranging from biomedical, mechanical engineering and chemistry to material science. 3D printing applications have driven innovations in particle technology, especially through tackling particle-related issues arising from the development of particle-based printing feedstocks across such application areas. Therefore, in this review, established 3D printing processes are described to include their prototyping mechanisms, advantages and limitations. Various particulate systems, including dry and wet systems, as printing feedstock materials are introduced. The main motivation for this paper is to outline the current state of particulate feedstock systems and to attempt to outline future directions for enhancing these particle applications. This paper would be valuable for individuals, researchers and companies who need adequate and comparative information regarding the state of particle applications in the AM industry.     

3D printing of living structural biocomposites

Nature fabricates organic/inorganic composites under benign conditions, yet, in many cases, their mechanical properties exceed those of the individual building components it is made from. The secret behind the evolutionary pivot is the unique ability of nature to control structure and local composition of its materials. This tight control is often achieved through compartmentalization of the reagents that can be locally released. Inspired by nature, we introduce an energy-efficient process that takes advantage of the compartmentalization to fabricate porous CaCO₃-based composites exclusively comprised of nature-derived materials whose compressive strength is similar to that of trabecular bones. The unique combination of nature-derived materials, 3D printability, and good mechanical properties is achieved through the formulation of these materials: We combine microgel-based granular inks that inherently can be 3D printed with the innate potential of engineered living materials to fabricate bacteria-induced biomineral composites. The resulting biomineral composites possess a porous trabecular structure that comprises up to 93 wt% CaCO₃ and thereby can withstand pressures up to 3.5 MPa. We envisage this system to have the potential to be used in art restoration, serve as artificial corals to help the regeneration of marine reefs, and, with additional work, might even allow the reparation of broken or partially disintegrated natural mineral-based materials such as certain parts of bones.