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.     

Smart polymers and nanocomposites for 3D and 4D printing

Smart materials, also known as intelligent materials, which are responsive to the external stimuli including heat, moisture, stress, pH, and magnetic fields, have found extensive applications in sensors, actuators, soft robots, medical devices and artificial muscles. Using three-dimensional (3D) printing techniques for fabrication of smart devices allows for complex designs and well-controlled manufacturing processes. 4D printing is attributed to the 3D printing of smart materials that can be significantly transformed over time. Herein the smart materials including hydrogels and polymeric nanocomposites used in 4D printing were reviewed and the fundamental mechanisms responsible for the functionalities were discussed in detail. In this report, 4D printing of smart systems and their applications in sensors, actuators and biomedical devices were reviewed to provide a deeper understanding of the current development and the future outlook.     

Direct Fused Deposition Modeling 4D Printing and Programming of Thermoresponsive Shape Memory Polymers with Autonomous 2D-to-3D Shape Transformations

Herein, direct 4D printing of thermoresponsive shape memory polymers (SMPs) by the fused deposition modeling (FDM) method that enables programing of 2D objects during printing for autonomous 2D-to-3D shape transformations via simply heating is focused on. The programming process during printing is investigated through designs and experiments. The capability of programming SMPs during printing is illustrated by prestrain and bending capabilities, which are highly related to printing settings, such as nozzle temperature, print speed, layer height, infill patterns, and ratio of active parts in a bilayer structure. A nearly linear relationship for prestrain and bending parameters is experimentally revealed for different printing factors. Quantitative results are presented to be used as a guidance for designing complex 3D structures via 4D printing of 2D structures. Helix structure, twisting structure, DNA-like structures, and functional gripper are designed to demonstrate the potential of direct FDM 4D printing for creating complex 3D structures from simple 2D structures with advantages over traditional manufacturing methods. It is shown that, by removing the need for a layer-by-layer stacking process to achieve a complex 3D shape, FDM can promote sustainability via 4D printing of autonomous 2D-to-3D shape transformer structures with lower materials, time, energy, and longer service life.     

Two-Way 4D Printing: A Review on the Reversibility of 3D-Printed Shape Memory Materials

The rapid development of additive manufacturing and advances in shape memory materials have fueled the progress of four-dimensional (4D) printing. With the right external stimulus, the need for human interaction, sensors, and batteries will be eliminated, and by using additive manufacturing, more complex devices and parts can be produced. With the current understanding of shape memory mechanisms and with improved design for additive manufacturing, reversibility in 4D printing has recently been proven to be feasible. Conventional one-way 4D printing requires human interaction in the programming (or shape-setting) phase, but reversible 4D printing, or two-way 4D printing, will fully eliminate the need for human interference, as the programming stage is replaced with another stimulus. This allows reversible 4D printed parts to be fully dependent on external stimuli; parts can also be potentially reused after every recovery, or even used in continuous cycles—an aspect that carries industrial appeal. This paper presents a review on the mechanisms of shape memory materials that have led to 4D printing, current findings regarding 4D printing in alloys and polymers, and their respective limitations. The reversibility of shape memory materials and their feasibility to be fabricated using three-dimensional (3D) printing are summarized and critically analyzed. For reversible 4D printing, the methods of 3D printing, mechanisms used for actuation, and strategies to achieve reversibility are also highlighted. Finally, prospective future research directions in reversible 4D printing are suggested.     

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.     

4D打印复合软材料力学性能预测研究进展

4D打印是一门新兴的制造技术,所打印结构的形状、属性或功能在外部环境的刺激下会随着时间的推移而变化。智能软物质材料由于变形大,激励响应机制多,响应速度快等特点被广泛使用于4D打印中,尤其是形状记忆水凝胶和形状记忆聚合物。目前对复合软材料的刚度和弯曲形状的控制是4D打印在应用上的两个难题,建立4D打印复合结构的等效模量和曲率预测模型对复合软材料的力学性能的设计具有指导意义。本文对现有的4D打印复合结构的等效模量及弯曲曲率模型进行了概述,首先介绍了4D打印结构在静态和动态下的弹性模量预测模型,然后,重点综述了Stoney理论,Timoshenko理论和复合材料力学在复合软材料弯曲曲率建模上的应用。最后探讨了现有4D打印复合软材料力学预测模型存在的问题及主要发展的方向。     

Colloidal Nanosurfactants for 3D Conformal Printing of 2D van der Waals Materials

Printing techniques using nanomaterials have emerged as a versatile tool for fast prototyping and potentially large-scale manufacturing of functional devices. Surfactants play a significant role in many printing processes due to their ability to reduce interfacial tension between ink solvents and nanoparticles and thus improve ink colloidal stability. Here, a colloidal graphene quantum dot (GQD)-based nanosurfactant is reported to stabilize various types of 2D materials in aqueous inks. In particular, a graphene ink with superior colloidal stability is demonstrated by GQD nanosurfactants via the π–π stacking interaction, leading to the printing of multiple high-resolution patterns on various substrates using a single printing pass. It is found that nanosurfactants can significantly improve the mechanical stability of the printed graphene films compared with those of conventional molecular surfactant, as evidenced by 100 taping, 100 scratching, and 1000 bending cycles. Additionally, the printed composite film exhibits improved photoconductance using UV light with 400 nm wavelength, arising from excitation across the nanosurfactant bandgap. Taking advantage of the 3D conformal aerosol jet printing technique, a series of UV sensors of heterogeneous structures are directly printed on 2D flat and 3D spherical substrates, demonstrating the potential of manufacturing geometrically versatile devices based on nanosurfactant inks.     

Investigating the shape memory properties of 4D printed polylactic acid (PLA) and the concept of 4D printing onto nylon fabrics for the creation of smart textiles

3D printing is an ever growing industry that provides many benefits to the advanced manufacturing and design industry. However, parts tend to be static, rigid, and lack multi-purpose use. Recently, a new technology has emerged that uses 3D printing to print parts with the ability to change shape over time when exposed to different external stimuli. This new technology has been called 4D printing. Creation of a new material that is capable of changing shape when exposed to different stimuli and possess the ability to be 3D printed can be a difficult and a long process. Due to this strenuous process, the potential of a common fused deposition modelling material, poly(lactic) acid (PLA), for use in 4D printing is investigated and the concept of combining PLA with nylon fabric for the creation of smart textiles is explored. PLA possesses thermal shape memory behaviour and maintains these abilities when combined with nylon fabric that can be thermomechanically trained into temporary shapes and return to their permanent shapes when heated.     

A novel near-infrared light responsive 4D printed nanoarchitecture with dynamically and remotely controllable transformation

Nano Research - Four-dimensional (4D) printing is an emerging and highly innovative additive manufacturing process by which to fabricate pre-designed, self-assembly structures with the ability to...     

Development of Bioimplants with 2D, 3D,and 4D Additive Manufacturing Materials

Over the past 30 years, additive manufacturing (AM) has developed rapidly and has demonstrated great potential in biomedical applications. AM is a materials-oriented manufacturing technology, since the solidification mechanism, architecture resolution, post-treatment process, and functional application are based on the materials to be printed. However, 3D printable materials are still quite limited for the fabrication of bioimplants. In this work, 2D/3D AM materials for bioimplants are reviewed. Furthermore, inspired by Tai Chi, a simple yet novel soft/rigid hybrid 4D AM concept is advanced to develop complex and dynamic biological structures in the human body based on 4D printing hybrid ceramic precursor/ceramic materials that were previously developed by our group. With the development of multi-material printing technology, the development of bioimplants and soft/rigid hybrid biological structures with 2D/3D/4D AM materials can be anticipated.     

三维打印碳纤维增强聚合物复合材料热残余解析解

三维打印碳纤维增强聚合物（CFRP）复合材料因层间材料失配和打印过程中梯度降温而产生热残余现象,影响工件成形质量。本文取代简单的同步降温假设,提出了符合实际制备工艺的梯度降温概念,据此建立了三维打印正交铺层复合材料板和梁的热残余变形和应力的解析解。为反映三维打印过程中随时序动态变化的制备和降温过程,考虑每层制备轮次的降温梯度并进行热残余分析,最后合成得到热残余变形和应力。讨论了4种梯度降温模式,覆盖了所有可能的三维打印工艺。以CFRP复合材料三维打印为例,验证了本文解析解的精度和可靠性,显示了同步降温假设会产生显著的误差,表明热残余水平与降温梯度成正比,讨论了铺层方式对热残余的影响。为优化三维打印CFRP复合材料的结构设计和制备工艺、降低热残余水平提供了可靠的分析方法。      

印刷法制备功能芯片的研究进展

目的概述印刷芯片的制备方法和研究现状,开拓印刷技术的研究思路和应用场景,为印刷芯片的发展提供参考。方法从印刷材料、印刷方法和芯片应用3个方面介绍近年来印刷芯片的研究进展,重点对比各种印刷方法的关键科学问题及特点,并且指出芯片印刷的发展方向。结果基于印刷方法在大面积制备、材料兼容性、绿色环保等方面的优势,印刷芯片在显示、能源、生物、智能包装等诸多方面快速发展,不过仍然面临高精度、规模化、功能集成方面的挑战。结论通过更好地调控印刷过程中液滴成型,构筑功能材料精细微纳结构,实现高精度器件与芯片全印刷制造。未来在实现智能、自动、互联化功能芯片制造的同时,发展绿色可持续印刷新策略。     

人体植入医用材料的3D打印技术研究进展

3D打印技术是一种与传统制备方式完全不同的新兴技术,是基于三维数学模型,通过逐层增加材料来实现成型的技术。3D打印技术在个性化设计以及复杂结构产品制备方面具有独特的优势,在人体植入物的结构设计和制造领域具有巨大潜力和研究价值,吸引了国内外工业界、医学界和社会媒体的广泛关注。目前制约该技术发展的主要因素是可打印材料种类有限。综述了几种人体植入医用材料及其3D打印成型技术,如骨支架、心脏血管支架以及药物定向运输材料的3D打印制备技术,并分析了以上技术各自的特点。最后结合各种3D打印成型技术的特点以及几个应用案例,对3D打印在人体植入物医学领域的发展进行了展望。     

Current status of 4D printing technology and the potential of light-reactive smart materials as 4D printable materials

The onset of multi-material 3D printing and the combination of smart materials into the printable material has led to the development of an exciting new technology called 4D printing. This paper will introduce the background and development into 4D printing, discuss water reactive 4D printing methods and temperature reactive 4D printing, modelling and simulation software, and future applications of this new technology. Smart materials that react to different external stimuli are described, along with the benefits of these smart materials and their potential use in 4D printing applications; specifically, existing light-reactive smart materials. 4D printing has the prospective to simplify the design and manufacturing of different products and the potential of automating actuation devices that naturally react to their environment without the need for human interaction, batteries, processors, sensors, and motors.     

计量性与未来制造业

总结了未来制造业的三种模式,即智能制造、网络化制造和增材制造。从未来制造业的技术发展出发,讨论了产品制造及质量保证对计量测试的需求,重点讨论了产品全寿命周期的计量性设计对未来制造业发展的基础作用及引领作用,提出以数字化计量、智能计量和增材制造装备计量,分别应对未来制造业的3种模式。     

Electrohydrodynamic 3D Printing of Aqueous Solutions

Among the various electrohydrodynamic (EHD) processing techniques, electrowriting (EW) produces the most complex 3D structures. Aqueous solution EW similarly retains the potential for additive manufacturing well-resolved 3D structures, while providing new opportunities for processing biologically derived polymers and eschewing organic solvents. However, research on aqueous-based EHD processing is still limited. To summarize the field and advocate for increased use of aqueous bio-based materials, this review summarizes the most significant contributions of aqueous solution processing. Special emphasis has been placed on understanding the effects of different printing parameters, the prospects for 3D processing new materials, and future challenges.     

3D Printing of Textiles: Potential Roadmap to Printing with Fibers

3D printing (3DP) has transformed engineering, manufacturing, and the use of advanced materials due to its ability to produce objects from a variety of materials, ranging from soft polymers to rigid ceramics. 3DP offers the advantage of being able to print at a variety of lengths scales; from a few micrometers to many meters. 3DP has the unique ability to produce customized small lots, efficiently. Yet, one crucial industry that has not been able to adequately explore its potential is textile manufacturing. The research in 3DP of textiles has lagged behind other areas primarily due to the difficulty in obtaining some of the unique characteristics of strength, flexibility, etc., of textiles, utilizing a fundamentally different manufacturing technology. Textiles are their own class of materials due to the specific structural developments that occur during the various stages of textile manufacturing: from fiber extrusion to assembly of the fibers to fabrics. Here, the current 3DP technologies are reviewed with emphasis on soft and anisotropic structures, as well as the efforts toward 3DP of textiles. Finally, a potential pathway to 3DP of textiles, dubbed as printing with fibers to create textile structures is proposed for further exploration.     

基于智能制造的交互系统设计需求与产品化

目的为智能制造系统的设计需求获取与产品化提供一种可行的研究思路与辅助设计方法。方法以笔者参与的智能3D打印系统研发与实际设计过程为研究对象,对其需求的定义、类型、获取与设计一致性进行实例验证研究与比较研究。结果提出交互系统设计需求与产品化的映射模型(DMP),同时利用设计实践对需求获取与产品化的方法进行可行性验证,为智能制造领域的系统开发提供可行的需求获取与产品化的设计方法。结论合理的需求获取方法对基于智能制造的设计需求产品化与品牌化有积极辅助作用,同时对其他相关领域的新型智能设备与系统的设计、品牌策略、产业策略提供可适用的辅助设计方法与工具。