State of art on evaluation of three- to six-dimensional novel additive manufacturing technology for biomedical applications

Critical appraisal and systematic review of 3D & 4D printing in sustainable and environment-friendly smart manufacturing technologies

4D printing: Pragmatic progression in biofabrication

Shape memory polymers are smart materials that produce shape changes under external stimulus conditions. Four-dimensional (4D) printing is a comprehensive technology originate from deformable materials and three-dimensional (3D) printing technology. At present, 4D printed shape memory polymers and shape-changing structures have been applied in various fields, especially in the field of biomedical science. 4D printing technology has made a breakthrough of personalized customization in the traditional medical field, providing a new direction for the further development of the biomedical field. In this review, the recent research and development of shape memory polymer, 3D printing technology, 4D printed shape memory polymers and shape-changing structures in biomedical area are present. The examples and applications of 4D printed shape memory polymers and their structures in the area of biomedical are also introduced. Based on 4D printing, stimulated by different conditions, 3D printed objects can be fabricated into various biomedical applications such as cell scaffolds, vascular stents, bone scaffolds, tracheal stents and cardiac stents by different 3D printing techniques. Finally, the application prospects, existing technical restriction and future development directions of 4D printed shape memory polymers and their structures in the biomedical field are summarized.

Three-dimensional (3D) and four-dimensional (4D) printing have emerged as the next-generation fabrication technologies, covering a broad spectrum of areas, including construction, medicine, transportation, and textiles. 3D printing, also known as additive manufacturing (AM), allows the fabrication of complex structures with high precision via a layer-by-layer addition of various materials. On the other hand, 4D printing technology enables printing smart materials that can alter their shape, properties, and functions upon a stimulus, such as solvent, radiation, heat, pH, magnetism, current, pressure, and relative humidity (RH). Myriad of biomedical materials (BMMs) currently serve in many biomedical engineering fields aiding patients’ needs and expanding their life-span. 3D printing of BMMs provides geometries that are impossible via conventional processing techniques, while 4D printing yields dynamic BMMs, which are intended to be in long-term contact with biological systems owing to their time-dependent stimuli responsiveness. This review comprehensively covers the most recent technological advances in 3D and 4D printing towards fabricating BMMs for tissue engineering, drug delivery, surgical and diagnostic tools, and implants and prosthetics. In addition, the challenges and gaps of 3D and 4D printed BMMs, along with their future outlook, are also extensively discussed. The current review also addresses the scarcity in the literature on the composition, properties, and performances of 3D and 4D printed BMMs in medical applications and their pros and cons. Moreover, the content presented would be immensely beneficial for material scientists, chemists, and engineers engaged in AM manufacturing and clinicians in the biomedical field. Graphical abstract. 3D and 4D printing towards biomedical applications

Objective This study aims to explain the mechanisms of the four-dimensional (4D) printing technique and its potential applications in dental and orthodontic practice. General Information Rapid advances in science and technology have led to significant developments in production systems. Described as additive manufacturing or rapid prototyping, a positive innovation has been the introduction of three-dimensional (3D) printers in the 1980s. The technology quickly became popular because it allowed complex structures to be produced using less material compared to traditional manufacturing methods. Objects are designed in three dimensions using dedicated computer programs and 3D printed using materials such as composites, resins, metals, and polymers. Orthodontics has also benefitted from 3D printing in the fields of clear aligner treatment, indirect bonding using bracket transfer trays, dental modelling, and the production of guides for mini-screw and implant placement, as well as the manufacture of removable appliances. As 3D printers continued to evolve and new ‘smart’ materials were specifically developed, 4D printing techniques emerged. 4D printing allows objects, produced by 3D printers to change shape in response to stimuli, usually in the form of heat and light, thereby enabling the performance of specific functions. The objects can also self-assemble into larger structures without external intervention. The applications of 4D printing are expanding across a wide range of clinical fields. Conclusion 4D printing is an evolving technology that requires further research. However, if integrated into dentistry, it holds great potential as an efficient printing method, similar to its applications in other fields.

The scientific community is and has constantly been working to innovate and improve the available technologies in our use. In that effort, three-dimensional (3D) printing was developed that can construct 3D objects from a digital file. Three-dimensional printing, also known as additive manufacturing (AM), has seen tremendous growth over the last three decades, and in the last five years, its application has widened significantly. Three-dimensional printing technology has the potential to fill the gaps left by the limitations of the current manufacturing technologies, and it has further become exciting with the addition of a time dimension giving rise to the concept of four-dimensional (4D) printing, which essentially means that the structures created by 4D printing undergo a transformation over time under the influence of internal or external stimuli. The created objects are able to adapt to changing environmental variables such as moisture, temperature, light, pH value, etc. Since their introduction, 3D and 4D printing technologies have extensively been used in the healthcare, aerospace, construction, and fashion industries. Although 3D printing has a highly promising future, there are still a number of challenges that must be solved before the technology can advance. In this paper, we reviewed the recent advances in 3D and 4D printing technologies, the available and potential materials for use, and their current and potential future applications. The current and potential role of 3D printing in the imperative fight against COVID-19 is also discussed. Moreover, the major challenges and developments in overcoming those challenges are addressed. This document provides a cutting-edge review of the materials, applications, and challenges in 3D and 4D printing technologies.

4D printing and stimuli-responsive materials in biomedical aspects

Owing to the success of three-dimensional (3D) printing in biomedical applications, the latest addition to the technology is four-dimensional (4D) printing, which has gained tremendous interest since 2012. 4D printing is being considered as an upgradation and extension of 3D that includes time as a fourth dimension with the utilization of smart biomaterials, and upon the application of any external stimulus, the shape and size of the printed structure change with time. In this review, we highlight the basic techniques involved in 4D printing, the shape memory effect, and various stimuli like light, temperature, pH, etc., that cause the shape change, leading to the transformation of the structures fabricated. 4D printing using smart materials demonstrates shape memory property and their possible applications in the field of biomedicine and regenerative medicine are discussed in detail. The authors have focused on 4D printing of various tissues, with a special highlight on bone and dental tissue.Graphical abstract

Over the last two decades, researchers, technologists, designers, and manufacturers have made enormous efforts to commercialize additive manufacturing (AM) or 3D printing technology in an array of fields including textile, apparel, and fashion industries. Recently, a great advancement in AM of complex architectures, which are impossible or difficult to produce otherwise, has been reported. Following the success of making metal/polymer-based 3D printed stiff structures, researchers have also explored the potential of this technique for creating flexible materials such as smart textiles. This chapter presents 3D printing as a novel method for the manufacturing of more flexible, cost-effective, and functional textiles via techniques such as screen printing and ink-jet printing and for fabricating smart textile structures which are slightly different from the conventional knitted or woven fabrics but possessing intelligent properties. Specifically, in this chapter, an overview of 3D printing technology, different 3D printing techniques, material selection, and properties of 3D printed objects in the context of manufacturing of smart and functional textiles is discussed. Emerging smart textiles enabled by 4D printing have also been explored which can exhibit transformation in their structure or colour as a function of time in the presence of an external stimulus. Therefore, the transition from 3D to 4D printing, the basic aspects of 4D printing, and materials selection for 4D printing of smart textiles and fashion products are presented here. The subsequent section discusses the potential applications of textiles enabled by 3D and 4D printing. Finally, current challenges and future perspectives of 3D and 4D printing of smart textiles are summarized.

Development in additive manufacturing is exceptionally rapid than the expected forecast so far and it has traced out new dimensions in engineering applications. 3D printing technology becomes more glamorous when Skylar Tibbits incorporated the concept of “Time” as a fourth dimension by encapsulating smart materials in current additive manufacturing technique. Materials having an explicit response to external stimuli over a certain time span are designated as smart materials and additive manufacturing of such time-dependent, programmable, and intelligent materials is termed as 4D printing. In 4D printing, primary 3D printed configuration switched exclusively into a transformed shape when exposed to an external stimuli, e.g. heat, light, water, chemical, electric current, magnetic field or pH. Perhaps, additive manufacturing technology seems to be superseded exclusively by this modern technology in forthcoming years, and much effort is demanding from every discipline to actualize this technology. A task-oriented entire landscape of 4D printing followed by a comprehensive smart material perspective is presented in this review. Graphical abstract set forth a route to the complete process comprehension. Moreover, other components of 4D technology like customary techniques, computational challenges, reversibility and current stature of 4D printing are probed through recent experimental and theoretical literature. Finally, potential applications of 4D printing are summarised with promising research directions and outlook. 4D printing: A future insight in additive manufacturing.

Chapter 7 - Polymers for additive manufacturing and 4D-printing for tissue regenerative applications

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.

Chapter 5 - Additive manufacturing (AM) of medical devices and scaffolds for tissue engineering based on 3D and 4D printing

The addition of the time dimension to three-dimensional (3D) printing has introduced four-dimensional (4D) printing technology, which has gained considerable attention in different fields such as medical, art, and engineering. Nowadays, bioscience has introduced some ideas which can be fulfilled by 4D printing. Blending time with variations caused by the situation has many beneficial aspects such as perceptibility and adaptability. Since 4D printing can create a dynamic structure with stimuli-responsive materials, the applications of smart materials, stimulus, and 3D printing are the effective criteria in 4D printing technology. Smart materials with their flexible properties can reshape, recolor, or change function under the effect of the internal or exterior stimuli. Thus, an attractive prospect in the medical field is the integration of the 4D printing approach along with smart materials. This research aims to show the most recent applications of 4D printing technology and smart materials in medical engineering which can show better prospective of 4D printing applications in the future. Also, it describes smart medical implants, tissue engineering, and bioprinting and how they are being used for the 4D printing approach in medical engineering applications. In this regard, a particular emphasis is dedicated to the latest progress in the innovation and development of stimuli-responsive materials that are activated and respond over time to physical, chemical, and biological stimuli and their exploitation through 3D printing methods to fabrication 4D printing smart parts such as intelligent tissue-engineered scaffolds, smart orthopedic implants, and targeted drug delivery systems. On the other hand, major challenges in this technology are explained along with some suggestions for future works to address existing limitations. It is worth noting that despite significant research that has been carried out into 4D printing, it might be more valuable if some investigation is done into 4D bio-printing applications and how this approach will be developed.

Stimuli-responsive materials for 4D Printing: Mechanical, Manufacturing, and Biomedical Applications