AI-enhanced magnetically controlled 4D printing: Reshaping the future of medical robotics

4D printing: Pragmatic progression in biofabrication

Modular 4D Printing Assisted by Dynamic Chemical Bonds

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 Perhaps, additive manufacturing technology seems to be superseded exclusively by this modern technology in forthcoming years, and much effort is demanding from every discipline to actualize this technology.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.

With the approval of first 3D printed drug “spritam” by USFDA, 3D printing is gaining acceptance in healthcare, engineering and other aspects of life. Taking 3D printing towards the next step gives birth to what is referred to as “4D printing”. The full credit behind the unveiling of 4D printing technology in front of the world goes to Massachusetts Institute of Technology (MIT), who revealed “time” in this technology as the fourth dimension. 4D printing is a renovation of 3D printing wherein special materials (referred to as smart materials) are incorporated which change their morphology post printing in response to a stimulus. Depending upon the applicability of this technology, there may be a variety of stimuli, most common among them being pH, water, heat, wind and other forms of energy. The upper hand of 4D printing over 3D printing is that 3D printed structures are generally immobile, rigid and inanimate whereas 4D printed structures are flexible, mobile and able to interact with the surrounding environment based on the stimulus. This capability of 4D printing to transform 3D structures into smart structures in response to various stimuli promises a great potential for biomedical and bioengineering applications. The potential of 4D printing in developing pre-programmed biomaterials that can undergo transformations lays new foundations for enabling smart pharmacology, personalized medicine, and smart drug delivery, all of which can help in combating diseases in a smarter way. Hence, the theme of this paper is about the potential of 4D printing in creating smart drug delivery, smart pharmacology, targeted drug delivery and better patient compliance. The paper highlights the recent advancements of 4D printing in healthcare sector and ways by which 4D printing is doing wonders in creating smart drug delivery and tailored medicine. The major constraints in the approach have also been highlighted.
 Keywords: 4D printing, smart, drug delivery system, patient compliance, biomaterials, tailored medicine

PurposeThis study aims to discuss the state-of-the-art digital factory (DF) development combining digital twins (DTs), sensing devices, laser additive manufacturing (LAM) and subtractive manufacturing (SM) processes. The current shortcomings and outlook of the DF also have been highlighted. A DF is a state-of-the-art manufacturing facility that uses innovative technologies, including automation, artificial intelligence (AI), the Internet of Things, additive manufacturing (AM), SM, hybrid manufacturing (HM), sensors for real-time feedback and control, and a DT, to streamline and improve manufacturing operations.Design/methodology/approachThis study presents a novel perspective on DF development using laser-based AM, SM, sensors and DTs. Recent developments in laser-based AM, SM, sensors and DTs have been compiled. This study has been developed using systematic reviews and meta-analyses (PRISMA) guidelines, discussing literature on the DTs for laser-based AM, particularly laser powder bed fusion and direct energy deposition, in-situ monitoring and control equipment, SM and HM. The principal goal of this study is to highlight the aspects of DF and its development using existing techniques.FindingsA comprehensive literature review finds a substantial lack of complete techniques that incorporate cyber-physical systems, advanced data analytics, AI, standardized interoperability, human–machine cooperation and scalable adaptability. The suggested DF effectively fills this void by integrating cyber-physical system components, including DT, AM, SM and sensors into the manufacturing process. Using sophisticated data analytics and AI algorithms, the DF facilitates real-time data analysis, predictive maintenance, quality control and optimal resource allocation. In addition, the suggested DF ensures interoperability between diverse devices and systems by emphasizing standardized communication protocols and interfaces. The modular and adaptable architecture of the DF enables scalability and adaptation, allowing for rapid reaction to market conditions.Originality/valueBased on the need of DF, this review presents a comprehensive approach to DF development using DTs, sensing devices, LAM and SM processes and provides current progress in this domain.

Abstract4D printing extends conventional additive manufacturing (AM) by enabling dynamic shape‐morphing structures that adapt to environmental stimuli. However, the spatial resolution of conventional 4D printing is often constrained by nozzle size, laser spot diameter, and material rheology, limiting its adoption in precision‐demanding engineering applications. High‐resolution 4D printing, integrating micro/nanoscale AM techniques with sub‐100 μm to sub‐100 nm structural resolution and stimuli‐responsive smart materials, has emerged as a promising solution to these challenges. Over the past decade, this approach has made significant strides in fields such as soft robotics, biomedical devices, flexible electronics, and microfluidic systems. This review summarizes recent progress in high‐resolution 4D printing, emphasizing key printing technologies such as digital light processing, PolyJet, projection micro‐stereolithography, two‐photon polymerization, and direct ink writing. A range of smart materials, including shape memory polymers, hydrogels, liquid crystal elastomers, and composite systems, are examined alongside their external stimuli, such as heat, light, humidity, and magnetic fields. Furthermore, the engineering applications enabled by high‐resolution 4D printing are discussed. Finally, the review highlights current challenges in material development, structural design, actuation speed, and scalable fabrication while offering future perspectives to stimulate further research and accelerate the industrial translation of high‐resolution 4D printing technologies.

Recent advances in multi‐material 3D and 4D printing (time as the fourth dimension) show that the technology has the potential to extend the design space beyond complex geometries. The potential of these additive manufacturing (AM) technologies allows for functional inclusion in a low‐cost single‐step manufacturing process. Different composite materials and various AM technologies can be used and combined to create customized multi‐functional objects to suit many needs. In this work, several types of 3D and 4D printing technologies are compared and the advantages and disadvantages of each technology are discussed. The various features and applications of 3D and 4D printing technologies used in the fabrication of multi‐material objects are reviewed. Finally, new avenues for the development of multi‐material 3D and 4D printed objects are proposed, which reflect the current deficiencies and future opportunities for inclusion by AM.

Additive manufacturing has evolved over the last few decades. Three-dimensional printing is a digital manufacturing technology that provides nearly endless options for the creation of an accessible instrument for all parts of various medical practices, including tissue engineering, through meticulous optimization of material, processing, and geometry for every point in an object. Three-dimensional printing has opened up a new, faster, and safer manufacturing process, despite its incapability to fabricate complex structures and objects. Recently, novel four-dimensional printing techniques have been developed for the transformation of typical stable three-dimensional printed parts into smart objects. The limitations of three-dimensional printing could be remedied with four-dimensional printing, by applying time as the fourth dimension. Self-repairing and speedy printing are two additional benefits of this technology's by using smart materials. By adapting this technology, numerous medical domains could be profited. Four-dimensional printing does not have the ability to produce curved complicated forms. However, five-dimensional printing overcomes the flaws seems in four-dimensional printing. Five-dimensional additive manufacturing relies on the rotation of both the print bed and the extruder head. Five-dimensional printing outlasts in terms of durability than three- and four-dimensional printing. Currently, a combination of the principles of four- and five-dimensional printing into a single process is called six-dimensional printing. In six-dimensional printing, the form changes over time due to the reaction of environmental factors, which is primarily used in biomedical applications. This paper summarizes extensive research on biomaterials in the field of biomedical science and discusses the present implications of three-, four-, five-, and six-dimensional printing techniques.

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.

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

The existing 3D printing methods exhibit certain fabrication-dependent limitations for printing curved constructs that are relevant for many tissues. Four-dimensional (4D) printing is an emerging technology that is expected to revolutionize the field of tissue engineering and regenerative medicine (TERM). 4D printing is based on 3D printing, featuring the introduction of time as the fourth dimension, in which there is a transition from a 3D printed scaffold to a new, distinct, and stable state, upon the application of one or more stimuli. Here, we present an overview of the current developments of the 4D printing technology for TERM, with a focus on approaches to achieve temporal changes of the shape of the printed constructs that would enable biofabrication of highly complex structures. To this aim, the printing methods, types of stimuli, shape-shifting mechanisms, and cell-incorporation strategies are critically reviewed. Furthermore, the challenges of this very recent biofabrication technology as well as the future research directions are discussed. Our findings show that the most common printing methods so far are stereolithography (SLA) and extrusion bioprinting, followed by fused deposition modelling, while the shape-shifting mechanisms used for TERM applications are shape-memory and differential swelling for 4D printing and 4D bioprinting, respectively. For shape-memory mechanism, there is a high prevalence of synthetic materials, such as polylactic acid (PLA), poly(glycerol dodecanoate) acrylate (PGDA), or polyurethanes. On the other hand, different acrylate combinations of alginate, hyaluronan, or gelatin have been used for differential swelling-based 4D transformations. TERM applications include bone, vascular, and cardiac tissues as the main target of the 4D (bio)printing technology. The field has great potential for further development by considering the combination of multiple stimuli, the use of a wider range of 4D techniques, and the implementation of computational-assisted strategies.

Four-dimensional (4D) printing is one of the emerging technologies. The fourth dimension in 4D printing refers to the ability of 3D printed material objects to alter its geometric configuration from one to another in a fully controllable manner, thus providing additional functional capabilities and performance-driven applications. With the additional dimension, 4D printing is emerging as a novel technique to enable configuration switching in 3D printed items. The purpose of this paper is to briefly discuss the 4D printing and to review some applications to demonstrate the potential of 4D printing.

Over the last decade, image-guided production of three-dimensional (3D) haptic biomodels, or rapid prototyping (RP), has transformed the way surgeons conduct preoperative planning. In contrast to earlier RP techniques such as stereolithography, 3D printing has introduced fast, affordable office-based manufacturing. We introduce the concept of 4D printing for the first time by introducing time as the fourth dimension to 3D printing. The bones of the thumb ray are 3D printed during various movements to demonstrate four-dimensional (4D) printing. Principles and validation studies are presented here. 4D computed tomography was performed using "single volume acquisition" technology to reduce the exposure to radiation. Three representative scans of each thumb movement (i.e., abduction, opposition, and key pinch) were selected and then models were fabricated using a 3D printer. For validation, the angle between the first and the second metacarpals from the 4D imaging data and the 4D-printed model was recorded and compared. We demonstrate how 4D printing accurately depicts the transition in the position of metacarpals during thumb movement. With a fourth dimension of time, 4D printing delivers complex spatiotemporal anatomical details effortlessly and may substantially improve preoperative planning.

4D printing and stimuli-responsive materials in biomedical aspects

The biomedical industry has witnessed a transformative evolution with the advent of 3D printing technology. However, inherent limitations, such as the inability to produce dynamic human tissues due to the absence of the temporal dimension, have persisted, resulting in static and inanimate printed products. To address this challenge and enable the creation of dynamic and living constructs, the concept of 4D printing has emerged, marking a paradigm shift in additive manufacturing. In 4D printing, time becomes the fourth dimension, breathing life into previously static creations. This review paper explores the journey from 3D to 4D printing and the pivotal role of time in the additive manufacturing process. Specifically, it highlights the integration of time-dependent responsive materials, focusing on stimuli-responsive hydrogels, as a cornerstone in 4D printing advancements. These materials exhibit a remarkable ability to adapt and respond to various stimuli, encompassing physical, chemical, and biological signals. The review delves into recent publications on the synergy between these stimuli and responsive materials, shedding light on their intricate interactions and potential applications. One of the primary areas of interest lies in medical applications, notably tissue engineering, where 4D printing holds immense promise. The paper explores the utilization of 4D printing in creating biomimetic scaffolds that can dynamically adapt to complex tissue environments. Furthermore, the review discusses the technical considerations and prospects of 4D printing technology, emphasizing its potential to revolutionize the biomedical landscape. The amalgamation of 4D printing and stimuli-responsive materials opens new avenues for personalized medicine, localized drug delivery, and regenerative therapies, bridging the gap between static 3D printing and the dynamic requirements of modern healthcare. The present review offers a complete examination of the evolution, challenges, and prospects of 4D printing in biomedical applications, paving the way for transformative innovations in the field.