Progress in 4D/5D/6D printing of foods: applications and R&D opportunities.

4D printing is a result of 3D printing of smart materials which respond to diverse stimuli to produce novel products. 4D printing has been applied successfully to many fields, e.g., engineering, medical devices, computer components, food processing, etc. The last two years have seen a significant increase in studies on 4D as well as 5D and 6D food printing. This paper reviews and summarizes current applications, benefits, limitations, and challenges of 4D food printing. In addition, the principles, current, and potential applications of the latest additive manufacturing technologies (5D and 6D printing) are reviewed and discussed. Presently, 4D food printing applications have mainly focused on achieving desirable color, shape, flavor, and nutritional properties of 3D printed materials. Moreover, it is noted that 5D and 6D printing can in principle print very complex structures with improved strength and less material than do 3D and 4D printing. In future, these new technologies are expected to result in significant innovations in all fields, including the production of high quality food products which cannot be produced with current processing technologies. The objective of this review is to identify industrial potential of 4D printing and for further innovation utilizing 5D and 6D printing.

Methods for biomaterials printing: A short review and perspective.

Printing technologies have opened larger windows of innovation and creativity to biomaterials engineers by providing them with the ability to fabricate complex shapes in a reasonable time, cost, and weight. However, there has always been a trouble with function adjusting in printing technologies in view of the multiplicity of materials and apparatus parameters. 3D printing, also known as additive manufacturing, revolutionized biomaterials engineering by the conversion of a digital subject into a printed object (implants, scaffolds, or diagnostics and drug delivery devices/systems).Inspired by the lessons learned from 3D printing, the concept of 4D printing (better called shape-morphing fabrication) was conceptualized and put into practice to reply on the need for responsiveness of the printed platforms to a stimulus (light, pH, temperature, voltage, humidity, etc.) in a programmable manner. Later, the next milestone in printing technology was reached by 5D printing, by which the desired objects could be printed from five axes compared to the upward one-point printing by 3D printers. 5D printers use ≈20-30% fewer materials comparatively, enabling the printing of curved surfaces. Nevertheless, all bioprinters need a bio-ink with qualified characteristics for the biomedical applications. Thus, we discussed briefly the cell viability, scaffold biomimicry, scaffold biodegradation and affordability.

Future trends of additive manufacturing in medical applications: An overview.

Additive Manufacturing (AM) has recently demonstrated significant medical progress. Due to advancements in materials and methodologies, various processes have been developed to cater to the medical sector's requirements, including bioprinting and 4D, 5D, and 6D printing. However, only a few studies have captured these emerging trends and their medical applications. Therefore, this overview presents an analysis of the advancements and achievements obtained in AM for the medical industry, focusing on the principal trends identified in the annual report of AM3DP.

The clinical significance of 4D printing.

4D printing is the next step on from 3D printing involving the fourth dimension of 'time'. The programmed 4D-printed objects are capable of changing their shape in response to external stimuli, such as light, heat, or water, differentiating them from 3D-printed static objects. This technique promises new possibilities for cancer treatment, drug delivery, stent development, and tissue engineering. In this review, we focus on the development of 4D-printed objects, their clinical use, and the possibility of 5D printing, which could revolutionize the fields of biomedical engineering and drug delivery.

Artificial Intelligence Assisted Fabrication of 3D, 4D and 5D Printed Formulations or Devices for Drug Delivery.

5D & 4D printings are an advanced version of 3D printing class and are one of the most revolutionary and powerful fabrication methods used for preparing innovative structures and solid substances using precise additive manufacturing technology. It captures the imagination of one with its potential to produce flexible designing and fabrication of innovative products with high complexity and speed. This technology with the assistance of AI (Artificial Intelligence) facilitates real-time sensing, adapting to change, and predicting the state of printing. 3D printing works by employing advanced materials utilizing a computer aided design with tomography scan under AI control which deposits printing material in accordance with the nature of a file usually in STL format, but it requires time for printing. This shortcoming can be overcome by 4D printing where smart materials are incorporated with time as 4th dimension. This technique has self-repair and self-assembly properties that will save around 80% of time. Some printed materials are made sensitive to temperature, humidity, light, and other parameters so that they can respond to stimulus, but it's one limitation of not being able to print complex shapes having curved surfaces can be overcome by utilising 5D printing where additive manufacturing is done by rotation of extruder head and rotation of print bed to print in 5 different axes. This review evaluates the prospective of these techniques with AI interference in medicine and pharmacy, with its effective and efficient production for the required design precision.

From Three-Dimensional (3D)- to 6D-Printing Technology in Orthopedics: Science Fiction or Scientific Reality?

Over the past three decades, additive manufacturing has changed from an innovative technology to an increasingly accessible tool in all aspects of different medical practices, including orthopedics. Although 3D-printing technology offers a relatively inexpensive, rapid and less risky route of manufacturing, it is still quite limited for the fabrication of more complex objects. Over the last few years, stable 3D-printed objects have been converted to smart objects or implants using novel 4D-printing systems. Four-dimensional printing is an advanced process that creates the final object by adding smart materials. Human bones are curved along their axes, a morphological characteristic that augments the mechanical strain caused by external forces. Instead of the three axes used in 4D printing, 5D-printing technology uses five axes, creating curved and more complex objects. Nowadays, 6D-printing technology marries the concepts of 4D- and 5D-printing technology to produce objects that change shape over time in response to external stimuli. In future research, it is obvious that printing technology will include a combination of multi-dimensional printing technology and smart materials. Multi-dimensional additive manufacturing technology will drive the printing dimension to higher levels of structural freedom and printing efficacy, offering promising properties for various orthopedic applications.

Effect of Elevation and Surface Roughness on Naturalness Perception of 2.5D Decor Prints.

Naturalness is a complex concept. It can involve a variety of attributes. In this work, we considered the effect of elevation and surface roughness on naturalness perception of 2.5D decor prints for four material categories. We found that elevation has an impact on the naturalness perception of 2.5D decor prints and that it is linked with content. The observers found lower elevation to be more natural for wood and glass 2.5D prints while there was no clear tendency for stone and metal 2.5D prints. We also found the perceptual attributes used for naturalness assessment of 2.5D decor prints. The top five ones are color, roughness, gloss, elevation, and lightness. The obtained findings can be useful for companies that produce 2.5D prints.

What Elevation Makes 2.5D Prints Perceptually Natural?

Elevation plays a considerable role in naturalness perception of 2.5D prints. The necessary level of elevation to make 2.5D prints look perceptually natural may vary from application to application. Therefore, one needs to know the right elevation for specific applications to make the prints look perceptually natural. In this work, we investigated what elevation makes 2.5D prints of wood images perceptually natural. We worked with various wood content images such as wooden wicker, wall, roof, and floor. We found that the optimal elevation that makes 2.5D prints of wood images perceptually natural is content-dependent and in a range between 0.3 mm and 0.5 mm. Moreover, we found that the optimal elevation becomes 0.5 mm if we consider images of wood regardless of the wood content. In addition, there was a high correlation between majority of observers on naturalness perception of 2.5D prints of wood images.

Artificial Intelligence-Empowered 3D and 4D Printing Technologies toward Smarter Biomedical Materials and Approaches.

In the last decades, 3D printing has played a crucial role as an innovative technology for tissue and organ fabrication, patient-specific orthoses, drug delivery, and surgical planning. However, biomedical materials used for 3D printing are usually static and unable to dynamically respond or transform within the internal environment of the body. These materials are fabricated ex situ, which involves first printing on a planar substrate and then deploying it to the target surface, thus resulting in a possible mismatch between the printed part and the target surfaces. The emergence of 4D printing addresses some of these drawbacks, opening an attractive path for the biomedical sector. By preprogramming smart materials, 4D printing is able to manufacture structures that dynamically respond to external stimuli. Despite these potentials, 4D printed dynamic materials are still in their infancy of development. The rise of artificial intelligence (AI) could push these technologies forward enlarging their applicability, boosting the design space of smart materials by selecting promising ones with desired architectures, properties, and functions, reducing the time to manufacturing, and allowing the in situ printing directly on target surfaces achieving high-fidelity of human body micro-structures. In this review, an overview of 4D printing as a fascinating tool for designing advanced smart materials is provided. Then will be discussed the recent progress in AI-empowered 3D and 4D printing with open-loop and closed-loop methods, in particular regarding shape-morphing 4D-responsive materials, printing on moving targets, and surgical robots for in situ printing. Lastly, an outlook on 5D printing is given as an advanced future technique, in which AI will assume the role of the fifth dimension to empower the effectiveness of 3D and 4D printing for developing intelligent systems in the biomedical sector and beyond.