4D-printed hybrids with localized shape memory behaviour: Implementation in a functionally graded structure

Multi-color dual wavelength vat photopolymerization 3D printing via spatially controlled acidity

Dual wavelength vat photopolymerization (DW-VP) has emerged as a powerful approach to create multimaterial objects. However, only a limited range of properties have been showcased. In this work, we report the 3D printing (3DP) of multi-color objects from a single resin vat using DW-VP. This was accomplished by concurrently curing resin with visible light and modulating local resin color with 365-nm ultraviolet (UV) light. The key advance was to use a photoacid generator (PAG) in combination with pH responsive dyes in the 3DP resins. The specific color is dictated by the extent of reaction, or local acidity in our case, and controlled by the light dosage and pattern of UV light applied. Multi-color object formation was implemented in two-step processes involving first 3DP to set the object structure, followed by UV exposure, as well as single processes that leveraged DW-VP to create a broad range of vibrant colors and patterns.

Nanomaterials in 4D Printing: Expanding the Frontiers of Advanced Manufacturing

As an innovative technology, four-dimentional (4D) printing is built upon the principles of three-dimentional (3D) printing with an additional dimension: time. While traditional 3D printing creates static objects, 4D printing generates "responsive 3D printed structures", enabling them to transform or self-assemble in response to external stimuli. Due to the dynamic nature, 4D printing has demonstrated tremendous potential in a range of industries, encompassing aerospace, healthcare, and intelligent devices. Nanotechnology has gained considerable attention owing to the exceptional properties and functions of nanomaterials. Incorporating nanomaterials into an intelligent matrix enhances the physiochemical properties of 4D printed constructs, introducing novel functions. This review provides a comprehensive overview of current applications of nanomaterials in 4D printing, exploring their synergistic potential to create dynamic and responsive structures. Nanomaterials play diverse roles as rheology modifiers, mechanical enhancers, function introducers, and more. The overarching goal of this review is to inspire researchers to delve into the vast potential of nanomaterial-enabled 4D printing, propelling advancements in this rapidly evolving field.

A novel technology for preparing the placebos of vortioxetine hydrobromide tablets using LCD 3D printing

This study aimed to describe the use of liquid crystal display (LCD) three-dimensional (3D) printing technology to prepare moulds for vortioxetine hydrobromide (VOR) tablet placebos and provide an economical, convenient, and flexible method for the small-batch preparation of special-shaped, scored, and coated placebo tablets. First, LCD 3D printing was used to generate different placebo moulds of VOR tablets based on VOR tablet digital models subtracted from the digital models of cuboid moulds by Boolean operation to optimise the structures of moulds. The better placebo mould had a parting surface located at the 7/10 height of the packing cavities and the positioning columns and slots were three pairs, and the efflux space had slender efflux channels combined with wide efflux tanks. Next, the placebo mould was corrected by the dimensional compensation method due to the shrinkage rates of the packing cavities (2.42%) and placebo prescription (1.12%) and the thickness of the film coating (25.08 μm). The placebo prescription was 8% hydroxypropyl methylcellulose (SH K15M) hydroalcoholic gel, and its mass ratio to lactose was 0.8:2. The placebos were coated with 13% gastric-soluble film coating solution for 30 min and polished with the 30% PEG 4000 solution. The National Bureau of Standards value between the VOR tablets and their placebos was 1.22 ± 0.10 (less than1.5). Finally, the mass of the placebos was similar to that of the VOR tablets. Their dimensional differences were less than 0.1 mm. Their mass, colour, odour, shape, and texture were all similar, which were assessed by manual evaluation. In conclusion, the preparations of VOR tablet placebos can be applied in placebo-controlled trials, and LCD 3D printing has an extensive application value in preparing placebo tablets.

Effect of Printing Process Parameters on the Shape Transformation Capability of 3D Printed Structures

The aim of our research was to investigate and optimise the main 3D printing process parameters that directly or indirectly affect the shape transformation capability and to determine the optimal transformation conditions to achieve predicted extent, and accurate and reproducible transformations of 3D printed, shape-changing two-material structures based on PLA and TPU. The shape-changing structures were printed using the FDM technology. The influence of each printing parameter that affects the final printability of shape-changing structures is presented and studied. After optimising the 3D printing process parameters, the extent, accuracy and reproducibility of the shape transformation performance for four-layer structures were analysed. The shape transformation was performed in hot water at different activation temperatures. Through a careful selection of 3D printing process parameters and transformation conditions, the predicted extent, accuracy and good reproducibility of shape transformation for 3D printed structures were achieved. The accurate deposition of filaments in the layers was achieved by adjusting the printing speed, flow rate and cooling conditions of extruded filaments. The shape transformation capability of 3D printed structures with a defined shape and defined active segment dimensions was influenced by the relaxation of compressive and tensile residual stresses in deposited filaments in the printed layers of the active material and different activation temperatures of the transformation.

Materials for Smart Soft Actuator Systems

In contrast to conventional hard actuators, soft actuators offer many vivid advantages, such as improved flexibility, adaptability, and reconfigurability, which are intrinsic to living systems. These properties make them particularly promising for different applications, including soft electronics, surgery, drug delivery, artificial organs, or prosthesis. The additional degree of freedom for soft actuatoric devices can be provided through the use of intelligent materials, which are able to change their structure, macroscopic properties, and shape under the influence of external signals. The use of such intelligent materials allows a substantial reduction of a device's size, which enables a number of applications that cannot be realized by externally powered systems. This review aims to provide an overview of the properties of intelligent synthetic and living/natural materials used for the fabrication of soft robotic devices. We discuss basic physical/chemical properties of the main kinds of materials (elastomers, gels, shape memory polymers and gels, liquid crystalline elastomers, semicrystalline ferroelectric polymers, gels and hydrogels, other swelling polymers, materials with volume change during melting/crystallization, materials with tunable mechanical properties, and living and naturally derived materials), how they are related to actuation and soft robotic application, and effects of micro/macro structures on shape transformation, fabrication methods, and we highlight selected applications.

Extrusion-Based 3D Printing Applications of PLA Composites: A Review

Polylactic acid (PLA) is the most widely used raw material in extrusion-based three-dimensional (3D) printing (fused deposition modeling, FDM approach) in many areas since it is biodegradable and environmentally friendly, however its utilization is limited due to some of its disadvantages such as mechanical weakness, water solubility rate, etc. FDM is a simple and more cost-effective fabrication process compared to other 3D printing techniques. Unfortunately, there are deficiencies of the FDM approach, such as mechanical weakness of the FDM parts compared to the parts produced by the conventional injection and compression molding methods. Preparation of PLA composites with suitable additives is the most useful technique to improve the properties of the 3D-printed PLA parts obtained by the FDM method. In the last decade, newly developed PLA composites find large usage areas both in academic and industrial circles. This review focuses on the chemistry and properties of pure PLA and also the preparation methods of the PLA composites which will be used as a raw material in 3D printers. The main drawbacks of the pure PLA filaments and the necessity for the preparation of PLA composites which will be employed in the FDM-based 3D printing applications is also discussed in the first part. The current methods to obtain PLA composites as raw materials to be used as filaments in the extrusion-based 3D printing are given in the second part. The applications of the novel PLA composites by utilizing the FDM-based 3D printing technology in the fields of biomedical, tissue engineering, human bone repair, antibacterial, bioprinting, electrical conductivity, electromagnetic, sensor, battery, automotive, aviation, four-dimensional (4D) printing, smart textile, environmental, and luminescence applications are presented and critically discussed in the third part of this review.

3D-Printed Objects for Multipurpose Applications

3D printing is a popular nonconventional manufacturing technique used to print 3D objects by using conventional and nonconventional materials. The application and uses of 3D printing are rapidly increasing in each dimension of the engineering and medical sectors. This article overviews the multipurpose applications of 3D printing based on current research. In the beginning, various popular methods including fused deposition method, stereolithography 3D printing method, powder bed fusion method, digital light processing method, and metal transfer dynamic method used in 3D printing are discussed. Popular materials utilized randomly in printing techniques such as hydrogel, ABS, steel, silver, and epoxy are overviewed. Engineering applications under the current development of the printing technique which include electrode, 4D printing technique, twisting object, photosensitive polymer, and engines are focused. Printing of medical equipment including artificial tissues, scaffolds, bioprinted model, prostheses, surgical instruments, COVID-19, skull, and heart is of major focus. Characterization techniques of the printed 3D products are mentioned. In addition, potential challenges and future prospects are evaluated based on the current scenario. This review article will work as a masterpiece for the researchers interested to work in this field.

Significant advancements of 4D printing in the field of orthopaedics

Researchers, engineers and doctors are continuously focusing on the development of orthopaedics parts characterised by the required responses. So, advanced manufacturing technologies are introduced to fulfil various previously faced challenges. 4D printing provides rapid development with its capability of customization of smart orthopaedics implants and appropriate surgical procedure. This technology opens up the making of innovative, adaptable internal splints, stents, replacement of tissues and organs. Thus, to write this review based article, relevant papers on 4D printing in medical/orthopaedics and smart materials are identified and studied. 4D printed parts show the capability of shape-changing and self-assembly to perform the required functions, which otherwise manufactured parts are not providing. Smart orthopaedics implants are used for spinal deformities, fracture fixation, joint, knee replacement and other related orthopaedics applications. This paper briefs about the 4D printing technology with its major benefits for orthopaedics applications. Today various smart materials are available, which could be used as raw material in 4D printing, and we have discussed capabilities of some of them. Due to the ability of shape-changing, smart implants can change their shape after being implanted in the patient body. Finally, twelve significant advancements of 4D printing in the field of orthopaedics are identified and briefly provided. Thus, 4D printing help to provide a significant effect on personalised treatments.

Two-Way and Multiple-Way Shape Memory Polymers for Soft Robotics: An Overview

Shape memory polymers (SMPs) are smart materials capable of changing their shapes in a predefined manner under a proper applied stimulus and have gained considerable interest in several application fields. Particularly, two-way and multiple-way SMPs offer unique opportunities to realize untethered soft robots with programmable morphology and/or properties, repeatable actuation, and advanced multi-functionalities. This review presents the recent progress of soft robots based on two-way and multiple-way thermo-responsive SMPs. All the building blocks important for the design of such robots, i.e., the base materials, manufacturing processes, working mechanisms, and modeling and simulation tools, are covered. Moreover, examples of real-world applications of soft robots and related actuators, challenges, and future directions are discussed.