4D Printing Materials Research Articles

Isolation of Fiber-Cellulose and Characterization from Oil Palm Frond for 3D and 4D Printing Materials Application

The oil palm frond (OPF), a primary biomass derived from agricultural waste in oil palm production, holds significant potential for evolving into cellulose fiber. Leveraging natural materials for cellulose extraction aligns with environmental sustainability. In this study, we focus on separating cellulose fibers from OPF biomass. The OPF is divided into its leaflet and frond-axial parts, undergoing a sequence of steps: dewaxing, alkaline treatment, delignification, hydrogen peroxide treatment, and final filtration. These steps assess both efficacy and cellulose fiber outputs. Notably, the axial and leaflet portions yield cellulose fibers, effective as an initial extraction step before progressing to nanoscale slicing. Quantitatively, extraction yields indicate that 14.13% and 19.52% of the 100 g leaflet and frond-axial portions can be harvested. SEM images confirm well-dispersed individual fibers. Additionally, GCMS results reveal slightly higher carbon dioxide gas in the palm leaflet sample than in the palm frond-axial sample after five days of water soaking. This procedure efficiently initializes OPF for cellulose extraction, positioning it as an initial ingredient for subsequent 3D/4D printing material production.

Fluorescent Polylactic acid composite incorporating lignin-based carbon quantum dots for sustainable 4D printing applications

Fluorescent 4D printing materials, as innovative materials that combine fluorescent characteristics with 4D printing technology, have attracted widespread interest and research. In this study, green lignin-derived carbon quantum dots (CQDs) were used as the fluorescent module, and renewable poly(propylene carbonate) polyurethane (PPCU) was used for toughening. A new low-cost fluorescent polylactic acid (PLA) composite filament for 4D printing was developed using a simple melt extrusion method. The strength of the prepared composite was maintained at 32 MPa, while the elongation at break increased 8-fold (34 % increase), demonstrating excellent shape fixed ratio (∼99 %), recovery ratio (∼92 %), and rapid shape memory recovery speed. The presence of PPCU prevented fluorescence quenching of the CQDs in the PLA matrix, allowing the composite to emit bright green fluorescence under 365 nm ultraviolet light. The composite exhibited shear thinning behavior and had an ideal melt viscosity for 3D printing. The results obtained demonstrated the versatility of these easy-to-manufacture and low-cost filaments, opening up a novel and convenient method for the preparation of strong, tough, and multifunctional PLA materials, increasing their potential application value.

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

Four-dimensional printing (4DP) is an interesting field of study that integrates intelligent materials into three-dimensional printing (3DP). Using this method, objects that can gradually change form in response to environmental stimuli, such as moisture, electric or magnetic fields, UV light, temperature swings, pH variations, or alterations in the composition of ions, can be created. Intelligent materials, such as shape memory polymers, alloys, hydrogels, ceramics, and composites, which can react to external stimuli, are essential for 4DP. Unlike traditional 3D printing, the ability of 4D printed materials to undergo structural and/or property alterations expands their applications across industries such as aerospace, biomedical, soft robotics, engineering, and fashion, potentially revolutionizing manufacturing. This review provides an overview of current advancements in 4D printing and discusses both established and emerging smart materials with shape-changing capabilities and their responses to stimuli. It explores the differences between 4D and 3D printing technologies, traces the origins of 4D printing, and examines the materials involved, with emphasis on shape-memory polymers. This paper also highlights the applications of 4D printing in pharmaceuticals and biomedicine, particularly in dynamic polymers, and in the development of drugs for genetic diseases. In addition, it discusses progress in creating implantable biomedical devices and pharmaceutical medications. Despite being in its early stages, 4D printing technology has immense potential and promising exciting possibilities in the future.

4D printing and simulation of body temperature-responsive shape-memory polymers for advanced biomedical applications

Four-dimensional (4D) bioprinting holds significant promise in precision medicine, enabling the emulation of dynamic changes in the human body and tissues to provide personalized treatments. Smart materials for 4D printing (i.e., responsive to specific stimuli) should exhibit properties, such as biodegradability, biocompatibility, and ease of processing, while also enabling the prediction of time-dependent behavior in programmed geometry. This study focused on the development of a body temperature-responsive shape-memory polymer (SMP). The thermal properties of the SMP were analyzed, and its biodegradability and biocompatibility were assessed through structures fabricated by three-dimensional printing techniques. The simulation calculated with this finite element (FE) solution was in good agreement with those measured in experiments. The findings contribute to our understanding of the behavior of SMP under various conditions, validating the effectiveness of the developed material for potential applications in precision medicine and 4D bioprinting. It has the potential for use in medical devices, such as catheters, stents, and artificial scaffolds, prepared by 4D bioprinting.  

Bioprinting of gelatin-based materials for orthopedic application.

Bio-printed hydrogels have evolved as one of the best regenerative medicine and tissue engineering platforms due to their outstanding cell-friendly microenvironment. A correct hydrogel ink formulation is critical for creating desired scaffolds that have better fidelity after printing. Gelatin and its derivatives have sparked intense interest in various biomedical sectors because of their biocompatibility, biodegradability, ease of functionalization, and rapid gelling tendency. As a result, this report emphasizes the relevance of gelatin-based hydrogel in fabricating bio-printed scaffolds for orthopedic applications. Starting with what hydrogels and bio-printing are all about. We further summarized the different gelatin-based bio-printing techniques explored for orthopedic applications, including a few recent studies. We also discussed the suitability of gelatin as a biopolymer for both 3D and 4D printing materials. As extrusion is one of the most widely used techniques for bio-printing gelatin-based, we summarize the rheological features of gelatin-based bio-ink. Lastly, we also elaborate on the recent bio-printed gelatin-based studies for orthopedics applications, the potential clinical translation issues, and research possibilities.

PH and temperature responsive UV curable lignin-based hydrogels with controllable and outstanding compressive properties

Functional hydrogels have been widely researched in various fields. However, preparing bio-hydrogels with several functionalities, such as desirable mechanical properties, high swelling ability, and stimuli-responsive properties, still presents a challenge. In this study, a UV-curable lignin-based bio-hydrogel was produced via methacrylation using glycidyl methacrylate, followed by cross-linking with acrylamide. The synthesized lignin hydrogel showed outstanding compressive performance, durability properties, and rheological behaviors, which could be engineered by changing the lignin content. With the increase in lignin concentration, the crosslinking density and storage/loss modulus were increased, whereas tan δ was decreased. Additionally, the hydrogels exhibited excellent swelling ratios (up to several thousand %), meanwhile their swelling behavior and dimensional changes varied with the lignin concentration, and strongly depended on temperature and pH. Finally, a smart strip-shaped hydrogel was designed to explore an actuator behavior, showing a fast and reversible swelling-deswelling response between pH 3 and 9. This can indicate that the lignin-based hydrogel could be a promising material for biomedical applications and 4D printing materials.

Revolutionizing manufacturing: A review of 4D printing materials, stimuli, and cutting-edge applications

The concept of four-dimensional (4D) printing emerged from the addition of the time dimension into the more established additive manufacturing (AM) methods, namely 3D printing technologies. Incorporating the element of time into 4D printing allows the resulting structures to change and adapt over time in response to external or internal stimuli such as light, heat, magnetism, electricity, solvent, pH, etc. Thus, only smart materials such as shape memory polymers, alloys, hydrogels, ceramics, and composites that possess the ability to respond to a stimulus can be used. In comparison to 3D printing, the change in structure and/or property allows for broader applications of 4D printed materials in the aerospace, biomedical, soft robotics, engineering, and fashion industries, and it has the potential to completely revolutionize the manufacturing industry. Herein, we have reviewed in detail the current developments in 4D printing, the available and new smart (shape-changing) materials, and how they respond to internal or external stimuli, following a short description of the definition, concept, and background of 4D printing. The cutting-edge current and potential applications of the 4D printed structures in the field of aerospace, biomedical, soft robotics, engineering, and fashion and apparel are reviewed in detail. Lastly, the review addresses future prospects including the potential future research areas, and market trends, as well as the challenges that need to be overcome for its widespread adoption. Although 4D printing technology is still in its very early phases of development, the possibilities are unlimited, and much like 3D printing, the future seems exciting. This document provides a cutting-edge review of this fascinating new field of 4D printing technology.

A REVIEW ON 4D ADDITIVE MANUFACTURING - THE APPLICATIONS, SMART MATERIALS & EFFECT OF VARIOUS STIMULI ON 4D PRINTED OBJECTS

Additive Manufacturing, often known as 3D printing, is a process that uses a variety of materials to manufacture highly accurate items layer by layer. However, this technology has its limitations. One such limitation is the inability to print components larger than the printer's size due to the limited size of the build chamber. 4D additive manufacturing or 4D printing is an innovative development based on 3D printing that allows objects to be reshaped after printing, using stimuli-responsive materials that require external stimuli. This article present a review on 4D printing. Four databases, Google Scholar, ScienceDirect, IEEE Xplore, and Scopus database, were systematically searched for relevant review articles to identify and classify research studies. Specific keywords (4D printing, additive manufacturing, smart materials, stimuli, and application) were identified and used to guide the discovery of relevant studies. A total of 28 full articles were reviewed to study the applications of 4D printing, smart materials for 4D printing, as well as the effect of various stimuli on 4D printed objects. In conclusion, this review gives a summary of 4D printing and highlights its potential for revolutionizing manufacturing and further research is required to solve the limitations posed by this technology.

Sustainable feedstocks for 4D printing: biodegradable polymers and natural resources

Additive manufacturing is an emerging technology supported by ‘Industry 4.0’. When combined with a stimulus-responsive behavior, incorporating the fourth dimension of time, it results in a manufacturing technique known as four-dimensional (4D) printing. 4D-printed entities have the distinctive characteristic of property transformation, under the influence of a drafted stimulus, which can be cleverly engineered for the desired application. The conventional stimulus-driven smart printing inks deployed in 4D printing are non-biodegradable polymers that pose a challenge to sustainability. Hence, it is imperative to appraise the utilization of sustainable raw materials, composed of natural and synthetic biodegradable polymers, as feedstocks for 4D printing. Natural resources have fluctuating properties, which make them receptive toward intelligent engineering. This review is an effort toward the implementation of sustainable feedstocks as printing inks for 4D printing, for eventual environmental benignity. It covers several sustainable raw materials for 4D printing and the strategies to use them in conjunction with conventional inks in order to bring down the volume of non-biodegradables. This review can serve as a reference for designers and engineers wishing to use sustainable inks for 4D printing, thereby boosting the momentum needed to consolidate this next-generation technology in line with the UN Sustainable Development Goals.

Dental Materials Applied to 3D and 4D Printing Technologies: A Review.

As computer-aided design and computer-aided manufacturing (CAD/CAM) technologies have matured, three-dimensional (3D) printing materials suitable for dentistry have attracted considerable research interest, owing to their high efficiency and low cost for clinical treatment. Three-dimensional printing technology, also known as additive manufacturing, has developed rapidly over the last forty years, with gradual application in various fields from industry to dental sciences. Four-dimensional (4D) printing, defined as the fabrication of complex spontaneous structures that change over time in response to external stimuli in expected ways, includes the increasingly popular bioprinting. Existing 3D printing materials have varied characteristics and scopes of application; therefore, categorization is required. This review aims to classify, summarize, and discuss dental materials for 3D printing and 4D printing from a clinical perspective. Based on these, this review describes four major materials, i.e., polymers, metals, ceramics, and biomaterials. The manufacturing process of 3D printing and 4D printing materials, their characteristics, applicable printing technologies, and clinical application scope are described in detail. Furthermore, the development of composite materials for 3D printing is the main focus of future research, as combining multiple materials can improve the materials' properties. Updates in material sciences play important roles in dentistry; hence, the emergence of newer materials are expected to promote further innovations in dentistry.

4D printing system stimulated by curcumin/whey protein isolate nanoparticles: A comparative study of sensitive color change and post-processing

In order to provide a more reliable curcumin stabilization scheme and efficient post-treatment process in food 4D printing system, this study innovatively introduced nano-embedding technology and catalytic infrared drying (CID) method to develop interesting color-changing materials for 4D printing based on thermal response stimuli. Firstly, curcumin (C) was encapsulated into whey protein isolate (WPI) to form nanoparticles (C-WPI-NPs), which were further added to potato starch-xanthan gum base to fabricate printing ink. The effects of C-WPI-NPs addition on the rheological properties, moisture distribution, and FTIR spectra of printing ink were investigated. It was demonstrated that the addition of C-WPI-NPs increase water-holding capacity and viscosity of the printing ink, and formation of a dense gel network while reducing water molecule movement. This resulted in excellent elastic solid-like behavior and mechanical strength against compression deformation of the printing ink. Subsequently, the effects of three drying post-treatment methods were compared, including catalytic infrared drying (CID), microwave drying (MD) and hot air drying (HAD). Compared with MD and HAD, CID showed a more uniform color change. The retention rate of curcumin under CID treatment reached 62.17%, which avoiding significant degradation of nutrients. Moreover, CID also showed great advantages in antioxidant capacity. The scavenging rate of DPPH radical was 52.69%, which was much higher than that of HAD (38.99%) and MD (36.04%). In addition, the appearance of the printed product was better preserved, and the dimensional offset rate was only 7.64%. • Curcumin/whey protein isolate nanoparticles (C-WPI-NPs) are fabricated successfully. • The 3D printing ink show preferable printability after addition of C-WPI-NPs. • The color change is achieved by heating the 3D printing product with C-WPI-NPs. • Catalytic infrared drying (CID) technology exhibit excellent post-treatment effects.

Mass-producible near-body temperature-triggered 4D printed shape memory biocomposites and their application in biomimetic intestinal stents

Despite the burgeoning interest in manufacturing highly complex and dynamically reconfigurable implants using the 4D printing technique, one of the most critical challenges is to develop near-body temperature (NBT)-triggered 4D printing materials in a facile and scale-up manner. The currently reported 4D printed biomaterials for implants have inappropriate transition temperatures or are limited to demonstration production of small amounts of materials in the laboratory. Here, 4D printed shape memory biocomposites with controllable transition temperature were developed through facile manufacturing technology, and the shape memory process of triggering printed constructs under NBT was realized. Customized, reconfigurable, biodegradable, and biocompatible 4D printed biomimetic intestinal stents were developed using NBT-triggered biocomposites, filling the blank of 4D printed intestinal stents. The 4D printed biomimetic intestinal stents were designed based on wavy biomimetic networks that can mimic the nonlinear stress-strain response of biological tissues, demonstrating high flexibility and facilitating reduced irritation of the intestinal wall. More importantly, the biodegradability of the 4D printed biomimetic intestinal stent can avoid the secondary endoscope removal required by the metal intestinal stent. This work not only offers an efficient and facile methodology to fabricate NBT-triggered 4D printing shape memory biocomposites but also demonstrates the attractive application potential of 4D printed intestinal stents in next-generation intelligent implants.

Review on development and application of 4D-printing technology in smart textiles

4D printed products can change shape under external stimulation, and the deformation design of material and structure is directly built into the material, which simplifies the manufacturing process from design concept to physical object and allows the object to be automatically assembled and conformed, realizing the integration of product design, manufacturing, and assembly. In recent years, 4D printing technology has also received widespread attention in the smart textile industry. This paper aims to promote the diversified and efficient development of the smart textile industry and expand the scope of the application of additive manufacturing technology. First, the evolution of 4D printing and its intrinsic relationship with 3D printing are examined. Then, the types of 4D printing smart textile technologies and their characteristics are presented, and the influence of relevant parameters of each type of technology on the molding quality, deformation mechanism, and driving performance of printed models is discussed. Materials for 4D printing of smart textiles are further described, including shape memory materials, hydrogels, and elastic liquid crystals. To adapt to the specific properties of textile applications, 4D printing technology has developed from the structural level of textiles to create smart textiles with adjustable shapes, properties, or functions. Then, the applications of 4D printed smart textiles in different fields are summarized. Finally, some problems currently faced by 4D printed smart textiles are discussed, and their prospects are projected.

Structurally Dynamic Gelatin-Based Hydrogels with Self-Healing, Shape Memory, and Cytocompatible Properties for 4D Printing.

Three-dimensional (3D) printable hydrogels with a shape memory effect have emerged as a new class of 4D printing materials recently and found wide applications in various fields. However, synergistically endowing such materials with good mechanical strength and biocompatibility for biomedical uses remains challenging. In this study, a series of multiresponsive hydrogels have been prepared through a dynamic covalent imine/Diels-Alder network from biocompatible starting materials of modified gelatin and poly(ethylene glycol)-based polymers. By further secondary crosslinking with a hyperbranched triethoxysilane reagent (HPASi) that contains multiple supramolecular hydrogen bonding, the hydrogels presented a strengthened self-healing and temperature-responsive shape memory effect. With the additional features of superior stretchability (elongation at break up to 523%), good cytocompatibility, and 3D printable properties, these multifunctional hydrogels showed great potential for broad biomedical applications.

Bioprinting for bone tissue engineering.

The shape transformation characteristics of four-dimensional (4D)-printed bone structures can meet the individual bone regeneration needs, while their structure can be programmed to cross-link or reassemble by stimulating responsive materials. At the same time, it can be used to design vascularized bone structures that help establish a bionic microenvironment, thus influencing cellular behavior and enhancing stem cell differentiation in the postprinting phase. These developments significantly improve conventional three-dimensional (3D)-printed bone structures with enhanced functional adaptability, providing theoretical support to fabricate bone structures to adapt to defective areas dynamically. The printing inks used are stimulus-responsive materials that enable spatiotemporal distribution, maintenance of bioactivity and cellular release for bone, vascular and neural tissue regeneration. This paper discusses the limitations of current bone defect therapies, 4D printing materials used to stimulate bone tissue engineering (e.g., hydrogels), the printing process, the printing classification and their value for clinical applications. We focus on summarizing the technical challenges faced to provide novel therapeutic implications for bone defect repair.

4D Printing of Freestanding Liquid Crystal Elastomers via Hybrid Additive Manufacturing.

Liquid crystal elastomers (LCE) are appealing candidates among active materials for 4D printing, due to their reversible, programmable and rapid actuation capabilities. Recent progress has been made on direct ink writing (DIW) or Digital Light Processing (DLP) to print LCEs with certain actuation. However, it remains a challenge to achieve complicated structures, such as spatial lattices with large actuation, due to the limitation of printing LCEs on the build platform or the previous layer. Herein, a novel method to 4D print freestanding LCEs on-the-fly by using laser-assisted DIW with an actuation strain up to -40% is proposed. This process is further hybridized with the DLP method for optional structural or removable supports to create active 3D architectures in a one-step additive process. Various objects, including hybrid active lattices, active tensegrity, an actuator with tunable stability, and 3D spatial LCE lattices, can be additively fabricated. The combination of DIW-printed functionally freestanding LCEs with the DLP-printed supporting structures thus provides new design freedom and fabrication capability for applications including soft robotics, smart structures, active metamaterials, and smart wearable devices.

Role of 4D printing materials, process and potentials for dentistry

With the advancement of existing technology, every sector requires assistance in fast changing its working style. New technologies are improving manufacturing speed, lowering industrial process costs, and so on. To improve efficiency, technical professionals do ongoing research and development. The ability of 4D printing to change shape over time is a big improvement over 3D printing since external elements such as air, pressure, water, heat, and so on utilizes controlled impact. Instead of three "Ds," 4D Printing has one, and the fourth is time. As a result, 4D printing's ability to change shape over time is a substantial improvement over 3D printing methods. Manufacturers would undoubtedly benefit much from four dimensional printing in terms of features and advancements in dentistry. Surgical guide manufacturing, medical modelling, prosthodontics, orthodontics, dentistry, dentistry equipment and implantology are among its uses. This paper provides an overview of four dimensional printing and how it might be used to manufacture smart materials. The diagrammatic presentation of the Bio-Oriented 4D printed smart materials and process workflow for dentistry. The report also explores and recognizes the great potential of 4D printing in dentistry.

4D printing of soybean oil based shape memory polymer and its magnetic-sensitive composite via digital light processing

ABSTRACT With the awakening of environmental awareness and the development of 4D printing, the availability of renewable materials for 4D printing has become increasingly important. A kind of soybean oil-based photosensitive resins were prepared to fabricate SMP parts with acrylate epoxy soybean oil/isobornyl methacrylate/nano-Fe3O4 (AESO/IBOMA/nano-Fe3O4) networks. The effects of IBOMA and nano-Fe3O4 concentration on mechanical and shape memory properties were systematically studied. The polymer can achieve high curing rate and printing accuracy. Break elongation of SMPs with 40 wt% IBOMA can up to 45.3% and tensile strength of SMPs with 60 wt% IBOMA can reach 44.3 MPa. The tensile-unload test results showed that the shape fixation rate and shape recovery rate of all formulations were higher than 90%. SMPs with 5 wt% Fe3O4 can be actuated by a magnetic field and complete an 82.47% shape recovery process in 40 s.

Research Progress of Four-dimensional Hydrogels in Implantable Medical Devices

Four-dimensional (4D) printing is an emerging technology that combines science and engineering techniques. The term, "4D printing" was coined in 2013 and since then it has attracted a lot of interests due to its unique ability to have structural or functional transformations over time in response to external stimuli. The most important element of 4D printing is the responsive material. The recent progress research of hydrogels and related new technologies for 4D printing was summarized in the field of implanted medical devices at home and abroad in this paper. Then, it was pointed out the problems of responsive materials for 4D printing. Finally, it was prospected that the development of 4D printing technology in the field of implantable medical devices.

Hygromorphic Response Dynamics of 3D-Printed Wood-PLA Composite Bilayer Actuators.

The use of wood particles in wood-plastic composites (WPC) is well known and similar use could occur in materials for fused deposition modeling (FDM) 3D printing. Wood particles could be one of the possible solutions in the search for natural-based materials to minimize the use of synthetic-origin materials in additive manufacturing. Wood particles for 3D printing filaments can be made from wood waste and could serve as a cheap filler or as a value-added reinforcing component, depending on their properties and incorporation. The disadvantages of wood (dimensional changes due to water adsorption and desorption) could be used as functions when dimensional change is desirable, such as in shape-changing 4D printing materials. In this research, FDM printing materials made of polylactic acid (PLA), with different amounts of wood particles, were used to design moisture-induced shape-changing bilayer actuators, which could serve as a principle for active façade or ventilation valves. The initial research shows that the wood content in the WPC causes dimensional changes and thus shape changes of the designed actuators under changing climates. The shape change depends on the ratio of the materials in the two-layered actuator and the wood content in the wood-PLA composite used, and thus on sorption. The rate of the shape change behaves in the same way: the higher the wood content, the greater the change observed. The dynamics of the hygromorphism of bimaterial composites is greater with a small amount of added hygromechanically active material.