Application of 4D printing in dentistry: A narrative review.

4D printing is an innovative digital manufacturing technology that originated by adding a fourth dimension, i.e., time, to pre-existing 3D technology or additive manufacturing (AM). AM is a fast-growing technology used in many fields, which develops accurate 3D objects based on models designed by computers. Dentistry is one such field in which 3D technology is used for manufacturing objects in periodontics (scaffolds, local drug-delivering agents, augmentation of ridges), implants, prosthodontics (partial and complete dentures, obturators), oral surgery for reconstructing jaw, and orthodontics. Dynamism is a vital property needed for the survival of materials used in the oral cavity since the oral cavity is constantly subjected to various insults. 4D printing technology has overcome the disadvantages of 3D printing technology, i.e., it cannot create dynamic objects. Therefore, constant knowledge of 4D technology is required. 3D printing technology has shortcomings, which are discussed in this review. This review summaries various printing technologies, materials used, stimuli, and potential applications of 4D technology in dentistry.

Tetrazine-based dynamic covalent polymers as degradable extraction materials in sample preparation.

BACKGROUND: Current trends in Analytical Chemistry are highly focused on the introduction of new extraction materials with a high selectivity towards the target analytes, high extraction capacity as well as sustainable characteristics. In this context, the introduction of smart materials able to respond to an external stimulus constitutes a promising approach in the field. However, investigations regarding the development of such stimuli-responsive polymers have been basically centered on their synthesis and the control of their properties, and hardly on exploiting such properties to generate polymers that, once their extraction function is fulfilled, they can be degraded into fragments with little or negligible toxicity, or even into their constituent monomers for an efficient recycling. RESULTS: The applicability of a degradable and recyclable dynamic covalent polymer based on the use of tetrazine as a linker was assessed as sorbent for the extraction of a group of 37 persistent organic pollutants, including 10 polycyclic aromatic hydrocarbons, 11 organochlorine pesticides, 14 polychlorinated biphenyls, and 2 antibacterial agents, from water samples. A microdispersive solid-phase extraction procedure was developed for the selective extraction of the target analytes, while their separation, determination, and quantification were achieved by gas chromatography coupled to mass spectrometry. The optimized procedure was validated for seawater and wastewater obtaining mean relative recovery values between 72 and 112 % for almost all the analytes, with satisfactory relative standard deviation values (<18 %). After extraction, the polymer could be degraded by adding the amino acid L-tyrosine, being possible a quantitative recovery of the initial functional monomer. SIGNIFICANCE: A responsive polymer based on the chemical versatility of the tetrazine ring was used as sorbent in sample preparation providing excellent results, showing good physicochemical properties and the ability to be degraded after use. This polymer constitutes an interesting alternative to reduce chemical waste through the recycling of monomers, contributing to the development of more sustainable analytical methodologies.

Structural Health Monitoring of Fiber Reinforced Composites Using Integrated a Linear Capacitance Based Sensor.

The demand for fiber-reinforced polymers (FRPs) has significantly increased in various industries due to their attributes, including low weight, high strength, corrosion resistance, and cost-efficiency. Nevertheless, FRPs, such as glass and Kevlar fiber composites, exhibit anisotropic properties and relatively low interlaminar strength, rendering them susceptible to undetected damage. The integration of real-time damage detection processes can effectively mitigate this issue. This paper introduces a novel method for fabricating embedded capacitive sensors within FRPs using a coating technique. The study encompasses two types of fibers, namely glass and Kevlar fiber/epoxy composites. The physical vapor deposition (PVD) technique is employed to coat bundle fibers with conductive material, thus creating embedded electrodes. The results demonstrate the uniform distribution of nanoparticles of gold (Au) along the fibers using PVD, resulting in a favorable resistance of approximately ≈100 Ω. Two sensor configurations are explored: axial and lateral embedding of the coated yarn (electrodes) to investigate the influence of load direction on the coating yarn. Axial-sensor configuration specimens undergo tensile testing, showcasing a linear response to axial loads with average sensitivities of 1 for glass and 1.5 for Kevlar fiber/epoxy composites. Additionally, onset damage is detected in both types of fiber composites, occurring before final fracture, with average stress at the turning point measuring 208 MPa for glass and 144 MPa for Kevlar. The lateral-sensor configuration for glass fiber-reinforced polymer (GFRP) exhibits good linearity towards strain until failure, with average gauge factors of 0.25 and -2.44 in the x and y axes, respectively.

Liquid Crystal Orientation and Shape Optimization for the Active Response of Liquid Crystal Elastomers.

Liquid crystal elastomers (LCEs) are responsive materials that can undergo large reversible deformations upon exposure to external stimuli, such as electrical and thermal fields. Controlling the alignment of their liquid crystals mesogens to achieve desired shape changes unlocks a new design paradigm that is unavailable when using traditional materials. While experimental measurements can provide valuable insights into their behavior, computational analysis is essential to exploit their full potential. Accurate simulation is not, however, the end goal; rather, it is the means to achieve their optimal design. Such design optimization problems are best solved with algorithms that require gradients, i.e., sensitivities, of the cost and constraint functions with respect to the design parameters, to efficiently traverse the design space. In this work, a nonlinear LCE model and adjoint sensitivity analysis are implemented in a scalable and flexible finite element-based open source framework and integrated into a gradient-based design optimization tool. To display the versatility of the computational framework, LCE design problems that optimize both the material, i.e., liquid crystal orientation, and structural shape to reach a target actuated shapes or maximize energy absorption are solved. Multiple parameterizations, customized to address fabrication limitations, are investigated in both 2D and 3D. The case studies are followed by a discussion on the simulation and design optimization hurdles, as well as potential avenues for improving the robustness of similar computational frameworks for applications of interest.

4D bioprinting of programmed dynamic tissues.

Setting time as the fourth dimension, 4D printing allows us to construct dynamic structures that can change their shape, property, or functionality over time under stimuli, leading to a wave of innovations in various fields. Recently, 4D printing of smart biomaterials, biological components, and living cells into dynamic living 3D constructs with 4D effects has led to an exciting field of 4D bioprinting. 4D bioprinting has gained increasing attention and is being applied to create programmed and dynamic cell-laden constructs such as bone, cartilage, and vasculature. This review presents an overview on 4D bioprinting for engineering dynamic tissues and organs, followed by a discussion on the approaches, bioprinting technologies, smart biomaterials and smart design, bioink requirements, and applications. While much progress has been achieved, 4D bioprinting as a complex process is facing challenges that need to be addressed by transdisciplinary strategies to unleash the full potential of this advanced biofabrication technology. Finally, we present future perspectives on the rapidly evolving field of 4D bioprinting, in view of its potential, increasingly important roles in the development of advanced dynamic tissues for basic research, pharmaceutics, and regenerative medicine.

Advanced Ceramics with Dual Functions of Healing and Decomposition.

This study developed advanced ceramic materials with both healing and decomposition functions using a metastable product generated under superheated steam. The developed composite material comprises ZrC particles dispersed in a yttria-stabilized zirconia (YSZ) matrix. After introducing a surface crack of approximately 120 µm on the composite specimen, it showed a complete strength recovery rate after one hour of heat treatment under superheated steam at 400 °C, while it exhibited a decomposition behavior after one hour of heat treatment in air at 400 °C. The XRD analysis of the heat-treated specimens showed that the final product was monoclinic ZrO2 under both steam and air conditions. In other words, full strength recovery in superheated steam was achieved by a chain reaction involving metastable intermediate products derived from H2O, unlike the reaction in air.

Electro-Mechanical Characterisation and Damage Monitoring by Acoustic Emission of 3D-Printed CB/PLA.

Even though the influence of the printing direction on the mechanical properties of 3D-printed samples by fused filament fabrication is established in the literature, very little is known about mechanical and electrical coupling. In this study, electrically conductive polylactic acid filled with carbon black particles undergoes monotonic and repeated progressive tensile loading to better understand the influence of the printing direction on the electro-mechanical properties of three-dimensional-printed samples. The objective is to analyse the electro-mechanical behaviour of this composite for its potential application as an actuator. The classical laminate theory is also applied to evaluate the relevance of this theory in predicting the mechanical characteristics of this material. In addition, a comprehensive damage analysis is performed using acoustic emission, infrared thermography, scanning electron microscopy, and X-ray microcomputed tomography imaging. Results show that the degradation of the mechanical and electrical properties is highly influenced by the printing direction. The appearance and development of crazes in 0° filaments are highlighted and quantified. The conclusions drawn by this study underline the interest in using longitudinal and unidirectional printing directions to improve the conductive path within the samples. Furthermore, the evolution of the resistance throughout the experiments emphasizes the need to control the implemented voltage in the design of future electro-thermally triggered actuators.

Diol or Hydrogen Peroxide-responsive Micellar Systems and Their Rheological Properties.

External stimuli-responsive worm-like micelles (WLMs) have the potential for a wide range of applications. In particular, sugar (a polyol compound)-responsive WLMs have the potential for use in smartdrug release systems. Phenylboronic acid (PBA) functions as a cis-diol sensor in a similar manner it does as a glucose sensor. Thus, WLMs, primarily composed of surfactants and PBA, are expected to function as cis-diol-responsive viscoelastic systems. PBA also reacts irreversibly with hydrogen peroxide (H2O2 ) and is converted into phenol and boric acid. H2O2 is one of reactive oxygen species crucial for several physiological processes. Therefore, H2O2 -responsive WLMs have the potential for various applications. In this review, we describe cis-diol- and H2O2 -responsive micellar systems composed of cetyltrimethylammonium bromide and PBA moieties that shift their viscosities in response to stimuli.

Multimodal Autonomous Locomotion of Liquid Crystal Elastomer Soft Robot.

Self-oscillation phenomena observed in nature serve as extraordinary inspiration for designing synthetic autonomous moving systems. Converting self-oscillation into designable self-sustained locomotion can lead to a new generation of soft robots that require minimal/no external control. However, such locomotion is typically constrained to a single mode dictated by the constant surrounding environment. In this study, a liquid crystal elastomer (LCE) robot capable of achieving self-sustained multimodal locomotion, with the specific motion mode being controlled via substrate adhesion or remote light stimulation is presented. Specifically, the LCE is mechanically trained to undergo repeated snapping actions to ensure its self-sustained rolling motion in a constant gradient thermal field atop a hotplate. By further fine-tuning the substrate adhesion, the LCE robot exhibits reversible transitions between rolling and jumping modes. In addition, the rolling motion can be manipulated in real time through light stimulation to perform other diverse motions including turning, decelerating, stopping, backing up, and steering around complex obstacles. The principle of introducing an on-demand gate control offers a new venue for designing future autonomous soft robots.

Smart Materials Design for Antibacterial Application.

In response to the escalating issue of antibiotic-resistant bacteria adhering to and thriving on medical equipment, scientists are pioneering innovative "intelligent" materials and coatings. These advancements entail the targeted release of antimicrobial substances, specifically activated when bacteria are detected. The next section discusses three revolutionary substances: hydrogels, nanoparticles, and thin films. Furthermore, intelligent antibacterial materials are divided into 2 groups based on the triggering source: those that react to biological stimuli and those that react to non-biological ones, like temperature and electric cues associated with bacterial presence, such as pH shifts or bacterial enzyme discharge. Moreover, because of their simple construction technique, outstanding biocompatibility, and robust antibacterial characteristics derived from polyphenols and metal ions, metallic-polyphenolic nanoparticles (MPNs) have obtained substantial interest in tackling antimicrobial infections. This article presents an introduction to several MPN-centered biomaterials (like nanoparticles, coatings, capsules, and hydrogels) and highlights the latest advancements in research in its applications for addressing microbial threats in the field of biomedicine. Furthermore, the usage of smart materials is classified based on their application domains, encompassing medical implants, waste reduction, and nano-engineered systems.

Design of a Shape-Memory-Alloy-Based Carangiform Robotic Fishtail with Improved Forward Thrust.

Shape memory alloys (SMAs) have become the most common choice for the development of mini- and micro-type soft bio-inspired robots due to their high power-to-weight ratio, ability to be installed and operated in limited space, silent and vibration-free operation, biocompatibility, and corrosion resistance properties. Moreover, SMA spring-type actuators are used for developing different continuum robots, exhibiting high degrees of freedom and flexibility. Spring- or any elastic-material-based antagonistic or biasing force is mostly preferred among all other biasing techniques to generate periodic oscillation of SMA actuator-based robotic body parts. In this model-based study, SMA-based spring-type actuators were used to develop a carangiform-type robotic fishtail. Fin size optimization for the maximization of forward thrust was performed for the developed system by varying different parameters, such as caudal fin size, current through actuators, pulse-width modulation signal (PWM), and operating depth. A caudal fin with a mixed fin pattern between the Lunate and Fork "Lunafork" and a fin area of approximately 5000 mm2 was found to be the most effective for the developed system. The maximum forward thrust developed by this fin was recorded as 40 gmf at an operation depth of 12.5 cm in a body of still water.

Expeditious Discovery of Small-Molecule Thermoresponsive Ionic Liquid Materials: A Review.

Ionic liquids (ILs) are a class of low-melting molten salts (<100 °C) constituted entirely of ions, and their research has gained tremendous attention in line with their remarkably growing applications (>124,000 publications dated 30 August 2023 from the Web of ScienceTM). In this review, we first briefly discussed the recent developments and unique characteristics of ILs and zwitterionic liquids (ZILs). Compared to molecular solvents and other conventional organic compounds, (zwitter) ionic liquids carry negligible volatility and are potentially recyclable and reusable. For structures, both ILs and ZILs can be systematically tailor-designed and engineered and are synthetically fine-tunable. As such, ionic liquids, including chiral, supported, task-specific ILs, have been widely used as powerful ionic solvents as well as valuable additives and catalysts for many chemical reactions. Moreover, ILs have demonstrated their value for use as polymerase chain reaction (PCR) enhancers for DNA amplification, chemoselective artificial olfaction for targeted VOC analysis, and recognition-based affinity extraction. As the major focus of this review, we extensively discussed that small-molecule thermoresponsive ILs (TILs) and ZILs (zwitterionic TILs) are new types of smart materials and can be expeditiously discovered through the structure and phase separation (SPS) relationship study by the combinatorial approach. Using this SPS platform developed in our laboratory, we first depicted the rapid discovery of N,N-dialkylcycloammonium and 1,3,4-trialkyl-1,2,3-triazolium TILs that concomitantly exhibited LCST (lower critical solution temperature) phase transition in water and displayed biochemically attractive Tc values. Both smart IL materials were suited for applications to proteins and other biomolecules. Zwitterionic TILs are ZILs whose cations and anions are tethered together covalently and are thermoresponsive to temperature changes. These zwitterionic TIL materials can serve as excellent extraction solvents, through temperature change, for biomolecules such as proteins since they differ from the common TIL problems often associated with unwanted ion exchanges during extractions. These unique structural characteristics of zwitterionic TIL materials greatly reduce and may avoid the denaturation of proteins under physiological conditions. Lastly, we argued that both rational structural design and combinatorial library synthesis of small-molecule TIL materials should take into consideration the important issues of their cytotoxicity and biosafety to the ecosystem, potentially causing harm to the environment and directly endangering human health. Finally, we would concur that before precise prediction and quantitative simulation of TIL structures can be realized, combinatorial chemistry may be the most convenient and effective technology platform to discover TIL expeditiously. Through our rational TIL design and combinatorial library synthesis and screening, we have demonstrated its power to discover novel chemical structures of both TILs and zwitterionic TILs. Undoubtedly, we will continue developing new small-molecule TIL structures and studying their applications related to other thermoresponsive materials.

[4D bioprinting technology and its application in cardiovascular tissue engineering].

3D bioprinting technology is a rapidly developing technique that employs bioinks containing biological materials and living cells to construct biomedical products. However, 3D-printed tissues are static, while human tissues are in real-time dynamic states that can change in morphology and performance. To improve the compatibility between in vitro and in vivo environments, an in vitro tissue engineering technique that simulates this dynamic process is required. The concept of 4D printing, which combines "3D printing + time" provides a new approach to achieving this complex technique. 4D printing involves applying one or more smart materials that respond to stimuli, enabling them to change their shape, performance, and function under the corresponding stimulus to meet various needs. This article focuses on the latest research progress and potential application areas of 4D printing technology in the cardiovascular system, providing a theoretical and practical reference for the development of this technology.

Advantages and Prospective Implications of Smart Materials in Tissue Engineering: Piezoelectric, Shape Memory, and Hydrogels.

Conventional biomaterial is frequently used in the biomedical sector for various therapies, imaging, treatment, and theranostic functions. However, their properties are fixed to meet certain applications. Smart materials respond in a controllable and reversible way, modifying some of their properties because of external stimuli. However, protein-based smart materials allow modular protein domains with different functionalities and responsive behaviours to be easily combined. Wherein, these "smart" behaviours can be tuned by amino acid identity and sequence. This review aims to give an insight into the design of smart materials, mainly protein-based piezoelectric materials, shape-memory materials, and hydrogels, as well as highlight the current progress and challenges of protein-based smart materials in tissue engineering. These materials have demonstrated outstanding regeneration of neural, skin, cartilage, bone, and cardiac tissues with great stimuli-responsive properties, biocompatibility, biodegradability, and biofunctionality.

[Structural Transitions of Micellar Systems in Response to Diol Compounds Accompanied by Changes in Viscoelastic Properties to Yield Novel Functional Materials].

External-stimuli-responsive smart viscoelastic systems have the potential for diverse applications. Worm-like micelles (WLMs) are distinct viscoelastic systems. Several stimuli-responsive WLMs have been reported thus far, in which modifications are triggered by pH variations, redox reactions, temperature shifts, and light. However, sugar-responsive WLMs have not been reported. Phenylboronic acid (PBA) reversibly forms cyclic ester with cis-diol compounds; therefore, it serves as a cis-diol sensor for compounds such as glucose (Glc) and fructose (Fru). Adding PBA to cetyltrimethylammonium bromide (CTAB) in a basic medium induces the transition of spherical micelles to WLMs. This is accompanied by a substantial increase in the viscosity of the CTAB/PBA system. Notably, the addition of Glc to the CTAB/PBA system induces the transformation of the WLMs into spherical micelles or short rod-like micelles. In this review, we describe diol-responsive micellar systems based on PBA and their rheological properties.

Glyphosate Separating and Sensing for Precision Agriculture and Environmental Protection in the Era of Smart Materials.

The present article critically and comprehensively reviews the most recent reports on smart sensors for determining glyphosate (GLP), an active agent of GLP-based herbicides (GBHs) traditionally used in agriculture over the past decades. Commercialized in 1974, GBHs have now reached 350 million hectares of crops in over 140 countries with an annual turnover of 11 billion USD worldwide. However, rolling exploitation of GLP and GBHs in the last decades has led to environmental pollution, animal intoxication, bacterial resistance, and sustained occupational exposure of the herbicide of farm and companies' workers. Intoxication with these herbicides dysregulates the microbiome-gut-brain axis, cholinergic neurotransmission, and endocrine system, causing paralytic ileus, hyperkalemia, oliguria, pulmonary edema, and cardiogenic shock. Precision agriculture, i.e., an (information technology)-enhanced approach to crop management, including a site-specific determination of agrochemicals, derives from the benefits of smart materials (SMs), data science, and nanosensors. Those typically feature fluorescent molecularly imprinted polymers or immunochemical aptamer artificial receptors integrated with electrochemical transducers. Fabricated as portable or wearable lab-on-chips, smartphones, and soft robotics and connected with SM-based devices that provide machine learning algorithms and online databases, they integrate, process, analyze, and interpret massive amounts of spatiotemporal data in a user-friendly and decision-making manner. Exploited for the ultrasensitive determination of toxins, including GLP, they will become practical tools in farmlands and point-of-care testing. Expectedly, smart sensors can be used for personalized diagnostics, real-time water, food, soil, and air quality monitoring, site-specific herbicide management, and crop control.

Soft robotics towards sustainable development goals and climate actions.

Soft robotics technology can aid in achieving United Nations' Sustainable Development Goals (SDGs) and the Paris Climate Agreement through development of autonomous, environmentally responsible machines powered by renewable energy. By utilizing soft robotics, we can mitigate the detrimental effects of climate change on human society and the natural world through fostering adaptation, restoration, and remediation. Moreover, the implementation of soft robotics can lead to groundbreaking discoveries in material science, biology, control systems, energy efficiency, and sustainable manufacturing processes. However, to achieve these goals, we need further improvements in understanding biological principles at the basis of embodied and physical intelligence, environment-friendly materials, and energy-saving strategies to design and manufacture self-piloting and field-ready soft robots. This paper provides insights on how soft robotics can address the pressing issue of environmental sustainability. Sustainable manufacturing of soft robots at a large scale, exploring the potential of biodegradable and bioinspired materials, and integrating onboard renewable energy sources to promote autonomy and intelligence are some of the urgent challenges of this field that we discuss in this paper. Specifically, we will present field-ready soft robots that address targeted productive applications in urban farming, healthcare, land and ocean preservation, disaster remediation, and clean and affordable energy, thus supporting some of the SDGs. By embracing soft robotics as a solution, we can concretely support economic growth and sustainable industry, drive solutions for environment protection and clean energy, and improve overall health and well-being.

A comparative study of starch-g-(glycidyl methacrylate)/synthetic polymer-based hydrogels.

Chemical modification reactions and blending formation are two alternatives used to improve the properties of starch-based materials. This work used both approaches to evaluate how they would affect the properties of hydrogels. The hydrogels were based on corn starch (St), modified with glycidyl methacrylate (GMA; starch-g-GMA; GMASt), and blended with N,N'-dimethylacrylamide (DMAAm; GMAStxDMAAmy) or sodium acrylate (SA; GMAStxSAy). The results confirmed that the pure GMASt matrix had a low swelling degree (≈3 g g-1), but when blended with the synthetic polymers, this value reached ≈10 g g-1 (sample GMASt25DMAAm75). All matrices showed responsiveness towards pH variations. In general, they swelled more at pH 5 than at pH 7. While DMAAm had more influence on the swelling degree, SA was more efficient as a mechanical enhancer. Increasing 25 % of the amount of SA in the blend increased Young's Modulus by a factor of ≈10 times. It confirmed that both polymers effectively change the properties of GMASt, but in different ways.

In Situ-Forming Protein-Polymer Hydrogel for Glucose-Responsive Insulin Release.

Phenylboronic acid (PBA)-containing hydrogels (HGs), capable of glucose-responsive insulin release, have shown promise in diabetes management in preclinical studies. However, sustainable material usage and attaining an optimum insulin release profile pose a significant challenge in such HG design. Herein, we present the development of a straightforward fabrication strategy for glucose-responsive protein-polymer hybrid HGs (PPHGs). We prepare PPHGs by crosslinking polyvinyl alcohol (PVA) with various nature-abundant proteins, such as bovine serum albumin (BSA), egg albumin, casein, whey protein, and so forth, using formylphenylboronic acid (FPBA)-based crosslinkers. We showcase PPHGs with diverse bulk rheological properties that are appropriately modulated by the positions of aldehyde, boronic acid, and fluorine substitutions in the FPBA-crosslinker. The orthogonal imine and boronate ester bonds formed by FPBAs are susceptible to the acidic pH environment and glucose concentrations, leading to the glucose-responsive dissolution of the PPHGs. We further demonstrate that by an appropriate selection of FPBAs, glucose-responsive insulin release profiles of the PPHGs can be precisely engineered at the molecular level. Importantly, PPHGs are injectable, incur no cytotoxicity, and, therefore, hold great potential as smart insulin for in vivo applications in the near future.

4D bioprinting technology and its application in cardiovascular tissue engineering / 生物工程学报

3D bioprinting technology is a rapidly developing technique that employs bioinks containing biological materials and living cells to construct biomedical products. However, 3D-printed tissues are static, while human tissues are in real-time dynamic states that can change in morphology and performance. To improve the compatibility between in vitro and in vivo environments, an in vitro tissue engineering technique that simulates this dynamic process is required. The concept of 4D printing, which combines "3D printing + time" provides a new approach to achieving this complex technique. 4D printing involves applying one or more smart materials that respond to stimuli, enabling them to change their shape, performance, and function under the corresponding stimulus to meet various needs. This article focuses on the latest research progress and potential application areas of 4D printing technology in the cardiovascular system, providing a theoretical and practical reference for the development of this technology.