4D printing of shape memory polymer composites: A review on fabrication techniques, applications, and future perspectives

4D printing of shape memory polymer composites: A review on fabrication techniques, applications, and future perspective

Vitrimer chemistry for 4D printing formulation

Vitrimerization is one of the new methods under development to convert polymer wastes into high-value compounds. The chemistry of vitrimers is such that the presence of dynamic chemical bonds changes the permanent covalent bonds into covalent adaptable networks, which are reversible. This allows for recycling and reprocessing of polymers by maintaining their initial properties after several cycles, which is included in the preparation of polymer resins to convert polymer waste into materials that can be formulated for three-dimensional (3D) printing resins. Four-dimensional (4D) printing has also been recently introduced as sustainable 3D printing of responsive polymers with dynamic applications, such as soft robotics, medicine, and medicals. Therefore, the synthesis of polymers with dynamic chemistry based on vitrimers can add unique properties such as shape memory, shape recovery, self-healing, and flexibility to the 3D printed products. Vitrimerization chemistry could contribute to polymer waste by producing 4D-printed resins. This article presents the vitrimerization chemistry used in different polymers to produce 4D printing resins with the mentioned capabilities and lists their recipes for the preparation of formulations used in 4D printing so that the researchers can use them in a practical way to possibly achieve simultaneous shape-programmable, self-healing, and recyclable features in printed structures

Biopolymeric sustainable materials and their emerging applications

Advancements in polymer science and engineering have helped the scientific community to shift its attention towards the use of environmentally benign materials for reducing the environmental impact of conventional synthetic plastics. Biopolymers are environmentally benign, chemically versatile, sustainable, biocompatible, biodegradable, inherently functional, and ecofriendly materials that exhibit tremendous potential for a wide range of applications including food, electronics, agriculture, textile, biomedical, and cosmetics. This review also inspires the researchers toward more consumption of biopolymer-based composite materials as an alternative to synthetic composite materials. Herein, an overview of the latest knowledge of different natural- and synthetic-based biodegradable polymers and their fiber-reinforced composites is presented. The review discusses different degradation mechanisms of biopolymer-based composites as well as their sustainability aspects. This review also elucidates current challenges, future opportunities, and emerging applications of biopolymeric sustainable composites in numerous engineering fields. Finally, this review proposes biopolymeric sustainable materials as a propitious solution to the contemporary environmental crisis

4D printing: Technological developments in robotics applications

The idea of four-dimensional (4D) printing is the formation of intricate stimuli-responsive 3D architectures that transform into different forms and shapes upon exposure to environmental stimuli. 4D printing (4DP) of smart/intelligent materials is a promising and novel approach to generate intricate structures for biomedical, food, electronics, textile, and agricultural fields. Nowadays, soft robotics is a growing research field focusing on developing micro/nanoscale 4D-printed robots using intelligent materials. Herein, recent advancements in 4DP of soft robotics, actuators, and grippers are summarized. This review also highlights some recent developments in novel robotics technologies and materials including multi-material printing, electro-, and magneto-active soft materials (MASMs), and metamaterials. It also sheds light on different modeling mechanisms including numerical models and machine learning (ML) models for fabricating highly precise and efficient micro/macro-scaled robots. The applications of shape-memory polymers (SMPs), hydrogels, and liquid crystal elastomers (LCEs)-based 4D-printed soft and intelligent robots in different engineering fields are highlighted. Lastly, this review incorporates current challenges which are hindering the actual utilization of 4D-printed soft robotics and their possible remedies