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

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. • Use of biopolymers has emerged as a new paradigm of the ecological conservation. • Biopolymeric composites are easily degraded under the possible source of degraded environment. • Biopolymers have found their applications in biomedical, food, electronics, cosmetics and other emerging fields. • Further understanding on their mode of action through this comprehensive review will imparts knowledge. 

Biopolymeric Sustainable Materials and their Emerging Applications

Recent progress in soft material chemistry and enabling methods of 3D and 4D fabrication—emerging programmable material designs and associated assembly methods for the construction of complex functional structures—is highlighted. The underlying advances in this science allow the creation of soft material architectures with properties and shapes that programmably vary with time. The ability to control composition from the molecular to the macroscale is highlighted—most notably through examples that focus on biomimetic and biologically compliant soft materials. Such advances, when coupled with the ability to program material structure and properties across multiple scales via microfabrication, 3D printing, or other assembly techniques, give rise to responsive (4D) architectures. The challenges and prospects for progress in this emerging field in terms of its capacities for integrating chemistry, form, and function are described in the context of exemplary soft material systems demonstrating important but heretofore difficult‐to‐realize biomimetic and biologically compliant behaviors.

Biomimetic and Biologically Compliant Soft Architectures via 3D and 4D Assembly Methods: A Perspective

This research demonstrates how a combination of two-way shape memory alloy (SMA), low-temperature liquid epoxy cure composites, and fibre reinforced plastic (FRP) may be utilised to create a novel reversible actuator with built driven functionality. The novelty of this work is that the actuator can reverse its original shape and be mounted on different customized structures. The strategy is based on a knowledge of SMA wires and the manufacturing principle underlying composite structure, as well as experiments to see how soft SMA-FRP can be programmed to bend. The folding mechanism is studied in terms of fabrication factors such as SMA training and strong interfacial bonding between SMA and epoxy resin, which influence the programming process and shape change. The two-way SMA wires are trained using the pre-straining method to programme the SMAs. The technique has been used to assemble the SMA wires with bond reliability to enhance the actuator interface's thermal behaviour. The SMA elements are directly inserted into FRP strips and epoxy resin is used as an adhesive, resulting in dynamic hybrid composites. The module is actuated using an electrical board with a current value between 3 and 6 A. The robustness, controllability, mechanical properties, and 500 life cycles of the actuator are tested. Results indicate a bending angle of 58° with 30 mm of deflection in 7 s after actuating the module. Also, 3D printing is used to print a gripper inspired by human fingers and a structure to lift various weights. The actuator’s performance as a soft gripper is reliable in terms of grasping objects of different shapes. 

https://figshare.com/articles/journal_contribution/Adaptive_reversible_composite-based_shape_memory_alloy_soft_actuators/21308736/1/files/37807608.pdf

Adaptive Reversible Composite-based Shape Memory Alloy Soft Actuators

The integration of magneto-responsive shape memory polymers (SMPs) into 4D printing provides novel opportunities to create innovative and intelligent products controlled in a contactless method. In this study, a promising SMPs with robustly mechanical property and magneto-responsive behavior were proposed and fabricated into 3D printing feedstock based on polylactic acid (PLA), thermoplastic polyurethane (TPU) and Fe 3 O 4 particles. Results revealed that the 3D-printed PLA/TPU/Fe 3 O 4 possessed robust tensile strength and modulus with a homogeneous distribution of magnetic particles in polymer blends. Also, PLA/TPU/Fe 3 O 4 exhibited excellent shape fix ratio (∼100%), recovery ratio (>91%) and rapid magnetic response within as short as 40 s, suggesting the high efficiency of heat generation by magnetic particles. Moreover, smart structures including honeycomb and bionic flower-like model were designed and printed as an original shape. After programmed by an external force, the folded lattice structure at the temporary shape could recovered completely under a contactless magnetic field. The flower-bud structure sequentially restored layer-by-layer controlled by using three pedals with varied Fe 3 O 4 composites. Consequently, the high-load capacity, fast magneto-responsive behavior and high recovery performance of the proposed multi-material have great potentials in actuator or robots applications via 3D printing. • The PLA/TPU/Fe 3 O 4 composites with varying Fe 3 O 4 contents are capable to fabricate filaments for fused filament (FFF) 3D printing. • PLA/TPU/Fe 3 O 4 composite filaments show fast magneto-responsive shape memory and recovery behavior by heat or magneto stimulation. • Facile transformation are perfectly realized between designed structures with temporary shape fixed by heat or external force and then magneto-stimulated into original shape. 

4D printing of mechanically robust PLA/TPU/Fe3O4 magneto-responsive shape memory polymers for smart structures

Magneto‐/ electro‐responsive polymers toward manufacturing, characterization, and biomedical/ soft robotic applications

In this article, we introduce an array of uncoupled and cascaded microwave sensors with a novel structure for the dielectric characterization of liquid samples for biomedical applications. The developed array consists of four cascaded resonators and can measure the complex permittivity of multiple samples simultaneously and independently, contributing to microwell plate measurements. The fabricated sensors consist of couplers and defected grounded interdigitated capacitors (IDCs), yielding a high sensitivity. Each sensor in the array acts as a resonator, with the resonance frequency and quality factor changing according to the material under test (MUT). We have used water/ethanol mixtures in different concentrations to calibrate the sensor and later relate the changes in resonance behavior to the one in dielectric permittivity. The corresponding fitting functions based on IDC’s model have a high <inline-formula> <tex-math notation="LaTeX">$r$ </tex-math></inline-formula>-squared value and result in a high precision permittivity extraction of the liquids with the volume of 20 <inline-formula> <tex-math notation="LaTeX">$\mu \text{L}$ </tex-math></inline-formula> in the frequency range of 3.87 GHz (for the sample with the highest permittivity) to 8 GHz.

Design of Uncoupled and Cascaded Array of Resonant Microwave Sensors for Dielectric Characterization of Liquids

Accurate characterization of biological matter, for example, in tissue, cells, and biological fluids, is of high importance. For example, early and correct detection of abnormalities, such as cancer, is essential as it enables early and effective type-specific treatment, which is crucial for mortality reduction <xref ref-type="bibr" rid="ref1">[1]</xref>. Moreover, it is imperative to investigate the effectiveness and toxicity of pharmaceutical treatments before administration in clinical practice <xref ref-type="bibr" rid="ref2">[2]</xref>. However, biological matter characterization still faces many challenges. State-of-the-art imaging and characterization methods have drawbacks, such as the requirement to attach difficult-to-find and costly labels to the biological target (e.g., COVID-19 rapid tests), expensive equipment (e.g., magnetic resonance imaging), low accuracy (e.g., ultrasound), use of ionizing radiation (e.g., X-rays), and invasiveness <xref ref-type="bibr" rid="ref3">[3]</xref>. The characterization of biological matter using microwave (<italic>µ</italic>W), millimeter-wave (mmW), and terahertz (THz) spectroscopy is a promising alternative: it is label-free, does not require ionizing radiation, and can be noninvasive. Moreover, there is a significant difference in how different biological materials absorb, reflect, and transmit electromagnetic (EM) waves <xref ref-type="bibr" rid="ref4">[4]</xref> that is due to the difference in their dielectric properties. The dielectric properties are described by the frequency-dependent material parameter called the complex permittivity <inline-formula><tex-math notation="LaTeX">$\mathbf{\varepsilon}\left({\mathbf{f}}\right){,}$</tex-math></inline-formula> which expresses how the material responds to an external oscillating electric field. The complex permittivity of a material determines how the material absorbs, reflects, and transmits EM waves at different frequencies (<xref ref-type="fig" rid="fig1">Figure 1</xref>). Since each biological material’s permittivity spectrum is different, it acts as an EM fingerprint. A material’s complex permittivity can be calculated from the reflection and transmission of EM waves through the material, described by the S-parameters, which can be measured using a vector network analyzer (VNA) transmitting and receiving EM waves over a range of frequencies. The amplitude and phase of the transmitted and reflected EM waves at different frequencies are influenced by different underlying biological effects at different scales. That causes the entire spectrum to provide information from the supracellular to the molecular and even atomic scale.

Maede Chavoshi

Papers

Magneto‐/ electro‐responsive polymers toward manufacturing, characterization, and biomedical/ soft robotic applications

Design of Uncoupled and Cascaded Array of Resonant Microwave Sensors for Dielectric Characterization of Liquids

Dielectric Spectroscopy: Revealing the True Colors of Biological Matter