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Four-dimensional (4 D) printing is a novel emerging technology, which can be defined as the ability of 3 D printed materials to change their form and functions. The term 'time' is added to 3 D printing as the fourth dimension, in which materials can respond to a stimulus after finishing the manufacturing process. 4 D printing provides more versatility in terms of size, shape, and structure after printing the construct. Complex material programmability, multi-material printing, and precise structure design are the essential requirements of 4 D printing systems. The utilization of stimuli-responsive polymers has increasingly taken the place of cell traction force-dependent methods and manual folding, offering a more advanced technique to affect a construct's adjusted shape transformation. The present review highlights the concept of 4 D printing and the responsive bioinks used in 4 D printing, such as water-responsive, pH-responsive, thermo-responsive, and light-responsive materials used in tissue regeneration. Cell traction force methods are described as well. Finally, this paper aims to introduce the limitations and future trends of 4 D printing in biomedical applications based on selected key references from the last decade. [ABSTRACT FROM AUTHOR]

Developments by Labuschagné et al. (Patent, WO 2006/123284 A2, 2006) in the manufacture of Layered Double Hydroxides (LDHs) have led to a patent describing a new effluent free synthesis method. A promising application for the LDH is as an additive for a flexible poly(vinyl chloride) (PVC) compound used for the insulation for cables used in South African underground mines. Consequently, a new formulation is required. Unfortunately formulating a PVC compound is a complex problem. The purpose of the investigation is to develop a method that can be used to find an optimum PVC formulation where the material requirements are met while also allowing for the quantitative analysis of the effect of the ingredients on the material properties. This is achieved by modeling the thermal stability, fire retardancy, and basic mechanical properties of the compound as a function of the relative proportions of the ingredients using 2nd order Scheffé polynomials. The empirical models are determined using statistical experimental design. Each model is interpreted using statistical analysis of the model terms which allows for the quantification of the effects and interactions of all the ingredients on the various response variables. The models are also used as constraints in the optimization of the PVC formulation for minimum cost. Parametric analyses are done to demonstrate how the optimization can be used to analyze the entire system taking into account the cost performance of the ingredients. Finally, it is demonstrated how the above approach requires significantly less time and labor to find an optimum formulation than the traditional approach. J. VINYL ADDIT. TECHNOL., 25:E44–E58, 2019. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The semicrystalline morphology of injection moldings of polyamide 11 (PA 11) prepared using mold temperatures of 25, 50, and 80°C was investigated. Regardless of the mold temperature, position‐resolved X‐ray diffraction (XRD) and polarized‐light optical microscopy (POM) revealed presence of poor/imperfect α‐crystals with an almost hexagonal arrangement of molecular stems in a nonspherulitic superstructure in the skin, and formation of α‐crystals and spherulites in the core. With increasing mold temperature, the thickness of the skin layer decreased, and the perfection of α‐crystals and the spherulite size in the core increased. The experimental observations are discussed in terms of predicted crystallization temperatures, with the prediction based on cooling‐rate simulations for the various parts of the injection moldings using Moldflow® and analysis of crystallization of the relaxed melt using fast scanning chip calorimetry, XRD, and POM. It is shown that the structure gradient in PA 11 injection moldings can be forecast without considering the effects of shear for this particular polymer. POLYM. ENG. SCI., 58:1053–1061, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Polymer applications range from biomedical devices and structures, packaging, or toys to automotive and industrial items. So far, biopolymers could replace commodity polymers in a variety of products, especially for biomedical applications or food packaging. One of the most used and widely studied biopolymers is poly(lactic acid) (PLA). To generate new application fields and provide a broader application of PLA, research on processing behavior is still required. This chapter covers the processing relevant behavior of PLA and processing conditions for extrusion melt spinning, injection molding, and additive manufacturing. The processing-related behavior is compared to that of commodity polymers. The aim is to provide an overview of the state of the art and some recent new developments in this research field. [ABSTRACT FROM AUTHOR]

Modern polymer‐based technical components not only have to fulfill demanding mechanical‐structural properties but need to integrate different functions to yield hybrid systems for complex operations. Typically, neither materials nor processing technologies are fully compatible with each other. The aim of the work is to combine the advantages of seemingly incompatible manufacturing processes such as high‐volume injection molding (IM) and precision additive manufacturing to produce functional and customized hybrid materials. IM is widely used for polymer processing but stands against high investment costs for tailor‐made molds with high‐resolution features. They focus on overprinting of injection‐molded parts made of thermoplastic polyurethane (TPU) with microstructures via projection‐microstereolithography (PµSL) to generate hybrid polymer materials with spatially tailored stiffness, enabling selective reinforcement, resulting in an E modulus increase of 195% compared to mere IM‐processed TPU. With that, the hybridization of processing methods is showcased to extend the product properties of polymer materials obtained via either IM or PµSL printing that have, prospectively, a maximum degree of individualization as well as a multitude of structural and functional features at the same time. To achieve optimum interfacial adhesion, the influence of surface roughness is studied, and reinforcement effects of different overprinted microstructure types are evaluated. [ABSTRACT FROM AUTHOR]

In this study, a test scenario for the friction testing of electrically heated shape-memory alloy (SMA) wires against polymer surfaces was developed. As alloy, Nickel-Titanium (Nitinol, NiTi) was specially selected due to its high working capacity, the good corrosion resistance and the quick actor response at low bias forces. As the materials in contact with the actuator must resist friction forces and elevated temperatures up to 200 °C, a combination with high performance polymers is preferable. In many applications, the actuators use redirections to enhance the actuator capabilities or enable the use in complex structures. To better understand and compare the tribological properties of Nitinol against various polymer materials, it was needed to manufacture a customized testing device. [ABSTRACT FROM AUTHOR]

Four-dimensional (4 D) printing is a novel emerging technology, which can be defined as the ability of 3 D printed materials to change their form and functions. The term 'time' is added to 3 D printing as the fourth dimension, in which materials can respond to a stimulus after finishing the manufacturing process. 4 D printing provides more versatility in terms of size, shape, and structure after printing the construct. Complex material programmability, multi-material printing, and precise structure design are the essential requirements of 4 D printing systems. The utilization of stimuli-responsive polymers has increasingly taken the place of cell traction force-dependent methods and manual folding, offering a more advanced technique to affect a construct's adjusted shape transformation. The present review highlights the concept of 4 D printing and the responsive bioinks used in 4 D printing, such as water-responsive, pH-responsive, thermo-responsive, and light-responsive materials used in tissue regeneration. Cell traction force methods are described as well. Finally, this paper aims to introduce the limitations and future trends of 4 D printing in biomedical applications based on selected key references from the last decade.