Ultrasonic Molding Technology: Recent Advances and Potential Applications in the Medical Industry

Polypropylene-Based Polymer Locking Ligation System Manufacturing by the Ultrasonic Micromolding Process

In recent years, there has been a growing demand for biocompatible medical devices on the microscale. However, the manufacturing of certain microfeatures has posed a significant challenge. To address this limitation, a new process called ultrasonic injection molding or ultrasonic molding (USM) has emerged as a potential solution. In this study, we focused on the production of a specific microdevice known as Hem-O-Lok, which is designed for ligation and tissue repair during laparoscopic surgery. Utilizing USM technology, we successfully manufactured the microdevice using a nonabsorbable biopolymer that offers the necessary flexibility for easy handling and use. To ensure high-quality microdevices, we extensively investigated various processing parameters such as vibration amplitude, temperature, and injection velocity. Through careful experimentation, we determined that the microdevice achieved optimal quality when manufactured under conditions of maximum vibrational amplitude and temperatures of 50 and 60 °C. This conclusion was supported by measurements of critical microfeatures. Additionally, our materials characterization efforts revealed the presence of a carbonyl (C=O) group resulting from the thermo-oxidation of air in the plasticizing chamber. This finding contributes to the enhanced thermal stability of the microdevices within a temperature range of 429-437 °C.

Transient viscoelastic heating characteristics of polyethene under high frequency hammering during ultrasonic plasticizing

As a polymer molding technology developed in recent years, ultrasonic plasticizing micro-injection molding has great advantages in the manufacture of micro-nano parts by virtue of low energy consumption, less material waste and reduced filling resistance. However, the process and mechanism of transient viscoelastic heating for polymers under ultrasonic high-frequency hammering are unclear. The innovation of this research is that a combination of experiment and MD (molecular dynamics) simulation was adopted to study the transient viscoelastic thermal effect and microscopic behavior of polymers with different process parameters. To be more specific, a simplified heat generation model was first established and high-speed infrared thermal imaging equipment was applied to collect temperature data. Then, a single factor experiment was conducted to investigate the heat generation of a polymer rod with various process parameters (plasticizing pressure, ultrasonic amplitude and ultrasonic frequency). Finally, the thermal behavior during the experiment was supplemented and explained by MD simulation. The results showed that changes in ultrasonic process parameters produce different forms of heat generation, and there are three forms of heat generation, which are dominant heat generation at the ultrasonic sonotrode head end, dominant heat generation at the plunger end, and simultaneous heat generation at the ultrasonic sonotrode head end and the plunger end.

Current and Future Trends for Polymer Micro/Nanoprocessing in Industrial Applications

Polymers are widely used in optical devices, electronic devices, energy-harvesting/storage devices, and sensors, owing to their low weight, excellent flexibility, and simple fabrication process. With advancements in micro/nanoprocessing techniques and more demanding application requirements, it is becoming necessary to realize high-resolution fabrication of polymers to prepare miniaturized devices. This is particularly because conventional processing technologies suffer from high thermal stress and strong adhesion/friction, which can irreversibly damage the micro/nanostructures of miniaturized devices. In addition, although the use of advanced fabrication methods to prepare high-resolution micro/nanostructures is explored, these methods are limited to laboratory research or small-batch production. This review focuses on the micro/nanoprocessing of polymeric materials and devices with high spatial precision and replication accuracy for industrial applications. Specifically, the current state-of-the-art techniques and future trends for micro/nanomolding, high-energy beam processing, and micro/nanomachining are discussed. Moreover, an overview of the fabrication and applications of various polymer-based elements and devices such as microlenses, biosensors, and transistors is provided. These techniques are expected to be widely applied for multiscale and multimaterial processing as well as for multifunction integration in next-generation integrated devices, such as photoelectric, smart, and biodegradable devices.

Fabrication of Polymer Microfluidics: An Overview

Microfluidic platform technology has presented a new strategy to detect and analyze analytes and biological entities thanks to its reduced dimensions, which results in lower reagent consumption, fast reaction, multiplex, simplified procedure, and high portability. In addition, various forces, such as hydrodynamic force, electrokinetic force, and acoustic force, become available to manipulate particles to be focused and aligned, sorted, trapped, patterned, etc. To fabricate microfluidic chips, silicon was the first to be used as a substrate material because its processing is highly correlated to semiconductor fabrication techniques. Nevertheless, other materials, such as glass, polymers, ceramics, and metals, were also adopted during the emergence of microfluidics. Among numerous applications of microfluidics, where repeated short-time monitoring and one-time usage at an affordable price is required, polymer microfluidics has stood out to fulfill demand by making good use of its variety in material properties and processing techniques. In this paper, the primary fabrication techniques for polymer microfluidics were reviewed and classified into two categories, e.g., mold-based and non-mold-based approaches. For the mold-based approaches, micro-embossing, micro-injection molding, and casting were discussed. As for the non-mold-based approaches, CNC micromachining, laser micromachining, and 3D printing were discussed. This review provides researchers and the general audience with an overview of the fabrication techniques of polymer microfluidic devices, which could serve as a reference when one embarks on studies in this field and deals with polymer microfluidics.

Numerical Simulation on the Acoustic Streaming Driven Mixing in Ultrasonic Plasticizing of Thermoplastic Polymers

The acoustic melt stream velocity field, total force, and trajectory of fluorescent particles in the plasticizing chamber were analyzed using finite element simulation to investigate the acoustic streaming and mixing characteristics in ultrasonic plasticization micro-injection molding (UPMIM). The fluorescence intensity of ultrasonic plasticized samples containing thermoplastic polymer powders and fluorescent particles was used to determine the correlation between UPMIM process parameters and melt mixing characteristics. The results confirm that the acoustic streaming driven mixing occurs in ultrasonic plasticization and could provide similar shear stirring performance as the screw in traditional extrusion/injection molding. It was found that ultrasonic vibrations can cause several melt vortices to develop in the plasticizing chamber, with the melt rotating around the center of the vortex. With increasing ultrasonic amplitude, the melt stream velocity was shown to increase while retaining the trace, which could be altered by modulating other parameters. The fluorescent particles are subjected to a two-order-of-magnitude stronger Stokes drag force than the acoustic radiation force. The average fluorescence intensity was found to be adversely related to the distance from the sonotrodes' end surface, and fluorescence particles were more equally distributed at higher parameter levels.

Tuning Power Ultrasound for Enhanced Performance of Thermoplastic Micro-Injection Molding: Principles, Methods, and Performances

With the wide application of Micro-Electro-Mechanical Systems (MEMSs), especially the rapid development of wearable flexible electronics technology, the efficient production of micro-parts with thermoplastic polymers will be the core technology of the harvesting market. However, it is significantly restrained by the limitations of the traditional micro-injection-molding (MIM) process, such as replication fidelity, material utilization, and energy consumption. Currently, the increasing investigation has been focused on the ultrasonic-assisted micro-injection molding (UAMIM) and ultrasonic plasticization micro-injection molding (UPMIM), which has the advantages of new plasticization principle, high replication fidelity, and cost-effectiveness. The aim of this review is to present the latest research activities on the action mechanism of power ultrasound in various polymer micro-molding processes. At the beginning of this review, the physical changes, chemical changes, and morphological evolution mechanism of various thermoplastic polymers under different application modes of ultrasonic energy field are introduced. Subsequently, the process principles, characteristics, and latest developments of UAMIM and UPMIM are scientifically summarized. Particularly, some representative performance advantages of different polymers based on ultrasonic plasticization are further exemplified with a deeper understanding of polymer–MIM relationships. Finally, the challenges and opportunities of power ultrasound in MIM are prospected, such as the mechanism understanding and commercial application.

Manufacturing PLA/PCL Blends by Ultrasonic Molding Technology

Ultrasonic molding (USM) is a good candidate for studying the plasticization of polymer mixtures or other composite materials due to either the little amount of material needed for processing, low waste or the needed low pressure and residence time of the mold. Thus, the novelty of this research is the capability of USM technology to process PLA/PCL blends and their corresponding neat materials, encompassing all the production stages, from raw material to the final specimen. The major findings of the work revealed that the thermal properties of the blends were not affected by the USM process, although the crystallinity degree experienced variations, decreasing for PLA and increasing for PCL, which was attributed to the crystallization rate of each polymer, the high process speed, the short cooling time and the small particle size. The employed ultrasonic energy increased the molecular weight with low variations through the specimen. However, the degradation results aligned with the expected trend of these material blends. Moreover, this study also showed the effect pellet shape and dimensions have over the process parameters, as well as the effect of the blend composition. It can be concluded that USM is a technology suitable to successfully process PLA/PCL blends with the correct determination of process parameter windows.

Ultrasonic nodal point, a new configuration for ultrasonic moulding technology

Ultrasonic moulding is a new technology that uses high power ultrasound to melt and mould thermoplastic polymers to produce samples with mini and micro features. The main feature of this technology is the use of ultrasonic energy as the heating source instead of a conventional injection screw. Even if ultrasonic moulding overcomes some of the drawbacks of conventional mini and micro-injection moulding, it still presents two main limitations that are hindering its widespread applicability: the lack of stability of the process and the difficulty to obtain samples with good mechanical properties for some materials. This article presents a new configuration, called nodal point ultrasonic moulding (NPUSM), to surmount such limitations. This configuration improves the stability of ultrasonic moulding technology and it is capable of processing materials with good mechanical properties. To prove its efficacy, the nodal point ultrasonic moulding configuration is used to obtain the processing window of a polyoxymethylene material and these results are compared with standard ultrasonic injection and conventional injection moulding. The results obtained show that NPSUM configuration improves the capabilities of ultrasonic moulding technologies.

Ultrasonic Welding of PBT-GF30 (70% Polybutylene Terephthalate + 30% Fiber Glass) and Expanded Polytetrafluoroethylene (e-PTFE)

The ultrasonic welding of polymeric materials is one of the methods often used in practice. However, each couple of material subjected to ultrasonic welding is characterized by different values of technological parameters. Therefore, the main objective of the research presented in this paper is to optimize the parameters for the ultrasonic welding of two materials, namely PBT-GF30 (70% polybutylene terephthalate + 30% fiber glass) and expanded polytetrafluoroethylene (e-PTFE). In this sense, the research was carried out considering a plate-type part made of PBT-GF30, which had a thickness of 2.1 mm, and a membrane-type part made of e-PTFE, with a thickness of 0.3 mm. The condition imposed on the welded joints made, namely to correspond from a technical point of view, was that the detachment pressure of the membrane should be at least 4 bar. To this end, a test device was designed. Additionally, the topography of the material layer from the plate-type part was analyzed, as well as the chemical composition and surface condition for the membrane-type part. The obtained results allowed the optimization of the following parameters: The welding force; welding time; amplitude; and holding time. All experimental results were processed using STATISTICS software, which established how each parameter influences the characteristics of welded joints.

Thermal Welding by the Third Phase Between Polymers: A Review for Ultrasonic Weld Technology Developments

Ultrasonic welding (USW) is a promising method for the welds between dissimilar materials. Ultrasonic thermal welding by the third phase (TWTP) method was proposed in combination with the formation of a third phase, which was confirmed as an effective technology for polymer welding between the two dissimilar materials compared with the traditional USW. This review focused on the advances of applying the ultrasonic TWTP for thermoplastic materials. The research development on the ultrasonic TWTP of polycarbonate (PC) and polymethyl methacrylate (PMMA), polylactic acid (PLA) and polyformaldehyde (POM), and PLA and PMMA are summarized according to the preparation of the third phase, welded strength, morphologies of rupture surfaces, thermal stability, and others. The review aimed at providing guidance for using ultrasonic TWTP in polymers and a basic understanding of the welding mechanism, i.e., interdiffusion and molecular motion mechanisms between the phases.

Ultrasonic moulding: Current state of the technology

Ultrasonic moulding, also known as ultrasonic microinjection moulding, is a new technology that uses high-power ultrasound to melt and mould thermoplastic polymers to produce samples with mini- and micro-features. The main feature of this technology is the use of ultrasonic energy as the heating source instead of a conventional injection screw. Since 2002, several authors have experimentally and theoretically studied the ability of ultrasonic energy to mould polymers. However, different machine configurations and experimental design strategies have been used, which makes it very difficult to compare the results obtained from different articles. In this report, the authors have compiled experimental studies on the ultrasonic moulding process and analysed them along with providing a theoretical framework. An accurate description of the process and the machine configurations used in the literature is also presented. The results obtained from the analysis are summarized and discussed, and possible next steps to further the research in this field are suggested.

Development of Interfacial Adhesive Property by Novel Anti-Stripping Composite between Acidic Aggregate and Asphalt

Studies on control of and preventive measures against asphalt pavement moisture damage have important economic and social significance due to the multiple damage and repair of pavements, the reasons for which include the poor interfacial adhesive ability between acidic aggregates and asphalts. Anti-stripping agent is used in order to improve the poor adhesion, and decomposition temperature is regarded as being important for lots of anti-stripping products, because they always decompose and lose their abilities under the high temperature in the mixing plant before application to the pavement. A novel anti-stripping composite, montmorillonoid/Polyamide (OMMT/PAR), which possesses excellent thermal stability performance and is effective in preventing moisture damage, especially for acidic aggregates, was prepared. Moreover, the modification mechanisms and pavement properties were also investigated with reference to the composites. The results show that OMMT/PAR was prepared successfully, improving the interfacial adhesion between the acidic aggregate and the modified asphalt. Due to the nanostructure of OMMT/PAR, the thermal stability was enhanced dramatically and the interfacial adhesion properties were also improved. Furthermore, asphalts modified with OMMT/PAR and their mixtures showed excellent properties. Finally, the moisture damage process and the mechanisms by which OMMT/PAR improves the interfacial adhesion properties are explained through adhesion mechanism analyses.

Study on the Mechanism of Interfacial Friction Heating in Polymer Ultrasonic Plasticization Injection Molding Process

Ultrasonic Plasticization Injection Molding (UPIM) is an effective way to manufacture polymeric micro parts and has great potential for energy saving with processing polymeric materials of a small amount. To better control the UPIM process and improve the quality of micro parts, it is necessary to study the heat generation mechanism. In this paper, the interfacial friction heating process of UPIM was studied by finite element (FEM) simulation and experiment, and the temperature change in the friction interface was estimated. Then, the effects of different process parameters such as ultrasonic frequency and ultrasonic amplitude on the friction heating process were analyzed. The results showed that the rising trend of friction heating temperature was transient (finished within 1 s), and the change trend of FEM simulation was consistent with experimental results. Adjusting ultrasonic frequency and amplitude has a significant influence on the friction heating process. Increasing the ultrasonic frequency and amplitude can improve the efficiency of friction heating.