Recent progress in minimizing the warpage and shrinkage deformations by the optimization of process parameters in plastic injection molding: a review

The quality control of plastic products is an essential aspect of the plastic injection molding (PIM) process. However, the warpage and shrinkage deformations continue to exist because the PIM process is easily interfered with by several related or independent process parameters. Thus, great efforts have been devoted to optimizing process parameters to minimize the warpage and shrinkage deformations of products during the last decades. In this review, we begin by introducing the manufacturing process in PIM and the cause of warpage and shrinkage deformations, followed by the mechanism about how process parameters, like mold temperature, melt temperature, injection rate, injection pressure, holding pressure, holding and cooling duration, affect those defects. Then, we summarize the recent progress of the design of experiments and four advanced methods (artificial neural networks, genetic algorithm, response surface methodology, and Kriging model) on optimizing process parameters to minimize the warpage and shrinkage deformations. In the end, future perspectives of quality control in injection molding machines are discussed.

Study on the fabrication and characterization of tip-loaded dissolving microneedles for transdermal drug delivery

In order to increase the utilization rate of drug carried by microneedles and reduce waste, a two-step casting method was proposed to fabricate tip-loaded dissolving microneedles in this paper. The tip-loaded dissolving microneedles, also named layered microneedles, was consisted of two layers. The tip layer of the microneedles carried model drug, while the backing layer was fabricated with pure dissolving material. Polyvinyl alcohol, polyvinylpyrrolidone and hyaluronic acid were used as the base materials to fabricate the dissolving layers of the microneedle patches. Rhodamine B was chosen as the model drug to show the layered structure of tip-loaded microneedles. The material formulation and fabricating conditions of the tip-loaded dissolving microneedles and their transdermal insulin delivery efficiency were systematically studied. Nanoindentation testing showed that the tips of all three kinds of dissolving microneedles can bear the maximum loading of 50 mN with no damages, indicated sufficient mechanical strength for smooth skin puncturing as the minimum pressure required was 10 mN only. Moreover, our fabricated tip-loaded dissolving microneedles can greatly reduce the drug waste cause by unused backing layer in normal microneedles and realize a 30% enhancement of drug delivery efficiency after puncture treatment.

Progress in Microneedle-Mediated Protein Delivery

The growing demand for patient-compliance therapies in recent years has led to the development of transdermal drug delivery, which possesses several advantages compared with conventional methods. Delivering protein through the skin by transdermal patches is extremely difficult due to the presence of the stratum corneum which restricts the application to lipophilic drugs with relatively low molecular weight. To overcome these limitations, microneedle (MN) patches, consisting of micro/miniature-sized needles, are a promising tool to perforate the stratum corneum and to release drugs and proteins into the dermis following a non-invasive route. This review investigates the fabrication methods, protein delivery, and translational considerations for the industrial scaling-up of polymeric MNs for dermal protein delivery.

A simple and cost-effective approach to fabricate tunable length polymeric microneedle patches for controllable transdermal drug delivery

Polymeric microneedles (MNs) are attractive transdermal drug delivery systems because of their efficient drug delivery and minimal invasiveness. Master template fabrication is the most time-consuming and costly step in producing polymeric MNs using a micromoulding approach. Herein, this issue is addressed by modifying tattoo needle cartridges by adjusting the volume of a PDMS spacer, thus streamlining polymeric MN fabrication and significantly reducing its manufacturing cost. Using the fabricated master template, dissolvable polymeric MN systems containing poly(vinyl pyrrolidone) (PVP) and poly(vinyl alcohol) (PVA) were developed. This MN system exhibits several advantages, including controllable MN length, uniform distribution of each needle, and controllable drug release profiles. Overall, polymeric MN fabrication using this method is inexpensive, simple, and yields controllable and effective transdermal drug delivery.

A simple and cost-effective approach to fabricate tunable length polymeric microneedle patches for controllable transdermal drug delivery.

Microneedle System for Transdermal Drug and Vaccine Delivery: Devices, Safety, and Prospects

Microneedle (MN) delivery system has been greatly developed to deliver drugs into the skin painlessly, noninvasively, and safety. In the past several decades, various types of MNs have been developed by the newer producing techniques. Briefly, as for the morphologically, MNs can be classified into solid, coated, dissolved, and hollow MN, based on the transdermal drug delivery methods of "poke and patch," "coat and poke," "poke and release," and "poke and flow," respectively. Microneedles also have other characteristics based on the materials and structures. In addition, various manufacturing techniques have been well-developed based on the materials. In this review, the materials, structures, morphologies, and fabricating methods of MNs are summarized. A separate part of the review is used to illustrate the application of MNs to deliver vaccine, insulin, lidocaine, aspirin, and other drugs. Finally, the review ends up with a perspective on the challenges in research and development of MNs, envisioning the future development of MNs as the next generation of drug delivery system.

Efficient preparation of PDMS-based conductive composites using self-designed automatic equipment and an application example

In this paper, the fabrication process of polydimethylsiloxane (PDMS)-based microstructured conductive composites via differential temperature hot embossing was proposed based on the spatial confining forced network assembly theory. The mold temperature was kept constant throughout the whole embossing cycle in this method, whereas the setting temperatures of the upper and lower molds were different. To solve the problem of poor conveying performance, a double-station automatic hot embossing equipment was designed and developed. A “bullet-filled” accurate feeding system was designed aiming at the high viscosity and feeding difficulty of blended PDMS-based composites before curing. Dispersion mold and semifixed compression mold were designed according to different functional requirements of different workstations. The developed automatic hot embossing equipment had already been successfully applied to the continuous preparation of conductive composites with greatly improved processing precision and efficiency. Furthermore, the conductive composites with and without microstructures can be used as flexible sensors for pressure measurements.

Application of Biodegradable and Biocompatible Nanocomposites in Electronics: Current Status and Future Directions

With the continuous increase in the production of electronic devices, large amounts of electronic waste (E-waste) are routinely being discarded into the environment. This causes serious environmental and ecological problems because of the non-degradable polymers, released hazardous chemicals, and toxic heavy metals. The appearance of biodegradable polymers, which can be degraded or dissolved into the surrounding environment with no pollution, is promising for effectively relieving the environmental burden. Additionally, biodegradable polymers are usually biocompatible, which enables electronics to be used in implantable biomedical applications. However, for some specific application requirements, such as flexibility, electric conductivity, dielectric property, gas and water vapor barrier, most biodegradable polymers are inadequate. Recent research has focused on the preparation of nanocomposites by incorporating nanofillers into biopolymers, so as to endow them with functional characteristics, while simultaneously maintaining effective biodegradability and biocompatibility. As such, bionanocomposites have broad application prospects in electronic devices. In this paper, emergent biodegradable and biocompatible polymers used as insulators or (semi)conductors are first reviewed, followed by biodegradable and biocompatible nanocomposites applied in electronics as substrates, (semi)conductors and dielectrics, as well as electronic packaging, which is highlighted with specific examples. To finish, future directions of the biodegradable and biocompatible nanocomposites, as well as the challenges, that must be overcome are discussed.