In an injection moulding process, the cooling step takes up to 50% or more of the total cycle time. Therefore, any reduction of the cooling time directly results into an increase of the production rate. Furthermore, products are often rejected because of defects such as warpage or sink marks. The cause of these defects is often an unevenly distributed cooling in the mould due to complex product or mould shapes. A solution for both problems is Conformal Cooling, a technique in which the cooling channels are designed to follow the contour of the mould cavity to obtain an optimal cooling. These often curved cooling channels are difficult or even impossible to produce with conventional techniques such as milling, drilling and EDM. The recent development of the Selective Laser Melting (SLM) 3D printing technology can be used to overcome these limitations. In a previous work [1] the cooling channels of an existing mould to produce sorting trays were assessed and redesigned to achieve a conformal cooled mould. A mould cavity and insert were provided with these cooling channels by means of the SLM technique. In this work the performance of the conformal cooled mould is compared with the original mould based on process characteristics and product measurements. In particular the start-up losses, mould temperature during the cycle, cycle time and product warpage are assessed.

Microneedle arrays contain needlelike microscopic structures, which facilitate drug or vaccine delivery in a minimally invasive way. However, producing hollow microneedles is currently limited by expensive, time consuming and complex microfabrication techniques. In this paper, a novel method to produce hollow polymer microneedles is presented. This method utilizes a femtosecond laser to create hollow microneedle cavities in a mold insert. This mold insert is used in an injection molding process to replicate polymethyl methacrylate microneedles. The combined effect of the mold temperature, volumetric injection rate, and melt temperature on the replication fidelity was evaluated. It was found that the combination of high injection molding parameters facilitated the replication. Furthermore, the functionality of the manufactured hollow microneedles was successfully tested by injecting a controlled flow of colored water into an agarose matrix. The developed methodology enables the production of low-cost, high-volume microneedle devices, which could be a key asset for large scale vaccination campaigns.

Microneedles are sharp microscopic features, which can be used for drug or vaccine delivery in a minimally invasive way. Recently, we developed a method to produce polymer microneedles using laser ablated molds in an injection molding process. At this moment, extensive injection molding experiments are needed to investigate the replication fidelity. Accurate predictions of the injection molding process would eliminate these costly and time expensive experiments. In this study, we evaluated the replication fidelity of solid polymer microneedles using numerical simulations and compared the results to injection molding experiments. This study was performed for different sizes of microneedles, different thermoplastics (polypropylene and polycarbonate) and different mold materials (tool steel, copper alloy and aluminium alloy). Moreover, different processing conditions and different locations of the microneedles on the macroscopic part were considered. A good correlation with experimental findings was achieved by optimizing the heat transfer coefficient between the polymer and the mold, while using a multiscale mesh with a sufficient number of mesh elements. Optimal heat transfer coefficients between 10,000 and 55,000 W/m² K were found for the different combinations of polymer and mold materials, which resulted in an accuracy of the simulated microneedle replication fidelity between 94.5 and 97.0%.

Polymer surfaces are increasingly being functionalized with micro- and nano- surface features using mass replication methods such as injection moulding. An example of these are microneedle arrays, which contain needle-like microscopic structures, which facilitate drug or vaccine delivery in a minimally invasive way. In this study, the replication fidelity of two types of solid polycarbonate microneedles was investigated using injection compression moulding and conventional injection moulding. Using a full factorial design of experiments for the injection moulding process, it was found that the volumetric injection rate had the largest positive effect on the replication fidelity. The mould temperature and holding pressure were also found to have a positive effect, while the effect of the melt temperature was found to be insignificant for the considered temperature range. For the injection compression moulding process, it was found that a larger compression stroke resulted in a better replication fidelity. A comparison between the replication fidelity for the injection moulding and injection compression moulding indicated that the injection compression moulding process resulted in a higher and more uniform replication fidelity. Using finite element flow simulations, a higher and more evenly distributed cavity pressure was observed compared to the conventional injection moulding process.