Andrew V. Healy

Injection moulding (IM) is a precise manufacturing process capable of producing tight‐tolerance, functional plastic components with high‐quality surface finishes. However, the growing use of stereolithography (SLA) 3D printing for rapid, low‐cost mould fabrication presents a challenge, as the layer‐by‐layer process produces a stair‐step geometry that promotes a keying effect, leading to reduced surface quality, premature tool wear and poor part release during moulding. The study addresses the problem by examining the influence of print orientation on the stair‐step effect on SLA‐printed tooling by assessing how post‐processing (bead blasting, polishing) and CAD‐applied textures can improve surface integrity and tool longevity. A short production trial using polypropylene (PP) coupons measured surface roughness, contact angle and tool degradation. Post‐processed and CAD‐textured moulds effectively masked the stair‐step effect and improved lifespan, achieving Ra values consistent with IM standards (0.2–2.5 µm). In contrast, untreated moulds exhibited progressive wear and chipping before 20 cycles. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR), scanning electron microscopy (SEM) and energy‐dispersive X‐ray (EDX) spectroscopy confirmed mould material transfer causing surface contamination, while CT scans revealed warpage and dimensional variation of up to 13% due to print orientation. These findings demonstrate that targeted surface modification strategies significantly enhance the performance of SLA‐printed moulds, providing a viable solution for short‐run IM applications.

Injection moulding (IM) is a manufacturing technique used to produce intricately detailed plastic components with various surface finishes, enabling the production of high-tolerance functional parts at scale. Conversely, stereolithography (SLA) three-dimensional (3D) printing offers an alternative method for fabricating moulds with shorter lead times and reduced costs compared to conventional manufacturing. However, fabrication in a layer-by-layer fashion results in anisotropic properties and noticeable layer lines, known as the stair-step effect. This study investigates post-processing techniques for plaques with contrasting stair-step effects fabricated from commercially available SLA high-temperature resin, aiming to assess their suitability for IM applications. The results reveal that annealing significantly enhances part hardness and heat deflection temperature (HDT), albeit with a trade-off involving reduced flexural strength. Experimental findings indicate that the optimal stage for abrasive surface treatment is after UV curing and before annealing. Plaques exhibiting contrasting stair-step effects are characterized and evaluated for weight loss, dimensional accuracy, and surface roughness. The results demonstrate that abrasive blasting effectively removes the stair-step effect without compromising geometry while achieving polished surface finishes with roughness average (RA) values of 0.1 μm through sanding. Overall, a combination of abrasive blasting and sanding proves capable of precisely defining surface roughness without significant geometry loss, offering a viable approach to achieving traditional IM finishes suitable for both functional and aesthetic purposes.

The introduction of three-dimensional printing (3DP) has created exciting possibilities for the fabrication of dosage forms, paving the way for personalized medicine. In this study, oral dosage forms of two drug concentrations, namely 2.50% and 5.00%, were fabricated via stereolithography (SLA) using a novel photopolymerizable resin formulation based on a monomer mixture that, to date, has not been reported in the literature, with paracetamol and aspirin selected as model drugs. In order to produce the dosage forms, the ratio of poly(ethylene glycol) diacrylate (PEGDA) to poly(caprolactone) triol was varied with diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (Irgacure TPO) utilized as the photoinitiator. The fabrication of 28 dosages in one print process was possible and the printed dosage forms were characterized for their drug release properties. It was established that both drugs displayed a sustained release over a 24-h period. The physical properties were also investigated, illustrating that SLA affords accurate printing of dosages with some statistically significant differences observed from the targeted dimensional range, indicating an area for future process improvement. The work presented in this paper demonstrates that SLA has the ability to produce small, individualized batches which may be tailored to meet patients’ specific needs or provide for the localized production of pharmaceutical dosage forms.

Poly-l-lactic acid (PLLA) is one of the most common bioabsorbable materials in the medical device field. However, its use in load-bearing applications is limited due to its inferior mechanical properties when compared to many of the competing metal-based permanent and bioabsorbable materials. The objective of this study was to directly compare the influence of both annealing and biaxial expansion processes to improve the material properties of PLLA. Results showed that both annealing and biaxial expansion led to an overall increase in crystallinity and that the crystallites formed during both processes were in the α’ and α forms. 2D-WAXS patterns showed that the preferred orientation of crystallites formed during annealing was parallel to the circumferential direction. While biaxial expansion resulted in orientation in both axial and circumferential directions, with relatively equal sized crystals in both directions, Da (112 Å) and Dc (97 Å). The expansion process had the most profound effect on mechanical performance, with a 65% increase in Young’s modulus, a 45% increase in maximum tensile stress and an 18-fold increase in strain at maximum load. These results indicate that biaxially expanding PLLA at a temperature above Tcc is possible, due to the high strain rates associated with stretch blow moulding.

Biodegradable polymers play a crucial role in the medical device field, with a broad range of applications such as suturing, drug delivery, tissue engineering, scaffolding, orthopaedics, and fixation devices. Poly-l-lactic acid (PLLA) is one of the most commonly used and investigated biodegradable polymers. The objective of this study was to determine the influence low shear microbore extrusion exerts on the properties of high molecular weight PLLA for medical tubing applications. Results showed that even at low shear rates there was a considerable reduction in molecular weight (M_n = 7–18%) during processing, with a further loss (M_n 11%) associated with resin drying. An increase in melt residence time from ~4 mins to ~6 mins, translated into a 12% greater reduction in molecular weight. The degradation mechanism was determined to be thermal and resulted in a ~22-fold increase in residual monomer. The differences in molecular weight between both batches had no effect on the materials thermal or morphological properties. However, it did affect its mechanical properties, with a significant impact on tensile strength and modulus. Interestingly there was no effect on the elongational proprieties of the tubing. There was also an observed temperature-dependence of mechanical properties below the glass transition temperature.

There has been a substantial increase in the use and development of plastics over the last century. However, due to ever-diminishing petroleum feedstocks and growing concern for the environment, there has been a rise in the use of eco-friendly polymers affording similar properties to that of their depleting counterparts. Poly(ε-caprolactone) is one such polymer. This present study investigates the possibility of developing a degradable nanocomposite, suitable for fused filament fabrication, utilizing hot melt extrusion technology to blend poly(ε-caprolactone), poly(ethylene) oxide and the nanoclay halloysite at loadings of two and six weight percent. The extruded blends were characterized using common polymer testing techniques. The addition of poly(ε-caprolactone) to the poly(ethylene) oxide matrix provided a plasticizing effect which was apparent with the melt flow index and melting point of the blends reducing with an increase in poly(ε-caprolactone) content. Upon reinforcing the matrix with halloysite, there was a significant improvement in mechanical properties. The addition of halloysite significantly increased Young’s modulus 11% and 25% when the loading was two and six percent respectively. Furthermore, it was also possible to produce a filament with the desired properties, diameter 1.75 mm, for fused filament fabrication, with subsequent studies required to evaluate their printability.

Material choice is a fundamental consideration when it comes to designing a solid dosage form. The matrix material will ultimately determine the rate of drug release since the physical properties (solubility, viscosity, and more) of the material control both fluid ingress and disintegration of the dosage form. The bulk properties (powder flow, concentration, and more) of the material should also be considered since these properties will influence the ability of the material to be successfully manufactured. Furthermore, there is a limited number of approved materials for the production of solid dosage forms. The present study details the complications that can arise when adopting pharmaceutical grade polymers for fused-filament fabrication in the production of oral tablets. The paper also presents ways to overcome each issue. Fused-filament fabrication is a hot-melt extrusion-based 3D printing process. The paper describes the problems encountered in fused-filament fabrication with Kollidon^® VA64, which is a material that has previously been utilized in direct compression and hot-melt extrusion processes. Formulation and melt-blending strategies were employed to increase the printability of the material. The paper defines for the first time the essential parameter profile required for successful 3D printing and lists several pre-screening tools that should be employed to guide future material formulation for the fused-filament fabrication of solid dosage forms.