3D Printing in Cosmetics: Investigating New Skin Delivery Platform

3D printing is an innovative manufacturing technology that can produce bespoke objects through a precise, layer-by-layer deposition of materials. While its potential in pharmaceutical manufacturing is well acknowledged, its application in the cosmetics industry remains underexplored. This study investigates the use of 3D printing in developing innovative, effective and sustainable cosmetic delivery systems, focusing on Stereolithography (SLA) and Fused Deposition Modelling (FDM), two widely used 3D printing techniques.

The SLA 3D printer operates via free-radical based photopolymerisation process and was selected for its high-resolution capabilities and prior success in fabricating microneedles (MNs) for transdermal drug delivery. SG dental resin, a commonly used photopolymer, was employed due to its mechanical strength and biocompatibility. However, the SLA technique faced challenges, primarily due to limitations in the resolution of desktop SLA printers and the physical properties of SG resin, leading to blunt microneedle tips unsuitable for effective skin penetration. These findings underscore the need for advancements in SLA technology and material optimisation to meet the precision demands of cosmetic microneedle fabrication.

The extrusion-based FDM 3D printer was selected for its accessibility and specific capability to perform dual-material printing, enabling the fabrication of two-part skin patches. These patches comprised a hydrophobic polylactic acid (PLA) backing material and a hydrophilic polyvinyl alcohol (PVA) layer designed to interact directly with the cosmetic formulation. The dual-material approach allowed for the seamless integration of materials with distinct properties. The PVA layer served as the delivery platform for the cosmetic formulation, ensuring controlled release and effective adherence to facial contours, while the PLA backing provided structural support and durability. This design enabled precise customisation to fit various facial areas.

To explore controlled release mechanisms, these 3D-printed patches were loaded with hydrogels containing a model hydrophilic active ingredient, caffeine. Six gelling agents, including polysaccharides, cellulose derivatives, and a synthetic polyacrylate, were used at varying concentrations. The hydrogels were characterised using rheological tests (continuous flow and oscillatory methods with MARS iQ Air, Thermo Scientific, Germany) and thermal analyses (Discovery thermogravimetric analyser and Q2000 differential scanning calorimeter, TA Instruments, USA).

In vitro release studies using a vertical diffusion cell system with cellulose acetate and skinmimicking membranes demonstrated that the viscosity of the hydrogels significantly influenced caffeine release. Lower-viscosity gels exhibited higher flux rates through skinmimicking membranes. It was shown that the controlled release of caffeine could be achieved through the combined effects of the 3D-printed PVA insert and the caffeine-containing hydrogel.

This research provides valuable insights into optimising the design of skin delivery platforms, focusing on critical factors such as surface characteristics, thickness, and the selection of gelling agents informed by their rheological and thermal properties. The FDM method demonstrated success in producing dual-material cosmetic patches due to its capability for customisation and controlled integration of distinct material properties. However, the SLA method encountered challenges in microneedle fabrication, as the resolution limitations of desktop SLA printers and the mechanical properties of SG resin resulted in blunt microneedle tips. This highlighted the need for further advancements in SLA technology and material formulation to address these limitations and enhance its application for cosmetic microneedles.

The novel contributions of this thesis include the application of dual-extrusion FDM technology to create customisable cosmetic skin delivery systems and the development of a new in vitro Skin insertion test. This test simulates the elastic properties of human skin, improving the evaluation of microneedle performance. These findings offer a foundation for future research and practical applications in the development of 3D-printed cosmetic delivery platforms, particularly in terms of material selection, active ingredient loading, and production methodologies.