Current formulation approaches in design and development of solid oral dosage forms through three‐dimensional printing

Three-dimensional (3D) printing technologies are continuously applied to novel fields, laying the foundations for a new industrial revolution. With regard to pharmaceutical sciences, 3D printed drug products are emerging as attractive and innovative tools in personalised medicine. For example, solid oral dosage forms (e.g. tablets) can be printed in a wide range of dosages, release profiles, geometries and sizes by simply modifying a digital model, thus providing patients with tailored therapies.

Various 3D printing technologies have been applied to pharmaceutical manufacture in recent years, and different materials have been investigated to fabricate solid oral dosage forms in a broad range of properties. Therefore, the aim of this review is to describe the state of the art of 3D printing oral pharmaceuticals, with the view to provide formulation scientists with essential information to approach the development of 3D printed drug products, from digital design to final product quality control. Short- to long-term potential areas of application of 3D printed drug products and their relative regulatory pathway challenges are also presented.

Introduction
Automated production of solid oral dosage forms was introduced over two centuries ago. The main advantages of such dosage forms are based on their relatively undemanding and convenient manufacture, coupled with high patient compliance. Tablets, the most relevant exponent of the class, have been improved in the last decades introducing techniques such as film coating, double compression and osmotic systems to achieve controlled and targeted release. However, despite the technological advances, tablet production is still based on tableting machines whose design has not essentially changed for decades since the introduction of automated tablet presses [2]. Conventional tableting techniques still suffer from limitations, including challenges in direct compression of powders and the related need for granulation. A further drawback of conventional tableting relies on the increasing demand for personalised treatments, likely to represent a significant shift in future medicine [3, 4]. Indeed, conventional tableting machines based on punches and dies are designed for a mass production market, therefore they are inherently lacking in flexibility; hence, a more flexible platform would facilitate the design, production and dispensing of bespoke medicines in the near future.

Additive manufacturing (AM), a set of techniques including 3D printing, has recently aroused much interest in pharmaceutics due to its large flexibility, which makes it a promising tool to produce the bespoke drug delivery devices, including solid oral dosage forms.

Designing 3D printed solid oral dosage forms: from digital design to bespoke tablet properties

Computer-aided design tools for dosage form design
Prior to 3D printing solid oral dosage forms, it is essential to produce a digital model through computer-aided design (CAD) software. Digital modelling allows freedom of design such that the production of tablets, for instance, is no longer dependent on size and shape of dies and punches, eventually making the same equipment suitable for producing an unlimited variety of geometries. For example, our research group has used Tinkercad (Autodesk Inc., USA) to design a set of dosage forms with different shapes with the aim of assessing the feasibility of SLA 3D printing for future research. Download the full article by clicking on the image

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