Design and formulation strategies to modulate drug release from implantable devices

Implantable drug delivery systems (IDDSs) provide an attractive alternative for delivering drugs locally or systemically in a sustained manner. They offer a promising therapeutic option for patients with chronic conditions that traditionally rely on continuous drug administration via oral or injectable routes. Achieving these benefits, however, depends critically on the selection of materials and excipients used in the preparation of IDDSs. This review focuses on preformed solid IDDSs and how their design and formulation strategies can be adapted to optimise drug release. A wide range of aspects, such as implant design and formulation strategies, are explored. The review provides a comprehensive discussion of conventional formulation approaches adapted for IDDSs, including solubility enhancement, polymer degradation, porosity modulation, particle size reduction, and the incorporation of micro- or nano-encapsulation strategies. In addition, design parameters such as implant geometry and the use of rate-controlling membranes are discussed in detail. The article emphasises the importance of integrating advances in disciplines such as polymer science, manufacturing technologies, and drug formulation into the design of preformed IDDSs. Future directions emphasise personalised implant design, smart materials, and multi-drug delivery systems to address evolving clinical needs.