Abstract

POLYMER ENGINEERING IN BILAYER AND MULTILAYER TABLETS: FROM FORMULATION DESIGN TO DRUG RELEASE – A REVIEW

Muskan Soni*, Dr. Kamlesh Dashora

Abstract

Bilayer and multilayer tablets are advanced oral drug delivery systems that enable spatial and functional separation of active pharmaceutical ingredients (APIs) and excipients within a single dosage form, thereby overcoming the limitations of conventional single-layer tablets. These systems are particularly advantageous for chronic disease management and fixed-dose combination therapies, as they allow the integration of immediate, sustained, delayed, targeted, and sequential drug release profiles. Polymer engineering plays a central role in the design, performance, and manufacturability of bilayer and multilayer tablets, as polymers govern layer formation, interlayer adhesion, mechanical integrity, and drug release behavior. This review provides a comprehensive overview of polymer engineering strategies applied to bilayer and multilayer tablet systems, with a focus on formulation design and drug release control. Natural, semisynthetic, synthetic, and functional polymers used in immediate-release, sustained-release, delayed-release, gastroretentive, mucoadhesive, osmotic, and chronotherapeutic layers are critically discussed. Particular emphasis is placed on key polymer attributes such as viscosity grade, molecular weight, swelling behavior, permeability, and compressibility, and their influence on critical quality attributes including disintegration time, dissolution kinetics, interlayer adhesion, and mechanical strength. The application of Quality by Design (QbD) principles to polymer selection and optimization is highlighted, emphasizing critical material attributes, risk assessment, and design space establishment to ensure robust and reproducible product performance. In addition, polymer–drug and polymer–polymer compatibility considerations, manufacturing challenges, and scale-up issues associated with multilayer tablet production are addressed. Recent advances in smart and stimuli-responsive polymers, nanostructured and hybrid polymer systems, and engineered polymer architectures are also reviewed, highlighting their potential to enable controlled, targeted, and patient-centric oral drug delivery. Overall, this review underscores polymer engineering as a system-defining approach for the development of robust, effective, and regulatory-compliant bilayer and multilayer tablet formulations.

Keywords: Bilayer tablets; Multilayer tablets; Polymer engineering; Controlled drug release; Quality by Design (QbD); Drug–polymer compatibility; Targeted drug delivery.