Microcrystalline Cellulose in Direct Compression: Material Attributes, Compaction Behavior, and Tablet Performance

Direct compression (DC) is an efficient tablet manufacturing technique in which a powder blend containing the active pharmaceutical ingredient (API) and suitable excipients is compressed directly without an intermediate granulation step. Although DC offers advantages such as reduced processing time, lower energy consumption, fewer manufacturing operations, and limited exposure to heat and moisture, it requires excipients with appropriate flow and compaction properties. Microcrystalline cellulose (MCC) is one of the most widely used excipients in DC formulations because of its excellent compactibility, tabletability, dry-binding capacity, and favorable plastic deformation behavior. However, MCC performance is influenced by several material attributes, including particle size, particle-size distribution, morphology, porosity, density, moisture content, crystallinity, surface characteristics, and manufacturing conditions. This review critically examines the physicochemical and functional properties of MCC and their relationship with direct-compression performance. Particular emphasis is placed on MCC deformation and interparticle bonding mechanisms, compressibility, compactibility, tabletability, grade and source variability, lubricant sensitivity, and effects on tablet critical quality attributes. The review also discusses MCC-based co-processed excipients as an emerging approach to improve powder flow, compaction, multifunctionality, and formulation robustness. Furthermore, current developments in advanced material characterization, predictive formulation development, continuous manufacturing, and science-based excipient selection are highlighted. Understanding the relationships among MCC material attributes, powder behavior, compression mechanisms, and final tablet performance is essential for rational excipient selection and development of robust direct-compression formulations. Overall, MCC remains a critical multifunctional excipient for modern tablet manufacturing, while continued material engineering and predictive approaches may further enhance its performance and formulation versatility.