Breast Implants: Biomaterials, Surfaces, Biocompatibility—A Biomedical Engineering Perspective

Breast implants are among the most frequently used long-term implantable medical devices in aesthetic and reconstructive surgery. In addition to correcting anatomical deficits, they have significant psychosocial effects, influencing body image, self-esteem, and quality of life, particularly in patients undergoing postmastectomy reconstruction. This review provides a comprehensive overview of the historical development, biological interactions, material characteristics, and clinical outcomes of breast implants. Early reconstructive attempts using foreign materials and injectable substances were associated with severe complications, underscoring the need for safer technologies. The introduction of silicone gel implants in the 1960s marked a pivotal advancement, followed by the development of saline-filled devices and highly cohesive silicone gels with enhanced mechanical stability. Key surgical considerations, including incision type and implant placement plane (subglandular, submuscular, dual-plane, and subfascial), are discussed in relation to aesthetic outcomes and complication risk. Emphasis is placed on the implant–tissue interface and the foreign body response (FBR), a process involving protein adsorption, immune cell activation, fibrous capsule formation, and potential chronic inflammation. Persistent inflammatory stimulation, often associated with bacterial biofilm formation, contributes to capsular contracture, the most common long-term complication. Additional adverse events include implant rupture, silicone gel bleed, granulomatous reactions, infection, hematoma, implant malposition, and rare but clinically significant conditions such as breast implant-associated anaplastic large cell lymphoma (BIA-ALCL). The review also summarizes implant classification according to construction, filling material, shape, and surface topography, highlighting the influence of surface characteristics on host response and clinical outcomes. Advances in biomaterials, cohesive gel formulations, and surface engineering aim to enhance biocompatibility and long-term safety, supported by standardized mechanical and biological testing protocols.