Bioactive Polymer Composites for 3D-Printed Bone Implants: A Systematic Review

Polymer-based bioactive composites are one of the most rapidly advancing areas in contemporary regenerative medicine. This review aims to identify major trends and knowledge gaps in the development of bioactive polymer composites and examine their translational relevance from a materials design perspective, with a specific focus on synthetic thermoplastic polymer matrices suitable for load-bearing bone scaffold applications and filament-based additive manufacturing. A total of 546 publications spanning 2016-2025 were screened, with 106 selected according to predefined relevance criteria. Bibliometric and content analyses were performed to delineate the primary research trajectories of bioactive composite materials. The results revealed that the majority of studies focused on composites comprising synthetic aliphatic polyesters, primarily polylactic acid (PLA) or polycaprolactone (PCL), reinforced with hydroxyapatite (HA) or bioactive glass (BG), which confer osteoconductivity but rarely achieve multifunctionality. Antimicrobial agents, ion-releasing components, and naturally derived bioactive molecules-associated with biointeractive functionalities and reported effects related to osteogenesis, angiogenesis, and immune modulation-are significantly underrepresented. Fewer than 20% of the investigated studies include in vivo validation, underscoring considerable scope for further preclinical and translational research. This work consolidates current trends in synthetic bioactive polymer composite design and identifies critical directions for future research. The findings of this review provide a structured framework to support the selection of composite fabrication and modification strategies, functional additives, and targeted biological functionalities for next-generation, load-bearing bone tissue engineering materials.