3D-printed polylactic acid scaffolds for bone tissue engineering: Bioactivity enhancing strategies based on composite filaments and coatings

The advent of additive manufacturing has ushered in an era of customized bone scaffolds tailored to a patient 's unique physiological condition. These personalized scaffolds not only increase treatment success rates but also mitigate patient discomfort. A wide range of manufacturing methods and feedstock materials have emerged for crafting bone implants. Amongst these, extrusion-based 3D printing is widely preferred due to its costeffectiveness, rapid production capabilities, and compatibility with a wide range of materials. Polylactic acid (PLA), a biopolymer derived from natural sugar sources like sugarcane and corn is one of the most preferred polymers for fused deposition modeling (FDM) 3D printing of bone scaffolds. Approved by the US-based regulator FDA for 3D-printed medical devices, PLA shows exceptional biocompatibility and biodegradability within the human body. However, pure PLA scaffold exhibits inert properties, resulting in minimal interaction with cellular components in the human body 's microenvironment. To overcome this limitation, various methodologies have been adopted to enhance the bioactivity of 3D-printed PLA scaffolds, thereby increasing cell-material interactions. Two prominently employed strategies for enhancing bioactivity involve the incorporation of bioactive filler materials into the polymer filaments to create polymer-ceramic composite scaffolds. This addition not only enhances bioactivity but also reinforces mechanical strength. Another effective approach involves coating scaffolds with biopolymers, ceramics, and other biologically active substances. This will ensure coating with materials that are likely to degrade at the high temperatures that will be experienced during FDM 3D printing. This work delves into the diverse array of strategies employed to enhance the bioactivity of 3D-printed PLA scaffolds. Furthermore, this study also provides a perspective on the anticipated advancements in this field in the near future.