Abstract
<title>Abstract</title> <p>Achieving structurally and geometrically accurate bioprinted constructs on complex anatomical surfaces remains a major bottleneck in clinical in situ tissue engineering. Traditional three-axis planar bioprinting systems are inherently limited in printing fidelity on curved or inclined surfaces due to their layer-by-layer planar deposition strategy, which results in stair-stepping artifacts, nonuniform layer thickness, material overfill or underfill, and poor interlayer adhesion. These deficiencies ultimately impair the mechanical integrity and functional performance of the printed constructs. To address these limitations, this study presents a five-axis extrusion-based bioprinting platform that enables orientation-adaptive, multi-angle material deposition. A conformal slicing algorithm is used to make toolpaths that are aligned with the surface. This lets the nozzle's orientation always follow the surface normals and keep tangential deposition along complex shapes. The system underwent experimental validation utilizing gelatin-alginate bioinks on a representative hemispherical cranial defect model. Compared to traditional 3-axis printing, the proposed method showed better structural fidelity, consistent wall thickness, better bonding between layers, and no stair-stepping effects. Quantitative assessment indicated improved dimensional precision, diminished surface variation, and enhanced repeatability across trials. The printed constructs' mechanical performance improved interlayer cohesion through angle-adaptive deposition, which made them stronger and less likely to deform. These findings validate that multi-axis conformal bioprinting can significantly improve the quality, structural integrity, and clinical applicability of in situ bioprinted tissues, establishing a foundation for patient-specific defect reconstruction and advanced robotic bioprinting technologies.</p>