# Computed Tomography-Driven Design and Fused Filament Fabrication of Graded Density Bone Scaffolds
## 1 Introduction
### Previous Works  
Numerous studies in the literature highlight the advantages of lattice structures produced with AM for medical applications [8; 24; 25; 26].  
Numerous researchers have explored the manufacturability of various lattice architectures and porosity levels. For example, [PERSON] et al. [27; 28] analyzed manufacturing deviations in metal lattices, focusing on the pore size, strut thickness, porosity, and surface area.  
In parallel, other studies have investigated the mechanical behavior of different lattice configurations. [PERSON] et al. [29], for instance, examined complex strut-based lattice structures with spatially varying porosities designed to replicate the stiffness of distinct bone regions, such as cortical bone, the transition zone, and bone marrow.  
The influence of geometric parameters--particularly the pore size and lattice cell dimensions--on osseointegration performance has also been widely studied. [PERSON] et al. [30] assessed the impact of pore sizes ranging from 450 to 1200 \(\upmu\)m on osteoblast proliferation, noting that pores smaller than 600 \(\upmu\)m facilitated complete tissue ingrowth. [PERSON] et al. [31] extended this investigation under in vivo conditions, evaluating the effect of the pore size on the interfacial strength between the bone and implant. They identified 600 \(\upmu\)m pores as being optimal for long-term bone ingrowth and the development of robust bone-implant union. Similarly, [PERSON] et al. [32] reported that porous channels of 500 \(\upmu\)m offered the most favorable osseointegration outcomes within the tested range of 500-1200 \(\upmu\)m. A similar pore size range was reported by [PERSON] et al. [24], who observed that initial osteoblast cell colonization is enhanced by smaller pores, with faster colonization occurring when the pore sizes are below 600 \(\upmu\)m. However, the effective vascularization of pre-bone tissue requires larger pores--greater than 300 \(\upmu\)m--to accommodate blood vessel ingrowth. The lower pore size limit is also constrained by the specific combination of material and AM technology employed, as smaller pores may lead to powder entrapment and pore occlusion.  
Others have explored the use of biocompatible polymers. [PERSON] et al. [33] fabricated biomimetic HA scaffolds with TPMS structures using desktop-scale digital light processing (DLP), achieving improved degradation behavior and enhanced biological performance through process optimization. Similarly, [PERSON] et al. [34] developed 3D-printed poly-l-lactic acid (PLLA)-nano-hydroxyapatite (nHA) scaffolds with a high nHA content of up to 50% using FFF. These scaffolds exhibited a compressive strength of 14.2 MPa, which is comparable to that of human cancellous bone (2-12 MPa).  
A very similar approach to the one presented in this work was proposed by [PERSON] [35]. He presented a method that employs CT scans to construct patient-specific phantoms by controlling the filament extrusion rate in FFF technologies.  
Most recently, [PERSON] et al. [36] developed a heterogeneous scaffold by integrating medical imaging data with the octree-based adaptive subdivision technique. The scaffold was manufactured using selective laser melting (SLM) with a biocompatible Ti6 Al4V alloy.