Effect of architecture topology on the properties of YSZ scaffolds for bone regeneration by filament extrusion 3D printing
AXELRAD TINOCO V. 1, HIDALGO J. 1, BERGES C. 1, NARANJO J. 1, HERRANZ G. 1
1 Universidad de Castilla-La Mancha E.T.S.I. INDUSTRIAL – INEI | Avda. Camilo Jose Cela s/n 13071 Ciudad Real, Ciudad Real, Spain
Bone defects in which a large part of the bone is injured are among the biggest challenges in orthopaedics surgery and traumatology. The research efforts seeking synthetic substitutes to bone have resulted in a collection of materials including compounds similar to bone and bioactive polymers and ceramics with excellent osteointegration and osteoconductive properties. However, these materials cannot typically resist high loads and suffer from the brittleness. This restricts their use for critical-size skeletal defects and commonly entails the use of auxiliary plates to keep the integrity and position of the scaffold. Biological grade yttria stabilized zirconia (YSZ) shows interesting properties compared to other ceramics in replacing critical-size defects in skeletal parts requiring to withstand a significant load. Ceramic scaffold should be capable to mimic the structural properties of the bone concerning bioactivity, porosity, interconnectivity and mechanical strength. The architecture topology of the porous cell structure has revealed as a key factor determining the osteconductivity, osteointegration and mechanical properties of the scaffold. A trade-off between these properties has to be considered in the design of the pore size, though three dimensional structure patterns such as gyroids have proven their efficacy of maintaining good mechanical properties for high porous volume structures.
The arrival of additive manufacturing technologies for ceramics allows a precise engineering of the pore size, pore distribution and produce tailormade geometries for an effective scaffold integration and bone regeneration. This work investigates the manufacture of biological grade YSZ scaffolds by Fused Filament Fabrication (FFF). Filaments made of nanometer size YSZ powder with up to 50 vol% were successfully produced and used for printing miniature scaffolds prototypes intended to by tested in rodents as a first step in the long run for validating their use in humans. The low ceramic powder particle size (40 nm) is a challenge in the production of feedstock for FFF technology, though it is necessary for a good densification during sintering and to maintain the final grain size below the 400 nm to meet the standards. The main issues arising from the use of low powder size are discussed. Besides, scaffolds with different porous cell structure topology and porous size were processed to determine the influence of these parameters in the scaffold properties including mechanical and biological.