EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Laser additive manufacturing (AM) technologies allow the homogeneous densification of complicated shape bio-ceramic parts. Among AM techniques, the powder bed selective laser processing (PBSLP), also known as selective laser sintering/melting, could enable the production of convenient, fast, and individualized implants and shorten the production period of patient-matched tissue engineering scaffolds from bioactive calcium phosphate powders, as hydroxyapatite (HAP). HAP is a well-known bio-ceramic material in bone tissue engineering because of its ideal properties for bone tissue reparation. Its bioactivity and biocompatibility ensure good osseointegration of the implants, keeping good mechanical and chemical resistance.

The shaping of pure HAP bio-ceramic, or at least as the main mixture component, by a PBSLP machine is still a challenge. The unfavorable optical and thermal properties of the HAP calcium phosphate phase make it decompose before it can sinter/melt to produce proper densification of the parts. A deeper study of powder feedstock composition is required.

In this communication, the processability comparison of different HAP based powder feedstocks is discussed, considering the flowability, thermal stability and laser-material interaction, as key factors for its correct shaping (Figure 1). Powder flowability and its interaction with the laser were improved through a multi-step process involving the synthesis and modification of HAP particles and their mixing with laser absorption additives. An ion-substitution process of HAP powder was performed to produce substituted-HAP with improved thermal stability. The characterization of slurries stability (through rheological behavior, zeta potential, and granulometry measurements), as well as powder chemical and structural properties (SEM, UV-VIS spectrophotometry, FTIR, and XRD), was decisive to produce and study the different powder feedstocks.

Figure 1. Hydroxyapatite sintered part by powder bed selective laser processing with 1 euro cent coin for scale reference.