Tailoring selective laser melting process for titanium drug-delivering implants with releasing micro-channels

The use of drug-delivering implants can minimise implant failure due to infection through a controlled medication release into the surrounding tissues. In this study, selective laser melting (SLM) was employed to manufacture Ti-6Al-4 V samples, with internal reservoirs and releasing Micro-channels (MCs) to simulate what could be a drug-delivering orthopaedic or dental implant. Investigations were performed to optimise the design and SLM process parameters required to create the releasing MCs with minimum dimensional deviation to allow a controlled dosing of the drugs, while considering the process impact on the surface roughness and porosity of the builds. The build orientation, internal contour spacing, and laser process parameters were varied to assess their effect on the resolution of the MCs with diameters of ∼200–500 μm. It was found that, vertically oriented channels were found to have the least dimensional deviation from the target dimensions compared with horizontally-oriented or inclined channels. The dimensional deviation of the MCs was found in range of 220–427 μm, while the horizontal surface roughness (R_a) was in range of 1.46–11.46 μm and the vertical surface roughness (R_a) was in range of 8.5–13.23 μm when applying energy density varying from of 27–200 J/mm³. It was found that, there was a clear correlation between the energy density with both dimensional deviation and horizontal surface roughness, while no correlation was found for the vertical’ surface roughness. The study identified the optimum conditions to manufacture drug-delivering metallic implants, creating hollow samples with releasing MCs equivalent diameter of ∼271 μm, horizontal surface roughness (R_a) of 4.4 μm, vertical surface roughness of (R_a) 9.2 μm, and build porosity of 1.4% using an internal contour of 150 μm and energy density of 35.7 J/mm³.