Fabrication of anodic and atomic layer deposition-alumina coated titanium implants for effective osteointegration applications

Abstract

Biomimicking the chemical, mechanical, and topographical properties of bone on an implant model is crucial to obtain rapid and effective osteointegration, especially for the large-area fractures of the skeletal system. Titanium-based biomaterials are more frequently preferred in clinical use in such cases and coating these materials with oxide layers having chemical/nanotopographic properties to enhance osteointegration and implantation success rates has been studied for a long time. The objective of this study is to examine the high and rapid mineralization potential of anodized aluminum oxide (AAO) coated and atomic layer deposition (ALD)-alumina coated titanium substrates on large deformation areas with difficult spontaneous healing. AAO-coated titanium (AAO@Ti) substrates were fabricated via anodization technique in different electrolytes and their osteogenic potential was analyzed by comparing them to the bare titanium surface as a control. In order to investigate the effect of the ionic characters gained by the surfaces through anodization, the oxidized nanotopographic substrates were additionally coated with an ultrathin alumina layer via ALD (ALD@AAO@Ti), which is a sensitive and conformal coating vapor deposition technique. Besides, a bare titanium sample was also coated with pure alumina by ALD (ALD@Ti) to investigate the effect of nanoscale surface morphology. XPS analysis after ALD coating showed that the ionic character of each surface fabricated by anodization was successfully suppressed. In vitro studies demonstrated that, among the substrates investigated, the mineralization capacity of MG-63 osteosarcoma cells were highest when incubated on ALD-treated and bare AAO@Ti samples that were anodized in phosphoric acid (H3PO4_AAO@Ti and ALD@H3PO4_AAO@Ti). Mineralization on these substrates also increased consistently beginning from day 2 to day 21. Moreover, immunocytochemistry for osteopontin (OPN) demonstrated the highest expression for ALD@H3PO4_AAO@Ti, followed by the H3PO4_AAO@Ti sample. Consequently, it was observed that, although ALD treatment improves cellular characteristics on all samples, effective mineralization requires more than a simple ALD coating or the presence of a nanostructured topography. Overall, ALD@H3PO4_AAO@Ti substrates can be considered as an implant alternative with its enhanced osteogenic differentiation potential and rapid mineralization capacity.