Morphological, mechanical, and biocompatibility characterization of macroporous alumina scaffolds coated with calcium phosphate/PVA

In bone tissue engineering, a highly porous artificial extracellular matrix or scaffold is required to accommodate cells and guide the tissue regeneration in three-dimension. Calcium phosphate (CaP) ceramics are widely used for bone substitution and repair due to their biocompatibility, bioactivity, and osteoconduction. However, compared to alumina ceramics, either in the dense or porous form, the mechanical strength achieved for calcium phosphates is generally lower. In the present work, the major goal was to develop a tri-dimensional macroporous alumina scaffold with a biocompatible PVA/calcium phosphate coating to be potentially used as bone tissue substitute. This approach aims to combine the high mechanical strength of the alumina scaffold with the biocompatibility of calcium phosphate based materials. Hence, the porous alumina scaffolds were produced by the polymer foam replication procedure. Then, these scaffolds were submitted to two different coating methods: the biomimetic and the immersion in a calcium phosphate/polyvinyl alcohol (CaP/PVA) slurry. The microstructure, morphology and crystallinity of the macroporous alumina scaffolds samples and coated with CaP/PVA were characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM/EDX) analysis. Also, specific surface area was assessed by BET nitrogen adsorption method and mechanical behavior was evaluated by axial compression tests. Finally, biocompatibility and cytotoxicity were evaluated by VERO cell spreading and attachment assays under SEM. The morphological analysis obtained from SEM photomicrograph results has indicated that 3D macroporous alumina scaffolds were successfully produced, with estimated porosity of over 65% in a highly interconnected network. In addition, the mechanical test results have indicated that porous alumina scaffolds with ultimate compressive strength of over 3.0 MPa were produced. Concerning to the calcium phosphate coatings, the results have showed that the biomimetic method was not efficient on producing a detectable layer onto the alumina scaffolds. On the other hand, a uniform and adherent inorganic-organic coating was effectively formed onto alumina macroporous scaffold by the immersion of the porous structure into the CaP/PVA suspension. Viable VERO cells were verified onto the surface of alumina porous scaffold samples coated with PVA-calcium phosphate. In conclusion, a new method was developed to produce alumina with tri-dimensional porous structure and uniformly covered with a biocompatible coating of calcium phosphate/PVA. Such system has high potential to be used in bone tissue engineering.