Biological glass coating on ceramic materials: In vitro evaluation using primary osteoblast cultures from healthy and osteopenic rat bone

ZrO ₂ and Al ₂O ₃ substrates were successfully coated by a double layer of a silica-based glass named RKKP, using a low-cost firing technique. RKKP is a glass well known for its bioactivity; therefore, a RKKP coating on Al ₂O ₃ or ZrO ₂, allows to combine the excellent mechanical properties of these strong ceramic substrates with its bioactivity. ZrO ₂ samples were easily coated using a double layer of RKKP by a simple enamelling technique. To accommodate the thermal expansion coefficient mismatch between Al ₂O ₃ and RKKP, this substrate was coated using a multilayered composite approach. All of the coatings were characterised from a morphological and compositional point of view, and an extensive biological evaluation was performed using fresh rat osteoblasts. Osteoblast primary cultures were derived from the trabecular bone of femoral condyles harvested from intact (NB) and osteopenic (OB) rats. After characterisation of their phenotype, osteoblasts were seeded on material samples of ZrO ₂ or Al ₂O ₃ coated with RKKP, and cultured for 7 days. Cell proliferation (MTT test) and cell differentiation (alkaline phosphatase activity) were evaluated at the end of the experiment, to assess osteoblast behaviour in the presence of biomaterials and determine if the results were related to the host bone quality. Results of both materials showed a good level of biocompatibility. In particular, MTT significant higher values were detected in NB cultures on ZrO ₂-RKKP samples; ALP activity significantly increased in NB cultures on Al ₂O ₃-RKKP and in OB cultures on both coated samples.