The ceramic slurry for scaffold fabrication was prepared by gradually adding 60 or 65 g of TiO2 powder to 25 ml of sterilised water and the pH of the slurry was kept at 1.7 for the entire duration of the stirring with small additions of 1 M HCl. For double-coated scaffolds, the slurry for the second coating contained 40 g of TiO2 powder in 25 ml sterilised water. The TiO2 powder was stirred in to the water in several steps at low rotation speed of 1,000 rpm (Dispermat Ca-40, VMA-Getzmann GmbH, Reichshof, Germany). The temperature of the slurry was adjusted to room temperature during the low rotation speed stirring. When the slurry mixture was homogenous, the rotation speed was increased to 5,000 rpm and the slurry was stirred for 5 h at this rotation speed. Temperature of the slurry was reduced to 15°C during high speed stirring.
The polyurethane (PU) foam templates (60 ppi, Bulbren S, Eurofoam GmbH, Wiesbaden, Germany) were washed and cut to appropriate size as described in [18 (link)]. The cylindrical templates were then immersed in the ceramic slurry, and excess slurry was either squeezed between two polymer foam sheets or centrifuged (1 min @ 1,000 rpm; Biofuge 22R Heraeus Sepatech, Osterode, Germany) out of the foam templates to ensure that only a thin layer of slurry covered uniformly the entire surface area of the polymer template without blocking the pores. The samples were then placed on a porous ceramic plate and allowed to dry at room temperature for at least 16 h before sintering.
For the burnout of the polymer, the scaffolds were slowly heated to 450°C at a heating rate of 0.5 K/min. After 1 h holding time at 450°C, temperature was raised to 1,500°C at a rate of 3 K/min and the sintering time at this temperature was set to 40 h. The sintered scaffolds were then cooled back to room temperature at the cooling rate of 5 K/min (HTC-08/16, Nabertherm GmbH, Bremen, Germany).
The polyurethane (PU) foam templates (60 ppi, Bulbren S, Eurofoam GmbH, Wiesbaden, Germany) were washed and cut to appropriate size as described in [18 (link)]. The cylindrical templates were then immersed in the ceramic slurry, and excess slurry was either squeezed between two polymer foam sheets or centrifuged (1 min @ 1,000 rpm; Biofuge 22R Heraeus Sepatech, Osterode, Germany) out of the foam templates to ensure that only a thin layer of slurry covered uniformly the entire surface area of the polymer template without blocking the pores. The samples were then placed on a porous ceramic plate and allowed to dry at room temperature for at least 16 h before sintering.
For the burnout of the polymer, the scaffolds were slowly heated to 450°C at a heating rate of 0.5 K/min. After 1 h holding time at 450°C, temperature was raised to 1,500°C at a rate of 3 K/min and the sintering time at this temperature was set to 40 h. The sintered scaffolds were then cooled back to room temperature at the cooling rate of 5 K/min (HTC-08/16, Nabertherm GmbH, Bremen, Germany).
