Sodium silicate gel induced self-mineralization of different compact and porous polymeric structures

In the present work a new methodology to produce bioactive coatings on the surface of starch based or other polymeric biomaterials is proposed. A sodium silicate gel is employed as an alternative nucleating agent to the more typical bioactive glasses, for inducing the formation of a calcium-phosphate (Ca-P) layer. The method has the advantage of being able to coat compact materials and porous 3D architectures to be used on tissue replacement and as tissue engineering scaffolds. By using this treatment, only after 6 hours of SBF immersion, it is already possible to observe the formation of very cohesive apatite-like layers that became then fragmented due to the swelling of the polymers. For the porous materials, this layer could be also observed inside the pores, clearing covering the cell walls. Furthermore, it was observed an increase of the surface hydrophilicity raising the amount of polar groups in the surface that might contribute to the formation of silanol groups that also act as apatite inductors. After 30 days of SBF immersion, the apatite-like films exhibit a partially amorphous nature and the Ca/P ratios became very closer to the value attributed to hydroxyapatite (1.67). These results are very promising for the developing of cancellous bone replacement materials and for pre-calcifying bone tissue engineering scaffolds. The present methodology can be used to coat biodegradable polymers in spite of all the correspondent difficulties arising from the continuous pH and surface changes as function of time.