Mineralized scaffolds for hard tissue engineering by ionotropic gelation of alginate
R. Dittrich, F. Despang, A. Bernhardt, A. Mannschatz, Th. Hanke, G. Tomandl, W. Pompe, M. Gelinsky
Advances in Science and Technology 49, 159 (2006)
Alginates form gels with tube-like pores when covered with solutions of di- or trivalent cations. This phenomenon also referred to as ionotropic gelation has been known for more than 30 years. By mixing a calcium phosphate powder and an alginate as the starting material, the mineral phase of bone is incorporated. Such porous structures can be used for scaffolds in hard tissue engineering. The starting materials and stabilizing additives are dispersed in an aqueous solution. Then a solution of Ca-ions is deposited onto the surface of the slurry. The slurry can be gelled by ion exchange of Na-ions in the alginate with Ca-ions. A primary thin gel layer with the function of a membrane is immediately formed. By diffusional control of cation transport through the membrane, the slurry gradually transforms to the gel forming tube-like pores in direction of cation diffusion. Like the gelation of pure alginate the concentration of electrolyte and the kind of cations and anions influence the size (diameter and length) and size growth of the pores, but the tolerance in the preparation conditions is much smaller. The diameters of the pores can be adjusted between 50 and 500 m which fits the optimum size for cell seeding and blood capillary ingrowth very well. By selecting the proper drying method the inherent shrinkage can be controlled. Hydroxyapatite sintered at high temperatures loses the ability to be resorbed by osteoclasts in vivo. Therefore, we have developed scaffolds with channel-like pores from alginate/calcium phosphate composites without the necessity for heating them to higher temperatures.