gms | German Medical Science

Objectives: In the past, strontium ions were shown to influence the bone remodeling process: the bone formation of osteoblasts is stimulated whereas bone resorption by osteoclasts is downregulated. Osteoporotic patients take advantage of Sr ions by the orally administered drug strontium ranelate. Herein, we have used a recently developed strontium-modified premixed calcium phosphate cement (Sr-CPC) [1] to produce highly porous scaffolds by additive manufacturing utilizing low temperature 3D plotting. We expected an enhanced Sr release from these scaffolds due to the higher surface/volume ratio in comparison to bulk scaffolds.

Methods: Sr-free calcium phosphate cement (CPC) and Sr-modified calcium phosphate cement (Sr-CPC) were prepared as described recently [1]. Both pastes were rheologically characterized for shear thinning, oscillatory response and viscosity and yield stress were obtained from the data. Scaffolds were produced by extrusion-based 3D-plotting using the Bioscaffolder 3.1 (GeSiM mbH, Radeberg, Germany). Scaffolds had cuboid shape and were plotted with needle sizes of 230 µm, 410 µm, 610 µm and 840 µm, respectively. As controls, bulk scaffolds of the same mass were produced. After production, scaffolds were allowed to set for 3 days in humidity [2] and washed over night in acetone. Scaffolds were evaluated by micro computed tomography and Sr release into cell culture medium was measured over 28 days.

Results: Both pastes, CPC and Sr-CPC showed shear thinning behaviour, highlighting the applicability for 3D plotting. Viscosity and yield stress were comparable for both cements. The extrusion trough the plotting needles did not provoke filter pressing, hence scaffolds of high shape fidelity could be fabricated without limitations in time. Micro computed tomography revealed, that the surface/volume ratio of the scaffolds increased with decreasing strand widths of the scaffolds, which were controlled by the various needle diameters while scaffold production. As expected, Sr release of the scaffolds was dependent on the surface/volume ratio. Bulk scaffolds released less Sr in comparison with their macroporous, plotted equivalents. Moreover, the normalized release was the highest for those scaffolds, which revealed the highest surface/volume ratio.

Conclusion:Scaffolds comprised of Sr-CPC were fabricated by 3D plotting and tested for their Sr release in vitro. By changing the needle dimension while fabrication process, Sr release could be influenced. The obtained scaffolds may be used in vivo for local application of Sr ions with controlled doses.