Additive manufacturing of bioactive and biodegradable porous iron-akermanite composites for bone regeneration

Advanced additive manufacturing techniques have been recently used to tackle the two fundamental challenges of biodegradable Fe-based bone-substituting materials, namely low rate of biodegradation and insufficient bioactivity. While additively manufactured porous iron has been somewhat successful in addressing the first challenge, the limited bioactivity of these biomaterials hinder their progress towards clinical application. Herein, we used extrusion-based 3D printing for additive manufacturing of iron-matrix composites containing silicate-based bioceramic particles (akermanite), thereby addressing both of the abovementioned challenges. We developed inks that carried iron and 5, 10, 15, or 20 vol% of akermanite powder mixtures for the 3D printing process and optimized the debinding and sintering steps to produce geometrically-ordered iron-akermanite composites with an open porosity of 69-71%. The composite scaffolds preserved the designed geometry and the original α-Fe and akermanite phases. The in vitro biodegradation rates of the composites were improved as much as 2.6 times the biodegradation rate of geometrically identical pure iron. The yield strengths and elastic moduli of the scaffolds remained within the range of the mechanical properties of the cancellous bone, even after 28 days of biodegradation. The composite scaffolds (10-20 vol% akermanite) demonstrated improved MC3T3-E1 cell adhesion and higher levels of cell proliferation. The cellular secretion of collagen type-1 and the alkaline phosphatase activity on the composite scaffolds (10-20 vol% akermanite) were, respectively higher than and comparable to Ti6Al4V in osteogenic medium. Taken together, these results clearly show the potential of 3D printed porous iron-akermanite composites for further development as promising bone substitutes. STATEMENT OF SIGNIFICANCE: : Porous iron matrix composites containing akermanite particles were produced by means of multi-material additive manufacturing to address the two fundamental challenges associated with biodegradable iron-based biomaterials, namely very low rate of biodegradation and insufficient bioactivity. Our porous iron-akermanite composites exhibited enhanced biodegradability and superior bioactivity compared to porous monolithic iron scaffolds. The murine bone cells proliferated on the composite scaffolds, and secreted the collagen type-1 matrix that stimulated bony-like mineralization. The results show the exceptional potential of the developed porous iron-based composite scaffolds for application as bone substitutes.

Sonochemical Synthesis of Vaterite-Type Calcium Carbonate Using Steamed Ammonia Liquid Waste without Additives

Herein, metastable spheroidal vaterite calcium carbonate (CaCO3) was prepared using a simple ultrasound technique. The fabricated material comprises an irregular nanoparticle aggregate when steamed ammonia liquid waste, that is, (CaCl2) and (NH4)2CO3, is used as the raw material at atmospheric temperature, without any surfactants. The effects of ultrasound amplitude, probe immersion depth, and solution volume on particle properties were investigated. The obtained samples were identified and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and the Brunauer-Emmett-Teller technique. Our experiments show that the probe immersion depth and the reaction volume are the key parameters that impact the diameter size and size distribution of the fabricated spheroidal vaterite CaCO3 particles. The ultrasound amplitude considerably affected the particle size and the specific surface area. A possible formation mechanism for pure vaterite is proposed herein, which suggests that simple vaterite CaCO3 is formed owing to the special properties of steamed ammonia liquid waste and the synergistic effects of the ultrasonic system. This study may provide a new method for vaterite CaCO3 synthesis.