Nano-particles of hydroxyapatite are made using a cold reaction method. This synthesis is required to make particles that can serve as a future bone scaffold.
2) Heat Treatment
To reach the desired crystalline phase of hydroxyapatite, the amorphous product of the synthesis is heat treated. The results are confirmed by x-ray diffraction.
3) Ball Milling
After the heat treatment, the particles became partially fused. To return our particles to their desired size they are repeatedly crushed in a ball mill for a prescribed length of time.
4) Sieving
Sieving is the process by which we can assess the post ball milling particle size distribution. This process is also known as gradation. This ensures particle size is fine enough to be made into slurry for extrusion.
5) Slurry Preparation
The non-toxic slurry is engineered to flow smoothly through the pump system and cure rapidly upon exposure to air. To reach the desired flow profile, the samples were tested using a rheometer. Additionally, materials were chosen that are non-reactive with hydroxyapatite.
6) Extrusion
At the extrusion step, we use our specially modified 3D printer to create an external mold made of PLA and a second extruder to print the piece from our innovative slurry.
7) Burnout
This step is necessary to remove the outer mold made in PLA because it is an undesired mold. After the burnout, no traces of PLA will be left on our product. The pores that are left from binder burnout will be filled with bio-resorptive polymer during infusion.
8) Sintering The ceramic is chemically bonded at this point. We found that several hours of 1100°C results in adequate sintering. At this temperatures the ceramic nano-particles are able to fuse together via atomic diffusion.
9) Infusing
Now that the ceramic has been fused, the last step in the fabrication process is to fill the voids with the bioresorptive polymer. This is done by dissolving the polymer in a non-toxic solvent and soaking the sample for a prescribed period of time under vacuum.
10) User
Prior to implantation, the component undergoes UV sterilization and ultrasonic crack detection. Then it is ready to be used to help those in need. Our goal is that after a few years, the part will be indistinguishable from the patient's original bone.