Gelatin freeze casting of biomimetic titanium alloy with anisotropic and gradient pore structure

Abstract

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Abstract. Titanium metal and its alloys are materials commonly used for dental and orthopaedic implants. However, due to large difference in properties between the titanium metal and the natural bone, stress shielding has been observed around the surround area, resulting in bone atrophy, and thus has raised concerns of the use of this material. Ideally implant materials should possess similar properties to the surrounding tissues in order to distribute the load as the joint would naturally, while also possessing a similar porous structure to the bone to enable interaction with the surrounding material. In this paper we report the formation of aligned porous titanium alloy scaffolds with the use of unidirectional freeze casting with a temperature gradient. The resulting scaffolds had a dense bottom part with sufficient strength for loading, while the top part remaining porous in order to allow bone growth in the scaffold and fully integrating with the surrounding tissue. The anisotropic nature of the pores within the titanium alloy samples were observed via micro computed tomography, where a gradient structure similar to bone was observed. The compressive strength of the fabricated scaffolds was found to be up to 427 MPa when measured with the pores aligned with the applied load, depending on the pore density. This is within the range of cortical bone.

The effect of gelation on statically and dynamically freeze‐cast structures

“…Introducing an initial gelation of the solvent by adding gelatin and leaving it to harden causes the medium in which the ice grows to change, thereby changing the final morphology of the ice crystals and thus the resulting pores . While the macroporosity of the gelated structures are still lamellar and the perpendicular pore shape is overall ellipsoidal, as is evident from Figure , the general morphology is significantly different.…”

“…Combining gelation and freeze‐casting using gelatin was introduced by Fukushima et al, who showed that initial gelation of samples completely alters the morphology of the pores while achieving complex shapes throughout the entire ceramic body. The gelated freeze‐cast structures have, however, primarily been used for processing of insulating materials, membranes, and biomedical purposes, where the latter utilizes the hierarchical nature of freeze‐cast structures, as previously mentioned. However, until now gelated freeze‐cast structures have been processed using primarily static freezing profiles .…”

“…The gelated freeze‐cast structures have, however, primarily been used for processing of insulating materials, membranes, and biomedical purposes, where the latter utilizes the hierarchical nature of freeze‐cast structures, as previously mentioned. However, until now gelated freeze‐cast structures have been processed using primarily static freezing profiles . For a static freezing profile the cold side is kept at a constant temperature below the freezing temperature of the solvent throughout the freeze‐casting process.…”

“…However, until now gelated freeze-cast structures have been processed using primarily static freezing profiles. [16][17][18][19] For a static freezing profile the cold side is kept at a constant temperature below the freezing temperature of the solvent throughout the freeze-casting process. Static freezing profiles lead to a changing freezing front velocity during casting, resulting in structures with varying macropore sizes.…”

Engineering biological gradients

“…Although the inverse relationship between pore size and mechanical properties was confirmed, temperature influence was not detected. 87 Although the three components are usually combined, it is also possible to exploit the freeze-casting technique without the presence of a powder, which results in a physical but not a chemical gradient. An anisotropic frozen alginate scaffold was produced by gradual cooling of the polymer solution, lyophilization, and final immersion in a solution with a high concentration of CaCl 2 for structural stabilization.…”