Pore structures and mechanical properties of porous titanium scaffolds by bidirectional freeze casting

Abstract

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms ABSTRACTPorous titanium scaffolds with long-range order lamellar structure were fabricated using a novel bidirectional freeze-casting method. Compared with the ordinarily porous titanium materials made by traditional freeze casting, the titanium walls can offer the structure of ordered arrays with parallel to each other in the transverse cross-sections. And titanium scaffolds with different pore width, wall size and porosity can be synthesized in terms of adjusting the fabrication parameters. As the titanium content was increased from 15 vol.% to 25 vol.%, the porosity and pore width decreased from 67 % to 50 % and 41μm to 32 μm, respectively. On the contrary, as the wall size was increased from 9 μm to 23 μm, the compressive strength and stiffness were increased from 58 ± 8 MPa to 162 ± 10 MPa and from 2.5 ± 0.7 GPa to 6.5 ± 0.9 GPa, respectively. The porous titanium scaffolds with long-range lamellar structure and controllable pore structure produced in present work will be capable of having potential application as bone tissue scaffold materials.Keywords: Porous titanium, Bidirectional, Lamellar structure, Freeze casting, Mechanical strength 1.IntroductionAs a kind of low density and modulus, high strength and good chemical resistance material, titanium is quite suitable for medical implants and other technological applications [1,2]. For example, when titanium is used as a bone substitute material, the elastic modulus of titanium with a proper level (1~30 GPa) was adjusted to avoid bone resorption and the loosening of the implant [3,4]. The 2 increase of porosity is an effective method to reduce the elastic modulus of materials and promotes osteocyte proliferate inside the porous titanium block [5]. The mechanical properties of the materials can be controlled by the porosity, pore size and pore morphology through a variety of manufacturing methods [6]. So far, many manufacturing techniques have been reported to produce porous titanium such as bubble generation [7,8], replication of polymeric sponge [9,10], rapid prototyping method [11,12], space holder method [13,14] and freeze casting [15,16].Freeze casting is a promising method to prepare porous materials with unique aligned and elongated pore structure by driving particles of the slurry to self-assemble along the ice growth direction [6,17]. The pore morphologies are mainly determined by matrix powder kinds, solvent types and frozen temperature gradient [18].Generally, matrix powder is divided into two categories: one is ceramic powder, and the other is metal powder. Currently, most of investigations are focused on the ceramic powders, because they can keep stable in the slurry and form obvious layered structure easily compared with metal powders [19]. To get porous metal with uniform layer structure, a certain amount of dispers...

Customizing the Pore Structure and Properties of Freeze‐Cast Porous Titanium by Zirconium Acetate Additive

“…This size was very close to most of the porous titanium scaffolds (41-80 μm) prepared by the icetemplating method. [12,13,18] After modification with zirconium acetate additive, the pore size of porous titanium scaffolds mainly distributed in a larger range; moreover, the upper limit value also becomes bigger. With the increase in zirconium acetate concentration, the average pore size first increased from 43 AE 10 to 126 AE 35 μm and then decreased to 88 AE 23 μm.…”

“…[11] In recent years, freeze casting (ice-templating) has attracted much attention due to the ability to fabricate porous materials with high open porosity and controlled pore size. [12,13] Moreover, ice-templating is a promising method to fabricate porous biomaterials because the pores produced by this method show many similarities (aligned, elongated pores, anisotropic mechanical properties) to natural biological materials such as bone and nacre. [14,15] Ice-templating method consists of freezing an aqueous suspension, followed by the sublimation of the ice crystals under vacuum and subsequent sintering and densify the walls.…”

“…Still, the problem is that the pore size of the titanium scaffold is almost smaller than 100 μm. [12,13,24] DOI: 10.1002/adem.202000519…”

Effect of spark plasma sintering temperature on the pore characteristics, porosity and compression strength of porous titanium foams

“…Ahmad et al [8] used the slurry foaming method in conjunction with vacuum sintering to produce titanium foams. The use of the freeze casting technique was recently reported by Yan et al [9]. Torres et al [10], reports the feasibility of obtaining a porous structure by simply sintering a loose powder in a furnace, while, Szyniszewski et al [11] and Novák et al [12] suggest the use of hollow powder sphere and powder reactive sintering methods, respectively.…”

Extra low interstitial titanium based fully porous morphological bone scaffolds manufactured using selective laser melting

“…Traditional Ti orthopaedic scaffolds have received significant criticism in relation to its higher elastic stiffness (E) in comparison to the cortical bone spectrum of 3 to 30 GPa [21,22] resulting in stress shielding. Even though research efforts [23][24][25][26][27][28] have focused on the lattice-based reduction of the elastic stiffness of Ti scaffolds, published literature mimicking the mechanical characteristics of the host section without altering the loading pattern are scarce. Dissimilar mechanical properties between the scaffold and bone lead to many undesirable effects.…”