Seung Mi Baek

Superior Pre-Osteoblast Cell Response of Etched Ultrafine-Grained Titanium with a Controlled Crystallographic Orientation

Ultrafine-grained (UFG) Ti for improved mechanical performance as well as its surface modification enhancing biofunctions has attracted much attention in medical industries. Most of the studies on the surface etching of metallic biomaterials have focused on surface topography and wettability but not crystallographic orientation, i.e., texture, which influences the chemical as well as the physical properties. In this paper, the influences of texture and grain size on roughness, wettability, and pre-osteoblast cell response were investigated in vitro after HF etching treatment. The surface characteristics and cell behaviors of ultrafine, fine, and coarse-grained Ti were examined after the HF etching. The surface roughness during the etching treatment was significantly increased as the orientation angle from the basal pole was increased. The cell adhesion tendency of the rough surface was promoted. The UFG Ti substrate exhibited a higher texture energy state, rougher surface, enhanced hydrophilic wettability, and better cell adhesion and proliferation behaviors after etching than those of the coarse- and fine-grained Ti substrates. These results provide a new route for enhancing both mechanical and biological performances using etching after grain refinement of Ti.

On the rule-of-mixtures of the hardening parameters in TWIP-cored three-layer steel sheet

Although twinning-induced plasticity (TWIP) steels have high tensile strength with high strain hardening and large uniform elongation due to the formation of deformation twins during plastic deformation, sheet formabilities of TWIP steels are relatively poor. In this study, to overcome this problem, TWIP-cored three-layer architectured steel sheets are produced using cladding with low carbon steel sheaths. For an optimum design of layer architectured materials, strain hardening exponent n and strain rate sensitivity m of the layer sheets are theoretically and experimentally investigated. The forced-based rule-of-mixtures well reproduces the experimental values of the equivalent n and m. Contrary to the conventional rule-of-mixtures, the equivalent n and m of the TWIP-cored mild steel-sheath layered sheets are governed not only by volume fractions and n and m of parent materials but also by the strength of strong layer.

Molybdenum Disulfide Surface Modification of Ultrafine-Grained Titanium for Enhanced Cellular Growth and Antibacterial Effect

The commercially pure Ti (CP Ti) and equal-channel angular pressing (ECAP) processed Ti can contribute to the downsizing of medical devices with their superior mechanical properties and negligible toxicity. However, the ECAP-processed pure Ti has the risk of bacterial infection. Here, the coarse- and ultrafine-grained Ti substrates were surface-modified with molybdenum disulfide (MoS2) to improve the cell proliferation and growth with antibacterial effect for further dental applications. According to in vitro tests using the pre-osteoblast of MC3T3-E1 cell and a bacterial model of Escherichia coli (E. coli), MoS2 nanoflakes coated and ECAP-processed Ti substrates showed a significant increase in surface energy and singlet oxygen generation resulting in improved cell attachment and antibacterial effect. In addition, we confirmed the stability of the surface modified Ti substrates in a physiological solution and an artificial bone. Taken together, MoS2 modified and ECAP-processed Ti substrates might be successfully harnessed for various dental applications.

Surface Abrasive Torsion for Improved Mechanical Properties and Microstructure

A novel process of discrete surface abrasion during simple torsion (ST), named “surface abrasive torsion (SAT),” is proposed to overcome the limitation of ST, i.e., insufficient strain for severe plastic deformation (SPD) due to cracks initiated on the surface, by removing the roughened surface region. The effect of SAT on delayed crack initiation was explained using finite element simulations. Larger shear deformation applicable to the specimen in SAT than ST was demonstrated experimentally.