What's New
2022（July－December）
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2022.12.26
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2022.10.26
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2022.9.24
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2022.9.13
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2022.9.11
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2022.7.28
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2022.7.4
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2022.12.26
The paper was published as an OA article in MDPI's Materials (IF=3.748).
Kazuhisa Sato*, Shunya Takagi, Satoshi Ichikawa, Takuya Ishimoto, Takayoshi Nakano:
Microstructure and Solute Segregation Around the Melt Pool Boundary of Orientation-Controlled 316L Austenitic Stainless Steel Produced by Laser Powder Bed Fusion,
Materials, 16(1), (2023), 218; 1-10.
DOI: https://doi.org/10.3390/ma16010218click here for this paper.
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2022.10.26
A paper on an international collaborative study that found boronated hydroxyapatite to have a strong affinity with osteoblasts was published as an OA article in Ceramics International (IF=5.532).
Ozkan Gokcekaya, Celaletdin Ergun*, Thomas J. Webster, and Takayoshi Nakano:
Influence of precursor deficiency sites for borate incorporation on the structural and biological properties of boronated hydroxyapatite,
Ceramics International, (2022),
DOI: https://doi.org/10.1016/j.ceramint.2022.10.232Abstract
The biological properties of hydroxyapatite (HA) are significantly influenced by its compositional characteristics especially doping elements and/or Ca/P ratio, which can be altered by precursor chemistry. In this study, a group of boronated (B-incorporated) hydroxyapatite (BHA) was synthesized using a precipitation method by setting the Ca/P ratio to the stoichiometric value of HA (1.67), while altering the precursor chemistry by adjusting either (Ca + B)/P (Ca-deficient precursor, BC) or Ca/(P + B) (P-deficient precursor, BP). After heat-treatment, the partial decomposition of the BC was observed, forming tricalcium phosphate as the byproduct, however, the BP showed phase stability at all temperatures. The B-ionic species in the form of (BO2)− and (BO3)3− were incorporated into the HA structure at the (PO4)3− and (OH)− positions, respectively. The incorporation of the B species also facilitated the incorporation of (CO3)2− groups specifically in the BPs. This is the first finding on BHA reporting that preferential (CO3)2− incorporation depends on the precursor chemistry used. As a result, osteoblast adhesion was superior on the BPs compared to pure HA owing to the carbonated structure, increasing cell spreading area. As such, this in vitro study highlighted that the present P-deficient precursor approach for synthesizing BHA improved biocompatibility properties and should, thus, be further considered for the next-generation of improved orthopedic applications. -
2022.9.24
A paper elucidating how to control tissue and mechanical properties based on Scalmalloy(R) scanning strategies has been published as an OA paper in Crystals (IF=2.670).
Yusufu Ekubaru, Ozkan Gokcekaya, Takayoshi Nakano*,
Effects of Scanning Strategy on the Microstructure and Mechanical Properties of Sc-Zr-Modified Al-Mg Alloy Manufactured by Laser Powder Bed Fusion,
Crystals, 12, (2022), 1348; 1-13.
DOI: https://doi.org/10.3390/cryst12101348Abstract
Laser powder bed fusion (LPBF)-manufactured Sc-Zr-modified Al-Mg alloy (Scalmalloy) has a bimodal microstructure comprising coarse grains (CGs) in the hot melt pool area and ultrafine grains (UFGs) along the melt pool boundaries (MPBs). Owing to these microstructural features, an increase in the MPBs can increase the UFGs, leading to enhanced mechanical properties. However, the effects of the LPBF process parameters, especially the laser scan strategy, on the microstructure and mechanical properties of Scalmalloy are still unclear. Here, a comparative study was conducted between X- and XY-mode laser scan strategies, with the same volumetric energy, based on the melt pool configuration, grain size distribution, and precipitation behaviors. The X-scan exhibited mechanical properties superior to those exhibited by the XY-scan, attributed to the higher volume fraction (VF) of UFGs. An increase in the VF of UFGs was observed, from 46% for the XY-scan to 56% for the X-scan, owing to an increase in MPBs. Consequently, the tensile strength of the X-scan was higher than that of the XY-scan. The maximum yield strength (271.5 ± 2.7 MPa) was obtained for the X-scan strategy, which was approximately twice that obtained for casting. The results of this study demonstrate that the microstructure and mechanical properties of Scalmalloy can be successfully tuned by a laser scanning strategy.Keywords: laser powder bed fusion; Scalmalloy; ultrafine grain; precipitation; melt pool
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2022.9.13
The following four commentary papers will be published as OA papers in Materials Transactions.
Ryosuke Ozasa, Aira Matsugaki, Takuya Ishimoto, Takayoshi Nakano*:
Review - Research and development of titanium-containing biomedical high entropy alloys (BioHEAs) utilizing rapid solidification via laser-powder bed fusion,
Materials Transactions, (2022), in press.Ishimoto Takuya, Takayoshi Nakano*:
Review - Microstructural control and functional enhancement of light metal materials via metal additive manufacturing,
Materials Transactions, (2022), in press.Aira Matsugaki*, Tadaaki Matsuzaka, Takayoshi Nakano:
Review - Metal additive manufacturing of titanium alloys for control of hard tissue compatibility,
Materials Transactions, (2022), in press.Hiroki Amano*, Takuya Ishimoto, Takayoshi Nakano
Review - Importance of Atmospheric Gas Selection in Metal Additive Manufacturing: Effects on Spatter, Microstructure, and Mechanical Properties,
Materials Transactions, (2022), in press. -
2022.9.11
JBMR-B (IF=3.405) has accepted a paper showing that nanoapatite (n-HA) coating is an effective tool for bone penetration and will be published as an OA article.
Ryota Watanabe, Hiroyuki Takahashi, Aira Matsugaki, Toru Uemukai, Yasumichi Kogai, Takashi Imagama, Kiminori Yukata, Takayoshi Nakano, Takashi Sakai*:
Novel nano-hydroxyapatite coating of additively manufactured 3D porous implants improves bone ingrowth and initial fixation,
Journal of Biomedical Materials Research: Part B - Applied Biomaterials, (2022), in press. -
2022.7.28
A paper on laser metal 3D fabrication methods for optimizing the strength-ductility balance of ScalmalloyR has been published as an OA paper in Materials and Design (IF=9.417).
Yusufu Ekubaru, Ozkan Gokcekaya, Takuya Ishimoto, Kazuhisa Sato, Koki Manabe, Pan Wang, Takayoshi Nakano*: Excellent strength–ductility balance of Sc-Zr-modified Al–Mg alloy by
tuning bimodal microstructure via hatch spacing in laser powder bed fusion, Materials & Design, 221, (2022), 110976; 1-13.
DOI:https://doi.org/10.1016/j.matdes.2022.110976click here for this paper
abstract
The bimodal microstructure, which comprises ultrafine grains (UFGs) forming along the melt pool boundary and relatively coarse grains inside the melt pool, is a characteristic of the Sc-Zr-modified Al–Mgbased alloy (Scalmalloy) microstructure manufactured using laser powder bed fusion (LPBF). Focusing on this microstructural feature, we investigated the improvement in the mechanical properties of
LPBF-fabricated Scalmalloy by tailoring the volume fraction of UFGs. Our approach was to decrease the laser hatch spacing (d) from 0.1 to 0.04 mm, while the volume fraction of UFGs increased from 34.6 ± 0.6 (d = 0.1 mm) to 59.5 ± 0.5 (d = 0.06 mm). The tensile yield stress increased from 296 ± 9 (d = 0.1 mm) to 380 ± 6 MPa (d = 0.06 mm), while maintaining a large elongation (14.8 ± 1.2 ). The yield stress and
elongation were superior to those of the cast counterparts by 2.9 and 4.0 times, respectively. In the sample with d = 0.04 mm, pores formed owing to excessive thermal energy input. Additionally, we investigated multiple strengthening mechanisms of the as-fabricated alloy. This is the first study to improve the mechanical properties of LPBF-fabricated Scalmalloy by optimizing the track-to-track interval and tuning the UFG fraction. -
2022.7.4
Our paper on establishing a bone culture model of collagen/apatite orientation under ex vivo (ex vivo) loading has been accepted for publication in Int. J. Mol. Sci. (IF=6.208) and published as an OA article.
Ryota Watanabe†, Aira Matsugaki†, Takuya Ishimoto, Ryosuke Ozasa, Takuya Matsumoto, Takayoshi Nakano:
A Novel Ex Vivo Bone Culture Model for Regulation of Collagen/Apatite Preferential Orientation by Mechanical Loading,
International Journal of Molecular Sciences, 23, (2022), 7423; 1-10.
DOI: https://doi.org/10.3390/ijms23137423
† The authors contributed equally to this work.Click here for this paper.
Abstract
The anisotropic microstructure of bone, composed of collagen fibers and biological apatite crystallites, is an important determinant of its mechanical properties. Recent studies have revealed that the preferential orientation of collagen/apatite composites is closely related to the direction and magnitude of in vivo principal stress. However, the mechanism of alteration in the collagen/apatite microstructure to adapt to the mechanical environment remains unclear. In this study, we established a novel ex vivo bone culture system using embryonic mouse femurs, which enabled artificial control of the mechanical environment. The mineralized femur length significantly increased following cultivation; uniaxial mechanical loading promoted chondrocyte hypertrophy in the growth plates of embryonic mouse femurs. Compressive mechanical loading using the ex vivo bone culture system induced a higher anisotropic microstructure than that observed in the unloaded femur. Osteocytes in the anisotropic bone microstructure were elongated and aligned along the long axis of the femur, which corresponded to the principal loading direction. The ex vivo uniaxial mechanical loading successfully induced the formation of an oriented collagen/apatite microstructure via osteocyte mechano-sensation in a manner quite similar to the in vivo environment.Keywords
collagen/apatite orientation; ex vivo; mechanical loading; osteocyte morphology; endochondral ossification