KEIO RESEARCHERS INFORMATION SYSTEM

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Profile 【 Display / hide 】

• My research interests are centered in the field of physics and mechanics of thin and slender structures, focusing on their tunable mechanical functionalities. As their deformation relies primarily on geometric nonlinearities, studies of specific structures would provide common knowledge in seemingly different physical phenomena. The goal of my research is to clarify how and why the complex mechanical functions emerge resulting from physics and mechanics, embracing instabilities of structures. The methodologies of the study are analytical calculus and computational modeling, combined with desktop-scale experiments.

Message from the Faculty Member 【 Display / hide 】

Message from the Faculty Member 【 Display / hide 】

• After seeing its foundations, the field of mechanics diverges as several branches, such as structural mechanics, material science, biomechanics, and earthquake physics. Despite its long history of research, mechanics remains an active field of research through the paradigm shift. Instead of avoiding the failure of structures, we harness the Structural Instabilities in Geometry and MAterials to predict new forms and functionalities.

Career 【 Display / hide 】

Career 【 Display / hide 】

• 2014.04

  -

  2016.03

  Yukawa Institute for Theoretical Physics, Kyoto University, JSPS Research Fellowships for Young Scientists (DC2)

• 2016.04

  -

  2019.03

  Ritsumeikan University,  Research Organization of Science and Technology, JSPS Research Fellowships for Young Scientists (PD)

• 2019.04

  -

  2021.03

  École polytechnique fédérale de Lausanne, JSPS Overseas Research Fellowships

• 2021.04

  -

  Present

  Faculty of Science and Technology, Keio University, Department of Mechanical Engineering, Senior Assistant Professor

Academic Background 【 Display / hide 】

Academic Background 【 Display / hide 】

• 2007.04

  -

  2011.03

  Kyoto University, Faculty of Science

  University, Graduated, Other

• 2011.04

  -

  2013.03

  Kyoto University, Graduate School of Science, Division of Physics and Astronomy

  Graduate School, Completed, Master's course

• 2013.04

  -

  2016.03

  Kyoto University, Graduate School of Science, Division of Physics and Astronomy

  Graduate School, Completed, Doctoral course

Academic Degrees 【 Display / hide 】

Academic Degrees 【 Display / hide 】

• Ph.D. (Science), Kyoto University, Coursework, 2016.03

  Studies on non-equilibrium fluctuating motion as a rectifier

Research Areas 【 Display / hide 】

Research Areas 【 Display / hide 】

• Natural Science / Biophysics, chemical physics and soft matter physics (Mechanics of slender structures, Buckling instability, Soft robotics)

• Manufacturing Technology (Mechanical Engineering, Electrical and Electronic Engineering, Chemical Engineering) / Mechanics of materials and materials (Mechanics of slender structures, Buckling instability, Soft robotics)

Research Themes 【 Display / hide 】

Research Themes 【 Display / hide 】

• Physics of Soft Robotic Matter, 

  2021.04

  -

  Present

• Predictive framework for morphing materials in contact, 

  2021.04

  -

  Present

• Mechanics of tangled structures, 

  2021.04

  -

  Present

Papers 【 Display / hide 】

Papers 【 Display / hide 】

• Buckling of knitted fabric wrapped around a rigid cylinder

  K Tajiri, TG Sano

  Journal of Applied Mechanics 93 (5), 051004 93 ( 5 )  2026.05

  Research paper (scientific journal), Joint Work, Last author, Corresponding author, Accepted,  ISSN  00218936

  　View Summary

  Knitted fabrics exhibit high flexibility due to their periodic loop structures formed by bent yarns. Under compressive loading, they develop three-dimensional (3D) wrinkling patterns that reflect nonlinear interactions between yarn elasticity and local loop deformations, as observed when the sleeves of a sweater are rolled up. Despite their widespread use in garments and medical textiles, the relationship between loop-level geometry and macroscopic buckling remains less understood. Here, we investigate the 3D deformation of knitted fabrics wrapped around a rigid cylinder under uniaxial compression. Circumferential and axial stitch numbers are systematically varied to determine how loop geometry affects the evolution of wrinkle patterns. Samples with a small number of circumferential stitches exhibit sequential wrinkle formation from the compressed end, leading to an accordion-like wrinkle pattern, whereas those with a larger number of stitches form helical wrinkles simultaneously across the surface. Wrinkle morphology changes progressively with stitch geometry, accompanied by systematic variations in compressive force, loop deformation, and helical wrinkle angle. The development of helical wrinkles originates from subtle structural asymmetries introduced during manufacturing processes, including the tension applied during knitting and the direction of sample assembly. These results demonstrate that small variations in local loop deformation can lead to substantial differences in wrinkle morphology, highlighting the sensitivity of macroscopic buckling to microscopic structural features. The study establishes a direct link between loop-level mechanics and global deformation behavior, providing a basis for the predictive design of knitted structures with tailored mechanical responses and complex 3D patterns.

  • Access to Document (DOI)

• Sliding of a cylindrical shell into a rigid hole

  Y Matsumoto, K Yoshida, TG Sano

  Physical Review E 113 (3), 035501 113 ( 3 )  2026.03

  Research paper (scientific journal), Last author, Corresponding author, Accepted,  ISSN  24700045

  　View Summary

  Fitting two different materials is a versatile methodology in manufacturing complex structures. One of the canonical models for fitting is the snap-fit model, in which flexible materials and rigid structures are assembled by pushing their interlocking components together. The assembly via snap-fit is often accompanied by large deformations of flexible structures and abrupt force drops, highlighting the role of elasticity, geometry, and contact friction. Despite several model studies revealing fundamental mechanics for snap-fit, the current snap-fit design relies on prototyping and empirical rules. In this paper, we analyze a snap-fit model in which a naturally curved beam slips into a rigid hole. We construct an analytical model based on the theory of elastica with contact friction and demonstrate that its predictions are in excellent quantitative agreement with both simulations and experiments. We find three distinct sliding modes: folding, pinning, and unfolding. The classification is systematically organized in a phase diagram based on the geometric parameters of the shells and the hole. Our study complements existing approaches by providing a predictive framework for contact-based structures that involve friction, elasticity, and geometry, and sheds light on a unified understanding of the interactions between an elastic and a rigid body.

  • Access to Document (DOI)

• (Dis) continuous buckling transition in elastic shell mediated by contact

  T Abe, TG Sano

  Physical Review Research 8 (1), 013065 8 ( 1 )  2026.01

  Research paper (scientific journal), Joint Work, Last author, Corresponding author, Accepted,  ISSN  26431564

  　View Summary

  Snap buckling is a rapid shape transition in slender structures, appearing as a fundamental switching mechanism of natural and man-made systems. Boundary conditions of structures are crucial to predict and control their snap buckling behavior. However, the general framework that relates boundary conditions, geometry, and performance of structures is still absent to date. Here, we study the snap buckling of hemispherical shells in contact with rigid cylinders of different diameters to uncover the roles of boundary conditions in dynamic performance of shells. Specifically, we analyze the jumping dynamics of the pneumatically inverted shells placed on the rigid cylinder by combining experiments and analytical theory. We find the characteristic diameter of the cylinder determined from the shell geometry that can switch between continuous and discontinuous buckling associated with the jumping behavior. The analytical predictions for jumping performance of the shell supplemented with the characteristic diameter are in excellent agreement with our experimental results. Our study clarifies that contact geometry is crucial in predicting the pathway of snap buckling, indicating that dynamic performance of soft robots would be optimized by tuning their surface geometry.

  • Access to Document (DOI)

• Twist deformation of physical trefoil knots

  T Goto, S Nomura, TG Sano

  Extreme Mechanics Letters 78, 102369 78 2025.08

  Research paper (scientific journal), Last author, Corresponding author, Accepted

  　View Summary

  Knots across various length scales, from micro to macro-scales, such as polymers, DNA, shoelaces, and surgery, serving their unique mechanical properties. The shapes of ideal knots have been extensively studied in the context of knot theory, while those of physical knots have only been recently discussed in the literature. The complex interplay of elasticity and geometry, such as bending, twisting, and contact, needs to be disentangled to predict their deformation. Still, the unified understanding of the deformation of physical knots is insufficient. Here, we focus on the trefoil knot, a closed knot with a nontrivial topology, and study the relationship between the shapes of the trefoil knot and applied physical twists, combining experiments and simulations. As we twist the elastomeric rod, the knot becomes either tightened or loosened, preserving the original three-fold symmetry, and then buckles and exhibits symmetry breaking at critical angles. The curvature profiles computed through the X-ray tomography (μCT) analysis also exhibit similar symmetry breaking. The transition would be triggered by the mechanical instability, where the imposed twist energy is converted into the bending energy. The phase transition observed here is analogous to the classical buckling phenomena of elastic rings known as the Michell instability. We find that the twist buckling instability of the trefoil knot results from the interplay of bending, twisting, and contact properties of the rod. In other words, the buckling of the knot is predictable based on the elasticity and geometry of rods, which would be useful in avoiding or even utilizing their buckling in practical engineering applications such as surgery and the shipping industry.

  • Access to Document (DOI)

• Curling morphology of knitted fabrics: Structure and Mechanics

  K Tajiri, R Murakami, S Kobayashi, R Tarumi, TG Sano

  Extreme Mechanics Letters 76, 102300 76 2025.05

  Research paper (scientific journal), Last author, Corresponding author, Accepted

  　View Summary

  Knitted fabrics are two-dimensional-like structures formed by stitching one-dimensional yarn into three-dimensional curves. Plain stitch or stockinette stitch, one of the most fundamental knitting stitches, consists of periodic lattices of bent yarns, where three-dimensional (3D) curling behavior naturally emerges at the edges. The elasticity and geometry of knitted fabrics have been studied in previous studies, primarily based on 2D modeling. Still, the relation between 3D geometry and the mechanics of knitted fabrics has not been clarified so far. The curling behavior of knits is intricately related to the forces and moments acting on the yarns, geometry of the unit knitted loops, mechanical properties, and contacts, hence requiring a 3D analysis. Here, we show that the curling of plain knits emerges through the elasticity and geometry of the knitted loops, combining desktop-scale experiments and reduced elasticity-based simulations. We find that by changing the horizontal and vertical knitting numbers, three types of curl shapes emerge: side curl and top/bottom curl shapes, which are curled only horizontally and vertically, and double curl shape, in which both curl shapes appear together. We uncover that the knit is side-curled when the knitted loop is vertically elongated, while we observe double curl and then top/bottom curl as the loop becomes horizontally elongated. Furthermore, we find that this characteristic loop shape affects the mechanical properties of knitted fabrics. The fundamental mechanism of intricate shape deformation is clarified through the force and moment balance along yarn whose centerline shape is discretized through the B-spline curves, where elastic stretching, bending, and contact mechanics are taken into account. We reveal that the 3D structure of the single knitted loop plays a critical role in the curling behavior. Our results imply that the change in shape per a single knitted loop has the potential to control the 3D natural overall shape of knitted fabrics. The 3D curling behavior of knitted fabrics is useful for industrial applications such as composite materials, wearable devices, and actuators. Our findings could be applied in predicting or designing more complex 3D shapes made of knitted fabrics.

  • Access to Document (DOI)

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Papers, etc., Registered in KOARA 【 Display / hide 】

Papers, etc., Registered in KOARA 【 Display / hide 】

• Wrinkling instability in rotating thin sheets

  Sano, Tomohiko

  福澤諭吉記念慶應義塾学事振興基金事業報告集 (福澤基金運営委員会)  2023

• Designing principles of mechanical metamaterials based on the studies of heterogeneous elastic materials

  Sano, Tomohiko

  科学研究費補助金研究成果報告書 2023

• Toward the predictive framework for the mechanical performance of flexible robotic arms

  Sano, Tomohiko

  学事振興資金研究成果実績報告書 (慶應義塾大学)  2022

• Mechanics of disordered slender structures : fabrication and computation

  Sano, Tomohiko

  学事振興資金研究成果実績報告書 (慶應義塾大学)  2021

Reviews, Commentaries, etc. 【 Display / hide 】

Reviews, Commentaries, etc. 【 Display / hide 】

• しなやかさとともに，かたちあり――弾性と幾何

  佐野友彦，和田浩史

  日本物理学会誌 74 ( 12 )  2019.12

  Article, review, commentary, editorial, etc. (other), Lead author

Presentations 【 Display / hide 】

Presentations 【 Display / hide 】

• Shapes of knits and knots

  Tomohiko G. Sano

  [International presentation]  WPI–AIMR & WPI–SKCM2 International & Interdisciplinary Math–Materials Workshop, 

  2025.07

  , 

  Oral presentation (general)

• Morphing structures inspired by plants and toys —useless and useful mechanical engineering—

  Tomohiko G. Sano

  [International presentation]  ICTAM2024, Daegu, Korea, 

  2024.08

  , 

  Oral presentation (invited, special)

• Morhing materials as building blocks of soft robots

  Tomohiko G. Sano

  [International presentation]  IUTAM Symposium on Mechanics of Soft Materials and Soft Robots., 

  2024.05

  , 

  Oral presentation (invited, special)

• Crack propagation on bilayer spherical shells

  Tomohiko G. Sano, Naoki Sekiya, Yuri Akiba

  [International presentation]  APS March Meeting, Minneapolis, 

  2024.03

  , 

  Oral presentation (general)

• Soft robots and structures inspired by foods and toys

  Tomohiko G. Sano

  [International presentation]  Japan-China Workshop on Bio-Soft Matter 2023 , 

  2023.09

  , 

  Oral presentation (invited, special)

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Research Projects of Competitive Funds, etc. 【 Display / hide 】

Research Projects of Competitive Funds, etc. 【 Display / hide 】

• High-resolution Magnetic Patterning for Soft Robotics

  2024.04

  -

  2028.03

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (A), No Setting

  　View Summary

  ソフトロボティクス分野の発展とともに柔軟な駆動構造に注目が集まっている．その中でも外部からの磁場により駆動する磁性柔軟材料は，配線なしに空間を介してエネルギー供給可能であり複雑な動きを生み出すことができるため，体内で駆動可能な医療ロボットへの応用等が期待されている．本研究では微細化可能な高い解像度および設計自由度を有する駆動構造作製プロセスを開発する．同時に，幾何学的に非線形な３次元変形を数理的に予測可能な理論的枠組みを構築し，設計手法を完成させる．最終的に，生体の繊毛群挙動や軟体動物腹足類の這行運動を例に取り上げ，柔軟な駆動体の大変形を磁場によって精緻に制御可能であることを実証する．
  ２０２４年度の研究では，シリコーンゴムをベースとした磁場駆動構造において，繊毛群の協調運動を実現しました．また，pneumaticな変形とのハイブリッド駆動方式を新たに提案しました．さらに，ゲル材料の駆動に関する研究では磁場駆動以外の変形についても検討しつつ，ゲル材料の磁化パターニングに関する研究も遂行しました．レーザを用いた新しいプロセスを改良しすることで，50マイクロメートル程度の高い解像度を達成しました．さらに，ゲルとレジンとの接着技術も確立しました．これらの成果により，柔軟な駆動構造の設計と制御に関する知見が大きく進展しました．
  今後，これらの成果を基盤とし，さらなる高解像度化と人工繊毛群の応用研究を進めていきます．具体的にはシリコーンゴムをベースとした磁場駆動構造の解像度をさらに向上させ，より精密な動作制御を実現することを目指します．ゲル材料の磁化パターニング技術についても，解像度の向上とプロセスの最適化を図ります，人工繊毛群への応用研究を進めます．
  2024年度の研究では，シリコーンゴムをベースとした磁場駆動構造において，繊毛群の協調運動を実現することに成功しました．この成果はシリコーンゴムの柔軟性と磁場による駆動の特性を活かし，複雑な動きを精密に制御することが可能であることを示しています．さらに，オプショナルな研究としてpneumaticな駆動様式とのハイブリッド駆動法を新たに提案しました．このハイブリッド方式は磁場駆動と空気圧駆動の両方の利点を組み合わせることで，より多様かつ自由度の高いな動作を実現できます．
  また，ゲル材料の駆動に関する研究では，磁場駆動以外の変形についても検討しました．これにより，ゲル材料の多様な応用可能性が広がり，より柔軟で適応性の高い駆動構造の設計が可能となりました．特にゲル材料の磁化パターニングに関する研究ではレーザを用いた新しいプロセスを改良し，50マイクロメートル程度の高い磁化パターニング解像度を達成しました．この高解像度の磁化パターニング技術は，微細な構造を精密に制御するための重要なステップとなります．
  さらに，ゲルとレジンとの接着技術も確立しました．この技術は，異なる材料間の強固な接着を可能にし，今後の多様な駆動製造の作製において重要な役割を果たします．これらの成果により，柔軟な駆動構造の設計と制御に関する知見が大きく進展し，特にバイオ流体系への応用可能性がさらに広がりました．
  今後の計画では，昨年度の成果を基盤とし，さらなる高解像度化を目指すとともに人工繊毛群の応用研究を進めていく予定です．具体的には，磁場駆動構造の解像度をさらに向上させ，より精密な動作制御を実現することを目指します．これにより，マイクロチップ上でのバイオ系流体研究分野などの応用研究を進めます．
  また，昨年度に提案したpneumaticな変形とのハイブリッド駆動方式についても，さらなる検証と改良を行います．このハイブリッド方式は磁場駆動と空気圧駆動の利点を組み合わせることでより多様な動作を実現できるため，応用範囲を広げることに期待できます．
  さらに，ゲル材料の磁化パターニング技術についても解像度の向上とプロセスの最適化を図ります．特に50マイクロメートル以下の微細な構造を精密に制御するための技術開発を進め，より高度な駆動構造の設計を目指します．
  人工繊毛群の応用研究についても，生体模倣技術の発展に寄与することを目指します．柔軟な駆動構造の設計と制御に関する知見がさらに深まり，バイオメディカル分野での新たな応用の可能性を広げることを目指します．

• 高速計算と精密実験がひもとく幾何学材料の相転移機構の解明

  2022

  -

  2028

  科学技術振興機構, 戦略的な研究開発の推進/創発的研究支援事業, No Setting

  　View Summary

  モノの変形を記述する「力学」の礎が築かれて以来、力学は様々な分野に派生しています。ここ20年では構造の不安定性を既知のものとし、逆に新たな力学的機能が発現したとみなすパラダイムシフトを経て、力学は新たな展開を見せています。私は薄い構造物のしなやかさと幾何学に着目し、構造同士がお互いに力を及ぼし合うことにより創発される新奇な力応答のメカニズムを精密実験、理論、数値計算を組み合わせて明らかにすることを目指します。

• Designing principles of mechanical metamaterials based on the studies of heterogeneous elastic materials

  2018.04

  -

  2024.03

  MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Early-Career Scientists , Principal investigator

  　View Summary

  複雑な内部自由度をもつ構造物の力学応答をデザインする指針を明らかにする。一般に、自然な構造物では通常起こり得ない特異な力学特性を示す材料は、メカニカルメタマテリアルと呼ばれる。構造を圧縮すると通常は圧縮方向に垂直にふくらむ(ポアソン比が正)が、逆に垂直にも縮むもの(ポアソン比が負)が例として挙げられる。メカニカルメタマテリアルは対称性の高い内部構造を用いて開発されており、その非対称性や乱れが全体に与える影響は明らかにされていない。本研究は構造の乱れと不均一性がメカニカルメタマテリアルに与える影響を系統的に考察することにより、力学応答を自在にデザインするための指針を解明する。
  本研究はくしゃくしゃに丸めた紙に代表される内部構造を持つ弾性材料の力学特性を明らかにすることを目的にしている。初年度は、丸めた紙の皺を系統的に生成する方法を確立し、皺が発生する過程での力学的性質を実験的に明らかにした。同じ直径の金属柱を二つ用意し、一つをリニアステージに取り付ける。そしてもう一つをロードセルと共に光学定盤に固定する。金属柱に紙(Mylar sheet)を巻きつけ、巻きつけた紙を金属柱より少し大きな直径をもつアクリル円筒内に入れ、紙のもう一端を光学定盤に固定した金属柱に固定する。リニアステージの変位制御により、巻きつけた紙に対して圧縮と伸張を繰り返し、その際に発生する力を変位の関数として測定した。この繰り返しにより系統的に皺を発生することができる。ロードセルで測定した力変位曲線の結果から、皺を発生させる力にも先行研究で知られている「皺の全長」と圧縮伸張回数の関係に類似した関係式が実験的に得られた。紙に皺を発生させるという一見乱雑な過程にも普遍的な数理構造があることが示唆された。研究成果は未だ公表に至っていないが、共同研究者との議論を重ね解析を続けている。またアメリカ物理学会に参加し関連研究の情報収集を行なった。
  内部構造を持つ弾性材料の簡単な問題として、円筒に切れ込みを入れたシェル構造体の力学特性を定量的にあきらかにした。切れ込みの入った円筒は、切れ込みのない円筒の場合と比べ、変形の緩和長が大きくなることがわかった。切り紙のような構造デザインを考える際の指針になりうると考えている。

Awards 【 Display / hide 】

Awards 【 Display / hide 】

• 材料力学部門部門一般表彰　優秀講演表彰

  2023, 日本機械学会M&M2023カンファレンス, ポテトチップスはどのように曲がるか

  Type of Award： Award from Japanese society, conference, symposium, etc.

• 材料力学部門部門一般表彰　優秀講演表彰

  2022, 日本機械学会M&M2022カンファレンス, ランダムに積み上げたシェル集合体のしなやかな力学応答

  Type of Award： Award from Japanese society, conference, symposium, etc.

• 材料力学部門部門一般表彰　優秀講演表彰

  2021, 日本機械学会M&M2021カンファレンス, 磁化したしなやかな弾性体の縮約理論とその実験的検証

  Type of Award： Award from Japanese society, conference, symposium, etc.

• Emerging Talents 2021

  2021, Journal of Physics A: Mathematical and Theoretical, Reduced theory for hard magnetic rods with dipole–dipole interactions

  Type of Award： International academic award (Japan or overseas)

• the Winners of the Most Watched Poster/Prerecorded Videos

  2020, Virtual Technical Meeting Society of Engineering Sciences 2020, A Kirchhoff-like theory for hard magnetic rods under three-dimensional geometrically nonlinear deformation

  Type of Award： Award from international society, conference, symposium, etc.

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Courses Taught 【 Display / hide 】

Courses Taught 【 Display / hide 】

• DOCTORAL RESEARCH ON MATHEMATICAL AND PHYSICAL SCIENCES

  2026

• GRADUATE RESEARCH ON INTEGRATED DESIGN ENGINEERING 2

  2026

• GRADUATE RESEARCH ON ENGINEERING AND DESIGN 1

  2026

• MECHANICAL ENGINEERING PRACTICAL RESEARCH C

  2026

• GRADUATE RESEARCH ON MATHEMATICAL AND PHYSICAL SCIENCES 1

  2026

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Media Coverage 【 Display / hide 】

Media Coverage 【 Display / hide 】

• （扉）日常にひそむ「やわらか物理」　ひもやゴムにルール、月面探査にも応用？

  朝日新聞,  (朝刊 (教育科学誌面) 18ページ) , 2025.12

Memberships in Academic Societies 【 Display / hide 】

Memberships in Academic Societies 【 Display / hide 】

• 日本機械学会, 

  2021

  -

  Present

• American Physical Society, 

  2018

  -

  2024

• 日本物理学会, 

  2011

  -

  Present

Committee Experiences 【 Display / hide 】

Committee Experiences 【 Display / hide 】

• 2026

  -

  Present

  日本物理学会Jr.セッション委員会委員

• 2024

  -

  2026

  日本物理学会新著紹介委員

• 2022.10

  -

  2023.09

  日本物理学会領域12運営委員

• 2022

  -

  Present

  日本機械学会材料力学カンファレンスOS委員