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1. Ultrasound Imaging by Thermally Tunable Phononic Crystal Lens

   https://doi.org/10.3390/ijms22157966  

   Jin, Yuqi; Neogi, Arup (August 2021, International Journal of Molecular Sciences)

   null (Ed.)

   This work demonstrates the detections and mappings of a solid object using a thermally tunable solid-state phononic crystal lens at low frequency for potential use in future long-distance detection. The phononic crystal lens is infiltrated with a polyvinyl alcohol-based poly n-isopropyl acrylamide (PVA-PNIPAm) bulk hydrogel polymer. The hydrogel undergoes a volumetric phase transition due to a temperature change leading to a temperature-dependent sound velocity and density. The temperature variation from 20 °C to 39 °C changes the focal length of the tunable solid-state lens by 1 cm in the axial direction. This thermo-reversible tunable focal length lens was used in a monostatic setup for one- and two-dimensional mapping scans in both frequency domain echo-intensity and temporal domain time-of-flight modes. The experimental results illustrated 1.03 ± 0.15λ and 2.35 ± 0.28λ on the lateral and axial minimum detectable object size. The experiments using the tunable lens demonstrate the capability to detect objects by changing the temperature in water without translating an object, source, or detector. The time-of-flight mode modality using the tunable solid-state phononic lens increases the signal-to-noise ratio compared to a conventional phononic crystal lens. 

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2. Novel 2D Dynamic Elasticity Maps for Inspection of Anisotropic Properties in Fused Deposition Modeling Objects

   https://doi.org/10.3390/polym12091966  

   Jin, Yuqi; Yang, Teng; Heo, Hyeonu; Krokhin, Arkadii; Shi, Sheldon Q.; Dahotre, Narendra; Choi, Tae-Youl; Neogi, Arup (September 2020, Polymers)

   null (Ed.)

   In this study, a novel ultrasonic non-destructive and non-invasive elastography method was introduced and demonstrated to evaluate the mechanical properties of fused deposition modeling 3D printed objects using two-dimensional dynamical elasticity mapping. Based on the recently investigated dynamic bulk modulus and effective density imaging technique, an angle-dependent dynamic shear modulus measurement was performed to extract the dynamic Young’s modulus distribution of the FDM structures. The elastographic image analysis demonstrated the presence of anisotropic dynamic shear modulus and dynamic Young’s modulus existing in the fused deposition modeling 3D printed objects. The non-destructive method also differentiated samples with high contrast property zones from that of low contrast property regions. The angle-dependent elasticity contrast behavior from the ultrasonic method was compared with conventional and static tensile tests characterization. A good correlation between the nondestructive technique and the tensile test measurements was observed. 

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3. Anisotropic Elasticity, Spin–Orbit Coupling, and Topological Properties of ZrTe2 and NiTe2: A Comparative Study for Spintronic and Nanoscale Applications

   https://doi.org/10.3390/nano15020148  

   Fazeli, Yasaman; Nourbakhsh, Zahra; Yalameha, Shahram; Vashaee, Daryoosh (January 2025, Nanomaterials)

   The present work investigates the interfacial and atomic layer-dependent mechanical properties, SOC-entailing phonon band structure, and comprehensive electron-topological–elastic integration of ZrTe2 and NiTe2. The anisotropy of Young’s modulus, Poisson’s ratio, and shear modulus are analyzed using density functional theory with the TB-mBJ approximation. NiTe2 has higher mechanical property values and greater anisotropy than ZrTe2. Phonon dispersion analysis with SOC effects predicts the dynamic stability of both compounds. Thus, the current research unifies electronic band structure analysis, topological characterization, and elastic property calculation to reveal how these transition metal dichalcogenides are influenced by their structural, electronic, and mechanical properties. The results obtained in this work can be used in the further development of spintronic and nanoelectronic devices. 

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4. Rational hydrogel design to improve brain modulus matching for implantation

   https://doi.org/10.1016/j.matlet.2025.138187  

   Garifo, Molli; Bethel, Keturah; Davis, Eric M; Larsen, Jessica (April 2025, Materials Letters)

   Treating the brain is challenging due to the restrictive blood–brain barrier, and modulus-mismatched implants often cause problems. Herein, we have fabricated copolymer hydrogels from thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAAm), -r-hydrophilic polymer, poly(acrylic acid) (PAA), which are injectable and transform into soft implants above their lower critical solution temperature (LCST). PAA concentration can be leveraged to tune the LCST and viscosity of the PNIPAAm–r–PAA hydrogel in solution. Furthermore, the Young’s moduli of these materials, ranging from 1-4 kPa, are close to rat and human brain tissue, potentially leading to less inflammation and rejection due to significant modulus mismatch. 

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5. Printable homocomposite hydrogels with synergistically reinforced molecular-colloidal networks

   https://doi.org/10.1038/s41467-021-23098-9  

   Williams, Austin H.; Roh, Sangchul; Jacob, Alan R.; Stoyanov, Simeon D.; Hsiao, Lilian; Velev, Orlin D. (May 2021, Nature Communications)

   Abstract The design of hydrogels where multiple interpenetrating networks enable enhanced mechanical properties can broaden their field of application in biomedical materials, 3D printing, and soft robotics. We report a class of self-reinforced homocomposite hydrogels (HHGs) comprised of interpenetrating networks of multiscale hierarchy. A molecular alginate gel is reinforced by a colloidal network of hierarchically branched alginate soft dendritic colloids (SDCs). The reinforcement of the molecular gel with the nanofibrillar SDC network of the same biopolymer results in a remarkable increase of the HHG’s mechanical properties. The viscoelastic HHGs show >3× larger storage modulus and >4× larger Young’s modulus than either constitutive network at the same concentration. Such synergistically enforced colloidal-molecular HHGs open up numerous opportunities for formulation of biocompatible gels with robust structure-property relationships. Balance of the ratio of their precursors facilitates precise control of the yield stress and rate of self-reinforcement, enabling efficient extrusion 3D printing of HHGs. 

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