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1. Energy-momentum tensor in Φ**4 theory at one loop

   https://doi.org/10.1103/PhysRevD.111.076001  

   Maynard, Brean (April 2025, Physical Review D)

   The energy-momentum tensor form factors are studied in Φ**4 to one-loop order with particular focus on the D-term, a particle property which has attracted a lot of attention in the recent literature. It is shown that the free Klein-Gordon theory value of D = -1 is reduced to D = − 1/3 even if the Φ**4 interaction is infinitesimally small. A companion work in Φ**3 theory confirms this result which may indicate that it is independent of the type of interaction as long as the scalar theory is renormalizable. Dispersion relations are studied. Various definitions of mean square radii including the mechanical radius are investigated. The findings contribute to a better understanding of the energy momentum tensor properties of particles and their interpretation. 

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2. Evolution and Morphology of Genitalia in Female Amniotes

   https://doi.org/10.1093/icb/icac115  

   Brennan, Patricia L. R. (July 2022, Integrative And Comparative Biology)

   Abstract Despite their evolutionary and biomedical importance, studies of the morphology and function of female genitalia have continued to lag behind those of male genitalia. While studying female genitalia can be difficult because of their soft, deformable and internal nature, recent advances in imaging, geometric analyses of shape and mechanical testing have been made, allowing for a much greater understanding of the incredible diversity of form and function of female genitalia. Here, we summarize some of these methods, as well as discuss some big questions in the field that are beginning to be examined now, and will continue to benefit from further work, especially a comparative approach. Topics of further research include examination of the morphology of female genitalia in situ, in-depth anatomical work in many more species, studies of the interplay between natural and sexual selection in influencing features of vaginal morphology, how these diverse functions influence the mechanical properties of tissues, and studies of clitoris morphology and function across amniotes. Many other research topics related to female genitalia remain largely unexplored, and we hope that the papers in this issue will continue to inspire further research on female genitalia. 

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3. Forming Covalent Crosslinks between Polymer‐Grafted Nanoparticles as a Route to Highly Filled and Mechanically Robust Nanocomposites

   https://doi.org/10.1002/adfm.201905168  

   Kubiak, Joshua_M; Macfarlane, Robert_J (August 2019, Advanced Functional Materials)

   Abstract Filler aggregation in polymer matrix nanocomposites leads to inhomogeneity in particle distribution and deterioration of mechanical properties. The use of polymer‐grafted nanoparticles (PGNPs) with polymers directly attached to the particle surfaces precludes aggregation of the filler. However, solids composed of PGNPs are mechanically weak unless the grafted chains are long enough to form entanglements between particles, and requiring long grafts limits the achievable filler density of the nanocomposite. In this work, long, entangled grafts are replaced with short reactive polymers that form covalent crosslinks between particles. Crosslinkable PGNPs, referred to as XNPs, can be easily processed from solution and subsequently cured to yield a highly filled yet mechanically robust composite. In this specific instance, silica nanoparticles are grafted with poly(glycidyl methacrylate), cast into films, and crosslinked with multifunctional amines at elevated temperatures. Indentation and scratch experiments show significant enhancement of hardness, modulus, and scratch resistance compared to non‐crosslinked PGNPs and to crosslinked polymer films without nanoparticle reinforcement. Loadings of up to 57 wt% are achieved while yielding uniform films that deform locally in a predominantly elastic manner. XNPs therefore potentially allow for the formulation of robust nanocomposites with a high level of functionality imparted by the selected filler particles. 

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4. Microfluidic deformability-activated sorting of single particles

   https://doi.org/10.1038/s41378-019-0107-9  

   Choi, Gihoon; Nouri, Reza; Zarzar, Lauren; Guan, Weihua (February 2020, Microsystems & Nanoengineering)

   Abstract Mechanical properties have emerged as a significant label-free marker for characterizing deformable particles such as cells. Here, we demonstrated the first single-particle-resolved, cytometry-like deformability-activated sorting in the continuous flow on a microfluidic chip. Compared with existing deformability-based sorting techniques, the microfluidic device presented in this work measures the deformability and immediately sorts the particles one-by-one in real time. It integrates the transit-time-based deformability measurement and active hydrodynamic sorting onto a single chip. We identified the critical factors that affect the sorting dynamics by modeling and experimental approaches. We found that the device throughput is determined by the summation of the sensing, buffering, and sorting time. A total time of ~100 ms is used for analyzing and sorting a single particle, leading to a throughput of 600 particles/min. We synthesized poly(ethylene glycol) diacrylate (PEGDA) hydrogel beads as the deformability model for device validation and performance evaluation. A deformability-activated sorting purity of 88% and an average efficiency of 73% were achieved. We anticipate that the ability to actively measure and sort individual particles one-by-one in a continuous flow would find applications in cell-mechanotyping studies such as correlational studies of the cell mechanical phenotype and molecular mechanism. 

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5. Particle Deformability Enables Control of Interactions between Membrane-Anchored Nanoparticles

   https://doi.org/10.1021/acs.jctc.3c00687  

   Nambiar, Nikhil; Loyd, Zachary A; Abel, Steven M (October 2023, Journal of Chemical Theory and Computation)

   Nanoparticles adsorbed on a membrane can induce deformations of the membrane that give rise to effective interactions between the particles. Previous studies have focused primarily on rigid nanoparticles with fixed shapes. However, DNA origami technology has enabled the creation of deformable nanostructures with controllable shapes and mechanical properties, presenting new opportunities to modulate interactions between particles adsorbed on deformable surfaces. Here we use coarse-grained molecular dynamics simulations to investigate deformable, hinge-like nanostructures anchored to lipid membranes via cholesterol anchors. We characterize deformations of the particles and membrane as a function of the hinge stiffness. Flexible particles adopt open configurations to conform to a flat membrane, whereas stiffer particles induce deformations of the membrane. We further show that particles spontaneously aggregate and that cooperative effects lead to changes in their shape when they are close together. Using umbrella sampling methods, we quantify the effective interaction between two particles and show that stiffer hinge-like particles experience stronger and longer-ranged attraction. Our results demonstrate that interactions between deformable, membrane-anchored nanoparticles can be controlled by modifying mechanical properties of the particles, suggesting new ways to modulate the self-assembly of particles on deformable surfaces. 

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