Grad Students to Present Research Nov. 6

The next Graduate Student Seminar hosted by the Beckman Institute will be at noon Wednesday, Nov. 6 in Room 1005. Three graduate students will discuss their research: Pin-Chieh “Jenny” Huang, bioengineering; Parham Mostame, psychology; and Charles Young, chemical and biomolecular engineering. Lunch will be provided.

“Stiffness-inferred Thermotherapy Dosimetry via Magnetomotive Optical Coherence Elastography”

Pin-Chieh “Jenny” Huang, bioengineering, Biophotonics Imaging Lab

scientific illustration of research by Jenny Huang

Magnetic hyperthermia (MH) is an emerging cancer treatment based on the magnetically induced heat released from in-tissue magnetic seeds, such as magnetic nanoparticles (MNPs). To avoid collateral damage to healthy tissue during MH treatment, accurate evaluation of thermal dosage is critical. Typically, MH thermal dosage is evaluated by the temperature change of tissues over time, which may not directly reflect the underlying physiological changes. Alternatively, tissue viscoelasticity can be a physiologically meaningful indicator of the induced thermal damage, as protein denaturation and coagulative necrosis can both lead to tissue stiffening. In addition to being magnetic seeds in MH, MNPs can be utilized independently in magnetomotive optical coherence elastography (MM-OCE), an optical imaging technique that probes the biomechanical properties of the tissues with high spatial resolution. Therefore, a novel and physiologically meaningful MH dosimetry technique is developed via a “theranostic” platform — inferring the necessary thermal dosage based on the alteration of tissue viscoelasticity characterized by MM-OCE, where the magnetic seeds delivered to the targeted tumor sites are used both in (1) MH as heating sources (therapeutic agents), and in (2) MM-OCE as mechanical perturbative sources (diagnostic/dosage evaluating agents).

"Phase Coupling Versus Amplitude Coupling: Two Distinct but Spatially Associated Modes of Neural Connectivity"

Parham Mostame, psychology, Connect Lab

scientific illustration of research by Parham Mostame

Functional connectivity (FC), thought to provide a window into neural communication, has become a core focus in the study of brain function and cognition. However, there is no consensus on how to conceptualize large-scale FC in electrophysiology. Phase coupling (PhC), defined as coupling between the phases of two signals, reflects the synchronization of rhythmic oscillation cycles. Conversely, amplitude coupling (AmpC), defined as coupling between the envelopes of two signals, reflects correlation of activation amplitude. Despite quantifying different electrophysiological properties, the relationship between PhC and AmpC remains largely unknown. We assessed spatial and temporal correspondence between PhC and AmpC during a word recognition task over 5 canonical frequency bands using electrocorticography (ECoG) in 10 patients (4 females) undergoing epilepsy surgery. Significant correspondence between the spatial pattern of PhC and AmpC was detected during stimulus processing across all subjects and frequency bands (R≈0.44 for theta, decreasing with increasing frequency). Stimulus processing in-/decreased PhC and AmpC, however in a spatially independent manner. The cross-measure spatial correlation vanished almost entirely when accounting for the portion of FC equally present during pre- and post-stimulus intervals, suggesting that the spatial correlations reflect intrinsic FC independent of stimulus processing. Examining the temporal correlation, we found no evidence for a dependence between PhC and AmpC. We conclude that PhC and AmpC reflect intrinsic FC similarly across space, but exhibit divergent stimulus-related FC changes across time. Succinctly, PhC and AmpC constitute two distinct but spatially associated modes of neural communication.

“Dynamics of Semidilute Comb Polymer Solutions in Extensional Flow"

Charles Young, chemical and biomolecular engineering, Sing Research Group

The dynamics and rheology of non-dilute solutions of polymers with lightly grafted branches (combs) are of relevant to a wide range of industrial processing methods as well as the behavior biomacromolecular environments. The time scale over which a polymer relaxes stress is intrinsically related to diffusion at equilibrium and the solution viscosity when deformed by flow. In this collaborative effort between Beckman faculty, we combine coarse-grained molecular dynamics simulations and single molecule imaging to gain insight into the dynamics of comb polymers during the startup of extensional flow and relaxation of the polymer conformation following the cessation of flow. In particular, we focus on the semidilute regime, where polymers significantly overlap. However, polymer weight percent is still relatively low such that both solvent dynamics and polymer dynamics must both be accurately modeled. We find unexpected relaxation behavior in which polymer relaxation time can decrease when branches are added due to these solvent-mediated hydrodynamic interactions. Additionally, we find diverse and unique stretching conformations of combs relative to analogous linear polymers.