Department of Engineering Science & Mechanics, and Bioengineering
Virus-Inspired Biomimetic Design of Nanoparticles as Nanocale Drug Carriers
Animal viruses invade their hosts in a rather controlled fashion, a process known as endocytosis. Biological studies revealed that virus invasion is bothtype selective: i.e., certain viruses are engulfed but not the others, as well assize selective, i.e., 50nm viruses are engulfed preferably but not 100nm ones. This fascinating adhesion-driven process makes one wonder: what are the fundamental mechanisms that govern specificities of endocytosis?
In this talk, we use synthesized viruses, nanoparticles (NPs) to elucidate the governing factors for endocytosis. The NP surface is coated with proteins (ligands) that are complementary to the receptors on the cell membrane. The molecular recognition and interaction of the ligand-receptor pairs enable specific targeting, which enhances drug efficacy and reduces adverse side effects during chemotherapy. Through thermodynamic arguments, we reveal that, unlike the adhesion between two inanimate objects, the adhesion strength between an NP and a living cell is a non-local, variable quantity that depends on not only the particle size and the ligand density, but also the receptor density that is actively regulated by the cell. The cellular uptake depends interrelatedly on theparticle size and ligand density, featuring a two-dimensional phase diagram in the particle size and ligand density space. The variableadhesion strength specifies a lower and an upper phase boundary beyond which the cellular uptake vanishes. The design principles of the NPs obtained from our studies are validated by comparisons to the characteristics of viruses and existing experimental data. Our findings are not only important for understanding the biological behaviors and evolutionary design of viruses, but also for engineering NP-based therapeutic and diagnostic agents. Extension of the thermodynamic analysis to coarse-grained molecular dynamics modeling will also be discussed.
In-Situ Lithiation Mechanics of Nanostructures
Recent independent TEM studies evidenced highly anisotropic swelling and size-dependent fracture of silicon nanowires (SiNWs) upon lithiation. The origin of such anisotropic behavior and the underlying fracture mechanism remain elusive. Here, we develop a multiscale chemo-mechanical model to study the phase evolution, morphological changes, stress generation and fracture in lithiated SiNWs. The model couples the reaction-diffusion of lithium with the lithiation-induced elasto-plastic deformation. We show that the apparent anisotropic swelling is critically controlled by the orientation-dependent mobility of the atomically sharp phase boundary between the crystalline core and amorphous shell. We further reveal an intriguing crack propagation mechanism using monolayer graphene: the stress gradient around the crack tip drives the diffusion of lithium from far to the crack tip, which subsequently weakens the crack-tip bonds, featuring a lithiation induced self-weakening mechanism. Our modeling results agree strikingly well with the experimental data. The study sheds light on the lithiation-mediated degradation in nanostructured electrodes. The multiscale modeling framework is generic and provides a basis for simulating the morphological evolution, stress generation and fracture in high-capacity electrodes for the next-generation lithium-ion batteries.
Dr. Sulin Zhangreceived his BS fromDalianUniversityof Technology, MS fromTsinghuaUniversityin 1997, and PhD from theUniversityofIllinois, Urbana-Champaign (UIUC) in 2002, all from Engineering Mechanics. He is currently an Associate Professor in the Department of Engineering Science and Mechanics and Department of BioEngineering at The Pennsylvania State University. Dr. Zhang’s research interests generally lie in multiscale modeling of nanostructured and bio-inspired materials and of processes that occur at nano-bio interfaces, and experimental cell mechanics. Dr. Zhang is the recipient of The Oak Ridge Ralph E. Powe Junior Faculty Enhancement Award in 2006, the Early Career Development Award from National Science Foundation in 2007, andICS Fellow and Rustum and Della Roy Innovation in Materials Research Award at PSU.