Effect of Thermal History and Hydrocarbon Core Size on Perfluorocarbon Endoskeletal Droplet Vaporization.

Vaporizable hydrocarbon-in-fluorocarbon endoskeletal droplets are a unique category of phase-change emulsions with interesting physical and thermodynamic features. Here, we show microfluidic fabrication of various morphologies, such as solid-in-liquid, liquid-in-solid, and Janus-type, of complex solid n-C20H42 or n-C21H44 and liquid n-C5F12 droplets. Furthermore, we investigated the vaporization behavior of these endoskeletal droplets, focusing on the effects of heat treatment and core size. Comparison of vaporization and differential scanning calorimetry results indicated that vaporization occurs prior to melting of the bulk hydrocarbon phase for C20H42/C5F10 droplets and near the rotator phase for C21H44/C5F10 droplets. We found that heat treatment of the droplets increased the fraction of droplets that vaporized and also increased the vaporization temperature of the droplets, although the effect was temporary. Furthermore, we found that changing the relative size of the solid hydrocarbon core compared to the surrounding liquid shell increased the vaporization temperature and the vaporizing fraction. Taken together, these data support the hypothesis that surface melting behavior exhibited by the linear alkane may trigger the fluorocarbon vaporization event. These results may aid in the understanding of the interfacial thermodynamics and transport and the engineering of novel vaporizable endoskeletal droplets for biomedical imaging and other applications.

Characterization of Single-Cell Osmotic Swelling Dynamics for New Physical Biomarkers.

Characterization of cell physical biomarkers is vital to understand cell properties and applicable for disease diagnostics. Current methods used to analyze physical phenotypes involve external forces to deform the cells. Alternatively, internal tension forces via osmotic swelling can also deform the cells. However, an established assumption contends that the forces generated during hypotonic swelling concentrated on the plasma membrane are incapable of assessing the physical properties of nucleated cells. Here, we utilized an osmotic swelling approach to characterize different types of nucleated cells. Using a microfluidic device for cell trapping arrays with truncated hanging micropillars (CellHangars), we isolated single cells and evaluated the swelling dynamics during the hypotonic challenge at 1 s time resolution. We demonstrated that cells with different mechanical phenotypes showed unique swelling dynamics signature. Different types of cells can be classified with an accuracy of up to ∼99%. We also showed that swelling dynamics can detect cellular mechanical property changes due to cytoskeleton disruption. Considering its simplicity, swelling dynamics offers an invaluable label-free physical biomarker for cells with potential applications in both biological studies and clinical practice.

Nuclear Stiffness Decreases with Disruption of the Extracellular Matrix in Living Tissues.

Reciprocal interactions between the cell nucleus and the extracellular matrix lead to macroscale tissue phenotype changes. However, little is known about how the extracellular matrix environment affects gene expression and cellular phenotype in the native tissue environment. Here, it is hypothesized that enzymatic disruption of the tissue matrix results in a softer tissue, affecting the stiffness of embedded cell and nuclear structures. The aim is to directly measure nuclear mechanics without perturbing the native tissue structure to better understand nuclear interplay with the cell and tissue microenvironments. To accomplish this, an atomic force microscopy needle-tip probe technique that probes nuclear stiffness in cultured cells to measure the nuclear envelope and cell membrane stiffness within native tissue is expanded. This technique is validated by imaging needle penetration and subsequent repair of the plasma and nuclear membranes of HeLa cells stably expressing the membrane repair protein CHMP4B-GFP. In the native tissue environment ex vivo, it is found that while enzymatic degradation of viable cartilage tissues with collagenase 3 (MMP-13) and aggrecanase-1 (ADAMTS-4) decreased tissue matrix stiffness, cell and nuclear membrane stiffness is also decreased. Finally, the capability for cell and nucleus elastography using the AFM needle-tip technique is demonstrated. These results demonstrate disruption of the native tissue environment that propagates to the plasma membrane and interior nuclear envelope structures of viable cells.

Advanced nanostructures for cell membrane poration.

Nanostructured devices are able to foster the technology for cell membrane poration. With the size smaller than a cell, nanostructures allow efficient poration on the cell membrane. Emerging nanostructures with various physical transduction have been demonstrated to accommodate effective intracellular delivery. Aside from improving poration and intracellular delivery performance, nanostructured devices also allow for the discovery of novel physiochemical phenomena and the biological response of the cell. This article provides a brief introduction to the principles of nanostructured devices for cell poration and outlines the intracellular delivery capability of the technology. In the future, we envision more exploration on new nanostructure designs and creative applications in biomedical fields.

First principles study of oxygen molecule interaction with the graphitic active sites of a boron-doped pyrolyzed Fe-N-C catalyst.

We study the adsorption and the dissociation of O2 molecules on the active sites of a boron-doped pyrolyzed Fe-N-C catalyst using density functional theory. Initially, we determine the possible structure of the FeN4 active site of the pyrolyzed Fe-N-C catalyst doped with a boron atom by considering the presence of a nitrogen atom as a metal-free site. The most stable configuration of the structure occurs when the boron and nitrogen atoms coalesce with the FeN4 site forming a complex site. This structure has higher stability compared to the undoped FeN4 site. The doped FeN4 possesses the unique ability to adsorb an oxygen molecule in a side-on mode due to the presence of the boron-nitrogen pair acting as a supporting site. One O atom of the O2 molecule sticks strongly to the top of the iron atom, while the other binds with the boron atom. This O2 side-on adsorption stretches the O-O bond length by 15%. Furthermore, the examined catalyst surface can dissociate the oxygen molecule easily with only half the energy barrier of the undoped FeN4 structure.

Acoustically manipulating internal structure of disk-in-sphere endoskeletal droplets.

Manipulation of micro/nano particles has been well studied and demonstrated by optical, electromagnetic, and acoustic approaches, or their combinations. Manipulation of internal structure of droplet/particle is rarely explored and remains challenging due to its complicated nature. Here we demonstrated the manipulation of internal structure of disk-in-sphere endoskeletal droplets using acoustic wave. We developed a model to investigate the physical mechanisms behind this interesting phenomenon. Theoretical analysis of the acoustic interactions indicated that these assembly dynamics arise from a balance of the primary and secondary radiation forces. Additionally, the disk orientation was found to change with acoustic driving frequency, which allowed on-demand, reversible adjustment of the disk orientations with respect to the substrate. This dynamic behavior leads to unique reversible arrangements of the endoskeletal droplets and their internal architecture, which may provide an avenue for directed assembly of novel hierarchical colloidal architectures and intracellular organelles or intra-organoid structures.

A frugal microfluidic pump.

Manipulation of fluid flow is paramount for microfluidic device operation. Conventional microfluidic pumps are often expensive, bulky, complicated, and not amenable in limited resource settings. Here, we introduce a Fully self-sufficient, RobUst, Gravity-Assisted, Low-cost (FRUGAL) microfluidic pump. The pump consists of a syringe, a syringe holder and loading masses. The system is easy to assemble, inexpensive, portable, and electrical power-free. Inside the syringe, the fluid is driven by the pressure from the weight of the loading masses. During operation, the exerted pressure is dynamically controllable and stable for hours. These features are useful for optimization of microfluidics assays and dynamic temporal studies. We demonstrate the application of this system to control the formation of water-in-oil droplet emulsion. Benefitting from its simplicity and versatility, the frugal microfluidic pump will enable global adoption of microfluidic technology in chemistry and biomedical applications, especially in limited resource environments.

Emerging on-chip surface acoustic wave technology for small biomaterials manipulation and characterization.

A surface acoustic wave (SAW) is a sound wave travelling on the surface of an elastic material. SAW offers a robust control of the acoustic energy leading to an unparalleled versatility. As an actuator, SAW can exert acoustic forces on particles and fluids thus enabling dexterous micro/nanoscale manipulations. As a sensor, SAW has a unique sensing capability upon changes in the environment. On-chip SAW technology, in which SAW is integrated with modern lab-on-a-chip (LOC), has drawn a lot of attention in recent years and found various exciting applications in micro/nanosystems. In particular, its well-known biocompatibility provides on-chip SAW technology as an exceptional platform for biomaterials research at the small-scale. In this minireview, we highlighted recent advances of on-chip SAW technology for biomaterials manipulation and characterization with a focus on cell-based (e.g. single-cell and multicellular) biomaterials. We also discussed and shared our perspective on future directions for this emerging research field.

A review of emerging physical transfection methods for CRISPR/Cas9-mediated gene editing.

Gene editing is a versatile technique in biomedicine that promotes fundamental research as well as clinical therapy. The development of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) as a genome editing machinery has accelerated the application of gene editing. However, the delivery of CRISPR components often suffers when using conventional transfection methods, such as viral transduction and chemical vectors, due to limited packaging size and inefficiency toward certain cell types. In this review, we discuss physical transfection methods for CRISPR gene editing which can overcome these limitations. We outline different types of physical transfection methods, highlight novel techniques to deliver CRISPR components, and emphasize the role of micro and nanotechnology to improve transfection performance. We present our perspectives on the limitations of current technology and provide insights on the future developments of physical transfection methods.