Microflow and crack formation patterns in drying sessile droplets of liposomes suspended in trehalose solutions

Leveraging the Coffee Ring Effect for a Defect-Free Electroformation of Giant Unilamellar Vesicles

We took advantage of the microflow hydrodynamics in the evaporation of sessile droplets to increase the height uniformity of thin lipid films for the subsequent electroformation of defect-free giant unilamellar vesicles (GUV). By serially casting progressively larger liposome suspension droplets on the same spot of an indium-tin-oxide (ITO) electrode, we managed to leverage the coffee ring effect (CRE) in the evaporation of each droplet to generate a smeared multilayer film of uniform thickness. This multidroplet technique of lipid film formation outperformed the traditional single-droplet deposition, improving the final quality of electroformed GUV samples. The proposed film formation technique constitutes a solvent-free method that results in a dramatic reduction (∼20×) in the appearance of undesirable structures like nonspherical (NSV), multilamellar (MLV), and multivesicular (MVV) vesicles.

Extracellular Trap-Mimicking DNA-Histone Mesostructures Synergistically Activate Dendritic Cells

Extracellular traps (ETs), such as neutrophil extracellular traps, are a physical mesh deployed by immune cells to entrap and constrain pathogens. ETs are immunogenic structures composed of DNA, histones, and an array of variable protein and peptide components. While much attention has been paid to the multifaceted function of these structures, mechanistic studies of ETs remain challenging due to their heterogeneity and complexity. Here, a novel DNA-histone mesostructure (DHM) formed by complexation of DNA and histones into a fibrous mesh is reported. DHMs mirror the DNA-histone structural frame of ETs and offer a facile platform for cell culture studies. It is shown that DHMs are potent activators of dendritic cells and identify both the methylation state of DHMs and physical interaction between dendritic cells and DHMs as key tuning switches for immune stimulation. Overall, the DHM platform provides a new opportunity to study the role of ETs in immune activation and pathophysiology.

The calorimetric properties of liposomes determine the morphology of dried droplets

The evaporation of liquid droplets deposited on a substrate is a very complex phenomenon. Driven by capillary and Marangoni flows, particle-particle and particle-substrate interactions, the deposits they leave are vestiges of such complexity. We study the formation of patterns during the evaporation of liposome suspension droplets deposited on a hydrophobic substrate at different temperatures. We observed that as we change the temperature of the substrate, a morphological phase transition occurs at a given temperature T_m. This temperature corresponds to the gel-fluid lipid melting transition of the liposome suspension. Optical microscopy and atomic force microscopy are used to study the morphology of the patterns. Based on the radial density profiles we found that all structures can be classified into two groups: patterns composed by nearly uniform deposition (below T_m) and prominent structures containing randomly distributed voids (above T_m).

A Raman microspectroscopy study of water and trehalose in spin-dried cells

Long-term storage of desiccated nucleated mammalian cells at ambient temperature may be accomplished in a stable glassy state, which can be achieved by removal of water from the biological sample in the presence of glass-forming agents including trehalose. The stability of the glass may be compromised due to a nonuniform distribution of residual water and trehalose within and around the desiccated cells. Thus, quantification of water and trehalose contents at the single-cell level is critical for predicting the glass formation and stability for dry storage. Using Raman microspectroscopy, we estimated the trehalose and residual water contents in the microenvironment of spin-dried cells. Individual cells with or without intracellular trehalose were embedded in a solid thin layer of extracellular trehalose after spin-drying. We found strong evidence suggesting that the residual water was bound at a 2:1 water/trehalose molar ratio in both the extracellular and intracellular milieus. Other than the water associated with trehalose, we did not find any more residual water in the spin-dried sample, intra- or extracellularly. The extracellular trehalose film exhibited characteristics of an amorphous state with a glass transition temperature of ?22°C. The intracellular milieu also dried to levels suitable for glass formation at room temperature. These findings demonstrate a method for quantification of water and trehalose in desiccated specimens using confocal Raman microspectroscopy. This approach has broad use in desiccation studies to carefully investigate the relationship of water and trehalose content and distribution with the tolerance to drying in mammalian cells.

Glass-forming property of hydroxyectoine is the cause of its superior function as a desiccation protectant

We were able to demonstrate that hydroxyectoine, in contrast to ectoine, is a good glass-forming compound. Fourier transform infrared and spin label electron spin resonance studies of dry ectoine and hydroxyectoine have shown that the superior glass-forming properties of hydroxyectoine result from stronger intermolecular H-bonds with the OH group of hydroxyectoine. Spin probe experiments have also shown that better molecular immobilization in dry hydroxyectoine provides better redox stability of the molecules embedded in this dry matrix. With a glass transition temperature of 87°C (vs. 47°C for ectoine) hydroxyectoine displays remarkable desiccation protection properties, on a par with sucrose and trehalose. This explains its accumulation in response to increased salinity and elevated temperature by halophiles such as Halomonas elongata and its successful application in ``anhydrobiotic engineering'' of both enzymes and whole cells.

Late embryogenesis abundant proteins protect human hepatoma cells during acute desiccation

Expression of late embryogenesis abundant (LEA) proteins is highly correlated with desiccation tolerance in anhydrobiotic animals, selected land plants, and bacteria. Genes encoding two LEA proteins, one localized to the cytoplasm/nucleus (AfrLEA2) and one targeted to mitochondria (AfrLEA3m), were stably transfected into human HepG2 cells. A trehalose transporter was used for intracellular loading of this disaccharide. Cells were rapidly and uniformly desiccated to low water content (<0.12 g H(2)O/g dry weight) with a recently developed spin-drying technique. Immediately on rehydration, control cells without LEA proteins or trehalose exhibited 0% membrane integrity, compared with 98% in cells loaded with trehalose and expressing AfrLEA2 or AfrLEA3m; surprisingly, AfrLEA3m without trehalose conferred 94% protection. Cell proliferation across 7 d showed an 18-fold increase for cells dried with AfrLEA3m and trehalose, compared with 27-fold for nondried controls. LEA proteins dramatically enhance desiccation tolerance in mammalian cells and offer the opportunity for engineering biostability in the dried state.

Cryopreservation of spin-dried mammalian cells

This study reports an alternative approach to achieve vitrification where cells are pre-desiccated prior to cooling to cryogenic temperatures for storage. Chinese Hamster Ovary (CHO) cells suspended in a trehalose solution were rapidly and uniformly desiccated to a low moisture content (<0.12 g of water per g of dry weight) using a spin-drying technique. Trehalose was also introduced into the cells using a high-capacity trehalose transporter (TRET1). Fourier Transform Infrared Spectroscopy (FTIR) was used to examine the uniformity of water concentration distribution in the spin-dried samples. 62% of the cells were shown to survive spin-drying in the presence of trehalose following immediate rehydration. The spin-dried samples were stored in liquid nitrogen (LN(2)) at a vitrified state. It was shown that following re-warming to room temperature and re-hydration with a fully complemented cell culture medium, 51% of the spin-dried and vitrified cells survived and demonstrated normal growth characteristics. Spin-drying is a novel strategy that can be used to improve cryopreservation outcome by promoting rapid vitrification.

Temperature distribution inside an evaporating two-dimensional droplet lying on curved or flat substrates

The temperature field inside an evaporating two-dimensional droplet resting on curved or flat isothermal substrates is studied under various evaporation conditions. An analytical solution for the temperature is derived, which can be directly used in the cases of pinned and depinned contact lines as well as in stick-slip evaporation modes. It is found that the temperature drop at the free surface of a droplet on a convex, hydrophobic substrate is far greater than that for flat or concave substrates of the same hydrophobicity. The analytical solution for the temperature field allows the direct estimate of the local temperature gradient and, hence, of the local surface tension gradient that gives rise to Marangoni flow directed from the contact lines to the top of the droplet.