Lipid sponge droplets as programmable synthetic organelles.

Living cells segregate molecules and reactions in various subcellular compartments known as organelles. Spatial organization is likely essential for expanding the biochemical functions of synthetic reaction systems, including artificial cells. Many studies have attempted to mimic organelle functions using lamellar membrane-bound vesicles. However, vesicles typically suffer from highly limited transport across the membranes and an inability to mimic the dense membrane networks typically found in organelles such as the endoplasmic reticulum. Here, we describe programmable synthetic organelles based on highly stable nonlamellar sponge phase droplets that spontaneously assemble from a single-chain galactolipid and nonionic detergents. Due to their nanoporous structure, lipid sponge droplets readily exchange materials with the surrounding environment. In addition, the sponge phase contains a dense network of lipid bilayers and nanometric aqueous channels, which allows different classes of molecules to partition based on their size, polarity, and specific binding motifs. The sequestration of biologically relevant macromolecules can be programmed by the addition of suitably functionalized amphiphiles to the droplets. We demonstrate that droplets can harbor functional soluble and transmembrane proteins, allowing for the colocalization and concentration of enzymes and substrates to enhance reaction rates. Droplets protect bound proteins from proteases, and these interactions can be engineered to be reversible and optically controlled. Our results show that lipid sponge droplets permit the facile integration of membrane-rich environments and self-assembling spatial organization with biochemical reaction systems.

Self-Calibration 3D Hybrid SERS Substrate and Its Application in Quantitative Analysis.

Surface-enhanced Raman spectroscopy (SERS) has been widely applied in many fields as a sensitive vibrational fingerprint technique. However, SERS faces challenges in quantitative analysis due to the heterogeneity of hot spots. An internal standard (IS) strategy has been employed for correcting the variation of hot spots. However, the method suffers from limitations due to the competitive adsorption between the IS and the target analyte. In this work, we combined the IS strategy with the 3D hybrid nanostructures to develop a bifunctional SERS substrate. The substrate had two functional units. The bottom self-assembly layer consisted of Au@IS@SiO2 nanoparticles, which provided a stable reference signal and functioned as the calibration unit. The top one consisted of appropriate-sized Au octahedrons for the detection of target analytes, which was the detection unit. Within the 3D hybrid nanostructure, the calibration unit improved the SERS performance of the detection unit, which was demonstrated by the 6-fold increase of SERS intensity when compared with the 2D substrate. Meanwhile, the reproducibility of the detection was greatly improved by correcting the hot spot changes through the calibration unit. Two biomedical molecules of cotinine and creatinine in ultrapure water and artificial urine, respectively, were sensitively determined by the 3D hybrid substrate. We expect that the developed bifunctional 3D substrate will open up new ways to advance the applications of SERS.

One-Dimensional Anomalous Diffusion of Gold Nanoparticles in a Polymer Melt.

We investigated the dynamics of polymer-grafted gold nanoparticles loaded into polymer melts using x-ray photon correlation spectroscopy. For low molecular weight host matrix polymer chains, normal isotropic diffusion of the gold nanoparticles is observed. For larger molecular weights, anomalous diffusion of the nanoparticles is observed that can be described by ballistic motion and generalized Lévy walks, similar to those often used to discuss the dynamics of jammed systems. Under certain annealing conditions, the diffusion is one-dimensional and related to the direction of heat flow during annealing and is associated with an dynamic alignment of the host polymer chains. Molecular dynamics simulations of a single gold nanoparticle diffusing in a partially aligned polymer network semiquantitatively reproduce the experimental results to a remarkable degree. The results help to showcase how nanoparticles can under certain circumstances move rapidly in polymer networks.

Highly Stable Artificial Cells from Galactopyranose-Derived Single-Chain Amphiphiles.

Single-chain amphiphiles (SCAs) that self-assemble into large vesicular structures are attractive components of synthetic cells because of the simplicity of bilayer formation and increased membrane permeability. However, SCAs commonly used for vesicle formation suffer from restricted working pH ranges, instability to divalent cations, and the inhibition of biocatalysts. Construction of more robust biocompatible membranes from SCAs would have significant benefits. We describe the formation of highly stable vesicles from alkyl galactopyranose thioesters. The compatibility of these uncharged SCAs with biomolecules makes possible the encapsulation of functional enzymes and nucleic acids during the vesicle generation process, enabling membrane protein reconstitution and compartmentalized nucleic acid amplification, even when charged precursors are supplied externally.

Reliable quantitative detection of uric acid in urine by surface-enhanced Raman spectroscopy with endogenous internal standard.

Abnormal levels of uric acid (UA) in urine serve as warning signs for gout and metabolic cardiovascular diseases, necessitating the monitoring of UA levels for early prevention. However, the current analytical methods employed suffer from limitations in terms of inadequate suitability for home-based applications and the requirement of non-invasive procedures. In this approach, creatinine, a metabolite with a constant excretion rate, was incorporated as an endogenous internal standard (e-IS) for calibration, presenting a rapid, pretreatment-free, and accurate strategy for quantitative determination of UA concentrations. By utilizing urine creatinine as an internal reference value to calibrate the signal fluctuation of surface-enhanced Raman spectroscopy (SERS) of UA, the quantitative accuracy can be significantly improved without the need for an external internal standard. Due to the influence of the medium, UA, which carries a negative charge, is selectively adsorbed by Au@Ag nanoparticles functionalized with hexadecyltrimethylammonium chloride (CTAC) in this system. Furthermore, a highly convenient detection method was developed, which eliminates the need for pre-processing and minimizes matrix interference by simple dilution. The method was applied to the urine detection of different volunteers, and the results were highly consistent with those obtained using the UA colorimetric kit (UACK). The detection time of SERS was only 30 s, which is 50 times faster than UACK. This quantitative strategy of using urinary creatinine as an internal standard to correct the SERS intensity of uric acid is also expected to be extended to the quantitative detection needs of other biomarkers in urine.

Mechanism of structural colors in binary mixtures of nanoparticle-based supraballs.

Inspired by structural colors in avian species, various synthetic strategies have been developed to produce noniridescent, saturated colors using nanoparticle assemblies. Nanoparticle mixtures varying in particle chemistry and size have additional emergent properties that affect the color produced. For complex multicomponent systems, understanding the assembled structure and a robust optical modeling tool can empower scientists to identify structure-color relationships and fabricate designer materials with tailored color. Here, we demonstrate how we can reconstruct the assembled structure from small-angle scattering measurements using the computational reverse-engineering analysis for scattering experiments method and use the reconstructed structure in finite-difference time-domain calculations to predict color. We successfully, quantitatively predict experimentally observed color in mixtures containing strongly absorbing nanoparticles and demonstrate the influence of a single layer of segregated nanoparticles on color produced. The versatile computational approach that we present is useful for engineering synthetic materials with desired colors without laborious trial-and-error experiments.

Single-Chain ß-d-Glycopyranosylamides of Unsaturated Fatty Acids: Self-Assembly Properties and Applications to Artificial Cell Development.

Amphiphilic molecules undergo self-assembly in aqueous medium to yield various supramolecular structures depending on their chemical structure and molecular geometry. Among these, lamellar membrane-bound vesicles are of special interest due to their resemblance to cellular membranes. Here we describe the self-assembly of single-chain amide-linked amphiphiles derived from ß-d-galactopyranosylamine and various unsaturated fatty acids into vesicles. In contrast, the analogous amphiphiles derived from ß-d-glucopyranosylamine self-assemble into nanotubes. Fluorescence spectroscopy, X-ray diffraction, and differential scanning calorimetry are used to determine various physical parameters pertinent to the self-assembly process. The vesicular architecture is characterized using optical microscopy and transmission electron microscopy. Moreover, we show that the vesicles derived from these amphiphiles can encapsulate molecules of various sizes and host model biochemical reactions. Our work demonstrates that single-chain glycolipid-based amphiphiles could serve as robust building blocks for artificial cells and have potential applications in drug delivery and microreactor design.

Effects of angiopoietin-1 on inflammatory injury in endothelial progenitor cells and blood vessels.

Endothelial progenitor cells (EPCs) and angiopoietin-1 (Ang-1) play important roles in vasculogenesis and angiogenesis, respectively. Thus, targeting both aspects of cardiovascular tissue regeneration may offer promising therapeutic options for cardiovascular disorders. To this end, we constructed a lentiviral vector (pNL) with the Ang-1 gene and transfected EPCs with it (Ang-1-EPCs) to investigate vasculogenesis in both cellular and animal models. Compared to controls, intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) increased significantly in both untreated EPCs and in the pNL vector group. After Ang-1 transcription, ICAM-1 and VCAM-1 decreased considerably in those treatment groups. Ang-1-modified EPCs alleviated inflammatory responses induced by tumor-necrosis factor-α (TNF-α) in vitro. Moreover, Ang-1-EPC implantation inhibited neointimal hyperplasia after balloon catheter injury in rats, dramatically diminishing the intimal-media (I/M) ratio and decreasing the neointimal area. Proliferating cell nuclear antigen expression in the Ang-1-EPC group was lower than the EPC non-treatment group as well, suggesting that Ang-1-EPC improved cell survival during inflammation and promoted endothelialization in damaged blood vessels.

Effect of transplanted mesenchymal stem cells from rats of different ages on the improvement of heart function after acute myocardial infarction.

BACKGROUND: Mesenchymal stem cells (MSCs) transplantation is of therapeutic potential after ischemic injury in both experimental and clinical studies. Clinically, elderly patients are more vulnerable to acute myocardial infarction (AMI). But little is known about the characteristics of young donor-derived MSCs transplanted to old patients with AMI. The present study was designed to investigate the effect of transplanted MSCs from rats of different ages on the improvement of heart function after AMI. METHODS: MSCs from Sprague-Dawley (SD) rats were isolated and cultured in vitro. The apoptosis characteristics of MSCs were observed under conditions of ischemia and anoxia. SD rats underwent MI received intramyocardial injection of MSCs from young donor rats (n = 8), old donor rats (n = 8), respectively. AMI control group received equal volume physiological saline. Immunofluorescence was used to observe the differentiation of the grafted cells into cardiomyocytes. Four weeks after cell transplantation, reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry for vascular endothelial growth factor (VEGF), VIII-factor immunohistochemistry for vessel density, TUNEL, caspase-3 for cardiomyocyte apoptosis, echocardiography and hemodynamic detection for heart function were performed. RESULTS: The apoptosis rate of the old donor-derived MSCs group was significantly higher than that of the young donor-derived MSCs group under conditions of ischemia and anoxia (P < 0.05). Engrafted MSCs survived, proliferated and differentiated into myocardium-like cells. VEGF gene expression and capillary density in the old donor-derived group were lower than those in the young donor-derived group but higher than those in the control group (P < 0.05). The transplantation of old donor-derived MSCs attenuated apoptosis of cardiomyocytes in the peri-infarct region compared with the control group and the effect was elevated in young donor-derived MSCs (P < 0.05). The heart functions (left ventricle ejection fraction (LVEF), left ventricle fractional shortening (LVFS)) were improved more significantly in the old donor-derived MSCs group than in the control group and the heart function in the young donor-derived MSCs group further improved (P < 0.05). CONCLUSIONS: Young donor-derived MSCs can improve heart function significantly through angiogenesis and decreasing cardiomyocyte apoptosis when transplanted to the infarcted area.