Biomedical subjects

Sheng Meng

Publications and source records attributed to Sheng Meng.

13 recordsLinked to original sources

PubMed2007

Structure and release behavior of PMMA/silica composite drug delivery system.

The preparation, characterization, and in vitro release of aspirin from polymethylmethacrylate (PMMA)/silica composites prepared via a sol-gel route are reported. The in vitro drug release test revealed that the release rate of aspirin in PBS increased with the silica content in the composites; on the contrary, the increase of the content of 3-(trimethoxysilyl) propyl methacrylate (MSMA), a coupling agent, decreased the drug release rate. The drug release rate/composite structure relationship was studied using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and swelling ratio (SR) measurement. The results indicated that the interface between polymer matrix and inorganic fillers has significant influence on the drug release behavior of the composite materials. In addition, models of mass transfer based on Fickian diffusion law at constant temperature and pressure were employed to analyze the results of the in vitro drug release experiments. The drug release behaviors of the composite samples fitted well with the Fickian diffusion model. The values of k, which is in direct proportion to drug release rate, increased with the increasing content of silica while decreased with that of MSMA in the composite samples.

Aspirin↗

PubMed2007

DNA nucleoside interaction and identification with carbon nanotubes.

We investigate the interaction of individual DNA nucleosides with a carbon nanotube (CNT) in vacuum and in the presence of external gate voltage. We propose a scheme to discriminate between nucleosides on CNTs based on measurement of electronic features through a local probe such as scanning tunneling spectroscopy. We demonstrate through quantum mechanical calculations that these measurements can achieve 100% efficiency in identifying DNA bases. Our results support the practicality of ultrafast DNA sequencing using electrical measurements.

DNA↗

PubMed2006

Structural model of eumelanin.

Melanin is a ubiquitous pigment in living organisms with multiple important functions, yet its structure is not well understood. We propose a structural model for eumelanin protomolecules, consisting of 4 or 5 of the basic molecular units (hydroquinone, indolequinone, and its tautomers), in arrangements that contain an inner porphyrin ring. We use time-dependent density functional theory to calculate the optical absorption spectrum of the structural model, which reproduces convincingly the main features of the experimental spectrum of eumelanin. Our model also reproduces accurately other important properties of eumelanin, including x-ray scattering data, its ability to capture and release metal ions, and the characteristic size of the protomolecules.

Animals↗

PubMed2006

Assembly-controlled biocompatible interface on a microchip: strategy to highly efficient proteolysis.

A biocompatible interface was constructed on a microchip by using the layer-by-layer (LBL) assembly of charged polysaccharides incorporating proteases for highly efficient proteolysis. The controlled assembly of natural polyelectrolytes and the enzyme-adsorption step were monitored by using a quartz-crystal microbalance and atomic force microscopy (AFM). Such a multilayer-assembled membrane provides a biocompatible interconnected network with high enzyme-loading capacity. The maximum digestion rate of the adsorbed trypsin in a microchannel was significantly accelerated to 1600 mM min(-1) microg(-1), compared with the tryptic digestion in solution. Based on the Langmuir isotherm model, the thermodynamic constant of adsorption K was calculated to be 1.6 x 10(5) M(-1) and the maximum adsorption loading Gammamax was 3.6 x 10(-6) mol m(-2), 30 times more than a monolayer of trypsin on the native surface. The tunable interface containing trypsin was employed to construct a microchip reactor for digestion of femtomoles of proteins and the produced peptides were analyzed by MALDI-TOF mass spectroscopy. The efficient on-chip proteolysis was obtained within a few seconds, and the identification of biological samples was feasible.

Biocompatible Materials↗

PubMed2006

Atomic structure and bonding of water overlayer on Cu(110): the borderline for intact and dissociative adsorption.

By carefully comparing the calculated and measured work function data, energetics, and vibrational spectroscopy, we determine explicitly the water structure in c(2 x 2) periodicity on Cu(110) to be an intact water overlayer with a majority component of H-down bilayer (95%) in low temperature experiments. Water dissociation is accessible by heating or ultraviolet illumination, resulting in a sensitive change in electron density at the surface and could therefore be monitored by work function measurement.

Journal Article↗

PubMed2006

Tuning solid surfaces from hydrophobic to superhydrophilic by submonolayer surface modification.

Molecular-scale understanding and manipulation of the wetting behavior of water on solids remains a fundamental challenge. Using diamond as a model system, we show that the naturally hydrophobic behavior of a hydrogen-terminated C(111) surface can be manipulated by replacing the H termination with a monolayer of adsorbate. In particular, a mixed monolayer of 1/3 Na and 2/3 F atoms leads to superhydrophilic behavior, as shown by first-principles calculations. The physical origin of the superhydrophilic behavior is attributed to the ionic nature of the Na adatoms, which mediate the right degree of binding strength between water molecules and the substrate.

Journal Article↗

PubMed2006

Formation and interaction of hydrated alkali metal ions at the graphite-water interface.

Ion hydration at a solid surface ubiquitously exists in nature and plays important roles in many natural processes and technological applications. Aiming at obtaining a microscopic insight into the formation of such systems and interactions therein, we have investigated the hydration of alkali metal ions at a prototype surface-graphite (0001), using first-principles molecular dynamics simulations. At low water coverage, the alkali metal ions form two-dimensional hydration shells accommodating at most four (Li, Na) and three (K, Rb, Cs) waters in the first shell. These two-dimensional shells generally evolve into three-dimensional structures at higher water coverage, due to the competition between hydration and ion-surface interactions. Exceptionally K was found to reside at the graphite-water interface for water coverages up to bulk water limit, where it forms an "umbrellalike" surface hydration shell with an average water-ion-surface angle of 115 degrees . Interactions between the hydrated K and Na ions at the interface have also been studied. Water molecules seem to mediate an effective ion-ion interaction, which favors the aggregation of Na ions but prevents nucleation of K. These results agree with experimental observations in electron energy loss spectroscopy, desorption spectroscopy, and work function measurement. In addition, the sensitive dependence of charge transfer on dynamical structure evolution during the hydration process, implies the necessity to describe surface ion hydration from electronic structure calculations.

Journal Article↗

PubMed2006

Construction of a biomimetic surface on microfluidic chips for biofouling resistance.

A biomimetic surface has been formed on the poly(methyl methacrylate) (PMMA) microfluidic chips for biofouling resistance on the basis of a simple modification. Accordingly, an amphiphilic phospholipid copolymer of 2-methacryloyloxyethyl phosphorylcholine and n-butyl methacrylate (PMB) was developed to introduce the phosphorylcholine functional groups onto the PMMA surface via the anchoring of hydrophobic n-butyl methacrylate units. The 2-methacryloyloxyethyl phosphorylcholine segments could form hydrophilic domains, considered to be located on the surface, to provide a biocompatible surface. X-ray photoelectron spectroscopy and Fourier transform infrared spectra confirmed the success of surface functionalization. The PMB-modified microchips containing phosphorylcholine moieties exhibited more stable electroosmotic mobility compared with the untreated one. In addition to being characterized for minimized nonspecific adhesion of serum proteins and plasma platelets, the PMB-functionalized microchannels have been exemplified by electrophoresis of proteins. This one-step procedure offers an effective approach for a biomimetic surface design on microfluidic chips, which is promising in high-throughput and complex biological analysis.

Biomimetics↗

PubMed2006

Deposition of PEG onto PMMA microchannel surface to minimize nonspecific adsorption.

A protein-resistant surface has been constructed on the poly(methyl methacrylate) (PMMA) microfluidic chips based on a one-step modification. The copolymer of butyl methacrylate (BMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) is synthesized to introduce a dense PEG molecular brush-like coating on the PMMA microchannel surfaces via the anchoring effect of the hydrophobic BMA units. The PEGMA segments could produce hydrophilic domains formed on the interface so as to achieve stable electroosmotic flow, and less nonspecific adsorption toward biomolecules. The modification procedure and the properties of the poly(BMA-co-PEGMA)-coated surface have been characterized by FT-IR spectroscopy, confocal fluorescence microscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The water contact angle and electroosmotic flow of PEG-modified PMMA microchip are measured to be 36 degrees and 5.4 x 10(-4) cm(2) V(-1) s(-1), while those of 73 degrees and 1.9 x 10(-4) cm(2) V(-1) s(-1) for native one, respectively. The PEG-modified microchip has been applied for the electrophoresis separation of proteins, corresponding to the theoretical efficiencies about 16 300 and 412 300 plates m(-1). In the interest of achieving efficient separation while minimizing biofoulings from the serum and plasma, the fabrication of PEG-coated microfluidic chips would provide a biocompatible platform for complex biological analysis.

Adsorption↗

PubMed2005

Dissolution dynamics of NaCl nanocrystal in liquid water.

The dissolution dynamics of a NaCl nanocrystal in liquid water was studied using molecular dynamics simulations. The dissolution process was found to start with a Cl(-) ion at a corner site, followed by a Na(+) ion nearby. Both show directional preference in the dissolution path. An ion sequence with alternating charge, i.e., Cl(-), Na(+), Cl(-), Na(+), etc. was found to dominate the dissolution process. This image can be understood from the ionic hydration structures and the Coulomb interaction between the ions.

Journal Article↗

PubMed2004

Two-dimensional hydration shells of alkali metal ions at a hydrophobic surface.

We study the hydration shell formation of alkali metal ions at a graphite surface. Two-dimensional shell structures are found in the initial stage of hydration, in contrast to the three-dimensional structures in bulk water and clusters. Comparison of vibrational spectra with experiments identifies the shell structures and the thermally induced transition from the first to the second shell. We also found intriguing competition between hydration and ion-surface interaction, leading to different solvation dynamics between K and Na. Implications of these results in ionic processes at interfaces are elaborated.

Journal Article↗

PubMed2004

Ice tessellation on a hydroxylated silica surface.

The adsorption of water on a fully hydroxylated silica surface is studied by using density-functional total-energy and molecular dynamics calculations. The (100) surface of beta(alpha)-cristobalite covered by geminal hydroxyls has been taken as the substrate. A well-ordered and stable two-dimensional ice with quadrangular and octagonal patterns of hydrogen bond (H-bond) networks-an ice tessellation-is found on the surface for the first time. With the vibrational recognition, the four water molecules in the quadrangle are found to be bonded by strong H bonds while the quadrangles are connected to each other by weak H bonds. This configuration is the most stable, because all the water molecules are fully saturated with H bonds either to each other or to the surface hydroxyl groups.

Journal Article↗

PubMed2002

Vibrational recognition of hydrogen-bonded water networks on a metal surface.

The adsorption of water on Pt(111) surface has been studied with ab initio molecular dynamics simulation. Both the energetics and vibrational dynamics indicate the existence of a well-ordered molecular bilayer on this surface. This conclusion is in contrast to the recent result of water on Ru(0001) surface, but agrees with available experiments. In addition, our calculation identifies two different hydrogen bonds in the bilayer. Both can be directly recognized from the vibrational spectra of the OH stretch modes.

Journal Article↗