Biomedical subjects

Ying Mei

Publications and source records attributed to Ying Mei.

11 recordsLinked to original sources

PubMed2006

Gradient substrate assembly for quantifying cellular response to biomaterials.

Using quantitative fluorescence microscopy in conjunction with a method of gradient substrate assembly established in their group, the authors were able to introduce and measure reproducible changes in cellular morphology and cell density by manipulating polymer grafting density. The mechanism behind this change in cellular behavior was explained by a semiempirical, geometric model that describes the effect of the spatial distribution of the polymer on protein attachment. A 10-fold increase in graft density of poly(2-hydroxyethyl methacrylate) [PHEMA] along the surface of a gradient sample, preexposed to bovine fibronectin, caused a change in the size of fibroblasts on the surface (i.e., cell spreading) from (1238 +/- 704) to (377 +/- 216) microm(2). The results were in quantitative agreement with those obtained on three separate gradient samples. Both cellular response and fibronectin adsorption (as measured via ellipsometry) were found to vary sigmoidally with graft density of PHEMA, demonstrating the high degree of correlation between the two phenomena. A simple, rigid-disk model accounting for the surface coverage of PHEMA was able to predict the amount of adsorbed fibronectin with a correlation coefficient of 0.97. Maximal cell adhesion and cell spreading were found to occur at fibronectin surface densities of 50 and 100 ng/cm(2), respectively. The results demonstrate the role of gradient substrate assembly as a method for quantifying the relationship between protein and cellular response to technologically relevant polymeric materials.

Adsorption↗

PubMed2006

The effect of surface chemistry on the formation of thin films of native fibrillar collagen.

In this study, we used well-defined, homogeneous, gradient and patterned substrates to explore the effects of surface chemistry on the supramolecular structure of adsorbed type I collagen. Type I collagen (320microg/mL) was allowed to adsorb onto self-assembled CH(3)-, COOH-, NH(2)- and OH-terminated alkylthiolate monolayers at 37 degrees C. Atomic force microscopy, ellipsometry and phase microscopy indicated that large supramolecular collagen fibril structures (approximately 200nm in diameter, several microns long) assembled only at the hydrophobic CH(3)-terminated surfaces. By varying the surface energy using a mixture of OH- and CH(3)-terminated thiols during monolayer formation, we found that large fibril assembly occurred at surfaces with a water contact angle above 83 degrees , but not on surfaces with a water contact angle below 63 degrees . Examining a surface with a linear hydrophobicity gradient revealed that the assembly of large collagen fibrils requires a hydrophobic surface with a water contact angle of at least 78 degrees . Collagen fibril density increased over a narrow range of surface energy and reached near-maximum density on surfaces with a water contact angle of 87 degrees . These studies confirm that the supramolecular structure of adsorbed collagen is highly dependent on the underlying substrate surface chemistry. We can take advantage of this dependency to pattern areas of fibrillar and non-fibrillar collagen on a single surface. Morphology studies with vascular smooth muscle cells indicated that only collagen films formed on hydrophobic substrates mimicked the biological properties of fibrillar collagen gels.

Adsorption↗

PubMed2005

Tuning cell adhesion on gradient poly(2-hydroxyethyl methacrylate)-grafted surfaces.

A simple yet versatile method was developed to prepare a low-density polymerization initiator gradient, which was combined with surface-initiated atom transfer radical polymerization (ATRP) to produce a well-defined poly(2-hydroxyethyl methacrylate) (HEMA) gradient substrate. A smooth variation in film thickness was measured across the gradient, ranging from 20 A to over 80 A, but we observed a nonmonotonic variation in water contact angle. Fits of X-ray reflectivity profiles suggested that at the low graft density end, the polymer chain structure was in a "mushroom" regime, while the polymer chains at high graft density were in a "brush" regime. It was found that the "mushroom" region of the gradient could be made adhesive to cells by adsorbing adhesion proteins, and cell adhesion could be tuned by controlling the density of the polymer grafts. Fibroblasts were seeded on gradients precoated with fibronectin to test cellular responses to this novel substrate, but it was found that cell adhesion did not follow the expected trend; instead, saturated cell adhesion and spreading was found at the low grafting density region.

Adsorption↗

PubMed2005

Synthesis and characterization of tapered copolymer brushes via surface-initiated atom transfer radical copolymerization.

Tapered copolymer brushes of methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) were synthesized via surface-initiated atom transfer radical polymerization (ATRP) by gradual addition of HEMA to a reaction mixture that originally only had MMA as monomer. The copolymer brush grew linearly with polymerization time. The tapered copolymer brushes responded to selective solvent treatments. For the same tapered copolymer brush, pretreating the surface with methylene chloride made the surface more hydrophobic; pretreating the surface with methanol increased the surface hydrophilicity. This change in surface properties was reversible and considered to be caused by the solvent induced rearrangement of the polymer brushes, which is supported by atomic force microscopy images of the surface. Our work demonstrates that the properties of the tapered copolymer brush could be finely tuned by careful control of the composition profile.

Journal Article↗

PubMed2005

Correlation between gene expression of CCK-A receptor and emptying dysfunction of the gallbladder in patients with gallstones and diabetes mellitus.

BACKGROUND: The incidence of gallstone is higher in patients with diabetes mellitus than in general population because of hypomotility and lowered emptying function. The aim of this study was to investigate the gene expression of cholecystokinin-A (CCK-A) receptor in patients with gallstones and diabetes mellitus and its correlation with the hypomotility of the gallbladder. METHODS: Smooth muscle was taken from the gallbladder after cholecystectomy and total RNA was extracted from it by Trizol reagent to compose cDNA. CCK-A receptor was enlarged by reverse transcription-polymerase chain reaction (RT-PCR) and identified by electrophoresis. Based on the analysis of images, the relative expression of the CCK-A receptor was obtained after comparison of the CCK-A receptor and beta-action. The emptying function of the gallbladder was measured with B ultrasound before operation. RESULTS: Gallbladder ejection fraction (GBEF2) (%) (24.9+/-12.7) decreased more significantly in patients with gallstones and diabetes mellitus than in those with simple gallstone (61.5+/-8.5) (P<0.01). In the two groups, a fraction of 540bp of CCK-A receptor could be testified respectively, but the relative expression was different. Compared to the expression of beta-action, it was 0.400+/-0.068 in patients with gallstones and diabetes mellitus, but 0.622+/-0.070 in those with gallstone only (F=7.169, Pu0.01). The result was consistent with the decreased contractility. CONCLUSIONS: The gene expression of CCK-A receptor on the smooth muscle of the gallbladder may decrease more significantly in patients with gallstone and diabetes mellitus than in those with gallstone only; this result is consistent with the decreased motility. Thus the lowered expression of CCK-A receptor is probably the cause of hypomotility in patients with gallstones and diabetes mellitus.

Adult↗

PubMed2004

A new synthetic method for controlled polymerization using a microfluidic system.

While many parallel synthesis methods developed by the pharmaceutical and life science communities are being applied to polymer synthesis, there remains a need to construct "libraries" of polymeric materials that explore a wider range of polymer structures with accuracy, flexibility, and rapid, often small, changes. We report the use of microfluidics to create an environment for continuous controlled radical polymerization. Varying either the flow rate or the relative concentrations of reactants (i.e., stoichiometry) controls the molecular properties of the products. Molecular variables, here molecular weight, can then be varied continuously. Well-defined materials with narrow molecular weight distributions are produced inside the microfluidic reactor and are available for processing, such as further mixing, deposition, or coating on surfaces. Preliminary kinetic data appear to agree well with literature values reported for larger-scale reactions.

Journal Article↗

PubMed2004

Solid-phase ATRP synthesis of peptide-polymer hybrids.

A versatile methodology to prepare hybrid biomaterials by atom transfer radical polymerization from resin-supported peptides has been established. As an example, we have synthesized a GRGDS-functionalized poly(2-hydroxyethyl methacrylate). The peptide-polymer was characterized by solid-state (13)C NMR and GPC and found to have a number average molecular weight of 4420 and a polydispersity of 1.47. These values are comparable to those obtained from solution-phase syntheses, suggesting the ATRP reaction is successful from a peptide-conjugated solid support. Solid-state (13)C NMR was used to characterize multiple steps in the reaction, and the synthesis was found to be near quantitative. We have performed cell adhesion experiments and observed the GRGDS sequence-promoted cell adhesion, whereas unfunctionalized poly(2-hydroxyethyl methacrylate) did not. By incorporating cell-signaling moieties in materials with defined molecular architecture, it will be possible to control the interactions between polymeric materials and biological systems.

Animals↗

PubMed2004

Construction of a targeting adenoviral vector carrying AFP promoter for expressing EGFP gene in AFP-producing hepatocarcinoma cell.

AIM: To construct a recombinant adenoviral vector carrying AFP promoter and EGFP gene for specific expression of EGFP gene in AFP producing hepatocellular carcinoma (HCC) HepG2 cells. METHODS: Based on the Adeno-X expression system, the human immediate early cytomegalovirus promoter (PCMV IE) was removed from the plasmid, pshuttle, and replaced by a 0.3 kb alpha-fetoprotein (AFP) promoter that was synthesized by polymerase chain reaction (PCR). The enhanced green fluorescent protein (EGFP) gene was inserted into the multi-clone site (MCS), and then the recombinant adenovirus vector carrying the 0.3 kb AFP promoter and EGFP gene was constructed. Cells of a normal liver cell line (LO2), a hepatocarcinoma cell line (HepG2) and a cervical cancer cell line (HeLa) were transfected with the adenovirus. Northern blot and fluorescence microscopy were used to detect the expression of the EGFP gene at mRNA or protein level in three different cell lines. RESULTS: The 0.3 kb AFP promoter was synthesized through PCR from the human genome. The AFP promoter and EGFP gene were directly inserted into the plasmid pshuttle as confirmed by restriction digestion and DNA sequencing. Northern blot showed that EGFP gene was markedly transcribed in HepG2 cells, but only slightly in LO2 and HeLa cells. In addition, strong green fluorescence was observed in HepG2 cells under a fluorescence microscopy, but fluorescence was very weak in LO2 and HeLa cells. CONCLUSION: Under control of the 0.3 kb human AFP promoter, the recombinant adenovirus vector carrying EGFP gene can be specially expressed in AFP-producing HepG2 cells. Therefore, this adenovirus system can be used as a novel, potent and specific tool for gene-targeting therapy for the AFP positive primary hepatocellular carcinoma.

Adenoviridae↗

PubMed2004

Biocompatibility of sorbitol-containing polyesters. Part I: Synthesis, surface analysis and cell response in vitro.

A series of sorbitol-containing polyesters were synthesized via a one-pot lipase-catalyzed condensation polymerization. Thin films were prepared by spin coating on silicon wafers and surfaces were analyzed by tapping mode atomic force microscopy and contact angle measurements. Surface morphologies and surface energies across the series of polyester films, including a poly(epsilon-caprolactone) (PCL) control were nearly indistinguishable. Biocompatibility of the sorbitol-containing polyester series was evaluated against a PCL control by measuring cell spreading and proliferation of a mouse fibroblast 3T3 cell line in vitro. Results confirmed that the sorbitol-containing polyester surfaces elicited cell behavior similar to the PCL control. These results establish the sorbitol-containing polyester series as a promising material for tissue engineering research and development.

3T3 Cells↗

PubMed2004

[Study on ligustrazine in reversing multidrug resistance of HepG2/ADM cell in vitro].

OBJECTIVE: To study the reverse effect of ligustrazine (TMP) on HepG2/ADM, a herd of hepatocellular carcinoma cell, multidrug resistance (MDR) and the influence of P-gp170 expression. METHOD: The reverse effect of ligustrazine on HepG2/ADM cell was observed, with the methods of cell culture, MTT's analyze, RT-PCR and Flow cytometric, etc. RESULT: Ligustrazine could make MDR of cell line of HepG2/ADM reduce the expression of P-gp170, enhance the density of adriamycin in cell and increase the adriamycin's cytotoxicity. With the Flow cytometric, the results of RT-PCR showed the transcriptional activity of the MDR1 decreased. CONCLUSION: Ligustrazine can reverse MDR of HCC cell line of HepG2/ADM and has prospect in clinical use.

ATP Binding Cassette Transporter, Subfamily B↗

PubMedDate not supplied

Imaging the distribution and secondary structure of immobilized enzymes using infrared microspectroscopy.

Synchrotron infrared microspectroscopy (SIRMS) was used for the first time to image the distribution and secondary structure of an enzyme (lipase B from Candida antarctica, CALB) immobilized within a macroporous polymer matrix (poly(methyl methacrylate)) at 10 microm resolution. The beads of this catalyst (Novozyme435) were cut into thin sections (12 microm). SIRMS imaging of these thin sections revealed that the enzyme is localized in an external shell of the bead with a thickness of 80-100 microm. Also, the enzyme was unevenly distributed throughout this shell. Furthermore, by SIRMS-generated spectra, it was found that CALB secondary structure was not altered by immobilization. Unlike CALB, polystyrene molecules of similar molecular weight diffuse easily throughout Novozyme435 beads. Scanning electron micrograph (SEM) images of the Novozyme435 beads showed that the average pore size is 10 times larger than CALB or polystyrene molecules, implying that there is no physical barrier to enzyme or substrate diffusion throughout the bead. Thus, the difference between polystyrene and enzyme diffusivity suggests that protein-matrix and protein-protein interactions govern the distribution of the enzyme within the macroporous resin.

Candida↗