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Biomedical subjects

J Tien

Publications and source records attributed to J Tien.

11 recordsLinked to original sources
PubMed2001

Self-assembly of 10-microm-sized objects into ordered three-dimensional arrays.

This paper describes the self-assembly of small objects--polyhedral metal plates with largest dimensions of 10 to 30 microm--into highly ordered, three-dimensional arrays. The plates were fabricated using photolithography and electrodeposition techniques, and the faces of the plates were functionalized to be hydrophobic or hydrophilic using self-assembled monolayers (SAMs). Self-assembly occurs in water through capillary interactions between thin films of a hydrophobic liquid (a liquid prepolymer adhesive) coated onto the hydrophobic faces of the plates; coalescence of the adhesive films reduces the interfacial free energy of the system and drives self-assembly. By altering the size and surface-patterning of the plates, the external morphologies of the aggregates were varied. Curing the adhesive furnished mechanically stable aggregates that were characterized by scanning electron microscopy (SEM). For assemblies formed by plates partially composed of a sacrificial material, a subsequent etching step furnished fully open, three-dimensional microstructures. This work validates the use of capillary interactions for three-dimensional mesoscale self-assembly in the 10-microm-size regime and opens new avenues for the fabrication of complex, three-dimensional microscructures.

Electroplating↗
PubMed2000

Forming electrical networks in three dimensions by self-assembly

Self-assembly of millimeter-scale polyhedra, with surfaces patterned with solder dots, wires, and light-emitting diodes, generated electrically functional, three-dimensional networks. The patterns of dots and wires controlled the structure of the networks formed; both parallel and serial connections were generated.

Journal Article↗
PubMed1999

Design and self-assembly of open, regular, 3D mesostructures

Self-assembly provides the basis for a procedure used to organize millimeter-scale objects into regular, three-dimensional arrays ("crystals") with open structures. The individual components are designed and fabricated of polyurethane by molding; selected faces are coated with a thin film of liquid, metallic alloy. Under mild agitation in warm, aqueous potassium bromide solution, capillary forces between the films of alloy cause self-assembly. The structures of the resulting, self-assembled arrays are determined by structural features of the component parts: the three-dimensional shape of the components, the pattern of alloy on their surfaces, and the shape of the alloy-coated surfaces. Self-assembly of appropriately designed chiral pieces generates helices.

Journal Article↗
PubMed1999

A strategy for the generation of surfaces presenting ligands for studies of binding based on an active ester as a common reactive intermediate: a surface plasmon resonance study.

This paper describes the immobilization of ten proteins and two low-molecular-weight ligands on mixed self-assembled monolayers (SAMs) of alkanethiolates on gold generated from the tri(ethylene glycol)-terminated thiol 1 (HS(CH2)11(OCH2CH2)3OH) (chi(1) = 1.0-0.0) and the longer, carboxylic acid-terminated thiol2(HS(CH2)11(OCH2-CH2)6OCH2CO2H) (chi(2) = 0.0-1.0). The immobilization was achieved by a two-step procedure: generation of reactive N-hydroxysuccinimidyl esters from the carboxylic acid groups of 2 in the SAM and coupling of these groups with amines on the protein or ligand. Because this method involves a common reactive intermediate that is easily prepared, it provides a convenient method for attaching ligands to SAMs for studies using surface plasmon resonance spectroscopy (and, in principle, other bioanalytical methods that use derivatized SAMs on gold, silver, and other surfaces). These SAMs were resistant to nonspecific adsorption of proteins having a wide range of molecular weights and isoelectric points. The pH of the coupling buffer, the concentration of protein, the ionic strength of the solution of protein, and the molecular weight of the protein all influenced the amount of the protein that was immobilized. For the proteins investigated in detail--carbonic anhydrase and lysozyme--the highest quantities of immobilized proteins were obtained when using a low ionic strength solution at a value of pH approximately one unit below the isoelectric point (pI) of the protein, at a concentration of approximately 0.5 mg mL-1. Comparisons of the kinetic and thermodynamic constants describing binding of carbonic anhydrase and vancomycin to immobilized benzenesulfonamide and N-alpha-Ac-Lys-D-Ala-D-Ala groups, respectively, on mixed SAMs (by methods described in this paper) and in the carboxymethyl dextran matrix of commercially available substrates yielded (for these systems) essentially indistinguishable values of Kd, koff, and kon.

Adsorption↗
PubMed1999

Geometric control of switching between growth, apoptosis, and differentiation during angiogenesis using micropatterned substrates.

Past studies using micropatterned substrates coated with adhesive islands of extracellular matrix revealed that capillary endothelial cells can be geometrically switched between growth and apoptosis. Endothelial cells cultured on single islands larger than 1500 microm2 spread and progressed through the cell cycle, whereas cells restricted to areas less than 500 microm2 failed to extend and underwent apoptosis. The present study addressed whether island geometries that constrained cell spreading to intermediate degrees, neither supporting cell growth nor inducing apoptosis, cause cells to differentiate. Endothelial cells cultured on substrates micropatterned with 10-microm-wide lines of fibronectin formed extensive cell-cell contacts and spread to approximately 1000 microm2. Within 72 h, cells shut off both growth and apoptosis programs and underwent differentiation, resulting in the formation of capillary tube-like structures containing a central lumen. Accumulation of extracellular matrix tendrils containing fibronectin and laminin beneath cells and reorganization of platelet endothelial cell adhesion molecule-positive cell-cell junctions along the lengths of the tubes preceded the formation of these structures. Cells cultured on wider (30-microm) lines also formed cell-cell contacts and aligned their actin cytoskeleton, but these cells spread to larger areas (2200 microm2), proliferated, and did not form tubes. Use of micropatterned substrates revealed that altering the geometry of cell spreading can switch endothelial cells among the three major genetic programs that govern angiogenesis-growth, apoptosis and differentiation. The system presented here provides a well-defined adhesive environment in which to further investigate the steps involved in angiogenesis.

Animals↗
PubMed1997

Using microcontact printing to pattern the attachment of mammalian cells to self-assembled monolayers of alkanethiolates on transparent films of gold and silver.

This paper describes a convenient methodology for patterning substrates for cell culture that allows the positions and dimensions of attached cells to be controlled. The method uses self-assembled monolayers (SAMs) of terminally substituted alkanethiolates (R(CH2)11-15S-) adsorbed on optically transparent films of gold or silver to control the properties of the substrates. SAMs terminated in methyl groups adsorb protein and SAMs terminated in oligo(ethylene glycol) groups resist entirely the adsorption of protein. This methodology uses microcontact printing (microCP)-an experimentally simple, nonphotolithographic process-to pattern the formation of SAMs at the micrometer scale; microCP uses an elastomeric stamp having at its surface a pattern in relief to transfer an alkanethiol to a surface of gold or silver in the same pattern. Patterned SAMs having hydrophobic, methyl-terminated lines 10, 30, 60, and 90 microm in width and separated by protein-resistant regions 120 microm in width were prepared and coated with fibronectin; the protein adsorbed only to the methyl-terminated regions. Bovine capillary endothelial cells attached only to the fibronectin-coated, methyl-terminated regions of the patterned SAMs. The cells remained attached to the SAMs and confined to the pattern of underlying SAMs for at least 5-7 days. Because the substrates are optically transparent, cells could be visualized by inverted microscopy and by fluorescence microscopy after fixing and staining with fluorescein-labeled phalloidin.

Actin Cytoskeleton↗
PubMed1995

Endogenous bacterial toxins are required for the injurious action of platelet-activating factor in rats.

BACKGROUND & AIMS: Platelet-activating factor (PAF), an endogenous mediator for experimental sepsis, has been shown to induce shock and intestinal necrosis in vivo. However, it is unclear whether PAF exerts its injurious effects on the intestinal tissue directly or via synergism with other endogenous products. The aim of this study was to examine the role of endogenous bacterial products, such as endotoxin, in PAF-induced intestinal injury. METHODS: PAF (3 micrograms/kg) was injected intravenously into normally colonized rats, germfree rats, and normal rats pretreated with a combination of antibiotics, and the systemic response and intestinal injury were assessed. RESULTS: PAF did not cause prolonged shock, leukopenia, hemoconcentration, and bowel necrosis in germfree rats. When germfree rats were primed with a low dose (0.5 mg/kg) of endotoxin, the protection was lost. Combined treatment of the normally colonized rats with neomycin, polymyxin B, and metronidazole for 7 days largely protected the animal from PAF-induced shock and intestinal necrosis. CONCLUSIONS: PAF does not directly induce prolonged hypotension, hemoconcentration, persistent leukopenia, and gross intestinal necrosis but causes these changes via a synergism with endogenous bacterial toxins, presumably from the gut flora.

Analysis of Variance↗
PubMed1982

Asian nursing students in the United States.

It is obvious that there is a great need to familiarize faculty and students with the Asian culture and heritage and to sensitize them to the difficulties and problems that Asian nursing students encounter in their adjustment to the university nursing program in the United States. Recommendations and strategies to achieve the above goals are: (1) Organizing cross-cultural courses for Asians and non-Asians to familiarize them with different cultures, (2) sensitizing faculty and counselors to the detrimental effects of existing nursing programs on international students, and (3) helping Asian nursing students better adjust to the American culture by providing English tutorial classes, support groups and host families that will act as socializing agents during the student's adjustment process. Through such educational and support programs, it is hoped that Asian nursing students will experience fewer difficulties which in turn will make their studies more meaningful and applicable.

Acculturation↗
PubMedDate not supplied

A new approach to reproducibility assessment: clinical evaluation of SpaceLabs Medical oscillometric blood pressure monitor.

The SpaceLabs Medical oscillometric blood pressure monitor was evaluated in both neonatal and adult populations according to the 1992 AAMI SP-10 standard for electronic or automated sphygmomanometers. For the neonatal study, the umbilical artery pressure was used as a reference. Fifteen newborn ICU patients were enrolled in the study, yielding a total of 150 pairs of comparison readings. For the adult study, the first and fifth phases of the Korotkoff sounds were used as a reference. One hundred twelve adults were enrolled in the study, yielding a total of 336 pairs of comparison readings. Accuracy was analyzed by the AAMI SP-10 standard. For systolic and diastolic pressures, respectively, the mean differences +/- standard deviations of oscillometric accuracy were 0.1 +/- 4.3 and 2.7 +/- 4.8 mmHg for the neonatal study and -0.6 +/- 5.9 and 0.9 +/- 6.4 mmHg for the adult study, which are within the AAMI SP-10 accuracy standard. Reproducibility was analyzed by a new approach developed from the sequential technique of the 1990 British Hypertension Society protocol. For systolic and diastolic pressures, respectively, the mean differences +/- standard deviations of the oscillometric reproducibility were estimated to be -0.1 +/- 3.3 and 0.1 +/- 3.4 mmHg for the neonatal study and -0.3 +/- 3.2 and 0.1 +/- 3.5 mmHg for the adult study.

Adult↗