Nanopatterned polymer brushes as switchable bioactive interfaces.

We report convenient methods for synthesis of nanopatterned, thermally responsive brushes of poly(N-isopropyl acrylamide) over large areas (e.g., 1 cm(2)) to form model, dynamic, biofunctional surfaces. The new nanopatterned brush structure can be used to control (i) the rate of both nonspecific and biospecific adsorption processes at the polymer-graft-free regions of the substrate, and (ii) the rate of cell detachment. These capabilities have potential implications in a number of areas of biotechnology including biosensing, separations and cell culture.

Micrometer and nanometer scale photopatterning of proteins on glass surfaces by photo-degradation of films formed from oligo(ethylene glycol) terminated silanes.

Exposure of films formed by the adsorption of oligo(ethylene glycol) (OEG) functionalized trichlorosilanes on glass to UV light from a frequency-doubled argon ion laser (244 nm) causes photodegradation of the OEG chain. Although the rate of degradation is substantially slower than for monolayers of OEG terminated thiolates on gold, it is nevertheless possible to form micrometer-scale patterns by elective adsorption of streptavidin to exposed regions. A low density of aldehyde functional groups is produced, and this enables derivatization with nitrilotriacetic acid via an amine linker. Complexation with nickel enables the site-specific immobilization of histidine-tagged yellow and green fluorescent proteins. Nanometer-scale patterns may be fabricated using a Lloyd's mirror interferometer, with a sample and mirror set at right angles to each other. At low exposures, partial degradation of the OEG chains does not remove the protein-resistance of the surface, even though friction force microscopy reveals the formation of patterns. At an exposure of ca. 18 J cm(-2), the modified regions became adhesive to proteins in a narrow region ca. 30 nm (λ/8) wide. As the exposure is increased further the lines quickly broaden to ca. 90 nm. Adjustment of the angle between the sample and mirror enables the fabrication of lines of His-tagged green fluorescent protein at a period of 340 nm that could be resolved using a confocal microscope.

Large area nanopatterning of alkylphosphonate self-assembled monolayers on titanium oxide surfaces by interferometric lithography.

We demonstrate that interferometric lithography offers a fast, simple route to nanostructured self-assembled monolayers of alkylphosphonates on the native oxide of titanium. Exposure at 244 nm using a Lloyd's mirror interferometer caused the spatially periodic photocatalytic degradation of the adsorbates, yielding nanopatterns that extended over square centimetre areas. Exposed regions were re-functionalised by a second, contrasting alkylphosphonate, and the resulting patterns were used as templates for the assembly of molecular nanostructures; we demonstrate the fabrication of lines of polymer nanoparticles 46 nm wide. Nanopatterned monolayers were also employed as resists for etching of the metal film. Wires were formed with widths that could be varied between 46 and 126 nm simply by changing the exposure time. Square arrays of Ti dots as small as 35 nm (λ/7) were fabricated using two orthogonal exposures followed by wet etching.

Photopatterning, etching, and derivatization of self-assembled monolayers of phosphonic acids on the native oxide of titanium.

Electron-hole pair formation at titania surfaces leads to the formation of reactive species that degrade organic materials. Here, we describe the degradation of self-assembled monolayers of alkylphosphonic acids on the native oxide of titanium following exposure to UV light. The rate of degradation was found to decrease as the length of the adsorbate molecule increased. Increasing order in the monolayer, resulting from the enhanced dispersion forces between longer adsorbates, impedes the progress of oxygen-containing molecules to the oxide surface and slows the rate of oxidation. Rates of degradation on titanium oxide are substantially greater than rates of degradation on aluminum oxide because of the photocatalytic effect of the titanium oxide substrate. Micrometer-scale patterns may be fabricated readily using a UV laser in conjunction with a mask, and nanometer-scale patterns may be fabricated using a scanning near-field optical microscope coupled to a UV laser. Photodegraded adsorbates may be replaced by contrasting molecules to yield chemical contrast. Such patterned materials have been utilized to fabricate patterns from polymer nanoparticles. The resist character is switchable--at lower exposures, the monolayer behaves as a positive tone resist, but at higher exposures, it exhibits negative tone behavior. Patterned samples may also be utilized as resists for solution-phase etching of the underlying substrate.

Pattern of admissions to the medical intensive care unit of Addis Ababa University Teaching Hospital.

A case-series study of all admissions using patient registers was carried out to analyse patterns of medical admissions into the Medical Intensive Care Unit (MICU) of the Addis Ababa University Teaching Hospital, and evaluate for any changes in that pattern over a study period. All patients admitted to the MICU of a 500-bed Teaching Hospital in Addis Ababa between 1985-2000 were the study subjects. Demographic variables, specific categories of diagnoses and their outcomes were recorded A total of 3548 patients (male to female ratio of 1.4:1, mean age 37.10 +/- 17.29) were admitted from September 1985 to August 2000. Acute infectious and cardiovascular diseases accounted for half of the entire critical care admissions with infectious diseases accounting for 30%. Among specific diagnoses, diabetic ketoacidosis was the leading cause of admission followed by acute myocardial infarction and severe and complicated malaria, each accounting for 10.7, 9.8 and 9.3% of all admissions respectively. Trends of admissions over the sixteen-year period showed steady increase in relative frequency of acute complications of non-communicable diseases consisting of diabetes, acute myocardial infarction and stroke while infectious diseases showed interspersed peaks of admissions coinciding with epidemics. The overall mortality of the MICU was 32%, with proportionally more female deaths, 34.8 versus 29% (P = 0.0002). Severe and complicated malaria was the leading cause of death (10.3%) followed by tetanus (6.4%) and acute myocardial infarction (6.3%). The increase in relative and absolute frequency of acute complications of non-communicable diseases most probably heralds an emerging epidemic of non-communicable diseases related to life style changes in the urban well to do in addition to existing problems of infectious diseases of poverty.