Biomedical subjects

Frantisek Svec

Publications and source records attributed to Frantisek Svec.

27 records · Page 2Linked to original sources

PubMed2003

Fabrication of porous polymer monoliths covalently attached to the walls of channels in plastic microdevices.

UV-initiated grafting of plastic tubes and microfluidic chips with ethylene diacrylate followed by the preparation of porous polymer monoliths has been studied. The first step affords a thin grafted layer of polymer with a multiplicity of pendent double bonds that are then used in the second step for covalent attachment of the monolith to the wall. As clearly seen on scanning electron micrographs, this procedure prevents the formation of voids at the monolith-channel interface a problem that has always plagued approaches involving bulk polymerization in nontreated channels due to the shrinkage of the monolith during the polymerization process and its lack of compatibility with the material of the device. Irradiation with UV light through a photomask allows precise patterning specifying both the area subjected to surface modification and the location of the monolith within specific areas of the device.

Microfluidics↗

PubMed2003

Monolithic valves for microfluidic chips based on thermoresponsive polymer gels.

The direct preparation of thermoresponsive monolithic copolymers by photopatterning of a liquid phase consisting of an aqueous solution of N-isopropylacrylamide, N-ethylacrylamide, N,N'-methylenebisacrylamide, and 4,4'-azobis(4-cyanovaleric acid) has been studied and the products used as valves within the channels of microfluidic devices. The volume change associated with the polymer phase transition at its lower critical solution temperature (LCST) leads to the rapid swelling and the deswelling of the 2.5% cross-linked monolithic gel thus enabling the polymer to close or open the channel and to function as a nonmechanically actuated valve. The LCST at which the valve switches was easily adjusted within a range of 35 degrees C-74 degrees C by varying the proportions of the monovinyl monomers in the polymerization mixture. The closed valve holds pressures of up to 18 MPa without noticeable dislocation, structural damage, or leakage. In contrast, following deswelling by raising the temperature above LCST the valve offers no appreciable flow resistance since its large, micrometer-size pores are open. Laser-triggered photobleaching of a fluorescent dye contained in the liquid phase enabled monitoring of flow through the device and determination of the times required to open and close the valve. The valves are characterized by very fast actuation times in a range of 1-4 s depending on the type of device. No changes in performance were observed even after repeated open-close cycling of the valves.

Acrylamides↗

PubMed2002

Enzymatic microreactor-on-a-chip: protein mapping using trypsin immobilized on porous polymer monoliths molded in channels of microfluidic devices.

Enzymatic microreactors have been prepared in capillaries and on microfluidic chips by immobilizing trypsin on porous polymer monoliths consisting of 2-vinyl-4,4-dimethylazlactone, ethylene dimethacrylate, and acrylamide or 2-hydroxyethyl methacrylate. The azlactone functionalities react readily with amine and thiol groups of the enzyme to form stable covalent bonds. The optimized porous properties of the monoliths lead to very low back pressures enabling the use of simple mechanical pumping to carry out both the immobilization of the enzyme from its solution and the subsequent analyses of substrate solutions. The Michealis-Menten kinetic characteristics of the reactors were probed using a low molecular weight substrate: N-alpha-benzoyl-L-arginine ethyl ester. The effects of immobilization variables such as the concentration of trypsin in solution and percentage of azlactone functionalities in the monolith, as well as the effect of reaction time on the enzymatic activity, and of process variables such as substrate flow velocity and residence time in the reactor, were studied in detail. The proteolytic activity of the enzymatic microreactor on chip was demonstrated at different flow rates with the cleavage of fluorescently labeled casein used as a substrate. The excellent performance of the monolithic microreactor was also demonstrated with the digestion of myoglobin at the fast flow rate of 0.5 microL/min, which affords a residence time of only 11.7 s. The digest was then characterized using MALDI-TOF MS, and 102 out of 153 possible peptide fragments were identified giving a sequence coverage of 67%.

Animals↗

PubMed2002

Effect of multivalency on the performance of enantioselective separation media for chiral HPLC prepared by linking multiple selectors to a porous polymer support via aliphatic dendrons.

Chiral stationary phases (CSPs) containing L-proline indananilide chiral selectors attached through a multivalent dendritic linker to monodisperse macroporous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) beads have been prepared using two different approaches. The convergent method involves the preparation of ligands in solution and their subsequent attachment to the support. The divergent approach is based on the stepwise "on-bead" formation of the linker using methods that are typical of solid-phase synthesis. While the convergent CSPs feature well-defined ligands, their loading is relatively low. In contrast, the divergent technique affords CSPs with higher loading but with more limited control over precise ligand architecture. Excellent enantioselectivities characterized by separation factors of up to 31 were achieved for the separation of racemic N-(3,5-dinitrobenzoyl)-alpha-amino acid alkyl amides with these new CSPs under normal-phase HPLC conditions.

Alanine↗

PubMed2002

Polymeric monolithic stationary phases for capillary electrochromatography.

This review summarizes the contributions of a number of groups working in the rapidly growing area of monolithic columns for capillary electrochromatography (CEC), with a focus on those prepared from synthetic polymers. Monoliths have quickly become a well-established stationary phase format in the field of CEC. The simplicity of their in situ preparation method as well as the good control over their porous properties and surface chemistries make the monolithic separation media an attractive alternative to capillary columns packed with particulate materials. A wide variety of approaches as well as materials used for the preparation of the monolithic stationary phases are detailed. Their excellent chromatographic performance is demonstrated by numerous separations of different analytes.

Chromatography↗

PubMed2002

Capillary electrochromatography: a rapidly emerging separation method.

This overview concerns the new chromatographic method--capillary electrochromatography (CEC)--that is recently receiving remarkable attention. The principles of this method based on a combination of electroosmotic flow and analyte-stationary phase interactions, CEC instrumentation, capillary column technology, separation conditions, and examples of a variety of applications are discussed in detail.

Buffers↗

PubMed2002

Porous polymer monoliths: an alternative to classical beads.

Porous polymer monoliths are a new category of materials developed during the last decade. These materials are prepared using a simple molding process carried out within the confines of a closed mold. Polymerization of a mixture that typically contains monomers, free-radical initiator, and porogenic solvent affords macroporous materials with large through-pores that enable flow-through applications. The versatility of the preparation technique is demonstrated by its use with hydrophobic, hydrophilic, ionizable, and zwitterionic monomers. The porous properties of the monolith can be controlled over a broad range. These, in turn, determine the hydrodynamic properties of the devices that contain the molded media. Since all the mobile phase must flow through the monolith, the mass transport within the molded material is dominated very much by convection, and the monolithic devices perform well even at very high flow rates. The applications of monolithic materials are demonstrated on the chromatographic separation of biological compounds and synthetic polymers, electrochromatography, gas chromatography, enzyme immobilization, molecular recognition, and in advanced detection systems. Grafting of the pore walls with selected polymers leads to materials with completely changed surface chemistries.

Chromatography↗

PubMedDate not supplied

Chiral recognition: design and preparation of chiral stationary phases using selectors derived from ugi multicomponent condensation reactions and a combinatorial approach.

Combinatorial approaches together with high-throughput screening have been used to develop highly selective stationary phases for chiral recognition. Libraries of potential chiral selectors have been prepared by the Ugi multicomponent condensation reactions and screened for their enantioselectivity using the reciprocal approach involving a chiral stationary phase with immobilized model target compound N-(3,5-dinitrobenzoyl)-alpha-l-leucine. The best candidates were identified from the library of phenyl amides of 2-oxo-azetidineacetic acid derivatives. This screening also enabled specification of the functionalities of the selector desired to achieve the highest level of chiral recognition. The substituents of the phenyl ring adjacent to the chiral center of the selector candidates exhibited the most profound effect on the chiral recognition. The best candidate was then synthesized on a larger scale, resolved into single enantiomers using preparative enantioselective HPLC, and attached to porous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) beads via an ester linkage to afford the desired stationary phase. Selectivities alpha as high as 3.2 were found for the separation of a variety of amino acid derivatives.

Acetates↗

PubMedDate not supplied

High-throughput peptide mass mapping using a microdevice containing trypsin immobilized on a porous polymer monolith coupled to MALDI TOF and ESI TOF mass spectrometers.

An enzymatic microreactor with a volume of 470 nL has been prepared by immobilizing trypsin on a 10 cm long reactive porous polymer monolith located in a 100 microm i.d. fused silica capillary. This reactor affords suitable degrees of digestion of proteins even after very short residence times of less than 1 min. The performance is demonstrated with the digestion of eight proteins ranging in molecular mass from 2848 to 77 754. The digests were analyzed using mass spectrometry in two modes: off-line MALDI and in-line nanoelectrospray ionization. The large numbers of identified peptides enable a high degree of sequence coverage and positive identification of the proteins. The extent of sequence coverage decreases as the molecular mass of the digested protein increases.

Peptide Mapping↗