Biomedical subjects

Martin Moeller

Publications and source records attributed to Martin Moeller.

9 recordsLinked to original sources

PubMed2006

Blood cell and plasma protein repellent properties of star-PEG-modified surfaces.

The implantation of biomaterials, medical devices or prostheses can instigate a rejection response or initiate an undesirable adsorption of plasma proteins, as well as blood cells on the implant surface, thus triggering diverse defense mechanisms against the supposed pathologic invader. The extent of this inflammatory reaction depends in part on the biocompatibility of the used materials or coatings. Although adsorption and coagulation responses can appear during the total in vivo lifetime of the implant, they are initially and crucially formed within the first 2-4 weeks of implantation. This early phase is of decisive importance for the consecutive in-growth and healing process. The present study was intended to elucidate the effects of blood contact to surfaces modified with reactive six-arm star-shaped poly(ethylene glycol-stat-propylene glycol) pre-polymers (Star PEG). Taken together, for Star-PEG-covered substrates we could demonstrate a profound reduction of various blood-biomaterial interactions compared to non-coated substrates, indicating the promising potential of this material as future coating for biomaterials with blood contact.

Adsorption↗

PubMed2005

A novel star PEG-derived surface coating for specific cell adhesion.

In this study a novel approach for the coating and functionalization of substrates for cell culture and tissue engineering is presented. Glass, silicon, and titanium panes were coated with an ultrathin film (30 +/- 5 nm) of reactive star-shaped poly(ethylene glycol) prepolymers (Star PEG). Homogeneity of the films was checked by optical microscopy and scanning force microscopy. These coatings prevent unspecific protein adsorption as monitored by fluorescence microscopy and ellipsometry. In order to allow specific cell adhesion the films were modified with linear RGD peptides (gRGDsc) in different concentrations. After sterilization, fibroblast, SaOS, and human mesenchymal stem cells (hMSC) were seeded on these substrates. Cell adhesion, spreading, and survival was observed for up to 30 days on linear RGD peptide (gRGDsc)-modified coatings, whereas no cell adhesion could be detected on unmodified Star PEG layers. By variation of the RGD concentration within the film the amount of cells that became adhesive could be controlled. When differentiation conditions are used for cultivation of hMSCs the cells show the expression of osteogenic marker genes after 14 days which is comparable to cultivation on cell culture plastic. Thus, the Star PEG/RGD film did not negatively influence the differentiation process. The high flexibility of the system considering the incorporation of biologically active compounds opens a broad field of future experiments.

Adult↗

PubMed2005

Ultrathin coatings from isocyanate terminated star PEG prepolymers: patterning of proteins on the layers.

This study presents the easy and fast patterning of low molecular weight molecules that act as binding partners for proteins on Star PEG coatings. These coatings are prepared from isocyanate terminated star shaped prepolymers and form a highly cross-linked network on the substrate in which the stars are connected via urea groups and free amino groups are present. Streptavidin has been patterned on these layers by microcontact printing (muCP) of an amino reactive biotin derivative and consecutive binding of streptavidin to the biotin. Patterns of Ni(2+)-nitriltriacetic acid (NTA) receptors have been prepared by printing amino functional NTA molecules in freshly prepared Star PEG layers that still contain amino reactive isocyanate groups. Complexation of the NTA groups with Ni(II) ions enabled the binding of His-tag enhanced green fluorescent protein (EGFP) in the desired pattern on the substrates. Since the unmodified Star PEG layers prevent unspecific protein adsorption, His-EGFP could selectively be bound to the sample by immersion into crude, nonpurified His-tag EGFP containing cell lysate.

Biotin↗

PubMed2005

Self-assembly of the perfluoroalkyl-alkane F14H20 in ultrathin films.

Scanning force microscopy on monomolecular films of eicosylperfluorotetradecane, F(CF(2))(14)(CH(2))(20)H, on mica, silicon oxide, or water revealed spontaneous organization to well-defined nanoscopic ribbon and spiral or toroidal superstructures. Whether ribbons or nanospirals were formed depended on the solvent from which the molecular monofilm was cast. Ribbons were observed when a hydrocarbon or a perfluorocarbon solvent was used, e.g., decalin or perfluorodecalin. When the compound, however, was deposited from nonselective hexafluoroxylene, the molecules assembled into spirals of defined size. The spirals/toroids transformed to ribbons when exposed either to decalin or perfluorodecalin vapor, and the ribbons transformed to toroids when exposed to hexafluoroxylene vapor. These changes could be observed in situ. Scanning force microscopy yielded an identical height and width for the bands forming the spirals and for the parallel flat ribbons. X-ray reflectivity yielded a height of 3.61 +/- 0.05 nm, again identical for both morphologies. Yet, the length of the extended F(CF(2))(14)(CH(2))(20)H molecule, i.e., 4.65 nm, exceeds the layer thickness obtained from X-ray reflectometry. It is, however, consistent with an arrangement where the fluorinated chains are oriented normal to the surface layer and where the alkyl segments are tilted with a 122 degrees angle between the two segments. Within the plane defined by the tilt, this angle allows a dense packing of the alkyl segments compensating for the larger cross-section of the fluorocarbon segment. The tilt plane defines an "easy" direction along which the monolayer structure can preserve order. In the plane perpendicular to this axis, long-range ordered dense packing of the alkyl chains is not possible. Incommensurable packing can in principle explain the finite and regular width of the ribbons and the stepwise turn in the spirals.

Journal Article↗

PubMed2005

Ultrathin coatings from isocyanate-terminated star PEG prepolymers: layer formation and characterization.

In this study we present the preparation of thin and ultrathin coatings from six-arm star-shaped isocyanate-terminated prepolymers on amino-functionalized silicon wafers. The backbone of the stars is a statistical copolymer of ethylene oxide and propylene oxide in the ratio 80:20 (Star PEG). Film preparation by spin coating from aqueous THF resulted in a variety of film morphologies that are determined by the water content of the solvent. Water is indispensable for activation of the isocyanate-terminated stars in solution and for proper cross-linking of the coatings on the substrate. This cross-linking results in a dense network of PEG chains on the substrate linked via urea groups with a mesh size of the network that corresponds to the arm length of the stars. Layer thickness variations between 3 and 500 nm revealed a strong dependence of the contact angle with water on the layer thickness which is explained by the chemical composition of the coatings. Due to the high functionality of the star-shaped prepolymers, free amino groups remain in the films that were detected by fluorescence microscopy after reaction with 4-chloro-7-nitrobenzofurazan (NBF). To test the system for the ability to prevent unspecific interaction with proteins, adsorption of fluorescence-labeled avidin was examined with fluorescence microscopy. For layer thicknesses between 3 and 50 nm, no protein adsorption could be detected.

Journal Article↗

PubMed2005

Nanostructured ordering of fluorescent markers and single proteins on substrates.

Highly ordered hexagonal nanopatterns of gold clusters on glass substrates were used as anchoring points for the specific attachment of fluorescence dyes and proteins labeled with fluorescence dyes. Thiol- or disulfide-containing linker molecules were used for the binding to the gold dots. In order to ensure specific binding on the gold dots only, the surface area in between the dots was protected against unspecific adsorption. For the attachment of polar low-molecular-weight fluorescence dyes, an octadecyltrichlorosilane self-assembled monolayer was prepared on the surface in between the gold dots, whereas a layer prepared from star-shaped poly(ethylene oxide-stat-propylene oxide) prepolymers was used to prevent unspecific adsorption of proteins between the gold dots. Fluorescence microscopy proved the specific binding of the dyes as well as of the proteins. Scanning force microscopy studies show that each gold dot is only capable of binding one protein at a time.

Avidin↗

PubMed2003

Measuring molecular weight by atomic force microscopy.

Absolute-molecular-weight distribution of cylindrical brush molecules were determined using a combination of the Langmuir Blodget (LB) technique and Atomic Force Microscopy (AFM). The LB technique gives mass density of a monolayer, i.e., mass per unit area, whereas visualization of individual molecules by AFM enables accurate measurements of the molecular density, i.e., number of molecules per unit area. From the ratio of the mass density to the molecular density, one can determine the absolute value for the number average molecular weight. Assuming that the structure of brush molecules is uniform along the backbone, the length distribution should be virtually identical to the molecular weight distribution. Although we used only brush molecules for demonstration purpose, this approach can be applied for a large variety of molecular and colloidal species that can be visualized by a microscopic technique.

Journal Article↗

PubMed2002

Optimizing the technique of contrast transcranial Doppler ultrasound in the detection of right-to-left shunts.

BACKGROUND AND PURPOSE: A cardiac right-to-left shunt (RLS) can be identified by transesophageal echocardiography and transcranial Doppler ultrasound (TCD) with contrast agents and a Valsalva maneuver (VM) as a provocation procedure. This article applies the modalities of these tests detailed in previous studies to a large patient cohort and compares 2 contrast agents (saline and Echovist-300). METHODS: Eighty-one patients were investigated by both transesophageal echocardiography and bilateral TCD of the middle cerebral arteries. The following protocol with injections of 10 mL agitated saline was applied in a randomized way: (1) no VM, (2) VM for 5 seconds starting 5 seconds after the beginning of contrast injection, and (3) repetition of the test with VM if the first test with VM was negative. The VM was performed for 5 seconds starting exactly 5 seconds after the beginning of saline injection. Thereafter, the same protocol was repeated with 10 mL Echovist-300 instead of saline. RESULTS: Thirty-one patients had a cardiac RLS. The Echovist-300 investigation disclosed all these 31 shunts, but saline disclosed only 29 of them. Twenty-two had an RLS only in at least 1 of the above TCD tests, some of them even with a considerable shunt volume. CONCLUSIONS: Contrast TCD performed with Echovist-300 but not with saline yields a 100% sensitivity to identify transesophageal echocardiography-proven cardiac RLSs. The TCD test should be repeated if negative the first time. This article gives detailed information for the optimization of the contrast TCD technique. Extracardiac shunts detected only during contrast TCD can have a considerable shunt volume and may allow for paradoxical embolism.

Adult↗

PubMedDate not supplied

Ultrathin functional star PEG coatings for DNA microarrays.

In this study, star PEG coatings on glass substrates have been used as support material for oligonucleotide microarrays. These coatings are prepared from solutions of six armed star shaped prepolymers that carry reactive isocyanate endgroups. As described earlier, such films prevent the adsorption of proteins and the adhesion of cells but can easily be functionalized for specific biological recognition. Here we used the high functionality of these coatings for the covalent immobilization of amino terminated 20mer oligonucleotides, both by microcontact printing and spotting techniques. The permanent immobilization of fluorescently labeled DNA as well as hybridization of 20mer oligonucleotides have been monitored by fluorescence microscopy. The hybridization efficiency as determined by fluorescence intensity varied from 30% to 80% depending on the way of layer preparation. The direct spotting without additional activation and blocking steps of the surface demonstrates the potential of star PEG coatings as ultrathin surface modification for microarrays.

Base Sequence↗