High mass clearance of autoantibodies from a murine model of lupus nephritis by immunoadsorption using star-configured polyethylene glycols

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.

Surface Grafting of PEO-Based Star-Shaped Molecules for Bioanalytical and Biomedical Applications

This article reviews surface grafting of star-shaped PEO. The use of star-shaped polymers is compared to linear PEO chains regarding the layer preparation and the ability of the resulting surfaces to resist protein adsorption. We then focus on the use of end-functionalized, star-shaped, PEO-based prepolymers that are able to form covalent crosslinks and functional polymer networks on the substrate. Examples are given for specific protein adsorption as well as for cell adhesion on such layers by covalent embedding of biofunctional molecules. The possibility of coating biomedically relevant polymer substrates in three-dimensional geometries is discussed and examples are shown for poly(ethylene terephthalate) monofilament constructs.

Synthesis, patterning and applications of star-shaped poly(ethylene glycol) biofunctionalized surfaces

Poly(ethylene) glycol (PEG) is an excellent material to modify surfaces to resist non-specific protein adsorption. Linear PEG has been extensively studied both theoretically and experimentally and it has been found that resistance of PEG-coated surfaces to protein adsorption depends mainly on the molecular weight of the polymer and the surface grafting density. End-functionalized star-shaped PEGs allow for interpolymer crosslinking to form a dense layer. An excellent example of such a system consists of a 6-arm PEG/PPG (4 : 1) star polymer functionalized with isocyanate using IPDI. The end functionalization may be further biofunctionalized to recognize specific biomolecules such as streptavidin, His-tagged proteins, amino-terminated oligonucleotides and cell receptors. This functionalization may be patterned into specific geometries using stamping techniques or randomly distributed by statistical reaction of the end group with the biofunctional molecule in solution. The surface preparation uses simple spin-, dip- or spray-coating and produces smooth layers with low background fluorescence. These properties, together with the advantageous chemical properties of PEG, render the surfaces ideal for immobilizing proteins on surfaces with detection limits down to the single molecule level. Proteins immobilized on such surfaces are able to maintain their folded, functional form and are able to completely refold if temporarily exposed to denaturing conditions. Immobilized enzyme molecules were able to perform their function with the same activity as the enzyme in solution. Future directions of using surfaces coated with such crosslinked star polymers in highly sensitive and robust biotechnology applications will be discussed.

Plasmaperfusion on triptophan columns can improve the clinical outcome of patients affected with myasthenia gravis

Myasthenia Gravis (MG) is a neuromuscular disease often associated with thymic pathology due to neuromuscular transmission impairment by circulating antibodies directed against the cholinergic postsynaptic receptor on the neuromuscular junction (Anti-AchR-Ab). The treatment of MG includes cholinesterase inhibitors, steroids and thymectomy. Plasmapheresis can remove Anti-AchR-Ab but more recently plasma-perfusion (PP), a more specific apheresis for selective removal of noxious plasma components, has been developed.

AIM OF THE STUDY

To study the effect of PP treatment, performed by using specific immunocolumns for Anti-AchR-Ab, on the clinical outcome of MG patients non-responder to steroid therapy or thymectomy.

MATERIALS AND METHODS

We treated 8 patients suffering from severe MG by a cycle of 6 sessions of PP. We used columns containing triptophan as a specific ligand for Anti-AchR-Ab. In order to evaluate the effectiveness of treatment we used functional tests (muscular tests, respiratory function, electromyography) and laboratory tests (Anti-AchR-Ab; immunoglobulins, complement fractions, immunocomplexes).

RESULTS

After one to three PP sessions, early clinical improvement in bulbar and respiratory symptoms were found in all patients and EMG showed improvement of neuromuscular transmission. Serum concentration of immunological markers decreased progressively and significantly during the treatment. Clinical improvements were progressive despite the tendency for Anti-AchR-Ab to reach initial values between one session and another. We observed no side effects due to the type of immunocolumns used.

CONCLUSIONS

Triptophan columns appear to be able to remove large quantities of Anti-AchR-Ab and immunological markers from plasma. Our experience shows that PP performed using triptophan columns in patients suffering from severe MG provides good clinical results, improving patients' outcome, without any risk linked to the procedure.

Survey of the year 2001 commercial optical biosensor literature

We have assembled references of 700 articles published in 2001 that describe work performed using commercially available optical biosensors. To illustrate the technology's diversity, the citation list is divided into reviews, methods and specific applications, as well as instrument type. We noted marked improvements in the utilization of biosensors and the presentation of kinetic data over previous years. These advances reflect a maturing of the technology, which has become a standard method for characterizing biomolecular interactions.