Grafting | EPFL Graph Search

Grafting or graftage is a horticultural technique whereby tissues of plants are joined so as to continue their growth together. The upper part of the combined plant is called the scion (ˈsaɪən) while the lower part is called the rootstock. The success of this joining requires that the vascular tissues grow together. The natural equivalent of this process is inosculation. The technique is most commonly used in asexual propagation of commercially grown plants for the horticultural and agricultural trades. The scion is typically joined to the rootstock at the soil line; however, top work grafting may occur far above this line, leaving an understock consisting of the lower part of the trunk and the root system. In most cases, the stock or rootstock is selected for its roots and the scion is selected for its stems, leaves, flowers, or fruits. The scion contains the desired genes to be duplicated in future production by the grafted plant. In stem grafting, a common gr

Surface modification of PES virus filtration membrane

Claire Roulin

Virus filtration by size exclusion is a robust means of eliminating viruses in blood or pharma products. Porous polymer membranes with a narrow size distribution are used to allow passage of the protein product but retain viruses. The chosen polymer must resist process-induced physical and chemical wear and is therefore generally inert and hydrophobic material. When filtrating potentially heterogeneous products such as IgG from pooled blood samples, protein adsorption on the polymer surface causes high fouling. This eventually blocks the filter and reduces total filtration volume. A solution to this adsorption problem is to graft a hydrophilic gel-like polymer layer on the membrane inner surface to reduce protein adsorption. The surface properties are thus changed while retaining the stability of the bulk polymer. The grafting was initiated with an electron beam, which creates free radicals by unspecific scission of the polymer backbone through electron irradiation. Two acrylate monomers were used for polymerization, a monofunctional monomer and a bifunctional one, used as a crosslinker to form the gel structure. Two different grafting method were tested. The first grafting method is simultaneous grafting, where the membrane is impregnated with the monomer solution then irradiated. Initiation and polymerization thus occur almost simultaneously. The grafted membrane properties were assessed using flow measurements, protein adsorption tests, FTIR absorbance measurements, virus retention tests and filter integrity tests. Comparing the various grafting approaches, it can be seen that simultaneous grafting lowers considerably protein adsorption, to the price of a highly reduced buffer flow. These filters therefore run slowly but can process more volume before fouling. The sequential grafting method using peroxides as initiators did not show significant filtration improvements compared to the reference membrane when the solution with monomer and crosslinker was used. However, when only monofunctional monomer was used for peroxidation grafting, the protein filtration capacity was increased with limited buffer flow loss. Generally, the sequential method is interesting for graft polymerization of porous membranes because it allows higher degree of grafting and the versatile grafting parameters involved give many development options depending on the application

2010

Silicone elastomer stamp with hydrophilic surfaces and method of making same

Emmanuel Delamarche, Christian Donzel, Bruno Michel, Heiko Wolf

A method for fabricating silocone elastomer stamps with hydrophilic surfaces is provided. The concept of polymer grafting is used to produce the stamps. The stamps thus produced have the great advantage that grafting of a thin hydrophilic polymer on a hydrophobic PDMS surface can render PDMS stamps permanently hydrophilic. With such stamps it becomes possible to print aqueous or highly polar inks reproducibly over days and weeks.

2002

Tuning the Properties of Hydrogel Microspheres by Adding Chemical Cross-linking Functionality to Sodium Alginate

Françoise Borcard, Léo Bühler, Virginia Crivelli, Sandrine Gerber, Redouan Mahou, François Rémi Pierre Noverraz, Solène Marcelle Françoise Marie Passemard, Christine Wandrey

Two novel types of hydrogel microspheres (MS) are presented. First, one-component microspheres (1-comMS) were produced from sodium alginate (Na-alg) equipped with thiolfunctionalized hydroxyl groups. The functionalization pathway included the conversion of Na-alg into tetrabutylammonium alginate, insertion of new carboxyl groups, grafting of α-amine-ω- thiol poly(ethylene glycol), and restoration of the sodium salt. This modification conserves all original carboxyl groups of Na-alg and allows for covalent disulfide bond formation in addition to ionic cross-linking. Second, two-component microspheres (2-comMS) were obtained from a mixture of Na-alg and Na-alg functionalized with cysteamine. This functionalization was achieved by grafting cystamine dihydrochloride on some carboxyl groups followed by the reduction to cysteamine. Using the one-step MS formation process developed for both MS types, very fast ionic gelation with calcium ions conserves the spherical shape of the polymer solution droplets upon extrusion into the gelation bath, while simultaneously occurring slow covalent cross-linking reinforces the hydrogels. The physical properties of both MS types are adjustable by varying the polymer concentration, the degree of grafting, and the mixing ratio. In vitro cell microencapsulation studies confirmed the cytocompatibility of 1-comMS and 2-comMS.

American Chemical Society2015

Surface modification of PES virus filtration membrane

Claire Roulin

2010