Michaela Müller

Plasma functionalization of polypropylene with acrylic acid

Tailor-made surfaces of polymer materials are required, e.g. for the improvement of their printability or adhesion and for many applications concerning medical equipment or life science products. Polypropylene (PP) is one of the few common polymers widely used in technical applications. But often the surface chemistry has to be modified by introducing special chemical functionalities like carboxylic groups or by coating the PP with thin films, e.g. with poly(acrylic acid). The radio frequency plasma technique was used for functionalization and coating of PP by using acrylic acid as monomer gas. After optimization of the plasma parameters, high concentration of carboxylic groups as well as solvent-stable thin films with good adhesion to the PP substrates could be obtained. Characterization of the plasma-modified PP substrates was performed by using the captive bubble method, ESCA (Electron Spectroscopy for Chemical Analysis) and fluorescence spectroscopy in combination with derivatization techniques and FTIR (Fourier Transformation Infrared Spectroscopy). The thickness of the polymer films was analyzed by AFM (Atomic Force Microscopy).

Plasma grafting : a method to obtain monofunctional surfaces

Tailor-made surfaces are needed for many applications concerning medical equipment or life-science polymer material. The polymers should only reveal one type of functionality (carboxyl groups), homogeneously distributed with a defined density over their total surface. Many attempts have been made to obtain those monofunctional surfaces on polymers via plasma treatments. The commonly used plasma treatment (with oxygen) results in a host of different functionalities often with a low stability. The latter is caused by damaging processes also occuring during the plasma treatment (fragmentation by charged particle bombardment or radiation damage). Therefore, it is desirable to minimize or, if possible, to completely avoid these effects. In principle, two kinds of strategies are used: first, minimising the applied energy (e.g. use of low power or pulsed powered plasmas) and minimising the kind and density of damaging particles during treatment in the plasma; second, separating substrate functionalisation from plasma in space (down stream) or in time (grafting). Both methods lead to a more homogenous distribution of functionalities and a better retention of the precursor structure. The aim of this contribution is to give a comparison of several approaches to produce homogeneously finished polymer surfaces. Attention is focused on plasma grafting. As substrate, polypropylene is chosen because of its widespread applications and its simple chemical composition, which makes observation of grafting yields easy to analyse. As functional groups, hydroxyl, carboxyl and epoxy groups are chosen. These are introduced by direct plasma treatment and also by grafting methods. Functional groups are observed by ESCA and IR measurements. The influence of the gases used to activate the polymer surface for grafting carboxyl groups is also discussed.

Glow-discharge treatment for the modification of textiles

Abstract Increased requirements on the finishing of textile products like environmental protective production, new kinds of synthetic fibers and, above all, optimized surface properties, demand innovative production technics. The advantages of the glow discharge treatment have been well known in the laboratories for a long time. Nevertheless, this technique is hardly used in the textile industry. This can be due to less knowledge about the semicontinous and continous plasma-finishing of textiles as well as an insufficent permanence of the achieved properties. On the example of water and oil repellence finishing, the optimization of the experimental parameter has been made. It can be shown that only dry textiles enables a good hydrophobic finishing. This is due to the water desorption which leads to changes of the gas phase composition. Oleophobic finishing with wash permanence could be obtained by using perfiuoroacrylates.

Plasma aminofunctionalisation of PVDF microfiltration membranes: comparison of the in plasma modifications with a grafting method using ESCA and an amino-selective fluorescent probe

Microfiltration membranes of polyvinylidenefluoride (PVDF) are promising materials for the development of functional polymeric membranes. The aim of this work is the investigation of typical plasma processes such as continuous plasma, pulse plasma and plasma graft polymerisation concerning their effect of functionalisation with primary amino groups using a mixture of nitrogen and hydrogen, ammonia, allylamine and diaminocyclohexane. The relative amounts of surface-incorporated nitrogen and primary amino groups are determined using electron spectroscopy and the binding of a selective fluorescent probe (Atto Tag FQ). No correlation of the relative amount of surface-bound nitrogen, determined by ESCA, and the relative amount of primary amino groups, determined with Atto Tag FQ, is found. The interpretation of the chemical shift of nitrogen with ESCA is limited. This is due to the unknown ionisation states of the primary amino groups resulting in peak shifts and their overlap with various other nitrogen compounds. The comparison of experiments performed with the same electric energy input but different powers show that the formation of primary amino groups on the surface of PVDF is higher, the lower the power of the plasma is. The formation of primary amine groups is maximised when a grafting method is applied. We explain this phenomenon as a fragmenting plasma effect. This results in an increased abstraction of hydrogen at higher plasma intensities and an augmented formation of a greater variety of nitrogen compounds. Furthermore the effectiveness of diaminocyclohexane as precursor is higher than allylamine, resulting in a higher grafting density.

Nano-hydroxyapatite-coated metal-ceramic composite of iron-tricalcium phosphate: Improving the surface wettability, adhesion and proliferation of mesenchymal stem cells in vitro

Thin radio-frequency magnetron sputter deposited nano-hydroxyapatite (HA) films were prepared on the surface of a Fe-tricalcium phosphate (Fe-TCP) bioceramic composite, which was obtained using a conventional powder injection moulding technique. The obtained nano-hydroxyapatite coated Fe-TCP biocomposites (nano-HA-Fe-TCP) were studied with respect to their chemical and phase composition, surface morphology, water contact angle, surface free energy and hysteresis. The deposition process resulted in a homogeneous, single-phase HA coating. The ability of the surface to support adhesion and the proliferation of human mesenchymal stem cells (hMSCs) was studied using biological short-term tests in vitro. The surface of the uncoated Fe-TCP bioceramic composite showed an initial cell attachment after 24h of seeding, but adhesion, proliferation and growth did not persist during 14 days of culture. However, the HA-Fe-TCP surfaces allowed cell adhesion, and proliferation during 14 days. The deposition of the nano-HA films on the Fe-TCP surface resulted in higher surface energy, improved hydrophilicity and biocompatibility compared with the surface of the uncoated Fe-TCP. Furthermore, it is suggested that an increase in the polar component of the surface energy was responsible for the enhanced cell adhesion and proliferation in the case of the nano-HA-Fe-TCP biocomposites.

Oligonucleotide and Parylene Surface Coating of Polystyrene and ePTFE for Improved Endothelial Cell Attachment and Hemocompatibility

In vivo self-endothelialization by endothelial cell adhesion on cardiovascular implants is highly desirable. DNA-oligonucleotides are an intriguing coating material with nonimmunogenic characteristics and the feasibility of easy and rapid chemical fabrication. The objective of this study was the creation of cell adhesive DNA-oligonucleotide coatings on vascular implant surfaces. DNA-oligonucleotides immobilized by adsorption on parylene (poly(monoaminomethyl-para-xylene)) coated polystyrene and ePTFE were resistant to high shear stress (9.5 N/m2) and human blood serum for up to 96 h. Adhesion of murine endothelial progenitor cells, HUVECs and endothelial cells from human adult saphenous veins as well as viability over a period of 14 days of HUVECs on oligonucleotide coated samples under dynamic culture conditions was significantly enhanced (P < 0.05). Oligonucleotide-coated surfaces revealed low thrombogenicity and excellent hemocompatibility after incubation with human blood. These properties suggest the suitability of immobilization of DNA-oligonucleotides for biofunctionalization of blood vessel substitutes for improved in vivo endothelialization.

Side chain thiol-functionalized poly(ethylene glycol) by post-polymerization modification of hydroxyl groups: synthesis, crosslinking and inkjet printing

Polymers with a poly(ethylene glycol) backbone and mercaptomethyl side chains were synthesized by post-polymerization modification of hydroxymethyl side chains in three steps. As the starting point of the synthetic route, linear copolymers of ethylene oxide and glycidol with molar contents of glycidol repeating units of approximately 20, 40, 60, 80 and 100% were used. The polymer-bound hydroxyl groups were converted to thiol groups in three steps, comprising tosylation, introduction of a triphenylmethyl protected thiol and thiol deprotection by acid treatment. The degree of thiol-functionalization was controlled by the degree of functionalization of the starting material. The degree of conversion of hydroxyl groups to thiol groups determined by 1H NMR spectroscopy was quantitative for copolymers with approximately 20 and 40% glycidol repeating units and 92, 81 and 87% for copolymers with approximately 60, 80 and 100% glycidol repeating units, respectively. Exemplarily, poly(glycidylthiol) obtained by conversion of poly(glycidol) was crosslinked with poly(ethylene glycol) diacrylate (PEG-DA) to yield hydrogels which supported adhesion and proliferation of human fibroblasts 48 h after cell seeding. Spatially defined and surface attached gel structures were fabricated by subsequent inkjet printing of poly(glycidylthiol) and PEG-DA solutions onto acrylated glass slides.

Plasma polymerization and grafting of ethylene oxide on polysiloxane surfaces.

Polysiloxane films were prepared by plasma polymerization and dip coating. Upon these films PEG was grafted by conventional methods, and ethylene oxide by plasma activation. Before and after grafting the films were analyzed by contact angle and ESCA measurements as well as by FTIR-ATR-spectroscopy and TOF-SIMS. Furthermore results of protein adsorption measurements are reported. The polysiloxane structures obtained by the plasma polymerization of HMDSO are rather similar to those ones yielded by dip coating. The two types of grafting applied on the polysiloxane substrates led to different structures of the grafted layers as was revealed by TOF-SIMS spectra.

Reconstitution of the membrane protein OmpF into biomimetic block copolymer–phospholipid hybrid membranes

Summary Structure and function of many transmembrane proteins are affected by their environment. In this respect, reconstitution of a membrane protein into a biomimetic polymer membrane can alter its function. To overcome this problem we used membranes formed by poly(1,4-isoprene-block-ethylene oxide) block copolymers blended with 1,2-diphytanoyl-sn-glycero-3-phosphocholine. By reconstituting the outer membrane protein OmpF from Escherichia coli into these membranes, we demonstrate functionality of this protein in biomimetic lipopolymer membranes, independent of the molecular weight of the block copolymers. At low voltages, the channel conductance of OmpF in 1 M KCl was around 2.3 nS. In line with these experiments, integration of OmpF was also revealed by impedance spectroscopy. Our results indicate that blending synthetic polymer membranes with phospholipids allows for the reconstitution of transmembrane proteins under preservation of protein function, independent of the membrane thickness.

The Emptying Behavior of Highly Viscous Liquids. Part I: Polymeric Surfaces and Plasma Coatings

Abstract Residues of fill goods on the inner side of packages are a problem not only from the economical point of view but also from an ecological perspective. For example, the cost of recycling increases with increasing amount of residues. Another point is the consumer satisfaction that declines when too much product remains in the package. The compositions of products as well as the packaging material have been optimized to provide specific characteristics, e.g., a particular taste or temperature resistance in case of viands, and, e.g., mechanical properties in case of packages. To achieve good anti-adhesive quality between such optimized systems one possible approach is to minimize adhesion forces between the inner side of the package and the fill good. This can be achieved by modifying the packages surfaces, e.g., by the use of plasma enhanced chemical vapor deposition (PECVD) with which deposition of defined nano-scale layers is possible. In this work plasma polymer coatings are compared with standard packaging material (PET) and typical anti-adhesive materials like PTFE with regard to emptying properties, surface free energy and work of adhesion. It will be shown that a low surface free energy is important for minimizing the residue. These low energetic surfaces can be designed by PECVD using two different chemical classes (PTFE- and silicone- analogous). The results show that besides surface free energy other physical-chemical characteristics of the packaged system influence the macroscopic amount of adhered fill goods.