Plasma Polymerized Allylamine Research Articles

Synthesis of Allylamine Plasma Polymer Films: Correlation between Plasma Diagnostic and Film Characteristics

Synthesis of Allylamine Plasma Polymer Films: Correlation between Plasma Diagnostic and Film Characteristics

Plasma-polymerized multistacked bipolar gate dielectric for organic thin-film transistors

A 10-layer stack of bipolar gate dielectric was formed by sequential layer-by-layer deposition using pulsed radio frequency (RF) plasma polymerization of allylamine and vinyl acetic acid monomers. Due to polar groups localized at the interfaces between each consecutive layer by alternating amine (–NH 2) and carboxylic acid (–COOH) functional groups, a 60 nm thick multilayer structure demonstrated relatively high dielectric constant of 4.4 with extremely smooth and crack/pin-hole free surfaces. Without any post-deposition thermal annealing, a 10-layer stack of bipolar dielectric layers shows a low leakage current density (∼1 × 10 −6 A/cm 2 at 2 MV/cm) with high breakdown fields (>4 MV/cm). With a 10-layer stack of bipolar gate dielectrics, low supply voltage regioregular poly-(3-hexythiophene) (P3HT) organic thin-film transistors (OTFT) were tested. P3HT OTFTs demonstrated low-voltage operation and moderate field-effect mobility up to ∼3.4 × 10 −3 cm 2/V s in the saturation region with the drain voltage a −12 V. The threshold voltage in the saturation region and on–off current ratio were measured to be +1.4 V and ∼1.2 × 10 2, respectively.

Positively Charged Material Surfaces Generated by Plasma Polymerized Allylamine Enhance Vinculin Mobility in Vital Human Osteoblastss

AbstractSeveral studies suggest that the modification of an implant surface by chemical means plays an important role in bone tissue engineering. Previously we have shown that osteoblast cell adhesion and spreading can strongly be increased by a positively charged surface. Cell adhesion and migration are two vital processes that are completely dependent on coordinated formation of focal adhesions. Changes in the organization of the actin cytoskeleton and the focal adhesions are essential for numerous cellular processes including cell motility and tissue morphogenesis. We examined the mobility of the cytoskeletally associated protein vinculin on functionalized surfaces using plasma polymerized allylamine (PPAAm), a homogenous plasma polymer layer with randomly distributed amino groups. In living, GFP–vinculin transfected osteoblastic cells we determined a significant increase in vinculin mobility and vinculin contact length on PPAAm compared to collagen I coated surfaces during the initial adhesion phase. We suggest that positive charges control the cell physiology which seems to be dominant over the integrin receptor binding to collagen I. The results emphasize the role of the surface charge for the design of artificial scaffolds in bone repair.

Influence of the Solution on Adhesion Layer Polymerized in Radio Frequency Pulsed Plasma for DNA Hybridization Assay

A radio frequency (RF) pulsed plasma polymerized allylamine (PPPAA) film as an adhesion layer to adsorb DNA probe and then hybridize with a complementary or a mismatch DNA target is investigated in this paper. The possible application of plasma polymerization film as an adhesion layer for DNA hybridization assay is evaluated by DNA hybridization reactions. It was found, by surface plasmon enhanced fluorescence spectroscopy (SPFS), that the DNA hybridization reactions in phosphate buffered saline (PBS) solution can be remarkably revealed by fluorescence signals, but it heavily depends on the solution conditions. The influence of the solution pH value and the ionic strength on the PPPAA film thickness and adsorption is explored in detail.

Antibacterial surfaces by adsorptive binding of polyvinyl-sulphonate-stabilized silvernanoparticles

This paper presents a novel and facile method for the generation of efficient antibacterialcoatings which can be applied to practically any type of substrate. Silver nanoparticleswere stabilized with an adsorbed surface layer of polyvinyl sulphonate (PVS). This stericlayer provided excellent colloidal stability, preventing aggregation over periods of months.PVS-coated silver nanoparticles were bound onto amine-containing surfaces, here producedby deposition of an allylamine plasma polymer thin film onto various substrates. SEMimaging showed no aggregation upon surface binding of the nanoparticles; they were welldispersed on amine surfaces. Such nanoparticle-coated surfaces were found to be effective inpreventing attachment of Staphylococcus epidermidis bacteria and also in preventingbiofilm formation. Combined with the ability of plasma polymerization to apply the thinpolymeric binding layer onto a wide range of materials, this method appearspromising for the fabrication of a wide range of infection-resistant biomedical devices.

Clinical observations of biofouling on PEO coated silicone hydrogel contact lenses

Silicone hydrogel contact lenses, which have been a major advance in the field of vision correction, require surface modification or coatings for comfort and biocompatibility. While current coatings show adequate clinical performance, advanced coatings may improve the biocompatibility of contact lenses further by reducing biofouling and related adverse clinical events. Here, we have produced coatings on Lotrafilcon A contact lenses by deposition of a thin film of allylamine plasma polymer (ALAPP) as a reactive interlayer for the high density grafting of poly(ethylene oxide) dialdehyde (PEO(ALD) 2), which had previously shown complete resistance to protein adsorption in vitro. The performance of these contact lenses was evaluated in a controlled clinical study over 6 h using Focus ® Night and Day™ (also known as Air Optix ® Night & Day ®) contact lenses as control lenses. Surface modified lenses were characterised by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) before and after wear. Clinical data showed a high level of biocompatibility of the PEO coated lenses equivalent to control lenses. Surface analysis of worn contact lenses demonstrated that the high density PEO coating is effective in reducing biofouling in vivo compared to control lenses, however small amounts of protein deposits were still detected on all worn contact lenses. This study highlights that elimination of biofouling in vivo can be much more demanding than in vitro and discusses issues that are important for the analysis of worn contact lenses as well as the design of improved contact lenses.

Deposition of Functional Organic Thin Films by Pulsed Plasma Polymerization: A Joint Theoretical and Experimental Study

AbstractThe pulsed plasma polymerization of allylamine and cyclopropylamine is investigated to study the influence of the precursor chemical structure on the process selectivity toward the primary amine groups. Both systems are compared under similar mean powers injected in the discharges (Pmean). The results reveal an increase in the precursor fragmentation in the plasma and a decrease in the primary amine content of the film (%NH2) as Pmean increases. Nevertheless, below a critical Pmean value, different behaviors are observed depending on the precursor, cyclopropylamine being less plasma‐fragmented than allylamine. As a result, plasma polymer films (PPF) synthesized from cyclopropylamine yield the largest %NH2. These results are rationalized with the help of theoretical calculations pointing to a preferential opening of the cyclopropylamine ring structure. Cyclopropylamine activation in the plasma can thus be achieved without fragmentation reactions, leading to a more efficient incorporation of the NH2 group of the precursor in the PPF.magnified image

Plasma Surface Modification of 316L Stainless Steel for Cardiovascular Stent Coating

Coronary stents are metallic (316L stainless steel) devices employed during balloon angioplasty to reopen and prevent the re-obstruction of a diseased narrowed area within a coronary artery. To reduce restenosis rate, bare metal stent coating is a promising solution. The coating can act as an anticorrosive barrier against the aggressive properties of biological environment, improving the long-term safety of the device. The goal of this study is to develop a dry process to isolate metallic surface from the biological environment by depositing a thin plasma polymerized allylamine (CH2=CH-CH2-NH2) film on the metallic surface. Plasma polymerized allylamine films were deposited on flat electropolished 316L stainless steel samples in a low pressure plasma reactor (70 kHz). Chemical composition of the coatings has been analysed as a function of the discharge power and treatment time. Moreover, special attention has been paid on the stability of the coating after immersion during 24 hours in D.I. water. Finally, to mimic stent expansion conditions, a “small punch test” has been used to investigate the adhesive properties of the coating. Our results demonstrate that is possible to deposit a stable, cohesive and adhesive plasma polymerized allylamine thin film which can be used as a coating for cardiovascular stents

Osteoblast Sensitivity to Topographical and Chemical Features of Titanium

The titanium-osteoblast-interaction can be influenced both by surface roughness and by chemical modifications. We have ascertained that a positively charged titanium surface boosts osteoblast cells adhesion due to their negatively charged cellular hyaluronan coat. In current experiments, chemical surface modifications were combined with different topographies. Titanium disks of technical purity were modified (i) in their roughness by polishing (P), machining (M) and corundum blasting (CB), and (ii) by subsequently chemical functionalization by a thin film (d≤0.1 µm) of microwave plasma polymerized allylamine (PPAAm). In addition, collagen I was immobilized on PPAAm via the bifunctional linker polyethylene glycol diacid or glutar dialdehyde, respectively. The cell shape and material's contact of human osteoblasts was analyzed by FE-SEM and time dependent cell adhesion measured by flow cytometry. The cell dynamic of the adhesion component vinculin was observed in living cells. Amino-functionalization (PPAAm) considerably enhances the adhesion of osteoblasts in combination with topographical features, which was in contrast to collagen modified surfaces. PPAAm allows the cells to literally melt into the groove structure of the titanium. The bone cells lie over a large area and very close to the surface, so that the edges of the cells can hardly be distinguished from the structure of the surface. The combinatory effect of topography and plasma modification could improve bonding of the implant to the bone tissue.

Time-Dependent Metabolic Activity and Adhesion of Human Osteoblast-Like Cells on Sensor Chips with a Plasma Polymer Nanolayer

To improve orthopedic implant ingrowth, knowledge of the effect of chemical surface modifications on vital cell function in vitro is of importance. Early in our investigations we recognized that amino groups, positively charged via plasma polymerized allylamine, increased cell growth and the actin-filament formation in the initial cell-material contact phase. To gain insight into continuous vital cell behavior on this plasma polymer layer, here we present the metabolic activity of osteoblasts and their time-dependent adhesion using the sensor chip technology. We demonstrate a new method for continuous 24 hour-measurements with vital human osteoblast-like cells (MG-63, ATCC) on sensor chips (Bionas® SC 1000) modified with plasma polymerized allylamine (PPAAm). The PPAAm film deposited on the chip is a cross-linked, strongly fixed plasma polymer with relatively high amino functionality and well defined chemical surface composition. We assessed continuous cell adhesion and the metabolic activity, i.e., oxygen consumption and acidification. We determined that adhesion of vital cells on PPAAm is not only enhanced shortly (1 h) after cell seeding but remained continuously higher for 24 h, which is significant. This nanometer-thin PPAAm layer did not change the overall metabolic activity of MG-63 cells during 24 h. This tool--using adhesion and metabolic sensor chips--appears to be a suitable method for the recognition of vital cell physiology in biocompatibility measurements of plasma chemical treated surfaces.

Low-energy electrons and X-ray irradiation effects on plasma-polymerized allylamine bioactive coatings for stents

Radiation used in biomedical applications causes chemical changes to biomedical materials. This work is an ex situ simulation of the influence of low-energy electron (LEE) impact and X-ray irradiation on the chemical properties of plasma-polymerized allylamine (PPA) bioactive and biocompatible stent coatings. Preliminary X-ray photoelectron spectroscopy (XPS) results show that PPA coatings oxidize in contact with ambient air by the detection of C–O and C O bonds which are typical of polymer oxidation. Chemical changes after LEE and X-ray irradiation are mainly a loss of oxygen, assuming a surface deoxidizing and not a complete destruction of the surface. XPS survey analyses show that the amine groups remain stable during irradiation. LEE impact measurements by TOF mass spectrometry show that the main ionic losses are H − ions. It appears that CN groups are stable under irradiation and we observe a loss of hydrogen and oxygen as the main chemical modifications. In conclusion, these results suggest that PPA coatings are stable under biomedical radiation, and they can therefore be used for bioactive and biocompatible stent coatings.

Nanopores in Single- and Double-Layer Plasma Polymers Used for Cell Guidance in Water and Protein Containing Buffer Solutions

To investigate the behavior of plasma polymers in biomaterial applications, we studied plasma polymerized hexane (ppHex) and plasma polymerized allylamine (ppAAm) in pure, buffered, and protein containing aqueous solutions. We report for the first time on nanoscale pores formed on ppHex deposits upon exposure to water and surface blistering of ppHex deposited on ppAAm in water. We demonstrate that the nature of the solution influenced the feature formation. These studies are necessary to monitor the changes of the plasma polymer surfaces applied in cell guidance. The surface chemical and topographical data from single- and double-layer plasma polymer films were compared. We further demonstrate that the differences in surface chemistry and topography that develop during aqueous exposure between the single- and double-layer plasma polymer deposits do not affect the adhesion of cells to the surface. These novel nanostructured surfaces may prove useful as membranes or structured films in biotechnological applications.

Laser-based patterning for transfected cell microarrays

The spatial control over biomolecule- and cell-surface interactions is of great interest to a broad range of biomedical applications, including sensors, implantable devices and cell microarrays. Microarrays in particular require precise spatial control and the formation of patterns with microscale features. Here, we have developed an approach specifically designed for transfected cell microarray (TCM) applications that allows microscale spatial control over the location of both DNA and cells on highly doped p-type silicon substrates. This was achieved by surface modification, involving plasma polymerization of allylamine, grafting of poly(ethylene glycol) and subsequent excimer laser ablation. DNA could be delivered in a spatially defined manner using ink-jet printing. In addition, electroporation was investigated as an approach to transfect attached cells with adsorbed DNA and good transfection efficiencies of approximately 20% were observed. The ability of the microstructured surfaces to spatially direct both DNA adsorption and cell attachment was demonstrated in a functional TCM, making this system an exciting platform for chip-based functional genomics.

In vivo investigation of the inflammatory response against allylamine plasma polymer coated titanium implants in a rat model

Titanium (Ti) is an established biomaterial for bone replacement. However, facilitation of osteoblast attachment by surface modification with chemical groups could improve the implant performance. Therefore, this study aimed to evaluate the effect of a plasma polymerized allylamine (PPAAm) layer on the local inflammation in a rat model. Three series (RM76AB, RM78AB, RM77AB) of PPAAm-treated Ti plates were prepared using different plasma conditions. Twelve male LEW.1A rats received one plate of each series and one uncoated control plate implanted into the back musculature. After 7, 14 and 56 days, four rats were euthanized to remove the implants with surrounding tissue. Total monocytes/macrophages, tissue macrophages, T-cells and MHC-class-II-positive cells were morphometrically counted. On day 14, the macrophage/monocyte number was significantly higher for the controls than for the PPAAm samples. On day 56, the RM76AB and RM78AB samples had significantly lower numbers than RM77AB and the controls. The same was found for the tissue macrophages. No change over time and no differences between the implants were found for the T-cells. For the number of MHC-class-II-positive cells, a significant decrease was found only for the RM78AB implants between day 14 and day 56. Physico-chemical analysis of the PPAAm implants revealed that the RM77AB implants had the lowest water absorption, the highest nitrogen loss and the lowest oxygen uptake after sonication. These results demonstrate that the PPAAm samples and the controls were comparable regarding local inflammation, and that different plasma conditions lead to variations in the material properties which influence the tissue reaction.

Preparation and Multi‐Characterization of Plasma Polymerized Allylamine Films

AbstractPlasma polymerized allylamine (ppAA) films were deposited in a radio‐frequency glow discharge plasma reactor using a continuous‐wave mode and varying the discharge power from 15 to 125 W. The deposition rate reached 26 nm · min−1 and was constant within at least half an hour of process. The chemical structure and elemental composition of the deposited films were investigated by Fourier transform infrared and X‐ray photoelectron spectroscopies, whereas surface properties were analyzed by atomic force microscopy and surface free energy measurement. A special focus is given to the stability of ppAA in aqueous media and primary amine quantification. The use of fluorescent microscopy and UV‐Visible spectroscopy enabled us to detect and quantify the primary amine, respectively. All the studied parameters varied widely with enhanced power with a transition point around 50 W. Over this value, the results remain relatively unchanged.magnified image

Mechanical characterization of anti-infectious, anti-allergic, and bioactive coatings on orthopedic implant surfaces

In total joint replacement much effort has been made to reduce implant loosening. We investigated different implant coatings (copper integrated titanium dioxide (TiO2–Cu), titanium nitride (TiN), plasma polymerized allylamine (PPAAm), and calcium phosphate (CaP)) regarding the adhesion strength and wear resistance. Standardized scratch and adhesive tests were applied. Abrasive wear was measured with artificial bone and bone cement using a special testing machine. All tested coatings have higher bonding strengths than the 22 N/mm2 required for medical implant surface coatings by ASTM standard 4711-F. Using bone cement, wear testing revealed higher wear rates in most cases. Polished surfaces reduce the amount of wear, whereas rough surfaces highly increase the wear rate due to three-body wear, especially ceramic surfaces. In general, the application of bone cement in conjunction with modified implant surfaces can lead to an increase in wear rate.

Covalent attachment of trypsin on plasma polymerized allylamine

This paper focuses on the immobilization of a proteolytic enzyme, trypsin, on plasma polymerized allylamine (ppAA) films. The later have been deposited onto silicon substrate by means of radiofrequency glow discharge. The covalent attachment of the enzyme was achieved in three steps: ( i) activation of the polymer surface with glutaraldehyde (GA) as a linker, ( ii) immobilization of trypsin and ( iii) imino groups reduction treatment. The effects and efficiency of each step were investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Fluorescent spectroscopy was used to evaluate the change of the biological activity following the immobilization steps. The results showed that enzyme immobilization on GA-modified substrate increases the enzyme activity by 50% comparing to adsorbed enzymes, while the imino reduction treatment improves the enzyme retention by about 30% comparing to untreated samples. In agreement with XPS and AFM data, UV–vis absorption spectroscopy, used to quantify the amount of immobilized enzyme, showed that allylamine plasma polymer presents a high adsorption yield of trypsin. Although the adsorbed enzymes exhibit a lower activity than that measured for enzymes grafted through GA linkers, the highest catalytic activity obtained was for the enzymes that underwent the three steps of the immobilization process.

Multifunctional Polymer Coatings for Cell Microarray Applications

Biocompatible coatings with suitable chemistries for the immobilization of biomolecules are increasingly in demand, as they can be applied in a wide range of biomedical applications. In particular, multifunctional polymer coatings displaying reactive functional groups for the immobilization of specific biological factors that can influence the cellular response while at the same time exhibiting low nonspecific protein adsorption and cell attachment properties have the potential to significantly advance the fields of biomaterials and regenerative medicine. In this study, multifunctional polymer surface chemistries were developed for a cell microarray application with the aim of screening cellular interactions with surface immobilized factors. Coatings were prepared by the deposition of an allylamine plasma polymer pinning layer followed by the deposition of random copolymers of glycidyl methacrylate (GMA) and poly(ethylene glycol) methacrylate (PEGMA). Coatings were characterized by X-ray photoelectron spectroscopy (XPS), infrared spectroscopy, ellipsometry, and contact angle measurements. A variety of proteins as well as synthetic polymers were printed onto copolymer-coated slides using a high-precision contact microarrayer. Printing conditions were optimized for a fluorescently labeled model protein in regard to the temperature, humidity, pin geometry, concentration, and pH of the printing solution. Finally, the suitability of the surface chemistry for the evaluation of cellular responses to surface immobilized factors in a microarray format was demonstrated using HeLa cells.

The support of neural stem cells transplanted into stroke-induced brain cavities by PLGA particles

Stroke causes extensive cellular loss that leads to a disintegration of the afflicted brain tissue. Although transplanted neural stem cells can recover some of the function lost after stroke, recovery is incomplete and restoration of lost tissue is minimal. The challenge therefore is to provide transplanted cells with matrix support in order to optimise their ability to engraft the damaged tissue. We here demonstrate that plasma polymerised allylamine (ppAAm)-treated poly( d, l-lactic acid- co-glycolic acid) (PLGA) scaffold particles can act as a structural support for neural stem cells injected directly through a needle into the lesion cavity using magnetic resonance imaging-derived co-ordinates. Upon implantation, the neuro-scaffolds integrate efficiently within host tissue forming a primitive neural tissue. These neuro-scaffolds could therefore be a more advanced method to enhance brain repair. This study provides a substantial step in the technology development required for the translation of this approach.

Synthesis of Allylamine Plasma Polymer Films: Correlation between Plasma Diagnostic and Film Characteristics

AbstractPrimary amine‐based plasma polymer films (NH2‐PPF) were synthesized using plasma polymerization of allylamine in continuous wave (CW) and pulsed radio‐frequency (RF) modes. Plasma chemistry, studied by residual gas analysis mass spectrometry, revealed that the precursor fragmentation is a function of the equivalent power (Peq) dissipated in the discharge, independently of the plasma mode used. X‐ray photoelectron spectroscopy combined with time‐of‐flight secondary ion mass spectrometry suggests as the precursor fragmentation in the plasma increases: (i) a decrease of the primary amine concentration in the NH2‐PPF (%NH2) and (ii) an increase of the cross‐linking degree. For a given Peq, similar to the precursor fragmentation in the plasma, the NH2‐PPF characteristics were found to be independent of the plasma mode used. Therefore, the main advantage of using pulsed RF processes over CW ones is the possibility to work at very low Peq which enables low precursor fragmentation, optimization of %NH2, and reduction of the film cross‐linking degree. The chemical composition and the cross‐linking degree of the NH2‐PPF synthesized by allylamine plasma polymerization can thus be tailored by adjusting the equivalent RF power injected in the plasma.magnified image