Plasma Polymerized Allylamine Research Articles

Construction of Polyfunctional Coatings Assisted by Gallic Acid to Facilitate Co-Immobilization of Diverse Biomolecules

Designing a multifunctional surface based on the coimmobilization of two or more diverse biomolecules with synergic action is very important in certain cases. In this work, a facile method by two-step aimed to construct a polyfunctional coating containing -COOH, -NH2, and phenol/quinine groups was reported. The first-step was to introduce amine groups onto target modified-surface by coating with plasma polymerized allylamine (PPAam), followed by the second-step conjugation of gallic acid (3,4,5-trihydroxybenzoic acid) onto the PPAam surface. The density of -COOH, -NH2, and phenol/quinone groups could be regulated easily by adjusting the reaction time of GA conjugation, making it possible to coimmobilize two or three diverse molecules. This has been shown by the successful coimmobilization of anti-CD34 antibody and vascular endothelial growth factor (VEGF). The surface coimmobilized with the anti-CD34 antibody and VEGF presented significant enhancement in the capture of endothelial progenitor cells (EPCs) and the growth of human umbilical vein endothelial cells (HUVECs). These data suggest the huge potential of such polyfunctional coating for tailoring the desired interfacial properties of materials through selectively conjugating two or more diverse bioactive molecules with synergic action.

Tuneable and robust long range surface plasmon resonance for biosensing applications

A multilayered biosensing architecture based on long range surface plasmons (LRSPs) is reported. LRSPs originate from the coupling of surface plasmons on the opposite sides of a thin metal film embedded in a symmetrical refractive index environment. With respect to regular SPs, LRSPs are characterized by extended electromagnetic field profiles and lower losses, making them of high interest in biosensing, especially for large biological entities. LRSPs-supporting layer structures are typically prepared by using fluoropolymers with refractive indices close to that of water. Unfortunately, fluoropolymers have low surface energies which can translate into poor adhesion to substrates and sub-optimal properties of coatings with surface plasmon resonance-active metal layers such as gold. In this work, a multilayered fluoropolymer structure with tuneable average refractive index is described and used to adjust the penetration depth of LRSP from the sensor surface. The proposed methodology also provides a simple solution to increase the adhesion of LRSP-supporting structures to glass substrates. Towards taking full advantage of long range surface plasmon resonance sensors, a novel approach based on the plasma-polymerization of allylamine is also described to improve the quality of gold layers on fluoropolymers such as Teflon AF. Through these advancements, long range surface plasmon resonance sensors were fabricated with figures of merit as high as 466RIU−1. The remarkable performance of these sensors combined with their high stability is expected to foster applications of LRSPR in biosensing.

Influence of Film Stability and Aging of Plasma Polymerized Allylamine Coated Quartz Particles on Humic Acid Removal

Plasma polymerized allylamine (ppAA) films have been successfully deposited on to the surface of quartz particles via a rotating barrel plasma reactor for humic acid removal. The films were deposited at a power of 25 W, allylamine flow rate of 4.4 sccm and polymerization times of 5 to 60 min. X-ray photoelectron spectroscopy was used to investigate the influence of short-term stirring in water and film age on surface chemistry. Stirring results in a reduction in the nitrogen concentration, which was greatest for shorter polymerization times. Film aging of up to 52 weeks appeared to result in a reduction in the concentration of C-N species. The influence of batch, recycling, and film age on humic acid removal was investigated. Humic acid removal appeared to be reproducible across three separate batches for polymerization times of 20 min or more, which was attributed to film thickness. Recycling of the ppAA films was most successful at pH 11 for up to 4 humic acid removal/regeneration cycles. Successful regeneration at pH 11 was attributed to electrostatic repulsion of the adsorbed humic acid molecules. Decreasing the pH of the regeneration solution reduced the number of successful regeneration cycles due to greater retention of adsorbed humic acid via electrostatic attraction. Film age appears to have minimal effect on humic acid removal where freshly deposited and 52-week-old films removed similar masses of humic acid. Successful production and development of ppAA coated quartz particles has resulted in a functional material that can be incorporated into a water treatment system to improve water quality.

Creation of biofunctionalized plasma polymerized allylamine gradients

ABSTRACTA chemical gradient possessing gradual change of amine concentration for every 100 carbon atoms (NHx/100 C) from 4.03 to 1.98 was prepared by plasma polymerization of allylamine on polypropylene films. Electron spectroscopy for chemical analysis and water contact angle (WCA) measurements revealed that the nitrogen incorporation resulted in the amine functionality (CN binding) and, therefore, the formation of the wettability gradient. The gradient showed the WCAs varied from 15° to 90° as the change of amine concentration on the gradient from the nitrogen rich end to the nitrogen deprived end. Furthermore, the interactions between the gradient with mammalian cells revealed that more than twofold cell density was found at the nitrogen rich end when compared with the nitrogen deprived end. Plasma polymerization was demonstrated as an effective method to create controllable chemical gradient and the obtained allylamine gradient was useful for biomaterial applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1361–1367

Stem Cells: Surface Bound Amine Functional Group Density Influences Embryonic Stem Cell Maintenance (Adv. Healthcare Mater. 4/2013)

The back cover image shows an octadiene–allylamine plasma polymer gradient surface with colonies of embryonic stem cells attached, as described by Nicolas H. Voelcker and co-workers on page 585. Stem cell colonies spread out on regions of the surface with higher amine group density, differentiating into more mature cell types. In contrast, smaller rounded colonies, consisting of proliferating stem cells, form high methyl group density areas.

Two-dimensional amine-functionality gradient by plasma polymerization

A two-dimensional (2D) gradient was created by employing two-step diffusion-controlled plasma polymerization of allylamine on polypropylene membrane, with varied deposition durations composed of two stages. The wettability gradient was examined by water contact angle measurements which clearly demonstrated that the gradient was well manipulated by varying the treatment duration, thus controlled the surface coverage and resulted in the average water contact angle ranged from 110° to 25°. On the created 2D gradients, the cell responses toward the distribution of nitrogen content were imaged by confocal laser microscopy. Moreover, a correlation based on experimental data revealed a linear relationship between the nitrogen content and water contact angle. The addition of serum proteins assisted also the adhesion and growth of L-929 cells. The methodology in fabricating the 2D gradient demonstrated the flexibility of the plasma technique which can be further used to create different types of well-defined gradients for applications in surface functionalization, biomedical devices, and material screening.

Plasma-Enhanced Synthesis of Poly(allylamine)-Encapsulated Ruthenium Dye-Sensitized Titania Photocatalysts

Photocatalysis for sustainable hydrogen production from water is becoming one of the core challenges for an efficient conversion of solar energy into a clean and renewable fuel, enabling the growth of a carbon-free hydrogen economy. In dye-sensitized TiO2, performances were obtained to be unstable over time due to weak covalent bonding of the molecule at the surface leading to detachment of the dye from the TiO2 surface and dye self-aggregation, with recombination of charge carriers at the dye/TiO2 interface being the second major factor for efficiency losses. Our strategy for improvement of the stability of the dye/TiO2 catalyst is the encapsulation of the assembly by a plasma-polymerized allylamine layer, providing a chemically and mechanically stable nanoconfinement of the dye in close proximity of the titania surface. The TiO2-layer was synthesized by a plasma-enhanced DC magnetron sputtering process on FTO substrates, resulting in homogeneous porous semiconductor layers. The stability of the PPAAm la...

Plasma polymerization in a microcapillary using an atmospheric pressure dielectric barrier discharge

Atmospheric pressure plasma deposition is a beneficial technology due to its low cost and flexibility in terms of its operation and integration for in-line processing. This paper presents the use of an atmospheric pressure dielectric barrier discharge (DBD) to deposit an amine functional polymer film onto the inner surface of a glass microcapillary. A micro discharge was generated in a DBD chip made from a rectangular borosilicate glass capillary using externally attached parallel plate electrodes. A new microplasma configuration which consists of a perforated high voltage electrode and a ground electrode with large surface area is implemented to sustain a stable glow discharge at atmospheric pressure and a temperature of 35°C. Polymerization was performed using a laboratory made plasma source working at a frequency of 8kHz with 50% duty ratio of the inverter. The monomer precursors allylamine and ethylenediamine were selected to optimize the polymerization conditions at atmospheric pressure. The hydrophobicity and philicity of the deposited surface were controlled as functions of plasma power. The atmospheric pressure plasma polymerized (APPP) films were characterized using Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), plasma emission spectroscopy, contact angle measurements and growth rate analysis. An average growth rate of 1.18μgs−1 for plasma polymerized ethylenediamine (PPEDA) and 1.91μgs−1 for plasma polymerized allylamine (PPAA) was obtained at a discharge power of 15W and 10sccm of monomer flow rate. The film thickness of 0.9μm for PPEDA and 2.1μm for PPAA was determined using AFM for deposition time of 10min. Polymerization results showed that the properties of APPP films can be controlled through optimization of parameters such as discharge power, treatment time and flow rates of the main gas and monomer vapors.

Immobilization of Heparan Sulfate on Electrospun Meshes to Support Embryonic Stem Cell Culture and Differentiation *

As our understanding of what guides the behavior of multi- and pluripotent stem cells deepens, so too does our ability to utilize certain cues to manipulate their behavior and maximize their therapeutic potential. Engineered, biologically functionalized materials have the capacity to influence stem cell behavior through a powerful combination of biological, mechanical, and topographical cues. Here, we present the development of a novel electrospun scaffold, functionalized with glycosaminoglycans (GAGs) ionically immobilized onto the fiber surface. Bound GAGs retained the ability to interact with GAG-binding molecules and, crucially, presented GAG sulfation motifs fundamental to mediating stem cell behavior. Bound GAG proved to be biologically active, rescuing the neural differentiation capacity of heparan sulfate-deficient mouse embryonic stem cells and functioning in concert with FGF4 to facilitate the formation of extensive neural processes across the scaffold surface. The combination of GAGs with electrospun scaffolds creates a biomaterial with potent applicability for the propagation and effective differentiation of pluripotent stem cells.

Surface Bound Amine Functional Group Density Influences Embryonic Stem Cell Maintenance

Gradient surfaces are highly effective tools to screen and optimize cell- surface interactions. Here, the response of embryonic stem (ES) cell colonies to plasma polymer gradient surfaces is investigated. Surface chemistry ranged from pure allylamine (AA) plasma polymer on one end of the gradient to pure octadiene (OD) plasma polymer on the other end. Optimal surface chemistry conditions for retention of pluripotency were identified. Expression of the stem cell markers alkaline phosphatase (AP) and Oct4 varied with the position of the ES cell colonies across the OD-AA plasma polymer gradient. Both markers were more strongly retained on the OD plasma polymer rich regions of the gradients. The observed variation of expression across the plasma polymer gradient increased with duration of stem cell culture. While maximum cell adhesion to the gradient substrate occurred at a nitrogen- to-carbon (N/C ratio) of approximately 0.1, Oct4 and AP expression was best retained at an N/C ratio < 0.04. Stem cell marker expression correlated with colony size and morphology: more compact, multilayered colonies with prominent F-actin staining arose as the N/C ratio decreased. Disruption of actin polymerization using Y-27632 ROCK inhibitor resulted in a collapse of the multilayer colony structure into monolayers with limited cell-cell contact. A corresponding decrease in expression of AP and Oct4 was observed. Oct4 expression along with 3D colony morphology was partially rescued on the OD plasma polymer rich regions of the gradient.

In vitro corrosion inhibition on biomedical shape memory alloy by plasma-polymerized allylamine film

To improve the corrosion resistance of biomedical nickel titanium (NiTi) alloy, a polymeric allylamine film is deposited by plasma polymerization. The chemical composition, surface morphology, and thickness of the polymer film are investigated with X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The corrosion behavior of the coated NiTi and bare NiTi samples is compared by polarization test and electrochemical impedance spectroscopy (EIS) in simulated body fluid. The results show that the polymeric film lowers the corrosion current density and increases the polarization resistance, indicating improved corrosion resistance. The plasma polymerized coating is expected to reduce corrosion risks of biomedical NiTi alloy in clinical use.

Direct thrombin inhibitor-bivalirudin functionalized plasma polymerized allylamine coating for improved biocompatibility of vascular devices

The direct thrombin inhibitor of bivalirudin (BVLD), a short peptide derived from hirudin, has drawn an increasing attention in clinical application because it is safer and more effective than heparin for diabetic patients with moderate- or high-risk for acute coronary syndromes (ACS). In this study, BVLD was covalently conjugated on plasma polymerized allylamine (PPAam) coated 316L stainless steel (SS) to develop an anticoagulant surface. QCM-D real time monitoring result shows that 565 ± 20 ng/cm2 of BVLD was bound to the PPAam surface. Infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS) confirmed the immobilization of BVLD. The conjugation of BVLD onto the PPAam coating led to enhanced binding of thrombin, and the activity of the thrombin adsorbed on its surface was effectively inhibited. As a result, the BVLD immobilized PPAam (BVLD-PPAam) substrate prolonged the clotting times, and exhibited inhibition in adhesion and activation of platelets and fibrinogen. We also found that the BVLD-PPAam coating significantly enhanced endothelial cell adhesion, proliferation, migration and release of nitric oxide (NO) and secretion of prostaglandin I2 (PGI2). In vivo results indicate that the BVLD-PPAam surface restrained thrombus formation by rapidly growing a homogeneous and intact endothelium on its surface. These data suggest the potential of this multifunctional BVLD-PPAam coating for the application not only in general vascular devices such as catheters, tubes, oxygenator, hemodialysis membranes but also vascular grafts and stents.

Focal Adhesion of Osteoblastic Cells on Titanium Surface with Amine Functionalities Formed by Plasma Polymerization

To enhance the focal adhesion of osteoblastic cells on a titanium surface, plasma polymerized allyl amine (AAm) thin films were deposited by plasma polymerization. This plasma polymer functionalization of titanium is advantageous for osteoblastic focal adhesion formation. Such Ti surfaces are useful for the fabrication of titanium-based dental implants for enhancement of osseointegration.

Construction and hemocompatibility study of highly bioactive heparin‐functionalized surface

A simple method is developed to construct anticoagulant surfaces via passive adsorption of heparin onto the protonated plasma-polymerized allylamine (PPAam) films from phosphate-buffered saline (PBS). These protonated PPAam surfaces are found to have high affinity to heparin. Importantly, the heparin-functionalized PPAam (Hep-PPAam) surfaces show good retention of heparin after long-term immersion in PBS. The Hep-PPAam surface prolongs the activated partial thromboplastin time for about 20 s as compared to 316L stainless steel even though the adsorption amount of heparin is only about 300 ng/cm(2). This indicates that the heparin bound to the protonated PPAam surfaces in this way maintains a high bioactivity. Blood platelet adhesion and activation on this surface is remarkably reduced and adsorption and activation of fibrinogen is inhibited. Thus, Hep-PPAam surface modification leads to a significant improve of the hemocompatibility.

The role of heparin binding surfaces in the direction of endothelial and smooth muscle cell fate and re-endothelialization

In this work, the effects of a heparin-functionalized coating on the growth behavior of vascular cells were studied. To retain its functionality, heparin was bound to a cationic plasma polymerized allylamine coating through electrostatic interaction. The heparin binding surface significantly inhibited human umbilical artery smooth muscle cell (HUASMC) adhesion and proliferation. In contrast, human umbilical vein endothelial cells (HUVECs) showed significant enhancement in cell adhesion, proliferation and migration, release of nitric oxide (NO) and secretion of prostaglandin I2 (PGI2). The test of acute thrombogenicity assessed using human blood exhibited an excellent antithrombotic performance of the heparin grafted surface. The heparinized surface significantly promoted in vivo re-endothelialization and effectively inhibited thrombosis formation. These observations form an important framework for further deciphering the biological functions of heparin. It is highlighted that these striking findings may serve as a guide for the design of multifunctional vascular devices.

Impact of plasma chemistry versus titanium surface topography on osteoblast orientation

Topographical and chemical modifications of biomaterial surfaces both influence tissue physiology, but unfortunately little knowledge exists as to their combined effect. There are many indications that rough surfaces positively influence osteoblast behavior. Having determined previously that a positively charged, smooth titanium surface boosts osteoblast adhesion, we wanted to investigate the combined effects of topography and chemistry and elucidate which of these properties is dominant. Polished, machined and corundum-blasted titanium of increasing microroughness was additionally coated with plasma-polymerized allylamine (PPAAm). Collagen I was then immobilized using polyethylene glycol diacid and glutar dialdehyde. On all PPAAm-modified surfaces (i) adhesion of human MG-63 osteoblastic cells increased significantly in combination with roughness, (ii) cells resemble the underlying structure and melt with the surface, and (iii) cells overcome the restrictions of a grooved surface and spread out over a large area as indicated by actin staining. Interestingly, the cellular effects of the plasma-chemical surface modification are predominant over surface topography, especially in the initial phase. Collagen I, although it is the gold standard, does not improve surface adhesion features comparably.

Plasma polymerized allylamine coated quartz particles for humic acid removal

Allylamine plasma polymerization has been used to modify the surface of quartz particles for humic acid removal via an inductively coupled rotating barrel plasma reactor. Plasma polymerized allylamine (ppAA) films were deposited at a power of 25W, allylamine flow rate of 4.4sccm and polymerization times of 5–60min. The influence of polymerization time on surface chemistry was investigated via X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectrometry (ToF-SIMS) and electrokinetic analysis. Acid orange 7 adsorption/desorption quantified the number of surface amine groups. Humic acid removal via ppAA quartz particles was examined by varying pH, removal time, humic acid concentration, and particle mass. Increasing the polymerization time increased the concentration of amine groups on the ppAA quartz surface, thus also increasing the isoelectric point. ToF-SIMS demonstrated uniform distribution of amine groups across the particle surface. Greatest humic acid removal was observed at pH 5 due to electrostatic attraction. At higher pH values, for longer polymerization times, humic acid removal was also observed due to hydrogen bonding. Increasing the initial humic acid concentration increased the mass of humic acid removed, with longer polymerization times exhibiting the greatest increases. Plasma polymerization using a rotating plasma reactor has shown to be a successful method for modifying quartz particles for the removal of humic acid. Further development of the plasma polymerization process and investigation of additional contaminants will aid in the development of a low cost water treatment system.

Rapid micropatterning of cell lines and human pluripotent stem cells on elastomeric membranes

Tissue function during development and in regenerative medicine completely relies on correct cell organization and patterning at micro and macro scales. We describe a rapid method for patterning mammalian cells including human embryonic stem cells (HESCs) and induced pluripotent stem cells (iPSCs) on elastomeric membranes such that micron-scale control of cell position can be achieved over centimeter-length scales. Our method employs surface engineering of hydrophobic polydimethylsiloxane (PDMS) membranes by plasma polymerization of allylamine. Deposition of plasma polymerized allylamine (ppAAm) using our methods may be spatially restricted using a micro-stencil leaving faithful hydrophilic ppAAm patterns. We employed airbrushing to create aerosols which deposit extracellular matrix (ECM) proteins (such as fibronectin and Matrigel™) onto the same patterned ppAAm rich regions. Cell patterns were created with a variety of well characterized cell lines (e.g., NIH-3T3, C2C12, HL1, BJ6, HESC line HUES7, and HiPSC line IPS2). Individual and multiple cell line patterning were also achieved. Patterning remains faithful for several days and cells are viable and proliferate. To demonstrate the utility of our technique we have patterned cells in a variety of configurations. The ability to rapidly pattern cells at high resolution over macro scales should aid future tissue engineering efforts for regenerative medicine applications and in creating in vitro stem cell niches.

Inspired Chemistry for a Simple but Highly Effective Immobilization of Vascular Endothelial Growth Factor on Gallic Acid‐functionalized Plasma Polymerized Film

AbstractBiomolecules with thiol or amine groups can be easily covalently immobilized onto a material substrate equipped with quinone groups in a simple mild alkali buffer solution based on Schiff base and Michael addition reaction. In this study we report a novel two‐step approach to creating a functional coating with abundant quinone groups for a facile immobilization of vascular endothelial growth factor (VEGF) in chemical mild phosphate buffered saline (PBS, pH = 7.4). This approach firstly involves the deposition of plasma polymerized allylamine (PPAam) thin coating onto a substrate to introduce the amine groups. Then gallic acid (3,4,5‐trihydroxybenzoic acid, GA) is chosen to functionalize PPAam for introducing phenol groups through a water‐soluble carbodiimide (WSC) coupling procedure. The results of infrared spectroscopy (IR), X‐ray photoelectron spectroscopy (XPS), and water contact angles reveal the effective conjugation of GA to PPAam and further immobilization of VEGF to GA functionalized PPAam. The results of quartz crystal microbalance equipped with dissipation monitoring (QCM‐D) show that 120 ng · cm−2 of VEGF is successfully immobilized onto GA functionalized surface. The VEGF functionalized surface shows a significant enhancement of human umbilical vein endothelial cell (HUVEC) proliferation, revealing a good bioactivity of VEGF. This functional coating not only provides a novel facile strategy for the covalent immobilization of biomolecules in a chemical mild reaction condition, but also can be adapted for a wide range of materials without surface pretreatment. magnified image

Serum profile of pro- and anti-inflammatory cytokines in rats following implantation of low-temperature plasma-modified titanium plates

Surface modification of Titanium (Ti) by low-temperature plasma influences cell-material interactions. Therefore, this study aimed at examining serum cytokine levels and associations after intramuscular implantation (n = 8 rats/group) of Ti-plates with Plasma Polymerized Allyl Amine (Ti-PPAAm), Plasma Polymerized Acrylic Acid (Ti-PPAAc), and without such layers (Ti-Controls). Pro-inflammatory (IL-2, IFNγ, IL-6) and anti-inflammatory (IL-4, IL-10, IL-13) cytokines were measured weekly for 56 days. Ti-PPAAm caused increased IL-2 (d7-14, d35), increased IFNγ (d35) and decreased IL-10 (d35, d49-56). Ti-PPAAc induced divergent anti-inflammatory cytokine changes with increased IL-4 (d28-56) and decreased IL-10 (d42-56). Ti-Controls elicited increased IL-2 (d42) and IFNγ (d35-42, d56). IL-6 was not detected and IL-13 only in three samples, thus they do not influence the response against these Ti implants. Correlation analysis revealed surface-dependent associations between cytokines indicating the involvement of different inflammatory cell populations. Concluding, different plasma modifications induce specific serum cytokine profiles and associations indicating distinct inflammatory responses.