Carina Jensen

Increased connective tissue attachment to silicone implants by a water vapor plasma treatment

Polydimethylsiloxane (PDMS) is the most common type of silicone polymer for the fabrication of implantable medical devices. Because of its inherent hydrophobic nature, the PDMS surface does not readily promote cellular adhesion, which leads to diverse clinical issues. Previously, we reported a simple water vapor plasma treatment of PDMS surfaces that resulted in stable long-term wettability and excellent in vitro cell compatibility. In this work, we report investigation of the in vivo local responses to PDMS implants treated by water vapor plasma using a subcutaneous rat model. The local tissue responses were assessed after 2 and 4 weeks of implantation by means of macroscopic and histomorphometric analysis. After 2 weeks of implantation, the plasma-treated implants elicited the formation of fibrous tissue capsules that were significantly thinner, more adherent, and vascularized than the control counterparts. The improved cell adhesion was correlated with an increased amount of cells attached to the implant surface after retrieval. There was no difference in the inflammatory response between untreated and treated samples. This study provides a rational approach to optimize the long-term performance of silicone implants, which is likely to have a significant impact in clinical applications demanding enhanced tissue integration of the implants.

Electrochemical properties of titanium nitride nerve stimulation electrodes: an in vitro and in vivo study.

The in vivo electrochemical behavior of titanium nitride (TiN) nerve stimulation electrodes was compared to their in vitro behavior for a period of 90 days. Ten electrodes were implanted in two Göttingen minipigs. Four of these were used for electrical stimulation and electrochemical measurements. Five electrodes were kept in Ringers solution at 37.5°C, of which four were used for electrical stimulation and electrochemical measurements. The voltage transients measured in vivo were 13 times greater than in vitro at implantation and they continued to increase with time. The electrochemical properties in vivo and the tissue resistance (Rtissue) followed a similar trend with time. There was no consistent significant difference between the electrochemical properties of the in vivo and in vitro electrodes after the implanted period. The differences between the in vivo and in vitro electrodes during the implanted period show that the evaluation of electrochemical performance of implantable stimulation electrodes cannot be substituted with in vitro measurements. After the implanted period, however, the performance of the in vivo and in vitro electrodes in saline was similar. In addition, the changes observed over time during the post-implantation period regarding the electrochemical properties of the in vivo electrodes and Rtissue were similar, which indicates that these changes are due to the foreign body response to implantation.

Triazine-based H2S Scavenging: Development of a Conceptual Model for the Understanding of Fouling Formation

The authors studied the applicability of a previously suggested model to describe the reaction between 1,3,5-tri-(2-hydroxypropyl)-hexahydro-s-triazine and H2S and thereby predict formation of fouling. To investigate the reaction system, electrospray ionization mass spectrometry was employed to analyze the composition of the generated mixture as H2S is bubbled through the scavenger. The results of the study confirm that the suggested model is capable of explaining how the scavenger reacts with H2S, which may be used to explain from where and how the fouling originates, and how a scavenging process can be designed to avoid fouling.

Stable Hydrophilic Polydimethylsiloxane Surfaces Produced by Plasma Treatment for Enhanced Cell Adhesion

Polydimethylsiloxane (PDMS) is a widely used polymer for medical implants due to its excellent physical properties, low cost and ease of fabrication. However, in some applications the hydrophobic nature of the material remains an issue. To increase PDMS hydrophillicity, a variety of surface treatments based on plasma discharge have been proposed. In this study, we investigated the effect of water-vapor based plasma on PDMS surfaces. Surface topography was analyzed by means of atomic force microscopy (AFM) while surface chemistry was obtained by Fourier transform infrared spectroscopy (FTIR). To analyze the stability of the treatment, surface wettability was assessed over a period of seven months by contact angle measurement. Furthermore, using primary human fibroblasts,in vitro cell growth and morphology was investigated. It was found that plasma treament produced long-term stable hydrophillic surfaces (contact angle between 70° to 80°). This property was correlated with hydroxylation of the surface and was accompanied by a slight increase in RMS roughness. Concomitantly, there was a significant increase in the number of cells growing on the plasma-treated surfaces, which was linked with a more spread cellular morphology. The results presented here suggest that water-vapor plasma treatment may be useful to enhance cell adhesion on PDMS implants.

Comparison of Different UV-activated AOP methods

Abstract In this study the photonic efficiency of different UV activated AOP methods are compared in regard to the oxidation of the dye p-nitrosodimethylaniline (RNO). The UV activated methods include heterogeneous photocatalysis (TiO2/UV), UV activated persulfate (UV/S2O82-) and hydrogen peroxide (UV/H2O2), vacuum UV irradiation (VUV) and combination of these. The photonic efficiencies were determined both by measuring the bleaching of RNO by UV/VIS and by measuring the decomposition by TOC. The results of this investigation showed that the highest photonic efficiency was observed for the system consisting of VUV/H2O2 (3.06%). Similar photonic efficiencies were observed for the UV/H2O2, UV /TiO2 (suspension), and UV/S2O82- process. These numbers suggest that only around 3% of the emitted photons are used in the bleaching of RNO. The photonic efficiency for the mineralization of RNO for the UV/H2O2 process was determined to around 20%. No synergistic effect was observed when combining photocatalysis with H2O2, S2O82- or VUV irradiation. In all the latter cases it was found that the bleaching rates for these techniques alone were higher than those observed combined with photocatalysis. The only process showing synergistic effects was the system consisting of VUV/H2O2.

Influence of fibrous encapsulation on electro-chemical properties of TiN electrodes

The aim of this study was to investigate how the electrochemical properties of porous titanium nitride stimulation electrode are affected by fibrous encapsulation in vivo. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry and voltage transient (VT) measurements were performed in vivo and in phosphate buffered saline, where the encapsulation process is absent. EIS was used as a non-invasive measurement to follow the inflammation, healing and encapsulation process. EIS showed that the healing and encapsulation process lasted 3-4 weeks. The VTs increased during the first 3-4 weeks, after which they stabilized. The charge storage capacity (CSC) decreased most during the first 3-4 weeks. The increasing VTs and decreasing CSC during the first 3-4 weeks after implantation of the in vivo electrodes seem related to healing and fibrous encapsulation. It is suggested that the charge injection pathway during the encapsulation process changes, which implies that charge injection limits are underestimated with conventional methods.