Holger Testrich

Aging effects of plasma polymerized ethylenediamine (PPEDA) thin films on cell-adhesive implant coatings.

Thin plasma polymer films from ethylenediamine were deposited on planar substrates placed on the powered electrode of a low pressure capacitively coupled 13.56 MHz discharge. The chemical composition of the plasma polymer films was analyzed by Fourier Transform Infrared Reflection Absorption Spectroscopy (FT-IRRAS) as well as by X-ray photoelectron spectroscopy (XPS) after derivatization of the primary amino groups. The PPEDA films undergo an alteration during the storage in ambient air, particularly, due to reactions with oxygen. The molecular changes in PPEDA films were studied over a long-time period of 360 days. Simultaneously, the adhesion of human osteoblast-like cells MG-63 (ATCC) was investigated on PPEDA coated corundum blasted titanium alloy (Ti-6Al-4V), which is applied as implant material in orthopedic surgery. The cell adhesion was determined by flow cytometry and the cell shape was analyzed by scanning electron microscopy. Compared to uncoated reference samples a significantly enhanced cell adhesion and proliferation were measured for PPEDA coated samples, which have been maintained after long-time storage in ambient air and additional sterilization by γ-irradiation.

Investigations on the stability of the low pressure positive column in oxygen

The stability of the low pressure positive column in oxygen was investigated in a pressure range from 0.5 to 0.9?Torr within a discharge current interval from 0.5 to 90?mA. The transition between the well-known T- and H-modes has been studied. The H- to T-mode transition showed a marked hysteresis in the E(I) characteristic which is affected by wall processes. For the first time temporally resolved electric field measurements were realized. At small discharge current the electric field showed a significant modulation, characterized by incoherent fluctuations with a broadband Fourier spectrum. With increasing current the discharge operates in the T-mode, where a mode selection with high modulation degree occurred, resulting in a periodic oscillation of the electric field at a discrete frequency spectrum. The dynamic state in the T-mode is expressed by T-waves moving from the cathode to the anode. It seems that they were excited by oscillations in the cathode region. The waves were damped in the direction of the anode and show no dispersion.The discharge stability was studied using a hydrodynamic model considering electrons, positive and negative ions as well as metastable O2(a?1?g) molecules. Here the negative O?-ions play a crucial role. In good agreement with the experiments the transition between the H-and T-modes was explained as a linear unstable equilibrium state where the energy dependence of the corresponding rate coefficients is the driving mechanism (attachment-induced instability).

Dynamic behaviour of an oxygen dc discharge

The dynamic behaviour of a positive column oxygen plasma is investigated both experimentally and theoretically. In the experiment the response of the discharge current to small external perturbations of the electrical field is measured. Using these data the electrical impedance of the plasma is obtained dependent on the frequency of the external perturbation. A drift approximation model is presented, which covers the experimental findings over a wide range of the perturbation frequency. It appears that the influence of the fluctuations of the neutral species is negligible and the dynamic behaviour of the plasma is mostly governed by the charged particles. This provides a simple expression for the plasma impedance which allows the reaction rate and transport coefficients, as well as discharge parameters. to be validated.

Quantification of osseointegration of plasma-polymer coated titanium alloyed implants by means of microcomputed tomography versus histomorphometry.

A common method to derive both qualitative and quantitative data to evaluate osseointegration of implants is histomorphometry. The present study describes a new image reconstruction algorithm comparing the results of bone-to-implant contact (BIC) evaluated by means of µCT with histomorphometry data. Custom-made conical titanium alloyed (Ti6Al4V) implants were inserted in the distal tibial bone of female Sprague-Dawley rats. Different surface configurations were examined: Ti6Al4V implants with plasma-polymerized allylamine (PPAAm) coating and plasma-polymerized ethylenediamine (PPEDA) coating as well as implants without surface coating. After six weeks postoperatively, tibiae were explanted and BIC was determined by µCT (3D) and afterwards by histomorphometry (2D). In comparison to uncoated Ti6Al4V implants demonstrating low BIC of 32.4% (histomorphometry) and 51.3% (µCT), PPAAm and PPEDA coated implants showed a nonsignificant increase in BIC (histomorphometry: 45.7% and 53.5% and µCT: 51.8% and 62.0%, resp.). Mean BIC calculated by µCT was higher for all surface configurations compared to BIC detected by histomorphometry. Overall, a high correlation coefficient of 0.70 (p < 0.002) was found between 3D and 2D quantification of BIC. The μCT analysis seems to be suitable as a nondestructive and accurate 3D imaging method for the evaluation of the bone-implant interface.

Anti-Adhesive Finishing of Temporary Implant Surfaces by a Plasma-Fluorocarbon-Polymer

Titanium implant surfaces should ideally be designed to support the subsequent clinical application. Therefore temporarily used implants have to fulfill both the mechanical stabilization of the bone stock and furthermore in trauma surgery the disintegration into the bone because the implant should be removed after fracture healing. The anti-adhesive plasma-fluorocarbon-polymer (PFP) films were synthesized using two different low-pressure plasma sources, the 2.45 GHz microwave (mw) and the 13.56 MHz capacitively coupled radio-frequency (rf) discharge in a mixture of the precursor octafluoropropane (C3F8) and hydrogen (H2). The film properties were characterized using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, water contact angle measurements, and abrasive strength tests. Cell adhesion and spreading of human osteoblasts were clearly reduced on these PFP surfaces. First in vivo data on the biocompatibility of the PFP films deposited in the rf-discharge demonstrate that the local inflammatory tissue response for PFP coating was comparable to controls, while a PFP coating deposited in mw plasma induced stronger tissue reactions.

Plasma-deposited fluorocarbon polymer films on titanium for preventing cell adhesion: a surface finishing for temporarily used orthopaedic implants

The design of a titanium implant surface should ideally support its later application in clinical use. Temporarily used implants have to fulfil requirements different from permanent implants: they should ensure the mechanical stabilization of the bone stock but in trauma surgery they should not be integrated into the bone because they will be removed after fracture healing. Finishing of the implant surface by a plasma-fluorocarbon-polymer (PFP) coating is a possible approach for preventing cell adhesion of osteoblasts. Two different low pressure gas-discharge plasma processes, microwave (MW 2.45 GHz) and capacitively coupled radio frequency (RF 13.56 MHz) plasma, were applied for the deposition of the PFP film using a mixture of the precursor octafluoropropane (C3F8) and hydrogen (H2). The thin films were characterized by x-ray photoelectron spectroscopy, Fourier transform infrared reflection absorption spectroscopy, and water contact angle measurements. Cell culture experiments show that cell adhesion and spreading of MG-63 osteoblasts were clearly reduced or nonexistent on these surfaces, also after 24 h of storage in the cell culture medium. In vivo data demonstrated that the local inflammatory tissue response for the PFP films deposited in MW and RF plasma were comparable to uncoated controls.

Influence of the longitudinal magnetic field on the length of the Faraday dark space region

Magnetized plasma is used in many technological applications. Investigation of the magnetic field influence is therefore of great interest. In present paper a low pressure gas discharge in neon in presence of the longitudinal magnetic field is investigated. Experiments were performed on the cylindrical discharges with three different value of tube radius. The length of the faraday dark space region was recorded as a function of magnetic field value and the discharge current. The length has shown a steep increase with the magnetic field. Under some conditions almost whole interval between the electrodes was dark. A simple hydrodynamic model of the faraday dark space is considered in order to explain observed phenomena. Intensive diffusion processes lead to the field reversal in this region. With increasing magnetic field the effective losses of the charged particle to the wall become smaller. This serves as a reason for the extension of the dark space. The applied description yields good qualitative agreement with experiment. The discrepancies in quantitative values are discussed.