Sophie Lerouge

Plasma Sterilization: A Review of Parameters, Mechanisms, and Limitations

Low-temperature plasma is a promising method for destroying microorganisms, an alternative to “conventional” methods which have numerous drawbacks. Several plasma-based sterilization technologies are presently under development, but their mechanisms of action are still incompletely understood. Since more than five years, we have investigated the effects of plasma on microorganisms (killing efficacy, and related mechanisms), as well as on the materials being sterilized. This article reports some important observations made during this work, using the commercialized so-called “plasma sterilizers” and “real” low-pressure plasma systems. The mechanism of etching (volatilization) of microorganisms by plasma that we have observed, leads us to believe that plasma may constitute a powerful solution to the clinical problems of deactivating also prions and endotoxins. However, plasma effectiveness is influenced by numerous experimental parameters, which we review here. This inherent complexity, and the weak penetrating power of plasma species, that severely limits plasma effectiveness in the presence of organic residues, packaging material, or complex geometries, are the main limitations of plasma sterilization.

Characterization of in vivo wear debris from ceramic—ceramic total hip arthroplasties

In contrast to the much-studied mechanism of aseptic loosening of the metal-polyethylene joint couple, the mechanism responsible for failure of ceramic-ceramic (CC) total hip arthroplasties (THAs) has not been evaluated. The aim of this study was to conduct a systematic characterization of the in vivo wear debris from 15 cases of CC THAs revised for aseptic loosening. Two methods were used to evaluate the wear debris; a semiquantitative histological analysis of H&E-stained periprosthetic pseudomembranes; and an evaluation of isolated debris particles using SEM, energy-dispersive X-ray analysis, and image analysis. The three main types of particulate debris identified were titanium alloy (TiAlV) and alumina ceramic (Al2O3) of prosthetic origin, and zirconium dioxide (ZrO2) from the contrast agent used in the cement for prosthetic fixation. Alumina debris was present in the smallest proportion (12%) and was consistent with the low wear rate of the CC joint couple. Zirconium dioxide debris was present in the greatest proportion (76%) and was an unexpected finding. The ZrO2 debris represented microstructural grains of the original ZrO2 particles added as contrast agent to the cement. The presence of a histiocytic foreign body reaction to ZrO2 debris on histologic sections leads us to believe that these particles play an important role in aseptic loosening of the CC THAs evaluated in this study.

CERAMIC-CERAMIC AND METAL-POLYETHYLENE TOTAL HIP REPLACEMENTS: COMPARISON OF PSEUDOMEMBRANES AFTER LOOSENING

We made a semiquantitative study of the comparative histology of pseudomembranes from 12 loose cemented ceramic-ceramic and 18 metal-polyethylene total hip replacements. We found no significant difference in cellular reaction between the two groups, but there was a major difference in the origin of the particulate debris. In the metal-polyethylene group, polyethylene of articular origin was predominant, while in the ceramic-ceramic group the cellular reaction appeared to be a response to zirconia ceramic particles used to opacify cement used for fixation. Isolation and characterisation of the debris showed that the zirconia particles formed the greatest proportion (76%) in ceramic-ceramic hips, while alumina debris of articular origin formed only 12%. Our study has indicated that aseptic loosening of ceramic cups is not due to a response to debris generated at the articular interface, but to mechanical factors which lead to fragmentation of the cement.

Sterilization by Low-Pressure Plasma: The Role of Vacuum-Ultraviolet Radiation

Low-pressure plasma is a promising method for destroying microorganisms, an alternative to “conventional” methods, which have numerous drawbacks. Several plasma-based sterilization technologies are presently under development, even though the exact role of the various plasma constituents, for example ultraviolet radiation, on the sterilization mechanism is still unknown and subject to controversy. In this study, we first report high sporicidal activity of a microwave (MW) plasma compared to its radio-frequency (RF) counterpart, which we believe to be due to the higher concentration of reactive particles in the former plasma. We then report a relatively low sporicidal efficacy of vacuum ultraviolet (VUV) radiation (between 115 and 170 nm) emitted by an hydrogen MW plasma, in spite of the high effectiveness of these photons to break chemical bonds. We discuss these results in terms of etching (ablation), which we have observed for both synthetic polymers and spores, and in terms of other possible mechanisms proposed in the literature. The sporicidal effectiveness of VUV/UV radiation appears to vary markedly with wavelength and intensity, on account of spore structure and molecular absorption.

Ceramic-ceramic And Metal-polyethylene Total Hip Replacements: Comparison Of Pseudomembranes After Loosening

We made a semiquantitative study of the comparative histology of pseudomembranes from 12 loose cemented ceramic-ceramic and 18 metal-polyethylene total hip replacements. We found no significant difference in cellular reaction between the two groups, but there was a major difference in the origin of the particulate debris. In the metal-polyethylene group, polyethylene of articular origin was predominant, while in the ceramic-ceramic group the cellular reaction appeared to be a response to zirconia ceramic particles used to opacify cement used for fixation. Isolation and characterisation of the debris showed that the zirconia particles formed the greatest proportion (76%) in ceramic-ceramic hips, while alumina debris of articular origin formed only 12%. Our study has indicated that aseptic loosening of ceramic cups is not due to a response to debris generated at the articular interface, but to mechanical factors which lead to fragmentation of the cement.

Plasma-based sterilization: effect on surface and bulk properties, and hydrolytic stability of reprocessed polyurethane electrophysiology catheters

Plasma-based sterilization is a promising alternative to ethylene oxide (EO) for reprocessing of electrophysiology catheters. To assess its safety in terms of material damage, modifications of surface and bulk properties as well as hydrolytic stability of sterilized catheters were evaluated. Polyurethane (PU) single-use electrophysiology catheters were subjected to one, five, and ten sterilization cycles by Sterrad-100S and Plazlyte, as well as by pure EO for comparison. Surface analysis techniques (ATR-FTIR, XPS, DCA) showed oxidation limited to the near-surface layer induced by both plasma-based sterilizers, whereas EO induced slight but deeper alkylation. Using bulk analysis techniques (RP-HPLC, SEC), oligomer alteration was observed after all three sterilization techniques, without modification of molecular weights. Hydrolytic stability of catheters was slightly changed by plasma-based sterilization, with a small increase in released oligomers. Finally, although Plazlyte and Sterrad are both plasma-based techniques, they induced different impacts on catheters, such as the degradation of an additive with Sterrad, and a clear difference in coloration with Plazlyte.

Implant Degradation and Poor Healing after Endovascular Repair of Abdominal Aortic Aneurysms: An Analysis of Explanted Stent-Grafts

Purpose: To study explanted stent-grafts to achieve a better understanding of the mechanisms of failure after endovascular treatment of abdominal aortic aneurysms (AAA). Methods: Twelve stent-grafts were harvested at autopsy (n=3) or during surgical conversion (n=9). Device alterations were investigated by macroscopic examination, radiography, and surface analysis techniques. Healing around the implants was studied via histology and immunohistochemistry, with particular attention to the stent-graft/tissue interface. Results: Degradation was more important with Vanguard stent-grafts (off the market) than with AneuRx and Talent stent-grafts, but rupture of nitinol wires and poor surface finish in Talent stent-grafts raise concern about their corrosion resistance and long-term stability. Poor healing was observed around stent-grafts even after several years of implantation, with absence of vascular smooth muscle cells, fibroblasts, and collagen formation. In addition to the well-known foreign body reaction around the graft, numerous polymorphonuclear cells characteristic of the first step of healing were present in tissues around stent-grafts retrieved at surgical conversion. Factors explaining the lack of tissue organization around stent-grafts are discussed. Conclusion: The long-term stability of implants remains a concern and requires more transparency from manufacturers regarding the surface properties of their devices. Lack of neointima formation impairs biological fixation of the implant to the vessel wall, leading to possible endoleaks and migration. New-generation stent-grafts promoting biological fixation should be developed to improve clinical outcomes of this minimally invasive treatment.

Chondroitin Sulfate Coatings Display Low Platelet but High Endothelial Cell Adhesive Properties Favorable for Vascular Implants

This study highlights the advantages of chondroitin sulfate (CS) as a sublayer combining selective low-fouling properties, low-platelet adhesion and pro-adhesive properties on endothelial cells, making CS promising for vascular graft applications. These properties were evaluated by comparing CS with well-known low-fouling coatings such as poly(ethylene glycol) (PEG) and carboxymethylated dextran (CMD), which were covalently grafted on primary amine-rich plasma polymerized (LP) films. Protein adsorption studies by quartz crystal microbalance with dissipation monitoring (QCM-D) and fluorescence measurements showed that CS is as effective as PEG in reducing fibrinogen adsorption (~90% reduction). CS also largely reduced adsorption of bovine serum albumin (BSA) as well as fetal bovine serum (FBS) but to a lower extent than PEG and CMD surfaces (72% vs 85% for BSA and 66% vs 89% for FBS). Whole blood perfusion assays indicated that, while LP surfaces were highly reactive with platelets, PEG, CMD, and CS grafted surfaces drastically decreased platelet adhesion and activation to levels significantly lower than polyethylene terephthalate (PET) surfaces. Finally, while human umbilical vein endothelial cell (HUVEC) adhesion and growth were found to be very limited on PEG and CMD, they were significantly increased on CS compared to that on bare PET and reached similar values as those for tissue culture polystyrene positive controls. Interestingly, HUVEC retention during perfusion with blood was found to be excellent on CS but poor on PET. Overall, our results suggest that the CS surface has the advantage of promoting HUVEC growth and resistance to flow-induced shear stress while preventing fibrinogen and platelet attachment. Such a nonthrombogenic but endothelial-cell adhesive surface is thus promising to limit vascular graft occlusion.

Endovascular Aortic Aneurysm Repair with Stent-Grafts: Experimental Models Can Reproduce Endoleaks

PURPOSE To develop canine aneurysm models that can reproduce type II endoleaks after endovascular aneurysm repair (EVAR) with stent-grafts. MATERIALS AND METHODS A fusiform infrarenal abdominal aortic aneurysm model (AAA) was surgically created with a jugular vein patch, while preserving collateral vessels (n = 3). To allow comparative studies within the same animal, a bilateral iliac aneurysm model was also constructed with venous patches and surgical re-implantation of the sacroiliac trunk (n = 3). Stent-grafts were implanted by femoral approach at least 2 months later in both aortic and iliac models. Follow-up imaging was performed by Doppler ultrasound (US) and angiography until animals were killed 3 months after EVAR. RESULTS Angiography revealed immediate type II leaks in all cases. Leaks were still present at autopsy 3 months after EVAR in all cases, and were revealed at pre-death angiography in all but one case. At autopsy, leaks were characterized by the presence of large endothelialized channels that formed within the thrombus between the stent-graft and the aneurysmal wall. CONCLUSION As shown in this pilot study, persistent type II leaks after EVAR can be reproduced in aortic and iliac animal models. The iliac model can be created bilaterally in the same animal, thus allowing for comparative evaluation of different therapies. These models could be used to better understand the mechanisms of endoleak, and to assess future developments aimed to improve the outcomes after EVAR.

Chitosan thermogels for local expansion and delivery of tumor-specific T lymphocytes towards enhanced cancer immunotherapies.

The success of promising anti-cancer adoptive cell therapies relies on the abilities of the perfused CD8(+) T lymphocytes to gain access to and persist within the tumor microenvironment to carry out their cytotoxic functions. We propose a new method for their local delivery as a living concentrate, which may not only reduce the numbers of cells required for treatment but also enhance their site-specific mobilization. Using combinations of sodium hydrogen carbonate and phosphate buffer as gelling agents, novel injectable chitosan-based biocompatible thermogels (CTGels) having excellent mechanical properties and cytocompatibility have been developed. Three thermogel formulations with acceptable physicochemical properties, such as physiological pH and osmolality, macroporosity, and gelation rates were compared. The CTGel2 formulation outperformed the others by providing an environment suitable for the encapsulation of viable CD8(+) T lymphocytes, supporting their proliferation and gradual release. In addition, the encapsulated T cell phenotypes were influenced by surrounding conditions and by tumor cells, while maintaining their capacity to kill tumor cells. This strongly suggests that cells encapsulated in this formulation retain their anti-cancer functions, and that this locally injectable hydrogel may be further developed to complement a wide variety of existing immunotherapies.