Mode of action of brown rot decay resistance in modified wood: A review

Chemically or physically modified wood materials have enhanced resistance to wood decay fungi. In contrast to treatments with traditional wood preservatives, where the resistance is caused mainly by the toxicity of the chemicals added, little is known about the mode of action of nontoxic wood modification methods. This study reviews established theories related to resistance in acetylated, furfurylated, dimethylol dihydroxyethyleneurea- treated, and thermally modified wood. The main conclusion is that only one theory provides a consistent explanation for the initial inhibition of brown rot degradation in modified wood, that is, moisture exclusion via the reduction of cell wall voids. Other proposed mechanisms, such as enzyme nonrecognition, micropore blocking, and reducing the number of free hydroxyl groups, may reduce the degradation rate when cell wall water uptake is no longer impeded. © 2014 Walter de Gruyter GmbH, Berlin/Boston

Initial Rhodonia placenta Gene Expression in Acetylated Wood: Group-Wise Upregulation of Non-Enzymatic Oxidative Wood Degradation Genes Depending on the Treatment Level

Acetylation has been shown to delay fungal decay, but the underlying mechanisms are poorly understood. Brown-rot fungi, such as Rhodonia placenta (Fr.) Niemelä, K.H. Larss. & Schigel, degrade wood in two steps, i.e., oxidative depolymerization followed by secretion of hydrolytic enzymes. Since separating the two degradation steps has been proven challenging, a new sample design was applied to the task. The aim of this study was to compare the expression of 10 genes during the initial decay phase in wood and wood acetylated to three different weight percentage gains (WPG). The results showed that not all genes thought to play a role in initiating brown-rot decay are upregulated. Furthermore, the results indicate that R. placenta upregulates an increasing number of genes involved in the oxidative degradation phase with increasing WPG

Incipient brown rot decay in modified wood : patterns of mass loss, structural integrity, moisture and acetyl content in high resolution

The study of degradation and growth patterns of fungi in modified wood may increase the understanding of their mode of action and may lead to more accurate service-life predictions. The aim of this paper was to study the degradation and growth patterns of brown rot fungi in modified wood and to measure moisture content (MC), structural integrity and the acetyl content by frequent monitoring over 300 days. Mass loss (ML) in the modified wood materials increased slowly up to 3% for 50–100 days after which it flattened out and remained constant during the remainder of the test. Structural integrity and acetyl content were maintained in the modified wood materials and MC was lower compared to untreated wood throughout the decay test. ML results of untreated wood indicate that fungi in solid wood go through distinct phases; the degradation patterns in the modified wood materials were more difficult to interpret

Susceptibility of surface-modified superhydrophobic wood and acetylated wood to mold and blue stain fungi

The susceptibility of surface-modified wood, surface-modified acetylated wood and acetylated wood to mold and blue stain fungi was investigated. The surface modifications were based on fluorinated and non-fluorinated silicone nanofilaments for increased hydrophobicity. Results showed an increased mold resistance of the surface-modified superhydrophobic wood with mold appearing later or with less intensity on the modified surfaces than on the untreated wood in accelerated mold chamber tests due to the increased water resistance of the samples. All acetylated wood samples exhibited good mold resistance as the available water in acetylated wood was reduced. The surface modifications on acetylated wood had a slightly negative effect on mold resistance due to side effects from the modification. The surface-modified wood showed high blue stain fungi coverage, whereas almost no blue stain fungi were observed on the acetylated wood and surface-modified acetylated wood. The surface-modified superhydrophobic wood showed high mold coverage after conditioning in a high-humidity environment or after exposure to UV irradiation. Meanwhile, the acetylated wood and surface-modified superhydrophobic acetylated wood showed a small amount of mold coverage in these conditions.

Covered versus uncovered self-expandable nitinol stents in the palliative treatment of malignant distal biliary obstruction: results from a randomized, multicenter study

Background: Covered biliary metal stents have been developed to prevent tumor ingrowth. Previous comparative studies are limited and often include few patients. Objective: To compare differences in stent patency, patient survival, and complication rates between covered and uncovered nitinol stents in patients with malignant biliary obstruction. Design: Randomized, multicenter trial conducted between January 2006 and October 2008. Setting: Ten sites serving a total catchment area of approximately 2.8 million inhabitants. Patients: A total of 400 patients with unresectable distal malignant biliary obstruction. Interventions: ERCP with insertion of covered or uncovered metal stent. Follow-up conducted monthly for symptoms indicating stent obstruction. Main Outcome Measurements: Time to stent failure, survival time, and complication rate. Results: The patient survival times were 116 days (interquartile range 242 days) and 174 days (interquartile range 284 days) in the covered and uncovered stent groups, respectively (P = .320). The first quartile stent patency time was 154 days in the covered stent group and 199 days in the uncovered stent group (P = .326). There was no difference in the incidence of pancreatitis or cholecystitis between the 2 groups. Stent migration occurred in 6 patients (3%) in the covered group and in no patients in the uncovered group (P = .030). Limitations: Randomization was not blinded. Conclusions: There were no significant differences in stent patency time, patient survival time, or complication rates between covered and uncovered nitinol metal stents in the palliative treatment of malignant distal biliary obstruction. However, covered stents migrated significantly more often compared with uncovered stents, and tumor ingrowth was more frequent in uncovered stents. (Clinical trial registration number: NCT00280709.) (Gastrointest Endosc 2010;72:915-23.