Current projects bio-engineered wood

Mycowood: improved acoustic properties for violins
Fungi growth on Norway spruce, on top and close up view of hypea inside the earlywood (left) and latewood (right) lumens, imaged by synchrotron X-ray microtomography (@TomCAT/PSI)

The quality of wood for the manufacture of music instruments (tone wood) is determined by its physical properties. Wood with a low density and high velocity of sound and modulus of elasticity is favored for string instruments making. The objective of our investigations is to improve the physical quality of tone wood, e.g. reduce the density, and thus increase the sound radiation by exposing it to specific decay fungi under controlled conditions. The latter fungi differ from most other fungi, as they reduce density but do not degrade highly lignified cell wall regions resulting only in negligible changes in the stiffness and velocity of sound which are thought to be important for the sound quality of string instruments. 

With the support of the Walter Fischli-Foundation we have developed a procedure which did result in mycowood of optimised quality and physical stability. Violins have been built by two different makers using the incubated mycowood and its non-incubated controls. Studies are being designed which will show the differences of these violins in sound characteristics and acoustic properties at Empa, and their psycho-acoustic differences by CD recordings at the sound design studio "Idee und Klang" in Basel. A first mycowood violin, a copy of the "Caspar Hauser" violin by Guarneri del Gesú, was recorded with a movement of the violin concerto by Ludwig van Beethoven with soloist Oleg Kaskiv and the Gstaad Festival Orchestra, and demonstrates its fine and differentiated sound. 


Microstructure-property relationship in varnished wood of string instruments
Left the close up of "old looking" made varnish (courtesy of M. Baumgartner), and right, 3D rendered micro-tomography image of the wood and varnish interface close to the edge in a cello, made in Turin by Henricus Casner (1740-60).

Wood varnish coatings are not only aesthetically important, but also preserve the musical instrument from wear and fluctuations in the ambient humidity. Depending on the thickness, extent of penetration into the wood and the physical and mechanical properties after hardening, varnishes may change the mechanical and also vibro-acoustical properties of the coated wood. Although some recent studies suggest that solists cannot distinguish between high quality contemporary violins and historical ones still the soloists and collectors believe in the superior quality of sound of the former violins manufactured by Cremonese masters, and the quality of their timber and varnish. Our ultimate goal is to contribute to the scientific understanding of the role of the varnish composition and its structure at the wood-varnish interface on the vibro-acoustics of string instruments. This knowledge helps to develop a generation of high quality varnishes for string instruments. 



Enhanced permeability of spruce by fungi modification

Aspiration of bordered pits in Norway spruce wood is the main reason why the treatibility with preservatives is greatly inhibited for increasing the durability against micro-organisms. If this restriction could be overcome wood could be treated more effectively. For this purpose Norway spruce wood is exposed to the white-rot fungus Physisporinus vitreus that selectively degrades the pit membranes, without altering the mechanical properties of wood.  At present we are undertaking studies to optimize conditions under which the colonization of wood by the fungus is improved with the objective to upscale our patented procedure as a biotechnological method for industrial purposes.



Environmental, health and safety perspective of copper nanoparticle-based wood preservatives
Intact wood (top left), raw wood after incubation with Trichoderma harzianum (top right), copper treated wood after incubation with serpula himantoides (bottom left), raw wood after incubation with antrodia serialis (bottom right).

Aqueous dispersions of copper particles with a size range from 1 nm to 25 micro-meter have just begun to be exploited commercially for the preservative treatment of wood. Hence, wood preservatives with copper nanoparticles have the potential to become one of the largest end uses for wood products worldwide, but if copper nanoparticles can accumulate in the mycelium of copper-tolerant fungi, during the decomposition of treated wood they may end up in spores and be widely dispersed in the environment. Despite broad knowledge of copper toxicity, it is difficult to assess the potential risk of copper nanoparticles without knowing the potential release/demobilization of the copper from impregnated wood. 

The current project will help to determine the opportunities and risks of nanoCu-based wood preservatives.



Development of high-quality wood-fibre insulation boards based on laccase-catalyzed reactions with natural polymers

A future-oriented production of fibreboards using sustainable resources should take the binder used and the type and quantity into account. In developing an enzyme-linked resin-free wood fiber insulation board with a cost optimized production process we aim to guarantee not only competitiveness, but also the consumer demands for an environmentally friendly wood-based material. In this project the conditions will bedeveloped to technically and economically integrate the enzyme laccase into the process chain of the fiberboard production. For this purpose the application of the enzyme to activate the natural binding forces of wood will be integrated in the production process of fiber boards and gradually optimized in collaboration with the Swiss company Pavatex SA, a leading provider of high-quality wood fiber insulating systems for modern buildings.



Laccase-catalysed iodination of wood for achieving antimicrobial effects and protection against microbial degradation
Figure: Principle of laccase-iodide treatment of wood for achieving antimicrobial effects and protection against wood degrading fungi.

Current methods of functionalization of wood and wood-based materials for antifungal and antibacterial effects rely mainly on the adsorption of bioactive (toxic) compounds. Exposure to physical  and chemical forces of the environment, particularly to water, mostly leads to rapid loss of efficacy of antimicrobial surfaces due to leaching. Our studies show that laccase-catalysed oxidation of iodide can be used for generating leaching resistant antimicrobial wood surfaces which effectively prevent colonization against different classes of heterotrophic microorganisms, including enteric bacteria, yeast, bluestain and wood decay fungi.  



Development of a biological control method to eradicate the inoculum of copper tolerant fungi in the soil of wood products using antagonists

Wood poles impregnated with copper based wood preservatives are popular and used in the telecommunication and power supply industries all over the world because of their high strength per unit weight, low installation and maintenance costs and excellent durability. Premature failure of wood poles is often the result of wood decay caused by copper tolerant fungi. The objective of this project is to develop a biological control method that can be applied for eradicating copper tolerant fungi of the genus Poria in the soil surrounding wood products. For the purpose we will isolate a range of antagonists from soils on different sites in Europe in which early failure of wood poles are commonly encountered. Once we have isolated and  identified the copper tolerant fungi we will complete a range of in intra and in vivo studies that we will enable identification of an antagonist. If this approach is successful it should be possible to drastically reduce the number of early failures of wood poles and other wood products in Europe.

Figure above: Early failure of a wood pole, which was impregnated with a chromium copper formulation. The copper tolerant fungus Poria placenta = Rhodonia placenta was isolated from the decayed wood. Pic.A: Dense, with mycelium has colonized the wood of an incubated control specimens. Pic.B: After pre-treatment with the antagonist T-Cu+ wood specimens were not colonized by Rhodonia placenta.