Silica-cast replicas for morphology studies on spruce and birch xylem

Sol-gel mineralization has been used and evaluated as a tool for morphological studies on Picea abies and Betula verrucosa. Wood specimens and a pulped spruce sample were impregnated with a silica sol-gel and subsequently heated (calcined) to condense the surfactant-templated polysilicic acid into structured mesoporous silica. During this calcination process, the wood substance and the surfactant were removed and a silica-cast replica of the sample was obtained. The sol-gel mineralization method produced replicas that were studied by environmental scanning and transmission electron microscopy (ESEM, TEM) without additional sample preparation. The calcination induced some shrinkage above the fiber level, but the ultrastructural dimensions were not discernibly affected. The silica-cast replica method may therefore be a useful tool for studies of the wood ultrastructure, including the cell-wall pore structure (microcavities), down to the nanometer level.