Assessment of the Micropore System in Wood for Drug Delivery

Drug delivery in biomaterials requires consideration of the pore network to store and deliver greater concentrations over an extended period of time. The porous structure in wood is used for delivery of water and therefore presents a possible pore architecture for storing fluids. The goal was to determine the pore characteristics of dried and pyrolysed wood and then investigate the ability to uptake water into the porous network. Balsa (Ochroma Pyramidale Urb) and oak (American: Quercus Alba and European: Quercus Robus) were selected based on the large pore size (100 – 200 μm). The microstructure was characterized by scanning electron microscopy and the pore volume determined by mercury intrusion porosimetry. The open and closed porosity was determined by the Archimedes method. Wood was pyrolyzed in a non-oxiding atmosphere between 800 and 1400 oC, the pore structure evaluated and the water uptake determined. Oak provides an open porosity 2.8 times greater than balsa. Pyrolysis of the wood open the pits, connecting vertically oriented tracheids with the other channel systems in wood (vessels and rays) for greater pore interconnectivity. The uptake of water, as determined by a liquid permeability test shows an initial linear uptake of 60% of the total water capacity, followed by a slower uptake of the remaining volume. This study shows that American oak has a larger open porosity and that pore connectivity can be improved by pyrolysis at 800 oC. Such a bimodal interconnected pore structure may find use for drug delivery in biomaterials applications