Cellulose is the most abundant polysaccharide on Earth. It can be obtained from a vast number of sources, e.g. cell walls of wood and plants, some species of bacteria, and algae, as well as tunicates, which are the only known cellulose-containing animals. This inherent abundance naturally paves the way for discovering new applications for this versatile material. This review provides an extensive survey on cellulose and its derivatives, their structural and biochemical properties, with an overview of applications in tissue engineering, wound dressing, and drug delivery systems. Based on the available means of selecting the physical features, dimensions, and shapes, cellulose exists in the morphological forms of fiber, microfibril/nanofibril, and micro/nanocrystalline cellulose. These different cellulosic particle types arise due to the inherent diversity among the source of organic materials or due to the specific conditions of biosynthesis and processing that determine the consequent geometry and dimension of cellulosic particles. These different cellulosic particles, as building blocks, produce materials of different microstructures and properties, which are needed for numerous biomedical applications. Despite having great potential for applications in various fields, the extensive use of cellulose has been mainly limited to industrial use, with less early interest towards the biomedical field. Therefore, this review highlights recent developments in the preparation methods of cellulose and its derivatives that create novel properties benefiting appropriate biomedical applications.

Water is the liquid of life. Nature has therefore evolved countless enzymes that catalyse the addition of water to C=C bonds, isolated or conjugated. These reactions are regio- and enantioselective, they are part of primary metabolism as well as the secondary metabolism. The enzymes that catalyse these reactions (hydratases or hydro-lyases) are applied industrially in selected cases. However, they are not generally used in the laboratory although they outperform all currently available catalytic chemical methodologies. This feature article highlights the potential that hydratases have for chemistry compared to the acid catalysed addition of water.

The flavoenzyme vanillyl alcohol oxidase (VAO, EC 1.1.3.38) from Penicillium simplicissimum is active on a range of phenolic compounds [1,2]. It contains a covalently linked FAD cofactor, and the holoprotein forms stable octamers. VAO was the first histidyl-FAD-containing flavoprotein for which the crystal structure was determined [3], and serves as a prototype for a specific flavoprotein family [4]. Mutagenesis studies have shown that the covalent flavin-protein bond is crucial for efficient catalysis, and that covalent flavinylation of the apoprotein proceeds via an autocatalytic event [5,6]. As well as oxidizing alcohols, the fungal enzyme is also able to perform amine oxidations, enantioselective hydroxylations, and oxidative ether-cleavage reactions [7,8]. Several substrates can serve as vanillin precursors (e.g. vanillyl alcohol, vanillyl amine and creosol) [9,10]. Recently, VAO has been used in metabolic engineering experiments with the aim of creating a bacterial whole cell biocatalyst that is able to form vanillin from eugenol [11,12]. However, VAO is poorly expressed in bacteria, resulting in a relatively low intracellular VAO activity [12] and low yields of A gene encoding a eugenol oxidase was identified in the genome from Rhodococcus sp. strain RHA1. The bacterial FAD-containing oxidase shares 45% amino acid sequence identity with vanillyl alcohol oxidase from the fungus Penicillium simplicissimum. Eugenol oxidase could be expressed at high levels in Escherichia coli, which allowed purification of 160 mg of eugenol oxidase from 1 L of culture. Gel permeation experiments and macromolecular MS revealed that the enzyme forms homodimers. Eugenol oxidase is partly expressed in the apo form, but can be fully flavinylated by the addition of FAD. Cofactor incorporation involves the formation of a covalent protein-FAD linkage, which is formed autocatalytically. Modeling using the vanillyl alcohol oxidase structure indicates that the FAD cofactor is tethered to His390 in eugenol oxidase. The model also provides a structural explanation for the observation that eugenol oxidase is dimeric whereas vanillyl alcohol oxidase is octameric. The bacterial oxidase efficiently oxidizes eugenol into coniferyl alcohol (K M ¼ 1.0 lm, k cat ¼ 3.1 s )1 ).Vanillyl alcohol and 5-indanol are also readily accepted as substrates, whereas other phenolic compounds (vanillylamine, 4-ethylguaiacol) are converted with relatively poor catalytic efficiencies. The catalytic efficiencies with the identified substrates are strikingly different when compared with vanillyl alcohol oxidase. The ability to efficiently convert eugenol may facilitate biotechnological valorization of this natural aromatic compound.Abbreviations EUGO, eugenol oxidase; PCMH, p-cresol methylhydroxylase (EC 1.17.99.1); VAO, vanillyl alcohol oxidase (EC 1.1.3.38).