# Recent Advances in Bio-Based Wood Protective Systems: A Comprehensive Review
## 4 Bio-Based Fillers
### Bio-Based Additives for Antimicrobial Wood Systems  
Over time, wood preservatives have seen a steady enhancement in their effectiveness, safety during usage, and eco-friendliness. This progress has been driven by the gradual replacement of certain chemical elements, prompted by concerns about their efficiency and impact on the environment. While numerous wood preservatives effectively hinder fungal decay, their adverse environmental effects have led to restrictions on their usage in numerous countries. Hence, there is a notable ongoing pursuit for novel, ecologically friendly, and environmentally conscious antimicrobial supplements. In particular, researchers are exploring inventive bio-based fillers to enhance wood coatings, equipping them with the ability to combat fungi. This is vital because fungi pose a significant risk to the durability of wooden materials. Considering this, a recent investigation conducted an assessment of the impact of certain chosen organic substances and modified versions thereof (including tea tree oil, propyl gallate, hydrogenated gum oil, salicylic acid, cinnamon bark oil, butylene oxide, and furfural) on the suppression of blue stain and mould fungi [105]. The study's findings indicated that salicylic acid, tea tree oil, and cinnamon bark oil exhibited the lowest level of mould proliferation following a four-week exposure within a mould chamber experiment. However, the literature is full of recent studies on the fungicidal effect of natural extracts. For instance, a raw extract obtained from crude heartwood, which contains the compounds pinosylvin (PS) and pinosylvin monomethyl ether (PSM), was employed as an antifungal treatment for Scots pine sapwood [92]. The study demonstrated that saturating the wood with a substantial amount of these stilbene compounds (at a rate of 60 milligrams per gram of dry wood) effectively inhibited fungal growth and notably decelerated the wood degradation process, particularly when dealing with the _G. trubeum_ fungus. Furthermore, coffee extracts have exhibited effective antifungal properties as well. For instance, [PERSON] et al. [120] highlighted the promise of cinnamates derived from used coffee as agents against microorganisms. When used at concentrations of 1% and higher, spent coffee substantially inhibited the growth of various fungi under examination, indicating its potential utility as an environmentally friendly ingredient in the composition of wood preservatives. Likewise, a recent examination explored the potential application of coffee silverskin, a byproduct generated during coffee roasting, as a raw material for antifungal components in wood preservatives [106]. In this subsequent scenario, the attempt to repurpose silverskin from industrial leftovers did not prove effective as a wood preservative. Nevertheless, it continued to hold promise as a prospective reservoir of antifungal compounds for the development of wood preservative formulations. However, various extracts exhibiting favourable antifungal characteristics are readily available in the natural world. For instance, [PERSON] et al. [100] conducted an investigation into the effectiveness of propolis's extract in safeguarding Scots pine wood against the brown-rot fungus _C. puteana_. The findings indicated that, when wood was treated with propolis's extract at concentrations exceeding 12%, the advancement of fungal decay was restricted. Furthermore, the propolis's extract employed for wood treatment was abundant in phenolic compounds, notably chrysin, pinocembrin, and galangin, all of which possess antimicrobial properties. These findings suggest that the propolis's extract derived from Poland holds potential as a promising natural wood preservative, ensuring safety for both humans and the environment. Lastly, [PERSON] et al. [99] conducted an experiment involving 41 individual monoterenes to assess their toxicity against wood white-rot fungi, namely _T. hirsuta, S. commune_, and _P. sanguineus_.