Introduction

Growing concerns regarding plastic pollution, fossil resource depletion, and climate change have intensified the search for sustainable alternatives to petroleum-based polymers. In this context, bio-based and biodegradable materials have gained increasing scientific and industrial attention due to their potential to reduce environmental impacts while maintaining functional performance in engineering applications. Among these materials, PolyLactic Acid (PLA) is one of the most widely investigated bio-based thermoplastics because of its renewable origin, biodegradability, and compatibility with conventional polymer-processing and additive manufacturing technologies1,2. PLA is commonly derived from renewable agricultural feedstocks such as corn starch or sugar cane and exhibits favourable properties including relatively high stiffness, dimensional stability, low processing temperatures, and good printability. These characteristics have contributed to its widespread use in Material Extrusion Additive Manufacturing (MEX AM), a three-dimensional 3D-printing technology that fabricates components layer-by-layer directly from digital geometries3,4. Consequently, PLA is frequently employed for lightweight structures, rapid prototyping, and sustainable manufacturing applications.

Despite these advantages, PLA also exhibits several limitations, including intrinsic brittleness, limited thermal resistance, and relatively low impact strength, which restrict its broader use in load-bearing and structural applications3,4. To overcome these limitations, the incorporation of natural lignocellulosic fillers has attracted increasing scientific interest. In particular, wood particles are considered promising bio-based fillers due to their low density, renewability, widespread availability, and low cost5,6. When incorporated into PLA filaments, wood particles form bio-based composites in which the lignocellulosic filler can influence stiffness, deformation behaviour, and printability depending on the particle characteristics, filler content, and interfacial adhesion between the wood particles and the PLA matrix7,8. The mechanical response of PLA/wood composites is influenced by several factors, including the nominal wood-particle content, filament formulation, processing conditions, additive manufacturing parameters, and the characteristics of the incorporated wood particles, such as their size and morphology9–11. Commercially available PLA/wood composite filaments have already been investigated with respect to their mechanical properties and processability in MEX AM3,5,11. However, little is known about how post-printing fungal colonisation and the associated processing conditions affect the tensile behaviour of these material combinations. Understanding this interaction is essential for the development of fungal-colonised additively manufactured bio-based composites.

More recently, mycelium-based materials have attracted increasing scientific attention as sustainable biological materials. Mycelium, the filamentous vegetative network of fungi, can grow on lignocellulosic substrates and form lightweight bio-based structures12,13. Although fungal colonisation is not primarily intended to improve the tensile strength of PLA/wood composites, it may provide additional functionalities that are not available in the untreated material. Mycelium can create biologically active or biodegradable surface layers, improve the integration of printed components into bio-based systems, and enable the development of hybrid living or biofabricated materials. Such approaches are increasingly being investigated for applications in sustainable construction, packaging, insulation, architectural components, and circular material systems. Before these applications can be realised, however, it is essential to understand how fungal colonisation influences the mechanical behaviour of the printed substrate. Due to their biological origin and cultivation-based fabrication process, mycelium materials are increasingly investigated for applications in packaging, architecture, thermal insulation, and biofabrication. In parallel with these developments, researchers have begun exploring the integration of fungal-based materials with additively manufactured structures. In recent approaches involving thermoplastic components, mycelium is generally not incorporated directly into the molten polymer during manufacturing. Instead, fungal colonisation is typically applied after fabrication onto previously manufactured structures14–17. In such systems, fungal growth may influence the surface condition and mechanical response of the fabricated components.

Although PLA/wood material combinations and mycelium-based materials have each been investigated individually, only limited research has addressed their combined use within additively manufactured hybrid material combinations. For example, Sharma and Le Ferrand17 recently reported mycelium-bound composites enabled by 3D-printed gyroid scaffolds, demonstrating the growing interest in combining additive manufacturing with fungal-based materials. However, their work focused on scaffold-supported mycelium composites, whereas the mechanical response of MEX-manufactured PLA/wood material combinations following fungal colonisation and the associated processing conditions remains largely unexplored. In particular, there is limited understanding of how different nominal wood-particle contents affect the mechanical response of PLA/wood material combinations before and after fungal colonisation. Furthermore, systematic comparisons between untreated and fungal-colonised specimens across several PLA/wood material combinations are still lacking. Consequently, the present study addresses an important and timely research gap in the field of bio-integrated additively manufactured materials.

Therefore, the present study investigates the tensile behaviour of additively manufactured PLA/wood biocomposites containing nominal wood-particle contents between 10 and 50 wt.%, both in the untreated condition and after post-printing colonisation with the fungus Fomes fomentarius. The underlying hypothesis of this work is that PLA/wood composites subjected to post-printing fungal colonisation and the associated processing conditions exhibit a modified mechanical response compared with untreated specimens, while providing a basis for future bio-integrated applications. Therefore, quantifying changes in tensile properties following fungal colonisation and the associated processing conditions represents an essential first step toward the development of functional hybrid bio-composite systems. The study focuses on experimentally comparing mean Young’s modulus (E), mean Ultimate Tensile Strength (UTS), and fracture behaviour under uniaxial tensile loading as a function of wood-particle content and post-printing fungal colonisation treatment. In addition, a supplementary screening-level Life Cycle Assessment (LCA) is conducted to compare the environmental impacts associated with the investigated material combinations during the MEX AM fabrication stage.

Figure 1 summarises the overall workflow of the study, including the fabrication of PLA/wood composite specimens by MEX AM, the subsequent fungal colonisation process, tensile characterisation, and the assessment of mechanical and environmental performance.

Fig. 1: Overview of the Make–Break–Simulate workflow applied in this study: (a) design of the ASTM D3039 tensile specimen, (b) post-printing fungal colonisation using Fomes fomentarius, (c) fabrication of PLA/wood specimens using MEX AM, (d) tensile testing using a universal testing machine, (e) evaluation of engineering stress–strain behaviour and determination of mean E and mean UTS, (f) statistical analysis of untreated and fungal-colonised specimens, and (g) screening-level LCA of the investigated material combinations.

The following research questions are addressed in this work: How does the mechanical response of PLA/wood material combinations with different wood-particle contents differ between untreated specimens and specimens subjected to post-printing fungal colonisation and the associated processing conditions?How do the investigated PLA/wood material combinations compare in terms of their screening-level environmental impacts during the MEX AM fabrication stage?