How Does Hot-Pressing Affect Fomes Fomentarius Mycelium? From Hydrophobic To Hydrophilic

Hot-pressing fundamentally reverses the natural wetting behavior of Fomes fomentarius mycelium. The process transitions the material from a naturally water-repellent (hydrophobic) state to a water-absorbing (hydrophilic) one. This drastic shift occurs because the simultaneous application of heat and pressure destroys both the chemical and physical mechanisms that originally allowed the mycelium to repel water.

The transition to hydrophilicity is driven by two simultaneous mechanisms: the thermal denaturation of hydrophobic surface proteins and the physical collapse of air-trapping micropores.

Mechanisms of Surface Alteration

To understand why this change occurs, we must look at how the hot-pressing environment affects the mycelium's biological structure.

Thermal Denaturation of Proteins

Natural mycelium relies on specific surface hydrophobic proteins to repel water.

When exposed to the high temperatures of a heated laboratory press (often around 160 °C), these proteins undergo denaturation.

The heat alters the structural conformation of the proteins, stripping them of their functional hydrophobic properties.

Elimination of Surface Microstructure

Hydrophobicity is not just chemical; it is also morphological.

Natural mycelium contains a network of micropores that trap air, preventing water from fully wetting the surface.

The extreme pressure applied during processing (up to 100 MPa) causes the elimination of these air-trapping micropores.

Without these pockets of air to act as a barrier, water can make direct contact with the surface material, leading to rapid wetting.

Understanding the Trade-offs

While the loss of hydrophobicity may seem like a disadvantage, it is a direct consequence of structural densification.

The Cost of Densification

The hot-pressing process compresses the mycelium to extreme degrees, often reducing its height by over 95%.

This transforms a loose, porous network into a high-density sheet.

While this destroys the porous structure required for water repellency, it facilitates close contact and bonding between hyphae.

Mechanical Gain vs. Surface Loss

The trade-off for becoming hydrophilic is a significant increase in tensile strength and stiffness.

You are effectively exchanging the material’s natural surface protection for superior mechanical integrity.

Users must recognize that the "loose" structure required for hydrophobicity is incompatible with the "dense" structure required for high stiffness in this specific process.

Implications for Material Application

The decision to use hot-pressing should be dictated by the specific performance requirements of your final application.

If your primary focus is mechanical load-bearing: You should proceed with hot-pressing to achieve high density and stiffness, but you must anticipate that the material will require a secondary coating to resist water.
If your primary focus is natural water repellency: You must avoid high-pressure densification, as retaining the native hydrophobic proteins and porous microstructure is essential for this property.

Ultimately, hot-pressing essentially re-engineers the mycelium from a porous biological foam into a dense, hydrophilic composite.

Summary Table:

Factor	Natural State	Post-Hot-Pressing State
Wetting Behavior	Hydrophobic (Water-Repellent)	Hydrophilic (Water-Absorbing)
Surface Proteins	Functional & Repellent	Thermally Denatured
Microstructure	Porous (Air-trapping)	Dense (No Micropores)
Density	Low (Porous Foam)	High (95% Compression)
Mechanical Strength	Lower	Significantly Increased
Best Application	Moisture Resistance	Load-bearing Components

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References

Huaiyou Chen, Ulla Simon. Structural, Mechanical, and Genetic Insights into Heat‐Pressed <i>Fomes Fomentarius</i> Mycelium from Solid‐State and Liquid Cultivations. DOI: 10.1002/adsu.202500484

This article is also based on technical information from Kintek Press Knowledge Base .