Cells in the bark of ficus trees temporarily repair ruptures by secreting latex into the wound site which cures upon exposure to air.

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After a break or tear in its bark, ficus trees secrete pre-made latex at the site of the wound. When exposed to air, this complex emulsion coagulates into an elastic polymer that serves several defensive functions including halting any further tearing (i.e., increasing tensile strength) and sealing the wound from infection until cell growth can permanently mend the injury. Thirty minutes after the damage is sustained by the ficus, latex has already coagulated enough at the damage site for about 55% of the materials original, un-wounded tensile strength to be restored. This added strength is maintained for hours or days until cellular growth can restore the materials complete strength (latex protects from further tearing but does not provide stiffness). Even before 30 minutes after the injury, when latex is still largely uncoagulated, it serves to support the mechanical properties of the damaged material perhaps acting like a sticky, glue-like substance.

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"[C]oagulation of Ficus benjamina (weeping fig) latex [contributes] to a restoration of the mechanical properties of the bark after external lesions...A significant increase in the tensile strength of bark samples until 30 min after injury was found, and this effect could be attributed to the coagulation of plant latex alone. The tensile strength remains nearly constant until several hours or days after injury. Then, very probably due to other mechanisms such as cell growth and cell proliferation, the tensile strength begins to increase slightly again...The coagulation of latex seals lesions and serves as a quick and effective pre-step of subsequent, more effective, long-lasting self-healing mechanisms...Upon external injury of a plant stem, the latex oozes out and quickly coagulates. For the plant it is important to seal lesions originating from external injury. Besides the prevention of the entry of pathogens (fungi, bacteria and viruses) into underlying tissues, the restoration of the mechanical properties is also a crucial factor. Therefore, in particular the recovery of the mechanical properties of the peripheral region (e.g. the bark) of a plant stem is important, as stresses in plant stems are largest in these regions of the stem and lesions are at risk of expanding due to such stresses...A faster mechanism, such as the coagulation of plant latices, enabling at least a partial restoration of the mechanical properties, could act as a first quick step of the complete recovery of these properties by cell and tissue growth in later repair phases." (Bauer 2012:807)

"The tensile strength of bark samples immediately after injury...decreased to 42% of the values obtained for uninjured bark. Up to a latency time of 30 min the tensile strength increases to a significantly higher value..., representing 55% of the value obtained for uninjured bark, and remains nearly constant for a considerable time, until 150 min after injury. Not before several hours or days after injury does the tensile strength begin to increase again slightly." (Bauer 2012:808)

"The observed increase in tensile strength of the whole bark taking place during the first 30 min after injury cannot be caused by an additional absorption of stresses by the coagulated latex alone. Thus, we propose a mechanism that can be compared with the mechanism of wet adhesion and/or the adhesion supported by a glue between two surfaces: in the case of both the uncoagulated and the coagulated, but still sticky, latex, the contact surfaces (i.e. the two sides of the lesion) remain in close contact with each other and are only separated by a thin layer of the uncoagulated (liquid) or coagulated latex ('glue'). We hypothesize that the latex acts as a 'crack stopper' hindering the crack propagation in the lesion and thus increasing the tensile strength (but not the Young’s modulus). Cross-linking taking place during coagulation increases this 'crack-stopping' function but will not increase the Young’s modulus significantly. Although the described repair effect may restore the mechanical properties of the plant stem only partially, the coagulation of the latex seals the lesion and reduces the crack propagation under tensile loading. Additionally, it serves as a quick and effective pre-step of subsequent, more effective but much longer lasting mechanisms such as cell growth and proliferation." (Bauer 2012:810)

Journal article
Restoration of tensile strength in bark samples of Ficus benjamina due to coagulation of latex during fast self-healing of fissuresAnnals of BotanyDecember 30, 2011
G. Bauer, T. Speck

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