Luffa sponges have been in fashion for some time. They are sponges of natural origin, with a hard and rough texture, which soften when wet, and with a great exfoliating property. There are several ways to present the product; some are made from braided and interwoven fibers; others, much more rudimentary, present themselves directly with the same appearance, elongated and irregular, that they originally had.
Unlike marine sponges, of animal origin and belonging to the poriferous group, Luffa sponges are of plant origin and are obtained from the fruit of a plant.
It is the genus Luffa —hence its name—, with several very representative species, among which Luffa aegyptiaca stands out, an annual climbing plant native to South and Southeast Asia, from the Cucurbitaceae family.
How is a sponge extracted from a fruit?
The fruit of L. aegyptiaca looks very similar to zucchini —a plant from the same botanical family—, elongated and about 30 centimeters long. In some places, the young fruit is consumed as food, in fact, it has traditionally been cultivated in Asia for that purpose.
When the fruit ripens, however, it becomes extremely stringy and dries up on the plant itself, rendering it inedible. In the process it loses practically all the pulp, and only the vascular bundles of the xylem remain, like a hard and rigid mesh. These vascular bundles form the fiber that will become the sponge.
The first step after harvesting is to peel the ripe fruit. It can be peeled freshly harvested, but it is easier to do it after hydration: the peel almost falls off on its own. Then you have to remove the seeds, which is traditionally done by beating: hitting the fruit against a mesh or against a piece of wood, causing the seeds to detach and fall.
Several washings are necessary to remove the remains of pulp. Once the sponge is clean, it is allowed to dry and is ready for use.
The whole fruit can be used, or cut into pieces with specific shapes, or through a process that extracts the fiber in the form of thread, which is then braided or woven to make more elaborate products.
This way of making the sponge dates back to ancient times . Although its use in Europe is relatively recent, Luffa sponges have a tradition in the tropical regions of Asia and America. The oldest records of the use of this plant are found in Israel, in some temple mosaics from the Byzantine era.
It’s not just a sponge
The fiber obtained from L. aegyptiaca is not only very useful as an exfoliating sponge. This material has been the object of study in the field of materials technology, due to its specific properties .
Due to their origin, vascular bundles of the fruit xylem, the simple fibers have a high porosity, and are composed mainly of a matrix of lignin, cellulose and hemicellulose. This makes it a material with a resistance similar to that of wood. In addition, the way in which the fibers are arranged in the fruit make it a very light structure, but at the same time firm and resistant to deformation. In fact, its structure has even been suggested as a model for the production of foams with applications such as the manufacture of lighter anti-crushing devices.
On the other hand, its high porosity makes it an extraordinarily adsorbent material capable of retaining dissolved substances on its surface —not to be confused with ‘absorbent’—. This fact adds to its biodegradable nature, to make it a very promising material as an alternative to other less sustainable adsorbents. In this sense, applications have been cited in sectors such as medicine, cosmetics, industry and, particularly relevant, wastewater treatment .
Another possible utility of the Luffa sponge points towards the field of microbiology and cell biology , particularly for cell immobilization. In this sense, the sponge would serve as a kind of exoskeleton or scaffold that facilitates the growth of cell cultures. Its high porosity allows the cultured cells to settle properly in its structure, while its lightness makes it very easy to handle. In addition, it is resistant to changes in pH, and very easy to sterilize.
References:
Anastopoulos, I. et al. 2020. Environmental applications of Luffa cylindrica-based adsorbents. Journal of Molecular Liquids, 319, 114127. DOI: 10.1016/j.molliq.2020.114127
Chen, Q. et al. 2014. A multiscale study on the structural and mechanical properties of the luffa sponge from Luffa cylindrica plant. Journal of Biomechanics, 47(6), 1332-1339. DOI: 10.1016/j.jbiomech.2014.02.010
Oboh, I. et al. 2009. Luffa cylindrica-an emerging cash crop. African Journal of Agricultural Research, 4, 684-688.
Saeed, A. et al. 2013. Loofa (Luffa cylindrica) sponge: Review of development of the biomatrix as a tool for biotechnological applications. Biotechnology Progress, 29(3), 573-600. DOI: 10.1002/btpr.1702
