Eggs are a basic food for almost the entire world population, although their consumption and handling generates a significant volume of waste products. Logically, the main waste generated in this food sector is the shell, which accounts for approximately 10% of the total weight of the egg.
What you may not have known is that shells can be transformed and reused in multiple ways to obtain materials with various technological and industrial applications, complying with the principles of the circular economy in the food industry.
For example, they can be part of fertilizers and food supplements for animals and be used as a decontamination agent for wastewater, as well as in the development of materials aimed at tissue regeneration. This last biomedical use is the one we will explore later.
The formation of the chicken eggshell can be considered the fastest controlled process of mineral calcification in nature. It is a very complex biological structure and perfectly designed, from a physiological and mechanical point of view, for the embryonic development of the chick.
This protective coating is formed by a calcified layer (calcium carbonate crystals in the form of calcite) adhered to the external surface of a membrane that looks like a thin film, as we can see when breaking an egg.
In order to take advantage of its biomineral qualities, a recent study has proposed an experimental methodology to transform the mineral component of the shell into calcium phosphate particles. In this way, its composition would be analogous to that found in bones and teeth, and it would partially maintain the organic composition of the original structure.
The results of this research are useful for designing and manufacturing biocompatible materials with osteoinductive properties, that is, capable of regenerating mineral tissues in the field of tissue engineering and dentistry. The ultimate objective is to convert this waste into particles of biomedical interest, establishing a profitable procedure (with a reduced number of processing operations) and respectful of the environment. This would be achieved through a low-temperature hydrothermal chemical transformation method.
Now we are going to look at the membrane, the thin layer adhered to the inside of the egg and that can be easily separated with our hands when we break the shell to make any recipe. This membrane has a high content of numerous proteins, such as lysozyme, ovotransferins and clusterin, as well as different types of collagen. The composition of this natural polymer makes it interesting for cosmetic use, as a nutritional supplement or in the development of dressings for burns or wounds.
Another research proposes developing a new biomaterial by mineralizing the membrane. What is intended is to replicate the formation and construction present in mineralized tissues and the mechanical behavior of other collagen-based systems, such as those found in bones and teeth.
The scientists managed to precipitate apatite (a mineral composed of calcium phosphate) on the external surface of the membrane through a controlled crystallization system, while the internal surface remained unmineralized. The composition of apatite, together with the collagen present in the membrane, is similar to that which is part of mineralized tissues.
Furthermore, biological assays indicate that this biohybrid material (which incorporates a biological tissue) is biocompatible and non-cytotoxic (that is, it would not affect the development of certain cells on its surface), inducing the proliferation and differentiation of different cell types involved in the bone metabolism.
The goal of this work was to manufacture a two-dimensional biomaterial with a double function: regenerate tissue on its mineralized external surface and protect against cell invasion on the internal part. In other words, it would play a role similar to that of the shell membrane during egg formation when produced by laying hens.
The cited studies take advantage of the characteristics and biological design of the eggshell to replicate the structure and composition of mineralized tissues. The development of these materials could be used in future applications of guided bone regeneration and dental treatments, such as coating the dental pulp in cases of possible tissue exposure in deep caries.
And also, of course, it is interesting in terms of circular economy, since it proposes the conversion of waste from the food industry into materials with promising biomedical properties.
This article was originally published on The Conversation. Pedro Álvarez Lloret is a professor of Crystallography and Mineralogy at the University of Oviedo,
