If the stakeholders play it right, we could see the birth of a new industry whose essential raw material is something that is dumped as waste — eggshells.

In recent years, the scientific community has been discovering the usefulness of eggshells in making bioceramics — materials used to repair bones and teeth. Eggshells, non-toxic and plentifully available at practically no cost, are rich in calcium carbonate, which can be converted into a variety of calcium phosphates, the basic building material of bones and teeth. Recent research by Prof TS Sampath Kumar of the Medical Materials Laboratory, Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Madras, identifies several pathways for the use of eggshell-derived chemicals in medicine — as bone fillers, dental fillers, cements and drug delivery systems.

This is of particular interest to India, home to the world’s third largest poultry sector, where 730 million birds lay about 120 billion eggs a year — roughly, 600,000 tonnes of eggshells. Kumar calls it a ‘gold mine’.

His research, published in the Journal of the Indian Institute of Science, tried to find out why eggshells are so suited to be made into bioceramics. When a doctor injects a paste into a fractured bone, it is expected to bond with the bone environment and become a part of it. Basic chemistry tells us that any bonding involves the attraction of ions, which are atoms that have more electrons than protons (negatively charged) or fewer (positively charged). So, proper bonding calls for the presence of ions. Bones have tiny amounts of magnesium, strontium, silicon and sodium. Kumar’s research showed that eggshells, too, have these. In fact, without these, the birds couldn’t have made the eggs in the first place.

Cooking up a solution

Eggshells are made up of calcium carbonate (94 per cent), calcium phosphate (1 per cent) and other organic matter (4 per cent). Calcium phosphates (CaPs) have been known to be good bone substitutes. Among the various CaPs, hydroxyapatite (HA) and its variant, calcium-deficient hydroxyapatite (CDHA), are known to help bone healing and bone regeneration.

Kumar’s Medical Materials Laboratory is tucked away in a nondescript, tiled shed that once used to house electrical generators. It has none of the glitzy sophistication of a buzzing chemical research centre. But, as it turns out, the researchers here didn’t need anything more than a ream of writing paper and a microwave oven.

Using the microwave oven, Kumar and his team (comprising K Madhumathi and R Jayasree) synthesised HA and CDHA from cleaned chicken eggshells. (Eggshells were heated to 900 degrees C for three hours to convert calcium carbonate into calcium oxide, which, in turn, becomes calcium hydroxide on exposure to air. Adding diammonium hydrogen phosphate to this yielded nano CDHA).

The process was novel — it was indeed a sort of cooking, with eggshells and phosphoric acid. The team was also able to ‘tune’ the CDHA to vary the ratio of calcium to phosphorous for application-specific compositions.

While CDHA is a sort of flagship product, the team came up with a bunch of other products too. For example, they heated HA to 1,100 degrees C, and came up with tricalcium phosphate (TCP). Heat HA to 1,400 degrees C, you get tetra-calcium phosphate (TTCP), an excellent material for making cement to fix broken bones.

The nano carriers

Further, any material that is introduced into the skeletal system to fill gaps or build back bones or gum together broken bones should ideally be capable of conducting drugs to wherever they are required. For example, if there is a bone infection, the man-made material should be a good drug carrier. Kumar says eggshell-derived materials are good at this too. It is not difficult to synthesise calcium phosphate in nano form. Nano materials distribute drugs well. Calcium phosphate nanoparticles offer more reaction sites for drug binding due to their high surface-to-volume ratios compared with bulk form. The researchers found out that eggshell-derived nano CDHA, tuned to a calcium-to-phosphate ratio of 1.61, was best suited for delivery of antibiotics, while eggshell-derived TCP was best for ibuprofen loading.

Thus, the team was able to produce a phalanx of products from eggshells, such as HA, CDHA (with variable calcium-to-phosphate ratios), carbonated apatite, amorphous calcium phosphate, TCP and TTCP, to suit specific medical applications. Kumar stressed that many more products could be derived from eggshells — any calcium-based product. For example, carbonated apatite, a good cancer fighter, can be produced from eggshells.

It is pertinent to note that calcium phosphates have always been used for bioceramics. What’s new is that it can be made from eggshells. Kumar notes that people generally keep away from natural raw materials because they are non-homogenous. For instance, different eggshells from different parts of the country could have varying properties. The solution is to procure eggshells from a single source. On the other hand, eggshell-based bioceramics are better than synthetic bioceramics because they contain ions of magnesium, strontium, silicon and sodium. “The various ions present in eggshell can not only play a key role in bone regeneration but also influence the binding of therapeutic molecules like proteins and drugs,” Kumar says.

He says that the research is at a technology readiness level of 4 (TRL-4), which means it is ripe for the industry to scale it up. Further, the use of eggshells is still under-explored — there would be many more specific applications. For example, 3D bioprinting with eggshell-derived biomaterials could lead to the fabrication of more functional tissues and organs.

One should also not forget the role of this eggshell-derived bioceramics in the circular economy. Indiscriminate disposal of eggshells leads to microbial contamination, a harm that we hardly take notice of. A push from the government towards collection of eggshells would be a big help, Kumar says.