Advances in medical uses for alumino-silicate clay minerals

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Published: Wednesday, 03 September 2014

Frank Hart* addreses the importance of clays in medicine, including kaolin used to cure stomach upset and the promising future of halloysite nanotubes.

Kaolin has long been associated with medicinal qualities. The internal use of kaolin and morphine for diarrhea and stomach upsets, as well as the external use of kaolin preparations, as facemasks or poultices, to improve skin condition and reduce swellings is well documented.

There are three long established grades of kaolin approved to British Pharmacopoeia: BP Light, BP Light Natural and BP Heavy.

Kaolin and morphine helps to heal stomach upsets by absorbing toxins from the gut and bulking faeces.

Facemasks meanwhile absorb oil and dirt from pores in the skin while poultices provide localised heat and moisture to relieve pain and draw pus.

For the last 20 years or so, Goonvean Ltd, now part of Imerys, has supplied the bulk of the global BP kaolin market, estimated at 1,500 tpa. Prices range from £600/tonne to £1,200/tonne ($1,010-2,020**/tonne) depending on the grade.

Montmorrillonite, a smectite, has been used for its detoxifying effects for many years.

It can be taken either internally, as an aqueous preparation, or applied externally as a cream, taking advantage of the body’s ability to excrete heavy metals through the pores of the skin.

In many cases medical benefits from kaolin and smectite occur due to their absorptive power in removing unwanted matter such as heavy metals, pollutants and fungi.

In such cases more highly refined clays with finer particle size and greater surface area are likely to be more effective. However, in the case of bacteria and virus elimination, the reverse seems to be true, in that unrefined clays that contain specific trace metals are better.

Both kaolinite and smectite have a layer lattice structure. Smectites are much finer and have the ability to swell significantly and absorb water.



A brief summary, covering some new ideas and research, is shown below:

Halloysite

Halloysite is chemically very similar to kaolinite but the alumino-silicate sheets are rolled into tubes. Major deposits occur at Matauri Bay in New Zealand, owned by Imerys, and at the Dragon mine in Utah, owned by Applied Minerals. I-Minerals is currently developing a new deposit near Bovill in northern Idaho, which is characterised by a high aspect ratio (longer tube length).

Halloysite nanotubes (HNT) have been the subject of intense investigation in recent years due to their ability to hold, and slowly release, pharmaceutical preparations at a uniform and sustained rate with no initial surges (overdose).

Halloysite tubes can be enlarged internally to increase volume capacity by etching the lumen with suitable acids. Active pharmaceutical preparations are loaded into the hollow tubes by vacuum techniques. The release rate can be tailored from hours to days by ‘capping’ the ends of the tubes, which is achieved by reacting the internal chemical agents with metal ions, or using starch. An alternative method that is also used, is to encapsulate the HNT with polymers such as polyethyleneimine.

Most research to date has been done with halloysite from the Dragon mine supplied via Sigma Aldrich to research institutes.

HNT competes against synthetic engineered carbon nanotubes but is significantly cheaper at approximately $140/lb versus $4000/lb, depending on the supplier and grades. Additionally, there are concerns that carbon nanotubes may have adverse health effects whereas halloysite is non-toxic.

A review of some new applications is shown below:

1. Cancer. HNT has been shown to be effective in capturing circulating tumor cells in the bloodstream eg. leukemic cells.

2. Drug release through transdermal patches. Drugs such as stimulants and hormones can be applied using HNT. Fewer drugs per patch are required and improved delivery rates are possible.

3. The controlled, slow release, of antibacterials, antiseptics, enzymes and proteins.

4. The slow release of glycerol in face creams to act as a moisturiser for skin care.

5. The slow release of Chitosan in dental applications such as toothpaste or fillings.

6. The slow release of antibiotics

in PMMA (polymethylmethacrylate) bone cement. The HNT component also brings improvements to mechanical properties such as tensile and flexural strength.

7. Wound care. HNT loaded with appropriate drugs can be embedded into the base layer of bandages. The treatment of burns is a good example where risk of infection and scarring is reduced.



Potential side effects

As with all cures there are potential side affects. These include the absorption of useful nutrients, vitamins or drugs and eventual removal through the gut system, as well as a reduced rate of absorption of such materials due to particle coatings on the digestive tract.

Further research

Clay minerals have been shown by a number of different research institutes to have great potential in curing various health problems; in particular, the work done on HNT looks promising.

HNT is confined to in vitro testing at present, with the exception of some face creams on sale in Europe and South Korea.

Full approval for internal use of new medicines by regulatory bodies such as the FDA and MHRA can of course take years.

Future commercial implications for suppliers are for low volumes but high value. Sales will be priced in lbs or kgs rather than tonnes.

*Frank Hart, director at First Test Minerals Ltd., has been involved in the manufacture and quality control of BP Kaolin at Goonvean Ltd for nearly 30 years and, more recently, through First Test Minerals Ltd, in the sale of small lots. He welcomes any questions or comments from anyone across the world, especially technical ideas, which might progress the development of minerals in this important sector. Contact him at frank.hart7@btinternet.com

**Conversion made August 2014