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