Bone is another
readily-available by-product from the meat industry. This has the
potential to be used in production of 'biomaterials' - substances that
come into contact with living tissues (Mucalo & Worth, 2008). One
use is in protheses, to replace damaged joints or missing bone.
Research into biomedical use of bone products is interdisciplinary
- but chemistry plays a major role because of its importance in
science. Research chemist Michael Mucalo
and his team have been investigating the use of biomaterials
in replacing bone lost through disease or accident. They are working on
the development of xenografts - manmade bone substitutes. While
don't contain any living cells (unlike natural bone, which
is a living tissue), they can act as a scaffold supporting the
growth of new bone.
Michael Mucalo (left) and research students Dougal Laird &
Ashley Easter, working with some of the biomedical materials they have developed from cow bone..
Bone is made up of a matrix of calcium
phosphate and the protein
collagen that supports the living component: cells and blood vessels.
However, it's not a homogenous substance. There's an outer hard layer,
called cortical bone, that surrounds the soft, spongy inner cancellous
bone. A xenograft replacement for bone must reproduce all this if it's
to be successful. In addition it has to be compatible with the body's
tissues and also able to be remodelled - reshaped and penetrated by new
bone - as the graft heals. Michael's team has focused on developing
xenograft materials from cow bone, as this is easy to obtain and - in
New Zealand at least - free of notifiable diseases such as Bovine
Spongieform Encephalitis (BSE). This research "has the potential
to produce a cheaper, high value biomedical commodity out of a
traditionally low value material currently used for fertiliser or
disposed of into the environment" (Mucalo & Worth, 2008).
Section of cow femur & prepared bone specimens.
To prepare bone for a xenograft, cubes of bone are cut from the knee
end of a cow femur (thigh bone). The cubes are then boiled and treated
chemically to remove blood and fat, before soaking them in an oxidising
agent such as hydrogen peroxide to remove collagen
. This leaves a
chalky cube of carbonated hydroxyapatite, which can be cut to a
suitable shape before being used as an implant. The material can also be
produced as a powder, which could then be sprayed onto artificial joint
surfaces, improving bonding between the artificial joint and new bone
Do the xenografts work?
In 2007 the research team reported their use in a labrador with a bone lesion in its right foreleg (Worth et al.
The usual treatment for such bone damage involves draining the cavity
& removing the damaged tissue (leaving a cavity), with or without
use of a bone graft. (In really severe cases the leg would be
In the case of the labrador, the dog's owner gave permission for the
surgical team at Massey University's Veterinary School to use the
Waikato xenografts as part of their treatment. The xenograft was cut to
fit the cleaned-out cavity in the dog's foreleg, and any gaps between it and the undamaged bone were packed with
healthy bone from the dog itself.
Two months after the operation, X-rays showed that new bone was forming
in the cavity and integrating with the graft. And after 10 months the
bone had completely healed.
M.R. Mucalo & A.J. Worth (2008) Biomedicals from bone. Chemistry in New Zealand
January 2008: 13-18
A.J. Worth, K.G. Thompson, M.C. Owen, M.R. Mucalo & E.C. Firth
(2007) Combined xeno/auto-grafting of a benign osteolytic lesion in a
dog, using a novel bovine cancellous bone biomaterial. NZ Veterinary Journal 55