The specialised stomach compartments fround in ruminant animals (e.g. cows, sheep) contain symbiotic microbes that digest the cellulose in the animals' diets. Because conditions in the various parts of the digestive system vary so widely, this may impact on the metabolism of drugs that are given orally, such as drenches for gut parasites. There is a lot of interest in developing ways of placing a reservoir of drugs into the rumen that can be slowly released over a relatively long period of time. But due to the complex chemical environment in the rumen, there are a number of challenges to overcome.

A group of researchers from Waikato University, Dexcel Ltd, InterAg NZ, and the University of Canterbury investigated the use of 'smart' polymers as a tool for the controlled release of drugs into the rumen.  Smart polymers are useful in this context because their molecular structure can change reversibly when environmental conditions alter. The team investigated the use of microcapsules made of a smart polymer that released their contents at low pH but retained them at a neutral pH. This would mean that similar capsules containing drugs could have their release targeted for a particular region of the gut.

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 biomaterials polymer 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 xenografts 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.


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).


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 growth.

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., 2007). 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 amputated.)

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.

References:
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(3): 143-148.