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Engineering joints and arteries

by LPS Special Correspondent

SCIENTISTS are building complete blood vessels and the inner surfaces of joints in their laboratories. The aim is to make these and other completely engineered structures available for transplant into patients suffering from conditions such as coronary thrombosis and osteoarthritis.

Eventually the researchers - at the universities of Manchester and Liverpool - plan to assemble complete replacements for parts of organs including kidney and liver, as well as muscle, heart and even brain tissue.

These products of tissue engineering, as the process of building them is called, will come equipped with the ability to communicate with their surroundings in the body they are implanted into, by sending the correct signals to attract blood vessels to grow into them to supply their needs.

This is part of the programme of the new United Kingdom Centre for Tissue Engineering, which has been set up to build on pre-existing skills, at Manchester and Liverpool, in areas including cartilage cultivation and wound healing,(Manchester) and the development of biocompatible materials for uses such as heart valves (Liverpool).

One of the centre's first targets is the so far intractable and, with an ageing population, increasingly common problem of chronic ulcers of the lower leg. These are seen at their worst in some diabetics in whom such disfiguring ulcers, which refuse to heal, are a constant source of discomfort and incapacity.

Such patients do not lack the inherent capacity to heal a skin wound; what are lacking are the biological signals, the chemical messengers which initiate the several events of wound healing; cell migration, blood vessel formation and tissue assembly. "If we can provide these biological signals in a tissue engineered package, we can kick-start a repair process which the patient's own tissues can then go on to complete" says Professor Tim Hardingham, director of the new Centre for Tissue Engineering (CTE).

A new type of skin graft for such patients is one of the CTE's first targets. Ordinary skin grafts act as a template which is soon replaced by the patient's own skin.

Leg tissue affected by chronic ulcers cannot send the signals required to attract the migrating cells and growth of blood vessels needed to build new skin tissue.

the skin grafts being developed at the new CTE, unlike today's skin grafts, will contain cells engineered to produce the missing signals. Much research at the CTE is being devoted to identifying more such signals, and finding the best ways to deliver them.

Small blood vessels made from cells cultured in the laboratory are also being developed, to act as replacements for blocked branches of the coronary arteries, which normally supply the muscle of the heart itself with food and oxygen.

Completely engineered ready-to-impact small arteries made from living tissue are badly needed because blood flowing through arteries made of synthetic material which are less than three millimetres in diameter tends to clot and cause more blockages.

Narrow ducts, such as those which carry urine to the bladder may be replaced in the same way. Another component which is being engineered from living cells is a complete replacement for the bearing surface of the main joint of the thumb, made of cartilage grown in the laboratory and intended for implantation to replace joint surfaces crippled by osteoarthritis. Ultimately the same approach may be used in replacing hip and knee joints.

The cells used in some of these and other made-to-order spare parts will be stem cells harvested from the patients themselves.

In other engineered tissues the cells will come from foreskins removed from male babies by circumcision.

Because they come from very young infants and are grown for long periods in culture, cells obtained in this way are not rejected or only very weakly rejected when they are transplanted. They can be grown to provide massive quantities of material, "One foreskin can provide a sheet of tissue the size of a football pitch" says Tim Hardingham.Stem cells, the unspecialised ever-youthful cells which are stored deep in the body, ready to migrate to the sites of injury and divide and differentiate to repair damage, are also the target of research at the CTE.

One aim is to discover the signals which attract such cells, so those signals can be used by implanted engineered structures to attract stem cells to the sites where they are needed, to augment and eventually to replace the implants.

Further in the future, the scientists hope to engineer replacements for damaged liver, kidney and heart tissue.

This will involve creating three dimensional structures including chambers and ducts.

One way in which this may be done is by using a device like an ink jet printer, which squirts a jet of quick hardening biocompatible polymer and is programmed to produced the required microscopic three-dimensional structures.

The first products of tissue engineering are already in experimental use and some are expected to be in clinical use within five to 10 years, ready to meet the growing demands of an ageing population, for whom tissue engineering can, hopefully, offer several different forms of genuine rejuvenation. (MED)

Professor Tim Hardingham, Wellcome Trust Centre for Cell Matrixn Research, School of Biological Sciences, University of Manchester, 2.205 Stopford Building, Oxford Road, Manchester, United Kingdom, M13 9PT. Telephone: +44 161 275 5511. Fax: +44 161 275 5752.

E-mail: [email protected]

New Superabsorbent Polymers

by Pradeesha Warnasooriya

Superabsorbent polymers play a large role in our personal hygiene and fast-paced lifestyle. These aptly named polymers are composed of cross-linked polyelectrolytes with an Interconnected structure ideally suited for absorbing large amounts of water and other aqueous solutions without dissolving. As a result, ninety percent of the superabsorbent polymers manufactured today go into such personal care items as baby diapers as well as adult incontinence and feminine hygiene products.

This technology in which new grades of superabsorbent polymers (SAPs) are created through the process of hydrolysis and aqueous emulsions of ultra high molecular weight polyacrylonitrile are converted into polyacrylic acid with sodium hydroxide. The patented process enables the hydrolysis to be controlled closely, producing SAPs with a wide range of properties.

Cross-linking reaction of polyacrylic acid is typically required to produce superabsorbing properties, but with this new technology, two cross-linking alternatives can be used, including starting with a slightly cross-linked polyacrylonitrile emulsion and cross-linking through controlled intermolecular reactions during hydrolysis.

Device to ensure effective metal detection in the food industry

by Ruvini Liyanage

jL Lenard of Australia has introduced a system designed to guarantee that a metal detection system is working effectively. The patented Audit Check system guarantees that the detection system is operating as it should and that the products are as safe as possible from metal contamination.

Audi Check allows the metal detector to automatically monitor the sensitivity performance of the system by passing a test shuttle coincides with the product, validating the reject function. The resultant signal is compared with calibration information. The test can be conducted as frequently as desired. If there is any drift in the detector owing to product build up or product effect changes, a warning will be given. More serious deviations from normal will trigger an alarm.

A third - generation digital signal processor (DSP3) released by Goring Kerr is offered by JL Lennard. The DSP3 provides sensitivity performance "never before possible". Advances in electronic circuitry and sophisticated signal processing algorithms make the DSP3 up to 25 percent more signals with greater distinction across a range of applications, both wet and dry such as meat, bread, cheese and almost any food containing moisture.

This ability results in improved sensitivity to metal contaminants and fewer false rejects owing to unwanted masking signals.

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