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Details of the latest tissue engineering techniques to benefit
patients were presented to conference delegates in a session devoted
to stem
cell technology.
Molly Stevens, of the Imperial College of Science and Technology, London,
explained that conventional approaches to tissue engineering — adding
stem cells to solid scaffolds in the presence of growth factors — are
still commonly used but are associated with problems when engineering
highly vascularised or complex tissues. The approach being developed
in Dr Stevens’s research group overcomes some of these problems.
The technique involves developing an in vivo bioreactor — using
the patient’s own body as a cell source and scaffold. There is
no need to harvest cells or to culture them in vitro. “This means
that immune rejection is not an issue,” Dr Stevens explained.
The methodology has been tested in rabbits to grow new bone. “The
results were dramatic,” said Dr Stevens. “After six weeks
there was a huge amount of new bone.” Not only was it revascularised,
the bone cells were also organised correctly. Adding growth factors did
not affect bone growth significantly and an average patient would not
need them, she said. After it had grown, bone could be easily harvested
and transplanted into a non-healing defect where it fully integrated.
Sheila MacNeil, of CellTran Ltd and the University of Sheffied, described
the surface technology and cell culture techniques being used to improve
skin replacement materials. The conventional technique involves collecting
cells from the intact skin of patients. These are then cultured and grown
as sheets on a donor dermis layer.
One of the drawbacks is that the cultured cells take several days to
form an integrated sheet. The functional shelf-life of the sheets is
inflexible. It takes nine to 10 days for the sheets to grow and they
have to be used within one to two days or the sheets blister and will
not attach to the patient.
“Even when we have the same people managing the patient and growing
the cells it is difficult to time the sheets to benefit the patients,” said
Professor MacNeil. The sheet of cells produced is also fragile and difficult
to handle.
“This methodology has been around for a long time and has helped
many patients survive,” she said. However, it relies on mouse fibroblasts
to provide a feeder layer, as well as a combination of growth factors
and bovine fetal calf serum. “It is a combination of man, mouse
and cow,” she continued.
Because of these problems the technique has not been routinely adopted
in clinical practice. “We needed a simpler way of getting the cells
from the lab to the patient,” she added.
Professor MacNeil’s research group used plasma polymerisation to
develop a surface that keratinocytes would attach to, grow on and then
leave to go into the wound bed. Improvements to the technique have led
to the development of a product called MySkin.
The first proof of concept study was in six patients with diabetic foot
ulcers — healing was seen in six out of nine ulcers and one ulcer
reduced in size. MySkin has also been tested in burns patients and in
patients with post burns complications and those with long-standing ulcers
resistant to standard therapy.
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The
Pharmaceutical Journal