Biomedical Engineering Reference
In-Depth Information
12.4 Hemoperfusion and biosorbents
The first successful use of artificial cells in routine clinical therapy was
hemoperfusion.
4,5,43,44
This is because 10 ml of artificial cells have a total
surface area of about 20 000 cm
2
, equivalent to that of a hemodialysis machine.
This, together with the ultra-thin membrane of 0.02 m and membrane
equivalent pore radius of 1.4 nm, allows for extremely fast equilibration of
molecules smaller than large proteins. Thus artificial cells containing adsorbents
are much more effective than standard hemodialysis in removing toxins and
drugs from the blood of patients.
43,44
This is now being used extensively in
many countries for the treatment of suicidal or accidental overdose of drug or
poisons, especially where regular dialysis machines are not readily available.
12.5 Cell encapsulation: hepatocytes, islets, stemcells
and others
12.5.1 Cell therapy
The encapsulation of biological cells was reported in 1964 based on a drop
method
2
and it was proposed that `protected from immunological process,
encapsulated endocrine cells might survive and maintain an effective supply of
hormone'
3,5
(Fig. 12.1). Conaught Laboratory was approached to develop this
for use in islet transplantation for diabetes. Sun from Conaught and his colla-
borators later extended this drop-method by using milder physical cross-
linking.
45
This resulted in alginate±polylysine±alginate (APA) microcapsules
containing cells. They showed that after implantation, the islets inside artificial
cells remain viable and continued to secrete insulin to control the glucose levels
of diabetic rats.
45
Cell encapsulation for cell therapy has been extensively developed by many
groups especially using artificial cells containing endocrine tissues, hepatocytes
and other cells for cell therapy.
7,45±51
Cheng and coworkers have been studying
the use of implantation of encapsulated hepatocytes for liver support.
52±57
It was
found that implantation increases the survival of rats in acute liver failure;
53
maintains a low bilirubin level in hyperbilirubinemic Gunn rats;
54
prevents
xenograft rejection.
55
A two-step cell encapsulation method was developed to
improve the APA method resulting in improved survival of implanted cells.
57
12.5.2 Stem cells
Using this two-step method plus the use of co-encapsulation of stem cells and
hepatocytes we have further increased the viability of encapsulated hepatocytes
both in culture and also after implantation.
58±59
One implantation of the co-
encapsulated hepatocyte-stem cells into Gunn rats lowered the systemic
bilirubin levels and maintained this low level for 2 months, instead of only 1
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