Page 179 - Biomedical Engineering and Design Handbook Volume 2, Applications

158 MEDICAL DEVICE DESIGN

The investigators have found that the RAD bioreactor was able to reabsorb glucose, glutathione, 1-25
dihydroxy-vitamin D , etc. In addition, the RAD bioreactors were able to generate ammonia in a quan-
3
tity comparable to the natural kidney. Clinical trials are currently ongoing.
The bioengineered artificial kidney with real tubular cells from the kidney seeded onto synthetic
polymeric hollow fibers is promising. These RAD bioreactors form the beginning of bioengineered
artificial kidney devices and provide a foundation for the development of artificial devices for full
restoration of the kidney function. Perhaps, one day, the renal glomerular cells can also be grown on
hollow fiber polymer cartridges to form a bioengineered glomerulus and Bowman’s capsule, which,
together with the RAD, could form a total bioengineered artificial kidney device.

5.7 CONCLUSION

The purpose of the artificial kidney device is to remove urea and other toxic waste molecules. Blood
flows on one side of a semipermeable membrane and dialysate solution flows on the other side of
the membrane. The toxic waste molecules are removed by either diffusion, or convection, or both.
Diffusion is the primary mechanism of waste product removal in the conventional low flux dialysis.
High flux dialysis involves solute removal by convection and diffusion, but convection is the primary
mechanism. Toxic middle molecules (e.g., β -microglobulin) are effectively eliminated in the high
2
flux dialysis. However, high flux dialysis may lead to the loss of blood serum albumin, which is
closer in molecular weight to the toxic middle molecules. Biocompatibility is a major requirement
of hemodialysis membranes. The conventional cellulose base membranes are associated with bio-
compatibility problems, including complement activation and lucopenia. Substituted cellulose and
synthetic membranes have significantly improved biocompatibility. Polyacrylonitrile based and
polysulfone membranes have excellent biocompatibility. There are stringent water quality require-
ments for use in dialysis fluid. Quantitative measures such as Kt/V are clinically useful for the pre-
scription and assessment of adequacy of dialysis. Designing a membrane to effectively remove toxic
middle molecules without the loss of blood serum albumin presents continuing challenge. The pre-
sent artificial kidney systems do not duplicate all the functions of the kidney. The future direction is
toward tissue-engineered renal assistive devices in series with hemodialysis cartridges.

REFERENCES

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