Anatomical Design Considerations

Intravascular Administration and Blood Collection. Drug administration and blood collection can be accomplished by syringe, vac-u-tainer and cannula in most fish species. The major determinants for method selection are anatomical, size, and experimental design considerations. 

After resolving the issue of matrix design, the next step was to determine a desirable anatomical location. Several considerations were used in determining possible implant sites. The first is the size of the implant and the requirement that it be placed in juxtaposition to well-vascularized tissue. A transplant matrix constructed as a porous sheet-like structure could be at most 200 mm thick, based on estimates of nutrient transport limitations (66). The size of a device required to replace about 5% of the mass of an adult liver would then be about 0.5 m2. Surgical trauma must be avoided when implanting the device, because such trauma produces fibrin clots and hematoma formation around the wounded area, which creates a poor environment for cell survival. Also, the implant may behave better if supplied by the portal circulation rather than the systemic, because the portal circulation contains potential hepatotrophic factors. For these reasons, the mesentery—the vascularized membrane which secures the intestines—was selected as the best potential site (Fig. 15). 

The design of any device to be implanted in the intervertebral space must incorporate considerations of the biomechanics of the particular spinal level to be implanted. Among other factors, the primary biomechanical factors to be considered can be characterized as the kinematics (motion), kinetics (applied forces), and load sharing (distribution of stress between anatomic components). The device should allow the expected kinematics, it should be able to withstand millions of cycles of the expected loads, and it should attempt not to disrupt the distribution of the tissue level stresses and strains experienced in a healthy intervertebral joint. The kinematics, kinetics, and load sharing of the spine vary significantly as one moves from the cervical to the thoracic to the lumbar spine. 

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