Date of Award
Master of Science in Biomedical Engineering - (M.S.)
Biomedical Engineering Committee
David S. Kristol
This study established protocols for extrusion of collagen tubes from an extruder made by the ZOKO Corporation of Czechoslovakia. Using a viscous collagen base material, collagen tubes can be formed with changes in rotation rates from 0 rpm to 260 rpm and linear draw speeds from 383 mm/min to 1270 mm/min with a constant extrusion rate of 50 cm2/min. These tubes, with further research and treatment, can be used for various medical applications including vascular implants and nerve conduits.
Post-extrusion, chemical crosslinking of the collagen increased the cohesiveness and mechanical integrity of the tubes. Microscopic photographs confirmed higher orientation of the fibers on the surface with less orientation on the interior surface of the tube. The collagen tubing displayed high affinity for water and was able to change mass by at least 100%. The tube volume changes ranged from 80% to 123% with length changes from 8% to 13% depending on thickness of the tube and the applied rotation rate.
The tensile properties supported the idea of collagen as a short fiber-reinforced material. The maximum tensile strength was attained with low to medium rotation rate and a medium thickness tube. There was increased modulus of the initial toe region and a decreased end region modulus as the rotation rate increased.
Thermal analysis showed differences between the shapes of energy versus temperature curves when comparing the tubes which were "normal" and those which were dehydrated before testing. Distinct water peaks increased in range for nondehydrated and decreased for dehydrated tubes with increasing rotation rate. An exothermic region also appeared which was either some form of shrinkage or denaturing/degradation of the collagen molecules. The actual degradation of the material had a beginning range of temperatures from 250° C to 257° C which apparently increased with increasing rotation rate.
Hoppe, Richard Peter, "Partial characterization of extruded collagen tubes with varied material deposition and orientation based on rotation rate and linear draw speed" (2001). Theses. 736.