Lecture 4

Question 1

Radial Testing

Answer 1

• used to determine radial pressure from radial force
• equation: P = Fr / (pi * D * L)
• D = current stent expanded outer diameter
• L = L0 (length change < 10%), expanded stent length for balloon-expandable stents and unconstrained length for self-expanding stents
• L = L(D) (change > 10%), current length of stent as function of the current diameter

Question 2

Uniform Radial Loading

Answer 2

• applied over the entire stent surface at minimum of three evenly distributed circumferential locations over stent’s length
• loading is focused inward

Question 3

Equivalent Diameter for Segmented Head

Answer 3

• diameter of the segmented head is defined by the inscribed circle within the contact segments
• D = sqrt(3) / 2 * H

Question 4

General Procedure

Answer 4

• inflate stent to the labelled diameter, then deflate the balloon and measure the expanded stent length
• insert the stent into the testing apparatus, load to a compression point that goes beyond significant plastic deformation, and use the generated curve

Question 5

Radial Test Data

Answer 5

• radial stiffness can be determined from the slope of the linear region

Question 6

Radial Testing Data contd.

Answer 6

• to determine radial strength, offset the unloading line to any point in the plastic region (typically use clinical relevance to determine this offset)
• peak load prior to the intercept of the experimental curve and the offset line = radial strength

Question 7

Sling Apparatus

Answer 7

• another way to perform radial testing, which uses a tensile testing machine
• sling material has low friction, high tensile stiffness, and flexibility in bending

Question 8

Sling Apparatus equation(s)

Answer 8

• F(radial) = pi * F (linear tensile)
• to approximate change in stent diameter…
  D = D0 - 2 / pi * (delta x - F(linear tensile)/K)
  where K is offset from sling stretch