Question 2. 120 pts] As the Society for

Biomaterials notes: "Sutures are one of

the most important medical devices that

is used in surgery. In cardiovascular

procedures the sutures can be used to

suture tissue with tissue, or tissue with

an implantable device. These are the

available in various sizes (suture diameter) and polymers (absorbable and non-absorbable).

Further, the sutures vary in forms, they can be either braided, monofilament, or knotless sutures."

You have been asked to evaluate a new suture thread material for use in cardiovascular surgery.

The material is highly biocompatible and could set a new standard for sutures, but there are

concerns that it is not strong enough. Surgeons have complained that the suture thread break too

easily when being pulled through tissue. You have been hired to model this form of failure and

make design recommendations.

A. [4pts] Draw a free body diagram that models a section of suture thread being pulled straight

through a block of tissue. Assume the needle pulls on one end of the cylindrical thread with force

F (N), the block of tissue has length B (such that B

thread is L, and that the tissue applies a uniformly distributed load to the thread of w (N/m) that

exactly resists the needle's force, such that the thread is in static equilibrium. The thread has a

radius of R and elastic modulus of E. You can also ignore the part of the thread that has not yet

been pulled through the tissue. Hint: This model contains 2 sections,

B. [4pts] What is the relationship between F and w.

C. [4pts] What part of the thread is most likely to break due to the tensile load? For that section

find the normal stress in terms of x, B, L, F, w, R, and/or E. Hint: Draw a FBD of each section.

not all variables have to be used.

D. [4 pts] Through empirical experiments, you discover that a thread of radius (rinitial) breaks when

a tensile load of greater than 20N is applied. To be competitive with other sutures on the market,

the thread must be able to handle a tensile load of at least 60N. Determine the minimum radius

(new) thread that you can sell competitively. Give your answer by creating a relationship between

Tinitial and new.

D. [4 pts] Create an equation that models the total deformation of the suture in terms of x, B, L, F,

w, R, and/or E. Not all variables have to be used.