Sensor Development for Measuring Capsule Contracture


Author:  Mandi Black


Introduction

The objective of our research is to find a method to prevent capsule contracture around surgically implanted objects in the body.  Currently, our short-term task is to develop a quantitative scale that measures the degree of contracture around the object in vivo.  Once we can obtain accurate measurements of capsule contracture, we can begin to experiment with variables to determine their effect on the contracture process and the body's reaction.

 

Background

Whenever a foreign object enters the body, the body’s immune response triggers a capsule to form around it.  The same response occurs for surgically implanted objects.  The capsule tries to protect the body against the possibly harmful effects of the implanted object.  Sometimes, the capsule will contract in an effort to either eject or destroy the implant.  Capsule contracture can be painful for the host and cause deformation, migration, and/or hardening of the implant.  The consequences can only be corrected with another surgery.  The cause for capsule contracture is unclear, but it is hypothesized that the amount of contracture is proportional to the strength of the immune response.  Many inconclusive histological studies of capsule contracture have been published, but there are no engineering solutions to the problem yet.

 

Research Team

Due to the interdisciplinary nature of our area of research, our research team is a collaboration of the University of South Carolina School of Medicine (Departments of Surgery and of Cellular and Developmental Biology and Anatomy), College of Engineering and Information Technology (Departments of Chemical and of Mechanical Engineering).  The following people have been involved: 

        

Mechanical Engineering
 		Chemical Engineering
 		Medical Fields
Dr. Victor Giurgiutiu
 Dr. Jonathan Bender
 Dr. Harold Friedman
Joel Bost
 Christopher Stewart
 Dr. Thomas Borg
Mandi Black
 Stephanie Lareau
 Dr. Michael Yost
LongDa Yin
 Lee Thompson
 Dr. William Newcomb
LAMSS
 Dan-Victor Giurgiutiu
 Dr. Christopher Watson
 

Sensor Concepts

Two different concepts for this sensor have been explored.  Initially, Piezoelectric Wafer Active Sensors (PWAS) were adapted for use in vivo.  Dr. Victor Giurgiutiu and the Labratory of Adaptive Materials and Smart Strucures (LAMSS) have a great amount of experience using PWAS for structural health monitoring purposes.  Since this project is interested in monitoring the structural properties of the collagen capsule, PWAS seemed to be a feasible solution.  PWAS operate on the basis of the piezoelectric effect.  Piezoelectric effect means that a mechanical input to the system will yield an electrical output and vice versa.  In order to exhibit this behavior, the asymmetrical crystalline structure of the material must cause a dipole.  In the 7mm diameter PWAS used for our sensors, the dipole produces thickness and radial vibrations as shown in the figure below.  Piezoelectric materials are extremely sensitive to mass changes and are therefore applicable to a variety of fields, especially the medical field.


Since the trial run of PWAS did not yield conclusive results, it was necessary to redesign the PWAS and look into another sensor concept.  Recently, attempts to use strain gauges have been made.



Experiments

Numerous experiments have been conducted both in vivo and in vitro with both sensor concepts.  A list of experiments peformed and a brief description are below.  For more information and results obtained follow the particular link.