Investigation of Stickiness in Voice Prosthesis Model

Abstract

A voice prosthesis is a medical device that helps people who have undergone a total laryngectomy to speak again. It is placed in the wall that separates the trachea and esophagus and consists of a valve that opens when speaking. Atos Medical is one of the few companies that manufactures voice prostheses. One of their voice prosthesis models is called Provox ActiValve. A problem with this model is that the valve flap is prone to sticking to the valve seat in situ, which makes it difficult for the user to speak.

The aim of this thesis was to investigate the problem of stickiness in ActiValve and to propose and investigate several hypotheses to the problem. The goal was also to develop a test method that measures the degree of stickiness, in vitro.

Through a pre-study, the focus of the thesis was determined to be on surface properties and PVDF, the material of the valve flap in ActiValve. Contact angle and surface energy measurements were conducted to explore the surface properties of PVDF, before and after different surface treatments: sodium etching, plasma treatment and polymer coating. A test method for measuring stickiness was developed and was used in the work to compare untreated to sodium etched PVDF.

In conclusion, the test results indicate that the surface properties of the valve flap and valve seat influence the degree of stickiness. Untreated and polymer coated PVDF showed less wettability than plasma treated and sodium etched PVDF, which indicates a reduced risk for stickiness. To prove these results, further testing is needed. It was concluded that the developed test method is too unreliable for any solid conclusions to be drawn. It needs to be ameliorated in order for the reproducibility to be increased.

Popular Abstract

How can the problem with stickiness in voice prostheses be solved?

A voice prosthesis consists of a valve that is placed in the wall that separates the trachea and esophagus. It helps people who have had their vocal cords removed, to speak again. However, there is one major issue with the device. In some models, the valve flap sticks to the valve seat, which makes it difficult for the user to speak. The question is: why does it stick and how can it be solved?

Due to the placement of the voice prosthesis, it comes into direct contact with airway mucus. The mucus seeks into the cavity of the prosthesis and adheres to the valve flap and valve seat. Mucus is therefore believed to be the number one factor that causes the valve to stick. The second most important factor is the surface properties of the valve flap and valve seat, as they determine how well the mucus sticks.

Atos Medical is one of the few companies in the world that manufactures voice prostheses. In this work, a pre-study was conducted to find out what makes the valve flap stick in one of their models. It was followed up by a literature study focused on adhesion, to understand why the valve flap sticks. As mucus, the most important factor in the stickiness problem, cannot be removed, focus was determined to be on surface properties instead. A potential solution to the problem was found when it was discovered that the surface properties of a material can be changed. By a surface treatment, it is possible to either make it easier or more difficult for a substance (mucus in this case) to adhere to a surface. A treatment that makes the surface non-stick would be favorable in this situation.

To explore this potential solution, the surface properties of the valve flap and valve seat material were investigated, before and after different surface treatments. This was done by measuring the contact angle, the surface energy, and the opening pressure. The contact angle and surface energy gives an indicative measure of adhesion. The opening pressure, which is the minimum pressure needed to open the valve in a voice prosthesis, gives a direct measure of stickiness, when airway mucus is present at the interface. However, slime was used instead of mucus in the measurements and it cannot be guaranteed that the two substances have the same adhesive properties. The results indicate that the surface properties play a role in the stickiness problem, but no solid conclusions could be drawn.

In the end, surface treatments are extensively used in many industries to change the properties of a surface. The problem with stickiness in voice prostheses could potentially be solved by a surface treatment of the valve flap and valve seat, but further testing is needed to confirm this.

• author: Danielsson, Johanna
• supervisor: Ingrid Svensson
• organization: Department of Biomedical Engineering
• course: BMEM01 20201
• year: 2020
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• language: English
• additional info: 2020-09
• id: 9026094
• date added to LUP: 2020-08-25 15:24:12
• date last changed: 2020-08-25 15:24:12