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Development of devices for self-injection: using tribological analysis to optimize injection force

Authors Lange J, Urbanek L, Burren S

Received 18 February 2016

Accepted for publication 14 April 2016

Published 11 May 2016 Volume 2016:9 Pages 93—103

DOI https://doi.org/10.2147/MDER.S106675

Checked for plagiarism Yes

Review by Single-blind

Peer reviewers approved by Dr Javeed Shaikh Mohammed

Peer reviewer comments 3

Editor who approved publication: Dr Scott Fraser

Jakob Lange, Leos Urbanek, Stefan Burren

Ypsomed Delivery Systems, Ypsomed AG, Burgdorf, Switzerland

Abstract: This article describes the use of analytical models and physical measurements to characterize and optimize the tribological behavior of pen injectors for self-administration of biopharmaceuticals. One of the main performance attributes of this kind of device is its efficiency in transmitting the external force applied by the user on to the cartridge inside the pen in order to effectuate an injection. This injection force characteristic is heavily influenced by the frictional properties of the polymeric materials employed in the mechanism. Standard friction tests are available for characterizing candidate materials, but they use geometries and conditions far removed from the actual situation inside a pen injector and thus do not always generate relevant data. A new test procedure, allowing the direct measurement of the coefficient of friction between two key parts of a pen injector mechanism using real parts under simulated use conditions, is presented. In addition to the absolute level of friction, the test method provides information on expected evolution of friction over lifetime as well as on expected consistency between individual devices. Paired with an analytical model of the pen mechanism, the frictional data allow the expected overall injection system force efficiency to be estimated. The test method and analytical model are applied to a range of polymer combinations with different kinds of lubrication. It is found that material combinations used without lubrication generally have unsatisfactory performance, that the use of silicone-based internal lubricating additives improves performance, and that the best results can be achieved with external silicone-based lubricants. Polytetrafluoroethylene-based internal lubrication and external lubrication are also evaluated but found to provide only limited benefits unless used in combination with silicone.

Keywords: injection pen, injection force efficiency, coefficient of friction, lubrication, testing, material selection

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