Beamlines | I22 - Case Study

What becomes of the broken heart valves?

Artificial heart valves have been used since the 1960s to replace natural heart valves damaged through disease. Each of four valves enables unimpeded blood flow through the heart itself and from the heart to the major arteries. As the heart beats the valve opens and closes, subjecting it to pressure loading and unloading. Artificial heart valves must be able to withstand repeated cycles of tensile loading and unloading in realistic conditions. Scientists from the University of Cambridge and the Politecnico di Milano have been using I22, Diamond’s SAXS beamline, to study samples of thermoplastic elastomers experiencing stress in real time, to evaluate their potential for use in artificial heart valves.

 A prototype valve
A prototype valve

Evaluating materials with potential for use in biomedical applications requires a detailed understanding of their mechanical properties on the macro and microscopic scale, and knowledge of their performance under realistic biomedical conditions. Thermoplastic elastomers have good elasticity and fatigue properties and are gaining popularity in biomedical applications. For these materials to be considered for use in prosthetic heart valves it is important to understand their behaviour under cyclic loading and unloading. Evidence of hysteresis during the process and the minimum number of pre-conditioning cycles before the material can be considered in steady state is also important.

The high photon flux available from synchrotrons allows in situ structural studies during mechanical deformation, with high time resolution unavailable for a lab-based source. The materials were subjected to cyclical deformation of up to 10,000 cycles at a frequency of 67 beats/minute. Real time dynamic SAXS measurements were used to determine the relationship between macroscopic and microscopic deformation, in order to understand the extent of reversibility with repeated deformation.

Nick Terrill, Principal Beamline Scientist on I22, says, “The unique combination of an undulator source and the time frame capabilities of the 2D RAPID detector system (consecutive 10µs frames are possible) have played an important role in enabling the experimental team to collect real time anisotropic data on their samples.”

“This study allowed us to examine the morphological evolution from the initial state to the stressed state and how this linked to the mechanical properties. We were able to observe real time micro-structural developments over the cycle time and over 10,000 cycles and measure the response of the material to applied mechanical stress on the ms timescale. It showed that these materials have both the long term stability and microstructural mechanical properties to be very promising for use in prosthetic heart valves.”

Geoff Moggridge, University of Cambridge

A real time SAXS study of oriented block copolymers during fast cyclical deformation, with potential application for prosthetic heart valves, Joanna Stasiak, Adriano Zaffora, Maria Laura Costantino and Geoff D. Moggridge, Soft Matter, 2011
DOI: 10.1039/C1SM06503C