Within valvular diseases (e.g. calficitation) an impaired function of the valvular leaflets can lead to incomplete opening/closing behavior of the heart valve and the need of a valve replacement. The number of patients requiring a heart valve replacement is rapidly increasing. Bioprosthetic heart valves (allografts) are commonly used as a replacement, although the principal disadvantage of these valves is progressive calcific and non-calcific deterioration, which limits durability. The onset of the degeneration of the allografts is not fully understood. However, cryopreservation techniques (to preserve the heart valve between donor death and the moment of implantation) and storage duration/temperature may contribute to the onset of the deterioration of these valves.
In a previous study we indeed observed structural damage (looser appearance of spongiosa, fragmented and disrupted fibrosa, and cracks in collagen; Fig 1) in the cryopreserved valve leaflets stored at -80°C and -196°C. Probably two different processes play a role in the development of damage during cryopreservation: 1) recrystallization of ice crystals during storage at -80°C and 2) mechanical stresses that occur around the glass transition temperature during thawing after storage at -196°C. However, it is not yet elucidated what the effects are of prolonged storage duration (e.g. storage duration times that exceed the ‘legal’ storage duration of 10 years). Therefore we (in collaboration with the Dutch Heart Valve Bank) would like to study the effects of long-time storage (>10 years) of human cryopreserved heart valves.
In this Master’s research project, you will study several human aortic heart valves that have been stored in either liquid nitrogen (-196°C) or in a mechanical freezer (-80°C) for approximately 10 years. The human cryopreserved heart valves will be obtained from the Dutch Heart Valve Bank (Euro Tissue Bank, Beverwijk, The Netherlands). These cryopreserved heart valves are assumed to be unfit for implantation, so that we can use them for research purposes. You will study the tissue properties by histology and other stainings and mechanical testing Next to that, you will study valve functionality by using a pulse duplicator. Subsequently, fatigue of the valves can also be tested.
It is not known if the observed structural damage is related to bioprosthetic valve deterioration commonly observed in patients with time. It is hypothesized that this deterioration is due to accelerated calcification of the bioprosthesis. Therefore, we would like to study the potential onset of calcification in human cryopreserved heart valves. To this end, you will culture human cryopreserved heart valves in normal and osteogenic medium, preferably in a pulse duplicator, and study tissue properties and functionality as stated above.