Biomedical subjects

S Willeke

Publications and source records attributed to S Willeke.

3 recordsLinked to original sources

PubMed1992

Detachable shape-memory sewing ring for heart valves.

The novel sewing ring concept consists of a detachable ring snap connection between valve housing or stent and suture cuff. The suture cuff itself is a memory metal ring of nickel-titanium (NiTi) that is embedded within a textile fabric torus. After a special training program the ring can assume two geometric shapes when alternately cooled and heated. Due to this physical property, the sewing ring can be safely fixed within a groove of the housing or stent by changing between room and physiological temperature. This allows the surgeon first to implant the sewing ring followed by arbitrary positioning and final fixation of the valve by the shape-memory effect. Additional advantages are an increased stiffening of the valve base for minimizing potential leaflet dysfunction, and reduced time and risk of implantation, particularly when a reoperation is necessary.

Heart Valve Prosthesis↗

PubMed1991

New J-3 flexible-leaflet polyurethane heart valve prosthesis with improved hydrodynamic performance.

The aim of this new three-leaflet valve development was to design a leaflet with minimum membrane stresses during performance. This is achieved by manufacturing the valve leaflets shaped almost flat in a medium opening position. Thus, the leaflets have two stable positions, one with maximum opening area and the other with favorable stress distribution in the closed position. The transition between the two end positions is achieved through a two-dimensional rolling motion without buckling and with minimum membrane stresses (bulge forces). The manufacturing technique is dip-coating in polyurethane. Hydrodynamic evaluation of the J-3 valve in steady and pulsatile flow showed minimum pressure drop compared to other commercially available valves. Laser-Doppler-anemometry studies indicated very low shear stresses in the flow field downstream of the valve. In durability tests prototypes have reached lifetimes of up to 17 years. In conclusion, the J-3 valve shows superior hydrodynamic performance thereby reducing potential thrombus formation. Minimization of stresses within the valve leaflets through design could reduce calcification.

Biomechanical Phenomena↗

PubMedDate not supplied

Advances in design principle and fluid dynamics of a flexible polymeric heart valve.

The three leaflet J-3 valve is manufactured in a medium open position with almost flat leaflets, whereby the stent is expanded by a cone shaped mold. After manufacturing, the dipcoated leaflets have stable closed and open positions. The transition succeeds with very low membrane stresses. Due to this design, the J-3 polymer valve showed superior hydrodynamic performance compared with commercial valves. In durability tests, prototypes have reached lifetimes up to 17 years. While animal tests are encouraging, they also reveal needed manufacturing improvements.

Animals↗