Features of the pulmonary valve

The aortic and the pulmonary valves are anatomical structures of high complexity . The assessment , and the treatment methodology is developed for the disorders of the two semilunar , tricuspid valves . The proper functioning mechanism of the semilunar valve is represented by the closed phase during systole , and the open one during diastole ( figure 1 ) . The valve stenosis is generated by the inability of the valve to open successfully . The regurgitation of the blood is caused by the incapacitation of the valve to close shut .

Figure 1 . The internal videoscopic view of the pulmonary valve in the reanimated human heart , sagittal superior ( a , b ) , sagital inferior ( c , d ) , in systole ( a , c ) , in diastole ( b , d ) . Copyright ( 2013 ) Springer .

The three dimensional arrangement of the pulmonary valve is maintained by the histological structure designed with the fibrosa , the spongiosa , and The Nodulus Arantii ( figure 2 ) . The mean value for the annular diameter of the pulmonary valve is 25 . 4 ± 3 . 2 ( N = 3997 ) , and the mean value for the aortic valve is 22 . 4 ± 2 . 7 ( N = 3370 ) .

Figure 2 . The idealised three - dimensional structure of the semilunar valve . Copyright ( 2013 ) Journal of Cardiovascular Translational Research .

The surgery on the pulmonary valve presents less risk because the pressure gradient across the valve is low , comparing to the one for the aortic valve . Both the pulmonary and the aortic valve have similar dimensions , with slightly different material properties ( figure 3 ) . The pulmonary valve is considered as autograft replacement for the aortic valve in some patients with congenital heart disorders .

Figure 3 . The name of the leaflets for the semilunar valves . Copyright ( 2013 ) Springer .

Four of the 3861 hearts analysed by The European Homograft Bank have the pulmonary valve with two leaflets . Eight of the 109571 autopsies present an aneurysm of the pulmonary artery . A patient with both these conditions may have had an anomaly in the embryonic development .

References :

Batesman M . G . , Hill A . J . , Quill J . L . , Iaizzo P . A . ( 2013 ) “ The clinical anatomy and pathology of the human arterial valves : implications for repair or replacement ” , Journal of Cardiovascular Translational Research , 6 ( 2 ) , 166 - 175 .

Capps S . B . , Elkins R . C . , Fronk D . M . ( 2000 ) “ Body surface area as a predictor of aortic and pulmonary valve diameter ” , The Journal of Thoracic and Cardiovascular Surgery , 119 , 975 - 982 .

Iaizzo P . A . , Bianco R . W . , Hill A . J . , Louis J . D . S . ( 2013 ) “ Heart valves : from design to clinical implantation ” , Springer , part I . 2 , 27 - 45 .

Hybrid bioprosthetic heart valve

The peer - reviewed publication Engineering of a bio – functionalized hybrid off – the – shelf heart valve caught my interest . The growth factor signalling mechanism inside the bioprosthetic heart valve is different from the native valve . The Young ' s modulus quantifies the remodeling behaviour after implantation .

The chosen method to generate the scaffold is the electrospinning of either poly - lactide acid ( PLA ) or equal amounts of it and poly - ethylene glycol dimethacrylate ( PEGdma ) . The performance of the polymeric scaffold is tested under physiological conditions . The blood is assumed to interact with the heart valve leaflet at large amplitude , in a laminar flow , under oscillatory shear stress . The nonlinear flow properties affect the response of the heart valve .

Valvular endothelial and interstitial cells are seeded in the scaffold . The protein configuration is visualised on the cell – seeded polymeric scaffolds using immunofluorescence staining . The cell viability is assessed with 3 - ( 4 , 5 - dimethyl – 2 - thiazolyl ) - 2 , 5 - diphenyl - 2 H - tetrazolium bromide ( MTT assay ) . The cells are compatible with both the PLA and the PEGdma – PLA scaffold . The valvular endothelial cells adhere in a greater amount onto the PEGdma – PLA scaffold than on the one with PLA fibres . The valvular interstitial cells adhere similarly on both polymeric scaffolds . The valvular actin cytoskeleton for both the endothelian and the interstitial cells is more visible in the PEGdma – PLA than in the plain PLA scaffold .

Native porcine aortic valve tissue , unseeded and cell – seeded polymeric scaffolds are analysed using the scanning electron microscopy ( SEM ) . The PLA scaffold has 30 times greater fibre diameter and 1160 times greater pore size than the native leaflet .

The atomic composition of the surfaces is determined using the electron spectroscopy for chemical analysis ( ESCA ) . The comparison of the data is made using literature values for single components . The PLA – PEGdma scaffold has both PLA and PEGdma groups on the analysed surface .

The mechanical properties of both native and polymeric scaffolds are using the atomic force microscopy ( AFM ) . The spongiosa is the softest layer of the native porcine leaflet , with a Young ' s modulus twice as small as the one for the ventricularis and fibrosa layer . The Young ' s modulus of the PLA – PEGdma scaffold is 10 times greater than the ventricularis and fibrosa native layer .

Uniaxial tensile testing provides information regarding the Young ' s modulus , the tensile strength and the elongation values . Both the PLA scaffold and the native leaflet is soft , with similar values for the Young ' s modulus . The computed Young ' s modulus for the PLA – PEGdma scaffold is twice the value for the PLA scaffold . The PLA scaffold is 55 times more expansible than the native leaflet . The tensile strength value is similar for both the PLA and PLA – PEGdma scaffold .

The polarity of the molecules on the surface is detected using the contact angle goniometry technique . The PLA scaffold is highly hydrophobic . The PEGdma scaffold is hydrophilic . The PLA – PEGdma scaffold is highly hydrophilic . The PLA – PEGdma is highly hydrophilic .

The capacity of water - holding of both the native and the polymeric scaffolds is compared . The PLA scaffold has 11 % water intake capacity , the PEGdma scaffold has high value , while the native leaflet has 90 % . The PLA – PEGdma scaffold has 5 times more water intake capacity than the PLA scaffold .

The protein expression patterns are revealed in the early development for the human heart tissue . Collagen type 1 is present in the leaflets , Versican in the atria – ventricular valves and in the outflow tract , in the first trimester of the fetal development . Collagen type 1 is present in the fibrosa layer of the aortic valve , Versican in the leaflet tip and close to the arterial wall , in the second semester of the fetal development . The valvular histoarchitecture in the 19 years old adolescent is similar to the one in the second semester of the fetal development .

The bio – functionalised prosthetic leaflet has PLA – PEGdma scaffold , Collagen type 1 gel layer , and Versican tip , in a proof – of – principle experiment . The polymeric scaffold requires further structural modifications to have a biocompatible material with a set of mechanical properties closer to the one of the human heart valve .

References :

Hinderer S . , Seifert J . , Votteler M . , Shen N . , Rheinlaender J . , Schaffer T . E . , Schenke – Layland K . ( 2014 ) “ Engineering of a bio – functionalized hybrid off – the – shelf heart valve ” , Biomaterials , 35 ( 7 ) , 2130 – 2139 .

Hyun K . , Wilhelm M . , Klein C . O . , Cho K . S . , Nam J . G . , Ahn H. , Lee S . J . , Ewoldt R . H . , McKinley G . H . ( 2011 ) “ Progress in Polymer Science ” , 36 ( 12 ) , 1697 – 1753 .