Small patients – Big needs: A material-based approach to develop miniaturised valves for congenital heart diseases

Figures

• 

  Fig. 1. Hypoplastic left heart syndrome and the treatment using a stent. A) Architecture of the patients with HLHS and ductus arteriosus stent placement. The colours within the heart signify oxygen enrichment, with blue being oxygen-poor blood, red oxygen-rich blood, and purple being a mixture of both. B) Schematic of the ductus arteriosus, including our concept to improve flow behaviour. Specifically, a miniaturised valve (dark blue) is integrated into a stent and placed in the ductus arteriosus. The valve prevents the backflow through the ductus arteriosus, leading to a more balanced flow ratio between pulmonary and systemic circuits and reduced systemic pressure on the heart.

• 

  Fig. 2. Electrospinning of TPU scaffold. A) SEM images of TPU scaffold fibres before and after treatment with 70 % ethanol. B) Measurement of wall thickness of a tubular scaffold both before and after ethanol treatment. C) Evaluation of fibre diameter from SEM images before and after ethanol treatment.

• 

  Fig. 3. Layer-by-layer dip-coating process of the electrospun TPU scaffolds with ELRs. A) Schematic of the coating procedure. B) Verification of coating by cross-sections of ELR-coated TPU with optical microscopy and fluorescent microscopy of 5 μm sections. Fluorescent microscopy makes use of the auto-fluorescent properties of the ELR hydrogel. The arrows point to the interface between the TPU and the ELR, with evident infiltration. C) Design of custom dip-coating holders to guarantee adequate coating on both the inner and outer surface of the tubular scaffold. D) Schematic of single point attached commissures technique (SPAC) [46,47], adapted to a tubular structure in a stent.

• 

  Fig. 4. Biological compatibility testing of the biohybrid scaffold. A–C: Cell cytotoxicity testing by indirect incubation of the material with HUVECs. A) Fluorescent images of HUVECs stained with DAPI and Phalloidin-iFluor™ 488 to visualise cell morphology after 24 h of incubation. B) Cell viability measured by metabolic activity after 24 h of incubation with extraction media. C) Normalised cell count after 24 h of incubation with extraction media based on the number of nuclei in fluorescent images. D–F: Haemocompatibility testing with platelets. D) SEM images of the platelets incubated for 1 h on the materials. Round platelets were coloured pink and activated, spread-out platelets were coloured yellow and blue depending on their extent of activation. E) Evaluation of platelet roundness in confocal images. F) Evaluation of platelet-covered area in confocal images.

• 

  Fig. 5. Mechanical properties of TPU scaffolds. A) Images of the material during the tensile test of tubular samples. B) Representative stress-strain curves for each thickness. C) Mechanical parameters from tensile testing of different thicknesses of electrospun TPU ring samples. Only samples that broke in the middle were considered for analysis. The whiskers extend to the minimum and maximum values; the middle of the box is the median. D) Burst pressure of ELR-coated TPU samples of different thicknesses. The burst pressure increased with the TPU scaffold thickness, and the ELR successfully sealed the TPU scaffold, resulting in burst pressure values up to 2000 mmHg. Without ELR-coating, no burst pressure could be measured since the TPU scaffolds were permeable to water. The whiskers extend to minimum and maximum values; the middle of the box is the median. E) Stress and strain shift during cyclic stretching and relaxing over 10,000 cycles. The ELR-coated TPU scaffold was subjected to force-dependent stretching and recoiling at 1 Hz for 10,000 cycles.

• 

  Fig. 6. Hydrodynamic testing of non-coated valve designs with varying skirt lengths. A) Valve designs with increasing skirt length. The white arrows indicate the length of the skirt. B) Bioreactor pulsatile flow setup. C) Regurgitation of different skirt designs. Only significant differences between the design with no skirt and the other skirt lengths were measured. D) Representative graph of pressure and flow measurements during the recording for a design with a high skirt.

• 

  Fig. 7. Hydrodynamic testing of the ELR-coated miniaturised valve with a low skirt. A) Visual assessment of the valve from the top during one cycle of opening and closing. B–E) Regurgitation, positive pressure difference ΔP, effective orifice area (EOA), and closing time for physiological flow and pressure conditions for ELR-coated TPU miniature valves. N = 5 valves were tested in all conditions.

• 

  Fig. 8. Hydrodynamics of the ELR-coated TPU valve in a native-like vascular graft with dimensions matching the ductus arteriosus vessel. A) On the left: crimping of the miniaturised valve (8 mm diameter) to fit into a delivery tube with inner diameter of 4.5 mm. Top right: Visual inspection of proper arrangement of the stent struts in the crimped state. B) Miniaturised valve after delivery into a native-like vascular graft [50]. The stent self-expanded when released from the delivery tube. C) Hydrodynamic performance of the miniaturised valve located in the native-like vascular graft. The parameters in the table were calculated from measurements with peak flow rate of around 1500 mL/min and a maximal pressure of 75 mmHg.

• 

  Fig. 9. Reinforcement and fatigue testing of the biohybrid scaffold and assembled valve. A) Break point of non-reinforced ELR-coated TPU valves in fatigue tester after approximately 50,000 cycles. The scaffold broke at one of the three top commissural points that shape the three leaflets of the valve. B) Sketch of construction of the three-leaflet valve with reinforcement. The textile was attached while suturing the top commissures. The textile was also attached at the bottom when shaping the skirt. Blue: Suture lines, Orange: Textile for reinforcement. Drawing of the stent is only schematic. C) Suture retention testing of a non-reinforced scaffold and a reinforced scaffold. A simple reinforcement increased the break force. D) Duration of fatigue testing until damage. N = 3 for non-reinforced valves and N = 4 for reinforced valves. The shape of the individual data points indicates the break locations.