Spatially Heterogeneous Tubular Scaffolds for In Situ Heart Valve Tissue Engineering Using Melt Electrowriting

Abstract

Heart valve tissue engineering (HVTE) aims to provide living autologous heart valve implants endowed with regenerative capabilities and life-long durability. However, fabrication of biomimetic scaffolds capable of providing the required functionality in terms of mechanical performance and tunable porosity to enable cellular infiltration remains a major challenge. Here, the additive manufacturing of bioinspired, spatially heterogeneous, tubular scaffolds enclosing the leaflets, inter-leaflet triangles, and their interface for in situ HVTE using melt electrowriting (MEW) is demonstrated. The innovative platform enables the digital fabrication of scaffolds with ad hoc architecture (e.g., tunable location, specific fiber pattern, and orientation) and customizable geometry via a custom-made control software. The user-friendly interface allows for the definition of areas of the scaffold with specific patterns to obtain properties such as tunable J-shaped stress-stain curve and anisotropy typical of the heart valve leaflet, compliant inter-leaflet triangles, and reinforced curvilinear boundary between them. Heterogeneous, tubular, heart valve MEW scaffolds are then embedded with a microporous elastin-like recombinamer (ELR) hydrogel to develop a soft-network composite favoring cell infiltration and ensuring hemocompatibility. The acute systolic hemodynamic functionality of the MEW/ELR composite satisfies the ISO 5840 requirements, under aortic and pulmonary conditions.

Natural, synthetic and commercially-available biopolymers used to regenerate tendons and ligaments

“…In contrast, MEW offers a solvent-free biofabrication method with excellent control over scaffold architecture and porosity. It is a high-resolution biofabrication strategy that permits the accurate deposition of micrometre-scale fibres, enabling tunable mechanical properties, macro-porosities, and patterns [ 158 ]. However, MEW is limited to thermoplastic (synthetic) biopolymers, with PCL currently the ‘gold standard’ material [ 103 , 159 , 160 ].…”

Programmable melt electrowriting to engineer soft connective tissues with prescribed, biomimetic biaxial mechanical properties

“…However, to the best of our knowledge, the dependency of these required print path adjustments -prescribed amplitude growth rate (PAGR) and prescribed phase shift rate (PPSR) -on the print path itself, particularly wave amplitude, has not been studied. Additionally, here we showed that printing at a sub-millimeter working distance between the needle and the collector substrate enabled the fabrication of sinusoidal structures with wave amplitudes an order of magnitude smaller than what was achieved in the previous studies 14,20,22 .…”

“…Scaffolds were fabricated using MEW of polycaprolactone (PCL) via printing on sinusoidal paths after novel comprehensive print path characterizations. The characterization and optimization of the print path enabled the fabrication of scaffolds composed of sinusoidal fibres with versatile architectures and with wave amplitudes an order of magnitude smaller than what was reported previously 14,20,22 . A second step of DOE and parametric modelling via linear regression was implemented to finely tune the scaffolds' mechanical properties via optimization of their architecture and closely recapitulate the biaxial tension-strain behaviour of the three target tissues.…”

“…Such scaffolds are suitable for soft connective tissue engineering as they can provide load-bearing properties comparable to native soft connective tissues due to their fibrous structures and, to some extent, can emulate the intricate architecture of their native counterpart 14 . In particular, scaffolds with sinusoidal or serpentine fibre patterns have shown promise in tissue engineering applications as they provide nonlinear, strainstiffening stress-strain behaviour, similar to that of soft connective tissues such as heart valves 20,22 .…”

Biohybrid elastin-like venous valve with potential for in situ tissue engineering

“…In order to evaluate the mechanical response of the EVV, equibiaxial tensile testing and burst strength tests of the textile-reinforced elastin-like hydrogels were carried out. Stress-strain curves revealed (i) radial to circumferential anisotropy, matching the textile design (Supplementary Information, Figure S1) and (ii) a marked nonlinear response, analogous to the J-shaped profile characteristic of native valve tissues (Huang and Lu, 2017;Lu and Huang, 2018;Benson and Huang, 2019;Saidy et al, 2022). Specifically, three distinct regions were identified within the exponential stress-strain curves (Figure 1C): (i) a fairly linear region at the beginning (with low tangent modulus), followed by (ii) a non-linear transition region, and (iii) relatively a linear region at the highest values of strain, with the highest tangent modulus.…”