Recreating the heart's helical structure-function relationship with focused rotary jet spinning

Abstract

Helical alignments within the heart's musculature have been speculated to be important in achieving physiological pumping efficiencies. Testing this possibility is difficult, however, because it is challenging to reproduce the fine spatial features and complex structures of the heart's musculature using current techniques. Here we report focused rotary jet spinning (FRJS), an additive manufacturing approach that enables rapid fabrication of micro/nanofiber scaffolds with programmable alignments in three-dimensional geometries. Seeding these scaffolds with cardiomyocytes enabled the biofabrication of tissue-engineered ventricles, with helically aligned models displaying more uniform deformations, greater apical shortening, and increased ejection fractions compared with circumferential alignments. The ability of FRJS to control fiber arrangements in three dimensions offers a streamlined approach to fabricating tissues and organs, with this work demonstrating how helical architectures contribute to cardiac performance.

Fig. 1.. Focused rotary jet spinning for producing helical structures.

(A) Schematic diagram of the helical alignment of a human heart. (B and C) FRJS uses focused air to separate fiber manufacture into formation (B, i) and patterning (C) phases, allowing for controlled alignments during deposition. (B, ii) Differential contrast projection of the fiber stream (maximal projection; scale bar, 5 cm). (D) Image of polycaprolactone spun onto a mandrel (scale bar, 5 mm), with corresponding scanning electron microscopy (SEM) image, showing aligned fiber formation (mean fiber diameter, ~900 nm; scale bar, 5 μm). (E) Schematic diagram showing that collection angle (θ) dictates fiber deposition alignment (i), with OOP indicating the relative average alignment (error bars, mean ± SD) (ii). SEM micrographs (iii to v; 0°, 60°, and 90°, respectively) with corresponding 2D Fourier transforms inset, indicating that the degree of alignment is based on collection angle (scale bars, 5 μm). (F) Schematic diagram showing HA fiber manufacture based on angle (i), α, with a representative fiber-coated rod (ii) and reconstructed micro–computed tomograph of a HA scaffold (iii; scale bar, 200 μm).

Fig. 2.. Tissue scaffolds with controlled helical alignments.

(A) Bright-field micrograph of a HA ventricle model (gelatin fibers seeded with NRVMs; scale bar, 2 mm). (B) SEM micrograph of fibers from CA [(i), α = 0°] and HA [(iii), α = 45°] cylinders, with corresponding immunofluorescent staining of cardiomyocytes (ii and iv) [NRVM; blue, DAPI (4′,6-diamidino-2-phenylindole); green, f-actin; red, sarcomeres], showing that fibers help direct tissue alignment (scale bars, 50 μm). Circ., circumferential. (C) Isochrones (top) with corresponding still frames (bottom), indicating calcium transience along an extended ventricle surface, showing increased transverse wave propagation for HA scaffolds. Tissues were point-stimulated apically [(i), CA; (ii), HA] (scale bars, 5 μm). (D) Schematic diagram of a CA (left) and HA (right) ventricle, illustrating differences in wall displacement during contraction. CA contracts as concentric rings, whereas HA follows a wringing motion, resulting in different predicted EFs [k, strain, q, apical shortening, H(α), radial shortening]. (E) Deformation maps generated by CA (left) and HA (right) ventricle models during contraction (scale bar, 2 mm).

Fig. 3.. Alignment dictates ventricular ejection fractions.

(A) (i) Bright-field micrograph of a tissue-engineered ventricle, with (ii) a magnified view of the ventricular basal region. ROI, region of interest. (iii) Maximum intensity projection of fluorescent beads taken over a single contraction cycle, showing particle displacement. (iv) High-magnification image of the boxed region in (iii); the arrow indicates the direction of fluid displacement [scalebars in (i) to (iii), 2 mm; in (iv), 0.5 mm]. (B) Side view of the ventricle (scale bar, 10 mm). (C) (i) Schematic diagram of PIV measurement, with velocity fields [(ii) and (iii)] taken from the base of a HA ventricle scaffold during peak systole [(ii), t = 0.3 s] and diastole [(iii), t = 0.7 s]. (D) Representative measurements of the instantaneous mass flux (N_flux) in the region of interest as function of contraction time and ventricle angle. (E) Ensemble measurements of EF for CA and HA ventricle scaffolds (n = 8 ventricles for each angle; *P < 0.05 by Student’s t test; box plot given in quartiles).

Fig. 4.. Multiscale heart models.

(A) Simplified design of a trilayered DCV that mimics the native ECM alignment of the heart, highlighting the four-step manufacturing process. (B) (i) μCT imaging of the DCV suspended on the collection mandrel, with corresponding coronal cross sections (ii) (scale bars, 5 mm). (iii to v) High-magnification mCT images taken from the intraventricular septum (highlighted in purple), showing trilayer alignments (scale bars, 25 μm). RV, right ventricle; LV, left ventricle. (C) DCV in culture seeded with NRVMs, as viewed from the side [(i), coronal] and looking into the two chambers [(ii), transverse]. (D) 3D extrusion printing scales as a power law with respect to feature size, showing that the throughput of FRJS is ~10⁶ times greater than that of 3D extrusion printing for single-micrometer features. (E) Left ventricle width for different species. (i to iv) Single-layer ventricles of different sizes, which can be rapidly manufactured owing to increased fiber production rates, while maintaining a single-micrometer feature scale [scale bars (left to right), 5 mm; 15 mm; 4 cm; and 8 cm). (F) Full-scale four-chambered human heart model composed of single-micrometer fibers (scale bar, 2 cm).