A Tubular Biomaterial Construct Exhibiting a Negative Poisson's Ratio

Abstract

Developing functional small-diameter vascular grafts is an important objective in tissue engineering research. In this study, we address the problem of compliance mismatch by designing and developing a 3D tubular construct that has a negative Poisson's ratio νxy (NPR). NPR constructs have the unique ability to expand transversely when pulled axially, thereby resulting in a highly-compliant tubular construct. In this work, we used projection stereolithography to 3D-print a planar NPR sheet composed of photosensitive poly(ethylene) glycol diacrylate biomaterial. We used a step-lithography exposure and a stitch process to scale up the projection printing process, and used the cut-missing rib unit design to develop a centimeter-scale NPR sheet, which was rolled up to form a tubular construct. The constructs had Poisson's ratios of -0.6 ≤ νxy ≤ -0.1. The NPR construct also supports higher cellular adhesion than does the construct that has positive νxy. Our NPR design offers a significant advance in the development of highly-compliant vascular grafts.

Fig 1. (Left) Schematic diagram of a projection based 3D printing system with a digital micro-mirror device (Right) Schematic showing the step-and-print process for scale-up printing.

Fig 2. Geometry design of the unit-cells.

The walls of the unit-cells (denoted as ribs) are approximately 40 micrometers wide and 100 micrometers deep.

Fig 3. Stress-strain simulations of tubular constructs composed of unit-cells with cut missing-rib and intact-rib architectures.

Fig 4. The fabricated tubular constructs.

A) PPR construct having intact rib unit-cells. B) NPR construct with cut-missing rib unit-cells.

Fig 5. Measured Poisson’s ratio as a function of the expansion ratio for the tubular constructs composed of the cut-missing rib (NPR), and intact rib (PPR) unit-cell geometries.

(Three strain-dependent experiments were performed for each type of construct; each strain test was conducted with a different construct. Dark blue: test 1; orange: test 2; green: test 3; red: average of NPR constructs; blue: average of PPR constructs. Circles: NPR constructs; squares, PPR constructs. Dotted red lines: logarithmic fits to the average of NPR constructs; Dotted blue lines: logarithmic fits to the average of PPR constructs.)

Fig 6. Optical images of the pulling test of PPR and NPR tubular constructs.

A) a PPR construct showing a radial contraction and B) an NPR construct demonstrating a radial expansion in the tubular construct.

Fig 7. Stress-strain plot of the simulation and experiment at the PPR and NPR constructs.

(Large blue-color square: simulation result at PPR construct, Large red-color circle: simulation result at NPR construct, small blue-color square: experiment result at PPR construct, small red-color circle: experiment result at NPR construct.)

Fig 8. Microscopic images of stained actin filaments (A, D), nuclei (B, E) and merged results (C, F) on the constructs (day 7).

A) ~ C) Cut-missing rib (NPR) construct, D) ~ F) Intact rib (PPR) construct.

Fig 9. Cell proliferation results on Cut-missing rib (PPR, white) and Intact rib (NRP, grey) constructs.

Bars: 1 S.D., n = 6. Asterisks: columns below line are significantly different (p < 0.05)