Texture analyser

The cutting strength was analysed using a Texture Analyser (Stable Micro Systems, Godalming, Surrey, UK). The cutting strength was measured from directions both perpendicular and longitudinal to the flow of the material inside the long cooling die. The dimensions of the samples were 20 mm (width) × 30 mm (length) × 10 mm (height), and five replicates from each sample were measured. A one-sided razor blade (width: 39 mm, height: 19 mm) was used to cut across the sample, either horizontally in the direction of the flow (longitudinal) or vertically in the direction of the flow (perpendicular). The settings for the measurements were: load cell, 5 kg; pre-test speed, 1 mm/s; test speed, 1 mm/s; post-test speed, 5 mm/s; cutting distance, 10 mm. The cutting strength was determined as the maximum force from the force-distance curve. Anisotropy index (AI) was calculated as the ratio of the perpendicular-to-longitudinal cutting forces.

The evaluation of the mucoadhesive properties of the Ch/P fibers was carried out by a texture analyser (Stable Micro Systems, Surrey, UK) with a 50 N load cell equipped with a mucoadhesive test ring.
Fresh pig mucosal tissue was rinsed with phosphate-buffered saline (PBS) at pH 6.8, cut into pieces of 2.5 × 2.5 cm and placed in the mucoadhesion test ring. The mucoadhesion test ring/pig mucosal tissue were equilibrated at 37 °C in PBS, pH 6.8. Ch/P fibers collected on aluminium foil were pasted on a probe (1 cm diameter) using carbon pads prior the test. The assay consisted of placing fibers in contact with the mucosal tissue with 20 g of force for 1 min, and then withdrawn. To calculate the work of adhesion necessary to separate Ch/P fibers from the mucosal tissue the area under the curve of force versus the distance obtained from the software (Exponent, Stable Micro Systems, Surrey, UK) of the texture analyzer was determined. Teflon films of 1 cm in diameter were used as control samples. All the samples were tested three times.

Polymer films were left to equilibrate
for 10 min at 20.5 °C, 40% relative humidity (RH) prior to measurements.
The probe tack measurement was conducted using both polypropylene
and steel probes (diameter of 25.4 mm) on a mechanical testing apparatus
(Texture Analyser, Stable Micro Systems, Godalming, UK). The surface
of the probe was cleaned with acetone before each test. The probe
was lowered onto the film at a velocity of 0.1 mm/s until a force
of 4.9 N was reached, and then left in contact for a time of 1 s,
before being withdrawn from the film surface at a constant velocity
of 0.1 mm/s. For each type of probe, five measurements of each film
were made both before and after UV radiation, and the mean values
are reported here. The contact area (A) and thickness
(h₀) of the films were measured using
a digital caliper. Dividing the force (F) by A to obtain stress (σ), and dividing the probe’s
vertical displacement (Δl) from the surface
by h₀ to obtain the strain, (ε),
probe-tack curves were obtained. The tack adhesion energy was obtained
from the area under the stress–strain curve as given by (eq 1)

The middle and outer layer of the bio-inspired SDVGs containing PCL fibre/GEAL sublayers were tested in uniaxial tension using a Texture analyser (Stable Micro Systems, TA.XT.plus, Surrey, UK) equipped with a 5 N load cell. Rectangular samples of the construct were tested to determine their circumferential and longitudinal stress–strain profiles. Three samples were cut and tested in both directions, circumferentially and longitudinally for each layer. Sample thickness and width were measured using a micrometer with 10 µm accuracy. For preconditioned samples, the constructs were subjected to five loading and unloading cycles of applied strain at a constant rate of 10 mm min⁻¹. The preconditioning loading/unloading cycles of the outer graft layer in the longitudinal and circumferential direction were conducted to a strain level of 13% and 30%, respectively. Differences in strain level were iteratively adjusted to the desired target J-shaped strain–stress curves matching human coronary arteries. In the case of the middle graft layer, the strain for preconditioning was 35% and 30% in the circumferential and longitudinal tensile testing, respectively. Uniaxial testing for both circumferential and longitudinal samples was performed at a constant rate of 10 mm min⁻¹ (Supplementary Fig. 2a).

180° peel tests were performed in
accordance with the FINAT test method.³⁹ Polymer films on PET sheets were allowed to equilibrate for 10 min
at 20.5 °C, 40% RH. Then, a silicone release liner was applied
to the free surface using a roller. Test pieces of the laminate were
cut into 25 mm wide strips. After removing the release liner, the
film was bonded to a steel plate, by rolling twice under the weight
of a 2 kg roller. The sample was left for a 20 min dwell time. In
some experiments, the peel test was performed immediately after; in
other experiments, the films were irradiated through the PET sheet
before the peel test. In this latter case, the sample was subjected
to UV radiation at 365 nm for 10 min, and the peel test was performed
immediately after. For each test piece, the peel adhesion at a 180°
angle was measured by pulling the film back on itself at a velocity
of 5 mm/s using a 5 kg load cell (texture analyser, Stable Micro Systems,
Godalming, UK). The average of five measurements is reported here.