Performance Evaluations by Synthetic Blood Penetration Resistance Test:
A vertical setup has been assembled with culture media filtration assembly connected to a pressured unit of medical sphygmomanometer as shown in Figure-4. The pressure was exerted manually from chamber-A with the help of a rubber bulb. Setup was first tested with non-porous material, nitrile glove material for its pressure holding ability and leakages, if any. It was confirmed that, pressure once exerted persists without any leakage up to tested pressure of 300 mmHg. Our setup qualified for precise pressure creation and holding criteria without any leakage.
The fabric samples A-K were subjected to SBPR-test in a pressure range of 0 - 300 mmHg or up to the breaking/leaking pressure point. The fabrics were first exposed to the fluid for 5 min at atmospheric pressure. Pressure was applied in an increasing order in steps of 20 mmHg for 5 mins at each pressure point. The results of the test w.r.t. the sustained pressure, the corresponding JIST 8122 classification and their utility classes are given in Table 1. The effect of radiation in degrading/deterioration of Fabrics A and B is also evident from this Table. For Fabric-A, the pressure holding ability decreased from 80 to 60 mmHg and Fabric-B lost its ability to hold 40 mmHg fluid pressure post-irradiation. The Fabrics C, I, J and K did not reach the breaking point even up to a pressure of 300 mm Hg, before and after radiation sterilization. It was observed that Fabrics-D, E, F, G and H were able to sustain at atmospheric pressure but could not resist at 40 mmHg fluid pressure, started leaking heavily, both before and after radiation sterilization. For all fabrics, the test was repeated three times to confirm the results.
For Fabrics-I and J, resistances were also tested at the fabric joints (sewed and taped). It was observed that, at improperly taped joints, some creases trapped inside the taping line acted as a passage for fluid to reach to the sewed line and penetrate through it (Figure-5). However, in case of samples with properly taped joints, the highest pressure was sustained by the fabric. It is emphasized that quality of taping plays a crucial role irrespective of performance of the fabric as a whole.
Method of detection of Fluid Penetration Through the Fabric:
Fluid penetration through the fabric was detected at three levels, first level of detection was visual through naked eye, following ISO 16603 protocols. To enhance sensitivity of the detection, swipe test was performed, wherein leaked surface was swiped with absorbent paper and spot created on it, if any, was observed to confirm leakage (adapted from Shimashaki et al 2017) (12). The test was added assuming that micro amount of fluid penetrating through the fabric may not be visible by naked eye but can be detected by swipe test. Presence or absence of spots on absorbent paper was further confirmed by observation under a magnifying hand-lens. These levels of detection helped us to define cut off pressure holding point for each tested fabric.
Figure 6 shows visual observations of the samples showing the leakages through the fabric at varying pressure points, both before and after irradiation. On the other hand, Figure 7, shows the three levels of detection adopted to confirm the leakage at the breaking point pressure.
Fabric Evaluations by Splash Resistance Test:
Performances of fabrica-A, B and C were further evaluated by Synthetic Blood Splash Resistance Test using the test setup developed (Figure-8). A ~2 cm diameter of fabric sample was placed in the fabric holder and 8 ml of SB was splashed on it at a pressure range of 280 - 300 mmHg from a distance of 30 cm. This was repeated three times on each sample so that effectively 24 ml of SB was splashed on each tested fabric sample. As per ISO reference protocol 2 ml of SB should be splashed on the test fabric, with 60 - 160 mmHg pressure range from a distance of 30 cm (13). No fluid penetration was detected for all the three fabrics (Figure-9). Since the fabrics did not leak at the higher pressure ranges and for large volumes over longer duration, there was no need to evaluate their performances at lower pressure ranges. All three levels of detections were followed as described earlier and are depicted in Figure-10.
Microscopic Examination of Fabrics:
To observe structural changes induced in the fabrics by radiation sterilization, microscopic examinations were carried out. It was observed that post irradiation, number and size of voids increased in the mesh region of the fabrics A and B, however not much detectable changes were observed in pressed regions (figure-11). This increased number and size of voids was responsible for decreased fluid pressure holding ability. No structural changes were observed (both in mesh and pressed regions) in fabric-C, before and after radiation sterilization as illustrated in figure-12. Information gathered by microscopic examination of fabric-A, B and C was in accordance with our SBPRT findings and it provided supplementary structural and mechanistic support to our observations.