CO2 whole area irradiative processing and patterning of nylon 6,6 and the effects thereof on osteoblast cell response in relation to wettability

It has previously been shown that CO2 laser patterning of nylon 6,6 can modify its wettability characteristics, resulting in the material becoming more biomimetic. This paper discusses comparatively the differences between using a CO2 laser for surface patterning and large area processing and details the effects of these modifications on the characteristic wettability and osteoblast cell response. The surface topography was analysed using white light interferometry which found that the largest increase in surface roughness, with an Sa of 4 µm was obtained with the large area processed sample using an irradiance of 510 Wcm-2 and a scanning speed of 25 mms-1. By employing X-ray photoelectron spectroscopy the surface oxygen content was found to increase by up to 5 %at for all laser irradiated samples. Wettability characteristics were determined using a sessile drop device which found that the laser patterned samples gave rise to an increase in contact angle where as a decrease in contact angle was observed for the large area patterned samples in comparison to the as-received nylon 6,6. It is believed that the increase in contact angle is a result of the likely existence of a mixed- state wetting regime in which both Wenzel and Cassie-Baxter regimes are present. The bioactive nature of the samples were analysed by seeding osteoblast cells onto the nylon 6,6 samples for 4 days. At 24 hours and 4 days the seeded samples were observed using optical microscopy and SEM. Also on day 4, the cells were counted using a haemacytometer. From this study it was found that the laser patterned samples gave rise to a more biomimetic surface whereas the osteoblast cells did not preferentially grow on the whole area processed samples with increasing irradiances. It is believed that this may be owed to the fact that the large area processed samples became excessively hydrophilic and did not promote sufficient cell growth and proliferation.