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The Enhancement of Biomimetic Apatite Coatings on a Nylon 6,6 Biopolymer by Means of KrF Excimer Laser Surface Treatment
D.G. Waugh and J. Lawrence

Simulated body fluid (SBF) has been widely used as a screening method in determining the bioactivity of numerous biomaterials. Owed to the insufficient surface properties of polymers it has been seen to be of great advantage to modify the surfaces of these materials to allow the polymer to become more biomimetic. This paper discusses for the first time the results and differences between using a KrF excimer laser for large area processing and surface patterning of a nylon 6,6 biopolymer. Both 50 and 100 μm dimensioned trench and hatch patterns were induced at a fluence of 858 mJ/cm2. The large area irradiative processing covered an area of 2.76 cm2, which was almost 57% of the entire sample surface, with fluencies ranging from 36 to 90 mJ/cm2. White light interferometry (WLI) was employed to determine 3-D continuous axonometric and profile extractions for each sample and found that the surface was significantly modified for the patterned samples with the average roughness, Sa, increasing by up to 1.5 μm when compared to the as-received sample. The large area processed samples were found to have Sa values equivalent to that of the as-received sample of around 0.1 μm. This was significant as a sessile drop device was used to find that the contact angle decreased by up to 20° for the large area processed samples. As the surface topography was negligible compared to the as-received sample this can be explained by the possibility of surface chemistry or surface charge being the dominant parameter. However, the increase in contact angle can be explained through a change in wetting regime on account of the surface patterning in which both Wenzel and Cassie-Baxter regimes are present over the liquid-surface interface. After 14 days of immersion in SBF each sample was analysed using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) to ascertain the presence of apatite crystals formed on the as-received and excimer laser treated surfaces of the nylon 6,6. An increase in mass of up to +0.03 g indicated that the laser processed samples gave rise to more accelerated formation of apatite crystals in comparison to the as-received sample. This suggests that through excimer laser surface treatment osteoblast cell adhesion and proliferation can be enhanced.

Keywords: KrF excimer laser, nylon 6,6, biopolymer, wettability characteristics, contact angle, surface free energy, bioactivity, simulated body fluid (SBF)

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