Laser Surface Engineering of Nylon 6.6 and the Effects Thereof on Adhesion and Biomimetic Apatite Coating Formation

Within the field of bioengineering, simulated body fluid (SBF) has been widely implemented as a technique to screen for the bioactivity of materials. Furthermore, SBF can be used in the biological industry to promote the adhesion of apatite coatings to assist with making materials more biomimetic. This paper details the use of CO2 and KrF excimer lasers for the surface treatment of nylon 6,6 to modulate apatite formation following immersion in SBF for 14 days. Following CO2 laser surface treatment, using white light interferometry, the surface roughness increased to a maximum of Ra and Sa of 1.3 and 4.4 μm, respectively. X-ray photoelectron spectroscopy (XPS) analysis showed a maximum increase in surface oxygen content of 5.6 %at. CO2 laser-induced surface modifications gave rise to a modulation in the wettability characteristics such that the contact angle, θ, decreased for the whole area processed samples, as expected, and increased for the patterned samples. For the KrF excimer laser processed samples, it was found that Sa increased by up to 1.5 μm when compared to the as-received sample. After 14 days of immersion in SBF each sample was analysed using SEM and EDX to ascertain the presence of apatite crystals formed on the as-received and laser treated nylon 6,6 surfaces. It was seen for all samples that calcium phosphate formed on each surface following 14 days. An increase in mass for the laser processed samples indicated that these modified surfaces gave rise to an accelerated formation of apatite when compared to the as-received sample. This, along with strong correlations between θ, the surface energy parameters and the calcium phosphate formation, for whole area processed samples, highlights the potential for this surface treatment technique for predicting and enhancing the bone forming ability of laser processed materials.