Using UV laser surface treatment to modify the wettability characteristics of polyamide 6,6 and its effects on osteoblast cell activity

Lasers can be used to modify the surface characteristics of a number of different materials for many applications. This paper details the way in which a KrF 248 nm excimer laser can be utilized to surface pattern and whole area irradiate nylon 6,6. 50 and 100 µm dimensioned trench and hatch patterns were induced in addition to the whole area irradiative processing which covered an area of 3.75 cm2 with fluencies ranging from 26 to 70 mJcm-2. The surface topography and roughness were determined with the use of a white light interferometer. From this it was found that the largest roughness, Sa, was 1.53 µm which arose from the 100 µm hatch excimer patterned sample. Wettability characteristics were obtained for each sample using a sessile drop device in which it was observed that the contact angle increased by up to 25° for the patterned samples and decreased by up to 15° for the large area processed samples. It is believed that the observed increase in contact angle can be attributed to the likely existence of a mixed-state wetting regime in which both Wenzel and Cassie-Baxter regimes are present over the liquid-solid interface. As a result of the small variation in surface roughness for the large area processed samples the observed decrease in contact angle can be explained by a modification of the surface chemistry and an increase in polar component (γp) and total surface energy (γT). Osteoblast cell activity was analyzed by carrying out cytotoxicity and alkaline leukocyte phosphatase (ALP) activity experiments, two major factors which are linked to sufficient cell growth and proliferation

Modulation of osteoblast cell response through laser surface processing of nylon 6,6

With an ageing population demand on medical facilities is growing, especially for bio-implants. Therefore, there is a need for cheaper, more efficient implants. This paper details how CO2 and KrF excimer lasers can be employed to modulate osteoblast cell growth on nylon 6,6 in relation to laser-modified wettability characteristics. Through patterning the contact angle, θ, increased by up to 19°, indicating the presence of a mixed state wetting regime; whereas θ decreased by up to 20° for the whole area irradiative processed samples. After 24 hours and 4 days incubation the cell cover density and cell count was somewhat modulated over the laser-modified samples compared to the as-received sample. A likely increase in surface toxicity gave rise to a hindered cell response for those samples with high energy densities and high incident pulse numbers. No strong correlations were determined for the laser-induced patterned samples which can be attributed to the likely mixed-state wetting regime. Correlative trends were found between the cell response, θ, polar component and surface oxygen content for the whole area irradiative processed samples. Thus, allowing one to identify the potential for this technology in regenerative medicine

The Transition Probability of the qq-TAZRP (qq-Bosons) with Inhomogeneous Jump Rates

In this paper we consider the $q$-deformed totally asymmetric zero range process ($q$-TAZRP), also known as the $q$-boson (stochastic) particle system, on the ${\mathbb Z}$ lattice, such that the jump rate of a particle depends on the site where it is on the lattice. We derive the transition probability for an $n$ particle process in Bethe ansatz form as a sum of $n!$ $n$-fold contour integrals. Our result generalizes the transition probability formula by Korhonen and Lee for $q$-TAZRP with a homogeneous lattice, and our method follows the same approach as theirs

Generic parameters governing the wettability characteristics of laser-modified nylon 6,6

Wettability is an interesting subject which spans any discipline that takes into account any form of adhesion. As such, it is imperative to identify generic parameters that govern the wetting nature of materials. This paper details the use of CO2 and KrF excimer lasers to modify the surface of nylon 6,6 in order to modulate the wettability characteristics. White light interferometery allowed one to establish that the surface roughness (Ra) was dramatically increased by up to 4.5 µm in comparison to the as-received sample. Using a sessile drop device it was determined for all samples that the polar component had a strong inverse relationship with the contact angle, θ. For the patterned samples an increase in θ indicated the likely formation of a mixed-state wetting regime and highlighted the significant influence of surface topography on θ. X-ray photoelectron spectroscopy determined that the surface oxygen content had increased by up to 5.7 %at. for all samples. Due to the highly modulated nature of θ over all samples it was concluded that surface oxygen content was not a dominant parameter; whereas the polar component and surface pattern were the most dominant parameters governing the wettability characteristics of the laser-surface-modified nylon 6,6

Wettability characteristics variation of PMMA by means of CO2 laser generated surface patterns

CO2 lasers can be seen to lend themselves to materials processing applications and have been used extensively in research and industry. This work investigated the surface modification of PMMA with a CO2 laser in order to vary wettability characteristics. The wettability characteristics of the PMMA were modified by generating a number of patterns of various topography on the sample surfaces using a CO2 laser. Through white light interferometry it was found that for all laser patterned samples the surface roughness had significantly increased by up to 3.1 μm. The chemical composition of selected samples were explored using X-ray photoelectron spectroscopy and found that the surface oxygen content had risen by approximately 4% At. By using a sessile drop device it was found that 50 μm dimensions gave rise to a more hydrophilic surface; whereas 100 μm dimensions gave rise to either no change or an increase in contact angle making the PMMA hydrophobic. This can be explained by the possibility of different wetting regimes taking place owed to the variation of topographies over the as-received and laser patterned sample

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

CO2 laser processing of nylon 6,6 can modify its wettability and biomimetic characteristics. This paper discusses comparatively the use of a CO2 laser for surface patterning and whole area processing, detailing the effects on the wettability and osteoblast cell response. White light interferometry 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. The surface oxygen content was increased by up to 5 %at for all laser irradiated samples. A sessile drop device determined that the laser patterned samples gave rise to an increase in contact angle, whereas a decrease in contact angle was observed for the large area patterned samples in comparison to the as-received nylon 6,6. The increase in contact angle is explained by the likely existence of a mixed-state wetting regime.The bioactive nature of the samples were analysed by seeding osteoblast cells onto the nylon 6,6 samples for 4 days. It was found that most laser surface treated samples gave rise to a more biomimetic surface. Some samples gave a less enhanced biomimetic which can be attributed to an increase in surface toxicity. Also, generic wettability characteristics have been forged which can predict the biomimetic nature of laser surface treated nylon 6,6