Generic parameters governing the biofunctionality of laser surface engineered nylon 6,6

On account of an ever increasing demand on medicine there is a need and a drive by the biomedical industry to develop robust and predictable implant technology. This paper gives an account of the implementation of CO2 and KrF excimer laser systems to modulate the biofunctionality of nylon 6,6 in terms of osteoblast cell response. There were correlative trends between the cell response, contact angle, 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. However, no strong correlations were determined for the laser-induced patterned samples which can be attributed to the likely mixed-state wetting regime. Through analytical analysis, governing equations are discussed, showing how different parameters can be used to predict the wettability of, and biological cell response to, laser surface engineered nylon 6,6

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

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

CO2 laser surface patterning of nylon 6,6 and the subsequent effects on wettability characteristics and apatite response

Simulated body fluid (SBF) has been used previously to predict the osseointegration potential of materials by assesing the apatite response. This paper details a study carried out using a CO2 laser to induce a number of surface patterns which inherently modified both the surface chemistry and surface topography of nylon 6,6 and gave rise to a difference in apatite response. These induced patterns caused a reduction in hydrophilicity with increased contact angles of up to 10°. Following immersion in SBF for 14 days each sample was weighed revealing an increase in weight of up to 0.029 g indicating that an apatite layer had begun to form. Energy dispersive X-ray (EDX) analysis identified the presence of calcium and phosphorous, two elements which support osteoblast cell response. It was found that the laser induced patterned samples gave rise to more layer crystals forming suggesting a more optimized surface for osteoblast cell growth

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

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

Osteoblast cell response to a CO2 laser modified polymeric material

Lasers are an efficient technology which can be applied for the surface treatment of polymeric biomaterials to enhance insufficient surface properties. That is, the surface chemistry and topography of biomaterials can be modulated to increase the biofunctionality of that material. By employing CO2 laser patterning and whole area processing of nylon 6,6 this paper details how the surface properties were significantly modified. Samples which had undergone whole area processing followed current theory in that the advancing contact angle, θ, with water decreased and the polar component, γp, increased upon an increase in surface roughness. For the patterned samples it was observed that θ increased and γP decreased. This did not follow current theory and can be explained by a mixed-state wetting regime. By seeding osteoblast cells onto the samples for 24 hours and 4 days the laser surface treatment gave rise to modulated cell response. For the laser whole area processing, θ and γP correlated with the observed cell count and cover density. Owed to the wetting regime, the patterned samples did not give rise to any correlative trend. As a result, CO2 laser whole area processing is more likely to allow one to predict biofunctionality prior to cell seeding. What is more, for all samples, cell differentiation was evidenced. On account of this and the modulation in cell response, it has been shown that laser surface treatment lends itself to changing the biofunctional properties of nylon 6,6

Investigation into time dependant degradation and atmospheric conditions on the wettability of nylon 6,6 which has undergone CO2 laser surface modification

Modification of the wettability of polymers has been demonstrated previously; however, it is known that the wettability modifications of these materials can degrade or vary over time. This can be seen to be crucial from a commercial point of view as this would indicate that a shelf-life has to be established. But at the same time, atmospheric parameters may affect the contact angle and must therefore be accounted for as a control variable in any long-term study of wettability. In this study four CO2 laser patterned nylon 6,6 samples with differing topographical patterns and one as-received sample were analysed over a 30 week period whilst stored in ambient air. By obtaining the characteristic contact angle every two weeks it was found that the contact angle varied erratically before ultimately increasing for all samples after the 30 weeks. White light interferometry analysis determined that the laser patterning gave rise to peak heights of up to 3 μm with roughness parameters Ra and Sa of up to 0.305 and 0.408 μm, respectively. X-ray photoelectron spectroscopy found that surface oxygen content increased by up to 7 %At. It was identified that there was a significant correlation between changes in barometric air pressure and contact angle, highlighting the need for further study to determine if this is a dominant factor

Nonlinear analysis of T-shaped concrete walls subjected to multi-directional displacements

Structural walls are often used to resist lateral loads applied to buildings. Structural walls have historically been very successful at limiting damage to both structural and non-structural elements. Researchers at the University of Minnesota (UMN), Iowa State University (ISU), the University of Puerto Rico at Mayaguez, and a consulting engineer from the Nakaki Bashaw Group, Inc. in California tested and analyzed five cast-in-place concrete structural walls, three rectangular walls and two T-walls. All of the walls were analyzed using the open source finite element package OpenSees. Both pre- and post-test analysis of the walls was done to understand the simulation capabilities, and improvements that are required to improve the simulation and prediction of the response of the structural walls. The OpenSees software was modified to include a new concrete model that improves the simulation of the response of concrete flexural members. The details of the concrete models are presented along with the modifications from a concrete model proposed by Chang and Mander in 1995. The global force-displacement response of the structural walls are compared with the responses recorded during the testing at the University of Minnesota\u27s Multi-Axial Subassemblage Testing Facility. The analysis was generally capable of capturing the measured response within 5-10%. The contribution of various displacement components were examined and compared with the contributions from the OpenSees analysis. The final T-wall response was successfully predicted using the modeling technique. In addition to the global force-displacement, the local responses including the location of the neutral axis, curvature, and strain profiles are examined. The local response was well captured for the post-testing analysis and acceptably predicted for the pretesting analysis. In general the fiber based modeling approach used in this investigation of the structural walls tested at the MAST facility was very successful at capturing both the global and local responses of both rectangular and non-rectangular walls under various applied loads. Recommendations for the simulation of concrete structural walls are given, and future research to further advance the simulation of concrete structural walls