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Experimental
Materials selection
Three substrate materials: poly(methyl methacrylate) (PMMA), glycol-treated poly(ethylene terephthalate) (PETG), and polytetrafluoroethylene (PTFE) were selected for full evaluation. Two other materials, low-density polyethylene and poly(ether ether ketone) were selected for evaluation as well, but later eliminated from testing due to their inherent fluorescence in the green and red wavelength regions discovered under fluorescence microscopy conditions. LDPE and PEEK were eliminated because this fluorescence made examination of the cell culture products impossible with the procedure used. PMMA and PETG were selected due to the differences in ablation characteristics as described by the literature. PTFE was chosen because of its wide use in biomedical applications and its little-known ablation characteristics. All of the materials were obtained in extruded sheet form in either 1/8” or 1/16” thicknesses from McMaser-Carr.
Both the PETG and the PMMA sheets came with a protective cover sheet that was removed prior to treatment or examination by other means. Prior to ablation or other treatment, the materials were cleaned with deionized water and a Kimwipe. No solvents were used to clean the material surfaces so as to prevent any contamination of the surfaces with foreign organic functional groups. While it is possible that there were other metallic contaminants on the sample surfaces, these would be easily identified during the surface compositional analysis with XPS and steps to remove contamination without damaging the samples could be taken. This was not necessary however, as metallic contaminants did not prove to be an obstacle in these experiments.
Laser treatment
A Lambda Physik LPX300 Kr-F laser was used to surface treat each polymers. Initial exploratory experiments were run to determine optimal spot size and energy for ablation. Spot size was manipulated by varying the dimensions of an internal aperature. Three spot sizes as defined by the aperture (8mm x 3mm, 5mm x 2mm, and 3mm x 1.5 mm) and 5 energies (306, 438, 672, 900, and 1026 mJ) were used. Upon observation of the results of these experiments, the medium spot size 5mm x 2mm and maximum energy of approximately 1000 mJ were chosen for further experimentation. This choice of energy and spot size delivered a dose per pulse of 3.3 x 109 W/cm2. This spot size and
energy were chosen in order to maximize the area to be ablated while still producing results observable with the naked eye. With this energy and spot size there was a visibly observable modification of the surface of all three polymers. Translation of the laser beam was done using a Stepper Motor Controller STP57D317 mounted on a rastering lens. This stepper motor moved the lens 1.8° /step at a speed of 20 steps/min. The experimental setup is shown in Figure 6 below.The distance between the rastering lens and the sample was 21 cm and the distance between the rastering lens and focusing lens was 11.3 cm. The laser was pulsed at 5 Hz as the beam translated across the polymer surface. All experiments were run in air with a fan to prevent ablation products from depositing on the rastering lens by blowing the plume away. The plume formed was consistent with effects seen in previous experiments described in the introduction. Plumes associated with polymer ablation are typically caused by the vaporization of surface materials due to the fast heating of the surface material with radiation
1. Introduction
1.1. Need for bioadhesion modulation
1.1.1. Implanted materials and biosensors
1.1.2. Biofouling
1.2. Surface properties of biomaterials
1.2.1. Hydrophilicity
1.2.2. Surface texture effects
1.2.3. Inherent surface toxicity
1.2.4. Culture environmental effects
1.3. Modification of surface properties of polymers for biomedical uses
1.4. Laser ablation for surface modification
1.4.1. Morphological influences
1.4.2. Surface chemical influences
1.4.3. Roughening
1.4.4. Poly(ethylene terephthalate)
1.4.5. Poly(methyl methacrylate)
1.4.6. Polytetrafluoroethylene
2. Experimental
2.1. Materials selection
2.2. Laser treatment
2.3. Cell culture1
2.4. Contact angle
2.5. Surface composition
2.6. Surface topography
2.6.1. Scanning electron microscopy
2.6.2. Optical microscopy
2.7. Other materials characterization
3. Results and Discussion
3.1. Laser treatment
3.2. Cell culture
3.3. Surface energy
3.4. Surface composition
3.5. Surface topography
4. Conclusions
5. Future Work.
6. References
7. Appendix
8. Vita
