Abstract

The objectives of this project were to assess the effect of laser surface modification
on the biocompatibility of polymeric biomaterials when used as a substrate for stem
cell culture. Human mesenchymal stem cells were cultured on a pair of polymeric
material substrates with varied incubation times and surface parameters. Poly ether
ether ketone was selected due to its chemical and physical robustness as well as its
use in load bearing implants as well as the potential to improve its efficacy via
improved osteogenicity. The second material was Nylon 6’6 a common member of
the Nylon family that is regularly used in a number of medical instruments and has
been shown in literature to have potential in tissue engineering applications.
Samples of both materials were cleaned and prepared for processing. The wattage
of laser power used, the traverse speed, the pattern and the spacing between lines
of the pattern were modify the material surface were all varied to produce differing
surface patterns. A number of the surface characteristics of the processed samples
were assessed in order to evaluate the effect of the individual processing parameters
modified. These included:
• Material Wettability
• Surface Roughness
• Surface Chemistry
• Surface topography via SEM
Another objective of this project was to assess the effect of laser modified material
surfaces on the growth rate of hMSCs. Alongside this, a proteomic assay as
performed to assess if any differentiational bias enforced upon hMSC's by materials
that have undergone processing. The was assessed via the expression of Bone
Daniel George Cosgrove University of Lincoln Student ID: COS10175497
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Morphogenic Protein 7 (BMP-7). Alongside this, the effect of laser surface
modification was assessed using a cytotoxicity assay to assess cell growth rates
using an incubation time course. The results of this study showed that PEEK was
found to be the more hydrophobic material post processing though lower levels of
laser energy per mm2 squared were found to be more hydrophobic than samples
that received higher amounts of laser energy. Nylon 6’6 samples on the other hand
was much more hydrophilic in comparison to PEEK. Surface roughness was varied
in both material, though the highest level of roughness was seen in PEEK as
opposed to Nylon 6’6. That being said, PEEK generally was more difficult to produce
a pattern on, this resulted in the some of the rougher surfaces as the surface simply
vaporised at higher laser energy per mm2. Both materials that underwent surface
processing had totally different responses. When laser energy was applied to Nylon
6’6 it resulted in liquefaction which allowed for greater infiltration of atmospheric
gasses. This resulted in an increase in an improved ration of nitrogen to carbon.
PEEK on the other hand scorched as opposed to liquefying which resulted in a large
increase in the level of carbon present. Cell response to modified surfaces was
assessed using stem cell incubation followed by a 3-(4,5-dimethylthiazol-2-yl)-2,5-
diphenyltetrazolium bromide (MTT) cytotoxicity assay to assess growth rates of
hMSCs. Cells were incubated at 24 hours, 48 hours and 4 days to assess the effect
over time. A statistically significant difference was found between the 24 hour and 48
hours and the 24 hours and 4 days. Cell growth rates were higher on samples that
had undergone modification as opposed to unmodified control samples. Finally, the
proteomic assay ELISA assay performed showed that there was no statistically
significant difference between unmodified and modified material samples.