Inspired
by the cell membrane surface as well as the ocular tissue,
a novel and clinically applicable antifouling silicone hydrogel contact
lens material was developed. The unique chemical and biological features
on the surface on a silicone hydrogel base substrate were achieved
by a cross-linked polymer layer composed of 2-methacryloyloxyethyl
phosphorylcholine (MPC), which was considered important for optimal
on-eye performance. The effects of the polymer layer on adsorption
of biomolecules, such as lipid and proteins, and adhesion of cells
and bacteria were evaluated and compared with several conventional
silicone hydrogel contact lens materials. The MPC polymer layer provided
significant resistance to lipid deposition as visually demonstrated
by the three-dimensional confocal images of whole contact lenses.
Also, fibroblast cell adhesion was decreased to a 1% level compared
with that on the conventional silicone hydrogel contact lenses. The
movement of the cells on the surface of the MPC polymer-modified lens
material was greater compared with other silicone hydrogel contact
lenses indicating that lubrication of the contact lenses on ocular
tissue might be improved. The superior hydrophilic nature of the MPC
polymer layer provides improved surface properties compared to the
underlying silicone hydrogel base substrate.
Materials taking
advantage of the characteristics of biological
tissues are strongly sought after in medical science and bioscience.
On the natural corneal tissue surface, the highly soft and lubricated
surface is maintained by composite structures composed of hydrophilic
biomolecules and substrates. To mimic this structure, the surface
of a silicone hydrogel contact lens was modified with a biomimetic
phospholipid polymer, poly(2-methacryloyloxyethyl phosphorylcholine)
(PMPC), and the nanoscaled morphology and mechanical properties of
the surface were confirmed with advanced surface characterization
and imaging techniques under an aqueous medium. Concavities and convexities
on the nanometer order were recognized on the surface. The surface
was completely covered with a PMPC layer and remained intact even
after 30 days of clinical use in a human ocular environment. The mechanical
properties of the natural corneal tissue and the PMPC-modified surface
were similar in the living environment, that is, low modulus and frictional
properties comparable to natural tissues. These results show the validity
of material preparation by biomimetic methods. The methodologies developed
in this study may contribute to future development of human-friendly
medical devices.
Plasma-functionalized polytetrafluoroethylene (PTFE) nanoparticles were employed to evaluate their utility in improving the lubrication property of a group III mineral oil with a significantly low amount of zinc dialkyl dithiophosphate (ZDDP). The particles were coated with two consecutive films; the initial coating contained silica to enhance amorphous glassy tribofilm formation, followed by a methacrylate film to protect the silica coating and enhance dispersibility in the oil. The functionalized nanoparticles were evaluated for their tribological performance using a high-frequency reciprocating rig, in a cylinder-on-flat configuration. The oil formulations containing ZDDP (350 ppm phosphorus level) and the functionalized nanoparticles resulted in dramatic reductions in the friction coefficient and overall wear compared to the samples containing nonfunctionalized PTFE nanoparticles, ZDDP (350 ppm P), and samples devoid of nanoparticles but containing ZDDP with a 700 ppm P treat rate. XPS and XANES spectroscopy were employed to characterize the tribological films formed on the test samples. The samples with functionalized particles and ZDDP clearly exhibited tribofilms with Si- and F-doped polyphosphates of Zn coupled with the presence of ZnS at the metal-tribofilm interface. On the other hand, oils without the functionalized nanoparticles have oxides of Fe and to a lesser extent short-chain phosphates of Zn. The overall results suggest that the synergism between plasma-coated PTFE nanoparticles and ZDDP contributed to the development of protective tribofilms even at reduced amount of phosphorus in the oil. This new method of employing nanoparticles to deliver novel antifriction and antiwear chemistries at the tribological interfaces stands out as a promising approach to further reduce P levels in oils without compromising friction and wear performance.
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