Wettability modification of human tooth surface by water and UV and electron-beam radiation.

The wettability of the human tooth enamel and dentin was analyzed by measuring the contact angles of a drop of distilled water deposited on the surface. The samples were cut along the transverse and longitudinal directions, and their surfaces were subjected to metallographic mirror-finish polishing. Some samples were also acid etched until their microstructure became exposed. Wettability measurements of the samples were done in dry and wet conditions and after ultraviolet (UV) and electron beam (EB) irradiations. The results indicate that water by itself was able to increase the hydrophobicity of these materials. The UV irradiation momentarily reduced the contact angle values, but they recovered after a short time. EB irradiation raised the contact angle and maintained it for a long time. Both enamel and dentin surfaces showed a wide range of contact angles, from approximately 10° (hydrophilic) to 90° (hydrophobic), although the contact angle showed more variability on enamel than on dentin surfaces. Whether the sample's surface had been polished or etched did not influence the contact angle value in wet conditions.

Surface roughness and wettability of dentin ablated with ultrashort pulsed laser.

The aim of this study was to evaluate the surface roughness and wettability of dentin following ultrashort pulsed laser ablation with different levels of fluence and pulse overlap (PO). Twenty-five extracted human teeth crowns were cut longitudinally into slices of approximately 1.5-mm thick and randomly divided into nine groups of five. Samples in groups 1 to 8 were ablated with an ultrashort pulsed laser through a galvanometric scanning system. Samples in group 9 were prepared using a mechanical rotary instrument. The surface roughness of samples from each group was then measured using a three-dimensional profile measurement laser microscope, and wettability was evaluated by measuring the contact angle of a drop of water on the prepared dentin surface using an optical contact angle measuring device. The results showed that both laser fluence and PO had an effect on dentin surface roughness. Specifically, a higher PO decreased dentin surface roughness and reduced the effect of high-laser fluence on decreasing the surface roughness in some groups. Furthermore, all ablated dentin showed a contact angle of approximately 0 deg, meaning that laser ablation significantly improved wettability. Adjustment of ultrashort pulsed laser parameters can, therefore,significantly alter dentin surface roughness and wettability.

Effect of ultraviolet-mediated photofunctionalization for bone formation around medical titanium mesh.

PURPOSE: The new technology of photofunctionalization with ultraviolet (UV) light for titanium implants has earned considerable attention. We hypothesized that UV light treatment would enhance bone formation on titanium mesh. MATERIALS AND METHODS: We implemented in vitro and in vivo experiments to examine the effectiveness of UV treatment for bone formation on titanium mesh surfaces. Titanium mesh for medical use was prepared as samples, which were autoclaved and stored under dark ambient conditions for 4 weeks. UV treatment was performed for 12 minutes. Carbon contamination, hydrophilicity, and protein adhesion of the titanium mesh surface were examined in an in vitro model. Bone tissue formation around the titanium mesh was observed in a rat femur bone model. The Mann-Whitney U test was used to examine differences between the untreated and UV-treated groups. P values of < .05 were considered significant. RESULTS: UV-mediated photofunctionalization reduced carbon contamination rates on the untreated titanium mesh surfaces. The hydrophobic surface of the untreated titanium mesh became superhydrophilic after UV-mediated photofunctionalization (P < .01). The amount of protein adsorbed onto the titanium was 1.5 to 3 times greater on the photofunctionalized titanium mesh surfaces than on the untreated titanium mesh surfaces (P < .01). In the animal experiment, the newly formed bone on the UV-treated titanium mesh was approximately 2.5 times greater than that on the untreated mesh (P < .05). CONCLUSIONS: UV-mediated photofunctionalization is effective, as demonstrated by the enhanced bone tissue formation on the titanium mesh. Future studies will focus on bone augmentation using an UV-mediated photofunctionalized titanium implant and mesh.

Vibration characteristics of aluminum surface subjected to ultrasonic waves and their effect on wetting behavior of solder droplets.

The vibration characteristics of an aluminum surface subjected to ultrasonic waves were investigated with a combination of numerical simulation and experimental testing. The wetting behavior of solder droplets on the vibrating aluminum surface was also examined. The results show that the vibration pattern of the aluminum surface is inhomogeneous. The amplitude of the aluminum surface exceeds the excitation amplitude in some zones, while the amplitude decreases nearly to zero in other zones. The distribution of the zero-amplitude zones is much less dependent on the strength of the vibration than on the location of the vibration source. The surface of the liquid solder vibrates at an ultrasonic frequency that is higher than the vibration source, and the amplitude of the liquid solder is almost twice that of the aluminum surface. The vibration of the surface of the base metal (liquid solder) correlates with the oxide film removal effect. Significant removal of the oxide film can be achieved within 2s when the amplitude of the aluminum surface is higher than 5.4 µm or when the amplitude of the liquid solder surface is higher than 10.2 µm.

Poly(ether-ether-ketone) orthopedic bearing surface modified by self-initiated surface grafting of poly(2-methacryloyloxyethyl phosphorylcholine).

We investigated the production of free radicals on a poly(ether-ether-ketone) (PEEK) substrate under ultraviolet (UV) irradiation. The amount of the ketyl radicals produced from the benzophenone (BP) units in the PEEK molecular structure initially increased rapidly and then became almost constant. Our observations revealed that the BP units in PEEK acted as photoinitiators, and that it was possible to use them to control the graft polymerization of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC). This "self-initiated surface graft polymerization" method is very convenient in the absence of external photoinitiator. We also investigated the effects of the monomer concentration and UV irradiation time on the extent of the grafted PMPC layer. Furthermore, as an application to improving the durability of artificial hips, we demonstrated the nanometer-scale photoinduced grafting of PMPC onto PEEK and carbon fiber-reinforced PEEK (CFR-PEEK) orthopedic bearing surfaces and interfaces. A variety of test revealed significant improvements in the water wettability, frictional properties, and wear resistance of the surfaces and interfaces.

Modification and patterning of nanometer-thin poly(ethylene glycol) films by electron irradiation.

In this study, we analyzed the effect of electron irradiation on highly cross-linked and nanometer-thin poly(ethylene glycol) (PEG) films and, in combination with electron beam lithography (EBL), tested the possibility to prepare different patterns on their basis. Using several complementary spectroscopic techniques, we demonstrated that electron irradiation results in significant chemical modification and partial desorption of the PEG material. The initially well-defined films were progressively transformed in carbon-enriched and oxygen-depleted aliphatic layers with, presumably, still a high percentage of intermolecular cross-linking bonds. The modification of the films occurred very rapidly at low doses, slowed down at moderate doses, and exhibited a leveling off behavior at higher doses. On the basis of these results, we demonstrated the fabrication of wettability patterns and sculpturing complex 3D microstructures on the PEG basis. The swelling behavior of such morphological patterns was studied in detail, and it was shown that, in contrast to the pristine material, irradiated areas of the PEG films reveal an almost complete absence of the hydrogel-typical swelling behavior. The associated sealing of the irradiated areas allows a controlled deposition of objects dissolved in water, such as metal nanoparticles or fluorophores, into the surrounding, pristine areas, resulting in the formation of nanocomposite patterns. In contrast, due to the distinct protein-repelling properties of the PEG films, proteins are exclusively adsorbed onto the irradiated areas. This makes such films a suitable platform to prepare protein-affinity patterns in a protein-repelling background.

Simplifying corneal surface regeneration using a biodegradable synthetic membrane and limbal tissue explants.

Currently, damage to the ocular surface can be repaired by transferring laboratory cultured limbal epithelial cells (LECs) to the cornea using donor human amniotic membrane as the cell carrier. We describe the development of a synthetic biodegradable membrane of Poly D,L-lactide-co-glycolide (PLGA) with a 50:50 ratio of lactide and glycolide for the delivery of both isolated LECs and of cells grown out from limbal tissue explants. Both isolated LECs and limbal explants produced confluent limbal cultures within 2 weeks of culture on the membranes without the need for fibroblast feeder layers. Outgrowth of cells from explants was promoted by the inclusion of fibrin. Membranes with cells on them broke down predictably within 4-6 weeks in vitro and the breakdown was faster for a lower molecular weight (MW) (44 kg/mol) rather than a higher MW (153 kg/mol) PLGA. Membranes could be reproducibly produced, sterilised with gamma irradiation and stored dry at -20 °C for at least 12 months, and the ability to support cell outgrowth from explants was retained. We demonstrate transfer of cells (both isolated LECs and of cells grown out from limbal explants) from the membranes to an ex vivo rabbit cornea model. Characterisations of the cells by immunohistochemistry showed both differentiated and stem cell populations. A synthetic membrane combined with limbal explants in theatre would avoid the need for tissue banked human amniotic membrane and also avoid the need for specialist laboratory facilities for LEC expansion making this more accessible to many more surgeons and patients.

Light-induced switching of the wettability of novel asymmetrical poly(vinyl alcohol)-co-ethylene membranes blended with azobenzene polymers.

Novel composite asymmetrical membranes based on poly(vinyl alcohol)-co-ethylene (EVAL) as the host material and new polyethers that contain azobenzene moieties in the side chain were prepared by dry-cast phase inversion after dissolving the azo polymers in tetrahydrofuran and EVAL in dimethylsulfoxide and subsequently mixing the resulting solutions. By taking advantage of the proper temperature variation in the oven used for solvent evaporation, asymmetrical membranes that exhibited a dense, crystalline layer on the bottom and a porous, mainly amorphous layer on the top were obtained. Remarkable changes in the surface morphology and the contact angle with water were observed on the top surfaces of the composite membranes. This was ascribed not only to the enhanced concentration of azo polymer on the top surface but mostly to a conformational change in EVAL induced by the photoisomerization of the guest azo groups, as shown by HRMAS (1)H NMR. The morphological and structural changes in EVAL could be reversed on exposing the membrane to visible light for 24 h.