Langmuir films study on lipid-containing artificial tears.

Lipid-containing artificial tears are a type of artificial tears that use lipid components in order to restore the lipid layer of the tear film. One of these components is lecithin which can be applied in spray solutions containing lecithin liposomes. In this work the behavior of three of these commercial tears based on lecithin, Innoxa, Opticalm and Optrex, are studied using the Langmuir technique. The obtained isotherms are presented, discussed and compared. This technique seems useful in order to see the film behavior of the lipid components of these tears and determine some important parameters such as fluidity and extension at the air-water interface, and allows us to discern differences between these commercial tears. Innoxa and Optrex tears are more similar to each other than to Opticalm tears. Opticalm presents more fluidity, probably due to the presence of more insaturations in the fatty acid chains of the phospholipids of the lecithin used in fabrication.

AFM in mode Peak Force applied to the study of un-worn contact lenses.

Contact lenses (CLs) are of common use and the biocompatibility, topography and mechanical properties of the used materials are of major importance. The objective of this contribution is to apply the AFM in mode Peak Force to obtain surface topography and mechanical characteristics of un-worn CLs of different materials. One material of hydrogel, two of siloxane-hydrogel and one of rigid gas-permeable were used in the study. The results obtained with different materials have been compared, at a nanoscopic level, and the conclusions are diverse. There is no significant influence of the two environments used to measure the characteristics of the CLs, either water or saline solution. The pHEMA hydrogel CL (Polymacon of Soflens) shows the highest values of roughness, adhesion and elastic modulus. The siloxane-hydrogel CL named Asmofilcon A of PremiO presents the lowest values of mean roughness (Ra), root-mean-square roughness (RMS or Rq), adhesion (Adh) and elastic modulus (Ym), meanwhile the siloxane-hydrogel CL named Lotrafilcon B of Air Optix presents the lowest value of skewness (Rsk) and the rigid gas-permeable CL, named RXD, presents the lowest values of kurtosis (Rku) and maximum roughness (Rmax).

Characterization of Langmuir and Langmuir-Blodgett films of a thiomacrocyclic ionophore by surface pressure and AFM.

The new synthesized thiomacrocyclic ionophore 4-phenyl-4-sulfide-11-(1-oxodecyl)-1,7-dithia-11-aza-4-phosphacyclotetradecane has proven to form Langmuir and Langmuir-Blodgett (LB) films. This ionophore shows a large affinity for copper(II) ions. Thus, the influence of the subphase composition on the surface pressure-area isotherms has been studied. The LB films have been observed by AFM and the effect of the subphase composition and the deposition surface pressure on the LB films is discussed. AFM image morphology has been correlated to the ionophore molecular structure. Surface pressure-area isotherms and AFM images show that the presence of copper(II) ions has an important role in the film structure.

Adsorption of recombinant human bone morphogenetic protein rhBMP-2m onto hydroxyapatite.

Recombinant human mature bone morphogenetic protein 2 (rhBMP-2m) has been expressed to study its adsorption onto precipitated hydroxyapatite (HA). The influence on the adsorption process of different parameters such as pH and concentrations of calcium, phosphate or NaCl has been investigated. Although the adsorption proceeds rapidly at the initial stages, the maximum adsorbed amount is reached after four hours. The process is notably influenced by adding calcium or phosphate to the system but, while calcium ions increase the adsorption of rhBMP-2m onto HA, phosphate ions inhibit it. The influence of pH and NaCl concentration are notable but less important than those of calcium and phosphate. The adsorption data fit well to a Langmuir adsorption isotherm. The values of the isotherm parameters have been calculated and discussed, and an adsorption mechanism has been proposed.