Study of in situ adsorption kinetics of polyelectrolytes and liposomes using quartz crystal microbalance: Influence of experimental layout

Controlling Growth of Poly (Triethylene Glycol Acrylate-Co-Spiropyran Acrylate) Copolymer Liquid Films on a Hydrophilic Surface by Light and Temperature

A quartz crystal microbalance with dissipation monitoring (QCM-D) was employed for in situ investigations of the effect of temperature and light on the conformational changes of a poly (triethylene glycol acrylate-co-spiropyran acrylate) (P (TEGA-co-SPA)) copolymer containing 12-14% of spiropyran at the silica-water interface. By monitoring shifts in resonance frequency and in acoustic dissipation as a function of temperature and illumination conditions, we investigated the evolution of viscoelastic properties of the P (TEGA-co-SPA)-rich wetting layer growing on the sensor, from which we deduced the characteristic coil-to-globule transition temperature, corresponding to the lower critical solution temperature (LCST) of the PTEGA part. We show that the coil-to-globule transition of the adsorbed copolymer being exposed to visible or UV light shifts to lower LCST as compared to the bulk solution: the transition temperature determined acoustically on the surface is 4 to 8 K lower than the cloud point temperature reported by UV/VIS spectroscopy in aqueous solution. We attribute our findings to non-equilibrium effects caused by confinement of the copolymer chains on the surface. Thermal stimuli and light can be used to manipulate the film formation process and the film's conformational state, which affects its subsequent response behavior.

Self-Assembled Multilayer Films for Time-Controlled Ocular Drug Delivery

The patient's compliance on the therapeutics to treat glaucoma is significantly low contributing for a fast evolution of the disease. This article presents an autonomous system with controlled release using an alpha2-adrenergic receptor agonist, brimonidine, usually used to treat glaucoma. More specifically, biocompatible and layer-by-layer drug delivery films containing monolayers with brimonidine encapsulated in polymer-β-cyclodextrin were prepared with the objective to obtain a system able to release precise amounts of drug at specific times. To delay the erosion-controlled drug release, we included nanosheets of graphene oxide and layers of a biodegradable polymer (poly-β-aminoester) between the drug-containing monolayers to obtain a time-controlled drug delivery system. An increase in the number of graphene oxide layers is proportional to the brimonidine release delay and its kinetic release can be tuned as a function of the number of layers. Two types of films with brimonidine encapsulated in β-cyclodextrin were analyzed. One of them composed of barrier layers with PBAE and another with two types of barrier layers, PBAE and graphene oxide. The results indicate that one graphene oxide bilayer can delay the brimonidine release for more than 24 h. In vitro assays confirmed that the films have a cell viability of 100%.

In Situ AFM Imaging of Adsorption Kinetics of DPPG Liposomes: A Quantitative Analysis of Surface Roughness

The adsorption of intact liposomes on surfaces is of great importance for the development of sensors and drug delivery systems and, also, strongly dependent on the surface roughness where the liposomes are adsorbed. In this paper, we analyzed, by using atomic force microscopy in liquid, the evolution of the morphology of gold surfaces and of poly(allylamine hydrochloride) (PAH) surfaces with different roughness during the adsorption of liposomes prepared with the synthetic phospholipid 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-(1-glycerol)]. Our results reveal the following. On smooth surfaces of Au only and Au with PAH, the liposomes open and deploy on the substrate, creating a supported-lipid bilayer, with the opening process being faster on the Au/PAH surface. On rough substrates of Au coated with polyelectrolyte multilayers, the liposomes were adsorbed intact on the surface. This was corroborated by power spectral density analysis that demonstrates the presence of superstructures with an average lateral size of 43 and 87 nm, in accordance with two and four times the mean liposome hydrodynamic diameter of about 21 nm. In addition, this work presents an adequate and effective methodology for analysis of adsorption phenomena of liposomes on rough surfaces.

DPPG Liposomes Adsorbed on Polymer Cushions: Effect of Roughness on Amount, Surface Composition and Topography

The adsorption of intact liposomes onto solid supports is a fundamental issue when preparing systems with encapsulated biological molecules. In this work, the adsorption kinetic of 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (sodium salt) liposomes onto cushions prepared from commom polyelectrolytes by the layer-by-layer technique was investigated with the main objective of finding the surface conditions leading to the adsorption of intact liposomes. For this purpose, different cushion surface roughnesses were obtained by changing the number of cushion bilayers. The adsorbed amount per unit area was measured through quartz crystal microbalance, surface morphology was characterized by atomic force microscopy, and the surface composition was assessed by X-ray photoelectron spectroscopy. The results show that (1) the amount of adsorbed lipids depends on the number of cushion bilayers, (2) the cushions are uniformly covered by the adsorbed lipids, and (3) the surface morphology of polymer cushions tunes liposome rupture and its adsorption kinetics. The fraction of ruptured liposomes, calculated from the measured amount of adsorbed lipids, is a function of surface roughness together with other surface morphology parameters, namely the dominating in-plane spatial feature size, the fractal dimension, and other textural features as well as amplitude and hybrid parameters.