Investigation on the Nanomechanics of Liposome Adsorption on Titanium Alloys: Temperature and Loading Effects.

Yiqin Duan,Jinjin Li,Hongdong Wang,Yuhong Liu,Shizhu Wen

doi:10.3390/polym10040383

Abstract

The mechanical properties of liposomes, determined by the lipid phase state at ambient temperature, have a close relationship with their physiological activities. Here, atomic force microscopy (AFM) was used to produce images and perform force measurements on titanium alloys at two adsorbed temperatures. The mechanical properties were evaluated under repeated loading and unloading, suggesting a better reversibility and resistance of gel phase liposomes. The liquid phase liposomes were irreversibly damaged during the first approach while the gel phase liposomes could bear more iterations, resulting from water flow reversibly going across the membranes. The statistical data offered strong evidence that the lipid membranes in the gel phase are robust enough to resist the tip penetration, mainly due to their orderly organization and strong hydrophobic interactions between lipid molecules. This work regarding the mechanical properties of liposomes with different phases provides guidance for future clinical applications, such as artificial joints.

Highlights

Phosphatidylcholine (PC) liposomes are widely used in various technologies [1,2,3,4,5,6], such as drug delivery systems in medicine, additives in cosmetics, gene delivery and food engineering, due to their biocompatibility
DPPC liposomes were characterized by atomic force microscopy (AFM) to obtain their morphology on Ti6Al4V
In order to obtain individual vesicles dispersing on substrate following nanomechanical measurements, the lipid concentration was set as 0.1 mg/mL

Summary

Introduction

Phosphatidylcholine (PC) liposomes are widely used in various technologies [1,2,3,4,5,6], such as drug delivery systems in medicine, additives in cosmetics, gene delivery and food engineering, due to their biocompatibility. On account of their highly hydrated PC head-groups and robust hydration shells [14,15], liposomes have been widely studied in different applications, such as surface force apparatuses and ex vivo cartilage devices [16,17] Among these applications, the mechanical properties of the liposomes and bilayers are of critical importance. It is of great importance to evaluate mechanical properties under repeated loading and unloading and to investigate the effects of temperature on the nanomechanical properties of liposomes In addition to these factors, the choice of substrate should not be underestimated. A polished titanium alloy, Ti6Al4V, was chosen as the substrate It had been used widely in joint lubrication due to its excellent biocompatibility and mechanical properties [40,41]. The statistical data from all force-distance curves was summarized to better explain the bearing capacity of lipid membrane at the two phases

Materials

Preparation of Liposomes and Adsorbed Surfaces

Atomic Force Microscopy

Characterization of Liposomes Adsorbing on Surfaces

Statistical Research on Comprehensive Bearing Capacity of DPPC Vesicles

Conclusions