Proliposome Powders for the Generation of Liposomes: the Influence of Carbohydrate Carrier and Separation Conditions on Crystallinity and Entrapment of a Model Antiasthma Steroid

Formulation effects on the entrapment of beclometasone dipropionate (BDP) in liposomes generated by hydration of proliposomes were studied, using the high-density dispersion medium deuterium oxide in comparison to deionized water (DW). Proliposomes incorporating BDP (2 mol% of the lipid phase consisting of soya phosphatidylcholine (SPC) and cholesterol; 1:1) were manufactured, using lactose monohydrate (LMH), sorbitol or D-mannitol as carbohydrate carriers (1:5 w/w lipid to carrier). Following hydration of proliposomes, separation of BDP-entrapped liposomes from the unentrapped (free) BDP at an optimized centrifugation duration of 90 min and a centrifugation force of 15,500g were identified. The dispersion medium was found to have a major influence on separation of BDP-entrapped liposomes from the unentrapped drug. Entrapment efficiency values were higher than 95% as estimated when DW was used. By contrast, the entrapment efficiency was 19.69 ± 5.88, 28.78 ± 4.69 and 34.84 ± 3.62% upon using D2O as a dispersion medium (for LMH-, sorbitol- and D-mannitol-based proliposomes, respectively). The similarity in size of liposomes and BDP crystals was found to be responsible for co-sedimentation of liposomes and free BDP crystals upon centrifugation in DW, giving rise to the falsely high entrapment values estimated. This was remedied by the use of D2O as confirmed by light microscopy, nuclear magnetic resonance ((1)HNMR), X-ray diffraction (XRD) and entrapment studies. This study showed that carrier type has a significant influence on the entrapment of BDP in liposomes generated from proliposomes, and using D2O is essential for accurate determination of steroid entrapment in the vesicles

Vibrational and AFM studies of adsorption of glycine on DLC and silicon-doped DLC

A better understanding of protein adsorption onto surfaces of materials is required to control biocompatibility and bioactivity. Diamond-like carbon (DLC) is known to have excellent biocompatibility. Various samples of a-C:H and silicon-doped a-C:H thin films (Si-DLC) were deposited onto silicon substrates using plasma-enhanced chemical vapour deposition (PECVD). Subsequently, the adsorption of the simplest amino acid glycine onto the surfaces of the thin films was investigated to elucidate the mechanisms involved in protein adhesion. The physicochemical characteristics of the surfaces, before and after adsorption of glycine, were investigated using Raman spectroscopy and atomic force microscopy (AFM). The Raman study highlighted a slight decrease in the I D/I G ratio with increasing the silicon dopant levels. Following exposure to glycine solutions, the presence of bands at ~1735 and ~1200 cm−1 indicates that the adsorption of glycine onto the surfaces has taken place. Glycine was bound to the surfaces via both deprotonated carboxyl and protonated amino groups whilst, as the silicon content in the DLC film increased the adsorption of glycine decreased. AFM analysis showed that the surface roughness increased following exposure to glycine. These results show that at low silicon doping the adsorption of the amino acid was enhanced whilst increased doping levels led to a reduced adsorption compared to undoped DLC. Therefore, doping of DLC may provide an approach to control the protein adsorption