Pegi Ahlin Grabnar

Thermoresponsive polymers: insights into decisive hydrogel characteristics, mechanisms of gelation, and promising biomedical applications.

Thermally induced gelling systems have gained enormous attention over the last decade. They consist of hydrophilic homopolymers or block copolymers in water that present a sol at room temperature and form a gel after administration into the body. This article reviews the main types of thermoresponsive polymers, with special focus on decisive hydrogel characteristics, mechanisms of gelation, and biocompatibility. Promising biomedical applications are described with a focus on injectable formulations, which include solubilization of small hydrophobic drugs, controlled release, delivery of labile biopharmaceutics, such as proteins and genes, cell encapsulation, and tissue regeneration. Furthermore, combinations of thermoresponsive hydrogels and various nanocarriers as promising systems for sustained drug delivery are discussed through selected examples from the literature. Finally, there is a brief overview of current progress in nano-sized systems incorporating thermoresponsive properties.

The manufacturing techniques of drug-loaded polymeric nanoparticles from preformed polymers

Over the past few decades, nanoparticle (NP) formulation has been the subject of extensive research. The choice of a suitable NP formulation technique is dependent on the physicochemical properties of the drug, such as solubility and chemical stability. Different NP manufacturing methods enable modification of the physicochemical characteristics such as size, structure, morphology and surface texture, but also affect the drug loading, drug entrapment efficiency and release kinetics. This review covers an update on the state of art of the manufacturing of polymeric NPs from preformed polymers. Both, conventional methods for NP preparation, such as spontaneous formulation and emulsification-based methods, and new approaches in NP technology are presented. A comparative analysis is given for polymer, drug and solvent nature, toxicity, purification, drug stability and scalability of the method. The information obtained allows establishing criteria for selecting a method for preparation of NPs according to its advantages and limitations.

Thermoreversible in situ gelling poloxamer-based systems with chitosan nanocomplexes for prolonged subcutaneous delivery of heparin: design and in vitro evaluation.

In situ forming systems including thermoreversible hydrogels, which undergo sol-gel transition upon an increase in temperature have been used for various biomedical applications. Heparins are the standard of anticoagulation in the prophylaxis and treatment of deep vein thrombosis and pulmonary embolism. Both conditions require long-lasting treatment with frequent subcutaneous administrations of heparin. The objective of this study was to prepare and evaluate in situ forming gel systems designed by combination of two poloxamers (P407 and P188) and hydroxypropylmethylcellulose (HPMC) for prolonged release of heparin. Thermoreversible hydrogels were prepared with heparin solution and dispersion of heparin/chitosan nanocomplexes. Nanocomplexes formed by self-assembly of heparin with chitosan at various mass ratios were thoroughly characterized. A heparin/chitosan mass ratio of 1:1 with pH 5.20 was the most appropriate for preparation of small, homogenous and stable nanocomplexes (mean diameter 123 nm; polydispersity index 0.22 and zeta potential+35.5 mV). Thermoreversible hydrogels were evaluated by gelation temperature, viscosity over the temperature range 20-40 °C, rate of hydrogel dissolution, and heparin release in vitro. The addition of P188 to P407 gel formulations resulted in an increase in gelation temperature, decrease in viscosity at room temperature and faster gel dissolution. The opposite effects were observed with formulations containing HPMC which demonstrated 18-day-long gel dissolution and complete heparin release in 9days from gels containing heparin solution. Considerable prolongation of heparin release was achieved with incorporation of heparin/chitosan nanocomplexes into the gelling systems. It may be concluded that with poloxamer mixtures at specific concentrations, addition of HPMC and use of heparin/chitosan nanocomplexes dispersions, thermoreversible formulations for prolonged subcutaneous release of heparin are feasible.

High celecoxib-loaded nanoparticles prepared by a vibrating nozzle device.

Drug delivery research has resulted in the availability of several enabling technologies for formulating poorly water-soluble compounds. In this study the vibrating nozzle device, originally used for encapsulation of drugs, cells and microorganisms, has been used to formulate nanoparticles (NP) with high loading capacity. Celecoxib was incorporated in NP of polylactic acid (PLA) and poly(lactic-co-glycolic acid) (PLGA) and the influence of polymers, initial drug : polymer ratio and stabilizer concentration on NP size and surface properties, entrapment efficiency, drug loading and in vitro release profile were investigated. NP were in the size range of 230–270 nm, with a polydispersity index less than 0.25 and a spherical shape. The highest celecoxib loading (13% w/w) was obtained at initial ratio celecoxib : Resomer RG 502 (PLA/PGA = 50/50) of 1 : 5 and 0.1% w/w polyvinyl alcohol concentration. Thermal analysis and X-ray diffraction suggested that celecoxib was amorphous or molecularly dispersed in the polymeric matrix. The release profile exhibited an initial burst followed by sustained release. The freeze-dried NP could be completely dispersed on addition of lyoprotectants. The production of NP by the vibrating nozzle device is highly reproducible, time saving, can be performed under aseptic conditions and offers the possibility of scale-up.

Structural characterization of liposomes made of diether archaeal lipids and dipalmitoyl-L-α-phosphatidylcholine.

The physicochemical properties of binary lipid mixtures of diether C(25,25) lipids and dipalmitoyl-L-α-phosphatidylcholine (DPPC) were studied using photon correlation, fluorescence and electron paramagnetic resonance spectroscopy, and transmission electron microscopy. These two types of lipids can be mixed at all molar ratios to form unilamellar and multilamellar liposomes. Fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatrien in mixed liposomes indicates that the abrupt changes in order parameter in the hydrophobic part of bilayer membranes made of DPPC lipids disappears with increasing mol%C(25,25) lipids. Electron paramagnetic resonance spectroscopy shows that at temperatures below 50 °C, the interfacial regions of membrane bilayer of mixed liposomes is more fluid than for pure DPPC liposomes, while at higher temperatures, the impact of the long isoprenoid chains on the membrane stability becomes more pronounced. Photon correlation spectroscopy and transmission electron microscopy show that mixed liposomes do not fuse or aggregate, even after 41 days at 4 °C.

Development and validation of a simple and sensitive size-exclusion chromatography method for quantitative determination of heparin in pharmaceuticals

Abstract Heparin is widely used as an anticoagulant for the treatment and prevention of various thrombotic diseases. However, due to its high anionic charge, heterogeneity in size distribution and high polarity, its analysis is very challenging. In this paper, a novel method based on size-exclusion chromatography (SEC) for quantitative determination of intact heparin in pharmaceuticals is presented. Analyses were performed on a BioSep-SEC-S 2000 column with Larginine solution at pH 6.5 as mobile phase and UV detection at 210 nm. The proposed method was found to be selective, linear (R2 > 0.997) over the concentration range of 3.1 to 1222 μg mL-1, with a limit of detection of 1.0 μg mL-1. Intraday and inter-day precision were below 5.1 % and inaccuracy expressed as bias did not exceed 6.5 %. The reported method is simple, selective, sensitive, and requires no laborious sample preparation, which makes it appropriate for routine quantitative analysis of heparin in pharmaceuticals

Aggressive conditions during primary drying as a contemporary approach to optimise freeze-drying cycles of biopharmaceuticals

&NA; Freeze‐drying is the method of choice to dry formulations with biopharmaceutical drugs, to enhance protein stability. This is usually done below the glass transition temperature of maximally freeze‐concentrated solutions (Tg′), to avoid protein aggregation, preserve protein activity, and obtain pharmaceutically ‘elegant’ cakes. Unfortunately, this is a lengthy and energy‐consuming process. However, it was recently shown that drying above Tg′ or even above the collapse temperature (Tc) is not necessarily detrimental for stability of biopharmaceuticals, and hence provides an attractive option for freeze‐drying cycle optimisation. The goal of the present study was to optimise the freeze‐drying cycle for a model IgG monoclonal antibody (20 mg/mL) in sucrose and sucrose/glycine formulations, by reducing primary drying time. To study the impact of shelf temperature (Ts) and chamber pressure on product temperature (Tp), one conventional and five aggressive cycles were tested. Aggressive conditions during primary drying were achieved by increasing Ts from −20 °C (conventional cycle) to 30 °C, with chamber pressure set to 0.1 mbar, 0.2 mbar or 0.3 mbar. These combinations of Ts and chamber pressure resulted in Tp well above Tg′, and in some cases, even above Tc, without causing macrocollapse. Other critical quality attributes of the products were also within the expected ranges, such as reconstitution time and residual water content. Physical stability was tested using size exclusion chromatography, dynamic light scattering, and micro‐flow imaging. All of the lyophilised samples were exposed to stress and the intended storage conditions, with no impacts on the product seen. These data show that implementation of aggressive conditions for the investigated formulations is possible and can significantly contribute to the reduction of primary drying times by up to 54% (from 48 to 22 h) in comparison to conventional freeze‐drying. Graphical abstract Figure. No caption available.

Impact of Carrier Systems on the Interactions of Coenzyme Q10 with Model Lipid Membranes

We investigated the influence of carrier systems for different commercially available water-soluble formulations for coenzyme Q10 on structural changes of model lipid membranes formed by 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and by a mixture of phosphatidylcholine and sphingomyelin (2.4:1). Structural changes in the membranes were measured using fluorescence anisotropy, electron paramagnetic resonance, and differential scanning calorimetry. Two fluorophores and two spin probes were used to monitor membrane characteristics close to the water-lipid interface and in the middle of the bilayer of the model lipid membranes. Different water-soluble carrier systems were tested. These data show that different systems can facilitate penetration of CoQ10 in the lipid membranes, where an increase in the lipid order parameter was observed. In addition, water soluble CoQ10 formulations better protect lipids from oxidation in liposome solution. With the exception of the carriers in an emulsified formulation of CoQ10, those in the other samples did not have any significant effects on membrane fluidity.