Pharmaceutical Physical Chemistry

The goal with our research is to clarify the relationships between the molecular structure of drug molecules, their physicochemical properties and the possibilities to control how they are stored in and released from different types of particulate drug carriers and formulations. The purpose is to create new knowledge making it possible to develop new or improved systems for the administration of drugs, including macromolecular drugs such as peptides and proteins, and small and amphiphilic drug molecules including cancer drugs. In our investigations we use a combination of experimental and theoretical methods. The experimental techniques include static and dynamic light scattering, small-angle x-ray scattering, small-angle neutron scattering, micropipette-assisted microscopy, confocal microscopy, atomic force microscopy, ellipsometry, and static and time-resolved fluorescence methods.

Ongoing projects

Table of contents:

                    Image of flow pipette microscopy of single microgels with LRI Olympus BX-51 light microscope

Subcutaneous drug delivery

The rapidly growing biopharmaceutical market has been driven by the discovery of new molecules and innovative therapies with great medical potential. However, large classes of the newly available molecules are not suitable for oral and intravenous administration. Subcutaneous (SC) injection is an important alternative administration route but the way biopharmaceuticals behave immediately after administration is still largely unknown. SC therapies used today are characterized by incomplete and variable bioavailability often related to the use of widely different types of formulations, different sites and methods of injection, and the physiological responses to the tissue damage and stress that might be the consequence of an injected formulation.

Our research in this field is part of the parenteral drug delivery platform of the Swedish Drug Delivery Forum (SDDF). We develop novel in vitro methods that can predict the behaviour of drug formulations after SC administration. As part of the work we study how the constituents of the extracellular matrix in human SC adipose tissue interact with formulations of biotherapeutics such as polypeptides, human growth hormone, and monoclonal antibodies, with focus on polyelectrolyte-based formulations.

→ Novel in-vitro models. In this project we develop and evaluate novel in vitro methods to model the behavior of pharmaceutical products administered subcutaneously. The purpose is to improve the mechanistic understanding to facilitate the innovation and development of formulations with high bioavailability of the active pharmaceutical ingredient (API) and small variability between patients. A special focus is on pharmaceutical products based on biologics. By constructing a physiologically relevant model of the extracellular matrix, we will mimic in vitro the fate of different types of drug formulations after administration in humans, including the rate of release and absorption of the API by uptake into the blood and lymph capillaries. The goal is to determine the key factors governing the transport of the pharmaceutical product in the SC environment and the absorption kinetics of the API and to establish in vitro methods useful in the development of drug formulations intended for subcutaneous administration (Fig.1). 

Fig.1: Subcutaneous administration

Contact persons: Per Hansson (principal investigator)

→ Physicochemical aspects. In this project we investigate how active pharmaceutical ingredients (APIs) and excipients in subcutaneously administered drug formulations interact with the components in the extracellular matrix in the subcutaneous adipose tissue (hypodermis). The purpose is to provide a basis for the development of novel in vitro methods to model the behavior of pharmaceutical products administered subcutaneously. The aim is to improve the mechanistic understanding to facilitate the innovation and development of formulations with high bioavailability of the APIs and small variability between patients. A special focus is on pharmaceutical products based on biologics. To increase our knowledge about the factors controlling the drug release rate and absorption by blood and lymphatic vessels we investigate how biological and self-associating drugs organize and interact with the biopolymers in the subcutaneous environment.

Contact persons: Marcus Wanselius (PhD student), Per Hansson (principal investigator).

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Amphiphilic properties of drug molecules

Many pharmacologically active compounds are made up of amphiphilic molecules and possess many similar properties to ordinary surface active agents. Amphiphilic drugs may be found within several classes of drugs including tranquilizers, analgesics, antibiotics, antidepressants, antihistamines, local anaesthetics, anti-inflammatory drugs and anticancer drugs. The amphiphilic nature of these molecules is expected to play a crucial role for their pharmacological activity as well as important properties related to toxicity and haemolysis. In drug formulations the amphiphilic properties of the active substance is decisively important for the molecular mechanisms of solubilisation and drug delivery.

In this research program, we study various aspects of the self-assembly process of amphiphilic drugs in presence of relevant drug delivery components such as phospholipid bilayers, surfactants, proteins and other biomacromolecules. The structural behaviour is mainly investigated using various scattering techniques such as static and dynamic light scattering, small-angle x-ray scattering (SAXS) and small-angle neutron scattering (SANS), but also complementary techniques such as cryo-TEM electron microscopy (Fig.2).

Fig.2: Cryo-TEM image of mixed sodium dodecyl sulfate/adiphenine hydrochloride vesicles.

Contact persons: Magnus Bergström(principal investigator).

→ Amphiphilic properties of drug molecules and their self-assembly in presence of phospholipids

Molecular components such as phospholipids, surfactants, proteins and drug molecules consist of both hydrophilic and lipophilic parts and are involved in various drug delivery systems. As a result, these components are able to self-assemble and interact strongly with one another in ways that usually determine molecular release mechanisms in drug delivery systems. The aim of the project is to study the interactions and self-assembly in mixtures of different amphiphilic drug molecules and phospholipids. The study includes structural characterization of the drug-phospholipid aggregates (micelles, liposomes, bilayer structures) as well as investigating the location and impact of drug molecules on phospholipid bilayers, by mainly using various small-angle scattering techniques.

Contact persons: Vahid Motlaq (PhD student), Magnus Bergström (principal investigator).

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Gels for drug delivery

Charged polymer networks have the possibility to absorb water to form hydrogels, soft materials with interesting mechanical properties. In drug delivery they are useful as carriers of various types of drugs, including small molecules for cancer therapy and large molecules of biological origin for treatment of infections and genetic diseases. Microgels are microscopic hydrogel particles that can be injected into the body or applied to the skin. Hydrogels are useful in drug delivery, in part because they have the capacity to encapsulate and store large amounts of drugs in an environment that protects the drugs from degradation, and in part because the polymer network offers ways to control the rate of release of the drug.

Our research in this field is mainly focused on fundamental aspects of the interaction between hydrogels and different categories of drugs and excipients (helper molecules) where the interplay between electrostatic and hydrophobic interactions and the elastic properties of the polymer networks is important. To this end we study the microstructure and stability of complexes formed between polyelectrolyte networks, drug molecules and excipients. A combination of experimental and theoretical methods are used to explain how the charge of proteins and peptides and the self-assembling properties of amphiphilic molecules determine their partitioning between the hydrogel and the surroundings, how they are distributed inside a hydrogel and between different hydrogels. To study the dynamics we measure the rate of binding and release and the related hydrogel volume response and make determinations of microstructures and compositions during intermediate stages. The aim is to reach a mechanistic understanding of the interactions to be able to predict the kinetics of drug release from hydrogels, and to develop new principles for controlled and triggered release from hydrogel based formulations (Fig 3).

Fig 3: The rheological study on hyaluronic acid gel (hydrogel)

→ Amphiphilic drugs in microgels. Amphiphilic drug molecules is an important group of active substances which are commonly used in cancer therapy, as antidepressants and antihypertensive agents. They have properties in common with regular micelle-forming surfactants but the relationships between their molecular structure and self-assembling properties are not well understood. To realize the potential of polyelectrolyte microgels as drug delivery system for amphiphilic drugs we study the basic principles governing the drug loading and release properties. The aim is to relate the microstructure and thermodynamic stability of drug self-assemblies in microgels to the molecular properties of drugs and microgel networks and to the mechanisms and kinetics of release under physiological conditions. We use two in-house developed micromanipulator techniques to monitor the size and internal morphology of single microgels during binding and release of drugs in the microscope. With the ‘flow-pipette’ we study microgels in contact with bulk solutions under conditions of controlled liquid flow (Fig.4); with the ‘micro-drop’ we study microgels in contact with a small solution volume under unstirred conditions (Fig. 5). In addition, we use a µDiss profiler to determine equilibrium binding isotherms and to monitor the kinetics of binding and release, and scattering techniques to determine the microstructure of complexes. The determined equilibrium and dynamic properties are compared with theoretical models developed within the group. The goal is to construct release models that contribute to the development of novel release systems for amphiphilic drugs. In a project run in collaboration with the Biopharmaceutical research group (Prof. H. Lennernäs) at the department we investigate in vitro a system of therapeutic microgels (DC bead®) for parenteral delivery of the amphiphilic drug doxorubicin used clinically for palliative treatment of liver cancer.

Fig.4: Schematic representation of the experimental setup. A single gel bead is immersed in the bulk solution and held in place in the center of the flow pipette.

Fig 5: Schematic illustrations of single-microgel inverse microscopy experiments in  which the microgel is selected from the aqueous solution and then transferred into a drug´s solution by using the micropipette.

Contact persons: Per Hansson (principal investigator).

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Lipid membrane-based nanoparticles and supported structures as nanocarriers and biomimetic systems

Lipid membranes play a key role in nature: they build the barriers separating living cells from their environment. These membranes are self-assembled structures, meaning that they form spontaneously when the lipids are mixed with water. The same phenomenon can be easily reproduced in the laboratory, giving rise to structures that strongly resemble biological membranes.

Dispersed systems based on self-assembled lipid bilayer structures, such as liposomes and lipodisks, are widely studied due to their unique properties as, e.g., biomimetic structures and drug carriers.

Development of lipid-based nanoparticles as drug nanocarriers

We study the suitability of novel lipid-based nanoparticles as carriers for molecules of therapeutic interest, as, e.g., antimicrobial peptides. The interactions between the carriers and the drugs are characterized in order to understand the physicochemical parameters affecting the loading and release of the molecules of interest into and from the carriers. We also study and characterize any structural changes caused by the inclusion of amphiphilic or hydrophobic drugs into the lipid membrane structure.

Fundamental studies on lipid membrane behavior

We perform fundamental physicochemical studies on the behavior of lipid membranes and lipid-based nanoparticles. Of particular interest is the interaction between lipid-based nanoparticles with each other, with other nanoparticles, and with solid substrates. The results from this project have proven useful to improve lipid-based formulations and avoid unwanted interactions with either other particles or the containers.  We have, e.g., developed methods to decrease the unwanted and non-specific interactions of liposomes with glass and quartz surfaces via surface and/or liposome modifications.

We also develop new experimental approaches to characterize the properties of lipid membranes, such as their permeability towards solutes and their mechanical properties. The new methods thus developed are helpful to characterize the effect of different components of the lipid membrane, to understand the effect of  membrane-embedded molecules on the nanoparticle’s structure, to predict the suitability of novel nanoparticles as drug nanocarriers, etc.

Supported lipid bilayer structures as biomimetic systems

Lipid bilayers are found at the core of all cellular membranes and they are key elements in building the barriers enclosing different organelles and the cell itself. Therefore, all interactions of a cell with its surroundings, including the uptake of therapeutic drugs, are at some point mediated by a lipid bilayer.

My research focuses on the design and use of immobilized lipid membrane structures in order to set the basis for the development of new lipid-modified surfaces suitable for fundamental studies on lipid-membrane behavior, as well as for electrochemical and nanogravimetric analyses to characterize membrane-analyte interactions. The lipid-based structures most commonly used in my research are lipodisks (are planar lipid bilayer structures whose rim is stabilized by lipids modified with polyethyleneglycol), liposomes (lipid membrane vesicles), and supported bilayer lipid membranes (sBLMs). These structures can even include integral membrane proteins in an environment mimicking the native cell membrane, thus allowing studies of protein/analyte interactions.

The figure below shows a schematic representation of the objectives, strategies, and methods used in my research.