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- Evertsson, Hans
(författare)
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Molecular dynamics and aggregation behaviour in aqueous polymer-drug model systems
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Pharmaceutical formulations often contain polymers used as binders, swelling agents, etc., to give the formulation mechanical stability or specific drug release features. Many drug substances, as well as polymers, are amphiphilic which will give an associative polymer-drug interaction, affecting the dissolution rate and drug release. This thesis focuses on the molecular dynamics of model nonionic polymer-anionic drug complexesformed in aqueous solution. Two low molecular weight amphiphiles with different surface activities are used; the surfactant sodium dodecyl sulfate (SDS) and the sodium salt of ibuprofen. The polymers studied are a set of cellulose ethers of different hydrophobicity, with special emphasis on ethyl(hydroxyethyl)cellulose (EHEC).Fluorescence probe techniques and nuclear magnetic resonance (NMR) are the main methods used. The molecular dynamics of the EHEC/SDS system is strongly composition dependent. Mixed EHEC/SDS micelles with low SDS aggregation numbers and a high relative content of EHEC is more than three times as rigid as mixed micelles with a high relative content of SDS, as monitored by the fluorescent probe 1,3-di(1-pyrenyl)propane(P3P) and 1H NMR transverse relaxation.The microviscosities as monitored by P3P of a set of ten cellulose ethers with different hydrophobicity, interacting with SDS, are compared. A correlation between the microviscosity and the polymer-SDS interaction energy, as qualitatively estimated from the SDS concentration at onset of polymer-SDS association, is found. This correlation is further described by principal component analysis for a subset of six EHEC samples. The microviscosity of mixed polymer-SDS micelles as monitored by P3P is found to be a valuable parameter for the characterization of polymer samples, and can be used to predict the surface tension of the polymer.The interaction between EHEC and the sodium salt of ibuprofen resembles the normally accepted model for polymer-surfactant interaction, but is more complex. Fluorescence probe- and pulsed gradient spin echo self diffusion NMR- (PGSE-NMR) measurements indicate that premicellar aggregates of ibuprofen adsorb onto EHEC below the onset of cooperative adsorption with respect to the ibuprofen concentration. The thesis shows theimportance of detailed knowledge of the molecular dynamics for design of controlled release preparations.
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- Evertsson, Maria, et al.
(författare)
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Frequency- and Phase-Sensitive Magnetomotive Ultrasound Imaging of Superparamagnetic Iron Oxide Nanoparticles
- 2013
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Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. - 0885-3010. ; 60:3, s. 481-491
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Tidskriftsartikel (refereegranskat)abstract
- It has recently been demonstrated that superparamagnetic iron oxide nanoparticles can be used as magnetomotive ultrasound contrast agents. A time-varying external magnetic field acts to move the particles and, thus, the nanoparticle-laden tissue. However, the difficulty of distinguishing this magnetomotive motion from undesired movement induced in regions without nanoparticles or other motion artifacts has not been well reported. Using a high-frequency linear-array system, we found that displacements outside nanoparticle-laden regions can be similar in magnitude to those in regions containing nanoparticles. We also found that the displacement outside the nanoparticle regions had a phase shift of approximately p radians relative to that in the nanoparticle regions. To suppress signals arising from undesirable movements, we developed an algorithm based on quadrature detection and phase gating at the precise frequency of nanoparticle displacement. Thus, clutter at other frequencies can be filtered out, and the processed signal can be color-coded and superimposed on the B-mode image. The median signal-to-clutter ratio improvement using the proposed algorithm was 36 dB compared with simply summing the movement energy at all frequencies. This clutter rejection is a crucial step to move magnetomotive ultrasound imaging of nanoparticles toward in vivo investigations.
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- Evertsson, Maria, et al.
(författare)
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In vivo magnetomotive ultrasound imaging of rat lymph nodes - a pilot study
- 2015
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Ingår i: 2015 IEEE International Ultrasonics Symposium (IUS). - 1948-5719.
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Konferensbidrag (refereegranskat)abstract
- The drive to gain a better understanding of how diseases arise and how to provide ever-earlier detection are some of the key factors for the development of molecular imaging. Compared to other imaging modalities ultrasound has not received the same attention for molecular imaging mainly due to its limited contrast resolution, together with contrast agents confined to the intravascular space. To overcome these issues, new nano-sized contrast agents and new ultrasound imaging techniques e.g. photo acoustic imaging, have been developed. Another such imaging technique under development is magnetomotive ultrasound imaging (MMUS). We have previously developed a frequency and phase tracking algorithm which is able to detect superparamagnetic iron oxide nanoparticles (SPIO NPs) using MMUS, where our suggested first clinical application is to detect sentinel lymph nodes (SLNs) in breast cancer surgery. Recently we have shown detection of SPIO laden rat SLNs in situ. Here we present the feasibility of in vivo detection of SLNs in rats. The algorithm clearly pinpoints the NP laden SLN, even in presence of significant artefactual tissue movement. The magnetomotive displacement increased when a higher voltage was applied on the coil creating the magnetic field (e.g. 56.6% increasing the voltage from 20V to 50V). An uneven concentration distribution of NPs in the SLN was found. The maximum magnetomotive displacement difference between two different cross sections in one SLN was 9.76 times. The study also showed that for a higher concentration of NPs a lower magnetic coil excitation voltage could be used in order to create a magnetomotive displacement of a certain magnitude. The result from this in vivo study shows that the method has potential for future clinical use.
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- Evertsson, Maria, et al.
(författare)
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Magnetomotive Ultrasound Imaging Of Rat Lymph Nodes In Situ: Assessment Of Imaging Parameters
- 2013
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Ingår i: 2013 IEEE International Ultrasonics Symposium (IUS). - 9781467356855 ; , s. 600-603
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Konferensbidrag (refereegranskat)abstract
- Detection and removal sentinel lymph nodes (SLN) is important in the diagnosis and treatment of breast cancer and malignant melanoma. The SLN is the first regional lymph node draining the cancer tumor and if the cancer has spread it is most likely to find cancer cells in the SLN. In this study we have been able to detect multimodal superparamagnetic iron oxide nanoparticles (SPIO-NP) in rat SLNs in situ using magnetomotive ultrasound imaging (MMUS). In MMUS a time-varying external magnetic field acts to move the NPs and, thus, the NP-laden tissue. This movement can be detected by proper processing of ultrasound data. We have recently developed an MMUS algorithm, based on quadrature detection and phase gating at the frequency of NP displacement, and this is the first study where the algorithm is evaluated in animals. For both higher NP-concentration, as well as smaller NPs, we found that the MMUS data showed a larger displacement (1.56 +/- 0.43 and 1.94 +/- 0.54 times larger, respectively). The MMUS displacement also increased with a lower excitation frequency (1.95 +/- 0.64 times larger for 5 Hz compared to 15 Hz) and higher excitation voltage (2.95 +/- 1.44 times larger for 30V compared to 10V). The results from this study show that the MMUS technique has potential to be used as bedside guidance during SLN surgery, well as being used as standalone technique in a number of other applications such as stem cell tracking and cardiovascular research.
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