| 1. |
- Jing, Yujia, 1985, et al.
(författare)
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Asymmetric cationic liposomes designed for heat-activated association with cells
- 2017
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Ingår i: Colloids and Surfaces B: Biointerfaces. - : Elsevier BV. - 0927-7765 .- 1873-4367. ; 151, s. 112-118
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Tidskriftsartikel (refereegranskat)abstract
- Improved anticancer drugs and drug carriers are needed in combination therapies, such as hyperthermia-assisted chemotherapy. Liposomal drug carriers with advanced functions are attractive candidates for targeted accumulation and drug release in response to heat stimulus. We report on the design of liposomes with a heat-activated surface function. Our design is based on asymmetric lipid membranes with a defined gel to liquid-crystalline phase-transition temperature around 41 °C. Asymmetry between the inner and the outer membrane leaflets was generated through selective PEGylation of cationic lipids in the outer membrane leaflet. In a physiological buffer, the PEGylated asymmetric liposomes had a neutral zeta potential and did not bind to planar anionic model membranes. In contrast, following upon heat-activation, binding of liposomes to the model membranes occurred. Release of a hydrophilic dye encapsulated in the asymmetric liposomes occurred at 40 °C. Enhanced uptake of the asymmetric liposomes by hypopharyngeal carcinoma cells (FaDu cells) was observed when hyperthermia was applied compared to experiments performed at 37 °C. These results show the potential of asymmetric liposomes for localized delivery of drugs into cells in response to (external) temperature stimulus.
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| 2. |
- Jing, Yujia, 1985
(författare)
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Characterization of supported lipid membranes towards the development of nano-sized drug carriers for hyperthermia applications
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- So called thermosensitive liposomal drug carriers for temperature-controlled drug release under hyperthermal conditions have recently attracted great attention and advanced lipid membrane - nanoparticle assemblies are emerging at an increasing rate to meet the demands for multifunctional drug carriers in medicine. The rational design of these drug delivery systems will require understanding of lipid membrane physicochemical properties under conditions relevant to the medical treatment. Towards this aim, the present thesis is devoted to studies of the formation and the function of lipid membrane coatings on planar solid supports, focusing on lipid compositions yielding a gel to liquid phase transition temperature in the range 40 - 45 °C. In the first study, DPPC (glass transition temperature, Tg = 41 oC) liposomes ranging from 90 nm to 160 nm in diameter were prepared and used for studies of the formation of supported lipid membrane on silica using the quartz crystal microbalance with dissipation (QCM-D) technique. It was found that, at a temperature (50 oC) well above the glass transition temperature, DPPC liposomes smaller than 100 nm spontaneously rupture on the surface at a critical surface coverage, following a well-established pathway. DPPC liposomes larger than 160 nm do not rupture on a silica surface at 50 oC, but can overcome the threshold to form membranes when first adsorbed to the surface at 22 oC, after which the temperature is increased to 50 oC. This study contributes to the understanding of the liposome-to-membrane formation process, where the critical coverage of adsorbed liposomes and the liposome shape play important roles. In the second study, a new method of preparing asymmetric lipid membranes on solid surfaces by combining two leaflets in different phase states is demonstrated. It includes a proof-of-concept, where phase transition induced flip-flop between the lipid leaflets is employed to control what lipid head groups are presented at the membrane surface. The process was monitored by QCM-D and dual polarization interferometry (DPI). The asymmetric structure was stable at a temperature below the effective Tg of the lower leaflet, while lipid flip-flop was induced upon increasing of the temperature above the effective Tg. Transmembrane lipid exchange was demonstrated by detecting, through streptavidin binding, biotinylated lipids appearing at the surface of the top leaflet after ‘temperature-activation’ of an asymmetric structure where these lipids were first located in the lower leaflet. The understanding of the fundamental physicochemical properties of lipid membranes, in particular the distinct transition between the gel phase and the fluid phase in response to temperature, is an important key to successful designs of hyperthermia-responsive nanodrugs for medical applications. The described strategy for constructing asymmetric membranes on flat titania surfaces provides a guide to ‘smart’ drug carriers upon transfer to spherical titania nanoparticle templates. The presented results also suggest that QCM-D can be a useful method to measure liposome content release, which is important in drug carrier development.
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| 3. |
- Jing, Yujia, 1985, et al.
(författare)
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Formation of supported lipid bilayers on silica: relation to lipid phase transition temperature and liposome size
- 2014
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 10:1, s. 187-195
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Tidskriftsartikel (refereegranskat)abstract
- DPPC liposomes ranging from 90 nm to 160 nm in diameter were prepared and used for studies of the formation of supported lipid membranes on silica (SiO2) at temperatures below and above the gel to liquid-crystalline phase transition temperature (T-m = 41 degrees C), and by applying temperature gradients through T-m. The main method was the quartz crystal microbalance with dissipation (QCM-D) technique. It was found that liposomes smaller than 100 nm spontaneously rupture on the silica surface when deposited at a temperature above T-m and at a critical surface coverage, following a well-established pathway. In contrast, DPPC liposomes larger than 160 nm do not rupture on the surface when adsorbed at 22 degrees C or at 50 degrees C. However, when liposomes of this size are first adsorbed at 22 degrees C and at a high enough surface coverage, after which they are subject to a constant temperature gradient up to 50 degrees C, they rupture and fuse to a bilayer, a process that is initiated around T-m. The results are discussed and interpreted considering a combination of effects derived from liposome-surface and liposome-liposome interactions, different softness/stiffness and shape of liposomes below and above T-m, the dynamics and thermal activation of the bilayers occurring around T-m and (for liposomes containing 33% of NaCl) osmotic pressure. These findings are valuable both for preparation of supported lipid bilayer cell membrane mimics and for designing temperature-responsive material coatings.
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| 4. |
- Jing, Yujia, 1985, et al.
(författare)
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Heat-activated liposome targeting to streptavidin-coated surfaces
- 2015
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Ingår i: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier BV. - 1879-2642 .- 0005-2736. ; 1848:6, s. 1417-1423
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Tidskriftsartikel (refereegranskat)abstract
- There is a great need of improved anticancer drugs and corresponding drug carriers. In particular, liposomal drug carriers with heat-activated release and targeting functions are being developed for combined hyperthermia and chemotherapy treatments of tumors. The aim of this study is to demonstrate the heat-activation of liposome targeting to biotinylated surfaces, in model experiments where streptavidin is used as a pretargeting protein. The design of the heat-activated liposomes is based on liposomes assembled in an asymmetric structure and with a defined phase transition temperature. Asymmetry between the inside and the outside of the liposome membrane was generated through the enzymatic action of phospholipase D, where lipid head groups in the outer membrane leaflet, i.e. exposed to the enzyme, were hydrolyzed. The enzymatically treated and purified liposomes did not bind to streptavidin-modified surfaces. When activation heat was applied, starting from 22 degrees C, binding of the liposomes occurred once the temperature approached 33 +/- 0.5 degrees C. Moreover, it was observed that the asymmetric structure remained stable for at least 2 weeks. These results show the potential of asymmetric liposomes for the targeted binding to cell membranes in response to (external) temperature stimulus. By using pretargeting proteins, this approach can be further developed for personalized medicine, where tumor-specific antibodies can be selected for the conjugation of pretargeting agents.
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| 5. |
- Jing, Yujia, 1985
(författare)
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Hyperthermia-responsive liposomal systems
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Abstract Sophisticated liposomal systems are emerging at an increasing rate to meet the demands for multifunctional drug carriers in chemotherapies in combined with hyperthermia. For example, liposomal drug carriers for temperature-controlled drug release under hyperthermic conditions have recently been tested in clinical trials. More advanced designs of liposomes are expected to release encapsulated contents and activate hidden surface-functions in response to heat stimulus. Towards this aim, the present thesis is focused on formulating asymmetric lipid systems that can preserve functional moieties, and reactivate the targeted function as well as release the encapsulated compounds upon local heating. The design of the asymmetric liposomal systems utilizes the heat-activated transmembrane lipid diffusion during gel to liquid-crystalline phase transitions of the lipid membranes.Rational design of advanced liposomal drug-delivery systems will require understanding of the physicochemical properties of lipid membranes under, e.g., hyperthermic conditions. Here, supported lipid membranes on planar solid surfaces were used for model studies of lipid composition yielding a gel to liquid crystalline phase-transition temperature in the range 40 – 45 °C. It was found that the liposome-to-membrane formation process is not only size-dependent but also governed by temperature. Two methods of preparing supported asymmetric lipid membranes were investigated. As a proof-of-concept, the upper leaflets were either replaced or chemically transformed by enzymatic hydrolysis. The processes were monitored using surface sensitive techniques such as quartz crystal microbalance with dissipation (QCM-D) and dual polarization interferometry (DPI). The asymmetric structures were stable at a room temperature, while lipid flip-flop was induced upon increasing of the temperature. Transmembrane lipid exchange in the asymmetric structure under hyperthermic conditions was demonstrated by detecting, through streptavidin binding, biotinylated lipids appearing at the top leaflet which were first located in the lower leaflet. The protocols developed for the supported lipid systems were adapted for the preparation of asymmetric liposomes. Biotinylated asymmetric liposomes were used as a model system to demonstrate the principle of heat-activated targeting of asymmetric liposomes to streptavidin-coated surfaces. More biologically relevant interaction was utilized to replace the biotin-streptavidin function, where asymmetric cationic liposomes were binding to anionic supported membrane immobilized surfaces upon heating. The described strategies for assembly of asymmetric supported membranes provide a guide to the development of multifunctional drug carriers. The protocols used in experiments with supported membranes were readily adapted to the preparation of asymmetric liposomes. The ongoing study tests the asymmetric liposomes in vitro, which is designed to demonstrate hyperthermia treatment can enhance accumulation of liposomes in FaDu cells, and at the same time activate release of the encapsulated components. The results of in vitro tests can be used to analyze the feasibility of utilizing the asymmetric liposomes as a platform in vivo to explore further improvement in their functions upon microwave hyperthermia.
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| 6. |
- Jing, Yujia, 1985, et al.
(författare)
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Phase Transition-Controlled Flip-Flop in Asymmetric Lipid Membranes
- 2014
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 118:9, s. 2389-2395
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Tidskriftsartikel (refereegranskat)abstract
- Lipid membrane asymmetry is of fundamental importance for biological systems and also provides an attractive means for molecular control over biomaterial surface properties (including drug carriers). In particular, temperature-dependent changes of surface properties can be achieved by taking advantage of distinct phase transitions in lipid membrane coatings where lipids exchange (flip-flop) between leaflets. In this study, temperature is used to control flip-flop of lipids in asymmetric lipid membranes on planar solid supports, where the two leaflets of the lipid membrane are in different phase states. More specifically, the lower leaflet is prepared from a supported lipid membrane composed of a high T-m lipid mixture of phosphocholine (PC), phosphatidylserine (PS), and a bioactive lipid on TiO2, followed by selective removal of the top leaflet by detergent. Next, at a lower temperature, where the remaining leaflet is in the gel state, a top leaflet of a different lipid composition and in the fluid phase is formed. Phase transition-induced changes in membrane surface properties following upon temperature-activation of the prepared asymmetric membrane are demonstrated by the detection of biotinylated lipids, which were initially located (thus "hidden") in the lower-gel phase leaflet, at the surface of the top leaflet. These processes were monitored in real-time by the quartz crystal microbalance with dissipation (QCM-D) and the dual polarization interferometry (DPI) techniques, allowing modeling of the mass and the anisotropic property of the lipid structures in different phase states.
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| 7. |
- Liu, Johan, 1960, et al.
(författare)
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Stem Cell Growth and Migration on Nanofibrous Polymer Scaffolds and Micro-Fluidic Channels on Silicon-Chip
- 2009
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Ingår i: Proceedings of the 2009 Electronic Components and Technology Conference. - 0569-5503. - 9781424444762 ; , s. 1080-1085
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Konferensbidrag (refereegranskat)abstract
- Stem cell growth and migration on nanofibrous scaffolds and micro-fluidic channels on Silicon-Chip were studied by using neural stem cells isolated from adult rats' brain. Electrospinning and lithographic technique were used for developing nanofibrous-polylactic acid (PLA) and polyurethane (PU) based-scaffolds and micro-fluidic channels on Si-Chips respectively. Immunocytochemical and morphological analysis showed better cell-matrix interaction with profound adhesion, proliferation and migration on the developed scaffolds. Cell culture assay with microfluidic channel revealed the ability of developed channel system in guiding neuronal stem cell growth towards specified directions. These studies extend the possibility of using developed nanofibrous scaffolds and micro-fluidic channel system for future electrical signal transmission based on living neural stem cells.
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| 8. |
- Wayment-Steele, H. K., et al.
(författare)
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Effects of Al3+ on Phosphocholine and Phosphoglycerol Containing Solid Supported Lipid Bilayers
- 2016
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 32:7, s. 1771-1781
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Tidskriftsartikel (refereegranskat)abstract
- Aluminum has attracted great attention recently as it has been suggested by several studies to be associated with increased risks for Alzheimer's and Parkinson's disease. The toxicity of the trivalent ion is assumed to derive from structural changes induced in lipid bilayers upon binding, though the mechanism of this process is still not well understood. In the present study we elucidate the effect of Al3+ on supported lipid bilayers (SLBs) using fluorescence microscopy, the quartz crystal microbalance with dissipation (QCM-D) technique, dual-polarization interferometry (DPI), and molecular dynamics (MD) simulations. Results from these techniques show that binding of Al3+ to SLBs containing negatively charged and neutral phospholipids induces irreversible changes such as domain formation. The measured variations in SLB thickness, birefringence, and density indicate a phase transition from a disordered to a densely packed ordered phase.
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